Excretion In Humans and osmoregulation - The kidneys

Question 1

What are the three main roles of the kidneys and how do they do this?

Answer 1

1) removal of urea from the blood
2) adjustment of salt levels in the blood
3) adjustment of water content of the blood
They do this by filtering stuff out of the blood under high pressure, and then reabsorbing the useful things. The end product is urine.

Question 2

What is the first step of blood passing through the nephron?

Answer 2

Ultrafiltration:

1) blood from the renal artery flows through the glomerulus.
2) a high pressure is built up which squeezes water, urea, salts and glucose out of the blood and into the Bowman’s capsule.
3) the membranes between the blood vessels in the glomerulus and the Bowman’s capsule act like filters, so big molecules like proteins and blood cells are not squeezed out. They stay in the blood. The filtered liquid in the Bowman’s capsule is known as the glomerular filtrate.

Question 3

What is the glomerulus?

Answer 3

A bundle of capillaries at the start of the nephron

Question 4

What is the second step of blood passing through the nephron?

Answer 4

Reabsorption:
As the filtrate flows along the nephron, useful substances are selectively reabsorbed back into the blood:
1) all the glucose is reabsorbed from the proximal convoluted tubule. This involves the process of active transport across the concentration gradient.
2) sufficient salt is reabsorbed. Excess salt isn’t.
3) sufficient water is reabsorbed from the collecting duct into the bloodstream.

Question 5

What is the third step of blood passing through the nephron?

Answer 5

Release of wastes:
The remaining substances (including water, salt and urea) form urine. This continues out of the nephron, through the ureter and down to the bladder, where it is stored before being realised via the urethra.

Question 6

How is water lost from the body?

Answer 6

Sweating, breathing and weeing

Question 7

How is water taken into the body?

Answer 7

Food and drink

Question 8

What is osmoregulation?

Answer 8

The body has to constantly balance the water coming in against the water going out

Question 9

What is ADH?

Answer 9

Anti-diuretic hormone which controls the amount of water reabsorbed in the kidney nephrons

Question 10

What does ADH do?

Answer 10

ADH makes the nephrons more permeable so more water is reabsorbed back into the blood

Question 11

What is negative feedback?

Answer 11

If the water content gets too high or too low a mechanism will be triggered that brings it back to normal

Question 12

Low blood water content means…

Answer 12

Increased ADH production and more water reabsorbed into the kidneys

Question 13

High blood water content means…

Answer 13

Decreased ADH production and less water reabsorbed

Question 14

Where is urea produced?

Answer 14

In the liver

Question 15

Is blood entering the glomerulus under high pressure or low pressure?

Answer 15

High pressure

Question 16

Where is urine stored before being released from the body?

Answer 16

The bladder

Question 17

What is the bladder?

Answer 17

Where urine is held in the body before it is released into the environment.

Question 18

What is the Bowman’s capsule?

Answer 18

The cup shaped structure at the start of a nephron where ultrafiltration occurs.

Question 19

What is a collecting duct?

Answer 19

The tube at the end of a nephron, where additional water is reabsorbed from urine.

Question 20

What are convoluted tubules?

Answer 20

The two sections of a nephron closely associated with a capillary; selective reabsorption of glucose takes place in the proximal convoluted tubule.

Question 21

What is the glomerular filtrate?

Answer 21

The liquid in the Bowman’s capsule produced by ultrafiltration.

Question 22

What is the glomerulus?

Answer 22

A small knot of capillaries associated with a Bowman’s capsule.

Question 23

What is the hypothalamus?

Answer 23

The part of the brain that monitors water content of the blood.

Question 24

What is the loop of henlé?

Answer 24

A large loop of the nephron which dips into the medulla of the kidney.

Question 25

What is a nephron?

Answer 25

A tiny kidney tubule where ultrafiltration and reabsorption take place to produce urine.

Question 26

What is osmoregulation?

Answer 26

The regulation of the concentration of water in the blood.

Question 27

What does the urinary system include?

Answer 27

Kidneys, ureters, bladder and urethra

Question 28

What is selective reabsorption?

Answer 28

The reabsorption of more of some substances than others.

Question 29

What is ultrafiltration?

Answer 29

Filtration on a molecular scale, as happens between the glomerulus and Bowman’s capsule.

Question 30

What are the ureters?

Answer 30

Tubes that connect the kidneys to the bladder. The urethra is a tube that connects the bladder to the outside of the body.

Question 31

What is urine?

Answer 31

A liquid waste produced by kidneys, containing water, urea and salts.