renal physiology, nephron structure, function,jga. hussein f. sakr

Dr./ Hussein F. Sakr

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Renal Physiology

Anatomy of the kidney

• The kidney is a retroperitoneal organ, about 150 gm in weight (2 kidneys 0.5 % of the body weight).• It is covered by a renal capsule

and renal fascia.

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Structure of the kidney• The kidney is divided into an outer

cortex and inner medulla.- The medulla is composed of renal pyramids, separated by renal columns.- The renal pyramids empty urine into the calyces that drain into the renal pelvis. From there urine flows into the ureter and is transported to the bladder to be stored.

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General function of the kidney

• Regulate ECF volume.• Regulation of electrolytes.• Regulation of arterial blood pressure.• Regulation of pH (acid-base balance).• Excretion of waste products.• Endocrinal function (renin- erythropoietin- active vitamin D).• Degradation of hormones.

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Functional organization of the kidney

• Renal cortex:Red and dotted.Contains glomeruli.Contains proximal tubules,

distal convoluted tubules and cortical collecting duct.

• Renal medulla:Pale and radial.Contains renal pyramids which

contain minor calyces that unite to form major calyces.

Contains loop of Henle and medulary collecting ducts.

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Blood supply of the kidney

• The kidneys receives its blood through the renal artery.• The renal artery is divided into

anterior and posterior branches each one divides into 5 segmental branches interlobar arcuate interlobular afferent glomerular capillaries efferent arteriole.

• Efferent arteriole peritubular capillary and vasa recta interlobular vein interlobar vein segmental renal vein IVC.

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Nephron it is the structural and functional unit of the kidney

Renal corpuscle • Formed of:

1) glomerulus: 20-40 loop of capillaries between afferent

and efferent arteriole.2) Bowman’s capsule: which is

the blind end of the proximal tubule.

Renal tubules• Formed of:

1) Proximal tubule.2) Intermediate tubule (loop of

Henle).3) Distal tubule (distal

convoluted tubule, connecting tubule and collecting duct.

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Types of nephrons

Superficial cortical • 85-90 % .

• Glomerulus in the outer 2/3 of the cortex.

• Loop of Henle is formed of DLH and ALH.

• Loop of Henle makes a bend at the junction between outer and inner

medulla.• Small in size with low capacity to

reabsorb salt and water.

Juxta medullary • 10-15 %.

• Glomerulus in the inner 1/3 of the cortex.

• Loop of Henle is formed of DLH , thin ALH and thick ALH.

• Loop of Henle makes a bend at the tip of inner medulla.

• Large in size with high capacity to reabsorb Na and water.

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Types of nephrons

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Juxta-glomerular apperatus

• It is system formed of modified:1) Macula densa cells.2) Juxta- glomerular granular

cells.3) Extra-glomerular mesengial

cells.

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Macula densa cells

• Modified tubular epithelial cells.• Present at the transitional zone between thick ALH and DCT.• Monitor Na and chloride concentration in the tubular fluid.

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Juxta glomerular granular cells

• Present in the wall of the afferent arteriole.• Smooth muscles with epitheliod apperance.• Forms , stores and secretes renin.• Contains B1 adrenergic receptors.• Acts also as baroreceptors.

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Extraglomerular mesengial cells

• It is a continuation of the intraglomerular mesengial cells.• It is in direct contact with the macula densa and juxtaglomerular

granular cells.

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Stimuli for renin release

• Sympathetic stimulation.• Renal ischemia.• Decrease Na+ and Cl- concentration in the tubular fluid.

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Mechanisms of stimulation:

Renin releaseIn cases of hemorrhage

with decreased circulating blood volume

stimulation of low and high pressure

baroreceptors located in the great vessels of the thorax stimulation of

the sympathetic nervous system stimulation of B receptors on JGG cells

renin release

With renal artery stenosis or thrombosis decreased renal perfusion pressure

stimulation of the juxta glomerular granular cells

renin release.

Decreases Na & Cl concentration of the

tubular fluid stimulation of the macula densa that

stimulates the JGGcells via Prostaglandins renin

release.

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Renin Angiotensin Aldosterone system

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Inhibitors of renin release

• Aldosterone .• Atrial Nariuretic Peptide (ANP).• AII.• Hypernatremia.

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Function of the renin angiotensin system

Salt and water retention 1- angitensin II increases Na

reabsorption from proximal tubules.

2- AII stimulates the zona glomerulosa of the adrenal cortex to secrete aldoseterone that increases Na reabsorption from distal tubules.

Vasoconstriction 1- arteriolar constriction

increasing the afterload (arterial blood pressure).

2- Venoconstriction increasing the preload (venous return).

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Pharmacological Inhibitors of the RAAS

• Angiotensin converting enzyme inhibitors: decreased the formation of AII.• Angiotensin II blockers: decreased aldosterone release.• B- blockers.

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