Cardiovascular System Flashcards
What are the three essential components of the human cardiovascular system?
Heart, blood and blood vessels
What is the pulmonary circulation?
A ‘loop’ through the lungs where blood is oxygenated
What is the systemic circulation?
A ‘loop’ through the rest of the body to provide oxygenated blood and receive deoxygenated blood
What does it mean to have a closed cardiovascular system?
Blood never leaves the network of arteries, veins and capillaries
How much blood does an average adult have?
5.0 litres of circulating blood, 2.0 litres is red cells and 3.0 litres is plasma
Out of 5 litres of circulating blood, how many litres will be in the veins?
3.25 litres
Out of 5 litres of circulating blood, how many litres will be in the heart and lungs?
1 litre
Out of 5 litres of circulating blood, how many litres will be in the peripheral arteries?
0.5 litres
Out of 5 litres of circulating blood, how many litres will be in the capillaries?
0.25 litres
What is an end artery?
An end artery (or terminal artery) is an artery that is the only supply of oxygenated blood to a portion of tissue
What are some examples of functional end arteries?
Coronary arteries, splenic artery, cerebral arteries and renal arteries
What is the best example of an absolute end artery?
Central artery to the retina
Describe blood flow in the aorta during systole and diastole
In systole, left ventricle contraction causes blood pressure in the aorta to rise to approximately 120 mm Hg. The walls of the aorta stretch.
In diastole, the aortic semilunar valve closes and the walls of the aota recoil, maintaining pressure on the blood and moving it towards the heart and smaller vessels. Aotic pressure drops to 70-80 mm Hg.
What are the three layers of the walls of arteries and veins called?
Tunica intima, tunica media and tunica adventitia
In the tunica media of the aorta, which cells produce the elastin, collagen and matrix?
Smooth muscle cells
Which is the most common site of an aneurysm?
Infrarenal abdominal aorta
Why are most abdominal aortic aneurysms infrarenal?
Less elastin fibres, weak point, predisposition to aneurysm
What is the main feature of the tunica media?
40 layers of smooth muscle cells connected by gap junctions for coordinated contraction
What are arteries with a diameter of less than 0.1mm considered to be?
Arterioles
What are arteries that supply blood to capillary beds called?
Metarterioles
What is a precapillary sphincter?
A precapillary sphincter is a band of smooth muscle that adjusts blood flow into capillaries mainly in the mesenteric microcirculation.
What can most arterioles dilate to?
60-100% of their resting diameter, or maintain up to 40% contriction fo along time
When is blood velocity at its lowest at 0.3 mm/s?
During passage through the capillaries to allow time for gas and nutrient exchange with surrounding tissues
What is a capillary made up of?
A single layer of endothelium and its basement membrane
What are pericytes?
Pericytes are contractile cells that wrap around the endothelial cells of capillaries and venules throughout the body. These cells are capable of dividing into muscle cells or fibroblasts.
Where do postcapillary venules receive blood from?
Capillaries
Why does fluid tend to drain into postcapillary venules?
This is because their pressure is lower than that of capillaries or the surrounding tissue
Where is the preferred location for emigration of leukocytes from the blood?
Postcapillary venules
How is the diameter and thickness of veins compared to arteries?
Veins have a larger diameter and thinner wall with more connective tissue and fewer elastic and muscle fibres
What do large veins have diameters of?
> 10mm
Why do superficial veins of the legs have a well-defined muscular wall?
Possibly to resist distension caused by gravity
What is capacitance?
The ability of a blood vessel to increase the volume of blood it holds without a large increase in pressure - inversely proportional to elasticity
How does blood get back to the heart through veins?
The return of blood to the heart is assisted by the action of the skeletal-muscle pump. Veins also have valves to prevent backflow.
In which veins are there no valves?
Intra-abdominal, intrathoracic and neck veins
What does calf muscle pump failure lead to?
Venous hypertension
