Chapter 18 - Cardiovascular System: The Heart



Chapter 18 - Cardiovascular System: The Heart

I. Heart Anatomy

A. 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

B. coverings

1. enclosed by double walled sac of membrane - pericardium

a. pericardium - 2 layers:

-fibrous: superficial; tough white 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

C. 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

D. 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

E. 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 (called main pulmonary artery)

a. blood pumped from right ventricle

b. blood goes to lungs

4. aorta

a. blood pumped from left ventricle

b. largest artery in body

c. blood goes to all parts of body

F. 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

G. Coronary circulation

-right and left coronary arteries

a. provide functional blood supply of heart

b. branch from root of aorta

H. 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 atria 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. 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 His bundle - to all branches/fibers

b. atrioventricular (av) node

-located in lower interatrial septum

-causes ventricular contraction

c. av bundle (His bundle)

–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

B. 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)

C. 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 – amount of blood pumped by each ventricle in 1 minute

b. peripheral resistance

c. blood volume

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