Homeostasis

Question 1

What are the keys to homeostatic systems?

Answer 1

1. Coordinated in the HYPOTHALAMUS
2. have a “set point” maintained by eff mechanims
3. Require sensors, afferents, integrator and efferents

Question 2

How do you avoid over heating using local and central mechanisms?

Answer 2

Locally: Local temperature sensors sense HEAT which leads to the release of NO. NO is a vasodilator and increases surface blood flow leading to HEAT LOSS.

Centrally:

Core temp sensors send signals to the CNS to activate sympathetic nerve outflow to INCREASE skin blood flow and increase sweating.

Question 3

What are local and central mechanisms used to avoid to low of temperatures?

Answer 3

Locally:

Cold stimulates skin sensors which lead to NE release. NE causes vasoconstriction > decreased blood flow > you lose less heat!

Centrally:

Core temperature sensors stimulate the CNS to increase nervous sympathetic outflow to DECREASE skin blood flow.

Question 4

How does a fever increase heat in the body?

Answer 4

Fevers involve pyrogens

pyrogens stimulate the hypothalamus

hypothalamus produces PGE2 in medial preoptic area

causes SHIVERING and INCREASED metabolic rate

Question 5

What is the formula for BP?

Answer 5

BP = HR X SV x TPR

Question 6

What are the sympathetic components that regulate BP

Answer 6

NE (Symp) acts on:

B1- increase HR

B1- increase SV

Alpha 1- increase resistance

Question 7

What is the parasympathetic component that affects BP?

Answer 7

Vagus Nerve (parasympathetic)

Releases Ach on muscarinic receptors in the heart leading to DECREASED HR.

Question 8

How do stretch receptors respond to an increase in blood pressure?

Answer 8

Baroreceptors in the carotid sinus stretch > increased firing rate which activates CN 9 and 10 and stimuluates the NTS which inhibits the rostral ventrolateral medulla which is connected to the sympathetic system so therefore it inhibits it!

Question 9

How do stretch receptors respond to a decrease in firing?

Answer 9

Baroreceptors feel no stretch so there’s less firing, less activation of CN 9 and 10, less inhibition of rostral ventrolateral medulla and therefore increased activation of sympathetics leading to increased HR, SV and R.

Question 10

How is breathing controlled?

Answer 10

A pace maker in the PBA of the ventrolateral medulla inititates breathing. It is simulated by the C2-C3 via the phrenic nerve to innervate the diaphram.

The PBA is stimulated by the parafacial respiratory center which is acativated when there is increasd CO2.

The parafacial respiratoryp center also direcly excites muscled involved in active expiration.