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233 Cards in this Set
- Front
- Back
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4 tunics or coats of the gut
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(From internal to external) Mucoas, submucosa, muscularis externa, and adventitia/serosa
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In what layer of the gut are the glands found?
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In the lamina propria of the tunica mucosa.
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Composition of the submucosa of the gut
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Dense irregular fibroeslatic CT with no glands (except esophagus and duodenum).
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Where is Meissner's plexus found?
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In the tunica submucosa of the gut
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Composition of muscularis externa of gut
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Inner circular and outer longitudinal layers of smooth muscle.
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Where is the myenteric (Auerbach's) plexus found?
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In the tunica muscularis externa of the gut between the circular and longitudinal muscle layers
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Make-up of serosa/adventitia of the gut
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The inner serosa is simple squamos epithelium and the outer adventitia is dense irregular CT that adheres to the body wall
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Function of myenteric (Auerbach's) plexus
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It is a single plexus that runs from esophagus to anus and it stimulates contraction of the gut
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Function of Meissner's plexus
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It controls local secretion, absorption, and blood flow
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How does the esophageal mucosa differ from the mucsal layer of other areas of the gut?
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In has only a single layer of longitudinally arranged smooth muscle. It also has esophageal cardiac glands that produce mucus
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What are the only 2 regions with glands in the submucosa of the gut?
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The esophagus and the duodenum
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What two enzymes are produced by serous cells in tubuloacinar glands of the esophagus?
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Pepsinogen and lysozyme
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What are gastric pits and where are they found?
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They are found in the stomach and 5-7 gastric glands empty into each pit
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What is unusual about the muscularis mucosa of the stomach?
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It has 3 layers, inner circular, then longitudinal, then outer circular layer.
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What is unusal about the muscularis externa of the stomach?
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It has 3 layers, an inner oblique, middle circular, and outer longitudinal layer.
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Gastric glands
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They are named for where they are found. Cardiac, fundic, and pyloric. They are found in the lamina propria of the mucosa. They are simple or branched tubular glands.
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Fundic glands
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Produce gastric acid, intrinsic factor, and mucus. The glandular epithelium are mucus neck cells, parietal cells, chief cells, and enteroendocrine cells
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What is the function of surface lining cells in the stomach?
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They are simple columanr cells that line the gastric pits and produce thick mucus for protection
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Parietal cells
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Secrete HCL and gastric intrinsic factor. They are pyramid-shaped and are located in the neck of the fundic gland.
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Chief cells
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Secrete pepsinogen and gastric lipase. Located in the base of fundic gland.
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Cardiac glands
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Mostly surface lining cells with some mucus neck cells. Mainly secretes protective mucus
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Pyloric glands
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Mostly mucus neck cells that secrete mucus and lysozyme. Some DNES cells that make gastrin. Deep gastric pit
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Are there goblet cells in the stomach?
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Nope
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To what degree is surface area in the small intestine increased?
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There is a 400-600 fold increase due to transverse folds, villi and microvilli
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What are the crypts of Lieberkuhn (intestinal crypts)
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They are invaginations into the lamina propria that are simple or branched tubular glands. They secrete various enzymes including sucrase, maltase, and enteropeptidase
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Function of goblet cell in small intestine
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They secrete mucinogen. There are increasing numbers of them as you go down the GI tract
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Paneth cells
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Located in the intestinal crypts, they secrete lysozyme, defensin, and TNF-alpha
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Brunner's glands
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Located in the submucos of the duodenum. They are tubuloalveolar glands that open into the intestinal crypts and produce mucus, a bicarbonate rich fluid, and epidermal growth factor
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Glandular epithelium of the large intestine
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There are no paneth cells, but an increased number of goblet cells and absorptive cells. They open into crypts of Lieberkuhn
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Where are Peyer's patches found?
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In the lamina propria of the ileum (small intestine)
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Major difference between small and large intestine
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Large intestine doesn't have villi like the small intestine, but it does have intestinal crypts
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Approximately how many taste buds are in the mouth?
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about 3,000
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Types of cells in a taste bud
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basal (type 4) --> dark cell (type 1) --> light cell (type 2) --> intermediate cell (type 3). It is believed that the cells follow the path of differentiation outlined above
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Ion channel taste buds
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Perception of salty and sour
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G-protein coupled receptor taste buds
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Perception of bitter and sweet
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Parotid gland
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compound tubulo-alveolar serous gland. Produces about 20-30% of resting saliva volume
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Submandibular gland
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Compound tubulo-alveolar gland that produces 60-65% of resting saliva volume. It is a mixed gland, predominantly serous
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Sublingual gland
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Compound tubulo-alveolar gland that produces 2-5% of resting saliva volume. Mixed gland but predominantly mucous
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Function of myoepithelial cells
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They have long processes that envelop the secretory acinus and intercalated ducts of salivary glands.
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Function and location of centroacincar cells
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They form the lumen of the intercalated ducts of the pancreas. They secrete a bicarbonate rich solution when stimulated by secretin
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Pancreatic acinar cells
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They secrete digestive enzymes in an exocrine manner when stimulated by cholecystokinin and acetylcholine
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What stimulates I-cells of DNES to secrete cholecystokinin?
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Fatty acids or monoglycerides (not triglycerides), peptides and single AA's, and acid.
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What is the function of cholecystokinin?
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It is a potent stimulator of enzyme secretion. Stimulates emptying of gallbladder and inhibits gastric emptying
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What stimulates S-cells of DNES to secrete secretin?
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Presence of acid in duodenum (pH <4.5) or fatty acids in duodenum
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What is the function of secretin?
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It stimulated pancreatic bicarbonate secretion and inhibits gastric acid secretion
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Make-up of pancreatic exocrine secretions
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There is an enzyme rich secretion and and enzyme poor secretion that are produced by different cells that are under different control. They can be released together or separate
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Mechanism of action of secretin
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It acts to open Cl- channels which exchange Cl- for bicarbonate (Cl- comes in and bicarbonate goes out into lumen)
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Five types of cells in Islets of Langerhans
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Alpha, beta, delta, G, and F cells.
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Function of pancreatic delta cells
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They secrete somatostatin which acts to reduce secretions and peristalsis of GI tract
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Function of pancreatic G cells
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They secrete gastrin which acts to stimulate production of HCL by parietal cells in the stomach
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Which cells in the liver are responsible for its endocrine and exocrine functions?
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The hepatocytes are responsible for both types of secretions.
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Functions of liver
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Synthesize blood proteins, maintain blood glucose, deaminate AA's, detox of drugs and toxins, Vit A storage, metabolism of chylomicrons, and bile production
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Blood supply to the liver
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The liver has a dual blood supply. 75% is nutrient rich blood from the hepatic portal vein and 25% is oxygenated blood from the hepatic artery
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Portal triads
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At each corner of hexagonal hepatocytes is a hepatic artery, portal vein, and bile duct that run together.
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Blood flow through liver
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Blood from the portal triads mixes together in the sinusoids and flows into the central vein.
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Classic liver lobule concept
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each hexagonal cell is a lobule, bile enters into bile canaliculi and flows to the periphery
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Portal lobule concept
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All hepatocytes that deliver their bile to a particular interlobular duct constitute a lobule. Forms a triangular region with portal are in the center and central veins at the apices.
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Liver acinus concept
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Oval are split into 3 zones according to oxygen concentration of blood. Zone 1 reichest and zone 3 poorest in oxygen
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What is the function of bile?
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It emulsifies fats to aid in their digestion and absorption (separates fat into smaller molecules)
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Perisinusoidal space (space of Disse)
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Space in the liver between the hepatocyte plate and the sinusoid. Blood plasma enters this space and nutrients/wastes are absorbed by liver cells. It contains type III collagen and fat storing Ito cells.
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Function and location of sphincter of Oddi
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It is the final sphincter before the duodenum. It must remain closed so that the bile will back up into the gallbladder for storage
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Bile release from gall bladder
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Cholecystokinin stimulated contraction of gall b ladder, relaxation of sphincter of Oddi, and injection of bile into duodenum. Acetylcholine also stimulates contraction of gall bladder
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What is the first step in digestion?
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Mastication
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What enzyme is contained in the serous portion of saliva?
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Alpha-amylase (ptyalin) for digesting starch.
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Primary saliva secretion
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Isotonic secretion with sodium, potassium, chloride, and bicarb levels nearly equal to plasma. Powered by sodium-potassium ATP pump
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Ductal modification of saliva
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Sodium actively reabsorbed, chloride follows. Potassium and bicarb are secreted. Net result--> much less sodium and chloride and much more potassium and bicarb
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Effect of saliva secretory rate on ionic composition
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As flow rate increases ion concentrations approach plasma values because there is less time for ductal modification
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Nervous regulation of salivary secretion
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Controlled from the brain stem, mainly under parasympathetic control. Stimulated by taste and tactile stimuli
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Slow waves in GI tract
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Rhythmic changes in membrane potential (5-15mV)caused by variations in sodium conductance, not action potentials
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Spike potentials (waves) in GI tract
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Action potentials that occur when the resting potential becomes greater than -40mV
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Where in the stomach does food mixing and chyme formation take place?
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In the antrum, assisted by the pyloric muscle. Chyme is then propelled into the duodenum.
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Functions of mucous
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Lubricates and prtoects the gut wall. Resistant to digestion and amphoteric (can buffer acids and bases)
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Three phases of gastric secretion
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Sight, smell, or taste stimulates via vagus. Local nervous reflexes (accounts for 70% of secretions). Presence of food in upper stomach.
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Stimulators of HCL production
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Acetylcholine, histamine, and gastrin
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Inhibitors of acid secretion
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Somatostatin acts to inhibit G cells and ECL cells and prostaglandins and gastric inhibitory peptide (GIP) act directly on parietal cells
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Acid response to a meal
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Right after a meal the pH is pretty high, it can take a couple of hours for the acid to build and pH to drop significantly
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Pepsinogen
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Secreted by chief cells in response to acetylcholine and acid. Low pH cleaves it and activates it. This is the first proteolytic enzyme encountered by food
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Helicobacter pylori
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Found in 95% of pts with gastric ulcers. It produces NH4+ that damages epithelial cells. Aspirin and alcohol also contribute to ulcers
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Brunner's glands
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Secrete alkaline mucous in response to irritating stimuli or the mucosa, secretin, or vagal stimulation.
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Structure of sucrose
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a glucose and fructose molecule bound by alpha1-2 glycosidic bond
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Structure of lactose
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A glucose and galactose molecule bound by beta1-4 glycosidic bond
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Digestion of three classes of foods
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All are digested by hydrolysis but the enzymes that catalyze hydrolysis differ with each one
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Membrane or contact digestion
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Therre are enzymes on brush border of enterocytes (surface absorptive cells). These are integral membrane proteins.
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Membrane digestion enzymes
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Enterokinase, sucrase, maltase, lactase, alpha-dextrinase, amino-oligopeptidase, dipeptidase
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Digestion of starches
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Ptyalin (alpha-amylase) is active for about an hour until pH drops below 4. Pancreatic amylase kicks in in duodenum for 15-30 minutes
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Final digestion of carbs
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Occurs at the brush border, products are mostly glucose with some galactose and some fructose.
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Enterokinase (enteropeptidase)
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Secreted from Brunner's glands. They activate trypsinogen to trypsin
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Proteolytic enzymes in pancreatic secretions
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All are zymogens that become activated by trypsin. They are trypsinogen, chymotrypsinogen, proelastase, and procarboxypeptidase A and B
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Endopeptidase function
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THey cleave in the middle of a polypeptide chain at certain amino acid sequences
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Final stage of protein digestion
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The intramembrane peptidases and intracellular peptidases eventually break down the small peptides into single AA's
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Lipid digestion
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Occurs largely in the small intestine. Bile emulsifies the fat and then pancreatic lipase breaks it down to 2-monoglyceride and 2 fatty acids. Bile salts form micelles to transport these to the brush border
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Water secretion in intestine
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cAMP activates Cl- channels which transport Cl- into the lumen. Na+ follows electrical gradient and H2O is pulled along by osmotic gradient into the lumen.
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Water absorption in intestine
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Sodium is actively transported out of the cells into extracellular fluid. More sodium flows into the cells and osmotic gradient brings water through epithelial junctions out of lumen.
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Carbohydrate absorption
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Active transport of Na+ coupled to glucose or galactose brings them into the cell. Fructose comes in by diffusion and converted to glucose inside cell
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Protein absorption
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AA's are coupled to Na+ transport and small peptides have a different carrier system that is faster.
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Lipid absorption
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2-monoglyceride and fatty acids are absorbed into cell and made into triglyceride in SER. They are assembled into chylomicrons and exocytosed out into lacteals
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Water secretion in intestine
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cAMP activates Cl- channels which transport Cl- into the lumen. Na+ follows electrical gradient and H2O is pulled along by osmotic gradient into the lumen.
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Water absorption in intestine
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Sodium is actively transported out of the cells into extracellular fluid. More sodium flows into the cells and osmotic gradient brings water through epithelial junctions out of lumen.
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Carbohydrate absorption
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Active transport of Na+ coupled to glucose or galactose brings them into the cell. Fructose comes in by diffusion and converted to glucose inside cell
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Protein absorption
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AA's are coupled to Na+ transport and small peptides have a different carrier system that is faster.
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Lipid absorption
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2-monoglyceride and fatty acids are absorbed into cell and made into triglyceride in SER. They are assembled into chylomicrons and exocytosed out into lacteals
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Where does synthesis and degradation of cholesterol take place?
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In the liver
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Effect of insulin on fatty acid storage (during feed state)
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It inhibits hormone sensitive lipase (which normally hydrolizes triglycerides). Also stimulates triglyceride synthesis and storage via liopprotein lipase
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Effect of insulin on fatty acid storage (during fasting state)
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Drop in insulin activates hormone sensitive lipase which hydrolyzes triglycerides and frees fatty acids
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Lipoprotein composition and function
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Made up of lipids plus apoproteins. Contains a lipid layer with polar heads facing out and cholesterol and triglycerides in the center. This is a way to solublize and transport lipids in the blood
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Apoprotein function
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They are in the outer lipid shell of lipoproteins. They are binding sites for receptors, activators or co-enzymes for lipid metabolism. They direct fate of lipoproteins
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Size vs. density of lipoproteins
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The larger ones (chlyomicrons and VLDL) are larger and less dense due to higher content of triglycerides. LDL and HLD are smaller and more dense due to more protein and less triglycerides
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Which 2 apoproteins can't co-exist on the same lipoprotein particle?
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apoB100 and B48 can't be on the same particle or exchange
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Chlyomicrons
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Largest and least dense lipoprotein. Most triglyceride rich and relatively short lived. Nearly absent in the fasting state. Assembled in intestinal mucosal cells
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VLDL
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Contain mostly TG but more cholesterol as well. Contain apo B100 and function in transporting endogenously synthesized TG to extra hepatic tissues. Acted upon by LPL to liberate fatty acids
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IDL
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50% of VLDL are lipolytically converted to IDL. Fatty acids are liberated from VLDL by LPL and this smaller more cholesterol ester enriched lipoprotein remains
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LDL
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Represents 70% of cholesterol in plasma. It is also a VLDL remnant formed from lipolysis of VLDL. High levels of plasma LDL is best predictor for atherosclerosis
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Lipoprotein lipase (LPL)
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Located in the capillary walls, activated by apo CII. It excises FFA from triglycerides in chylomicrons and VLDL's
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LCAT enzyme
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Function in the blood, activated by apo A1. Extracts cholesterol from cells and attaches it to HDL to carry to liver for clearance.
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Statins
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They lower cholesterol by inhibiting HMG-CoA reductase that functions in production of cholesterol in the liver. they raise HDL and lower LDL
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Liporpotein clearance
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Most lipoproteins hava a relatively short half life, but LDL can stay in circulation for 2-3 days because the LDL receptor has a lower affinity for B100 than apo E
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Consequence of oxidation of LDL
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Contributes to atherosclerosis/CAD. Induces chemokine production that brings macrophages to arterial walls. They contribute to atherosclerotic plaque
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Function of renal podocytes
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They are modified epithelial cells that cover the glomeruli capillaries with cytoplasmic extensions. They serve a filtering function by creating filtering slits
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Intraglomerular mesangial cells
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They sit between capillaries in glomeruli. Their two functions are to phagocytose any proteins or large molecules trapped by basal lamina and cause vasoconstriction when stimulated by angiotensin II
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Renal ultrafiltration in Bowman's capsule
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Fluid leaves capillaries via fenestrae. Basal lamina trapes > 69kDa and neg charged molecules. Filtration slit allows < 4nm and uncharged molecules to pass through.
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Function of proximal tubule
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Recovers 67-80% of Na+, Cl-, and water. Recovers all glucose, AA's, and proteins. Eliminates organic solutes, drugs, and toxins.
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Henle complex
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Squamous epithelium. Descending limb is permeable to water, urea, Na+, Cl-, and other ions. Ascending limb only moderately permeable to water.
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Function of distal tubule
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Impermeable to water or urea. Possesses a Cl- and Na+ pump that actively transports them from the lumen
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Action of aldosterone
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Causes distal tubule to actively resorb remaining sodium and passively resorb chloride. Water follows and this increases blood volume and pressure
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Juxtaglomerular apparatus
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Consists of macula densa of distal tubule that comes in contact with juxtaglomerular cells of afferent arteriole. These cells monitor the composition of filtrate and contain ACE, angiotensin I/II.
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Epithelium of ureters and urinary bladder
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Transitional epithelium that can becomes flattened at the bladder stretches
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Cortical collecting ducts
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Made up of principal and intercalated cells that can actively secrete H+ to modify acid-base balance. Impermeable to water except in presence of ADH.
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Which cells serve as pacemaker cells?
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Specialized cardiac muscle fibers form the sinoatrial node
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Function of internodal fibers
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Propagate the electrical signal through atrial syncytium and connect with AV node
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Function of AV node
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Connects to bundle branch fibers that conduct signal to ventricular syncytium
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What allows the automaticity of the SA node fibers?
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"funny" Na+ channels that are slowly activated at membrane voltages below -55mV, at which point they open and the membrane is depolarized quickly.
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Effect of sympathetic stimulation of B1 receptors on "funny" Na+ channels in SA node?
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cAMP is produced that in turn makes funny channels more sensitive to repolarization and increases the rate of depolarization (ie stronger heart contraction)
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Effect of parasympathetic stimulation on SA nodal cells
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G-protein coupled receptor (muscarinic) activates K+ channel that hyperpolarizes SA cells and reduces rate of depolarization
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Transitional fibers
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Small fibers that slow conduction of impulses from the atria to the ventricles. Prone to breakage causing an AV block
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Bundle branches
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One on each side of the heart, carry impulses from the AV node to the ventricles. Contain Purkinje fibers
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Mechanism of action of digitalis
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It is given to pts with a weak heartbeat. It inhibits the sodium-potassium pump so cellular sodium increases. This inhibits sodium-calcium exchanger so calcium levels remain higher in the cytosol = contractions are stronger
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P-R interval in EKG
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Corresponds to the depolarization of the atria and a delay of conduction to the ventricles.
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QRS complex in EKG
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Corresponds to the depolarization of the ventricles.
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T wave of EKG
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Corresponds to the repolarization of the ventricles
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What does an inverted T wave indicate?
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Damage to ventricular muscles causing them to repolarize in the same direction as depolarization. These cells could produce arrythmias
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How does "re-entry" cause arrythmia?
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Ventricular fibers are stimulated and pass that stimulation back to the original fiber which propagates it into the same muscle again (unless its still refractory)
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Causes of arrythmias
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Enlarged heart, reduced conduction velocity, shortened refractory period, and ischemic cells that can become pacemakers.
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Isovolemic contraction of the ventricles
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Ventricles contract but the aortic valve remains closed briefly and pressure builds for a short period
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How is blood flow and pressure maintained during diastole?
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The elastic recoid of the aorta keeps blood pressure and flow going even after ventricular relaxation.
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Left ventricular fillings
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It is actually mostly due to blood flowing through the atria and mitral valve from pulmonary veins into the ventricle...atrial contraction doesn't contribute that much
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How is cardiac output calculated?
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Stroke volume x heart rate
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Frank-Starling curve (law of the heart)
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The more the ventricles fill during diastole, the more cardiac fibers are stretched and the more forceful the contraction
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How to calculate total peripheral resistance
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Mean arterial pressure / cardiac output
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Control of blood flow to capillaries
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Sympathetic stimulation of alpha-1 promotes contraction of sphincters in arterioles and local factors (CO2, low pH, and temp) promote relaxation.
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What is the orthostatic reflex?
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It preserves blood pressure to the head via baroreceptors in the carotid sinus.
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Advantages of extensive vascular branching
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You get an increase in cross sectional area with no increase in resistance to blood flow. You can effectively cover more area
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Venous systemic circulation
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Blood pressure is very near zero, most of the blood volume is in the systemic venous circulation
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Sympathetic stimulation of veins
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Causes vasoconstriction of large veins so that venous return is increased. This contributes to increased cardiac output
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Mechanism of action of nitroglycerin
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It causes dilation of major veins which reduces venous return and in turn reduces work load on the heart
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Starling forces
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Blood pressure in capillaries slightly exceeds osmotic pressure from albumin in blood. This results in a net loss of water from capillaries
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How much fluid from plasma is lost as interstitial fluid each day?
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3 L/day goes from plasma to interstitial fluid which will be picked up by lymphatics
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Consequence of protein loss from plasma to interstitial fluid
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Osmotic forces will pull more fluid into ISF and lymphatics will be overwhelmed...result is edema
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At what pressure does pulmonary hypertension lead to serious edema?
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At or above a left atrail pressure (=pulmonary venous pressure) of 25 mmHg
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How do coronary arteries fill?
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They are the first branches off the aorta after the valve. When the valve shuts and the aorta recoils, the coronary arteries fill.
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What is thrombosis?
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Inappropriate clost formation
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What is embolism?
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Migration of blood clots
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Function of endothelin after vascular injury
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It is secreted by local endothelia and causes a vasoconstrictor reflex to help slow bleeding. However, it's effect is transient
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Primary hemostasis
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Endothelial injury exposes subendothelial ECM. Platelets adhere to it and become activated and change shape. They secrete products that recruit additional platelets (aggregation) to form a plug.
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von Willebrand's factor
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Plasma protein that binds collagen in subendothelial ECM and glycoprotein 1b in the platelet membrane.
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What factors do bound, activated platelets secrete?
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ADP and thromboxane A2. They activate an integrin that can bind fibrinogen in the plasma.
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How does Aspirin inhibit clot formation?
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It is a cyclooxygenase inhibitor that inhibits a precursor for thromboxane A2 (which is needed for fibrinigen binding to platelets)
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What are the areas of concern for thromboembolism formation?
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Pooled venous blood and areas of atherosclerotic plaques with high concentrations of clotting factors
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How does Plavix work to stop clot formation?
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It is an irreversible inhibitor of ADP binding. Doesn't allow it to bind to platelet and cause aggregation
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Secondary hemostasis
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Tissue factor produced by local endothelia activate thrombin, which cleaves fibrinogen into insoluble fibrin. It also induces further platelet aggregation. A permanent plug is thus formed.
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Intrinsic clotting pathway
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factor XII --> XI --> IX --> VIII --> X --> Prothrombin --> thrombin. Factor XII (Hageman factor) binds to negatively cahrged surfaces on exposed collagen to start the cascade
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Extrinsic clotting pathway
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Tissue factor --> factor VII --> X --> V --> prothrombin --> thrombin. Tissue factor on local endothelia starts the cascade
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What is the common point between extrinsic and intrinsic clotting cascades?
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Factor X. From that point the steps are identical up to activation of fibrin
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What mineral is necessary for binding of coagulation factors on platelet membranes?
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The end point of both pathways happens on platelet membranes and requires calcium ions for factor binding.
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Role of VIt K in clotting
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It is a cofactor needed to allow factors to bind to platelets for clotting rxns. Coumadin and warfarin act to block Vit K action and stop intrinsic pathway
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What are the antithrombotic factors released to prevent clot formation where it isn't needed?
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Tissue plasminogen activator (t-PA) which breaks up clots, and thrombomodulin which blocks the coagulation cascade
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Antithrombin III
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The most powerful inhibitor of clot formation. It is activated by heparin, so heparin is used to stop clot formation before surgery or dialysis.
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Tissue plasminogen activator (t-PA)
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It activates plasminogen to plasmin, which is a proteolytic enzyme that dissolves clots
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How much of the extracellular fluid does plasma represent?
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Only about 3L out of 42L approximately. Plasma volume is regulated by the kidneys
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Two different types of capillary beds around a nephron
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Peritubular capillaries that are located in the cortex around the tubules, and vasa recta which is located in the medulla around the Henle complex
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Two types of nephrons
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Samller cortical nephrons in the cortex, and longer juxtamedullary nephrons (which only make up about 15% of total nephrons)
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What is the avergage glomerular filtration rate (GFR) in the kidneys?
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About 125ml/min or 180L/day, which is about 20% of the total plasma flow passing through the glomeruli
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How is GFR calculated?
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By administering inulin and monitoring the amount excreted in a set amount of time. Called inulin clearance
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What test is used to evaluate kidney function?
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24 hour urinary creatinine output or blood creatinine concentrations. If blood creatinine is high, then GFR is probably reduced
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Functional role of the proximal tubule
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~70% of Na and Cl and H2O is absorbed here. 100% of glucose and AA's are absorbed and organic wastes (uric acid, toxins, drugs, etc) are secreted.
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Functional role of loop of Henle
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25% of NaCl and 15% of H2O absorbed here. Sets up osmotic gradient in peritubular fluid
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Functional role of the distal tubule
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7% NaCl and 8-17% of H2O are absorbed here. Responsible for maintaining sodium/potassium balance
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Functional role of collecting duct
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Reabsorption of NaCl and H2O. This is the site of final urine concentration, regulated by antidiuretic hormone
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How does glucose enter proximal tubule cells?
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Via a Na+-glucose symport protein called a SGLT. There are limited number of them, so with high filtered load glucose can appear in the urine
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How does bicarbonate enter proximal tubule cells?
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It is coupled to the secretion into the lumen of H+ via a Na+-H+ antiport protein. This is why urine is acidic.
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What part of the Henle complex is involved in active transport of ions?
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The thich ascending loop. It has a Na+/K+ pump in the basal membrane that drives the cotransport of Na+, K+, and 2Cl- ions out of the lumen and into the cell. They are then transported out to the ISF
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How does Furosemide (Lasix) work as a diuretic?
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The Na+, K+, and 2CL- (NKCC) cotransport protein is inhibited by lasix. This means these ions can't move out of the lumen so more water stays in the lumen as well.
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Describe counter current multiplication
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The ascending think loop dilutes fluid entering the distal tubule and concentrates the ISF and this draws water out of the descending loop.
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How does glucose enter proximal tubule cells?
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Via a Na+-glucose symport protein called a SGLT. There are limited number of them, so with high filtered load glucose can appear in the urine
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How does bicarbonate enter proximal tubule cells?
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It is coupled to the secretion into the lumen of H+ via a Na+-H+ antiport protein. This is why urine is acidic.
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What part of the Henle complex is involved in active transport of ions?
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The thich ascending loop. It has a Na+/K+ pump in the basal membrane that drives the cotransport of Na+, K+, and 2Cl- ions out of the lumen and into the cell. They are then transported out to the ISF
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How does Furosemide (Lasix) work as a diuretic?
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The Na+, K+, and 2CL- (NKCC) cotransport protein is inhibited by lasix. This means these ions can't move out of the lumen so more water stays in the lumen as well.
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Describe counter current multiplication
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The ascending think loop dilutes fluid entering the distal tubule and concentrates the ISF and this draws water out of the descending loop.
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What does aldosterone do and how does it work?
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It is a mineralocorticoid that stimulates Na+ reabsorption and K+ secretion. Blockers of aldosterone limit salt retention and thus water retention.
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mechanism of action of antidiuretic hormone
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It stimulates expression of an aquaporin in the apical membrane of the collecting duct. This allows more water to be reabsorbed.
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Juxtaglomerular apparatus control mechanism
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Macula densa senses tubular fluid composition and transmits signal to juxtaglomerular cells, which release renin.
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Function of renin
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Produced by juxtaglomerular cells, goes to the kidney and activates angiotensin 1. This goes to the lung and is cleaved by ACE enzyme to make angiotensin 2. A2 travels to the adrenals and stimulates aldosterone production
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What 2 hormones does angiotensin 2 stimulate?
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ADH and aldosterone
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Action of ACE inhibitors
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Doesn't allow angiotensin 2 to be formed, so this limits vasoconstriction and fluid retention thus reducing blood pressure
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What are the most important inspiratory muscles?
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The external intercostals raise the rib cage and the diaphragm lowers the floor of the thoracic civity
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What are the most important expiratory muscles?
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The abdominal recti pull the ribs down and push the abdominal contents up. The internal intercostals pull the rib cage in.
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What is pleural pressure?
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The outward force of the inspiratory muscles after a tidal breath. It is about -5cmH2O.
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Under tidal breathing, how much negative pressure is usually needed to draw air in?
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About -2.5 cmH2O. So, the total pleural pressure is -7.5 cmH2O during a tidal breath
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What is lung compliance?
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It is the amount of filling per unit of pressure gradient
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Where is surfactin made?
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It is made by type II epithelial cells in the alveoli and helps to reduce the surface tension so that they can inflate properly
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Composition of surfactant
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It is composed of 90% lipid and 10% protein. 90% of the lipid content is phospholipid
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Emphysema
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The alveoli fuse and elastic elements break down. They inflate easily but don't deflate
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Partial pressure gradients in arterial blood
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PO2 = 100 mmHg
PCO2 = 40 mmHg |
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Partial pressure gradients in venous blood
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PO2 = 40 mmHg
PCO2 = 46 mmHg |
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Partial pressure gradients in alveoli
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PO2 = 100 mmHg
PCO2 = 40 mmHg |
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Why is the partial pressure gradient of CO2 so much less than that for O2?
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Because CO2 is about 20 times more soluble than O2, so it has a much higher diffusion coefficient
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Why is PO2 of alveolar air and that of pulmonary venous blood not equal?
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Because pulmonary venous blood gets mixed with oxygen poor systemic venous blood supplying the lung tissue itslef. This is called an anatomical shunt.
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Function of dorsal respiratory group in brainstem
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Controls quiet or tidal breathing (only inspiration, expiration is passive)
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Function of ventral respiratory group
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Increases alveolar ventilation with exercise. Controls inspiration and expiration
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What does the pneumotaxic center do?
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It regulates the depth of inspiration and can increase frequency of inspiration.
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What is the Hering Breuer reflex?
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It is the control and modification of intrinsic breathing patterns by stretch receptors in the lungs
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What is the primary stimulator of ventilation?
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A decrease in pH of the cerebrospinal fluid due to an increase in PCO2. This is sensed by chemoreceptors in the medulla
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Factors that favor unloading of oxygen in the tissues
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A drop in pH due to higher PCO2, increasing temperature, and 2,3-BPG from the glycolytic pathway
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What are the three forms of transporting CO2 in the blood and which is more prominant?
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Some CO2 is dissolved in the blood, some is present as carbamino CO2 (bound to Hb), and most is in the form of bicarbonate.
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Path of pulmonary arteries and veins in the lungs
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The pulmonary arteries run alongside the conducting ariway, the pulmonary veins run in connective tissue septae, not along conducting airways
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What are the arteries that bring systemic blood from to the lungs?
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The bronchial arteries supply the parenchyma of the lungs.
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What are the areas of gas exchange in the lungs?
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Respiratory bronchioles, alveolar duct, alveoli
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Function of respiratory neuroendocrine cells
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They detect hypoxia and release neurotransmitters BASALLY to affect the underlying tissue
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What is the difference between bronchi and bronchioles?
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Bronchi will have some cartilage surrounding it, bronchioles don't but they have more smooth muscle
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What is metaplasia?
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It is a shift of epithelium in the lungs from pseudostratified columnar to stratified squamous due to pollution or tobacco smoke. It is reversible but can lead to cancer
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Clara (domed) cells
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They are found in the respiratory bronchioles in place of other epithelial cells (simple cuboidal). They produce surfactant and serous fluid.
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What are pores of Kohn?
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They are holes between alveoli that connect them and allow macrophages to crawl from one alveolus to the next
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Type I pneumocytes
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Squamous cells joined by tight junctions. Majority of gas exchange occurs across these cells.
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Type II pneumocytes
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They make surfactant and store it in lamellar bodies. They are also the stem cells of the alveoli
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