Lecture33

Question 1

What is the percentage of total body water?

Answer 1

55-60% depending on gender.

Question 2

Individual compartments of water storage?

Answer 2

Majority 2/3 stored in ICF (cells)

1/3 stored in ECF of that 1/5 is stored as plasma and 4/5 stored as interstitial fluid of ECF (fluid between cells)

Question 3

Why do females have a lower body water percentage.

Answer 3

Females have a greater fat mass.

Question 4

How often is plasma filtered by kidneys?

Answer 4

60 times a day.

Question 5

What is osmolarity?

Answer 5

Based on the number of osmolarity active ions or solutes , can be estimated by specific gravity.

Question 6

What is the concentration of sodium chloride in ECF?

Answer 6

145mM

Question 7

What are the variations of osmolarity?

Answer 7

Ismo, hypo, hyper osmotic

Question 8

What is Tonicity ?

Answer 8

based on the effect of a solution on cells. An isotonic solution does not change water homeostasis between cells.

Question 9

What is the concentration of Sodium in ECF and ICF?

Answer 9

145 in ECF and 15 in ICF

Question 10

What is the concentration of Potassium in ECF and ICF?

Answer 10

4-5 in ECF and 150 in ICF.

Question 11

Osmolarity of ECF and ICF

Answer 11

Is the same `

Question 12

Where do we lose water?

Answer 12

Breathing
Diffusion and sweat
Kidney filtration
Small intestine

Question 13

What is the driver for water reabsorption?

Answer 13

Sodium

Question 14

Is there active sodium secretion in the kidney?

Answer 14

No this happens in the intestine

Question 15

Where is odium reabsorbed?

Answer 15

67% in Proximal Tubule 
25% in the thick ascending limb
5%n in Distal Tubule 
3% in distal Tubule and collecting duct
Excrete 1%

Question 16

Does the PCT have a tight or leaky epithelium?

Answer 16

leaky

Question 17

Where is tight and leaky epithelium found?

Answer 17

Leaky in PCT

Tight in DCT

Question 18

Reabsorption of water in the nephron?

Answer 18

67% PCT
25% tDLH
2-8% collecting duct

Question 19

What is the main driver of water reabsorption in the PCT?

Answer 19

Glucose transporter SGLT

Question 20

What changes osmolarity?

Answer 20

Changing water content

Question 21

What happens when there is a change in osmolarity?

Answer 21

Water moves between ICF and ECF

Question 22

What allows water to move compartments?

Answer 22

A change in plasma ECF osmolarity is detected by osmoreceptors in hypothalamus which stimulates the pituitary to secrete more or less ADH as ADH alters the permeability of the renal collecting duct. Water will be retained or excreted to balance TBW and stabilize plasma osmolarity and cell volume.

Question 23

Without ADH?

Answer 23

Without ADH, you can easily flush out extra volume = Diuresis

Question 24

With ADH?

Answer 24

Tight epithelium becomes more leaky, water can be absorbed (aquaporins) = anti-diurese (urine becomes more concentrated.

Question 25

What is the role of Macula Densa cells?

Answer 25

Can sense changes in sodium reaching the distal tubule and therefore perfusion of the nephron, if it is too low this leads to release of renin for juxtamedullary cells.

Question 26

What is Aldosterone?

Answer 26

a corticosteroid hormone which stimulates absorption of sodium by the kidneys and so regulates water and salt balance