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Introduction to physiology with pharmacology > Absorption + secretion > Flashcards

Absorption + secretion Flashcards

Semester 1 year 1

1
Q

What is secretion in the GI tract controlled by?

A

Hormonal, paracrine + neurocrine agents

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2
Q

Where is fluid absorbed in the GI tract?

A

-most absorbed in small intestine
-rest in large intestine or lost in faeces

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3
Q

What does the salt and water balance help do?

A

-regulate ECF volume
-maintain blood pressure

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4
Q

What are 3 main functions of the stomach?

A

-secretions
-motor - regulate food intake/transit, mix to decrease food particle size
-humoral regulation - gastrin + somatostatin (regulate secretions)

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5
Q

What are the proximal secretions in the stomach?

A

-HCl - decrease stomach pH
-pepsinogens - precursor to pepsins (hydrolysed to become active pepsins)
-intrinsic factor
-mucins/bicarbonate ions

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6
Q

Why do pepsins begin as pepsinogens?

A

Ensure the enzymes don’t attack the wall as they’re in inactive form

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7
Q

What are the distal secretions in the stomach?

A

-gastrin
-somatostatin
-pepsinogens

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8
Q

What are basal secretions from the stomach secretory cells rich in?

A

-Na+
-when stimulated, become rich in H+ (from HCl)

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9
Q

What cells make up oxyntic glands in the body and what do they secrete?

A

-epithelial cells - HCO3^-
-mucous neck cells - mucus
-parietal cells - HCl + intrinsic factor
-enterochromaffin-like cells - histamine
-chief cells - pepsinogen
-enterochromaffin cells - serotonin, VIP, substance P
-D cells - somatostatin (hormone)

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10
Q

What cells make up antrum pyloric glands and what do they secrete?

A

-same as the body oxyntic glands, except no parietal cells
-also have G cells - gastrin hormone

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11
Q

What is the structure of resting parietal cells?

A

-cytoplasmic pool of tubulovesicular membrane on apical side
-contain acid secreting H, K-ATPase

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12
Q

What is the structure of stimulated parietal cells?

A

-stimulation induces cytoskeletal changes
-fusion of tubulovesicular + canalicular membranes
-increase SA
-appearance of microvilli
-insertion of H, K-ATPase pump + K+ Cl- channels

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13
Q

Describe the process of gastric acid secretion

A

-H2CO3 dissociates
-H+ secreted across apical membrane via H+-K+ ATPase - Cl- follows via channel
-HCO3^- absorbed into blood via Cl-, HCO3^- exchanger
-net secretion of HCl + absorption of HCO3^-
-K+ recycled into lumen via K+ channels

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14
Q

Are the structures and functions of the small and large intestine similar or not?

A

-similar
-both have crypts of Lieberkühn

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15
Q

What do the small and large intestine absorb?

A

-absorb fluids + electrolytes via villus cells/surface epithelia respectively
-Na+, K+, Cl-, HCO3^-

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16
Q

What additional thing does the small intestine absorb that the large doesn’t?

A

-hydrolysed food after digestion
-via luminal + border brush enzymes

17
Q

What do crypt epithelial cells do?

A

-secrete fluid + electrolytes
-protects against bacteria + toxins

18
Q

What do ‘polar’ cells have?

A

Apical + basolateral membranes separated by tight junctions

19
Q

What is transcellular movement?

A

Usually active across at least 1 membrane

20
Q

What is paracellular movement?

A

Generally passive + determined by tight junctions

21
Q

What is fluid movement?

A

-coupled to solute movement
-sometimes the reverse - solvent drag

22
Q

Why does the small intestine have a large surface area?

A

-folds of Kerckring (plica)
-villi (+ crypts)
-microvilli

23
Q

What are the duodenum + jejunum in the small intestine?

A

Primary site of Na+, Cl-, K+, HCO3^- absorption

24
Q

In the large intestine, what is absorbed and secreted?

A

-net absorption - H2O, Na+, Cl-
-secretes K+, HCO3^-

25
Q

Describe cellular transport (absorption) in the jejunum

A

-all Na+ transcellular absorption occurs via Na+-K+ ATPase
-low IC Na+ acts as driving force for Na+ entry via Na+ channels or Na-H ion exchanger + Na+-glucose transporter (secondary active transport)
-luminal HCO3^- increases Na+ reabsorption by stimulating the apical Na-H ion exchanger
-net absorption of NaHCO3

26
Q

Describe cellular transport (absorption) in the ileum

A

-same transport mechanism as jejunum + Cl-, HCO3^- exchanger + Cl- transporter
-H+ and HCO3^- generated, H+ secreted into lumen via Na-H ion exchanger
-HCO3^- secreted into lumen by Cl-,HCO3^- exchanger
-net absorption of NaCl

27
Q

Describe how pancreatic secretion occurs using ductal cells

A

-acinar cells secrete enzymes (CDK receptors)
-centroacinar cells secrete isotonic aqueous portion
-HCO3^- secreted into pancreatic juice by Cl-HCO3 exchanger
-H+ transported into blood via Na-H exchanger
-net secretion of HCO3^- + absorption of H+

28
Q

Describe how absorption occurs in the large intestine (colon)

A

-synthesis of Na+ channels induced by aldosterone
-increased Na+ channels = increased Na+ entry across apical membrane = increased Na+ across basolateral membrane via Na-K ATPase
-causes increase in K+ in cell = increased K+ secretion across apical membrane

29
Q

Describe how carbohydrates are absorbed in the small intestine

A

-glucose + galactose - co-transport against electrochemical gradient (high intracellular conc.)
-use sodium gradient to drive movement - low Na intracellular conc. due to ATPase on basolateral
-fructose - facilitated diffusion

30
Q

Describe how proteins are absorbed in the small intestine

A

-amino acids move in with Na down electrochemical grad. (secondary active transport)
-dipeptides + tripeptides move in with H+ using co-transport
-peptidase converts them to amino acids which then move into blood via facilitated diffusion

31
Q

Describe the first part of lipid absorption in the small intestine (prior to moving into the cell)

A

-pancreatic + other lipases, aided by bile salts complete lipid hydrolysis in duodenum + jejunum
-products of lipid digestion - cholesterol, lysophospholipids, monoglycerides + free fatty acids
-lipid digestion products solubilised in mixed micelles
-micelle exterior lined with amphipathic bile salts

32
Q

Describe the second part of lipid absorption in the small intestine (moving into the cell)

A

-mucus gel layer lining epithelial surface contain fatty acids that become protonated + cross luminal surface of enterocyte
-once inside cell, products are re-esterified with free fatty acids in SER
-packaged into chylomicrons
-cross basolateral membrane + absorbed into lacteals - glycerol enters blood supply
-bile salts are recycled - enterohepatic circulation

33
Q

How can the fatty acids in the mucus gel layer cross the luminal surface of enterocyte?

A

-diffusion
-incorporated into enterocyte membrane
-carrier mediated method

Introduction to physiology with pharmacology (29 decks)

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