7. Excretory system and osmoregulation

Question 1

Which mediators are produced by the kidneys?

Answer 1

The kidneys produce the enzyme renin, the hormone erythropoietin and the “vitamin” calcitriol.

Question 2

How are the kidney functions influenced?

Answer 2

The physiological functions of the kidney are influenced by ADH, aldosterone, parathyroid hormone,
ANP, BNP and angiotensin II.

Question 3

What is the route of waste products from blood to urine?

Answer 3

1. Blood enters the kidney nephron
2. The blood is filtered in the glomerulus into the Bowman’s capsule, part of the renal tube
3. Waste products enter the proximal convoluted tube and travel through the loops of Henle
4. First part: descending loop. Second part: ascending loop. In the loops of Henle, osmoregulation takes place
5. Waste products travel to the distal convoluted tube
6. Multiple distal convoluted tubes coming from different nephrons join together at the collecting duct, travels towards a papilla
7. Minor calyx –> major calyx
8. Into the renal pelvis which empties in the ureter

Question 4

What is the function of ADH in the kidneys?

Answer 4

The amount of water removed from the collecting ducts is controlled by a hormone called antidiuretic hormone (ADH) produced by the pituitary gland, situated at the base of the brain. When the blood becomes more concentrated, as happens when an animal is deprived of water, ADH is secreted and causes more water to be absorbed from the collecting ducts so that concentrated urine is produced. When the animal has drunk plenty of water and the blood is dilute, no ADH is secreted and no or little water is absorbed from the collecting ducts, so dilute urine is produced. In this way the concentration of the blood is controlled precisely.

Question 5

Describe the reabsorption of molecules and location in the nephron

Answer 5

Proximal convoluted tube: reabsorption of glucose, amino acids, potassium, calcium ions and water
Henle’s loop (descending): water
Henle’s loop (ascending): sodium
Distal convoluted tube: hydrogen and potassium ions entre the filtered fluid to be secreted
Collecting duct: concentration of fluid because of reabsorption of water

Question 6

What is the name for the entry point to the kidney for nerves, blood vessels, ureters and lymphatics?

Answer 6

Hilum is the name of the point of attachment between an organ
and its supply services.

Question 7

Where are all of the glomeruli of the kidney located?

Answer 7

in the cortex

Question 8

What structure does the blood from the afferent arteriole enter?

Answer 8

Afferent (incoming) arteriole enters the glomerulus, the efferent
arteriole leaves the glomerulus.

Question 9

Which part of the nephron is impermeable to water?

Answer 9

The ascending limb. Hence volume of filtrate does not change as it passes through the ascending limb.

Question 10

How is the high blood pressure (or, hydrostatic pressure) in the glomerulus maintained?

Answer 10

The efferent (outgoing) arteriole has a smaller diameter than the afferent arteriole, hence the glomerulus is a high pressure area. This aids the movement of dissolved substances through the filtration membrane.

Question 11

What molecule catalyses the formation of angiotensin I?

Answer 11

Renin is an enzyme that catalyses the reaction that forms angiotensin I from angiotensinogen.

Question 12

What is the kidney tubule’s response to a rise in blood pH?

Answer 12

Bicarbonate ions are secreted into the filtrate, while hydronium ions are absorbed from the filtrate into the blood.

Question 13

Describe the blood (not filtrate fluid) flow in the kidney

Answer 13

afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries.

Question 14

The descending limb of the Loop of Henle is permeable to water so water diffuses out of the descending limb into the interstitial fluid. What happens to this water?

Answer 14

Water (and solutes) that are reabsorbed from the filtrate diffuse into the peritubular capillaries and ascending vasa recta for return to the blood.

Question 15

What is the macula densa?

Answer 15

The macula densa cells are chemoreceptors that respond to
changes in Na + & Cl − ions.

Question 16

What part of the nephron performs the majority of the reabsorption of materials from the filtrate?

Answer 16

The proximal convoluted tubule (the fi rst part or the renal tubule) absorbs most of the required material.

Question 17

What is the function of columns and pyramids in the kidney?

Answer 17

In the medulla, columns are filled with blood vessels and pyramids with collecting ducts

Question 18

What is the resulting effect of renin being released by the kidney?

Answer 18

Renin catalyses the formation of angiotensin I from angiotensinogen. ACE then converts angiotensin I to angiotensin II. Aldosterone is released from the adrenal cortex due to angiotensin II. Angiotensin II also promotes systemic vasoconstriction (not just in efferent arteriole).

Question 19

Which hormone causes increased sodium reabsorption in the kidney?

Answer 19

Aldosterone stimulates the active absorption of sodium (and the secretion of potassium) from the filtrate.

Question 20

To what does the “juxtaglomerular apparatus” refer?

Answer 20

The “juxtaglomerular apparatus” refers to certain cells of the distal convoluted tubule where it touches the afferent arteriole. The juxtaglomerular = macula densa cells (of the DCT wall) andgranular cells (of the afferent arteriole wall).

Question 21

In the nephron, if the afferent arteriole dilates and the efferent arteriole constricts, what happens?

Answer 21

The granular cells of the afferent arteriole respond to low blood
pressure by releasing renin. As a result, angiotensin II would form which causes systemic vasoconstriction, which increases blood pressure, which dilates the afferent arteriole and increases glomerular filtration rate.

Question 22

What effect does aldosterone have?

Answer 22

Aldosterone stimulates the active absorption of sodium (Na) from the filtrate (and the secretion of potassium).

Question 23

What is the purpose of ANP in urine production?

Answer 23

2 things: ANP triggers the dilation of the afferent arterioles and constriction of efferent arterioles which increases GFR. It also decreases sodium reabsorption from the filtrate. Hence urine volume increases (and blood volume and pressure decreases).

Question 24

The nephron of the kidney consists of which of the following structures?

Answer 24

glomerulus and renal tubule

Question 25

What is the function of angiotensin II?

Answer 25

Angiotensin II promotes general vasoconstriction (which raises
blood pressure), and stimulates the adrenal cortex to release aldosterone.

Question 26

Which section of the renal tubule is permeable to urea?

Answer 26

PCT is permeable to urea, so as volume of filtrate in PCT
decreases due to absorption of water, urea concentration in filtrate increases. This promotes passive reabsorption of urea along its concentration gradient.