2What is the Human Heart?It is an electro-mechanical muscular pump receiving blood from all parts of the body and pumps blood back to them.It measures about 12 cm in length and 8.5 cm widthWeighs about 300 grams in men and 250 grams in womenBeats about 100,000 times per dayBeats 2.5 billion times in an average 70 yr. lifetimePumps about 9000 litres of blood each dayCirculates blood completely 1000 times each day
3Where is the heart situated? It is situated in the thorax (chest cage) to the left side of the chestThe lungs are its neighboursIt is guarded by the ribs.
4What Does the Heart Do?Its function is to receive deoxygenated [‘impure’] blood through veinsSend it to the lungs for oxygenation [‘purification’]Collect oxygenated [‘purified’] blood from lungsPump oxygenated [‘purified] blood into the rest of the body through the arteries
6What roles do various parts of the heart play? The heart has two veins flowing into the right atrium carrying deoxygenated (‘impure’) blood from various parts of the body called:Superior Vena Cava (SVC)Inferior Vena Cava (IVC)SVC drains head, neck & upper limbsIVC drains blood from the thoracic & abdominal organs and the lower limbsSVC and IVC drain into the right atrium (RA)There is a valve allowing unidirectional flow between the RA & RV called tricuspid valve (TV)SVCRATVIVC
7What roles do various parts of the heart play? Blood then enters the right ventricle (RV) from the RA across TVThe RV pumps blood to the lungs via pulmonary artery (PA).The main pulmonary artery (MPA) or the pulmonary trunk divides into two i.e. Left pulmonary artery (LPA) and right pulmonary artery (RPA) thereby carrying blood to the left and right lungs respectively.There is a unidirectional valve between RV and PA known as the pulmonary valve (PV)SVCLPARPAMPARAPVTVRVIVC
8What roles do various parts of the heart play? Blood is then oxygenated (‘purified’) in the lungs.Flow of blood from lungs back to the heart is through four pulmonary veins (PV) known as left upper (LAPV), left lower (LLPV), right upper (RUPV) and right lower (RLPV) pulmonary veins respectivelyBlood from the PV flows into the left atrium (LA)There is a unidirectional valve separating LA from left ventricle (LV) called the mitral valve (MV)SVCLPARPARUPVMPALUPVLLPVRLPVLARAPVMVTVRVIVC
9What roles do various parts of the heart play? Blood enters LV through MVOxygenated (‘pure’) blood is pumped out of the LV to the rest of the body into the main artery called aorta (AO).There exists an unidirectional valve between LV and AO known as the Aortic valve (AV)The atria are separated from each-other by a muscular wall known as inter-atrial septum (IAS)The ventricles are separated from each-other by a muscular wall known as inter-ventricular septum (IVS)SVCAOLPARPAMPALUPVRUPVLLPVRLPVLARAPVAVMVTVIVSLVRVIVCAO
10The Left Ventricle & the arterial system is a high pressure – high resistance circuit. The right sided chambers and lungs are a low pressure – low resistance.
12How Does the heart pump? It is first electrically activated. The impulse forming point of the heart is known as the Sino-atrial (SA) nodeThe impulse of activation then passes through the atriaThen on to the Atrio-ventricular (AV) nodeThe impulse is delayed at the AV node for a few hundredths of a second (nodal delay) and then passes to the bundle of HisThe bundle of His divides into left & right branches, activating the corresponding ventricles.The muscle fibres of the ventricles are supplied by Purkinje fibres.
13How can heart’s electrical activity be captured on paper? The graphic representation of heart’s electrical activity is known as the electrocardiogram (ECG / EKG)
14What happens to the heart after it is electrically activated? Electrical activation triggers mechanical action i.e. contraction. In other words it is the electrical activation that activate the muscle to contract in an orderly & rhythmic manner.Thereby enabling reception & distribution of blood Slides that follow will explain heart’s mechanical action
15Blood Flows Into the Heart… Form the veins and then on to SVC and IVCsvcEnters RARATricuspid Valve opensTVRVBlood then enters the Right Ventricle Atria ContractIVC
16Then….Into the Lungs Exits the heart through the Pulmonary Valve Ventricles ContractLPARPAMPAEnters Pulmonary TrunkPVThen Into Lungs
17Blood Returns to Heart From Lungs enters Pulmonary veins. Enters Heart in Left AtriumPVPVPVPVLAMitral valve opensBlood flows into Left VentricleAtria contractMVLV
18Then …Pumped Back Into the Body Ventricles contractBlood flows through Aortic Valve.AO ArchBlood enters Ascending Aorta (coronary arteries i.e. arteries supplying the heart are at the aortic root)Asc.AoAortic Arch (arteries supplying head and upper limbs are situated here)AVLVDescending Aorta (thoracic, abdominal organs & lower limbs are thus supplied)Des. AO
19The Normal Heart and Regional Circulation LungsThe Normal Heart and Regional CirculationAnterior Cutaway ViewPulmonary ValveAortaSuperior Vena CavaLeft Pulmonary ArteryLeft Pulmonary VeinsLeft AtriumRight Pulmonary ArteryAorticValveMitral ValveRight Pulmonary VeinsTricuspid ValveInferior Vena CavaSeptum
20Blood Supply to the Heart Heart is supplied by coronary arteries.They have their origin just above the aortic root. [Aortic root is the area of the aorta just above the aortic valve i.e. the point of attachment of aorta to the heart]There are two of coronary arteries i.e. the left and rightThe left main coronary artery (LMCA) bifurcates into two i.e. the left anterior descending (LAD) and left circumflex (LCx)The right coronary artery (RCA) continues as such and gives off its branches.Majority of the venous drainage of the heart is from the corresponding coronary veins which drain into the coronary sinus which empties into RA
22Paths of Circulation Pulmonary Circuit Systemic Circuit Consists of vessels that carry blood from the heart to the lungs and back to the heartSystemic CircuitCarries blood from the heart to all other parts of the body and back againIncludes coronary circulation (supplies the heart)
23Pulmonary Circuit Right Ventricle Pulmonary Trunk Right and Left Pulmonary ArteriesCapillary Networks associated with walls of alveoli (air sacs in lungs where gas exchange occurs between air and blood)Pulmonary VenulesPulmonary veins – 2 from each lungLeft atrium
24Systemic Circuit Left Atrium (oxygenated blood) To Left Ventricle Aorta and its branches that lead to all body tissuesAccompanying system of veins returns blood to Right Atrium
25The Normal Heart and Regional Circulation LungsThe Normal Heart and Regional CirculationAnterior Cutaway ViewPulmonary ValveAortaSuperior Vena CavaLeft Pulmonary ArteryLeft Pulmonary VeinsLeft AtriumRight Pulmonary ArteryAorticValveMitral ValveRight Pulmonary VeinsTricuspid ValveInferior Vena CavaSeptum
27Blood VesselsThey are a closed circuit of tubes that carry blood from heart to cells and backThey include: arteries, arterioles, capillaries, venules, and veins100,000 Km of blood vessels in the body (2 ½ times around the world)
28ArteriesStrong elastic vessels adapted for carrying blood away from the heart under high pressureSubdivide into progressively thinner tubes and give rise to arterioles (finer branched tubes that connect artery to capillary)Walls of artery consist of 3 layersArterioles have 3 layers similar to arteries, but thin as they approach capillaries.
29Internal Structure of Arteries Tunica intima(endothelium)Elastic membraneTunica mediaExternalelasticlaminaTunica externa(adventitia)ArteryCourtesy Servier
30Tunica Intima (Interna) Innermost layerComposed of endothelium (squamous epithelium) and collagenous and elastic connective tissueHelps prevent blood clotting by providing a smooth surface that allows blood cells and platelets to flow through without being damaged.Secretes chemical substances that inhibit platelet aggregation (thereby preventing establishment of blood clots)May help regulate blood flow by secreting substances that dilate or constrict blood vessels.
31Tunica Media Middle layer Bulk of arterial wall Comprises of - Smooth muscle fibers encircling it- Thick layer of elastic connective tissue
32Tunica Adventitia (Externa) Outer layerConnective tissue with irregularly organized elastic and collagen fibersAttaches the artery to surrounding tissues.
33Nerve Supply to Blood Vessels Sympathetic branches of the autonomic nervous system use vasomotor fibers to innervate smooth muscle in artery and arteriole wallsVasoconstriction: vasomotor impulses stimulate contraction which reduces diameter of vesselVasodilation: vasomotor impulses are inhibited, muscle fibers relax and diameter of vessel increases.Changes in diameter of vessels greatly influence blood flow and pressure.
34Capillaries Smallest-diameter blood vessels Connect the smallest arterioles and smallest venulesComposed of extensions of the inner linings of arterioles in that their walls are endotheliumThin walls form semipermeable layer through which substances in blood are exchanged with tissue fluid surrounding body cells
35CapillariesOsmotic Pressure: force due to salts etc. in the blood that brings water into vessel.Blood Pressure: force exerted by the heart in contractions.BP changes as the arteries get further away from heart.OP remains the same.Difference between BP & OP determines materials movement in or out of vessel.
36Capillaries Arterial end Venous end Osmotic 21 Osmotic 21 BP15 BP 30 Diff: 6InwardDiff: 9Outward
37CapillariesAt arterial end: nutrients, oxygen etc. move from vessel to cells.At venous end: waste, carbon dioxide etc. move from cells to vessel.But not all fluid moves into the vessels.A third vessel found along vein, Lymphatic Vessel.
38Exchanges in capillaries Gases, nutrients, and metabolic by-products are exchanged by diffusion, filtration and osmosisDiffusionSubstances diffuse down concentration gradient.Plasma proteins remain in blood. Too large to diffuse through membrane pores and also are not soluble in the lipid portion of capillary cell membranes.
39Venules and VeinsVenules: microscopic vessels that continue from capillaries and merge to from veins.Veins: carry blood back to the atria following pathways that roughly parallel arteries.
42Venous Valves Found in many veins, especially in lower limbs Project inward from the liningComposed of 2 leaflets that close if blood begins to back up in a vein.Aid in returning blood to the heart (open if flow is toward the heart)
43Veins as Blood Reservoirs In a hemorrhage accompanied by a drop in arterial pressure, sympathetic nerve impulses reflexively stimulate venous constriction of the walls.This helps maintain blood pressure by returning more blood to the heart.Normal flow can be maintained when even as much as 25% volume is lost.