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BIO169-Renal
Renal System
| Question | Answer |
|---|---|
| what does the renal corpuscle consist of? | the glomerular capsule (aka Bowman's capsule) and the glomerulus (highly permeable capillary bed) |
| what does the nephron consist of? | the renal corpuscle and the tubular portion: PCT, loop of Henle, DCT, collecting duct |
| what 3 features must an anatomical structure have to be classified as a counter current system: | 1) must consist of either 2 parallel tubes or a single U-shaped tube (vasa recta & loop of Henle), 2) the flow through these tubes must be in opposite directions, 3) the tubes must be in close proximity to each other |
| what occurs in all counter current systems? | something (i.e. a substance or heat) is transferred from one tube to the others |
| what makes a counter current system a multiplier? | active transport must occur in the transfer |
| what makes a counter current system an exchanger? | if only diffusion occurs in the transfer |
| What are the 2 types of nephrons? What percentage does each constitute? | cortical: 80%; juxtamedullary: 20% |
| Describe cortical nephrons | have short loops which don't extend out of the cortex |
| What type of urine do cortical nephrons form? | isotonic and hypotonic |
| Describe juxtamedullary nephrons | have long loops of Henle which extend deep into the medulla of the kidney |
| what is filtration? | the movement of liquid from high hydrostatic pressure to low hydrostatic pressure, thru the glomerular capillary |
| how does liquid flow through the glomerulus? | thru the glomerular capillary into Bowman's capsule |
| what methods are used for reabsorption? | active transport (for reabsorption of many solutes such as glucose & amino acids); simple diffusion (used for reabsorption of lipid soluble solutes); osmosis (reabsorption of water) |
| what method is used for secretion? | active transport (it occurs against the concentration gradient) |
| What types of urine do juxtamedullary nephrons form? | iso-, hypo-, and hypertonic urine |
| How do juxtamedullary nephrons function? | as counter current multipliers as they actively concentrate urea & salts in the medulla of the kidneys |
| what happens when urea & salts are concentrated in the medulla of the kidneys? | it creates an environment with a high osmotic pressure so that water may be reabsorbed from the forming urine by osmosis if needed |
| What is the vasa recta? | a specialized system of blood vessels |
| how does the vasa recta function? | as a counter current exchanger; it picks up reabsorbed waer and leaves the solutes (salts & urea) behind in the medullary tissue |
| what is filtrate? | the fluid flowing from the blood to the glomerular capsule; contains the same substances as plasma, except it does not contain large proteins or RBCs |
| what is the "raw material" for urine formation? | blood plasma; once filtered into Bowman's capsule, it is called filtrate; as filtrate traverses the nephron tubules, desirable substances are reabsorbed back to the blood and additional wastes are secreted into filtrate; end product is urine |
| what are the 2 factors that drive glomerular filtration? | 1) permeabillity of the glomerular capillary endothelium which is fenestrated (more porous) 2) pressure gradient |
| what are the 3 components of the pressure gradient? | 1) glomerular hydrostatic pressure; 2) glomerular osmotic pressure; 3) capsular hydrostatic pressure |
| what is hydrostatic pressure? | pressure exerted by a fluid against the walls of its container; blood pressure is a hydrostatic pressure |
| what is osmotic pressure? | pressure due to the number of solute particles in a solution; water will move from an area of lower osmotic pressure to higher osmotic pressure |
| what is the glomerular hydrostatic pressure? | is is about 55 mm Hg; it is aka blood hydrostatic pressure; the pressure exerted by the blood against the glomerular capillaries; it is the blood pressure in the glomerulus (it pushes blood out of the capillaries and into Bowman's capsule |
| what is the glomerular osmotic pressure? | aka colloid osmotic pressure; about 30 mm Hg; due to large plasma proteins in the blood; pressure w/in capillaries due to non-diffusable, non-filterable solutes in the blood; the pressure is negative, as it tends to pull fluid back from Bowman's capsule |
| what is the capsular hydrostatic pressure? | it is about 15 mm Hg; it is the pressure of Bowman's capsule due to presence of filtrate; it is also negative because it tends to push fluid back into the glomerulus |
| what is the capsular osmotic pressure? | pressure in Bowman's capsule due to solutes in the filtrate; normally 0, but can be > 0 in case of disease; in this case it would be an outward pressure, pulling filtrate into capsule |
| what is the net filtration pressure? | the difference between opposing pressures: NFP = GHP - (GOP + CHP) |
| how is the pressure gradient formed? | due to the difference in size of afferent & efferent arterioles |
| what are the 2 outward pressures in the glomerulus? | GHP and COP (COP is normally 0) |
| what are the 2 inward pressures in the glomerulus? | CHP and GOP |
| what is the normal glomerular filtration rate? | 125 ml/min; 180 L/day; 48 gallons/day |
| what is the effect of GFR on urine production? | when rate increases, production increases; decrease in rate, decrease in urine |
| what is renal autoregulation? | self-regulating mechanism which assures that GHP is the dominant pressure, assuring a net filtration pressure |
| what are the 4 renal autoregulation mechanisms? | myogenic mechanism, tubuloglomerular feedback mechanism, renin-angiotensin mechanism, atrial natriuretic factor (ANF) aka atriopeptide |
| how does the myogenic mechanism work? | it involves the smooth muscle of the afferent glomerular arterioles; when stretche, it responds by contracting or constricting |
| what happens in the myogenic mechanism when there is an increase in systemic blood pressure? | the afferent arteriole is constricted, decreasing the amt of blood in the glomeruli and decreasing the GHP, preventing the loss of increased amts of blood plasma into the filtrate |
| what happens in the myogenic mechanism when there is an decrease in systemic blood pressure? | the afferent arteriole is dilated, increasing the volume of blood in the glomeruli and increasing the glomerular hydrostatic pressure to ensure that filtrate will be made |
| when is the myogenic mechanism most effective? | when blood pressure is between 110 and 200 mm Hg |
| how does the tubuloglomerular feedback mechanism work? | it is controlled by the macula densa cells of the juxtaglomerular apparatus, located in the distal tubule; it monitors the flow and osmolarity of the filtrate in the distal tubule |
| what happens in the tubuloglomerular feedback mechanism when there is low osmolarity and slow flow? | the afferent arteriole is dilated, resulting in an increase in GHP, increase in GFR, and accordingly more filtrate formed |
| what happens in the tubuloglomerular feedback mechanism when there is high osmolarity and fast flow? | the afferent arteriole is constricted, resulting in an decrease in GHP, decrease in GFR, and accordingly less filtrate formed |
| how does the renin-angiotensin mechanism work? | it is a powerful, long-term regulator of blood pressure and glomerular filtration and is controlled by the hormone renin? |
| what is renin work and what is its stimulus? | it is a hormone produced by the juxtaglomerular cells of the juxtaglomerular apparatus and its stimulus is decreased blood pressure or decreased flow in the afferent arteriole |
| what does renin do? | it activates the plasma protein angiotensinogen into angiotensin I |
| what is angiotensinogen? | it is the inactive form of angiotensin I and it is produced by the liver and circulates in the plasma |
| what is angiotensin convertine enzyme? | aka ACE; it converts angiotensin I to angiotensin II |
| what are the 2 effects of the renin-angiotensin mechanism? | 1) systemic vasoconstriction, which increases blood pressure; 2) release of aldosterone from the adrenal cortex, causing reabsorption of sodium chloride, and water |
| how does aldosterone impact GFR? | the reabsorption of water and NaCl increases blood pressure because by reabsorbing more NaCl, more water is drawn into the blood, increasing systemic blood volume |
| what is atrial natriueretic factor? | aka ANF, aka atriopeptide, aka atriopeptin; it is a hormone produced by the atria (right atrium?) of the heart |
| what is the stimulus and action of ANF? | stimulus: increased pressure in the right atrium; action: inhibits the secretion of renin and aldosterone, causing vasodilation which decreases blood pressure and volume |
| what is renal reabsorption? | the uptake of desirable substances from the filtrate back into the blood by way of the peritubular capillaries |
| where does renal reabsorption take place? | desirable substances are moved from the lumen of the renal tubules into the lumen of the peritubular capillaries |
| how much water is reabsorbed in the peritubular capillaries and where does it occur? | 99% of water is reabsorbed; 60-80% of filtered water is reabsorbed in the proximal convoluted tubule; 15% of filtered water is reabsorbed in the loop of Henle |
| how much solute is reabsorbed? | it varies depending on the solute; nearly all glucose, amino acids, and small proteins are reabsorbed in the PCT |
| how are glucose, amino acids, and small proteins reabsorbed? | in the PCT, by active transport |
| what is the role of the collecting duct in reabsorption? | only water is reabsorbed here; it is the 2nd largest place where water is reabsorbed; regulated by ADH |
| what is the impact of aldosterone on the reabsorption of water? | aldosterone regulates the reabsorption of extra sodium; stimulated when body fluids are too dilute |
| what is the impact of ADH on reabsorption of water? | ADH regulates the reabsorption of water from the collecting duct and is released when body fluids become too concentrated; it targets the water channels in the collecting duct, opening them, to cause water to be reabsorbed |
| where is ADH released from? | the psterior pituitary |
| what happens to urine volume and urine concentration when ADH is released? | because water is reabsorbed into the peritubular capillaries, urine volume decreases and becomes more concentrated |
| what is the relationship between ADH and aldosterone | when aldosterone is released, ADH is suppressed, closing up the water channels in the collecting duct |
| what is secretion? | movement of substances from the peritubular capillaries to the epithelial cells of the tubules into the lumen of the tubules |
| how is secretion accomplished and regulated? | by active transport; regulated by hormones |
| what substances are secreted? | creatinine, H+, K+, many organic molecules, drugs, and drug metabolites |
| what is creatinine? | a metabolic waste product |
| where is H+ secreted? What is it linked with? | H+ is secreted in the distal nephron tubules and is coupled with bicarbonate reabsorption by the tubular cells to control pH of body fluids |
| what is the secretion of potassium linked with? How is it regulated? | potassium secretion is linked with Na+ reasborption; it is regulated by aldosterone from the adrenal cortex |
| what happens to most substances secreted? | they eventually are excreted in the urine |
| what are the 2 components of the countercurrent mechanism in the nephron? | both involve the juxtamedullary nephron; 1) the vasa recta serves as a counter current exchanger; 2) the long loop of Henle serves as a counter current multiplier |
| what is the importance of the juxtamedullary nephron? | it is capable of forming hypertonic urine |
| how is hypertonic urine formed? | ADH opens water channels in the collecting ducts; because of high solute concentration in the medulla, H2O flows down its concentration gradient so that it is reabsorbed into the blood |
| what is the normal osmolarity of body fluids? What is the maximum concentration of urine? | 320 mOsm; 1800 mOsm |
| describe the permeability of the descending and ascending limbs of the loop of Henle | the descending limb is impermeable to solutes, permeable to H2O; the ascending limb is permeable to solutes, impermeable to H2O |
| how and what is moved in the ascending limb of Henle? | active transport is used to transport solutes out to the medulla; solutes include Na+, K+, Cl-; the transport of these solutes depends on the Na+/K+ pump; Na+, K+, Cl- are co-transported all at the same time |
| what is the vasa recta and what is its function? | it is a special portion of the peritubular network of blood vessels that surrounds and runs parallel to the nephron tubules (inc. loop of Henle) and functions to maintain solute concentration |
| how does the vasa recta maintain solute concentration? | it carries off reabsorbed water, keeping solutes behind in the medulla, due to the slow flow of blood in the vasa recta and concentration gradients |
| describe osmolarity in the medullary tissue | osmolarity increases as you get deeper into the medulla, due to active transport of solutes (primarily sodium and urea) from filtrate to medulla |
| where is ADH produced and released from? | produced by the supraoptic nuclei of the hypothalamus; released from the posterior pituitary |
| when is ADH released? | when body fluids become too concentrated |
| where are the receptors for ADH release? | osmoreceptors in the hypothalamus and baroreceptors in the carotid bifurcation and aortic arch |
| what is the purpose of the osmoreceptors? | they monitor osmotic concentration of blood; stimulates ADH release when osmolarity increases |
| what is the purpose of the baroreceptors? | they detect changes in systemic blood pressure; when pressure increases, ADH is inhibited (i.e. if blood pressure increases, the blood already contains enough water) |
| what is the target of ADH? | the collecting ducts; it increases permeability of the collecting duct by opening water channels (aquaporins) |
| what is the function of ADH and its result? | water reabsorption; result - production of small volume of concentrated urine |
| what happens to the contents of the tubule once it flows thru the collecting duct? | no further processing occurs; the finished product is called urine |
| what is the pathway for urine elimination? | collecting ducts -> renal calyces -> renal pelvis -> ureter -> urinary bladder -> ureter -> out |
| how is urine carried from the kidneys to the urinary bladder? | by ureteral peristalsis |
| what is the stimulus for micturition? | stretch of bladder wall stimulates stretch receptors |
| which nerve signals are involved in micturition? | 1) afferent nerve signal to sacral spinal cord 2) efferent nerve signal to the parasympathetic motor fibers of the pelvic nerve |
| which muscles are involved in micturition? | 1) contraction of detrusor muscle of the bladder 2) relaxation of internal urethral sphincter 3) voluntary relaxation of external urethral sphincter (skeletal muscle) |
| which part of the nervous system controls the relaxation of the external urethral sphincter? | CNS both facilitates and inhibits the external sphincter; voiding is voluntary and the reflex can be overridden |
| what happens in the body when an individual is well hydrated? | decreased serum osmolarity (<270 mOsm), increased blood pressure, decreased serum sodium concentration |
| What is the body's response to decreased serum osmolarity? | osmoreceptors in the hypothalamus sense the decreased osmolarity, thirst is decreased, and ADH secretion is decreased |
| What is the body's response to increased blood pressure? | baroreceptors in the carotid bifurcation and aortic arch (sinuses) and volume receptors in the atria detect the increase in pressure; increased secretion of atriopeptide (ANF), which causes inhibition of renin (which accordingly reduces angiotensin I and |
| does vasoconstriction increase or decrease systemic blood pressure? | vasoconstriction increases blood pressure (think of high blood pressure caused by arteriosclerosis); vasodilation decreases blood pressure |
| what is the body's response to decreased serum sodium concentration? | aldosterone production is increased, causing increased reabsorption of sodium |
| what is the renal response to large volume of dilute urine (well hydrated)? | vasodilation of the afferent glomerular arteriole to increase filtration |
| what causes vasodilation and vasoconstriction of the afferent glomerular arteriole? | 1) myogenic mechanism and 2) juxtaglomerular apparatus |
| what happens in the body when an individual is poorly hydrated or dehydrated? | increased serum osmolarity (>320 or >300 mOsm), decreased blood pressure |
| What is the body's response to increased serum osmolarity? | osmoreceptors in the hypothalamus sense the increased osmolarity, thirst is increased, and ADH secretion is increased, causing increased reabsorption of water from tubules |
| What is the body's response to decreased blood pressure? | baroreceptors and volume receptors in the atria detect the decrease in pressure; secretion of ANF is decreased, allowing production of renin (which accordingly increases angiotensin I and II), increasing vasoconstriction and aldosterone production |
| what is the renal response to small volume of concentrated urine (poorly hydrated)? | vasoconstriction of the afferent glomerular arteriole to decrease filtration |
| where is renin produced? | in the walls of the afferent & efferent arterioles |
| where does angiotensin I come from? | converted from the inactive protein angiotensinogen, which is produced in the liver |
| what is the relationship between ANF, renin, angiotensin I and II, and aldosterone? | increase in ANF, decreases renin, angiotensin I and II; decrease in ANF, increases renin, angiotensin I and II and aldosterone |
| how is calcium homeostatis regulated? | by parathyroid hormone (PTH) and calcitonin |
| how does PTH work? What are its targets? | parathyroid hormone is released from the parathyroid glands when calcium levels are low; its targets are bone (increased osteoclast activity and release of calcium from the bone), kidney (increased absorption of calcium), and small intestine (increase abs |
| how does calcitonin work? What is its target? | calcitonin is released from the thyroid gland when calcium levels are high; it targets the bone by increasing the bones' uptake of calcium |
| how is sodium homeostasis regulated? | by the renin-angiotensin system; by aldosterone and atriopeptide (ANF) |
| what is aldosterone and where is it produced? | it is a steroid hormone, produced by the adrenal glands and is secreted in response to angiotensin II |
| what is the trigger for aldosterone secretion? When is aldosterone secretion inhibited? | when Na+ levels are low; it causes increased reabsorption of Na+ from the nephron tubules; also triggered in response to angiotensin II; aldosterone secretion is inhibited by ANF, which is released when Na+ levels are high |
| what is the role of atriopeptide in sodium homeostatis? | atriopeptide, aka ANF, is released when Na+ levels are high, which inhibits renin, angiotensin I and II, and aldosterone |
| how is potassium homeostasis regulated? | by the reninangiotensin system |
| what is the role of aldosterone in potassium homeostatis? | increase in potassium levels, increase in aldosterone (so K+ is secreted into tubules), increase in potassium excretion; decrease in potassium levels, decrease in aldosterone, less potassium excreted |
| what is the role of atriopeptide in sodium homeostasis? | atriopeptide, aka ANF, is inhibited when K+ levels are high, which stimulates renin, angiotensin I and II, and aldosterone |
Created by:
debmurph
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