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Phys U4 - Renal

Physiology Unit 4 - Renal - Fofi

Functions of kidney regulation of body fluid osmolality, volume; excretion of H20 & NaCl regulated w/ cardiovascular, endocrine, & CNS
Regulation of electrolyte balance daily intake of organic ions should be matched by daily excretion through kidneys
Regulation of acid-base balance kidneys work in concert with lungs to regulate the pH in narrow limits of buffers within body fluids
Excretion of metabolic products and foreign substances urea from amino acid metabolism, uric acid from nucleic acids, creatinine from muscles, end products of hemoglobin metabolism, hormone metabolites, foreign substances
Renin activates the renin-angiotensin-aldosterone system (RAAS), thus regulating blood pressure & Na+K+ balance
Prostaglandins/kinins-braykinin vasoactive, leading to modulation of renal blood flow and along w/ angiotensin II affect systemic blood flow
Erythropoietin stimulates RBC formation by bone marrow
Functional unit of the kidney nephron
Nephron function production of filtrate, reabsorption of organic nutrients, reabsorption of water and ions, secretion of waste products into tubular fluid
Types of nephrons cortical and juxtamedullary
Cortical nephrons 85% of all nephrons; located in cortex
Juxtamedullary nephrons closer to renal medulla; loops of Henle extend deep into renal pyramids
Blood supply to kidnesy blood travels from afferent arteriole to capillaries in nephron (glomerulus); blood leaves nephron via efferent arteriole; blood travels from efferent arteriole to peritubluar capillaries and vasa recta
Glomerular filtration produced from blood plasma; must pass thru pores b/t entothelial cells of glomerular capillary, basement membrane, podocyte filtration slits
Filtrate similar to plasma in terms of concentrations of salts, organic molecules, but it is essentially protein free.
Glomerular filtration barrier restricts filtration of molecules on basis of size and electrical charge
What drives filtration? starling forces across glomerular capillaries; changes in these forces and in renal plasma flow alter glomerular filtration rate (GFR)
Glomerulus is more efficient than other capillary beds…why? filtration membrane is significantly more permeable, glomerular blood pressure is higher, higher net filtration pressure
Plasma proteins and filtrate not filtered and are used to maintain oncotic (colloid osmotic) pressure of the blood
Net filtration pressure (NFP) pressure responsible for filtrate formation; equals the glomerular hydrostatic pressure (HPg) minus the oncotic pressure of glomerular blood (OPg) plus capsular hydrostatic pressure (HPc); NFP = HPg- (OPg + HPc)
Glomerular filtration rate (GFR) total amt filtrate formed/min by kidneys; factors include total surface area available for filtration & membrane permeability, net filtration pressure (NFP); GFR directly proportional to NFP; changes in GFR result of changes in glomerular capillary BP
GFR too high needed substances cannot be reabsorbed quickly enough and are lost in urine
GFR too low everything is reabsorbed, including wastes that are normally disposed of
Control of GFR normally result from adjusting glomerular capillary blood pressure; 3 mechanisms—renal autoregulation (intrinsic system), neural controls, hormonal mechanism (renin-angiotensin)
Autoregulation of GFR two mechanisms—myogenic mechanism, tubuloglomerular feedback
Myogenic mechanism autoregulation of GFR; arterial pressure rises, afferent arteriole stretches, vascular smooth muscles contract, arteriole resistance offsets pressure increase; RBF & hence GFR remain constant
Tubularglomerular feedback mechanism autoregulation of GFR; feedback loop of flow rate (increased NaCL) sensing mechanism in macula dena of juxtaglomerular apparatus; increased GFR & RBF triggers release of vasoactive signals; constricts afferent arteriole leading to decreased GFR & RBF
Juxtaglomerular apparatus arterial walls have JG cells—enlarged smooth muscle cells; have secretory granules containing renin; act as mechanoreceptors
Macula densa tall, closely packed distal tubule cells; lie adjacent to JG cells; function as chemoreceptors or osmoreceptors
Extrinsic controls at rest renal blood vessels are maximally dilated, autoregulation systems prevail
Extrinsic controls under stress Norepi released by sympathetic NS; Epi released by adrenal medulla; afferent arterioles constrict, filtration inhibited; drop in filtration pressure stimulates JGA to release renin and erythropoietin
Renin-angiontensin mechanism renin release triggered by reduced stretch of JG cells, stimulation of JG cells by macula densa cells, direct stimulation of JG cells by renal nerves; renin acts on angiotensin to release angiotensin I, which is converted to angiotensin II
Angiotensin II causes mean arterial pressure to rise; stimulates adrenal cortex to release aldosterone; results in both systemic & glomerular hydrostatic pressure to rise
Prostaglandins affect glomerular filtration; vasodilators produced in response to sympathetic stimulation and angiotensin II; thought to prevent renal damage when peripheral resistance increased
Nitric oxide vasodilator produced by vascular endothelium
Adenosine vasoconstrictor of renal vasculature
Control of surface area mesangial cells have contractile properties, influence capillary filtration by closing some of the capillaries; effects surface area; podocytes change size of filtration slits
Process of urine formation glomerular filtration, tubular reabsorption of substance from tubular fluid into blood, tubular secretion of substance from blood into tubular fluid
Mass balance amount excreted in urine = amount filtered through glomeruli into renal proximal tubule minus amount reabsorbed into capillaries plus amount secreted into tubules
Reabsorption and secretion accomplished via diffusion, osmosis, active and facilitated transport; carrier proteins have transport max Tm which determines renal threshold for reabsorption of substances in tubular fluid; carriers saturation = excess of that substance is secreted
Transport maximum (Tm) reflects the number of carriers in the renal tubules available; exists for nearly every substance actively reabsorbed
Sodium reabsorption almost always by active transport via NKATpase pump; provides energy and means for reabsorbing most other solutes, i.e. water by osmosis, organic nutrients & selected cations by secondary active transport
Reabsorption—secondary active transport Na linked secondary active transport; key site is proximal convoluted tubule (PCT); reabsorption of glucose, ions, amino acids
Non-reabsorbed substances substances that lack carriers, are not lipid soluble, too large to pass through membrane pores; urea, creatinine, uric acid most important
Tubular secretion basically reabsorption in reverse; substances move from peritubular capillaries/tubule cells into filtrate; important for disposal of substances not already in filtrate, eliminating undesirable substances (urea, uric acid); controlling blood pH
PCT reabsorption & secretion glomerular filtration produces fluid similar to plasma (but no proteins); PCT reabsorbs 60-70% of filtrate produced; Na, all nutrients, cations, ions, water, urea, lipid soluble solutes, small proteins; H+ secretion also occurs here
DCT reabsorption & secretion performs final adjustment of urine; active absorption of Na and Cl; secretion of K and H based on blood pH; water regulated by ADH/vasopressin; Na and K regulated by aldosterone
Atrial natriuretic peptide activity (ANP)—reduces Na decreases blood volume, lowers blood pressure
ANP lowers blood Na by acting on medullary ducts to inhibit Na reabsorption; antagonistic to aldosterone & angiotensin II; promotes Na and H20 excretion in urine by kidney; indirectly stimulates increase in GFR reducing H20 reabsorption
Regulation by ADH released by posterior pituitary when osmoreceptors detect increase in plasma osmolality; dehydration or excess salt intake produces thirst sensation; stimulates H20 reabsorption from urine
Control of urine volume & concentration regulated by controlling water and sodium reabsorption; precise control allowed via facultative water reabsorption
Osmolality number of solute particles dissolved in 1L water; reflects solution’s ability to cause osmosis; body fluids measured in milliosmols (mOsm); kidneys keep solute load of body fluids at about 300mOsm by countercurrent mechanism
Countercurrent mechanism interaction b/t filtrate flow through loop of Henle (countercurrent multiplier) and flow of blood through vasa recta (countercurrent exchanger)
Countercurrent multiplication—loop of Henle vasa recta prevents loss of medullary osmotic gradient—equilibrates w/ interstitial fluid; maintains osmotic gradient, delivers blood
Descending loop of Henle relatively impermeable to solutes; highly permeable to water
Ascending loop of Henle permeable to solutes; impermeable to water
Collecing ducts of deep medullary region permeable to urea
Countercurrent multiplier and exchange medullary osmotic gradient; H20ECFvasa recta vessels
Formation of concentrated urine ADH inhibits diuresis; equalizes osmolarity of filtrate, interstitial fluid; presence of ADH99% filtrate water reabsorbed; ADH is signal to produce concentrated urine; kidney ability to respond depends on high medullary osmotic gradient
Facultative water reabsorption ADH dependent water reabsorption
Formation of dilute urine diluted in ascending loop if ADH not secreted; created by allowing filtrate to continue into renal pelvis; collecting ducts remain impermeable to water—no further water reabsorption occurs; Na and selected ions removed via active/passive mechanisms
ADH mechanism action formation of water pores; ADH dependent water reabsorption is called facultative water reabsorption
Renal clearance volume of plasma that is cleared of a particular substance in a given time; =UV/P; U = conc mg/ml of certain substance in urine; v = flow rate of urine (ml/min); P = conc of same substance in plasma
Renal clearance tests used to determine GFR, detect glomerular damage, follow progress of diagnosed renal disease
Creatinine clearance amount of creatinine in urine, divided by concentration in blood plasma, over time. UcreatininV/Pcreatinine
Glomerular filtration can be calculated by measuring any chemical that has a steady level in the blood, and is filtered but neither actively absorbed or excreted by the kidneys; creatinine fulfills these requirements and is produced naturally by the body
Inulin freely filtered @ glomerulus & neither reabsorbed/secreted; therefore its clearance measures GFR; substances filtered and reabsorbed will have lower clearances than inulin (Ux¯); substances filtered and secreted have greater clearances than inulin (Ux­)
PAH freely filtered at glomerulus; most of remaining PAH actively secreted into tubules so that >90% plasma is cleared of its PAH in one pass through kidney; can be used to measure plasma flow through kidneys (renal plasma flow)
Excretion all filtration products not reabsorbed; excess ions, H20, molecules, toxins, excess urea, “foreign molecules,” kidneyureterbladderurethraout of body
Characteristics of urine color and transparency; yellow due to urocrhome; concentrated = deep yellow; drugs, vitamin supplements, diet, can change color of urine; cloudy urine may indicate UTI
pH of urine slightly acidic (pH 6); diet can alter pH
specific gravity of urine ranges from 1.001 to 1.035; dependent on solute concentration
Chemical Composition of Urine 95% water, 5% solutes; Nitrogenous wastes include urea, uric acid, & creatinine; Other normal solutes--Na, K, phosphate, and sulfate ions, Ca, Mg, and HCO3 ions; Abnormally high concentrations of urinary constituents may indicate pathology
Micturition from kidneys, urine flows down ureters to bladder (peristalsis); fills bladder; contraction of detrusor muscle empties bladder; greater volumes stretch bladder walls—initiate micturition reflex
Micturition reflex spinal reflex; Psymp stimulation causes bladder to contract; internal sphincter opens, external sphincter relaxes due to inhibition
Created by: michellerogers



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