Vascular System & Vessels

What are the 2 components of the circulatory system?

• Cardiovascular system

• Lymphatic system

What are the 2 main events which are occurring in the cardiovascular system?

• Pulmonary circulation: oxygen-poor blood travels to the lungs for oxygenation via the pulmonary arteries

• Systemic circulation: oxygen-rich blood is returned to the heart via the systemic veins and is sent to the body for circulation

What are the 2 main events which are occurring in the lymphatic system?

• Draining of surplus tissue fluid & plasma proteins, & removal of debris from cellular decomposition & infection

What are the 4 main constituents of the lymphatic system?

• Plexuses

• Vessels

• Nodes

• Tissues

What is the vascular system derived from & hence where is it found?

• Derived from mesoderm

• Only present in mesoderm-derived structures (e.g. muscles, connective tissue, & dermis)

Provide some examples of avascular & non-lymph structures

• Epidermis (ectoderm)

• Surface epithelium (endoderm)

• Articular cartilage (exception for the mesoderm-derived cartilage)

State the 3 types of blood vessels

• Arteries

• Veins

• Capillaries

What type of blood leaves the arteries, & where is this blood delivered to?

• Blood under high pressure leaves the arteries

• Oxygen-rich blood is delivered to capillaries

  • Except for blood leaving the right ventricle (which goes to the lungs to be oxygenated via the pulmonary arteries)

What do the pulmonary arteries carry?

De-oxygenated blood

What is lumen?

Open area that exists in the centre of the blood vessels

What are tunics?

The 3 layers of all blood vessels

What are the 3 tunics in blood vessels, from deep → superficial?

• Tunica intima: Innermost lining, flattened epithelial cells supported by delicate connective tissue

• Tunica media: the middle tunic layer which is composed of smooth muscle, and is highly variable in its thickness relative to the lumen (which determines whether it produces arteries, veins, or lymphatic ducts)

• Tunica adventitia: outermost connective tissue layer

What are capillaries made of?

Tunica intima + basement membrane

Define the 3 types of arteries

• Conducting arteries: large elastic arteries

• Distributing arteries: medium muscular arteries

• Small arteries & arterioles

Describe conducting arteries

• Large elastic arteries

• Many elastic layers → smooth blood flow

• Near the heart, aorta & its major branches

• Endothelium < fibrous/collagenous tissues < elastic tissue < smooth muscle

Describe distributing arteries

• Medium muscular arteries

• Circular smooth muscle fibres

• Capable of vasoconstriction & blood flow regulation

• Majority of names arteries

• Endothelium < elastic tissues < fibrous/collagenous tissues < smooth tissue

Describe small arteries & arterioles

• Narrow lumina

• Thick, smooth muscle walls

• Flow into capillary beds

• Tonus regulates arterial pressure in vascular system

• Endothelium < elastic tissues < fibrous/collagenous tissues < smooth muscle

Why is elasticity in conducting arteries the highest?

• the heart pumps blood out at a very high velocity → lots of pressure behind the blood

• need to ensure smooth blood flow to the rest of the body

• elasticity in large conducting layers compensates for the spurting of high velocity blood → smooths it out for the rest of the body

Why are distributing arteries found in the periphery?

Want to vasoconstrict blood vessels when it is cold to divert blood to major organs & away from the extremities

Describe arterial bleeding & its clinical importance

• Blood flow in elastic & muscular arteries is pulsatile & at high pressure

  • Majority of larger blood vessels are arteries

  • Pulsatile blood flow reflects systole (contraction) & diastole (relaxation) BP

• Laceration to any arterial vessels (elastic or muscular) → pulsatile blood flow

Describe venous bleeding

• Larger lumen + v elasticity + v smooth muscles → lumen are largely open just by the amount of blood they have (lots of blood b/c of large lumen)

• Laceration → continuous low pressure flow

  • Happens usually from capillaries & thin-walled veins

Define & describe anastomoses

Links b/w arteries or b/w arterioles

• Provide potential detours for blood flow (collateral flow) if usual pathway is obstructed

• Adjacent arteries tend to anastomose

• Occur around joints, are significant only in muscle belly that crosses the joint

Provide an example of an anastomoses joint

Knee & elbow joints

• Joints are flexed → constriction of major blood vessel → anastomoses which occur across the major arteries allow for an alternative path of blood flow

What are end arteries?

Arteries which do not link with other arteries i.e. no anastomoses

• Not a ‘dead end’ - still branches into capillary beds drained by veins

What are the 5 principles of arteries of the limb?

1. Single stem artery

2. Changes name according to the region it traverses

3. Travels on the flexor aspect of a joint

4. Where it crosses a hinge joint the artery will anastomose to avoid compression

5. Terminal branches are generated as the artery crosses the middle joint

Provide an example of how arteries change names in response to the region it traverses

Brachiocephalic artery → axillary artery → brachial artery → radial & ulnar arteries

• Stem artery travels on the flexor aspect of a joint (anterior aspect)

• Similar to the knee; external iliac artery → femoral artery

  • Proceeds down the flexor (posterior side of the knee)

Describe the abundance & structure of arteries

• More abundant than arteries

• Walls are thinner, but diameter is larger than the corresponding artery

  • Have larger capacity for expansion than arteries

• Typically 80% of blood occupies veins

• Usually depicted as a single vessel but are typically double or multiple

  • Deep arteries accompanied by venae comitantes

    • ~ 2 or more veins : artery

What are venae comitantes?

Paired or multiple veins that closely accompany an artery, with arterial pulsations aiding venous return

How are veins named?

From distal → proximal

• Smallest caliber → largest caliber

Describe the structure of venules & small veins

• Venules = smallest drain capillary beds

  • Unnamed b/c there are so many of them)

• Small veins unite to form venous plexuses

  • Also unnamed

Describe the structure & function of medium veins

• Similar makeup to large veins

• Drain venous plexuses, accompany medium arteries

• Often named according to the artery they accompany

• Contain valves located where blood flow opposes gravity

  • Enforces one-way blood flow, preventing accumulation

Describe the structure & function of large veins

• Wide bundles of longitudinal smooth muscle

• Well-developed tunica adventitia

• Found nearer to the heart

Describe the relative tissue makeup of capillaries, venules & veins

• Capillaries: 100% endothelium

• Venules: endothelium < smooth muscle < fibrous/collagenous tissues

• Vein: Elastic tissue < endothelium < smooth muscle < fibrous/cartilaginous tissue

What are the valves in veins made of? Describe their structure

• Made of folds of the endothelium lining of the veins

• Usually a pair of cups

• Often located distal to the entry of the major tributary

How do valves enforce unidirectional blood flow?

• Enforce unidirectional flow from distal → proximal

What are the 4 key principles of veins of the limbs?

1. Superficial system of veins drains skin & superficial fascia only

2. Deep system of veins drains deeper structures

3. Paired venae comitatnes are found distally, whereas single vessels accompany arteries proximally

4. A set of communicating veins connects superficial & deep veins

   1. Superficial veins outside the deep fascia → communicating veins connect through fascial layers

What are capillaries?

Single endothelial tubes connecting arterial & venous sides of circulation

Describe the structure & function of capillaries

• Arranged in beds that connect arterioles & venules

  • Many beds named according to organs & body regions

• Allow exchange of materials w/ interstitial & extracellular fluid