Unit 10 - Kidney & Nephron

Question 1

What is the functional filtration unit of a kidney

Answer 1

A nephron

Question 2

How many nephrons are in each kidney?

Answer 2

1 to 1.5 million

Question 3

What does the nephron do?

Answer 3

Filter, reabsorb & secrete stuff that is in the blood.

Question 4

What are the two basic divisions of the nephron?

Answer 4

Renal corpuscle and renal tubule

Question 5

What is the Renal corpuscle?

Answer 5

Bowmans camsule - Cup-shaped portion of the renal tubule. Inner layer forms part of the filter that helps clean your blood.
Glomerulus - a small knot of capillaries tucked into bowman’s capsule. Blood enters via the afferent arteriole & exits via the efferent arteriole. Maintains relatively high pressure in glomerulus which ensures good filtration. The capillary cells are “holey” & so form the other parts of the filter.

Question 6

How much of your total body blood supply passes through the kidneys every minute?

Answer 6

20-25%!

Question 7

What is the glomerulus filtration rate?

Answer 7

125 mL/min

Question 8

What is the proximal convoluted tubule?

Answer 8

Located nearest Bowman’s capsules & very twisted. Most reabsorption occurs here.

Question 9

What is the Loop of Henle?

Answer 9

Hairpin portion of the nephron. Long descending limb, a loop, then a straight ascending limb. Water reabsorption.

Question 10

What is the distal convoluted tubule?

Answer 10

From the ascending limb, the tubule once again gets twisty. Secretion & some reabsorption occurs.

Question 11

What are the collecting tubules?

Answer 11

Extensions of the DCT that ultimately merge thus collecting filtered material from several nephrons & ultimately draining into the renal calyces.

Question 12

What are the facts that affect the glomerular filtration rate? (GFR)

Answer 12

Prerenal, renal, postrenal

Question 13

What are pre renal factors? Cardiac output

Answer 13

Normal cardiac output is about 5000 mL/min
20% or 1200 mL/min is routed through both kidneys.
Varies between 12-30%
Any decrease in cardiac output - decreased GFR
Any increase in cardiac output - increased GFR

Question 14

What are pre renal factors? Arteriole pressure

Answer 14

Increases in blood pressure - increased glomerular pressure - increased GFR

Question 15

What are pre renal factors? Blood Volume

Answer 15

Decreased blood volume - decreased RBF - reduced GFR

Increase in blood volume would result in renal blood flow and increased GFR

Question 16

What are renal factors? Glomerular blood pressure

Answer 16

Pressure inside the capillaries that causes fluid to pass through the glomerular membrane into Bowman’s capsule, is about 8kPa (60 mm Hg).

Question 17

What is Filtration pressure

Answer 17

The net pressure forcing fluid through the glomerular membrane

Question 18

What is the permeability of glomerular membrane

Answer 18

The glomerular membrane is approximately a hundred time more porous than other capillaries found in the body.

Question 19

Number of viable nephrons

Answer 19

The GFR is a function of the number of viable nephrons.
Not a direct relationship (there is some reserve capacity within each nephron to increase the filtration rate if the total number of nephrons declines).

Question 20

what is tubular necrosis (death)

Answer 20

The effect of tubular necrosis is reduced GFR
Two possible causes:
Casts and cellular debris obstruct tubular lamina increasing the intratubular pressure, the net effect - decreased net filtration pressure and GFR.
Glomerular filtrate leaks back across the damaged renal tubular epithelium - “break-leak” hypothesis

Question 21

What is renal calculi?

Answer 21

Urinary obstruction causes a significant reduction in the pressure gradient across the glomerular capillaries, which in turn reduces the GFR.
Similar to the “break leak” idea

Question 22

What are post renal Factors?

Answer 22

Extrarenal Obstruction
Urethral occlusion can result from blasser, pelvic, or prostatic neoplasms; pro statism; surgical accidents; medications; calculi; pus; and blood clots.
The impact on the GFR is the same as in the case of renal calculi

Question 23

What do the kidneys do?

Answer 23

Filter blood of metabolic wastes
Reabsorb any “good” stuff that was filtered
Recrete unwanted ions, drugs, hormones out of the blood into urine.
Regulate blood volume, blood pressure & composition (pH, ions)
Regulate red blood cell synthesis (erythropoietin)
Activate Vit D

Question 24

What is fluid balance?

Answer 24

Fluid losses - Fluid gains

Question 25

Water is ….

Answer 25

50 to 60 % of our body weight
55% is found inside our cells (ICF)
45% is in the ECF

Question 26

Fluid Functions

Answer 26

Fluids can move between compartments relatively easily, so a change in one compartment will ultimately affect ALL compartments.

Question 27

Plasma is used to..

Answer 27

transport nutrients & wastes throughout the body - its volume is fairly stable. A change in this fluid volume alters blood volume (& P), which impacts blood flow

Question 28

Fluid balance within body compartments

Answer 28

Body fluids are more than just water.
The types and amounts of solutes are also important to overall homeostasis
Electrolytes (ions-charged particles) and proteins are the major solutes in the body fluids
A solute is any dissolved substance & that water follows solutes.

Question 29

Factors affecting fluid balance

Answer 29

Pressure
If fluid pressure is higher in any one compartment, this pressure difference will cause fluids to move, until fluid pressure is equal in both compartments
Normally, blood pressure is fairly constant, so it already has little effect on fluid movements in the body.
Solute concentration and Osmosis
Electrolyte levels not only impact fluid levels, BUT also affect the functioning of all excitable cells.
So changes in electrolytes can impact blood volume and cell function.

Question 30

Three categories that affect water balance

Answer 30

Organic compounds of low molecular weight
Organic compounds of high molecular weight
The inorganic electrolytes.

Question 31

What are Organic compounds of low molecular weight?

Answer 31

Small molecular size compounds such as glucose, urea, amino acids, and lactate diffuse rather freely across capillary membranes but not across cell membranes.
Have little tendency to effect the movement of water. However, if present in large quantities, they cause the retention of water and thereby do influence the total body water.

Question 32

what are the Organic compounds of high molecular weight?

Answer 32

The organic substances considered in this category are mainly the plasma proteins which are the only dissolved substances in plasma that do not diffuse readily through the capillary membranes.
It is the plasma proteins that are responsible for the osmotic gradient at the plasma capillary membranes.

Question 33

What are inorganic electrolytes?

Answer 33

The osmolality of substances that ionize in solution is higher than that of substances that do not ionize.
The main cation in the ECF is sodium and the main cation in the intracellular fluid is potassium.

Question 34

How can plasma osmolality be calculated?

Answer 34

Osmolality equals 2 x [Na+] + [glucose] + [urea nitrogen]

Question 35

Na equation

Answer 35

[ ( Na+ + K+ ) ] TB

[ Na+ ]s = [ H2O ] TB

Question 36

What is the tubule adjustment of water? (relation to the kidneys)

Answer 36

As the kidneys can only process blood, they rely on a countercurrent exchange mechanism to significantly adjust water levels.
This occurs in the Loop on Henle

Question 37

What are the conditions necessary for countercurrent exchange in the kidneys?

Answer 37

1. The flow of fluid in the tubules be in opposite directions.
2. The tubules be in close proximity to one another.
3. An osmotic gradient exists between the tubular fluid compartment and interstitial fluid
4. there is a low medullary blood flow.

Question 38

What is fluid regulation?

Answer 38

A balance between GFR and tubular reabsorption.

Question 39

remember…

Answer 39

When the GFR is 125 mL/min, net tubular absorption is 124 mL/min resulting in the formation of 1.0 mL/min of urine for a 24 hr volume of 1440 mL.

At a GFR of 150 mL/min, tubular reabsorption is145 mL/min resulting in the production of 5 mL of urine each minute. The 24-hour urine output would then be 7200 mL (5 times the normal output)

Question 40

What are the two major methods of controlling water levels?

Answer 40

ADH
When the hypothalamus detects that blood has too much solute (too salty) it releases ADH from the post. Pit. ADH opens the water channels in the collecting ducts which returns water to the blood, lowering the saltiness of the blood.
Aldosterone
When the juxtaglomerular apparatus detects low renal blood volume or changes in solute levels, they release renin. Renin activates angiotensin II which in turn does 3 things. Increases BP, releases aldosterone to cause the kidneys to absorb more Na, and stimulates the release of catecholamines from the adrenal medulla and increases sympathetic activity.