Lab 6- Renal

what are the key functions of the kidneys?

regulation of water concentration and fluid volume (blood), regulation of inorganic ion concentrations, acid-base balance, synthesis of hormones, excretion of metabolic waste products

what are four essential renal processes?

filtration, reabsorption, secretion, excretion

define filtration

substances move from glomerular capillary to lumen

define reabsorption

substances reclaimed from lumen to blood (peritubular capillary)

define secretion

substances move from blood (peritubular capillary) to tubule lumen

define excretion

substances are removed via urine

define nephron

the functional unit of the kidney; has both a medulla and cortex

what is in the nephron medulla?

renal pyramid, loop of Henle, medullary collecting ducts

what is in the nephron cortex?

corpuscle, convoluted tubule, cortical collecting ducts

what determines how much a tubule can concentrate urine?

the depth which the tubules extends into the medulla

describe the renal corpuscle

includes glomerulus and bowman's capsule, connected to proximal convoluted tubule to pass on filtrate, input is afferent arteriole, output is efferent arteriole

define the glomerulus

the capillary filtration unit

define bowman's capsule

surrounds the glomerulus to capture filtrate in bowman's space

describe the features of the glomerulus that allow for filtration

fenestrated endothelial cells, basement membrane that surrounds endothelial cells, podocytes around basement membrane that leave gaps for flow-through, and large, negatively charged proteins are repelled, only small solutes can pass through

what drives filtration of plasma?

pressure differences

what is the net driving force that favors ultrafiltraion?

the difference between hydrostatic pressure difference and oncotic pressure difference between the capillary and bowman's capsule

what are the parts of the tubular system?

proximal and distal convoluted tubules, loop of henle, collecting ducts

what lines the tubules?

epithelial cells that express different channels and pumps at different sections of the tubule

define peritubular capillaries

a second capillary bed that comes off the efferent arteriole and surrounds the tubule system

describe tubular secretion

important for acid-base balance and occurs by active transport across epithelial membranes

describe tubular reabsorption

occurs by passive transport (using gradients) or active transport (using pumps or exchangers); glucose, water, NaCl, and most bicarbonate are all reabsorbed

describe potassium balance

most uncontrollably reabsorbed in proximal tubule and loop of henle and depending on balance, secretion occurs in cortical and medullary collecting ducts (regulated by hormones)

describe potassium active transport

requires H-K ATPases; H+ secretion to reabsorb potassium and important for plasma acid-base balance

what promotes potassium secretion?

aldosterone, hypernatremia (high sodium in blood), volume depletion, ACTH

what reduces potassium secretion?

dopamine and ANP

describe sodium balance

most of it uncontrollably reabsorbed at proximal convoluted tubule and loop of henle, but rest of reabsorption os regulated by hormones at distal tubules and collecting ducts

what hormones increase sodium reabsorption?

aldosterone and AVP/ADH

what hormone increases sodium excretion/inhibits sodium reabsorption?

ANP

why is NaCl the most important contributor of plasma osmolarity?

where sodium goes, water follows to keep osmotic balance and chloride follows to keep electrical balance; most diuretics acts on sodium reabsorption

describe water balancw

uncontrolled reabsorption at proximal tubule and loop of henle, but regulated by ADH in distal tubules and collecting duct depending on the fluid need

what hormones increase water reabsorption?

aldosterone and ADH

describe acid-bace balance

under normal conditions, bicarbonate is reabsorbed in the proximal tubule and loop of henle and acid H+ is secreted with buffers

define intercalate cells

found in the collecting duct to transport acid and bicarbonate to balance pH

define type A intercalated cells

function during acidosis, usually more active under physiological conditions, uses H-K ATPases, excretes H+, reabsorbs bicarbonate and potassium

define type B intercalated cells

function during alkalosis, excrete bicarbonate and potassium, reabsorb H+

define GFR

the volume of fluid filtered into bowman's capsule per unit time; found by multiplying ultrafiltration coefficient by net filtration pressure

why can we not directly measure GFR?

due to the small size of the renal corpuscle

how do we estimate GFR?

by using substances that are freely filtered, but not secreted or reabsorbed (creatinine)

define clearance

the virtual volume of blood plasma per unit time needed to supply the amount of solute that appears in the urine

why do we use clearance to estimate GFR?

since all solute excreted into urine comes from the blood plasma perfusing the kidneys, the rate at which the kidneys excrete a solute into urine equals the rate at which solute disappears from the plasma

what does the clearance equation describe?

the virtual volume of blood plasma that will be totally cleared of a solute in a given time; conc of solute in urine * urine flow rate / conc of solute in blood plasma

what does it mean if clearance of a solute is equal to GFR?

solute is freely filtered, but not secreted or reabsorbed?

what does it mean if clearance is not equal to GFR?

if clearance > GFR: net secretion of solute

if clearance < GFR: net absorption of solute

describe creatinine

main source of plasma creatinine is metabolism of creatinine phosphate in muscles, and it is produced at a relatively constant rate

is creatinine clearance a perfect estimate of GFR?

no, it is secreted in small amounts by proximal tubule, so it overestimates GFR by 10-20%

define specific gravity

the ratio of the density of a material to the density of water; used as an index of osmolarity

what does it mean if specific gravity is more than 1.000?

the solution has more total solute than pure water (specific gravity decreases as urine becomes more diluted)

describe the juxtaglomerular apparatus

area where convoluted tubule comes between afferent and efferent arterioles; key site for RAAS; contains macula densa, granular cells, and extraglomerular mesangial cells

define macula densa

detect NaCl concentration in arterioles and signal to granular cells (when nacl low); secretes vasodilator and vasoconstrictor chemicals to arterioles (to regulate GFR)

define granular cells

secrete renin in response to macula densa cells when NaCl is low

define extraglomerular mesangial cells

specific function not fully understood, may work with RAAS system

what are the components of the RAAS system?

renin, angiotensin I and II, aldosterone

describe renin

made in kidney; activates angiotensinogen form live to produce angiotensin I

describe angiotensin I

converted to angiotensin II by ACE in the lungs

describe angiotensin II

stimulates adrenal glands to produce aldosterone, hypothalamus to produce ADH, hypothalamic thirst drive, and arteriolar vasoconstriction

what does aldosterone stimulate?

kidney sodium reabsorption

describe ADH/AVP

hormone made in hypothalamus that contains osmoreceptors to sense changes in osmolality

how is ADH/AVP release controlled?

by blood pressure, plasma osmolality, and angiotensin II: high plasma osmolality and low blood pressure --> renin release --> angiotensin II --> AVP/ADH

what is the action of AVP/ADH?

increases water permeability of distal tubules and collecting ducts --> increase water reabsorption; also acts as a vasoconstrictor

describe alcohol's effect on renal systen

inhibits release of ADH, so you will excrete dilute urine, leading to dehydration, and contributing to symptoms of a hangover

describe ANP

synthesized and secreted by cells in the atria and released when pressure/stretch in atrium gets too high (i.e. high blood pressure)

describe ANP's action

causes relaxation of afferent arteriole into the renal corpuscle, causing increased renal blood flow and GFR and inhibits the release of renin

how does ANP affect water and sodium?

reduces sodium and water reabsorption at distal tubule and collecting duct; increases excretion of sodium and water