Cardio Vascular System Fundamentals YouTube Lecture Handouts

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Illustration: Cardio Vascular System Fundamentals YouTube Lecture Handouts
Illustration: Cardio Vascular System Fundamentals YouTube Lecture Handouts

CARDIOVASCULAR SYSTEM

Includes:

  • Heart &
  • Blood Vessels
    • Arteries
    • Arterioles
    • Capillaries &
    • Veins
Illustration: CARDIOVASCULAR SYSTEM
Illustration: CARDIOVASCULAR SYSTEM

Functions of CVS

  • To provide pressure head so as to keep blood flowing. Pressure in Lt. Ventricle is up to 120 while in Rt. Atrium it is only about 0 mmHg.
  • To maintain BP during rest as well during various activities
  • Ensures more supply to active tissues
  • During emergencies such as in case of severe hemorrhage

Blood flow to vital organs like brain & heart is maintained, this can be even at the expense of reducing flow to other tissues & at times it can lead to total renal shut down so total anuria

Secondary Functions (Blood)

  • Distribution of metabolites & oxygen
  • Collection of waste products & CO2
  • Thermoregulation
  • Distribution of hormones to the target tissues

Physiological Anatomy of Heart

  • Located in the mediastinal space of thoracic cavity between two lungs.
  • Measures about 12 cm from base to apex and 6 cm anteroposteriorly
  • Weight approx. 300 gms in males and 250 gms in females
  • Works throughout the life
  • Contracts about one lakh times in a day
  • Pumps about 7200 liters of blood in 24 hrs.
Illustration: Physiological Anatomy of Heart
Illustration: Physiological Anatomy of Heart

Cut Section

  • Four chambered 2 atria & 2 ventricles
  • Atria and ventricles are separated by a fibrous ring and are two separate units
  • Atria are divided by interatrial septum
  • Ventricles are divided by intraventricular septum

Atria

  • Atria are thin walled and receive blood
  • Rt atrium from systemic circulation via superior & inferior vena cavae
  • Lt atrium from lungs via pulmonary veins

Ventricles

  • Ventricles are thick walled and serve as pumps
  • Lt ventricle pumps blood in systemic circulation
  • Rt ventricle pumps in pulmonary circulation

Structure of Heart

Illustration: Structure of Heart
Illustration: Structure of Heart
Illustration: Structure of Heart

Valves of Heart

Two types

  • Atrioventricular
    • Mitral
    • Tricuspid
  • Semilunar
    • Aortic
    • Pulmonary

Structure of Valves

Illustration: Structure of Valves

Functions of Valves

  • They open in one direction.
  • Keep circulation unidirectional
  • Prevent backflow of blood.
  • Produce heart sounds which have clinical significance

Wall of the Heart

Pericardium

  • Fibrous
  • Serous
  • Parietal
  • Visceral

Myocardium

  • Specialized tissue of heart
  • Cardiac muscles

Endocardium

Specialized Tissue of Heart

Is made of modified cardiac muscles

Phylogenitically primitive

  • Sinoatrial node (SAN)
  • Interatrial tract (Bachman՚s bundle)
  • Internodal fibers: three pathways
  • Ant. pathway of Bachman
  • Middle pathway of Wenckebach
  • Post. Pathway of Thorel
  • Atrioventricular node (AVN)
  • Bundle of His
  • Purkinje fibers
Illustration: Specialized Tissue of Heart

Histological Features

  • Pace maker is rich in P (pacemaker) cells, which are primitive and less striated
  • P cells are pale, round with few organelles they are connected by gap junctions.
  • P cells are more in SA node and less in AV node

Sino Atrial Node

  • Located near the junction of superior venacava & the rt. atrium
  • Acts as pacemaker because the rate of impulse generation is highest here

Ectopic pacemaker: is pacemaker other than SAN.

  • Some other part discharge at a higher rate
  • Impulse blockage from SAN to AVN

Atrioventricular Node

  • Located at the rt. lower part of the interatrial septum

Functions

  • Normally it is the only path of impulse conduction from atria to ventricles
  • Produces A-V delay

A-V Delay

  • Is gap between atrial & ventricular contraction
  • Conduction is slow in different parts of A-V Node because of less number of Gap Junctions. So each succeeding cell is slow to be excited.
  • Normal A-V delay is about 0.13 sec.
  • It ensures that Ventricular contraction is always after the Atrial contraction.
Illustration: A-V Delay

Bundle of His & Purkinje fib.

  • Is continuation of AVN. Present on the rt. side of the intraventricular septum
  • Divides into 2 branches
    • Rt. Bundle Branch &
    • Lt. BB
  • Purkinje fib. arise from both branches
Illustration: A-V Delay

Innervation

By both divisions of ANS

  • Sympathetic: from 1 to 5 thoracic seg.
  • Distibited to all parts of heart
  • Parasympathetic: from Vagi
    • Mainly inn. SAN & AVN
    • Lesser extent muscles of atria
    • Even lesser to ventricular muscles or practically no inn. To ventricles
Illustration: Innervation

Sidedness

Innervation of nodes

  • SA Node
  • Parasympathetic … Rt. Vagus
  • Sympathetic … Rt. sided nerves
  • AV Node
  • Parasympathetic … Lt. Vagus
  • Sympathetic … Lt sided nerves

Properties of Cardiac Mus

  • Automaticity & Rhythmicity
  • Conductivity
  • Excitability
  • Contractility
  • All or none response
  • Staircase phenomenon
  • Refractory period
  • Tone

Properties of Specialized Tissue

  • Automaticity
  • Rhythmicity
  • Conductivity

Specialized Tissue

Automaticity

Heart can generate its own impulse that is why transplantation is possible

Rate of Impulse Generation

  • SA node … 70 - 80 per minute
  • AV node … 40 - 60
  • Atrial muscle … 40 - 60
  • Ven. muscle … 20 - 40
    Illustration: Rate of Impulse Generation

Automaticity & Rhythmicity

  • Normally impulses are generated automatically & rhythmically
  • It is because of presence of pacemaker potential or prepotential
  • Pacemaker potentials are prominent in SA and AV nodes

Latent Pacemaker

Comes into action when normal pacemaker stops functioning

  • Latent pacemaker are present in the conducting system
  • Atria and ventricles normally have no pacemaker but can discharge when injured

Pacemaker Potential

  • RMP is not stable
  • RMP is -55 to -60 mV
  • Rapid depolarization begins at threshold level -40 mV
  • Depolarization peaks up to + 5 mV
  • Then Repolarization begins
  • Normally it goes on throughout the life

Ionic Basis of PP

  • At the beginning of repolarization there is potassium efflux
  • Prepotential caused by opening of T (transient) calcium channels
  • Rest of Depolarization is by opening of L (long lasting) calcium channels
  • Repolarization by potassium efflux

Pacemaker Potential

Illustration: Pacemaker Potential

Pacemaker Potential

Illustration: Pacemaker Potential

Effect of ANS

  • Vagal stimulation
  • Membrane becomes hyperpolarized (more negative)
  • Slope of prepotential decreases
  • Acetylcholine increases potassium conductance
  • Firing rate hence HR decreases
  • Strong stimulation can stop heart
Illustration: Effect of ANS

Vagal Escape

  • Vagal stimulation by tetanising current
  • Slowing of heart
  • After some time heart starts beating even if the stimulation is continued
  • It is called Idioventricular Rhythm

Sympathetic Stimulation

Results in

  • Rapid fall in repolarization
  • No change in RMP
  • Beta 1 receptors stimulated
  • Mediated via cAMP
  • HEART RATE INCREASES

SYMPATHETIC STIMULATION

Illustration: SYMPATHETIC STIMULATION

Conductivity

Tissue and Its Rate of Conduction. (M/S)

  • SAN
  • Atrial muscles
  • AVN
  • Bundle of His
  • Purkinje system
  • Ven. Muscles

Pathway of Impulse

Illustration: Pathway of Impulse

Last to Depolarize

  • Poster basal region of left ventricle
  • Pulmonary conus
  • Upper portion of interventricular septum

Time Required

Illustration: Time Required

Specialized Tissue

Illustration: Specialized Tissue

Cardiac Muscle

  • Are involuntary
  • There are two functional units
    • Atrial syncytium
    • Ventricular syncytium

Types of Muscles

Illustration: Types of Muscles

Cardiac Muscle

Histology

  • Size Length … 80 µm Width … 15 µm
  • Fibers are striated
  • Branching and anastomosis present
  • Nucleus is central
Illustration: Histology

Intercalated Disc

  • Present at the junction of two cells
  • Intercalated disks 0.5 to 1 µ in thickness
  • Desmosomes ensure tight junctions
  • Gap junctions help in fast conduction
Illustration: Intercalated Disc

Sarcotubular System

  • Sarcoplasmic reticulum less developed as compare to skeletal muscles
  • “T” tubules and “L” tubules present
  • “T” -tubules are wider
  • One triad per sarcomere
  • Triads are at Z lines
  • Dyads are often seen
  • Dyads have “T” tubule and one cistern of “L” tubule

Triads

Histology

Illustration: Histology
Illustration: Histology

Properties of Cardiac Muscles

  • Excitability
  • Automaticity & Rhythmicity
  • Contractility
  • Conductivity
  • All or none law
  • Staircase phenomenon
  • Fatigue

Excitability

Shows following changes

  • Electrical changes
  • Ionic changes
  • Mechanical changes
  • Metabolic changes

Electrical Changes

Table of Electrical ChangesTable of Electrical Changes
PhaseState
ORapid depolarization
1Rapid repolarization
2Plateau
3Slow depolarization
4Resting
Illustration: Electrical Changes

Ionic Changes

Table of Ionic ChangesTable of Ionic Changes
PhaseChange
0Na influx
1Na channels closed & K efflux
2Ca influx
3K efflux
4RMP

Contractility

Shows:

  • All or none Law
  • Staircase phenomenon
  • Refractory period

Cardiac Muscles Do Not Fatigue

Following reasons:

  • Aerobic metabolism so lactic acid does not accumulate
  • Rich blood & O2 supply
  • Mitochondria in plenty

Contractility

  • Basic mechanism similar to skeletal muscle contraction
  • Depends more on extracellular Ca++ level
  • Isotonic as well as isometric

Characteristics of Contraction

Refractory period is long

  • Absolute RP (0.20 to 0.30 sec.)
  • Relative RP (0.05 sec.)
  • Because of long refractory period muscle cannot be Tetanized

ELECTRICAL ACTIVITY

Illustration: ELECTRICAL ACTIVITY

Metabolic Changes

  • Mainly aerobic
  • Normally only 1% anaerobic
  • During hypoxia up to 10% anaerobic

Energy Sources

  • Fat … 60%
  • Carb … 35%
  • Ketones & A. A … 5%

Contractility in Heart

Regulation

  • Heterometric regulation
    • Frank- Starlings Law of heart
  • Homometric regulation
    • by Autonomic Nervous System