Vascular System

Question 1

Understand the layered structure of vessels and describe how these layers differ between arteries, veins and lymphatic vessels

Answer 1

• All blood vessels have 3 layers (tunics) surrounding
  the lumen
• Veins have thinner tunics, larger lumen

Tunics of blood vessel walls
- Tunica intima
- Innermost lining, flattened epithelial cells
supported by delicate connective tissue
- Capillaries have only this tunic + basement
membrane
- Tunica media
- Middle layer, mainly smooth muscle
- Most variable – thickness relative lumen
differentiates arteries, veins, lymphatic ducts
- Tunic adventitia
- Outermost connective tissue layer or sheath

Question 2

Name the types of arteries and arterial branches and understand their structural components

Answer 2

• Blood passes through arteries of decreasing calibre,
  which is a continuum

1. Large Elastic Arteries (conducting):
   
   • Many elastic layers, resulting in the smooth flow of
     blood
   • Near the heart, aorta and its major branches
2. Medium muscular arteries (distributing):
   
   • Circular smooth muscle fibres, capable of
     vasoconstriction + blood flow regulation
   • Majority of named arteries
3. Small arteries and arterioles:
   
   • Narrow lumina, thick smooth muscle walls
   • Flow into capillary beds, tonus regulated arterial
     pressure in the vascular system

Question 3

Describe the functional role of anastomoses

Answer 3

• Anastomoses are links between arteries or between
  arterioles
• Provide potential detours for blood flow (collateral
  flow) if usual pathway is obstructed
• By joint position, pathology, surgical ligation
• Adjacent arteries tend to anastomose
• Occur around joints, are significant only in muscle belly
  that crosses a joint

Question 4

Describe the anatomical components of veins and venous tributaries

Answer 4

Types of Veins:
- Return low O2 blood from capillary beds to the heart, are more abundant than arteries

 Venules + small veins:
o Venules are the smallest drain capillary beds, and are unnamed
o Small veins unite to form venous plexuses, which are unnamed

 Medium veins:
o Drain venous plexuses, accompany medium arteries
o Often named according to artery they accompany
o Contain valves where blood flow opposed gravity (e.g. limbs)

 Large veins:
o Wide bundles of longitudinal smooth muscle
o Well-developed tunica adventitia

Valves in veins:
- Folds of endothelium lining veins, usually a pair of cusps
- Enforce unidirectional blood flow from distal to proximal
- Often located distal to the entry of major tributary

Principles of veins of the limbs:
1. Superficial system of veins drains skin and superficial fascia
2. Deep system of veins drains deeper structures (muscles vs skin)
3. Paired venae comitantes distally, single vessels proximally accompanying arteries
4. A set of communicating veins connects superficial and deep vein
> superficial veins outside of deep fascia, communicating veins connect through fascial layers

Question 5

Understand the principles of venous return including the thoracic and musculovenous pump

Answer 5

• Vascular smooth muscle has tone (continuous partial contraction)
• Modulated by visceral motor nerves – vasomotor nerves from neighbouring peripheral nerves
• Almost exclusively part of the sympathetic nervous system

Vascular venous pumps
- Venous flow returning to atria due to blood pressure, contraction of skeletal muscle, respiratory oscillation of intrathoracic pressure

 Vascular venous pumps result of the arrangement of venae comitantes
o Connective tissue resists expansion, arterial pulsation compresses blood in veins, valves direct flow proximally

 Musculovenous pump
o Main method of venous return from limbs
o Expansion of contracting muscles limited by fascia
o Muscles contraction “milks” blood superiorly

 Thoracic venous pump
o Double pump mechanism linked to respiration
o Descent of diaphragm during inspiration shortens IVC (emptying it) and lengthens SVC (filling it)
o In expiration diaphragm ascends, SVC shortens and empties, IVC lengthens and fills

Question 6

Understand the functional role of lymph vessels and lymph nodes

Question 7

Name the major sites of lymph nodes and other lymphoid tissues

Question 8

Describe the principles of lymph nodes and other lymphoid tissues

Question 9

Describe the principles of lymph flow and the neurovascular supply of lymph vessels

Question 10

Understand the two divisions of the circulatory/vascular system

Answer 10

1. Cardiovascular system
   > Pulmonary circulation
   
   • O2 poor blood going from the heart to the lungs for
     oxygenation via the pulmonary arteries coming from
     the right ventricle of the heart
   • The oxygenated blood then returns through the
     pulmonary veins to the left atrium and then the left
     ventricle
   • The blood then enters systemic circulation

> Systemic circulation
- Left ventricle pumps O2-rich blood to the body for
circulation
- involves circulating oxygen rich blood to capillary
beds, and the O2 poor blood returns via systemic
veins

2. Lymphatic system
   
   • Drains surphus tissue fluid (fluid that’s accumulated
   • in the interstitial spaces/space between cells), drains
   • plasma proteins, removal of debris from cellular
   • decomposition, removes infection material
   • Composed of Lymph plexuses (dense
     concentrations of lymph tissues), lymph vessels,
     lymph nodes + lymph tissues

Question 11

Describe the three types of blood vessels