Endocrine system Flashcards
What are some key features common to all control systems, including those in the body involved in homeostasis?
- Communication - NS and endocrine system
- Control centre
- Receptor
- Effectors
- Feedback
What is paracrine control?
Endocrine control caused by the local release of hormones (rather than into the blood) which act locally
What is autocrine control?
Endocrine control caused by a variety of agents which effect the releasing cell itself, not others around it or large distances away from it
What is the afferent branch of the peripheral nervous system?
The peripheral nerves that carry signals from the sensory input towards the brain
What is the efferent branch of the peripheral nervous system?
The peripheral nerves that carry signals from the brain towards the motor output
What are the two important control centres in the brain for homeostasis?
- Hypothalamus in the diencephalon
2. Medulla oblongata in the brain stem
What is the role of the control centre in a control system?
To determine the reference set point, to analyse the afferent input and determine the appropriate response
The hypothalamus is involved in the control of what system?
Endocrine system
Regions of the medulla are involved in the control of what systems?
Ventilation -movement of air between lungs&environment
Cardiovascular system
What do body sensors usually consist of?
Specialised nerve endings
What is the role of sensors in the body?
To detect stimuli such as changes in the environment
What do chemoreceptors respond to?
chemical stimuli
What do thermoreceptors respond to?
absolute and relative changes to temperature
What do proprioreceptors respond to?
Movement and position of body
What do nocireceptors respond to?
potentially damaging stimuli and sends signals which are usually detected as pain
What are effectors?
Agents that receive outputs from the control centres down efferent pathways and cause a change e.g. sweat glands responding to efferent signals from the control centre in response to high temperature afferent signals form thermoreceptors
What is feedback?
When the output (effect) has an effect on the control centre
What is negative feedback?
When the output inhibits the function of the control centre and the effector acts to oppose the stimulus
What is the purpose of negative feedback in control systems?
It gives them stability by allowing the set point to be controlled within fine limits
What is positive feedback?
The stimulus produces a response which tends to increase its effect rather than counteract it. Therefore positive feedback creates a rapid catastrophic change in state
There are not many examples of positive feedback in the human body, give two
- Blood clotting cascade - change in state of blood from liquid to solid
- Ovulation - build up of FSH causes release of an oocyte form a follicle in the ovary
What is meant by biological rhythms?
When the set point of a control system varies throughout the day instead of being a fixed steady value
Explain the biological rhythm that cortisol shows and the effect of this on cortisol measurments
The levels of cortisol in blood vary throughout the day from a peak at 7am to a trough at 7pm.
Therefore you should always note the time of day that a blood sample was taken for cortisol measurement and repeated measurement should be taken at the same time of day
The menstrual cycles is an example of a biological rhythm. What varies throughout the cycle?
A woman’s core body temperature. A sudden increase in body temperature can be used as a marker for ovulation
Where is the “biological clock” of the brain found?
Suprachiasmatic nucleus in the hypothalamus
List 4 nucleases in the hypothalamus and their functions
- Suprachiasmatic nucleus - “biological clock”
- Supraoptic nucleus - oxytocin
- Paraventricular nucleus - ADH (vasopressin)
- Arcuate nucleus - satiety centre
What is a meant by a CNS nucleus?
A cluster of neurones in the brain
What is meant by human’s “natural diurnal cycle”?
We keep on a 24 hr 11min cycle maintained by keys in the environment (Zeitgebers)
What is the cause of jet-lag?
A mismatch between environmental keys and our “body clocks”