Transcript Dr. Jasra Chapter 14 Cardiac A

Cardiovascular Physiology
• The circulatory system is the transport system of the body.
• The three basic components of the circulatory system
• Anatomy of the heart as a specialized organ pumping blood
to the whole body
• Cardiac muscle with its specialized pacemaker and
contractile cell
• The origin and conduction of the cardiac impulse
• The excitation –contraction coupling in the heart muscle
Three basic components
• The heart : serves as a pump imparting pressure to the blood.
This establishes the pressure gradient needed for the blood to flow
to the tissues.
• The blood vessels : serves as a passage way through
which blood is directed and distributed from the heart to all parts of
the body and subsequently returned to the heart.
- Arteries
- Veins
• The blood: serves as the transport medium.
Hemoglobin ?
A muscular organ
•Pericardium
•Pericardial Fluid
Four chambers
•Atria
•Ventricles
Septum
Heart Valves
• Right and left atrioventricular (AV) valves
The right side valves -tricuspid
The left side valves – bicuspid (mitral)
Chordae tendineae
 Papillary muscles
• Right and left Semi lunar valves
No valves between atria and the veins.
Flow of Blood
Overview of Circulation
•Pulmonary circulation
•Systemic circulation
•Oxygenated
•Deoxygenated
Pelvis and Legs
How Blood Flows?
• Pressure gradient- Highest in chambers of heart
- Lowest in the vena cava
• Loss of pressure- Friction between fluid and
blood vessel walls
Ischemia
Myocardial infarction
Changes in Pressure
• Pressure decreases over distance
Hydraulics- Study of fluid in motion
• Compression raises pressure
Velocity of Flow
• Resistance opposes flow
• Flow rate
• Cross sectional area
Velocity = Flow rate / cross–sectional area
The cardiac Muscle
• Most of the heart wall is composed of cardiac
muscle or the myocardium consisting of bundles
of cardiac muscle fibers arranged spirally
around the circumference of the heart.
• The individual cardiac muscle fibers form
interconnecting branching fibers . The adjacent
cells are joined end to end with specialized
structures –Intercalated disks.
Intercalated disks
The intercalated disks have two types of membranous
junctions: –
• The desmosomes -provide mechanical support
• The gap junctions -areas of low electrical resistance
allowing action potential to spread from one cell to the other.
No gap junctions between the atrial and ventricular contractile
cells
Cardiac Muscle Fibers
Cardiac Muscle Fibers
Myocardial cells
• Myocardial cells are striated
• Have sarcomeres
• Much smaller than skeletal muscle fibers
• Connected by gap junctions at intercalated discs
• Lots of mitochondria. Why?
• Lots of blood flow to myocardial cells
More about myocardial cells
• Large branching t-tubules
• Sparse sarcoplasmic reticulum
• Source of Ca++ is largely extra cellular
Autorhythmic cells /Pace makers
• Specialized myocardial cells which set the rate
of the heart beat.
• Ability to contract without any outside signal.
• Smaller and have few contractile fibers
• Initiate and conduct the action potential
Autorhythmic cells /Pace makers
• Don’t have a resting potential ,display pacemaker
activity i.e. their membrane potential slowly depolarizes
or drifts between action potentials until threshold is
reached. At that time the membrane fires an action
potential.
• The most important changes in ion movement giving rise
to pacemaker potential are the decreased outward K+
current coupled with a constant inward Na+ and
Ca++ current.
Myogenic
Neurogenic
Where are Autorhythmic cells?
• The sinoatrial node (SA node): a small specialized
region in the right atrial wall near the opening of the
superior vena cava
• The AV node : a small bundle located at the base of the
right atrium near the septum
• The bundle of His :a tract of specialized cells originating
at the AV node and enters the inter ventricular septum
• The purkinje fibers: small terminal fibers that extend
from the bundle of His and spread throughout the
ventricular myocardium.
Specialized Conduction System
Conduction in the Heart
• An action potential in an autorhythmic cell
• Spreading of depolarization through gap junctions
• Depolarization wave followed by a wave of contraction
• Atria contract followed by the ventricles
Internodal pathways connecting SA to AV node conduct faster than the contractile
cells of the atrium
Apex to base contraction of ventricles?
AV node delay?