The document discusses the heart and circulatory system. It notes that the heart is a hollow muscle that pumps blood through arteries and veins via rhythmic contractions. The circulatory system consists of two circuits - the pulmonary circuit which pumps blood to the lungs, and the systemic circuit which pumps blood to all body tissues. The cardiac cycle refers to the heart's alternating periods of contraction (systole) and relaxation (diastole) with each heartbeat. Blood pressure is maintained through mechanisms that regulate blood volume, resistance, and response to sympathetic/parasympathetic impulses.

1. By- Chintan Chavda

2. The Heart
 The heart is a hollow muscle that pumps approximately
4.7-5.7 litres of blood per minute throughout the blood
vessels to various parts of the body by repeated,
rhythmic contractions.
 It is found in all animals with a circulatory system, which
includes the vertebrates.
 The adjective cardiac means "related to the heart"
 The average human heart, beating at 72 beats per
minute, will beat approximately 2.5 billion times during
an average 66 year lifespan.
 It weighs approximately 250 to 300 grams in females and
300 to 350 grams in males.

4. Circulatory System
The systemic and pulmonary
circuits. The right
 side of the heart pumps blood
through the pulmonary circuit* (to
the lungs and back to the left side
of the heart).
 The left side of the heart pumps
blood through the systemic circuit
to all body tissues and back to the
right side of the heart.
 The arrows indicate the direction
of blood flow.
 *For simplicity, the actual number
of two pulmonary arteries and four
 pulmonary veins has been reduced
to one each.

6. The Cardiac Cycle
 The heart undergoes some dramatic movements as it
alternately contracts, forcing blood out of its chambers,
and then relaxes, allowing its chambers to refill with
blood.
 The term systole refers to these periods of contraction,
and diastole refers to those of relaxation.
 The cardiac cycle includes all events associated with the
blood flow through the heart during one complete
heartbeat—atrial systole and diastole followed by
ventricular systole and diastole.
 These mechanical events always follow the electrical
events seen in the ECG.

7. The Cardiac Cycle
 Cardiac output is the amount of blood pumped out by
each ventricle in 1 minute. It is the product of heart rate
(HR) and stroke volume (SV).
 Stroke volume is defined as the volume of blood
pumped out by one ventricle with each beat.
 In general, stroke volume correlates with the force of
ventricular contraction.
 CO = HR x SV
 Notice that cardiac output varies directly with SV and HR.
 This means that CO increases when the stroke volume
increases or the heart beats faster or both, and it
decreases when either or both of these factors decrease.

8. BloodVessels

9. Arterial System
1. Elastic arteries are the thick-walled arteries near the
heart—the aorta and its major branches. These arteries
are the largest in diameter, ranging from 2.5 cm to 1 cm,
and the most elastic. Also called conducting arteries.
2. Muscular Arteries- elastic arteries give way to the
muscular arteries, which deliver blood to specific body
organs (and so are sometimes called distributing arteries).
3. Arterioles The smallest of the arteries, arterioles have a
lumen diameter ranging from 0.3 mm down to 10 μm.
 Smaller arterioles, which lead into the capillary beds.

10. Capillaries
 The microscopic capillaries are the smallest blood
vessels.
 Average capillary length is 1 mm and average lumen
diameter is 8–10 μm, just large enough for red blood
cells to slip through in single file. Most tissues have a
rich capillary supply, but there are exceptions
 Capillaries are ideally suited for their role—exchange
of materials (gases, nutrients, hormones, and so on)
between the blood and the interstitial fluid

12. Venous System
 Venules - Capillaries unite to form venules, which
range from 8 to 100 μm in diameter.
 Veins - Venules join to form veins.
 The walls of veins can be much thinner than arterial
walls without danger of bursting because the blood
pressure in veins is low.
 However, the low-pressure condition demands
several structural adaptations to ensure that veins
return blood to the heart at the same rate it was
pumped into the circulation.

13. Physiology of Circulation
 Blood flow is the volume of blood flowing through a
vessel, an organ, or the entire circulation in a given period
(ml/min).
 Blood pressure (BP), the force per unit area exerted on a
vessel wall by the contained blood, is expressed in
millimeters of mercury (mm Hg).
 The term blood pressure means
systemic arterial blood pressure
in the largest arteries near the
heart.

14. Physiology of Circulation
 Resistance is opposition to flow and is a measure of the
amount of friction blood encounters as it passes through
the vessels.
 Because most friction is encountered in the peripheral
(systemic) circulation, well away from the heart, we
generally use the term peripheral resistance.
 There are three important sources of resistance:
1. blood viscosity,
2. vessel length, and
3. vessel diameter.

15. Maintaining Blood Pressure
 Clearly, blood pressure varies directly with CO and R. Additionally, blood
pressure varies directly with blood volume because CO depends on
blood volume

16.  Activation of
Sympathetic
Impulse- Increase
in BP
 Activation of
Parasympathetic
Impulse-
Decrease in BP

17. The Direct Renal Mechanism
 The direct renal mechanism alters blood
volume independently of hormones.
 When either blood volume or blood
pressure rises, the rate at which fluid
filters from the bloodstream into the
kidney tubules speeds up.
 In such situations, the kidneys cannot
reabsorb the filtrate rapidly enough,
and more of it leaves the body in urine.
 As a result, blood volume and blood
pressure fall.

18. Indirect Renal Mechanism
Renin Angiotensin Aldosterone System
 The kidneys can also regulate blood pressure indirectly via the
renin-angiotensin-aldosterone mechanism.
 When arterial blood pressure declines, certain cells in the
kidneys release the enzyme renin into the blood.
 Renin enzymatically cleaves angiotensinogen, a plasma
protein made by the liver, converting it to angiotensin I.
 In turn, angiotensin converting enzyme (ACE) converts
angiotensin I to angiotensin II.
 Angiotensin II acts in four ways to stabilize arterial blood
pressure and extracellular fluid volume

20. Factors Increasing Blood Pressure