Body Temperature Regulation

Introduction

Overview

• Humans have a normal core internal temperature of approximately 37ºC (98.6ºF).
• Thermoregulation:
  • Regulation of body temperature Body Temperature The measure of the level of heat of a human or animal. Heatstroke is independent of external temperature.
  • 3-step pathway:
    • Afferent Afferent Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology sensing
    • Central control
    • Efferent Efferent Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology responses
• The hypothalamus Hypothalamus The 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 is the main thermoregulatory center in the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification.

Physiologic processes related to thermoregulation

• Fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever:
  • Controlled increase in body temperature Body Temperature The measure of the level of heat of a human or animal. Heatstroke most commonly due to an infection
  • Triggered by pyrogens Pyrogens Substances capable of increasing body temperature and cause fever and may be used for fever therapy. They may be of microbial origin, often polysaccharides, and may contaminate distilled water. Fever (e.g., bacterial and nonbacterial molecules)
  • Pyrogens Pyrogens Substances capable of increasing body temperature and cause fever and may be used for fever therapy. They may be of microbial origin, often polysaccharides, and may contaminate distilled water. Fever reaching the preoptic area (POA) of the hypothalamus Hypothalamus The 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 stimulate cyclooxygenase-2 (COX-2).
  • COX-2 expression in the endothelial cells of the POA of the hypothalamus Hypothalamus The 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 results in prostaglandin (PG)E₂ production.
  • PGE₂ acts through local EP3 receptors Receptors Receptors 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 to inhibit the activity of the hypothalamic POA neurons Neurons The 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 that function to reduce body temperature Body Temperature The measure of the level of heat of a human or animal. Heatstroke, resulting in fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever.
• Sleep Sleep A readily reversible suspension of sensorimotor interaction with the environment, usually associated with recumbency and immobility. Physiology of Sleep: 
  • Sleep Sleep A readily reversible suspension of sensorimotor interaction with the environment, usually associated with recumbency and immobility. Physiology of Sleep onset coincides with a decline in body temperature Body Temperature The measure of the level of heat of a human or animal. Heatstroke.
  • During sleep Sleep A readily reversible suspension of sensorimotor interaction with the environment, usually associated with recumbency and immobility. Physiology of Sleep phases (i.e., REM phase), thermoregulation is significantly inhibited.
• Appetite and regulation of food intake: Energy generated from food is used for temperature homeostasis Homeostasis The processes whereby the internal environment of an organism tends to remain balanced and stable. Cell Injury and Death.
• Fluid homeostasis Homeostasis The processes whereby the internal environment of an organism tends to remain balanced and stable. Cell Injury and Death: Adequate hydration is necessary for effective sweat production.

Afferent Thermoregulatory Pathway

Peripheral temperature sensing

• Afferent Afferent Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology signaling starts from the peripheral tissues.
• Tissues that provide thermoregulatory input:
  • Skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions
  • Spinal cord Spinal cord The 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
  • Abdominal viscera
  • Brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification:
    • The POA of the hypothalamus Hypothalamus The 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 is the most thermosensitive site in the body.
    • The POA of the hypothalamus Hypothalamus The 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 receives signals from the peripheral tissues and also acts as an autosensor.
• There are 2 classes of temperature-sensitive afferent Afferent Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology neurons Neurons The 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:
  • Neurons Neurons The 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 activated by warmth (approximately 34–42ºC (93–107ºF))
  • Neurons Neurons The 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 activated by cold (approximately 14–30ºC (57–86ºF))
  • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology neurons Neurons The 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 have cell bodies located in:
    • Trigeminal ganglion Trigeminal ganglion The semilunar-shaped ganglion containing the cells of origin of most of the sensory fibers of the trigeminal nerve. It is situated within the dural cleft on the cerebral surface of the petrous portion of the temporal bone and gives off the ophthalmic, maxillary, and part of the mandibular nerves. Trigeminal Neuralgia (for innervation of the head and face)
    • Dorsal root ganglia (for innervation of the rest of the body)
  • Axons Axons Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. Nervous System: Histology split into 2 branches:
    • The 1st branch innervates the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions or viscera.
    • The other branch projects to the dorsal horn Dorsal horn One of three central columns of the spinal cord. It is composed of gray matter spinal laminae i-vi. Brown-Séquard Syndrome of the spinal cord Spinal cord The 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 or the trigeminal nucleus Nucleus Within 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 in the brainstem.

Circumventricular organs Circumventricular organs Highly vascularized and specialized tissues distributed principally along the midline of the ventricular system from the forebrain to the hindbrain. They are distinguished by their lack of normal blood-brain barrier and fenestrated capillaries and contain either neurosecretory neurons or chemoreceptors. Ventricular System: Anatomy (CVOs)

• Areas of the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification with absent or very limited blood-brain barrier Blood-brain barrier Specialized non-fenestrated tightly-joined endothelial cells with tight junctions that form a transport barrier for certain substances between the cerebral capillaries and the brain tissue. Systemic and Special Circulations
• Can sense signals in the blood and pass that information neurally to other areas of the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification
• Permeable to PGs
• 2 CVOs important for thermoregulation due to their proximity to the hypothalamus Hypothalamus The 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:
  • Subfornical organ
  • Organum vasculosum of the lamina terminalis (OVLT)
• Other CVOs:
  • Median eminence
  • Posterior pituitary Pituitary A 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 gland
  • Pineal gland Pineal gland A light-sensitive neuroendocrine organ attached to the roof of the third ventricle of the brain. The pineal gland secretes melatonin, other biogenic amines and neuropeptides. Hormones: Overview and Types
  • Area postrema Area Postrema A small, rounded eminence on each side of the fourth ventricle, which receives nerve fibers from the solitary nucleus; spinal cord; and adjacent areas of the medulla oblongata. The area postrema lies outside the blood-brain barrier and its functions include acting as an emetic chemoreceptor. Antiemetics

Central Control and Efferent Responses

Central control

• The preoptic area and anterior hypothalamus Hypothalamus The 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 are key control sites for thermoregulation in the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification.
• Efferent Efferent Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology pathways to thermoregulatory effectors activate negative feedback Negative feedback Hypothalamic and Pituitary Hormones responses if the core body temperature Body Temperature The measure of the level of heat of a human or animal. Heatstroke deviates from 37ºC (98ºF).

Efferent Efferent Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology responses

Four physiologic effectors are particularly important for thermoregulation in mammals:

• Brown adipose tissue Brown adipose tissue A thermogenic form of adipose tissue composed of brown adipocytes. It is found in newborns of many species including humans, and in hibernating mammals. Brown fat is richly vascularized, innervated, and densely packed with mitochondria which can generate heat directly from the stored lipids. Adipose Tissue: Histology (BAT):
  • Specialized organ for the rapid production of heat Heat Inflammation
  • Highly innervated by sympathetic nerves
  • Norepinephrine Norepinephrine Precursor 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 release induces a mitochondrial leak that produces heat Heat Inflammation.
  • The rostral raphe Raphe Testicles: Anatomy pallidus is the primary site within the preoptic nucleus Nucleus Within 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 where descending signals to BAT exit the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification.
• Control of blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure to the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions:
  • Heat Heat Inflammation exchange between the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions and the environment is dependent on blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure to the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions.
  • Vasoconstriction Vasoconstriction The physiological narrowing of blood vessels by contraction of the vascular smooth muscle. Vascular Resistance, Flow, and Mean Arterial Pressure prevents heat Heat Inflammation loss in cold environments.
  • Vasodilation Vasodilation The physiological widening of blood vessels by relaxing the underlying vascular smooth muscle. Pulmonary Hypertension Drugs allows for heat Heat Inflammation loss in hot environments.
  • Controlled by adrenergic and cholinergic innervation of blood vessels in the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions
• Shivering:
  • Fast, repetitive contraction of skeletal muscle to generate heat Heat Inflammation (“ chills Chills The sudden sensation of being cold. It may be accompanied by shivering. Fever”)
  • Occurs when the core body temperature Body Temperature The measure of the level of heat of a human or animal. Heatstroke falls below 35ºC (95ºF)
• Evaporative heat Heat Inflammation loss:
  • Thermoregulatory strategy to dissipate heat Heat Inflammation
  • Achieved primarily by sweating
  • Occurs through stimulation of the sweat glands Sweat glands Sweat-producing structures that are embedded in the dermis. Each gland consists of a single tube, a coiled body, and a superficial duct. Soft Tissue Abscess by cholinergic postganglionic innervation

Conditions That Affect Thermoregulation

• Age: Aging is associated with diminished cold-induced thermoregulation, which is due to a combination of increased heat Heat Inflammation loss and decreased metabolic heat production Heat Production Fever.
• Exercise
• Extreme environmental conditions leading to:
  • Hypothermia Hypothermia Hypothermia can be defined as a drop in the core body temperature below 35°C (95°F) and is classified into mild, moderate, severe, and profound forms based on the degree of temperature decrease. Hypothermia
  • Heatstroke Heatstroke Heatstroke is an illness characterized as a core body temperature exceeding 40°C (104°F) with accompanying neurological symptoms including ataxia, seizures, and/or delirium. Heatstroke is usually due to the body’s inability to regulate its temperature when challenged with an elevated heat load. Heatstroke
• Hormone levels: Menopause Menopause Menopause is a physiologic process in women characterized by the permanent cessation of menstruation that occurs after the loss of ovarian activity. Menopause can only be diagnosed retrospectively, after 12 months without menstrual bleeding. Menopause is associated with impaired thermoregulation and occurs due to estrogen Estrogen Compounds that interact with estrogen receptors in target tissues to bring about the effects similar to those of estradiol. Estrogens stimulate the female reproductive organs, and the development of secondary female sex characteristics. Estrogenic chemicals include natural, synthetic, steroidal, or non-steroidal compounds. Ovaries: Anatomy depletion and elevated central sympathetic stimulation.
• Drugs can impair thermoregulation through:
  • Diuresis and electrolyte imbalance
  • Sedation and cognitive impairment
  • Reduced thirst recognition
  • Reduced sweat production
  • Hypotension Hypotension Hypotension 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 and reduced cardiac output Cardiac output The 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
  • Commonly implicated drugs:
    • Diuretics Diuretics Agents that promote the excretion of urine through their effects on kidney function. Heart Failure and Angina Medication
    • ACE inhibitors ACE inhibitors Truncus Arteriosus
    • ARBs ARBs Agents that antagonize angiotensin receptors. Many drugs in this class specifically target the angiotensin type 1 receptor. Heart Failure and Angina Medication
    • Anticholinergics Anticholinergics Anticholinergic drugs block the effect of the neurotransmitter acetylcholine at the muscarinic receptors in the central and peripheral nervous systems. Anticholinergic agents inhibit the parasympathetic nervous system, resulting in effects on the smooth muscle in the respiratory tract, vascular system, urinary tract, GI tract, and pupils of the eyes. Anticholinergic Drugs
    • Psychotropics
• Alcohol use:
  • Impaired sweating and skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions vasodilation Vasodilation The physiological widening of blood vessels by relaxing the underlying vascular smooth muscle. Pulmonary Hypertension Drugs
  • Behavioral changes
• Metabolic conditions:
  • Diabetes Diabetes Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus mellitus
  • Hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto’s disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism
  • Hyperthyroidism Hyperthyroidism Hypersecretion of thyroid hormones from the thyroid gland. Elevated levels of thyroid hormones increase basal metabolic rate. Thyrotoxicosis and Hyperthyroidism
  • Hypoadrenalism Hypoadrenalism Conditions in which the production of adrenal corticosteroids falls below the requirement of the body. Adrenal insufficiency can be caused by defects in the adrenal glands, the pituitary gland, or the hypothalamus. IPEX Syndrome
  • Hypopituitarism Hypopituitarism Hypopituitarism is a condition characterized by pituitary hormone deficiency. This condition primarily results from a disease of the pituitary gland, but it may arise from hypothalamic dysfunction. Pituitary tumors are one of the most common causes. The majority of cases affect the anterior pituitary lobe (adenohypophysis), which accounts for 80% of the gland. Hypopituitarism

Temperature Measurement

Clinical Relevance

The following conditions occur when thermoregulation mechanisms are overwhelmed by environmental conditions:

• Hyperthermia: occurs when the core body temperature Body Temperature The measure of the level of heat of a human or animal. Heatstroke increases due to intensive physical stress and the mechanisms of heat Heat Inflammation emission are insufficient. In its extreme state, hyperthermia is referred to as heatstroke Heatstroke Heatstroke is an illness characterized as a core body temperature exceeding 40°C (104°F) with accompanying neurological symptoms including ataxia, seizures, and/or delirium. Heatstroke is usually due to the body’s inability to regulate its temperature when challenged with an elevated heat load. Heatstroke and is accompanied by a systemic inflammatory response causing multiple organ dysfunction that can lead to death. Treatment includes rapid external and internal cooling.
• Hypothermia Hypothermia Hypothermia can be defined as a drop in the core body temperature below 35°C (95°F) and is classified into mild, moderate, severe, and profound forms based on the degree of temperature decrease. Hypothermia: A decrease in core body temperature Body Temperature The measure of the level of heat of a human or animal. Heatstroke to < 35ºC (95ºF) can be classified as mild (32–35ºC (90–95ºF)), moderate (28–32ºC (82–90ºF)), or severe (< 28ºC (82ºF)) hypothermia Hypothermia Hypothermia can be defined as a drop in the core body temperature below 35°C (95°F) and is classified into mild, moderate, severe, and profound forms based on the degree of temperature decrease. Hypothermia. Symptoms progress from shivering to confusion, lethargy Lethargy A general state of sluggishness, listless, or uninterested, with being tired, and having difficulty concentrating and doing simple tasks. It may be related to depression or drug addiction. Hyponatremia, coma Coma Coma is defined as a deep state of unarousable unresponsiveness, characterized by a score of 3 points on the GCS. A comatose state can be caused by a multitude of conditions, making the precise epidemiology and prognosis of coma difficult to determine. Coma, and ultimately death. Individuals with alcohol- or substance-use disorders who lose consciousness in cold environments are particularly susceptible. Treatment requires passive and active rewarming.
• Frostbite Frostbite Injuries due to cold weather are common among children and athletes who are involved in sports played in cold conditions. Frostbite is a direct freezing injury to the peripheral tissues and occurs when the skin temperature drops below 0°C (32°F). Common sites of frostbite include the nose, ears, fingers, and toes. Frostbite: a direct freezing injury to peripheral tissues that occurs when the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions temperature drops below -0.5ºC (31.1ºF). Common sites of frostbite Frostbite Injuries due to cold weather are common among children and athletes who are involved in sports played in cold conditions. Frostbite is a direct freezing injury to the peripheral tissues and occurs when the skin temperature drops below 0°C (32°F). Common sites of frostbite include the nose, ears, fingers, and toes. Frostbite include the nose Nose The nose is the human body’s primary organ of smell and functions as part of the upper respiratory system. The nose may be best known for inhaling oxygen and exhaling carbon dioxide, but it also contributes to other important functions, such as tasting. The anatomy of the nose can be divided into the external nose and the nasal cavity. Nose Anatomy (External & Internal), ears, fingers, and toes. Gangrene Gangrene Death and putrefaction of tissue usually due to a loss of blood supply. Small Bowel Obstruction may develop and severely affected tissue may autoamputate. Treatment is with rewarming and local tissue care. Surgery is sometimes necessary if necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage occurs.