Structure & Function of Blood Vessels - Lecture 5 Flashcards
What are the three main layers of a blood vessel wall?
○ Tunica intima
○ Tunica media
○ Tunica adventitia
Components of the tunica intima
○ Endothelium (simple squamous epithelium)
○ Basal lamina of the epithelial cells
○ Subendothelial connective tissue
Components of the tunica media
○ Smooth muscle fibres in loose connective tissue
○ May contain elastic fibres
Components of the tunica externa/adventia
○ Connective tissue
○ Merges with surrounding connective tissue
○ May contain vasa vasorum
Key differences between arteries and veins
○ Arteries: High pressure, thick walls, smaller lumen, maintain shape, more resilient, no valves
○ Veins: Low pressure, thin walls, larger lumen, may have valves to prevent backflow
what are the three types of arteries
○ Elastic (conducting) arteries
○ Muscular (distributing) arteries
○ Arterioles (resistance vessels)
Describe elastic (conducting) arteries
○ Examples: Aorta, brachiocephalic & common carotid
○ Up to 2.5cm
○ Function: Withstand pressure changes during the cardiac cycle and ensure continuous blood flow
○ Structural Adaptations: Thick tunica media with many elastic fibres and few smooth muscle cells
Describe muscular (distributing) arteries
○ Examples: Most named arteries, e.g., brachial & femoral
○ Diameter: 0.5mm - 0.4cm
○ Function: Distribute blood to muscles and organs, capable of vasodilation and vasoconstriction
○ Structural Adaptations: Smooth muscle cells +++ in tunica media, distinct internal and external elastic laminae, thick tunica externa
Describe arterioles (resistance vessels)
○ Capable of vasoconstriction & vasodilation
○ Control blood flow to organs
○ Involved in blood pressure control
○ Diameter: ≤ 30µm
○ Structural Adaptations: one to two layers of smooth muscle cells in tunica media, poorly defined tunica externa
What are capillaries and what is their function?
○ Connect arterioles and venules (microcirculation)
○ Site of gaseous exchange
○ Thin walls facilitate diffusion, blood flow is slow
○ Blood flow through capillaries is slow
○ 2- way exchange
○ 8µm in diameter
What are the three types of capillaries?
○ Continuous
○ Fenestrated
○ Sinusoidal
Describe continuous capillaries
○ Majority of capillaries are continuous
○ Found in skeletal and smooth muscle, connective tissue, and the lungs
Describe fenestrated capillaries
○ Contain pores in the endothelial lining, facilitating rapid exchange of water or large solutes
○ Found in the kidney, choroid plexus, and endocrine glands
Describe sinusoidal capillaries
○ Have spaces between endothelial cells, incomplete or absent basement membrane, allow for exchange of large solutes
○ Specialized lining cells (e.g. in the liver)
○ Blood moves slowly through sinusoid
What are metarterioles?
○ Supplies a single capillary bed
○ Continues as a thoroughfare channel
○ Constriction = reduced blood flow to whole capillary bed
What is the function of precapillary sphincters
○ Guard the entrance to each capillary
○ Contraction = narrows entrance and decreases blood flow
○ Relaxation = dilates entrance and increases blood flow
What are arteriovenous anastomoses?
○ Form direct communication between the arteriole and venule
○ Dilation = allows blood to bypass capillary bed and flow directly to venous circulation
What are venules?
○ Collect blood from capillary beds and deliver it to small veins
○ Diameter: average 20µm
○ Structural adaptations:
Small - endothelium on a basement membrane
Large - increasing numbers of smooth muscle cells located outside endothelium
What are veins
○ Low pressure system
○ Easily distensible
○ Structural adaptations:
- Thin walled
- Tunica externa is predominant
- Valves to aid blood flow
Classification of veins
○ Small: < 2mm in diameter
○ Medium: 2-9mm in diameter
○ Large: > 9mm in diameter e.g. superior and inferior vena cavae
What does superior (anatomical) mean?
Towards the head or upper part of the body
What does inferior (anatomical) mean?
Away from the head or towards the lower part of the body
What does medial (anatomical) mean?
Towards the midline of the body
What does lateral (anatomical) mean?
Away from the midline of the body
