Normal Renal Physiology II

Question 1

What are some humoral and glomerular regulations of RBF?

Answer 1

Adenosine (local vasodilation)

Angiotensin II

Atrial Naturitic Peptide (ANP)

Aldosterone

Renal Prostaglandins (helps with vascular tone changes)

Macula Densa feedback

Question 2

What is ANP?

Answer 2

Atrial Naturitic Peptide

• Generated in the heart: the more the atrium stretches, the more ANP is released
• Causes release of salt which gets excreted in the kidneys (acts as a diueretic)

Question 3

How much blood does the proximal tubule of the nephrone in the glomerulus absorb back?

Answer 3

70%-80%; less at higher velocities (which indicates increased volume anyhow)

Question 4

Which part of the nephron reabsorbs back most of the blood that is filtered in the kidneys?

Answer 4

The proximal tubule (absorbs 80-90% of the blood that flows through)

Reabsorption rate will vary depending on speed of passing filtrate (high speed indicates lots of volume and will = less reabsorption of filtrate back into systemic circulation)

Question 5

How does the macula densa work to influence RBF?

Answer 5

When it detects lower NaCl content in blood passing through proximal tubule, it signals for increased renin secretion (low NaCl content = low blood volume = low blood flow velocity)

• RAA system will increase efferent arteriolar resistance, resulting in increased difficulty for blood to leave the glomerulus, allowing more NaCl to be reabsorbed (Water follows)
  
  • At the same time, macula densa also signals for decreased afferent arteriolar resistance, helping the process of forcing more filtrate into the glomeruli (it all leads to increased GFR –> more reabsorption of NaCl –> water retention)

**It uses detection of Cl- and pressure to send out the appropriate signals

Question 6

What is normal GFR? How much of cardiac output is devoted to the kidneys?

Answer 6

125 mL/min

20% of CO

Question 7

What makes up the membranes of the glomeruli?

Answer 7

Potocytes make up the inner membrane and endothelial cells make up the outer membrane.

Question 8

Describe how the glomerulus filters out our blood.

Answer 8

The size and charge of potocyte membrane pores determines what is filtered from our blood.

Large/charged subtances will not pass through the membrane and will remain in the blood - electrolytes, bacteria, fluids, smaller proteins pass through into the filtrate (which eventually becomes urine)

Question 9

What is GFR a mathematical function of?

Answer 9

A constant that represents membrane properties x the net filtration pressure which represents blood flow velocity

OR

Essentially: CO X (20% TRBF X 55% Plasma Volume X 20% Filtration Percentage)

Question 10

How many liters of fluids does the kidney filter a day?

Answer 10

180 L/day

Question 11

What is the effect of Angiotensin II on GFR?

Answer 11

It maintains GFR and prevents it from decreasing

Question 12

What do prostaglandins do to GFR?

Answer 12

They increase GFR

Question 13

What does NE and epi do to GFR?

Answer 13

They decrease GFR

Question 14

How are pedi nephrons different from adult nephrons? How does it effect our choice of carrier fluids for them?

Answer 14

They are more primitive and less able to compensate for fluids/electrolyte shifts.

We use more dilute saline (quarter normal) as carrier fluids as a result.

Question 15

Describe the cell layers around a nephron.

Answer 15

Nephrons start as endothelial cells in the glomerulus, surrounded by mesangial cells bordered by podocytes.

Mesangial cells and podocyte cells (Bowman’s capsules) make up the filtration layer.

Mesangial cells have contractile abilities that can change funtion and diameter of nephron tubules.

Question 16

Describe the anatomy of the nephron tract pathway.

Answer 16

Bowman’s capsule (glomerulus) –> proximal convoluted tubule –> loop of Henle –> distal convoluted tubule –> collecting duct

Question 17

At the proximal tubule, what components of our blood are predominantly reabsorbed from the filtrate?

Answer 17

Na+, H2O, and bicarb (for pH maintenance)

Question 18

Describe the activity of electrolytes at the proximal tubule.

Answer 18

Na/K ATPase selectively pumps Na+ back into the blood from the filtrate side; Water follows Na+ back

Cl- follows Na+ to maintain electrolyte neutrality

Every sodium pumped back into the blood results in a K+ or H+ pumped out into the filtrate (impacts acid-base balance)

H+ is preferentially pumped out if our body pH is low (acidosis) over K+

Mg++, Ca++ also make it into the filtrate

Question 19

What is the effect of angiotensin and NE on sodium reabsorption?

Answer 19

Angiotensin and NE enhance reabsorption of Na+ (makes body think it is hypovolemic)

Question 20

What actions occur at the proximal tubule (general)?

Answer 20

Reabsorption of electrolytes and fluids via active pumps and passive filtration.

Signal induction through the macula densa.

Secretion of substances in the bloodstream via active pumps [cephalosporins, ASA, IV dyes (indigo), cimetidine (a histamine blocker), and diuretics]

Question 21

Where is renin released from? what does it affect?

Answer 21

macula densa; affects efferent arteriole diameter

Question 22

How does aldosterone increase Na+ reabsorption and decrease K+?

Answer 22

By increasing the amount of Na+/K+ channels in the proximal tubule