PBL 4 Flashcards
how does the heart beat?
- the heart has its own pacemaker cells — contract on their own without any external nervous input
- collection of pacemaker cells at top right of atrium = sinoatrial node (SA)
- the electrical impulse generated here will spread throughout both atria and will reach the AV node
- impulse reaches the AV node before the left atrium has finished contracting
- the impulse is slowed down through the AV node, which allows the left atrium to finish contracting
- from the AV node, the impulse goes down the bundle of His and the wave of depolarisation will go down through the left and right bundle branches and then they’ll spread through both ventricles via the Purkinjie fibres.
what effect does the SNS have on the heart?
- increase HR
- increase contraction strength
- dilate coronary arteries to increase myocardial blood flow
what effect does the PNS have on the heart?
decreases HR
what makes up the cardioregulatory centre and where are they?
cardioaccelatory/pressor centre in the upper part of hte medulla oblongata, and the cardioinhibitory/depressor centre in the lower part of the MO
where does the SNS act and where does the PNS act?
SNS = pressor centre PNS = depressor centre
how does the SNS increase HR? PNS?
acts on the SAN to speed up depolarisation rate
PNS does the opposite
what nerve do the sympathetic fibres and parasympathetic fibres run down into the cardiac plexus, from which they enter the heart?
vagus nerve
where do sympathetic and parasympathetic fibres arise and originate from?
sympathetic: superior, middle and inferior cervical ganglia — T1-T4/5 (but originate in MO)
parasympathetic: originate in MO
what is rheumatic fever?
an autoimmune disease in which antibodies produced to fight a bacterial infection also attack the mitral and aortic valves. results from a streptococcal infection
what immunoglobins are most likely to cause rheumatic fever?
IgM
what happens to the heart valves in rheumatic fever?
heart valves are infiltrated with T cells — which are reacting against cardiac myosin, having been activated against the M antigen
what is rheumatic heart disease?
= a chronic condition caused by irreversible damage to the heart as a result of rheumatic fever
- leading cause of heart disease in children and young adults in the developing world
what valve is most commonly affected in rheumatic heart disease (RHD)?
mitral valve
what can the valves suffer from in RHD? are some more severe than others?
any valve can suffer from stenosis, regurgitation or both — mitral stenosis typically causes more severe disease than mitral regurgitation
how can mitral stenosis cause atrial fibrillation? mitral regurgitation?
very high atrial pressure — atrium becomes dilated — becomes very electrically active — irregular HB (fibrillation)
regurgitation: LA can become stretched — more electrically active — etc
