PSIO Exam 4 Flashcards
Smooth Muscle
- modulates luminal pressure/tension
- tissue is present in sheets, bundles or sheaths around tissues
Innervation and Stimulation of Smooth Muscle
- primarily under control of ANS “involuntary”
- diffuse branching of nerve fibers
- transmitters include ACh and NE
- membrane potential ~ -50 to -60mV
Smooth Muscle Cells type categorized based on excitation
- single/unitary (visceral)
- multi-unit
Unitary Smooth Muscle Cells
- walls of digestive tract, gall bladder, urinary bladder
- may not have direct contact with any motor neuron
- AUTORHYTHMIC. Adjacent cells connect via gap junctions and transmit AP from one fiber to another
- cell membranes adhere to one another: transmission of force
- slow synchronized “graded” contraction
- entire sheet of muscle contracts as a “functional syncytium”
Diffuse Junctions
general area of smooth muscle fiber where numerous viscosities are located and release neurotransmitters into
Structure of Smooth Muscle Cells
- sarcoplasmic reticulum is poorly developed relative to skeletal muscle
- thick filaments of SM have actin-gripping heads along their entire length
- thick and thin filaments are arranged diagonally within the cell contraction results in twisting motion
Special Features of SM
- capable of sustained contraction without fatigue and at little energy cost
- maintains a low level of tension or tone even in the absence of action potentials
- stress relaxation response
SM Stretch Relaxation Response
- stretch causes initial increase in tension
- tension decreases within 1-2 minutes
- allows SM to change length but maintain ability to contract (important for storage organs)
Length-Tension Relationship in SM
- smooth muscles operate over a wider range of resting lengths
- generally broader length-tension relationship in smooth muscle compared to skeletal muscle
Parts of Stomach
- cardia
- fundus
- body
- pylorus
- pyloric sphincter
Stomach Anatomy
- stomach filling triggers secretions and motility
- stomach empties slowly into the duodenum as small squirts of chyme leave through the pyloric sphincter
Parietal Cell Function
secrete HCl
Mechanical Digestion in Stomach
- gentle mixing waves occur in the stomach to mix the blouse of food with gastric juice (enzyme, acid, water) and turn it into chyme (a thin liquid)
- more vigorous waves traveling from the body of stomach to the pyloric region move the chyme along
- intense waves near the pylorus lead to opening of the pyloric sphincter- squirting 1-2 teaspoons into the duodenum with each wave
Chemical Digestion in Stomach
- protein digestion begins in the stomach
- fat digestion continues
- HCl kills microbes in food
- mucous cells secret mucus to protect the stomach walls from being digested
Protein digestion in stomach
- HCl denatures (unfolds) protein molecules
- HCl activates pepsinogen into pepsin- an enzyme that breaks peptide bonds between certain amino acids
Fat digestion continues
gastric lipase splits the triglycerides in milk fat, although this is most effective at pH 5-6 (infant stomach)
Absorption of Nutrients by the Stomach
- water
- electrolytes
- some drugs (aspirin) and alcohol
- fat content in the stomach slows the passage of alcohol to the intestine, where absorption is more rapid
- alcohol is absorbed more slowly if taken with a meal
Regulation of Stomach Function: Neural Influences
- stretch receptors & chemoreceptors (pH) signal bolus entry, and this leads to an increase in parasympathetic nerve impulses to effectors in the stomach
- vigorous peristalsis and gastric gland secretions result
- chyme periodically released into the duodenum until return to homeostasis
Regulation of Stomach Function: Endocrine (hormonal) influences
distention and presence of food in stomach cause G cells to secrete gastrin into the bloodstream; gastrin increases gastric gland secretions and motility, and cause pyloric sphincter relaxation
Anatomy of the Small Intestine
- 3m (10 feet) in length
- 2.5 cm (1.0 in) in diameter
- large surface area
- site of most digestion and absorption
- divided into sections
Sections of Small Intestine
- duodenum 25 cm (10 in) starts at pyloric sphincter
- jejunum 1 m (3 ft)
- ileum 2m (6 ft) ends at ileocecal sphincter valve
Total length of small intestine in cadavers
6.5 m (21 ft) due to loss of smooth muscle tone
Functions of Villi and Microvilli
- increase surface area for absorption
- brush border enzymes found on the surfaces of microvilli participate in chemical breakdown of carbohydrates, proteins, and nucleosides
- cell division within intestinal glans produces new cells that move up to replace old cells that have been lost
Brush border enzymes on microvilli
- pancreatic juice is present in the lumen with chyme, and contains amylase, proteases, lipase and nucleases
- no brush border lipase or nucleases present
Pancreatic Juice (~2L produced per day)
clear colorless liquid (pH of 7.1 to 8.2) consisting of:
- water
- salts
- sodium bicarbonate
- several enzymes
Enzymes secreted by the pancreas
- pancreatic amylase
- trypsin
- chymotrypsin
- carboxypeptidase
- elastase
- pancreatic lipase
- ribonuclease
- deoxyribonuclease
Proteases
secreted as inactive precursors (like pepsinogen in the stomach)
Enteropeptidase (on brush-border cells)
activates trypsinogen to trypsin, trypsin then activates chymotrypsinogen, procaboxypeptidase, and proleasease
Digestion of carbohydrates
- mouth: salivary amylase
- stomach: mechanical only
- pancreas: pancreatic amylase in pancreatic juice
- small intestine: brush border enzymes maltase, sucrase, and lactase
Small intestine brush border enzymes: carbohydrates
- act on disaccarides (maltose, sucrose, and lactose)
- produce monosaccharides (fructose, glucose, and galactose)
Lactose Intolerance
those without lactase will have bacteria ferment lactose, and the result will be gas and diarrhea
Absorption of Monosaccharides
- Absorption into epithelial cells
- glucose & galactose: sodium symporter (secondary active transport)
- fructose: facilitated diffusion - Movement out of epithelial cell into bloodstream
- by facilitated diffusion
Digestion of Proteins
- mouth: mechanical only
- stomach: Hal denatures or unfolds proteins, and pepsin breaks proteins into smaller polypeptides -smaller chains of amino acids
- pancreas: pancreatic enzymes (proteases) in pancreatic juice continue to split peptide bonds between amino acids
- small intestine: brush border enzymes amino peptidase and dipeptidase
Small intestine brush border enzymes: proteins
- split off amino acids at the amino end of polypeptides (amino peptidase)
- split apart two-amino acid chains (dipeptidase)
Absorption of Amino Acids & Dipeptides
- Absorption into epithelial cells of duodenum and jejunum
- active transport with Na+ of H+ ions (symporters using secondary active transport) - Movement out of epithelial cell into blood
- by facilitated diffusion
Digestion of Lipids
-begins in the mouth thanks to lingual lipase in saliva
-continues in the stomach thanks to gastric lipase
(gastric lipase is especially important for digestion in infant)
-pacreas: pancreatic lipase in pancreatic juice continues to split triglycerides into fatty acids and monoglycerides
-liver: bile emulsifies lipids to form tiny micelles
-there is no digestion of lipids by the small intestine itself (no lipase enzymes in the membranes of brush border cells)
Absorption of Lipids
- short-chain fatty acids are absorbed by simple diffusion
- long-chain fatty acids and monoglycerides (products of lipases) are sequestered within tiny micelles after emulsification by bile; will also enter cells by simple diffusion, leaving bile salts behind
- bile salts are also reabsorbed and later recycled (into bile) by the liver
- fat-soluble vitamins (A, K, D3, E) are able to enter cells with lipids. - inside epithelial cells fats are rebuilt and coated with protein to form chylomicrons
- chylomicrons leave intestinal cells by exocytosis into interstitial fluid where they can only enter lacteals (too big for capillaries)
- travel in lymphatic system to reach subclavian veins
- removed from the blood by the liver and fat tissue
Absorption of Electrolytes
- source of electrolytes (GI secretions, ingested foods and liquids)
- enter epithelial cells by diffusion and secondary active transport
- Intestinal Ca2+ absorption requires vitamin D and parathyroid hormone.
Active transport by electrolytes
- sodium and potassium move by active transport
- chloride, iodide and nitrate follow passively
- iron, magnesium, and phosphate ions use active transport
Absorption of vitamins
- fat soluble vitamins (A, K, D3, E)
- travel in micelles and are absorbed by simple diffusion with lipids - water-soluble vitamins
- absorbed by diffusion - vitamin B12 must combine with intrinsic factor from the stomach parietal cells before it is transported into the cells of the ileum
- absorbed by receptor mediated endocytosis
Absorption of Water
- 9L fluid enters the GI tract per day
- small intestine absorbs 8L
- large intestine absorbs 90% of the last liter
- absorption of its accomplished by osmosis- through cell membranes into cells and then from the cells into the capillaries inside the intestinal villi
The Manifold Functions of the Liver
- metabolism of carbohydrates, proteins, and lipids
- detoxifies the blood by removing or altering drugs and hormones (thyroid and estrogen)
- removes bilirubin (waste product of red blood cell breakdown)
- releases bile salts to help digestion by emulsification of lipids
- stores fat-soluble vitamins (A, D3, E, K)
- stores iron, copper and vitamin B12
- phagocytosis of worn out blood cells and bacteria
- plays a role in the vitamin D activation pathway
Blood Flow through the Liver
blood from the hepatic arteries and hepatic portal vein mixes, and the mixed blood flows through the sinusoidal capillaries of the liver before returning to venous circulation
Liver’s Functional Unit: The Liver Lobule
- hepatocytes are the primary cells of the liver, doing most of the work
- hepatocytes arranged in grids in lobules
- spaces between hepatocytes are either blood-filled sinusoid or bile canaliculi
- kupffer cells phagocytize microbes and foreign matter
Pathway of Bile Secretion
- bile canaliculi join to form bile ducts which form hepatic ducts
- L & R hepatic ducts form the common hepatic duct
- the cystic duct from gallbladder and the common hepatic duct join to form common bile duct
- common bile duct & main pancreatic duct empty into duodenum
Carbohydrate Metabolism Liver Function
- turn amino acids into glucose (gluconeogenesis)
- turn triglycerides into glucose (gluconeogensis)
- turn excess glucose into glycogen & store in the liver (glycogenesis)
- turn glycogen back into glucose as needed (glycogenolysis)
Lipid Metabolism Liver Function
- synthesize cholesterol
- synthesize lipoproteins such as HDL and LDL, which are used to transport fatty acids and cholesterol in the bloodstream
- stores some fat
- breaks down some fatty acids
Protein Metabolism Liver Function
- deamination
- convert resulting toxic ammonia (NH3) into urea for excretion by the kidney
- transamination
- synthesizes plasma proteins utilized in the clotting mechanism and immune system
Deamination
removes -NH2 (amine group) from amino acids so we can use what is left as an energy force
Transamination
converts one amino acid into another
Functions of Large Intestine
- smooth muscle: mechanical digestion
- peristaltic waves (3 to 12 contractions/minute)
- haustral churning
- bacteria ferment undigested carbohydrates into carbon dioxide and methane gas, and undigested proteins into simpler substances
- gastroilial reflex, gastrocolic reflex, defecation reflex
Haustral Churning
relaxed pouches are filled from below by muscular contractions; when full, they contract and move contents to next pouch
Gastroilial reflex
when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty into large intestine
Gastrocolic reflex
when stomach fills, a strong peristaltic wave moves contents of transversals colon into rectum
Defacation reflex general
when rectum fills, input to sacral spinal cord return commands to expel feces
Defacation reflex detailed
- gastrocolic reflex moves feces into rectum
- stretch receptors signal sacral spinal cord
- parasympathetic nerves contract muscles of rectum and relax internal sphincter
(external anal sphincter is voluntarily controlled)
Regulation of digestion
- cephalic phase
- gastric phase
- intestinal phase
Cephalic phase (anticipation)
- prepare the mouth and stomach for food
- cerebral cortex: sight, smell, taste, and thoughts of food stimulate the parasympathetic nervous system to stimulate salivation (facial and glossopharyngeal) and gastric glands to secrete gastric juice (vagus)
Gastric phase (breakdown of material)
- neural influences
- endocrine influences
Neural influences over stomach activity
- stretch receptors and chemoreceptors (pH) signal bolus entry
- vigorous peristalsis and gastric gland secretions
- chyme periodically released into the duodenum
Endocrine influences over stomach activity
distention and presence of food in stomach cause G cells to secrete gastrin into the bloodstream; gastrin increases gastric gland secretions and motility, and causes pyloric sphincter relaxation
Gastric emptying increased as bolus of food enters stomach
- distention of the stomach and presence of undigested contents increase the secretion of gastrin hormone and vagal nerve impulses
- this stimulates contraction of the lower esophageal sphincter and the stomach, as well as relaxation of the pyloric sphincter for emptying
Intestinal phase (controlled release of chyme)
entry of chyme into duodenum slows gastric activity and increases intestinal activity
Neural influences over intestinal activity
distention of the duodenum and chemical contents of the chyme activate sympathetic nerves, which slow gastric activity (enterogastric reflex)
Endocrine influences over intestinal activity
distention of duodenum and contents of chyme trigger hormonal release from enteroendocrine cells in the duodenum
- secretin hormone decreases stomach secretions
- cholecystokinin (CCK) decreases stomach emptying
Enterogastric reflex: regulates the amount of chyme released into the duodenum
- initiated by distention of duodenum and contents of the chyme
- sensory impulses sent to the medulla inhibit parasympathetic stimulation of the stomach
- cause CCK and secretin release from the duodenum and stimulate sympathetic impulses, both of which inhibit gastric emptying
Regulation of pancreatic secretions by enteroendocrine cells
- secretin: acidity in intestine causes increased sodium bicarbonate release
- CCK (cholecystokinin): fats and proteins cause increased digestive enzyme release
Regulation of bile secretion by enteroendocrine cells
- parasympathetic impulses along vagus nerves stimulate bile production by liver
- fatty acids and amino acids in chyme entering the duodenum stimulate secretion of CCK into blood. acidic chyme entering duodenum stimulates secretion of secretin into blood
- CCK causes contraction of gallbladder
- secretin enhances flow of bile rich in HCO3- from liver
Catabolic reaction
breaks down complex organic compounds, providing energy
Anabolic reaction
synthesize complex molecules from small molecules, requiring energy
ATP’s central role in metabolism
- each cell has 1 billion ATP molecules (equals ~2 seconds of max contraction for skeletal muscle); rapid ADP-ATP turnover
- over half of the energy released from ATP is lost as heat
Energy Transfer
- energy is found in the bonds between atoms
- oxidation is a decrease in the energy content of a molecule: electrons lost, plus H+
- reduction is an increase in the energy content of a molecule: electrons gained, plus H+
- sometimes an intermediate molecule is involved in electron transfer: coenzyme (NAD+ and FADH)
4 Steps of Glucose Catabolism
- glycolysis
- formation of acetyl coenzyme A
- Krebs cycle
- electron transport chain (ETC)
Transport of Lipids by Lipoproteins
- most lipids are non polar and must be combined with protein to be transported in blood
- lipoproteins are spheres containing hundreds of molecules
- lipoproteins are categorized by function and density
- 4 major classes of lipoproteins
Classes of Lipoproteins
- chylomicrons
- very low-density (VLDLs)
- low-density (LDLs)
- high-density (HDLs)
Chylomicrons
- 2% protein, 85% TG
- form in intestinal epithelial cells to transport dietary fats to adipose cells
VLDLS (ver low-density)
- 10% protein, 50% TG
- form in hepatocytes to transport triglycerides to adipose cells
LDLs (low-density)
- 25% protein, 50% Cholesterol
- bad cholesterol
- carry blood cholesterol to body cells
HDLs (high-density)
- 40% protein, 20% Cholesterol
- good cholesterol
- carry cholesterol from cells to liver for elimination
Fate of Lipids
- oxidized to produce ATP
- excess stored in adipose tissue or liver
- synthesize structural or other important molecules
Other important lipid molecules
- phospholipids of plasma membrane
- lipoproteins that transport cholesterol
- thromboplastin for blood clotting
- myelin sheaths to speed up nerve conduction
- cholesterol used synthesize bile salts and steroid hormones
Thromboplastin
phospholipids and tissue factor are needed to activate the extrinsic pathway of blood clotting
Lipolysis
triglycerides are broken down into glycerol and fatty acids within liver or adipose cells in the presence of epinephrine, norepinephrine, cortisol
- beta oxidation
- ketogenesis
Lipogenesis
triglycerides are synthesized from amino acids or glucose within liver or adipose cells in the presence of insulin
Beta oxidation
fatty acids undergo beta oxidation in mitochondria to produce Acetyl CoA and lots of ATP
Ketogenesis
occurs in liver cells; ketone bodies are used by heart muscle and kidney cortex for ATP production
Fuel sources for lipogenesis
- amino acids, glycolysis metabolites, and ketone bodies for fatty acid production from Acetyl-CoA
- glycolysis metabolites for glycerol production
