The cardiac system Flashcards
What are the 6 main differences between cardiac and skeletal muscle?
- Cardiac has a long action potential whereas skeletal has a short one
- Skeletal muscle can have tetanus but cardiac cannot due to the long A.P. the heart must relax before it contracts again
- Some cardiac cells have an unstable AP
- The intercalated disks of cardiac muscles have alternating gap junctions and desmosomes
- Where skeletal muscle have multiple nuclei per cell cardiac has only one but acts as a syncytium
- Calcium from outside of the cell can regulate contraction strength as it does not saturate troponin
describe the process of non-pacemaker action potential
- Resting membrane potential: high resting PK+
- Initial depolarisation: Increase in PNa+
- Plateau: increase in PCa2+ (l-type), decrease in PK+
- Repolarisation: Decrease in PCa2+ (l-type), increase in PK+
Describe the process of a pacemaker action potential
- Action potential: Increase in PCa2+ (L-type)
- Pacemaker potential (pre-potential): Gradual decrease of PK+, early increase in PNa+ and a late increase in PCa2+ (t-type)
What type of drugs modulate electrical activity?
- Ca2+ channel blockers: decrease the force of contraction
- Cardiac glycosides: Increase the force of contraction
What (other than drugs) modulate electrical activity?
- Temperature (increases about 10 beats/min/*C)
- Hyperkalaemia: fibrillation + heart block
- Hypokalaemia: Fibrillation + heart block
- Hypercalcaemia: Increases force of contraction + HR
- Hypocalcaemia: Decreases force of contraction + HR
name the different parts of the heart that are for conducting
- sinoatrial node: pacemaker (fastest)
- atrioventricular node: delay box
- Bundle of His
- Purkinje fibres: rapid conducting system
What does the P wave correspond to?
atrial depolarisation
What does the QRS complex correspond to?
Ventricle depolarisation
What does the T wave correspond to?
Ventricle repolarisation
What is an atheroma?
The formation of large focal elevated lesions (plaques) in the intima of large and medium sized arteries
What is the earliest significant lesion and when does it form?
The earliest significant lesion is a fatty streak which forms in young children. It is a yellow linear elevation of the intimal lining and comprises of masses of lipid-laden macrophages. It has no clinical significance and may go away, however, patients are at risk of going on to form atheromatous plaques.
What are the early atheromatous plaques and when are they formed?
Formed in young adults, early atheromatous plaques are smooth yellow patches in the intima made of lipid-laden macrophages and can progress to form established plaques
What are fully developed atheromatous plaques?
They have a central lipid core with a fibrous tissue cap and is covered by the arterial endothelium. They are soft, highly thrombotic and often have a rim of foamy macrophages.
Why are the macrophages in atheromatous plaques described as foamy?
Due to the uptake of oxidised lipoproteins via specialised membrane bound scavenger receptors
Where do the atheromatous plaques tend to form
Bifurcations or at branching points (turbulent flow)
What is the fibrous tissue cap composed of?
There is collagen (produced by smooth muscle cells) in the cap to provide structural strength along with inflammatory cells recruited from the endothelium.
What happens in late development of the atheromatous plaques?
There is extensive dystrophic calcification and the plaques are confluent and cover large areas.
What are the risk factors of atheroma?
- Hypercholesterolaemia
- Smoking
- Hypertension
- Diabetes mellitus
- Male
- Elderly
- Obesity
- sedentary lifestyle
- Low socioeconomic status
- Low birthweight
- Role of microorganisms
How is an atheromatous plaque formed?
- A microscopic injury to the endothelial lining of the artery
- Chronic inflammation and healing response of the vascular wall to the agent causing injury
- Accumulation of lipoproteins (LDL) in the vessel wall
- Monocyte adhesion to the endothelium results in migration to the intima and transformation into foamy macrophages
- Platelet adhesion
- Factor release from activated platelets
- Smooth muscle cell proliferation, extracellular matrix production and T cell recruitment - Chronic/ episodic exposure of the arterial wall to these processes cause the formation of atheromatous plaque
What are the causes of endothelial injury?
- Haemodynamic disturbances (turbulent flow)
- Hypercholesterolaemia
How are the injured endothelial cells functionally altered?
- Enhanced expression of cell adhesion molecules (ICAM-1, E-selection)
- High permeability for LDL
- Increased thrombogenicity
- Inflammatory cells in the intima causes plaques
What is plaque growth initiated by?
small areas of endothelial loss
What are the clinical manifestations of progressive lumen narrowing due to high grade plaque stenosis?
- Stenosis of 50-75% of the vessel lumen causes a critical reduction in blood flow in a distal arterial bed which, in turn, causes reversible ischaemia
- e.g. stenosis of the atheromatous coronary artery can cause stable angina
- Very severe stenosis causes ischaemic pain at rest (unstable angina)
- e.g. ileal, femoral, popliteal artery stenosis results in intermittent claudication (peripheral arterial disease)
- Longstanding tissue ischaemia results in atrophy of affected organ
What are the clinical manifestations of an acute atherothrombotic occlusion?
- Major complications: rupture of plaque results in an acute event
- Rapture exposes highly thrombotic plaque contents (collagen, lipid, debris) to the bloodstream which results in the activation of a coagulation cascade and thrombotic occlusion in a very short time
- Total occlusion causes ischemia which leads to necrosis of tissue
What are the clinical manifestations of embolisation of the arterial bed?
- Detachment of thrombus fragments from thrombosed atheromatous arteries which embolise distally to ruptured plaque
- Embolic occlusion of small vessels cause small infarcts in organs
What are the clinical manifestations of ruptured atheromatous abdominal aortic aneurism?
- Media beneath atheromatous plaques generally weakened
- This results in gradual dilation of the vessel
- Slow but progressive, seen in elderly, often asymptomatic
- Sudden rupture results in a massive retroperitoneal haemorrhage
- Mural thrombosis results in an embolism to the legs
What are the clinical manifestations of a vulnerable atheromatous plaque?
- Typically have a thin fibrous cap, a large lipid core and prominent inflammation
- Pronounced inflammatory activity results in degradation and weakening of the plaque which results in an increased risk of plaque rupture
- Secretions of proteolytic enzymes, cytokines and reactive oxygen species by plaque inflammatory cells
- Highly stenotic plaques often have a large fibrocalcific component with little inflammation
What is the preventative therapy of atheroma?
- Stop smoking
- Control blood pressure
- Weight loss
- Regular exercise
- Dietary modifications
- Cholesterol lowering drugs
- Surgical options
What are the complications of Hypertension?
- Brain: stroke, haemorrhage, cognitive decline
- Heart: LV hypertrophy, coronary heart disease, congestive heart failure and MI
- Kidneys: Renal failure, dialysis, transplantation and proteinurea
- Peripheral vascular disease
- Retinopathy (eyes)
What is the definition of hypertension?
-Blood pressure above which the benefits of treatment outweigh the risks
What is the definition of stage 1 hypertension?
- Clinical blood pressure: 140/90 or higher
- ABPM: 135/85 or higher
What is the definition of stage 2 hypertension?
- Clinical blood pressure: 160/100 or higher
- ABPM: 150/95 or higher
What is sever hypertension?
Clinical BP: 180/110 or higher
What are the underlying causes of secondary hypertension?
- Chronic renal disease
- Renal artery stenosis
- Endocrine disease, cushings, Conn’s syndrome, phaeochromocytoma, GRA
- Pregnancy (pre-eclampsia)
- Coarctation of the aorta
- Sleep apnoea
What are the drugs that ca cause hypertension?
- NSAIDs
- Oral contraceptives
- Corticosteroids
What are the risk factors of hypertension?
- Smoking
- Diabetes myelitis
- Renal disease
- Male
- Hyperlipidaemia
- Previous MI or stroke
- LV hypertrophy
- Age
- genetics
- Environment
- Weight
- Alcohol intake
- Race
- Diet
What is the aetiology of Hypertension?
- Polygenic: Major genes, Poly genes
- Polyfactorial: environmental, individual and shared
What do you have to think about if you’re thinking of treating hypertension?
- Identifying true hypertension
- Assess risk (look at risk factors)
- Assess end organ damage
- screen for treatable causes
- treatment should be started at an overall CVD risk of 20%/10 years
When should the young (under 80) with stage 1 hypertension be given treatment?
If they have one of the following
- established cardiovascular disease
- target organ damage
- renal disease
- diabetes
- CV risk > 20%/10 years
When should the young be given treatment with stage 2 hypertension?
whenever they have it
What is the step 1 treatment for over 55 year olds or Afro-Caribbeans?
- Calcium channel blocker (CCB)
- if CCB not suitable or if there is evidence or a high risk of HF: Thiazide-like diuretic
What is step 1 treatment for under 55’s
ACEI/ARB
What is step 2 treatment?
Add thiazide-like diuretics to CCB or ACEI/ARB
What is step 3 treatment?
-Add all three classes (CCB, ACEI, Diuretic) together
What is step 4 treatment?
- Blood K+ < 4.5mmol/l: low dose spirnolactone
- Blood K+ > 4.5mmol/l: higher dose thiazide-like diuretic
Give an example of an ACEI
Rampril
What does ACEI do?
competitively inhibit the actions of ACE
What are the contraindications of ACEI?
- Renal artery stenosis
- Renal failure
- Hyperkalaemia
What are the adverse drug reactions of ACEI
- Cough
- First dose hypo-tension
- taste disturbance
- Renal impairment
- angioneurotic oedema
What are the drug-drug interactions of ACEI?
- NSAIDs (precipitate acute renal failure)
- Potassium supplements (Hyperkalaemia)
- Potassium sparing diuretics (Hyperkalaemia)
give 4 examples of ARB (angiotensin II agonists)
Losartan, Valsartan, Candesartan, Irbesartan
What does ARB do?
competitively block the actions of angiotensin II at the angiotensin ATI receptor
What advantage does ARB have over ACEI?
No cough
Give two examples of vasodilator calcium channel blockers
Amlodipine and Felodipine
Give two examples of rate limiting calcium channel blockers
Verapamil and Diltiazem
What are the contraindications of CCBs?
- Acute MI
- HF, bradycardia
What are the adverse drug reactions of CCBs?
- Flushing
- Headache
- Ankle oedema
- Indigestion and re-flux esophagus
- Rate limiting: Bradycardia and/or constipation
Name two Thiazide type diuretics
Indamide and clortidone
Where has Thiazide type diuretics proven beneficial?
MI an stroke reduction
What does thiazide type diuretics do?
Urinary excretion of sodium but it may take weeks to be fully effective
What are the adverse drug reactions of thiazide type diuretics?
- Gout
- Impotence
Give two examples of vasodilators
Minoxidil and Hydralazide
Give an example of an alpha-adrenoreceptor antagonist
Doxazosin
What does alpha-adrenoreceptors do?
selectively blocks post-synaptic alpha 1-adrenoreceptors
What are the adverse reactions of alpha-adrenoreceptors?
- First dose hypertension
- Dizziness
- dry mouth
- headache
Give two examples of centrally acting agents
Methyldopa and Moxonidine
What are the adverse reactions of Methyldopa?
- Sedation
- drowsiness
- Dry mouth
- Nasal congestion
- Oethostatic hypotension
What is the definition of stable angina?
A discomfort in the chest and/or adjacent areas with myocardial ischaemia but without myocardial necrosis.
What is the overall pathophysiology of angina?
A mismatched supply of O2 and metabolites to the myocardium and the myocardial demand for them.
What are the 4 causes of angina?
- A reduction in blood flow
- Reduced O2 transport: anaemia
- Pathological increased demand for O2
- Thyrotoxicosis
What is the reduction in blood flow to the myocardium caused by?
- Obstructive coronary atheroma
- Coronary artery spasm
- coronary inflammation/ arteritis
What might increase the myocardial demand for O2?
LV hypertrophy: as seen in persistent hypertension, significant aortic stenosis and hypertrophic cardiomyopathy.
What is the characteristics of the pain of angina?
- Site: retrosternal
- character: tight band/ pressure/ heaviness
- Radiation: neck and/or jaw, down arms
- Aggregation: exercise, emotional stress
- relieving factors: rapid improvement with GTN (1-3mins) or physical rest
What other symptoms will there be if there is no pain?
- Breathlessness on exertion
- Excessive fatigue for activity undertaken
- Near syncope on exertion
What 6 features make angina less Likely?
- Sharp/ stabbing pain: pleuritic or pericardial (worse in different positions)
- Associations with body movements or respiration
- very localised site
- No pattern to pain, particularly if occurring at rest
- Begins sometime after rest
- Lasting for hours
What are the risk factors of angina?
- age
- gender
- creed
- family history
- Genetic factors
- smoking
- Life style: diet and exercise
- Diabetes myelitis
- Hypertension
- Hyperlipidaemia
What bloods would you have done to diagnose angina?
- full blood count
- lipid profile
- fasting glucose
- electrolytes
- liver and thyroid tests
What is the reason for taking a CXR in angina?
It shows pulmonary oedema
What will an electrocardiagram show in angina?
- Evidence of an MI: pathological Q waves
- LV hypertrophy: high voltages, lateral ST-segment or “strain pattern”
What are the advantages of a myocardial perfusion test?
Superior to ETT in detection of CAD, localisation of ischaemia and assessing size of affected area
What are the disadvantages of the myocardial perfusion test?
- Expensive
- Involves radioactivity
What are the drugs that are used for pharmacological induced stress?
- adenosine
- dipyramidamole
- dubutamine
What happens in a myocardial perfusion test if the heart is normal?
It takes up the tracer both before and after stress
What happens in a myocardial perfusion test if the heart is ischaemic?
tracer seen at rest but not after stress
What happens in a myocardial perfusion test if there was an infarction?
Tracer would not be seen at rest or stress
What happens in a myocardial perfusion test if there is angina?
Tracer would not be seen at rest but would be seen in stress
What are the general measures of treatment of stable angina?
address risk factors: BP, cholesterol, lifestyle
What drugs are used to treat angina?
- statins
- ACEI
- Aspirin
- beta blockers
- calcium channel blockers
- IK channel blockers
- Nitrates
- Potassium channels blockers
When do you consider the use of statins in the treatment of angina?
If the total cholesterol is > 3.5 mmol/l
What do statins do?
They reduce the deposition of LDL-cholesterol in atheroma reducing plaque ruptures and ACS
When are ACE inhibitors used in the treatment of angina?
If there is an increased cardiovascular risk and atheroma
What do ACE inhibitors do in the treatment of angina?
They stabilise the endothelium and also reduce plaque ruptures
What is the alternative drug for aspirin in the treatment of angina?
Clopidogrel
What does aspirin do in the treatment of angina?
It protects the endothelium and reduces platelet activation/ aggregation
What are the beta blockers for?
to achieve resting HR, reducing myocardial work and has anti-arrhythmic effects
What do the CCBs do?
achieve resting heart rate and it is central acting
What does IK channel blockers do?
achieve resting heart rate. Ivabradine reduces sinus rhythm
What do nitrates do?
produces vasodilation
Name a potassium channel blocker
nicorandil
What is a percutaneous coronary investigation (PCI)
A surgeon crosses a stenotic lesion with a guide wire and squashes the atheromatous plaque into the walls with a balloon and stent
what medication is needed if this coarse of action is taken?
-take aspirin and clopidigrel together whilst the endothelium covers the stent. Disease modifying drugs are still needed though.
Does this work?
There is no evidence of an improved prognosis in angina
When is coronary artery bypass grafting (CABG) the best option?
In diffuse multivessel
What is the advantages of CABG?
Good lasting benifit
What is the disadvantages of CABG?
you must continue the disease modification medications and the graft deteriorates after 10 years.
name 7 problems that can cause defects in blood flow
- Thromboembolism
- Atheroma
- Hyperviscosity
- Spasm
- External compression (tumour)
- Vasculitis
- Vascular steel (vessel steels blood from another)
What are the three factors that cause thrombosis?
- Changes in the blood vessel wall
- Changes in the blood constitutes
- Changes in the pattern of blood flow
What are the outcomes of thrombosis?
- resolution
- Organisation/ recanalisation
- Death
- Propagation which leads to an embolism
What is an embolism?
Movement of abnormal material in the blood stream and its implantation in the vessel, blocking the way
What are the different types of embolism?
- Thrombosis
- Systemic thrombosis
- Paradoxical embolism
- Fat embolism
- Gas embolism
- tumour
- trophoblast
- septic material
- Amniotic fluid
- Foreign bodies
what are the sources of a thrombosis?
- Mural thrombosis
- aortic aneurysm
- atheromatous plaques
- valvular vagitation
What is a paradoxical embolism?
In the venous circulation and causes what is effectively known as a stroke
What is a systemic thrombosis?
It travels to a wide verity of sites: lower limbs (most common), brain, other organs
What are the consequences of a systemic thrombosis?
depends on vulnerability of effected tissue to ischaemia, calibre of occluded vesicle, collateral circulation but usually infarction occurs
What are the most common signs of a fat embolism?
- confusion
- renal disease
- rash
From where to where does standard limb lead 1 go (negative to positive)?
Right arm to left arm
From where to where does standard limb lead 2 go (negative to positive)?
From the right arm to the left leg
From where to where does standard limb lead 3 go (negative to positive)?
Left arm to left leg
What type of events are transmitted better on an ECG? fast or slow events?
Fast
What is the heart doing at each point in the ECG?
-P wave: SA node depolarises
-Q wave: the AV node depolarises and the interventricular septum depolarises from left to right
-R wave: Atrial relaxation and the bulk of the ventical depolarises from the endocardial to the epicardial surface
-S wave: The upper part of the interventricular septum depolarises
T wave: ventricle repolarisation
What does each wave of the ECG signify?
P wave: atrial depolarisation
QRS complex: Ventricle depolarisation
T wave: ventricle repolarisation
Why is the T wave positive?
The action potential is longer in the endocardial cells than the epicardial cells and the wave for repolarisation runs in the opposite direction to the wave of depolarisation
What does STEMI mean?
ST elevated myocardial infarction
What does NSTEMI mean?
Non ST elevated myocardial infarction
What is worse a STEMI or a NSTEMI and why?
A STEMI as an elevated ST segment seems to indicate something has gone seriously wrong
What are the 5 major stages of heart development?
- Bilateral Heart primordia
- Primitive heart tube
- Heart looping
- Arterial and ventricular septation
- Outflow tract septation
When does the primordial heart start to develop?
at the beginning of week 4 as the embryo is rapidly growing and so diffusion is not fast enough
What is the real name foe paired endothelial strands and when and where do they appear?
angioblastic cords appear in the carcinogenic medoderm in the third week
What is the pericardium derived from?
intra-embryonic coelom
What is each layer of the pericardium developed from?
- parietal (fibrous + serous): somatic mesoderm
- Visceral (Serous): Splanchnic mesoderm
Where does each horn of the sinus venosus get blood from?
- The yolk sac (viteline v.)
- The placenta (Umbilical v.)
- Body of the embryo (common cardinal v.)
Where do the aortic arches arise from?
The aortic sac
Where do the aortic arches terminate?
dorsal aorta
Why does the heart loop?
The bulbous cordis and the ventricle grows faster than the other regions forming a U-shaped bulboventricular loop
What is dextrocardia?
Heart tube loops to the left side instead of the right
When is atrial and ventricular septation seen?
around the 27-30th day of embryonic development
When does the partitioning of the primordial atrium into left and right start?
At the end of week 4
What is the opening between the septum primum and the endocardial cushion
Ostium primum
What is the role of the oval foreman before birth?
- Allows most of the blood o pass through the right atrium to the left atrium (non-functioning lung)
- Prevents passage of blood in the opposite direction
What are the roles of the oval foremen after birth?
- normally closes (increased pulmonary blood flow and shift of pressure to the left atrium)
- Septum primum fuses with septum secundum
- Oval fossa of an adult heart is a ruminant of the oval foremen
Name the four clinically significant types of atrial septum defects
- Foremen secundum defect
- Endocardial cushion defect
- Sinus venosus defect
- common atrium
What is the opening in the muscular ventricular septum called?
Interventricular foremen
How does the interventricular foremen close?
Aorticopulmonary septum rotates and fuses with the muscular ventricular septum
When does the partitioning of the bulbous cordis and truncus arteriosus happen?
During the 5th week of development
What are the early pacemakers?
Primordial atrium and then sinus venosus
When does the SA node develop?
During the 5th week
What is the aetiology of CHD?
- Rubella infection in pregnancy
- Maternal alcohol abuse
- Maternal drug treatment and radiation
- genetics
- Chromosomal: down’s syndrome and turner’s syndrome
What are the causes if transposition of great vessels?
- Failure of aorticopulmonary septum to take a spiral coarse
- Defect migration of neural crest cells
What is the first stage of the cardiac cycle?
Late diastole: both sets of chambers are relaxed and the verticals fill passivly
What is the second stage of the cardiac cycle?
Atrial systole: Atrial contraction forces a small amount of additional blood into the ventricals
What is the third stage of the cardiac cycle?
isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed bat does not create enough pressure to open the semilunar valves
What is the fourth stage of the cardiac cycle?
ventricular ejection: as ventricular pressure rises and exceeds the pressure in the arteries, the semilunar valve opens and blood is ejected
What is the fifth stage of the cardiac cycle?
isovolumic ventricular relaxation: as the ventricles relax, pressure in the ventricles falls, blood flows back into cusps of the semilunar valves and snaps them closed
What is the first heart beat noise?
The mitral and the tricusped valves closing
What is the second heart beat noise?
The aortic and the pulmonary valves closing
What is it that the sympathetic nervous system releases?
Noradrenaline plus circulating adrenaline from adrenal medulla
What receptors do adrenaline and Noradrenaline act on in the heart?
Beta 1 receptors on the sinoatrial node
What does the binding of adrenaline and Noradrenaline to beta 1 receptors do to the heart?
Increases the slope of action potential increasing the heart rate (tachycardia)
What does the parasympathetic system release and from where?
acetylcholine from the Vegas nerve
What receptors does acetylcholine work on in the heart?
Muscurinic receptors on the sinoatrial node
What does the binding of acetylcholine to muscurinic receptors do to the heart?
It hyperpolarises cells and decreases and decreases the slope of the pacemaker potential decreasing the heart rate (bradycardia)
What is preload?
The energy of contraction is proportional to the initial length of cardiac muscle
What is preload effected by in vivo?
It is effected by the end diastolic volume
What happens to stroke volume if there is a decreased venous return
decreased EDV and therefore decreased stroke volume
What is afterload?
The load against which the muscle tries to contract
What happen to stroke volume if the total peripheral resistance increases?
Aortic pressure will increase and so the ventricles will have to work harder to push open the aortic valve and it will have less energy to do the useful bit of contraction i.e. stroke volume will decrease
How does the sympathetic nervous system effect stroke volume?
It increases contractility: gives stronger, shorter contractions
How does the parasympathetic system effect stroke volume?
It has little effect, probably because the vagus nerve doesn’t innervate the ventricular muscles
How does hypercalcemia effect stroke volume?
it increases stroke volume
How does hypocalcaemia effect stroke volume?
it decreases stroke volume
How does ischaemia effect stroke volume
it decreases stroke volume
How do barbiturates effect stroke volume?
it decreases stroke volume
What structures are anterior to the heart?
- Sternum
- Left costal cartilages 4-7
- Anterior edges of lungs and pleura
- Thymic ruminants
What structures are posterior to the heart
- Esophagus
- Descending aortic arch
- Thorasic vertebrae 5-8
What structures are lateral to the heart?
- Lungs
- Phrenic nerve
What structures are inferior to the heart?
Central tendon of the diaphragm
What are the layers of the heart wall (in order of inside to outside)?
- Endocardium
- Myocardium
- Intercalated disks
- Epicardium
- Epithelium
What tissues make up the Endocardium?
- Simple squamous epithelium
- Basement membrane
- Connective tissue
What is the role of the Endocardium?
- Lines the heart chambers
- Forms valves
Describe the myocardium
- Cardiac muscles (myocytes)
- Striated muscles, lots of mitochondria
- Rich capillary bed
- myocytes connected by intercalated disks
Describe intercalated disks
- Complex junctions that connect myocytes
- Desmosomes: connects at horizontal interface to bind myocytes together
- Gap junctions: connects at vertical interface for electrical communication, this is essential to the cardiac cycle
Describe the Epicardium
- connective tissue, basement membrane and simple squamous epithelium
- The epicardium contains the main branches of the coronary arteries
- -may be fatty
What is the endothelium?
The same layer as the visceral pericardium
What holds the heart in place?
- Hangs by great vessels within the fibrous pericarium
- Dense connective tissue bag
- Attachments: Central tendon of diaphragm, sternum, roots of great vessels
- Lined by serous pericardium
What is the serous pericardium made from?
Epithelium
What does the serous pericardium do?
It secretes pericardial fluid (lubricant) that allows freedom of movement during the cardiac cycle
What are the three layers of a basic blood vessel?
- Tunica intima
- Tunica media
- Tunica adventisia
What type of cells does the tunica intima have?
- Simple squamous epithelium
- Basement membrane
- connective tissue
What is the tunica media made up of?
- Smooth muscle
- Elastic tissue
What is the tunica adventitia made up of?
Fibrous connective tissue
What are the differences between arteries and veins?
- Arteries have a smaller diameter than accompanying veins
- Arteries have thicker walls
- Arteries have a thick tunica media and a thin tunica adventitia
- Veins have a thin tunica media and a thick tunica adventitia
What are the three types of arteries?
- Elastic
- Muscular
- Arterioles
What type of vessel is elastic arteries
Large conducting
Give some examples of elastic arteries
- The aorta
- The common carotid
- Pulmonary
What do elastic arteries do?
- Pressure reservoir
- Stretched during systole
- During diastole the heart relaxes, the pressure falls and the artery recoils maintaining pressure on the blood
Why are elastic arteries so stretchable and able to recoil?
There is an excessive amount of elastic fibres in the tunica media in the form of layers (laminae). These layers are stretched by smooth muscles
What type of vessel are muscular arteries?
distrabuting
Give some examples of muscular arteries
- Coronary arteries
- Radial
- Femoral
What do muscular arteries do?
Control the distribution of blood to regions
What are muscular arteries composed of?
- T. intima: endothelial cells, BM
- Thick T. media has smooth muscle cells
- No elastic lamina between the muscle cells in the T. media
- Elastic fibres are concentrated in two defined sheets called the internal elastic lamina (IEL) just under the spithelium and the extenal/outer elastic lamina (OEL) between the T. media and the T. adventitia
What do arterioles do?
- they are terminal branches which supply blood to the capillary bed
- Controls blood flow to the capillary beds (local)
- Controls blood pressure (systemic)
What are arterioles made of?
- T. intima: endothelium, BM, no IEL
- 1-2 layers of smooth muscle in the t. media
- no t. adventitia
- Rich sympathetic nerve innervation
What do capillaries do?
main exchange site for nutrients and gasses
What are capillaries made up of?
- Very thin walled
- T. intima only: endothelium on BM
- no T. media
- no T. adventitia
- Pericytes: incomplete layers of cells surrounding the BM, they have contractile properties which help control the flow of blood in the capillaries
Is the BP in capillaries low or high?
Low
What are the three types of capillaries?
- Continuous
- Fenestrated
- Discontinuous
What is the role of continuous capillaries?
- Control of what is exchanged
- Material must pass through the cell or between the cell (junctions can control)
- Selective transport mechanisms
How do the protein diaphragms in some of the fenestrations filter molecules?
-MW and/ or charge
How is there free passage of fluid and cells in discontinuous capillaries?
There are gaps between the endothelial cells (and BM)
Where would you find continuous capillaries?
Muscles
Where would you find fenestrated capillaries
endocrine glands, kidney, renal capuscle
Where would you find discontinuous capillaries?
Liver, spleen and bone marrow
What are sinusoids?
- Large diameter discontinuous capillaries
- Found where a large amount of exchange is taking place (liver, some endocrine glands)
- T. intima contains a large amount of phagocytic cells
What is the structure of veins?
- Thin T. intima
- IEL or OEL is thin ir absent
- T. media is very thin or absent
- T. adventitia: collagenous tissue valves (to prevent backflow) endothelial projections into the lumen
Describe superficial veins
- Thick walled
- No surrounding support
Describe Deep veins
- Thin walled
- Surrounding support from the deep fascia and muscles
What does the lymphatic system do?
- Drains tissue fluid from lost blood capillaries
- Drains into the venous system
- Nodes found alongside major veins and around the origin of major arteries
- Valves direct flow
- Clinically important in tumour cell metastasis
Describe lymph capillaries
- Blind ended capillaries
- Lines by very thin endothelium
- No fenestrations
- Absent/ rudimentary basal lamina
- Lumen maintained at negative hydrostatic pressure
- Anchoring filaments: fine collegenous filaments link endothelial cells to surrounding tissue keeping lumen open
- No red blood cells in lumen
What does ischaemia mean?
relative lack of blood supply to a tissue/organ leading to inadequate O2 supply to meet the needs of the tissue or argan
What is hypoxic hypoxia?
- Low inspired O2 level
- Normal inspired O2 but low PaO2
What is anaemic hypoxia?
normal inspired O2 but blood abnormal
What is stagnant hypoxia?
Normal inspired O2 but abnormal delivery
- Local e.g. occlusion of vessel
- systemic e.g. shock
What is cytoxic hypoxia
Normal inspired O2 but abnormal at tissue level
What factors effect Oxygen supply?
- Inspired O2
- Pulmonary function
- Blood constitutes
- Blood flow
- Integrity of vasculature
- Tissue mechanisms
- Supply issues
- Demand issues
- Localised accumulation of lipid and fibrous tissue in the intima of arteries
What sort of supply issues affect oxygen delivery?
- coronary artery atheroma
- Cardiac failure (flow)
- Pulmonary function- other disease or pulmonary oedema
- Anaemia
- Previous MI
What sore of demand issues affect oxygen delivery?
- Heart as high as intrinsic demand
- Exertion/ stress increases the demand
What are the clinical consequences of ischaemia?
- MI
- TIA
- Cerebral infarction
- Abnormal aortic aneurysm
- Peripheral vascular disease
- Cardiac failure
- coronary disease
What are the different effects ischaemia has?
- Functional
- Acute (you will see the changes)
- Chronic (may go unnoticed for a while)
- Acute on chronic (sudden worsening of a chronic event)
- Biochemical
- Cellular
- Clinical
What are the functional effects Ischaemia has?
- Blood/ O2 supply fails to meet the demand due to decreased supply, increased demand or bith
- Related to rate of onset
What are the biochemical effects ischaemia has?
-Decreased O2 leads to anaerobic respiration which can causes cell death (the change in biochemistry leads to cell death)
What are the cellular effects ischaemia has?
-Different tissue have variable O2 requirements and are variably susceptible to ischaemia
What are the clinical effects of ischaemia?
- Dysfunction
- Pain
- Physical damage (specialised cells are effected the most)
What is the outcome of ischaemia?
- No clincal effect
- Resolution verses therapeutic intervention
- May lead to infarction
What is infarction?
Ischaemic necrosis within a tissue/organ in a living body produced by occlusion of either the arterial supply or venous damage
What is the aetiology of infarction?
- Thrombosis
- Embolism
- Trauma
What are the four thing the scale of damage depends on?
- time period
- Tissue/ organ
- Pattern of blood supply
- Previous disease
What happens if a myocardial infarction happens for seconds?
Anaerobic metabolism, onset of ATP depletion