Introduction to Circulation Flashcards
What is the function of the heart and blood vessels?
Heart and blood vessels evolved to transport oxygen, nutrients, waste products and heat around the body quickly
Diffusion vs the cardiovascular system
Diffusion is sufficient for small, primitive organisms
It is vital for transport over short distances
Cardiovascular system is in place due to the limitations of diffusion
What is diffusion?
Diffusion is a passive process driven by the random thermal motion of molecules
Metabolic energy does not play a part
How do particles move in diffusion?
The path is known as a random walk (example of brownian motion)
When a concentration gradient is present, the random walk leads to a net movement of solute down its concentration gradient.
Why is rate of diffusion important?
It needs to keep up with cellular demand
What formulas relate diffusion time?
x^2 is directly proportional to t where x is the distance of the particle from starting position and t is time
t = x^2/D where D is the diffusion coefficient
Hence diffusion is faster over small distances (eg. 0.1um neuromuscular junction) but slow over larger ones (eg. O2 over 1m of tissue takes 7 years)
What factors affect the diffusion coefficient?
- Size of the molecule
- Temperature
- Viscosity of medium
Describe how convection (bulk flow) in the body works
The cardiovascular system dissolves substances in a fluid and flows it to where it is needed
The energy for this is provided by the contraction of the heart.
What is the primary function of the cardiovascular system?
The primary function of the CV system is rapid convective transports of nutrients and waste
What are the two circulation circuits called?
Systemic and Pulmonary Circulation
Give one similarity between the two circuits of the heart
They both originate and terminate at the heart
Name the chambers of the heart
Upper chambers: right and left atria
Pumps: right and left ventricles
Blood in the two halves do not mix
Is the heart connected in series or in parallel? Comment on the volume and pressures of blood pumped
They are connected in series so the same volume of blood is pumped through both sides but the pressures differ
How do the right and left side of the heart differ?
The right side
- Pumps deoxygenated blood through the pulmonary artery to the lungs
- Low pressure
The left side
- Pumps oxygenated blood through the aorta to the body
- High pressure
Is systemic circulation parallel or series?
Parallel
Heart directly connects to organs such as brain, heart wall etc.
Ensures good perfusion
Name type of system connected in series and some of the disadvantages
Portal systems eg. liver and kidney
Secondary organs receive partially deoxygenated blood under lower pressure
Downstream tissue vulnerable to damage during hypotension (low arterial pressure)
Name the 3 layers of blood vessels (except capillaries)
- Tunica intima (innermost)
- Tunica media (middle)
- Tunica adventitia (outermost)
Describe the tunica intima
- Endothelial cells on basal lamina
- Main barrier to escape of plasma
- Secretes vasoactive agents such as the vasodilator NA
Describe the tunica media
- Smooth muscle allows contraction
- Collagen fibers provide strength
- Elastin fibers allows stretchiness
Describe the tunica adventitia
- Maintains large arteries by having a blood supply
- Tethers vessel to surrounding tissue
- Few mechanical advantages
What are the adaptations of the aorta and other large arteries?
- Elastic as they contain a lot of elastin
- Allows expansion by 10% each heart beat to accommodate ejected blood
- Recoil during diastole smoothes out flow downstream
- Collagen prevents over distension
What are the adaptations of arteries?
- Tunica media thicker and contains more smooth muscle
- Can contract and relax (rich autonomic innervation)
- Spasm and contract to close in injury
What are the functions and adaptations of terminal arteries and arterioles (resistance vessels)?
- Regulate BP and control blood flow
(Vasodilation: resistance falls, blood flow increases)
(Vasoconstriction: resistance rises, blood flow decreases) - Large drop in pressure due to large increase in resistance
(Small lumen and few vessels) - Sympathetic innervation do so by contracting posses lots of smooth muscle
What are the adaptations of capillaries?
- Large network of vessels (most tissue cells are within 10-20um of a capillary)
- Wall is a single endothelial cell thick (allows fast diffusion)
- Capillary bed has low resistance despite narrow vessels due to large parallel array
What do most capillary venules do (15 - 50um)
- Some exchange also occurs here
- Lacks a smooth muscle coat
What are the adaptations of capacitance vessels?
Veins ( 50 - 200um)
- Thin walls contain a thin layer of smooth muscle and collagen (intima of limb veins contain semilunar valves )
- Net resistance is low
- Contains 2/3 of circulating blood at one instant
- Easily distended or collapsed (act as a variable store, many are innervated by vasoconstrictor fibers, can constrict and displace blood into heart and arteries)
What is laplace’s law?
- Larger vessels must have thicker walls are they are under greater tension for the same internal fluid pressure
- T = Pr
- T = tension of vessel per unit length
- P = pressure
- r = radius of vessel
