this is a sample question i came across in a book i'm reading  
Describe the role of chemoreceptors, stretch receptors, higher brain
centres and temperature in regulating breathing

Hi Jonesy,

There are a number of websites that discuss the regulation of
breathing, especially the roles of chemoreceptors and stretch
receptors.  I'm giving you a few links (below) that will help you out.

MSN Encarta - Respiratory System: III: Regulation
http://encarta.msn.com/encyclopedia_761577180/Respiratory_System.html#s26

Control of Respiration
http://www.ursa.kcom.edu/Department/LectureNotes/Summer/ContRespiration.doc
NOTE: MS WORD file!  This is a set of lecture notes on respiration
from Baer's Physiology Site

University of California at Berkeley MCB 136: Control of Respiration
http://mcb.berkeley.edu/courses/mcb136/topic/Respiration/SlideSet5/index.htm
These are the PDF slides for this lecture.  Main website for the
respiration unit from the course is
http://mcb.berkeley.edu/courses/mcb136/topic/Respiration/

Biology Mad: Heart and Exercise
http://www.biologymad.com/HeartExercise/HeartExercise.htm

There are a lot more sites out there that discuss these processes and
the roles of the different receptors.  I found the above by doing a
search of the Google engine for: "role chemoreceptors breathing
stretch receptors".  Please let me know if I can clarify this answer
further!

Librariankt

Hey, the main chemoreceptor for breathing is found in the brainstem,
and it senses the amount of CO2 in the blood. It actually senses the
acidity of the blood, because CO2 + H20 --> H2CO3, which gives off a
proton or two, causing acidity. This sends a signal to the thalamus of
the brain to increase respiration, and by breathing faster you exhale
more CO2, restoring the pH of the blood. You also have O2
chemoreceptors, which make the heart beat faster if O2 levels fall.
Stretch receptors, also called baroreceptors, are found in the carotid
arteries and aorta, and they will sense this increase in pressure
(because the heart is beating harder), and this makes a negative
feedback system mediated by control centers in the medulla oblongata.
(This works by decreasing sympathetic output {alpha receptors of
norepinephrine} and increasing parasympathetic output {through beta-1
and muscarinic receptors}. This increase in sympathetic activity makes
you breath faster. (It also releases hormones that affect the kidneys,
but I'll try not to get too detailed). There are also chemoreceptors
in the bronchiol tubes, which is how inhalers work-- they activate the
B2 receptors, opening up the passageways. Cold temperatures can induce
an asthma attack, so I'm guessing that heat helps open up the
bronchiole tubes and allows better respiration. Hope that helps!