Homoeostasis IA%%+(+

Question 1

Tissue

Answer 1

Tissues: groups of cells that share the same characteristics or specialisation

.

Question 2

Organs

Answer 2

Collections of tissues, usually of several different types, that synchronise to perform a particular function.

Question 3

Negative feedback operation

Answer 3

• Magnitude of change in a monitored variable is sensed by a receptor
• receptor feeds that information to an integrating centre, where it is compared with a reference level.
• Any difference between the actual level and the reference level generates another signal, which is fed to an effector mechanism,
• a response is produced which corrects the original change.

Question 4

Feed forward control

Answer 4

Its a more sophisticated form of negative feedback. Additional receptors permit system to anticipate change and therefore activate response earlier.

Question 5

Positive feedback

Answer 5

Initial disturbance set off a train of events that lead to an even greater disturbance. e.g action potential

Question 6

Water compartments

Answer 6

1. Intraceullular fluid (2/3)
2. Extracellular fluid (1/3): Interstitial fluid (80%) & Plasma (20%)

Question 7

Trend in % water content (of mass) with weight and age

Answer 7

• From puberty onwards women show proportionally less body water then men.
• Both sexes show a decline in body water with age (after puberty), as muscle mass decreases.

Question 8

Plasma

Answer 8

• Plasma is the fluid component of blood.
• Plasma freely exchanges nutrients (e.g. O₂, glucose, ions) and waste (e.g. CO₂ and urea) with the ISF.
• Exchanges occur as blood passes through the capillaries of the body
• The composition of plasma and ISF are virtually identical except for plasma proteins, which are too large and so are restricted to the plasma.

Question 9

how do you measure body fluids?

Answer 9

Based on the DILUTION PRINCIPLE

1. c = m/v,
2. Only compartments of which plasma is a component can be measured directly (plasma, ECF, TBW).
3. The NATURE of BARRIERS which separate compartments is crucial in determining the test substance.

Question 10

Compartments that can be measured directly using the Dilution Principle:

Answer 10

1. Plasma Volume (PV): plasma proteins can’t cross capillary walls, can use dyes that attach to plasma proteins, e.g. Evans blue.
2. Extracellular Volume (ECF): Need something that freely crosses capillary walls, but cannot cross cell membranes, e.g. inulin which is too large to cross cell membrane or ²⁴Na+ , ³⁶Cl-, which are actively extruded from cells.
3. Total Body Water (TBW): There is no barrier to water in the body, so can use a loading dose of heavy water/ deuterated water (D₂O).

Question 11

Terminology

Answer 11

• Hyper = greater than normal
• Hypo = less than normal
• Aemia/emia = means in the blood
• Uria = means in the urine
• Glyc = related to glucose

e.g:

• Glycosuria = glucose in the urine
• Hypoglycaemia = low blood glucose levels

Question 12

Method of practice of dilution principle

Answer 12

1. Inject a substance that will stay in one compartment only (plasma, ECF, TBW)
2. Then calculate the volume of distribution V=M/C:

= amount injected (minus any removed by excretion or metabolism), divided by the concentration in the sampled fluid.

Question 13

Homeostasis water example►

Answer 13