The functional unit of the kidneys is the _____________________. • Urine is eliminated from the bladder through the ______________. • The two regions of the kidney are an outer ______________and an inner _______________. • Tubular _____________________ and tubular _____________________ are selective processes that occur in the nephron.
The specialized cells of the _____________________, located within the _____________________, detect changes in the rate at which fluid is flowing past them through the distal tubule.
Regional differences in nephron structure • Cortical nephrons • have glomeruli located in the -------------------------. • have ______________loops of Henle that penetrate only a short distance into the ________________
Regional differences in nephron structure (cont.) • Juxtamedullary nephrons. • have glomeruli that lie ______________cortex near the medulla • have ______________loops of Henle that dip deeply into the _________________. • have specialized peritubular capillaries _________________
The kidney produces following hormones : • Erythropoietin • 1,25 dihydroxycholecalciferol (Vitamin D3, calcitriol) • Renin
The fluid within the Bowman’s capsule virtually the same as in the plasma. • Except • It is free from: • _______________ • ________________
Fluid filtered pass through three layers of the glomerular membrane • ________________________ • _________________________ • __________________________
GFR: Definition: The volume of plasma filtered from both kidneys per minute. • GFR = _______ ml/min = _______ liters/day • GFR=_____________ x ______________
Forces determining Net Filtration Pressure (NFP) • ___________________ • ____________________ • ________________________
NFP = ( PGC+ BC) - ( PBC+ GC)
Calculate NFP if • Glomerular capillary hydrostatic pressure = 60 • Plasma colloidal osmotic pressure is = 40 • Bowman's capsule hydrostatic pressure is = 10 • Ans = 10
Increase of PBc can be caused by • _________________________ • _________________________ • _________________________ • plasma colloid osmotic pressure increases ________________ Decreases __________________
Adjustments of Afferent Arteriole Caliber to Alter The GFR
Baroreceptor Reflex Influence on the GFR
Autoregulation The major function of autoregulation in the kidneys is to maintain a relatively constant GFR and renal blood flow despite considerable arterial pressure fluctuations that can occur. Autoregulation: TWO THEORIES • Myogenic autoregulation • Tubuloglomerular feedback
Myogenic Mechanism Vascular smooth muscle contraction in response to increased stretch Arterial Pressure Stretch of Blood Vessel Cell Ca++ Permeability Vascular Resistance Intracell. Ca++ Blood Flow
Macula Densa Feedback (Tubuloglomerular feedback) GFR Distal NaCl Delivery Macula Densa NaCl Reabsorption (macula densa feedback) Afferent Arteriolar Resistance GFR (return toward normal)
What is a Glomerular Filtration Fraction? • The Filtration Fraction (FF) is the ratio of the GFR to the renal plasma flow (GFR/TRPF). • Renal blood flow = 1.1 L/min • 20-25% of total cardiac output (5 L/min). • Of the 625 ml of plasma enters the glomeruli via the afferent, 125 (the GFR) filters in the Bowman’s capsule, the remaining passing via efferent arterioles into the peritubular capillaries • Filtration fraction = (GFR/TRPF) = 0.2 • So, GFR is About 20% of the Renal Plasma Flow
The filtration fraction The Filtration Fraction (FF) is the ratio of the GFR to the renal plasma flow = (GFR/TRPF).
Reabsorption and Secretion The amount of a substance filtered into Bowman's space per unit time is called the filtered load: • Filtered load = _____ _________ • Excretionrate = _____ __________ • Reabsorption/secretion rate = FL – Excretion rate
Reabsorption - Transport Mechanisms WHAT ARE THE DIFF MECHANISMS ? • Primary active transport EXAMPLE ? • Sodium-potassium pumps in basolateral membrane only • Secondary active transport • EXAMPLE ? • co-transport (glucose, amino acids) • counter-transport (K+, H+) • Passive Reabsorption • EXAMPLE ? • Osmosis (H2O) • Electrostatic attraction (Cl-)
Glucose Reabsorption SGLT 2 GLUT 2
Reabsorption Transport Maximum(Tmax) • DEF:_________________________________________ • WHAT creates a limit to the rate of substances transport. ? SATURATION OF TRANSPORT PROTEINS • Therefore, excess of that substance is ____________ • EXCRETED
Glucose Transport Maximum Figure 27-4; Guyton and Hall
RENAL THRESHOLD FOR GLUCOSE • DEFINITION ? • The is the plasma level at which the glucose first appears in the urine . • The actual renal threshold is about • 200 mg/dL of arterial plasma, • which corresponds to a venous level of about 180 mg/dL. • What causes in splay ? • TmGin all the tubules is not identical and • All the glucose were not removed from each tubule when the amount filtered was below the TmG.
GFR = 120ml/min, Plasma glucose of 200 mg/dl (2mg/ml), transport max (Tm) 200 mg/min What is the glucose excretion for this patient?
Passive Reabsorption • Passive reabsorption depends on: • Electrical gradient (electrostatic attraction). • Concentration gradient • Membrane permeability • Time available in the tubule for reabsorption
Passive Reabsorption Secondary water Reabsorption via osmosis Sodium reabsorption makes both intracellular and extracellular fluid hypertonic to the tubular fluid. Water follows with sodium into the peritubular capillaries. Na+ Na+ H2O capillary Tubular lumen Tubular cell
Passive Reabsorption Secondary ion reabsorption via electrostatic attraction Negative ions (Cl-) tend to follow with the positive sodium ions by electrostatic attraction. Na Na+ Cl- capillary Tubular cell Tubular lumen
Urea–Example of Passive Reabsorption Na+ reabsorption H2O reabsorption Increase concentration of urea in tubular fluid Passive reabsorption of urea
Mechanisms by which Water, Chloride, and Urea Reabsorption are Coupled withSodium Reabsorption Figure 27-5; Guyton and Hall
PAH –EXAMPLE OF SECRETION • PAH is an organic acid • Used for measurement of renal plasma flow • Both filtered and secreted • PAH transporters located in peritubular membrane of proximal tubular cells. • There are parallel secretory mechanism for secretion of organic bases like quinine and morphine
References • Human physiology by Lauralee Sherwood, seventh edition • Text book physiology by Guyton &Hall,11th edition • Text book of physiology by Linda .s contanzo,third edition