Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!think!mit-eddie!genrad!decvax!wanginst!masscomp!ts
From: ts@masscomp.UUCP (Tony Schene)
Newsgroups: sci.bio,sci.med
Subject: Re: HEART RATE
Message-ID: <1154@masscomp.UUCP>
Date: Sat, 1-Nov-86 21:10:27 EST
Article-I.D.: masscomp.1154
Posted: Sat Nov  1 21:10:27 1986
Date-Received: Tue, 4-Nov-86 00:07:26 EST
References: <768@mtx5w.UUCP>
Sender: news@masscomp.UUCP
Reply-To: ts@masscomp.UUCP (Tony Schene)
Distribution: na
Organization: MASSCOMP - Westford, Ma
Lines: 16
Xref: mnetor sci.bio:10 sci.med:156

In article <768@mtx5w.UUCP> drv@mtx5w.UUCP writes:
> Does anyone know the underlying mechanism that
> "causes" the heart to beat faster during exercise?

Basically, it's a physiological reaction to lower pH levels, and lower oxygen
partial pressures in the blood (the lower pH is caused by increased carbon
dioxide).  Sensory receptors in the carotid and aortic arteries respond
to lower oxygen levels, and a cardio-accelerator center in the hindbrain
responds directly to pH values.  I don't know for sure how this information
gets to the heart itself, but presumably it is carried by sympathetic
nerves to the pacemaker region of the heart, causing it to speed the
heartbeat.  By the way, these same carotic and aortic bodies, in
conjuction with other pH sensors in the brain, also cause increased
breathing rates during exercise.

	-Tony Schene      UUCP: {decvax, ihnp4, ...}!masscomp!ts