5.2 Excretion

Question 1

What is the function of the renal artery?

Answer 1

Carries oxygenated blood (containing urea and salts) to kidneys

Question 2

What is the function of the renal vein?

Answer 2

Carries deoxygenated blood (that has had urea and excess salts removed) away from kidneys

Question 3

What is the function of the kidney?

Answer 3

Regulates water content of blood and filters blood

Question 4

What is the function of the ureter?

Answer 4

Carries urine from kidneys to bladder

Question 5

What is the function of the bladder?

Answer 5

Stores urine (temporarily)

Question 6

What is the function of the urethra?

Answer 6

Releases urine outside of the body

Question 7

What are the three main areas of he kidney?

Answer 7

• The cortex (contains the glomerulus, Bowman’s capsule, proximal convoluted tubule, and distal convoluted tubule of the nephrons)
• The medulla (contains the loop of Henle and collecting duct of the nephron)
• The renal pelvis (where the ureter joins the kidney)

Question 8

How does blood flow to the nephrons?

Answer 8

• The afferent arteriole (carrying blood from the renal artery) supplies the glomerulus with blood
• Capillaries of the glomerulus rejoin to form the efferent arteriole
• Blood then flows from the efferent arteriole into a network of capillaries that run alongside the nephron and eventually flows into the renal vein.

Question 9

Describe the process of ultrafiltration

Answer 9

• As the afferent arteriole is wider then the efferent arteriole, there is a higher blood and hydrostatic pressure in the glomerulus
• Forces smaller molecules - passes through the basement membrane which acts as a filter and sops large molecules from getting through - out by diffusion into the Bowmans capsule (area of lower hydrostatic pressure) to form filtrate

Question 10

What is the structure of the Bowmans Capsule?

Answer 10

Blood in glomerular capillaries is eparated from the lumen of the Bowmans capsule by:
- 1st layer = endothelium of capillary - each cell perforated by thousands of tiny membrne lined circular holes
- 2nd layer = basement membrane - network of collagen and glycoproteins
- 3rd layer = epithelium of Bowmans capsule - many finger like projections with gaps = cells called podocytes

Question 11

What the adaptations of the proximal convoluted tubule epithelial cell for selective reabsorption?

Answer 11

• Many microvilli on the luminal membrane = increases SA
• Many co transporter proteins in the luminal membrane = aid transport of specific solutes
• Many mitochondria = provide energy for sodium-potassium pump in basal membranes
• Cells tightly packed together = no fluid can pass between the cells

Question 12

Describe the process of selective reabsorption

Answer 12

• Blood that is close to the PCT has very little plasma/water/ions etc
• Sodium-potassium pump in basal membranes diffuse sodium ion out of cells into blood
• Lowers Na+ concentration inside cells = Na+ in filtrate to diffuse into cell down concentration gradient through co transporter proteins - transport another speciic solute with it (e.g glucose)
• Solutes diffuse down concentration gradient into blood = decreases water potential of the blood and creates steep water potential gradient as water moves by osmosis into the blood

Question 13

Describe the process of water reabsorption

Answer 13

• The ascending limb wall is impermeable to water
• Cl- and Na+ are actively pumped out of ascending limb which decreases the water potential in the medulla
• This causes water to move out of the descending limb down the water potenial gradient into the blood
• Na+ and Cl- diffuse into the descending limb down the concentration gradient
• At the Loop of Henle, Cl- and Na+ diffuse out into the medulla, decrease water potential and causes water to move out via diffusion at descending lim and collecting duct = reabsorbed by the blood.

Question 14

How does the liver get a good blood supply?

Answer 14

• Oxygenated blood from heart carried to the liver = hepatic artery= provides oxygen for aerobic respiration
• Blood from the digestive system = hepatic portal vein = allows to absorb nutrients from blood in small intestines
• Deoxygenated blood leaves liver = hepatic vein = flow back to heart

Question 15

What is the function of the gall bladder?

Answer 15

Stores bile which contains
-bile salts for lipid digestion
- bile pigments from the breakdown of hamoglobin
Releases bile into the duodenum via the bile duct

Question 16

What is the internal structure of a liver?

Answer 16

• Made up of hepatocytes
• Arranged in lobules - each supplied with blood by branches of the hepatic artery and hepatic portal vein
• Blood from both mix inside sinusoids (wide capillaries) which exchanges substances from the blood with hepatocytes to perform the livers function
• Each lobule has a central vein = hepatic vein that drains blood away from lobule

Question 17

How does the liver store glycogen?

Answer 17

• Glycogenesis = conversion of glucose to glycogen - insulin triggers this process after pancreas detects too high blood glucose concentration - synthesis of glycogen removes glucose from blood and deceases levels

Question 18

How does the liver store urea?

Answer 18

• Deamination - amino group is removed from each amino acid and combined with an extra H+ to form ammonia
  -The amino acid part that remains = keto acid and can enter the krebs cycle, be converted to glucose or converted to glycogen for storage.
• Ornithine cycle - ammonia combines ith carbon dioxide to form urea which diffuese through the membrane of the hepatocytes and transported to the kidneys for excrretion
• Ammonia is very soluble and highly toxic

Question 19

How does the liver undergo the detoxification of alcohol?

Answer 19

• Alcohol (ethanol) absorbed i stomach is transported in the blood to hepatocytes
• In hepatocytes, alcohol dehydrogenase coverts ethanol to ethanal, the to other molecules that can be used for respiration
• Can cause liver problems - metabolism of ethanol generates ATP = fat stores not used = fatty liver = reduced hepatocyte ability to function = possible cirrhosis

Question 20

Describe the term osmoregulation

Answer 20

The control of water potential of the blood

Question 21

How does ADH help regulate low water levels in the blood?

Answer 21

1. Hypothalamus detects decrease in water potential + stimulates the posterior pituitary gland to release ADH
2. ADH is released in the blood + travels to the collecting duct in the kidney
3. ADH binds to receptors on plasma membrane of collecting duct cells = a series of enzyme controlled reactions + leads to active phosphorylase enzyme
4. Enzyme activates aquaporins that are contained in vesicles = vesicles travel and fuse with the plasma membrane
5. Creates aquaporin channels where water can diffuse into the cell via osmosis down the water potential gradient and into the blood

Question 22

What is the urine like with high ADH levels?

Answer 22

Concentrated + small volume of urine

Question 23

What is urine like when there are low ADH levels?

Answer 23

dilute + large volume of urine

Question 24

What is GFR and how is it used to diagnose kidney failure?

Answer 24

GFR= glomerular filtration rate
If kidney fails, salt and toxins are retained and not excreted = less blood filtered by glomerulus= build up of toxins = decreased GFR

Question 25

What problems can a build up of sodium and potassium ions cause?

Answer 25

Excess potassium ions = ab cramps, tiredness, muscle weakness, paralysis ~ If increase too much, frequency of impulses from SA node may decrease = arrhythmia and cardiac arrest Excess sodium ions = disorientation, muscle spasms, higher blood pressure + general weakness

Question 26

What is hemodialysis?

Answer 26

Ongoing dialysis via the arm (3-5x a week) Counter current flow between blood and dialysis fluid to maintain concentration gradient so that excess urea and ions are diffused out Net movement of useful (glucose + amino acids) = 0 so conc of these in dialysis fluid = conc in blood Anticoagulant added as system is below body temp = stop blood lotting in machine

Question 27

What is peritoneal dialysis?

Answer 27

Ongoing dialysis (daily) Collects waste and blood from washing the peritoneal cavity with dialysis fluid then draining the fluid after a set period of time Pros - increases lifespan, more freeing then hemodialysis Cons - diet restrictive, expensive

Question 28

What is a kidney transplant?

Answer 28

Non functioning kidney is surgically replaced with a functioning kidney Pros - More freedom, diet less restrictive Cons - have to weight for a donor to be found, need to take immunosuppressant drugs, could be rejected or infected

Question 29

How does a pregnancy test work?

Answer 29

Contain monoclonal antibodies specific to hCG (hormone secreted by early embryo) 1. Absorbent membrane dipped into urine sample with hCG 2. hCG binds to complementary monoclonal antibodies which are attached to a dye on test strip 3. hCG complexes diffuse up strip and binds to immobilized antibodies, forming a line of coloured dye

Question 30

How does a urine test for steriods work?

Answer 30

Anabolic steriods are detected in urine via gas chromatography or mass spectrometry It measures the time taken for urine to pass the column compared to time taken for steroids to pass through

Question 31

How is steriod test different to pregnancy test?

Answer 31

In steriod test, sample is vaporized + passed down tube lined with absorption agent = measures retention time Pregnancy test uses liquid urine + antibodies