Transcript Cardiovascular Physiology

Cardiovascular
Physiology
Blood Pressure
 =force
exerted by the blood against
the walls of the blood vessel;
Changes throughout cardiac cycle
– Systolic Blood pressure=maximal
pressure achieved by ventricular
contraction
– Diastolic Blood pressure=lowest
pressure remaining in blood vessels
after ventricle contracts
Blood Pressure
Blood flow - amount of blood flowing at
any given time. Dependent on Cardiac
output (CO).
 Blood pressure - force per unit area
exerted on wall of blood vessel

 Autonomic
Nervous System
– Sympathetic – causes
vasoconstriction of arterioles
 Increases
blood pressure
– Parasympathetic – causes
vasodilation
 Decreases
blood pressure
Blood Pressure
 Systolic
pressure
 Diastolic pressure
 Pulse pressure = systolic - diastolic
 MAP = Diastolic + (Pulse pressure/3)
 Hypotension - Low blood pressure
(Nutritional, anesthesia)
 Hypertension - High blood pressure
(increased peripheral resistance,
high blood viscosity)
Pressure
 Systemic
circulation-high hydraulic
pressure required to overcome
gravitational forces and resistance
 Arteriole-vessels with high resistance
to reduce pressure before reaching
capillary beds
 Pulmonary Circulation-low pressure,
due to low resistance to blood flow
Effects of High Blood Pressure
 Abnormally
high blood pressure
within veins-can cause leaking of
fluid from blood vessels
– Result-edema
– Congestive heart failure
 Right
cava
heart failure-leaking of fluid from vena
– Pleural effusion
 Left
heart failure-leaking of fluid within
lungs
– Pulmonary edema
Distribution of Blood Flow
 Pulmonary
Circulation – 15%
 Systemic Circulation – 80%
– 65% in veins
– 10% in arteries and arterioles
– 5% in capillary beds
 Heart
– 5%
Functions of the CV System
 Maintain
blood pressure within the
arteries
 Maintain blood flow to the tissues
 Maintain normal blood pressures
within the capillaries and veins
=Perfusion
Perfusion
 Allows
delivery of oxygen and
nutrients (i.e. glucose)
 Removal of waste products
– Carbon dioxide
 Transport
of hormonal messages
from one part of the body to another
Forces
 Heart
must adjust contractility
(inotropic state) based on forces
working on the heart.
– Preload
– Afterload
Afterload
 =Sum
of forces the ventricles must
contract against to make blood flow
forward
 Increased systemic blood pressure
– Increases or Decreases Afterload????
– Chronic blood pressure-increases the
work of the heart-heart enlarges!
Preload
 =Amount
of blood in the heart just
prior to contraction of the ventricle
 =Venous Return or amount of blood
returning to the heart
– Leaky valves-regurgitate blood back
into the atrium
 Increases
or Decreases Preload??
Inotropic State
 Adjustments
in contractility based on
Calcium and contractile protein
interactions
– Sympathetic tone (norepinephrineneurotransmitter)
– Increases heart rate and contractility by
increasing Calcium availability
– Starling’s law-increased contractility
with stretching of sarcomere
The Cardiac Cycle
 “Pacemakers”
of the heart-send
electrical signal through heart
– Systole-ventricular contraction
– Diastole-Heart is relaxed allowing filling
of the heart
**Based on Ventricle, although atria also
contract and relax
The Cardiac Cycle
 End
of Diastole-maximal ventricular
filling
 Electrical signal-triggers ventricular
contraction.
 Pressure in Ventricle > Atria = closes
AV valves; semilunar valves not
open yet
The Cardiac Cycle


First Heart Sound =closure of AV valves
Semilunar Valves open once pressure in
ventricle is greater than aorta or
pulmonary artery

Stroke Volume = amount of blood ejected
(end diastolic volume-end systolic volume)

Second Heart Sound= Closure of the
Semilunar valves
The Cardiac Cycle
Semilunar Valve-open
 AV valves-closed
 Ventricle Relaxes
 Once pressure in the ventricle is less than
the atrium-AV valves open allowing filling
of ventricle
 Third heart sound =passive filling of the
ventricle

– Normal to hear in horses and ruminants-not
carnivores
Ventricular Filling
 Initial,
rapid filling phase-passive
 Slow-filling phase-atrial contraction
 Fourth
heart sound =atrial
contraction
– Normal in ruminants and equine, not in
carnivores
Cardiac Muscle
 Striated
muscle
 Impulse from cell to cell
 Automaticity-cells can become selfexcitable
– Small portion of the muscle cells
Activation of cell
 Depolarization=Opening
of fast
sodium channels
 Wave of depolarizations travels down
myocardium-Ca++ channels open in
sarcoplasmic reticulum
– Crosslink of myocardium
 Refractory
Period-resting between
depolarization, unable to contract
Cardiac Impulse Propagation
 Automatic
Tissues-generate action
potentials
 Sequence of activation
– Sinoatrial (SA) node-fastest rate!
 Atrial
Contraction
– AV node
– Bundle of His
– Rt. And Lt. Bundle Branch to v. apex
– Purkinje fibers to myocardium
Conduction Propagation
Action Potential


THE WHOLE PICTURE
Na + influx creates (+) internal
charge
1
+
CHARGE
INSIDE 0
CELL
-
2
Repolarization
3
0 Depolarization
K+ leaves cell
and cell
returns to it’s
resting or
repolarized
4
state
Resting cell
TIME
**Purple numbers indicate phase numbers
Action Potential
0-Sodium enters cell
via fast channels
 1-fast sodium
channels close
 2-Ca and Na enter cell
via slow channels
 3-K exits cells
 4- Na and K
equilibrium

Intrinsic Rate
 SA
node-fastest
 AV note-40-60 bpm
 Sympathetic and Parasympathetic
Nervous System-alter the intrinsic
rate
– SNS-increase rate of depolarization
– PNS-decrease rate of depolarization
Heart Rate Regulation
 Baroreceptors-in
heart chamber
blood vessels and
– If blood pressure decreases
 Brain>>Increased
Sympathetic nervous
system
 Increases Heart rate and vasoconstricts to
increase blood pressure
– If blood pressure increases?
Excitation-Contraction Coupling
 See
muscle physiology!!
 Ca++ influx
 Myofibrils couple via
troponin/tropomysin complex
The Electrocardiogram (ECG)
 Recording
of electrical activity of the
heart
 Waves-positive vs. negative
depending on the direction the
impulse is traveling
ECG
P
wave-
– Atrial depolarization
 QRS
complex
– Ventricular
depolarization
T
wave-ventricular
repolarization
Conduction
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