Cardiovascular system Flashcards
Main functions
- distributes oxygen and nutrients around the body
- distributes water, electrolytes & hormones through the body
- transports metabolic waste & CO2 from tissues
- thermoregulation
- contribute to structure of immune system
Where?
- In the thoracic cavity (mediastinum)
sits behind the sternum - Above diaphragm and in front of lungs
- In front of oesophagus and spine
- Oblique shape of heart means its apex points down to the left
- Size of fist
Layers of the heart:
- Pericardium
- Heart wall
Pericardium
- Membrane/sac surrounding heart
- Confines the heart to its position in the mediastinum whilst allowing sufficient freedom of movement for vigorous and rapid contraction
- two main parts: the fibrous pericardium and the serous pericardium.
- The superficial fibrous pericardium is composed of tough, inelastic, dense irregular connective tissue.
- serous membrane of the pericardium cavity is a thinner, more delicate membrane
- serous fluid between the layers
Heart wall
3 layers:
- Epicardium: external
- composed of two tissue layers.
- contains blood vessels, lymphatics, and vessels that
supply the myocardium.
- Myocardium: middle, containing striated cardiac muscle tissue responsible for the pumping action of the heart
- Endocardium: thin inner layer
- thin layer of endothelium overlying a thin layer of
connective tissue. It provides a smooth lining for the
chambers of the heart and covers the valves
- continuous with the endothelial lining of the large
blood vessels attached
Right atrium
- receives deoxygenated blood from body
- receives blood from three veins: the superior vena cava, inferior vena cava, and coronary sinus
Left atrium
Receives oxygenated blood returning from lungs
Right ventricle
- Sends deoxygenated blood to lung to be oxygenated
- ventricles pump blood under higher pressure over greater distances, their walls are thicker
Left ventricle
- Send oxygenated blood to body
- ventricles pump blood under higher pressure over greater distances, their walls are thicker
Atrioventricular valves
- bicuspid and tricuspid
- located between an atrium and a ventricle
- blood moves from a higher pressure in the atria to a lower pressure in the ventricles
Bicuspid valve/ left atrioventricular valve
- Opens to allow oxygenated blood to move from the left atrium to the left ventricle and close when left ventricle ejects blood
- two cusps
Semi lunar valves
- Aortic valve & pulmonary valve
- made up of three crescent moon–shaped cusps
- The SL valves allow ejection of blood from the heart into arteries but prevent backflow of blood into the ventricles.
Tricuspid valve/right atrioventricular valve
- Opens to allow deoxygenated blood to move from the right atrium to the right ventricle and close when right ventricle sends blood to the lungs
- it consists of three cusps or leaflets composed of dense connective tissue covered by endocardium
Pulmonary valve
- semi lunar valve
- between the lower right heart chamber (right ventricle) and the artery that delivers blood to the lungs (pulmonary artery)
Aortic valve
- semi lunar valve
- separates the lower left heart chamber (left ventricle) and the body’s main artery (aorta)
Ascending aorta
First receives oxygenated blood from the left ventricle
Arch of aorta
Has branches which take blood to head and arms
Descending aorta
Takes blood to rest of the body
Vena cava
Takes deoxygenated blood from the body
Capillaries:
- Site of exchange
- O2, nutrients, ions and electrolytes from blood moves into cells
- Thin walled, single endothelial cell layer surrounded by basement membrane
- 3 types:
• Continuous - most common
• Fenestrated - larger pores, allow larger molecules to pass through
• Sinusoid - large gaps, least common - Form an extensive network to make contact with body cells
- Allows efficient exchange of substances between blood and interstitial fluid
Left and right pulmonary artery
Deoxygenated blood is carried to the lungs
Left and right pulmonary veins
Carry oxygenated blood to the left atrium
Blood flow types through the body:
- Heart circulation: atria & ventricles
- Systemic circulation: arteries, arterioles, -systemic capillaries, venules & veins
- Pulmonary circulation: pulmonary arteries, pulmonary capillaries, pulmonary veins
Heart circulation steps
- Deoxygenated blood return to the right atrium via superior and inferior vena cava
- Deoxygenated blood moves from right atrium into the right ventricle via tricuspid valve
- Deoxygenated blood is pumped from right ventricle to the lung via the pulmonary valve to be reoxygenated
- Oxygenated blood is returned to the left atrium via the pulmonary veins
- Oxygenated blood is passed from the left atrium to the left ventricle via the bicuspid valve
- Oxygenated blood is pumped from the left ventricle to aorta via aortic valve
Artery
- Carries blood away from heart to tissues (oxygenated except for pulmonary arteries)
- More pressure
- Thicker wall
Veins
- Carries blood away from tissues to heart (deoxygenated except for pulmonary veins)
- Less pressure
- Thinner wall
Pulmonary circulation:
- Deoxygenated blood from body enters heart through superior vena cava, inferior vena cava and coronary system into the right atrium
- Deoxygenated blood passes through the tricuspid valve into right ventricle
- Deoxygenated blood passes through the pulmonary valve into pulmonary arteries
- Blood reached the lungs where gas exchange occurs (blood is oxygenated)
- Oxygenated blood leaves the lungs via the pulmonary veins
- Oxygenated blood enters the left atrium
- Passing through the bicuspid valve blood enters the left ventricle
- Passing through the aortic valve the oxygenated blood exits the heart to the body via aorta and systemic arteries
Arterioles:
- Smooth muscle cells wrap around allowing diameter to be controlled
- Regulates blood flow into capillary networks
- Sympathetic nerve supply allowing diameter to be controlled
Coronary circulation:
- Heart itself needs blood to pump
- Via coronary arteries & veins
Blood vessels
- Transport system of the body
- Made up of: arteries, arterioles , capillaries, venules & veins
- Parallel delivery to all organs
Arteries:
- Thick, elastic walls for high pressure
- Carry blood away from the heart
- 3 (tunics) wall structure layers:
• External
• Middle - aids elasticity, (stretch/recoil to propel blood onward while ventricles are relaxing) and contractibility (to maintain vessel pressure and tone)
• Internal
Venules:
- Drain the capillary blood
- Begin to return flow of blood back to the heart
Sulcus
- mark the separation between ventricles
- contain coronary blood vessels and a variable amount of fat
Atrioventricular (AV) Node
- At base of right atrium
- At AV node, action potential slows allowing both atria to empty their blood into ventricles
Veins:
- Return blood to the heart
- Serve as blood reservoirs
- 3 layers:
• External
• Middle
• Internal - Valves (especially in limbs) aid venous return of blood to heart
Conduction pathway
For each heartbeat, electrical signals travel through the conduction pathway of your heart
Vessel lumen size:
Decreases artery to capillary
Increases capillary to vein
Action potential and contraction of contractile fibres
- Depolarisation
- Plateau
- Repolarisation
Autorhythmic fibres
self-excitable.
Autorhythmic fibres repeatedly generate action potentials that trigger heart contractions. They continue to stimulate a heart to beat even after it is removed from the body
Sinoatrial (SA) Node
- Origin of every heart beat
- Located in right atrium wall
- SA node cells repeatedly depolarise to threshold spontaneously (~75/min)
- Act as pacemakers & set the rhythm of electrical excitation that causes contraction of heart
- Each action potential from the SA node propagates throughout the both atria & contract simultaneously
- No stable resting membrane potential, continuously moving towards threshold (pacemaker potential)
Systole
- During systole, the two ventricles develop pressure and eject blood into the pulmonary artery and aorta.
- At this time the AV valves are closed and the semilunar valves are open.
Atrio-ventricular bundle (bundle of His)
- Originates at AV node & enters the interventricular septum
- Only electrical connection between the atrial & ventricles
- Autorhythmic in own right (~25/40/min)
Purkinje fibres
- Conduct the action potential-beginning at the apex of the heart upwards to the remainder of ventricular myocardium
- Sub-endocardial in ventricular walls
Diastole
- the phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood.
- The semilunar valves are closed and the atrioventriular valves are open during diastole.
Right & left bundle branches
- Action potential enters both R & L bundle branches which extend through interventricular septum towards the apex of the heart
Diastolic pressure
- the lowest pressure within the arteries during ventricular filling
- heart in diastole 2/3 of the time
Blood pressure
The amount of pressure exerted on the vessel walls by the blood
Systolic pressure
- The highest pressure within the arteries during ventricular emptying
- Measures the pressure in your arteries when your heart beats
- Heart in systole 1/3 of the time
Pulse pressure
= systolic pressure - diastolic pressure
Mean arterial pressure
- The mean value of pressure being exerted
- MAP = diastolic BP + 1/3(pulse pressure)
Stoke volume (SV)
- Amount of blood pumped out of the ventricle
- SV = EDV - ESV
(EDV = end diastolic volume, ESV = end systolic volume)
Ejection fraction (EF)
- % of blood leaving the heart at each contraction
- EF = (SV/EDV) x 100%
- Normal: 53 ≤ x ≤ 73, 45 or lower indicates heart problem
Factors affecting MAP
- Vascular resistance
- Cardiac output (CO) -L/min
Vascular resistance impact on MAP
- Amount of resistance to blood flow in the blood vessels
- Caused by the friction between the blood & the vessel walls
- Dependant on: the size of the vessel lumen, blood viscosity & blood vessel length
Cardiac output (CO) -L/min impact on MAP
- The amount of blood circulated through the blood vessels in one minute
- CO = SV x heart rate (HR) - BPM
- Increased HR &/or SV increases CO increases MAP
Why is it important to regulate MAP
- Excess high blood pressure (hypertension) can damage blood vessels & the surrounding tissues
- Low blood pressure can result in poor blood perfusion, leaving the tissues starved of oxygen and other nutrients
Electrocardiogram
- The P wave represents atrial depolarisation, which spreads from the SA node through contractile fibres in both atria.
- The second wave, called the QRS complex, begins as a downward deflection, continues as a large, upright, triangular wave, and ends as a downward wave. The QRS complex represents rapid ventricular depolarisation, as the action potential spreads through ventricular contractile fibres.
- The third wave is a dome-shaped upward deflection called the T wave. It indicates ventricular repolarisation and occurs just as the ventricles are starting to relax. The T wave is smaller and wider than the QRS complex because repolarisation occurs more slowly than depolarisation.
- During the plateau period of steady depolarisation, the ECG tracing is flat.
