The anatomy and physiology of the circulatory system

Question 1

Heart location

Answer 1

-mediastinum- extends from sternum anteriorly to the vertebral column
-lies medially between lungs
-2/3 mass is to the left of midline
-base (top) of heart tipped up medially and posteriorly
-apex projects inferiorly and laterally

Question 2

The pericardium
what is it, what it does, what its composed of

Answer 2

-membrane surrounds the heart
-helps retain hearts position within mediastinum
-composed tough outer fibrous layer and lined by delicate serous membrane
-serous membrane divided into parietal layer (outer) and visceral layer (inner)
-between these layers there’s serous fluid

Question 3

Layers of heart wall

Answer 3

-epicardium- thin, transparent outer layer, also called visceral layer of pericardium
-myocardium- thick middle layer, composed of cardiac muscle
-endocardium- squamous epithelium, known throughout circulatory system as endothelium

Question 4

Atrial kick

Answer 4

-when atria contract
-responsible for only a 20% increase in amount of blood ejected by the ventricles

Question 5

Heart valves

Answer 5

-atrioventricular valves- between atria and ventricles
-outflow/ semi lunar valves- from ventricles to outflow vessels

Question 6

Atrioventricular valves

Answer 6

Right AV valve= tricuspid valve as has 3 leaflets/ cusps
Left AV valve= bicuspid/ mitral valve

Question 7

Outflow valves
names

Answer 7

-right= pulmonary valve
-left= aortic valve

Question 8

How heart valves (av) work by preventing backflow

Answer 8

-AV valves tethered to walls of ventricles by heart strings/ chordae tendinae attached to papillary muscles
-papillary muscles pull on AV valves via chordae tendinae, slowing their closure and preventing damage to valve

Question 9

Outflow valves

Answer 9

-firm cusps that each look like a semi full moon
-each cusp makes up a third of the valve

Question 10

Why there are no valves between vena cava and right atria and pulmonary vein and left atria

Answer 10

-small amount of blood does flow backwards
-but minimised by the way the atria contracts
-this compresses and nearly collapses the vessels

Question 11

Arteries

Answer 11

-blood away form heart
-contain oxygenated blood
-thick walls, exposed to high pressures and friction forces
-outer layer= tunica externa
-middle layer= tunica media
-inner layer= tunica interna/ endothelium

Question 12

Veins

Answer 12

-blood back to heart
-contain deoxygenated blood
-thin walls as exposed to low pressures and minimal friction forces
-same 3 layers as artery- tunica externa, media, interna
-layers just not as thick as an artery
-valves

Question 13

Arteries and vein that attach to heart

Answer 13

-arch of the aorta
-pulmonary trunk
-coronary arteries
-superior and inferior vena cava
-4 pulmonary veins
-coronary sinus

Question 14

Arterioles- 3 layers and structures

Answer 14

-thin tunica interna with thin fenestrated elastic lamina
-tunica media consists of one or two layers of smooth muscle cells
-tunica externa consists of connective tissue and sympathetic nerve supply that can vary the rate of flow

Question 15

Capillaries

Answer 15

-smallest vessels
-one RBC through at a time
-allow exchange of substances between blood and interstitial fluid
-lack tunica media and externa
-single layer endothelial cells

Question 16

Systemic circuit

Answer 16

-ejects blood into aorta, systemic arteries, and arterioles, powered by left side of heart

Question 17

Pulmonary circuit

Answer 17

-ejects blood into pulmonary trunk, powered by right side of heart

Question 18

Coronary circulation

Answer 18

-passive process
-blood flows through coronary arteries only during relaxation phase of ventricular diastole
-LCA- goes to anterior interventricular and circumflex branches
-RCA- to marginal and posterior atrioventricular branches
-coronary veins collect in coronary sinus at the back of heart
-coronary sinus empties into right atrium to be oxygenated by lungs

Question 19

Cardiac muscle tissue

Answer 19

-shorter fibres than skeletal muscle
-branch
-only have on centrally located nucleus
-communicate with neighbouring cells through gap junctions in intercalated discs

Question 20

Autorhythmicity

Answer 20

-doesn’t rely on CNS
-just happens automatically
-autorhythmic cells spontaneously depolarise
-when they reach the threshold, an AP is reached causing all cells in that area to depolarise

Question 21

Myocytes- 2 roles

Answer 21

-form the conduction system
-act as pacemakers

Question 22

Normal pacemaker of the heart
name, why, location

Answer 22

-sino atrial node (SAN)
-due to fastest rate of depolarisation
-located right atrial wall

Question 23

How often the SA node fires

Answer 23

-once every 0.8 seconds or 75 AP per min

Question 24

Cardiac conduction

Answer 24

-AP generated at SAN
-then propagates throughout wall of atria via the bachmann’s bundle to the AVN in the interatrial septum
-at AVN, signal is slowed allow atria chance to mechanically move blood into ventricles
-spreads down bundle of his which separates to the right and left bundle branches to the purkinje fibres

Question 25

How contractions are coordinated

Answer 25

-band of muscle wind around the heart, working as a unit
-this forms a functional syncytium
-this allows the top and bottom parts to contract in their own way

Question 26

Role ANS

Answer 26

-regulate changes in BP, blood flow and blood volume
-maintain enough cardiac output to provide for all organs

Question 27

Refractory period

Answer 27

-longer than the contraction itself, unlike skeletal muscle
-therefore tetanus (maintained contraction) cannot occur in cardiac muscle

Question 28

ECG

Answer 28

Electrocardiogram
-records electrical changes on surface of the body caused by depolarisation and repolarisation of myocardium
-measures presence or absence of certain waveforms

Question 29

PQRST waves

Answer 29

P= atrial systole
QRS= ventricular systole
T= diastole/ repolarisation of ventricle
PQ interval- excitation goes from SAN to AVN for the pause to occur

Question 30

Cardiac cycle

Answer 30

-includes all events associated with one heartbeat
-systole and diastole
-during atrial systole, ventricles are relaxed and vice versa
-lub (S1)= closure of mitral and tricuspid valves
-dub (S2)= closure of aortic and pulmonary valves

Question 31

Average stroke vol

Answer 31

70 ml

Question 32

Cardiac output calculation

Answer 32

stroke volume x heart rate
resting adult= 70ml x 75bpm= 5.25 l/min
-on average whole blood volume flows through pulmonary and systemic circuits every minute

Question 33

3 factors affect stroke volume

Answer 33

-amount of ventricular filling before contraction (preload)
-contractility of ventricle
-resistance in blood vessels the heart is pumping into (afterload)

Question 34

Cardiac reserve

Answer 34

-difference between cardiac output at rest and the maximum cardiac output the heart can generate

Question 35

Starlings law of the heart

Answer 35

-the more the heart muscle is preloaded/ stretched, the more forcefully the heart will contract

Question 36

Functions of blood

Answer 36

-transportation- O2, CO2
-regulation- pH, temp
-protection- clotting, immune system