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Bs1060 > gastrointestional physiology > Flashcards

gastrointestional physiology Flashcards

1
Q

GI Tract

A

-a hollow tube open at both ends and is considered external

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2
Q

layers of the GI tract:mucosa

A

-epithelium layer= lines the lumen of GI tract
-lamina propria= loose layer of connective tissue containing capillaries,,lymph and immune cells (mast cells)

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3
Q

layers of the GI tract:submucosa

A

-larger blood vessels and nerves
-glands
-loose collagenous connective tissue

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4
Q

layers of GI tract:muscularis externa

A

-nerves between the muscle layers
-contains smooth muscle

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5
Q

Enteric nervous system

A
  • the nerves in the GI tract
  • a division of the autonomic nervous system and contains a lot of neurones hence the name ‘mini-brain’
    -a reflex circuit = function without input
    -controls motility, secretion and absorption
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6
Q

serosa

A

-outermost layer
-a layer of connective tissue
-keepseverything inside the GI

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7
Q

lumen

A
  • the middle of the GI tract
    -food goes through (chyme = food that has been chewed)
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8
Q

structure of the stomach

A

-forms gastric pits lined by epithelial cell, mucous cells, stem cells, chief cells,pariteal cells and endocrine cells
-consist of the GI tract

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9
Q

functions of the stomach

A

-where digestion starts
-secretion
-defence
-motility

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10
Q

digestion of proteins in the stomach

A

-chief cells= secrete pepsinogens
-pepsinogen are activated to pepsins in the acid stomach lumen
-pepsins initiate protein digestion by hydrolyzing specific peptide bonds
-parietal cells= changes shape when you smell or eat food and so is stimulated to secrete acid
-the tubolovesicular structure rearranges into a canalicular structure increases surface area up to one hundred-fold to create a larger surface area for the insertion of proton
pumps for increased acid secretion

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11
Q

explain the cellular mechanism for gastric acid secretion

A

-parietal cells secrete acid through transporters and pumps
-sodium pump=sodium gradient
-carbon dioxide and water diffuses into the parietal cell which is converted by carbonic anhydrase into to H+ and HCOthree-
-proton pump transports H+ into the lumen of stomach for exchange of K+
-* H+ - Na+ exchanger on the basolateral membrane is important
for pH control of cytoplasm
* The HCO3- leaves the cell via the HCO3– Cl- cotransporter..
* Cl- flows by passive movement through a Cl- channel down
electrochemical gradient
* Cl- enters the lumen to form HCl

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12
Q

regulation of acid secretion (HCL)

A

-The vagus nerve
stimulates the parietal
cell directly
-Vagal stimulation of enterochromaffin-like cell (ECL) increases histamine release
-Histamine stimulates acid secretion
- Vagal stimulation of G cells triggers gastrin release
-Gastrin directly stimulates acid secretion
from the parietal cell
-Gastrin indirectly stimulates acid secretion by increasing histamine
release from ECL cells
-Luminal acid
stimulates cells to release somatostatin
-Somatostatin inhibits acid secretion directly at the parietal cell
-Somatostatin inhibits gastrin release at the G cell
-Somatostatin inhibits histamine
release at the ECL cell

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13
Q

mucus protection layer

A
  • Mucus creates a diffusion barrier for H+ and pepsin
  • This creates a neutralization zone which protects the gastric
    epithelia from H+ and inactivates pepsins
    -pH in the lumen can be as low as pH1 yet at the apical membrane
    of surface epithelium it is pH7
    -Mucus is secreted by mucus neck cells
    -HCO3- is secreted by surface epithelia
    -Mucus traps HCO3- forming a protective
    ‘mucus gel layer’
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14
Q

defence of the stomach

A

-First line of defence as it is the first of the hollow
organs to receive external food- chyme
-Acid pH of the stomach lumen kills most bacteria

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15
Q

motility of the stomach

A

-Motility serves two functions
i. Movement of food by
propulsive movements along
the GI tract.
ii. Mechanically mix food to
maximise exposure of particles
to digestive enzymes by
churning (mixing) movements.

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16
Q

structure of the small intestine

A

-villi=which is the mucosa of the small intestine . contains surface epithelial cells and has blood vessels,lacterls and nerves
-has crypts of leiberkuhn
-alos has a lumen,submocosa=glands and muscularis externa

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17
Q

folds of the small intestine

A
  • folds of kerckring
    -villi and crypts
    -when you zoom in further you can see microvilli
    =x600 increase in surface area
18
Q

general functions of the GI system

A

-digestion
-adsorption
-secretion
-defence
-motility
-excrertion

19
Q

digestion of the small intestine

A

-digestive juices from the pancreas are secreted into the duodenum and enzymes within them breakdown
-fats by lipase
-carbohydrates by amylase
-protein by trypsin and protease

20
Q

the brush border

A

-enzymes are present on the brush border for protein and carbohydrate digestion into small units which can be absorbed
-oligosaccharides for carbohydrate digestion are at the brush border
-amino-peptidases are also present for protein digestion on the apical membrane

21
Q

absorption of the small intestine

A

-absorption of glucose is driven by the Na+ driven glucose symprter
-absorption of the amino acids is driven by the Na+ driven amino acid symporter
-water is absorbed passively via the osmotic gradient generated can either go through the paracellular pathway or transcellular pathway
-adsorption of Na+ in the small intestine I don via Na+/H+ exchnsger also for fat adsorprtion

22
Q

adsorption of fatty acids in the small intestine

A

-Lipases secreted from
the pancreas digest fats in the small intestine into simple lipids in the small intestine
-fats form micelles in water stabilised by bile salts released from the gallbladder ‘
-the micelles are small enough to diffuse amongst the microvilli
-the micelles migrate into the unstirred layer close to the brush border which Is acidic
-because of the acidity the micelles fall apart and the free fatty acids get absorbed

23
Q

re-synthesis of fats in epithelial cells

A

-the fatty acids go into the smooth endoplasmic reticulum and get reformed into triglycerides, phospholipids and cholesterol ester
-intracellular micelles called chylomicrons are formed with a lipoprotein coat
-chylomicrons leave the basolateral membrane by exocytosis and diffuse into the villi lacteals

24
Q

non-immune defence of the small intestine

A

goblet cells= secrete mucin and create a protective mucus layer
-paneth cells= specialised for the secretion of antibacterial enzymes
-tight junctions between cells form a barrier

25
Q

immune cells of the small intestine

A

-immune cells in the villi and peyers patch

26
Q

motility of the small intestine

A

-movement of material in the GI tract as a result of coordinated contractions of smooth muscle

27
Q

migrating motor complex (motility of the small intestine)

A

-for ‘housekeeping’ between meals by sweeping remnants into the large intestine
-rhythmic contraction of the stomach and small intestine in the fasting stateto puh remnats out

28
Q

peristalsis (motility of the small intestine )

A
  • forward movements
    -progressive waves that move food forward to the next area of the GI tract
    -circular muscles contract whilst longitudinal muscles relax just behind the bolus of food
    -receiving end the circular muscles relax and the longitudinal muscle contract
29
Q

segmental movement(motility of the small intestine)

A

-mixing and churning for breaking up the chyme

30
Q

slow waves

A

-Oscillations in the membrane potential of GI smooth muscle cells are called ‘slow waves’
-There are several slow waves per minute (~6)
- When slow waves exceed the electrical threshold (~-40mV) action potentials will fire stimulated Electrical threshold
Action potentials
-When action potentials fire the force of smooth contraction is higher

31
Q

hypovolemic shock

A

-serve blood loss
-when you lose thirty per cent or more blood

32
Q

baroreceptors

A
  • responds to a changes in blood pressure detected as changes in stretch
    -high blood pressure=high strech=increased firing rate=signals to a decrease in vasoconstrictors=vasodilation
    -low blood pressure=low strech=decreased firing rate=increase in vasoconstrictors=vasoconstriction
33
Q

mechanism of high-pressure baroreceptor cells

A
  • the change in stretch causes the mechanosensitive channels to open
    -Na+ and calcium enter via the channels causing depolarisation until the action potential is fired which goes to the brain stems
34
Q

relationship between phasic aortic blood pressure and firing rate of a single afferent nerve from carotid sinus

A

the carotid sinus it fires action potentials with each heartbeat

35
Q

low-pressure baroreceptors

A

-measures blood pressure in the atria and sends signals to the medulla and pituitary which leads to a sympathetic response

36
Q

sympathetic responses

A

-release of noradrenaline from sympathetic postganglionic neurones
-sympathetic response triggers the adrenal medulla to release adrenaline and noradrenaline
leads to increased heart rate, blood pressure and force of contraction due to sympathetic stimulation of beta-adrenoreceptors

37
Q

cerebral and coronary vascular beds

A

not affected by neuronal influences
-they autoregulated themselves
-during hypovolemia shock, the blood flow to the brain and heart will initially drop but very rapidly autoregulate back to normal thus preventing these essential organs

38
Q

renin-angiotensin-aldosterone

A

-decrease in blood pressure picked up by baroeceptors
-the cells release renin which converts angiotensinogen made in the liver into angiotensin one
-Ace coverts in into angiotensin two which is a vasoconstrictor that helps maintain blood pressure
-can stimulate thirst and water loss from the kidney
-causes the release of aldosterone from the adrenal gland

39
Q

aldosterone

A

-promotes Na+ reabsorption in the collecting ducts in the kidney
-which preserves water after hypovolemic shock

40
Q

symptoms of hypovolemic shock

A

-rapid and weak pulse= due to tachycard[ia
- Cold and clammy =Sympathetic vasoconstriction in the skin
and Sympathetic stimulation of sweat glands
-Low urine output =Effects of vasopressin (antidiuretic hormone)
-Na+ retention=Effects of aldosterone= Thirst

Bs1060 (11 decks)

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