The cardiovascular system, is a complex network of organs and vessels that is responsible for the transportation of blood, nutrients, oxygen, carbon dioxide, hormones, and waste products throughout the body.

It plays a crucial role in maintaining homeostasis, supporting the immune system, and ensuring the proper functioning of various organs and tissues

Functional components of the cardiovascular system

Heart

Blood Vessels

Blood

Transportation

Everything transported by the blood

Regulation

Of the cardiovascular system

Intrinsic v extrinsic

Protection

Against blood loss

Production/Synthesis

The circulation is divided into the systemic or peripheral circulation and the pulmonary circulation

Arteries transport blood under high pressure and their muscular walls are thick.

The veins are conduits for transport of blood from tissues back to the heart.

The pressure in the venous system is very low and the walls of the veins are thin

The heart is a hollow muscular organ whose wall is thickened to act as a regulated pump.

The heart is the major determinant of systemic blood pressure

APEX

Formed mainly by left ventricle

Apex beat heard here, Located in the 5th intercostal space in the midclavicular line approximately 9cm from the midline.

It is were the sounds of mitral valve can be heard

Point of maximum pulsation

The cardiac wall consists of three layers

Endocardium, consisting of an endothelial lining and sub endothelial connective tissue.

Myocardium, a functional syncytium of striated cardiac muscle fibers forming three major types of cardiac muscle: atrial muscle, ventricular muscle, and specialized excitatory and conductive muscle fibers.

Pericardium. The epicardium, the visceral layer of the pericardium, is a low-friction surface lined by a mesothelium in contact with the parietal pericardial space.

Vessels returning blood to the heart include

Superior and inferior venae cavae

Right and left pulmonary veins

Vessels conveying blood away from the heart include

Pulmonary trunk, which splits into right and left pulmonary arteries

Ascending aorta (three branches) –

Brachiocephalic

Left common carotid

Left Subclavian artery

The heart’s modest size is Only about the size of a fist

Typically it weighs between 250 and 350 grams—less than a pound.

The heart lies in the thorax posterior to the sternum and costal cartilages and rests on the superior surface of the diaphragm

It is the largest organ in the mediastinum, which is the region between the two lungs (and pleural cavities)

The four heart chambers are

Right atrium

Left atrium

Right ventricles

Left ventricles

Atria are the receiving chambers of the heart

Each atrium has a protruding auricle

Pectinate muscles mark atrial walls

Blood enters right atrium from superior and inferior venae cavae and coronary sinus

Blood enters left atrum from pulmonary veins

Ventricles are the discharging chambers of the heart

Papillary muscles and trabeculae carneae muscles mark ventricular walls

Right ventricle pumps blood into the pulmonary trunk

Left ventricle pumps blood into the aorta

Thickness of myocardium varies according to the function of the chamber

Atria are thin walled, deliver blood to adjacent ventricles

Ventricle walls are much thicker and stronger

right ventricle supplies blood to the lungs (little flow resistance)

left ventricle wall is the thickest to supply systemic circulation

The heart valves—the paired atrioventricular (AV) and semilunar valves—enforce the one-way flow of blood through the heart, from the atria to the ventricles and into the great arteries that leave the superior part of the heart.

Each heart valve consists of two or three cusps, which are flaps of endocardium reinforced by cores of dense connective tissue

Located at the junctions of the atria and their respective ventricles are the atrioventricular valves:

The right atrioventricular (tricuspid) valve, which has three cusps

The left atrioventricular (bicuspid) valve, or mitral valve which has only two cusps.

Heart valves open (to allow blood flow) and close (to prevent the backflow of blood) in response to differences in blood pressure on each side of the valves.

The two atrioventricular valves prevent the backflow of blood into the atria during contraction of the ventricle

The two semilunar valves prevent backflow from the great arteries into the ventricles

The closing of the valves causes vibrations in the adjacent blood and heart walls that account for the familiar “lub dup” sounds of each heartbeat

The “lub” sound is produced by the closing of the AV valves at the start of ventricular contraction; the “dub” is produced by the closing semilunar valves at the end of ventricular contraction

This corresponds to mitral and tricuspid valve closure at the onset of systole

This corresponds to aortic and pulmonary valve closure following ventricular ejection

Heart muscle is supplied by two coronary arteries which encircle the heart in the manner of a crown.

Latin word corona=crown

Two coronary arteries, namely

Right coronary artery

Left coronary artery

Originates from the right aortic sinus of the ascending aorta

It passes anteriorly and to the right between the right auricle and the pulmonary trunk and then descends vertically in the coronary sulcus, between the right atrium and right ventricle

Right coronary artery supplies whole of the right ventricle and posterior portion of left ventricle.

The right conus artery

Supplies the anterior surface of the pulmonary conus (infundibulum of the right ventricle) and the upper part of the anterior wall of the right ventricle

The anterior ventricular branches

Are two or three in number and supply the anterior surface of the right ventricle.

The posterior ventricular branches

Are usually two in number and supply the

diaphragmatic surface of the right ventricle.

The posterior interventricular (descending) artery

It supplies branches to the posterior part of the ventricular septum but not to the apical part, which receives its supply from the anterior interventricular branch of the left coronary artery.

The atrial branches

Supply the anterior and lateral surfaces of the right atrium. One branch supplies the posterior surface of both the right and left atria.

Sinu-atrial nodal branch, which passes posteriorly around the superior vena cava to supply the Sinu- atrial node

The left coronary artery originates from the left aortic sinus of the ascending aorta.

It passes between the pulmonary trunk and the left auricle before entering the coronary sulcus.

Left coronary artery supplies mainly the anterior and lateral parts of left ventricle.

The anterior interventricular (descending) branch supplies

The right and left ventricles with numerous

branches that also supply the anterior part of the ventricular septum.

The circumflex artery It winds around the

left margin of the heart in the atrioventricular groove. It has the following branches

Left marginal artery

Anterior ventricular and posterior ventricular branches

Atrial branches

Anastomoses between the terminal branches of the right and left coronary arteries (collateral circulation) exist, but they are usually not large enough to provide an adequate blood supply to the cardiac muscle should one of the large branches become blocked by disease.

The sinuatrial node is usually supplied by the right but sometimes by the left coronary artery.

The atrioventricular node and the atrioventricular bundle are supplied by the right coronary artery.

The RBB of the atrioventricular bundle is supplied by the left coronary artery;

The LBB is supplied by the right and left coronary arteries

Normal blood flow through coronary circulation is about 200 mL/minute.

It forms 4% of cardiac output.

It is about 65 to 70 mL/minute/100 g of cardiac muscle.

Blood flow through coronary arteries is not constant.

It decreases during systole and increases during diastole

Intramural vessels or final arteries supplying

myocardium are perpendicular to the cardiac muscles.

During systole, the intramural vessels are compressed and blood flow is reduced.

During diastole, the compression is released and

the blood vessels are distended. So, the blood flow increases.

Autoregulation

Coronary blood flow is not affected when

mean arterial pressure varies between 60 and 150 mm Hg

Several factors are involved in the autoregulation mechanism

Need for oxygen

Metabolic factors

Coronary perfusion pressure

Nervous factors.

Amount of blood passing through coronary circulation is directly proportional to the consumption of oxygen by cardiac muscle.

Thus, the need for oxygen, i.e. hypoxia immediately causes coronary vasodilatation and increases the blood flow to heart

Coronary vasodilatation during hypoxic

conditions occurs because of some

metabolic products, which increase the coronary blood flow by vasodilatation.

Metabolic Products which Increase the Coronary Blood Flow

Adenosine

Potassium

Hydrogen

Carbon dioxide

Adenosine phosphate compounds.

Perfusion pressure is the balance between mean arterial pressure and venous pressure

coronary perfusion pressure is the balance between mean arterial pressure in aorta and the right atrial pressure.

Since right arterial pressure is low, the mean arterial pressure becomes the major factor that maintains the coronary blood flow

Coronary blood vessels are innervated both by parasympathetic and sympathetic divisions of autonomic nervous system.

Stimulation of sympathetic nerves increases the rate and force of contraction of heart.

This in turn, causes liberation of more metabolites which dilate the blood vessels and increase the coronary blood flow.

Similarly, when parasympathetic nerves are stimulated, the cardiac functions are inhibited and the production of metabolites is less.

Coronary blood flow decreases

Coronary artery disease (CAD) is the heart disease that is caused by inadequate blood supply to cardiac muscle due to occlusion of coronary artery.

It is also called coronary heart disease.

Myocardial infarction

Cardiac pain – angina pectoris

Conductive system of the heart is formed by the modified cardiac muscle fibers.

These fibers are the specialized cells, which conduct the impulses rapidly from SA node to the ventricles.

Conductive tissues of the heart are also called the junctional tissues.

The contractions of the various parts of the heart have to be carefully synchronized.

It is the prime function of the electrical conduction system to ensure this synchronization.

The atria should contract first to fill the ventricles before the ventricles pump the blood in the circulation.

Sinoatrial (SA) node

Atrioventricular (AV) node

Bundle of His (and bundle branches)

Purkinje fibers.

SA node is situated in right atrium, just below the opening of superior vena cava.

The sinus node (also called sinoatrial node) is a small, flattened, ellipsoid strip of specialized cardiac muscle about 3 millimeters wide, 15 millimeters long, and 1 millimeter thick.

Impulses from SA node are conducted throughout right and left atria.

Impulses also reach the AV node via some specialized fibers called internodal fibers

AV NODE

The excitation starts in the sinus node consisting of special pacemaker cells.

The electrical impulses spread over the right and left atria.

The AV node is normally the only electrical connection between the atria and the ventricles.

The impulses slow down as they travel through the AV node to reach the bundle of His.

There are three types of internodal fibers

Anterior internodal fibers of Bachman

Middle internodal fibers of Wenckebach

Posterior internodal fibers of Thorel.

All these fibers from SA node converge on AV node and interdigitate with fibers of AV node.

The bundle of His, the distal part of the AV junction, conducts the impulses rapidly to the bundle branches.

The fast conducting right and left bundle branches subdivide into smaller and smaller branches, the smallest ones connecting to the Purkinje fibers.

The Purkinje fibers spread out all over the ventricles beneath the endocardium and they bring the electrical impulses very fast to the myocardial cells.

Fetal circulation is the circulatory system of a fetus.

The term usually encompasses the entire fetoplacental circulation, which includes the umbilical cord and the blood vessels within the placenta that carry fetal blood

CIRCULATION

Maternal blood is the source of oxygen and food to fetus through placenta because the fetal lungs and digestive system are non-functional. foetal blood reaches the placenta via two umbilical arteries and returns by one umbilical vein.

CIRCULATION

Blood from the placenta is carried to the foetus by the umbilical vein.

About half of this enters the foetal ductus venosus to bypass the liver carried to the inferior vena cava and remain half enters the liver proper from the inferior border of the liver.

The blood then moves to the right atrium of the heart.

CIRCULATION

In the foetus, there is an opening between the right and left atrium (the foramen ovale), and most of the blood flows through this hole directly into the left atrium from the right atrium, thus bypassing pulmonary circulation.

CIRCULATION

Some of the blood entering the right atrium does not pass directly to the left atrium through the foramen ovale, but enters the right ventricle and is pumped into the pulmonary artery

In the foetus, there is a special connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the lungs

CIRCULATION

The continuation of this blood flow is into the left ventricle, and from there it is pumped through the aorta into the body

At birth, when the infant breathes for the first time, there is a decrease in the resistance in the pulmonary vasculature, which causes the pressure in the left atrium to increase relative to the pressure in the right atrium.

This leads to the closure of the foramen ovale, which is hence referred to as the fossa ovalis.

CIRCULATION

Additionally, the increase in the concentration of oxygen in the blood leads to a decrease in prostaglandins, causing closure of the ductus arteriosus.

These closures prevent blood from bypassing pulmonary circulation, and therefore allow the neonate’s blood to become oxygenated in the newly operational lungs

CIRCULATION

12.After closure, the duct becomes the ligamentum arteriosum, which connects the left pulmonary artery (near its origin) with the aortic arch. The ductus venosus shuts down by an unknown mechanism, its fibrous remnant is the ligamentum venosum

The fetal circulation consists of parallel systemic and pulmonary pathways in contrast to the normal postnatal circulation, in which the systemic and pulmonary circulations exist in series

OVALE

When blood starts flowing through the pulmonary circulation, the oxygenated blood from the lungs returns to left atrium.

It causes increase in the left atrial pressure. Simultaneously, due to stoppage of blood from placenta, pressure in inferior vena cava is decreased It leads to fall in right atrial pressure.

OVALE

Thus, the pressure in right atrium is less and the pressure in left atrium is already high.

This causes the closure of foramen ovale.

Within few days after birth, the foramen ovale closes completely and fuses with the atrial wall.

VENOSUS

Due to the contraction of smooth muscle near junction between umbilical vein and ductus venosus, the constriction and closure of ductus venosus occurs.

Later, the ductus venosus becomes fibrous band.

VENOSUS

Ductus arteriosus starts closing due to narrowing.

It closes completely after 2 days and the adult type of circulation starts.

In some rare cases, the ductus arteriosus does not close.

VENOSUS

It remains intact producing a continuous murmur.

This condition with intact ductus arteriosus is known as patent ductus arteriosus

Arteries – vessels that transport blood away from the heart

Veins – return blood back to the heart

Capillaries – microscopic blood vessels that allow exchanges between blood and tissues

Tunica externa (adventitia) – outermost layer made of loose connective tissue. Serves to anchor, protect and prevent overstretching.

Tunica media – middle layer composed of smooth muscle; functions in dilation and constriction of blood vessels.

Tunica interna(intima) – innermost layer made of endothelium (s.squamous epithelium)

From the heart blood flows into

Aorta

Arteries

Arterioles

Capillaries

Venules

Veins

Superior/ Inferior Vena Cava

Back to the heart

Elastic (conducting) arteries

Larger arteries

Muscular ( distributing) arteries

Medium arterties

Arterioles

Tiny, tiny arteries

Metarteriole

Microscopic vessels that connect arterioles and Venules.

Walls consist of a single layer of simple squamous epithelial cells that allow the exchange of gases.

Precapillary sphincters regulate blood flow.

Continuous/Fenestrated capillaries

Venules merge to form veins.

Have 3 distinct layers; thinner walled than arteries due to thin tunica interna and media.

Large lumens and posses valves.

Varicose veins.

Blood reservoir

The aorta and its major branches

Arterial supply to neck and head

Arterial supply to upper extremities

Arterial supply to thorax

Arterial supply to abdomen

Arterial supply to pelvic region and lower extremities

Venous drainage of the head and neck

Major tributaries of the inferior vena cava

Venous drainage of the upper extremities

Venous drainage of the lower extremities

Routes blood from the stomach, spleen, pancreas, small and large intestines to the liver.

Blood from these structures all drain into the hepatic portal vein, then into the liver.

Blood is returned to the inferior vena cava via the hepatic vein

Blood Flow

Blood pressure

Resistance

Blood flow – is the amount of blood flowing through a tissue in a given period of time.

Velocity of blood flow is inversely related to the diameter of the blood vessel.

Blood flows most slowly in areas of greatest width

Force that the blood exerts against the walls of a blood vessels.

Factors affecting BP include cardiac output, blood volume, viscosity, resistance, and the elasticity of the arteries.

CO=Stroke volume X Heart Rate

Any factor that increases SV or HR will increase blood pressure

Resistance to blood flow due to the force of friction between vessel wall and blood.

Resistance affected by blood viscosity, vessel length and vessel radius.

Blood viscosity- how thick or thin the blood is. Measured by hematocrit.

Vessel length- longer the vessel, the greater the resistance, the greater the BP

Vessel radius- smaller the vessel the greater the resistance

Renin- angiotensin pathway

Angiotensin II – powerful vasoconstrictor thus raising resistance.

Stimulates secretion of aldosterone from the adrenal gland promoting sodium retention.

ADH – antidiuretic hormone from the pituitary causing the kidneys to reabsorb more water

The function of the heart is to maintain a constant circulation of blood throughout the body.

Cardiac cycle is the term referring to all or any of the events related to the flow of blood that occurs from the beginning of one heartbeat to the beginning of the next.

During ventricular systole, there is closure of atrioventricular valves, producing the first heart sound.

While the second heart sound is produced by closure of aortic and pulmonary valves during diastole.

The frequency of the cardiac cycle is the heart rate.

Cardiac output = stroke volume X heart rate.

References• Seeley, R. R., Stephens, T. D., &Tate, P. (2003). Anatomy and Physiology. New York:McGraw-Hill.• Shier, A., Butler, J., & Lewis, R. (2004). Hole’s Human Anatomy & Physiology. NewYork: McGraw-Hill.• Standring, S. (2008). Grays’s Anatomy The anatomical basis of clinical practice. UnitedKingdom: Churchill Livingstone Elservier

What is cardiac circle?

What is the meaning of diastole?

What is the meaning of systole?

Mention 3 factors affecting the heart rate