Lecture 1 - Homeostasis, Body Fluids, pH & Temperature

Question 1

Define homeostasis + name 4 things that need to be maintained constant in the internal environment.

Answer 1

Homeostasis is the physiological process by which internal systems of the body are maintained at equilibrium, despite variations in internal and external factors.

• Concentration of O2, CO2 + electrolytes
• Concentration of nutrients (glucose, AA’s etc)
• pH
• Temperature

Question 2

What are the 4 components required for a homeostatic feedback loop to work?

Answer 2

• The variable (e.g.: temperature/blood glucose)
• The sensor (e.g.: nerve cells in skin)
• The control centre (e.g.: hypothalamus)
• The effector (e.g.: muscle)

Question 3

Describe how an increase or decrease in temperature. is controlled by a negative feedback loop & Describe at least 3 effector mechanisms for heating up and cooling down.

Answer 3

1) Receptors in skin alert brain of temp change
2) Hypothalamus then alerts effectors
3) Effectors return temp to set point

• Vasodilation vs Vasoconstriction
• Sweating vs Shivering
• Pilorelaxation vs piloerection

Question 4

Give 2 examples of positive feedback loops + how they work.

Answer 4

1) Blood clotting - break in blood vessel wall causes release of chemokines which attract platelets to adhere to blood vessel wall. This causes further attraction of platelets until clot is formed and loop is stopped.
2) Stretching of cervix during birth - causes oxytocin release from pituitary. This binds to cervix wall and causes further stretching.

Question 5

What is core body temperature? When does it fluctuate?

Answer 5

• 37 degrees C +/- 0.5

- Throughout the day or during menstrual cycle for women (decreases during ovulation)

Question 6

What is the normal body pH range & What are the 2 major organs that control Acid-Base balance?

Answer 6

• 7.35-7.45
  1) Lung-respiratory balance
  2) Kidney-metabolic balance

Question 7

What are the 2 main buffer systems used to regulate pH levels?

Answer 7

• Carbonic-Bicarbonate Buffer System

- Phosphate buffer system

Question 8

In a standard 70kg male, what % does water make up?

How much water is in the IC and EC? - describe compartments for EC

Answer 8

• 60% (42L)
• 2/3 of water is ICF = 28L
• 1/3 of water if ECF = 14L
• of the 1/3, 75% is IF (10.5L) & 25% is in plasma (3.5L)

Question 9

How much blood is there in a standard 70kg male?

Answer 9

• 5L

Question 10

State the total body water (TBW) % in normal, lean and obese males, females and infants.

Answer 10

Males - 60%, 70%, 50%
Females - 50%, 60%, 42%
Infants - 70%, 80%, 60%

Remember - more % body fat = less % water

Question 11

In terms of red blood cells, explain the terms isotonic, hypotonic & hypertonic

Answer 11

Isotonic = Same amount of water on both sides of membrane.
Hypotonic = Less water inside the cell
Hypertonic = Less water outside the cell

Question 12

What happens to hypotonic and hypertonic RBC’s?

Answer 12

Hypo = Cell bursting/lysis
Hyper = Cell shrinkage/shrivelling

Question 13

What happens in the body during dehydration (due to sweating, vomiting, burns etc) ]

What happens to the body in water toxicity?

Answer 13

• Water loss, leading to increase in plasma osmolality –> ADH release –> oliguria (decreased urine)
• High osmotic pressure –> Cells absorb water and swell –> enzymes and proteins stop working –> patients need isotonic solution.

Question 14

What is oedema? Describe the process of oedema.

Answer 14

• Oedema is fluid retention in interstitial space.
• This occurs when hydrostatic pressure (pressure from blood vessels) exceeds oncotic pressure (pressure trying to put water back into capillaries), therefore water is drawn out into interstitial spaces and accumulated.