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S1 Intro To Physio With Pharmacology > L26 Absorption And Secretion > Flashcards

L26 Absorption And Secretion Flashcards

1
Q

What are the three primary control systems that regulate gastrointestinal (GI) actions and secretions?

A

Hormonal, paracrine and neurocrine control.

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2
Q

How many L of fluid is handle by the GI per day and what happens to them?

A

> 9L per day and most are absorbed in the SI and the remaining fluid is lost in the LI or lost in faeces

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3
Q

How does the body regulate extracellular fluid (ECF) volume and maintain blood pressure?

A

By integrating salt and water balance, primarily through the kidneys

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4
Q

What is the key factor in regulating ECF volume?

A

Adjusting the total body sodium chloride (NaCl) content

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5
Q

Describe the steady state of sodium balance.

A

In a steady state, the sodium (Na+) intake through the gastrointestinal (GI) tract equals the Na+ output through renal (and other) pathways

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6
Q

What are the three main functions of the stomach? (3)

A
  1. Secretion
  2. Motor - regulates food intake, mixing, decreasing food particle size
  3. Humoral - gastrin activity
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7
Q

What are the distal secretions of the stomach? (3)

A
  1. Gastrin
  2. Somatostatin
  3. Pepsinogens
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8
Q

What are the proximal secretions of the stomach? (4)

A
  1. HCl
  2. Pepsinogens
  3. Intrinsic factor
  4. Mucins/HCO ions.
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9
Q

Name the oxyntic glands and what they secrete? (7)

A
  1. Epithelial cells - HCO3
  2. Mucous neck cells - Mucus
  3. Parietal cells - HCl, intrinsic factors
  4. Enterochromaffin-like cells histamine
  5. Chief cells - pepsinogens
  6. Enterochromaffin cells – serotonin, VIP, substance P.
  7. D cells – somatostatin (H)
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10
Q

Describe the secretion/function of epithelial cells

A

HCO3- - combines with mucus to form protective barrier + neutralises acid

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11
Q

Describe the secretion/function of mucous neck cells

A

Mucus – protects epithelia from other agents harmful to stomach lining

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12
Q

Describe the secretion/function of parietal cells

A

HCl – activates pepsinogen, denatures proteins, inhibits pathogens

Intrinsic factor – required from B12 absorption

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13
Q

Describe the secretion/function of Enterochromaffin - like cells

A

Histamine – ↑ parietal cell HCl secretion

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14
Q

Describe the secretion/function of Enterochromaffin cells

A

Serotonin – regulates motility & secretion
VIP – motility, secretions, vasodilation, ↓HCl
Substance P – smooth muscle contractions

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15
Q

Describe the secretion/function of Chief cells

A

Pepsinogen (precursor of pepsin – cleavage results in digestion of protein)

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16
Q

Describe the secretion/function of D cells

A

Somatostatin (hormone) – inhibits gastrin release (feedback mechanism)

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17
Q

Describe the secretion/function of G cells

A

Gastrin hormone - ↑parietal cell HCl secretion, ↑motility, ↑pepsinogen release

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18
Q

Where is the location of the tubulovesicular membrane?

A

Apical side

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19
Q

In resting parietal cells, what enzyme is responsible for acid secretion?

A

H/K- ATPase

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20
Q

Stimulation induces cytoskeletal changes. Which membranes fuse together in the parietal cells?

A

Tubulovesicular and canalicular membrane

21
Q

Stimulation induce cytoskeletal changes, How much does the surface area (SA) of parietal cells increase by?

A

50-100x

22
Q

What structural changes occurs to the parietal cells on the cell surface during cytoskeletal changes?

A

Microvilli appearace

23
Q

Describe the mechanism of gastric acid secretion in parietal cells

A
  1. H2CO3 in dissociated
  2. H+ will be sectreted across the apical membrane through H+-K+ ATPase.(Cl- follows)
  3. Bicarbonate ion is absorbed into the blood via Cl - HCO3 exchanger.
  4. Secretion of HCl and absorption of HCO3 occurs.
  5. K is recycled into lumen by K channels.
24
Q

How does regulation of HCl secretion occur?

A
  1. Stimulation of H+ secretion: histamine, Ach and Gastrin
  2. Inhibition : leading to low pH and secretion of somatostatin and prostaglandins.
25
Q

What is somatostatin?

A

Somatostatin is a hormone that inhibits the release of other hormones

26
Q

What are the key electrolytes that the SI and LI need to absorb?

A

Na+, K+, Cl-, HCO3- via villus cells/surface epithelia respectively

27
Q

What do Cyrpt epithelial cells do?

A

They secrete fluid and electrolytes

28
Q

What are the two main intestines and its sections?

A

1) Small intestine - Dudodenum, jejunum and ileum
2) Large intestine - colon and cecum

29
Q

What are the primary sites for absorption of Na+, Cl-, K+ and HCO3-?

A

Duodenum and jejunum

30
Q

What do the crypt epithelial cells do?

A

They secrete fluid and electrolytes

31
Q

Do SI me LI have similar structures?

A

Yes they do

32
Q

What seperates the apical and basolateral membranes in polar cells?

A

Tight junctions

33
Q

How do both SI and LI absorb + secrete solutes?

A

Via active and passive mechanisms.

Transcellular movement is usually active
Paracellular movement is generally passive

34
Q

How are ions transported into the cell from the blood in the intestines?

A

Na+K+Cl- cotransporter

35
Q

Describe the general mechanism of secretion of NaCl in epithelial cells of crypts

A

1) NKCC2 brings Na+, K+, 2Cl - into cell from the blood
2) Cl- ion diffuses into the lumen through Cl- channels in the apical membrane
3) Na+ follows Cl- secretion passively (paracellularly) which draws water allowing the movement/ secretion of NaCl

36
Q

How is water secreted into the lumen of the intestines?

A

Na+ follows Cl- secretion passively (paracellularly) - water drawn following the movement of NaCl

37
Q

Describe the mechanism of electrolyte absorption in the jejunum

A
  • All Na+ transcellular absorption via Na+/K+ ATPase
  • Low IC Na+, so allows Na+ entry via Na+/H+ exchanger or Na+/ glucose cotransporter
  • Luminal HCO3- increases Na+ absorption by stimulating the apical Na+/H+ ion exchanger (think about previous lecture on HCO3- with NHE3 cotransporter)
38
Q

Describe the mechanism of electrolyte absorption in the ileum

A
  • Same transport mechanisms as jejunum in the top half, however have CL–/HCO3- exchanger on apical membrane
  • H+ secreted into the lumen via Na+/H+ exchanger. HCO3- secreted into lumen via CL-/HCO3- exchanger
  • Net effect - movement NaCl- into cell (absorbed into blood)
39
Q

What is different between the mechanisms of the ileum and jejunum?

A
  • HCO3- is on basolateral membrane in the jejunum however in the ileum, it’s on the apical membrane
  • Has a chloride ion channel on basolateral membrane
40
Q

Describe the mechanism of electrolyte pancreatic secretion

A
  • HCO3- secreted into pancreatic juice (lumen) by Cl-/ HCO3- exchanger
  • H+ transported into blood via Na+/H+ exchanger
  • Net effect: secretion of HCO3- +absorption of H+
41
Q

Describe the mechanism of absorption of the large intestine (colon)

A
  • Synthesis of Na+ channels induced by aldosterone
  • Increased Na+ channels –> Increased Na+ entry –> Increased Na+ across basolateral membrane via NaK ATPase
  • Increased K+ in cell due to ATPase –> Increased K+ secretion across apical membrane
42
Q

Name me 6 carbohydrate which are located across the brush border

A

α-amylase
α-dextrinase
Maltase
Sucrase
Trehelase
Lactase
The products absorbed into villus blood

43
Q

Name me 5 proteases

A

Pepsin
Tryosin
Chymotrypsin
Elastase
Carboxypeptidases
- Products into villus blood

44
Q

Some products may go into the lacteals instead of the villus blood within the villus. What substances are the causes of that?

A

The products produced are the result of lipases and bile salts

45
Q

Describe the mechanism of absorption of carbohydrates in the epithelial cell of SI

A
  • Na/K ATPase establishes a Na+ gradient within cell so that Na+ can cotransport glucose and galactose via SGLT1 cotransporters and fructose via GLUT5
  • GLUT2 on the basolateral membrane allows glucose, galactose and frutose to diffuse into blood
46
Q

Describe the mechanism behind the absorption of proteins in the SI

A
  • Na/K ATPase establishes Na+ gradient inside the epithelial cell of SI
  • This allows amino acids and dipeptides and tripeptides to be contransported from apical membrane into the cell
  • Dipeptides and tripeptides are hydrolysed into amino acids via peptidase where it diffuses into the blood
  • There is a Na+/H+ exchanger on the apical membrane
47
Q

Describe the mechanism behind lipid absorption of the small intestine (7)

A
  • Pancreatic lipase + other lipases, aided by bile salts complete lipid hydrolysis in duodenum + jejunum
  • Products of lipid digestion: cholesterol, monoglycerides + fatty acids have been made soluble in mixed micelles
  • Micelle exterior lined with amphipathic bile salts
  • In the mucous gel layer lining the epithelial surface FAs become protonated + cross luminal surface of enterocyte by 3 methods: diffusion, incorporated into enterocyte membrane and carrier mediated transport
  • Products re-esterified with FA in SER which is then pacakaged into chylomicrones
  • Cross basolateral membrane and absorbed into lacteals
  • Bile salts recycled
48
Q

What are the 3 methods for surface Fas to become protonated and cross the luminal surface of enterocyte?

A

-Diffusion
-Incorporated into enterocyte membrane
-Carrier mediated transport

S1 Intro To Physio With Pharmacology (32 decks)

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