3: The CV System Flashcards
functions of the CV system
transport - nutrients, oxygen, hormones, waste
maintenance - heat, pH, hydration
protection - WBCs
components
fluid - blood
system of channels - blood vessels
pump - heart
2 circuits
pulmonary circuit - blood to and from lungs
systemic circuit - blood to and from rest of body
location of heart
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
the heart
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
pericardium
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)
myocardium
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
intercalated discs
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
endocardium
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
ventricular differences
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
supporting heart structures
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
the heartbeat
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
electrical system of the heart
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
cardiac cycle
- SA node activity and atrial activation begin
- stimulus spreads across the atrial surface and reaches AV node
- 100 millisecond delay at AV node whilst atrial contraction begins
- 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
- impulse is distributed by the Purkinje fibres and relayed throughout the ventricular myocardium, atrial contraction completed and ventricular contraction begins
heart rate regulation
autonomic nervous system
catecholamines (e.g. adrenaline)
changes in carbon dioxide/oxygen levels
changes in BP
autonomic nervous system control
two main branches - sympathetic nervous system increased HR and parasympathetic slows down
both innervate the heart directly at SA node
catecholamines
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
chemoreceptors
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
baroreceptors
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
