5.2 Excretion as an example of homeostatic control

Question 1

Define excretion (1)

Answer 1

The removal of metabolic waste from the body.

Question 2

What are the 3 main excretory products?

Answer 2

Carbon dioxide
Nitrogenous waste compounds
bile pigments

Question 3

In what three ways is C02 transported around the body? (3)

Answer 3

5% dissolved in plasma
10% carbaminohaemoglobin
85% HCO3- hydrogen carbonate

Question 4

How does carbon dioxide lower the pH of blood? (2)

Answer 4

CO2+H20—–> H203 carbonic acid

H203 dissociates——-> H+ + HCO3-

Question 5

How do deamination and urea formation occur? (2)

Answer 5

AA + Oxygen—->keto acid + ammonia

ammonia + co2——>urea + H20

Question 6

Name three functions of the liver (3)

Answer 6

storage of glycogen/maintain glucose conc
bile synthesis
breakdown RBC's
breakdown of hormones
storage of vitamins
breakdown excess AA- urea
detoxification of alcohol

Question 7

Describe the process of the detoxification of alcohol.

Answer 7

ethanol dehydrogenase breaks down ethanol into ethanal
ethanal is dehydrogenated again by ethanal dehydrogenase
forming ethanoic acid
The hydrogen ions are conbined with NAD to form reduced NAD

Question 8

What are the four tubes running through/along side a hepatocyte?

Answer 8

Bile duct
hepatic vein
hepatic portal vein
hepatic artery

Question 9

What does a kupffer cell do? (1)

Answer 9

digests old RBC’s

Question 10

In which direction does the hepatic artery carry blood? Is the blood oxygenated or deoxygenated?

Answer 10

away from heart to hepatocytes (oxygenated)

Question 11

In which direction does the hepatic portal vein carry blood? Is it oxygenated/deoxygenated?

Answer 11

from digestive system to liver

Question 12

In which direction does the hepatic vein carry blood?

Answer 12

Away from liver towards heart vena cava

Question 13

Define ultrafiltration. (1)

Answer 13

The filtration of the blood at a molecular level under pressure.

Question 14

The renal artery splits to form many afferent arterioles which each lead to a knot of capillaries called the WHAT?

Answer 14

Glomerulus

Question 15

What is each glomerulus surrounded by

Answer 15

Bowman’s capsule

Question 16

What are the 3 layers of the barrier between the capillary’s blood and the lumen of the bowmans capsule?(6)

Answer 16

Endothelium of the capillary- gaps between cells, and pores in the cells allowing plasma out of capillary
Basement membrane- collagen fibres and glycoproteins stops big molecules through like RECs
Epithelial cells of Bowmans capsule- called podocytes, have foot processes ensure gaps between cells so fluid can pass into Bowmans capsule

Question 17

What does the blood plasma contain? (5)

Answer 17

Water
Amino acids
Glucose
Urea
Inorganic materials ions (sodium, chloride, potassium)

Question 18

Why is peritoneal dialysis fluid replaced four times a day whereas haemodialysis patients only need treatment three times a week?

Answer 18

peritoneal removes less waste than heamo
haemodialysis is constantly refreshed
haemodialysis maintains conc grad but peritoneal conc grad reduces

Question 19

Where is glucose selectively reabsorbed into the kidneys?

Answer 19

the proximal convoluted tubule

Question 20

How are glucose and amino acids selectively reabsorbed?

Answer 20

sodium ions are actively pumped out of the cell
so conc of sodium decreases creating conc grad
sodium ions diffuse into cell through cotransport protein carrying either glucose or AA
water moves into cell by osmosis
glucose and aa diffuse into blood

Question 21

How are the cells lining the tubule specialised to achieve reabsorption? (4)

Answer 21

microvilli increase sa
cotransport proteins in membrane
other end of cell also folded to increase sa and has sodium potassium pumps
many mitochondria for lots of atp

Question 22

How are the cells lining the tubule specialised to achieve reabsorption? (4)

Answer 22

microvilli increase sa
cotransport proteins in membrane
other end of cell also folded to increase sa and has sodium potassium pumps
many mitochondria for lots of atp

Question 23

How do we alter the permeability of our collecting ducts? (4)

Answer 23

ADH detected by cell surface receptors
enzyme controlled reactions
causing vesicles containing water peprmeable channels (aquaporins) to fuse with membrane
so more water can be reabsorbed

Question 24

How do we alter the concentration of ADH in the blood?

Answer 24

Osmoreceptors in hypothalamus shrink when wp is low
stimulates neurosecretory cells in hypothalamus
ADH made in cell body (in hypo) moves down axon to terminal bulb in pituitary gland where its stored in vesicles.
when neurosecretory cells are stimulated by osmoreceptors, they carry actionpotentials down the axon and release ADH by exocytosis

Question 25

How do pregnancy tests work? (5)

Answer 25

urine onto stick
hCG binds to antibodies attached to blue bead
mobile antibodies move down test stick
if hCG is present it binds to fixed antibodies holding bead in place forming blue line
mobile antibodies with no hCG attached bind to another fixed site to show test is working

Question 26

Define the ornithine cycle

Answer 26

A series of biochemical reactions that convert ammonia to urea