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Physiology (MPP 3202) > Ch. 18 Day 2 > Flashcards

Ch. 18 Day 2 Flashcards

1
Q

Ability of bile salts to emulsify fat

A

conversion of hydrophobic cholesterol into amphipathetic bile acids
–occurs in liver

PRO and CHO water-soluble, fat isn’t water-soluble

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2
Q

Digestion and Absorption of Fats

A

Digestion begins in duodenum: bile stabilizes fat emulsion and lipase (from pancreas) breaks it down into fatty acids and glycerol

Phospholipase A (from pancreas) digests phospholipids into fatty acids and lysolecithin

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3
Q

Fat Emulsification and Digestion

A

Digestion products of fat (free fatty acids) incorporated into micelles, producing mixed micelles; these diffuse into absorptive surface and fatty acids pass into cells

In micelles, hydrophilic parts sticking out, hydrophobic parts sticking in

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4
Q

Absorption and Transport of Fats

A

Fatty acids, monoglycerides, and lysolecithin move into bile micelles and are transported to brush border

Fat molecules then leave micelles and diffuse into epithelial cells of villi

Inside epithelial cells, they are regenerated into triglycerides, cholesterol, and phospholipids and combined with proteins to form Chylomicrons

Chylomicrons are secreted by exocytosis into the central lacteal of villus

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5
Q

What is the Central Lacteal?

A

Main collection point for lymph; eventually chylomicrons secreted int there will be returned to blood at thoracic duct at subclavian vein

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6
Q

Fluid and electrolyte secretion and absorption

A

Oral fluid intake = 2,000 mL/day; digestive secretions = 7,000 mL/day; all but 100mL is reabsorbed, mainly in small intestine but also in large intestine

Mostly water and ions (Na+, K+, Cl-, HCO3-, H+).

Secreted ions are reabsorbed, water follows osmotic gradients created by solute transfer

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7
Q

Where is most of the water coming into the gut coming from?

A

The GI tract itself and accessory organs
–some comes from food

Most of water being secreted by GI tract going to be reabsorbed

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8
Q

Control of digestive function occurs at each level of the GI tract. What are the 3 phases?

A
  1. Cephalic phase
    - -stimulation of gastric activity
  2. Gastric phase
    - -stimulation of gastric activity
  3. Intestinal phase
    - -inhibition of gastric activity, stimulation of digestion in intestine
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9
Q

Cephalic Phase

A

Short duration, prepares stomach for arrival of food

Mechanism: neural - reflex signals from medulla oblongata via vagal preganglionic fibers to synapses in submucosal plexus

Actions:

  • 1: direct neural stimulation of acid, mucus, enzyme secretion
  • 2: indirect via stimulation of gastrin release from G cells, gastrin stimulates motility and acid secretion
  • 3: indirect via stimulation of histamine release from ECL cells

Vagal signals stimulate acid secretion via 3 mechanisms occurring simultaneously in both fundus and antrum:

  • -a) direction signal via ACh
  • -b) indirect via histamine
  • -c) indirect via gastrin
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10
Q

Gastric Phase

A

Duration: 3-4 hours, enhances secretion, mix, acidify, and increase surface area of chyme, begin hydrolysis of protein

Mechanisms:

  • 1: neural reflexes triggered by stretch, rising pH
  • 2: hormonal (gastrin) release triggered by vagal signals, peptides, AA’s
  • 3: local release of histamine (stimulates acid secretion) triggered by stretch

Actions: increased production and secretion of acid and pepsinogen, increased motility and mixing waves

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11
Q

Gastric Emptying

A

Chyme metered out into duodenum as stomach empties

Emptying is regulated by intestinal signals to prevent “dumping”

Liquids empty fastest, solids slowest, nutrient-specific control (sensing of physiochemical properties, e.g. H+, fat)

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12
Q

Intestinal Phase

A

Duration: hours, acts to control gastric emptying rate, to limit gastric acid secretion, and to optimize conditions for enzymatic digestion in intestinal lumen

Mechanisms:

  • 1: neural - short reflex (enterogastric reflex) triggered by distention of duodenum
  • 2: hormonal - stimulation of secretin, CCK, GIP, by presence of H+, CHO, AAs, lipids

Actions: feedback inhibition of gastric acid/pepsinogen secretion, gastric motility, promotion of intestinal/pancreatic/biliary secretion, intestinal motility

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13
Q

Gastrin (KNOW FOR EXAM)

A

Secreted by stomach

Effects:

  • -stimulates parietal cells to secrete HCl
  • -stimulates chief cells to secrete pepsinogen
  • -maintains structure of gastric mucosa
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14
Q

Secretin (KNOW FOR EXAM)

A

Secreted by small intestine

Effects:

  • -volume and HCO3- secretion from pancreas: raises pH of incoming chyme –> allows pancreatic enzymes to be active
  • -promotes favorable environment for enzymatic digestion
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15
Q

CCK (KNOW FOR EXAM)

A

Secreted by small intestine

Effects:

  • -1) pancreatic enzyme secretion
  • -2) bile secretion via stimulation of gallbladder contraction - responsible for enzymatic digestive activity, fat emulsion stability, and absorption of digestion products of fat
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16
Q

Regulation of pancreatic juice and bile secretion

A

When chyme enters duodenum, 2 hormones produced:

  • a) secretin is produced in response to drop in pH (production stops w/ rise in pH)
  • b) cholecystokinin (CCK) is produced in response to presence of partially digested proteins and fats in chyme (production stops when food leaves small intestine)

Pancreatic enzyme production of trypsin, lipase, and amylase is stimulated by ACh from vagus nerve and CCK

Pancreatic bicarbonate production is stimulated by secretin

Liver produces bile continuously, but arrival of food into duodenum stimulates increased bile production

Happens when:

  • -bile acids are returned to liver after intestinal absorption via enterohepatic circulation (so we don’t have to continually make bile salts)
  • -secretin and CCK stimulate increased bicarbonate secretion into bile
  • -CCK (in response to presence of fat in chyme) stimulates gallbladder contraction
17
Q

Enterohepatic Circulation

A

Recycling of bile salts regulates hepatic synthesis of bile acids from cholesterol, and therefore, controls plasma cholesterol levels
–can “exploit” this process to reduce plasma cholesterol levels to help patients w/ higher levels

~5% of bile salts lost in feces, rest are reabsorbed

Bile acid-binding resins:

  • -Questran (cholestryamine)
  • -Welchol (colesnvelam)
  • -Colestipid/Colestid (colestipol)
  • -disrupt enterohepatic circulation, reduce cholesterol levels
18
Q

Pancreatic and Biliary Secretion

A

Control by both vagal stimulations and intestinal hormones

Pancreatic Exocrine Secretion:

  • -acid in duodenum –> secretin –> stimulates secretion of HCO3- by pancreas
  • -fat, AA’s in duodenum –> CCK –> stimulates secretin of enzymes by pancreas

Biliary Secretion:
–fat in duodenum –> CCK –> stimulation of bile secretion by gallbladder and relaxation of Sphincter of Odi

19
Q

Pancreatic Exocrine Secretion

A

Enzymes from acing cells: trypsinogen, chymotrypsinogen, lipase, amylase; HCO3- form ductal cells

Proteases secreted as inactive, zymogen form - activated ONLY in lumen of gut

20
Q

What is a Zymogen?

A

aka proenzyme

Inactive enzyme precursor. Requires a biochemical change (such as hydrolysis reaction releasing active site, or changing configuration to reveal active site) for it to become an active enzyme

21
Q

Pancreatic Enzymes

A

most are inactive (zymogens) until they reach small intestine:

  • -enteropeptidase activates trypsinogen –> trypsin (to digest protein)
  • -trypsin activates other enzymes

Enteropeptidase is also called enterokinase; expressed w/in brush border

22
Q

What are the fat soluble vitamins?

A

A, D, E, and K vitamins (“ADEK” vitamins)

–absorbed w/ fat

23
Q

What are the water soluble vitamins?

A

Vitamin C and most B vitamins

–carrier mediated transport

24
Q

Vitamin B12

A

Requires gastric secreted Intrinsic Factor (IF), uptake by enterocytes in terminal ileum

IF is produced and secreted into stomach by parietal cells - the SAME cells which secrete gastric acid

Thus, if anything which affects acid secretion is going to similar affect IF secretion –> absorption of vitamin B12 is affected

Vitamin B12 deficiency manifests as anemia

25
Q

Almost all physiologically significant digestion/absorption occurs in ____ ____.

A

Small intestine

26
Q

With the exception of ____, most nutrients enter the blood and go to the liver via Hepatic Portal System.

A

Fat

27
Q

Fat absorption and transport

A

via chylomicrons (CM) in lymph, CM enter circulation at thoracic duct (bypasses liver) –> delivers fat to muscle, adipose –> reduced size “remnant” particle then taken up by liver

28
Q

Why does fat transport via chylomicrons occur in lymph instead of directly in blood?

A

Chylomicrons (100-500 nm) too large to pass through relatively tight vascular endothelium

Unique aspect to transport of absorbed fat

29
Q

How does the colon concentrate waste?

A

By reabsorbing water and electrolytes, remaining residue is moved distally for elimination

30
Q

Colonic Motility

A

Segmenting contractions (esp. in ascending colon)

Mass movement triggered by gastro-colic reflex

Entry into and distension of rectum triggers defecation reflex

31
Q

The mucosal barrier of the GI tract is?

A

Gut mucosa in host defense

Defensins - secreted by Paneth cells

32
Q

Immune-inflammatory response is normally self-limiting, but dysregulation can cause disease such as?

A

Inflammatory Bowel Disease (IBD)

33
Q

What is “FAE”?

A

Follicular associated epithelium

Physiology (MPP 3202) (32 decks)

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