homeostasis

Question 1

what’s the equation of life?

Answer 1

nutrients + O2 = energy (ATP) + waste (CO2)

Question 2

How does homeostasis allow humans to live in hot countries without illnesses?

Answer 2

High temperature
Vasodilation of arteries
More blood near skin
Increase in rate of sweating
Helps lose heat

Question 3

How does homeostasis allow us to eat a doughnut without being ill?

Answer 3

Increase blood glucose concentration
Insulin directs other cells to store/use glucose
Blood glucose returns to normal

Question 4

what is negative feedback loop?

Answer 4

when the condition that triggered the homeostatic response beocmes switched off/ removed by that response.

Question 5

give an example of negative feedback loop (increased/ decreased body temp)

Answer 5

sweating to lose heat until returns to normal

shivering to gain heat until it returns to normal

self limiting response

Question 6

Explain a negative feedback loop e.g. a person working outside on a hot, dry day, how is his body temperature and water levels maintained?

Answer 6

sweating, as the arteries vasodilate and blood rushes to the skin

thirst response to counteract the loss of water through sweating and returns the concentration of bodily fluids to their normal range

Question 7

Explain a negative feedback loop e.g. homeostatic control of blood glucose

Answer 7

When you eat a meal [BG] increases, which causes a response releasing Insulin.

Insulin causes cells to uptake glucose.

Then you decrease [BG].

Question 8

What is a positive feedback loop?

Answer 8

reinforces the stimulus rather than decreasing or removing it. Instable.

Question 9

Explain a positive feedback loop e.g. in a diabetic person; breakdown of homeostatic regulation.

Answer 9

When a diabetic person eats a meal, [BG] increase, but there is either no response to release insulin or insulin has no effect.

The liver receptors pick this up and perceives that there is no glucose in the blood, so it produces its own glucose.

This leads to an even more increase in [BG].

Question 10

give an exampe of positive feedback looop (childbirth)

Answer 10

When the baby is ready to be delivered, it drops lower in the uterus and begins to put pressure on the cervix, the opening of the uterus.

releases oxytocinc
uterus contracts and push the baby’s head against the cervix, stretching it, and causing more oxytocin release.

This goes on until the baby is delivered.

Question 11

Explain a positive feedback e.g. in the case of an action potential in a nerve cell.

Answer 11

When Na+ enters a nerve cell in influx, it becomes more positive on the inside (depolarization)

the cell membrane becomes more permeable to Na+

allows more Na+ to go inside.

Question 12

What are feed-forward control/systems?

Answer 12

allows the body to predict that a change is about to occur and start the response loop in anticipation of the change.

Question 13

Give an example of feed-forward control (anticipatory responses) e.g. What does the kidney do when a person is working outside on a hot, dry day?

Answer 13

the thirst response.

kidney detects increased bodily fluid concentration and anticipates a state of dehydration.

produces smaller but more concentrated volumes of urine

conserves water.

Question 14

what percentage of water makes up our body weight?

Answer 14

60%

Question 15

where is water located in our body?

Answer 15

ICF (2/3)
ISF + Plasma (extracellular fluid - 1/3)

Question 16

Why are Plasma (3L) and ISF (11L) not completely identical in composition?

Answer 16

Because plasma contains plasma proteins which are too large to pass to the ISF through the capillaries NOT the arteries.

Question 17

what are the things to remember when you measure body fluid volumes?

Answer 17

1. c = m/v, v = m/c = Dilution Principle
2. ONLY plasma can be sampled, only compartments of which plasma is a component can be measured directly (plasma, ECF, TBW).

Question 18

what do you use to measure Plasma Volume using the Dilution Principle? why?

Answer 18

use dyes or radioactive labels that attach to plasma proteins

e.g. Evans blue or l125albumin.

We chose plasma proteins because they cannot cross the capillary walls so they stay in the arteries.

Question 19

what substances do you use to measure Extracellular Volume (ECF) using the Dilution Principle? why?

Answer 19

We can use inulin, sucrose, mannitol, because they can freely cross capillary walls but cannot cross cell membranes.

We can use 24Na+ or 36Cl- which are actively extruded from cells.

Question 20

what substances do you use to measure the Total Body Water (TBW) using the Dilution Principle? why?

Answer 20

Since there’s no barrier to water in the body, we can use a loading dose of heavy water or deuterated water (D2O)

Question 21

How do you measure the volume of ISF and ICF where plasma is not a belonging component?

Answer 21

For Interstitial Fluid Volume
ISF = ECF - PV

For Intracellular Fluid Volume
ICF = TBW - ECF

Question 22

How do you practice the Dilution principle?

Answer 22

1- Inject a substance that will stay in one compartment only (plasma, ECF, TBW)

2- Calculate the volume of distribution v = m/c
V = mass (minus any removals by excretion or metabolism) / concentration

Question 23

What happens if homeostasis does not operate effectively e.g. ECF [K+] increases beyond the normal range? and how is it regulated?

Answer 23

Loss of concentration gradient between ECF and ICF

nerve and muscle function disrupted, including cardiac muscle, leads to ventricular fibrillation and death.

Kidney regulates ECF ion composition; by excreting the excess ions through the urine

maintains homeostasis and prevent disease

Question 24

Why do females and older people have less water in their bodies?

Answer 24

females and older people contain higher proportion of body fat, which has less water content than muscle.

Muscle contains 70% water by weight, while fat only 10% water.

Question 25

Why is it important to know the proportions of water/fat content in the body and not just refer to a standard (e.g. 70kg, 21yr male)?

Answer 25

proportions of body water varies with age and gender.

also affect drug therapy treatments; rate of drug elimination (lipid or H2O soluble drugs) is changed by the water/fat content.

Lipid soluble drugs persist longer female body (contains more fat).

Question 26

a healthy 20 yr old female with [K+] ECF of 4.2 mmol/l doubles her K+ intake. After a week what’s her [K+] plasma?

Answer 26

4.2 mmol/l as a healthy individuals kidney will sort out the excess K+ and excret the excess in urine