Gastro Intestinal Physiology Flashcards
Digestion Process Steps
- Ingestion
- Propulsion
- Digestion
- Abosorbtion
- Defecation
Ingestion
- Mastication
- Deglutition
Mastication
chewing
Deglutition
swallowing
GI PHYSIOLOGY
Propulsion
movement of food
Digestion
breakdown of food by:
1. Mechanical action
2. Chemical processes
Digestion
Mechanical Action
chewing food into smaller pieces
Digestion
Chemical Processes
mixing food with acids, enzymes, and emulsifiers to breakdown food
Absorbtion
passage of nutrients into circulatory and lymphatic systems for distribution throughout the body
Defecation
elimination of indigestible substances
Divisions of the GI system
- Alimentary Canal
- accessory Digestive Organs
Alimentary Canal
tube that winds through the body
mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum
Accessory Digestive Organs
contribute to the breakdown of food
teeth, tongue, salivary glands, pancreas, liver, gall bladder
4 Layers of the Alimentary Canal Wall
- Tunica Mucosa
- Tunica Submucosa
- Tunica Muscularis
- Tunica Serosa
Innermost to outermost
Alimentary Canal Wall
Sublayers of the Tunica Mucosa
- Epithelium lining
- Lamina Propia
- Muscularis Mucosa
innermost to outermost
Epithelium Lining of the Tunica Mucosa
absorbtion/protection/secretion, mucous production, glands-digestive enzymes
inner layer
stratified squamous or simple columnar
Lamina Propia of the Tunica Mucosa
immune protection, contains capillaries and lymphatics
middle layer
loose connective tissue
Muscularis Mucosa of the Tunica Mucosa
folds to increase surface area, local movement of GI epithelium
outer layer
Alimentary Canal Wall
Tunica Submucosa
highly vascularized, innervated by the ANS, binds tunica mucosa to tunica muscularis, contains meissners plexus
2nd from middle
dense irregular connective tissue,
meissners plexus
tells glands to secrete, tells muscularis mucosae to contract
Alimentary Canal Wall
Tunica Muscularis
mechanical digestion, propulsion, contains Auerbach’s Plexus,
3rd from middle
smooth muscle, controlled by ANS
Auerbach’s Plexus
located between muscle layers, controls GI motility
Tunica Serosa
fluid secreting membrane, visceral peritioneum on organs, parietal peritoneum lines cavities
outermost layer
simple squamous epithelium
Blood Flow of GI system
25% of cardiac output, liver recieves blood from hepatic artery and portal veins from organs.
Liver Functions
- Carbohydrate Metabolism (stores glycogen, releases glucose)
- Lipid Metabolism (manufacture of cholesterol (HMG CoA Reducatse)
- Protein Synthesis (albumins, fibrinogens, prothrombin)
- Breakdown of old RBC hemoglobin into bilirubin
- Bile Production (used for emulsification of fats)
- Detoxification (chemically alters alcohol, drugs, etc into kidney exretable compounds such as urea, ammonia, uric acid)
Portal Triad
portal vein, hepatic artery, bile duct
portal vein
deoxygenated blood into the liver
hepatic artery
oxygenated blood into the liver
Hepatic Sinusoids process
- Kuffler cells break down RBC’s
- Hemoglobin broken down into Iron + Bilirubin
- Bilirubin binds to Albumin
- Absorbed by Liver cell
- Processed into Bile Salts
- Stored by the Gall Bladder
- Released by common bile duct
- bile salts are recirculated multiple times per day in GI tract
Jaundice Causes
bile tract blockage, liver failure, hemolysis
Nutrient Absorbtion
most enzymes from Pancreas, bile for fat emulsification, from liver
Carbohydrate Absorbtion steps
- broken down by Amylase (pancreas)
- absorbed in mono and disaccharide form into capillaries
- absorbtion coupled with Na+ down concentration gradient
- secondary active transport
- transport into liver via hepatic portal system
Protein Absorbtion steps
- Broken down by stomach acid, pepsin, trypsin(pancreas)
- absorbed as AA’s and small peptides into capillaries
- absorbtion coupled with Na+ down concentration gradient
- Secondary active transport
- Transport to liver via hepatic portal sytem
Fat and Cholesterol Absorbtion
- Emulsified via action of Bile(liver)
- broken down into fatty acids or monogylcerides by lipases(pancreas)
- Lipids absorbed as FFA’s and monoglycerides in small intestine
- conjugated with Apoproteins by mucosal cell form Chylomicron
- exocytosis via mucosal cells releases Chylomicrons
- forms lacteals of lymphatic system for transport
- stored as peripheral fat in the venous system
normal cholesterol level
200 mg/dl and below
LDL
low density lipoprotein, remains in circulation and promotes plaque formation
bad cholesterol
HDL
high density lipoprotein, promotes storage of cholesterol in the liver
good cholesterol
Ideal LDL level
LDL<130mg/dl
Ideal HDL level
HDL>45mg/dl
At risk cholesterol levels
cholesterol 240mg/dl or above
LDL>160mg/dl
HDL<35mg/dl
Natural Treatment of High Cholesterol
low fat diet with moderate alcohol
Cholestyramine
binding resin, forms insoluable bile/fat complexes that are excreted
Statins
binds to HMG CoA Reductase, reduce cholesterol synthesis by Liver, decreases LDL’s, increases HDL’s
Lovastatin(mevacor), Simvastatin(Zocor), Atorvastatin(Lipitor), Pravastatin(Pravachol), Rosuvastatin(Crestor)
Ezetimibe(Zetia)
binds to NPC1L1 protein on enterocytes and hepatocytes, mediator of dietary absorbtion,
lower absorbtion rate enhances uptake of LDL by peripheral cells
Vytorin
Zocor + Zetia
Inputs of Water Balance
1200ml drinking/food
1500ml saliva
2000ml stomach
500ml bile
1500ml pancreas
1500ml small intestine
8200ml total
Reabsorbtion in water balance
8500ml small intestine
350ml large intestine
exrete 150ml in feces
8850ml total
Water Absorbtion
water is absorbed until is is isoosmotic with plasma, the max urine flow is 16ml/min
Water Intoxication
Water intake above the max urine flow or if too much exogenous ADH is administered, swelling of brain, convulsions, coma, death
max urine flow is 16ml/min
Minimum Amount of Water Excreted
600mosm/L/day
Kidney Max Urine Concentration of Water
1200 mosm/L/day
Amount of Water Excreted in Urine
0.5L/day
Max Kidney Urine Concentration of Seawater
1400 mosm/L
Digestion
Sight and Smell of food
stimulates salivary and gastric secretions
Chemoreceptors in the Stomach
detects HCl levels
Mechanoreceptors in the Stomach
detects distension and pressure in the stomach
Neural Control of Digestion
Long Relex Innervation
connects parts of the GI tract together, connects to CNS, stimulated by Vagus nerve, ACh, and Serotonin,
activates Meissners and Auerbachs Plexus, Splanchnic Nerves are inhibitory
Splanchnic Nerves
sympathetic fibers that inhibit Long Reflex Innervation
stimulated by NE and E
Short Reflex Innervation
mediated through nerves confined to the GI tract, stimulated by chemicals, hormones, and distension
activates endocrine glands and smooth muscles in the tract
Components of GI System
Mouth
Ingestion and digestion, contains salivary glands, buccal glands, parotid glands, submandibular glands, submaxillary glands, and sublignual glands.
entrance of Alimentary Canal, Mucosa lined
Salivary Glands
saliva production, contains Compound Acinar Gland
accessory digestive organs
Compound Acinar Gland
makes Amylase for starch digestion, makes Lipase for fat digestion
serous and mucous
Mumps
virus that causes inflammation of the parotid glands
Deglutition Steps
- Medulla Signals Swallowing
- Trigeminal, Glossopharyngeal, Vagus, and Hypoglossal Innervate
- Mouth Closes
- Tongue pushes food back
- Contraction of Pharynx
- Inhibition of respiration (Larynx raises, epiglottis closes)
- Upper Esophageal Sphincter Relaxes
- Peristaltic Wave initiated
- Lower esophageal sphincter relaxes
- Second painful Peristaltic wave if unsuccessful
Liquids via gravity
Stomach
widest part of Alimentary Canal, distentable/contractable, produces enzymes and acids
food storage, mechanical and chemical digestion
Cardiac Sphincter
sphincter at the upper end of the stomach
Heartburn
reflux of acid at the cardiac sphincter
Mucosa
protects from acids, secretes mucous, acids, and enzymes, absorbes water, alcohol, and drugs
has folds called Rugar, made from Simple Columnar Epithelium
Gastric Pits
contains stomach glands which produce Chyme, contains specialized cells
Gastric Pit Cells
Mucous Neck Cells
produce mucous for protection
Gastric Pit Cells
Parietal Cells
produce HCl, absorb Vitamin B12
Pernicous Anemia
insufficient RBC production due to Vitamin B12 deficiencies
can be caused due to issues with Parietal Cells
Gastric Pit Cells
Chief Cells
secretes Pepsinogen with acid to activate Pepsin, acts in protein digestion
these cells can be digested by the enzymes they secrete (autolyse)
Gastric Pit Cells
G Cells or “APUD”
activated by food in the stomach and releases Gastrin into the blood causing increased Parietal Cell acid secretion and increased GI motility
when activated they speed up digestion
Gastric Pit Cells
Enterochromaffin Cells
produce histamine, acid secretion stimulator
Gastric Pit Cells
D Cells
produces somatostatin, acid secretion inhibitor
Tunica Muscularis Layers
- Inner Oblique
- Middle Circular
- Outer Longitudinal
Innermost to Outermost
Pyloric Sphincter
controls the emptying of the stomach into the duodenum
Acid Production in the Stomach
- H+ is exchanged with K+ and moves into the gastric lumen
- HCO3- is exchanged with Cl-
- cAMP activates protein kinase which drives the pump
- ACh and Gastrin both increase Ca++ and also stimulate protein kinases
- Histamine will activate cAMP
- PGE2 will deactivate cAMP
HCl moved into gastic lumen and HCO3- is moved into the blood
Stomach Acid Inhibitors
- ACh antagonists (Atropine)
- Histamine blockers
- Gastrin Blockers
Omeprazole
blocks H+/K+ ATPase pump
Acidity and Gastrin
high acidity in the stomach inhibits gastrin release and slows down the movement of HCl into the stomach
Acid Production
high protein meals
high protein meals buffer acidity and stimulate acid production
Acid Production
Empty Stomach
An empty stomach is high in acidity and inhibits Gastrin release
Ulcers
caused from a hyper secretion of acid or a lack of mucous protection, lesser curvature, pyloris, and duodenum are the most vulnerable,
usually caused by bacteria
Ulcer Treatments
H2 blockers, Omeprazole, Vagotomy(removal of part of the vagus nerve)
Vomiting Process
- Irritation trigger vomiting center in the brain
- Saliva Secretions Stimulated
- Squeezing of the stomach beginning with the diaphragm and abdominal muscles (increased pressure)
- Sphincters open
excessive vomiting can cause alkalosis due to vomiting out acids which would cause more acid to move into the stomach and more base to move into the blood
Small Intestine
longest portion of the Alimentary Canal, basic pH
Small Intestine Functions
- Enzymatic Digestion (enzymes from pancreas)
- Emulsification of Fats (via bile from the liver)
- Absorbtion of Nutrients (capillaries and lacteals)
- Secretion of Hormones
Main Parts of the Small Intestine
- Duodenum
- Jejunum
- Ileum
Cell Types of the Small Intestine
- Absorbative
- Goblet (mucous)
- Enteroendocrine (hormones)
- Paneth (antibacterial enzymes)
Small Intestine
Tunica Mucosa
different from usual as it has a greater surface area due to three modifications
Small Intestine
Tunica Mucosa Modifications
- Simple Columnar Epithelium with Microvilli
- Arranged in Villi (contain artery, capillary, and vein)
- Plica Sircularis (folds of mucosa and submucosa, where Enteroendocrine and Paneth cells are located)
Small Intestine Hormones
- GIP-Gastric Inhibitory Peptide
- CCK-PZ Cholecystokinin-Pancreozymin
- Secretin
- Motilin
- VIP
produced by Enteroendocrine cells
Small Intestine Hormones
GIP-Gastrin Inhibitory Peptide
released from duodenal filling or inceased acid in duodenum, inhibits GI motility and acid production,
increases time for absorbtion
Small Intestine Hormones
CCK-PZ Cholecystokinin-Pancreozymin
released from duodenal filling, increased acid, increased protein, or increased fat in the duodenum, inhibits GI motility, stimulated Gall Bladder Contraction, stimulates Pancreatic secretion(digestive enzymes)
gall bladder releases bile for fat emulsification and pancreas releases enzymes for protein digestion
Small Intestine Hormones
Secretin
released due to acid in duodenum, stimulates HCO3- release from Pancreas,
makes intestine basic which shuts down its secretion
Small Intestine Hormones
Motilin
responsible for MMC(migrating motor complex), emptys stomach
Migrating Motor Compex (MMC)
peristaltic wave from esophagus to small intestine
during the interdigestive period, emptys stomach
Small Intestine Hormones
VIP
decreases smooth muscle motility, dilation for peripheral vessels, inhibits acid secretion
Small Intestine
Segmentation
mixing of Chyme and Enzymes, brings digested nutrients into contact with villi and microvilli for absorbtion
controlled by ANS(Auerbach’s Plexus) and hormones
Small Intestine
Peristalsis
propulsion of chyme along the small intestine, pumping up and down of villi and microvilli by Mucous Mucosa
controlled by ANS(Auerbach’s Plexus) and hormones, Meissners Plexus
Pancreas
Exocrine Functions
secretion into a duct of digestive enzymes and alkaline juice
Acinar Cells
produce Pancreatic Juice and digestive enzymes secreted into Pancreatic duct and moved into the Small Intestine
Alkaline Juice
neutralizes stomach chyme, HCO3- secretion in lumen, H+/Na+ exchange, Na+ secretion in lumen
Enzymatic Digestion Enzymes
Amylase, Trypsin, Lipase
the pancreas can digest all portions of a meal
Pancreas
Endocrine Function
hormonal regulation of blood sugar with insulin and glucagon hormones
Large Intestine Functions
- Abosrbtion of water and electrolytes
- Vitamin production, K and B
- Expulsion of Feces by mass peristalsis movements
Parts of the Large Intestine
- Cecum
- Colon (ascending, transverse, descending, sigmoid)
- Rectum
First to Last
Large Intestine
Tunica Muscosa Tissue Makeup
simple columnar but statified squamous at rectum
Large Intestine
Tunica Muscularis Structure
contains Taenia Coli and Haustra
Taenia Coli
rope-like thickening of longitudinal muscle
Haustra
puckered pouches that form as a result of distension of one haustra, causes propulsion of contents into next haustra
Diverticulitis
diet lacks bulk causing outward herniation of Haustra wall
can become infection
Hirschsprung’s Disease
constriction of large intestine wall (aganglionic megacolon)
feces backs up
Hemmorroids
varicose veins in anal canal, itching throbing, bleeding
destroyed by burning, cutting, or rubber banding