10. Blood vessels Flashcards
On entering the circulation, what is the route that newly formed red blood cells travel?
Venule —> intermediate vein —> larger vein —-> vena cava
When do red cells become mature?
During circulation RBCs become mature – 2 days
What route does newly formed white blood cells take?
Venule —> intermediate vein —> larger vein —-> vena cava
When do white cell become mature?
- T cells need the actions of the thymus and lymphatics
* B cells already mature
How are sinusoids different from continuous and fenestrated capillaries?
Sinusoids have a discontinuous endothelium and an incomplete basement membrane. Thus permit the free exchange of water and large solutes like plasma proteins.
What controls flow in capillaries?
precapillary sphincters (little muscles)
Where are precapillary sphincters (little muscles)located?
• Located between arterioles and capillaries
How do precapillary sphincters work?
- Contain smooth muscle - contraction of smooth muscle of sphincter narrows capillary entrance
- When open, blood flows freely to the capillary beds
- When closed (sphincters contracted), blood is not allowed to flow through the capillary beds
What is the function of precapillary sphincters?
- Controls fluid exchange between the capillaries and the body tissues takes place at the capillary bed
- Larger cells cannot pass through capillaries and bypass the capillary bed
What is a vein?
A vein is an elastic blood vessel that transports blood from various regions of the body to the heart
What are the 3 layers of veins?
- Tunica intima – endothelial cells
- Tunica media – elastic fibres and smooth muscle cells
- Tunica externa – elastic fibrous capsule
What in veins assist flow towards the heart?
Non-return fibroelastic cartilaginous valves assist flow towards the heart - prevent backflow
What kind of a pressure system are veins?
Low pressure system
Why wold vein problems occur?
due to either a blood clot or a vein defect behind the valves
What are the 4 main vein types?
- Pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart
- Systemic veins return non-oxygenated blood from the rest of the body to the right atrium of the heart
- Superficial veins that are located close to the surface of the skin and are not located near a corresponding artery
- Deep veins are located deep between tissues and are typically located near a corresponding artery with the same name (for example femoral artery and vein). They are surrounded by viscera and organs
Describe vein size
• A vein can range in size from 1 mm to 1-1.5 cm in diameter
• Smallest veins in the body are venules - They receive blood from arterioles and capillaries
• The venules branch into larger veins - eventually carry the blood to the largest veins in the body, the
vena cavae
• The superior vena cava and inferior vena cava drain into
the right atrium of the heart
• Superior and inferior vena cavae are the largest veins
What are arteries?
Arteries are elastic blood vessels that convey blood away from the heart
What are the 3 layers of arteries?
- Tunica Intima - composed of an elastic membrane lining and smooth endothelium (non-fenestrated)
- Tunica Media - composed of smooth muscle and elastic fibres. This layer is thicker in arteries than in veins and has two distinct elastic layers
- Tunica Externa (adventia) - the strong outer covering composed of collagen and elastic fibres
How does the structure of arteries help with its function
ARTERIES have thick, strong walls, elastic fibres and smooth muscle which help to provide the strength and elasticity needed to withstand high blood pressure, maintain the pressure and prevent bursting. The smooth muscles contract to increase the blood pressure and relax to lower the blood pressure. They have a narrow lumen to maintain high blood pressure.
How does the structure of capillaries help with its function
CAPILLARIES have very thin walls and very narrow lumen to bring blood into close contact with body tissue to allow diffusion of substances between capillary an surrounding tissue. No need for strong walls as most of the blood pressure has been lost
How does the structure of veins help with its function
Have thin walls as no need for strong walls as most of the blood pressure has been lost. Wide lumen offers less resistance to blood flow. Valves work against gravity to help prevent back flow. Low pressure system so needs contraction of muscles to aid blood flow
What are the differences between arteries and veins?
- Walls of arteries are much thicker to deal with the higher BP - tunica media of an artery contains more smooth muscle
- Veins have a larger lumen
- veins have valves and arteries don’t
- veins have less elastic fibres and smooth muscle as lower blood pressure so low risk of bursting
What are collateral blood vessels?
Collateral blood vessels are small capillary-like branches of an artery that form over time in response to narrowed coronary arteries. The collaterals “bypass” the area of narrowing and help to restore blood flow.
When are collateral blood vessels formed?
- Some generated due to chronic disease such as ischaemia (reduced blood flow)
- Some produced during development (e.g. brain and joints)
What is vasculogenesis?
Formation of new blood vessels from angioblast precursors (bone marrow)
What is angiogenesis?
Formation of new blood vessels from existing blood vessels
Give examples of when angiogenesis occurs
During fetal development, collateral arteries, postnatal lung development
Describe the two types of vasculogenesis
First steps:
Production of a single vessel
• VEGF produced by endoderm
• Generates primary plexus, which folds into a primary vessel
- Sprouting: Angiogenesis
• FGF produced by mesenchymal cells • Pericytes convert into smooth muscle cells
• Slow, takes hours to days - Division of primary vessel: Intussusception
• Twinned vessels from primary vessel
(e.g. ‘splitting one vessel into two’)
• Needs multiple growth factors
• Explains why arteries and veins are close together in
‘neurovascular bundles’ •
Quick, takes minutes to hours
What is pericyte?
• Immature ‘smooth muscle-like’ cell Found inside the basal lamina close to basement membrane • Key component of capillaries • Have contractile properties • Also involved in nerve cell communication • Blood-brain barrier
What are pericytes able to differentiate into?
endothelial cell, smooth muscle cell or
fibroblast
What are the functions of pericytes?
• Prevents endothelial cell proliferation
• Maintains tight capillaries, e.g. blood
brain barrier, in the retina, etc.
Give examples of when vasculogenesis occurs
During embryo development
(heart and primitive vascular plexus), newly formed cancers, endometriosis, etc.
What are the functions of collateral blood vessels?
- Collateral vessels (usually arterioles) provide protection for tissues that may become compromised
- Provide alternative path for arterial blood flow
