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PR - Big book > 17.4 Digestive system > Flashcards

17.4 Digestive system Flashcards

1
Q

GI epithelium

A

innermost lining of lumen

EPITHELIAL CELLS (same as outer surface of the body and inner surface of respiratory tract)

TIGHT JUNCTIONS = impermeable

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2
Q

skeletal muscle and cardiac muscles are STRIATED (striped)

A

GI muscle is smooth

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3
Q

GI HAS functional syncytium

A

GI nerve impulses spread to neighboring cells

It’s own nervous system

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4
Q

two networks of neurons: MYENTERIC PLEXUS and SUBMUCOSAL plexus

A

MYENTERIC found between circular and longitudinal muscle layers, regulates GUT MOTILITY

SUBMUCOSAL regulates enzyme secretion, gut blood flow, and ion/water balance in the lumen (SPARSE in anus and esophagus)

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5
Q

EXOCRINE ORGANS

A

release of enzymes from LIVER, GALLBLADDER, and PANCREAS

also GASTRIC GLANDS of stomach are EXOCRINE - secrete pepsinogen (protease zymogen) and acid

MUSCUS-SECRETION from GOBLET cells (all over the GI tract) - produces mucous membrane

SECRETION OF WATER (GALLONS) are secreted and reabsorbed in the small intension or colon

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6
Q

salivary amylase = hydrolyzes starch

A

also called PTYALIN

saliva also contains LINGUAL LIPASE for fat digestion

NO DIGESTION OF PROTEINS IN MOUTH

Lysozyme = breaks down bacterial cell walls (innate immunity)

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7
Q

epiglottis

A

an cartilaginous flap that blocks water/food from trachea

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8
Q

lower esophageal sphincter

A

at end of esophagus, PREVENTS reflux

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9
Q

Stomach

A

pH = 2

  • HCl is secreted by parietal cells, located in the gastric mucosa (“Acidic parents”)
  • HCl converts of pepsinogen to pepsin (BREAKS PROTEINS DOWN TO AAs)
  • proenzyme (INACTIVE ZYMOGEN - activated by CLEAVAGE/PROTEOLYSIS at a specific site) is pepsinogen, which is released by the CHIEF cells of stomach wall; activated by HCl
  • pepsinogen unfolds in low acidity, and cleaves itself in AUTOCATALYTIC fashion (pepsin cleaves pepsinogen, removing 44 amino acids)
  • HCl hydrolyzes some polysaccharides
  • HCl hydrolyzes polypeptides into FRAGMENTS
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10
Q

chyme

A

food with gastric secretion

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11
Q

cholecystokinin (stomach emptying)

A

secreted by epithelial cells of the duodenum, which inhibits the opening of the pyloric sphincter (more food in duodenum) inhibits stomach emptying

Cholecystokinin releases digestive enzymes from pancreas and gallbladder

a hunger suppressant

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12
Q

small intenstine

A

duodenum, JEJUNUM, ILEUM

10 feet long, 25 feet long when dead

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13
Q

Peyer’s patches

A

immune system

lymphocytes dotting the villi, confer immunity to gut pathogens

ILEUM

Also known as aggregated lymphoid nodules

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14
Q

Pancreas

A

digestive enzymes and BICARB exits by PANCREATIC DUCT

shares the SPHINCTER OF ODDI with common bile duct

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15
Q

bile acid sequestrants BIND TO BILE ACIDS and are secreted into the DUODENUM as FECES

A

drugs which bind acids in the small intestine, causing them to remain in GI lumen and excreted as feces

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16
Q

Duodenal enzymes

A
  1. duodenal enterokinase (enteropeptidase) activates the pancreatic zymogen TRYPSINOGEN to TRIPSIN
  2. brush border enzymes - hydrolyze the smallest carbs and proteins (disaccharides and dipeptides) into monosaccharides and amino acids
17
Q

Duodenal hormones

A
  1. Cholecystokinin (CCK) - response to FATS, prevents stomach emptying, stimulates gallbladder contraction (bile release), decreases gastric motility
  2. Secretin - response to ACID, releases HCO3- in water, neutralizing the pH from stomach HCl. Duodenal pH must be kept NEUTRAL or slightly basic for pancreastic enzymes to function
  3. Enterogastrone - decreases stomach emptying
18
Q

cecum

A

first part of large intestine

19
Q

jejunum and ileum

A

substances not absorbed in duodenum must be absorbed here

LOWER small intestine (ILEUM) absorbs B12 (only when complexed with INTRINSIC FACTOR, a glycoprotein secreted by parietal cells of stomach)

Ileum leads to cecum, divided by the ILEOCECAL VALVE

20
Q

Colon (LARGE INTESTINE)

A

3-4 feet long

IMPORTANT for absorbing water and minerals, stores feces

CECUM is first part

appendix is finger-like appendage (lymphatic tissue)

Rectum is last part

21
Q

Internal anal sphincter

A

smooth muscle, under autonomic control

external anal sphincter, SKELETAL muscle

SAME AS URINARY SPHINCTERS

22
Q

Vitamin K

A

essential for blood clotting

gut bacteria supply vitamin K

23
Q

Pancreas (EXOCRINE)

A
  1. amylase - polysaccharides -> disaccharides
  2. lipase - hydrolyze triglycerides at micelle
  3. Nuclease -> hydrolyze DNA and RNA
  4. Proteases -> hydrolyzing polypeptides into di/tripeptides (released as ZYMOGENS)
  5. Enzymes activated by trypsin (see below)
24
Q

enzymes activated by Trypsin

A
  1. Chymotrypsinogen (active: chymotrypsin)
  2. Procarboxypeptidase (carboxypeptidase)
  3. Procollagenase (collagenase)

THESE BREAK DOWN PROTEINS TO DIPEPTIDES AND TRIPEPTIDES

25
Q

Pancreas (ENDOCRINE)

A

ISLETS OF LANGERHANS has 3 types of cells

  1. Alpha - glucagon - low blood sugar - stimulates liver to hydrolyze glycogen and release glucose, also stimulates adipocytes to release fats in the blood (INCREASE GLUCOSE AND FAT RELEASE) - catabolic
  2. Beta - secrete INSULIN (removes glucose into storage as glycogen and fat) - anabolic
  3. delta - secretes SOMATOSTATIN - INHIBITS DIGESTION
26
Q

raising blood glucose

A

Glucagon, epinephrine, cortisol

27
Q

Liver

A

exocrine: RELEASE BILE (1 liter a day)

bile is synthesized from cholesterol

bile contains bile acids (BILE SALTS in deprotonated form), cholesterol, bilirubin (RBC breakdown)

EMULSIFIES large fat particles in duodenum, creating MICELLES, reducing size and increasing surface area, making them better targets of hydrophilic LIPASES

Bile helps fat particles diffuse across the intestinal mucosal membrane

Bile is secreted into the duodenum or stored in gallbladder.

Gallstone = large crystal formed from bile

28
Q

Gallbladder

A

NO SECRETORY ABILITIES

NOT ESSENTIAL

controlled by nervous and endocrine system

CCK (released by duodenal cells) and parasympathetic NS stimulate contraction of gallbladder wall

29
Q

Liver (2)

A

receives OXYGENATED blood fo hepatic arteries

receives venous blood draining from stomach and intestines through HEPATIC PORTAL VEIN

HEPATOCYTES absorb nutrients

GLUCONEOGENESIS - when blood glucose is low, breaks glycogen down and GNG

STORES GLUCOSE AS GLYCOGEN (as well as skeletal muscles), only liver can release glucose to bloodstream

30
Q

glycogenolysis

A

the product is glucose-6-phosphate, which must be dephosphorylated by GLUCOSE-6-PHOSPHATASE, which then can be released into blood

31
Q

Liver (3)

A

waste products of protein catabolism regulated here

NH3 (ammonia) are byproducts of amino acid breakdown during starvation, converted into UREA. this circulates the blood and excreted by kidney in urine

32
Q

Liver lipid metabolism

A

chylomicrons degraded by lipases into triglycerides, glycerol, and cholesterol-rich chylomicron remnants

the remnants are taken up by hepatocytes and combined with proteins to make lipoproteins (HDL, LDL, VLDL) which enter the blood and are source of cholesterol and triglycerides

PLASMA PROTEINS (albumin, globulin, fibronogens, CLOTTING factors) are made in liver and secreted into blood

albumin prevents fluid from leaving bloodstream (OTHERWISE, EDEMA)

33
Q

Liver (detox)

A

reduces toxicity

smooth ER in hepatocytes contains enzyme pathways to break down drugs and toxins

34
Q

appetite

A

ghrelin - GRR I’m HUNGRY

leptin (released by white adipose tissue) - adipostat - maintains stable lipid content, released in response to increased triglyceride levels

Peptide YY - reduces appetite

impact the arcuate nucleus of the hypothalamus

35
Q

uptake of monosaccharides

A

actively transported by intestinal epithelial cells

apical SYMPORT transports 1 sugar INTO the cell while allowing sodium to flow IN (the Na/K ATPases are constantly pumping Na+ OUT, keeping INTRACELLULAR SODIUM very LOW)

Facilitated diffusion (Uniport) allows high concentration monosaccharides to flow into nearby capillaries

36
Q

uptake of peptides

A

SYMPORT specific to each amino acid uptakes AA and Sodium into INTESTINAL EPITHELIAL cell, and uniporter facilitates movement out into the INTERSTITIUM

AAs end up in liver, where it’s catabolized for energy or synthesis (anabolism)

37
Q

fat digestion (tri -> mono -> tri -> mono -> tri)

A

organized into huge hydrophobic droplets

CCK stimulates gallbladder contraction, in which BILE acids emulsify lipids = micelle

pancreatic lipase hydrolyzes triglycerides into monoglycerides and free fatty acids, which are SMELL enough to move into EPITHELIAL cells by simple diffusion (they are SMALL and HYDROPHOBIC).

they are converted back to triglycerides and packages into CHYLOMICRONS (fat + protein) which enter LACTEALS, eventually emptying into thoracic duct, emptying into large vein near heart

The chylomicrons CIRCULATE and removed by adipose and liver tissues which contain LIPOPROTEIN LIPASE, hydrolyzing chylomicron triglycerides into monoglycerides and free fatty acid

these diffuse into adipocytes and liver cells, remade into triglycerides

38
Q

Vitamins

A

FAT-SOLUBLE or WATER-SOLUBLE

FS requires bile acids for solubilization and absorption

FS vitamins stored in adipose tissue

Excess WS excreted in urine by kidneys

PR - Big book (29 decks)

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