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PHYSIOLOGY > Prelims - GIT ORGANIZATION & FUNCTION (Dr. Castro & Dr. Nobleza) > Flashcards

Prelims - GIT ORGANIZATION & FUNCTION (Dr. Castro & Dr. Nobleza) Flashcards

1
Q

How much does stomach secrete?

A

2L/day

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2
Q

Secretion of the stomach is

A

ISOTONIC with Plasma

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3
Q

When secretion is SODIUM RICH (by NON PARIETAL CELLS)

A

Basal Secretion

  • No food
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4
Q

When secretion is H+ RICH (PARIETAL CELLS)

A

Stimulated Secretion

  • Thinking of food
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5
Q

Describe CARDIA

A

No Parietal Cells

No Acid Secretion

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6
Q

Other term for PARIETAL CELLS

A

Oxyntic Cells

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7
Q

Other term for CHIEF CELLS

A

Peptic Cells

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8
Q

Parietal cells secrete

A

HCl and Intinsic Factor

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9
Q

Chief cells secrete

A

Pepsinogen

  • it also secretes GASTRIC LIPASE
  • not an acid
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10
Q

pH needed to activate Pepsinogen

A

pH < 3

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11
Q

Usual intraluminal pH range

A

4-6

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12
Q

Describe ANTRUM

A

No Parietal Cells

No Acid Secretion

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13
Q

Endocrine Cells include

A

G Cells

D Cells

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14
Q

G Cells secrete

A

GASTRIN

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15
Q

GASTRIN function

A

Gastric Acid Secretion

Trophic Effect

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16
Q

D Cells secrete

A

SOMATOSTATIN

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17
Q

SOMATOSTATIN function

A

Inhibit Gastrin release and Parietal acid secretion

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18
Q

What secretes HISTAMIN

A

Enterochromaffin-like (ECL) Cells

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19
Q

In Basal State, acid secretion is

A

LOW

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20
Q

Tubulovesicular membrane present in resting non-stimulated parietal cells have what pumps

A

H-K Pump

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21
Q

H-K pump is responsible for

A

Acid Secretion

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22
Q

With stimulation, pH of gastric secretion is

A

<2

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23
Q

Process of ACID SECRETION

A

(1) Stimulation
(2) Tubulovesicular membrane (with H-K Pump) fuse into Cannalicular membrane
(3) Increase surface area of Parietal cells
(4) Insertion of H-K Pumps, Potassium and Chloride channels into Cannalicular membrane
(5) GASTRIC H+ EXTRUDED INTO LUMEN EXCHANGE FOR K
(6) K+ is recycled, Passive moment of Cl- into gland lumen
(7) Active secretion of HCl
(8) Increase in Parietal cell pH
(9) Passive uptake CO2 and H2O; Carbonic Anhydrase convert to H+ and HCO3 (H+ substrate for H-K Pump)

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24
Q

2 Inhibitors of H-K Pump

A

(1) Substituted Benzimidazoles
* not inhibit Na-K pump
(2) Competitive inhibitors of K binding site

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25
Q

Mechanism of GASTRIN

A

(1) CCK 2
(2) Ga(q)
(3) PLC
(4) IP3
(5) Ca and Activation of PKC

  • Gastrin is from G Cells
  • CCK 1 - attached to CCK
    CCK 2 - equal affinity for CCK 2 and Gastrin
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26
Q

Mechanism of HISTAMIN

A

(1) H2 Receptor
(2) Ga(s)
(3) Adenylyl Cyclase
(4) CAMP
(5) PKC
(6) Phosphorylation of H-K pump

  • Histamine released from ECL cells
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27
Q

Mechanism of Ach

A

(1) M3 Receptor
(2) Ga(q)
(3) PLC
(4) Converts IP2 to IP3 (increases calcium release) & DAG (PKC)

  • Ach released from Vagal stimulation
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28
Q

Histamine/H2 receptor blockers example

A

Histidine

  • can be direct or indirect
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29
Q

ACID SECRETION by PARIETAL CELLS

A

(1) Water in Parietal cell dissociates into H+ and OH-
(2) H+ active secretion in exchange with K+ (H-K ATPase)
(3) K+ ions in Basolateral side leak into lumen (BUT RECYCLED)
(4) Basolateral pump creates low IC Na = Low Na+; REABSORPTION
(5) K+ and Na+ in cannaliculus is reabsorbed in CYTOPLASM; H+ in CANNALICULUS
(6) Increase OH- to accumulate; Form HCO3 from CO2 Carbonic Anhydrase
(7) HCO3 out across basolateral membrane into ECF; Exchange Cl
(8) Increase HCl in cannaliculus
(9) HCl secreted outside the lumen

30
Q

ACID SECRETIONS

Direct and Indirect Example

A

DIRECT: Gastrin, Histamine and Ach

INDIRECT: Gastrin and Ach stimulate ECL cells to secrete Histamine and act on parietal cells

31
Q

What secretes pepsinogen

A

Chief cells and Mucus cells

32
Q

What initiates hydrolysis of ingested protein in the stomach

A

Pepsin

33
Q

Group 1 Pepsinogen are secreted from

A

BASE OF GLANDS in Corpus of Stomach

34
Q

Group II Pepsinogens are secreted from

A

CHIEF CELLS and MUCUS NECK CELLS of Cardia, Corpus and Antral Area

35
Q

Basal secretion of Pepsinogen

A

20% of Maximal Secretion after stimulation

36
Q

Pepsinogen is released through

A

Compound Exocytosis

  • Allows RAPID SECRETION and SUSTAINED release
37
Q

Pattern of Pepsinogen release

A

INITIAL PEAK followed by PERSISTENT LOWER RATE of secretion

38
Q

STIMULATION of CHIEF CELLS

A

(1) Agonists via CAMP
(2) Activate CAMP
(3) Increase secretion of Pepsinogen

(1) M3 receptors for Ach/Gastrin/CCK 1

PATH 1
(2) Increase Ca release from intracellular stores by IP3 and increase Ca

PATH 2
(2) Ach release due to vessel stimulation
(3) Release pepsinogen; stimulate Parietal cell to secrete acid
(4) STOMACH: Dec pH, stimulate chief cells = Pepsinogen release
DUODENUM: Acid = release Secretin from S Cells; Chief cells release more Pepsinogen

39
Q

Barrier that prevents acid from destroying own cells

A

Mucous Bicarbonate Barrier

40
Q

In the Mucous Bicarbonate Barrier, HCl passes througn one pathway which is

A

Viscous Fingering

41
Q

Describe G-17

A

More Active; ANTRAL G cells

42
Q

Describe G-34

A

Slower degradation; DUODONENAL G Cells

43
Q

G-34 released from

A

Duodenal G Cells

44
Q

G-17 released from

A

Antral G Cells

45
Q

GASTRIN major effect on GI cells

A

> Stimulation of Acid Secretion by parietal cells
Release of Histamine by ECL cells
Regulation of mucosal growth (TROPHIC effect) on Corpus, SI and LI

46
Q

What releases SOMATOSTATIN

A

D cells

47
Q

What triggers D Cells Corpus

A

Neural and Hormonal Mechanism

  • endocrine
48
Q

What triggers D cells Antrum

A

Low intraluminal pH

  • Paracrine
49
Q

This D cell is stimulated by low intraluminal pH

A

D cells Antrum (PARACRINE)

50
Q

This D cell is triggered by Neural and Hormonal mechanism

A

D Cell Corpus (ENDOCRINE)

51
Q

SOMATOSTATIN 3 Mechanisms

A

(1) Bind to Ga(1) coupled receptor SST —> inhibit adenylyl cyclase —> antagonize stimulatory effect on Histamine
(2) CORPUS of stomach —> inhibit release of Histamine from ECL cells —> reduce gastric acid secretion
(3) ANTRUM of stomach —> inhibit release of Gastrin from G cells —> reduce gastric acid secretion

52
Q

Most potent inhibitor of gastric acid secretions

A

Lipid

53
Q

SECRETIN is released from

A

S Cells of Small Intestine/Duodenum

54
Q

SECRETIN functions

A

> Inhibition of release of GASTRIN from Antrum
Stimulation of SOMATOSTATIN release
Direct down regulation of PARIETAL H release

55
Q

GASTRIC INHIBITORY PEPTIDE (GIP) is released from

A

K Cells in the duodenum and jejunum

56
Q

Cholecystokinin (CCK) is released from

A

I Cells of duodenum/jejunum

57
Q

GASTRIC INHIBITORY PEPTIDE (GIP) function

A

> (directly) inhibit PARIETAL CELL ACID SECRETION

> (indirectly) inhibit ANTRAL GASTRIN RELEASE

58
Q

CHOLECYSTOKININ (CCK) function

A

> (feedback inhibition): directly reduces GASTRIC ACID secretion by PARIETAL CELLS

59
Q

Inhibit Histamine activation

A

Prostaglandin (PGE2)

60
Q

PARTS OF STOMACH and specific ENZYMES they secrete

A

CARDIA - Mucous Cells

FUNDUS - Parietal Cells (HCl)
                  Chief Cells (Pepsin)

BODY/CORPUS

ANTRUM - Mucous Cells
                   G Cells (Gastrin)

PYLORUS

61
Q

3 Phases of Gastric Acid Secretion

A

(1) Cephalic - 30% of total acid
(2) Gastric - 50-60% of total acid
(3) Intestinal - 5-10% of total acid

62
Q

Explain CEPHALIC PHASE

A

(1) Sight, smell, taste or thought and swallowing of food
(2) Mediated by VAGUS NERVE of (Medulla Oblongata)
(3) Parasympathetic stimulation
(4)
- Release of Ach: Parietal cell H+ secretion
- BODY of stomach Ach trigger Histamine release
- ANTRUM GRP induce Gastrin release
- ANTRUM and BODY inhibit D cells - reduce Somatostatin and background inhibition of Gastrin release

63
Q

Explain GASTRIC PHASE

A

(1) DISTENTION of Proximal Part of stomach (VASOVAGAL REFLEX), partially digested proteins stimulate Antral G cells
(2) Send impulse to medulla oblongata; Parasympathetic stimulation
(3) Active parietal cell; Increase Gastric Acid secretion
(4) Mixing of food and Gastric juices: CHYME

64
Q

Explain INTESTINAL PHASE

A

(1) Chyme in DUODENUM
(2) Decrease pH
(3) Inhibition of Gastric Acid
(4)
- Signal Medulla Oblongata inhibition of PS stimulation
- DISTENTION results to stimulation of reflex: decrease secretion
- Release of Secretin, GIP and CCK

65
Q

Contact of food with the Epithelium Stimulates Secretion - Function of ENS

A

(1) Tactile stimulation
(2) Chemical irritation
(3) Distention of the gut wall

66
Q

SYMPATHETIC STIMULATION has a dual effect

A

SYMPATHETIC - Slight increase in secretion

SYMPATHETIC plus PARASYMPATHETIC - with vasoconstriction = dec. blood supply —> decrease secretion

67
Q

TRUE or FALSE

Small increase in volume DOES increase intragastric pressue

A

FALSE

  • does not
68
Q

MECHANICAL ACTIONS of STOMACH

A

(1) PROPULSION - waves move from fundus to pylorus (Pyloric valve closed)
(2) GRINDING - most vigorous grinding and mixing occur close to pylorus (Pyloric valve closed)
(3) RETROPULSION - the pyloric end acts as pump that delivers small amounts of chyme into duodenum, simultaneously forcing most of its contents backward into the stomach (Pyloric valve slightly opened)

69
Q

Emptying of LIQUIDS

A

Function on SMOOTH MUSCLE (Proximal Part)

70
Q

Emptying of SOLIDS

A

Function of SMOOTH MUSCLE (Antral Part)

71
Q

Function on SMOOTH MUSCLE (Proximal Part)

A

Emptying of Liquids

72
Q

Function of SMOOTH MUSCLE (Antral Part)

A

Emptying of Solids

PHYSIOLOGY (6 decks)

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