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MG: Circulatory Tract; all lectures
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Medicine Groups: Circulatory TractIntroduction lecture 1
Learning outcomes
At the end, students will understand:
- The neuronal and hormonal regulatory mechanisms of the cardiovascular system: regulation of BP and
heart rate
- The physiology and pathophysiology of the CV-system and the main risk factors for the development of
diseases of this system: hypertension, angina pectoris, pulmonary hypertensin, arrhythmias, heart
failure, blood coagulation
- The pharmacology of the drugs for the circulatory system
o Beta blockers, calcium antagonists, nitrates, PDE inhibitors, ACE inhibitors, AT1 antagonists,
diuretics, anti-arrhythmics, digoxin, cholesterol-lowering drugs, anticoagulants
- The pharmacotherapy for CV-diseases: when to use which class of drug?
Circulatory system- Pharmacy
With pharmacy, the patient is in the center and medicinal drugs, disease, healthcare provision is the task.
The aspects that are important at medicinal drugs: efficacy, safety, mode of administration, production.
Disease: cause, mechanism, course. Also as a pharmacist, you are a healthcare provider; distribution,
supervision, consultation, therapy.
Cardiovascular system
Introduction – the cardiovascular system and the heart
The anatomy of the heart: the heart is a pump and delivers blood containing oxygen, nutrients, waste
products and glucose, hormones etc. to various organs. The blood is composed of CO2, nutrients,
hormones, H20, macrophages, RBC, etc.
A schematic representation of the CV system: low levels of O2 on the left and oxygenated blood on the
right. First, blood from veins goes to right atrium → right ventricle → pulmonary artery (lungs for exchange
CO2→O2) → pulmonary veins → left atrium → left ventricle → atrium → organs in body. The heart has its
own blood supply: coronary arteries provide blood for the heart. Blood clotting/other problems lead to
angina pectoris in the coronary arteries. Capillaries in organs are permeable for nutrients and O2 are there
for exchange of these factors. Deoxygenated blood goes via veins back to the heart. Veins contain valves
which prevent returning of blood flow. These valves are not included in arteries.
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,Heart anatomy
Vena cava transports blood from organs to the heart. Superior vena cava transports blood to right atrium
→ right ventricle (has valves to prevent blood going back into right atrium) → ventricle contracts → blood
goes via pulmonary artery to the lungs for exchange CO2 to O2 → pulmonary veins → left atrium → left
ventricle → descending aorta → body. Left ventricle is thicker than right because it has to contract much
harder for the blood throughout the whole body. The thickness of the muscle is significantly higher.
Mechanical events – heart rhythm
Diastole: phase during which the heart relaxes and fills with blood. Late diastole: atria fill with blood and
valves are all open to get filled. Systole: atria and ventricles contract. As this happens, the pressure
increases and when threshold is reached, the valves to pulmonary artery and aorta opens and blood is
pumped to the vessels. Isovolumetric ventricular relaxation is the next step.
Diastole: relaxed heart, valves open, just the volume increases and pressure does not increase. End
diastolic volume: heart is completely filled, atria start to contract. The pressure starts to increase.
Isocolumetric contraction: ventricles start to contract (rise in left ventricular pressure), the valves open and
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,blood gets ejaculated into the vessels. D: ventricular ejection: pressure in left ventricle drops and blood can
flow into ventricles and atria.
A: diastole, relaxed heart. B: filled heart, atria starts contracting.
C: isovolumetric contraction: valves open and blood gets
ejaculated into the vessels. D: ventricular ejection: pressure in
left ventricle drops and blood can flow into ventricles and atria.
Electrical conduction in the heart (pacemaker cells)
One heartbeat: why? → pacemaker cells in SA node. These cells have unstable membrane potential and
they give rise to electrical current to spread around the heart. The cardiomyocytes appropogate current
to next cells with their gap junctions (intercalated disk). The membrane depolarizes and causes contraction
→ next cell contracts → and so on. If there is damage to SA node (hypoxia, etc.), then there also are other
pacemaker cells: AV node, bundle of his, they also have pacemaker activity with a lower frequency. The
main pacemaker cell is still SA node. By an influx of calcium of pacemaker cells, the action potential is
reached. The repolarization is caused by potassium.
Electrical conduction in the heart
SA node goes via the internodal pathways to the AV node (depolarization)→ small delay (prevents
contracting ventricles) in electrical conductance → AV bundle (bundle of His) → Purkinje fibers →
activation cardiomyocytes in ventricle by contraction.
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, Excitation-contraction coupling
AV node via internodal pathways, Purkinje fibers spread out over ventricles. Action potentials have
different shapes.
Refractory period
With the heart, there is a long refractory period when compared to other skeletal smooth muscles.
Refractory period: after an action potential initiates, the cardiac cell is unable to initiate another action
potential for some duration of time. This period of time is referred to as the refractory period, which is
approx. 250ms in duration and helps to protect the heart. There can be accumulation in muscles; if you
want to lift something for example. With a cardiac muscle, the refractory period is much longer; the
refractory period for cardiac muscle is almost as long as it takes for the muscles to contract. There is no
accumulation possible because of this. This is to protect the heart.
Muscle tissues
Cardiac, skeletal, smooth muscle. These muscle types differ in action potential mechanism (skeletal vs.
heart) and contraction mechanism. These mechanisms are important because they are target sites for
medication.
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