Cardiovascular System I Flashcards
What are the functions of the cardiovascular system?
Transport - O2, nutrients, glucose, AA, fatty acids
Washout of metabolic waste products - CO2, urea, creatinine
Distributes hormones to tissues
Hormone secretion
Temp regulation - Heat from core to skin
Reproduction - Provides hydraulic mechanism
Describe the location of the heart and its surroundings
Located in the thorax centre
Surrounded by pericardium (fluid protection)
Describe the pericardium
Subdivided into visceral layer (outside) and parietal pericardium (water between layers)
Describe the parietal layer
Lines inner portion of pericardial sac, deep meshwork of collagen fibers
Restrains heart and prevents sudden dislocation
What are the 3 layers of the heart?
Epicardium, myocardium, endocardium
Describe the epicardium
Outer layer/visceral pericardium, has exposed mesothelium, underlain by layer of loose connective tissue
Describe the myocardium
A muscle
Muscular wall of heart, has cardiac muscle tissue/blood vessels/nerves
Describe the endocardium
Inner layer, squamous epithelium lines internal spaces of heart/covers valves
What are the left and right atria separated by?
Interatrial septum
What are the ventricles separated by?
Interventricular septum
How is a unidirectional flow of blood controlled?
Atria and ventricles separated by AV valves
What are the other valves lying between the atria and ventricles
Tricuspid valves - Between right atria and ventricle
Bicuspid valve - Between left atria and ventricle (mitral valve)
Describe the structure and function of the valves
Each valve has 2-3 flaps of connective tissue covered by endothelium
String-like chordae tendineae connect valve flaps to conical papillary muscles found on ventricular floor to prevent valve from bulging (prolapsing) into the atria
Describe the difference between tricuspid and bicuspid
Tricuspid valves have 3 cusps but bicuspid valves have 2 cusps
What are the 2 types of semilunar valves?
Pulmonary and aortic semilunar valves
Describe pulmonary SL valves
Prevents backflow of blood from pulmonary artery to right ventricles
Describe aortic SL valves
Prevents backflow of blood from aorta to left ventricle
Describe how the blood flow is divided
Blood vessels divided into pulmonary circuit (between heart and gas exchange surfaces of lungs) and systemic circuit (between heart and body)
What are cardiac cells?
Types of heart cells involved with heartbeat
What are the 2 types of cardiac cells?
Mechanical and Electrical
What are mechanical cardiac cells?
Contractile cells
What are electrical cardiac cells?
Conducting system
Describe mechanical cardiac cells
Form bulk of atrial/ventricular wall, perform mechanical work (Contraction - If stimulated)
Short, fat, branching, uninucleated myocytes striated
Cardiac myocytes joined by intercalated discs consist of
- Gap junctions to electrically couple the cells
- Desmosomes to mechanically couple the cells
99% cardiac myocytes contractile, 1% autorhythmic
Describe electrical cardiac cells
Consists of:
Sinoatrial node (SAN) - Initiate stimuli
Atrioventricular node (AV) - Delays stimuli
Bundle of His - Conducting bundle
Purkinje fibres - Conducting/distributing bundle
Describe how electrical impulses are conducted through the heart
Each heartbeat begins in SAN - Adjacent to superior vena cava opening to RA
SA node cells autorhythmic, depolarise, generate AP when membrane potential = -40mV
Impulse generated through AV node, slow conduction so takes longer for impulse to pass through AV node to Bundle of His - Delay allows atria to contract before ventricles
Describe further notes about the conduction of electrical impulses through the heart
AV node continues as Bundle of His to ventricles
Bundle branches to right/left bundle branches, then to Purkinje fibres
Impulse spreads through ventricles, initiate ventricular contraction
Contraction = Systole
Relaxation = Diastole
Atria and ventricle contract in sequence
What are the 4 stages of the cardiac cycle?
Mid-to-late diastole
Systole
Systole - Ventricular ejection
Isovolumetric relaxation
Describe mid-to-late diastole
Low pressure in diastolic atria, blood flows from veins to right atria
Ventricles are in diastole
Tricuspid and mitral valves open
70% of blood in atria flows into ventricles, atrial systole forces 30% blood to ventricles
Describe systole
Ventricles fill with blood, pressure rises forcing AV valves to close increasing ventricular pressure more.
When ventricular pressure is greater than atrial pressure, mitral valves close. ventricles closed chamber with fixed volume of blood
What is isovolumetric contraction?
Pressure in ventricles rises quickly reaching 80mmHg in 50ms
Describe systole - Ventricular ejection
When ventricular pressure greater than aortic, forces SL valves to open pumping blood to ventricles
Describe isovolumetric relaxation
Increased pressure in arteries close SL valves, begins ventricular diastole, contracting ventricular fibres so ventricle pressure drops.
When ventricle pressure below aortic, AV valves close, aortic pressure drops
What is stroke volume?
Size of left ventricle, degree of myocardial fiber shortening
What does myocardial shortening depend on?
Preload and afterload
What is load?
Force acting on/generated by heart muscle
What is preload?
Force acting on muscle before contraction (force stretching muscle before contraction)
Determines passive tension of muscle/initial length (part of total load muscle needs to overcome to shorten)
What is afterload?
Force added to preload that offers resistance to muscle shortening
What is total load?
Preload + Afterload
Define preload
Degree of stretching of myocardial fibers in ventricular diastole proportional to EDV
What is the link between EDV and preload?
The greater the EDV the greater the preload
What is the importance of preload?
Determines the ability of muscle fibres to shorten (develop tension), hence the higher the preload the higher the tension developed and greater stroke volume
What is EDV?
End-diastolic volume
Amount of blood in vent at end of VD
What is ESV?
End-systolic volume
Amount of blood in vent at end of VS
What is the relationship between EDV and force of contraction (Starling’s law)?
Stroke volume of heart increases in response to an increase in volume of blood filling the heart (at end of diastole volume) when all other factors stay constant
What is SVR?
Systemic vascular resistance
Describe SVR
Inverse relationship between cardiac output/SVR > If CO too low (eg hemorrhage) SVR is elevated (vasoconstriction)
If CO too high (septic shock) SVR will be low (vasodilation)
Describe SVR in terms of an anemic patient
They may have compensatory tachycardia due to bleeding/decreased O2 carrying capacity and elevated SVR
What happens when aortic regurgitation is present?
Back flow of blood causes increased cardiac output and lower SVR
Define afterload (cardiac output)
Amount of tension made by vent in contraction to open SV valves
Describe afterload in terms of systole and systolic volume
Greater afterload, shorter duration of ventricular ejection and larger end-systolic volume (stroke volume decreases with increased afterload)
When does afterload increase?
By factors that increase peripheral resistance, high afterload may lead to myocardial damage and heart failure
Describe the autonomic control of cardiac output
Heart innervated by SNS/PSNS and autonomic control is largely outside the influence of voluntary control (PS pathway usually dominant)
What occurs due to the inhibition of sympathetic nerves?
Decreased heart rate from 70-60 bts/min due to uncontrolled PS activity
What occurs due to the inhibition of parasympathetic nerves?
Increase in heart rate to 160 beats/min
Define intropy
An agent that alters force of muscular contractions
Describe the difference between negative and positive inotropic agents
Negative = Weaken force of contraction Positive = Increase strength of contraction
Describe heart pathology
Ventricular hypertrophy increases inotropic state
MI decreases inotropic condition
Many inotropes alter preload/afterload
Describe the difference between negative and positive chronotropic agents
Negative = Decrease heart rate Positive = Increase heart rate
Give examples of negative and positive chronotropic agents
Negative = Beta blockers, Ach Positive = Adrenergic agonists, atropine
What do parasympathetic nerves supply?
SA/AV nodes, atrial muscle, AV bundle
Describe parasympathetic nerves
Release ACh - Act on M2 receptors
Activate M2 receptors - Decreased force of contraction (Neg ino), Cardiac slowing (bradycardia - Neg chro), Inhibition results inc in heart rate to 160 bts/min
What do sympathetic nerves supply?
SA node, conducting tissue, myocardium
Describe sympathetic nerves
Effects Sym activation on heart mediated by catecholamines actions on B1-receptors
Sym stimulation result - Inc force of contraction (Pos ino), Inc heart rate (Pos chro), Inhibition results dec heart rate from 70-60 bts/min
Describe baroreceptors
Stretch sensitive receptors, tonically active, enhanced by stretching after dilation of vessels
Describe the baroreceptor reflex pathway
Activity of SNS/PSNS regulated by cardiovascular centres in brain in response to info from baroreceptors (Main found in carotid sinus and aortic arch)
