Chapter 23: The Small and Large Intestine

What is the main function of the small intestine?

Digestion and absorption

What does the length and structural modifications of the small intestine provide for the body?

Huge surface area for nutrient absorption

What are the three modifications of the small intestine, and describe each one

1. Circular Folds: force chyme to slowly spiral through lumen allowing more time for full nutrient absorption

2. Villi: has lymphatic capillaries lacteal for absorption

3. Microvilli: brush boarder containing brush boarder enzymes used for carbohydrates and protein digestion

What in the small intestine has a brush boader containing brush boarder enzymes used for carbohydrates and protein digestion?

Microvilli

What in the small intestine have lacteals for absorption?

Villi

What in the small intestine forces chyme to slowly spiral through lumen allowing more time for full nutrient absorption?

Circular folds

What are the cells found in the villi and crypts and describe each one

1. Enterocytes: bound by tight junctions and the villi absorbs nutrients/electrolytes and crypts produce intestinal juice

2. Goblet Cells: mucus secreting cells

3. Enteroendocrine cells: source of enterogastrones (CCK and secretin)

4. Paneth Cells: secrete antimicrobial agents (defensins &lysozyme)

5. Stem Cells: dive to produce other cells

How does MALT protect intestine against microorganisms?

The lamina propria due to the secretion of IgA and the peyer's patch where many microbes are found in the distal part of small intestine

What does the duodenal glands secrete?

Alkaline mucous to neutralize acidic chyme

Describe the characteristics and composition of intestinal juice

- 1-2 L secreted daily due to distension or irritation of mucosa.

- major stimulus for production is hypertonic or acidic chyme

- Alkaline and isotonic w/ blood plasma

- Consists of water and mucus that is secreted by duodenal glands and goblet cells

How is the mucus in the intestinal juice secreted?

By the duodenal glands and goblet cells

What is the major stimulus for intestinal juice to be produced?

Hypertonic or acidic chyme

What is the digestive process like in the small intestine?

Chyme from the stomach contains partially digested carbohydrates, proteins and undigested fats. Takes 3-6 hrs for small intestine to absorb all nutrients and water

What binds to the plasma membrane to perform final digestion of chyme?

Brush boarder enzymes

Which enzymes are imported from the liver and pancreas for digestion?

Bile, Bicarbonate and Digestive enzymes (NOT brush boarder enzymes)

When chyme enters the duodenum it is usually ______.

Hypertonic

Why does the delivery of chyme need to be slow?

To prevent osmotic loss of water from blood & the low pH of chyme must be adjusted upward

What does chyme need to be mixed with?

Bile and pancreatic juice to continue digestion

What does the Enterogastric reflex and Enterogastrones control and prevent

Control movement of food into duodenum and prevent duodenum from being overwhelmed

What is the motility of the small intestine after a meal?

Segmentation is initiated by _____ pacemaker cells and mixes/moves content toward _____ valve making intensity alter by ____ and ____ reflexes and hormone.

intrinsic, ileocecal, long, and short

How does the parasympathetic affect motility?

Enhances motiltiy

How does the sympathetic affect motility?

Decreases motility

What is the motility of the small intestine between meals?

Peristalsis _____ by the rise in hormone ____. Each wave starts ____ (migrating motor complex) and meal remnants, bacteria and debris move toward ______

increases, motilin, distally, large intestine

What happens in the ileocecal valve control?

- Ileocecal sphincter relaxes and admits chyme into lg intestine when gastroileal reflex enhances force of segmentation in ileum and when gastrin increases motility of ileum.

- Then ileocecal valve flaps close when chyme exerts backward pressure preventing regurgitation into ileum

When does the ileocecal sphincter relax and admit chyme into the large intestine?

When gastroileal reflex enhances force of segmentation in ileum and when gastrin increases motility of ileum.

When does the ileocecal valve flaps close?

When chyme exerts backward pressure preventing regurgitation into ileum

What are the unique features of the large intestine?

- Teniae coli (longitudinal smooth muscle)

- Haustra (sacs caused by tone of teniae coli)

- Epiploic appendages (fat patches of viceral peritoneum)

What is the first part of the large intestine?

Cecum

What is part of the MALT of immune system and considered a bacterial storehouse that is capable of recolonizing the gut?

The Appendix

What is the appendix?

Masses of lymphoid tissue, twisted shape of appendix makes it susceptible to blockages

The colon is retroperitoneal except for which regions?

Transverse and sigmoid parts

Describe the ascending colon

Travels up right side of abdominal cavity by the right kidney and ends at the right colic (hepatic) flexure

Describe the transverse colon

Travels across addominal cavity and ends at the left colic (splenic) flexture

Where does the sigmoid colon travel through?

The pelvis

The cecum, appendix, and rectum are all ________.

Retroperitoneal

The intraperitoneal regions are anchored to posterior abdominal wall by what?

Mesentery sheets called mesocolons

What is Appendicitis?

Acute inflammation of appendix, resulting form blockage by feces that traps infectious bacteria

- common in adolescence

- entrance to appendix is widest

What does the large intestine NOT contain?

circular folds, villi, or digestive enzymes

(only small intestine has these)

What is anal recesses?

secretes mucus to aid in emptying

In the pectinate line, visceral sensory nerves innervate superior to this line causing the region to be _________ to pain.

Insensitive

In the pectinate line, somatic sensory nerves innervate inferior to this line causing the region to be _________ to pain.

sensitive

What does the superficial venous plexus of anal canal form if inflamed?

Hemorrhoids

Where does bacterial flora enter from?

The small intestine or anus to colonize colon

What are the metabolic function of bacterial flora?

Fermentation and Vitamin synthesis

- fermentation: ferment indigestible cho and mucin releasing irritant acids and gases

- vitamin synthesis: synthesizes vitamin b and vitamin k

Describe fermentation in the bacterial floral?

Ferments indigestible carbohydrates, mucin & release irritating acids and gases

Describe vitamin synthesis in bacterial flora?

Synthesizes vitamin B and vitamin K needed by the liver to produce clotting proteins

What is needed by the liver to produce clotting factors?

Vitamin B and Vitamin K

How does bacterial flora keep pathogenic bacteria in check?

Immune system destroys bacteria trying to breach mucosal barrier. Epithelial cell recruit dendritic cells and present antigens to T cells triggering production of IgA that restricts microbes

What is the digestive process in the large intestine?

Residue remains for 12-24 hrs, no food breakdown occurs except when enteric bacteria digest. Vitamins, water, electrolytes (Na+ , Cl-) are reclaimed

What is the major function of the large intestine?

Propulsion of feces to anus and defecation

What are haustral contractions?

Contract in response to distension, slow segmenting movements are in the ascending and transverse colon

What is Gastrocolic Reflex?

initiated by presence of food in stomach, results in mass movements of peristaltic waves that are activated 3-4/day

What part of the large intestine acts as a storage reservoir?

Descending and Sigmoid colon

During defecation, distension initiates what?

Spinal defecation reflex

During defecation, what does the parasympathetic signals do?

Stimulate contraction of sigmoid colon and rectum to relax internal anal sphincter

During defecation, conscious control allows what?

Relaxation of external anal sphincter

What is Valsalva's maneuver?

closing of glottis, contraction of diaphragm and abdominal wall muscles increase intra abdominal pressure and levator ani muscle contracts. causing anal canal lifted and feces leave the body

What is Diarrhea?

Watery stool, results when large intestine does not have sufficient time to absorb remaining water.

- causes irritation of colon by bacteria, prolonged diarrhea may be from dehydration and electrolyte imbalance

What is Constipation?

When food remains in colon for extended periods of time and too much water is absorbed

- stool becomes hard and difficult to pass, result from insufficient fiber or fluid in diet, laxative abuse and improper bowel movements