Vascular System and Vessels Flashcards
Explain how blood vessels are derived differently from other avascular structures.
Blood vessels are mesoderm-derived structures. Avascular and non-lymph structures are usually:
- Ectoderm derived: epidermis
- Endoderm derived: surface epithelium
- Exception - articular cartilage: mesoderm-derived but subject to compression
Describe the structure of vessels. Differ between arteries, veins, and arteries.
It has three layers (tunics):
- Intima: endothelium
- Media: smooth muscle
- Adventitia: fibrous tissue
Arteries:
- Thicker walled
- Smaller lumen
- Elastic fibres in media
Vein
- Thinner walled
- Larger lumen
Lymphatics
- Thinner walled than veins
- Valves
Mention and describe the type of arteries.
- Elastic:
- closest to heart
- large quantities of elastic tissue
- act as ‘conducting’ vessels - Windkessel effect
- prevent a sudden drop in blood pressure
- Muscular:
- Most named arteries
- large amount of smooth muscle in media
- act as ‘distribution’ vessels
- progressively reducing in calibre
- redistribution, rechannelling possible
Mention the arterial branches to somatic structures
- Arterioles
- Small branches – small lumen, thick walls
- Controlled by vasomotor nerve fibres
- Mostly innervated by SNS
- Tonus determines blood pressure
- Approach capillary bed
- Capillaries
- Thinnest walled branches
- Exchange vessels - Exchange permitted by difference in hydrostatic pressure between arterioles (high) to venules (low)
- Arranged in networks of capillary beds
What are anastomoses and collateral circulation?
Anastomoses usually occur between arteries or arterioles. It involves lumen to lumen linking without capillary bed. This offer collateral blood supply in the case of occlusion and occurs often in highly vascular organs (such as muscle). There are true and potential (if necessary) anastomoses.
- Note: Atrio-venous (AV) Anastomoses:
- Between arteries and veins without capillary
- Help without regulation, sexual intercourse
Describe end arteries.
- End Arteries
- Do not link with other arteries
- Anatomical:
- Single artery that doesn’t anastomose with another – occlusion (thrombosis and embolus) means necrosis of tissue
- Thrombus: a blood clot that forms in a vessel and remains there.
- Embolus: an unattached mass that travels through the bloodstream
- Single artery that doesn’t anastomose with another – occlusion (thrombosis and embolus) means necrosis of tissue
- Functional
- Potential of small-calibre arteriole anastomosis
- If occlusion is gradual, existing collateral may dilate
- E.g. right and left coronary artery
Describe the function of veins.
- Carry deoxygenated blood away from capillary beds to the heart (except for pulmonary vein) - flows to the heart
- Has valves
- For directing of flow
- Against gravity in limbs towards heart
- From superficial to deep veins through the perforating veins
- Note: no valves in deep veins of the trunk – vertebral and azygos (blood can flow in either direction)
- For directing of flow
Describe venae comitantes.
They are a pair of veins, wrapped around an artery, which is primarily located in the limbs. Its main function is to conserve heat, transferring it from the warm arterial blood to the cool venous blood. The pulsations of the artery also aid venous return.
Describe methods in assisting blood return to the heart.
Thoracic Pump:
- During inspiration, SVC is stretched allowing venous collection of blood (from periphery and azygos) while blood in IVC is transferred into the heart
- During expiration, the diaphragm contracts and stretches the IVS, allowing it to collect venous blood while SVC dumps its contents to the heart
Musculovenous pump:
- In muscular pumps – muscles are wrapped around thick layers of fascia – when contract, deep veins is pressed allowing blood to return to blood
Mention the function of lymph vessels.
Lymph vessels:
- Carry lymph & foreign materials to lymph nodes where it is filtered and exposed to defence cells
- Lymph returned to the circulation (via the subclavian veins of the neck)
- Lymph capillaries drain into lymphatics and lymph trunks
- One-way valves help direct flow to the venous system
- Note: there are more afferent (into) compared to efferent (only one) lymph vessels
Describe the mechanisms resulting in lymph flow.
- The result of 3 mechanisms (similar to veins):
- ‘milking effect’ - close contact with veins (like vena comintates)
- ‘squeezing effect’ action of surrounding muscles
- ‘sucking effect’ intrathoracic pressure with respiration
- Flow in larger lymphatics is also aided by the presence of one-way valves
- Drain into larger lymph trunks and lymph ducts
- Thoracic duct drains all except upper right quadrant
- Right lymphatic duct drains upper right quadrant
- Ultimately returned to venous system
- Note:
- Sentinel lymph node: the first lymph node that collects the lymph
- Last sentinel lymph nodes can get inflamed if source (such as cancer) is persistent
- Lymph can pass through the axial line – lymph nodes can get inflamed on both sides
- All lymph drains through at least one set of lymph nodes before reaching the venous system
- Sentinel lymph node: the first lymph node that collects the lymph
Describe the neurovascular supply of vessels.
- Nerve Supply:
- Mostly SNS
- Vessels maintain continuous partial tone – exception: erectile tissue also receives PNS
- Blood Supply:
- Media and adventitia receive vasa vasorum - own blood supply
- Endothelium and intima receive nutrition through diffusion
Mention other sites for lymphoid tissue.
- Thymus –from upper thorax into the neck. Reaches its greatest size at puberty and involutes with age
- Spleen
- Tonsils – collections of lymphoid tissue encircling the pharynx & draining mucosa of alimentary & respiratory systems
- ‘Peyer’s patches’ – collections of lymphoid tissue in the mucosa of the GI Tract
