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: Sep 18, 2023
The rectum is the most posterior visceral organ in the pelvic cavity.
Similar 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.
Made up of 2 layers of smooth muscle:
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.
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