Download biology 206 chapter 19:heart

BIOLOGY 206
I.
II.
III.
CHAPTER 18:HEART: LAUREL SPRING 2007
Overview of Circulation
A. Blood exits the heart via arteries, which eventually become capillaries
where diffusion to and from the tissues takes place. Oxygen and
nutrients leave the blood and carbon dioxide and other wastes enter the
blood. Veins return blood to the heart where it is sent to the lungs to
remove the carbon dioxide and pick up fresh oxygen. Blood then returns
to the heart to be pumped throughout the body again.
Heart Anatomy
A. Size, location and orientation
1.
Heart is the pump that forces blood throughout the body
2.
Size = person's closed fist and generally weighs less than a pound
(250-350 g)
2.
Located within the pericardial cavity of the mediastinum (region
of thoracic cavity between the lungs).
3.
Apex = pointed inferior tip which points toward left hip
4.
Base = posterior, superior aspect of heart which points to right
shoulder
B. Coverings of the Heart
1.
Pericardium is the double-walled sac that encloses the heart and
origins of the great blood vessels
2.
Fibrous pericardium is the loose fitting superficial part that
protects and anchors the heart. It also prevents overfilling.
3.
The serous pericardium is deep to the fibrous pericardium.
4.
Recall serous membranes are membranes that enclose cavities that
do not exit to the outside.
5.
Parietal pericardium forms a strong protective sac for the heart
and serves to anchor it within the mediastinum (attaches to
diaphragm and great blood vessels).
6.
Visceral pericardium is deep to the parietal layer and constitutes
the outer layer of the heart wall or epicardium
6.
Pericardial cavity and its pericardial fluid lie between the parietal
and visceral layers.
C. 3 Layers of the heart
1.
Epicardium = Thin outer membrane (exterior of heart)
a.
Protection, anchorage
2.
Myocardium = actual cardiac muscle = thick middle layer
a.
Produces contractions to push blood
3.
Endocardium = inner layer of simple squamous epithelium
a.
Covers connective tissue skeleton of heart valves
Chambers and Great Vessels of the Heart
A. Overview
1.
2 upper = right and left atria
2.
2 lower = right and left ventricles
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B.
C.
D.
IV.
3.
4.
Atria
1.
2.
Interatrial septum = separates 2 atria
Interventricular septum = separates 2 ventricles
thin-walled receiving chambers
Auricles are small, wrinkled protruding appendages which slightly
increase atrial volume.
3.
Internally contain pectinate muscles .
4.
Also contain fossa ovalis which was the opening known as the
foramen ovale .
5.
Superior and inferior vena cava carry blood from tissue
capillaries to the right atrium from above and below the heart,
respectively.
6.
Cardiac veins collect blood from cardiac capillaries and dump into
the coronary sinus which carries blood to the right atrium..
a.
Note there are 3 openings into the right atrium.
7.
Pulmonary veins carry blood from lungs to left atrium..
Ventricles
1.
thick-walled discharging chambers.
2.
Internally contain trabeculae carneae.
3.
Pulmonary trunk and pulmonary arteries carry deoxygenated
blood from right ventricle to lungs.
4.
Aorta carries oxygenated blood from left ventricle to body tissues.
a.
Coronary arteries carry blood from aorta to myocardium.
One-way Valves
1.
Atrioventricular valves (AV) occur between each atrium and its
ventricle and prevents back flow into the atria when ventricles
.contract.
a.
Tricuspid = right AV valve
b.
Bicuspid /mitral = left AV valve
2.
Papillary muscles connect AV valves to heart muscle via
Chordae tendineae. When ventricles contract they prevent the
closed valves from inverting into the atria like an umbrella blown
inside out.
3.
Semilunar valves = found between ventricles and their blood
vessels to prevent back flow during ventricular diastole (when
ventricles relax).
a.
Pulmonary SL valve: between right ventricle and
pulmonary trunk.
b.
Aortic SL valve: between left ventricle and aorta.
Circulation
A. Simultaneous 2 pump system
1.
both atria and both ventricles pump at same time.
2.
right pump = pulmonary circulation which pumps deoxygenated
blood to the lungs back to the left side of the heart.
2
3.
B.
C.
left pump = systemic circulation which pumps oxygenated blood
all over the body.
4.
Recall function dictates structure, hence the left ventricle is much
larger than the right because although both chambers contain the
same volume of blood, the left ventricle must pump blood much
further than the right.
Pathway of blood through heart
superior/inferior vena cava-->right atrium-->tricuspid valve-->right
ventricle-->pulmonary semilunar valve-->pulmonary trunk-->pulmonary
arteries-->capillaries around alveoli of lungs for gas exchange-->right
and left pulmonary veins-->left atrium-->mitral valve-->left ventricle->aortic semilunar valve-->aorta-->systemic circulation through arteries->capillaries--> veins--> superior/ inferior vena cava.
Coronary circulation
1.
Heart chambers always have blood, but this blood does not nourish
the heart tissue because myocardium is too thick.
2.
Heart has its own set of arteries, capillaries, and veins that supply
myocardium with blood.
a.
This is the shortest circuit in the body.
3.
Right and left coronary arteries come directly off aorta and serve
respective sides of the heart.
a.
Run in Atrioventricular groove.
4.
Capillaries branch off arteries and gas/nutrient exchange occurs.
5.
Cardiac veins drain capillaries and empty into the coronary sinus
on posterior surface of heart which in turn dumps into the right
atrium.
6.
Vascular anastomoses = vascular channels that unite or
interconnect.
a.
Provide alternate channel for blood to flow if one is blocked.
7.
Arteries that lack anastomoses are called end-arteries.
a.
Tissue death can result if this type of artery is occluded.
b.
This situation frequently occurs in myocardium in a heart
attack.
8.
However, following a heart attack an entirely new capillary
network develops from a collateral channel = collateral
circulation.
9.
Angina is chest pain caused by fleeting deficiency of blood
delivery to heart. Usually from coronary artery spasm or increased
demand on heart.
a.
Cells do not die.
10. Myocardial Infarction (MI) is a heart attack and cardiac cells do
die from insufficient oxygen, or hypoxia.
a.
Caused by blood clot, atherosclerosis, etc.
b.
Because heart cells are non-mitotic, dead ones replaced by
scar tissue.
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V.
Conducting system of heart
A. Heart beat
1.
Influenced by extrinsic factors (hormones and nerves).
2.
Can be initiated solely by its own impulses = Intrinsic
mechanism.
3.
Components of intrinsic mechanism made up of cardiac cells but
they have nerve-like properties and are non-contractile.
B. Components of conduction system of the heart
1.
Sinoatrial node = (SA node)
a.
Pacemaker because its intrinsic pace is faster than other
cells.
b.
causes heart to beat on average of 75 beats/min, but without
external nervous or endocrine stimulation it would be 100
beats/min.
c.
Located near opening of Superior vena cava.
d.
Impulses which travel across and down both atria through
gap junctions and causes the atria to contract together from
top to bottom.
e.
Does not cause ventricles to contract because there is
electrically inert, non-contractile tissue between the atria and
ventricles.
2.
Impulses travel to Atrioventricular (AV) node just above the
tricuspid valve.
a.
delays impulse 0.1 sec for atria to empty.
3.
AV bundle (bundle of His) carries impulses out of AV node
4.
Branch into Right bundle branch and left bundle branch and go
through interventricular septum without causing contraction.
5.
Branches at bottom into left and right ventricles via in Purkinje
fibers which stimulate the ventricles to contract from bottom up
(fast conduction --> both ventricles contracting together).
D. Pathology of the Conduction System
1.
Arythmias are irregular heart rhythms.
2.
Fibrillation is a condition of rapid irregular or out-of phase
contractions resulting in writhing heart.
a.
Ventricles useless as a pump because there is no Cardiac
Output; death if not altered
VI.
Cardiac cycle
A. Overview
1.
Pumping of both atria and both ventricles = cardiac cycle
2.
Systole = contractile phase of a heart chamber.
a.
Atrial systole and ventricular systole.
3.
Diastole = relaxation phase of a heart chamber.
a.
Atrial diastole and ventricular diastole.
4.
When the atria are in systole the ventricles are in diastole.
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5.
VII.
****
When the ventricles are in systole the atria are in diastole and
remain there for a while when ventricles enter diastole.
*6.
Blood moves from an area of higher pressure to an area of lower
pressure.
a.
As a chamber fills with blood, pressure increases.
b.
When a chamber contracts, the internal size is smaller, so
pressure rises and flows to lesser pressure.
B. Heart sounds
1.
Heart sounds are sounds associated with closing of heart valves.
2.
First sound = Lubb which is a loud, low-pitched, relatively long
sound.
a.
Represents the closing of AV valves.
3.
The second sound is Dub/dup which is short, higher-pitched sound
with a sharp snap.
a.
This represent the closing of SL valves.
b.
Marks beginning of ventricular diastole.
4.
There is a pause after the dup which represents the quiescent
period of the cardiac cycle when the heart is totally relaxed.
5.
The total pattern = Lubb, dup, pause; lubb, dub, pause
C. Abnormal sound
1.
Murmur = any abnormal sound such as:
2.
Stenosis = thickening and narrowing of opening at valve.
Produces a high pitched sound.
a.
Forces heart to contract more forcibly than normal and may
ultimately weaken the heart, but there is some Cardiac
Output.
3.
Incompetent valve occurs when the valve leaks and blood flows
back into chamber it just left.
a.
Mitral Valve Prolapse is the most common valve disorder
where or more flaps of mitral valve weakens and bulges into
left atrium during ventricular systole.
Cardiac Output (CO)
A. Definitions
1.
Heart rate represents the number of times the heart beats in 1
minute.
a.
Measured as “beats/min”
**** 2.
Stroke volume = volume blood pumped from 1 ventricle in 1 beat
a.
Measured in “ml/beat”
b.
Same for each ventricle
3.
Cardiac ouput represents the amount of blood pumped out by
each ventricle in one minute (ml by 1 ventricle/min).
a.
Formula for cardiac output: CO= SV X heart rate
1000
b.
Example at rest: CO = 70 ml/beat X 72 beats/min = 5 L/min
5
c.
**
VII,
Example during exercise: CO = 200 ml/beat X 120 beats/min
= 24 L/min
B. Regulation of Stroke Volume
1.
End-diastolic volume = volume blood left in a ventricle at end of
diastole (120 ml).
2.
End-systolic volume = volume blood left in a ventricle at end of
systole (50 ml).
3.
Formula for Stroke volume: SV = end-diastolic volume minus
end-systolic volume.
a.
Example at rest: SV = 120 ml/beat - 50 ml/beat = 70 ml/beat
b.
During exercise: SV may increase to 200 ml/beat
4.
Frank-Starling Law of the heart states that increased venous
return (amount of blood going into right atrium) --> increased
Cardiac output:
a.
increase Venous return --> increased end-diastolic volume -> increased stretching of cardiac muscle fibers--> increased
strength of contraction --> increased stroke volume -->
increased CO
5.
Only works up to a point. If stretched too much fibers lose ability
to contract and get decreased CO as in congestive heart failure.
6.
We will discuss factors that influence venous return next chapter.
7.
Frank-Starling Law of the heart is an intrinsic control
mechanism.
8.
Extrinsic factors come from outside the heart and they too affect
contractility or the strength of the contraction of the heart.
3 Things that affect Stroke Volume
A. Preload
1.
This is the end-diastolic volume just discussed where we said as
venous return increases, EDV increases, and stroke volume
increases
B. Contractility
1.
this is the strength of the heart’s contraction independent of its
degree of stretch
2.
An increase in contractility will result in an increase in stroke
volume and a decrease in end systolic volume
3.
Factors that increase contractility include: increased
cardioacceleratory activity; hormones such as epinephrine and
thyroxine, drugs such as digitalis
4.
Drug types that decrease contractility include beta-blockers and
calcium channel blockers.
C. Afterload
1.
This is the pressure that must be overcome for the ventricles to
eject blood
2.
Recall that in order for ventricular ejections to occur, the semilunar
valve must be opened. In order for the SLV to open, ventricular
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IX.
pressure must exceed arterial pressure. The arterial pressure is
the equivalent to afterload.
3.
Anything that increases arterial blood pressure will increase
afterload. This makes the heart expend more energy on opening
the SLV and less on ejecting blood.
Extrinsic Regulation of Heart Rate
A. ANS (Autonomic Nervous system)
1.
Cardiac centers are located in medulla oblongata of brain.
2.
Cardioinhibitory center sends impulses to SA and AV node via
the vagus nerve of the parasympathetic NS to slow the heart.
a.
AcH = neurotransmitter.
3.
Cardioacceleratory center sends impulses to SA/AV nodes via
sympathetic NS fibers to:
a.
speed up the heart rate and
b.
increase stroke volume (by increasing strength of
contractions independently of end-diastolic volume).
c.
Norepinephrine = neurotransmitter.
4.
These 2 centers work antagonistically to control heart rate
5.
Cardiac center influenced by incoming signals from Baroreceptor/
pressoreceptors in aorta and carotid arteries which detect changes
in blood pressure.
a.
Increased pressure will cause a slowing of heart and
decreased pressure will cause increase in heart rate.
b.
Glossopharyngeal cranial nerve, # 9, carries impulses from
baroreceptor to cardiac centers.
c.
Impulses from higher brain centers work through the
hypothalamus to influence cardiac centers.
6.
Cardiac center also influenced by impulses from higher brain
centers working through the hypothalamus: fear, anger, pain, etc.
B. Chemical Regulation
1.
Hormones affect heart rate, especially epinephrine from adrenal
medulla.
a.
It increases heart rate and contractility.
a.
Mimics norepinephrine effects.
2.
Thyroxin is a hormone produced by the thyroid gland
a.
It increases metabolic rate and body heat
b.
In large quantities it causes slower bu more sustained
increases in heart rate when compared to epinephrine
3.
Intracellular and extracellular ions must be maintained for normal
heart function.
4.
Hypocalcemia (reduced Ca++) depress heart rate and
hypercalcemia may drastically increase heart rate and even lead to
prolonged contraction.
4.
Increased K+ --> decreased rate and cardiac arrest whereas
decreased K+ may lead to abnormal rhythms.
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C.
Other factors
1.
Increased temp --> increased rate and vice versa.
2.
Age: fastest in fetus and declines with age.
3.
Gender: females have generally higher rates than males.
4.
Exercise raises HR, but in the phyically fit HR is lower because of
increased SV.
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