Renal Blood Flow

Lecture 2Dr. Amal Mahmoud Saeed

Describe the renal blood flowDescribe the control of the renal blood flow

Objectives

The renal blood flow = 1.2 L/min

25% of the cardiac output

90% perfuse cortex, 10% perfuse medulla.

Renal Blood Flow

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

•Delivers oxygen , nutrient and hormones to cells of the nephron and return carbon dioxide and reabsorbed fluids and solutes to the circulation•Indirectly determining the glomerular filtration rate•Modifies the rate of solute and water re-absorbed in proximal tubules•Participates in the concentration and dilution of urine•Delivers substrates for secretion in urine

Functions of Renal Blood Flow

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

• Auto-regulation

• Neural regulation

• Hormonal regulation

04/22/23 14:49Lecture 2Dr. Amal Mahmoud Saeed

Regulation of Renal Blood Flow (RBF)

• Auto-regulation Is defined as the ability of the kidney

to maintain blood flow during changes in perfusion pressure.

Regulation of Renal Blood Flow (RBF)

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

Q= ΔP

• Renal blood flow is expressed by the following formula:

• Q flow • ΔP Pressure gradient• R Resistance

• To maintain flow Q constant while changing pressure ΔP, R must change.

• This change in resistance is mainly by alteration in arteriolar diameter, specially the afferent arteriole.

R

Regulation of Renal Blood Flow (RBF)

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

• The kidney auto-regulates in the perfusion pressure range of 80-180mmHg

Regulation of Renal Blood Flow (RBF)

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

• Auto- regulation depends on two mechanisms:

1. myogenic response: vascular smooth muscles contract when stretched by increasing pressure.

Regulation of Renal Blood Flow (RBF)

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

2. tubulo -glomerular feed back: the macula densa detects changes in perfusion pressure by detecting changes in tubular flow. A vaso-active substance is released which changes vascular resistance accordingly.

Regulation of Renal Blood Flow (RBF)

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

• Neural Regulation

Renal sympathetic nerve stimulation increases renal vascular resistance of both afferent and efferent arterioles this decreases renal blood flow.

Regulation of Renal Blood Flow (RBF)

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

• Hormonal Regulation

- angiotensin II constricts both afferent and efferent arterioles and reduces renal blood flow.

- Prostaglandins are produced within the kidney PGE1 and PGI2 are vasodilators and thromboxane A2 is a vasoconstrictor.

Regulation of Renal Blood Flow (RBF)

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

Renal blood flow is about 1.2L/minRegulated by auto regulation, neural and hormonal mechanisms

04/22/23 14:49

Summary

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

Functions of the Kidney

• Excretion of waste products

• Regulation of the concentration of electrolytes in E.C.F.

• Regulation of the osmolality of E.C.F.

Functions of the Kidney

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

• Regulation of the volume of E.C.F

• Regulation of the pH. of E.C.F.

• Regulation of blood pressure

Functions of the Kidney

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed

• Endocrine functions–erythropoietin

–1-25 dihydroxy cholecalciferol

–renin

–prostaglandins

Functions of the Kidney

04/22/23 14:49

Lecture 2Dr. Amal Mahmoud Saeed