the cardiovascular system heartmarketlabscentral.com/.../11/ch-18-heart-students.pdf · gross...
TRANSCRIPT
The Cardiovascular System
Heart
Biology 260
M. Iyengar
Embryonic Development of the Heart
• Week 2
– Somites have not fully developed.
– Towards the head, the ectoderm migrates down to engulf/ surround the endoderm
– Lateral plate mesoderm contains cells that will become cardiomyoblastsanterior to the gut tube.
– Lateral plate mesoderm splits and eventually surrounds the developing heart to create the pericardial cavity
Embryonic Development of the Heart
• Further development
– Two cardiac tubes fuse with a primitive atria and ventral
– As the embryo grows the heart elongates and bends forming an S-curve
• Atria move superior and ventricles inferior
– An interatrial and interventricular septa subdivide the heart.
– A gap between the two interatrial septa creates the foramen ovale.
• Allows blood flow from the right atrium into the left atrium →bypassing the pulmonary circuit.
• At birth this opening closes and the two circuits of the heart are separated.
Location of the Heart
• In mediastinum between second rib and fifth intercostal space
– Anterior to vertebral column, posterior to sternum
– Sits on the superior surface of diaphragm
• Two-thirds of heart is left of midsternal line
– Base leans toward right shoulder
– Apex points toward left hip
(c)
Superior vena cava
Left lung
AortaParietal pleura (cut)
Pericardium (cut)
Pulmonary trunk
Diaphragm
Apex of heart
Pericardium(cut)
Fat inepicardiumRib 5
Left lung
Aorta
Mediastinum
Apex ofheart(d)
Right auricleof right atrium
Superiorvena cava
Right ventricle
Diaphragm
(a)
Rib 2
Midsternal line
Location of the Heart
Heart
Posterior
Right lung
(b)
Mediastinum
Covering of the Heart
• Pericardium
– Fibrous pericardium – strong layer of dense CT• Anchors heart to surrounding structures
– Serous pericardium – formed from two layers• Parietal layer lines internal surface of fibrous pericardium
• Pericardial cavity (decreases friction) - fluid-filled between the parietal and visceral layers
• Visceral layer (AKA the epicardium) on external surface of the heart
Pulmonary
trunk
Heart
wall
Layers of the Heart
Layers of the Heart• Myocardium:
– Cardiac muscle arranged in circular and spiral patterns
– Space between cells (intercellular) filled with CT (endomysium)
– Cardiac muscle cells are short & branched, with:
• Mitochondria, sarcomeres, less T tubules & SR than skeletal muscle celss
• Desmosome: hold cells together; prevent cells from separating during contraction
• Gap junctions: allow ions to pass from cell to cell
Layers of the Heart
• Endocardium:
– Simple squamous epithelium
– Lines the internal walls of the heart and is continuation of blood vessel lining
Gross Anatomy of the Heart
1. Atria:
– Arriving chambers - Receive blood from the pulmonary and systemic circuits through veins
– Thin muscular wall
– Auricles (exterior surface):
» Folded extensions of the atria
» Increase volume
– Pectinate muscle (internal surface):
» Atrial muscle
Gross Anatomy of the Heart
2. Ventricles:
– The exit/pumping chambers of the heart
– Thick muscular walls
– Trabeculae carneae = irregular ridges of ventricular wall muscles
– Papillary muscles: project into ventricular cavity
• Anchor chordae tendineae that are attached to heart valves
– Right ventricle:
• Thinner wall
• Pumps to the lungs (pulmonary circuit)
– Left ventricle:
• 2-3x thicker than the RV muscles
• Pumps to the body (systemic circuit)
Gross Anatomy of the Heart
• Surface features
– Coronary sulcus
• Separates atria from ventricles on the posterior surface
– Auricles & coronary arteries
• Separates atria from ventricles on the anterior surface
– Anterior interventricular sulcus
• Marks the right and left ventricles on the anterior surface
– Posterior interventricular sulcus
• Marks the right and left ventricles on the posterior surface
(b) Anterior view
Anatomy of the Heart
(d) Inferior view; surface shown rests on the diaphragm.
Apex
Anatomy of the Heart
Gross anatomy of the Heart
• Internal divisions
– Atrioventricular valves
• Separates atria and ventricles
– Interatrial septum
• Separates right and left atria
– Interventricular septum
• Marks the right and left ventricles
• Fossa ovalis: remnant of foramen ovale of fetal heart
Left atrium
(e) Frontal section
Right atrium
Frontal section of the Heart
Gross Anatomy of the Heart
• Valves of the Heart - composed of endocardium with a connective tissue core
• Atrioventricular (AV) valves
– Between atria and ventricles
– Prevent backflow of blood to atria when ventricles are contracting.
• Tricuspid valve → right side
• Bicuspid valve or mitral valve → left side
• Semilunar (SL) valves
– Between ventricles and main arteries
– Prevent backflow of blood to ventricles when ventricles relax
• Pulmonary SL valve → right side
• Aortic SL valve → left side
The Heart Valves
Pulmonary valve
Aortic valve
Area of cutaway
Mitral valve
Tricuspid valve
Myocardium
Tricuspid(right atrioventricular) valve
Mitral(left atrioventricular)valve
Aorticvalve
Pulmonaryvalve
Cardiacskeleton Anterior
The Heart Valves
Chordae tendineae
attached to tricuspidvalve flap
Papillary muscle
Mitral valveChordae tendineae
Tricuspidvalve
Interventricularseptum
Myocardium of leftventricle
Rightatrium
Left atrium
Papillary muscles
Myocardium of right ventricle
Heart Sounds
•Caused by the closure of the heart valves.•LUB – First sound → AV valves closing
•DUB – Second sound →semilunar valves closing
•Murmur→ heart valve disorder
• Stethoscope placement:
–Aortic semilunar valve: 2nd intercostal space on right of sternum
–Pulmonary semilunar valve: 2nd
intercostal space on left of sternum
–Tricuspid valve: 5th intercostal space on right of sternum
–Mitral valve: 5th intercostal space on left of sternum
Right
atrium
Aorta
To body
To heart
To heart
To lungs
Mitral
valveLeft
ventricle
Left
atrium
Left
atriumAorta
Left
ventricle
Four pulmonary
veins
Right
ventricle
Superior vena cava (SVC)Inferior vena cava (IVC)
Coronary sinus
Right
atrium
Pulmonary
trunk
Pulmonary
veins
Pulmonary
arteries
Aortic
semilunar
valve
Tricuspid
valve
Tricuspid
valve
Pulmonary
trunk
Right
ventricle
Pulmonary
semilunar
valve
Pulmonary
semilunar valve
IVC
SVC
Two pulmonary arteries
carry the blood to the
lungs (pulmonary circuit)
to be oxygenated.
Oxygen-rich blood returns
to the heart via the four
pulmonary veins.
Oxygen-poor blood
returns from the body
tissues back to the heart.
Oxygen-rich blood is
delivered to the body
tissues (systemic circuit).
Oxygen-rich blood
Oxygen-poor blood
Mitral
valve
Aortic
semilunar
valve
Coronary
sinus
Blood Flow Through the Heart Pulmonary Circuit –carries CO2- rich blood to the lungs.1.CO2- rich blood from tissues moves thru the heart to the Lungs. 2.CO2 is removed, O2 is added to blood, and sent back to the heart.
Systemic Circuit –carries O2 – rich blood to all body parts.1.O2- rich blood from the Lungs moves thru the heart to the Body.2.O2 diffuses from blood to tissues, CO2 is added to blood, & sent back to the heart.
Physiology of the Heart
• Systems that control contraction of heart muscles:
1. Intrinsic conduction system/nodal system• Autorhythmicity
– Pacemaker cells: noncontractile cells that spontaneously depolarize
• Contractile cells: responsible for contraction
– All cardiomyocytes contract as unit, or none contract
» ensures effective pumping action
2. Extrinsic conduction system →Medulla oblongata
The Intrinsic Conduction System
• Sequence of excitation
– Cardiac pacemaker cells pass impulses, in following order, across heart in 0.22 seconds
1. Sinoatrial node → right atrial wall
2. Atrioventricular node → inferior interatrial septum
3. Atrioventricular bundle → superior interventricular septum
4. Right and left bundle branches → interventricular septum
5. Purkinje fibers (Subendocardial conducting network) →Complete pathway through interventricular septum into apex and ventricular walls
Intrinsic Conduction System
The sinoatrial (SA)
node (pacemaker)
generates impulses.
Internodal pathway
Superior vena cava Right atrium
Left atrium
Purkinje
fibers
Inter-
ventricular
septum
The impulses
pause (0.1 sec) at the atrioventricular
(AV) node.
The atrioventricular
(AV) bundle connects
the atria to the ventricles.
The bundle branches
conduct the impulses
through the interventricular
septum.
The Purkinje fibers
stimulate the contractile
cells of both ventricles.
1
2
3
4
5
Intrinsic Conduction System
The Electrocardiogram (ECG or EKG)
–Record of electrical events in heart– Used to diagnose cardiac abnormalities by looking for abnormal
wave patternsThree waves are recorded:
– P wave: atria depolarization =
contract
– QRS complex: ventricle
depolarization = contraction
– T wave: ventricle repolarization =
relaxation
Extrinsic Conduction System
Heartbeat
• Cardiac cycle: blood flow through heart during one complete heartbeat
– 75 beats/minute at rest
• Systole and diastole also refer to:
– Stage of heartbeat when ventricles contract and expand
– Systole – period of heart contraction
– Diastole – period of heart expansion/relaxation
Cardiac Cycle
Cardiac Cycle
Blood vessels of the Heart
Arteries - carry blood Away from the heart.
– Main arteries:
• Aorta: left ventricle → systemic circuit
• Pulmonary trunk: right ventricle → pulmonary circuit
VeIns - carry blood Into the heart.
– Main veins:
• Superior and inferior vena cava: transport blood from body to right atrium
• Pulmonary veins: transport blood from lungs to left atrium
Blood Supply to the Myocardium
• Coronary circulation
– Functional blood supply to heart muscle itself
– Shortest circulation in body
– Delivered when heart is relaxed
– Left ventricle receives most of coronary blood supply
Blood Supply to the Myocardium
• Coronary arteries – Supply nutrient & O2-rich blood to the muscles of the heart
– Arise from the aorta, encircle heart in coronary sulcus
– Left coronary supplies the interventricular septum, anterior ventricular walls, left atrium, and posterior wall of left ventricle; has two branches:
• Circumflex artery→ Anterior interventricular artery
– Right coronary - supplies right atrium and most of right ventricle; has two branches:
• Right marginal artery
• Posterior interventricular artery
Blood Supply to the Myocardium
Blood Supply to the Myocardium
• Coronary veins – Remove blood with waste from the heart muscles
– Cardiac veins collect blood from capillary beds
– Coronary sinus empties into right atrium; formed by merging cardiac veins
• Great cardiac vein of anterior interventricular sulcus
• Middle cardiac vein in posterior interventricular sulcus
• Small cardiac vein from inferior margin
– Several anterior cardiac veins empty directly into right atrium anteriorly
Auricle ofleft atrium
Left ventricle
Apex(b) Anterior view
Right atrium
Right ventricle
Blood vessels of the Heart
Left atrium
Mitral (bicuspid) valve
Aortic valve
Pulmonary valve
Left ventricle
(e) Frontal section
Right atrium
Tricuspid valve
Right ventricle
Blood vessels of the Heart
(d) Inferior view; surface shown rests on the diaphragm.
Left atrium
Left ventricle
Apex
Right atrium
Right ventricle
Blood Supply to the Myocardium
Blood Supply to the Myocardium