the circulatory system Flashcards
(27 cards)
what are the functions of circulation?
- maintain optimal environment for cells (transport nutrients and waste, maintain pH…)
- transport hormones: communication
what are the different types of blood vessels?
- Arteries – transport blood away from the
heart, therefore under high pressure - Veins – transport blood to the heart
- Capillaries – exchange transported material
with interstitial fluid (between vessels and
cells)
what is the anatomy of a blood vessel?
Vessel walls:
1. Adventitia: fibroblasts and fibrous elements gradually merge with
surrounding connective tissue
2. Media: elastic fibers, collagen fibers and circumferentially
arranged smooth muscle cells
3. Intima: endothelial cells, surrounded by subendothelium (
collagen and smooth muscle) and elastic fibers
what are the different types of arteries?
- Elastic arteries – convert pulsative flow into smoother continuous flow
- Muscular arteries – contain smooth muscle but less elastic fibers
resistance vessels: - Terminal arteries – diameter 100-150μm
- Arterioles – diameter 10-100 μm; control release of blood to capillaries
veins
- thinner walls than arteries but muscular so can act as reservoir (approx. 2/3 of blood is in veins)
- contain valves to ensure one-way blood flow
- small veins (50-200 μm diameter) are called venules
- helped by muscular pump
venules
Venules consist of an endothelial layer surrounded by longitudinal smooth muscle and occasional pericytes
What conditions will cause relaxation of the precapillary
sphincters?
- High CO2
- low pH
- increased body temperature (fever)
what are the different types of capillaries?
- continuous capilliaries: fat, muscle, nervous system
- fenestrated capilliary: intestinal villi, endocrine glands, kidney glomeruli
- discontinuous capilliary: liver, bone marrow, spleen
continuous capilliaries
- diffusion distance is around 300 μm
- solute exchange can occur through intercellular clefts or caveolae-mediated
transport - occur in fat, muscle and the nervous system
fenestrated capillaries
- Fenestrae have a diameter of 50-60 nm; usually closed by 4-5 nm membrane
- One order of magnitude more permeable to water and small water-soluble substances than continuous capillaries
- intestinal villi
- endocrine glands
- kidney glomeruli
discontinuous capillaries
- gaps may be 100 nm wide
- permeable to plasma proteins
- occur in liver, bone marrow and spleen
pericytes
repair blood vessels
hydrostatic pressure
The pressure in the circulatory system exerted by the volume of blood when it
is confined in a blood vessel
osmotic pressure
The pressure exerted by the flow of liquid through a semi-permeable
membrane separating two solutions with different concentrations of solute
what does Darcy’s law about blood flow tell us?
- blood flow is proportional to the difference in pressure between the two ends of the blood vessel
- flow ocurs from high to low pressure
what are the three different types of flow in blood vessels?
- laminar
- turbulent
- single- file
laminar flow
- most efficient
- fluid moves paralell to the walls of the vessel
- occurs in arteries, arterioles, venules and veins
turbulent flow
- occurs in the heart ventricles and also behind atherosclerotic lesions
- difficult to move perpendicular to wall
- if pressure difference is above a critical point, transition to
turbulent flow occurs
single-file flow
- occurs in capilliaries
- friction between blood cells and vessel wall minimised by glycocalyx or a thin film of plasma
- efficiency depends on erythrocyte ability to change shape; impaired in some clinical conditions
how is blood flow controlled?
- arterioles
- widespread constriction leads to increase in peripheral
resistance and blood pressure
what are the two sources of blood control?
- Intrinsic: blood flow control due to local factors
- Extrinsic: blood flow control by factors outside the organ (e.g. circulating
hormones, nerve stimulation); often capable of overriding intrinsic
system
intrinsic blood flow control
- myogenic response (response to stretching)
- vasodilator metabolites
- endothelial factors
- autocoids (local hormones)
- in skin: temperature
what are the properties of nitric oxide?
- Nitric oxide is a diatomic free radical consisting of one atom of nitrogen and one atom of oxygen
- Lipid soluble and very small for easy passage between cell membranes
- Short lived, usually degraded or reacted within a few seconds
- The natural form is a gas
in what way can smooth muscle contract?
- mechanical stretching
- electrical depolarisation
- hormones (eg: noradrenaline)
