Case 2 - The stomach Flashcards

1
Q

Explain how CO2 and HCO3- act as intraceullar buffers

A
  • CO2 is kept constant by respiration
  • the cell is highly permeable to CO2 which enters the cell via diffusion and reacts with water
  • H2O + CO2 = H+ + HCO3-
  • Carbonic anhydrase speeds up dissociation
  • if the hydrogen ions are in excess this will shift the equilibrium to form CO2 and H2O
  • Therefore more CO2 leaves the cell into the extracellular fluid
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2
Q

What is absorbed in the ileum?

A
  • Proteins
  • lipids
  • sodium
  • water
  • carbohydrates
  • bile acids
  • cobalamin (Vitamin B12)
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3
Q

What is the exocrine function of the stomach?

A
  • Releases pepsin for protein digestion,
  • HCL for stomach acidity
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4
Q

What is the paracrine function of the stomach?

A

Use of histamine to stimulate gastric acid secretion

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5
Q

What do the mucuous neck cells of gastric glands secrete?

A
  • Mucous secretion
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6
Q

What is intrinsic factor and what is its importance?

A
  • It is secreted by parietal cells
  • it binds to vitamin b12 (x2) and forms a complex that is resistant to digestion
  • Allows b12 to be absorbed in the terminal ileum
  • without intrinsic factor b12 is absobed inefficiently by passive diffusion - leads to pernicious anemia
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7
Q

Describe the basolateral secretion of parietal cells.

A
  • bircabonate leaves the cell passively by a 1:1 exchange for Cl-
  • basolateral Na+, K+ - ATPase maintains concentratins of [Na+<strong> </strong>] [K+]
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8
Q

What is the function of the fundus and corpus of the stomach

  • What types of cells are present
A
  • Fundus and corpus - main secretory and for storage, mainly gastric glands
    • Chief - pepsinogen
    • Parietal - HCl and intrinsic factor
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9
Q

What is absorbed in the jejunum?

A
  • Carbohydrates
  • proteins
  • lipids
  • sodium
  • water
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10
Q

What is the range of intracellular ph

A

6.8 - 7.2

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11
Q

In gastric glands what do the surface epithelial cells secrete?

A
  • Secrete mucous (HCO3-) to protect the stomach from secretions from acidity and proteases from gastric juice, neutralises acid
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12
Q

Explain how macromolecules control intracellular buffering

A
  • Macromolecules present in the cell have weak acid (COO-) and base groups (NH2)
  • These groups can pick up a proton
  • They help to minimsise pH fluctuations
  • They provide temporary relief as they have a limited capacity
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13
Q

What is absorbed in the duodenum?

A
  • Iron
  • carbohydrtaes
  • lipids
  • proteins
  • sodium
  • water
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14
Q

What are secretory canaliculi and what are their function?

A
  • An extension of the lumen
  • Full of microvilli, not just around the lumen
  • when the cell is stimulated there is a structural change and the canaliculi are released
  • Apical membrane is withdrawn into close vesicles during resting phase
  • Massive decrease in surface area
  • Stoping secretion pulls back the villi into the cell, due to PP they damage the cell therefore cell is restored during rest
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15
Q

What is the function of the stomach?

A
  • Acts as a reservoir
  • Mix and churns food with gastric secretions to form chyme
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16
Q

What is the MoA of PPI?

A
  • They are lipid soluble weak bases they enter the cell and accumulate in acid spaces i.e. canaliculi and tubulovesicles of parietal cells
  • They are activated in acid - chemically altered by H+ to an active sulphonamide form
  • Sulphonamides are cationic which are trapped in canaliculi
  • Forms irreversible disulphide bond with H+ - K+ - ATPase and blocks H+ secretion until new pumps are synthesized
  • They are given in encapsulated formulation to avoid breakdown by stomach acid, it is absorbed in the SI and travels to parietal cells via the blood (onset 1 - 2 hours)
17
Q

How is glucose absorbed in the SI

A
  • There is a Na+ - K+- ATPase at the basolateral membrane which extrudes Na+ out of the cell
  • This creates a Na+ gradient
  • Na+ and glucose come into the cell via a co-transporter (SGLT) symporter)
18
Q

What transporters act as acid extruders?

A

sodium hydrogen exchanger

proton pump e.g. parietal cells

sodium bicarbonate co - transppoter: import of bicarbonate ions into the cell to neutralise the acid within the cell

19
Q

How is fat absorbed in the SI?

A
  • Liver produces bile which emulsifies fat, fat lobules are broken down into smalelr fat droplets coated in bile salts
  • Increases surface area for an enzyme attack
  • Broken down further
  • THey pass through the membrane into the lacteal to venous circulation, to prevent accumulation of vascular pathology in vessels
20
Q

Describe the apical secretion of parietal cells

A
  • Active transport of H+ions by a proton pump: H+, K+ - ATPase, antiporter mechanism and conformational change is driven by phosphorylation
  • K+ recycles via a K+ channel, no net gain/loss (recycled)
  • Cl- ions recycle via Cl- ion channels
21
Q

What is the function of the pylorus and antrum of the stomach

What types of cells are present

A
  • Few parietal cells
  • mainly endocrine - gastrin - g cells
  • mixing and movements control of emptying into duodenum
22
Q

How does a high flow rate of gastric secretion affect the gastric juice composition?

A
  • Increase in
    • chloride ions
    • potassium ions
    • hydrogen ions
  • Decrease in sodium ions
  • Rate of parietal cells increases
  • Mucous cell secretion is passive therefore remains unaffected
  • Less dilution of chyme
23
Q

Why must pH be kept optimal

A

For the optimal functioning of proteins within the body:

  • Enzymes
  • Receptors
  • Transporters
  • Structural/contractile proteins
24
Q

What do the parietal cells release

A
  • Intrinsic factor
  • HCl
25
Q

What transporters act as base extruders?

A
  • Chloride bicarbonate exchanger - bicarbonate exits the cells
  • sodium bircabonate co transporter - 1: 3 bircabonate ratio
26
Q

What is the endocrine function of the stomach?

A
  • Releases the hormone gastrin from G cells, it acts locally on the stomach smooth muscle and mucosa to stimulate gastric motility
27
Q

Descibe acid secretion by parietal cells

  • Draw it out
A