Medical Physiology Block 4 Week 1 Flashcards
State the four major functions of the kidney.
regulation of water and electrolyte balance; filtering (removing metabolic products and toxins from the blood and excreting them through the urine); regulation of arterial blood pressure; Produce or activate hormones (Renin, erythropoeitin, vitamin D, prostaglandins and kinins)
Explain mass balance and how it applies to the kidney.
For any solute (X) that the kidney does not synthesize, degrade, or accumulate, the only route of entry to the kidney is the renal artery, and the only two routes of exit are the renal vein and the ureter
What is the renal pelvis? what are calyxes? renal pyramids?
renal pelvis and its extensions, the major and minor calyces sit in the renal sinus; The medulla is subdivided into 8 to 18 conical renal pyramids, whose bases face the cortical-medullary border; the tip of each pyramid (papilla) terminates in the renal pelvis (urine flows from the tip into the minor calyxes of the renal sinus through perforations)
Describe the renal medulla. What is the renal papilla?
Lacks glomeruli and consists of a parallel arrangement of tubules and small blood vessels; The renal papilla is the location where the medullary pyramids empty urine into the minor calyx in the kidney. Histologically it is marked by medullary collecting ducts converging to form a duct of Bellini to channel the fluid.
Define nephron, renal corpuscle, glomerulus, and tubule.
Nephron = glomerulus + tubule; Renal corpuscle = glomerulus, Bowman’s space, and Bowman’s capsule + mesangium; Glomerulus (vascular)= cluster of blood vessels from which the plasma filtrate originates; The tubule is an epithelial structure consisting of many subdivision, designed to convert the filtrate into urine.
Draw the relationship between glomerulus, Bowman’s capsule, and the proximal tubule.
plasma flows from the glomerular capillaries into Bowman’s space, which is contiguous with the lumen of the proximal tubule
Describe the three layers separating the lumen of the glomerular capillaries and Bowman’s space.
glycocalyx covering the luminal surface of endothelial cells (negatively charged proteins); endothelial cells; glomerular basement membrane (two thin exterior layers and a thick layer in the middle); epithelial podocytes (foot processes cover glomerular capillaries; filtration slits are spaces in between interdigitations of podocytes that cover GBM; connected together to form slit diaphragm surrounded by negatively charged glycoproteins)
Define glomerular mesangial cells and state their function.
similar to smooth muscle; secrete the extracellular matrix; contraction of mesangial cells reduces renal permeability; filtration occurs away from mesangial cells
List the individual tubular segments in order; state the segments that make up the proximal tubule, Henle’s loop, and the collecting duct system
proximal tubule (S1 & S2 = proximal convoluted tubule reabsorbs the bulk of the filtered fluid; S3 = proximal straight tubule; Henle’s loop (thin descending, thin ascending, thick ascending: tall interdigitations and numerous mitochondria maintain the hyperosmotic nature of the medullary interstitium); collecting duct (distal convoluted tubule, initial collecting tubule, and cortical collecting tubule) and medullary collecting tubule
Define principal and intercalated cells
cells found in the initial collecting tubule and cortical collecting tubule; Principal cells reabsorb sodium chloride and secrete potassium; Intercalated A cells secrete hydrogen ion and reabsorb potassium; Intercalated B cells secretes bicarbonate
List in order the vessels through which blood flows from the renal artery to renal vein; contrast the blood supply to the cortex and the medulla; define vasa recta and juxtame-dullary nephrons.
a high resistance arteriole (afferent), followed by a high-pressure glomerular capillary network for filtration, followed by a second high resistance arteriole (efferent), which is followed by a low-pressure capillary network that surrounds the renal tubules (peritubular capillaries) and takes up the fluid absorbed by these tubules (followed by the renal vein); Some 90% of the blood entering the kidney perfuses superficial glomeruli and cortex; only ∼10% perfuses juxtamedullary glomeruli and medulla; efferent arterioles of juxtamedullary nephrons descend into the medulla and form capillaries and hairpin vessel structures
Define juxtamedullary apparatus and describe its three cell types; state the function of the granular cells.
a region where each thick ascending limb contacts its glomerulus (extraglomerular mesangial cells, macula densa, and granular cells); When the afferent arteriole senses decreased stretch in its wall (baroreceptor), neighboring granular cells increase the release of renin into the circulation
Define the basic renal process: glomerular filtration, tubular reabsorption, and secretion.
volume of fluid filtered into Bowman’s capsule per unit time (the amount of X that appears in the urine per unit time is the same as the amount of X that the glomerulus filters per unit time); amount of solute filtered - amount of solute reabsorbed + amount of solute secreted = amount of solute excreted
Define renal blood flow, renal plasma flow, glomerular filtration rate, and filtration fraction and give normal values.
renal blood flow is 20% of the cardiac output (1 L/min); renal plasma flow = (1-hematocrit) x renal blood flow (600 mL/min); glomerular filtration rate- 125 mL/min or 180 L/day; filtration fraction = GFR/RPF (0.2)
State the formula relating flow, pressure, and resistance in an organ.
Flow = delta P/R
Describe the effects of changes in afferent and efferent arteriolar resistance on renal blood flow.
constriction of afferent arteriole and relaxation of efferent arteriole decreases glomerular capillary pressure; Constriction of only afferent arteriole decreases capillary pressure, renal plasma flow, and GFR; Constriction of only efferent arteriole increases capillary pressure and decreases renal plasma flow following administration of angiotensin II decreases renal plasma flow (Initially GFR increases because rising capillary pressure dominates; Later, GFR decreases because falling renal plasma flow dominates)
Describe the relative resistance of the afferent arterioles and efferent arterioles.
selective constriction or relaxation of the afferent and efferent arterioles allows for highly sensitive control of the hydrostatic pressure in the intervening glomerular capillary and thus of glomerular filtration.
Describe how molecular size and electrical charge determine filterability of plasma solutes; state how protein binding of a low-molecular weight substance influences its filterability.
The glomerular filtration barrier limits large, negatively charged, globular or rigid (non-deformable) solutes from entering into Bowman’s space; solutes bound to proteins have reduced filtration
State the formula for the determinants of glomerular filtration rate, and state, in quantitative terms, why the net filtration pressure is positive.
glomerular ultrafiltration depends on the product of the ultrafiltration coefficient (K f ) and net Starling forces (GC pressure is very high throughout the capillary; BS pressure is 10 mm Hg along the capillary; Oncotic pressure of the glomerular capillary increases along the capillary; there is virtually no oncotic pressure for Bowman’s space)
Define ultrafiltration coefficient and state how mesangial cells might alter the filtration coefficient; state the reason why glomerular filtration rate is so large relative to filtration across other capillaries in the body
Kf is the product of the hydraulic conductivity of the capillary (Lp) and the effective surface area available for filtration (very large compared to other capillary beds); contraction of mesangial cells reduces Kf
Describe how changes in renal plasma flow influence average glomerular capillary oncotic pressure.
At higher plasma flow (normal physiology), a hypothetical filtration equilibrium would be reached at a site actually beyond the end of the capillary (Capillary oncotic pressure rises more slowly along the length of the capillary)
Describe how arterial pressure influences peritubular capillary pressure.
Volume expansion inhibits the renin angiotensin system; Significant decrease in efferent arteriole resistance (increase in hydrostatic pressure entering peritubular capillary); Increases GFR, pGC, and RBF; decreases filtration fraction (renal plasma flow increases more relative to GFR, which saturates); Decreases oncotic pressure entering peritubular capillary; final outcome: decreased uptake by peritubular capillaries
Define autoregulation of renal blood flow and glomerular filtration rate.
The kidney autoregulates RBF by responding to a rise in renal arterial pressure with a proportional increase in the resistance of the afferent arterioles (changes in posture, sleeping, and light to moderate exercise)
