Gastrointestinal tract secretions

Question 1

How many litres is absorbed by the small intestine?

Answer 1

9 litres

Question 2

How does the GI tract regulate the ECF volume?

Answer 2

Na+ is taken up by GI tract

Question 3

What are the 3 main functions of the stomach?

Answer 3

1. secretion
2. motor - regulate food intake, mixing chyme, decrease food size
3. humoral - gastrin, somatostatin

Question 4

What are proximal secretions?

Answer 4

• HCI
• Pepsinogen (cleaved into pepsin (protease))
• intrinsic factor
• mucins/bicarbonate ions

Question 5

What are distal secretions?

Answer 5

• gastrin
• somatostatin
• pepsinogens

Question 6

How many litres does the mucosal layer of the stomach secretory cells?

Answer 6

2L/day

Question 7

What is basal secretions rich in?

Answer 7

rich in H+

Question 8

What are the different cells & their secretions in the oxyntic glands?

Answer 8

• Epithelial cells - HCO3
• Mucous neck cells - mucus
• Parietal cells - HCI, intrinsic factor
• Chief cells - pepsinogen

Question 9

How is the pyloric glands different from the oncotic glands?

Answer 9

pyloric glands don’t contain parietal cells

Question 10

What does intrinsic factor absorb?

Answer 10

Vitamin B12

Question 11

Describe resting parietal cells

Answer 11

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

Question 12

Describe the cytoskeletal changes when a parietal becomes active

Answer 12

• fusion of tubulovesicular & canalicular membranes]- 50-100x increase in surface area
• microvilli appearance
• insertion of H, K-ATPase pump, K+ + Cl- channels

Question 13

What is the major function of parietal cells?

Answer 13

gastric acid secretion

Question 14

What channels are found on the apical side of a parietal cell?

Answer 14

• H-K ATPase
• chloride channel
  (HCl secretion)

Question 15

What channels are found on the basolateral side of a parietal cell?

Answer 15

• Na-K ATPase
• HCO3 & Cl channel

Question 16

What stimulates ATPase releasing HCl acid?

Answer 16

the release of acetylcholine via the vagus nerve

Question 17

What do ECL cells release?

Answer 17

histamine, stimulating the H2 receptor, stimulating the H-K ATPase

Question 18

What can stimulate H+?

Answer 18

Histamine (ECL), ACh (vagus), gastrin (G cells)

Question 19

What inhibits gastrin?

Answer 19

low pH, therefore downregulating H+ secretions

Question 20

What similarity do SI & LI structures have?

Answer 20

• crypts of Leinerkuhn (SI - microvilli)
• absorpb fluid & electrolytes via villus cells/surface epithelia respectively

Question 21

What do crypt epithelial cells secrete?

Answer 21

fluid & electrolytes (Protective-bacteria/toxins)

Question 22

What is the difference in net absorption/secretion between the small & large intestine?

Answer 22

small - absorbs K+
large - secretes K+

Question 23

Is paracellular movement passive or active?

Answer 23

passive - determined by tight junctions

Question 24

Do the crypts cells secrete or absorb?

Answer 24

secrete

Question 25

Do the surface cells secrete or absorb?

Answer 25

absorb

Question 26

What can activate a chloride channel?

Answer 26

cAMP

Question 27

What does the Na+K+Cl- cotransporter bring?

Answer 27

brings ions into cell from blood

Question 28

What ATPase is in the intestine?

Answer 28

K-Na ATPase

Question 29

What ATPase is found on the basolateral side of the jejunum?

Answer 29

K-Na ATPase

Question 30

What exchanger is found on the apical side of the Jejunum?

Answer 30

Sodium-Hydrogen exchanger

Question 31

What is different in the Ileum compared to the Jejunum?

Answer 31

ileum has a chlorine-bicarbonate exchanger

Question 32

What is the main role of the ileum?

Answer 32

net absorption of NaCl

Question 33

What is the main role of the jejunum?

Answer 33

absorption of Na & bicarbonate

Question 34

What do acinar cells secrete?

Answer 34

enzymes (CCK recs)

Question 35

What do centroacinar cells secrete?

Answer 35

isotonic aqueous portion, modified by ductal cells

Question 36

How is HCO3 secreted into pancreatic juice?

Answer 36

using Cl-HCO3 exchanger

Question 37

What is the net effect of the pancreas?

Answer 37

- secretion of HCO3 - absorption of H+ (acidification of pancreatic venous blood)

Question 38

What are ductal cells receptors for?

Answer 38

CCK, Ach + secretin, which will upregulate production

Question 39

What induces the synthesis if Na+ channels in the large intestine?

Answer 39

aldosterone

Question 40

Is K secreted or absorbed in the large intestine?

Answer 40

secreted

Question 41

What happens to the products of carbohydrases?

Answer 41

products absorbed into villus blood

Question 42

What happens to the products of proteases?

Answer 42

products absorbed into villus blood

Question 43

What happens to lipases + bile salts?

Answer 43

products into the lacteals within villus (part of the lymphatic system)

Question 44

How does glucose get reabsorbed?

Answer 44

facilitated diffusion (cotransported with Na+)

Question 45

How do proteins get absorbed?

Answer 45

travel as dipeptides or tripeptides, which have been broken down by peptidase. - travels into the epithelial cell of SI, using facilitated diffusion & sodium as a cotransporter.

Question 46

How do micelles get transported across the epithelial cell of villi?

Answer 46

as chylomicrons

Question 47

What % of the pancreas does the islets of langerhans make up?

Answer 47

10-30% - 500,000

Question 48

What is the rest of the pancreas made of?

Answer 48

aciner & ductal cells - part of exocrine tissue that secrete enzymes, bicarbonate for digestion

Question 49

What are the islet main secretory cells?

Answer 49

- beta cells (65%) - alpha cells (20%) - delta cells (10%)

Question 50

What are other cells found in the endocrine tissue?

Answer 50

F cells (polypeptide cells) E cells Enterochromaffin cells

Question 51

What do B cells secrete?

Answer 51

insulin

Question 52

What do A cells secrete?

Answer 52

glucagon

Question 53

What do D cells secrete?

Answer 53

somatostatin

Question 54

What do F cells secrete?

Answer 54

pancreatic polypeptide

Question 55

What do E cells secrete?

Answer 55

Ghrelin protein (stimulates hunger)

Question 56

How does blood distribute via fenestrated capillaries?

Answer 56

small arteries enter islet core

Question 57

What allows communication & control between B & A cells?

Answer 57

gap junction between B & A cells

Question 58

What does somatostatin do?

Answer 58

somatostatin is a power inhibitor of glucagon & insulin secretion

Question 59

What are islets innervated by?

Answer 59

adrenergic - sympathetic innervation cholinergic - parasympathetic innervation

Question 60

How does glucose enter the B cells?

Answer 60

via GLUT2

Question 61

What are the 3 types of G-coupled receptors?

Answer 61

- B adrenergic - Glucagon - Somatostatin A

Question 62

What does the activation of B adrenergic agonist & glucagon lead to?

Answer 62

upregulates - adenyl cyclase - leading to more - Exocytosis of insulin

Question 63

What does activation of somatostatin A & adrenergic lead to?

Answer 63

down regulation of adenyl cyclase, leading to less exocytosis of insulin

Question 64

What does insulin encourage?

Answer 64

the insertion of GLUT4 (allows for glucose uptake) in the membrane of cells

Question 65

What is the name given to the conversion of glucose to glycogen?

Answer 65

glycogenesis

Question 66

What happens to excess glucose?

Answer 66

it converted into adipose tissue (lipogenesis)

Question 67

What 4 effects does insulin have on muscle?

Answer 67

1. promotes glucose uptake 2. promotes glycogen synthesis from glucose 3. promotes glycolysis & carbohydrate oxidation 4. promotes protein synthesis

Question 68

What is the action of insulin on adipocytes?

Answer 68

- glucose converted into FA (fatty acids) - stored as triglycerides - insulin prevents lipolysis

Question 69

What are biguanide drugs?

Answer 69

drugs that up-regulate receptors on target tissues

Question 70

What drives the mensural cycle?

Answer 70

the hypothalamic-pituitary gonadal axis