Physiology 2 Flashcards
The GI Tract is all smooth muscle except?
upper 1/3 of esophagus and anal sphincter (striated)
Types of Smooth Muscle Contraction?
- Phasic - parastalic
2. Tonic - can last hours
Chewing does?
- breaks down food particles
- mixes food with saliva
- increase surface are to digest better
Functions of stomach?
- storage-most in orad area
- break down food particles in small cubic sizes
- gastric emptying
GERD
- acid reflux
- heartburn
- hiatal hernia, pregnancy, failure of secondary peristalsis
Oxyntic Cells
Parietal Cells, in body of stomach, weak motility
Pyloric
antrum, very strong contractions, muscle is thicker in this area
accommodation
relaxation
Cells of Caja
-slow waves always present from these intestinal cells
“gastric pacemaker”
3-5 depolarizations/min
Vagal Stimulation effect on slow waves
-increase height of waves (so increase frequency of contraction)
What empties fastest in the stomach?
-isotonic water (everything becomes isotonic when it goes in duodenum)
CCK effect on emptying?
inhibits
Effect of acid on peristalsis?
decrease from neural reflex
Failure of Gastric Emptying
- fullness, loss of appetite, nausea
- obstruction-ulcer, nausea
- vagotomy
Increased Gastric Emptying
- inadequate regulation
- diarrhea, duodenal ulcer
Reason for irregular contractions in small intestine?
- mixing
- digesting
- absorption
Peristalsis
propulsion, moves food only 4-5cm at a time, short
Migrating Motor Complex
- “housekeeper” reflex
- goes away when you start to eat
- # of contractions per minute except areas of extreme contractility (90min) b/c of motiline (creates wave beginning in stomach)
Small Intestine Motility
-must have spikes to have contraction
Teniae Coli
-longitudinal muscle
Haustra
-segmentation in colon, can disappear and reappear in different areas
Achalsia
food stuck in esophagus
rectosphinteric reflex
when rectum is distended, it will contract external sphincter
absent in paraphalgicts (rectal sphincter causes defication)
voluntary rexed for deification
Salivary Secretion Components
- alpha amylase - pH 7, lingual lipase (acidic), solubilization (to taste food)
- lubrication - needed for speech
- protective function - allows drinking hot, dilute noxious substances, dec. cavities, sec. F, Ca, P, lysosomes to wash particles from teeth
Salivary Glands`
- Parotid - watery 25-40% of output
- Submaxilary - watery and mucus
- Submandibular
- recieve lots of blood flow, CN nerves VII & IX both sympathetic and parasympathetic
Acinar cells
secretion goes unchanged in intercalated duct, then modified: abs NaCl, sec. K+ and bicarb in striated duct
Xerostamia
-absence of saliva
Ion concentration with flow rate
- hypotonic at all rates
- high K+ concentration all the time
- Na+ concentration low at low rates
- bicarb high at high rates
Changes in concentration as saliva moves from acinus to duct opening?
- Na+ decreases, K+ increases (secreted into duct)
- more happens the longer it stays in the gland
Kallikrein
salivary glands secrete it into the blood stream, acts on plasma proteins to cause secretion of Bradykinin to increase blood flow
What happens if you denervate salivary glands
they shrink
What 5 things does the stomach secrete?
- Hydrogen Ion
- Pepsinogens
- Mucus
- Intrinsic Factor
- Water
Hydrogen Ion’s Job in Stomach?
- activates conversion of pepsinogen into pepsin
- kills bacteria
- digests protein
***absence increases infection for small bowel
Pepsinogen’s Job in Stomach?
-pepsin digests protein by cleaving interior peptide bonds
Mucus’ Job in Stomach?
- lubricates food
- protects lining of stomach
Intrinsic Factor’s Job in Stomach?
- lubricates food
- protects lining of stomach
Water’s Job in Stomach?
- dissolves and dilutes ingested material
- secretes 1.5L per day
How long can the liver’s stores of Vit B12 last?
5 years
What does the oxyntic gland mucosa secrete?
HCl
What does the pyloric mucosa release?
gastrin
What do mucus neck cells secrete?
mucus with vagal stimulation
What happens if you block carbanic anhydrase?
decrease acid secretion
How is H+ ion secreted?
down electrical gradient
against concentration gradient
into mucosa
What disrupts the cell membrane and cause the separation of charges across the mucosa to decrease pd?
aspirin and alcohol
What keeps acid from hurting stomach?
gastric mucosal barrier
Concentration of ions in gastric juice depending on the rate of secretion?
- Cl is constant
- H+ increases with increasing secretion
- Na+ decreases with increasing secretion
- K+ increases with increasing secretion
Electrolytes with chronic vomiting
hypokalemia, low Na+, loose H+
metabolic alkalosis
Chronic Diarrhea
metabolic acidosis
Non-oxyntic Fluids
- low volume with no acid production
- electrolytes like conc. in plasma
- produced continually at low rates, overwhelmed when secretion is stimulated from parietal cells
Increase in Oxyntic fluid due to?
acid stimulation
What are the 3 major stimulants of gastric acid secretion?
-gastrin: travels through circulation
-histamine: released from intracromlin like cells
stimulates acid secretion
-G cell
-Neuron
parital cell has all 3 receptors
gastrin + histamine decarboxylase activity (increased response)
Bile acid secretion
- independent of serum gastrin
- middle of the night
- peak is unrelated to plasmic gastrin levels
“fasting output”
-10% of max output of stomach
How much output does acid secretion peak at?
30mEq/hr
Cephalic Phase
- chew up food, then spit it out: 30% response of acid secretion (better the food, more acid)
- mechanisms are all in the head
What happens in the absence of gastrin?
vagus stimulates acid secretion
- direct stimulation of parietal cell via Ach
- release of gastrin via GRP
What part of food stimulates gastrin release?
protein (AA and peptides), lasts 1.5hr, 50-60% of acid secretion
What does distention do?
- parietal cells to secrete (short intermediate reflux) - local
- long-vaso-vagal reflux, stimulate gastric cells to release gastrin (GRP)
Mechanisms Regulating Gastrin Release
Vagus Nerve
-Ach at nicotenic receptor
-GR4 cell inhibits somatostatin release
Distention
Summary of all Mechanisms Stimulating Gastric Acid Secretion
- Cephalic: chewing, swallowing, smell, taste
- Gastric: distention, digested protein
- Intestinal: digested protein
Direct Inhibiters of Gastrin Release
- somatostatin
- secretin
- GIP
pH and volume in response to a meal
meal: pH increases to 5-6 b/c of protein buffers
volume increase: stomach begins to secrete
Regulation of Pepsin Secretion
- Ach stimulates pepsin secretion from cell
- H+ turns pepsinogen to pepsin
- pH of 4 or less, automatic conversion
- vagus nerve stimulates pepsin secretion
Effect of smoking on pancreatic secretions?
decreases them
How much does pancreas secrete per day?
1-2L
What is secreted from pancreatic duct cells?
water and bicarb
Acinus
in pancreas
-blind system “grapes”, elaborate enzymatic components
Ductal cells % of pancreas?
4%
Acinus cells % of pancreas?
80%
Absence of pancreatic secretion causes?
malabsorption, especially protein & fat
CCK with Pancreas?
major secretion regulator, triggers vago-vagal signals
-use ACh as receptor, we don’t have CCK-1 receptors
Duct Cell in Pancreas
Cations: Na+ (water follows in aquaporin 1)
transport mechanisms are proteins
-Na+/K+ATPase
secondary transport: Na+ in/ H+ out of cell
-passive conductance: Cl- in cell more to lumen (abnormal in cystic fibrosis)
Electrolytes in Pancreatic Secretion and Changes with Flow?
K+ & Na+ is constant: similar to plasma conc.
Low flow: dec. HCO3- inc. Cl-
High flow: inc. HCO3- dec. Cl-
Anion concentration in High Pancreatic Secretion Rates?
- Na+Cl- low secretion rates
- Na+HCO3- high secretion rates
- the slower the secretion the longer the exchanges (so more Cl-) can occur
The steps of pancreatic enzyme secretion?
- RER- proteins are secreted, move to smooth golgi, then condensing vacuoles (proenzymes)
- In zymogen granules, fuze with luminal membrane
- from condensing vacuole step on, need energy
What determines the types of enzymes found in pancreatic secretion?
what you eat
carbs-amylase
protein-trypsin
What protects the pancreas from the enzymes?
- Enzymes in membranes
- Enzymes are “pro” inactive form
- Trypsin responsible for activation of other enzymes
- Cell is antitrypsin
- Trypsin is autocatalytic
Pancreatic secretion after a meal?
- increase in protein
- acid secretion
- increase bicarb and volume
What stimulates pancreatic secretion?
vagus, from cephalic phase
-conditional stimuli, smell, taste, chewing, swallowing, hypoglycemia
- strong aciner cell stimulation
- weak duct cell stimulation
Secretin Release (pancreas)
-measure bicarb secretion
-threshold for release is 4.5 pH
-cells don’t respond to decreasing pH past 3
-if inc. volume, get higher rates of secretion
(when fat, protein, H+ enter duodenum, H+ acts on S cells to make secretin duct & aciner, also CCK cause ACh to release on duct cells)
Phe + Secretin
potent release of CCK the 2 combine have a huge response 1. conserves hormones 2. if needed lots of hormones, it would have other effects POTENTIATION
Pancreatitis
- decreased volume and bicarbonate
- may impair digestion
- 10% hereditary (gets rid of protective mechanisms)
Kwashiorkor
- a pancreatic insufficiency
- malnutrition
- decreased volume, bicarb, enzymes
- steatorrhea
Cystic Fibrosis
- no Cl- conductance in apical membrane
- mucus secretion
- decreased volume, bicarb, enzymes
- steatorrhea
Bile acids
- synthesized from cholesterol
- secreted by hepatocytes into ducts
Secretin Stimulates what into the Bile Ducts?
- HCO3-
- Na+
- H2O
Spincter of Oddi at rest?
-closed, so bile flows into gallbladder
CCK stimulates ACh to do what to gallbladder and sphincter of Oddi?
- gallbladder contractions
2. relaxes sphincter of Oddi
% of bile acid reabsorbed due to passive diffusion?
40%
Amount of bile salts in the pool?
2.5g
% of bile acids actively reabsorbed in the ileum?
55%
% of bile acids lost in stool?
5%
4 Important Bile Acids?
Primary: synthesized by liver 1) Cholic Acid 2) Chenodeoxycolic Secondary 3) Deoxycholic Acid 4) Lithocholic Acid
While have bile salt instead of bile acids?
Bile acids have pKa~7, the live conjugates them to amino acids (bile salts)
- glycine pKa~3.7
- taurine pKa~1.5
Micelle Formation
Polar Part: nucleus, hydroxyl group, ionized acidic group
Hydrophobic Part: hydrocarbon steroid body
-it solublizes products of fat digestion
Biliary Histology
-stuff is extracted from portal vein, secreted into bile duct, flow of bile is countercurrent from flow of blood (dec. conc. gradient)
How much bile aids secreted per day?
30g
Max synthesis of bile acids per day?
3-5g
Enterohepatic Circulation
bile acids actively transported into bile, stored in gallbladder, secreted in duodenum
- dehydroxylate bile salts
- if you inhibit 7 hydroxylase enzyme, stops production
Bile acids reabsorbed in blood
- continuous process
- secretion of bile acids osmotically drives electrolytes H20
- cholesterol and phospholipids still depend on bile acids
Bilirubin
- produced by metabolism of broken RBC
1. formation of Fe, chelated & disposed of
2. green-biliredin, yellow bilirubin (bound to plasma albumen in blood) - active process that excretes bilirubin from intestine (not very effective)
Bilirubin Glucuronide
water soluble
bacteria converts it to bilirubin
Stirkobiligin
makes poop brown (pigment)
Secretion of Water & Electrolytes
- osmotically drive secretion of H2O & electrolytes
- liver ducts secretin inc. Na+ bicarb and H2O
- Interdigestive phase: sphincter of Oddi, filling pressure of 10-20mmHg holds 20-50mL of bile
CCK on Gallbladder Function
- acts through vagal stimulation
- ACh causes contraction of gall bladder and relaxes sphincter of Oddi
Micellar Solution
- isotonic
- all cations are osmotically inactive by being bound to bile acids
Cholesterol Stones
- all bile produced is supersaturated with cholesterol - 50% normal
- bile acid pool reduced 50%
- crystal formation
Pigment Stones
10-20%
-bile saturated with unconjugated bilirubin
-high beta glucuronidase: causes it
-gall bladder wall damaged by bacteria - E. coli
surface is damaged, physical or bacteria
