chapter 15 p4

Question 1

The protective layer of fat around kidneys

Answer 1

(renal capsule) is impressive - these vital organs are well-cushioned from physical damage in the body

Question 2

strcutrie of real kidney diagram

Answer 2

Question 3

It is very difficult to see an entire tubule but different parts of the tubules can be identified :

Answer 3

Question 4

To make the nephrons more visible

Answer 4

• a drop of hydrogen peroxide can be applied onto the cut surface of the kidney (wearing safety glasses and gloves].
• There will be rapid effervescence (foaming), after this is wiped off, the renal tubules, collecting duct, and loops of Henle should be a little clearer to see as shown by strings of bubbles.
• In a section through the cortex you will see Bowman’s capsules and glomeruli, as well as sections through proximal and distal convoluted tubules.
• The lumen of the distal tubules tends to be bigger and more open than those of proximal tubules which can be helpful in identifying them.
• In a section through the medulla you will see mainly loops of Henle and collecting duct.

Question 5

In a transverse section you will see the

Answer 5

lumens of the tubules - the collecting ducts are larger than the thick ascending loops of Henle while the thin-walled descending limbs are only visible at very high magnifications.

Question 6

In a longitudinal section you will see

Answer 6

the parallel tubes - low magnifications give an overall impression whilst higher magnifications enable you to see individual tubules.

Question 7

kidney microscope

Answer 7

Question 8

The functions of the nephrons:
Ultrafiltration:
p1

Answer 8

• The first stage in the removal of nitrogenous waste and osmoregulation of the blood is ultrafiltration.
• Ultrafiltration in the kidney tubules is a specialised form of the process that results in the formation of tissue fluid in the capillary beds of the body and it is the result of the structure of the glomerulus and the cells lining the Bowman’s capsule
• The glomerulus is supplied with blood by a relatively wide afferent (incoming) arteriole from the renal artery.
• The blood leaves through a narrower efferent (outward) arteriole and as a result there is considerable pressure in the capillaries of the glomerulus.
• This forces the blood out through the capillary wall - it acts rather like a sieve.

Question 9

The functions of the nephrons:
Ultrafiltration:
p2

Answer 9

• Then the fluid passes through the basement membrane - scientists are increasingly recognising the basement membrane as an important factor in the filtration process.
• The basement membrane is made up of a network of collagen fibres and other proteins that make up a second ‘sieve’.
• Most of the plasma contents can pass through the basement membrane but the blood cells and many proteins are retained in the capillary because of their size.
• The wall of the Bowman’s capsule also involves special cells called podocytes that act as an additional filter.

Question 10

The functions of the nephrons:
Ultrafiltration:
p3

Answer 10

• They have extensions called pedicels that wrap around the capillaries, forming slits that make sure any cells, platelets, or large plasma proteins that have managed to get through the epithelial cells and the basement membrane do not get through into the tubule itself.
• The filtrate which enters the capsule contains glucose, salt, urea, and many other substances in the same concentrations as they are in the blood plasma
• The process is so efficient that up to 20% of the water and solutes are removed from the plasma as it passes through the glomerulus.

Question 11

glomerular filtration rate.

Answer 11

The volume of blood that is filtered through the kidneys in a given time

Question 12

ultrafiltration diagram

Answer 12

Question 13

Reabsorption:

Answer 13

• Ultrafiltration removes urea, the waste product of protein breakdown, from the blood but it also removes a lot of water along with the glucose, salt, and other substances which are present in the plasma.
• Many of these substances are needed by the body - for example, glucose is used for cellular respiration and is never normally excreted.
• The ultrafiltrate is also hypotonic to (less concentrated than) the blood plasma.
• The main function of the nephron alter the Bowman’s capsule is to return most of the filtered substances back to the blood.

Question 14

Answer 14

Question 15

The proximal convoluted tubule:

Answer 15

In the proximal convoluted tubule all of the glucose, amino acids, vitamins, and hormones are moved from the filtrate back into the blood by active transport.
Around 85% of the sodium chloride and water is reabsorbed as well - the sodium ions are moved by active transport while the chloride ions and water follow passively down concentration gradients.
The cells lining the proximal convoluted tubule have clear adaptations:

Question 16

The cells lining the proximal convoluted tubule have clear adaptations:

Answer 16

they are covered with microvilli, greatly increasing the surface area over which substances can be reabsorbed
they have many mitochondria to provide the ATP needed in active transport systems.

Question 17

Once the substances have been removed from the nephron

Answer 17

, they diffuse into the extensive capillary network which surrounds the tubules down steep concentration gradients.
These are maintained by the constant flow of blood through the capillaries.
The filtrate reaching the loop of Henle at the end of the proximal convoluted tubule is isotonic (at same concentration) with the tissue fluid surrounding the tubule and isotonic with the blood.
At this stage over 80% of the glomerular filtrate has been reabsorbed back into the blood.
This remains the same regardless of the conditions in the body.

Question 18

Answer 18

Question 19

The loop of Henle: p1

Answer 19

The loop of Henle is the section of the kidney tubule that enables mammals to produce urine more concentrated than their own blood.
Different areas of the loop have different permeabilities to water and this is central to the way the loop of Henle functions.
It acts as a countercurrent multiplier, using energy to produce concentration gradients that result in the movement of substances such as water from one area to another.

Question 20

The loop of Henle: p2

Answer 20

Cells use ATP to transport ions using active transport and this produces a diffusion gradient in the medulla.
The changes that take place in the descending limb of the loop of Henle depend on the high concentrations of sodium and chloride ions in the tissue fluid of the medulla that are the result of events in the ascending limb of the loop.

Question 21

diagram of the proximal convoluted tubule

Answer 21

Question 22

Answer 22

Question 23

The descending limb p1

Answer 23

• leads from the proximal convoluted tubule.
• This is the region where water moves out of the filtrate down a concentration gradient.
• The upper part is impermeable to water but the lower part of the descending limb is permeable to water and runs down into the medulla.
• The concentration of sodium and chloride ions in the tissue fluid of the medulla gets higher and higher moving through from the cortex to the pyramids, as a result of the activity of the ascending limb of the loop of Henle.
• The filtrate entering the descending limb of the loop of Henle is isotonic with the blood.
• As it travels down the limb, water passes out of the loop into the tissue fluid by osmosis down a concentration gradient.

Question 24

The descending limb p2

Answer 24

• It then moves down a concentration gradient into the blood of the surrounding capillaries (the vasa recta).
• The descending limb is not permeable to sodium and chloride ions, and no active transport takes place in the descending limb.
• The fluid that reaches the hairpin bend is very concentrated and hypertonic to the blood in the capillaries

Question 25

The first section of the ascending limb of the loop of Henle is very …

Answer 25

permeable to sodium and chloride ions and they move out of the concentrated solution by diffusion down a concentration gradient.

Question 26

In the second section of the ascending limb

Answer 26

• sodium and chloride ions are actively pumped out into the medulla tissue fluid against a concentration gradient.
• This produces very high sodium and chloride ion concentrations in the medulla tissue.
• Importantly, the ascending limb of the loop of Henle is impermeable to water, so water cannot follow the chloride and sodium ions down a concentration gradient.
• This means the fluid left in the ascending limb becomes increasingly dilute, while the tissue fluid of the medulla develops the very high concentration of ions that is essential for the kidney to produce urine that is more concentrated than the blood.
• This is a key part of the countercurrent multiplier system.
• By the time the dilute fluid reaches the top of the ascending limb it is hypotonic to the blood again, and it then enters the distal convoluted tubule and collecting duct.