Excretory Products and their Elimination

Question 1

Main function of the excretory system

Answer 1

Elimination of nitrogenous waste products

Question 2

Types of nitrogen excretion

Answer 2

1. Ammonotelism
2. Ureotilism
3. Uricotelism

Question 3

Ammonotelism

Answer 3

• Ammonia is formed as the result of deamination of amino acids
• Simplest form of nitrogenous waste and excreted from body surfaces or gill surfaces
• Ammoniotelic organisms- aquatic invertebrates, freshwater fish, aquatic amphibians

Question 4

Ureotelism

Answer 4

• Excretion of urea and uric acid as nitrogenous waste
• Ammonia metabolized is converted to urea, which is then sent to the liver. From the liver it is filtered out into the blood and excreted out by the kidneys.
• Ureotelic organisms- Mammals, aquatic reptiles, semi-aquatic amphibians

Question 5

Uricotelism

Answer 5

• The main nitrogenous waste product is uric acid
• The white part of the faeces excreted by birds contains uric acid and urates
• Uricotelic organisms- Birds, terrestrial reptiles, snails and insects

Question 6

Steps of urine formation

Answer 6

1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion

Question 7

Ultrafiltration

Answer 7

• Takes place in Glomerular Filtration step of urine formation
• Blood with waste products reaches the kidneys at the Bowman’s capsule.
• The network of capillaries in the glomerulus acts as a mesh and filters blood constituents except proteins.
• This is known as ultrafiltration.
• The filtered plasma is known as Glomerular filtrate

Question 8

How much blood is filtered

Answer 8

5 litres of blood in the body

Question 9

How much blood circulates in the kidneys per minute?

Answer 9

1250 ml

Question 10

Quantity of plasma in 1250 ml of blood

Answer 10

650 ml plasma

Question 11

How much glomerular filtrate is produced from 650 ml of plasma?

Answer 11

125 ml

Question 12

What is the composition of the glomerular filtrate?

Answer 12

H2O, Na+, H+, K+, Cl-, HCO3-, Glucose, Creatine, Amino acids, Urea and Uric acid

Question 13

Amount of
1. Glomerular filtrate produced per day
2. Urine formed per day

Answer 13

1. 180 litres of glomerular filtrate/day
2. 1.5 litres of urine/day

Question 14

Why is there such a drastic difference in the amount of urine formed per day and GFR formed per day?

Answer 14

• There are many useful substances that need to be sent back to the blood
• A concentrated hypertonic urine needs to be eliminated

Question 15

Tubular reabsorption

Answer 15

Filtrate that moves out of the glomerulus contains essential substances that need to be sent back to the body through the blood.
This is done by selective reabsorption by the renal tubules.

Question 16

what is reabsorbed

PCT

Answer 16

• Proximal convoluting tubule (70-80% of electrolytes and water)
• Reabsorption into the blood- H2O, Na+, K+, Glucose, amino acids, Cl-, HCO3-, Urea

Question 17

what is reabsorbed

DCT

Answer 17

• Distal convoluting tubule
• Reabsorption into the blood H2O, Na+, Cl-

Question 18

what is reabsorbed

Collecting duct

Answer 18

Reabsorption into the blood- H2O, Na+, HCO3-, Urea

Question 19

Tubular secretion

Answer 19

Tubular secretion is the transfer of materials from the peritubular capillaries to the renal tubular lumen and occurs mainly by active transport and passive diffusion

Question 20

what is secreted

PCT secretion

Answer 20

Secretion into the urine: H+, NH4, Urea, and Creatine

Question 21

Loop of Henle secretion

Answer 21

Secretion into the urine: Urea

Question 22

DCT secretion

Answer 22

Secretion into the urine: K+, H+, Drugs, antibiotics, anabolic steroids

Question 23

Composition of urine

Answer 23

• Creatinine, ammonia, and uric acid: 0.2%
• Dissolved salts and other ions: 2.8%
• Urea: 2%
• Water: 95%

Question 24

Countercurrent mechanism

Answer 24

Countercurrent mechanism in the kidneys is the process of using energy to generate an osmotic gradient that enables you to reabsorb water from the tubular fluid and produce concentrated urine

Question 25

Renal calculi

Answer 25

The crystals of salts (calcium, uric acid) present in the urine solidify into insoluble stones
Excruciating pain when the stone gets stuck in the ureter

Treatment:
* Surgery
* Shock wave lithotropy which pulverizes the stone so that the fragments are small enough to be passed out in the urine

Question 26

Glomerulonephritis

Answer 26

• Bright’s Disease
• Inflammation of the glomeruli in the nephrons of the kidney
• Glomerular membrane- highly permeable and it allows infiltration of blood and proteins

Symptoms
* Intense pain
* redness swelling and heat in the glomeruli of the nephrons

Question 27

Uraemia

Answer 27

• Accumulation of urea in the blood
• Reduced glomerluar filtration
• develops after seven days of anuria- absence of urine

Question 28

Renal failure

Answer 28

• Decrease or cessation of glomerular filtration

1. Acute renal failure- kidneys stop functioning abruptly
   * Suppression of urine flow
2. Chronic renal failure- progressive, irreversible decline of rate of glomerular filtration
   * Persons suffering from CRF need dialysis and possibly a kidney transplant operation.

Question 29

Effects of renal failure

Answer 29

Effects of renal failure
* Oedema- fluid retention
* Anaemia and osteomalacia- two main problems associated wwith renal failure
* Elevated blood potassium levels that can lead to cardiac arrest

Question 30

Where is the fistula created furing haemo-dialysis?

Answer 30

A fistula is created between the radial artery/branchial artery and the cephalic vein for haemo-dialysis to be carried out

Question 31

UTI

Answer 31

• Urinary tract infection
• Caused due to increased acidity of the urine and that region
• Acidity causes E. coli ( * underline) to multiply
• Intensity of UTI depends on the number of microorganisms and the region where is takes place

Symptoms
* Burning sensation while urinating
* Pain in the lower back
* Radiating pain