Unit 13 Excretion

Define Excretion

Removal of waste products of metabolism, toxic materials and substances in excess requirements

What are the excretory organs?

lungs, liver kidney

How is urea made?

Made in the liver from excess amino acids

How is urea excreted?

Urea is carried to the kidneys in the plasma where it is filtered out and leaves in the body in the form of urine

Why is excretion important?

To avoid carbon dioxide and urea build up in the tissues, the substances would reach a toxic level and destroy the tissues.

What is the difference between excretion and egestion?

Excretion is substances that have been produced in the body cells in metabolism, substances that are egested have been eaten and passed through the ailimentary canal without digestion. Eg- fibres

Define assimilation

The food molecules have been absorbed and have now become part of the cells.

Describe the functions of liver

1. Removes glucose from the blood storing it as glycogen, helps regulate the glucose concentration in the blood.
2. Uses amino acids to make proteins. Eg- fibrogens involved with blood clotting
3. Break down of excess amino acids
4. Converts fatty acids and glycerol into fat stored around the body (skin)
5. produces cholesterol from fats

What is deamination?

Breakdown of excess amino acids to form ammonia

Describe what happens to amino acids in the body?

After amino acids is made, one molecule is converted into carbohydrate or fat used as a source of energy. The other excess molecule gets taken to the liver and deaminated- producing urea, carbohydrate or fat.

What are the roles of the liver?

1. Breaks down hormones that have been circulated in the blood for a while
2. Breakdown of harmful substances such as alcohol and other drugs such as paracetamol

Assimilation

Making of Bile

What is the function of Bile?

1. Neutralisation of acid contents of small intestine
2. Emulsification of fats

What are the kidneys responsible for?

Removal of urea and excess ions from the blood

How are the kidneys protected

They are protected by the lower ribcage and the fat that surrounds them.

How do the molecules get filtered and/or reabsorbed?

In the kidney, there are kidney tubules which are filtering units. As the blood flows through the filtering units, small molecules like glucose, ions, water, urea are forced out the blood to form filtrate. The filtrate passes along the tubule, and the glucose and ions (useful substances) get reabsorbed into the blood

How does the volume of water reabsorbed change?

When you are dehydrated, the kidneys will take back as much water as needed. So your urine will be concentrated. On a cold day, the kidneys will reabsorb less water giving pale coloured and dilute urine.

Where is the urine stored?

Bladder

Function of Renal Vein?

takes cleaned blood away from the kidneys

Function of Renal artery?

brings waste blood to the kidneys

Function of ureter

Carry urine down to the bladder

Function of urethra

carries urine out of the body

What are the parts of the kidney?

Cortex, Medulla, Pelvis

What is the function of the kidney tubules?

To filter the blood, remove waste chemicals, determine how much water is excreted.

How is the blood filtered in the glomerulus?

The blood vessel entering the glomerulus is thicker than the one leaving, increased pressure that allows the blood to be filtered. The lining of the capillaries have small holes, blood proteins are too large to fit through the holes so they stay in the blood. Small molecules like urea, glucose, ions and water pass out of the glomerulus in the bowmans capsule.

Why does reabsorption occur?

All the glucose, some ions and water are still needed by the body so are reabsorbed back into the blood.

What are the adaptations in the cell wall associated with active transport?

1. Microvilli- to provide a large surface area for absorption
2. Mitochondria- for active transport