Homeostasis

Question 1

What are 5 relationships between physiological systems

Answer 1

Protection from the external environment

Provision and delivery of nutrients and oxygen

Excretion of waste products and carbon dioxide

Communication between cells

Reproduction of next generation

Question 2

What does the internal environment refer to

Answer 2

The fluid surrounding cells (extracellular/interstitial fluid)

Question 3

Define homeostasis

Answer 3

The ability of the body to maintain a condition of dynamic equilibrium within the internal environment when dealing with external changes

Question 4

Give some examples of controlled variables in the internal environment

Answer 4

Concentrations of ions: Na+, K+, Ca2+, Cl-, H+ (pH)

Concentrations of nutrients: glucose, amino acids

Concentrations of blood gases: pO2, pCO2

Physical characteristics of blood:
pressure, volume, flow, temperature, osmolarity

Question 5

What are some examples of normal ranges

Answer 5

Blood glucose, 3.5-6.0 mM

Blood osmolarity, 280-295 mOsM

Body temperature, 36.5-37.5 oC

Arterial blood pressure 120/80 mmHg

Arterial pO2 80-100 mmHg

Arterial pH 7.35-7.45

Question 6

Outline the homeostatic mechanism

Answer 6

A change in the controlled variable acts as a stimulus

This is picked up by the sensors

An afferent pathway is followed

Integration at control centre (compared to set point or reference value)

An efferent pathway is followed

This is picked up by the effectors which bring about a response

Question 7

Negative feedback

Answer 7

Increase or decrease in blood pressure is detected by receptors in blood vessels

The control centre in the brain that regulates heart rate responds

Heart rate decreases or increased

Blood pressure decreases or increases due to heart rate

Homeostasis is maintained

Question 8

Positive feedback

Answer 8

Constantly increasing or decreasing value

Question 9

Feed forward regulation

Answer 9

Involves anticipation of change

Anticipation of change in blood glucose when feeding

Sensory information from eating food and prescience of food in the stomach

Nervous afferent signals sent to hypothalamus

Nervous effector signals sent to pancreas to release insulin

Question 10

Changes in homeostatic control

Answer 10

Physiological:
Changes in cardiovascular variables during exercice
Rhythmic changes through the day to give circadian changes in physiological variables
Hierarchy of homeostasis

Pathological:
Hypotension in circulatory shock following haemorrhage
Loss of control of cell division in cancer
Pathogens influence temperature regulation in fever

Question 11

Intrinsic regulation

Question 12

Extrinsic regulation