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Chapter 18. Cardiovascular System. Cardiovascular = circulatory. Heart & closed system (arteries, veins, capillaries) Appears early in development – heartbeat at 4 wks. Heart.

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Chapter 18

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chapter 18

Chapter 18

Cardiovascular System

cardiovascular circulatory
Cardiovascular = circulatory
  • Heart & closed system (arteries, veins, capillaries)
  • Appears early in development – heartbeat at 4 wks.
  • In mediastinum – behind sternum, between 2nd & 6th ribs 2/3 to the left of midline, lies between 5th & 8th thoracic vertebrae
  • 4-chambered – size & shape of closed fist
  • CPR – cardiopulmonary resuscitation – heart compressions & artificial respiration
  • Apex – lower border of the heart, blunt point, lies on the diaphragm, points to the left
  • Base – upper border, below 2nd rib
Size of heart influenced by age, body type, & state of contraction
  • Between puberty and 25 yrs., reaches adult shape & weight
  • 310g avg. male
  • 225g avg. female
  • Shape resembles individual (tall = elongated, stocky = transverse) – avg. length 12cm, width 9cm, depth 6cm
heart coverings
Heart coverings
  • Pericardium – loose-fitting inextensible sac – 2 parts:

a. fibrous portion – tough white fibrous sac

b. serous portion – produces pericardial fluid – 2 layers:

i. parietal layer = lining inside fibrous pericardium

ii. visceral layer = adheres to heart

2. Epicardium = visceral layer

heart structure
Heart structure
  • Epicardium = outer layer – part of serous pericardium’s visceral layer
  • Myocardium = thick, contractile middle layer

- intercalated discs join cardiac cells to make a continuous mass = syncytium – muscles can pass action potential along large area of heart = compresses with great force – cells are autorhythmic

3. Endocardium = delicate layer lining interior of myocardial wall

- endothelial tissue

- covers trabeculae – muscular beam-like projections

- forms valves

chambers of the heart
Chambers of the Heart
  • 4 chambers (2 atria & 2 ventricles)
  • Right & left sides are separated by the septum
  • Atria – upper chambers

- “receiving chambers” – receive blood from veins

- myocardial wall not very thick

2. Ventricles – lower chambers

- “pumping chambers” – thicker myocardial wall than atria – left is thicker than right because pumps to most of the body

valves permit blood flow
Valves – permit blood flow
  • 2 atrioventricular (AV) valves – guard opening between atria & ventricles (also called cuspid valves)

- right has 3 flaps = tricuspid valve

- left has 2 flaps = bicuspid/mitral valve

- allows blood to flow from the atria to the ventricles without backflow

2 semilunar valves – opening between pulmonary artery or aorta and the ventricles

- prevents backflow into ventricles

- pulmonary semilunar valve – in between pulmonary artery & right ventricle

- aortic semilunar valve – in between aorta & left ventricle


skeleton of heart
Skeleton of Heart
  • Fibrous structure of connected rings – support for heart valves and attachment of myocardium – also electrical barrier between atria & ventricles
flow of blood through heart
Flow of Blood through Heart
  • Right atrium  right AV valve (tricuspid)  right ventricle  pulmonary semilunar valve  pulmonary artery  lungs  pulmonary veins  left atrium  left AV valve (mitral)  left ventricle  aortic semilunar valve  aorta  everywhere in body except lungs (vena cavas return blood to heart)

blood supply to heart tissue
Blood Supply to Heart Tissue
  • Coronary arteries – provide myocardial cells with blood

- come off of aorta

- ventricles get more blood because they get it directly from the coronary arteries, atria get blood from branches

Anastomoses – one or more branches from the artery – provides a detour for the blood to travel if the main route becomes blocked
  • Myocardial infarction – death of heart cells due to lack of blood flow
  • Cardiac veins – take oxygendepleted blood to the right atrium through coronary sinus (some drain directly into right atrium)

- path closely follows the path of coronary arteries

conduction system of heart
Conduction System of Heart
  • 4 structures (impulses):

1. Sinoatrial node (SA node, pacemaker) – right atrial wall, near superior vena cava

2. Atrioventricular node (AV node) – lower right atrium, along interatrial septum

3. Atrioventricular bundle (bundle of His) – 2 bundles of cardiac muscle fibers that extend from AV node down the sides of the interventricular septum

4. Purkinje fibers – small extensions from the AV bundle onto the ventricle walls

blood vessels
Blood Vessels
  • Artery – carries blood away from the heart

- all carry oxygenated blood, EXCEPT pulmonary artery

- color red

- small arteries = arterioles

2. Vein – carries blood to the heart

- all carry deoxygenated blood , EXCEPT pulmonary vein

- color blue

- small veins = venules

- sinuses – very large venous space

3. Capillaries – microscopic vessels, carry blood from arteries to veins

- sinusoids – take the place of capillaries in irregular, microscopic places

Circulation: heart  arteries  arterioles  capillaries  venules  veins  heart

structure of blood vessels 3 layers
Structure of blood vessels – 3 layers
  • Tunica adventitia – outermost layer – strong, flexible fibrous connective tissue

- holds vessels open, prevents tearing during movement

- thickest layer in veins

- 2nd thickest in arteries

2. Tunica media – middle layer – smooth muscle tissue sandwiched by an elastic connective tissue layer

- permits changes in diameter

- innervated by nerves and supplied with blood by vasa vasorum (tiny vessels)

3. Tunica intima – innermost layer – endothelial tissue, smooth lining, continuous with heart

*** only layer in capillaries

- thin, allows for efficient exchange of materials

- some capillary cells have fenestrations (numerous holes)

functions of capillaries
Functions of Capillaries
  • Most important because they deliver & collect essential materials
  • Very tiny, but very numerous – keep cells supplied with vital materials & rid injurious waste
  • “primary exchange vessels” of cardiovascular system
Efficient exchange because capillaries are so small that blood flows at its slowest rate (maximum contact time between blood & tissue) – this is called microcirculation

function of arteries
Function of Arteries
  • Arteries distribute blood to arterioles, arterioles distribute blood to capillaries
  • Also maintain normal blood pressure and circulation = “resistance vessels”
  • Smooth muscles in arteriole walls act as precapillary sphincters – reduce flow to capillaries when the muscles contract & constrict
  • Increase blood flow when they relax & dilate

functions of veins
Functions of Veins
  • Return blood to heart
  • Collectors and reservoir vessels
  • Can accommodate varying amount of blood without a change in blood pressure because of great ability to stretch capacitance = ease of stretch
  • Reservoir function is to maintain normal circulation
  • Heart is primary pump – keeps blood moving
circulatory routes
Circulatory Routes
  • Blood flow = from left ventricle through blood vessels of the entire body (except lungs) and back to the right atrium = systemic circulation
  • right ventricle to lungs to left atrium = pulmonary circulation
Systemic circulation:

left ventricle  ascending aorta  arteries  tissues, organs  arterioles  capillaries  venules  veins  vena cavas  right atrium

generals about arteries
Generals about arteries
  • Deliver blood from the heart to organs & tissues
  • Main artery can branch into arterioles, which branch into capillaries – these are called end-arteries – can cause serious damage if blocked
Some arteries branch into other branches of the same or other arteries = arterial anastomoses – these are more common further from the heart
  • Aorta = main artery that serves the trunk

- ascending aorta – first few cm, sends blood up out of left ventricle

- descending aorta – sends blood down thoracic cavity (thoracic aorta) to abdominal cavity (abdominal aorta)

generals about veins
Generals about veins
  • Return blood from body to heart to be oxygenated in the lungs
  • Superior vena cava – drains head, neck, thorax, upper extremity
  • Inferior vena cava – drains lower trunk & extremity
fetal circulation
Fetal Circulation
  • Differs before birth because fetal blood secures oxygen & nutrients from maternal blood instead of from fetal lungs and digestive organs
additional blood vessels structures in fetus
Additional blood vessels & structures in fetus
  • Umbilical arteries (2) – carry fetal blood to the placenta
  • Placenta – attached to uterine wall – exchange oxygen and other materials between maternal & fetal blood – NO MIXING of fetal & maternal blood (diffusion)
3. Umbilical vein – returns oxygenated blood from the placenta

* Umbilical cord = 2 umbilical arteries & umbilical vein

4. Ductus venosus – continuation of u. vein which drains into inferior vena cava

5. Foramen ovale – opening in the septum between the right & left atria so that the blood bypasses the fetal lungs because already oxygenated (and lungs not functioning yet)

6. Ductus arteriosus – connects the pulmonary artery with the descending thoracic aorta (another detour to avoid the lungs)

Almost all fetal blood is a mixture of oxygenated & deoxygenated
  • Special structures non longer needed shortly after birth – umbilical vessels, ductus venosus, and ductus arteriosus become fibrous ligaments over time
  • Foramen ovale becomes functionally closed when newborn takes first breath – complete closure takes about 9 mos.
  • Separation of oxygenated & deoxygenated blood occurs after birth