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The Heart Chapter 18.

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1 The Heart Chapter 18

2 Introduction The heart is the pump of our circulatory system
The cardiovascular system provides the transport system of the body Using blood as the transport medium, the heart continually propels oxygen, nutrients, wastes, and many other substances into the interconnecting blood vessels that move past the body cells

3 Introduction The heart is a muscular double pump with two functions
Its right side receives oxygen poor blood from the body tissues and then pumps it to the lungs Its left side receives oxygenated blood from the lungs and then pumps it to the body

4 Introduction The blood vessels that carry blood from the lungs form the pulmonary circuit The vessels that carry blood to all the body tissues form the systemic circuit

5 Heart Size, Location and Position
The heart is about the size of a fist It weighs between grams (less than a pound) Located in the medial cavity of the thorax, the mediastinum It extends from the 2nd rib to 5th intercostal space Rests on the superior surface of diaphram

6 Heart Size, Location and Position
The lungs flank the heart laterally and partially obscure it

7 Heart Size, Location and Position
The heart lies anterior to the vertebral column and posterior to the sternum Two thirds of the heart lies to the left of the mid- sternal line; the balance projects to the right Its broad flat base, or posterior surface, points to right shoulder The apex points toward the left hip

8 Location - 4 Corners The heart is has four corners projected onto the anterior thoracic wall Superior right - where the costal cartilage joins the 3rd rib Superior left - costal cartilage of 2nd rib a fingers breadth lateral to the sternum

9 Location - 4 Corners The inferior right - lies at the costal cartilage of the sixth rib, a finger’s breath lateral to the sternum The inferior left (apex) lies in the fifth intercostal space at the mid-clavicular line These points depict the normal heart size and placement

10 Coverings of the Heart The heart is enclosed in a triple-walled sac called the pericardium The loose fitting outer layer of the sac is the fibrous pericardium This tough, dense connective tissue layer 1) protects the heart; 2) anchors the heart; and 3) prevents overfilling

11 Coverings of the Heart Deep to the fibrous pericardium is the double-layered serous pericardium, a closed sac sandwiched between the fibrous pericardium and the heart The two layers are… Parietal layer Visceral layer

12 Coverings of the Heart The outer parietal layer adheres to the internal surface of the fibrous pericardium At the superior reflection of the heart, the parietal layer is continuous with the visceral layer of the serous pericardium or epicardium

13 Coverings of the Heart The visceral layer, also called the epicardium, is an integral part of the heart wall The two-layer membrane conforms around the heart much like pushing your fist into a double layer membrane with an air pocket in between

14 Coverings of the Heart Between the two layers of serous pericardium is the slitlike pericardial cavity The cavity contain pericardial fluid The serous membranes, lubricated by fluid, glide smoothly against one another during heart activity, creating a relatively friction-free environment

15 Inflammation Inflammation of the heart can lead to serious problems
Pericarditis / hinders production of serous fluid production causing the heart to rub Cardiac tamponade / inflammatory fluid seep into the pericardial cavity, compressing the heart and limiting its ability to pump blood

16 Layers of the Heart Wall
The heart wall is composed of three layers Superficial layer of epicardium Middle layer of myocardium Deep layer of endocardium All three layers are richly supplied with blood vessels

17 Layers of the Heart Wall
The epicardium is the visceral layer of the serous pericardium The epicardium is often infiltrated with fat, especially in older people

18 Layers of the Heart Wall
The myocardium is the layer of cardiac muscle that forms the bulk of the heart It is the layer that actually contracts The myocardium’s elongated circularly spirally arranged muscle cells squeeze the blood though the heart

19 Layers of the Heart Wall
Within the myocardium, the branching cardiac muscle cells are tethered to each other by crisscrossing connective tissue fibers also arranged in spiral or circular bundles These interlacing bundles effectively link all parts of the heart together

20 Layers of the Heart Wall
The connective tissue forms a dense network called the internal skeleton of the heart It reinforces the myocardium internally and anchors the cardiac muscle This network of fibers is thicker in some areas than in others to rein- force valves and where the major vessels exit

21 Layers of the Heart Wall
The internal skeleton prevents overdilation of vessels due to the continual stress of blood pressure Additionally, since connective tissue is not electrically excitable, it limits action potentials across the heart to specific pathways

22 Layers of the Heart Wall
The endocardium is a glistening white sheet of endothelium (squamous epithelium) resting on a thin layer of connective tissue

23 Layers of the Heart Wall
Located on the inner myocardial surface, it lines the heart chambers and covers the connective tissue skeleton of the valves The endocardium is continuous with the endothelial linings of the blood vessels leaving and entering the heart

24 Heart Chambers The heart has four chambers
Two superior atria Two inferior ventricles The longitudinal wall separating the chambers is called the Interartial septum Between atria Interventricular septum Between ventricles Atria Septum Ventricles

25 Heart Chambers The right ventricle forms most of the anterior surface of the heart The left ventricle dominates the inferio- posterior aspect of the heart and forms the heart apex Left Ventricle Right Ventricle

26 Heart Chambers Two grooves visible on the surface of the heart indicate the boundaries of its four chambers and carry the blood vessels that supply myocardium The Atrioventricular groove or coronary sulcus encircles the junction of the atria and ventricles Coronary Sulcus

27 Heart Chambers The anterior inter- ventricular sulcus, separates the right and left ventricles It continues as the posterior inter-ventricular sulcus which provides a similar landmark on the heart’s posterio- inferior surface Anterior Interventricular Sulcus Posterior Interventricular Sulcus

28 Heart Chambers Except for the small, wrinkled, protruding appendages called auricles, the atria are free of distinguishing surface features The auricles increase the atrial volume slightly Atria Auricles

29 Heart Chambers Internally, the posterior walls are smooth, but the anterior walls are ridged by bundles of muscle tissue These muscle bundles are called pectinate muscles Pectinate Muscle

30 Heart Chambers The interatrial septum bears a shallow depression, the fovea ovalis This landmark marks the spot where an opening, the foramen ovale, existed in the fetal heart Fovea Ovalis

31 Heart Chambers Functionally, the atria are receiving chambers for blood returning to the heart from the circulation Because they need to contract only minimally to push blood into the ventricles, the atria are relatively small, thin walled chambers As a rule they contribute little to the propulsive pumping of the heart

32 Atria: The Receiving Chambers
Blood enters the right atrium via three veins Superior vena cava Returns blood from body regions superior to diaphragm Inferiorn vena cava Returns blood from body areas below the diaphragm Coronary sinus Collects blood draining from the myocardium itself Superior vena cava Coronary sinus Inferior vena cava

33 Atria: The Receiving Chambers
Blood enters the left atrium via four veins Right and left pulmonary veins The pulmonary veins transport blood from the lungs back to the heart Right Pulmonary veins Left pulmonary veins Posterior view

34 Ventricles: Discharging Chambers
Marking the internal walls of the ventricle chambers are irregular ridges of muscle called trabeculae carneae The papillary muscles project into the cavity and play a role in valve function Papillary muscles Trabeculae carneae

35 Ventricles: Discharging Chambers
The ventricles are the discharging chambers of the heart Note the difference in thickness of the wall When the ventricles contract blood is propelled out of the heart and into circulation Atrial Wall Ventricular

36 Ventricles: Discharging Chambers
The right ventricle pumps blood into the pulmonary trunk, which routes blood to the lungs for gas exchange The left ventricle pumps blood into the aorta, the largest artery in the systemic circulation Aorta Left ventricle Pulmonary trunk Right ventricle

37 Pathway of Blood: Heart
The heart is actually two pumps, each serving a separate blood circuit Blood vessels that carry blood to the lung form the pulmonary circuit (gas exchange) Vessels carrying blood to the body form the systemic circuit

38 Pathway of Blood: Heart
The right side of the heart forms the pulmonary circuit Blood returning from the body enters the right atrium and passes into the right ventricle The ventricle pumps the blood to the lungs via the pulmonary trunk

39 Pathway of Blood: Heart
Blood in the pulmonary circuit is oxygen poor and carbon dioxide rich Once in the lungs the blood unloads carbon dioxide and picks up oxygen Freshly oxygenated is carried back to the heart by the pulmonary veins

40 Pathway of Blood: Heart
Note that the circulation of the pulmonary circuit is unique Typically veins carry oxygen poor blood to the heart and arteries carry oxygen rich blood The pattern is reversed in the pulmonary circuit with the pulmonary arteries carrying oxygen poor blood to the lungs and the pulmonary veins carrying oxygen rich blood back to the heart

41 Pathway of Blood: Heart
The left side of the heart is the systemic system pump Freshly oxygenated blood leaving the lungs enters the left atrium and passes into the left ventricle The left ventricle pumps blood into the aorta and from there into many distributing arteries

42 Pathway of Blood: Heart
Smaller distributing arteries carry the blood to all parts of the body Gases, wastes and nutrients are exchanged across capillary walls Blood then returns to the right atrium of the heart via systemic veins and the cycle continues

43 Pathway of Blood: Heart
Although equal volumes of blood are flowing in the pulmonary and systemic circuits at any one moment the two ventricles have very unequal work loads The pulmonary circuit, served by the right ventricle, is a low pressure circulation The systemic circuit, served by the left ventricle, circulates through the entire body and encounters about five times as much resistance to blood flow

44 Pathway of Blood: Heart
The fact that blood passes through heart chambers sequentially does not mean that the four chambers contract in that order Rather the two atria contract together, followed by the simultaneous contraction of the two venticles

45 Pathway of Blood: Heart
A single sequence of atrial contraction followed by the ventricular contraction is a called a heartbeat The heart of the average adult person at rest beats times a minute

46 Pathway of Blood: Heart
The contraction of a heart chamber is called a systole The time during which a heart chamber is relaxing and filling with blood is termed diastole Although both atrial and ventricular chambers experience systole and diastole the terms usually reference the ventricles which are the dominant heart chambers

47 Ventricles: Discharging Chambers
The difference in system work load is revealed in the comparative anatomy of the two ventricles The walls of the left ventricle are three times as thick as those of the right ventricle Left ventricle

48 Ventricles: Discharging Chambers
The cavity of the left ventricle is circular The right ventricle wraps around the left and is crescent shaped The left can generate much more pressure than the right and is a far more powerful pump Left ventricle

49 Pathway of Blood: System
Blood flows through the heart and other parts of the circulatory system in one direction Right atrium  right ventricle  pulmonary arteries  lungs Lungs  pulmonary veins  left atrium  left ventricle  body This one way flow of blood is controlled by four heart valves

50 Heart Valves Heart valves are positioned between the atria and the ventricles and between the ventricles and the large arteries that leave the heart Valves open and close in response to differences in blood pressure Bicuspid (mitral) valve Aortic valve Pulmonary valve Tricuspid valve

51 Heart Valves The valves of the heart allow for the blood to flow in only one direction Note: View of the heart with the superior atria removed

52 Atrioventricular (AV) Valves
The AV valves are located at each atrial-ventricular junction The valves are positioned to prevent a backflow of blood into the atria when the ventricles are contracting The valves are the Tricuspid valve Bicuspid valve Bicuspid (mitral) valve Tricuspid valve

53 Atrioventricular (AV) Valves
The right AV valve, the tricuspid, has three flexible cusps The left AV valve, the bicuspid, has two flexible cusps The cusps are flaps of endocardium reinforced by connective tissue Bicuspid (mitral) valve Tricuspid valve

54 Atrioventricular (AV) Valves
Attached to each of the AV valve flaps are tiny collagen cords called chordae tendoneae The cords anchor the cusps to the papillary muscles protruding from the ventricular walls Chordae tendoneae Papillary muscles

55 Atrioventricular (AV) Valves
When the heart is completed relaxed, the AV valve flaps hang limply into the ventricular chambers Blood flows into the atria and then through the open AV valves into the ventricles Atria contract, forcing additional blood into ventricles

56 Atrioventricular (AV) Valves
When the ventricles begin to contract, compressing the blood in the chambers, intra- ventricular pressure rises forcing blood superiorly against the valve flaps The chordae tendoneae and the papillary muscles anchor the flaps in their closed position

57 Semilunar (SL) Valves The aortic and pulmonary semilunar valves are located at the bases of the large arteries exiting the ventricles The valves prevent backflow of blood from the aorta and pulmonary trunk into the associated ventricles Aortic valve Pulmonary valve

58 Semilunar (SL) Valves Each semilunar valve is made up of three pocketlike cusps Their mechanism of closure differs from that of the AV valves When the ventricles contract intra- ventricular pressure exceeds the blood pressure in the aorta and pulmonary trunk

59 Semilunar (SL) Valves Blood pressure from the ventricle forces the semilunar valves open and blood is forced past the valve and into the artery When the ventricles relax, and the blood flows backward toward the heart it fills the cusps which closes the valves

60 Heart Sounds The closing of the heart valves causes vibrations in the adjacent blood and heart walls that account for the familiar “lub-dup” sounds of the heartbeat The “lub” is produced by the closing of the AV valves at the start of ventricular systole The “dup” is produced by the closing of the semilunar valves at the end of ventricular systole

61 Fibrous Skeleton The fibrous skeleton of the heart lies in the plane between the atria and the ventricles It surrounds the four valves It is composed of dense connective tissue

62 Fibrous Skeleton The fibrous skeleton has four functions
It anchors the valve cusps It prevents overdilation of the valve openings as blood pulses through them It is the point of insertion for the bundles of cardiac muscle in the atria and ventricles It blocks the direct spread of electrical impulses from the atria to the ventricles

63 Conducting System Cardiac muscle cells have an intrinsic ability to generate and conduct impulses that signal these same cells to contract rhythmically These properties are intrinsic to the heart muscle itself and do not depend on extrinsic nerve impulses Even if all nerve connections to the heart are severed, the heart continues to beat rhythmically

64 Conducting System The conducting system of the heart is a series of specialized cardiac muscle cells that carries impulses throughout the heart musculature, signaling the heart chambers to contract in proper sequence

65 Conducting System The components of the conducting system are:
Sinoatrial node Internodal fibers Atrioventricular node Atrioventricular bundle Right an left branches Purkinje fibers

66 Conducting System The impulse that signals each heartbeat begins at the sinoatrial (SA) node This is a crescent shaped mass of muscle cells that lies in the wall of the right atrium, below the entrance of the superior vena cava

67 Conducting System The sinoatrial node, the heart’s own pacemaker, sets the basic heart rate by generating impulses per minute

68 Conducting System The sequence that controls each heartbeat - atrial contraction followed by ventricular contraction is specific

69 Conducting System Impulses from the SA node spread in a wave along the cardiac muscle fibers of the atria signaling the atria to contract

70 Conducting System Some of these impulses travel along the intranodal pathway to the atrioventricular (AV) node in the inferior part of the interatrial septum, where they are delayed for a fraction of a second

71 Conducting System After this delay, the impulses race through the atrio- ventricular bundle which enters the interventricular septum and divides into right and left bundle branches

72 Conducting System About halfway down the septum, the Bundle fibers, (crura), become bundles of Purkinje fibers which approach the apex of the heart, then turn superiorly into the ventricular walls

73 Conducting System This arrangement of conducting structures ensures that the contraction of the ventricles begins at the apex of the heart and travels superiorly, so that the ventricular blood is ejected superiorly into the great arteries The brief delay of the contraction signaling impulses at the AV node enables the ventricles to fill completely before they start to contract

74 Conducting System Because the fibrous skeleton between the atria and ventricles is nonconducting, it prevents impulses in the atrial wall from proceeding directly on to the ventricular wall As a result, only those signals that go through the AV node can continue on

75 Conducting System Examination of the microscopic anatomy of the heart’s conducting system reveals that the cells of the nodes and AV bundle are small, but otherwise typical cardiac muscle cells Each Purkinje fiber, by contrast, is a long row of special, large-diameter cells called Purkinje myocytes

76 Conducting System Purkinje myocytes are cardiac muscle cells containing relatively few myofilaments because they are adapted more for conduction than contraction Their large diameter maximizes the speed of impulse conduction Purkinje fibers are located in the deepest part of the ventricular endocardium, between the endocardium and myocardium layers

77 Innervation Although the heart’s inherent rate of contraction is set by the SA node, this rate can be altered by extrinsic neural controls

78 Innervation The nerves to the heart consist of visceral sensory fibers
Parasympathetic fibers that slow heart rate Sympathetic fibers that increase the rate and force of heart contractions

79 Innervation Parasympathetic nerve fibers arise as branches of the Vagus nerve in the neck and thorax

80 Innervation Sympathetic nerves travel to the heart from the cervical and upper thoracic chain ganglia All nerves serving the heart pass through the cardiac plexus on the trachea before entering the heart

81 Innervation Although autonomic fibers project to cardiac musculature throughout the heart, they project most heavily to the SA and VA nodes and the coronary arteries

82 Innervation The autonomic input to the heart is controlled by cardiac centers in the reticular formation of the medulla of the brain In the medulla, the cardio-inhibitory center influences parasympathetic neurons, whereas the cardioacceleratory center influences sympathetic neurons

83 Innervation These medullary cardiac centers, in turn, are influenced by such higher brain regions as the hypothalamus, periaqueductal gray matter, amygdala, and insular cortex

84 Coronary Circulation The coronary circulation, the functional blood supply of the heart, is the shortest circulation in the body The arterial supply of the coronary circulation is provided by the right and left coronary arteries

85 Coronary Circulation The left coronary artery runs toward the left side of the heart and then divides into its major branches Anterior interventricular artery follows the sulcus and supplies blood to the inter- ventricular septum and walls of ventricle

86 Coronary Circulation The right coronary artery courses to the right side of the heart where it divides The marginal artery serves the myo-cardium of the lateral part of the right side of the heart The posterior inter-ventricular artery runs to the apex of the heart

87 Coronary Circulation There are many merging blood vessels that delivery blood to the heart muscle This explains how the heart can receive an adequate supply when one of its coronary arteries is almost entirely occluded

88 Coronary Circulation The coronary arteries provide an inter- mittent pulsating flow to the myocardium These vessels and their main branches lie in the epicardium and send branches inward to nourish the myocardium Although the heart represents only about 1/200 of body weight, it requires 1/20 of the body’s blood supply The left ventricle receives the largest proportion of the blood supply

89 Coronary Circulation After passing through the myo- cardium, the venous blood is collected by the cardiac veins The veins join together to form an enlarged vessel called the coronary sinus which empties into the right atrium

90 End of Material Chapter 18

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