lecture 25

Question 1

define secretion and absorption

Answer 1

secretion is the movement of solutes and water from the body into the lumen.
absorption is the movement of solutes and fluid into the body

Question 2

what are the three components of exocrine secretion in the GI tract

Answer 2

mucous, protection and lubrication of tissues and aids in mechanical digestion
digestive enzymes: these do chemical digestion and help absorption
electrolyte solute: dilutes food, provides optimal pH for enzymes, also aids chemical digestion

Question 3

about how much do we secrete a day, why don’t we die 2

Answer 3

we secrete about 8 litres a day, but we reabsorb most. whats lost in urine is replaced with drinking water

Question 4

how much is secreted from the salivary glands in each state and what are the components

Answer 4

about 1.5L, basal is 0.3ml/min 1.5ml/min when stimmed
made of digestive enzymes like amylase, has bicarbonate solution to provide optimal pH for enzymes, has mucous for taste, lubrication and protection

Question 5

functions of salivary secretions

Answer 5

aids in chewing, talking and swallowing as lubrication.
helps in hygiene as it irritates bacteria out of mouth when swallowed
also luminal digestion using lingual lipase and alpha amylase

Question 6

what are the 2 regulation methods of salivary secretion, describe

Answer 6

CNS regulation. producing saliva when we receive external signal of food, or when food is in mouth
PNS causes secretion of more saliva
SNS causes secretion of a viscous fluid in small volumes to augment the PNS response

Question 7

how much secretion is in stomach and whats the basal secretion like

Answer 7

2-3L per day. in a fasting basal state we have slow secretion, mostly just gastric pit cells secreting mucous and bicarbonate

Question 8

whats secretion like in the stomach when eating

Answer 8

this is above and beyond the basal level
surface epithelial cells secrete mucous and bicarb. parietal cells secrete the HCl and intrinsic factor to help B12 absorption
chief cells do pepsinogen

Question 9

what activates pepsinogen

Answer 9

the HCl in the stomach

Question 10

what is our source of H+

Answer 10

in the parietal cells carbonic anhydrase does:
CO2 + H2O –> H2CO3
H2CO3 then dissociates into
H+ and HCO3-

Question 11

outline the four steps of HCl secretion in the parietal cells

Answer 11

1 carbonic anhydrase makes HCO3- and H+
2 secretion of H+ using H+/K+ ATPase
3 source of chloride
4 secretion of chloride

Question 12

in secretion of HCl outline steps 3 and 4

Answer 12

3: source of chloride. uses anion counter transporter, serosal membrane of cell ejects HCO3- and imports Cl-
4: secretion of chloride. Cl- diffuses across cell, Cl- enters lumen via channel of the apical membrane

Question 13

what are the three phases of gastric secretion

Answer 13

cephalic secretion- CNS controlled
gastric secretion- stomach control
intestinal secretion - intestine control

Question 14

describe the cephalic phase

Answer 14

this is 20% of gastric secretions, this involves preparation for food arrival. the CNS will start secretions with stimuli of thought, smell, sight of food. chewing and taste will also stimm. in prep for food the extrinsic PNS will act via the enteric nervous system. this stimulates parietal, chief and goblet cells.
this PNS stimulation will also stimulate secretion of gastrin into the blood, which stimulates the parietal and chief cells.

Question 15

what is function of the gastric phase and how much secretion does it do?

Answer 15

70% of the secretions associated with a meal, this phase ensures there is enough secretions in the stomach to handle the ingested food.

Question 16

stimuli for the gastric phase of stomach secretions

Answer 16

stretch and distension of the stomach wall due to presence of food. having products of digestion in the lumen and, elevated PH of the stomach

Question 17

what are the regulations of the gastric phase what do they do?

Answer 17

enteric nervous system in a local reflex, long reflex with the PNS. both stimulate secretion of gastric glands, motility and gastrin secretion- which further stimulates secretion and motility

Question 18

how much and what it do- intestinal phase

Answer 18

its about 10% of gastric secretions, this phase serves to control the delivery of chyme into the small intestine

Question 19

stimuli for the intestinal phase of secretions in stomach

Answer 19

distenstion of the duodenum, also the arrival of acidic chyme and lipids and carbs in the small intestine

Question 20

what are the hormones release in the intestinal phase secreted in response to

Answer 20

secretin is released in response to decreased PH
CCK and GIP are released in response to lipid and carb presence in SI lumen

Question 21

what are the regulators of intestinal phase of gastric secretions

Answer 21

CCK, secretin and GIP. enterogastric reflex as well- duodenum to stomach to brain.
both regulate motility and gastric secretions

Question 22

how much and what does the pancrease secrete

Answer 22

1-1.5L per day secreting alkaline solution (duct cells make bicarb to neutralise acid and give good PH for enzymes), we also have enzyme secretion from acinar cells

Question 23

whats the secretory stimulation for pancreatic enzymes

Answer 23

secretion of digestive enzymes is stimulated by CCK. which itself is stimulated by carbs and lipids into duodenum

Question 24

hwo do we activate the proteolytic enzymes

Answer 24

the activation occurs in the small intestine using membrane bound enterokinase. this enterokinase converts trypsinogen to trypsin. trypsin then converts the other enzymes to active form, those enzymes being chymotripsin and carboxypeptidase

Question 25

what is secretion of alkaline fluid from pancreas caused by

Answer 25

secretin is secreted in small intestine by low PH, secretin then stimulates duct cells of pancreas to stimulate bicarbonnate secretion

Question 26

how much bile secretion do we have per day

Answer 26

about 0.5L per day, consisting of Bile salts
 HCO3
- rich fluid – ducts
 Excretory products
 Bile pigments – waste products
 Cholesterol

Question 27

describe regulation of biliary secretions

Answer 27

its under hormonal control by CCK hormone. CCK is released in response to fat in the duodenum, CCK causes gall bladder to contract and relaxation of hepatopancreatic ampulla. thus releasing bile. bile also causes own secretion in hepatopancreatic circulation

Question 28

describe hepatopancreatic circulation

Answer 28

Bile metabolically expensive to produce so 95% reabsorbed in ileum. it is Transported back to liver in enterohepatic circulation it is
 Reabsorbed and secreted
 Stimulation of bile secretion

Question 29

discuss intestinal secretions

Answer 29

1.5L per day. mucus for lubrication, digestive enzymes and sosmotic fluid to help neutralise. this is SI
LI just secreted mucus for lubrication