The respiratory control system comprises sensors in the brain and carotid bodies that detect levels of oxygen, carbon dioxide, hydrogen ions, and pH in the blood and cerebrospinal fluid. This information is sent to the central controller in the brain which coordinates the diaphragm and respiratory muscles as effectors to regulate breathing. Central chemoreceptors in the medulla are directly stimulated by increased carbon dioxide and hydrogen ions in the cerebrospinal fluid, triggering faster breathing. Peripheral chemoreceptors in the carotid and aortic bodies also sense decreased oxygen and increased carbon dioxide in the blood to stimulate the respiratory control center.

1. PRESENTER: Keagan Kirugo
DISCUSSANTS: The Circle

2.  Central controllers
 Effectors
 Sensors
 Integrated responses

4.  The main function of the lung is to exchange O2
and CO2 between blood and gas and thus
maintain normal levels of PO2 and PCO2.
 Despite the widely differing demands for O2
uptake and CO2 output made by the body, the
arterial PO2 and PCO2 are normally kept within
close limits through the mechanisms that will be
elaborated further.

5.  The respiratory control system comprises the
following:
 Sensors that gather information and feed into
the
 Central controller in the brain which co-
ordinates information and then sends impulses
to the
 Effectors which are the respiratory muscles.
They cause the ventilation to occur.

15.  Site Ventral surface of medulla
 Evidence Local application of H+ ions or
dissolved CO2 to this area stimulates breathing
within a few seconds.
 The central chemoreceptors are surrounded by
brain ECF-Extracellular fluid.

16.  ECF composition is governed by CSF, local blood
flow and local metabolism.
 CSF is the most important among the three. It is
separated from blood by the blood-brain barrier
(BBB).
 BBB is relatively impermeable to H+ and HCO3-
ions but not CO2.

17.  blood PCO2 diffusion of CO2 from
the cerebral blood vessels to CSF through ECF
 CO2 + H2O H+ + HCO3- and reduced
CSF pH
 H+ ions stimulate the chemoreceptors leading to
hyperventilation and finally decreased PCO2 in
blood and hence CSF.

18.  The cerebral vasodilation that accompanies an
increased arterial PCO2 enhances diffusion of
CO2 into the brain ECF and CSF.
 Normal CSF pH is 7.32

19.  Sites Carotid bodies at the bifurcation of the
common carotid arteries and the aortic bodies
above and below the aortic arch.
 Stimulants Decrease in arterial PO2 and PH
and Increase in arterial PCO2.
 Both receptors are responsible for increase in
ventilation that occurs due to hypoxemia.
 Response is rapid with PO2 <100 mmHg

20.  PCO2 response is less important compared to
the central chemoreceptors. However, the
response is rapid.
 PH response is by the carotid bodies and not the
aortic bodies.

29.  It is the most important factor in the control of
ventilation.
Factors leading to a decresa in ventilatory
response to CO2
 Sleep
 Increasing age
 Genetics
 Training: athletes and divers
 Increase in work of breathing

30.  There is an interaction to increase in PCO2 with
a fall in PO2 such that an increase in PCO2 leads
to increased response to a fall in PO2.
 Response to O2 is important in hypoxic
environments such as high altitude areas and in
patients with severe lung disease.

31.  Patients with severe lung disease have chronic
CO2 retention and the pH of the brain ECF has
returned to normal in spite of a raised PCO2 .
Therefore they have lost most of their increase in
stimulus to ventilation from CO2. In addition,
the initial depression of blood pH has been
nearly abolished by renal compensation hence
there is little pH stimulation of the peripheral
chemoreceptors. With these conditions; arterial
hypoxia becomes the chief stimulant to
respiration.

32.  Patients with a partly compensated metabolic
acidosis for example; uncontrolled DM who have
reduced pH and PCO2, show an increase in
ventilation which is responsible for the fall in
PCO2.

33. 