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Flashcards in Physiology Deck (31):
1

Atropine does what to parietal cells

Atropine blocks vagal stimulation of parietal cells but  vagal stimulation of G cells is unaffected as a different transmitter is used (not ACh)

2

Vagus stimulation of parietal cells

Stimulates ACh --> M3 receptor --> Gq --> IP3/Ca2+ --> H+/K+ ATPase --> H+ seceretion

Stimulates GRP --> +G cells --> Gastrin --> CCKb receptor --> Gq --> IP3/Ca2+ --> H+/K+ ATPase --> H+ secretion

3

ECL cells mechanism on parietal cells

What blocks?

Gastrin stimulates ECL --> histamine --> H2 receptor --> activate cAMP --> activate  H+/K+ ATPase --> H+ secretion

H2 blockers inhibit histamine from activating H2 receptors

4

Prostaglandins/misoprostol mechanism on parietal cells

PG/misoprostol --> Gi --> cAMP inhibited --> H+/K+ ATPase inhibited 

5

Somatostatin mechanism on parietal cells 

Somatostatin --> Gi --> inhibitory cAMP --> inhibit H+/K+ ATPase 

6

Proton Pump Inhibitor

Inhibits H+/K+ ATPase and H+ secretion into gastric lumen 

7

Brunner's Glands

Located in duodenal submucosa. Secrete alkaline mucus. Hypertrophy seen in peptic ulcer disease.

8

Pancreatic secretion

Isotonic fluid

Low flow --> high Cl-

High flow --> high HCO3-

9

alpha-amylase

Starch digestion

Secreted in active form

10

Lipase, phospholipase A, colipoase

Fat digestion

11

Proteases

Protein digestion

Includes trypsin, chymotrypsin, elastase, carboxypeptidases

Secreted as proenzymes also known as zymogens 

12

Trypsinogen

Converted to active enzymes trypsin --> activation of other proenzymes and creation of more trypsinogen (positive feedback loop)

Converted to trypsin by enterokinase/enteropeptidase, an enzyme secreted from duodenal mucosa 

13

Salivary amylase

Starts digestion, hydrolyzes alpha-1,4 linkages to yield disaccharides (maltose and alpha-limit dextrins)

14

Pancreatic amylase

Highest concentration in duodenal lumen, hydrolyzes starch to oligosaccharides and disaccharides

15

Oligosaccharides hydrolases

At brush border of intestine, the rate-limiting step in carbohydrate digestion, produce monosacchardies from oligo- and disaccharides

16

Carboyhydrate absorption

Only monosaccharides (glucose, galactose, fructose) are absorbed by enterocytes. Glucose and galactose are taken up by SGLT1 (Na+ dependent). Fructose is taken up by facilitate diffusion by GLUT-5. All are transported to blood by GLUT-2.

D-xylose absorption test: distinguishes GI mucosal damage from toher causes of malabsorption

17

Iron absorbed

Absorbed as Fe2+ in duodenum

18

Folate absorbed

Absorbed in jejunum

19

B12 absorbed

Absorbed in terminal ileum along with bile acids, requires intrinsic factor

20

Peyer's patches 

Unencapsulated lymphoid tissue found in lamina propria and submucosa of ileum. 

Contained specialized M cells that take up antigen.

21

Peyer's patches B cells

B cells stimulated in germinal centers of Peyer's patches differentiate into IgA-secreting plasma cells, which ultimately reside in lamina propria. IgA receives protective secretory component and is then transported across the epithelium to the gut to deal with intraluminal antigen. 

Think of IgA, the Intra-gut Antibody. And always say "secretory IgA"

22

Bile

Composed of bile salts (bile acids conjugated to glycine or taurine, making them water soluble), phospholipids, cholesterol, bilirubin, water, and ions. 

23

What catalyzes rate-limiting step of bile salts?

Cholesterol 7alpha-hydroxylase catalyzes rate-limitng step.

24

Function of bile 

Digestion and absorption of lipids and fat-soluble vitamins

Cholesterol excretion (body's only means of eliminating cholesterol)

Antimicrobial activity (via membrane disruption) 

25

Bilirubin

Removed how?

Product of heme metabolism. 

Removed from blood by liver, conjugated with glucuronate and excreted in bile.

26

Direct bilirubin

Conjugated with glucuronic acid - water soluble

27

Indirect biliburin 

Unconjugated - water insoluble

28

Macrophage role in breakdown of RBC

Macrophage breakdown RBC --> heme --> unconjugated bilirubin (indirect bilirubin - water insoluble)

29

Unconjugated bilirubin enters bloodstream by

Binding to albumin to form unconjugated bilirubin-albumin complex

30

Conjugated bilirubin forms from unconjugated by

UDP-glucuronosyl-transferase in the liver to form Conjugated bilirubin (water soluble)

31

Conjugated bilirubin to Urobilinogen

Gut bacteria take conjugated to urobilinogen 

80% of urobilinogen to excreted in feces as stercobilin, which gives characteristic color of stool

20% of urobilinogen to enterohepatic circulation --> 90% to liver and 10% to kidney --> excreted in urine as urobilin which gives characteristic color of urine