Mean arterial pressureMean Arterial PressureMean arterial pressure (MAP) is the average systemic arterial pressure and is directly related to cardiac output (CO) and systemic vascular resistance (SVR). The SVR and MAP are affected by the vascular anatomy as well as a number of local and neurohumoral factors.Vascular Resistance, Flow, and Mean Arterial Pressure (MAP) is the average systemic pressure in the arteriesArteriesArteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology. The MAP is tightly regulated to help maintain appropriate perfusion and is primarily determined by the cardiac outputCardiac outputThe volume of blood passing through the heart per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with stroke volume (volume per beat).Cardiac Mechanics (CO) and the systemic vascular resistanceResistancePhysiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow.Ventilation: Mechanics of Breathing (SVR). Cardiac outputCardiac outputThe volume of blood passing through the heart per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with stroke volume (volume per beat).Cardiac Mechanics is determined by the HR and the stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle (the volume of blood ejected by the heart each beat). The HR is primarily regulated by the effects of the ANSANSThe ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems.Autonomic Nervous System: Anatomy on the sinoatrial nodeSinoatrial nodeThe small mass of modified cardiac muscle fibers located at the junction of the superior vena cava and right atrium. Contraction impulses probably start in this node, spread over the atrium (heart atrium) and are then transmitted by the atrioventricular bundle (bundle of His) to the ventricle (heart ventricle).Heart: Anatomy in the heart, while stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle is determined by the preloadPreloadCardiac Mechanics, afterloadAfterloadAfterload is the resistance in the aorta that prevents blood from leaving the heart. Afterload represents the pressure the LV needs to overcome to eject blood into the aorta.Cardiac Mechanics, and inotropy (or contractile strength) of each heartbeat. The SVR is regulated by a number of factors, including the ANSANSThe ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems.Autonomic Nervous System: Anatomy, the arterial baroreflexBaroreflexA response by the baroreceptors to increased blood pressure. Increased pressure stretches blood vessels which activates the baroreceptors in the vessel walls. The net response of the central nervous system is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral vascular resistance and by lowering cardiac output. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Vascular Resistance, Flow, and Mean Arterial Pressure, circulating catecholaminesCatecholaminesA general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Adrenal Hormones, the RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones, and several other hormonesHormonesHormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types.
Mean arterial pressureMean Arterial PressureMean arterial pressure (MAP) is the average systemic arterial pressure and is directly related to cardiac output (CO) and systemic vascular resistance (SVR). The SVR and MAP are affected by the vascular anatomy as well as a number of local and neurohumoral factors.Vascular Resistance, Flow, and Mean Arterial Pressure (MAP) equations
Mean arterial pressureMean Arterial PressureMean arterial pressure (MAP) is the average systemic arterial pressure and is directly related to cardiac output (CO) and systemic vascular resistance (SVR). The SVR and MAP are affected by the vascular anatomy as well as a number of local and neurohumoral factors.Vascular Resistance, Flow, and Mean Arterial Pressure is the average systemic arterial pressure.
MAP = (CO x SVR) + CVPCVPThe blood pressure in the central large veins of the body. It is distinguished from peripheral venous pressure which occurs in an extremity.Central Venous Catheter
CO: cardiac outputCardiac outputThe volume of blood passing through the heart per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with stroke volume (volume per beat).Cardiac Mechanics, which = stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle x HR
SVR: systemic vascular resistanceResistancePhysiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow.Ventilation: Mechanics of Breathing
CVPCVPThe blood pressure in the central large veins of the body. It is distinguished from peripheral venous pressure which occurs in an extremity.Central Venous Catheter: central venous pressureCentral venous pressureThe blood pressure in the central large veins of the body. It is distinguished from peripheral venous pressure which occurs in an extremity.Central Venous Catheter (close to 0, often disregarded)
Can be approximated using systolic and diastolic blood pressures:
Because the heart spends more time in diastoleDiastolePost-systolic relaxation of the heart, especially the heart ventricles.Cardiac Cycle than in systoleSystolePeriod of contraction of the heart, especially of the heart ventricles.Cardiac Cycle, the diastolic blood pressure (DBP) contributes more to the MAP than the systolic blood pressure (SBPSBPAscites).
Mean arterial intravascular pressure throughout the cardiac cycle P: pressure
Image by Lecturio.
Factors affecting the mean arterial pressureMean Arterial PressureMean arterial pressure (MAP) is the average systemic arterial pressure and is directly related to cardiac output (CO) and systemic vascular resistance (SVR). The SVR and MAP are affected by the vascular anatomy as well as a number of local and neurohumoral factors.Vascular Resistance, Flow, and Mean Arterial Pressure
Mean arterial pressureMean Arterial PressureMean arterial pressure (MAP) is the average systemic arterial pressure and is directly related to cardiac output (CO) and systemic vascular resistance (SVR). The SVR and MAP are affected by the vascular anatomy as well as a number of local and neurohumoral factors.Vascular Resistance, Flow, and Mean Arterial Pressure is primarily affected by the CO and SVR:
CO = HR x stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle:
HR is determined by:
ANSANSThe ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems.Autonomic Nervous System: Anatomy (primary regulator) effects on the sinoatrial nodeSinoatrial nodeThe small mass of modified cardiac muscle fibers located at the junction of the superior vena cava and right atrium. Contraction impulses probably start in this node, spread over the atrium (heart atrium) and are then transmitted by the atrioventricular bundle (bundle of His) to the ventricle (heart ventricle).Heart: Anatomy in the heart
Other factors:
ThyroidThyroidThe thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck.Thyroid Gland: AnatomyhormonesHormonesHormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types
Circulating catecholaminesCatecholaminesA general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Adrenal Hormones
K+ levels
IschemiaIschemiaA hypoperfusion of the blood through an organ or tissue caused by a pathologic constriction or obstruction of its blood vessels, or an absence of blood circulation.Ischemic Cell Damage
Stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle is affected by:
Inotropy: contractile strength of each heartbeat
AfterloadAfterloadAfterload is the resistance in the aorta that prevents blood from leaving the heart. Afterload represents the pressure the LV needs to overcome to eject blood into the aorta.Cardiac Mechanics:
PreloadPreloadCardiac Mechanics (how much the ventricles have stretched/filled with blood by the end of diastoleDiastolePost-systolic relaxation of the heart, especially the heart ventricles.Cardiac Cycle), which is affected by:
Venous complianceComplianceDistensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure.Veins: Histology (how much blood the veinsVeinsVeins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology can hold)
Blood volume, primarily affected by renal Na+ and H2O handling
Systemic vascular resistanceResistancePhysiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow.Ventilation: Mechanics of Breathing is primarily affected by:
Vascular anatomy:
Arrangement of vessels in series or parallel
Anatomy of the vessel walls
Local factors secreted by vessel walls (e.g., NO, prostacyclinProstacyclinA prostaglandin that is a powerful vasodilator and inhibits platelet aggregation. It is biosynthesized enzymatically from prostaglandin endoperoxides in human vascular tissue. The sodium salt has been also used to treat primary pulmonary hypertension.Eicosanoids, thromboxane), which can cause vasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure and vasodilationVasodilationThe physiological widening of blood vessels by relaxing the underlying vascular smooth muscle.Pulmonary Hypertension Drugs
Neuronal factors:
Input from the ANSANSThe ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems.Autonomic Nervous System: Anatomy
Arterial baroreceptor reflexBaroreceptor reflexA response by the baroreceptors to increased blood pressure. Increased pressure stretches blood vessels which activates the baroreceptors in the vessel walls. The net response of the central nervous system is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral vascular resistance and by lowering cardiac output. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Vascular Resistance, Flow, and Mean Arterial Pressure
HormonesHormonesHormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types:
Circulating catecholaminesCatecholaminesA general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Adrenal Hormones released by the adrenal medullaAdrenal MedullaThe inner portion of the adrenal gland. Derived from ectoderm, adrenal medulla consists mainly of chromaffin cells that produces and stores a number of neurotransmitters, mainly adrenaline (epinephrine) and norepinephrine. The activity of the adrenal medulla is regulated by the sympathetic nervous system.Adrenal Glands: Anatomy
HormonesHormonesHormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types in the RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones
Natriuretic peptides
Antidiuretic hormoneAntidiuretic hormoneAntidiuretic hormones released by the neurohypophysis of all vertebrates (structure varies with species) to regulate water balance and osmolarity. In general, vasopressin is a nonapeptide consisting of a six-amino-acid ring with a cysteine 1 to cysteine 6 disulfide bridge or an octapeptide containing a cystine. All mammals have arginine vasopressin except the pig with a lysine at position 8. Vasopressin, a vasoconstrictor, acts on the kidney collecting ducts to increase water reabsorption, increase blood volume and blood pressure.Hypernatremia (ADH)
Factors that affect mean arterial pressure (MAP).
CO: cardiac output
SVR: systemic vascular resistance
Via α1-adrenergic receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors, which are coupled to Gq proteinsProteinsLinear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein.Energy Homeostasis
Uses inositol trisphosphateInositol trisphosphateIntracellular messenger formed by the action of phospholipase C on phosphatidylinositol 4, 5-bisphosphate, which is one of the phospholipids that make up the cell membrane. Inositol 1, 4, 5-trisphosphate is released into the cytoplasm where it releases calcium ions from internal stores within the cell’s endoplasmic reticulum. These calcium ions stimulate the activity of B kinase or calmodulin.Second Messengers (IP3) signal transductionTransductionThe transfer of bacterial DNA by phages from an infected bacterium to another bacterium. This also refers to the transfer of genes into eukaryotic cells by viruses. This naturally occurring process is routinely employed as a gene transfer technique.Bacteriology → contracts smooth muscle
↑ CO by increasing both HR and stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle
Directly, via β1-adrenergic receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors, which increases:
Contractility (leading to ↑ stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle)
cAMPcAMPAn adenine nucleotide containing one phosphate group which is esterified to both the 3′- and 5′-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and acth.Phosphodiesterase Inhibitors → ↑ rate of depolarizationDepolarizationMembrane Potential at the sinoatrial (SA) node) → ↑ HR
By inducing venoconstrictionVenoconstrictionVenous Function → forces more blood back to the heart → ↑ preloadPreloadCardiac Mechanics → ↑ stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle → ↑ CO
By ↑ blood volume through activation of the RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones → ↑ preloadPreloadCardiac Mechanics → ↑ stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle → ↑ CO
Parasympathetic stimulation
Parasympathetic stimulation decreases MAP by decreasing both SVR and CO:
↓ SVR by inducing vasodilationVasodilationThe physiological widening of blood vessels by relaxing the underlying vascular smooth muscle.Pulmonary Hypertension Drugs
↓ CO by decreasing HR
Via muscarinic M2receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors which are coupled to Gi proteinsProteinsLinear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein.Energy Homeostasis
Leads to ↓ cAMPcAMPAn adenine nucleotide containing one phosphate group which is esterified to both the 3′- and 5′-positions of the sugar moiety. It is a second messenger and a key intracellular regulator, functioning as a mediator of activity for a number of hormones, including epinephrine, glucagon, and acth.Phosphodiesterase Inhibitors → ↓ rate of depolarizationDepolarizationMembrane Potential at the SA node → ↓ HR
Regions of autonomic output regulation
HypothalamusHypothalamusThe hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems.Hypothalamus: regulates “automatic” ANSANSThe ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems.Autonomic Nervous System: Anatomy output
Medulla: coordinates baroreceptor reflexBaroreceptor reflexA response by the baroreceptors to increased blood pressure. Increased pressure stretches blood vessels which activates the baroreceptors in the vessel walls. The net response of the central nervous system is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral vascular resistance and by lowering cardiac output. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Vascular Resistance, Flow, and Mean Arterial Pressure responses (see below)
Cerebral cortexCerebral cortexThe cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex: Anatomy: adjusts ANSANSThe ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems.Autonomic Nervous System: Anatomy output based on cognitive thought processes (i.e., fear, stress, relaxation)
Spinal cordSpinal cordThe spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord: Anatomy: contains sympathetic efferents under reflexive control of the spinal cordSpinal cordThe spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord: Anatomy
The baroreceptor reflexBaroreceptor reflexA response by the baroreceptors to increased blood pressure. Increased pressure stretches blood vessels which activates the baroreceptors in the vessel walls. The net response of the central nervous system is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral vascular resistance and by lowering cardiac output. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Vascular Resistance, Flow, and Mean Arterial Pressure is the most important mechanism for acute BP regulation.
BaroreceptorsBaroreceptorsReceptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls.Diabetes Insipidus
Pressure-sensing neuronsNeuronsThe basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system.Nervous System: Histology
Fire continuously, though firing rate varies depending on the blood pressure
Location of baroreceptorsBaroreceptorsReceptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls.Diabetes Insipidus:
Carotid sinusCarotid sinusThe dilated portion of the common carotid artery at its bifurcation into external and internal carotids. It contains baroreceptors which, when stimulated, cause slowing of the heart, vasodilatation, and a fall in blood pressure.Carotid Arterial System: Anatomy:
Located where the common carotids divide into their internal and external branches
Innervated by the glossopharyngeal nerveGlossopharyngeal nerveThe 9th cranial nerve. The glossopharyngeal nerve is a mixed motor and sensory nerve; it conveys somatic and autonomic efferents as well as general, special, and visceral afferents. Among the connections are motor fibers to the stylopharyngeus muscle, parasympathetic fibers to the parotid glands, general and taste afferents from the posterior third of the tongue, the nasopharynx, and the palate, and afferents from baroreceptors and chemoreceptor cells of the carotid sinus.Pharynx: Anatomy (cranial nerve (CN) IX) nerve
Aortic archAortic archMediastinum and Great Vessels: Anatomy: innervated by the vagus nerveVagus nerveThe 10th cranial nerve. The vagus is a mixed nerve which contains somatic afferents (from skin in back of the ear and the external auditory meatus), visceral afferents (from the pharynx, larynx, thorax, and abdomen), parasympathetic efferents (to the thorax and abdomen), and efferents to striated muscle (of the larynx and pharynx).Pharynx: Anatomy (CN X)
Locations of the carotid and aortic baroreceptors
Image by Lecturio.
Baroreceptor reflexBaroreceptor reflexA response by the baroreceptors to increased blood pressure. Increased pressure stretches blood vessels which activates the baroreceptors in the vessel walls. The net response of the central nervous system is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral vascular resistance and by lowering cardiac output. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Vascular Resistance, Flow, and Mean Arterial Pressure
↑ Blood pressure or blood volume → ↑ vessel stretching
Baroreceptor nerves ↑ firing frequency when they sense ↑ stretch
Respond in milliseconds
Firing rate changes between systoleSystolePeriod of contraction of the heart, especially of the heart ventricles.Cardiac Cycle and diastoleDiastolePost-systolic relaxation of the heart, especially the heart ventricles.Cardiac Cycle of a single heartbeat
Signal sent through afferentAfferentNeurons which conduct nerve impulses to the central nervous system.Nervous System: Histology fibers → nucleusNucleusWithin a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus.The Cell: Organelles tractus solitarius in the medulla
Appropriate response is coordinated in the cardiovascular control centers of the medulla and sent out via ANSANSThe ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems.Autonomic Nervous System: Anatomy fibers
3 primary output centers in the cardiovascular control center:
Sympathetic centers:
Cardioacceleratory center: ↑ HR and inotropy when activated
Baroreceptors are neurons that sense the stretching of a blood vessel. P: pressure
Image by Lecturio.
Example: ↑ blood pressure
↑ Blood pressure → ↑ vessel stretch → ↑ rate of baroreceptor firing → leads to:
Activation of the vagal/parasympathetic center (i.e., cardioinhibitory center): ↓ HR
Inhibition of the sympathetic centers (i.e., cardioacceleratory and vasomotor centers):
↓ Inotropy
VenodilationVenodilationVenous Function → ↓ preloadPreloadCardiac Mechanics → ↓ stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle → ↓ CO
Responses of the baroreceptor reflex to increased blood pressure: HR: heart rate
CO: cardiac output
SVR: systemic vascular resistance
Image by Lecturio.
Example: ↓ blood pressure (that is, hypotensionHypotensionHypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension)
↓ Blood pressure → ↓ stretch → ↓ rate of baroreceptor firing → leads to:
Inhibition of the vagal/parasympathetic center (i.e., cardioinhibitory center): ↑ HR
Activation of the sympathetic centers (i.e., cardioacceleratory and vasomotor centers):
↑ Inotropy
VenoconstrictionVenoconstrictionVenous Function → ↑ preloadPreloadCardiac Mechanics → ↑ stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle → ↑ CO
Responses of the baroreceptor reflex to decreased blood pressure: HR: heart rate
CO: cardiac output
SVR: systemic vascular resistance
Image by Lecturio.
Baroreceptor reflex in response to hypotension:
The decrease in blood pressure is sensed by the aortic baroreceptors, which initiate the reflex. The induced sympathetic response causes peripheral arterial vasoconstriction, increasing systemic vascular resistance (SVR). Constriction of the veins increases preload, which increases stroke volume and thus cardiac output (CO). The sympathetic response also increases HR and cardiac inotropy. These all contribute to normalization of the blood pressure. MAP: mean arterial pressure
Image by Lecturio.
Adjusting baroreceptor function
BaroreceptorsBaroreceptorsReceptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls.Diabetes Insipidus are rapidly adapting → involved only in short-term (i.e., second to second) blood pressure regulation
Even if baseline blood pressure range is chronically elevated (or lowered), the body still needs to be able to make short-term adjustments to maintain appropriate blood pressure during normal activities (e.g., standing up, walking up stairs).
Certain situations require the normal range for baroreceptor firing to be “reset” or adjusted .
The baroreceptor reflexBaroreceptor reflexA response by the baroreceptors to increased blood pressure. Increased pressure stretches blood vessels which activates the baroreceptors in the vessel walls. The net response of the central nervous system is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral vascular resistance and by lowering cardiac output. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Vascular Resistance, Flow, and Mean Arterial Pressure follows a sigmoidal curve:
Arterial pressure plotted on the x-axis
Baroreceptor firing frequency plotted on the y-axis
Highest rate of firing is during the steepest part of the curve
Effects of chronically elevated blood pressure (e.g., chronic hypertensionHypertensionHypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension)
Shifts the curve to the right
BaroreceptorsBaroreceptorsReceptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls.Diabetes Insipidus do not increase firing rate until higher levels of stretch are sensed.
Other situations in which baroreflexBaroreflexA response by the baroreceptors to increased blood pressure. Increased pressure stretches blood vessels which activates the baroreceptors in the vessel walls. The net response of the central nervous system is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral vascular resistance and by lowering cardiac output. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Vascular Resistance, Flow, and Mean Arterial Pressure set point is adjusted for shorter periods of time:
Aerobic exercise
PainPainAn unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons.Pain: Types and Pathways
Relationship between arterial pressure and baroreceptor firing frequency in normotensive and hypertensive patients:
As arterial pressure increases, the baroreceptor afferent neurons fire more frequently in a sigmoidal relationship. Chronic hypertension decreases the sensitivity of the baroreceptors, shifting the curve to the right. MAP: mean arterial pressure
The RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones is the major long-term regulator of blood pressure.
EnzymesEnzymesEnzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes and hormonesHormonesHormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types in the RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones
ReninReninA highly specific (leu-leu) endopeptidase that generates angiotensin I from its precursor angiotensinogen, leading to a cascade of reactions which elevate blood pressure and increase sodium retention by the kidney in the renin-angiotensin system.Renal Sodium and Water Regulation:
Secreted by the maculaMaculaAn oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid.Eye: Anatomy densa cells within the kidneysKidneysThe kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine.Kidneys: Anatomy
Converts angiotensinogen (secreted by hepatocytesHepatocytesThe main structural component of the liver. They are specialized epithelial cells that are organized into interconnected plates called lobules.Liver: Anatomy) to angiotensin I
ACE:
Secreted by pulmonary vascular endotheliumEndotheliumA layer of epithelium that lines the heart, blood vessels (vascular endothelium), lymph vessels (lymphatic endothelium), and the serous cavities of the body.Arteries: Histology
Converts angiotensin I to angiotensin IIAngiotensin IIAn octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the c-terminal by angiotensin converting enzyme. The amino acid in position 5 varies in different species. To block vasoconstriction and hypertension effect of angiotensin II, patients are often treated with ace inhibitors or with angiotensin II type 1 receptor blockers.Renal Sodium and Water Regulation
Angiotensin IIAngiotensin IIAn octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the c-terminal by angiotensin converting enzyme. The amino acid in position 5 varies in different species. To block vasoconstriction and hypertension effect of angiotensin II, patients are often treated with ace inhibitors or with angiotensin II type 1 receptor blockers.Renal Sodium and Water Regulation:
Stimulates release of aldosteroneAldosteroneA hormone secreted by the adrenal cortex that regulates electrolyte and water balance by increasing the renal retention of sodium and the excretion of potassium.Hyperkalemia (secreted by the zona glomerulosaZona GlomerulosaThe narrow subcapsular outer zone of the adrenal cortex. This zone produces a series of enzymes that convert pregnenolone to aldosterone. The final steps involve three successive oxidations by cytochrome p-450 cyp11b2.Adrenal Glands: Anatomy in the adrenal cortexAdrenal CortexThe outer layer of the adrenal gland. It is derived from mesoderm and comprised of three zones (outer zona glomerulosa, middle zona fasciculata, and inner zona reticularis) with each producing various steroids preferentially, such as aldosterone; hydrocortisone; dehydroepiandrosterone; and androstenedione. Adrenal cortex function is regulated by pituitary adrenocorticotropin.Adrenal Glands: Anatomy)
↓ Venous complianceComplianceDistensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure.Veins: Histology through angiotensin type 1Type 1Spinal Muscular Atrophy (AT1) receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors
AldosteroneAldosteroneA hormone secreted by the adrenal cortex that regulates electrolyte and water balance by increasing the renal retention of sodium and the excretion of potassium.Hyperkalemia:
Stimulates Na+ and water reabsorption from the renal tubules
Stimulates excretion of K+ and H+ into the urine
Stimulation of RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones
Factors that stimulate the RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones (i.e., reninReninA highly specific (leu-leu) endopeptidase that generates angiotensin I from its precursor angiotensinogen, leading to a cascade of reactions which elevate blood pressure and increase sodium retention by the kidney in the renin-angiotensin system.Renal Sodium and Water RegulationsecretionSecretionCoagulation Studies) include:
↓ Renal perfusion:
↓ Blood pressure
↓ Effective circulating blood volume
↓ SodiumSodiumA member of the alkali group of metals. It has the atomic symbol na, atomic number 11, and atomic weight 23.Hyponatremia delivery to the kidney
↑ Sympathetic stimulation
End results of RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones activation
ReninReninA highly specific (leu-leu) endopeptidase that generates angiotensin I from its precursor angiotensinogen, leading to a cascade of reactions which elevate blood pressure and increase sodium retention by the kidney in the renin-angiotensin system.Renal Sodium and Water Regulation → angiotensin I → angiotensin IIAngiotensin IIAn octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the c-terminal by angiotensin converting enzyme. The amino acid in position 5 varies in different species. To block vasoconstriction and hypertension effect of angiotensin II, patients are often treated with ace inhibitors or with angiotensin II type 1 receptor blockers.Renal Sodium and Water Regulation → aldosteroneAldosteroneA hormone secreted by the adrenal cortex that regulates electrolyte and water balance by increasing the renal retention of sodium and the excretion of potassium.Hyperkalemia:
↑ BP: induces reabsorption of water and Na+, leading to ↑ blood volume → ↑ preloadPreloadCardiac Mechanics → ↑ stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle → ↑ CO → ↑ MAP
↑ Serum Na+ (by ↓ urinary excretion of Na+)
↓ Serum K+ (by ↑ urinary excretion of K+)
↑ Serum pHpHThe quantitative measurement of the acidity or basicity of a solution.Acid-Base Balance (by ↑ urinary excretion of H+)
Renin-angiotensin-aldosterone system:
A decrease in mean arterial pressure (MAP) is sensed by the juxtaglomerular apparatus, which then secretes renin. Renin catalyzes the synthesis of angiotensin I which is converted into angiotensin II by ACE. Angiotensin II induces the release of aldosterone from the adrenal cortex, which travels to the distal convoluted tubule, where it causes reabsorption of Na+ and water. CO: cardiac output
Other Hormones Involved in Arterial Pressure Regulation
Circulating catecholaminesCatecholaminesA general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Adrenal Hormones
Circulating catecholaminesCatecholaminesA general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Adrenal Hormones are secreted by the adrenal medullaAdrenal MedullaThe inner portion of the adrenal gland. Derived from ectoderm, adrenal medulla consists mainly of chromaffin cells that produces and stores a number of neurotransmitters, mainly adrenaline (epinephrine) and norepinephrine. The activity of the adrenal medulla is regulated by the sympathetic nervous system.Adrenal Glands: Anatomy directly into the bloodstream
Catecholamine hormonesHormonesHormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types:
EpinephrineEpinephrineThe active sympathomimetic hormone from the adrenal medulla. It stimulates both the alpha- and beta- adrenergic systems, causes systemic vasoconstriction and gastrointestinal relaxation, stimulates the heart, and dilates bronchi and cerebral vessels.Sympathomimetic Drugs (80%)
NorepinephrineNorepinephrinePrecursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers, and of the diffuse projection system in the brain that arises from the locus ceruleus.Receptors and Neurotransmitters of the CNS (20%)
Effects of catecholaminesCatecholaminesA general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Adrenal Hormones that ↑ blood pressure:
Via cardiac β1-adrenergic receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors → ↑ HR and ↑ stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle
Via renal β1-adrenergic receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors → ↑ RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones → ↑ blood volume
Via blood vessel α1receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors → vasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure
Other effects of catecholaminesCatecholaminesA general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Adrenal Hormones:
↑ Respirations and bronchodilation
↑ Blood glucoseGlucoseA primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement.Lactose Intolerance levels
↓ DigestionDigestionDigestion refers to the process of the mechanical and chemical breakdown of food into smaller particles, which can then be absorbed and utilized by the body.Digestion and Absorption
Circulating catecholaminesCatecholaminesA general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Adrenal Hormones are ↑ by:
Physical activity
Stress
Heart failureHeart FailureA heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction.Total Anomalous Pulmonary Venous Return (TAPVR)
ShockShockShock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock
PheochromocytomaPheochromocytomaPheochromocytoma is a catecholamine-secreting tumor derived from chromaffin cells. The majority of tumors originate in the adrenal medulla, but they may also arise from sympathetic ganglia (also referred to as paraganglioma). Symptoms are associated with excessive catecholamine production and commonly include hypertension, tachycardia, headache, and sweating. Pheochromocytoma
Natriuretic peptides
These hormonesHormonesHormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types act in opposition to the RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones.
2 types of natriuretic peptides:
Atrial natriuretic peptideAtrial natriuretic peptideA potent natriuretic and vasodilatory peptide or mixture of different-sized low molecular weight peptides derived from a common precursor and secreted mainly by the heart atrium. All these peptides share a sequence of about 20 amino acids.Renal Sodium and Water Regulation (ANP): stored in and released by atrial myocytesMyocytesMature contractile cells, commonly known as myocytes, that form one of three kinds of muscle. The three types of muscle cells are skeletal, cardiac, and smooth. They are derived from embryonic (precursor) muscle cells called myoblasts.Muscle Tissue: Histology
Brain-type natriuretic peptide (BNPBNPA peptide that is secreted by the brain and the heart atria, stored mainly in cardiac ventricular myocardium. It can cause natriuresis; diuresis; vasodilation; and inhibits secretion of renin and aldosterone. It improves heart function. It contains 32 amino acids.Renal Sodium and Water Regulation):
Stored in and released by ventricular myocytesMyocytesMature contractile cells, commonly known as myocytes, that form one of three kinds of muscle. The three types of muscle cells are skeletal, cardiac, and smooth. They are derived from embryonic (precursor) muscle cells called myoblasts.Muscle Tissue: Histology
Diagnostic marker for heart failureHeart FailureA heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction.Total Anomalous Pulmonary Venous Return (TAPVR)
ANP and BNPBNPA peptide that is secreted by the brain and the heart atria, stored mainly in cardiac ventricular myocardium. It can cause natriuresis; diuresis; vasodilation; and inhibits secretion of renin and aldosterone. It improves heart function. It contains 32 amino acids.Renal Sodium and Water Regulation have similar actions:
↓ ReninReninA highly specific (leu-leu) endopeptidase that generates angiotensin I from its precursor angiotensinogen, leading to a cascade of reactions which elevate blood pressure and increase sodium retention by the kidney in the renin-angiotensin system.Renal Sodium and Water Regulation release → ↓ angiotensin IIAngiotensin IIAn octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the c-terminal by angiotensin converting enzyme. The amino acid in position 5 varies in different species. To block vasoconstriction and hypertension effect of angiotensin II, patients are often treated with ace inhibitors or with angiotensin II type 1 receptor blockers.Renal Sodium and Water Regulation → ↓ aldosteroneAldosteroneA hormone secreted by the adrenal cortex that regulates electrolyte and water balance by increasing the renal retention of sodium and the excretion of potassium.Hyperkalemia → diuresis (water loss) and natriuresis (Na+ loss) → ↓ blood volume → ↓ preloadPreloadCardiac Mechanics → ↓ CO → ↓ MAP
Minor effects which ↓ CVPCVPThe blood pressure in the central large veins of the body. It is distinguished from peripheral venous pressure which occurs in an extremity.Central Venous Catheter and SVR
Angiotensin IIAngiotensin IIAn octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the c-terminal by angiotensin converting enzyme. The amino acid in position 5 varies in different species. To block vasoconstriction and hypertension effect of angiotensin II, patients are often treated with ace inhibitors or with angiotensin II type 1 receptor blockers.Renal Sodium and Water Regulation
Endothelin
Effects of atrial natriuretic peptide (ANP) on blood volume:
Atrial natriuretic peptide is released by atrial myocytes in response to distention and decreases the release of renin, which results in sodium loss (natriuresis) and water loss (diuresis) in the urine. The loss of volume through the urine decreases central venous pressure (CVP), preload, and systemic vascular resistance (SVR), decreasing blood pressure. GFR: glomerular filtration rate NEP: neutral endopeptidase
Image by Lecturio.
Antidiuretic HormoneAntidiuretic hormoneAntidiuretic hormones released by the neurohypophysis of all vertebrates (structure varies with species) to regulate water balance and osmolarity. In general, vasopressin is a nonapeptide consisting of a six-amino-acid ring with a cysteine 1 to cysteine 6 disulfide bridge or an octapeptide containing a cystine. All mammals have arginine vasopressin except the pig with a lysine at position 8. Vasopressin, a vasoconstrictor, acts on the kidney collecting ducts to increase water reabsorption, increase blood volume and blood pressure.Hypernatremia (ADH)
A neuropeptide secreted by the posterior pituitaryPituitaryA small, unpaired gland situated in the sella turcica. It is connected to the hypothalamus by a short stalk which is called the infundibulum.Hormones: Overview and Types
Also called vasopressin
Secreted in response to:
Angiotensin IIAngiotensin IIAn octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the c-terminal by angiotensin converting enzyme. The amino acid in position 5 varies in different species. To block vasoconstriction and hypertension effect of angiotensin II, patients are often treated with ace inhibitors or with angiotensin II type 1 receptor blockers.Renal Sodium and Water Regulation
Hyperosmolarity
Sympathetic stimulation
2 primary effects:
At typical levels:
Action is via vasopressin 2 (V2) receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors
Stimulates water reabsorption in the renal tubules and collecting system (primary effect) → ↑ blood volume → ↑ preloadPreloadCardiac Mechanics → ↑ CO → ↑ MAP
At high levels: vasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure via V1 receptorsReceptorsReceptors are proteins located either on the surface of or within a cell that can bind to signaling molecules known as ligands (e.g., hormones) and cause some type of response within the cell.Receptors → ↑ SVR
Hemorrhage: excessive blood loss that results in decreased blood volume, leading to ↓ preloadPreloadCardiac Mechanics, ↓ stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle, ↓ CO, ↓ MAP, and thus ↓ perfusion to vital organs. In order to maintain perfusion, the body will compensate by attempting to increase MAP by boosting CO through increases in HR and contractility, and by vasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure to increase systemic vascular resistanceResistancePhysiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow.Ventilation: Mechanics of Breathing. IV fluidsIV fluidsIntravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids and/or blood transfusionsBlood transfusionsThe introduction of whole blood or blood component directly into the bloodstream.Transfusion Products can help to restore blood volume.
Fight-or-flight response: activation of the sympathetic nervous systemNervous systemThe nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system.Nervous System: Anatomy, Structure, and Classification (SNS), which affects several aspects of the cardiac cycleCardiac cycleThe cardiac cycle describes a complete contraction and relaxation of all 4 chambers of the heart during a standard heartbeat. The cardiac cycle includes 7 phases, which together describe the cycle of ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation.Cardiac Cycle simultaneously. The SNS activation increases contractility of the heart, while causing vasoconstrictionVasoconstrictionThe physiological narrowing of blood vessels by contraction of the vascular smooth muscle.Vascular Resistance, Flow, and Mean Arterial Pressure and increasing venous return to the heart. These conditions result in synergistic effects, increasing stroke volumeStroke volumeThe amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Cardiac Cycle owing to effects on both ↑ preloadPreloadCardiac Mechanics and ↑ inotropy.
States of low cardiac outputCardiac outputThe volume of blood passing through the heart per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with stroke volume (volume per beat).Cardiac Mechanics, such as heart failureHeart FailureA heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction.Total Anomalous Pulmonary Venous Return (TAPVR), liverLiverThe liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: AnatomycirrhosisCirrhosisCirrhosis is a late stage of hepatic parenchymal necrosis and scarring (fibrosis) most commonly due to hepatitis C infection and alcoholic liver disease. Patients may present with jaundice, ascites, and hepatosplenomegaly. Cirrhosis can also cause complications such as hepatic encephalopathy, portal hypertension, portal vein thrombosis, and hepatorenal syndrome. Cirrhosis, and cor pulmonaleCor PulmonaleCor pulmonale is right ventricular (RV) dysfunction caused by lung disease that results in pulmonary artery hypertension. The most common cause of cor pulmonale is chronic obstructive pulmonary disease. Dyspnea is the usual presenting symptom. Cor Pulmonale from severe lung disease may cause abnormally high stimulation of the RAASRAASA blood pressure regulating system of interacting components that include renin; angiotensinogen; angiotensin converting enzyme; angiotensin i; angiotensin ii; and angiotensinase. Renin, an enzyme produced in the kidney, acts on angiotensinogen, an alpha-2 globulin produced by the liver, forming angiotensin I. Angiotensin-converting enzyme, contained in the lung, acts on angiotensin I in the plasma converting it to angiotensin II, an extremely powerful vasoconstrictor. Angiotensin II causes contraction of the arteriolar and renal vascular smooth muscle, leading to retention of salt and water in the kidney and increased arterial blood pressure. In addition, angiotensin II stimulates the release of aldosterone from the adrenal cortex, which in turn also increases salt and water retention in the kidney. Angiotensin-converting enzyme also breaks down bradykinin, a powerful vasodilator and component of the kallikrein-kinin system.Adrenal Hormones in an attempt to maintain adequate arterial pressures. The abnormally high aldosteroneAldosteroneA hormone secreted by the adrenal cortex that regulates electrolyte and water balance by increasing the renal retention of sodium and the excretion of potassium.Hyperkalemia, however, may lead to metabolic complications, such as hypokalemiaHypokalemiaHypokalemia is defined as plasma potassium (K+) concentration < 3.5 mEq/L. Homeostatic mechanisms maintain plasma concentration between 3.5-5.2 mEq/L despite marked variation in dietary intake. Hypokalemia can be due to renal losses, GI losses, transcellular shifts, or poor dietary intake.Hypokalemia and/or metabolic alkalosisAlkalosisA pathological condition that removes acid or adds base to the body fluids.Respiratory Alkalosis.
Baumann, B. M. (2016). Systemic hypertension. Chapter 57 of J. E. Tintinalli, J. S. Stapczynski, O. J. Ma, D. M. Yealy, G. D. Meckler & D. M. Cline (Eds.), Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8th ed. McGraw-Hill Education. accessmedicine.mhmedical.com/content.aspx?aid=1121496251
Klabunde R. E. (2021). Cardiovascular physiology concepts. Retrieved June 10, 2021, from https://www.cvphysiology.com/
Saladin, K.S., Miller, L. (2004). Anatomy and physiology, 3rd ed., pp. 753–760. McGraw-Hill Education.
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