Cardio Vascular System Fundamentals YouTube Lecture Handouts
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CARDIOVASCULAR SYSTEM
Includes:
- Heart &
- Blood Vessels
- Arteries
- Arterioles
- Capillaries &
- Veins
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.
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
Valves of Heart
Two types
- Atrioventricular
- Mitral
- Tricuspid
- Semilunar
- Aortic
- Pulmonary
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
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.
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
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
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
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
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
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
Conductivity
Tissue and Its Rate of Conduction. (M/S)
- SAN
- Atrial muscles
- AVN
- Bundle of His
- Purkinje system
- Ven. Muscles
Pathway of Impulse
Last to Depolarize
- Poster basal region of left ventricle
- Pulmonary conus
- Upper portion of interventricular septum
Time Required
Specialized Tissue
Cardiac Muscle
- Are involuntary
- There are two functional units
- Atrial syncytium
- Ventricular syncytium
Types of Muscles
Cardiac Muscle
Histology
- Size Length … 80 µm Width … 15 µm
- Fibers are striated
- Branching and anastomosis present
- Nucleus is central
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
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
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
Phase | State |
---|---|
O | Rapid depolarization |
1 | Rapid repolarization |
2 | Plateau |
3 | Slow depolarization |
4 | Resting |
Ionic Changes
Phase | Change |
---|---|
0 | Na influx |
1 | Na channels closed & K efflux |
2 | Ca influx |
3 | K efflux |
4 | RMP |
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
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