Homeostasis

Question 1

What is negative feedback? Give an example

Answer 1

This control system is inhibitory

• Oppose change by creating an opposite response
• Stabilise physiological variables by keeping them within or near normal ranges
• the response counteracts the stimulus, shutting off the response loop.
• Examples; thermoregulation, blood pressure regulation, ph regulation, release of neurotransmitters or hormones etc.

Question 2

Describe what happens homeostatically when we exercise

Answer 2

Factors being regulated : blood po2 and pco2
-Exercise increases muscle use of O2, increases CO2 production,
- increased breathing rate and depth to MAINTAIN BLOOD PO2 and PCO2
- selective vascular constriction and dilation directs greater blood flow to exercising muscles
- increased heart rate and force increases cardiac output
-Increased cardiac output and muscle blood flow maintains delivery of O2 and removal of CO2
- increased cardiac output increases pulmonary blood flow to pick up more o2 and to drop off more CO2.
Factors being regulated: core body temp
- exercise increases core body temp, by generating heat in muscles
- increased skin blood flow to increase sweat rate to cool the body

Question 3

Describe the flow chart of control systems with examples for each component

Answer 3

1) Stimulus - skin is exposed to cold
2) Sensor or receptor - detected by thermoreceptors in skin
3) Afferent pathway - towards brain - sensory nerve fibres
4) integrating centre - brain 0 hypothalamus (compares actual to set value)
5) efferent pathway - efferent nerve signals - away from brain
6) target or effector organ and its action - Shivering/ piloerection/cuteneous vasocontriction
7) response - body heat is retained - purpose on the pathway

Question 4

Describe control versus regulation

Answer 4

Control ; the act of modifying or modulating a physiological function eg, heart rate

Regulation: changes to physiological functions that specifically result in one or more physiological variables, eg blood pressure, being held relatively stable

Question 5

what are the two types of negative feedback?

Answer 5

Tonic control: accelerator
- uses only one control system (increase or decrease output) e.g., HR can be controlled by increasing and decreasing sympathetic nervous system activity

Antagonistic control: accelerator and brake

• uses two control systems - one positive and one negative
• insulin lowers blood glucose concentration, glucagon raises it

Question 6

describe positive feedback

Answer 6

• stimulatory
• amplify or reinforce the change
  examples: Childbirth, ion channel opening in transmitting an action potential, blood clotting etc

Question 7

describe feed forward control system

Answer 7

• response in anticipation of change

Eg, in digestion, or muscle flow prior to exercise.

Question 8

what are the levels of control?

Answer 8

• intracellular - genes and enzymes
• intrinsic controls - signals to nearby cells - autoregulation
• extrinsic controls - signals originate outside of the controlled organ eg endocrine and nervous

Question 9

What is pathophysiology and what are its origins in the body?

Answer 9

• when one or more of the body systems fail to function properly - so an optimal internal environment cannot be maintained.
• disruptions to homeostasis can lead to illness and death
  Origins of pathophysiologies:
• intrinsic defect in a homeostatic system
  -> hormonal tumour -> excessive hormone secretion
• normal response to an abnormal stimulus (an extrinsic defect)
  -> chronic high BP leading to adaptation of heart -> enlargement then heart failure
• chronic effects of a homeostatic compensatiry mechanism
  -> impaired renal blood flow invokes RAS -> chronic hypertension