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