Renal Physio

Front 1

reanal blood supply is app. what percentage of the cardiac output?

Back 1

Approximately 20%.
About 99% of the blood goes to the cortex and the remaining 1% goes to the medulla.

Front 2

Which part of the kidney contains most of the nephrons?

Back 2

The cortex.

Front 3

Where are the juxtamedullary nephrons found?

Back 3

In the medulla. These nephrons possess a greater concentrating ability.

Front 4

The kidney possesses two capillary beds arranged in a series. What are these 2 capillary beds?

Back 4

The glomerular capillaries
The peritubular capillaries

Glomerular capillaries are under high pressure for filtration.
peritubular- These are at low pressure, and are anatomically situated around the tubules.

Front 5

Each kidney has about 250,000 nephrons. True/False

Back 5

False. each kidney may contain up to 1 million nephrons.

Front 6

What exactly is a nephron?

Back 6

The nephron is made up of a glomerulus and its tubule.

Front 7

What are the regions that make up the tubule?

Back 7

The proximal tubule
Loop of Henle
Distal tubule(which continues and empties into the collecting duct).

Front 8

What is the three phase process that results in urine formation?

Back 8

Filtration
Reabsorption
Excretion

Front 9

Where exactly does filtration take place?

Back 9

It takes place through the semipermeable walls of the glomerular capillaries which are impermeable to proteins and large molecules.
The filtrate should be free of protein and cellular bodies.

Front 10

How is hydrostatic pressure controlled?

Back 10

Hydrostatic pressure is controlled by the afferent and efferent arterioles, and maintained by arterial pressure.

Front 11

Approximately how much renal plasma flow is filtered each minute?

Back 11

About 125ml/min. This is termed the glomerular filtration rate.

Front 12

What is intended by the term "autoregulation"?

Back 12

When there is a change in arterial blood pressure, there is a resultant constriction or dilation of the afferent and efferent arterioles.

Front 13

Define glomerular tubular balance.

Back 13

When there is a diminution of GFR, there is a resulting decrease in the fluid flow rate within the tubule.

Front 14

At the loop of Henle, there is greater time for reabsorption of sodium and chloride ions. Is this a true statement?

Back 14

It is. As a result, there is a decrease in the number of sodium and chloride ions reaching the distal tubule which is detected by the macula densa.

Front 15

Regarding the above answer, what affect or influence does this have on the afferent arteriole?

Back 15

It decreases the resistance in the afferent arteriole which causes an increase in renal blood flow.
Additionally, there is also a release of renin from the juxtaglomerular apparatus which activates angiotensin 11 production resulting in constriction of the efferent arteriole.

Front 16

Regarding answer # 16, what is the final result of this mechanism?

Back 16

These act to increase the hydrostatic pressure in the glomerular capillary bed and return the GFR to normal boundaries.

Front 17

What is the Juxtaglomerular complex?

Back 17

It is composed of macula densa cells and the juxtaglomerular cells.

Front 18

What are macula densa cells?

Back 18

These are specialized distal tubular epithelial cells which can detect concentrations of chloride and smooth muscle cells (juxtaglomerular cells) in the walls of the afferent and efferent arteriole.

Front 19

What do the macula densa cells secrete?

Back 19

They secrete renin, which is an enzyme that converts the plasma protein angiotensinogen to angiotensin 1.

Front 20

How is angiotensin 11 formed?

Back 20

This occurs via angiotensin converting enzyme(ACE) which is created in minute quantities in the lungs, the proximal tubule and other tissues.

Front 21

What is the effect of angiotensin 11?

Back 21

It causes vasoconstriction and an increase in systemic blood pressure.
It can stimulate as well, the adrenal gland to produce aldosterone, which results in sodium and water retention which also increases blood volume.

Front 22

What is the required stimulus necessary for the production of aldosterone?

Back 22

It is a fall in blood volume which leads to a fall in perfusion pressure in the kidneys. (Negative feedback)

Front 23

The proximal tubule reabsorbs about 65% of all solute. True/False

Back 23

True. This includes under normal conditions 100% of glucose and amino acids, 90% of bicarbonate and about 85% of inorganic phosphate and water.

Front 24

Regarding proximal tubule reabsorption, reabsorption is exclusively an active process. True/False

Back 24

False. It may be either active or passive.

Front 25

For reabsorption, what is meant by active transport?

Back 25

Active transport requires a sum of energy to move solute against an electrochemical or a concentration gradient. In fact, it is the main requirement for O2 consumption by the kidney.

Front 26

What is Passive transport?

Back 26

This is where reabsorption occurs down an electrochemical, pressure or concentration gradient.

Front 27

Within the tubule where is urine most likely to be concentrated?

Back 27

Within the loop of Henle. This is possible resulting from the high concentration of solute in the substance or interstitium of the medulla.

Front 28

Within the region of the loop of Henle how is high concentration maintained?

Back 28

This high concentration of solutes is maintained by the counter current multiplier. This system is an arrangement by which the high medullary interstitial concentration of solute is maintained giving the kidney the ability to concentrate urine.

Front 29

The loop of Henle is the counter current multiplier and the vasa recta is the counter current exchange. True/False

Back 29

True.

Front 30

Is the descending loop of Henle, permeable to water?

Back 30

Yes. It is however impermeable to solute. water moves out or exits via osmosis and the fluid in the tubule becomes increasingly hyperosmotic or hypertonic.

Front 31

How can the thin section of the ascending loop of Henle be described with regards to permeability?

Back 31

It is impermeable to water, but permeable to solute, especially sodium and chloride ions.

Front 32

What is the fluid tonicity within the ascending loop of Henle?

Back 32

As sodium and chloride ions move out down the concentration gradient, the fluid within the tubule becomes firstly isotonic then hypotonic as more ions leave.

Front 33

What is the activity of urea in this ascending region of the loop?

Back 33

Urea which was mostly absorbed into the medullary interstitium from the collecting duct, diffuses into the ascending limb.
This keeps the the urea within the interstitium of the medulla where it also plays an important role in urine concentration.

Front 34

The thick section of the ascending loop and early distal tubule are impermeable to water. True/False

Back 34

True. Sodium and chloride ions are activelt transported out resulting in increased fluid hypotonicity.

Front 35

What is the vasa recta?

Back 35

It is a portion of the peritubular capillary system which enters the medulla where the solute concntration in the interstitium is high.

Front 36

What is a function of the vasa recta?

Back 36

It acts with the loop of Henle to concentrate the urine by a mechanism of counter current exchange.

Front 37

What would happen if the vasa recta no longer functioned?

Back 37

The high concentration of solutes in the medullary interstitium would be washed out.

Front 38

What is the justification and purpose of the exchanger-multiplier system combined?

Back 38

Solutes diffuse out of the vessels conducting blood towards the cortex and into the vessels descending into the medulla while water is doing the opposite, moving from the descending vessels to the ascending vessels. As a result, this system allows the solutes to recirculate in the medulla and water, to bypass it.

Front 39

What is the affect of ADH on concentration?

Back 39

The final concentration of urine depends upon the quantity of ADH(antidiuretic hormone). ADH is secreted by the posterior lobe of the pituitary.
If ADH is present, the distal tubule and the collecting duct become permeable to water.

Front 40

There are cells within the hypothalamus, osmoreceptors, which are sensitive to changes in osmotic pressure of the blood. True/False

Back 40

True. if there is low water intake, there is a consequential rise in osmotic pressure of the blood, and if there is an excess of water intake, the reverse is true.