Chapter 8 part 1: Excretion in humans

Question 1

What are metabolic activities?

Answer 1

• Metabolic activities are the chemical activities that take place in our body to keep us alive.

Question 2

Are metabolic waste products and excretory products harmful (to humans)?

Answer 2

• Metabolic waste products and excretory waste products can be harmful to the body if they accumulate, so they must be removed from the body.

Question 3

What are the 4 examples of waste products?

Answer 3

1. Urea:
   - It is produced when excess amino acids undergo deamination (process that takes place in the liver) inside the liver.
   - An abnormally high level in urea can lead to Abdominal pain, nausea, and vomiting.
   - It may also cause irregular heartbeat and muscle cramps.
2. Carbon dioxide:
   - It is produced during aerobic respiration.
   - An abnormally high level in carbon dioxide results in Hypercarbia; whereby a person may suffer from headache, confusion, rapid breathing, and premature heartbeats.
3. Water:
   - Excess water increases the water potential of the blood.
   - Water enters cells through osmosis, and excess water entering the cells may cause them to swell and burst.
4. Mineral salts or ions:
   - Excess amounts of mineral salts/ions may lower the water potential of the blood which results in cells losing water through osmosis and becoming dehydrated.

Question 4

What is deamination?

Answer 4

• Deamination is the process that takes place in the liver

Question 5

What is excretion?

Answer 5

• Excretion is the removal of metabolic waste products, toxic substances, and other substances in excess of the body’s requirement.

Question 6

What are the 3 main excretory organs and products that they create?

Answer 6

1. Lungs
   Excreted product: Carbon dioxide
   Excreted gas: A component of exhaled air.
2. Kidneys:
   Excreted product: Excess water (mainly), excess mineral salts and urea.
   Excreted as: A component of urine.
3. Skin:
   Excreted product: Excess water (mainly), excess mineral salts and urea (but in small amounts).
   Excreted as: A component of sweat.

Question 7

What is the human urinary system consisted of?

Answer 7

• The human urinary system consists of a pair of kidneys, a pair or ureters, a urinary bladder, and a urethra.

Question 8

What are the 4 parts of the urinary system and their functions?

Answer 8

1. Kidneys:
   Description:
   - Bean-shaped organs.
   - The left kidney is slightly higher than the right kidney.
   Function:
   - Remove excess water, mineral salts and urea from the body.
2. Ureters:
   Description:
   - Narrow tube
   Function:
   - Connect kidneys to the urinary bladder.
3. Urinary bladder:
   Description:
   - Elastic muscular bag in front of the rectum
   Function:
   - Stores urine
4. Urethra:
   Description:
   - Duct
   Function:
   - Connects the urinary bladder to the outside of the body.

Question 9

What does the kidneys consist of?

Answer 9

• The kidneys consist of the outer dark red region and the inner pale red region.

Question 10

What are nephrons?

Answer 10

• Nephrons are the basic functional units of the kidney, and they are tin kidney tubules, where urine is formed.

Question 11

What is the nephron consisted of?

Answer 11

• Each nephron consists of a Bowman’s capsule, proximal convoluted tubule, a loop of Henle and distal (2nd/second) convoluted tube.
• Several nephrons lead into the collecting duct.

Question 12

What are the steps in which blood enters the kidney through the renal artery and leaves through the renal vein?

Answer 12

1. Blood enters the kidneys via the renal artery which branches out into different arterioles.
2. Blood in the different arteriole enters the glomerulus; the mass of blood capillaries i the Bowman’s capsule.
3. Blood leaves the glomerulus via the efferent arteriole and enters blood capillaries surrounding the nephron.
4. Blood from the capillaries enter the venules, which leads to the renal vein.

Question 13

How does the body remove excess water, mineral salts and nitrogenous waste products?

Answer 13

• The body removes excess water, mineral salts, and nitrogenous waste products through urine (process: urination).

Question 14

What substances does the renal artery and renal vein carry?

Answer 14

• The renal artery caries oxygenated blood, nutrients and wastes to the kidney for processing while the renal vein carries filtered blood away from the kidney.

Question 15

What are the 2 main processes that the urine formation in each nephron involve?

Answer 15

• Urine formation in each nephron involves:
  1. Ultrafiltration: of small molecules from the blood.
  2. Selective absorption: of useful substances.

Question 16

How does ultrafiltration occur?

Answer 16

• Ultrafiltration occurs in the glomerulus through a partially permeable membrane.

Question 17

What are the steps in the process of ultrafiltration?

Answer 17

1. The afferent arteriole that brings blood into the glomerulus is wider than the efferent arteriole that caries blood away.
2. This creates a high blood pressure in the glomerulus.
3. Water and small molecules (such as glucose, amino, mineral salts, and urea) are forced out of the glomerular capillary, and into the Bowman’s capsule.
4. Larger molecules (such as fats and proteins), blood cells and platelets are retained in the glomerular capillaries.

Question 18

What is the glomerular filtrate consisted of?

Answer 18

• The glomerular filtrate contains small and soluble molecules such as salts, waters, glucose, amino acids, and waste products such as urea.
• It passes from the Bowman’s capsule into the proximal convoluted tubule.

Question 19

When does the selective reabsorption occur?

Answer 19

• Selective absorption occurs in the proximal convoluted tube, loop of Henle, distal convoluted tube and collecting duct, and it returns substances required by the body to the blood.

Question 20

What are the different substances that are reabsorbed along the length of the nephron?

Answer 20

1. Proximal convoluted tubule:
   - Most of the water is reabsorbed by osmosis.
   - All glucose and amino acids are reabsorbed by diffusion, and active transport.
   - Most mineral salts are reabsorbed by diffusion and active transport.
2. Loop of Henle:
   - Some water is reabsorbed by osmosis.
   - Some mineral salts are absorbed by active transport.
3. Collecting duct:
   - Some water is reabsorbed by osmosis.
4. Distal convoluted tubule:
   - Some water s reabsorbed by osmosis.
   - Some mineral alts are reabsorbed by active transport.

Question 21

How does excess water, mineral salts, and metabolic waste products get out of the body?

Answer 21

• Excess water, mineral salts, and metabolic waste products pass out of the collecting duct as urine.

Question 22

What are the factors that can result in a change of the composition of urine?

Answer 22

• The composition of urine may change depending on a person’s diet and health.
• Protein–> rich foods mean that more urea formed from deamination of excess amino acids in the liver. Thus, there is more urea in urine.
• Salty foods mean that there are more slats in urine.
• More liquids mean that the water potential of blood increases and this results in a higher-greater volume of urine.

Question 23

What is diabetes mellitus?

Answer 23

• Diabetes mellitus means that the body cannot store excess glucose as glycogen and glucose filtered out of the glomerulus as a filtrate.
• The nephron is unable to reabsorb all the glucose fast enough, this results in a large amount of glucose in urine.

Question 24

What is osmoregulation?

Answer 24

• Osmoregulation is the control of water potential and solute concentration (level) in the blood to maintain a constant water potential in the body.
• It is important for proper functioning of the body.

Question 25

What happens when the water potential in the body is not kept constant?

Answer 25

1. Too much water in the body –> water moves into the blood cells (red and white blood cells, platelets, and plasma), and tissue cells by osmosis –> cells swell and burst.
2. Too little water in the body –> water moves out of the blood cells and tissue cells by osmosis –> cells become dehydrated and shrink (in terms of size –> become smaller)

Question 26

Why are kidneys osmoregulators?

Answer 26

• Kidneys are osmoregulators because they regulate the water potential and solute concentration in the blood.

Question 27

What is the antidiuretic hormone (ADH)?

Answer 27

• The ADH is a hormone that controls the amount of water in the blood plasma.
• It is also produced by the hypothalamus in the brain.
• It is also released by pituitary gland to increase the water reabsorption at nephrons.

Question 28

Is osmoregulation a form of homeostasis?

Answer 28

• Osmoregulation is a gorm homeostasis.
  (The mind map/diagram of how water potential is kept constant when there is an increase/decrease in the water potential of the blood can be found in chapter 8 of Revision Guide)