Cardiovascular System Flashcards
Functions of the CVS?
Delivers oxygen and nutrients around the body, removes waste products and maintains blood flow - determined by pressure and resistance.
Anatomy of the Heart? (4)
Left side = oxygenated blood
Right side = deoxygenated blood
The walls of the atria and ventricles are made of cardiac muscle tissue (myocardium)
The left ventricle is 3x thicker than the right because it generates more force.
Describe the blood flow through the heart.
Deoxygenated blood from the body returns to the heart through the vena cava. It enters the right atrium and into right ventricle. Blood is then pumped out of the right ventricle through the pulmonary trunk to the lungs.
Blood becomes oxygenated in the lungs
Oxygenated blood from the lungs travels back to the heart through the pulmonary veins into the left atrium. It then flows into the left ventricle and pumped into the aorta to flow around the body.
What are atrioventricular valves (AV Valves)?
Between the atria and ventricles (left - bicuspid, right - tricuspid).
They prevent the backflow of blood from the ventricles into the atria.
They are connected to papillary muscles by the chordae tendinea.
What are semilunar valves (SL Valves)?
Between the ventricles and arteries (right - pulmonary valve, left - aortic valve).
They prevent the backflow of blood from the major arteries into the ventricles.
They are thick cusps of connective tissue - fill with blood from the arteries to close without needing muscle.
What is the Sinoatrial (SA) Node?
The ‘pacemaker’ region of the heart. Produces action potentials to generate the heartbeat - the action potentials depolarise cells.
Whats the electrical signal pathway?
Sinoatrial node –> internodal pathway –> atrioventricular node –> moderator band –> purkinje fibres
What is an ECG?
Electro cardio gram - measures the electrical activity in the heart
What is diastole?
The relaxation phase (2/3 of cardiac cycle)
Ventricles relax and fill with blood
What is systole?
The contraction phase (1/3 of cardiac cycle)
Ventricles contract and pump blood out of the heart
Describe the start of the cardiac cycle.
All four chambers are relaxed, SA node spontaneously releases action potential.
Pressure in the atria is higher than in the ventricle - AV vales are open
Pressure in the artery is higher than in the ventricle - SL Valves are closed
What happens in step 1 of the cardiac cycle?
Ventricular filling 2 - diastole
Atria depolarise and contract = ECG P-wave
AV valves are open
SL valves are closed
What happens in step 2 of the cardiac cycle?
Isovolumetric contraction - systole
Ventricles depolarise and start to contract = QRS Complex
AV valves are closed
SL valves are closed
Pressure builds in ventricles but no volume change = isovolumetric
What happens in step 3 of the cardiac cycle?
Ventricular ejection - systole
Ventricles are still depolarised and continue to contract = no new electrical activity
AV valves are closed
SL valves are open
What happens in step 4 of the cardiac cycle?
Isovolumetric relaxation - diastole
Ventricles repolarise and relax = T-wave
AV valves are closed
SL valves are closed
What happens in step 5 of the cardiac cycle?
Ventricular filling 1 - diastole
All chambers are repolarised and relaxed
AV valves open
SL valves closed
What is heart sound 1?
“lub” happens with closing of the AV valves as the ventricles contract. Happens after the QRS complex, ventricles depolarise and contract
What is heart sound 2?
“dub” happens with closing of the SL valves as the ventricles relax. Happens after the T-wave, ventricles repolarise and relax
What is Heart rate?
How often the heart goes through one complete cardiac cycle. In a healthy adult, HR ~60-100bpm at rest
Slower = bradycardia
Faster = tachycardia
What is stroke volume?
How much blood the left ventricle pumps out in one heart beat. In a healthy adult, SV is ~70ml at rest
What is cardiac output?
CO = HR x SV
Volume of blood pumped per min. In a healthy adult, CO ~5L/min at rest
What is flow determined by?
F = P/R
Pressure gradient
Resistance
What is pressure gradient determined by?
By the pressure generated by the left ventricle during contraction.
Pressure in the arteries is higher than in the venous system
What is resistance proportional and inversely proportional to?
Resistance = 8nl/πr^4 (poiseuille’s law)
Proportional to: Fluid viscosity (n) and Blood vessel length (l)
Inversely to: Blood vessel radius (r)
Increased resistance = reduced flow
What is flow proportional and inversely proportional to?
Proportional to: pressure gradient (P) and blood vessel radius (r)
Inversely to: resistance (r), blood vessel length (l) and fluid viscosity (n)
What is laminar flow?
Smooth flow through vessels
What is turbulent flow?
Increases resistance and reduces flow
eg. plaque deposit in vessels
What are arteries? (5)
Arteries carry blood away from the heart
Have thick walls and large diameters
Combination of elastic tissue and smooth muscle layers
Low resistance vessels
Provide a pressure reservoir
What are elastic arteries? (4)
The aorta is an elastic artery.
Elastic arteries reduce fluctuations in flow and pressure from ventricle ejection.
Reduces pulsatile flow to provide steady blood flow into smaller arteries
High compliance vessels
What are muscular arteries? (3)
Medium-sized arteries
Contain more smooth muscle than elastic arteries
Distribute blood to skeletal muscle and internal organs through arterioles
What are arterioles? (4)
Arterioles are the smallest type of arteries
Contain smooth muscle and endothelium
Responsible for determining relative blood flow to individual organs
Main factor for determining mean arterial blood pressure
What is pulse pressure?
Pulse pressure is SP-DP
Systolic pressure (SP) - peak pressure in arteries, ~120mmHg
Diastolic pressure (DP) - ~80-90mmHg
What is mean arterial blood pressure (MABP)?
MABP = (1/3 x PP) + DP
MABP is tightly regulated as it drives blood flow to the tissue throughout the cardiac cycle
MABP = CO x TPR
What is Total Peripheral Resistance (TPR)?
The combined resistance to blood flow of all the systemic blood vessels.
It’s determined by:
- Vascular resistance
- Fluid viscosity
- Turbulence
What is the most common mechanism to alter blood flow?
To change the radius of the vessel (flow is proportional to radius)
What is vasodilation?
When blood vessels become wider.
Radius increases, resistance decreases, flow increases
What are physiological vasodilators? (4)
Adrenaline acting on Beta receptors in vessels
Increased nitric oxide released by endothelium
Atrial natriuretic peptide
Local increases in CO2 levels
What is vasoconstriction?
When blood vessels become narrower.
Radius decreases, resistance increases, flow decreases
What are physiological vasoconstrictors? (4)
Adrenaline acting on Alpha receptors in vessels
Endothelin - 1 release by endothelium
Vasopressin and angiotensin II
Local increases in O2 levels
What are sympathetic nerves? (4)
Innervate arterioles
Controlled by the brainstem
Release noradrenaline onto the smooth muscle cells of the blood vessel
Activates a-adrenergic receptors
What is hypermia?
Increased blood in vessels
It’s a physiological response to a regional increase in metabolic activity, eg. the skeletal muscle
Key response to maintaining blood flow to muscle during exercise
Increased activity in tissue/organ –> increased CO2, decreased O2 –> triggers regional vasodilation –> increased blood flow to tissue/organ
What is flow autoregulation?
The CVS tries to maintain blood flow. If arterial pressure is changed, the blood vessels themselves can respond to keep flow constant = myogenic autoregulation
What are capillaries?
Thin walled vessels made of endothelial cells, no smooth muscle layer.
Network of blood vessels between arterioles and venules and where exchange occurs
What are the 3 main types of capillaries?
- Continuous - least ‘leaky’
- Fenestrated - ‘In between types’
- Sinusoidal - most ‘leaky’
Of all the blood vessels, capillaries have:
Smallest diameter
Largest cross-sectional area
Lowest velocity of blood flow
What does capillary exchange involved a combination of?
Filtration
Diffusion
Osmosis
Where can capillary exchange occur?
Across the endothelial cell membrane (directly or through channels)
Through pores of fenestrated capillaries
By vesicle transport
What is filtration determined by?
Capillary hydrostatic pressure (CHP)
Blood colloid osmotic pressure (BCOP)
What is CHP?
Capillary Hydrostatic Pressure
Blood pressure within the capillaries
The driving force to PUSH fluid out of the blood stream
Highest at start of capillary bed
What is BCOP?
Blood colloid osmotic pressure
Osmotic pressure within the blood
Force which PULLS fluid into the blood stream
Increases when water leaves the blood but solutes left behind
What is net filtration pressure (NFP)?
The difference between CHP and BCOP
- CHP > BCOP = filtration = positive NFP (start of capillary)
- CHP < BCOP = reabsorption = negative NFP (end of capillary)
- CHP = BCOP = no net movement (middle of capillary)
What is diffusion determined by?
Concentration gradient
Solubility
Size
What are venules?
Smallest of the venous vessels, thin walled
They collect blood form the capillary beds
Venules unite to form the larger veins to return blood to the heart
What are veins? (6)
Veins carry blood back to the heart
Have thinner walls and less smooth muscle than arteries
Higher compliance vessels than arteries
Veins are highly distensible - can change volume easy
Provide a volume reservoir
The vena cavae are the largest veins in the body
What are red blood cells?
Largest component of the formed elements in whole blood (99.9%): erythrocyte
Major function is to carry oxygen - bound to haemoglobin
What are white blood cells?
Account for <0.1% of all blood cells
Critical function in the body’s defence against pathogens and toxins.
Neutrophils and lymphocytes are the most abundant
What are platelets?
<0.1% of the formed elements in blood
Flattened discs that are continuously replaced
Clump together and stick to damaged blood vessel walls and release chemicals to trigger blood clotting
What are the 3 steps of haemostasis?
- Vascular phase - vessel constricts to reduce blood flow
- Platelet Phase - platelets adhere to site of injury, them aggregate and clump
- Coagulation Phase - fibrous blood clot is formed
Where does the sympathetic pathway originate?
In the cardioacceleratory centre
Where does the parasympathetic pathway originate?
In the cardioinhibitory centre
What do nerves innervate?
Sinoatrial Node
Ventricular Myocardium (mostly sympathetic)
Atrial Myocardium
What do sympathetic nerves release?
Release noradrenaline which binds to beta-adrenergic receptors in the heart
Sympathetic nerve activity in the SA Node:
B-receptor activation reduces the resting repolarisation of the cells
Cells reach threshold faster = more action potentials
Heart rate increases
Sympathetic nerve activity in the ventricular and atrial myocardium:
B-receptor activation increases the amount of force produced during contraction
Atria and ventricles contract harder and faster and therefore can relax faster
Stroke volume increases
B-receptor activation speeds up calcium cycling inside the muscle cells
What do parasympathetic nerves release?
Release acetylcholine which causes potassium channels in the heart to open
Parasympathetic nerve activity in the SA node:
K+ channel activation hyperpolarises the nodal cells
Cells reach threshold slower = fewer action potentials
Heart rate decreases
Parasympathetic nerve activity in the atrial myocardium and ventricle muscle:
Atria contract less
Less filling of the ventricles
Stroke volume decreases
No significant effect in ventricle
What is postural hypotension when lying down?
When lying down, the gradient of pressure through our body is low because they are all at a similar height. Therefore gravity has minimal effect on blood pressure
What is postural hypotension when stand?
If you stand suddenly, blood will pool in the veins of the legs due to gravity. Increased blood in the veins means less blood returns to the heart = lower venous return.
Lower SV
Reduced CO
BP drops (hypotension)
How do we meet the increased metabolic demand during exercise?
Increasing Cardiac Output (CO)
What happens to our heart rate during exercise?
When we exercise, the brain responds by decreasing parasympathetic and increasing sympathetic activity to the SA node = Increased HR.
What happens to our stroke volume during exercise?
When we exercise, the brain responds by increasing sympathetic activity to the ventricle = increased SV
What happens to the cardiac cycle during exercise?
The cardiac cycle becomes shorter as heart rate increases. Most due to diastole shortening as the heart relaxes faster.
What happens to our venous system when we exercise?
Increased contractions in exercising muscle pushes more blood out of the veins back to the heart = increased venous return
Where is blood flow increased and decreased to during exercise?
Increased to: skeletal muscle, heart and the skin
- mainly due to local increase in metabolites
- stimulates local vasodilation
Decreased to: Kidneys, gut and abdominal organs
- mainly due to increased sympathetic activity to non-essential organs during exercise
- stimulates regional arteriole vasoconstriction
What happens to our blood pressure during exercise?
During exercise,
- large increase in CO
- some blood vessels dilate and some constrict so overall, TPR is slightly decreased
- MABP slightly increases (MABP = CO x TPR)
