Physiology Flashcards
how to calculate BMI & ranges
weight/(height 2)
<25= norm, <29.9=overweight, <39.9= obese, >40=morbidly obese
what is a tx for obesity
recombinant lectin therapy, drugs, surgery e.g. gastric by-pass surgery
what 3 things regulate satiety?
enterogastrones
hypothalamus
apetite controllers
what are 3 examples of enterogastrones
CCK, glucagon-like-peptide 1, Gherlin
what is 1 appetite controller that inc food intake and 1 that decreases food intake
glutamate
monoamines
other than satiety signalling, what two other mechanisms influence ANS and neuroendocrine activity?
adiposity -ve feedback signalling
food reward
what are the signalling molecules for adiposity -ve feedback and food reward pathways?
- leptin & insulin
- dopamine
what does leptin mimic?
fullness
what does insulin do
inc energy burn
what are the 2 mechanical activities of the 2 areas of the stomach?
orad stomach- tonic
caudad stomach- phasic
3 points of tonic activity in stomach…
relaxation driven by vagus to to accommodate mass
tonic contractions are weak due to thin muscle
NO SLOW WAVES
2 points of phasic activity in stomach…
intermittent contractions from mid stomach to gastro-duodenal junction propelling food through pylorus
CONSTANT SLOW WAVES
what is retropulsion?
inc velocity of contractions towards junction to overtake movement of chyme that rebounds against stomach
why is strength of antral waves important
determines how much chyme escapes through pyloric sphincter
what is the strength of antral waves determined by?
gastric factors: proportional to volume & viscosity of chyme
duodenal factors: neural (enterogastric reflex dec strength) & hormonal (enterogastrones)
what are the 2 types of gastric gland?
oxyntic glands (proximal 2/3rds of stomach) pyloric glands (distal 1/3rd of stomach (near pylorus))
what 5 secretions do oxyntic glands secrete & what does each do
histamine (stimulates HCl) HCl (pepsinogen>pepsin) pepsinogen intrinsic factors (vitB12 absorption) mucous (lubrication)
what 3 secretions do pyloric glands secrete & what does each do?
gastrin (HCl secretion)
somatostatin (inhibits HCl)
mucous
what are the main secretagogues of HCl and by which method do they secrete?
ACh, Gastrin, Histamine
direct
what is the indirect mechanisms of HCl secretion?
stimulation of ECL cells > release histamine > HCl secretion via signal transduction pathways
what are 2 substances that oppose histamine
somatostatin & prostaglandins
what are the 3 phases in which the stomach secretes its secretions?
cephalic: prepares stomach for food. vagus stimulates parietal cells
gastric: food in stomach distending it and activating acid secretion
intestinal: food has left
how are gastric secretions inhibited?
cephalic: vagal activity dec after eating
gastric: pH falls after emptying so somatostatin & prostaglandin E2 inc
intestinal: factors dec motility also dec secretion e.g. enterogastrones
what does small intestine secrete?
mucous & aqueous salts
what are the 2 phases of small intestine motility?
segmentation: contraction & relaxation of circular muscle mixing chyme
peristalsis: few localised strong contractions and migrating motor complex (MMC). clears SI of debris
what determines strength of segmentation contractions
para & sympathetic activity
True/False…
peristalsis is promoted by feeding
False…
peristalsis promoted by motilin, inhibited by feeding
what are 6 secretions of the small intestine & their function?
gastrin (stimulates HCl) secretin (HCO3- secretion) CCK GIP (insulin release- inhibits gastric emptying) GLP-1 (insulin release) Motilin (MMC initiation) Gherlin (apetite)
what 4 things does CCK do?
inhibits gastric emptying
secretes pancreatic digestive enzymes
ejection of bile into duodenum
potentiates secretin
what endocrine function does the pancreas have?
insulin, glucagon
what exocrine function does the pancreas have?
digestive enzymes, aqueous salts
what do duct cells do?
release alkaline solution to neutralise acidic chyme
what do acinar cells do?
store pancreatic enzymes
name an example of a pancreatic protease, amylase, lipase ?
protease: trypsinogen
amylase: pancreatic amylase
lipases: pancreatic lipase
True/False…
pancreatic enzymes are inactive in pancreas?
True…
inc Ca2+ cause them to migrate to duodenum where become active
what controls pancreatic secretion in each gastric phase?
Cephalic: vagal stimulation of acinar cells
Gastric: distention stimulates pancreatic cells
intestinal: acid in lumen causes secretin release & fat/ protein in lumen cause CCK release= digestive enzyme release
what 3 anatomical structures are found in large intestine?
caecum, appendix, colon
what does the caecum do?
receives undigestible residues from terminal ileum
what does appendix do?
has extensive lymphoid tissue connected to caecum via appendices orifice
what does colon do?
absorbs Na+/Cl and H2O to condense ileocaecal content into stool. also secretes K+, HCO3-, mucus.
which steroid hormone causes inc Na+ absorption and K+ secretion?
Aldosterone
what are the 3 cells of the colon and their function?
colonocytes: mediate electrolyte absorption
crypt cells: mediate ion secretion
goblet cells: secrete mucous and proteins
what are the 2 motility mechanisms of the large intestine?
Haustration: formation of haustra from contraction of circular muscle
Mass Movement: simultaneous movement of ascending & transverse colon driving faeces into rectum
what causes defection?
rectal stretch
what are the large intestine secretions?
bacteria that synthesise vitK and free fatty acids
how are carbs digested?
starch> oligosaccharides> monosaccharides
what are oligosaccharides?
membrane proteins that catalyse by cleavage of oligomers to monosaccharides e.g. glucose
how does amylase work?
breaks down linkages in starch
describe absorption of carbs
products of digestion transferred across apical and basolateral membrane of enterocytes
where are monosaccharides (glucose, fructose and galactose) absorbed?
duodenum & jejunum
what transmembrane proteins allow entry to enterocyte?
glucose & galactose- SGLT1
fructose= GLUT5
what transmembrane protein allows exit from enterocyte?
GLUT2 for all
True/False…
proteins digested by gastric and pancreatic digestion
True
describe the gastric element of protein digestion…
HCl denatures proteins in stomach
describe the pancreatic element of protein digestion…
pancreatic proteases, some of which present in duodenum and some in brush border and cytoplasm
True/False…
proteases at brush border break down small oligopeptides (di & tripeptides)
False….
brush border proteases break down large oligopeptides.
proteases in cytoplasm break down small peptides
how are proteins absorbed?
sigle AAs: Na+ dependent co-transporters for apical & basolateral membranes
large AAs: @ apical membrane= H+ dependent mechanisms. @ basolateral membrane= Na+ dependent system
what happens to proteins in enterocytes?
become hydrolysed
what is problematic about fat digestion
fats are insoluble in water so have to be converted into an emulsion
how are fat emulsions stabilised
addition of amphiphilic molecules that form a surface layer on droplets
what is the gastric phase of lipid digestion?
lipases secreted in response to gastrin
what is the pancreatic phase of lipid digestion?
pancreatic lipase secreted in response to CCK
how do bile salts facilitate digestion of fats?
released into duodenum in response to CCK to help emulsify large lipids to small ones
what does colipase do?
binds to pancreatic lipase and bile salts allowing lipase access to tri and di glycerides
what are the final products of fat digestion stored and released in…
micelles
how are fats absorbed?
free fatty acids and monoglycerides are transferred from micelles to apical membrane and enter enterocyte
through what mechanisms do fats enter enterocytes
passive diffusion, fat translocases and fatty acid binding proteins
how do short and medium fatty acids exit cell?
exit enterocyte via basolateral membrane and enter villi caps
what happens to long chains and monoglycerides?
are resynthesized into triglycerides in the endoplasmic reticulum and are incorporated into chylomicrons
What does iron have to be converted to to pass into enterocyte?
from Fe3+ to Fe2+ by HCl
how is vit B12 digested and absorbed?
stomach acid isolates protein B12 from protein, protein digested and heptacorin binds to B12 which releases IFs, B12 binds to IF and absorbed by terminal ileum
what happens to fat soluble vitamins
incorporated into micelles > diffuse into enterocyte > incorporated into chylomicron or VLDLs
how do water soluble vitamins enter enterocytes
via Na+ transport
what does reabsorption of Na+ provide?
the osmotic force that drives reabsorption of water
how is Na+ absorbed?
Na+/glucose co-transport
Na+/amino acid co-transport
what does Na+ transport provide?
a transepithelial potential that drives Cl- absorption
what type of Na+ exchange is present in jejunum and is stimulated by alkaline lumen?
Na+/H+ exchange
what type of Na+ exchange is 1y mode of Na+ absorption in inter-digestive periods and occurs in ileum and proximal colon?
parallel Na+/H+ and Cl-/HCO3- exchange
what type of Na+ exchange mediates Na+ absorption in distal colon and is inc by aldosterone and regulated by cAMP and cGMP?
epithelial Na+ channels
how is Cl- absorbed?
lumen’s -ve potential due to Na+ transport
how is Cl- secreted?
crypt cells have
- Na+/K+ ATPase pump
- Na+/K+/2Cl- co-transporters
- K+ channels
what happens if there is low intracellular Na+?
inward movement of Na+, K+ and Cl- occurs via NKCC1
how does the body deal with inc K+ and Cl- intracellularly due to NKCC1 system?
- K+ recycled via K+ channels
- inc intracellular Cl- provides gradient for Cl- to exit via CFTR on apical membrane
- CFTR activated via hormones, NTs etc
