Topic 8 Excretion and Osmoregulation

Question 1

What is excretion?

Answer 1

Removal of waste products from metabolism, along with excess water, salts and hormones

Question 2

What is egestion?

Answer 2

Passage of undigested food out of the system

Question 3

Why does excess salt need to be removed?

Answer 3

1. Too much salt in cells -> water travels from blood and tissue fluid surrounding cells (down concentration gradient by osmosis) to enter these cells
2. This lowers the volume of the blood and thus lowers the blood pressure
3. Extra water entering cells may make them burst

Question 4

What are amino acids converted to in the liver?

Answer 4

Amino acids that are not needed are converted to urea in the liver

Question 5

What waste product is produced and then exhaled by the lungs

Answer 5

Carbon dioxide (produced in respiration)

Question 6

What waste product is produced and then exhaled by the lungs, sweated from skin, removed from blood by kidneys

Answer 6

Water (produced in respiration and ingestion)

Question 7

How are salts excreted?

Answer 7

Removed from blood by kidneys, urinated out of body

Some sweated

Question 8

How is urea excreted?

Answer 8

After being converted from amino acids in the liver -> removed from blood by kidneys and excreted as urine
Some sweated out

Question 9

What is the function of the capsule

Answer 9

Fibrous skin covering the kidney

Question 10

What is the function of the cortex

Answer 10

Outer region of the kidney (blood filtered here)

Question 11

What is the function of the medulla

Answer 11

Inner region of the kidney

Question 12

What is the renal artery’s function?

Answer 12

Carries unfiltered blood to kidney

Question 13

What is the renal vein’s function?

Answer 13

Carries filtered blood from the kidney

Question 14

What is the pelvis’ function?

Answer 14

Area where ureter joins kidney (urine collects here)

Question 15

What is the ureter’s function?

Answer 15

Carries urine to the bladder

Question 16

What is the function of the nephron?

Answer 16

1. Remove all urea from blood
2. Remove excess water + salts

This is via ultrafiltration

Question 17

What is ultrafiltration?

Answer 17

1. Movement of small molecules from blood in glomerulus into bowman’s capsule under high pressure (across a partially permeable membrane)
2. Capillary leaving glomerlus (efferent) narrower, high pressure, resistance to blood flow, high pressure in glomerulus
3. Pressure forces smaller molecules into Bowman’s capsule to form glormerular filtrate

Question 18

What are the substances forced out of the capillaries (and filtered by the the Bowman’s capsule, which will not let large molecules like protein through)

Answer 18

1. Water
2. Glucose
3. Salt
4. Urea

Question 19

What is the composition of the glomerular filtrate?

Answer 19

1. Proteins : 740 mg per 100ml in renal artery, none in glomerular filtrate or urine, 740 mg per 100ml in renal vein
2. Glucose : 90 mg per 100ml in renal artery, 90 in filtrate, 0 in urine, 90 in renal vein
3. Urea: 30 mg per 100ml in renal artery, 30 in filtrate, 2000 in urine, 24 in renal vein

Question 20

Explain the composition of the glomerular filtrate

Answer 20

1. Protein : stays in blood, doesn’t enter filtrate as too large to be ultrafiltrated into bowman’s capsule
2. Glucose: removed from blood into filtrate, all goes into Bowman’s capsule then all selectively re absorbed into proximal tubule
3. Urea : all removed from blood into filtrate, some selectively re absorbed to support water potential of blood
   Urea in urine is more concentrated due to water re absorption in loop of Henle and collecting duct

Question 21

What is selective re absorption?

Answer 21

• kidneys re absorb molecules essential to the body via active transport with ATP

Eg. All glucose reabsorbed, as much water as needed (by osmosis) and as many ions as needed

Question 22

Where and why is glucose selectively reabsorbed?

Answer 22

1. Proximal convuluted tubule (lots of mitochondria present in nephron for active transport + microvilli for large sa)
2. Reabsorbed into capillary network around nephron

Question 23

Where and why is water selectively reabsorbed?

Answer 23

1. Needed in cytoplasm + tissue fluid
2. Absorbed via osmosis in loop of Henle and collecting duct

Question 24

What happens to the leftover urine?

Answer 24

Goes into collecting duct -> renal pelvis -> ureter -> bladder -> urethra

Question 25

What is osmoregulation?

Answer 25

Control of body’s water content

Question 26

How is water content controlled?

Answer 26

Lungs when we exhale
Skin by sweating
Body, in urine produced by kidneys

Question 27

What part of the brain detects and controls water content of tissue fluid (must be kept constant as too much water in tissue fluid will make cells swell up due to osmosis, and too little, cells will lose water via osmosis)

Answer 27

Hypothalamus

Question 28

What happens when there is too much water in the blood?

Answer 28

1. Detected by hypothalamus
2. Hypothalamus signals to pituitary gland to stop releasing ADH
3. Collecting duct becomes impermeable to water so no water is reabsorbed by osmosis
4. Greater volume of more dilute urine produced

Question 29

What happens when there is not enough water in the blood?

Answer 29

1. Detected by hypothalamus
2. Signals to pituitary gland to produce more ADH
3. Collecting duct becomes more permeable to water so more is reabsorbed by osmosis
4. Smaller volume of more concentrated urine is produced