1.04 Medical Sciences

what are the 3 main stages of atherosclerosis formation?

1) endothelial damage

2) uptake of LDLs and macrophage adhesion

3) smooth muscle proliferation to form fibrous cap

what causes endothelial damage?

- shear stress (increased by hypertension)

- toxic damage (cigarette smoke)

- exposure to high concs of LDLs

- glycosylation of proteins

how are LDLs and macrophages taken up? (4)

- LDLs enter the artery wall through damaged endothelium

- LDL gets modified by oxidation

- this causes endothelial cells to attract inflammatory cells

- monocytes cross endothelium and become macrophages

what do the macrophages do? (3)

- phagocytose modified LDLs unrestrictedly

- accumulated in large droplets called foam cells

- lipids released from foam cells and accumulate in subendothelial space

how does smooth muscle proliferation occur? (3)

- damaged endothelial cells release growth factors

- growth factors cause proliferation of smooth muscles cells and collagen which cover the plaque

- increases the size and forms a fibrous cap

what happens in plaque rupturing? (2)

- the fibrous cap can fissure, erode or rupture, exposing the lipid core

- triggers coagulation cascade

- blood clot is formed

what could happen to the thrombus?

- could completely occlude artery (lead to death)

- could embolise (small parts break off) and block off smaller distal arterial branches

what are the two types of risk factors for atherosclerosis?

- non-modifiable

- modifiable

what are some non-modifiable risk factors? (4)

- age

- gender

- family history

- race

what are some modifiable risk factors? (6)

- lipid intake

- smoking

- hypertension

- diabetes mellitus

- obesity

- lack of exercise

what can happen as a response to an occlusion of an artery?

reactive hyperaemia

what is reactive hyperaemia?

tissue ischaemia causes vasodilation, to try and increase the blood flow to the area

where can you auscultate the aortic valve?

2nd intercostal space - right of sternum

where can you auscultate the pulmonary valve?

2nd intercostal space - left of sternum

where can you auscultate the tricuspid valve?

4th intercostal space - on the right or left of sternum

where can you auscultate the mitral valve?

5th intercostal space - left midclavicular line

draw a diagram of the different auscultation sites of the heart

what is the first heart sound (S1)?

lub

what causes the lub sound?

closing of av valves

where can you hear the lub sound the best?

same as mitral valve:

- 5th intercostal space - left midlavicular line

what is the second heart sound (S2)?

dub

what causes the dub sound?

closing of the semilunar valves

where can you hear the dub sound the best?

same as pulmonary valve:

- 2nd intercostal space - left of sternum

where is erb's point?

third left intercostal space mid clavicular

what is the point of erb's point?

aortic regurgitation can be heard as a murmur here

what causes a positive deflection in an ecg?

depolarisation towards lead OR repolarisation away from lead

what causes a negative deflection in an ecg?

repolarisation towards the lead OR depolarisation away from lead

what does a normal ecg look like?

what causes the p wave?

atrial depolarisation

why does atrial depolarisation form a positive deflection?

depolarisation of atria towards the lead

what causes the flat line between the p wave and qrs complex?

the artioventricular septum temporarily blocking the depolarisation

what causes the qrs complex?

ventricular depolarisation

why does ventricular depolarisation have 3 parts?

1st part - depolarisation of interventricular septum - bundle of his

2nd part - depolarisation at apex

3rd part - depolarisation moving up lateral walls

what does the qrs complex hide?

atrial repolarisation

what causes the t wave?

ventricular repolarisation

why does ventricular repolarisation form a positive deflection?

repolarisation away from lead

what are the electrodes surrounding the heart called?

pre-cordial

how many pre-cordial electrodes are there?

6

where do you place v1?

4th intercostal space to the right of the sternum

where do you place v2?

4th intercostal space to the left of the sternum

where do you place v4?

5th intercostal space - midclavicular line

where do you place v3?

between v2 and v4

where do you place v6?

5th intercostal space - midaxillary

where do you place v5?

5th intercostal space - between v4 and v6 - anterior axillary line

where do you place the other 4 leads?

- right arm

- left arm

- right leg

- left leg

what is the lead going to the right arm called?

aVR

what does aVR stand for?

augmented vector/voltage right arm

what is the lead going to the left arm called?

aVL

what does aVL stand for?

augmented vector/voltage left arm

what is the lead going to the left leg called?

aVF

what does aVF stand for?

augmented vector/voltage foot

which lead is the ground lead?

right leg

what forms the 3 other views of the heart?

communication between:

- right arm and left arm (lead I)

- left leg and right arm (lead II)

- left arm and left leg (lead III)

(like a triangle)

which are the bipolar leads?

leads I, II and III

which leads are inferior?

II, III, aVF

what do the inferior leads detect?

inferior border of heart - receiving blood from right coronary artery

which leads are lateral?

I, aVL, V5, V6

what do the lateral leads detect?

lateral wall - receiving blood from left circumflex artery

which leads are septal?

V1, V2

what do the septal leads detect?

along the anterior interventricular septum - receiving blood from left anterior descending/anterior interventricular artery

which leads are anterior?

V3, V4

what do the anterior leads detect?

along anterior wall of heart - receiving blood from the left anterior descending/anterior interventricular artery

which leads would lead to an anterolateral MI?

II, aVL, V3, V4, V5, V6

which vessel would II, aVL, V3-6 detect?

left coronary artery - LCA

what are the 6 layers of the heart?

- endocardium

- myocardium

- epidcardium/visceral layer of serous pericardium

- pericardial cavity

- parietal layer of serous pericardium

- fibrous pericardium

what is the endocardium also called?

tunica intima

what does the endocardium line?

atria, ventricles and valves

what is the endocardium made up of?

simple squamous epithelium

what is another name for the myocardium?

tunica media

what does the myocardium contain?

cardiac muscle fibres and endomysial connective tissue with capillaries

what is another name for the epicardium?

tuncia adventitia/visceral layer of the serous pericardium

what does the epicardium consist of?

simple squamous mesothelium

what does the parietal layer of serous pericardium consist of?

simple squamous mesothelium

what does the fibrous layer of pericardium consist of?

connective tissue

what is the fibrous layer of the pericardium continuous with?

central tendon of the diaphragm

what is the pathway of conductivity in the heart? (5)

- sinoatrial node

- atrioventricular node

- His bundle

- either right or left bundles

- Purkinje fibres

what is the effect of parasympathetic innervation of SA node? (3)

- acetylcholine acts of M2 muscarinic receptors at SA node

- lengthens the interval between pacemaker potentials

- slows heart rate

which nerve delivers the parasympathetic innervation of the heart?

vagus nerve (CNX)

what is the effect of sympathetic innervation of the SA node? (3)

- noradrenaline acts on B1 adrenoceptors

- shortens interval between pacemaker potentials by making it steeper

- increases heart rate

which nerve supplies sympathetic innervation to the heart?

sympathetic cardiac nerves

what is the intrinsic heart rate without autonomic inputs?

100bpm

what is the actual normal resting rate and why?

60bpm - parasympathetic system dominates at rest

what is initial increase in heart rate caused by?

decrease in parasympathetic outflow

what is further increase in heart rate caused by?

increase in sympathetic outflow

what are the 3 types of blood vessels?

- arteries

- veins

- capillaries

what are the 4 types of arteries?

- large elastic (conducting) arteries

- medium muscular (distributing) arteries

- arterioles

- metarterioles

what are the 3 layers of large and medium arteries?

- tunica intima

- tunica media

- tunica adventitia

what are the 3 components of the tunica intima?

- endothelium

- subendothelium

- internal elastic lamina

what are the 3 components of the tunica media?

- myocytes

- elastin

- collagen

what lies in between the tunica media and tunica adventitia?

external elastic lamina

what are the 3 components of the tunica adventitia?

- fibres

- fibroblasts

- vasa vasorum (neurovascular bundle)

which layers do arterioles not have?

- internal elastic lamina

- external elastic lamina

how is smooth muscle arranged in metarterioles?

rings called precapillary sphincters

what are the 2 layers of capillaries?

- endothelium

- basement membrane

what are 3 types of capillaries?

- continuous

- fenestrated

- sinusoidal

where are continuous capillaries found? (2)

muscles and skin

what can pass through continuous capillaries? (2)

- water

- some ions

where are fenestrated capillaries found? (2)

kidneys and small intestine

what can pass through fenestrated capillaries?

slightly larger molecules

where are sinusoid capillaries found? (3)

spleen, liver and bone marrow