The rectum and anal canal are the most terminal parts of the lower GI tract/ large intestine Large intestine The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix: Anatomy that form a functional unit and control defecation Defecation The normal process of elimination of fecal material from the rectum. Gastrointestinal Motility. Fecal incontinence Fecal incontinence Failure of voluntary control of the anal sphincters, with involuntary passage of feces and flatus. Pediatric Constipation can occur if this function is disturbed. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis Puborectalis Vagina, Vulva, and Pelvic Floor: Anatomy muscle, and internal and external anal sphincters. Peristaltic waves within the rectal muscularis, involuntary relaxation of the internal anal sphincter (controlled by the ANS ANS The 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), and voluntary relaxation of the external anal sphincter (controlled by the cerebral cortex Cerebral cortex The 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) are essential for defecation Defecation The normal process of elimination of fecal material from the rectum. Gastrointestinal Motility to occur. The rich plexus of veins Veins Veins 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 surrounding the anal canal can develop into hemorrhoids Hemorrhoids Hemorrhoids are normal vascular cushions in the anal canal composed of dilated vascular tissue, smooth muscle, and connective tissue. They do not cause issues unless they are enlarged, inflamed, thrombosed, or prolapsed. Patients often present with rectal bleeding of bright red blood, or they may have pain, perianal pruritus, or a palpable mass. Hemorrhoids if dilated.
Last updated: 3 May, 2022
The rectum is the most posterior visceral organ in the pelvic cavity.
Anatomy of the internal female pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy
Image by BioDigital, edited by LecturioAnatomy of the internal male pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy
Image by BioDigital, edited by LecturioSimilar to other segments of the GI tract, the layers of the anorectal wall (from the inner lumen outward) are mucosa → submucosa → muscular layer → serosa. There are no villi or circular folds Circular folds Small Intestine: Anatomy in the anorectal wall like those in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy.
Histological image of the rectal mucosa (longitudinal section):
Rectal crypts with simple columnar
epithelium
Epithelium
The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions.
Surface Epithelium: Histology are visible and the stroma (
lamina propria
Lamina propria
Whipple’s Disease) is seen wrapping around the crypts.
Made up of 2 layers of smooth muscle:
Differences in anal neurovasculature above and below the pectinate line:
IMA:
inferior mesenteric artery
Inferior mesenteric artery
The artery supplying nearly all the left half of the transverse colon, the whole of the descending colon, the sigmoid colon, and the greater part of the rectum. It is smaller than the superior mesenteric artery and arises from the aorta above its bifurcation into the common iliac arteries.
Small Intestine: Anatomy
IMV
IMV
Invasive mechanical ventilation (IMV) is an advanced airway modality used for individuals with immediate or impending respiratory failure and/or in preparation for surgery. The IMV technique involves positive pressure ventilation delivered to the lungs through an endotracheal tube via a ventilator.
Invasive Mechanical Ventilation: inferior mesenteric vein
LN:
lymph
Lymph
The interstitial fluid that is in the lymphatic system.
Secondary Lymphatic Organs node
IVC
IVC
The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs.
Mediastinum and Great Vessels: Anatomy:
inferior vena cava
Inferior vena cava
The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs.
Mediastinum and Great Vessels: Anatomy
The primary roles of the rectum and anal canal involve controlled defecation Defecation The normal process of elimination of fecal material from the rectum. Gastrointestinal Motility.
The rectum contains stretch receptors Stretch receptors Stretch receptors found in the bronchi and bronchioles. Pulmonary stretch receptors are sensors for a reflex which stops inspiration. In humans, the reflex is protective and is probably not activated during normal respiration. Respiratory Regulation that stimulate the defecation Defecation The normal process of elimination of fecal material from the rectum. Gastrointestinal Motility reflex when the rectum begins to fill with feces.
Defecation
Defecation
The normal process of elimination of fecal material from the rectum.
Gastrointestinal Motility reflex:
1. Feces stretch the rectum and stimulate the
stretch receptors
Stretch receptors
Stretch receptors found in the bronchi and bronchioles. Pulmonary stretch receptors are sensors for a reflex which stops inspiration. In humans, the reflex is protective and is probably not activated during normal respiration.
Respiratory Regulation, transmitting the signal to 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.
2. A spinal reflex sends parasympathetic
motor
Motor
Neurons which send impulses peripherally to activate muscles or secretory cells.
Nervous System: Histology signals to the myenteric nerve plexus, resulting in contraction of the
smooth muscles
Smooth muscles
Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant.
Muscle Tissue: Histology within the rectum, pushing feces downward.
3. The same spinal reflex also sends parasympathetic
motor
Motor
Neurons which send impulses peripherally to activate muscles or secretory cells.
Nervous System: Histology signals to relax the internal anal sphincter.
4. Voluntary impulses from 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 prevent
defecation
Defecation
The normal process of elimination of fecal material from the rectum.
Gastrointestinal Motility by keeping the external anal sphincter contracted.
Defecation
Defecation
The normal process of elimination of fecal material from the rectum.
Gastrointestinal Motility will occur if voluntary signals allow the external anal sphincter to relax.