Lecture 1

Question 1

What is homeostasis?

Answer 1

The ability to maintain a relatively stable internal environment (steady state), even though the external environment changed continuously, through the use of homeostatic control systems (feedback loops)

Question 2

What are some diseases that the accumulation of damaged proteins is responsible for?

Answer 2

Alzheimer’s Disease and Creutzfeldt-Jakob Disease

Question 3

What does homeostatic control require, and what can accomplish that?

Answer 3

Nervous and endocrine systems, through the use of electrical impulses and hormones to carry information

Question 4

What are homeostatic mechanisms?

Answer 4

Reflexes that occur subconsciously (feedback loops)

Question 5

What is homeostasis constantly being disrupted by?

Answer 5

Changes to the internal and external environments

Examples:
Internal
- Drop in blood glucose due to lack of food

External
- Intense heat or lack of oxygen

Question 6

What is a variable?

Answer 6

The factor or condition being regulated

Question 7

What are some of the components of a homeostatic control mechanism?

Answer 7

• Receptor/Sensor
• Afferent pathway
• Set-point or reference value
• Integrator/Control center
• Efferent pathway
• Effector

Question 8

What do receptors do?

Answer 8

• monitors changes in a variable

- Receives the change and sends the input to the control centre through afferent pathways

Question 9

What does the control centre do?

Answer 9

• Brain (in general the hypothalamus)
• Determines the set point/reference value for a variable (e.g. normal body temperature range)
• Evaluates input received from receptors and generates an output command
• Nerve impulses, hormones

Question 10

What does the effector do?

Answer 10

• Receives output from the control centre via efferent pathways
• Produces a response or effect that changes the value of the variable (e.g. Shivering to generate heat and thereby increase body temperature)

Question 11

What are controlled variables?

Answer 11

Variables that are not themselves homeostatically regulated

Ex.

• Arterial blood pressure is regulated by changing heart rate, stroke volume and peripheral resistance
• Heart rate is not controlled around a set point, instead its main role is to contribute to blood pressure regulation

Question 12

Are homeostatic control mechanisms more often positive or negative feedback loops?

Answer 12

Negative

Question 13

Positive feedback?

Answer 13

• The response enhances the original stimulus
• The response is positive because it is in the same direction as the
  initial change
• The value of the variable deviates further from its original set value

e.g. child birth and blood clotting

Question 14

Negative feedback?

Answer 14

• Reverses a change in the variable by either shutting off the original effect of the stimulus or reducing its intensity
• The mechanisms cause the variable to change in the opposite direction to that of the initial change
• Variable returns back to set point.

e.g. regulation of blood pressure and body temperature

Question 15

Set point?

Answer 15

• Homeostatic control systems cannot maintain a variable at complete constancy, so any regulated variable will have a range of normal values depending on multiple factors e.g. age, time of day, external environmental conditions
• Set points can be physiologically reset to a new value
  e. g. During a fever, the body temperature is raised (≥37°C) in response to infection. This is an adaptation for fighting infection because it inhibits proliferation of some pathogens

Question 16

Adaptation?

Answer 16

• A characteristic that favours survival in specific environments
• Homeostatic control systems are inherited biological adaptations

Question 17

Acclimatisation?

Answer 17

• A type of adaptation, where there is improvement of an already existing homeostatic system
• Usually reversible with discontinuation of the environmental stress

Question 18

Circadian rhythm?

Answer 18

Many body function/processes have rhythmic changes over time, and the most common rhythm is once every 24h, which is called the circadian rhythm

e.g. waking and sleeping, body temperature, growth hormone release

Question 19

What do biological rhythms do?

Answer 19

Add an anticipatory (or feedforward) component to homeostatic control systems by activating them at times when change likely to occur (but before it actually does)

e.g. Body temperature increases prior to waking in a person on a typical sleep-wake cycle, which allows metabolic machinery of the body to operate most efficiently upon waking, as its partly temp dependant

Question 20

What are factors that affect performance of homeostatic mechanisms
(causing imbalance)?

Answer 20

– Aging
– Nutritional status
– Disease causing organisms
– Excessive stress
– Extreme environmental conditions beyond control

Question 21

Moderate imbalance?

Answer 21

• Disorder or abnormality of structure and function
• Disease specific for an illness with recognisable signs and symptoms
• Treatment leads to restoration of homeostasis

Question 22

Severe imbalance?

Answer 22

• Treatment fails to restore homeostasis

- Illness and death

Question 23

Homeostatic imbalance in type 1 diabetes?

Answer 23

• Beta cells of the pancreatic islets are destroyed.
• Insulin no longer produced
• Blood glucose continues to
  rise
• The condition is fatal if not treated

Question 24

What is the function of osteocytes?

Answer 24

• Important role as mechanosensors
• They detect changes in the bone, either chemical or physical changes, and release chemicals in response to either send out osteoblasts (build bone) or osteoclasts (remove bone)