Class Notes (810,488)
Canada (494,139)
BIOC33H3 (127)

BIOC33/BIOC34 Lec 5.docx

11 Pages
Unlock Document

University of Toronto Scarborough
Biological Sciences
Stephen Reid

BIOC34/BIOC33 Lec 5. Jan. 20/2014  Assignments o Just need to submit what is requested in instructions  Cardiac output o Amount of blood pumped per unit time o CO = SV x HR o MAP = CO x TPR  Autonomic regulation of heart rate o Have both types of parasympathetic innervation through vagus nerve o From brainstem, have a branch of the vagus nerve that innervates pacemaker (SA node) as well as a branch innervating theAV node connecting the electrical axis of atria to the ventricle o Have sympathetic nerve which also innervates the SAandAV nodes but it innervates ventricular myocardium as well o Ventricular muscle has 2 purposes:  Increase force of contractility  Helps to speed up the relaxation of the heart when it transitions from systole to diastole • Important because it allows heart to spend more time in diastole - can fill with more blood  Autonomic regulation of heart rate o Parasympathetic (Vagus): Have our cardiac branch of the vagus nerve that presynaptically releases acetylcholine onto ganglia where it binds to nicotinic receptors. Post-ganglionic cell also releases acetylcholine onto the heart. Acetylcholine interacts with muscarinic acetylcholine receptor (on the heart)  In this case, see it slows down the rate of depolarization of pacemaker cells and slows rate of conduction (waves of conduction fromAV node) o Sympathetic system does the opposite - haveACh released from preganglionic fibres onto ganglia  From post-ganglionic fibre have NE released as a neurotransmitter  NE speeds up pacemaker potential as well as speeds up conductivity from theAV node o Adrenal gland - also under control of sympathetic nervous system. Pre-ganglionic NT =ACh, reacts with nicotinic receptors on adrenal cells and release NE and epinephrine into the blood. These hormones have similar effects or opposite effects on the blood vessels. It depends on which organ is being talked about and at what concentration  Sympathetic regulation of heart rate o Speeds up depolarization of pacemaker cells and speeds up conductivity through AV node o Does this by enhancing influx of Na and Ca into the pacemaker cells orAV node cells, allowing for more rapid depolarization o When talking about NT from sympathetic nerve, it would be NE. if talking about hormone from adrenal gland, would be both E and NE. They interact with beta- adrenergic receptor on the cell membrane activating a stimulatory G protein, which then activatesAC, which catalyzes conversion ofATP into cAMP and cAMP leads to phosphorylation of protein kinase. o This then activates our funny channels which allow Na in and some K out during the first half of the pacemaker potential. More channels opening = more Na influx.Also enhance opening of T-type Ca2+ channels, which are responsible for the depolarization of the second half of the pacemaker potential. o In that slow pacemaker potential, have funny channels opening in the first half, T- type channels opening in the second half, and theAP carried by Ca current through L-type Ca channels.?? By having enhanced Na and Ca currents, have an enhanced rate of depolarization and heart rate increases  Parasympathetic Regulation of Heart Rate o Reduces rate of depolarization in SAandAV node through activation of inhibitory and stimulatory G protein o ACh interacting with cholinergic receptor - in this case, in cells of the heart, they are muscarinic receptors.AChR is described as muscarinic or nicotinic. In the heart, it is muscarinic R. o Get activation of inhibitory and stimulatory G protein.  Inhibitory protein acts to close the T-type Ca++ channels - reduces Ca current into cell and reduces the depolarization rate.  Stimulatory protein opens K+ channel - K leaves cell, reduces depolarization and enhances hyperpolarization o These both decrease the rate and magnitude of depolarization - leads to slower heart rate  Parasympathetic and sympathetic tone to the heart o Possible to quantify the amount of sympathetic and amount of parasympathetic using pharmacological measures o Amount of input is referred to as the TONE o Solid line = normal situation o With sympathetic stimulation, slope of pacemaker potential is enhanced and we get a faster heart rate due to action of Ca and Na current. o With parasympathetic (vagal) stimulation input to heart, it takes a longer time for pacemaker potential to meet threshold to be met so heart rate slows down o 2 competing inputs into the heart which are always providing some sort of tone to the heart o Parasympathetic dominates sympathetic  o parasympathetic (vagal) tone > sympathetic tone o Can think of parasympathetic as a braking system and sympathetic as an accelerator. Under normal conditions if pacemaker were allowed to depolarize on its own, without any input from sympathetic or parasympathetic, it depolarizes at a rate of 100-110 beats/min. This would be a neutral situation. Have pacemaker cells depolarizing at this high rate. Unless we are exercising, heart rate isn’t normally 100 beats a min. usually 60-70 beats/min o Since normal heart rate is lower than intrinsic rate of depolarization of the pacemaker cells, this means the pacemaker cells are being slowed under normal conditions. Vagal tone is having a greater effect than sympathetic tone  Quantification of Parasympathetic and Sympathetic Tone to the Heart o We can quantify how much vagal tone and sympathetic tone there is to the heart through pharmacological agents that are going to block the receptors on the cardiac cells that are responsible forACh and NE o Looking at parasympathetic tone from vagus nerve,ACh is being released onto heart cells. Type of cholinergic-R is a muscarinic-R. Classical anti-muscarinic drug that is injected to block muscarinic R is atropine - can block the effects of parasympathetic nervous system by putting atropine onto heart. o On sympathetic nervous side, the majority of action of NE on the heart is through B-adrenergic R. Adrenergic are alpha or beta. On cardiac contractile cells, Beta- Rs are predominant. There are a number of drugs that can block these Beta-Rs  beta blockers which are treatment for high blood pressure  E.g. atenolol - Blocks Beta R and will reduce action of sympathetic nervous system on the heart  If blocking with atenolol, expect heart rate to drop o If we block muscarinic R, expect heart rate to speed up becauseACh is normally slowing it down o Nicotinic (N) receptors are not blocked by atropine  Quantification of Sympathetic and Parasympathetic Effects (Tone; Inputs) on Heart Rate o Resting heart rate = 70 beats/min o If atenolol is given to a person, it will slow down the sympathetic nervous system and block NE actions. Expect heart rate to slow down because we are removing the accelerator. With atenolol, heart rate falls to 50 beats/min o Sympathetic tone/input is the difference between resting rate and rate that we see when we block the system (10 beats/min - 50 beats/min = 20 beats/min)  Sympathetic input increases HR by 20 beats/min o Parasympathetic tone -  Block muscarinic R with atropine, now removing the braking system and expect heart rate to go up  Goes from 70 to 100/min  Parasympathetic input causes heart rate to be reduced by 30 beats/min o Use drugs to determine the actions or to quantify extent of actions of autonomic nervous system on heart rate o Parasympathetic sends branches out directly from brainstem (medulla) and sympathetic system sends branches through sympathetic nerves starting at the spinal cord and going to spinal chain ganglia  Cardiovascular-Related Output from the Brainstem o In diagram, see parasympathetic and sympathetic innervation to the heart o Have sympathetic innervation going to blood vessels - arteries and veins o See that arteries are labelled as systemic resistance arteries and think of arterial circulation as being a pressure reservoir or a resistance reservoir  Pressure in arterial circuit is higher than in venous circuit therefore majority of pressure is in arteries. o Veins in venous side are called systemic capacitance veins - this means it has the greater capacity to hold blood. Majority of blood is in the venous circuit o Have innervation coming to arteries and veins and see that this causes the arteries and veins to dilate or constrict - by dilating or constricting, they alter blood flow and resistance to flow which can affect blood pressure o Resistance goes down to adrenal glands - inner region - adrenal medulla; where NE and E are produced.Adrenal cortex - produces a lot of steroid hormones important in osmoregulation o See some input into cardiovascular center. Key input = pressure R located in the carotid arteries and aortic arch o Look at baroR-reflex (reflex initiated by baroR in aorta and carotid arteries - key to regulating blood pressure) o Also have movement or proprioR in skeletal muscle that can send inputs to cardiovascular centers o Skeletal muscle R are interesting in a respiratory control POV  there is no known respiratory controls system that can account for the increased breathing during exercise  Oxygen and CO2 - stay the same during exercise  Cardiac output (CO) o HR regulation is parasympathetic/sympathetic regulation and effects of circulating hormones o CO = the rate at which the heart pumps blood o Measured in ml (or L)/min o CO = SV x HR  Stroke volume Regulation o SV = mL of blood pumped per beat o Compared to HR regulation, SV regulation is not more complicated, but involves more factors o 3 factors that affect SV  2 function on their own  3 - where complexity comes in (EDV) o 1. Ventricular contractility - if ventricle contracts with a greater force, will pump more blood out of the ventricle to aorta or pulmonary artery  Contractility of ventricle is affected mostly by sympa
More Less

Related notes for BIOC33H3

Log In


Don't have an account?

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.