Intro to GIT physiology

Question 1

where is the start to the end of GIT

Answer 1

oral cavity to the anus

Question 2

what long is the GIT as well as:
pharynx/oesohagus/stomach
small bowel
large bowel

Answer 2

about 8/9 metres
1m
6m
1.5m

Question 3

what are the 6 functions of the GIT

Answer 3

ingestion 
mechanical processing 
digestion 
secretion 
absorption 
excretion

Question 4

what is the role of the peritoneum

Answer 4

visceral and parietal
forms mesenteries which suspends them and support them
secretes peritoneal fluid which provides lubrication

Question 5

which organs lie retroperitoneally and therefore no surround by peritoneum

Answer 5

kidneys, pancreas and part of the duodenum

Question 6

what do mesenteries do

Answer 6

suspend organ and stop them from getting tangled - carry nerves, blood vessels and lymphatics as well as fat pads to cushion and protect organs

Question 7

what are the three arteries than stem from the abdominal aorta

Answer 7

coeliac
superior mesenteric
inferior mesenteric

Question 8

what vessels go into the liver and why

Answer 8

hepatic portal vein which comes from various abdominal organs and sites
hepatic artery stemming from the coeliac artery which is its main supply of oxygen

Question 9

what does the coeliac artery supply

Answer 9

stomach, spleen, gall bladder, pancreas as well as forms the hepatic artery

Question 10

what does the superior mesenteric artery supply

Answer 10

pancreas, small intestine and large intestine

Question 11

what does the inferior mesenteric artery supply

Answer 11

large intestine and rectum

Question 12

what are the general layers of the digestive tract from innermost to outermost

Answer 12

mucosa
submucosa
muscalris externa
serosa

Question 13

what is the difference between epithelia and glands

Answer 13

epithelia are layers of cells covering internal or external surfaces
glands are structures than produce secretions

Question 14

how does sheet of epithelial cells become and epithelial tube

Answer 14

sheet of epithelial cells are invaginated by an organised tightening of adhesion belts in sleeted regions of the cell sheet
the adhesion belt with associated actin filaments
epithelial tube pinches off from overly sheet of cells and becomes the tube

Question 15

what is special about epithelia cells and polarisation

Answer 15

epithelial cells are polarised which allows them to determine the ultimate site of expression of proteins
ie they are polarised and protein form at certain areas within the cell

Question 16

what are the four types of junctions between cells from apical to basal

Answer 16

apical side
occluding junction - tight junction sealing gaps between cells
cell-cell anchoring - adherent junction connects actin filament bundle in one cell with the next - desmosome
channel forming junctions - gap junction allows passage of small water soluble molecules from cell to cell
cell matrix anchoring junction - anchors celll to ECM (hemidesmosome)

Question 17

what are the two movements of solutes and water across epithelia

Answer 17

1) from external compartment (lumen) to the internal compartment (blood) - absorption
2) from internal compartment to external - secretion such as protons and potassium/phosphate

Question 18

what is net flux

Answer 18

absorptive flux - from lumen to capillary = Jabs
secretory flux - from capillary to lumen = Jsec
net flux = Jabs - J sec

Question 19

what are the three transcellular pathways

Answer 19

transcellular absorption
transcellualr secretion
paracellular secretion/absoprtion

Question 20

what are the barrier to trasncellular routes

Answer 20

basal and apical membrane

Question 21

what are the types of passive transport across membranes

Answer 21

non-coupled - solutes moving down their electrochemical gradient
can occur via pores or channels
transporters - facilitate diffusion of small non-electrolytes

Question 22

what are the two types of active transport

Answer 22

primary - energy to drive transport comes directly from ATP - substrate moves against an electrochemical gradient
secondary - energy to drive AT comes from electrochemical gradient which is set up by primary action - second substrate moves against electrochemical gradient

Question 23

describe the process of sugar absorption from the lumen of the intestine

Answer 23

glucose/Na co transporters on apical side work via secondary active from an area of low to high glucose inside the cell
glucose then passively moves out the basal surface from high to low conc - Na/k primary active trasnporter on basal side pumps na out basal and K+ into the cell

Question 24

what is the osmotic movement of water

Answer 24

water moves from an area of low osmotic pressure to areas of high osmotic pressure via para/trans routes or diffusion through aquaporins in lipids

Question 25

what is the vagus nerves role in the GIT

Answer 25

controls foregut and midgut derivatives

Question 26

what is the role of the splanchnic nerve

Answer 26

supply hindgut components

Question 27

how does the sympathetic system affect the GIT

Answer 27

inhibits gut activity due to fight or flight

Question 28

where do the vagus/splanchinic nerves stem from and innervate

Answer 28

vagus from medulla and stimulates parts of small/large intestine, stomach and oesophagus
splanchnic stems from s2 - s4 which stimulates some of the large intestine and anus

Question 29

where does sympathetic innervation stem from in the GIT

Answer 29

T5 - L1

Question 30

what is the enteric nervous system

Answer 30

gut autonomic control which lies underneaths the submucosa and controls most of gut motility

Question 31

describe the two types of extrinsic nerve supply to the GIT

Answer 31

check the home screen

Question 32

what are depolarisation sin the pacemaker cells of the submucosa

Answer 32

periodic shifts which provide underlying structure to the activity of smooth muscle
3-12 per minute

Question 33

what are interstitial cells of cajal

Answer 33

mediators of slow waves which conduct to smooth muscle cells
3-12 per minute