addsc excretory
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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