The Cardiovascular System: The Heart

1
The Cardiovascular SystemThe Heart

• Chapter 19

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
Heart Size, Location and Position

• The heart is about the size of a fist
• It weighs between 250 - 350 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

4
Heart Size, Location and Position

• The lungs flank the heart laterally and partially
  obscure it

5
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

6
Coverings of the Heart

• The heart is enclosed in a double-walled sac
  called the pericardium
• The loose fitting superficial part 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

7
Coverings of the Heart

• The loose fitting superficial part of the sac is
  the fibrous pericardium
• This tough, dense connective tissue layer
• Protects the heart
• Anchors it to surrounding structures
  (diaphragm/large vessels)
• Prevents overfilling of the heart with blood

8
Coverings of the Heart

• Deep to the fibrous pericardium is the serous
  pericardium, a thin slippery serous membrane
  composed of two layers
• Parietal layer
• Visceral layer

9
Coverings of the Heart

• The parietal layer lines the internal surface of
  the fibrous pericardium
• At the superior margin of the heart, the parietal
  layer attaches to the large arteries exiting from
  the heart
• It then turns inferiorly and continues over the
  external heart surface as the visceral layer

10
Coverings of the Heart

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

11
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

12
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

13
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

14
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

15
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

16
Layers of the Heart Wall

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

17
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

18
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

19
Layers of the Heart Wall

• The endocardium is a glistening white sheet of
  endothelium (squamous epithelium) resting on a
  thin layer of connective tissue

20
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

21
Chambers and Great Vessels

• 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
22
Chambers and Great Vessels

• 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
23
Chambers and Great Vessels

• 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
24
Chambers and Great Vessels

• 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
  hearts posterio- inferior surface

Anterior Interventricular Sulcus
Posterior Interventricular Sulcus
25
Atria The Receiving 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
26
Atria The Receiving 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
27
Atria The Receiving 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
28
Atria The Receiving 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

29
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
30
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
31
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
32
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 Wall
33
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
34
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

35
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

36
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

37
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

38
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

39
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

40
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

41
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
42
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
43
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

44
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
45
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

46
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
47
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
48
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
49
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

50
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

51
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
52
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

53
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

54
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

55
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

56
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

57
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

58
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 bodys blood
  supply
• The left ventricle receives the largest
  proportion of the blood supply

59
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

60
End of Material

• Chapter 19