Cardiovascular + Respiratory System 1 Flashcards
What is the role of the cardiovascular system?
A transport system for getting the right amount of blood to the right place at the right time and back again.
What are 5 key functions of the cardiovascular system?
- rapid transport and distribution of nutrients e.g glucose and O2 and waste products e.g. urea and CO2
- distribution of water
- infrastructure of immune system
- temperature regulation
- exchange between blood vessels and interestrial fluid
What is the key principle in physiology
= homeostasis
–> the maintenance of the internal environment, faced with variation in the external environment, activity and intake of nutrients.
What is the negative feedback loop in homeostasis?
= Core mechanism
Controller –> Effector –> Variable –> Receptor
What are the three ways that blood can circulate?
Pulmonary circulation –> lungs (lower resistance, lower pressure)
Systemic Circulation –> body (higher restance, higher pressure)
Arterial System and Venous system –> distribution of blood, venous return
Definition of systole:
= phase of heartbeat where muscle contracts and pumps blood from chambers into the arteries.
Definition of diastole:
= Phase of heartbeat where heart muscle relaxes and allows chambers to fill with blood.
Definition of stroke volume:
= how much blood is in the left ventricle each time it contracts
Definition of cardiac output:
= amount of blood that leaves the heart in L / min
What does pressure (P) mean?
= force per unit area (heart generates a ‘head of pressure’)
What does Resistance (R) mean?
how hard it is for flow (Q) to occur
What is normal arterial blood pressure?
= systolic / diastolic: very variable
What is the controlled variable in the Central Nervous System (CNS)
= mean arterial pressure
What is myocardium?
= heart muscle
What is endocardium?
The innermost layer of the heart. It lines the chambers and extends over structures such as the valves.
What is epicardium?
The outermost layer of the heart.
What is pericardium?
a fibrous sac that encloses the heart and great vessels.
What muscle is the heart made up of?
Cardiac (striated) muscle
What is annulus fibrousus?
a fibrocartilaginous tissue consisting of layers of lamellae with highly cross linked collagen fibrils.
What is the structure of the Atria?
- thin walled (compared to ventricles)
- Located above the ventricles
- receive venous blood
- right atrium receives systemic venous blood
- left atrium receives oxygenated venous blood
What is the function of the Atria?
acts a a pump to fill or ‘prime’ ventricles at low pressures
produces the hormone atrial natriuretic peptide (ANP)
What is the function of ventricles?
eject blood into the arterial systems including the lungs
Left ventricle has a thicker wall than the right ventricle which helps generate higher pressure - blood to systemic circulation
What initiates the heartbeat?
the sinoatrial node (SAN)
What is the sinoatrial node (SAN)
the physiological pacemaker
How does the sinoatrial node (SAN) function?
excitable cells generate action potentials
automaticity - (spontaneous)
rhythmicity - (regular)
dominance over other potential pacemakers
Causes cardiac muscle contraction
What is the electrophysiology of the Sinoatrial node (SAN) ?
Several ion currents are involved
No ‘fast’ outward sodium currents
Unstable resting membrane potential
How is a heart contraction stimulated by the sinoatrial node (SAN) ?
SAN sends signals to AVN
Signals sent to bundle of His
Travel down left and right bundle branches to purkinje fibres
Cause heart muscle to contract.
What is the resting membrane potential of the heart (myocardial cell)?
~ 90 mV
What are the components of an ECG and what do they mean?
P wave - atrial depolarisation
QRS complex (<0.10s) - Ventricular depolarisation
T wave - Ventricular repolarisation (some cells still depolarised)
PR interval (0.12 - 0.2s) - Atrioventricular conduction
QT interval (QTc < 0.44s) - Duration of ventricular activation
What is cardiac output?
the volume of blood ejected from the heart per minute
What is the equation for cardiac output?
Cardiac output = heart rate x stroke volume
CO (L/min) = HR (bpm) x SV (litres)
resting adult ~ 5 L/min
exercising adult ~ 20 L/min
What system controls the heart and blood vessels?
The Autonomic Nervous System
What controls the heart rate?
Parasympathetic nerves
Vagus nerve
Sympathetic nerves
What is the difference between a normal and intrinsic heart rate?
- at rest both parasympathetic and sympathetic systems are active
- pharmacological block of both systems causes a 50% increase in heart rate. At rest the parasympathetic effects are dominant.
What is the heart rate known a tachycardia and bradycardia?
tachycardia = >100/min
bradycardia = < 60 /min
What is the mean arterial pressure? (MAP)
the average blood pressure of the tissues that the heart has perfused blood to
What is the equation for Mean Arterial Pressure?
MAP = (CO x TPR) + CVP
TPR is the total peripheral resistance
CVP (central venous pressure) is very small (often ignored in the calculation)
What is the key controlled variable via cardiac output?
Blood pressure
What happens when blood pressure is too low or too high?
Too low blood pressure = poor perfusion e.g lack of blood to brain when you stand up
Too high bp = excessive afterload on heart and excessive pressure at small vessels in tissues - loss of fluid to tissue e.g. legs and lungs
What is the controlled variable for blood pressure?
Mean arterial pressure
Blood Pressure is critical for correct perfustion
What do baroreceptors measure?
Mean Arterial Pressure
What would happen if a sudden fall in blood pressure was detected?
- arterial pressure => - MAP => Baroreceptor firing –> - –> CNS –> + sympathetic TPR –> parasympathetic + –> CO
Why do arterioles change diameter (volume) ?
arterioles are the ‘taps’ of tissue perfusion
respond to local tissue factors
innervated by sympathetic system (alpha receptors)
= Vasoconstriction
= Vasodilation —> bring about changes in TPR
