Wall of the heart
3 parts-- from external to internal
1. visceral layer of serous pericardium
2. myocardium
3. endocardium--thin layer of endothelial tissue that is continuous
with the remainder of the cardiovascular system
Chambers of the heart
Atria--
-each atria has an auricle
(looks like a dogs ear)
-seperated by Interatrial
septum
Ventricles--
Interventriculer septum
Externally sulcus (sulci) separate the chambers of the heart
coronary sulcus--separates the
atria from the ventricles
**sulci contain coronary blood vessels and store fat
Blood flow through the heart
Superior Vena Cava (SVC), Inferior Vena Cava (IVC) and the coronary
sinus bring blood to the right atrium
Coronary sinus drains blood
from the heart wall (myocardium)
right atrium allows blood to flow to the right ventricle which pumps
blood to the lungs via the pulmonary
trunk that divides into the right and left
pulmonary arteries
pulmonary veins bring blood
from the lungs to the left atrium
left atrium allows blood to flow to the left ventricle
ascending aorta takes blood
from the left ventricle to the rest of the body
-control blood flow thought the chambers of the heart
Atrioventricular valves (AV valves)
tricuspid valve
-on the right
-three flaps (cusps)
bicuspid (mitral) valve
-found on the left
-2 cusps
chordae tendineae--fibrous
cord that connects the cusps to the papillary muscles
papillary muscles--anchor the
chordae tendineae to the ventricle walls
**these 2 structures function to keep the AV valves from being pushed
into the atria during ventricular contraction
Semilunar valves of the heart
pulmonary semilunar and
aortic semilunar
-both of these arteries that leave the heart have these valves
-prevent back flow of blood by permitting blood flow in one direction
only
Blood supply of the myocardium
left and right coronary
arteries originate from the ascending aorta (1st
branches) to carry oxygenated blood
coronary sinus returns deoxygenated blood
Anastomosis--
-2 different arteries connecting and supplying an area with blood
flow
-found throughout the body (numerous in the heart)
-provides collateral circulation for blood to reach an organ
Angina pectoris
-chest pain
-reduced oxygen supply weakens cardiac cells but doesn’t kill
them
symptoms:
-tightness or choking sensation
-squeezing pressure type of sensation for short durations
causes:
-stress, exertion, hypertension
Myocardial Infarction
(MI)
-heart attack
-infarction means death of tissue due to lack of blood supply
-myocardial tissue behind blocked artery dies
-dead tissue may disturb conducting system of the heart which could
lead to sudden death (ventricular fibrillation)
1. Sinoatrial node (SA node)
“pacemaker”
-found in right atrial wall inferior to the opening of the vena cava
opening
2. Atrioventricular node (AV node)- -found
near inferior portion of the interatrial septum
**impulse from the SA node travel across atria (which stimulates the
contraction
of the atria) then stimulates the AV node
3. AV bundle (bundle of his)
-conducting fibers that run from the AV node to top of
interventricular septum and branches into 2
-distributes potential over medial surface of the ventricles
4. Purkinje fibers (conduction myofibers)
-pass from bundle branches into the myocardium
-stimulates the contraction of the ventricles
P WAVE
-atrial depolarization
-fraction of a second after atria contraction
QRS WAVE
-downward deflection (Q)
-large upward peak (R)
-large downward deflection (S)
-ventricle depolarization
-fraction of a second after the completion of this wave the
ventricles may contract again
T WAVE
-ventricular repolarization
**atrial repolarization is hidden by the QRS wave
-2 things control the flow of blood through the heart
1. values opening and closing
2. myocardial contractions
PHYSIOLOGY OF CARDIAC CYCLE
2 atria contract while ventricles relax
2 ventricles contract while atria relax
Systole
-refers to the phase of contraction
Diastole
-refers to the phase of relaxation
Cardiac Cycle
-completer heart beat
-consist of systole and diastole of both atria and the systole and
diastole of both ventricles
4 steps in the cardiac cycle
1.
Atrial
systole
-continuous blood flow into the right atrium
-pulmonary veins bring blood into the left atrium
-Sinoatrial node “fires” and triggers the contraction of
the atria
-increase pressure forces the atrioventricular valves to open
2. Ventricular filling
3. Ventricular systole
-coincides with the 1st heart sound (lubb---louder and longer of the
two sounds)
-increase pressure slams the atrioventricular valves shut
-after the atrioventricular valves shut, pressure continues to build
until ventricular pressure exceeds arterial pressure-semilunar valves
open and blood leaves via arteries
4. Ventricular diastole
-arterial pressure remains relatively high and forces blood back
toward the heart
-semilunar valves close which causes the second heart
sound----dupp
-any condition that causes unusual sounds to be heard before or
after the lubb-dupp
-noises is causes by turbulent blood flow
Mitral and aortic stenosis
-narrowing of either valve by scar formation or congenital defect
Mitral and oartic
insufficiences
-backflow of blood because the cusp doesn’t close properly
-caused by a damaged cusp of chordae tendinae
Mitral
valve prolapse (MVP)
-inherited disorder in ehich the mitral valve is pushed back too far
during contraction
-condition usually asymptomatic
-about 10% of population has this disorder
Arteries--carry
blood away from the heart to tissues
Arterioles--enter the
tissues where they branch into microscopic capillaries
Capillaries-
-allow gasses to be exchanged
Venules--form after
capillaries and leave the tissue
Veins--carry blood back
to the heart
Vasa Vasorum
-blood vessels in the walls of vascular tissue
-nourish the vascular tissue
3 layers (tunics)
1. Tunica
Interna --Inner wall
(tunic)
-simple squamous epithelium
-basements membrane
-layer of elastic tissue (internal elastic lamina)
2. Tunica Media--Middle
tunic
-thickest
-smooth muscle
-elastic fibers
3. Tunica
Externa--Outer tunic
-composed of elastic and collagenous fibers
2 important properties
1.
elasticity--arteries
can expand and return to original shape
2.
contractility--smooth
muscle in the tunica media are arranged longitudinally and in rings
around the lumen
Types of arteries
1. Elastic conducting
arteries
-conduct blood from the heart to the medium sized arteries
-large diameter with relatively thin walls tunica media has more
elastic fibers and less smooth muscle
- must be able to withstand high blood pressures
examples: aorta, brachiocephalic,
common carotid, subclavian, vertebral and common iliac
2. Muscular distributing
arteries
-distribute blood to the rest of the body
-more smooth muscle in tunica media
-regulate blood needs of the structures they serve
-anastomoses likely to occur in this type of artery
examples: axillary, brachial, radial,
intercostal, splenic, mesenteric, femoral, popliteal (behind the
knee), and tibial arteries
Arterioles
-almost microscopic arteries that deliver blood to capillaries
-regulate amount of blood that goes into the capillaries
Capillaries
-primary function is to permit the exchange of nutrients and waste
between cells and blood
-capillary walls are only one epithelial cell layer thick
-diameter is one Red Blood Cell
-microscopic vessels that connect arterioles to venules
-found near almost every cell in the body
-the higher the tissues activity the more capillaries are present
examples:
liver, lungs and kidneys --- very numerous
cartilage and sclara of the eye --- very few
Metarterioles
-vessel that emerges from an arteriole and passes through the
capillary network and empties into the venule
“true”
capillaries--branch off of the metarteriole
precapillary
sphincter--regulates blood flow into the capillary
Venules
-collect blood from capillaries and drain into the veins
-leave the tissue
Veins
same 3 tunics as arteries
differences due to the pressure differences between arteries and
veins:
-named correspondingly to arteries
examples: subclavian, popliteal, etc.
Varicose Veins
-venous valves are weak which allow gravity to force large quantities
of blood into distal parts of the vein
-pressure stretches the vein and causes it to lose elasticity
-vein becomes stretched and flabby
-deep veins are not as susceptible
Treatments: rest and elevation with external pressure
sclerotherapy--injection
of chemical that causes vein to collapse
surgery
Blood flow
-amount of blood through a vessel in a given time
-determined by 2 things
1. Blood Pressure (BP)
-pressure on an artery wall due to the left ventricle contraction
-average aorta pressure is 100 mmHg
-average right atrium pressure is nearly 0 mmHg
-normal resting BP is 120 mmHg
(systolic)/ 80 mmHg (diastolic)
-measured with a
sphygomanometer
2. Resistance
-friction as blood travels
-related to:
Factors That Influence Arterial
Blood Pressure
1. Cardiac
output
-amount of blood ejected by the left ventricle into the aorta each
minute
-main factor in BP
2. Blood
volume
-average is about 5 liters
-decreased blood volume = decreased blood pressure
-increased blood volume = increased blood pressure
-high salt intake = retain water = increased blood volume
3. Peripheral
resistance
-all of vascular resistance offered by the cardiovascular system
-major function of arterioles is to control this resistance
4. Capillary
exchange
-blood flow is at its slowest to aid in exchange of gases and
nutrients
-depends on concentration differences
Factors that aid in Venous
Return
1. Velocity of blood flow
2. Skeletal muscles and valves in veins
3. Breathing--decreases
pressure in the thoracic cavity and increases pressure in the
abdominal cavity
Shock
-failure of the cardiovascular system to deliver adequate amounts
of
oxygen and nutrients to meet the metabolic need of body cells
because of an inadequate cardiac output
signs and symptoms:
1. systolic BP lower that 90 mmHg as a result of vasodilation and
decrease cardiac output
2. clammy, cool, pale skin due to vasoconstriction of blood vessels
in the skin
3. sweating due to increase levels of epinephrine
4. reduced urine formation
5. rapid heart rate
6. lactic acid build up
7. weak pulse
8. altered mental state
9. thirst due to extra cellular fluid loss
Checking circulation
Circulation routes
1. systemic--throughout the body
2. coronary
3. hepatic portal--runs from the GI tract to
the liver
4. pulmonary--right ventricle to lungs to the
left ventricle
Circulation time
-time required for blood to travel from the right atrium through
pulmonary circulation and systemic circulation and back to the right
atrium
-about one minute
Pulse
-alternating expansion and recoil of an artery wall
-stronger the close to the heart
-measured by counting for 15 seconds and multiplying by 4
-most commonly use artery is the radial artery
other arteries commonly used:
-temporal
-facial
-common carotid = lateral to the voice
box
-brachial artery = medial side of biceps
brachii
-femoral
-popliteal = behind the knee
-posterial tibial = posterior to the
medial malleolus
-dorsalis pedis = superior to the
longitudinal arch of the foot
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