Renal system Dr. Zainab - PowerPoint Presentation

Slide1

Renal system

Dr.

Zainab

H.H

Dept. of Physiology

Lec.1,2

Slide2

Objectives

List

the functions of

kidney

Describe the morphology of the typical

nephron

and its blood supply

.

Describe the concept of clearance

Slide3

What is excretion?

Throwing

out of waste product is known as excretion

.

The organs

through which excretion occurs.

1. Kidneys: Excrete water and water soluble waste products.

2. Lungs: Excrete carbon dioxide, water

vapour

and other volatile substances such

as acetone

.

3. Skin: Excretes water and salts mainly in the form of sweat.

4. Gastrointestinal tract: Excretes undigested food.

Slide4

The Role of the Kidneys in the Body

Includes:

Regulation of the volume and composition of the ECF, by maintaining a balance between intake and output of water and electrolytes in the body.

Excretion and elimination of waste products of metabolism, such as the excretion of urea,

creatinine

and uric acids; as well as the excretion of various toxins such as drugs and food additives.

The kidneys act as endocrine glands producing hormones, such as “erythropoietin hormone” and

renin

.

Slide5

Playing a dominant role in the long-term and short-term regulation of arterial blood pressure.

Kidneys along with the respiratory system contribute to acid-base regulation.

Finally, kidneys synthesize glucose from

amino acids

and other precursors

Slide6

Metabolic waste products excreted by kidneys are: Urea from protein.

Uric acid from nucleic acid

.

Creatinine

from muscle

creatine.

End products of

haemoglobin

breakdown.

Slide7

STRUCTURE OF NEPHRON

Nephron

is a structural and functional unit of the kidney.

Each

nephron

is capable

of forming

urine.

There

are

two types

of

nephrons

:

1.

Cortical

nephrons

.

Glomeruli

are present near the surface of the kidneys.

These

nephrons

constitute about 86% of total

nephrons

.

The

main function of

cortical

nephrons

is

absorption of sodium

.

Slide8

2. Juxtamedullary

nephrons

.

Glomeruli

lie at the junction of cortex and medulla of the kidney.

These constitute 14% of the

nephrons

.

The main role of

juxtamedullary

nephron

is to

increase concentration of

medullary

interstitial fluid.

Slide9

Slide10

Two kidneys together have two millions nephrons

.

Nephron

consists of two major parts:

Glomerulus

.

A long renal

tubule.

1.

Glomerulus

.

It is made up of tuft of capillaries which connect

afferent arteriole with

an

efferent

arteriole.

Capillaries

have single layer of endothelial cells attached to

a basement

membrane

.

Slide11

Bowman’s capsule encloses the glomerulus and is formed of two layers:

inner layer which covers the

glomerular

capillaries is called visceral layer,

outer layer is called parietal layer.

Space between visceral and parietal layers is continued as the lumen of the tubular portion.

Slide12

fluid-filled space, Bowman’s space, is formed within the capsule.

Blood of capillary and fluid of Bowman’s space are separated by the

glomerular

membrane.

From the Bowman’s capsule, tubule of the

nephron

extends, the lumen of which is continuous with the Bowman’s space.

Slide13

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2. Renal tubule.

It is mainly formed of three parts:

(a)

Proximal convoluted tubule

.

(b)

Loop of

Henle

consisting of:

Thin segment :

walls of descending limb and lower end of ascending limb are very thin. Therefore, they are termed thin segment.

Hair pin bend

.

Thick ascending limb

or segment

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Slide16

(c) Distal convoluted tubules.

open into initial arched collecting ducts called

cortical collecting ducts

present in renal

cortex.

Seven to ten such ducts form straight collecting duct which passes into medulla forming

medullary

collecting ducts.

Slide17

In the inner zone of medulla they form

papillary ducts

or ducts of Bellini.

These open into papilla of

minor calyces

.

Three or four minor calyces

unite to form

one

major calyx

.

The major calyces open into

pelvis of

ureter

.

The

pelvis

is an expanded portion present in renal sinus and it

continues as

ureter

Slide18

Slide19

Slide20

BLOOD FLOW TO KIDNEYS

Rate of blood flow to kidneys is 1200 ml/min.

This is quite high as compared to their size.

State peculiarities of renal circulation.

1.Very high blood supply

, about 21% of cardiac output.

2.Two sets of capillaries.

The

glomerular

capillaries

.

These combine to form efferent arteriole which in turn breaks into

peritubular

capillary network around the tubules of cortical

nephrons

.

Slide21

vasa

recta

which are loop-shaped vessels in

juxtamedullary

nephrons

the efferent arterioles continue as these loops dip into the

medullary

pyramids alongside the loops of

Henle

3.Glomerular capillary bed

has a high hydrostatic pressure because efferent arteriole is of a smaller diameter than afferent arteriole which offers considerable resistance to blood flow.

Slide22

Slide23

4. Peritubular

capillary bed

is a low pressure bed.

5. Only 1 to 2% of blood flows through

vasa

recta

. The flow is very sluggish.

6. Renal blood flow shows remarkable constancy

in face of blood pressure changes due to

autoregulation

Slide24

The kidneys regulate the hydrostatic pressure in both capillary beds (

glomerular

&

peitubular

) , by adjusting resistance of the afferent and efferent arterioles.

High hydrostatic pressure in

GC

(60 mmHg) causes

rapid fluid filtration

; whereas a much lower pressure in the

peritubular

capillaries

(13 mmHg) permits

rapid fluid

reabsorption

.

Slide25

The afferent arteriole is a short, straight branch of the interlobular artery.

The

efferent arteriole

, that drains the GC, has a

relatively high resistance

than the

afferent arteriole.

Slide26

The Process of Urine Formation:

Urine formation begins with the

Filtration of plasma through the GC

into the Bowman’s space.

As the filtered fluid flows through the remaining portions of the tubule, its composition is altered as a result of two main processes:

Tubular

reabsorption

.

Tubular secretion

.

and both processes will produce the final product,

urine

.

Slide27

Concept of Clearance:

The renal clearance of a substance is the volume of plasma that is completely cleared or cleaned of that substance by the kidney per unit of time. (usually expressed as

mL

/ minute).

However, renal clearance provides a useful way of quantifying renal excretory functions.

It can be used to quantify the rate at which blood flows through the kidneys, as well as to measure the basic kidney functions such as GFR.

Slide28

Concept of Clearance (continues):

Renal clearance of a substance (S) is calculated by dividing the urinary excretion rate of (S) (U

S

×

V

•

) by its plasma concentration (P

S

), as expressed below

:

U

S

× V

•

C

S

=

P

S

Where: U

S

= urine concentration of S.

V

•

= urine flow rate/ minute = (0.9

mL

/ minute).

P

S

= plasma concentration of S.

Slide29

Clearance

of any

substance

depends on the

behavior of the tubular cell

towards that substance:

If a substance like

inulin

, which is freely filtered at the

glomerulus

level and is neither reabsorbed nor secreted by the renal tubule, then its

clearance

equals

to

GFR.

On the other hand, if a substance is

reabsorbed by the renal tubule

, its

clearance

is

lower

than the

GFR

.

Finally, if a substance that is in addition to filtration is

secreted by the renal tubule

, then its

clearance

is

higher than the GFR.

Slide30

THANK YOU