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• 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.
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• The specialized cells of the _____________________, located within the _____________________, detect changes in the rate at which fluid is flowing past them through the distal tubule.
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Regional differences in nephron structure
Cortical nephrons - have glomeruli located in the
-------------------------. - have ______________loops of Henle that
penetrate only a short distance into the ________________
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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 _________________
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• The kidney produces following hormones :• Erythropoietin• 1,25 dihydroxycholecalciferol (Vitamin D3,
calcitriol)• Renin
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• The fluid within the Bowman’s capsule virtually the same as in the plasma.
• Except
• It is free from:– _______________– ________________
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• Fluid filtered pass through three layers of the glomerular membrane
• ________________________
• _________________________
• __________________________
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GFR:
Definition: The volume of plasma filtered from both kidneys per minute.
• GFR = _______ ml/min = _______ liters/day
• GFR= _____________ x ______________
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• Forces determining Net Filtration Pressure (NFP)
– ___________________
– ____________________
– ________________________
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• NFP = ( PGC + -BC ) - ( PBC + -GC )
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• Calculate NFP if– Glomerular capillary hydrostatic pressure = 60– Plasma colloidal osmotic pressure is = 40– Bowman's capsule hydrostatic pressure is = 10
– Ans = 10
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• Increase of PBc can be caused by
1. _________________________2. _________________________3. _________________________
• plasma colloid osmotic pressure increases ________________
Decreases __________________
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Adjustments of AfferentArteriole Caliber to AlterThe GFR
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Baroreceptor Reflex Influence on the GFR
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Autoregulation
• Myogenic autoregulation
• Tubuloglomerular feedback
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
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Myogenic Mechanism
Stretch ofBlood Vessel
Cell Ca++
PermeabilityArterial Pressure
Intracell. Ca++Blood Flow VascularResistance
Vascular smooth muscle contraction in response to increased stretch
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Macula Densa Feedback (Tubuloglomerular feedback)
GFR
Distal NaCl Delivery
Macula Densa NaCl Reabsorption
Afferent Arteriolar Resistance
GFR (return toward normal)
(macula densa feedback)
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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
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The filtration fractionThe Filtration Fraction (FF)
is the ratio of the GFR to the renal plasma flow = (GFR/TRPF).
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Reabsorption and Secretion
The amount of a substance filtered into Bowman's space per unit time is called the
filtered load:
• Filtered load = _____ _________
• Excretion rate = _____ __________
• Reabsorption/secretion rate = FL – Excretion rate
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Reabsorption ROUTES
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Reabsorption - Transport Mechanisms
WHAT ARE THE DIFF MECHANISMS ?– Primary active transportEXAMPLE ?
• 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-)
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Sodium Reabsorption
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Glucose Reabsorption
SGLT 2GLUT 2
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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
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Glucose Transport Maximum
Figure 27-4;Guyton and Hall
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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 ?
– TmG in all the tubules is not identical and – All the glucose were not removed from each tubule
when the amount filtered was below the TmG.
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GFR = 120 ml/min, Plasma glucose of 200 mg/dl (2mg/ml), transport max (Tm) 200 mg/min What is the glucose excretion for this patient?
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Passive Reabsorption
• Passive reabsorption depends on:– Electrical gradient (electrostatic attraction).
– Concentration gradient
– Membrane permeability
– Time available in the tubule for reabsorption
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Sodium reabsorption makes both intracellular and extracellular fluid hypertonic to the tubular fluid.
Water follows with sodium into the peritubular capillaries.
Passive Reabsorption Secondary water Reabsorption via osmosis
H2O
Na+Na+
capillary Tubular cell Tubularlumen
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Negative ions (Cl-) tend to follow with the positive sodium ions by electrostatic attraction.
Passive Reabsorption
Secondary ion reabsorption via electrostatic attraction
Na Na+
Cl-
capillary Tubular cell Tubularlumen
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Urea–Example of Passive Reabsorption Na+ reabsorption
H2O reabsorption
Increase concentration of
urea in tubular fluid
Passive reabsorption of urea
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Figure 27-5;Guyton and Hall
Mechanisms by which Water, Chloride, and Urea Reabsorption are Coupled withSodium Reabsorption
Mechanisms by which Water, Chloride, and Urea Reabsorption are Coupled withSodium Reabsorption
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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
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PAH Filtration, Secretion & Excretion
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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