Physiological control systems: Homeostasis

Question 1

What is homeostasis?

Answer 1

Maintenance of a steady-state/ internal environment

Question 2

What are the examples of controlled variables?

Answer 2

Physical entities - Blood Pressure, Care Temperature

Circulating concentrations of chemical substances- Ions e.g. Na+, Ca2+, Nutrients e.g. blood glucose concentration, Hormones

Regulation of body temperature - Shivering, vasoconstriction, increased metabolism (increase), Vasodilation, sweating (decrease)

Question 3

What can change the setpoint in temperature?

Answer 3

Pyrogens (Bacterial or viral infections) change the setpoint to a higher level resulting in fever.

Question 4

What are the benefits of a higher temperature?

Answer 4

Inhibits bacterial growth
Speeds up metabolic reactions
Increase delivery of white blood cells to infection sites

Question 5

What happens if there is an increase in blood pressure?

Answer 5

The baroreceptor detects the change, sends impulses to the Cardiovascular control center.

This leads to decreased sympathetic input, so a decrease in peripheral resistance.

Also, an increase in parasympathetic input, so a decrease in Cardiac output. The decrease in sympathetic input also decreases Cardiac output.

Question 6

What happens if there is a decrease in blood pressure?

Answer 6

Activation of sympathetic output increased CO and TPR.

Question 7

The hypothalamic-pituitary axis

Answer 7

Neurons in the hypothalamus synthesis and release hormones from the posterior pituitary.

Other neurosecretory cells in the hypothalamus release their hormones into the portal capillaries in which they are transported directly to endocrine cells of the anterior cells.

Question 8

What happens if there is hemorrhaging?

Answer 8

Blood volume and pressure decrease.
So: Stimulation of Vasopressin (ADH) to increase blood volume
The baroreceptor reflex to increase cardiac output and total peripheral resistance

Question 9

What does CRH do?

Answer 9

(Corticotropin-releasing hormone) stimulates ACTH. ACTH stimulates cortisol secretion.

Question 10

Positive feedback in labour

Answer 10

1. Labour Oxytocin stimulates contraction of uterine muscles
2. Cervix dilates and activates stretch receptors
3. Action potential signal to the hypothalamus
4. Stimulates the further release of oxytocin