Chemical control of respiration (7) Flashcards
What is a stable internal environment and what components must be maintained within a narrow range?
Homeostasis
- concentration of water and electrolytes within and outside the cells
- pressures and volumes
- pH
- Body temp
- conc of nutrients (glucose),O2 CO2 and waste products (urea)
What is the primary type of homeostatic control system?
Negative Feedback
What are the stages of negative feedback?
1) Sensor ( chemoreceptor)
2) integrating centre (medulla)
3) Effectors ( respiratory muscles)
4) Variable ( PO2/PCO2)
What are the arterial partial pressures of O2 and CO2 (set point)?
PO2- 100mmHg
PCO2- 40mmHg
What are the venous partial pressures of O2 and CO2 (set point)?
PO2- 40mmHg
PCO2-46mmHg
What do peripheral chemoreceptors do and where are they situated?
Sense tension of oxygen and carbon dioxide and [H+] in the blood and are situated in the carotid and aortic bodies
What is normal ventilation?
6-8L/min
What two values do you need to calculate inspired partial pressure(PO2)?
Atmospheric pressure and % of oxygen in inspired air (21%)
What happens when PO2 drops below 60mmHg?
Ventilation increases
What do chemoreceptors do?
Sense the values of gas tensions
What do peripheral chemoreceptors do?
Sense tension of oxygen and carbon dioxide and [H+] in the blood
What do central chemoreceptors do and where are they situated?
They respond to [H+] of the cerebrospinal fluid (CSF) and are situated near the surface of the medulla of the brainstem
What is Hypercapnia?
Increased arterial PCO2 and ventilation
What is Hypoxia?
Decreased arterial PO2 and ventilation (i.e. at high altitudes
What are neural and chemical factors that may increase ventilation?
- reflexes originating from body movement
- adrenaline release
- impulses from the cerebral cortex
- Increase in body temperature
