ADDITIONAL SCIENCE FORM 4

ADDITIONAL SCIENCE FORM 4

CHAPTER 13: EXCRETORY SYSTEMCHAPTER 13: EXCRETORY SYSTEM

13.1 FUNCTIONS OF THE KIDNEY AND SKIN IN EXCRETION

Excretion is the process of removing

metabolic waste products and toxic

materials.

Excretion and defecation are two

different processes.

Organ Metabolic waste products

Skin Urea, salts and water

Lungs Carbon dioxide and water

Kidneys Urea, salts and water

13.1 FUNCTIONS OF THE KIDNEY AND SKIN IN EXCRETION

Excretion Defecation

Differences

Remove metabolic waste products Remove undigested food from the digestive system

Waste are products of metabolism Faeces is a not a product of metabolism

Involves kidneys, skin and lungs Involves large intestine, rectum and anus

Similarities

Remove waste products from the body

13.1 FUNCTIONS OF THE KIDNEY AND SKIN IN EXCRETION

Urine is produced in the kidneys. The functional unit of the kidney is the

nephron.

Structure of the human kidney

13.1 FUNCTIONS OF THE KIDNEY AND SKIN IN EXCRETION

Blood is carried into the glomerulus

through the afferent arteriole from the

renal artery. Blood flows out of the

glomerulus through the efferent arteriole.

The afferent arteriole has bigger

diameter than the efferent arteriole. This

causes the high hydrostatic pressure of the blood in the glomerulus.

13.1 FUNCTIONS OF THE KIDNEY AND SKIN IN EXCRETION

Steps in the formation of urine

Step 1Ultrafiltration

• The high hydrostatic pressure of the blood causes the ultrafiltration process to occur in the glomerulus. Plasma components such as urea , amino acids, sugars, salts and water are filtered into the Bowman’s capsule

Step 2Selective

reabsorption

• At the proximal convulated tubule, about 65 % of water, sugars and amino acids are reabsorbed into the blood capillaries. At the loop of Henle, about 20 % of water and salt are reabsorbed. At the distal convulated tubule and collecting duct, only water and salt are reabsorbed

Step 3Secretion

• Occurs when substances not required by the body are secreted into the filtrate by the cells of the tubule wall. The remaining filtrate in the collecting duct is secreted as urine which contains urea, salts and water

13.1 FUNCTIONS OF THE KIDNEY AND SKIN IN EXCRETION

Skin can remove metabolic wastes from

the body through sweating. Sweat is a mixture of water, salts and

urea. When we sweat, our body become

cooler and metabolic waste products

are excreted.

13.1 FUNCTIONS OF THE KIDNEY AND SKIN IN EXCRETION

Structure of the human skin

Sebaceous gland

Blood vessel

Hair follicle

Epidermis

Dermis

Hypodermis

Sensory neurone

Sweat gland

Hair erector muscle

13.1 FUNCTIONS OF THE KIDNEY AND SKIN IN EXCRETION

How the skin regulate our body temperatureThe body temperature rises

The receptors in the skin send nerve impulses to the brain

The brain sends signal to the blood vessels and cause them to dilate

More blood flow to the skin and stimulates the sweat glands

The blood flow also carries waste products which diffuse into the sweat gland

The sweat is secreted from the sweat gland to the skin surface through sweat pores

13.2 DISEASES RELATED TO THE EXCRETORY SYSTEM

We can prevent kidney related diseases

by reducing salt and sugar intake in our

diet, drinking plenty of water and avoiding

drugs and alcohol.

Disease Symptoms Causes

Kidney failure Blood in the urineHigh blood pressure

DiabetesHigh blood pressureInfections Kidney stones

Kidney stones Pain in the middle of the upper abdomen

High concentration of uric acid and insufficient water in the kidneys to dissolve waste products

13.2 DISEASES RELATED TO THE EXCRETORY SYSTEM

Uric acid crystals can cause gout

13.3 HEALTHY EXCRETORY SYSTEM

Treatment for kidney

failure

Kidney transplant

Haemodialysis