3.7 Homeostasis And The Kidney

Question 1

What is homeostasis

Answer 1

Maintenance of a constant internal environment

Question 2

Why is homeostasis so important

Answer 2

Cells can function efficiently, independently of the fluctuations in the conditions of the external environment

Question 3

Some examples of homeostasis

Answer 3

Core body temperature
Glucose levels
Solute potential

Question 4

How does negative feedback work

Answer 4

Corrects deviations from the set point

Question 5

Examples of negative feedback

Answer 5

Insulin
Antidiuretic hormone

Question 6

Sequence of events that go on for a negative/positive feedback to happen

Answer 6

Input is detected by a receptor which monitors the condition and provides input to the control centre which then evaluates information and provides output to an effector which will initiate a response designed to take away the deviation and restore the norm

Question 7

How does positive feedback work

Answer 7

By enhancing the size of the stimulus

Question 8

Examples of positive feedback

Answer 8

Oxytocin during childbirth

Question 9

What parts of the nephron are in the cortex

Answer 9

Bowmans capsule
Proximal convoluted tubule
Distal convoluted tubule

Question 10

What parts of the nephron are in the medulla

Answer 10

Descending limb
Loop of henle
Ascending limb
Collecting duct

Question 11

Simply, what happens during ultrafiltration

Answer 11

Urea is removed from the blood as the glomerulus and Bowmans capsule work together to filter the blood under high pressure

Question 12

How is there high pressure during ultrafiltration

Answer 12

The Blood supply to the glomerulus enters through the afferent arteriole and leaves through the efferent arteriol
The efferent is narrower than the afferent which increases the hydrostatic pressure of the blood plasma

Question 13

3 part filter

Answer 13

• endothelium of capillaries of Glomerulus has fenestrations between the cells to increase filtration
• podocytes of Bowman’s Capsule have finger like projections called pedicels which wrap around the capillaries, the filtration slits between pedicels allow free passage of the filtrate from blood in the lumen of the Bowman’s capsule but not proteins and cells as they’re mostly too large
• basement membrane of capillaries and podocytes act as a selective barrier which allow water and small molecules to pass from the blood into the nephron

Question 14

How is the efficiency of ultrafiltration increased

Answer 14

• pedicels increase surface area
• there is a short diffusion distance between podoctyes and the capillary
• filtration slits between pedicels increase the concentration gradient between the tissue fluid

Question 15

What is the mechanism of ultrafiltration

Answer 15

• the large hydrostatic pressure causes small soluble molecules such as glucose, amino acids, salt, water and urea to be forced out of the plasma and they enter the channels between the pedicels and the capillary walls. The concentration then increases in the channels do they enter the Bowman’s capsule and form the glomerular filtrate
• the basement membrane of the capillary acts as a selective barrier between the blood and the nephron and allows small sized particles through whilst plasma proteins and cells remain in the blood due to their larger size

Question 16

Net filtration pressure of ultrafiltration

Answer 16

The hydrostatic pressure is greater than the combined effect of the osmotic pressure of the plasma and fluid pressure of the filtrate so water and small molecules pass out of the plasma

Question 17

What is osmoregulation

Answer 17

Control of the water content and solute composition of bodily fluids such as blood, tissue fluid and lymph

Question 18

What is excretion

Answer 18

Elimination of waste products of metabolism from an organism

Question 19

What biological molecule is used in excretion and why

Answer 19

Amino acids cannot be stored so excess amino acids are deaminated in the liver so the amino group forms ammonia which is converted to urea and transported into the blood plasma

Question 20

Where does selective reabsorption occur

Answer 20

Proxima convoluted tubule

Question 21

What is reabsorbed during selective reabsorption

Answer 21

All glucose
All amino acids
Most water
Most salts

Question 22

Adaptations for selective reabsorption

Answer 22

• cells lining the tubule have a large surface area due to the microvilli and basal channels and also due to the length and large numbers of nephrons per kidney
• cells contain many mitochondria which provide ATP for active transport
• the close association with capillaries provides a short diffusion distance between cells and peritubular capillaries
• tight junctions between adjacent cells prevent the seepage of reabsorbed materials back into the filtrate

Question 23

How are mineral ions and salts reabsorbed?

Answer 23

Facilitated diffusion and active transport into the epithelial cells

Question 24

How are glucose and amino acids reabsorbed?

Answer 24

Secondary active transport using a co-transport mechanism with Na+. Glucose is co-transported with 2 Na+ by facilitated diffusion into the cell. Na+ and glucose move separately into capillaries

Question 25

How is 90% of water reabsorbed?

Answer 25

Osmosis

Question 26

How are some filtered proteins and some urea reabsorbed

Answer 26

Diffusion

Question 27

What is the concentration of the filtrate at the end of the PCT, relative to the blood plasma

Answer 27

Isotonic

Question 28

Where does osmoregulation occur

Answer 28

Loop of Henle

Question 29

Permeability of ascending and descending limbs to water

Answer 29

Ascending - impermeable Descending - permeable

Question 30

Counter-current multiplier

Answer 30

1. Na+ and Cl- are actively pumped out of the filtrate in the ascending limb into the tissue fluid causing a low water potential in the tissue fluid 2. This causes water to leave the descending limb by osmosis and is carried away by the vasa recta 3. Contents of the descending limb become more concentrated as they reach the tip of the Loop of Henle due to the loss of water 4. As the filtrate passes up the ascending limb it becomes more dilute due to loss of ions

Question 31

Simply, the role of antidiuretic hormone

Answer 31

Role in negative feedback restoring the normal osmotic concentration in the blood

Question 32

How is antidiuretic hormone released

Answer 32

It is secreted by the hypothalamus and stored in the posterior lobe of the pituitary

Question 33

What happens in terms of ADH when someone is dehydrtated

Answer 33

• it is detected by the osmoreceptors in the hypothalamus which triggers the posterior pituitary gland to release more ADH This increases the permeability of the distal convoluted tubule and collecting duct so that more water is reabsorbed into the blood and more concentrated urine is produced

Question 34

Causes of kidney failure

Answer 34

Diabetes High blood pressure Auto-immune disease Infection Crushing injuries

Question 35

In general, what do all kidney failure treatments try to achieve

Answer 35

To balance the fluids in the blood

Question 36

What are some treatments for kidney failure

Answer 36

Medication to control blood K and Na levels Low protein diet Drugs to lower blood pressure Dialysis Kidney transplant

Question 37

Why must the medication to control blood K and Na levels be controlled

Answer 37

Can lead to heart disease and kidney stones

Question 38

How is a low protein diet a treatment for kidney failure

Answer 38

It reduces the concentration of excess amino acids hence the concentration of the yrea

Question 39

Examples of drugs to lower blood pressure

Answer 39

• beta blockers which reduce the effect of adrenaline • calcium channel blockers which dilate blood vessels which lowers the blood pressure • ACE inhibitors which reduce the effect of angiotensin which cause the blood to restrict

Question 40

What are the two kinds of dialysis

Answer 40

Haemodialysis Peritoneal dialysis

Question 41

Haemodialysis

Answer 41

• a dialysis machine removes excess water, urea and ions from the plasma as fresh dialysate is constantly moving in opposite direction to that of the blood flow to create a counter-current system so equilibrium is not reached • Hepain is used to prevent blood clotting • this takes several hours and is repeated several times each week

Question 42

Pertioneal dialysis

Answer 42

• dialysis fluid is passed into the peritoneum through a catheter. The peritoneum contains numerous capillaries which exchange materials with dialysis fluid which is changed after about 40 minutes • this is repeated several times a day • the patient can move around • this is less effective than haemodialysis and can cause fluid retention

Question 43

Kidney transplant as treatment

Answer 43

This is a final resort The transplanting one kidney from closely matched donor Immunosuppressants are used afterwards to prevent rejection

Question 44

What is the excretory product of freshwater fish and why?

Answer 44

Ammonia This is highly soluble and toxic so cannot be stored This is excreted immediately using large volumes of water to dilute it The large volumes of water is freely available to freshwater fish

Question 45

What is the excretory product of Birds. Reptiles and insects and why?

Answer 45

Uric acid This is virtually non-toxic Not much water is needed to dilute it - advantageous to birds as a reduced weight in flight The conversion of ammonia to uric acid requires much energy but allows these to survive in arid environments

Question 46

What is the excretory product of mammals and why?

Answer 46

Urea Much less toxic than ammonia so requires less water to dilute it and can be stored It required energy to convert ammonia to urea but is an adaptation to life on land as it helps to prevent dehydration because less water is needed to excrete it

Question 47

What does the length of Loop of Henle correspond to?

Answer 47

The typical availability of water

Question 48

Beavers length of Loop of Henle and effect of this

Answer 48

Short loop of Henle Live in freshwater and so water is plentiful Large volumes of dilute urine produced

Question 49

Kangaroo rat length of Loop of Henle and effect of this

Answer 49

Long Loop of Henle Live in arid environment Small volumes of highly concentrated urine due to higher ion concentration in medulla is created by counter-current multiplier Higher proportion of juxtamedullary nephrons where the Bowman's capsule is nearer to the medulla and the Loop of Henle penetrates deep into the medula

Question 50

Camel water supply

Answer 50

Metabolic water They largely respire fat stored in its hump

Question 51

Some behavioural adaptations to minimise waterloss

Answer 51

Nocturnal