Kidney
1. Functions:
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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 Kidney
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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 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
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Thin segment
Ascending limb loop of Henle
Distal convoluted tubule
Collecting duct
3. 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
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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
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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 Kidney
4.1 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•
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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.