KidneyKidney

1. Functions:• removal of metabolic waste products• regulation of the water content of body fluids• regulation of pH of body fluids• regulation of chemical composition of body

fluids

2. Structure of Kidney2. Structure of Kidney• Outer part – renal cortex • covered by tough fibrous connective tissue• Contain glomeruli, renal corpuscle, PCT,DCT• Inner part – renal medulla• Contain tubular part of nephron, blood vessels

2.1 Nephron2.1 Nephron• Basic unit of structure & function• Composed of diff. regions• Renal corpuscle/malpighian capsule

[bowman’s capsule & glomerulus]• Proximal convoluted tubule• Descending limb of loop of Henle

• Thin segment• Ascending limb loop of Henle• Distal convoluted tubule• Collecting duct

3. Formation of Urine3. Formation of Urine• The two kidneys in the body receive between

1100 – 2000 liters (1160 – 2100 quarts or 500 gallons) of blood per day – about the volume of a car!

• Because the body has only about 5.6 liters of blood, our blood runs through the kidneys to be cleaned about once every four minutes.

3.1 Ultrafiltration of blood• Occurs at the renal capsule• Filtration takes place due to high blood

pressure• Thin perforated endothelium tissue• Podocytes of renal capsule have slit pores• Except large molecules like proteis, red blood

cells and platelets gets filtered [glomerular filtrate].

3.2 Selective Reabsorption 3.2.1 Proximal convoluted tubule

• 80% of glomerular filtrate reabsorption occurs• Specialized for reasorption• Numerous microvilli & basal channels• Numerous mitochondria• Closeness of blood capillaries• Contain carrier protein

• Glucose, amino acids and ions actively transported by carrier protein

• Diffuse into the blood capillaries and are carried away

• Water moves along with these substances

3.2.2 The Loop of Henle• Conserve water and produce concentrated

urine• Loop of Henle with vasa recta and collecting

duct create and maintain osmotic gradient in medulla

• Glomerular filtrate flows in opposite directions in the two limbs of Henle's loop [counter current mechanism]

3.2.3 Descending loop of Henle

• Has thin wall • Highly permeable to water and permeable to other solutes

3.2.4 Ascending loop of Henle• Thick & impermeable to water• Sodium & other ions are actively reasorbed• Interstitial fluid becomes more concentrated• Water from descending limb & collecting duct are drawn

• The water quickly enters the vasa recta and is being carried away.

• This maintains a high concentration of solutes in the interstitial fluid

• Filtrate in the ascending limb becomes dilute as it is impermeable to water

3.2.4 Distal convoluted tubule & collecting duct

• Fine control of precise amounts of water & salts reasorbed takes place

• Water diffuses from the collecting duct into the tissue fluid of medulla

• Urine becomes concentrated

3.3 Secretion • Release of unwanted substances from the

blood into the nephron which are not present in glomerular filtrate.

• Occurs in the convoluted tubules• Aminohippuric acid, K+, H+, Creatinine,

Phosphate and antibiotics

4 Hormonal Regulation of 4 Hormonal Regulation of KidneyKidney4.1 Control of blood solute

level• The solute potential of blood is controlled by anti-

diuretic hormone [ADH].• Osmoreceptors in Hypothalamus detect change in

blood concentration.• Stimulate posterior pituitary gland• Pituitary gland release ADH• ADH travels through blood to Kidney• Increase the permeability of distal convoluted

tubule and collecting duct to water.

• Less and concentrated urine is produced • Once normal blood concentration is achieved,

production of ADH stops• High intake of water inhibits release of ADH• More and dilute urine is produced.• Insufficient release of ADH leads to diabetes

insupidus.

4.2 Control of blood sodium level [The renin-angiotensin system]

• Steady maintenance of blood sodium is brought by Aldosterone.

• It also influence water reasorption• Secreted by adrenal cortex• Decrease in blood sodium leads to a decrease

in blood volume

• Decrease in blood volume reduces blood pressure

• Decrease blood pressure and volume stimulates group of secretory cells [macula densa &juxtaglomerular- juxtaglomerular complex] located between DCT & Afferent arteriole

• It releases an enzyme – Renin• Renin activates inactive hormone angiotensin

present in blood plasma to active form.

• Active angiotensin performs tow functions: • it brings about vasoconstriction raising the

arterial pressure• it activates adrenal cortex to release

aldosterone. • Aldosterone stimulate sodium absorption in

the gut and reduce loss in sweat• Sodium absorption increases the reabsorption

of water.• Thus it maintains arterial pressure, overall

fluid and electrolyte balance.