Chapter 18 - Cardiovascular System: The Heart



Chapter 18 - Cardiovascular System: The Heart

I. Heart Anatomy

A. Interesting information

1. entire blood supply – 5 quarts (4.7L) pumped through body every minute

2. every 24 hours

a. 2,000 gallons pumped

b. 80,000-100,000 beats

3. 70 year lifetime

a. 51 million gallons of blood pumped

b. heart beats 2 ½ billion times

4. Red Blood Cells

a. 1 RBC has 250 million hemoglobin molecules

b. 1 hemoglobin molecule can carry 4 oxygen molecules

c. 1 hemoglobin molecule has 4 heme molecules

d. 1 heme group has 1 molecule of iron

e. oxygen binds to iron

f. 1 RBC has 1 billion iron molecules

g. 1 RBC has 1 billion oxygen molecules

B. General

1. size - about size of your fist; weighs less than 1 lb.

2. location

a. anterior to vertebral column

b. posterior to sternum

c. lungs lateral

d. tips slightly to left - oblique position

C. coverings

1. enclosed by double walled sac of membrane - pericardium

a. pericardium - 2 layers:

-fibrous: superficial; tough with fibrous ct; protects/anchors heart

-serous: deep; 2 layers

-parietal: lines internal surface of fibrous pericardium

-visceral: next to and part of heart wall; called epicardium

2. pericardial cavity

a. space between parietal and visceral membranes

b. serous fluid

D. heart wall - 3 layers

1. epicardium – see above

2. myocardium - bulk of heart - layer that actually contracts

3. endocardium - endothelial membrane (squamous epithelium) lines interior of heart and covers fibrous skeleton of valves

E. Chambers

1. components

a. 2 atria - right and left

-superior

-receive blood

-small; thin walled

-posterior inner wall smooth

-anterior inner wall – ridged – called pectinate muscles

b. 2 ventricles - right and left

-inferior

-pump blood

-on inner walls: trabeculae carneae - irregular muscle folds

- some form papillary muscles

papillary muscles - role in valve function

-right ventricle

-forms most of anterior surface of heart

-pumps blood into pulmonary trunk and into lungs

-left ventricle

-forms heart apex

-dominates posteroinferior surface

-pumps blood into aorta

-walls 3 times as thick as right one

c. associated structures

-interatrial/interventricular septum - divides heart longitudinally

-name depends on which chamber it separates

F. Great vessels associated with chambers

1. blood enters right atrium through 3 veins

a. superior vena cava

-returns blood from body areas superior to heart

b. inferior vena cava

-returns blood from body areas below heart

c. coronary sinus – collects blood draining from myocardium itself

2. blood enters left atrium by:

-4 pulmonary veins (2 right and 2 left) – carries blood from lungs to heart

3. pulmonary trunk

a. blood pumped from right ventricle

b. blood goes to lungs

4. aorta

a. blood pumped left ventricle

b. largest artery in body

c. blood goes to all parts of body

G. Pathway of blood through heart

1. pulmonary circuit

a. collects blood returning to heart from body – sends blood to lungs for oxygenation

b. right side of heart

c. short route/low pressure

d. strictly serves gas function

e. blood O2 poor/CO2 rich

f. blood enters right atrium - tricuspid valve - right ventricle -

pulmonary semilunar valve - pulmonary trunk -pulmonary arteries -

lungs - pulmonary veins - left atrium

2. systemic circuit

a. left side of heart

b. blood O2 rich/CO2 poor

c. long route

d. supplies entire body with oxygenated blood

e. lots of pressure

f. blood leaves lungs - pulmonary veins - left atrium - bicuspid valve (mitral) -

left ventricle - aortic semilunar valve - aorta - all parts of body – veins -

superior/inferior vena cava - right atrium

H. Coronary circulation

1. right and left coronary arteries

a. provide functional blood supply of heart

b. branch from root of aorta

c. left coronary artery divides into anterior interventricular artery and circumflex artery

d. right coronary artery divides into marginal artery and posterior

interventricular artery

2. cardiac veins and coronary sinus

a. cardiac veins collect venous blood

b. cardiac veins join to form coronary sinus - empties into right atrium

3. disorders

a. angina pectoris

-temporary

-deficient blood flow to heart

-weakens cells but don’t die

b. myocardial infarction

-prolonged coronary blockage

-cells die – infarct

-heart attack – coronary

-adult cardiac muscle amitotic

-areas of cell death repaired with scar tissue - noncontractile

-affects efficiency of heart

-survival depends on amt. of damage/location of damage

-left ventricle more serious

I. Heart valves

-blood flows in one direction: atria - ventricles - arteries

-enforced by presence of 4 valves: paired atrioventricular and semilunar valves

1. atrioventricular (av) valves

a. between atria and ventricles

b. prevents backflow of blood into aria when ventricles contract

c. right av valve – tricuspid valve – 3 flaps

d. left av valve – bicuspid valve (mitral valve) - 2 flaps

e. chordae tendineae

-collagen cords

-anchor cusps to papillary muscles

-also helps hold cusps closed

f. heart relaxed – av valves hang down into ventricular chamber

-ventricles contract

-blood forced up against valve flaps closing them

2. two semilunar valves

a. between ventricles and arteries

b. prevent backflow of blood into ventricles when ventricles relax

c. aortic semilunar valve – between left ventricle and aorta

d. pulmonary semilunar valve – between right ventricle and pulmonary trunk

e. ventricles contract forcing open semilunar valves, close when ventricles relax

II. Heart Physiology

A. Properties of cardiac muscle

1. microscopic anatomy

a. striated

b. short/fat

c. branched

d. interconnected by intercalated discs

-contain desmosomes and gap junctions

-desmosomes prevent separation of adjacent cells during contraction

-gap junctions allow ions to pass from cell to cell transmitting the electrical impulses

-heart works as 1 unit due to gap junctions

e. 1-2 large nuclei

f. lct matrix – endomysium with lots of capillaries

g. matrix connected to dense fct skeleton

-collagen and elastin fibers – link cardiac cells together

h. lots of mitochondria

2. energy requirements

a. continual supply of O2 for energy metabolism

b. relies mostly on aerobic respiration

-decrease in O2 not well tolerated

3. mechanism and events of muscle contraction

a. mostly same as skeletal muscle contraction (sliding filament mechanism)

b. differences

-all or none response at organ level – not cellular

-can be self-excited with rhythm

-refractory period (inexcitable pd.) longer – prevents tetanic contraction

(heart would stop)

B. conduction system of heart – intrinsic

1. components

-nodes

-specialized nervelike, noncontractile cardiac cells

-initiate and distribute impulses throughout heart

-therefore heart depolarizes and contracts in orderly/sequential manner

from atria to ventricles

-how heart beats as one cell

-characteristic rhythm called sinus rhythm

a. sinoatrial (sa) node

–pacemaker

-small mass located in upper right atrial wall

-causes atrial contraction

-depolarizes 70-80 times/minute

-initiates each depolarization wave – moves across heart – sets pace –

called sinus rhythm

-depolarization travels to av node – to bundle of His - to all branches/fibers

b. atrioventricular (av) node

-located in lower interatrial septum

-causes ventricular contraction

c. av bundle (bundle of His)

–located in interventricular septum

d. right/left bundle branches

-located in interventricular septum

e. Purkinje fibers

-penetrate into ventricular septum, apex, and turn superiorly into

ventricular walls

2. autonomic nervous system (extrinsic)

a. ans has 2 parts: sympathetic and parasympathetic nervous systems

b. sympathetic increases heart rate

c. parasympathetic decreases heart rate

d. hormones used

e. tachycardia

-heart beat to fast (100 beats or more/minute)

-if persistent, considered pathological – can cause fibrillation

f. bradycardia

-heart beat to slow (below 60 beats/minute)

-good for athletes

-in poor physical condition – not good

-may result in inadequate blood circulation

-often a warning of brain edema after head trauma

3. defects

a. arrhythmias – irregular heart beat

b. fibrillation

-out of phase contractions

-heart muscles appears as mass of writhing worms

-makes ventricles worthless as pumps

-circulation stops/brain dies

c. heart block

-impaired transmission of impulses from atrium to ventricles

-problem with av node

-need pacemaker

C. electrocardiography

1. ECG – electrocardiogram

– graphic recording of electrical changes during heart activity

2. 3 distinct waves – deflection waves:

a. P wave

-impulse sent from sa node to atria

-atrial depolarization

-atrial systole (contraction)

b. QRS complex

-ventricular depolarization /atrial repolarization

-ventricular systole (contraction)

-atrial diastole (relaxation)

c. T wave

-ventricular repolarization

-ventricular diastole (relaxation

3. P to R

-from atrial excitation to ventricular excitation

-also called P-Q interval

4. Q to T

-from ventricular depolarization to repolarization

-ventricular systole

5. S-T segment

-total myocardial ventricular contraction

-“plateau phase”

6. size, duration, timing of waves

a. consistent – good

b. change in waves – problems

D. Heart Sounds – closing of valves

1. normal

a. lub-dub

b. 1st sound – av valves close (lub)

c. 2nd sound – sl valves close (dub)

d. BTAP or MTAP

bicuspid (mitral), tricuspid, aortic semilunar, pulmonary semilunar

e. both atria contract at same time then both ventricles contract at same time

2. abnormal

a. murmurs

b. most often indicates valve problem (hear swishing noise)

E. Cardiac Cycle

1. terms

a. systole – contraction period (atria and ventricles)

b. diastole – relaxation period (atria and ventricles)

c. cardiac cycle – events occurring during 1 heartbeat

-marked by succession of pressure and blood volume changes within heart

-each ventricle pumps same volume of blood per heartbeat

2. route of blood

a. period of ventricular filling: mid to late diastole - begins with heart totally relaxed - quiescent period

-blood flows into atria and ventricles

-av valves open

-sl valves shut

-atria contract – atrial pressure increases

-residual blood in atria propelled into ventricles

-atria relax – diastole

b. ventricular systole

-atria in diastole

-ventricles begin contracting

-pressure rises sharply

-av valves close

-for split second ventricles completely closed – blood volume constant

-sl valves open due to more pressure in ventricles than in arteries

-blood forced into aorta and pulmonary trunk

-ventricular ejection phase

c. isovolumetric relaxation: early diastole

-ventricles begin to relax

-ventricular pressure decreases

-sl valves close due to blood pressure decreasing in ventricles causing

backflow of blood (in arteries) towards heart

-ventricles once again closed chambers for split second

-miscellaneous

-atria still in diastole

-atria filling with blood – so pressure on rise in atria

-av valves forced open

-ventricles begin filling

-atrial pressure drops/ventricular pressure rises – completing cycle

-flow of blood controlled by pressure changes

-blood flows along pressure gradient – higher to lower

3. blood pressure influenced by:

a. cardiac output

b. peripheral resistance

c. blood volume

F. Cardiac output (mL/min)

1. CO is amount of blood pumped by each ventricle in 1 minute

2. CO is determined by heart rate (hr) X stroke volume (sv)

- heart rate is beats per minute

- stroke volume is mL per beat

-or volume of blood pumped out by a ventricle with each contraction

-CO (mL/min) = HR X SV

-CO = 75 beats/minute X 70 mL/beat

-CO = 5250 mL/minute = 5.25L/minute

3. entire blood supply passes through each side of heart once each minute

4. normal blood volume = 4.7L (approximately 1 gallon)

5. hemorrhage with large loss of blood

-causes drop in blood pressure due to change in cardiac output

6. regulation of heart rate

a. autonomic nervous system regulation by cardiac centers in medulla oblongata

-sympathetic (increases heart rate) vs parasympathetic (decreases heart rate)

-predominant influence over heart rate is inhibitory

b. chemical regulation

-hormones

-norepinephrine, epinephrine, thyroxine – increases heart rate

-acetylcholine – decreases heart rate

-ions – Ca+, Na+, K+

-electrolyte balance important – if off, can be fatal – heart stops

c. physical factors

-age

-gender

-exercise

-body temperature

7. homeostatic imbalance of CO

a. CHF –congestive heart failure

-pumping ability of heart cant’ provide adequate circulation to meet body needs

-right side heart failure

-peripheral congestion

-blood stagnates in body organs, pools in tissue spaces

-tissues/organs deprived of oxygen/nutrients

-tissues can’t get rid of wastes

-systemic edema occurs (swelling in hands, feet, ankles, etc)

-left side heart failure

-right ventricle continues to propel blood to lungs

-left ventricle can’t adequately eject blood to body

-blood vessels in lungs become engorged

-fluid leaks into tissue

–pulmonary congestion/edema results

-untreated, person suffocates

G. Blood pressure

1. pressure/force of blood exerted against walls of arteries

2. systole – heart muscle contracting

diastole – heart muscle relaxing

3. normal BP: 120

80

-range of normal: 110-140

75-80

4. hypertension – high blood pressure – chronic: 140 and up

90 and up

5. hypotension - low blood pressure: below 100

below 60

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