W3 Cardiovascular Flashcards
Describe the external nerve supply to the heart
Pacemaker cells in the SA node spontaneously depolarise 100-110 times/min.
Rate of actual depolarisation controlled by input by the SNS and PNS. Resting HR is 70-80bpm and is set via vagal tone (activation of PNS Vagus nerve).
Normal generation of action potentials and HR known as sinus rhythm. ↓HR = PNS releases Acetylcholine ACh ↑ HR = SNS noephidrine
Describe the internal electrical system of the heart Explain the sequence of cardiac contraction
It is composed of five major structures:
Sinoatrial (SA) node: Triggers action potential.
Autorhythmicity - regular spontaneous depolarisation. Mygogenicity: heart beat originates within the heart and sets the rate.
Atrioventricular (AV) node: fibrous semiridgid insulation support for the heart valves for attachment of cardiac muscle of the myocardium.
AV (bundles of His): Velocity increases, the impulse is relayed through bundle of his.
Bundle branches: L & R bundle branches and subendocardial brances conduct impulses through the muscles of both ventricles, stimulating contract stimutaneously.
Subendocardial branches (purkinje fibres). Cardiac conduction - pacemaker cells are specialised they cannot contract. Action potentials propagate through the heart via gap junctions.
Explain how the SA node fires spontaneously and rhythmically
Pacemaker potential where there is a gradual depolarisation from -60mV due to leaky Na+ channels known as funny channels.
When this reaches threshold at -40mV fast Ca2+ channels open and there is rapid membrane depolarisation (Ca2+ in)
At +20mV fast Ca2+ channels close and repolarisation occurs when K+ channels open (K+ out) to restore membrane potential to -60mV. Pacemaker cells become a cardiomyocyte action potential
Describe the action potentials of cardiac muscle and relate to function
Resting membrane is -90mV
Phase 0: Depolarisation occurs when voltage gates Na+ channels open (Na+ in).
Phase 1: Na+ channels close at +30mV, K+ channels open (K+ out) to produce early repolarisation.
Phase 2: At this time Ca2+ channels open (Ca2+ in) and this delays repolarsation producing a plateau phase, ↑ intracellular Ca2+ activates release of more Ca2+ from sacroplasmic reticulum and this leaves to muscle contraction. The plateau ensures cardiac muscle stays contracted long enough.
Phase 3: Ca2+ channels close and continued K+ out repolarised membrane
Phase 4: Resting membrane potential restored by Na+/K+ exchanger. Ca2+ and ATP myosin interacts with actin and pulls on it
Interpret a normal ECG and relate to function
Records the electrical signals we see in the heart, used to measure the rate and rhythm of heartbeats, size and position of the heart chambers, presence of damage to heart muscles + the effects of cardiac drugs.
Their are 3 distinct wave forms to identify and associate with chamber (muscle) depolarization.
P wave: SA node fires, atrial depolarization - atrial systole
QRS complex: ventricular depolarisation (atrial repol and diastole)
ST segment: ventricular systole. resting.
T wave: ventricular repol.
Describe the structure and function of the different types of arteries
Muscular arteries - distal to elastic arteries; delivers blood to body organs, have thick tunica media, activate vasconstriction, distrubutes blood to specific organs.
Arterioles- smallest arteries; lead to capillary beds: control flow into beds via vasodilation and unstriction, SNS.
Metarterioles: short vessels connect arterioles to the capillaries bed,
Describe the structure and function of the 3 different types of capillaries
Microcirculation: musclular sphincters in metarterioles can regulate blood flow through capillary beds. Vasoconstriction ↓ flow - vasodilation ↑ flow.
Capillaries: smallest of blood vessels, wall consist of a thin tunica interna. Carry blood from arterioles to venules, together arterioles, capillaries and venules constitue microcirculation.
Continuous: lining of endothelial cells, openings (intracellular clefts) abundant in skin and muscles. Constitute blood-brain barrier.
Fenestrated: Filtrate formation characterised by holes, greater permeability than capillaries. Sinusoid: leakiest, large holes and lumens, found in liver bone, marrow, spleen. Allows large molecules to pass between blood and surrounding tissues.
Veins: act to ↓BP, have high capacitance.
- VENULES*: postcapillary venules more porous than capillaires, muscular venules have tunica media
- VENOUS SINUSES*: veins with thin walls, large lumens, no smooth muscle,
Describe a capillary bed and explain how they regulate blood flow
Capillary Beds is a microcirculation of interwoven networks of capillaries consisting of: Vascular shunts - metarteriole - thoroughfare cannel connecting an arteriole directly with a post capillary venule.
Precapillary sphincter: cuff of smooth muscle that surrounds each true capillary, regulates blood flow into the capillary. The use of SNS neurons uses contraction of noephinerine neurons, causing it to shut down the flow (constriction).
Outline the route of blood flow through the pulmonary circuit
Venous blood moves from R atrium to R ventricle to pulmonary artery to lung arterioles and capillaries, where gases are exchanged; oxygenated blood returns to L atrium by way of pulmonary veins; from L atrium, blood enter L ventricle.
Pulmonay capillaries near alveoli: basket like capillary bed surrounds alveoli
Identify and name the principal arteries (*) of the body
Ascending aorta: R and L coronary arteries supply heart.
Aortic arch - brachiocephalic:
R common carotid suppling R side of head.
R subclavian supplying R shoulder and Upp limb.
Left common carotid supplying L side of head.
L subclavian supplying shouder and upper limb.
Descending aorta:
Thoracic aorta above diaphragm.
Abdominal aorta below diaphragm.
Identify and name the principal veins (*) of the body
Veins are the ultimate extentions of capillaries; they unite into vessels of increasing size to form benule then veins.
Large veins of the cranial cavity are called dural sinuses.
Sysemic veins: venous blood from upper body and thoracic organs, except the lungs) drains directly into superior vena cava or azygoes vein. Venous blood from the lower extremities and abdomen drains into the inferior vena carva.
Hepatic portal circulation: veins from spleen, stomach, pancreas etc send their blood to the liver via hepatic portal vein.
Outline the flow of venous blood from any region or organ back to the heart
picture
Demonstrate understanding of foetal circulation and the changes that occur at birth
It steals dissolved oxygen from the mother through the placenta - this has implication for foetal circulation. Embryos develop in a sac full of fluid (amniotic sac) this is used to exchange nutrients, dissolved gasses and wastes (placenta).
The placenta is a series of spaces that the maternal blood leaks and circulates through. Finger like projections into these spaces, Villi ↑ surface area for max absorption. In utero the umbilical cord connects umbilical vessels to foetal circulation, two umbilical arteries that are extentions of the iliac pelvis arteries. The umbilical vein transports o2 blood from palcent to foetus → liver → giving two branches → ductus venosus drains into foetal inferior ven cava
Describe the cardiac cycle and relate its phases to pressure changes, volume changes, heart sounds and ECG
The cardiac cycle is one complete contraction (systole) and relaxation (diastole) of all 4 chambers of the heart.
Atrial systole: atrial contraction. Begins with P wave of ECG which triggers atrial contraction. Ventricles are relaxed and filling with blood from atria. AV valves are open; SL walves are closed.
Contraction of atria creates pressure gradient that pushes blood out of the atria and the relaxed ventricles. Filling completed by atrial contraction; ventricles now contain end-diastolic volume (EDV).
Ventricular ejection: ↑ pressure opens semilunar valves, rapid ejection of blood, followed by reduced ejection of blood (↓ pressure).
Stroke volume (SV): amount ejected, 70ml at rest. Ejection fraction: % of blood pumped out.
End-systolic volume (ESV): amount let in heart,
T-wave later in phase marking ventricular repolarisation. SV/EDV x100.
Isovolumetric Ventricular Relaxation: Ventricular diastole begins at this phase. SL valve closes (dupp).
Systolic sound (lubb): first sound contraction of the ventricles and by vibrations of the closing AV valves.
Diastolic sound (dupp): short, sharp sound, caused by vibrations of the closing SL valves
Explain how pressure and resistance determine the flow of a fluid
Hemodynamic describe the mechanisms that influence the active and changing flow of blood in vessles. Newtons first and second law of motion.
- Inertia: flow requires a pressure difference
- Force, mass, speed are related: more force, that faster it will flow. area ↑ pressure to ↓ pressure.
Perfusion pressure (PP) gradient is needed to maintain flow through a local tissue. Resistance and flow: resistant is a force that opposes flow, for blood to flow it much have more force than resistance. Resistance to flow in a blood vessel can be generated by: Blood viscosity, Vessel length, Vessel radius. ↑ pressure = faster flow. ↑ resistance = slower flow or resistance requires more pressure for the same flow
