The cardiovascular system functions to transport blood and nutrients throughout the body while removing waste. It is composed of the heart, which pumps blood through a closed system of arteries, capillaries and veins. The heart has four chambers and uses electrical conduction pathways to generate rhythmic contractions. Blood flows through two circuits - systemic circulation which oxygenates tissues, and pulmonary circulation which oxygenates blood in the lungs. The cardiovascular system is regulated through neural and hormonal mechanisms to maintain blood pressure and meet the body's needs.

1. 1
Physiology of
The Cardiovascular System

2. 2
FUNCTIONS OF THE CVS
• Transport and distribute essential substances to
the tissues.
• Remove metabolic byproducts.
• Adjustment of oxygen and nutrient supply in
different physiologic states.
• Regulation of body temperature.
• Humoral communication.

3. 3
Components of the CVS
CVS composed of
 Heart: Pumping center
 Blood vessels
 Arteries: Distributing system
 Capillaries: Exchange system
 Veins: Collecting system
 Blood: circulating connective tissue

4. 4
Division of the circulatory system
• In the CVS, blood passes through two (double)
circulations:
 Systemic circulation
 Pulmonary circulation
• Systemic circulation:
Starts in the LV→ Aorta → Systemic arteries
→Systemic capillaries →Veins →SVC & IVC
→ends in RA
• Pulmonary circulation:
Starts in the RV →Pulmonary trunk →Pulm.
arteries → Pulm. capillaries →Pulm. veins →ends
in the LA.

5. 5
Pathway of Blood Through the Heart and Lungs

6. 6

7. 7
The Heart
• Heart is the hollow, muscular organ that plays a
central pumping role
• Composed of 4-chambers;
• 2 atria and 2 ventricles
• Size: Approximately equivalent to clenched fist
• Weight: 280 to 320 gram in average adults
• It is situated between two lungs in the
mediastinum.

8. Anatomical location of the heart
8

9. 9
The Heart: Anterior View

10. 10
The Heart: Posterior View
Figure 18.4d

11. 11
Histology of the heart
Heart wall is made up
of 3 distinct layers:
1 - Endocardium -
innermost layer;
epithelial tissue that
lines the entire
circulatory system
2 - Myocardium -
thickest layer; consists
of cardiac muscle
3 - Epicardium - thin,
external membrane
around the heart

12. 12
Cardiac muscle (Myocardium)
•Myocardium is the middle layer of wall of the heart
•Cardiac muscle cells are straited, mononucleated
and branched
•connected to each other through intercalated disks
•Intercalated disks: Specialized cell-cell contacts:
• Desmosomes hold cells together and
• Gap junctions allow conduction of action
potentials.
•Electrically, cardiac muscle behaves as single unit

13. 13
Properties of cardiac muscles
• Cardiac muscles have 4 physiological
properties. These are;
 Autorhythmicity
 Excitability
 Conductivity
 Contractility

14. 14
Autorhythmicity
• It is the ability of the heart to generate
cardiac impulse and to beat regularly
independent of any external stimulus.
• The heart is provided with specialized
excitatory and conductive muscle systems
having two functions:
1. They generate rhythmic cardiac impulse
2. They conduct cardiac impulse

15. 15
Specialized excitatory and conducting system of
the heart
1. Sino-atrial node (SA-node):
Located on the posterior wall of the Rt-atrium
inferior to the opening of the SVC
The heart beat is initiated by the pacemaker (SA
Node)
SA-nodal fibres have a special capability to
discharge repetitive and rhythmic cardiac
impulse.
They repeatedly depolarize to threshold
spontaneously
It generates impulse at a frequency of 80-

16. Cont’d
2. Atrioventricular node (AV-node): in which
impulse from the atria delayed to be conducted to
the ventricle.
• Site of nodal delay
• located in the right atrium, close to the
interventricular septum.
• It is the Potential pacemaker (if SA node fails).
16

17. Cont’d
3. Atrioventricular bundle (bundle of His):
which conducts impulse from the atria to the
ventricle.
• The only site where action potentials can
conduct from the atria to the ventricles
• The rest of atrioventricular boundary
consist of unexcitable connective tissue
17

18. Cont’d
4. Right and left bundle branches
• They extend through the interventricular
septum toward the apex of the heart.
5. Purkinje fibers: conduct cardiac impulse
to the rest of ventricles
18

19. 19
Specialized excitatory and conductive system of the heart

20. 20

21. Cardiac valves
• Cardiac valves are made up of fibrous
connective tissues.
• The valves direct blood flow (One way valves)
• Each have fibrous connective tissue:
• Prevent enlargement of valve opening
• Anchor valve flaps.
• Opening and closing of valves occur passively
as a result of pressure differences.
• Valve closure prevents backflow of blood during
and after contraction.
21

22. Types of cardiac valves
 There are 4 types of heart valves:
– Inlet valves => AV (atrioventricular) valves.
Tricuspid(RAV) and mitral or Bicuspid(LAV).
– Outlet valves => Semilunar valves.
 Aortic and Pulmonary semilunar valves.
22

23. AV valves
• Formed from thin flaps of
tissue joined at base to
connective tissue ring.
23
• AV valves are not identical:
– Tricuspid : 3 flaps
– Bicuspid: 2 flaps : Also called
Mitral valve
– Open to ward the heart
• Open during diastole.

24. Semilunar valves (outlet valves)
• Pulmonary valves => b/n RV and pulmonary
artery.
• Aortic valve => b/n LV and aorta.
• Open towards blood vessels.
• Open during systole.
• Anatomical composition same as AV valves. 24

25. 25
Cardiac valves

26. 26
Blood supply to the heart
• The heart receives arterial blood from the coronary artery,
which is the branch of ascending aorta.
• Resting coronary blood flow = 250 ml/min, 5% CO
Ascending Aorta
L Coronary artery
R Coronary artery
Supplies
• Atrium
• Posterior ventricles
 R ventricle
 L ventricle
Circumflex a.
Supplies
Atrium
L ventricle
Anterior
descending a.
Supplies
R ventricle
L ventricle

27. 27
Coronary venous drainage
Small venules
Small veins
Great cardiac vein Middle cardiac vein
From the anterior part From the posterior part
of the heart of the heart
Coronary sinus
R Atrium

28. Cardiac innervation
• Sympathetic  innervates almost all parts of heart.
• increase myocardial contractility, accelerates heart rate
• Parasympathetic (from vagus):
 Mainly innervates: SA node, Atria and AV node.
 No ventricular innervations of parasympathetic.
 Strong stimulation of vagus, has no effect on ventricles
 decrease myocardial contractility, reduces heart rate
28

29. 29
Excitation-contraction coupling in cardiac muscle
• It is a mechanism by which an action potential causes
contraction of myocardium.
• It has the following sequences
Auto-rhythmicity Membrane depolarization T-
tubule depolarization Release of Ca2+ from SR +
from T-tubule (ECF) Ca2+ activates contractile
molecules Sliding of filaments Contraction
• The action potential of cardiac muscle has a prolonged
refractory period.
Advantage: prevents tetanic contraction of the heart

30. 30
Ca2+
signaling in cardiac muscle
DHPR
(DHPR)
Ca2+
Entry of Ca2+
during
action potential
1 Ca2+
out
for 3 Na+
in
Inhibited by digitalis & ouabain;
indirectly Na+
/Ca2+
exchange 
[Ca2+
]in
Affected by epinephrine () and ACh ()

31. The Cardiac Cycle
(diastole and systole)
• Activities in the heart in a single beat
• It refers to the repeating pattern of contraction and
relaxation of the heart.
– The period from the end of one heart contraction to the
end of the next.
– Systole:
• Phase of ventricular contraction.
– Diastole:
• Phase of ventricular relaxation.
• Diastole is longer than systole.
31

32. Cont’d
• There are 72 cycles completed per minute.
• During systole, heart contracts and pumps the
blood through arteries.
• During diastole, heart relaxes and blood is
filled in the heart.
• Duration of each cycle = 0.8 second:
 Ventricular diastole = 0.5 second.
 Ventricular systole = 0.3 second.
32

33. Heart sounds
• Heart sounds are associated (usually) with
valve closure.
• Heart sounds are the sounds produced by
mechanical activities of heart during each cardiac
cycle.
• First heart sound => Closure of AV valves:
 Occurs at beginning of isovolumic
contraction. 33

34. • Second heart sound => Closure of Aortic &
Pulmonic valves (Semilunar valves):
 Occur at end of ejection (at onset of
ventricular diastole)
• Third heart sound (sometimes): - due to rapid
ventricular filling.
• Fourth heart sound (occasionally): - during
atrial contraction.
Third and fourth sounds occur: normally in
children 34

35. Cont’d
• S1: is always audible, has a LUBB-sound
• S2: is always audible, has DUBB-sound
• Continuous heart sound: Lubb-Dubb, Lubb-
Dubb
• Heart sounds are produced by:
1. Flow of blood through cardiac chambers
2. Contraction of cardiac muscle
35

36. 36
Sites of heart sounds

37. 37
Electrophysiology of the heart
Phases and ionic bases of
myocardial action potential
It has 5-phases
Phase-0: Rapid depolarization
Caused by rapid Na-influx
Phase-1: Early partial repolarization
Caused by Cl- influx
Phase-2: The plateau (prolonged
depolarization)
Caused by Ca2+influx
Phase-3: Repolarization
Caused by K+ efflux
Phase-4: complete repolarization
RMP reestablished
Action potential of the ventricular muscle
RMP = -90 mv
↑PCl

38. Fetal circulation
38

39. Blood vessels
• Their role is to direct the flow of blood from the
heart to the capillaries, and back to the heart.
 Characteristics of blood vessels:
– Arteries and arterioles => carry blood away
from heart.
– Capillaries => site of exchange.
– Venules, veins => return blood to heart.
39

40. Types of blood vessels
1. Elastic vessels:
 Example: Aorta, big
arteries.
 Pressure storing
components
 High ability of stretching
and recoiling.
2. Resistance vessels:
 Example: small arteries and
arterioles.
 High muscular component.
 Develop high resistance
 Regulate blood flow.
40

41. Cont’d
3. Exchange vessels: made
up endothelium and
basement membrane.
 Thin enough for
exchange.
4. Capacitance vessels (big
to small veins).
 Very high capacity of
distension.
 It can accommodate
large volume of blood
(60-70% of blood
volume).
41

42. Blood vessel functions: overview
Strong and elastic arteries
Arterioles control blood
flow and pressure
Capillaries: thin and
with large area for
diffusional exchange
Veins: compliant, large, low resistance veins with
valves assures blood return

43. Important terminologies:
 Ventricular volumes: The volume of blood in the ventricles.
 Ventricular end diastolic volume (VEDV): The total
volume of blood in the ventricle at the end of ventricular
diastole.
VEDV = 120 -140 ml
 Ventricular end systolic volume (VESV): The volume of
blood that remains in the ventricle at the end of ventricular
systole.
VESV = 50 - 60 ml
43

44. Cardiac output (CO)
• CO is the volume of blood ejected from the heart per minute.
– CO = SV x HR, = 5 - 6 L/min
• HR is the number of heart beats per minute.
• Stroke volume (SV): the volume of blood ejected from the ventricle
during ventricular systole with each beat.
– SV = VEDV – VESV = 70 – 80 ml
• Ejection fraction: the proportion of ejected blood to Ventricular end
diastolic volume (VEDV).
– EF = SV/VEDV *100 = 55 - 70% is normal
44

45. Arterial blood pressue
• It is a pressure caused by the blood on the wall of the
blood vessels
• Normal Ps: 90 – 130 mm Hg (120 mm Hg)
Pd: 60 – 90 mm Hg (80 mm Hg)
Pp: Ps – Pd
Three factors determine ABP:
ABP = CO x TPR
1. Cardiac output
2. Peripheral vascular resistance
3. Blood volume

46. Blood Pressure Measurement

47. Regulation of blood
pressure
47

48. BP Regulation:
Baroreceptors
↑BP stimulates
baroreceptors
Impulse goes
to MO
Stimulation of PNS ↓BP

49. Regulation of Blood Pressure
Figure 15-22: The baroreceptor reflex: the response to increased blood pressure
Blood Pressure
Regulation

50. HORMONAL REGULATION
• Epinephrine & Norepinephrine
– From the adrenal medulla
• Renin-angiotensin-aldosterone
– Renin from the kidney
– Angiotensin, a plasma protein
– Aldosterone from the adrenal cortex
• Vasopressin (Antidiuretic Hormone-ADH)
– ADH from the posterior pituitary

51. Hypertension
• Hypertension is defined as arterial blood pressure that
exceeds 140/90mmHg at several determinations.
• More common in male than female before menopause.
• Severe hypertension 4 X more common in black men
than white.
 Possible reason => higher renal vascular
resistance.
51

52. Cardiac failure and hypotension
• Failure of the heart to pump enough blood to meet the need of the body
• Manifested by
1. A decreased in CO
2. Damping of blood in veins and in the heart
3. Edema
Circulatory shock: hypotension
• A generalized insufficiency of blood flow to the peripheral organs that
leads to multiple organ failure
Types of shock
1. Cardiogenic shock: Myocardial infarction, cardiac arrhythmia
2. Hypovolemic/hemorrhagic shock: bleeding ↓BP
3. Neurogenic shock: No VC ↑VD ↓BP
4. Septic shock: Infection excessive inflammatory agents
↑VD ↓BP
Treatments: Fluid, vasoconstrictors, antibiotics