Homeostasis and Biological Rhythms Flashcards
What is homeostasis?
The maintenance of a stable internal environment
What do homeostatic mechanisms act to do?
Counteract the changes in the internal environment
At what level does homeostasis occur?
All levels -
- Cellular
- Organ/system
- Whole body
What factors does homeostasis control?
- Supply of nutrients
- Supply of oxygen
- Blood flow
- Body temperature
- Removal of waste
- Control of CO2
- pH
What does failure of homeostasis lead to?
Disease
What are the components of the control systems in the body?
- Communication
- Control centre
- Receptor
- Effector
What are the main communication pathways in the body?
- Nervous system
- Endocrine system
What does the nervous system use?
Hormones
What is paracrine control?
Local release (via ducts/exocrine) and action
What is autocrine control?
When agents are released by a cell which affects the releasing cell
What can the peripheral nervous system be divided into?
The afferent branch (sensory input) and the efferent branch (motor output)
What does the control centre do?
- Establishes the reference set point
- Analyses the afferent input
- Dtermines the appropriate response
Give two important control centres in the brain
- Diencephalon
- Medulla oblongata
Where is the dicephalon located?
In the hypothalamus
Where is the medulla oblongata located?
In the brain stem
What is the hypothalamus involved in the regulation of?
The endocrine system
What are regions of the medulla involved in the control of?
- Ventilation
- Cardiovascular system
What are receptors required for in the bodies control systems?
Detect stimuli such as changes in the internal environment
Give two examples of receptors
- Chemoreceptors
- Thermoreceptors
What are receptors usually made of?
Specialised nerve endings
How do sensors communicate input to the control centre?
Via the afferent nerves
What do effectors do?
Cause change
What happens to the output produced by the control centre?
It is communicated via efferent pathways to the effectors
Give an example of an effector?
Sweat glands, which can be activated to produce more sweat, causing heat loss
Give an example of a control system in the body
The hypothalamic-pituitary-adrenal axis
What is it called when the set point for homeostasis varies over time?
Biological rhythm
Give an example of a level varies during the day
Level of the hormone cortisol
When does cortisol levels reach their peak?
Around 7am
When are cortisol levels at their lowest?
About 7pm
What is it known as when levels vary over roughly a 24 hour cycle?
Circadian rhythm
What is the clinical relevance of the circadian rhythm of cortisol?
The time should always be noted when taking a sample of blood for cortisol measurement, and when repeating a measurement it should be taken at the same time of day. Alternatively, the 24 hour urinary excretion of cortisol can be measured
Draw a diagram illustrating the HPA axis
What is the clinical condition of hypoactivity of the adrenal cortex called?
Addisons disease
What effect does Addisons disease have on blood cortisol levels?
Low blood cortisol
What is the clinical condition of hyperactivity of the adrenal cortex called?
Cushing’s syndrome
What effect does Cushings syndrome have on blood cortisol?
High blood cortisol
How can temperature be used as a marker of ovulation?
Women’s core body temperature varies during the menstural cycle, and a sudden increase in core body temperature can be used as a marker of ovulation
