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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 l.jpg

Chapter 18

Cardiovascular System

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Cardiovascular = circulatory

  • Heart & closed system (arteries, veins, capillaries)

  • Appears early in development – heartbeat at 4 wks.

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  • 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

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  • 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

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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

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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

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3. Endocardium = delicate layer lining interior of myocardial wall

- endothelial tissue

- covers trabeculae – muscular beam-like projections

- forms valves

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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

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2. Ventricles – lower chambers

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

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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

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  • 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


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Skeleton of Heart

  • Fibrous structure of connected rings – support for heart valves and attachment of myocardium – also electrical barrier between atria & ventricles

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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)

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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

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  • 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

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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

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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

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Blood Vessels

  • Artery – carries blood away from the heart

    - all carry oxygenated blood, EXCEPT pulmonary artery

    - color red

    - small arteries = arterioles

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2. Vein – carries blood to the heart

- all carry deoxygenated blood , EXCEPT pulmonary vein

- color blue

- small veins = venules

- sinuses – very large venous space

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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

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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

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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)

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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)

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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

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Function of Arteries blood flows at its slowest rate (

  • 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

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Functions of Veins blood flows at its slowest rate (

  • 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

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Circulatory Routes blood flows at its slowest rate (

  • 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

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  • Systemic circulation: blood flows at its slowest rate (

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

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Generals about arteries blood flows at its slowest rate (

  • 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

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  • 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)

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Generals about veins other arteries =

  • 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

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Fetal Circulation other arteries =

  • Differs before birth because fetal blood secures oxygen & nutrients from maternal blood instead of from fetal lungs and digestive organs

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Additional blood vessels & structures in fetus other arteries =

  • 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)

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3. other arteries = 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

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5. other arteries = 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)

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  • Almost all fetal blood is a mixture of other arteries = 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