3: The CV System

Question 1

functions of the CV system

Answer 1

transport - nutrients, oxygen, hormones, waste
maintenance - heat, pH, hydration
protection - WBCs

Question 2

components

Answer 2

fluid - blood
system of channels - blood vessels
pump - heart

Question 3

2 circuits

Answer 3

pulmonary circuit - blood to and from lungs
systemic circuit - blood to and from rest of body

Question 4

location of heart

Answer 4

located in thoracic cavity - near anterior chest wall directly posterior to sternum
between two lungs
top part of the head lies at third costal cartilage
apex of the heart lies between 5th intercostal space
heart sized influenced by: exercising, height, body mass, age

Question 5

the heart

Answer 5

4 chambers functioning as a double pump
system circuit > vena cava > right atrium > right ventricle > pulmonary artery > pulmonary circuit
pulmonary circuit > pulmonary vein > left atrium > left ventricle > aorta > systemic circuit
left ventricle and muscle mass surrounding it is bigger
contracts more than 100,000 times per day - 70 times a min
pumps about 5L/min at rest, 15-20 L/min during exercise = 8000 L/day at rest
systole = period of time when cardiac tissue is contracting
cardiac output = stroke volume x bpm

Question 6

pericardium

Answer 6

outer layer of the heart
fibrous tissue - collagen
stabilises heart position
lubrication from pericardial fluid in pericardial space
outer fibrous layer
pericardial space between the outer serous (parietal layer) and inner serous (visceral layer called epicardium)

Question 7

myocardium

Answer 7

the muscle tissue of the heart
thick muscular layer between epicardium and endocardium
thickness varies according to function of chamber
short wide Y shaped muscle cells
large central nucleus and large number of mitochondria
interconnections with other cardiac cells via intercalated discs
involuntary due to auto-rhythmicity because cardiac muscle is myogenic and controlled by ANS and endocrine system

Question 8

intercalated discs

Answer 8

they are the junction between cardiac cells
2 components
- gap junctions = allow for depolarisation to pass between cells, synchronising contraction
- desmosomes = bind adjacent myocytes together

Question 9

endocardium

Answer 9

covers all inner surfaces of the heart - the internal chambers and heart valves
consists of epithelial tissue and is continuous with epithelium of the great vessels

Question 10

ventricular differences

Answer 10

wall of left ventricle thicker - cylindrical shape whereas right ventricle is pouch shaped
LV delivers blood into systemic circuit so pressure is 80-100 mmHg
pumping blood round systemic circuit requires 4-6 times more pressure than pulmonary circuit
RV delivers blood to pulmonary circuit so pressure is <15 mmHg

Question 11

supporting heart structures

Answer 11

chordae tendineae - tenderness structure that tethers valves to ventricular wall through papillary muscles
papillary muscles - contract during ventricular systole to pull the chordae tendineae tight to make sure the valves don’t open in opposite direction

Question 12

the heartbeat

Answer 12

represents a single contraction of the heart
entire heart contracts in series - first atria then ventricles
2 types of cardiac muscle fibres
- contractile cells = produce contractions
- cardiac pacemaker cells (nodal/conducting) = Sino Atrial Node, Atrio Ventricular Node, Purkinje Fibres which all control and coordinate the contractile cells

Question 13

electrical system of the heart

Answer 13

SA node = natural pacemaker of heart, cells depolarise in SA node automatically, periodic electrical impulses, by itself it depolarises 60 times a minute equally 60 bpm
AV node = has a delay in response, 1/10th of a second delay before depolarising to allow atria to empty into ventricles first, auto-rhythmicity, SA node overrides it because it depolarises more (AV node 40 times a minute)
Purkinje fibres = pass impulse round ventricle, nodal cells so have auto rhythmicity but depolarises very slow (15 times a min)
auto rhythmicity of AV node and Purkinje fibres act as backup in case SA node fails

Question 14

cardiac cycle

Answer 14

1. SA node activity and atrial activation begin
2. stimulus spreads across the atrial surface and reaches AV node
3. 100 millisecond delay at AV node whilst atrial contraction begins
4. impulse travels along the interventricular septum within the AV bundle and the bundle branches to the Purkinje fibres and the papillary muscles of the right ventricle
5. impulse is distributed by the Purkinje fibres and relayed throughout the ventricular myocardium, atrial contraction completed and ventricular contraction begins

Question 15

heart rate regulation

Answer 15

autonomic nervous system
catecholamines (e.g. adrenaline)
changes in carbon dioxide/oxygen levels
changes in BP

Question 16

autonomic nervous system control

Answer 16

two main branches - sympathetic nervous system increased HR and parasympathetic slows down
both innervate the heart directly at SA node

Question 17

catecholamines

Answer 17

epinephrine (adrenaline) is released by adrenal medulla upon activation of sympathetic nerves innervating this tissue
exercise, stress and anxiety increase HR and contractility
works by bind to adrenergic receptors on the heart
norepinephrine initially increases HR and contractility but with longer exposure results in decreased HR and contractility
released by adrenal medulla (about 20%) but mostly from spill over from sympathetic nerves innervating blood vessels
works by bind to adrenergic receptors on the heart

Question 18

chemoreceptors

Answer 18

receptors that monitor chemical characteristics of the blood to help regulate function of both CV and respiratory systems
monitor blood pH and CO2
peripheral - in carotid bodies and aortic bodies
central - in medulla
high CO2 of low pH = increased HR
low CO2 or high pH = decreased HR

Question 19

baroreceptors

Answer 19

type of mechanoreceptor that detect changes in BP
carotid sinus - senses increases and decreases
aortic arch - senses only increase
low BP = low stretch of vessel = less stretch of receptor = decreased afferent firing = increase efferent sympathetic firing and decrease prismatic firing
increased HR and contractility, vasoconstriction, increased BP