Human Biology (Excretory System)

Question 1

What is excretion?

Answer 1

Excretion is the removal of wastes produced by metabolism within cells.

Question 2

Give 3 examples of organs that do excretion and their excreted substances.

Answer 2

Lungs: C2O
Sweat Glands: Water, Salt, Uric acid, Urea
Kidneys: Water, Urea, Salt

Question 3

What is and what organ primarily performs deamination?

Answer 3

The liver, and deamination is the process of breaking down proteins into amino acids, then further breaking them into amine groups, this breakage releases a carbohydrate and ammonia.

The carbohydrate formed is used for energy.
The ammonia formed is reacted with CO2 and energy to form urea a less toxic substance and water.

Question 4

Why does ammonia react with CO2 and energy to form urea?

Answer 4

Because Ammonia is a highly toxic substance and so needs to be neutralised. The reaction NH3 + CO2 + Energy —-> Urea + Water is good for neutralising the ammonia into urea which then is further distilled in water to be excreted through urine.

Question 5

When do the sweat glands release body odour?

Answer 5

When bacteria on the skin breakdown the urea.

Question 6

What is a nephron?

Answer 6

The structural and functional unit of the kidney. There are approximately 1.2M per kidney.

Question 7

What are the 3 main parts of the kidney and nephron?

Answer 7

Kidney:
- Cortex
- Medulla
- Renal Pelvis

Nephron:
- Glomerulus
- Tubules
- Collecting Duct

Question 8

What is the blood flow from the heart to the kidney?

Answer 8

Blood leaves the heart through the aorta. The aorta splits off into smaller arteries, one of these is the renal artery which brings blood to the kidneys.

The renal artery splits into smaller arteries. Each arteriole leads to the renal corpuscle of a nephron.

Question 9

What are the afferent and efferent arterioles?

Answer 9

The afferent arteriole brings blood to the glomerulus, coming from the renal artery which is from the heart’s aorta split into many arteries.

The efferent arteriole takes blood from the glomerulus and splits into smaller capillaries surrounding the nephron, called the peritubular capillaries, which eventually reform into the renal vein taking blood from the kidneys back to the heart.

Question 10

What are the 3 major processes involved in the formation of urine?

Answer 10

• Glomerular Filtration
• Selective Reabsorption
• Tubular Secretion

Note: Any material that stays in the nephron will be excreted. Substances that are reabsorbed move back into the blood (will stay in the body)

Question 11

What is the causation of the great pressure in the glomerulus?

Answer 11

The afferent arteriole is wider than the efferent arteriole creating the great pressure in the capilarries.

Question 12

What is Glomerular Filtration?

Answer 12

The process of when the pressure of the glomerulus causes materials in the blood plasma to move from the capillaries into the glomerular capsule. Because the glomerulus acts like a filter, the material that moves into the glomerular capsule is termed ‘filtrate’.

Question 13

What are substances that are moved through glomerular filtration?

Answer 13

The filtrate includes:
- Water
- Glucose
- Amino Acids
- Salts
- Fatty Acids
- Urea
- Creatine (Metbolic waste)
- Hormones & various ions

Question 14

Why can’t blood cells and proteins diffuse to the glomerular capsule?

Answer 14

Larger structures such as the blood cells and proteins are too large to fit through the membrane making up the walls of the glomerulus, and so stay in the blood.

Question 15

What is Selective Reabsorption?

Answer 15

Many materials in the filtrate are vital for survival and must be reabsorbed into the blood. This is termed selective reabsorption.

Question 16

Where are glucose and amino acids reabsorbed and form of movement?

Answer 16

Through active transport, glucose and amino acids are reabsorbed in the blood at the proximal convoluted tubule.

Question 17

What occurs at the descending limb during selective reabsorption and what occurs with the water?

Answer 17

The descending limb of the loop of Henle is impermeable to salt
Due to the high concentration of salts in the surrounding blood, water is reabsorbed into the blood through osmosis and the salt stays put due to the impermeability. The filtrate is now highly concentrated.

Question 18

What occurs at the ascending limb during selective reabsorption?

Answer 18

The ascending limb of the loop of Henle is impermeable to water.

Due to the high concentration of the filtrate in the nephron, the sodium and chlorine ions are reabsorbed into the blood. Water stays put due to its impermeability.

Question 19

What occurs at the distal convoluted tubule during selective reabsorption and what occurs with the water?

Answer 19

In the distal convoluted tubule, sodium ions are actively reabsorbed by active transport. Water is absorbed into the filtrate.

Question 20

What is faculative reabsorption?

Answer 20

The process of reabsorption that is controlled by hormones.

Question 21

What is tubular secretion?

Answer 21

Involves adding materials from the blood into the nephron to be excreted.

Question 22

What occurs during tubular reabsorption in the distal convoluted tubule?

Answer 22

Potassium and hydrogen ions, creatine (a metabolic waste), are moved into the nephron.