10. Blood vessels

Question 1

On entering the circulation, what is the route that newly formed red blood cells travel?

Answer 1

Venule —> intermediate vein —> larger vein —-> vena cava

Question 2

When do red cells become mature?

Answer 2

During circulation RBCs become mature – 2 days

Question 3

What route does newly formed white blood cells take?

Answer 3

Venule —> intermediate vein —> larger vein —-> vena cava

Question 4

When do white cell become mature?

Answer 4

• T cells need the actions of the thymus and lymphatics

* B cells already mature

Question 5

How are sinusoids different from continuous and fenestrated capillaries?

Answer 5

Sinusoids have a discontinuous endothelium and an incomplete basement membrane. Thus permit the free exchange of water and large solutes like plasma proteins.

Question 6

What controls flow in capillaries?

Answer 6

precapillary sphincters (little muscles)

Question 7

Where are precapillary sphincters (little muscles)located?

Answer 7

• Located between arterioles and capillaries

Question 8

How do precapillary sphincters work?

Answer 8

• 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

Question 9

What is the function of precapillary sphincters?

Answer 9

• 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

Question 10

What is a vein?

Answer 10

A vein is an elastic blood vessel that transports blood from various regions of the body to the heart

Question 11

What are the 3 layers of veins?

Answer 11

• Tunica intima – endothelial cells
• Tunica media – elastic fibres and smooth muscle cells
• Tunica externa – elastic fibrous capsule

Question 12

What in veins assist flow towards the heart?

Answer 12

Non-return fibroelastic cartilaginous valves assist flow towards the heart - prevent backflow

Question 13

What kind of a pressure system are veins?

Answer 13

Low pressure system

Question 14

Why wold vein problems occur?

Answer 14

due to either a blood clot or a vein defect behind the valves

Question 15

What are the 4 main vein types?

Answer 15

• 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

Question 16

Describe vein size

Answer 16

• 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

Question 18

What are arteries?

Answer 18

Arteries are elastic blood vessels that convey blood away from the heart

Question 19

What are the 3 layers of arteries?

Answer 19

• 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

Question 20

How does the structure of arteries help with its function

Answer 20

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.

Question 21

How does the structure of capillaries help with its function

Answer 21

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

Question 22

How does the structure of veins help with its function

Answer 22

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

Question 23

What are the differences between arteries and veins?

Answer 23

• 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

Question 24

What are collateral blood vessels?

Answer 24

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.

Question 26

When are collateral blood vessels formed?

Answer 26

• Some generated due to chronic disease such as ischaemia (reduced blood flow)
• Some produced during development (e.g. brain and joints)

Question 27

What is vasculogenesis?

Answer 27

Formation of new blood vessels from angioblast precursors (bone marrow)

Question 28

What is angiogenesis?

Answer 28

Formation of new blood vessels from existing blood vessels

Question 29

Give examples of when angiogenesis occurs

Answer 29

During fetal development, collateral arteries, postnatal lung development

Question 30

Describe the two types of vasculogenesis

Answer 30

First steps:
Production of a single vessel
• VEGF produced by endoderm
• Generates primary plexus, which folds into a primary vessel

1. Sprouting: Angiogenesis
   • FGF produced by mesenchymal cells • Pericytes convert into smooth muscle cells
   • Slow, takes hours to days
2. 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

Question 31

What is pericyte?

Answer 31

• 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

Question 32

What are pericytes able to differentiate into?

Answer 32

endothelial cell, smooth muscle cell or

fibroblast

Question 33

What are the functions of pericytes?

Answer 33

• Prevents endothelial cell proliferation
• Maintains tight capillaries, e.g. blood
brain barrier, in the retina, etc.

Question 34

Give examples of when vasculogenesis occurs

Answer 34

During embryo development

(heart and primitive vascular plexus), newly formed cancers, endometriosis, etc.

Question 35

What are the functions of collateral blood vessels?

Answer 35

• Collateral vessels (usually arterioles) provide protection for tissues that may become compromised
• Provide alternative path for arterial blood flow