Digestive System Flashcards
ingestion
introduction of food into stomach
mastication
chewing
- chem digestion requires large SA so breaking down large particles mechanically facilitates chem digestion
propulsion
- deglutition : swallowing
- peristalsis : move material thru digestive tract by waves of circulation smooth muscles ahead of bolus then relaxation waves
local: enteric nervous system
- sensory, motor, and interneurons
- coordinates peristalsis and regulate local reflexes
general nervous regulation
- Coordination with the CNS.
- May initiate reflexes because of sight, smell, or taste of food.
- Parasympathetic primarily
- Sympathetic input inhibits muscle contraction, secretion, and decrease of blood flow to the digestive tract.
saliva
- compound alveolar salivary glands to make saliva
- lubrications
- prevent bacteria infections
- contain salivary amylase
- form bolus for swallowing
- parasympathetic input cause salivary production
salivary glands
- parotid: largest, mostly serous
- submandibular: serous + mucous,
- sublingual: small, mostly mucous
- lingual glands: coiled tubular glands on tongue surface
swallowing: 3 phases
- voluntary: bolus of food moved by tongue from oral cavity to pharynx
- pharyngeal: reflex, controlled by medulla oblongata, soft palate elevate and upper esophageal sphincter relaxes, food pushed into esophagus by pharyngeal sphincters
- esophageal: reflex, stretching of esophagus cause ENS to initiate peristalsis
chyme
ingested food plus stomach secretions
mucus
surface, neck mucous cells
- viscous, alkaline
- protect from acidic chyme and enzyme pepsin
- irritation of stomach mucosa cause greater mucous
intrinsic factor
parietal cells.
- Binds with vitamin B12 and helps it to be absorbed.
- B12 necessary for DNA synthesis
HCl
parietal cells
- kill bacteria
- stop carb digestion by inactivate salivary amylase
- denature protein
- helps convert pepsinogen to pepsin
pepsinogen
packaged in zymogen granules released by exocytosis.
pepsin catalyzes breaking of covalent bonds in proteins
- inactive form of pepsinga
HCl production
- CO2 and H2O make H2CO3 (in presence of CA), extra H forced by ATP (dephosph into ADP) into gastric pit (active transport)
-K leaves as H enters gastric pit (antiport) - HCO3 down conc gradient and out of cell, Cl in (antiport/secondary active transport)
- Cl down into gastric pit
cephalic phase
- taste/smell food, tactile sensation in mouth or thoughts stimulate medulla oblongata
- vagus (X) cause increase in saliva production
- gastrin stimulated to make parietal cells (stomach acid)
(before food in mouth)
gastric phase
arrival of food in stomach
- myenteric and vagovagal reflex
- increase gastrin (HCl) and histamine
intestinal phase
further breakdown of food, and absorption
- CCK and secretin released
- sympathetic nervous system (inhibition)
- parasympathetic nervous system (stimulatory)
small intestine
most digestion and absorption of nutrients and water
- duodenum: first 25cm
- jejunum: 2.5m
- Ileum: 3.5m (Peyer’s patches)
modifications to increase surface area
Increase surface area 600 fold
-Plicae circulares (circular folds)
-Villi that contain capillaries and lacteals. Folds of the mucosa
-Microvilli: folds of cell membranes of absorptive cells
absorptive cells
w microvilli, produce digestive enzymes and absorb digested food
goblet cells:
produce protective mucous
endocrine cells:
produce regulatory hormones
granular (paneth) cells:
protect from bacteria
intestinal glands (crypts of Lieberkuhn):
tubular glands at base of villi
duodenal glands (brunner’s glands):
tubular mucous glands enter into intestinal glands
jejunum and ileum
- decrease in diameter, thickness as move away from stomach
- nutrient absorption (jeju)
- Peyer’s patches: lymph nodes
- ileocecal junction: ileum meet L int.
small intestine secretions
- Fluid (water, electrolytes, mucous)
- mucous (protect from acid and bacteria)
- Digestive enzymes:
disaccharidases: breakdown into mono
peptidases: hydrolyze peptide bond
nucleases: break down nucleic acids - duodenal glands (stimulated by vagus nerve, secretin)
movements in small intestine
- mixing, propulsion over short distance
- cecal distention cause local reflex, constrict (prevent backflow and too much chyme enter cecum)
liver histology
- CT branch from porta to interior
- lobules: portal triad (hepatic portal vein/artery/duct)
- central veins unite to form hepatic veins enter inf VC
liver parts
- hepatic portal cords composed of hepatocytes
- hepatic sinusoids: lined w epithelial, Kupffer cells
- bile canaliculis: btwn cells w/in cords
Liver functions
liver cell: hepatocyte
- bile production
-storage (glycogen, fat, vitamins, Cu, Fe)
- interconversion of nutrients
- detoxification (ammonia > urea)
- phagocytosis (get rid of old WBC and RBC)
- synthesize blood components
bile secretion and release
gastrin into blood system to release HCl, pepsinogen
- cholecystokinin excitatory to bile
- secretin excite bile production in gallbladder
- bile, pancreatic secretions raise pH (2-4 for pepsin, 6-8 for others)
pancreatic juice
aqueous; made by columnar epithelium; raise pH by HCO3 absorb ions
- enterokinase make trypsinogen > trypsin
- trypsin make chymotrypsinogen > chymotrypsin
- chymotrypsin make procarboxypeptidase > procarboxypeptides
bicarbonate ion production in pancreas
- CO2 + H20 = H2CO3 > H + HCO3 ; make ATP w H
- Na down conc gradient antiport/repulsion H out
bile
made in the liver and stored in the gallbladder
- emulsify fat so enzymes can work
Control of pancreatic secretion
cholecystokinin and secretin: pancreatic secretions and release HCl
cholecystokinin (CCK)
A hormone secreted by the small intestine (duodenum) in response to the presence of fats.
- excites: gallbladder to release bile into small intestine
- inhibit: gastric emptying
secretin
A hormone secreted by the small intestine (duodenum) in response to low pH
- excites: pancreatic fluid and HCO3 secretion
- inhibits: gastric acid secretion of stomach parietal cells
secretions of large intestine
- mucous provides protection
- pumps: bacteria produce acid and exchange HCO3 for Cl, and Na for H (repulsion as same charge)
- Flatus
- Vit K to be reabsorbed
- Feces (water, undigested food, sloughed off epithelial cells, etc)
Colon and rectum
- presence of chyme in duodenum stimulate mass mvmnt
-Cecum is full the ileocecal valve shuts and mass mvmnts in descending colon
-Peristalsis move material into intestines once ileocecal valve reopens
-Rectum pressure determines if bowel mvmnt occur (internal sphincter)
-Peristalsis food into cecum
digestion, absorption, transportation
digestion: mechanical and chemical breakdown of food for absorption into circulation
absorption/transport: molec out of digestive tract into circulation for distribution
carbohydrates hydrolyzed into monosaccharides
-Cotransport = symport (both move in same direction)
-Na down conc gradient and pull monosaccharide into cell (facilitated transport )then into capillary
transport lipids across intestinal epithelium
-Bile salts (emulsify fatty acid) & monoglycerides diffuse into epithelial cell, then form triglyceride (protein coated (chylomicron) and exocytosied) then into capillary then lacteal (lymphatic system)
-Simple diffusion, micelles, chylomicron, lymphatic system move into liver NOT circ syst
chylomicron
formed in the intestinal epithelium to transport long-chain triglycerides to the tissues
- 90% triglyceride, 5% cholesterol, 4% phospholipid, 1% protein
- enter blood stream and travel to adipose tissue
micelles
temporary compounds formed during the fat digestion and absorption process
lipoproteins
protein and fat clusters that transport fats in the blood
- VLDL
- HDL
- LDL
VLDL (very low density lipoprotein)
*92% lipid, 8% protein
-Form in which lipids leave the liver
-Triglycerides removed from VLDL and stored in adipose cells. VLDL has been converted to LDL.
HDL (High Density Lipoprotein)
- 55% lipid, 45% protein
-Transports excess cholesterol from cells to liver
LDL (low density lipoprotein)
*: 75% lipid, 25% protein
-Transports cholesterol to cells
-Cells have LDL receptors
-# of LDL receptors become less once cell’s lipid/cholesterol needs are met.
LDL into cells
-LDL receptors have pits to grab LDL
-Bind to each other and endocytize into cell
amino acid transport
-Na down conc gradient
-Tri/di peptide or AA into cell via cotransport (symport - move in at same time)
-Tri/di peptides broken into AA in cell , then via active transport into capillary, then to liver
-Much more energetic to absorb protein as need ATP
effects of aging
*Decrease in mucus layer, connective tissue, muscles and secretions
*Increased susceptibility to infections and toxic agents, increase in incidences of ulcerations and cancers
