GI: Physiology of GIT

Question 1

Function of the GI tract

Answer 1

Injestion, secretion, mixing, digestion, absorption and excretion

Question 2

Layers of the GI tract (out to in)

Answer 2

Mucosa (epithelium, NAV), submucosa (loose CT), muscularis (circular and longitudinal), serosa (peritoneum)

Question 3

What are villi used for

Answer 3

Absorption

Question 4

What are crypts used for

Answer 4

Secretion. ECF released into lumen, water follows. (Fluid derived from plasma)

Question 5

What is involved in the coordination if GI tract?

Answer 5

Nervous system, local (physical stretch or chemical), hormone

Question 6

Difference between enteric nervous system and ANS

Answer 6

• Enteric, short reflexes, communications in the gut.
• Enteric signals go up to CNS and become ANS. (long reflexes)

Question 7

Stomach motility stimulation and inhibition

Answer 7

Stimulated by stomach distension and peptides
Inhibited by dudodenal lumen, high peptides, high pressure, high osmolarity, low pH and high fat

Question 8

Process of stomach motility/ contractions

Answer 8

Meal-> acetylcholine + gastrin -> High threshold -> stomach contracts

Slow wave contractions (3-4mins)

Question 9

1. Cephalic phase (seeing food)

Answer 9

Release gastrin. Chief cells to pepsinogen and parietal cells to HCL.

Question 10

Phases of gut secretions

Answer 10

Cephalic phase, gastric phase, intestinal phase

Question 11

2. Gastric phase (food in stomach)

Answer 11

Through stretch receptors. Gastrin release, peptides stimulate gastrin release.

Question 12

Parietal cell secretions

Answer 12

Secretes HCl.
Stimulation: Vagus, Gastric, Histamine
Inhibition: Somatostatin + Low pH

Question 13

Alkaline tide

Answer 13

HCO3- by pancreas into duodenum to neutralize stomach H+ from stomach.

Question 14

What is the pancreatic mucus secretion used for

Answer 14

Protective layer against stomach acids

Question 15

How are the sphincters of the of the GIT controlled?

Answer 15

Controlled by enteric NS/ stretch (except external anal sphincter) and regulated by stretch. Found between each organ.

Question 16

Causes of vomiting (3)

Answer 16

Physiology, drugs and chemicals (through chemical trigger zone) and pathology

Question 17

Stages of vomiting (6)

Answer 17

1. Postural adaptation
2. Saliva stimulated (protect against acidity)
3. Respiratory (inspiration inhibited), glottis closed, larynx raised, increased SP
4. Diaphragm + abdominal muscles contract
5. High intragastric pressure, retching
6. Lower oesophageal sphincter relaxes, gastric contents expelled.

Question 18

3. Intestinal phase (What is secreted?)

Answer 18

Parietal cell secretions and mucus secretions

Question 19

What controls salivary secretion?

Answer 19

Complete neural control

Question 20

What comprises enteric NS? (2 nerve plexuses)

Answer 20

• Myenteric plexus (sensory, found btw and regulates muscles)
• Submucosal plexus (regulates mucosal gland secretions)

Question 21

Gastrin

Answer 21

Stimulation of HCl production and supports growth of mucosa. (distal stomach)

Question 22

Secretin

Answer 22

Stimulates production of bicarbonate by pancreas and Brunner’s glands. (duodenum)

Question 23

Cholecystokinin (CCK)

Answer 23

Stimulates enzyme production in pancreas and gall bladder by contraction. (duodenum)

Question 24

Gastric inhibitory polypeptide (GIP)

Answer 24

Reduces HCl production and stomach emptying. Stimulates insulin release. (Proximal small bowel)

Question 25

Somatostatin

Answer 25

Reduces acid secretion, gastric motility and stomach emptying. (intestines and pancreas)

Question 26

Leptin

Answer 26

Stimulates satiety

Question 27

Ghrelin

Answer 27

Stimulates feeding centre

Question 28

Peptide YY (PYY)

Answer 28

Stimulates satiety, inhibits eating.

Question 29

Small intestine function

Answer 29

Secretes fluid, mucus and HCO3- (from Brunner's glands)

Question 30

S.intestine motility (2)

Answer 30

- Segmentation: Alternating contractions, squeezing back and forth to mix - Peristalsis: Initiated at a point, contraction of circular muscles on oral side and relaxing on aboral side.

Question 31

Control of s.intestine motility

Answer 31

- Local distension, enteric peristalsis - Extrinsic: parasymp increase, sympathetic decreases

Question 32

Standing- gradient osmosis (how water is absorbed)

Answer 32

- Dependent on Na+ - Pump Na/Cl into lateral space between cells. Water follows - Pressure build and pushed out into tissue

Question 33

L. intestine function

Answer 33

- Absorbs remaining water and Na, vitamins produced by commensal bacteria, eliminates metabolic waste, etc.

Question 34

What happens in the rumen? (Carb and proteins) (2)

Answer 34

- Anaerobic bacteria fermenting carbs into short chain fatty acids - Microbes use ammonia (by-product) for protein. Flushed through, protein from dead bacteria

Question 35

Reticuloruminal motility

Answer 35

2nd rumenal wave - Antiperistalsis and eructation voided through nares

Question 36

Primary ruminal contractions

Answer 36

- Rumen fill = strength of mixing - Peristaltic to reticulum

Question 37

Secondary ruminal contractions

Answer 37

- Eructation of gas - Anti-peristaltic and follows half of primary ruminal contractions

Question 38

What do the Short chain fatty acids become? (Ruminant digestion)

Answer 38

Acetate > Proprionate > Butyrate (and ketone bodies)

Question 39

Acetate, proprionate or butyrate; which one directly produces glucose

Answer 39

Propionate

Question 40

Lactation ketosis

Answer 40

Ketone bodies replace glucose due to high energy demand and low oxaloacetates in Krebbs. - Acetyl-CoAs diverted to produce ketone bodies - Very acidic conditions

Question 41

Grain overload

Answer 41

- High fermentation rate, acidic rumen, high lactate, lactophiles thrive - High rumen osmolarity, low BP and dehydration - Renal and respiratory comprimise + metabolic acidosis.

Question 42

Uses of saliva (ruminant)

Answer 42

- pH buffer - plant wetting agent - anti-frothing proteins (to prevent bloat)

Question 43

Salivary glands (4)

Answer 43

Parotid, mandibular, zygomatic and sublingual

Question 44

Control of saliva

Answer 44

Parotid and sublingual nerve + food :)

Question 45

Chemical compound that provides energy when there isn't enough glucose (result of ketosis)

Answer 45

B-hydroxybutyrate