Download ANPS 020 Black 02-24

ANPS 020
February 24, 2012
Stomach (4) areas- 3 jobs
1. Cardiac
-mucous cells secrete
-junction with esophagus and sphincter (sm. Muscle)
2. Fundus and body (basically the same)
-mucous cells secrete
-chief cells (pepsinogen) specialized cells
-parietal cells (H+; Cl- and IF)
3. Pyloric
-mucous cells secrete
-junction with duodenum and sphincter (sm. Muscle)
FUNDUS/BODY
Mucous cells – mucous
Stem cells – differentiate to form all other cells)
Parietal cells (HCL and IF –B12)
Chief Cells (digestive enzyme – pepsinogen)
MUCOUS CELS
Store product in vesicles in the apical part of the cell
Release of product by exocytosis
Product goes to the lumen of the GI system
Mucous cells make mucous and HCO3 (bicarbonate to neutralize acid)
PROTECTING THE STOMACH CELLS
Tight junctions – inhibit any movement through lateral portion of cells
Mucous layer
HCO3 from mucous cells helps neutralize stomach acid
PARIETAL CELL
Produces H+ and ClProduces intrinsic factor – B12 absorption
Why have a pH of 2 in stomach???
1. Acid helps kill bacteria
2. A pH of 2 is optimal pH for pepsin activity (enzyme) and helps start digestion
Acid production
Diffusion of Cl- ion thru membranes
Exocytosis of intrinsic factor (IF) for B12 absorption
Chief Cells
Store product in vesicles in the apical part of the cell
Release product by exocytosis
Product foes to the lumen of the GI system
Chief Cell synthesize and release pepsinogen = zymogen
ENTEROENDOCRINE CELLS:
Like taste buds in the GI epithelium
Stimulants: proteins, carbohydrates, lipids, etc.
Results: release peptide hormones…hormones result in many effects
Function via paracrine and endocrine mechanisms
Ex. = G cells in stomach epithelium release gastrin – stimulates acid secretion in stomach... by parietal
cells
CEPHALIC PHASE
Sight, smell, thought of food causes:
-CNS (extrinsic) stimulation of sub mucosal plexus (parasympathetic cells)
Causes secretion of 
1. Mucous cells --- mucous
2. Parietal cells --- HCL (acid) and Intrinsic factor (IF)
3. Chief cells ------ pepsinogen
Prepares stomach to receive food
Also causes muscle to contract
GASTRIC PHASE (FOOD IN STOMACH)
Once food enters the stomach, the influence of the CNS remains – sensory feedback foes to the CNS and
information (efferent) returns to the nervous system of the gut
Neural control of the digestive system from sensory input is managed by the intrinsic – enteric nervous
system
STIMULI:
1. Food takes up space –mechanoreceptors (stretch) receptors recognize bulk
2. The acid secreted into the lumen – chemoreceptors recognized acid
3. Digestion products from proteins – enteroendocrine (G cells) recognize peptides
GASTRIC PHASE – EXTRINSIC CONTROL
Regulation of acid secretion
1. Vagal input via enteric neurons provides input to parietal cell, ECL cells (histamine) and G cell
(gastrin)
2. G cells releases gastrin activates parietal cells and ECL cells
3. ECL cell releases histamine – activates parietal cells
4. D cell releases somatostatin which inhibits parietal cells
Mechanoreceptors and chemoreceptors stimulate:
1. Intrinsic enteric plexuses
2. Extrinsic sensory fibers
Enteroendocrine cells sense peptides
causes::
Cells secrete and muscles contract
Mucous cells, Parietal cells, Chief Cells ----- mucous, HCL, pepsinogen
G cells – gastrin->circulation ->stimulates chief and parietal cells and muscle contraction
GASTRIC PHASE- INTRINSIC INPUT
Receptors: mechano- & chemo-receptors stimulate GI plexuses
GI plexuses stimulates cells to secrete and muscles to contract
Peptides stimulate G cells that release gastrin
Gastrin stimulates cells to secrete and muscles to contract
Stimuli = lumen contents
Neurons in the GI and hormones control the results
WHAT HAPPENS TO CHYME (FOOD AND ACID) IN THE SMALL INTESTINE
DIGESTION AND ABSORPTION ARE IMPORTANT HERE
Acid has to be neutralized
Pancreas release digestive enzymes and bicarbonate – rich fluid
Liber makes bile for lipid absorption
Gallbladder releases bile
Digestion continues
Water added and reabsorbed
Absorption of building blocks through enterocytes
Undigested material remains
DUODENUM
The folds in the lumen = plicae circulares
-similar to rugae in the stomach but permanent
Core of submucosa
4 LAYERS OF DIGESTIVE SYSTEM
1. Mucosa:
- epithelium – plicae/villi
- lamina propria (CT)
- muscularis mucosa
2. Submucosa (CT)
- submucosal glands
3. Muscularis externa
- inner circular
- outer longitudinal
4. Adventitia (mostly)
DUODENUM – STRUCTURE AND FUNCTION
Duodenum receives acidic chime from the stomach
-list all its functions
1. Protect the epithelial cells from destruction
- neutralize the acid from stomach
- protect from digestive enzymes – from pancreas
2. Continue digesting of food and being to absorb the nutrients
3. Signal the stomach that is has the food and the stomach can adjust or stop its work
DUODENUM – STRUCTURE AND FUNCTION
Mucous covers or hides the epithelial cells
-mucous from the submucosal (Brunner’s) glands
Raise the PH from ~2 to about ~7
-bicarbonate rich alkaline fluid from:
-pancreas
-submucosal (Brunner’s) gland
Together – mucous covers epithelial cells and alkaline watery secretions raise the pH to about 7
--if these don’t work, the stomach acid can cause an ulcer
DUODENUM – STRUCTURE AND FUNCTION
Digest the food and being to absorb the nutrients. Food contain carbohydrates, fats and proteins
Receive digestive enzymes from pancreas
Receive bile form liver/gallbladder to help absorb fats
Increased cell surface area is designed to absorb nutrients (Can only absorb “Building blocks”)
DUODENUM FUNCTIONS AND BEYOND
Accessory organs of the digestive system
1. Discuss pancreas
2. Discuss liver and gallbladder functions
3. Return to absorptive functions of the small intestine
PANCREAS FUNCTIONS
1. Secrete watery, bicarbonate – rich alkaline fluid (from duct cells) to neutralize stomach acid
2. Secrete digestive enzymes – an exocrine function to digest foods
3. Secrete hormones like insulin and glucagon etc.
PNACREAS STRUCTURE AND FUNCTION
Exocrine organ (polarized cells)
-pancreatic acinar cells synthesize digestive enzymes
-proenzymes (zygomens)
-inactive in duodenum
-secreted through ducts
Pancreatic ducts cells secrete water and HCO3 (bicarbonate)
Endocrine organ
--islet of Langerhans
-insulin
-glucagon
-others
EXOCRINE PANCREAS
Acinus cells: secrete pancreatic pro-enzymes
-trysinogen, chymotrypsinogen (proteins)
-lipases (fats)
-Amylase and carbohydrase (carbohydrates)
-trypsin activates pro-enzymes to allow digestion
Duct cells secrete water and ions (dilate and buffer stomach acid)