L1 Renal Intro

Question 1

• Define the general function of the kidneys.
• Define balance, steady state, positive andnegative balance.
• Review the functional anatomy of the kidney.
• Describe the filtration apparatus of the kidney.
• Know the route of blood flow in the kidney.
• Describe the innervation of the kidney.
• Understand the components of renal function.

Question 2

What are the functions of the kidney?

Answer 2

• Regulation of water and inorganic ion balance.
• Regulation of body fluid osmolality and volume.
• Excretion of metabolic waste.
  – urea, uric acid, creatinine
• Excretion of foreign chemicals.
  – drugs, pesticides, food additives
• Secretion of hormones.
  – Renin (enzyme) (juxtaglomerular [= granular] cells)
  – Erythropoietin (interstitial cells)
  – 1, 25-dihydroxycholecalciferol (Calcium homeostasis)

Question 3

What are 3 types of balance that the kidney maintains?

What is a positive or negative balance?

Answer 3

The kidney maintains, water, sodium and potassium balance.

A positive balance is when the input is greater than the output.

A negative balance is when the input is less than the output.

Steady state is when input = output

Question 4

What are some examples of negative and positive sodium and water balances?

Answer 4

Negative sodium and water balance:
– Diarrhea
– Diuretic medication
– Insufficient aldosterone (adrenal dysfunction)

Positive sodium and water balance:
– Excess steroids (anabolic substances)
– Congestive heart failure
– Salt-retaining renal disease

Question 5

Which area of the kidney appears granular and which appears striated?

Answer 5

The cortex (outer layer) is granular

The medulla is striated

Question 6

What occurs in the Renal Corpuscle?

Answer 6

The glomerulus w/ tufts of specialized capillaries filters water and electrolytes into bowman’s capsule but excludes proteins and RBCs

When plasma exits the glomerular capillaries and enters bowman’s capsule it becomes urine

Question 7

What occurs in the Proximal convoluted tubule?

Answer 7

Filters and reabsorbs 2/3 of water, electrolytes, glucose and proteins and secretes toxins or other waste products.

The PCT is isoosmotic and doesn’t concentrate urine but it changes the composition

Question 8

What occurs in the loop of henle (LOH)?

Answer 8

The LOH generates an osmotic gradient to dilute urine. Ion pumps pump ions into the interstitial space.

Urine is less concentrated in the ascending limb than descending limb.

Question 9

What occurs in the juxtaglomerular apparatus (JGA) and what are the specialized cell types?

Answer 9

The JGA is the tubular portion that comes in contact with the renal corpuscle between the afferent and efferent arterioles.

Macula Densa cells: monitor flow, helps control GFR

Extraglomerular mesangial cells: unknown function

Granular cells: secrete renin, controls BP and Volume

Mesangial cells: in capillary tufts, contract in respnse to AngII

Question 10

What occurs in the distal convoluted tubule?

Answer 10

– some reabsorption of water and
ions
– fluid is iso- or hyposmotic

Question 11

What occurs in the collecting duct?

Answer 11

• Collecting is target of hormones, other portions of tubule function “automatically”
  -water permeability controlled by
  vasopressin
  – site where final concentration of
  urine is adjusted (urine may be
  iso-, hypo- or hyperosmotic)

Question 12

What is the difference between cortical and juxtamedullary nephrons?

Are nephrons in parallel or series?

Answer 12

Cortical nephrons: glomeruli in out cortex, LOH don’t extend to inner medulla

Juxtamedullary nephrons: Glomeruli near
corticomedullary border. LOH long & extend
deep into the innermedulla.
-Ability to produce concentrated
urine is proportional to
the number of juxtamedullary
nephrons

All nephrons function in
parallel; collecting ducts
shared by many nephrons

Question 13

What are the 3 layers of the filtration barrier in the renal corpuscle?

Answer 13

1. capillary endothelium
2. basement membrane
   (basal lamina)
3. capsular epithelial cells
   » podocytes, foot
   processes
   » Slits between podocytes
   constitute the path of
   filtrate flow into BC

Question 14

What are the two renal capillary beds?

Answer 14

Two capillary beds:
– Glomerular
– Peritubular: (2 parts)
» Cortical
» Vasa Recta:
—–follow LOH of
juxtamedullary nephrons
—–found in medulla

Question 15

Describe the blood supply to the nephrons.

Answer 15

Cortical arteries give off afferent arterioles.

One afferent arteriole per glomerulus.

Fluid not filtered goes to efferent arteriole.

Then to peritubular capillaries.,
which supply blood to the nephron.

Note that there are two arterioles (afferent and efferent) and
two capillary beds (glomerular and peritubular) in series

Question 16

Describe the Vasa Recta.

Answer 16

Specialized peritubular capillaries of
juxtamedullary nephrons.

Long, hairpinshaped capillaries
that follow the LOH.

• *Supply nutrients to medullary tissue** and
• *important for recovery of water.**

Question 17

Describe renal sympathetic innervation.

Parasympathetic?

Answer 17

Renal sympathetic nerves release dopamine and norepinephrine that act on a-1 receptors (primarily on afferent arterioles) to cause vasoconstriction.

SNS reduces RBF and GFR but is counteracted by PGE₂ and PGI₂ which oppose the effect to maintain RBF and GFR when SNS increases.

Only extreme SNS innervation will reduce RBF and GFR.

SNS also innervates G cells (beta receptors) and causes release of the enzyme renin

NO Renal Parasympathetics