CARDIOVASCULAR SYSTEM

Cardio vascular system

•        The cardiovascular system consists of the heart, blood vessels and the approximately 5 liters of blood that the blood vessels transport.

•        Oxygen and carbon dioxide transport. Supplying oxygen to the body is the most essential function of the cardiovascular system.

•        Disease protection and healing.

•        Hormone delivery.

•        Body temperature regulation:

–       Cardio- heart

–       Vascular- blood vessels

•        Heart:

–       Whose pumping action ensures constant circulation of the blood.

•        Cardiac cells:

–       Cardiac muscle cells or cardiomyocytes (also known as microcytes or cardiac myocytes) are the muscle cells (myocytes) that make up the cardiac muscle (heart muscle)

•        Blood vessel:

–       Which form a lengthy network through which the blood flow

•        Blood vessels:

–       Arteries transport blood away from the heart and branch into smaller vessels, forming arterioles. 

–       Arterioles distribute blood to the capillary beds the sites of exchange with the body tissues.

•        Capillaries:
        any of the fine branching blood vessels that form a network between the arterioles and venules.

•        Vein and venule:
   a venule is a small blood vessel in the microcirculation that allows deoxygenated blood to return from capillary beds to larger blood vessels called veins. Venules range from 8 to 100μm in diameter and are formed when capillaries come together. Many venules unite to form a vein.

Capillary exchange (exchange of gases):
this dynamic displacement of materials between the interstitial fluid and the blood is named capillary exchange.
These substances pass through capillaries through three different systems or mechanisms: diffusion, bulk flow, and transcytosis or vesicular transport.

Heart

Position

The heart is located in the chest between the lungs behind the sternum and above the diaphragm. It is surrounded by the pericardium. Its size is about that of a fist, and its weight is about 250-300 g. Its center is located about 1.5 cm to the left of the midsagittal plane.

Organs associated with the heart

Anatomy of the heart:

•        The human heart consists of four chambers:

–       The left side and the right side each have one atrium and one ventricle.

–       Each of the upper chambers, the right atrium and the left atrium, acts as a receiving chamber and contracts to push blood into the lower chambers.

–       The right ventricle and the left ventricle: the ventricles serve as the primary pumping chambers of the heart, propelling blood to the lungs or to the rest of the body.

The heart walls:

The heart wall is composed of connective tissue, endothelium, and cardiac muscle. It is the cardiac muscle that enables the heart to contract and allows for the synchronization of the heartbeat. The heart wall is divided into three layers:

•        Epicardium: an outer protective layer of the heart

•        Myocardium: muscular middle layer wall of the heart

•        Endocardium: inner layer of the heart

Epicardium:
       the epicardium is the outer layer of the heart wall. It is also known as visceral pericardium as it forms the inner layer of the pericardium. The epicardium is composed primarily of loose connective tissue, including elastic fibers and adipose tissue. The epicardium functions to protect the inner heart layers and also assists in the production of pericardial fluid. This fluid fills the pericardial cavity and helps to reduce friction between pericardial membranes.

Myocardium:

   Myocardium is the middle layer of the heart wall. It is composed of cardiac muscle fibers, which enable heart contractions. The myocardium is the thickest layer of the heart wall, with its thickness varying in different parts of the heart.

Endocardium:

   Endocardium is the thin inner layer of the heart wall. This layer lines the inner heart chambers covers heart valves and is continuous with the endothelium of large blood vessels. The endocardium of heart atria consists of smooth muscle, as well as elastic fibers. An infection of the endocardium can lead to a condition known as endocarditis.

Heart valve:

The heart has four valves that help ensure that blood only flows in one direction:

•        Aortic valve: between the left ventricle and the aorta.

•        Mitral valve: between the left atrium and the left ventricle.

•        Pulmonary valve: between the right ventricle and the pulmonary artery.

•        Tricuspid valve: between the right atrium and right ventricle.

Septum:

•        An internal wall of tissue divides the right and left sides of your heart. This wall is called the septum. 

•        The area of the septum that divides the atria is called the atrial or interatrial septum. The area of the septum that divides the ventricles is called the ventricular or interventricular septum.

A cardiac conduction system is a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. The main components of the cardiac conduction system are the SA node, av node, bundle of his, bundle branches, and Purkinje fibers.

The heart automaticity is a fundamental physiological function in higher organisms. The spontaneous activity is initiated by specialized populations of cardiac cells generating periodical electrical oscillations.

Conduction system

Sinoatrial node:

•        The sinoatrial (SA) node: -is a collection of specialized cells (pacemaker cells) and is located in the upper wall of the right atrium, at the junction where the superior vena cava enters.

•        These pacemaker cells can spontaneously generate electrical impulses. The wave of excitation created by the SA node spreads via gap junctions across both atria, resulting in atrial contraction (atrial systole) – with blood moving from the atria into the ventricles.

•        The rate at which the SA node generates impulses is influenced by the autonomic nervous system:

–       Sympathetic nervous system: increases firing rate of the SA node, and thus increases heart rate.

–       Parasympathetic nervous system: decreases firing rate of the SA node, and thus decreases heart rate.

Atrioventricular node:

•        After the electrical impulses spread across the atria, they converge at the atrioventricular node – located within the atrioventricular septum, near the opening of the coronary sinus.

•        The av node acts to delay the impulses by approximately 120ms, to ensure the atria have enough time to fully eject blood into the ventricles before ventricular systole.

•        The wave of excitation then passes from the atrioventricular node into the atrioventricular bundle.

Atrioventricular bundle:

The atrioventricular bundle (bundle of his) is a continuation of the specialized tissue of the av node and serves to transmit the electrical impulse from the av node to the Purkinje fibers of the ventricles.

It descends the membranous part of the interventricular septum, before dividing into two main bundles:

Right bundle branch: conducts the impulse to the Purkinje fibers of the right ventricle.

Left bundle branch: conducts the impulse to the Purkinje fibers of the left ventricle.

Purkinje fibers:

The Purkinje fibers (sub-endocardial plexus of conduction cells) are a network of specialized cells. They are abundant with glycogen and have extensive gap junctions.

These cells located the subendocardial surface of the ventricular walls and can rapidly transmit cardiac action potentials from the atrioventricular bundle to the myocardium of the ventricles.

This rapid conduction allows coordinated ventricular contraction (ventricular systole) and blood is moved from the right and left ventricles to the pulmonary artery and aorta respectively.

Nerve supply to heart:

•        The efferent limb innervates the SA and av nodes via the vagus nerve and the parasympathetic ganglia and inhibits sympathetic nervous tone to the heart and blood vessels

Physiology of heart:

The right and left sides of the heart work together. The pattern described below is repeated over and over, causing blood to flow continuously to the heart, lungs, and body.

The right side of the heart:

•        Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart.

•        As the atrium contracts, blood flows from your right atrium into your right ventricle through the open tricuspid valve.

•        When the ventricle is full, the tricuspid valve shuts. This prevents blood from flowing backward into the atria while the ventricle contracts.

•        As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.

The left side of the heart:

•        The pulmonary vein empties oxygen-rich blood from the lungs into the left atrium of the heart.

•        As the atrium contracts, blood flows from your left atrium into your left ventricle through the open mitral valve.

•        When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts.

•        As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta, and to the body.

How does blood flow through your lungs?

Once blood travels through the pulmonic valve, it enters your lungs. This is called pulmonary circulation. From your pulmonic valve, blood travels to the pulmonary artery to tiny capillary vessels in the lungs.


Here, oxygen travels from the tiny air sacs in the lungs, through the walls of the capillaries, into the blood. At the same time, carbon dioxide, a waste product of metabolism, passes from the blood into the air sacs. Carbon dioxide leaves the body when you exhale. Once the blood is purified and oxygenated, it travels back to the left atrium through the pulmonary veins.

Circulation of blood

Systemic circulation:

The aorta is the largest artery in the body. The aorta begins at the top of the left ventricle, the heart's muscular pumping chamber. The heart pumps blood from the left ventricle into the aorta through the aortic valve.

•        Thoracic aorta

•        Abdominal aorta

Thoracic aorta:

•        Ascending aorta: the coronary arteries branch off the ascending aorta to supply the heart with blood. 

•        Arch of the aorta: the aortic arch has three branches, the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery. The aortic arch and its branches are shown in situ. From its branches, the upper body, arms, head, and neck.

Descending aorta:

the descending aorta is part of the aorta, the largest artery in the body. The descending aorta begins at the aortic arch that runs down through the chest and abdomen.

Abdominal aorta:

•        The abdominal aorta has three single anterior visceral branches:

–       Coeliac artery

–       Superior mesenteric artery

–       Inferior mesenteric artery

•        Three paired lateral visceral branches:

–       Suprarenal

–       Renal

–       Gonadal

•        Five paired lateral abdominal wall branches:

–       Inferior phrenic

–       Four lumbar

•        Three terminal branches:

–       Two common iliac

–       The median sacral

•        Celiac trunk

•        Arch of aorta

•        Common carotid artery

Systolic and diastolic:

Regulation of blood pressure

The kidneys provide a hormonal mechanism for the regulation of blood pressure by managing blood volume. The renin‐angiotensin‐aldosterone system of the kidneys regulates blood volume.  Angiotensin ii constricts blood vessels throughout the body (raising blood pressure by increasing resistance to blood flow).