homeostasis Flashcards
what are the components of a feedback system ?
- Regulated factor/controlled variable (set point, operating range, error signal)
- Detector/sensor that senses change (afferent path)
- Comparator/control centre – determines set point of variable, compares and maintains variable at set point. Initiate the response
Intrinsic: local – cell or tissue autoregulates
Extrinsic: endocrine system, nervous system - Effector – returns variable to set point (efferent path)
Response
what are some examples of regulated factors/controlled variables ?
- Blood pressure
- Core temperature
- Ions e.g. Na+, Ca2+
- Nutrients e.g. blood glucose concentration
- Hormones
what are the 4 mechanisms that the body uses for heat exchange to maintain homeostasis in an environment that is not thermoneutral ?
Conduction: The transfer of heat from two objects e.g. transfer of heat from skin to chair
Convection: is the transfer of heat to the air surrounding the skin
Radiation: is the transfer of heat via infrared waves e.g. sun warms the skin
Evaporation: is the transfer of heat by the evaporation of water e.g. sweating
Regulation of body temperature
* shivering, vasoconstriction, increased metabolism (increases)
* vasodilatation, sweating (decreases)
draw a diagram to show the elements of the homeostatic control of core body temperature: negative feedback control
draw a diagram to show the elements of the homeostatic control of core body temperature when infection is involved
what are the benefits of an increase in body temperature ?
- Pyrogens (bacterial or viral infections) change the set point to a higher level resulting in fever
Benefits of a higher temperature
* Inhibits bacterial growth
* Speeds up metabolic reactions
* Increases delivery of white blood cells to infection sites
How is temperature increased?
* Blood flow shifted to core to conserve heat
* Increased muscle activity (shivering)
* Chills stop when high temp reached
draw a diagram to show The homeostatic control of blood pressure – the baroreceptor reflex
- The baroreceptors in the walls of blood vessels(carotid sinus & aortic arch) detect an increase in BP
- Brain receives an input and signals blood vessels & heart
- Arterioles dilate and HR decreases leading to decreases in BP
draw a diagram to show the negative feedback system of hypertension
draw a diagram to show the Role of vasopressin in the control of blood pressure
Scenario: an accident caused a significant blood loss of blood that led to lower blood pressure (BP)
Question: what pathways will the body employ to restore BP??
- After a haemorrhage blood volume and hence blood pressure are reduced
- To help restore blood pressure several homeostatic control systems are activated - these include:
The baroreceptor reflex to increase cardiac output and total peripheral resistance
Stimulation of vasopressin (ADH) secretion to increase blood volume
describe the Integrated feedback loops in the control of sodium balance, blood pressure and fluid volume
- The kidneys: The glomerulus or the granule cells in the kidney will secrete Renin
- Renin converts angiotensinogen into angiotensin 1
- Angiotensin 1 under the action of ACE gets converted to Angiotensin 2
- Angiotensin 2 has many effects:
Adrenal Cortex: secretes Aldosterone
Hypothalamus: Secretes ADH and acts on the thirst Centre in the brain
On the smooth muscles cells of the arteries to constrict
draw a diagram to show the Control of circulating cortisol concentrations
draw a diagram to show the Control of circulating sex steroid concentrations
how is blood glucose controlled ?
- Blood sugar is a very tightly controlled in the body, the normal range is about 4.4 to 6.1 mmol/L (79 to 110 mg/dL)
- Our blood sugar will be subject to change after eating and digesting a meal- Blood sugar will rise
- The Beta cells of the pancreas will sense an increase in blood sugar and will secrete insulin
- Insulin circulates in the blood and will cause adipose tissue, muscle and liver to take up and store glucose -blood sugar drops
- Without eating our blood sugar level will fall –
- The Alpha cells of the pancreas can secrete glucagon
- Glucagon stimulates gluconeogenesis through glycogenolysis, and glucose release from liver - increasing blood sugar
draw a diagram to show the control of blood glucose
describe Positive feedback control in Haemostasis
- Less common physiologically as it is like a “runaway train” (less control)
- The response of the effector output reinforces the stimulus e.g. blood clotting, ovulation, childbirth
describe the Positive feedback in the control of uterine contractions in labour by oxytocin
- In labour oxytocin stimulates contraction of uterine muscles
- Cervix dilates and activate stretch receptors
- Action potentials signal to hypothalamus
- Stimulates further release of oxytocin
