Class Notes (834,804)
Canada (508,727)
BIOC33H3 (127)

Lecture V - Regulation of Cardiac Output.docx

4 Pages
Unlock Document

Biological Sciences
Stephen Reid

Thiruvarangan Regulation of Cardiac Output (Stroke Volume) **complex** Stroke Volume Regulation 1. Force of Ventricular Contraction 2. End-Diastolic Volume 3. Afterload (Blood Pressure) Stroke Volume Regulation: Ventricular Contractility The sympathetic nerve innervates a cardiac myocyte (muscle cell) by releasing noradrenaline by binding to β receptors. This leads to the production of adenylyl cyclase which leads to the production of cAMP. cAMP activates PKA which opens up Ca 2+ channels. This influx acts on the SR and triggers further release of Ca from the SR. An 2+ increase in Ca triggers contraction.  Force generation  Increase in cytosolic calcium leads to increase in the force of contraction  Circulating hormonal adrenaline has the same effect Increase in intracellular [Ca ] in cardiac muscle cells 2+ 1. Increased binding of Ca to troponin: more cross-bridge formation between the thick and thin filaments 2+ 2. Incr2+se in Ca permeability of the sarcoplasmic reticulum (Ca - induced calcium release). Therefore, ventricular contractility is regulated simply by sympathetic input enhancing calcium influx into the cardiac myocytes which enhance contraction End-Diastolic Volume – it is the ventricular volume (of blood) at the end of diastole available to be pumped when the heart contracts Starling law/curve – Greater amounts of blood entering the heart during diastole lead to greater amounts of blood leaving the heart during systole.  ↑ EDV  ↑ Force of ventricular contractio ↑ SV  ↑ CO  Prevents an increase in heart volume with increased venous return The starling effect is mediated by the position of the thick and thin filaments within the contractile cardiac muscle cells.  Cardiac muscle fibers are shorter than their optimal length (unlike skeletal muscles). **See Slide 15 if necessary** Thiruvarangan o At normal resting length, there is only a limited amount of space for the filaments to slide over each other (smaller contraction force). o Stretching (due to ↑ EDV) increases the potential for cross-bridge formation. The stretching allows the filaments to slide to a greater degree.  A stretched muscle can generate a greater force of contraction  Note: if the muscle stretches too much, it loses its muscle contractility (as in high b.p. – cardiac hypertrophy)  Starling Curves and Sympathetic Activity o Stroke volume can be regulated by altering EDV and/or sympathetic activity. (see slide 17 if necessary) o In order to get a normal stroke volume from a weaker heart, for example, we have to increase the EDV or increase sympathetic input Effects of Pre-Load on End Diastolic Volume Pre-load is the amount of blood within the ventricles just before contraction.  If the end-diastolic pressure (EDP: pre-load) increases then end-diastolic volume will increas SV  CO o Ways to increase pressure can be an increase in blood volume, posture, muscular activity, and venous return  Pre-load can be influenced by ventricular compliance o Compliance is a measure of how easily the ventricle expands o Compliance = Δ Volume / Δ Pressure o Stiffness = Δ Pressure / Δ Volume o compliance and stiffness can be measured from a single curve  A steep slope means are reduced compliance or a high stiffness  Compare Points 1, 2, and 3 (see slide 19) o Normal Curve Figure 1: this graph is a measure of stiffness (slopes) o As EDP↑, EDV ↑  Compare Points 1, 4, and 5 o Normal and Abnormal Curves o As compliance ↓, EDV ↓ at any given EDP Muscular Pump – The Skeletal Muscle Pump: moves bl
More Less

Related notes for BIOC33H3

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.