Excretion

Question 1

Describe the role of the loop of Henlé in osmoregulation

Answer 1

1. Filtrate moves into the descending limb of the loop of Henlé. Water moves out of the descending limb by osmosis
2. At the bottom of the LoH (hairpin bend) the filtrate has a low water potential as it has a very high concentration of solutes
3. Ions rapidly diffuse out of the ascending limb into the medulla which creates a very low WP in the medulla tissues
4. Further up the ascending limb, ions (Na+, Cl-) are actively transported out of the ascending limb
5. At the top of the collecting duct, there is a very high WP so water moves out of the collecting duct by osmosis

Question 2

Describe the role of ADH in osmoregulation

Answer 2

1. osmoreceptors in the hypothalamus detect a low WP
2. sends signal to posterior pituitary gland which secretes ADH
3. ADH binds to receptors on the cell surface membrane
4. Aquaporins fuse to membrane which increases permeability of collecting duct
5. WP increases and returns to set point

Question 3

Describe the gross structure of the kidney

Answer 3

Cortex, medulla, pelvis
- renal artery, renal vein

Question 4

State the blood vessels of the liver

Answer 4

Hepatic vein (takes blood away)
Hepatic portal vein (wider, blood from intestines/ digestive system)
Hepatic artery (narrow, blood from aorta - into liver)

Question 5

State 3 functions of the liver

Answer 5

• glycogen storage
• detoxification
• deamination

Question 6

Define excretion

Answer 6

Removal of metabolic waste products from the body

Question 7

Explain each function of the liver

Answer 7

Detoxification
- hepatocytes secrete catalase which breaks down hydrogen peroxide
- hepatocytes release alcohol dehydrogenase
Ethanol —> Ethanal Ethanal —> ethanoate

Ethanol is absorbed and transported in the blood until it reaches hepatocytes
Hepatocytes release enzyme alcohol dehydrogenase which converts ethanol into ethanal

Deamination
- remove amine group from amino acid
- forms ammonia (toxic and highly soluble)
- ornithine cycle
- urea is produced

Question 8

How do freshwater fish, mammals and birds excrete

Answer 8

Freshwater fish- ammonia
Mammals- urea
Birds- uric acid

Question 9

Where does ultrafiltration occur

Answer 9

Glomerulus

Question 10

What happens in ultrafiltration

Answer 10

• Salts, water, urea and glucose diffuse out of the glomerulus into the bowman’s capsule
• WBC’s, RBC’s, platelets are too large to pass through fenestrations in B.C
  Afferent and efferent arterioles

Question 11

What makes up glomerular filtrate

Answer 11

Water, urea, amino acids, inorganic ions

Question 12

Where does selective reabsorption occur

Answer 12

PCT

Question 13

What 4 things are selectively reabsorbed

Answer 13

Glucose, water, sodium, amino acids

Question 14

3 adaptations of PCT

Answer 14

• microvili (large SA)
• mitochondria
• Co transporter molecules

Question 15

3 things DCT does in selective reabsorption

Answer 15

• pH regulation
• ion reabsorption
• water reabsorption

Question 16

5 causes of kidney failure

Answer 16

• blood loss
• high BP
• overuse of certain drugs
• infection
• diabetes

Question 17

What happens if kidneys fail

Answer 17

• urea, water, salts, toxins are not excreted
• this leads to a build up toxins in blood
• less blood is filtered, glomerular filtrate rate decreases
• electrolyte balance is disrupted

Question 18

What problems occur if electrolyte balance is disrupted

Answer 18

K+ = abdominal cramps, muscle spasms, paralysis, cardiac arrest
Na+ = muscle spasms, general weakness, high BP, disorientation

Question 19

Define dialysis

Answer 19

Filtering of blood through a partially permeable membrane

Question 20

Describe the process of Haemodialysis

Answer 20

• blood passes through tubes of dialysis membrane surrounded by dialysate
• blood and dialysate flow in opposite directions - maintain concentration gradient
• lasts ~3 hours
• heparin (blood thinner) is given to prevent blood clots

Question 21

Drawbacks and side effects of haemodialysis

Answer 21

Drawbacks
- required several times a week for 3 hours
- restricts diet (low salt intake)
- decreases lifespan by 5-10 years

Side Effects
- muscle cramps
- low BP
- weakness
- nausea

Question 22

What is a kidney transplant

Answer 22

One kidney is replaced by a donor
- donor and recipient must have a compatible blood type

Question 23

Benefits and drawbacks of kidney transplant

Answer 23

Benefits
+ long term
+ better quality of life & freedom
+ no diet restrictions
+ cheaper

drawbacks
- must take immunosuppressants for life
- not enough donors for demand
- risk of rejection
- risks of surgery
- vulnerable to infection

Question 24

What 4 molecules/ions can urine testing be used for & problems with them

Answer 24

Proteins - high BP, kidney infection
Glucose/ketones -diabetes
Nitrate ions- bacterial infection, UTI

Question 25

How are anabolic steroids tested for

Answer 25

- gas chromatography - mass spectrometry

Question 26

How do pregnancy tests work

Answer 26

**First Zone** Mobile monoclonal antibodies bind to hCG bind to layer of fixed antibodies **Second Zone** Antibodies that didn’t bind to hCG bind to a second layer of antibodies (control line)

Question 27

What substances undergo detoxification in the liver

Answer 27

- alcohol - hydrogen peroxide - lactate - medicinal drugs