Renal physiology

Question 1

What does the kidney have to achieve?

Answer 1

Regulate the composition and volume of body fluids. Retain substances vital to the body such as protein, mineral salts and glucose. Maintenance of acid/ base balance (pH). Excretion of waste products, excess water, soluble toxins and drugs. They also have very important endocrine functions.

Question 2

Why are the kidneys needed?

Answer 2

The body does not have any active water or urea pumps Water can only move in or out of compartments in the direction dictated by osmotic forces i.e. it moves by passive transport

Question 3

To produce urine the nephrons and collecting ducts have to perform three basic functions, what are they?

Answer 3

Glomerular filtration Tubular re-absorption Tubular secretion

Question 4

Answer 4

Question 5

Path of urine drainage?

Answer 5

Question 6

Answer 6

Question 7

Tubular re-absorption

Answer 7

As the filtered fluid flows along the renal tubule and through the collecting duct/s, the tubule cells re-absorb
~99% of the filtered water and many useful solutes. These return to the blood flow, as it flows through the peritubular capillaries and vasa recta.

RE-ABSORPTION REFERS TO THE RETURN OF SUBSTANCES TO THE BLOOD STREAM

Question 8

Tubular secretion

Answer 8

As fluid moves along the renal tubule and through the collecting duct. The tubule and duct cells secrete other materials-wastes, drugs and excess ions.

The wastes are removed from the BLOOD STREAM and secreted by the cells of the tubule and duct into the urine.

(IV contrast agents are voided via this route)

Question 9

Brief explanation of how the kidneys work?

Answer 9

Glomerulus allows glucose, Na, K, H, Cl, HCO3 to pass through to the Bowmans capsule while blocking RBC and Proteins

Proximal tubule- amino acids, glucose, H2O and Na out

Descending limb- H2O out through osmosis, Na in through concentration gradient

Loop of Henle- Na pumped back out

Distal tubule- more filtering

Collecting duct- H2O out through osmosis and leaves behind urine

Question 10

What percentage of amino acids are re-absorbed?

Answer 10

100%

Question 11

What percentage of water is re-absorbed?

Answer 11

99.4%

Question 12

What percentage of Na+ is re-absorbed?

Answer 12

99.4%

Question 13

What percentage of K+ is re-absorbed?

Answer 13

93.3

Question 14

What percentage of HCO3- is re-absorbed?

Answer 14

100%

Question 15

What percentage of glucose is re-absorbed?

Answer 15

100%

Question 16

What percentage of urea is re-absorbed?

Answer 16

50-60%

Question 17

What percentage of inulin is re-absorbed?

Answer 17

0%

Question 18

What is ADH?

Answer 18

Anti-diuretic hormone

Question 19

Where is ADH produced and released from?

Answer 19

Produced by the hypothalamus

Released by the posterior pituitary in response to dehydration or drop in blood volume

Question 20

The effect of hormones on the re-absorption of water

Answer 20

The final portion of the tubule (collecting duct) passes through the hyper-osmotic environment of the medulla.

The epithelium of the collecting duct has the ability to insert (reversibly) aquaporins into the luminal surface, controlling the amount of water reabsorbed. This depends on instructions from a hormone ADH (anti-diuretic hormone), ADH is produced by the hypothalmus and released from the posterior pituitary in response to dehydration or drop in blood volume.

ADH also causes an increase in vasoconstriction, which increases blood pressure.

Question 21

What is ANP?

Answer 21

Atrial natriuretic peptide

Question 22

What does ANP do?

Answer 22

Influence the rate of water excretion vianthe urine.

ANP uses a different mechanism to ADH, when it is present in the blood it causes an increase in the rate of

glomerular filtration.

The NaCl pumps in the loop of Henle only work at a

fixed rate, so, the effect will be to lessen the hyper

-osmolailty of the renal medulla, reducing the osmotic

removal of water from the collecting tube.

ANP is released by the cells in the atria of the heart, it lowers blood pressure by causing vasodilation and promoting loss of water and salt in the urine, reducing blood volume.

Question 23

What is the flow chart of ANP from increase in blood volume to a decrease in blood pressure?

Answer 23

Question 24

Name 3 important endocrine and homeostatic functions of the kidneys?

Answer 24

• Production of the hormone erythropoietin, this stimulates the bone marrow to produce red blood cells.
• The production of renin which is important in the regulation of blood pressure.
• The active form of vitamin D is formed by the kidney, this is vital for healthy bones.