This PPT is prepared to understand Circulation of blood in the human body and the cardiac muscles involved and their function.

1. Heart - Circulation

2. Heart
Function:
- Pump blood to various parts of the body
- To lungs for oxygenation and for other parts of body for supply of oxygen

3. Circulation
Function:
 To serve the need of body tissue (nutrients, gases, waste products, hormones)
 Maintain appropriate environment in all tissue fluids for survival and function of cells
Rate of blood flow is directly proportional to the need of nutrition, except for kidney
(excretion)
Heart and blood vessels are controlled to provide necessary cardiac output and arterial
pressure.
Physical characteristics of circulation:
2 types:
Systemic or greater or peripheral circulation– supply blood to all parts except lungs
pulmonary circulation – supply blood to lungs

4. Circulation
Parts of circulatory system:
1. Arteries:
Transport blood to various tissues under high pressure
Thick vessel wall
Blood travel faster
2. Arterioles:
End of arteries- Small blood vessel before capillaries
Control blood release into capillaries
Have strong muscular wall that can close arterioles completely or dilates the vessels for blood flow – altering
blood flow in each tissue
3. Capillaries:
Smaller blood vessels in body
Exchange of fluid, nutrient, electrolyte, gases and hormones between blood and interstitial fluid occurs through
small pores in capillaries
4. Venules:
Collect blood from capillaries and gradually enters vein
5. Veins:
Transport blood to the heart
Reservoir of extra blood (depends on circulation)
Low Pressure
Blood vessel wall is thin
They have potential energy to contract and relax but never uses

5. Circulation
Volume of blood in various parts of circulation:
Systemic – 84%
64% vein
13% arteries
7% arterioles and capillaries
Pulmonary – 9%
Heart – 7 %

6. Circulation
Cross sectional area and velocity of blood flow:
Approx. cross sectional area of blood vessels:
Cross sectional area of arteries are lesser than vein (4 times) – explains larger storage
capacity
Velocity of blood flow:
Irrespective of the cross sectional area of the blood vessel, same volume of blood flow
(F) must passes through each segment of the circulation in each min.
Velocity of blood flow (v) is inversely proportional to vascular cross sectional area (A)
v=F/A

7. Circulation
Velocity of blood flow in various parts of circulation:
Under rest – velocity of blood flow averages about 33 cm/sec in aorta
In capillaries – 0.3 mm/sec as the capillaries are only 0.3 – 1 mm in length
Blood remain in the capillaries of only 1-3 sec which is surprising
Pressure in various portions of circulation:
Blood pumped into aorta at high pressure hence increase in arterial pressure (average-
100 mmHg)
Heart pumping is pulsatile
Systolic – contraction of heart to eject blood (120 mmHg)
Diastolic – relaxation of heart after ejecting blood (80 mmHg)
Systemic circulation pressure is high at the heart and pressure falls progressively to 0
mmHg by the time it reaches superior and inferior vena cava which opens in right
atrium.
Arteriole end – 35mmHG
Venule end at the end of capillaries – 10 mmHg
Average functional pressure of capillaries - 17 mmHg (low enough so little plasma leaks
through minute pores of capillary walls

8. Circulation
Pressure in various portions of circulation:
Pulmonary circulation pressure:
Pulsatile like aorta but has less pressure
pulmonary artery systole – 25mmHg
Pulmonary artery diastole – 8 mmHg
mean arterial pressure – 16 mmHg
mean pulmonary capillary – 7 mmHg
Even though the pressure is less the average,
blood flow of pulmonary system is same as
systemic circulation.
It has less pressure because blood is sent
through these vessels only for oxygenation

9. Circulation
Basic principles of circulatory system: 3 major principles
1. Blood flow to most tissue is controlled according to need of tissue :
Active tissue requires high blood flow
Heart can only increase the blood flow 4-7 times not more than that
It is not possible to increase the blood flow beyond this level.
Instead, micro vessels of each tissue control blood flow by contraction or relaxation
based on need
Nervous system and hormones also helps.
2. Cardiac output is the sum of all the local tissue flow:
Blood flow to tissue enters vein and inflow of blood increased in heart leading to
pumping of blood on to arterial system
Heart is a automaton which responds to demand of tissue need.
Heart needs special nerve functions to perform these functions

10. Circulation
3. Arterial pressure regulation is generally independent of either local blood flow
control or cardiac output control
Various system to regulate arterial pressure – Nervous reflex elicits a serious od
circulatory chages
a) Increased force of pumping
b) Contraction of vein so blood flow is high to heart
c) Constriction of arterioles so blood is there in larger arteries to increase the pressure
d) Kidney also plays a major role in regulating arterial pressure by releasing blood
pressure controlling hormones (Angiotensin)

11. Cardiac muscles

12. Cardiac muscles
3 major types:
1. Atrial muscle
2. Ventricular muscle
Contracts same way as skeletal muscle but the period of contraction is high
3. Specialized excitatory and conductive muscles
Contracts with less strength because they have less contractile fibrils but exhibit
automatic rhythemic electrical discharge in form of action potential.
Conduction of action potential leads to rhythemicity of heart
Anatomy:
Arranged in lattice work – fibers divide,
recombine and branches
Striated as SMCs
Have microfibrils containing actin and myosin
filaments which lies side by side during
contraction

13. Cardiac muscles
Physiological characteristics:
1. Excitable:
Respond to stimulus like membrane potential
If provided sufficient membrane potential these muscles contracts
Factors affecting: Bathmotrophic
Increase excitation – positive bathmotrop (Catecholamines)
Decrease excitation – negative bathmotrop (hypercarbia – less response to
Catecholamines)
2. Auto rhythemicity:
Self excitatory
Also influenced by nerves and hormones
3. Contractile:
Self explanatory
Contraction differs in different ways than SMCs
Factors affecting: inotropy – force of muscle contraction
Increase contraction: positive inotrophic (ventricular hypertrophy)
Decrease contraction: negative inotrophic (myocardial infarction)

14. Cardiac muscles
4. Conduct electrical impulses:
Intercalated disks helps cardiac muscle to conduct electric impulse
Speed is low
5. Syncytium: single cell or mass of cell having many nuclei formed by fusion of cells or
by division of nuclei.
Intercalated disks are cell membranes fused together to form gap junctions where ions
diffuse rapidly to intra cellular fluid
Action potential travels from one muscle cell to another easily
Since heart muscle cells are syncitious if once cell is activated or excited the action
potential spreads to all the cells
Types:
1. Atrial syncytium
2. Ventricular syncytium
Separated by fibrous tissue that surrounds atrio ventricular (A-V) openings between atria
and ventricles
Potentials are not conducted from atria to ventricle via these tissues
Potentials are conducted by AV bundles.

15. Cardiac muscles
6. All or none law in the heart applies to the entire syncytium:
If the stimuli exceeds the threshold potential, the nerve or muscle fiber will give a
complete response, otherwise there is no response.
7. The action potential in cardiac muscle is prolonged and has a long refractory period:
Action potential in ventricular muscle fiber
After stimuli – membrane remain depolarized for
0.2 sec exhibiting a plateau followed by
repolarization
Presence of plateau: cause ventricular
contraction 15 times more in cardiac muscle than
skeletal muscle

16. Cardiac muscles
Another characteristics: Refractory to restimulation during the action potential
Refractory – period of time during which a second action potential absolutely cannot be
initiated no matter how large the applied stimulus is.
Ventricular refractory period: 0.25 – 0.30 sec
Atrial refractory period: 0.15 sec
Relative refractive period: period which follows
immediately after refractory period. Initiation of
second action potential is inhibited but not
impossible
Early premature contraction- extra heart beat
which originates in ventricles
Later premature contraction - originates either
in atria or ventricles

17. Cardiac muscles
8. Cardiac muscle requires
calcium ions for
contraction:
a. Action potential created
b. Reaches cardiac muscle
membrane
c. spreads through cardiac
muscle and reaches T tubule
d. T tubules creates action
potential
e. Acts on sarcoplasmic reticulum
f. Release of Ca++ ions into
muscle sarcoplasm
g. Ca++ enters myofibrils and
catalyses chemical reactions
that promote sliding of the
actin and myosin filaments
along one another
h. Produce muscle contraction

18. Cardiac muscles
In addition,
Ca++ is taken in from T tubules
into sarcoplasm at the time
of action potential
Opens voltage dependent Ca++
channels in the membranes
of T tubules
Ca++ activates calcium release
channels called ryanodine
receptor channels in
sarcoplasmic reticulum that
leads to release of calcium
Calcium interact with troponin
and initiates cross link
formation and contraction
like SMCs

19. Cardiac muscles
Ca++:
Without calcium from T tubules the strength of cardiac muscle contraction would fall
Cardiac muscle is not well developed as SMCs and cannot store Ca++
Diameter of the T tubule is 5 times higher in cardiac muscle than in the SMCs hence
larger volume of Ca++
T tubule have high amount of mucopolysaccharide that are negatively charges and acts
as storage house for CA++
Strength of contraction depends on concentration of Ca++ in the extra cellular fluid
Heart placed in Ca++ free solution will stop working
9. Cardiac muscle contraction depends on the initial length of the muscle fiber:
(Frank Starling law of the heart and concept of preload and afterload)
Preload: Amount of ventricular stretch at the end of diastole (due to filling of blood)
The greater the volume the greater end diastolic pressure and greater stretch
Afterload: force or load against the ventricular stretch, in which the heart has to contract
to eject blood

20. Cardiac muscles
Frank Starling law:
States that the stroke volume of heart increases in response to an increase in volume of
blood in the ventricles before contraction, when all factors remain constant.
Stroke volume: volume of blood pumped from left ventricle per beat
Relationship of length to contraction can be modified in the presence of inotrophic
factors
a. Intense symphathetic stimuli can alter young adult heart rate from 70 beats/ min to
180-200 beats/min in some cases 250 beats/min
b. Increase the contraction force to increase the volume of blood pumped thereby
increasing ejection pressure
Rather than Frank Starling law symphathetic stimuli maximises the cardiac output 2-3
folds
Inhibition of symphathetic nervous
Decreases cardiac output
- decreasing heart rate
- decrease the strength of ventricular muscle contraction
- decrease cardiac output by 30% below normal

21. Cardiac muscles
Ventricular pressure – volume relationship during systole and diastole:
Systole- contraction of heart to eject blood
Diastole – relaxation of heart after contraction
Pumping mechanism of ventricle:
2 important component of curve
systolic pressure curve and diastolic
pressure curve – volume pressure curve
Diastolic pressure curve:
Fill heart with greater volume of blood and
measure diastolic pressure immediately before
ventricular contraction – end diastolic pressure
Systolic pressure curve:
Systolic pressure achieved during ventricular
contraction at each volume of filling

22. Cardiac muscles
Until the volume of blood reaches 150 ml the diastolic pressure does not increase
Upto this point the blood can flow into ventricle from atrium easily
During ventricular contraction, the systolic
pressure increases even at very low volume
The systolic pressure decreases at some point,
because at higher volume the actin and myosin
filaments are pull apart from each other,
leading to decrease in contraction less than
optimum
Normal left ventricular pressure – 250 -300
mmHg
Normal right ventricular pressure – 60 – 80
mmHg

23. Cardiac muscles
Volume pressure diagram demonstrating intraventricular volume and pressure during
single cardiac cycle:
1. Period of filling
2. Period of isovolumic contraction
3. Period to ejection
4. Period of isovolumic relaxation

24. Cardiac muscles
10. Contraction muscle does not fatigue because of the following reasons.
a. Increase refractory period
b. Increase blood flow to the heart– capillary density is 4 times higher
c. Aerobic metabolism – lactic acid formation is not there
d. Increase in mitochondria – one third of the cardiac muscle by weight