Final Exam Flashcards
Gastric glands
at the base of the gastric pits, contain endocrine cells that secrete hormones and exocrine cells that secrete an acidic, enzyme containing fluid called gastric juice
mucous neck cells
Secrete acidic mucus
parietal cells
Secrete hydrochloric acid (HCl)
Produce intrinsic factor - required for absorption of vitamin B12
Pepsinogen - enzyme that HCl activates
chief cells
Secrete inactive pepsinogen
When it encounters an acidic environment (HCl) it activates into the enzyme pepsin (begins protein digestion)
DNES cells
Endocrine cells
G cells - secrete hormone gastrin - gastrin stimulates the parietal cells to secrete HCl
3 phases of acid secretion in the stomach
- cephalic phase
- gastric phase
- intestinal phase
cephalic phase
Mediated by sight, smell, taste, thought of food
Prepares the stomach to receive food by increasing the release of hydrogen ions into it
These stimuli trigger the vagus nerve and result in 4 effects
- Direct stimulation of H+ release (from parietal cells)
- Stimulation of gastric secretion (from G cells)
- Stimulation of histamine secretion (from DNES cells)
- Inhibition of somatostatin secretion (from DNES cells)
- Somatostatin inhibits acid secretion (inhibit the inhibiter)
gastric phase
- Begins when food enters the stomach and continues the stimulation from the cephalic phase
- Two stimuli trigger acid secretion
- Presence of food in the stomach → distension of the stomach wall → stimulates the ENS and vagus nerve (same effects as above)
- Presence of partially digested proteins stimulate G cells to produce and secrete gastrin → stimulates acid secretion → which activates pepsin → catalyzing protein digestion (positive feedback loop)
intestinal phase
- Triggered by the presence of partially digested proteins in the fluid entering the duodenum
- Partially digested proteins trigger duodenal DNES cells (G cells) to release intestinal gastrin
- Enterogastric reflex - as chyme enters the duodenum, the declining pH and presence of lipids trigger this which decreases vagal activity and acid secretion
- Low pH of the duodenum also triggers the production of secretin and gastric inhibitory peptide (both hormones reduce acid secretion)
3 types of folds in intestines
- circular folds
- intestinal villi
- microvilli
migrating motor complex
- during fasting, the small intestine, exhibits slow rhythmic contractions along its length
- These contractions clear any remaining material
- Takes about 2 hours for digesting food to get from ileocecal valve
- Controlled by ENS and motilin (produced by cells of duodenal mucosa)
bacteria in the large intestines
Produce vitamins (K & B)
Metabolize undigested materials (eg. soluble fibers → byproduct = flatus)
Deter the growth of harmful bacteria/pathogens
Stimulate the immune system
Induce immune tolerance body’s own antigens
Stimulate production of MALT and antibodies
Cholecystokinin (CCK)
- a hormonal mediator of pancreatic secretion
- produced by duodenal DNES cells in response to the presence of lipids and partially digested proteins in the duodenum
- It acts on acinar cells to trigger the secretion of digestive enzymes and other proteins
secretin
Released by duodenal cells in response to acids and lipids in the duodenum. Primarily triggers duct cells to secrete bicarbonate ions
Porta Hepatis
Indentation where numerous blood vessels enter and exit the liver (including the hepatic artery, hepatic portal vein) also nerves, lymphatic vessels, and common hepatic duct
The Gallbladder and Its Relationship to the Liver
- Gallbladder stores bile, concentrates it (removes water), and releases it when stimulated
- Secretin triggers bile production and release from hepatocytes
- CCK triggers contraction of gallbladder
- This causes the gallbladder to release bile into the cystic duct
- Cystic duct + common hepatic duct = common bile duct
- Common bile duct + main pancreatic duct = hepatopancreatic ampulla
Digestion and Absorption of Carbohydrates
1) Polysaccharides are broken into oligosaccharides and disaccharides in reactions catalyzed by pancreatic amylase
2) Brush border enzymes (lactase, maltase, and sucrase) catalyze the breakdown of disaccharides into monosaccharides
3) The Na+/K+ pump creates a gradient for Na+ absorption from the fluid in the lumen
4) This gradient drives the secondary active transport of glucose and galactose via the Na+/glucose cotransporter
5) Fructose is absorbed by facilitated diffusion
6) All 3 monosaccharides cross the basal side of the enterocyte membrane and then diffuse into the blood
digestion and absorption of proteins
1) Oligopeptides are broken down into free amino acids in reactions catalyzed by pancreatic and brush border enzymes
2) The Na+/K+ pump creates a Na+ gradient
3) This gradient drives the secondary active transport of certain amino acids into the enterocyte
4) Amino acids cross the basal enterocyte membrane by facilitated diffusion and enter the blood
digestion and absorption of lipids
1) Lipids are broken apart by the stomach churning and broken down in reactions catalyzed by gastric lipase
2) Lipids enter the small intestine and are emulsified by bile salts
3) Pancreatic lipase catalyzes reactions that digest the lipids into free fatty acids and monoglycerides
4) Bile salts remain associated with the digested lipids to form micelles
lipid absorption
1) Micelles escort lipids to the enterocyte plasma membrane
2) Lipids diffuse through the phospholipid bilayer and enter the cytosol
3) Lipids are reassembled into triglycerides and packaged into chylomicrons
4) Chylomicrons are released into the interstitial fluid by exocytosis and then enter a lacteal
absorption of vitamins
Water soluble vitamins - polar
- Absorbed by small intestine dy diffusing through enterocytes plasma membranes
- Vitamin B12 - must bind to intrinsic factor to be absorbed in the ileum
- vitamin B & C
Fat soluble vitamins - non polar/lipid based
- Packaged into micelles with fats and lipids and are absorbed with them
- vitamin A, D, E, K
nutrient pool
anabolic activities require amino acids, some lipids, and few carbohydrates
Catabolic reactions break down carbohydrates first, then lipids, and rarely amino acids
glucose catabolism, 2 main stages
glycolysis
citric acid cycle
glycolysis
- series of reactions in the cytosol that split glucose
- Energy investment phase: requires “spending” of 2 ATP for every 6 carbon glucose, producing two 3 carbon glucose sugars (pyruvate)
- Energy payoff phase: phosphate groups of the 3 carbon sugars are transferred to ADP to produce ATP (net total of 2), and the compounds are oxidized to produce NADH
- Net gain: 2 ATP & 2 NADH
citric acid cycle
- series of reactions in the mitochondrial matrix that breaks down glucose further
- Starts and ends with the same compound, oxaloacetate
- Overall yield per glucose molecule
- 10 NADH (2 from glycolysis, 2 from pyruvate oxidation, 6 from citric acid cycle)
- 2 FADH2
- 4 ATP (2 from glycolysis, 2 from citric acid cycle)
oxidative phosphorylation
occurs after glycolysis and citric acid cycle. series of oxidation-reduction reactions that use the energy released by glucose catabolism. Involves the transfer of electrons between electron carriers known as the electron transport chain (ETC)
1) Transfer of electrons between electron carriers
2) Generation and maintenance of a hydrogen ion concentration gradient
3) Use of the steep electrochemical gradient to drive the release of ATP
- produces 34 ATP
substrate level phosphorylation
involves the transfer of a phosphate group directly from the phosphate containing chemical (substrate) to ADP to form ATP
how many ATP can 1 glucose molecule yield
38 ATP
fatty acid catabolism
- 3 fatty acid + glycerol
- glycerol goes to glycolysis then citric acid cycle
- fatty acids oxidized through beta oxidation
- produces:
- FADH2 → ETC
- NADH → ETC
- Acetyl-CoA → citric acid cycle
Oxidation of fats releases twice as much energy as carbohydrates or proteins
amino acid catabolism
- Amino acid = “carbon skeleton” + nitrogen-containing amino group
- Amino group removed via transamination → carbon skeleton + glutamate
- Carbon skeleton → undergo oxidation via glycolysis or citric acid cycle
- Glutamate undergoes oxidative deamination → ammonia (NH3)
vitamin B1
coenzyme in many catabolic pathways
vitamin B9 (folic acid)
coenzyme in many metabolic pathways
deficient during pregnancy