Physiology

Question 1

what three glands is salvia secreted from?

Answer 1

submandibular (70%)
parotid (25%)
sublingual (5%)

Question 2

what effect does parasympathetic enervation have upon salvia secretion?

Answer 2

increases it

Question 3

what are the functions of saliva?

Answer 3

lubrication, antibacterial, carb breakdown via amylase

Question 4

what two factors does the escape of chyme from to stomach depend on?

Answer 4

gastric factors (which are in favour of gastric emptying) and duodenal factors (which are against gastric emptying)

Question 5

where is hydrochloric acid secreted?

Answer 5

parietal cell via a proton pump - (oxyntic mucosa)

Question 6

what is the function of HCL in the stomach?

Answer 6

• activate pepsinogen to pepsin
• denatures protein
• kills micro-organisms

Question 7

what cells is pepsinogen secreted by and what is it function?

Answer 7

Chief cells (oxyntic mucosa)

function:- it is the inactive precursor to pepsin

Question 8

where is the intrinsic factor secreted from and what is its function?

Answer 8

intrinsic factor is secreted from parietal cells (oxyntic mucosa)

function:- needed for the absorption of B12

Question 9

where is histamine secreted from and what is its function?

Answer 9

they are secreted by enterochromaffin like cell (oxyntic mucosa)

function:- histamine stimulates HCL production

Question 10

where is gastrin secreted from and what is its function?

Answer 10

gastrin is secreted from G cells in the pyloric gland area

function:- stimulates HCL production

Question 11

where is somatostatin secreted and what is its function?

Answer 11

somatostatin is secreted by D cells in the pyloric gland area of the stomach

function:- it inhibits the secretion of HCL

Question 12

vagal stimulation has what effect on the secretions in the stomach?

Answer 12

vagal stimulation increases the secretion of substances in favour of acid production

Question 13

what 4 factors help protect the mucosa from HCl/pepsin?

Answer 13

• hydrophobic monolayer
• bicarbonate secretion
• H+ exchanged for sodium
• locally produced prostaglandins (they reduce acid secretion, increase mucous and bicarbonate secretion)

Question 14

what is the adverse effect of NSAIDs on the stomach?

Answer 14

NSAIDs inhibit the production of prostaglandin by COX 1 inhibition - which can then lead to gastric ulceration and bleeding

Question 15

how does H. Pylori cause gastric ulceration?

Answer 15

not fully understood,

H. Pylori produces urease which converts urea to ammonia

• this buffers H+, protects the H. pylori itself and caused epithelial damage to the mucosa
• lipases/proteases are secreted degrading the mucosa and damaging the layers underneath

there is also an increased number of G cells, decreased D cells and a increased level of alkaline induced gastrin secretion

Question 16

what drugs affect gastric acid secretion?

Answer 16

proton pump inhibitors (PPI)

H2 receptor agonists

Question 17

What is the mode of action of PPIs and give an example.

Answer 17

they decrease acid secretin by inhibiting active (membrane secreted) proton pumps - they only become active in acidic environments

example - omeprazole

Question 18

what is the mode of action of H2 receptor antagonists and give an example.

Answer 18

they are competitive antagonists and they block histamine mediate acid secretion

example - ranitidine, cimetidine

Question 19

where is secretin secreted and what is its function?

Answer 19

secretin is secreted from S cells in the duodenal mucosa

it inhibits gastric emptying and secretion ad stimulates secretion by the gall bladder

Question 20

where is cholecystokinin secreted and what is its function?

Answer 20

it is secreted from Endocrine I cells in the duodenal mucosa

it inhibits gastric emptying and secretion ad stimulates secretion by the gall bladder

Question 21

where is GIP (glucose dependent insulinotrophic peptide) secreted and what is its function?

Answer 21

endocrine K cells within the duodenal mucosa

it stimulates insulin release by the pancreas

Question 22

insulin and glucagon are examples of which type of pancreatic secretion?

Answer 22

endocrine secretions, secreted into the bloodstream

Question 23

give examples of pancreatic exocrine secretions and they functions.

Answer 23

digestive enzymes (from acing cells) and sodium bicarbonate (from duct cells)

they neutralise acidic chyme - protecting the mucosa and providing the optimum pH for pancreatic enzymes

(look at the document diagrams and it is explained really well)

Question 24

site of bile formation, storage and its function?

Answer 24

bile is secreted by bile duct cells and hepatocytes in response to chyme in the duodenum; this causes gallbladder smooth muscle to contract to release bile for the aid of fat digestion

Question 25

what is the process of carbohydrate digestion?

Answer 25

mouth salivary alpha amylase and stomach salivary alpha amylase attack 1-4 glycosidic links along with duodenum-pancreatic amylase

glucose and galactose are both absorbed by secondary active transport
fructose is absorbed by facilitated diffusion

Question 26

what is the process of protein breakdown?

Answer 26

HCl denatures proteins and pepsin clever proteins into peptides
- duodenum-pancraetic enzymes slit peptide binds between amino acids and brush border enzymes cleave amino acids apart

absorption is mostly by active transport, but hydrophobic amino acids are absorbed by passive diffusion

Question 27

what is the process of lipid digestion?

Answer 27

stomach-gastric lipase and pancreatic lipase

bile salts emulsify large lipid droplets to smaller liid droplets - to provide a larger surface area for the action of pancreatic lipase

absorption of free fatty acids happens through passive diffusion
long fatty acid chains are resynthesises into triglycerides in the ER and incorporated into chylomicrons.

Question 28

how/where is calcium absorbed in the body and that regulates its absorption?

Answer 28

passively through the small intestine, and active transport in the duodenum/jejunum

it is regulated by D3 and parathyroid hormone

Question 29

how is B12 absorbed?

Answer 29

B12 binds to intrinsic factor produced in the small intestine and stomach - the B12-intrinsic factor complex is then absorbed in the terminal ileum by endocytosis.