Topic 1 - Homeostasis

Question 1

Define Homeostasis.

Answer 1

• The process by which cells, tissues and organs maintain the status quo.
• Homeo = same, Stasis = standing still

Question 2

Give an example of a negative feedback loop.

Answer 2

• Body temp regulation: The body temp deviates from the normal range, this change is detected by the hypothalamus (internally) and the skin (externally), these receptors cause effectors to counteract the change (shivering, vasoconstriction, curl up, piloerection VS sweating, vasodilation, stretch out, pilorelaxion), this continues until the temp returns to normal (the effectors cease).

Question 3

Give an example of a positive feedback loop.

Answer 3

• Blood Clotting: Tear or break in blood vessel, platelets adhere to site to initiate clotting, platelets release chemicals (cytokines) which attract more platelets, clot grows.

Question 4

What is the normal range of human core body temperature?

Answer 4

36.5 - 37.5°C.

Question 5

When might a healthy person’s core body temperature fluctuate?

Answer 5

• during the day, and at night it may fall (circadian rhythm)
• falls during ovulation due to the menstrual cycle

Question 6

Why is human body temperature the level that it is?

Answer 6

• To allow for the metabolic processes to function including with enzymes, too hot = enzymes denature, too cold = not enough energy to react.

Question 7

Below what temp does severe hypothermia occur?

Answer 7

32°C

Question 8

Explain how infection causes pyrexia.

Answer 8

• Pyrexia (Fever) occurs when a pathogen enters the body and triggers an immune response, the hypothalamus raises the set point temp to fight the infection as the immune system works optimally at higher temperatures

Question 9

How might an elderly patient’s brain respond to pyrexia compared with a younger patient?

Answer 9

• delayed responses, hypothalamus acts less effectively at raising set point, immune system slow to fight infection

Question 10

What is the normal human body pH range?

Answer 10

7.35 - 7.45

Question 11

A change of 0.3 in pH leads to a what effect on H+ conc?

Answer 11

• doubling or halving

Question 12

Which antacid is the favoured choice for acid reflux and why?

Answer 12

• aluminium hydroxide

- because its insoluble (soaks up H+ ions and then excreted), mildly alkaline (neutralises acid)

Question 13

Name the two types of acidosis and the associated organs.

Answer 13

• Metabolic acidosis (Kidneys): Lactic acid build up
• Respiratory acidosis (Lungs): Hyperventilation leads to lots of dissolved CO2 in venous blood which makes it more acidic

Question 14

Explain water toxicity.

Answer 14

• Too much water in cell/tissue, metabolites are too far apart to react, metabolic rate decreases, metabolic failure.

Question 15

What are these for a 70kg male:

1. The percentage of total body weight water makes up?
2. Litres of blood in body?

Answer 15

1. 60%

2. 5 Litres

Question 16

Define these terms: Isotonic, Hypertonic and Hypotonic.

Answer 16

• Isotonic: The conc of solute is the same in the cell as in its surroundings.
• Hypotonic: Lower conc of water in the cell than in its surroundings.
• Hypertonic: Higher of solute in the cell than in the surroundings.

Question 17

Define Osmolality.

Answer 17

• The total number of solute particles per kg (L).

Question 18

How do you calculate osmolality?

Answer 18

• Use the concentrations of each individual ion/particle in mmol/Litre (if its a compound like NaCl then do each dissociative ion separately, Na+ and Cl-)
• Add them together
• Unit is mOsm/kg (MilliOsmoles per Kg)

Question 19

What is Oedema and what is it caused by?

Answer 19

• Fluid retention
• Caused by trauma to blood vessels (fenestrations enlarge and leak), taking on too much water, defective lymphatic sys (doesn’t drain as it should)

Question 20

Define Oncotic pressure and name the protein that mostly causes it in blood plasma?

Answer 20

• pressure caused by concentration of a solute (e.g. protein)
• albumen protein

Question 21

What would happen to a red blood cell placed into pure water?

Answer 21

• the solute concentration is much higher in the cell than in the surrounding water so water would move into the cell by osmosis down the conc gradient.
• the cell would swell and possibly burst due to osmotic pressure

Question 22

Which condition is caused by water intoxication?

Answer 22

• Hyponatraemia (low sodium content)