revision excretion

8/8/2019 Revision Excretion

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Revision: Excretion

Chapter 7


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Learning Objectives Define excretion and explain the importance

of removing nitrogenous and othercompounds from the body

Outline the function of kidney tubules withreference to ultra-filtration and selectivereabsorption in the production of urine

Outline the role of anti-diuretic hormone

(ADH) in the regulation of osmoticconcentration

Outline the mechanism of dialysis in the caseof kidney failure


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What is excretion?

Excretion - process where metabolic waste

products and toxic materials are removed

from the body of an organism

Egestion - removal of undigested matter from

the alimentary canal. Never been absorbed

into the cells hence not produced as a resultof metabolic changes


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An overview of excretion system

Excretory organs

Kidneys Lungs Skin Liver

Water

Urea

Uric acid

Creatinine

Some salts

Water

CO2

Water

Urea

Uric acid

Creatinine

Some salts

Bile pigments


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Functions of kidney

Main function ofkidneys is to form

urine through

ultrafiltration

Selective

reabsorption of

useful materials


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Functions of the kidneys

Regulates the pH and composition of the

blood plasma.

Regulates the salt and water balance of

the body fluid.


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Ultrafiltration

Blood pressure or hydrostatic

forces out small molecules like

water, salts, glucose and aminoacids and waste materials

include excess mineral salts,

nitrogenous wastes (urea,

creatinine, uric acid). All thesemake up the filtrate.

Selective reabsorption

Most water reabsorbed by

osmosis. Some mineral salts,all glucose and all amino acids

are actively reabsorbed through

the nephron


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The mammalian

urinary system

Structure

Urinary system

Longitudinal section of kidney

Structure of nephron

Function

Formation of urine (ultrafiltration and selective

reabsorption

Kidneys as osmoregulators


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Urinary system


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Theu

rinary system The urinary system comprises of:

- 2 kidneys

- 2 ureters

- 1 urinary bladder

- 1 urethra


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Longitudinal section of kidney


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Stru

ctu

re of a neph

ron Each nephron comprises of:

Bowmans capsule and glomerulus

Proximal and distal convoluted tubules

Loop ofHenl

Collecting duct


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Structure

of th

enephron


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Formation of urine


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Kidneys as osmoregu

lators Water potential of the blood has to be kept

relatively constant.

Control of water content of the body is

known as osmoregulation.

The kidney, together with thehypothalamus and pituitary gland, are

responsible for osmoregulation in humans.


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Kidneys as osmoregu

lators The hypothalamus continuously monitors

the concentration of the blood.

The pituitary gland secretes the hormone

called vasopressin oranti-diuretic

hormone (ADH).

Anti-diuretic hormone (ADH) increases

water re-absorption by the kidney tubules.


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Kidneys as

osmoregu

lators


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Dialysis


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Dialysismembrane


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Kidney failu

re1. In dialysis, blood is drawn from an artery

in the patients arm and allowed to flow

through the tubing in a dialysis machine.

2. The dialysis machine contains fluid

consisting of water and other substances

such as salt.


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Kidney failu

re3. As the patients blood passes through the

dialysis machine, it is separated from the

fluid by a partially permeable membrane.

4. Small molecules such as urea diffused

through the membrane into the fluid.

5. Big molecules, such as proteins and

blood cells, remains in the tubing.


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Kidney failure The filtered blood is then returned to a

vein in the patients arm.

Dialysis can be inconvenient and

expensive for the patients.

A better long-term solution for kidneyfailure is a kidney transplant. However,

there are drawbacks as well.


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Conclusions Excretion is process where metabolic waste

products and toxic materials are removed from thebody of an organism (different from egestion)

Kidneys produce urine through ultrafiltration and

selective reabsorption

Kidneys are involved in osmoregulation,regulation of pH in blood and regulation of bloodplasma composition.


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Each nephron consists of a renal (Bowmans)

capsule, the glomerulus, first (proximal)

convoluted tubule, loop ofHenl and second(distal) convoluted tubule).

Urine is formed by ultrafiltration and selective

reabsorption.

The hormone ADH regulates the amount of

water reabsorbed by the kidney tubules.

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