9 Flashcards
(24 cards)
the steps from mouth to large intestine
.mouth .pharynx/esophagus .sphincters (control movement of food) .stomach (food mixed with gastric juices) .pyloric sphincter .duodenum (most digestion receives secretion from gall bladder, liver, pancreas) .jejunum/ileum .large intestine
General Structure of the GI Tract Walls
• Mucosa - lines the inside of the tract = single layer of epithelial cells
• The lamina propria lies under the epithelial layer.
•the mucosa is usually ruffled into folds to increase its surface area.
A layer of smooth muscle (muscularis mucosa ) is responsible for the ruffling
what is the submucosa made of
The submucosa is made up of lots of connective tissues which gives strength to the GI tract, and also carries the larger blood vessels (leading in and out of capillaries) and lymph vessels.
Muscularis Externa = two layers of smooth muscle:
longitudinal - fibers arranged along length of the GI tract
circular - fibers arranged circularly around GI tract
•The smooth muscle is grouped into bundles electrically connected by gap junctions
serosa
an outer layer of connective tissue
The GI tract has its own internal nervous system
Enteric Nervous System
•extends all of the way from the esophagus down the GI tract
•regulates GI movements and secretions
how does the autonomic system control the enteric system
Parasympathetic— increases activity
Sympathetic— inhibits activity of GI tract, by inhibitory effect of norepinephrine both directly on muscle cells and on enteric nerves.
myenteric
plexus
controls
muscles
submucosal
plexus
controls
secretions and
absorption
The epithelium of the small intestine is
specialized for absorption of materials:
- absorbed material must be taken up by, and pass through, enterocytes to get to the capillaries
- The small intestine is specialized to increase the surface area (more enterocytes):
- the mucosa has large fold (circular folds)
- the folds have multiple finger-like projections
- the enterocytes themselves have protrusions of the membrane (brush border)
where does the final digestion take place
Enterocytes
Carbohydrates Breakdown:
from diet a mix of polysaccharides, disaccharides and monosaccharides
- Polysaccharides: starch, glycogen cellulose
- Disaccharides: sucrose, lactose
- Monosaccharides: glucose,fructose
- amylase from pancreas and salivary glands break down starches to smaller molecules
- enzymes on the enterocyte membrane digest them to monosaccharides
Protein Breakdown:
stomach:
•denatured by HCl
•digested to large peptides by pepsin
small intestine
•digested to amino acids and small peptides by pancreatic
proteases (trypsin, chymotrypsin and carboxypeptidase)
enterocyte surface
•further digestion by amino peptidase
•absorbed as amino acids, di- and tri-peptides
how are glucose/amino acids transported to lumen to capillaries
- The co-transport of Na+ or H+ down its concentration gradient allows the nutrients to be moved against their concentration gradients.
- The side of the enterocyte facing the interstitial fluid has facilitative transporters = allow the nutrients to flow out of the cell, down their concentration gradients
- Since the capillaries are constantly taking away the nutrients, there will be a steady flow pf nutrients into the capillaries (again, down a concentration gradient).
what does pancreatic enzyme lipase do
triglycerides»_space; fatty acids + glycerol
why are bile salts need and what are they produced from
fats are insoluble in water
cholesterol
where are bile salts made, stored and released
- bile salts are made in the liver and stored in the gallbladder
- bile is concentrated in the gallbladder by removal of water
- bile is released into the small intestine via the Sphincter of Oddi
emulsification of fats
The breakdown of fat globules in the duodenum into tiny droplets, which provides a larger surface area on which the enzyme pancreatic lipase can act to digest the fats into fatty acids and glycerol. Emulsification is assisted by the action of the bile salts
how does bile emulsify fat
Bile contains bile salts, which have hydrophobic and hydrophilic sides. The bile salts’ hydrophilic side can interface with water, while the hydrophobic side interfaces with lipids, thereby emulsifying large lipid globules into small lipid globules.
products of fat digestion are held in MICELLES
The bile salts surround fatty acids and monoglycerides, forming tiny spheres called micelles. The micelles move into the brush border of the small intestine absorptive cells where the fatty acids and monoglycerides diffuse out of the micelles into the absorptive cells, leaving the micelles behind in the chyme. The fatty acids and monoglycerides recombine in the absorptive cells (Enterocytes transported to smooth ER) to form triglycerides, which aggregate into globules and are then coated with proteins. These large spheres are called chylomicrons. Chylomicrons contain triglycerides, cholesterol, and other lipids; they have proteins on their surface. The surface is also composed of the hydrophilic phosphate “heads” of phospholipids. Together, they enable the chylomicron to move in an aqueous environment without exposing the lipids to water. Chylomicrons leave the absorptive cells via exocytosis, entering the lymphatic vessels.
what regulates passage down the esophagus to the stomach
upper and lower esophageal sphincters
how do you get the food to the stomach
•pressure of the food bolus against the pharynx sets off the SWALLOWING REFLEX - controlled by the swallowing center in the medulla.
Pharyngeal muscles contract to force the bolus into the esophagus.
•UVULA prevents food from going into the nasal passage
•EPIGLOTTIS prevents food from entering the trachea.
•the reflex continues in the esophagus, where a traveling ring of constriction “milks” the food down to the stomach
(a peristaltic contraction).
HCl
product of parietal cells - concentrated in the body region
•helps denature foods
•kills ingested bacteria
•activates pepsinogen
how is HCl produced in parietal cells
actively uses energy to pump protons outside cell H+ and K+ in = H+/K+ pump
K+channel on lumen - comes in/diffuses out
protons come from water (OH/H+)
cannot have OH- in cell = neutralized by CARBONIC ANHYDRASE > carbonic acid: H+/bicarbonate ions pumped out for Cl- ions inside the cell
