Cardiovascular Flashcards
What is the equation of stroke volume?
End Diastolic Volume (EDV) - End Systolic Volume (ESV)
What is the equation for mean arterial pressure (MAP)
diastolic pressure +1/3 pulse pressure
What is the equation for cardiac output?
Heart rate (HR) x Stroke volume (SR) Typically 5L/ minute
What is the definition of cardiac output?
The volume of blood each ventricle pumps as a function of time (litres per minute)
What is the equation for Ohm’s law and vessel resistance?
Flow = pressure gradient/ resistance
What is the equation for Poiseuille and blood flow
Flow = radius to the power of 4
What is the equation for pulse pressure?
systolic - diastolic pressure
What is the definition of preload?
the volume of blood in the left ventricle which stretches the cardiac myocytes before left ventricular contraction
What is the definition of after load?
the pressure the left ventricle must overcome to eject blood during contraction - dilate arteries = decrease in after load
What is the definition of contractility?
Force of contraction and the change in fibre length - how hard the heart pumps. When muscle contracts myofibrils stay the same length but the sarcomere shortens - force of heart contraction that is independent of sarcomere length.
What is the definition of elasticity?
myocardial ability to recover normal shape after systolic stress
What is the definition of compliance?
how easily the heart chamber expands when filled with blood volume
What is the definition of resistance?
Total peripheral resistance: the total resistance to flow in systemic blood vessels from beginning of aorta to vena cava - arterioles provide the most resistance.
Starlings Law of the heart
force of contraction is proportional to the end diastolic length of cardiac muscle fibre - the more ventricle fills the harder it contracts.
How long does systole last?
0.3 seconds. Ventricular contraction and blood ejection occurs.
How long does diastole last?
0.5 seconds. Ventricular relaxation and blood filling occurs.
What is isovolumetric contraction?
iso - equal/unchanging contraction of the ventricles. Increase in pressure but volume remain the same since valves remain closed.
What are the parasympathetic fibres transmitted by?
vagus nerve (CN10)
What is parasympathetic stimulation controlled by?
Acetylcholine which bind to muscarinic receptors
What are the effects of parasympathetic stimulation?
- Decreases heart rate (negatively chronotropic)
decreases force of contraction (negatively inotropic)
decreases cardiac output (by up to 50%)
What do sympathetic postganglionic fibres innervate?
The entire heart
What is the sympathetic stimulation controlled by?
Adrenaline and noradrenaline
What are the effects of sympathetic stimulation?
- Increases heart rate (positively chronotropic)
- increases the force of contraction (positively inotropic)
- increases cardiac output (by up to 200%)
Explain the 5 phases of myocyte action potential
Phase 0: rapid depolarisation, inflow of Na+
Phase 1: partial depolarisation, inward Na+ current deactivated & outflow of K+
Phase 2: plateau, slow inward Ca2+ current
Phase 3: depolarisation K+ outflow, Ca2+ current deactivated
Phase 4: pacemaker potential, slow Na+ inflow, slowing of K = outflow
Isovolumetric ventricular relaxation
Ventricular volume is not changing. Decrease in pressure but volume remains the same
Name the effectors in the central circulation control
Blood vessels, heart and kidneys
What is the main aim of control of circulation?
It is maintain mean systemic arterial pressure (MAP) - the average blood pressure in the arteries during the cardiac cycle
Function and structure of circulatory system: arteries
- contain mainly elastic, collagen and smooth muscle.
- the intima is composed of an inner surface lining of endothelial cells and a very small amount of collagen.
- the adventitia shows mainly collagenous connective tissue
- there are 2 elastic laminae, one at the interface of the intima and media and the other on the outer edge of the media.
Function and structure of circulatory system: arterioles
- may have an obvious media and adventitia
- smaller arterioles show only a few medial cells with a poorly defined elastic lamina
- a thin adventitia and normal intima also exist
Function and structure of circulatory system: endothelium
- single layer of spindle/pavement cells with tight adhesions between adjacent cells
- little cytoplasm and intra-cellular organelles-bit gap/adheren junctions are prominent
- they may be fenestrated (have pores in them for rapid diffusion) in the liver, kidney, glomeruli and endocrine tissue
- in some areas they may be very thin (lung) to enable rapid fluid and gas transfer
Function and structure of circulatory system: Capillaries
- tubes of endothelial cells (one cell thick wall - for rapid diffusion) bound to a basement membrane with co-existing pericytes.
- pericytes have muscle fibres and may regulate blood flow
Function and structure of circulatory system: Venules and veins
- show variable thickness
- veins generally have collagen and little muscle and elastic with the wall and a single internal elastic lamina
- veins contain valves for one way flow of the heart - prevent back flow
Some veins are surrounded by skeletal muscle which contracts to increase vein pressure and ensure blood flows back to the heart.
What is the pulmonary circulation?
Blood leaves the right ventricle via a single large artery, the pulmonary trunk, which divides into the two pulmonary arteries, one supplying the right and one supply the left lung. In the lungs the arteries continue to branch and connect to arterioles, leading to capillaries that unite into venules and then veins. The blood leaves the lungs via four pulmonary veins, which empty into the left atrium
What is the systemic circulation?
Blood leaves the left ventricle via single large artery, the aorta. The arteries of the systemic circulation branch off the aorta, dividing into progressively smaller vessels. The smallest arteries branch into arterioles, which branch into roughly 10 billion very small vessels, the capillaries, which unite to form larger-diameter vessels known as venules. The arterioles, capillaries & venules are collectively referred to as the MICROCIRCULATION. The venules then unite to form larger vessels, veins. The veins from the various peripheral organs and tissues unite to produce two large veins, the inferior and superior vena cava which drain into the right atrium
What are the two phases of the blood?
Cellular component (45%); Red cells (form 99% of blood cells), white cells &platelets
Fluid component (55%); plasma
What is haematocrit?
the volume of red blood cells i.e. haemoglobin in the blood, normal haematocrit is 0.45
What is haeopoiesis?
The process of the production of blood cells and platelets which continues throughout life.
Where does haemopoiesis occur in adults?
It is confined to the bone marrow
Where does haemopoiesis occur in embryonic life and early infancy?
It can occur at other sites.
What is the red blood cell lifetime?
120 days
What is the lifetime of a platelet?
7-10 days
What is the lifetime of a white blood cell?
6 hours
Do red blood cells and platelets have a nucleus?
No they are anucleate (have no nucleus)
Where are the precursor cells of RBCs located?
In the bone marrow
RBCs precursor cells: Where is this in adults?
In the axial skeleton: skull, ribs, spine, pelvis and long bones
RBCs precursor cells: where is this in children?
In all bones
RBCs precursor cells: where is this in utero?
yolk sac, then liver and spleen
Are precursor cells found in the blood?
No this is a sign of leukaemia
What is anaemia?
Reduction in haemoglobin in the blood
What are some examples of soluble plasma proteins?
Albumin, carrier proteins, immunoglobulins
What is the physiological function of platelets?
(organised anucleate particles) responsible for primary haemostasis = bleeding time: PT (prothrombin time), they adhere to damaged endothelium and aggregate to form platelet plug that blocks hole in vessel
Describe the structure of platelets
Small cytoplasmic anucleate cells that block up holes in blood vessels
• Made in bone marrow from cells called megakaryocytes
• Spherical, enucleate - cannot repair itself
• Lifespan: 5-10 days
• Normal number: 140-400 x 109/l
Name the types of white blood cells
- Neutrophils
- lymphocytes: B cells and T cells
How long does each cardiac cycle usually last?
0.8 seconds
What does systole involve?
Ventricular contraction and blood ejection