Homeostasis

Question 1

Define homeostasis

Answer 1

Homeostasis:
A state of dynamic equilibrium characterised by various responses to changes in the external environment.

Homeo = same
Stasis = standing still

Question 2

What is the percentage of water in a standard 70kg male?

Answer 2

60%

So 70kg x 0.6 = 42L

Question 3

State the body compartments where fluids accumulate

Answer 3

2/3 Intracellular (ICF)

1/3 Extracellular (ECF)

ECF > 3/4 interstitial / 1/4 plasma

Question 4

Compare and contrast water balance in males and females.

Compare in early life and older

Answer 4

Standard male is 60% water
Standard Female is 50% water (higher body fat)

Infants highest % TBW 70%

Higher body fat = lower TBW%

Question 5

Outline differences between water toxicity and dehydration.

Answer 5

Water toxicity:

• Body fluids become diluted.
• Reduction of sodium concentration in ECF causes shift in osmotic pressure.
• Cells and tissues swell.

Dehydration:

• Tissues and cells become dehydrated
• Cells not getting nutrients > lowers concentration
• Water > INTERSTITIAL fluid compartment - shrink.
• High HR
• Low BP

Question 6

Difference between positive and negative feedback loops

Answer 6

Positive:

• Change in condition reinforced
• Feedback stops when initiator stops

Negative:

• Change in condition reversed
• Feedback stops when effector stops

Question 7

Example of positive feedback loop

Answer 7

Birth:

• Baby pushes on cervix, causing stretch
• Stretch > nerve impulses to brain
• Pituitary releases oxytocin
• Oxytocin causes uterus to contract

Stops when baby born (initiator removed)

Question 8

Example of negative feedback loop

Answer 8

Body temperature regulation:

• Body temp exceeds 37°C
• Nerve cells in skin signal brain
• Hypothalamus activates cooling mechanisms

(Vasodilation, sweating, pilorelaxation)

• Temp decreases
• Cooling shut off

Question 9

Normal range for core body temperature

Answer 9

36.5-37.5°C

Question 10

Normal range for pH

How is it measured?

Answer 10

7.35-7.45

ABG
Arterial Blood Gas

Question 11

Explain importance of acid-base balance for normal human physiology

Answer 11

If blood pH falls below 6.8 or increases above 7.8 death is likely.
Represents very small change in free hydrogen ion concentration

Question 12

How is core body temperature measured?

Answer 12

Tympanic thermometer (ear canal)

Can also use oral cavity, axilla , rectum

Question 13

What is the homeostatic mechanism to regulate body temperature?

Answer 13

Thermoregulation

Question 14

How can heat be lost from the body?

Answer 14

Radiation
Conduction
Convection
Sweat evaporation

Question 15

What are the physiological responses to increase in core body temperature?

Answer 15

Cutaneous Vasodilation
Pilorelaxation
Sweating
Behaviour (stretch out)

Question 16

Define hypothermia

Answer 16

Core body temperature below 35C

Question 17

What is it called when core temp is above 41.5C?

Answer 17

Hyperpyrexia

Question 18

Increase in core temp due to infection is called..?

Answer 18

Pyrexia (fever)

Question 19

Which part of the brain acts as the heat regulation centre?

Answer 19

Hypothalamus

Question 20

What are the physiological responses to decrease in core body temperature?

Answer 20

Cutaneous vasoconstriction
Piloerection
Shivering
Behaviour (curl up)

Question 21

Describe the causes and process of oedema

Answer 21

Oedema causes:
- Raised hydrostatic pressure (capillary)
(fluid forced out)

• Decreased osmotic pressure (capillary)
  Low albumin e.g. Liver disease can’t keep fluid in
• Raised osmotic pressure (Interstitium)
  Fluid out of cell down gradient
• Impaired lymphatic drainage
  Fluid not taken back up

Question 22

Calculate osmolality using the below values:

[Na+] = 136.2 mmol/L
[K+] = 4.0 mmol/L

Answer 22

Osmolality = sum of osmotically active ions

For each +ve ion there is equal value Cl- ions

So:

136. 2 + 4 = 140.2
     (x2) = 280.4 mOsm/L