GI system

Question 1

what is the general function of the GI system?

Answer 1

take in food, digest it to extract and absorb metabolites for growth and energy needs of the body

Question 2

name the layers of the gut wall in order from the lumen out

Answer 2

mucosal
submucosal
muscularis
serosal

Question 3

what are the contents of the mucosal layer?

Answer 3

epithelium, lamina propria and muscularis mucosae

Question 4

what is the function of the musuclaris mucosae?

Answer 4

move villis to enhance exposure to absorptive surfaces

Question 5

what is the function of the submucosal plexus?

Answer 5

the neural control of secretion, absorption and villi movement

Question 6

what is the submucosal layer made up of?

Answer 6

submucosal plexus, connective tissue blood vessels

Question 7

what is the muscularis layer made up of ?

Answer 7

inner circular muscle, outer longitudinal muscle and the myenteric plexus

Question 8

what is the serosal layer?

Answer 8

outer sheath of the gut wall

Question 9

what is the core of the plicae circulares made of?

Answer 9

folds with a core of submucosa

Question 10

what is the core of the villi made of

Answer 10

mucosal layer

Question 11

what are microvilli?

Answer 11

finger like projections on the epithelial surface

Question 12

what is the macroscopic blood supply of the GI tract

Answer 12

gets 25% of cardiac output at rest
when eating the GI tract recives more blood flow
venous return goes via the liver through the hepatic portal vein to remove any toxins

Question 13

what is the microscopic blood supply of the GI tract?

Answer 13

blood and lymphatic vessels in each villi carry nutrients too and from the submucosa

Question 14

what are the structures of the enteric nervous system and what is their function?

Answer 14

submucosal plexus- controls the mucosa for secretion, absorption and movement of villi
myenteric plexus- controls the muscularis for motility

Question 15

what is the controlled variable for the regulation of the GI tract?

Answer 15

the conditions in the lumen, ie whats in there, how much etc.

Question 16

what are the two major effectors of regulation in the GI tract?

Answer 16

smooth muscle and GI tract epithelial cells

Question 17

what are the three phases of the GI tract, what are their detections and what are their preparations?

Answer 17

cephalic phase (prep), detected by scent or site of food, prep is through expansion of GIT lumen

gastric phase (digestive), detected by arrival of food in the stomach, pH and nutrients, prep is through sending ENS, CNS and hormone sending

intestinal phase (controlled release), detected by stretch, acid, osmolarity and nutrients. prep through ENS, CNS and hormones

Question 18

what is extrinsic reflex control of the GI tract?

Answer 18

involves the CNS- gut to brain and back
regulation over long distances

Question 19

what is intrinsic reflex control of the GI tract?

Answer 19

only involves the ENS- local control over small distance (cm’s)

Question 20

what neurotransmitters in the ENS cause stimulation?

Answer 20

acetylcholine and tachykinins

Question 21

what neurotransmitters in the ENS cause inhibition?

Answer 21

nitric oxide

Question 22

how does the sympathetic nervous system impact the GI tract?

Answer 22

inhibition of activity in GI tract- noradrenaline detected by alpha adrenic receptors
short preganglionic and long post ganglionic

Question 23

how does the parasympathetic system impact the GI tract?

Answer 23

stimulation of activity- acetylcholine detected by muscarinic receptors
long pre-ganglionic and short post ganglionic

Question 24

where are GI tract hormones released from?

Answer 24

enteroendocrine cells throughout intestinal tract

Question 25

name the components of the immune system in the GI tract?

Answer 25

epithelial barrier mesenteric lymph nodes peyers patches a range of immune cells- B cells, T cells, mast cells, macrophages, eosinophils

Question 26

what are the two phases of chemical digestion?

Answer 26

1) luminal digestion- enzymes into the lumen to initiate digestion 2) contact digestion- in the small intestine. enzymes from enterocytes attatch to brush boarder.

Question 27

what is involved in the luminal digestion of carbohydrates?

Answer 27

alpha amalyse- through pancreatic alpha amalyse hydrolyses alpha 1-4 glycosytic bonds **the amalyse cannot break the beta glycolytic bonds

Question 28

name of the enzyme that is involved with contact digestion of the dissachride?

Answer 28

dissacharidases- made by the GI tract epithelial cells break disaccarides into monosaccardies at the apical membrane

Question 29

what are the two types of monosaccaride digestion?

Answer 29

sodium dependent- secondary active transport, glucose (against its gradient) being brought into cell with sodium down its gradient. Na/K ATPase maintaining the gradient for sodium by pumping it out and bringing potassium in. glucose transporter on basolateral membrane transporting glucose out of the cell. sodium independent- specific transporter ie fructose transporter bringing into cell down conc gradient on apical side. basolateral side another glucose transporter transports it out of the cell.

Question 30

how is trypsinogen converted to its active form? what does it then do?

Answer 30

trypsinogen activated to trypsin by enterokinase enzyme. trypsin then activates other proteases.

Question 31

what proteases cleave internal peptide bonds of a protein?

Answer 31

trypsin, chymotripsin and elastase

Question 32

what protease cleaves peptide bonds from the C terminal?

Answer 32

carboxypeptidases.

Question 33

what is H+ dependent peptide transport?

Answer 33

di, tri and tetra peptides are transported into the cell through secondary active transport with H+. intracellular peptidases then cleave them into amino acids where they can then exit cell via amino acid transporters on basolateral membrane

Question 34

what are the initial steps 4 steps of fat digestion

Answer 34

1- emulsification- done through mixing, breaking up the fat into smaller parts. 2- stabilisation- occurs in duodenum. bile salts join on to stabilise small emulsion droplets. increased surface area increased rate of triglyceride digestion step 3- enzymatic digestion- occurs in lumen of intestines. Digests triglycerides to monoglyerides and fatty acids. colipase binding to emulsion droplet- allowing lipase to bind which hydrolyses triglycerides at the surface releasing monoglycerides and 2 fatty acids step 4- micelle formation- these are stabilised by bile salts on the surface. Forming smaller droplets to interact with brush boarder for absorption.

Question 35

what is the process of fat absorption?

Answer 35

ffa and monoglycerides from micelle simply diffuse across apical membrane into cell theyre then transported to er where they are made back into TAGS secreted by golgi as chlyomicrons, go to the basolateral membrane where theyre exocytosed as chylomicrons where they can enter the lymph through lacteals in the villi