Physiology - RENAL

Question 1

What is normal range of plasma oncotic pressure?

Answer 1

25 - 28 mmHg

Question 2

Identify the normal body volumes of (as a percentage): 
Water 
Proteins and related substances 
Minerals 
Fat

Answer 2

Water: 60%
Proteins and related substances: 18%
Minerals: 7%
Fat: 15%

Question 3

What factors affect total body water?

Answer 3

Age: Newborns (75%) have more water than older people (50%)
Obesity: Obese people have less boy water % (Due to higher fat content)
Gender: Females have less body water % than males (Due to higher fat content)

Question 4

Identify the tonicity of the following:

1. Isosmotic = ?
2. Hypoosmotic = ?
3. Hyperosmotic = ?

Answer 4

1. Isosmotic = Isotonic
2. Hypoosmotic = Hypotonic
3. Hyperosmotic = Hypertonic

Question 5

Which structure has the MOST water content percentage?

Bone, Fat or Organs

Answer 5

Organs = 70 - 80% 
Bone = 35 % 
Fat = 10 - 20 %

Question 6

How is body water calculated in L?

Answer 6

L = 60/100 (% of body water as a fraction) x 70 (Kg of individual)

Question 7

What does extracellular and intracellular fluid consist of?

Answer 7

Extracellular: Plasma + interstitial fluid
Intracellular: Fluid surrounding the cells which is separated from plasma

Question 8

Formula for volume distribution?

Answer 8

V = Q/C 
V = Volume distribution 
Q = Amount of dye known added to body compartment 
C =  Concentration measurement after mixing (body compartment + dye)

Question 9

What type of cells separate the plasma and interstitial fluid?

Answer 9

Endothelial cells

Question 10

Identify the % of body weight of the following and the volume fraction of the following:

Total body water (TBW) = ?
Extracellular volume (ECV) = ?
Intracellular volume (ICV) = ?
Plasma = ?
Interstitial fluid = ?

Answer 10

Total body water (TBW) = 60% of body weight 
Extracellular volume (ECV) = 20% of body weight (1/3 of TBW)
Intracellular volume (ICV) = 40% of body weight. (2/3 of TBW)
Plasma = 5% of body weight. (1/4 of ECV)
Interstitial fluid = 15% of body weight. (3/4 of ECV)

Question 11

What indicators can be use to measure total body water?

Hint: 2

Answer 11

• Antipyrine

- Tritiated water/heavy water

Question 12

What indicators can be use to measure extracellular fluid?

Hint: 4

Answer 12

• Na (Sodium)
• Inulin
• Thiosulfate
• I-iothalamate

Question 13

What indicators can be use to measure intracellular fluid ?

Answer 13

• Intracellular fluid = Total body water - extracellular fluid

Question 14

What indicators can be use to measure plasma volume?

Hint: 2

Answer 14

• Radioactive albumin

- Evans blue dye (strongly binds to albumin which stays in the plasma compartment)

Question 15

What indicators can be use to measure blood volume?

Hint: 3

Answer 15

• Radiolabelled chromium-51
• Techetium-99m
• blood volume = plasma volume/ haematocrit

Question 16

What indicators can be use to measure interstitial fluid?

Answer 16

• (Calculated as Extracellular fluid volume - plasma volume)

Question 17

How is interstitial fluid measured?

Answer 17

• Interstitial fluid = Extracellular fluid - plasma volume

Question 18

Compare the charge and osmolality of the intracellular compartment and extracellular compartment.

Answer 18

• The intracellular compartment has MORE total charges than the extracellular compartment. This is due to higher protein content in the intracellular compartment and that proteins are polyvalent.
• Osmolality in each compartment is the same
  1. Extracellular
  Plasma:
• Cations: Sodium, calcium, potassium, magnesium
• Anions: Chlorine, bicarbonate, protein
  Interstitial:
• Cations: sodium, potassium, calcium
• Anions: Chlorine, bicarbonate, sulphate

2. Intracellular
   - Cations: Potassium, magnesium, calcium, sodium
   - Anions: Organic phosphates e.g. ADP, proteins, proteins, bicarbonate

Question 19

Describe the extracellular fluid

Answer 19

Extracellular

• Both plasma and interstitial fluid is similar, containing similar amounts of sodium, chloride and bicarbonate
• There is more protein in the plasma compartment than interstitial
• There is more sodium and less chloride in plasma due to the negatively charged protein

Question 20

Describe the intracellular fluid

Answer 20

Intracellular

• Different cells = different functions, therefore different charges
• The main ion are organic phosphate e.g. ATP

Question 21

How is plasma and interstitial fluid composition maintained/controlled?

Answer 21

1. Capillaries - tend to hold more proteins, proteins don’t readily move across the membrane
2. The Gibbs-Donnan Effect….Proteins attracting cations (+) and repelling anions (-). Therefore plasma has a sodium and lower chloride than interstitial fluid.

Question 22

How is extracellular and intracellular fluid composition maintained/controlled?

Answer 22

1. Cell membrane is MORE selectively permeable than capillary endothelium
2. Selective ion pumps e.g. Na+/K+ -ATPase
3. The Gibbs-Donnan effect because of the proteins contained within cells

Question 23

How is total body water maintained/controlled?

Answer 23

• Thirst, kidney, Antidiuretic Hormone (ADH)

Question 24

What is the function of the kidneys

Answer 24

• Vitamin D production (active form 125-ihydryoxy) is made in kidneys
• Gluconeogenesis
• Regulation of RBC - erythropoietin
• Maintain arterial blood pressure - sodium balance, renin (causes vasoconstriction), vasoactive substances, prostaglandins (causes vasodilation)
• Detox
• Acid-base regulation (production of bicarbonate if needed)
• Water and electrolyte balance

Question 25

Describe the 4 types of filtration in the kidneys?

Answer 25

1. Free filtration - The substance is full secreted with urine - E.g. inulin 2. Partial reabsorption - Some of the substance is secreted, however some of it is reabsorbed back into the blood - E.g. Vitamin C 3. Complete reabsorption - The substance is 100% reabsorbed and is NOT secreted - E.g. Glucose (in healthy people) 4. Secretion - The substance is fully excreted with urine out the body - E.g. Para-amino

Question 26

What is normal renal blood flow in males and females?

Answer 26

``` Males = 1.2L/min Females = 900mL/min ```

Question 27

How is renal plasma flow (RPF) calculated?

Answer 27

Renal plasma flow = Renal Blood flow (RBF) x (100 - Hct%)/100 Hct% = % of hematocrit blood

Question 28

What is autoregulation? and the normal autoregulatory range

Answer 28

- Autoregulation is a compensatory mechanisms which helps to minimise the changes within the glomerular filtration rate (GFR) and real blood flow (RBF) at different blood pressure values - It is an intrinsic response (no hormonal or neural control) - There are 2 types of autoregulation: 1. Myogenic 2. Tubularglomeulerar feedback macular densa - Range = 80mmHg - 170mmHg

Question 29

Compare blood flow and oxygen levels in the kidneys

Answer 29

Kidneys have a high blood flow rate- accounting for 20-25% of blood flow from resting cardiac outflow, and is considerably higher than blood flow to other organs e.g. brain. This is necessary for the blood to be filtered and is by no means equilevant to the oxygen levels supplied to the kidneys (which is smaller)

Question 30

Renin is produced why which cells?

Answer 30

Granular cells (juxtaglomerular cells) located in the afferent arteriole

Question 31

Describe the Rennin-angiotensin system

Answer 31

1. Rennin is produced by granular cells in the afferent arteriole 2. Rennin cleaves angiotensinogen (produced in the liver) to produce angiotensin 1 3. Angiotensin I is then cleaved by angiotensin converting enzyme to angiotensin II. (Note angiotensin converting enzyme also metabolises bradykinin - stopping vasodilation). 4. Angiotensin II acts up AT1 and AT2 receptors (however action occurs mainly on AT1 receptors)

Question 32

What is a juxtaglomerular apparatus and what does it consist of?

Answer 32

- Function: Regulate blood pressure and the filtration rate of the glomerulus. - Located: Vascular pole of the glomerulus - It is formed by the distal convoluted tubule and the glomerular afferent arteriole. Four components - Juxtaglomerular cells: smooth muscle cells located in the walls of the afferent arterioles which produce rennin and are innervated by sympathetic nervous system - Macular dense cells: Are located between the thick acceding loop of Henle and distal convoluted tube. They sensitive to ionic content and water volume. - Mesangial cells and mesangial matrix: Located between the glomerular capillaries. Produces substances which contribute to the matrix and immune complex clearance via phagocytosis. - Glomerular capillaries

Question 33

How is Rennin release controlled?

Answer 33

1. Renal baroreceptor - drop in BP in afferent arteriole --> release of renin 2. Macular densa - reduction in NaCl delivery --> release of renin 3. Renal sympathetic nerves - increase renin release via B1 receptor 4. Feedback control a. Increase in intravasular volume, blood pressure and improved renal perfusion inhibit release (long feedback loop) b. Short feedback loop - AngII acts on JG cells to inhibit release 5. Other a. Increase - chronic hypokalaemia, PGE2 b. Decrease - acute hypernatremia, ADH, ANF

Question 34

What affects does angiotensin II have on the vascular system?

Answer 34

- Arteriolar vasoconstriction (most potent known vasoconstriction)

Question 35

What affects does angiotensin II have on the renal system?

Answer 35

- Vasoconstriction - Proximal sodium reabsorption - Contraction of mesangial cells - decrease the area for filtration

Question 36

What affects does angiotensin II have on the adrenal system?

Answer 36

- Aldosterone release

Question 37

What affects does angiotensin II have on the neural system?

Answer 37

- Facilitates sympathetic activity - Inhabits vagus = decrease of baroreflex - Increases ADH secretion - Increases ACTH secretion - Dipsogen - stimulates thirst

Question 38

Renal sympathetic nerve effects:

Answer 38

1. Vasoconstriction via a1-adrenoreceptors | 2. Renin release by B-adrenoreceptors on JG cells

Question 39

What type of renal neurons supply the major afferent and efferent arterioles of the kidney, JG cells and proximal tubules?

Answer 39

Sympathetic noradrenergic neurons

Question 40

What is normal Glomerular Filtration Rate (GFR)?

Answer 40

Males: 125ml/min - 180L/day

Question 41

Describe the histology of the glomerular structure

Answer 41

- Increased capillary loops = increase in SA filtration - Mesangial cells and mesangial matrix - located between capillary loops. The cells are phagocytic and contractile (alter SA for glomerular filtration) + substance secretion - Podocytes - located on the glomerular capillary and extend over the capillaries to form numerous filtration slits (that are covered by slit diaphragms). It functions to filtrate - only letting small molecules pass. Podocytes can reduce GFR by contracting close to slits = reduction in SA or filtration

Question 42

Identify the various filtration barrier features that regulate the movement across the basement membrane of the kidneys

Answer 42

- Fenestrations - Glycoialoprotein coat: negatively charged to prevent movements of ions e.g. in minimal change nephropathy - Slit diaphragm: Restrict substance size - Podocytes and foot processes: Form filtration slits - Basement membrane: three layers (main barrier)

Question 43

Identify the factors that can affect GFR

Answer 43

- Renal blood flow | - Changes in pressure glomerular capillaries (Pgc)