Question

1. Extreme challenges to an animal’s physiology allow us to explore and better understand the function of systems in the body.   Please address the following questions regarding the initial reflexive changes (before acclimatization) that occur in response to ascent to altitude.

1. Outline the initial global reflexes that occur in response to the low PO₂ at high altitude. Be sure to include all components of the reflex arcs for cardiovascular and respiratory systems.

1. Compare these global reflexes to local reflexes occurring in the lungs.

How do the global and local reflexes address the optimization of the ventilation : perfusion ratio (keeping it close to 1)

Answer 1

Acclimatisation

At high altitude barometric pressure decreases and there is decrease in po2 partial pressure of 02 while PCo2 and PH remain constant .In acclimatised child individual Oxygen delivery to tissues is maintained by Haemoconcentration.

1. Increase 2,3 DPG biphosphoglycric acid reduces the affinity of hb for Oxygen and increase in relaese of O2 at tissue levels help a lot.

2.Increase in erythropoetin secretion --- Polycythaemia vera ( increases RBC volume or Haematocrit ),red cheeks present .

3.Increase in number of mitochondria and tissue content of cytochrome oxidase

4. Increase myoglobin

5. Increased pulmonary ventillation

6. Barrel shape chest

7Alkaline urine is formed .

Baroreceptor reflex during acclimatisation --When there is hypoxia it causes vasodilation ,leading to Hypotension low blood pressure and

Whenever there is low BP baroreceptors which are stretch receptors are activated and impulses travel via carotid sinus nerve brach of glossopharyngeal nerve and Depressor nerve branch of vagus nerve and they are integrated in Nucleus tractus solitarius in Medulla and response is increased sympathetic vasoconstrictor tone to vessels and increasing sympathetic discharge to heart and increase the cardiac output and increasing the Blood pressure.

2) Chemoreceptor -- Central and peripheral

A)Central chemoreceptor present on ventrolateral surface of Medulla and it sense the Hypoxia low po2 and vaise stimulation through hyperventilation ,Vasoconstriction ( increased cardiac output,Increased heart rate ,increased blood pressure)

B)Peripheral Chemoreceptor consist of carotid and aortic bodies which contain chemosensitive glomus cells .They detect the changes in blood po2 ,PCo2 and PH .

Stimulus is Hypoxia decreased po2 and increased PCo2 integartion occur in Vasomotor centre and response is Hyerventilation and vasoconstriction .Vasoconstriction cause increase in Diastolic Bp.

Lungs - Low po2 stimulate the peripheral Chemoreceptor and cause hyperventilation removal of excess of CO2 and tachycardia and pulmonary artery hypertension