Colon and Urinary Excretion - RS

Question 1

What does the pontine micturition center control? What about the suprapontine centers?

Answer 1

It controls the detrusor muscle and urinary sphincters. The suprapontine centers control the pontine micturition center providing voluntary control.

Question 2

What is destroyed if there is an atonic bladder?

Answer 2

The afferents are destroyed

Question 3

What is destroyed if there is an uninhibited neurogenic bladder?

Answer 3

The sacral nerves are destroyed. It is caused by lack of inhibitory signals from the brain

Question 4

What is the order of sphincter relaxation during micturition (when you piss)?

Answer 4

Voiding begins with voluntary relaxation of the external urinary sphincter, followed by the internal sphincter.

Question 5

What happens when a small amount of urine reaches the proximal urethra?

Answer 5

The micturition reflex continues as pontine centers no longer inhibit the parasympathetic preganglionic neurons that innervate the detrusor muscle. As a result the bladder contracts.

Question 6

What do SNS fibers do in the micturition process?

Answer 6

They inhibit contraction of the detrusor (B-adrenergic response) and stimulate contraction of the internal sphincter muscles (a-adrenergic).

Question 7

What is automatic bladder caused by?

Answer 7

Spinal cord damage above the sacral region.

Question 8

What does the gastroileal reflex do?

Answer 8

It intensifies peristalsis in the ileum and emptying of the ileal contents into the cecum.

Question 9

What does the ascending colon do?

Answer 9

Extracts water and electrolytes

Question 10

What does the transverse colon do?

Answer 10

Removes electrolytes and water

Question 11

What does the descending colon do?

Answer 11

It stores feces

Question 12

Do meals mix in the large intestine?

Answer 12

Yes they do because of the long duration it takes feces to move through the colon

Question 13

What causes constipation?

Answer 13

Poor motility which leads to greater absorption of liquids and hard feces.

Question 14

What causes diarrhea? What about osmotic diarrhea? How about secretory diarrhea?

Answer 14

The rapid movement of fecal matter through the large intestine. Osmotic results from non-absorbable solutes in the lumen (e.g. lactase deficiency). Secretory results from excessive secretion of fluids by crypt cells due to bacterial overgrowth (e.g. cholera toxin)

Question 15

What are common causes of diarrhea?

Answer 15

bacterial infections, viral infections, food intolerances, parasites, intestinal diseases, reactions to meds, functional bowel disorders, psychogenic factors, long distance running

Question 16

What is the function of the ileocecal sphincter?

Answer 16

It prevents backflow from colon to ileum; emptying is regulated by stretch, composition & fluidity of chyme

Question 17

How is the colon epithelium distinct from that in the small intestine?

Answer 17

The colon performs both absorptive and secretory functions. The colon lacks the numerous villi and folds that characterize the small intestine it contains numerous crypts of invaginations of the epithelium. It contains solitary lymphatic nodules but few or no Peyer’s patches. It has mucus secreting goblet cells and columnar absorptive cells.

Question 18

What does the colon absorb? What does it secrete?

Answer 18

Absorbs Na+, Cl- and H20.
Secretes K+ and HCO3-
Major exchanges occur in the ascending and transverse colon

Question 19

Are tight junctions “tighter” in the large intestine?

Answer 19

Yes! They offer a greater resistance to fluid flow through the paracellular pathway than the small intestine. This prevents back-diffusion of ions and allows more complete absorption of Na+

Question 20

How is Na+ actively absorbed by the large intestine?

Answer 20

Na-H and Cl-HCO3 exchange is coupled by a change in intracellular pH that results in “electroneutral NaCl absorption” which is the primary mechanism for interdigestive Na+ absorption

Question 21

What causes mass movement in the large intestine?

Answer 21

The gastrocolic reflex.

Question 22

How is motility characterized in the large intestine?

Answer 22

Slow segmental propulsion, segmental mixing, and mass movements (motility is sluggish compared to the small intestine)

Question 23

What is Hirschsprung’s disease?

Answer 23

Also called megacolon it is present at birth. It results from a lack of ENS in the distal part of the GI tract. The aganglionic segment is tonically contracted due to lack of inhibitory motor neuron function. Surgery removes the agonglionic portion and often results in normal fecal excretion. (t is analogous to the aganglionosis in the esophagus. Acholasia in the esophagus.)

Question 24

What composes flatus?

Answer 24

Swallowed air, bacterial action, and diffusion from blood

Question 25

What is irritable bowel syndrome?

Answer 25

A common GI disorder that leads to crampy pain, bloating, gassiness, and altered bowel habits. There is not cure but you can treat the symptoms

Question 26

What is the defecation (rectosphincteric) reflex?

Answer 26

It is triggered by distension of the rectum by feces. Mechanoreceptors sense the pressure and activate the myenteric nerves, impulses are sent to relax in the internal sphincter. The urge signal is sent to the brain and reflex actions cause the voluntary contraction of the external anal sphincter until defecation occurs.

Question 27

What controls the act of defecation?

Answer 27

The cerebral cortex through connections in the spinal cord

Question 28

The intrinsic myenteric defecation reflex functioning by itself is normally weak, what else aids this reflex?

Answer 28

To be effective in causing defecation it is fortified by another type of defecation reflex, a parasympathetic defecation reflex that involves the sacral segments of the spinal cord