Physiology Flashcards
What are the layers of the GI wall?
Mucosa
Submucosa
Circular & longitudinal smooth muscle
Serosa
What is part of the mucosa?
Layer of epithelial cells specialized for absorption and secretion
Highly vascularized
Innermost layer
What is the submucosa consist of?
Consists of collagen, elastin, glands, and blood vessels
What is the circular and longitudinal smooth muscle for?
Motility for GI tract
Functions of the Mouth
Mostly mechanical digestion Mastication Food is broken down into small particles Chemically digested Bolus
Enzymes of the Mouth
Lingual amylase: carbs
Lingual lipase: lipids
What does lipase require to function appropriately?
Co-lipase
How many muscles and CN are used for swallowing?
26 muscles
5 CN
What CN are used for swallowing?
5 7 9 10 12
Esophageal Stage of Swallowing
Begins with crico-pharyngeal relaxation
Involuntary
What salivary gland matches up with Stenson’s duct?
Parotid gland
What salivary glands match up with Wharton’s ducts?
Submandibular glands
What salivary glands match up with the sublingual ducts?
Sublingual glands
How much saliva does the salivary glands produce a day?
1 liter
Functions of Saliva
Initial digestion of starches & lipids by salivary enzymes
Dilution & buffering of ingested foods
Lubrication of ingested food to aid its movement
Secretions Produced By:
Salivary glands
Gastric mucosal cells
Pancreatic exocrine cells
Liver
Functions of the Stomach
Short-term storage Absorption Digestion Secretion Chemical/enzymatic digestion Liquefaction of food Release slowly into sm. intestine Pepsin & peptidase to break down proteins Good environment for enzymes to work in
Functions of the Small Intestine
Absorption of nutrients
Function of the Large Intestine
Absorption of water
What does gastric juice convert food to?
Semiliquid called chyme
4 Parts of the Stomach
Cardia
Fundus
Body
Pylorus
What are the 3 phases of digestion?
Cephalic phase
Gastric phase
Intestinal phase
Parts of the brain that are part of the cephalic phase
Cortex
Amygdala
Hypothalmus
Vagus nerve
Important Hormones of the Gastric Phase
HCl
Pepsin
Define Enterogastrone
hormones in the GI tract as a group
Define Intestinal Phase
Enterogastrone hormones secreted in the duodenum & the lower GI tract
What does stimulation of the vagal nerve fibers cause release of?
Pancreatic juice and weak contractions of the gallbladder
What is released during the gastric phase of digestion?
Cholecystokinin into the blood stream
What happens when cholecystokinin reaches the pancreas?
Induces secretion of enzyme-rich pancreatic juice
What does secretin cause?
Copious secretion of bicarbonate-rich pancreatic juice
Gastric mucosal cells secrete what types of gastric juice?
HCl: protein digestion
Pepsinogen: protein digestion
Intrinsic factor: absorption of vit. B12
Cell Types of Gastric Mucosa in the Body of the Stomach
Parietal cells
Chief cells
What does parietal cells secrete?
HCl
Intrinsic factor
What do chief cells secrete?
Pepsinogen
Cell Types of Gastric Mucosa in the Antrum of the Stomach
G-cells
Mucous neck cells
What do G-cells secrete?
Gastrin
What does mucous neck cells secrete?
Mucus
HCO3
Pepsinogen
What stimuli releases gastrin?
Proteins
Distention of the stomach
Vagal stimulation
When is gastrin-releasing peptide released?
Vagal stimulation of the G cells
What does Gastrin promote?
H secretion by gastric parietal cells
What does gastrin stimulate?
Growth of gastric mucosa
Other Functions of Gastrin Hormone
Pepsinogen release
Increase stomach motility
Relax pylori sphincter
Contract LES
How does ACh regulate HCL secretion?
ACh released from vagus nerve
Binds receptors on parietal cells
Produces H secretion by parietal cells
What blocks muscarinic receptors on parietal cells?
Atropine
How does histamine regulate HCl secretion?
Released from mast like cells in gastric mucosa
Binds to H2 receptors on parietal cells
Produces H secretion by parietal cells
What blocks H2 receptors?
Cimetidine
How does gastrin regulate HCl secretion?
Released into circulation by G cells of stomach antrum
Binds to receptors on parietal cells
Stimulates H+ secretion
Define Segmentation Contractions
Circular muscle contracts sending chyme in both directions
Intestine then relaxes allowing chyme to merge back together
Define Peristaltic Contractions
Longitudinal muscle contracts propelling chyme along small intestine
How do varies occur?
Obstruction of the liver
When does a Mallory-Weise tear occur?
Frequent retching
What enzymes are released by the salivary glands?
Amylase
Lipase
What enzymes are released by the stomach?
Pepsin
Lipase
What enzymes are released by the pancreas?
Amylase Lipase & co-lipase Phospholipase Trypsin Chymotrypsin
What enzymes are released by the intestines?
Enterokinase
Disaccharidases
Peptidases
What does trypsin & chymotrypsin target?
Peptides
What does enterokinase activate?
Trypsin
What innervates the GI tract?
Autonomic nervous system
Parts of the Autonomic Nervous System
Extrinsic
Intrinsic
What does the extrinsic autonomic nervous system encompass?
Sympathetic
Parasympathetic
What does the intrinsic part of the autonomic nervous system do?
Communicates with the extrinsic component
What does the enteric nervous system do?
Myenteric plexus
Meissner’s plexus
Where does the parasympathetic nerve supply come from?
Vagus nerve
Where does the sympathetic nerve supply come from?
Cervical & thoracic sympathetic chain
What does the parasympathetic nervous system do for the GI tract?
Motor innervation to the esophageal muscular coat and secretomotor innervation to the glands
What does the sympathetic nervous system do for the GI tract?
Regulates blood vessel constriction, esophageal sphincters contractions, relaxation of the muscular wall, and increases in glandular and peristaltic activity
What is a special function of the intrinsic innervations?
Can direct all functions of GI in absence of extrinsic innervation
What does intrinsic innervation control?
Contractile, secretory, and endocrine functions of the GI tract
Where does the intrinsic part of the ANS receive input from?
Parasympathetic & sympathetic nervous systems
Mechanoreceptors & chemoreceptors in the mucosa
Where does the intrinsic ANS send information to?
Smooth muscle, secretory, and endocrine cells
4 Functionally Different Cell Types that Compose Glands
Mucous cells
Chief cells
Parietal cells
Enteroendocrine cell
What activity does gastrin have on the stomach?
Causes gastric glands to increase secretory activity
Stimulates gastric emptying
What activity does gastrin have on the small intestine?
Stimulates contraction of intestinal muscle
What activity does gastrin have on the ileocecal valve?
Relaxes ileocecal valve
What activity does gastrin have on the large intestine?
Stimulates mass movements
What activity does serotonin have on the stomach?
Causes contraction of the stomach muscle
What activity does histamine have on the stomach?
Activates parietal cells to release HCl
What activity does somatostatin have on the stomach?
Inhibits gastric secretion of all products
Inhibits gastric motility and emptying
What activity does somatostatin have on the pancreas?
Inhibits secretion
What activity does somatostatin have on the small intestine?
Inhibits GI blood flow
Inhibits intestinal absorption
What activity does somatostatin have on the gallbladder?
Inhibits contraction and bile release
What are the 3 parts of the small intestine?
Duodenum
Jejunum
Ileum
Function of the Small Intestine
Primary site for digestion and absorption of nutrients
What ducts empty into the duodenum?
Bile duct
Pancreatic duct
Where does the liver receive blood from?
Hepatic portal vein
Hepatic artery
What type of vascular resistance occurs in the liver?
Low vascular resistance
What happens to the liver circulation when someone has cirrhosis?
Vascular resistance increases
Blood flow decreases
Hepatic Functions
Carbohydrate metabolism Lipid metabolism Protein metabolism Removal of drugs and hormones Excretion/secretion of bilirubin Synthesis of bile salts Storage of some compounds (glucose) Phagocytosis Aids in synthesis of active vitamin D Urea formation from ammonium
Carbohydrate metabolism in the liver
Maintaining a normal blood glucose
Storage of glycogen
Why do alcohol abusers frequently have hypoglycemia?
Alcohol suppresses citrate cycle and impairs gluconeogenesis from amino acids
Why do patients with cirrhosis have hyperglycemia after a carbohydrate rich meal?
Liver insufficiency Decrease of glucose utilization Hyperglycemia Hyperinsulemia Down-regulation of insulin receptors Insulin resistence
Steps in Carbohydrate Breakdown
Disaccharides
Monosaccharides
Steps in Protein Breakdown
Peptides
Amino acids
Steps in Lipid Breakdown
Diglycerides
Monoglycerides & fatty acids
Where does most of our cholesterol come from?
Liver
Fat Metabolism in the Liver
Oxidation of fatty acids to supply energy
Synthesis of large quantities of cholesterol, phospholipids, and lipoproteins
Inactivation of steroids & excretion from the body
Disorders of Protein Metabolism
Ammonia detoxification disorder and failure of urea formation
Hyperammonemia
Hepatic coma
Ammonia Detoxification Disorder & Failure of Urea Formation
Ammonia comes from bacterial degradation of nitrogen substances in intestines, from intestinal mucosa during glutamine degradation, from degradation of amino acids in kidneys and muscles
Hyperammonemia SE
Mental changes: disorientation, sleeping disorders, chaotic speech, personality changes
Motor changes: increased muscle reactivity, hyperreflexia, tremor
Types of Hepatic Coma
Endogenous
Exogenous
Endogenous Hepatic Coma
Viral hepatitis and poisoning
Hepatic cell disintegration
Exogenous Hepatic Coma
Final status of chronic cirrhosis
Basics of Bile Secretion
Necessary for digestion and absorption of lipids
Mixture of bile salts, bile pigments, and cholesterol
Bile salts emulsify lipids
Bile Secretion and Recycling
Produced and secreted by liver
Stored in gallbladder
Ejected into sm. intestine
After lipid absorption, bile salts are recirculated to liver
Extraction of bile salts from portal blood
Formation of Bilirubin
Formed from hemoglobin Hemoglobin phagocytosed Iron release bound to transferrin Remainder of heme group covered to biliverdin Biliverdin reduced to bilirubin Bilirubin attached to albumin Secretion of bilirubin into bile
Processing Bilirubin by Hepatocytes
Albumin removed as unconjugated bilirubin passes through liver
Bilirubin conjugated
Secretion of Conjugated Bilirubin into Bile
Hepatocytes transport conjugated bilirubin into bile clinical
Conjugated bilirubin enters duodenum
Role of Small Intestine in Bile Metabolism
Bile & bile salts increase growth of intestinal bacteria
Intestinal bacteria metabolize conjugated bile to urobilirubin
Urobilirubin reabsorbed into blood
What happens to the bile when the duodenal orifice is closed?
Bile is stored and concentrated in the gallbladder
How much bile does the liver produce in a day?
500-1000 mL
Composition of Bile
Water Bile Salts Bile pigment Cholesterol Inorganic salts Fatty acids Lecithin Fat Alkaline phosphatase
What are the ways people become jaundice?
Too much production of bilirubin
Conjugation of bilirubin
Obstruction of path to the duodenum
Obstructive Jaundice
Bile prevented from flowing out of biliary duct
Conjugated bilirubin builds up in biliary duct
Conjugated bilirubin is returned to blood
Unconjugated bilirubin normal or decreased
Formation and Secretion of Bile
Detoxification of various substances Synthesis of plasma proteins Coagulation Blood reservoir Immunity Vitamins Relation to blood formation
Function of the Gallbladder
Blind pouch that stores bile
Ducts of the Gallbladder
Hepatic duct
Cystic duct
Common bile duct
What duct joins the common duct?
Pancreatic duct
Why is the pancreatic duct pressure greater than the common bile duct pressure?
Reflux of bile into the pancreas will give the patient severe pancreatitis
Innervation of the Pancreas
Sympathetic: splanchnic nerves
Parasympathetic: vagus
Exocrine Glands in the Pancreas
Secrete essential digestive enzymes through pancreatic duct into duodenum
Endocrine Gland of the Pancreas
Islets of Langerhans
Four Major Cell Types in the Islets of Langerhans
Alpha: glucagon
Beta: insulin
Delta: somatostatin
F cells: pancreatic polypeptide
What does the pancreatic polypeptide do?
Secretes insulin and glucagon into the blood stream
What do the exocrine pancreas enzymes digest?
Carbohydrates
Proteins
Fats
Major Stimulants of Bicarbonate Secretion
Secretin
Cholecystokinin
Gastrin
Acetylcholine
Major Inhibitors of Bicarbonate Secretion
Atropine
Somatostatin
Pancreatic polypeptide
Glucagon
Amylase from the Pancreas
Only enzyme to be released in active form
Hydrolyzes starch & glycogen to glucose, maltose, maltotriose, and dextrins
Function of Lipase from the Pancreas
Emulsify and hydrolyze fat in the presence of bile salts
How much of the islet cell mass must be removed before diabetes will become clinically apparent?
80%
Most Important Stimulant of Acinar Cells
CCK
Major Stimulant of Ductal Cells
Secretin
What is secretin secreted in response to?
H+ in intestine
Big Adipose Secretions
Resistin
Adiponectin
Leptin
Where is the pain when posterior ulcers erode?
Back pain
Where is the pain when anterior ulcers perforate?
Peritonitis
Why is the third portion most vulnerable to traumatic rupture?
It’s fixed
How do GI peptides regulate functions of the GI tract?
Contraction and relaxation of smooth muscle wall & sphincters
Secretion of enzymes for digestion
Secretion of fluid & electrolytes
Regulate secretion of other GI peptides
What activity does intestinal gastrin have on the stomach?
Stimulates gastric glands and motility
What activity does secretin have on the stomach?
Inhibits gastric gland secretion and gastric motility during gastric phase of secretion
What activity does secretin have on the pancreas?
Increases output of pancreatic juice rich in bicarbonate ions
Potentiates CCK’s action
What activity does secretin have on the liver?
Increases bile output
What activity does cholecystokinin (CCK) have on the liver/pancreas?
Potentiates secretin’s actions on these organs
What activity does cholecystokinin (CCK) have on the pancreas?
Increases output of enzyme-rich pancreatic juice
What activity does cholecystokinin (CCK) have on the gallbladder?
Stimulates organ to contract and expel stored bile
What activity does cholecystokinin (CCK) have on the hepatopancreatic sphincter of Oddi?
Relaxes sphincter to allow entry of bile and pancreatic juice into duodenum
What activity does vasoactive intestinal peptide (VIP) have on the duodenum?
Stimulates buffer secretion
Dilates intestinal capillaries
What activity does vasoactive intestinal peptide (VIP) have on the stomach?
Inhibits HCl production
What activity does vasoactive intestinal peptide (VIP) have on the small intestine?
Relaxes intestinal smooth muscle
What activity does motilin have on the proximal duodenum?
Stimulates migrating motility complex
How does digestion occur in the small intestine?
Hydrolysis then absorption
Causes of Malabsorption of Nutrients
Anything that interferes with delivery of bile or pancreatic juice
Damaged intestinal mucosa
Diarrhea
Functions of the Small Intestine
Electrolyte absorption
Water absorption
Electrolyte Absorption in the Small Intestine
Along whole length
Iron & calcium in duodenum
Sodium coupled with absorption of glucose & amino acid
Ionic iron stored in mucosal cells with ferritin
Potassium diffuses with osmotic gradients
Calcium absorption is regulated by vitamin D and PTH
Water Absorption in the Small Intestine
95% absorbed via osmosis
Net osmosis occurs when gradient is created via transport of solutes
Water uptake coupled with solute uptake
How does the intestinal lining increase absorptive surface area?
Villi
Microvilli
Define Villi
Finger-like projections of the mucosa
Define Microvilli
Tiny projections on luminal membrane of each intestinal cell
When do the final stages of chemical digestion occur?
Just prior to absorption of amino acids, glucose and fatty acids
What does carbohydrates have to be broken down to, to be absorbed?
Monosaccharides
What does protein have to be broken down to, to be absorbed?
Small peptides
Amino acids
What does fat have to be broken down to, to be absorbed?
Monoglycerides
Free fatty acids
Path of Absorption of Carbohydrate Digestion
Glucose/galactose co-transport with sodium ions
Fructose via facilitate diffusion
Path of Absorption of Protein Digestion
Co-transport with sodium ions
Path of Absorptions of Fat Digestion
Diffusion
Combine with proteins (chylomicrons)
Path of Absorption of Nucleic Acid Digestion
Active transport via membrane carriers
Emptying at the Ileocecal Valve
Fluidity of contents promotes emptying
Pressure & chemical irritation relax sphincter and excite peristalsis
Pressure or chemical irritation in cecum inhibits peristalsis of ileum and excites sphincter
Functions of the Large Intestine
Reabsorb water
Compact material into feces
Absorb vitamins
Store fecal matter
Physiology of the Ascending Colon
Processing chyme delivered from the terminal ileum
Physiology of the Transverse Colon
Storage and dehydration of feces
Primary site for removal of water & electrolytes
Storage of feces
Physiology of the Descending Colon
Conduit between transverse and sigmoid colon
Physiology of the Rectosigmoid Region
Maintains fecal continence
Types of Motions of the Colon
Haustrations- mixing movements
Mass movements- propulsive movements
Define Haustrations (Mixing Movements)
Ring-like contractions divide colon into pockets
When does net forward propulsion occur?
When sequential migration of hausfrau occurs the length of the bowel
Define Mass Movements (Propulsive Movements)
Starts in middle of transverse colon and precede by relaxation of the circular muscle and the downstream disappearance of austral contractions
What movements are inhibited during massive movements?
Haustral contractions
Physiology of the Large Intestine in Regards to Reabsorption
Water Vitamins K, biotin, B5 Organic wastes- urobilinogens & sterobilinogens Bile salts Toxins
Define Crypts
Tubular glands responsible for mucus secretion
What happens when crypts are occluded?
Diverticulitis
What is the last portion of the digestive tract?
Rectum
Where does the rectum terminate?
Anal canal
Rectum Function
Storage of feces
Define Feces
Particles of waste matter that is left over after the body has processed and absorbed nourishment from foods
What does feces contain?
Water Dietary fiber Inorganic salts Dead cells Bacteria Anything the body cannot or will not absorb
What type of sensory receptors does the rectum have?
Pain
Temperature
Touch
What structures maintain fecal continence?
Contraction of internal anal sphincter and puborectalis muscle
How does a bowel movement exit the anus?
Rectum fills with feces
Contraction of muscles increase intra-abdominal pressure
Increases intra-rectal pressure
Sphincter relax
Feces enter canal
Peristaltic waves push feces out
Relaxation of internal/external anal sphincters allows feces to exit