• 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

1. _________________________2. _________________________3. _________________________

• plasma colloid osmotic pressure increases ________________

Decreases __________________

Adjustments of AfferentArteriole Caliber to AlterThe GFR

Baroreceptor Reflex Influence on the GFR

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

Myogenic Mechanism

Stretch ofBlood Vessel

Cell Ca++

PermeabilityArterial Pressure

Intracell. Ca++Blood Flow VascularResistance

Vascular smooth muscle contraction in response to increased stretch

Macula Densa Feedback (Tubuloglomerular feedback)

GFR

Distal NaCl Delivery

Macula Densa NaCl Reabsorption

Afferent Arteriolar Resistance

GFR (return toward normal)

(macula densa feedback)

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 fractionThe 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 = _____ _________

• Excretion rate = _____ __________

• Reabsorption/secretion rate = FL – Excretion rate

Reabsorption ROUTES

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-)

Sodium Reabsorption

Glucose Reabsorption

SGLT 2GLUT 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 ?

– 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.

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?

Passive Reabsorption

• Passive reabsorption depends on:– Electrical gradient (electrostatic attraction).

– Concentration gradient

– Membrane permeability

– Time available in the tubule for reabsorption

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

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

Urea–Example of Passive Reabsorption Na+ reabsorption

H2O reabsorption

Increase concentration of

urea in tubular fluid

Passive reabsorption of urea

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

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

PAH Filtration, Secretion & Excretion

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