L1: general renal function and body fluids

Question 1

Location of the kidneys

Answer 1

• fist sized bean shaped organs located retroperitoneally in the flanks or mid-back region
• under the lower part of the rib cage either side of the vertebral column
• right kidney is slightly lower due to the liver

Question 2

Major functions of the kidneys

Answer 2

• filtration: clearance of metabolic waste products especially nitrogenous wastes and excess ions, drugs and toxins
• production of renin, erythropoietin, prostaglandins, vitamin D (more detail at 16:25)
• regulation of body fluids: volume of extracellular fluid; osmolality of body fluid; concentration of electrolytes; pH of blood, blood pressure, red blood cells

Question 3

Major waste products produced by the body

Answer 3

Ammonia:

• from protein catabolism
• extremely toxic and soluble in water
• converted to urea - breakdown of amino acids
• converted to uric acid - breakdown of nucleotides

Creatinine:

• continuously produced during muscle breakdown
• serum creatinine used as a test of kidney function
• high serum creatinine indicates poor kidney function or disease
• since much mass is relatively constant day to day creatinine production normally remains unchanged on a daily basis

Proteins are the major contributor to waste production

Question 4

Why do we need to regulate body fluids?

Answer 4

Cannot be dehydrated or over hydrated with water
Kidneys control urine volume

Osmolality of body fluids is very critical
Extreme variation in osmolality causes cells to shrink, swell and even burst
Damages cell structure and disrupts normal cell function

Question 5

Fluid compartment water location

Answer 5

Total volume of water = 60% of body weight, 45L in a 70kg male:
Intracellular fluid is all the fluid inside cells = 40% of body weight /30L
Extracellular fluid (20% of body weight/15L) is all fluid outside of cells = plasma (20% of ECF/3L) + interstitial fluid (80% of ECF/12L)

37:30

Question 6

Boundaries of the fluid compartments

Answer 6

Boundaries surrounding plasma which is the blood vessel. Functional barrier is the capillary endothelium.
Functional barrier for intracellular fluid is the cellular membrane.

Kidneys control volume of all compartments but only have access to the plasma.

Question 7

How does fluid move across the boundaries?

Answer 7

Fluid moves across the cellular membrane by osmosis.

Fluid moves via diffusion across the capillary endothelium.

Question 8

What forces are in place to allow the diffusion of fluid across capillaries?

Answer 8

Starlings forces:

• mmHg
• water and electrolytes freely cross
• moves by diffusion
• changes in hydrostatic pressure will lead to fluid movement

Osmotic pressure:

• mosm/Kg H2O
• water freely crosses but not ions
• moves by osmosis
• changes in the ionic content of IF and ICF will lead to H2O movement,

Question 9

Osmolality of fluids in each compartment

Answer 9

Fluid osmolality should be the same in each compartment - plasma, interstitium and intracellular fluid
However the composition of ions is different

Question 10

What is normal plasma osmolality?

Answer 10

Normal body osmolality is 275-295 mOsm/Kg H2O (285)