8. Cardiovascular & Muscle Flashcards
How much blood does the average human have, and what is its composition?
5L of blood. 2L of plasma and 3L erythrocytes.
Where does most of our blood lie ?
65% in our capillaries
20% heart and lungs
10% peripheral arteries
5% capillaries
What are the major arteries which supply the heart and where do they stem from?
The L and R coronary arteries which emerge from the aorta and divide further to supply the heart.
What is the only proper example of an absolute end artery?
Central artery to the retina
What are end arteries?
When a terminal artery supplies all or most of the blood to a body part without significant collateral circulation
E.g splenic artery, renal arteries, cerebral arteries and coronary arteries.
What develops in response to stenosis or blockage of an end artery?
Branching of the arteries to build collateral circulation.
Where is the tricuspid valve?
Right atrioventricular valve
Where is the mitral valve?
Left atrioventricular valve
What is the significant of atrioventricular delay?
The AV node delays nerve impulses to the ventricles to allow them to fill before stimulating contraction
What branches from the brachiocephalic trunk?
The right subclavian artery and the R carotid artery
What happens during systole?
The left ventricle contracts, causing blood pressure in the aorta to rise to 120 mmHg. The aortic walls stretch, elastic properties.
What happens during diastole?
The aortic semilunar valve closes and the aortic walls recoil, pressure drops to 80 mmHg.
Which layer of the arteries contains smooth muscle?
Tunica media
How do elastic arteries act as ‘pressure resovoirs’ or capacitor vessels?
During diastole, they act as auxiliary pumps, giving back the elastic energy stored during systole.
What is an aneurysm and where is the commonist site and why?
Dilation of a blood vessel. Most common in the infrarenal abdominal aorta because the junction of suprarental and infrarenal aorta contains less elastic fibres, making it weaker.
What is in the tunica adventitia?
Connective tissue containing lymphatic vessels, nerve fibres and vasa vasorum (blood vessels)
What is the different between arteries and arterioles in terms of their smooth muscle layer?
In tunica media of arteries there are 40 layers of smooth muscle, only 1-2 in arterioles
What structure regulates the flow of blood to the capillary beds?
Pre-capillary sphincters open and close to increase and reduce blood flow to the capillary beds.
How is blood flow regulated in arteries?
Most arteries can dilate 60-100% of their resting diameter. This can direct blood flow to where it is most needed. E.g during exercise increased blood flow to skeletal muscle.
Outline the structure of capillaries and how this is related to their function.
Single layer of endothelium and its basement membrane - think barrier for diffusion.
Large SA
small lumen - RBC’s virtually fill the entire lumen
Where are pericytes found?
They form a branching network on the outer surface of the endothelium in capillaries and postcapillary venues.
What are the properties of pericytes?
Capable of dividing into muscle cells and fibroblasts during angiogenesis, wound healing and tumour growth.
What is the role of post-capillary venules?
Receive blood from the capillaries and are even more permeable than capillaries with a lower pressure, so fluid is drawn into them.
They are the preferred location for leukocyte emigration from the blood.
Explain how veins act as capacitance vessels.
Capacitance is inversely proportional to elasticity. Veins have thin NON-ELASTIC so they can stretch a great deal but do not recoil.
Ability of the vessels to increase the volume of blood without increasing blood pressure.
What are 3 mechanisms which help venous return to the heart from the legs?
- Calf muscle pump
- Pressure changes in the thorax act as a ‘vacuum’ by increasing and decreasing atrial pressure
- One-way valves in veins of lower limbs, upper limbs and heart
Which veins contain NO valves?
Intrabdominal, intrathoracic and neck veins
What does the frank starling curve represent?
Stroke volume of the heart increases in response to increased filling.
As sarcomeres are more stretched, due to more filling, they can pump more effectively…up to a certain point when ‘over-stretched’ and cannot contract.
What is the consequence of calf muscle pump failure?
Venous hypertension
Why does left ventricular heart failure lead to pulmonary oedema?
It will lead to a back up of blood in the pulmonary arteries which will increase hydrostatic pressure,
Why is pulmonary oedema worse when lying flat?
More blood is returning to the heart
A symptom of LVF is Orthopnea, what does this mean?
Shortness of breath when lying flat
What are some causes of LVF?
Aortic stenosis - age related
Hypertension - increased ‘afterload’
What are 3 indicators of muscle injury?
Troponin 1 (cardiac muscle) - HF indicator Creatine Kinase (skeletal muscle, heart muscle) - MI indicator Myoglobin
What are some diseases caused by smooth muscle dysfunction?
Asthma, irritable bowel syndrome, primary hypertension
What is the first symptom of right sided heart failure?
Pitting oedema around the ankles. Back up of blood in vena cava, increased venous hydrostatic pressure.
What is the significance of fixed mottling?
indicated there is absolutely no circulation whatsoever, irreversible ischaemia.
What normally happens in post-capillary venules?
Fluid enters the vessel, as they are much lower pressure
What happens in post-capillary venules during infection?
Emigration of leukocytes and fluid
When would you see skin staining?
Venous hypertension, as red blood cells leave the capillaries and iron is oxidised to stain skin - dark appearance.
What does calf muscle pump failure cause?
venous hypertension
