17.4 Digestive system

Question 1

GI epithelium

Answer 1

innermost lining of lumen

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

TIGHT JUNCTIONS = impermeable

Question 2

skeletal muscle and cardiac muscles are STRIATED (striped)

Answer 2

GI muscle is smooth

Question 3

GI HAS functional syncytium

Answer 3

GI nerve impulses spread to neighboring cells

It’s own nervous system

Question 4

two networks of neurons: MYENTERIC PLEXUS and SUBMUCOSAL plexus

Answer 4

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)

Question 5

EXOCRINE ORGANS

Answer 5

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

Question 6

salivary amylase = hydrolyzes starch

Answer 6

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)

Question 7

epiglottis

Answer 7

an cartilaginous flap that blocks water/food from trachea

Question 8

lower esophageal sphincter

Answer 8

at end of esophagus, PREVENTS reflux

Question 9

Stomach

Answer 9

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

Question 10

chyme

Answer 10

food with gastric secretion

Question 11

cholecystokinin (stomach emptying)

Answer 11

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

Question 12

small intenstine

Answer 12

duodenum, JEJUNUM, ILEUM

10 feet long, 25 feet long when dead

Question 13

Peyer’s patches

Answer 13

immune system

lymphocytes dotting the villi, confer immunity to gut pathogens

ILEUM

Also known as aggregated lymphoid nodules

Question 14

Pancreas

Answer 14

digestive enzymes and BICARB exits by PANCREATIC DUCT

shares the SPHINCTER OF ODDI with common bile duct

Question 15

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

Answer 15

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

Question 16

Duodenal enzymes

Answer 16

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

Question 17

Duodenal hormones

Answer 17

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

Question 18

cecum

Answer 18

first part of large intestine

Question 19

jejunum and ileum

Answer 19

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

Question 20

Colon (LARGE INTESTINE)

Answer 20

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

Question 21

Internal anal sphincter

Answer 21

smooth muscle, under autonomic control

external anal sphincter, SKELETAL muscle

SAME AS URINARY SPHINCTERS

Question 22

Vitamin K

Answer 22

essential for blood clotting

gut bacteria supply vitamin K

Question 23

Pancreas (EXOCRINE)

Answer 23

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)

Question 24

enzymes activated by Trypsin

Answer 24

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

THESE BREAK DOWN PROTEINS TO DIPEPTIDES AND TRIPEPTIDES

Question 25

Pancreas (ENDOCRINE)

Answer 25

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

Question 26

raising blood glucose

Answer 26

Glucagon, epinephrine, cortisol

Question 27

Liver

Answer 27

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

Question 28

Gallbladder

Answer 28

NO SECRETORY ABILITIES NOT ESSENTIAL controlled by nervous and endocrine system CCK (released by duodenal cells) and parasympathetic NS stimulate contraction of gallbladder wall

Question 29

Liver (2)

Answer 29

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

Question 30

glycogenolysis

Answer 30

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

Question 31

Liver (3)

Answer 31

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

Question 32

Liver lipid metabolism

Answer 32

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)

Question 33

Liver (detox)

Answer 33

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

Question 34

appetite

Answer 34

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

Question 35

uptake of monosaccharides

Answer 35

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

Question 36

uptake of peptides

Answer 36

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)

Question 37

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

Answer 37

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

Question 38

Vitamins

Answer 38

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