Excretion

Question 1

Metabolic waste products

Answer 1

1. Carbon dioxoide
2. Urea
3. Mineral salts
4. Water

Question 2

Excretion

Answer 2

Excretion is the process of removing metabolic waste products, toxic and excess substances from the body

Importance: Excretion is important so that harmful substances do not build up in the body and cause harm

Question 3

Excretory Products and their Excretory Organs

Answer 3

1. Carbon dioxide is excreted by the:
   - Lungs (Gas)
2. Excess water is excreted by the:
   - Kidneys (Urine)
   - Skin (Sweat)
3. Excess mineral salts is excreted by the:
   - Kidneys (Urine)
   - Skin (Sweat)
4. Urea is excreted by the:
   - Kidney (Urine)
   - Skin (Sweat)

Question 4

Organs of the human urinary system

Answer 4

1. A pair of kidneys
2. A pair of ureters
3. Urinary bladder
4. Urethra

Question 5

Ureter

Answer 5

Function:
- Carry urine from the kidney to the bladder

Question 6

Bladder

Answer 6

Function:
- Stores urine

Question 7

Urethra

Answer 7

Function:
- Allow urine to be passed out of the body

Question 8

Nephron

Answer 8

It is the basic functional unit of the kidney tubule

Question 9

Formation of urine

Answer 9

1. Ultrafiltration
2. Selective reabsorption

Question 10

Ultrafiltration

Answer 10

• The first stage of urine formation
• Process by which small molecules are filtered out of the blood by the glomerulus into the Bowman’s capsule

Process:
1. The afferent arteriole has a wider diameter than the efferent arteriole, generating high hydrostatic pressure in the glomerulus

2. This forces blood plasma out of the glomerular capillaries into the Bowman’s capsule
3. The substances that are filtered include:
   - Mineral salts
   - Glucose
   - Amino acids
   - Water
   - Urea
4. The substances that remain in the glomerulus include:
   - Proteins
   - Blood cells
   - Platelets

Question 11

Adaptations of the glomerulus

Answer 11

1. The glomerulus is a network of blood capillaries
   - Provides a large surface area for greater rate of diffusion
2. The glomerular capillary have one cell thick walls that contain tiny pores
   - To maintain a shorter diffusion distance for greater rate of diffusion of substances

Question 12

Selective reabsorption

Answer 12

In the proximal convoluted tubule:
- Most water is absorbed via osmosis
- Most mineral salts are absorbed via diffusion and active transport
- All glucose and amino acids are absorbed via active transport

In the loop of Henle:
- Some water is absorbed via osmosis
- Some mineral salts are absorbed via active transport

In the distal convoluted tubule:
- Some water is absorbed via osmosis
- Some mineral salts are absorbed via active transport

In the collecting duct:
- Some water is absorbed via osmosis

• Remaining water, excess mineral salts and urea form urine

Question 13

Kidney failure

Answer 13

If both kidneys fail
- Might need a kidney transplant
- Kidney dialysis

Question 14

Function of kidneys

Answer 14

1. They are excretory organs
   - Secrete water, excess mineral salts and urea out of the body
2. They are osmoregulators
   - Regulate water potential to maintain a constant water potential level in the body

Question 15

Dialysis Process

Answer 15

1. Blood is drawn from a patient’s vein and pumped through a tubing
2. The tubing is bathed in dialysis fluid. Tubing walls are partially permeable
3. Small molecules such as urea diffuses out while cells like blood cells and platelets and large molecules like proteins remain in the tubing
4. The filtered blood is returned to the arm via a vein

Question 16

Features of a dialysis machine

Answer 16

1. Composition of dialysis fluid
   - Similar concentration of essential substances as blood to prevent nutrient loss
2. Long, narrow and coiled tubing
   - Increase SATV for greater rate of diffusion of wastes
3. Opposite flow of blood and dialysis fluid
   - To maintain a steep concentration gradient for greater rate of diffusion of wastes