Urine Formation

Question 1

Three main processes of urine formation

Answer 1

Glomerular filtration
Reabsorption
Tubular secretion

Question 2

First step in urine formation?
Which structure carries it out?
Name of this process?

Answer 2

Filtration of blood
Glomerular
Glomerular filtration

Question 3

On average, amount of blood filtered by the kidneys

Compare to blood pumped out by ventricles

Answer 3

1100-1200ml of blood per minute

1/5th of the blood pumped out by each ventricle in a minute

Question 4

What causes filtration of blood?
How many laters is the blood filtered through?
Name the layers

Answer 4

Glomerular capillary blood pressure
3
Endothelium of glomerular blood vessels
Epithelum of Bowman’s capsule
Basement membrane between the above two layers

Question 5

Cells of Bowman’s capsule:
Type
Name
Arranged how and why?

Answer 5

Epithelial
Podocytes
Arranged in an intricate manner so as to leave some minute spaces called filtration slits or slit pores

Question 6

Which constituent of the plasma does not pass onto lumen of Bowman’s capsule, in untrafiltration?

Answer 6

Proteins

Question 7

GFR
What is it?
Value

Answer 7

Glomerular Filtration Rate
Amount of filtrate formed by kidneys per minute
125ml/minute (18 litres per day)

Question 8

How is GFR regulated?

Name one example

Answer 8

Kidneys have built in mechanisms
One such efficient mechanism is carried out by JGA (Juxta Glomerulus Apparatus)
JGA is a special sensitive region formed by cellular modifications in the DCT and the afferent arteriole at the location of their contact
A fall in GFR can activate JG cells to release renin which can stimulate the glomerular blood flow and thereby the GFR back to normal

Question 9

Urine amount released

Answer 9

1.5 litres per day

Question 10

Why is urine amount released so less compared to filtrate volume?

Answer 10

Nearly 99% of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption

Question 11

Which cells perform reabsorption?

What type of mechanisms used?

Answer 11

Tubular epithelial cells in different segments of nephron

Active or passive mechanisms

Question 12

Which substances are reabsorbed actively?

Answer 12

Glucose
Amino acids
Na+

Question 13

Which substances are absorbed passively?

Answer 13

Nitrogenous wastes

Reabsorption of water also occurs passively in the initial segments of the nephron

Question 14

Which cells secrete certain substances during urine formation?
What substances are secreted?
Why is this an important step in urine formation?

Answer 14

Tubular cells
H+, K+, ammonia
Maintenance of ionic and acid base balance of body fluids