Vascular Physiology Flashcards
(48 cards)
What are the different types of blood vessels?
Aorta and Pulmonary artery Arteries Arterioles Capillaries Venules Veins
Describe the features of blood flow hydraulics
Blood flow will always be from an area of high pressure down to an area of low pressure.
As blood flows from the arteries, it goes down a pressure gradient.
As we get down to the veins and the venules we have a very low pressure.
What is the normal blood pressure in the different blood vessels?
Aortic pressure 120mmHg
Systemic pressure varies between 120-80mmHg
Pulmonary pressure varies between 25-10mmHg
Pressure in veins is virtually zero
Describe the structure of blood vessel walls
All vessels except capillaries have three layers:
- Tunica Intima- endothelial cells (barrier and secretions) on connective tissue basal lamina
- Tunica media- smooth muscle cells (circular- contraction) in elastin and collagen fibres
Internal and external elastic laminae = sheets of elastin at boundaries
- Tunica adventitia/ externa- connective tissue sheath to hold the vessel in place.
Large vessels have vasa vasorum- own vessels in adventitia; and sensory nerve fibres
What are the two different types of arteries?
Elastic arteries
Conduit or muscular arteries
Give examples of elastic arteries
Pulmonary artery
Aorta
Iliac artery
Describe the structural features of elastic arteries
1-2 cm diameter
Very distensible walls
Rich in elastin- protein more extensible than rubber
Expand to receive stroke volume
Recoil to produce continuous flow
Collagen in media to prevent over distension
Give examples of muscular arteries
Popliteal, radial, cerebral, coronary
Describe the structural features of muscular arteries
0.1-1cm Thick tunica media Lots of smooth muscle Low resistance Prevent vessel collapse at bends Rich autonomic nerve supply Contract or relax to regulate flow
Describe the features of arterioles
Resistance vessels
Large fall in pressure
Describe the functional features of elastic arteries
They are elastic and they recoil when they receive the flow of blood out of the heart.
Blood gets ejected into the aorta, the force of the blood causes the wall to expand.
As the pressure falls in the blood vessel, we will then see the recoil of that stretched artery. It acts as a pump in itself. It squeezes the blood into one part of the artery into the next.
Elastic arteries are able to expand as they have the protein elastin. There are lots of elastin fibres present in the artery walls.
The collagen fibres give them strength.
Describe the functional features of arterioles
These contain a large amount of smooth muscle, which gives them the capacity to have a lot of control to how the blood flow is directed through particular organs.
They supply the organs directly with blood.
They have a good nerve supply for control and so the blood flow can be regulated.
They are simpler structures compared to the arteries.
Describe the features of terminal arterioles
The terminal arterioles directly feed the capillaries.
Some are able to take part in gas exchange.
When the terminal arteriole is constricted, it will stop blood flow going through that particular capillary bed.
The reason that you get this vasomotion is because of the relaxation and constriction of the terminal arterioles.
Some terminal arteriole have a little muscle at the end of them called a pre capillary sphincter.
What blood vessels are capable of gas exchange
Terminal arterioles- oxygen Continuous capillaries Fenestrated capillaries Discontinuous capillaries Pericytic venules- fluid exchange
Where is the main area of gaseous exchange?
The main area of exchange in the capillaries.
The continuous capillaries is the typical capillary.
Discontinuous capillaries are in specialised tissues.
Depending on which capillaries are present depends on how much exchange can take place in each muscle.
What are the structural features of the capillaries?
4-7mm diameter Numerous- cells never more than 10-20mm Single layer of endothelial cells on basal lamina (connective tissue) Rapid diffusion Very large cross sectional area Modest resistance to flow for small size Slow velocity for exchange
What are the functional features of the capillaries?
There are millions of capillaries in our bodies.
Substances can be taken into the endothelial cell.
As well as substances passing from the blood into the tissues, we get substances moving in the opposite direction, from the tissues into the bloodstream.
The blood flow goes through the capillaries very slowly, this gives plenty of chances for the exchange to take place.
Describe the features of continuous capillaries
These are your general type of capillary.
Found in muscle, skin, lung, fat, connective tissue, nervous system
Circumference of 1-3 endothelial cells on basement membrane
Diffusion distance is very small
Pericytes envelop the capillary (provides nourishment to the endothelial cells)
Describe the features of fenestrated capillaries
Higher permeability
Specialist areas of fluid exchange
Renal glomerulus and tubules, glands, intestinal mucosa
Endothelium perforated by fenestrae or windows
Allow molecules to 0.1mm of extravascular space
Bridged by extremely thin membrane- fenestral diaphragm sandwiched between basement membrane and glycocalyx
Major pathway of water and metabolite transport
Signals (e.g. VEGF) induce fenestration
Describe the features of discontinuous (or sinusoidal) capillaries
Large gaps over 100nm wide Discontinuity in underlying basal lamina Permeable to plasma proteins Allow red cells to migrate between blood and tissues Bone marrow, spleen, liver
What is an arteriovenous anastomosis?
A vessel that shunts blood from an artery to a vein in order to bypass a capillary.
Describe the features of arteriovenous anastomoses?
Present in skin and nasal mucosa Wide shunt vessels 20-135µm Connect arterioles to venules Bypass capillaries Thick muscular walls Rich nervous innervation Temperature regulation
Describe the features of venules and veins
50- 200mm Venules
Thin wall with thin media
Limb veins have semilunar valves to prevent backflow of blood
Large central veins and and veins of head and neck have no valves
Low resistance
Low pressure 10-15 mmHg
Large number
Veins contain about 2/3 of blood volume- capacitance vessels
Distend or collapse easily- ‘reservoirs’
Vasoconstrictor nerve fibres to control reservoirs
What are the different types of vascular circuit?
Parallel circuits
- Most organ supplies arise separately from aorta
- Prevents loss of pressure
Series circuits
- Portal systems in series
- Get flow ‘second hand’ to transport substances
- Oxygen may be reduced
- Eg. Liver, kidney, brain
