structure and function of blood vessels

Question 1

explain the principles of angiogenesis

Answer 1

formation of new arteries and veins
1st stage: vasculogenesis = formation of blood vessels from endothelial progenitor cells (angioblasts issues from the mesoderm during embryogenesis)
2nd stage: angiogenesis = the sprouting of new capillaries from pre-existing vessels
occurs during:
- fetal and post-natal development (metabolivally active tissue needs to be “close” to a capillary for gaseous exchange)
- limited in adults (principally in female reproduction, uterine/ovarian changes and placental development)
- pathology (wound healing, skin/heart disease, tumour development)
- in response to hypoxia

switched on and off by pro-angiogenic factors or anti-angiogentic factors (angioblastin etc)

Question 2

describe the concept of the vascular tree and how this canv ary between species

Answer 2

vscular tree = the blood is sent in parallel: each tissue receives fresh blood from the heart and not from other tissues
- split into 2 parts: systemic circulation and pulmonary circulation
portal system: few organs connected in series and they obtain their blood second hand from other organs. advantage is to transport solute from one place to another without dilution in the general circulation (i.e. hepatic portal vein from Gi to liver and renal portal vein from hind limbs to kidney

Question 3

compare the pressure and volume of different blood vessels

Answer 3

arteries and arterioles: high pressure, contain ~15% of blood volume
venules and veins: low pressure. contain ~80% of blood volume (reservoid of blood
capillaries exchange system - intermediate pressure, contain ~5% of blood volume

Question 4

describe the structure of blood vessels from inside out

Answer 4

• lumen
• enothelium
• tunica intima (interna) (smooth muscles, collagen and elastin)
• interna elastic lamina (made of elastin)
• tunica media (smooth muscles, collagen and elastin)
• external elastic lamina (made of elastin)
• tunica adventitia (or externa) (made of collagen and elastin

veins contain valves within lumen to keep blood flow unidirectional

Question 5

why do arterioles need a lot of smooth muscle

Answer 5

increased contractile ability allows to decrease pressure before entering capillaries

elastin allows for recoil of vessel
collagen allows for strength or solidity of the vessel

Question 6

explain the pressure variance in different blood vessels

Answer 6

• a high level of elastin and collagen in the aorta damp the oscillating cardiac output when the blood leaves/is pushed out of the heart
• the arterioles are composed of smooth muscle cells that can contract diminishing the radius of the arterioles. a decrease in the readius results in a corresponding increase in blood pressure. as a result contraction of arterioles regulates the blood pressure and they provide resistance to blood flow (important for capillaries)
• **capillaries **have no collagen or elastin and have relatively low blood pressure. low pressure is a good design for capillaries because theyre fragile (high pressure would tear them) and they are very permeable. (high pressure forces a lot of fluid out = oedema)
• veins have high collagen but low elastin and dont need to recoil, just capture volume coming from capillaries

Question 7

describe the mechanism for nutrient exchange

Answer 7

• diffusion (O2, CO2, glucose, hormones, electrolytes diffue down concentration gradients)
• Lipid soluble molecules can pass through cell membrane easily (drugs/therapeutics)
• water soluble molecules generally require transport mechanisms to enter/exit cells

Question 8

what are the 3 types of capillaries

Answer 8

continuous: continuous lining of endothelial cells except for clefts between cells (found in majority of body)
fenestrated: fenestrations are not true holes but rather where the cell membrane is compressed to permit greater fluid transmission (found in glomerular capillaries in the kidney)
discontinuous sinusoid: some wider intercellular gaps permit increased exchange with surrounding tissues (found in liver, bone marrow, lymphoid tissue, some endocrine glands)

Question 9

describe mechanisms of venous return

Answer 9

• the venous return depends on the pressure difference between venules and RA (changes in the RA pressure changes venous return)
• smooth muscles contraction in the tunica media (small amount)
• inspiration/lower diaphragm/abdominal comression (physcial moevement)
• existence of venous valves to prevent backflow
• skeletal muscles (contraction against veins during movement)
• gravitation (for upper part of body)

Question 10

what are the main functions of blood circulation

Answer 10

• to transport gases to and from organs/tissues
• to deliver nutrients
• to remove waste
• to communicate
• to maintain cardiac output pressure
• to maintain a constant temperature (for warm blood animals)