Anatomy of the Large Intestine

The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid. The prostate consists of multiple lobes and is made up of glandular and fibromuscular tissue. The glandular tissue has ducts that empty into the prostatic portion of the urethra, and the fibromuscular tissue encircles the urethra.

The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal incontinence 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 muscle, and internal and external anal sphincters. Peristaltic waves within the rectal muscularis, involuntary relaxation of the internal anal sphincter (controlled by the ANS), and voluntary relaxation of the external anal sphincter (controlled by the cerebral cortex) are essential for defecation to occur. The rich plexus of veins surrounding the anal canal can develop into hemorrhoids if dilated.

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. The colon also contains many mucus-secreting glands to lubricate the stool passing through it. The colon receives its blood supply from colic branches of the superior and inferior mesenteric arteries, which form an important anastomosis along the transverse colon. The colon is regulated by the ANS and receives both sympathetic (inhibitory) and parasympathetic (stimulatory) input.