kidney

Primary functions of the kidney:

— Maintaining homeostasis through the regulation of

fluid and electrolytes and removing wastes through

the formation of urine.

ž Other important functions:

— Regulation of acid-base balance

— Control of blood pressure

— Renal clearance

— Regulation of RBC production

— Synthesizing vitamin D to the active form

— Secreting prostaglandins

— Regulating calcium and phosphorus balance.

Nephron

ž Each kidney has

about 1 million

nephrons

ž Two types

— Cortical nephrons

— Juxtamedullary

nephrons
FUNCTIONS OF THE

NEPHRON

1. Filtering plasma

through the

glomerulus

2. Reabsorb and

secrete substances

along tubular tract.

3. Form a filtrate (urine)

that is protein free.

4. Regulate filtrate

formation to

maintain body fluid

volume, electrolyte

composition, and pH

within limits.

URINE FORMATION

1. Glomerular Filtration

2. Tubular Reabsorption

3. Tubular Secretion

4. Excretion

GLOMERULAR

FILTRATION

ž This is the movement of fluid and

solutes out of the glomerulus, across the

glomerular capillary membrane, and into

Bowman’s capsule.

ž The filtrate that is formed here should NOT

contain any red blood cells or protein.

ž Filtrate contains mostly water, NaCl, K+,

bicarbonate, glucose, amino acids,

creatinine and urea

GLOMERULAR FILTRATION

PRESSURES

ž Rate of glomerular filtration is

affected by capillary pressure.

ž Capillary hydrostatic pressure

(CHP) is the main force

responsible for pushing water

and solutes into Bowman’s

capsule.

ž CHP is opposed by hydrostatic

pressure in Bowman’s space and

the effective oncotic pressure of

blood in the glomerular capillary.

ž Net filtration pressure is the sum

of all these forces combined.

GLOMERULAR FILTRATION

RATE

ž This is the measurement of how much

blood passes through glomeruli, each

minute.

ž 90-120 mL/min

ž The rate of glomerular filtration is

affected by the net filtration pressure in

the glomeruli.

TUBULAR SECRETION AND

REABSORPTION Proximal Convoluted

Tubule

ž This is where most of the

nephron’s reabsorption and

secretion occurs.

ž Reabsorbed: K+, NaCl,

H2O, amino acids,

glucose, and bicarbonate.

ž Secreted: uric acid and

foreign substances.

TUBULAR SECRETION AND

REABSORPTION

Loop of Henle

ž Urine can be concentrated

or diluted here

— Descending loop: water is

— Ascending loop: NaCl is

reabsorbed

reabsorbed.

ž Uromodulin: protein

produced by the loop

of henle that binds to

pathogens and prevents

UTIs, protects the tubule

from injury, and against

kidney stone formation.

TUBULARE SECRETION AND

REABSORPTION

Distal Tubule

ž Distal tubule: where the

final adjustments of urine

composition are made.

— Reabsortion: Na+, water (in

the presences of ADH) and

bicarbonate

.

— Secretion: K+, urea, H+,

ammonia, and metabolites are

secreted into the tubule

ž The distal tubule contributes

to the regulation of acid-base

balance.