excretion. definition excretion is the process by which metabolic waste products and toxic materials...

Excretion

Definition

Excretion is the process by which metabolic waste products and toxic materials are removed from the body of an organism.

The removal of the faeces is not regarded as excretion because the fibre which make up the faeces is not the product of a chemical reaction in the body. Instead, it is passed all the way through the intestines unaffected by enzymes.

Excretion

Metabolic process= anabolism + catabolism

Process metabolic waste products

Eg: deamination- ___________________

respiration - ___________________

break down haemoglobin - __________

Excretory Organ

Lungs Liver Kidney Skin

Excrete carbon dioxide and water vapour

-adaptation of the alveolus

Excrete bile via the intestine

Excrete metabolic waste products eg urea, uric acid, creatinine

Produces and get rid of sweat containing water, mineral salts, uric acid, creatinne

Why remove nitrogenous waste?

Accumulation of nitrogenous waste, like urea, poisons and kills the cells.

Kidney

Functions:

1. The removal of nitrogenous waste products (eg. urea), excess water and mineral salts in the form of urine.

2. The maintenance of constant concentration of blood plasma (osmoregulation)

The kidneys

The kidneys are two brown bean-shaped organs lying dorsally in the abdominal cavity

A

B

Longitudinal section of a kidney

Medulla

Cortex

Renal pelvis

Renal artery

Renal vein

ureter

Nephron

April 21, 2023 Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 9

Blood enters the kidney via the renal artery

branchof renalartery

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How blood enters the kidney tubule?

Renal artery branches into many arterioles

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afferent arteriole



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2


glomerulus

Arterioles further divide into a mass of blood capillaries (glomerulus)

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Blood leaves glomerulus and enters tubule

collecting tubule/duct

Malpighiancorpuscle

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venuleBlood capillaries unite to form venules

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branch ofrenal vein

Venules join to form renal vein

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1

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Blood capillaries unite to form venules



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Blood exits the kidney via the renal vein


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branch ofrenal vein

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Blood capillaries unite to form venules



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Venules join to form renal vein

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The formation of urine

Two main processes are involved in the formation urine:

1. Ultrafiltration

2. Selective reabsorption

Ultrafiltration

The blood pressure in the glomerulus is high because afferent ateriole is wider than the efferent arteriole. The blood pressure provides a great force for the blood to pass through from glomerulus to the renal capsule.

Renal capsule has a layer of cell membrane which is partially permeable . Only very small molecules are filtered off the blood. All the large molecules are retained.

Glomerulus and renal capsule

Composition of filtrate

Water We Glucose Go Amino acid And Mineral salts Make Urea Urine Uric acid Unitedly

At Proximal Tubule

80% of filtrate reabsorbed here,eg. all the glucose, amino acids, most sodium chloride and water

F

I

L

T

R

A

T

E

Blood capillary

Process of reabsorption

Process of reabsorption

Amino acids, glucose and ions diffuse into cells of proximal tubule.

These are absorbed into the blood capillaries by diffusion and active transport.

The constant removal of these substances from tubule cells causes a diffusion gradient.

What about water and NaCl ?

The uptake of Na,Cl ions causes water potential of tubule cells to decrease.

Therefore, water from filtrate enters by osmosis into tubule cells and blood capillaries.

Descending Limb?

Thin walls that are highly permeable to water. The water passes out of the filtrate by

osmosis, enters the capillaries and taken away.

Ascending Limb?

Has thick walls that are impermeable to water.

At the collecting duct.

The collecting duct is permeable to water. As filtrate moves down, water passes out of it

by osmosis and carried away in capillaries. Excess water, excess mineral salts and

nitrogenous waste, like urea, pass out of the collecting duct into renal pelvis.

THE PERMEABILITY OF COLLECTING DUCT IS AFFECTED BY ADH.

Group Work- data analysis- 10 mins

Main component

Blood plasma/ g/100ml

Filtrate/ g/100ml Urine g/100ml

Water 90 98 98

Dissolved mineral

0.72 0.72 1.1

Albumin 8.00 0.05 0.00

Glucose 0.10 0.10 0.00

urea 0.05 0.05 1.8

Based on the differences in the composition of plasma and filtrate, predict the functions of glomerulus.

Group Work- data analysis – (15 min)

Main component

Blood plasma/ g/100ml

Filtrate/ g/100ml

Urine g/100ml

Water 90 98 98

Dissolved mineral

0.72 0.72 1.1

Albumin 8.00 0.05 0.00

Glucose 0.10 0.10 0.00

urea 0.05 0.05 1.8

It was found that an average adult can produce 1-1.5 litres of urine per day. However, it was found that the average amount of filtrate produced per day is about 150 litres. Based on the data, explain why

(a) there is a decrease in the volume from filtrate to urine,(b) the glucose is no longer found in the urine.

Factors affecting the urine composition:

1. Intake of protein-rich diet

2. Weather

3. Salty food

4. Disease

5. Large intake of liquids

The kidneys as Osmoregulators

Osmoregulation is the control of water and solute levels in the blood to maintain a constant water potential in the body.

Why is it important to control the water potential in the body?

CAUSEs OF LOW WATER POTENTIAL

Little water is ingested Much sweating occurs Large amount of salts are ingested

LOW WATER POTENTIAL MEANS ...

High solute concentration High concentration of plasma

NORMAL WATER POTENTIAL OF BLOOD

Reduced water intake

Decreased water potential of blood ie. more concentrated plasma

Detected by receptors in hypothalamus in brain. Stimulated more.

Nerve impulse sent to pituitary gland

More ADH released

Wall of collecting duct more permeable to water

More water reabsorbed, less water leaves body

Urine is more concentrated

Thinking room Drinking too much alcohol is bad for your health. One

unpleasant effect of drinking too much alcohol is having a hangover. The symptoms of a hangover include a headache, a feeling of nausea and in extreme cases, shaking of the limbs. Many symptoms of a hangover are the result of dehydration rather than the direct effects of the alcohol itself. Alcohol causes dehydration because it reduces the production of ADH.

(a) Explain why does the body lose more water than it needs to in a hangover?

(b) State changes to the urine composition do you expect to find in a person with a hangover?

Kidney dialysis

If a person’s kidney stop working properly, there will be a build-up of urea and toxins in their blood which will eventually prove fatal. A kidney transplant may be possible if a donor with suitable tissue type is available. Otherwise, kidney dialysis may be used.

Features of the dialysis machine Dialysis tubing is partially permeable. Only small molecules in the

blood can pass from the tubing into the fluid. A kidney dialysis machine removes chemicals with small molecules (urea, toxins and ions) from a patient’s blood, but does not allow a larger molecules (such as plasma proteins) to leave the blood.

The dialysis fluid is continuously renewed, washed away the substances removed from the blood. By varying the concentration of substances in the washing fluid, the amount of those substances which leave the blood can be controlled.

The direction of blood flow is opposite to that of the dialysis solution, helping to maintain a diffusion gradient for removal of the urea.

Dialysis fluid is renewed

Features of the dialysis machine

Tubing is bathed in dialysis solution composition containing salts and glucose at similar to blood plasma to prevent the useful substances from leaving the blood plasma.

Differences between removal of waste material through:

nephron dialysis

Differences between removal of waste material through:

nephron

1. ultra-filtration occur at the glomerulus

2. active transport is involved to selectively reabsorb back molecules such as glucose and amino acids.

3. Osmosis, diffusion and active transport can take place.

dialysis1. filtration did not take

place

2. No active transport involved. The dialysis fluid need to have the similar composition of plasma (without the urea and salt)

3. It depends largely on diffusion.

Peritoneal dialysis

which uses a selectively permeable membrane called the peritoneum.

special solutions that facilitate removal of toxins are infused into the abdomen where they remain for some time before being drained out and replaced with fresh solution. This form of dialysis can be performed at home, but must be done continuously on a daily basis.

The end

excretion. definition excretion is the process by which metabolic waste products and toxic materials...

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