P9 Evacuation and fluid and electrolyte absorption.pdf

Question 1

What are the functions of the Colon?

Answer 1

1. Storage of Liquid chyme from ileum
2. Absorption of water and electrolytes
3. Providing a site for bacterial action
4. Expulsion of semisolid stool.

Question 2

Describe how the colon provides a site for bacterial action?

Answer 2

Colonic microflora catabolizes polysaccharides from food to short-chain FAs that are absorbed by the colon

Question 3

Describe the physiology of lactose intolerance

Answer 3

when lactose can’t be digested well in the small intestine, it passes into the colon. Bacteria in the colon break down some of the lactose, producing gas. The remaining lactose also draws water into the colon. The extra gas and water result in bloating and diarrhea

Question 4

What is the colonic micro-flora capable of digesting?

Answer 4

1. Lactose
2. Bilirubin
3. Bile acids
4. Fibers

Question 5

What triggers the relfex that empties the ileum?

Answer 5

distension of the ileum, this reflex is done by the enteric system

Question 6

Emptying at the ileo-ceacal valve

Answer 6

Distension of ileum is sensed by mechanoreceptors

Question 7

What events follow distension of the ceum

Answer 7

distension of cecum causes a negative feedback response that activats ENS to cause a decrease in ileal peristalsis and closure of ileocecal valve, to prevent more emptying into the cecum.

Question 8

What hormones play a role in opening of ilieocecal valve?

Answer 8

Gastrin + CCK combined with effects of ANS/ENS initated opening of valve and emptying of ileum

Question 9

What factors in the ileum promote emptying?

Answer 9

Fluidity of contents

Question 10

What factors in the ileum relax the sphincter and excite peristalsis?

Answer 10

Pressure and Chemical Irritatants

Question 11

What factors in the cecum excites the sphincter and inhibit peristalsis?

Answer 11

Pressure and Chemical irritants

Question 12

What role does the gastroileal reflex play in emptying of ileocecal valve?

Answer 12

1. it intensifies peristalsis in the ileum
2. promotes opening of the sphincter
3. emptying at the ileocecal valve

Question 13

Autonomic Innervation of the Colon

Answer 13

Parasympathetic stimulation increase motility while sympathetics inhibit motility

Question 14

Parasympathetic innervation to colon

Answer 14

1. Proximal colon [ascending + Proximal 2/3 of transverse]: Vagus nerve
2. Distal colon [Distal 1/3 of transverse + ascending]: Pelvic nerve

Question 15

Sympathetic innervation to the Colon

Answer 15

1. Proximal colon [ascending + Proximal 2/3 of transverse]: Superior mesenteric plexus
2. Distal colon [Distal 1/3 of transverse + ascending]: Inferior mesenteric + Superior Hypogastric plexus

Question 16

What reflex goes through the spinal cord?

Answer 16

defecation reflex

Question 17

What reflexes go through the ANS/ENS?

Answer 17

1. Enterogastric
2. Gastrocolic
3. Gastroileal
4. Colonoileal

Question 18

enterogastric reflex

Answer 18

signals from small intestine inhibit gastric emptying.

Question 19

gastrocolic reflex

Answer 19

signals from stomach elicit motility of colon

Question 20

gastroileal reflex

Answer 20

increased gastric activity induces motility and emptying of ileum

Question 21

colonoileal reflex

Answer 21

signals from colon to inhibit emptying of small intestine into colon

Question 22

Mixing movements of the colon?

Answer 22

Haustrations

Question 23

Propulsive movements of the colon

Answer 23

Mass Peristalsis

Reverse peristalsis

Question 24

What are Haustrations?

Answer 24

1. Contractions of inner circular muscles, which mainly occur at teniae coli. Haustrations are the result of structural and functional properties of the colon.
2. occur is cecum + entire colon

Question 25

What is Mass peristalsis?

Answer 25

strong peristalsis which directed aborally, occur several times a day in cecum and entire colon

Question 26

Reverse peristalsis

Answer 26

orally directed which gives more time to the fecal matter to be exposed for water absorption.

Question 27

Normal amouns of mass movements in colon?

Answer 27

1-3 times/day

Question 28

Normal amount of haustrations is proximal colon?

Answer 28

• major contraction of this segment
• lasts for 10 to 60 seconds at pressures between 10 to 50 mmHg

Question 29

role of Haustrations in proximal and distal colon

Answer 29

1. Proximal: propulsive [10-60s at 10-50 mmHg]
2. Distal: resistance to propulsion [stronger and more frequent segmental contractions]

Question 30

What four factors affect the motility of the colon?

Answer 30

1. Properties of smooth muscles [exhibit slow waves]
2. ENS [responsible for peristaltic reflex+ haustration]
3. ANS [modulatory effects, colonic reflex gave pathways in extrinsic nerves]
4. Hormones [Gastrin + CCK increase activity, while Epinephrine inhibits it]

Question 31

What pathology may cause diverticula and how?

Answer 31

Constipation, as it may lead to increased intra-colonic pressure

Question 32

Mechanism of diarrhea

Answer 32

inflammation irritates the colonic mucosa, thus the rate of secretion and motility increases rapidly

Question 33

What enhances the absorption of Na in the small intestines?

Answer 33

sugar and amino acids

Question 34

absorption of Na in small intestines

Answer 34

1. Na-H exchanger [apical side], Na-K+ ATPase [basal side]
2. Paracellularly

Question 35

absorption of K+ in small intestines

Answer 35

absorbed by passive diffusion

secreted when lumenal level is below 25mM

Question 36

secretion of HCO3- in small intestines

Answer 36

Via HCO3-/Cl- exchanger