PSYC340 Study Guide - Final Guide: Cystic Duct, Lactose Intolerance, Osmosis
24 Jun 2018
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1. Describe the location, anatomy, histology and functions of the large intestine.
A. Large intestine - The large intestine is the terminal portion of the GI tract. The
overall functions of the large intestine are the completion of absorption, the
production of certain vitamins, the formation of feces, and the expulsion of feces
from the body.
A.I. 1. Haustral churning, peristalsis, and mass peristalsis drive contents of
colon into rectum.
A.II. 2. Bacteria in large intestine convert proteins to amino acids, break down
amino acids, and produce some B vitamins and vitamin K.
A.III. 3. Absorption of some water, ions, and vitamins.
A.IV. 4. Formation of feces.
A.V. 5. Defecation (emptying rectum
A.VI. Anatomy
A.VII. Cecum - The opening from the ileum into the large intestine is guarded by
a fold of mucous membrane called the ileocecal sphincter (valve), which
allows materials from the small intestine to pass into the large intestine.
Hanging inferior to the ileocecal valve is the cecum, a small pouch about 6
cm
A.VIII. Appendix or vermiform appendix - Attached to the cecum is a twisted,
coiled tube, measuring about 8 cm (3 in.) in length, called the appendix or
vermiform appendix
A.IX. Colon - The open end of the cecum merges with a long tube called the
colon, which is divided into ascending, transverse, descending, and sigmoid
portions. Both the ascending and descending colon are retroperitoneal; the
transverse and sigmoid
colon are not.
A.X. Ascending colon - the ascending colon ascends on the right side of the
abdomen, reaches the inferior surface of the liver, and turns abruptly to the
left to form the right colic (hepatic) flexure
A.XI. Transverse colon/Descending colon
The colon continues across the abdomen to the left side as the transverse
colon. It curves beneath the inferior end of the spleen on the left side as
the left colic (splenic) flexure and passes inferiorly to the level of the iliac
crest as the descending colon.
A.XII. Sigmoid colon
A.XIII. The sigmoid colon begins near the left iliac crest, projects medially to the
midline, and terminates as the rectum at about the level of the third
sacral vertebra.
A.XIV. Rectum
A.XV. The rectum is about 15 cm (6 in.) in length and lies anterior to the sacrum
and coccyx
A.XVI. Anal canal - The terminal 2–3 cm (1 in.) of the large intestine is called the
anal canal
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A.XVII. Anal columns - The mucous membrane of the anal canal is arranged in
longitudinal folds called anal columns that contain a network of arteries and
veins.
A.XVIII. Anus/ Internal anal sphincter/External anal sphincter
A.XIX. The opening of the anal canal to the exterior, called the anus, is guarded
by an internal anal sphincter of smooth muscle (involuntary) and an
external anal sphincter of skeletal muscle (voluntary). Normally these
sphincters keep the anus closed except during the elimination of feces.
A.XX. Histology
A.XX.a. Mucosa
A.XX.b.The mucosa consists of simple columnar epithelium, lamina
propria (areolar connective tissue), and muscularis mucosae (smooth
muscle)
A.XX.c. The absorptive cells function primarily in water absorption; the
goblet cells secrete mucus that lubricates the passage of the colonic
contents. Both absorptive and goblet cells are located in long, straight,
tubular intestinal glands (crypts of Lieberkühn) that extend the full
thickness of the mucosa.
A.XX.d.Solitary lymphatic nodules are also found in the lamina propria of
the mucosa and may extend through the muscularis mucosae into the
submucosa.
A.XX.e. Compared to the small intestine, the mucosa of the large intestine
does not have as many structural adaptations that increase surface area.
There are no circular folds or villi; however, microvilli are present on the
absorptive cells. Consequently, much more absorption occurs in the small
intestine than in the large intestine
A.XX.f. Submucosa - The submucosa of the large intestine consists of
areolar connective tissue.
A.XX.g. Muscularis - The muscularis consists of an external layer of
longitudinal smooth muscle and an internal layer of circular smooth muscle
A.XX.h. Teniae coli - Unlike other parts of the GI tract, portions of the
longitudinal muscles are thickened, forming three conspicuous bands called
the teniae coli that run most of the length of the large intestine. The teniae
coli are separated by portions of the wall
with less or no longitudinal muscle
A.XX.i. Haustra (singular is haustrum)
A.XX.j. Tonic contractions of the bands gather the colon into a series of
pouches called haustra give the colon a puckered appearance
A.XX.k. Serosa - A single layer of circular smooth muscle lies between
teniae coli. The serosa of the large intestine is part of the visceral
peritoneum.
A.XXI. Mechanical digestion
A.XXI.a. Gastroileal reflex - Immediately after a meal, a gastroileal reflex
intensifies peristalsis in the ileum and forces any chyme into the cecum. The
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Document Summary
Describe the location, anatomy, histology and functions of the large intestine, large intestine - the large intestine is the terminal portion of the gi tract. The overall functions of the large intestine are the completion of absorption, the production of certain vitamins, the formation of feces, and the expulsion of feces from the body. Cecum - the opening from the ileum into the large intestine is guarded by a fold of mucous membrane called the ileocecal sphincter (valve), which allows materials from the small intestine to pass into the large intestine. Hanging inferior to the ileocecal valve is the cecum, a small pouch about 6 cm. Appendix or vermiform appendix - attached to the cecum is a twisted, coiled tube, measuring about 8 cm (3 in. ) in length, called the appendix or vermiform appendix. Colon - the open end of the cecum merges with a long tube called the colon, which is divided into ascending, transverse, descending, and sigmoid portions.
