Blood Vessels Flashcards
Week 6
General structure of vasculature
Artery -> arteriole -> capillaries -> venule -> vein
Arteries
Pulsatory flow, elastic
General structure of vessels
- Tunica Externa (external coat): collagen + elastic fibers
- Tunica Media (middle coat): smooth muscle cell
- Tunica Intima (inner coat): internal elastic membrane, connective tissue, endothelial cells, lumen
Longitudinal vs circular muscle
Longitudinal: vein
Circular: all other vasculature
Tunica Intima
- Single layer of endothelium
- Basal lamina: collagen, proteoglycans and glycoproteins
- subendothelial layer: loose connective tissue
Large arteries/veins: may contain smooth muscle bundles
Arteries/arterioles: internal elastic membrane
Vascular endothelium
- Selective barrier
- Non-thrombogenic barrier
- releases anti-coagulants
- modulation of blood flow/resistance
- regulates immune response
- synthesis and secretion of hormones
- stem cell growth factors
Vascular endothelium
Weibel-Palade bodies: electron dense organelles that contain:
- von Willebrand factor: released during injury to promote clooting
- P-selectin: adhesion molecule for neutrophils
Subendothelial layer and internal elastic membrane
- main cell type: smooth muscle
- separated from tunica media by an internal elastic membrane
Subendothelial layer and internal elastic membrane
- Main cell type: smooth muscle
- separated from tunica media by an internal elastic membrane
Tunica Media
- Primarily consists of smooth muscle, circumferentially arranged
- smooth muscle cells produce varying amounts of elastin, reticular fibers and proteoglycans
- External elastic membrane (only in elastic arteries): elastin
Vascular endothelium and blood flow - RELAXATION
communication between endothelium and tunica media
Responds to: shear stress and metabolic stress
Vascular endothelium and blood flow - CONTRACTION
Responds to: hormones, clotting factors, reduced NO
Tunica Adventitia (or externa)
- Outer layer of connective tissue
- Collagen and elastic fibers, merges with overlying connective tissue
- Vasa vasorum: vessels that supply to large arteries and veins
- Nervi vasorum: autonomic nerves
Large/Elastic Arteries
Size: >10 mm
EX) pulmonary arteries, aorta, and aortic branches (common carotid, brachiocephalic, subclavian)
Functions: conduction tubes
Layers:
1) Tunica Intima
- endothelium, connective tissue, and smooth muscle
- subendothelial layer: smooth muscle and elastic fibers
- internal elastic fibers
- prominent internal elastic membrane
2) Tunica Media
- Thickest layer
- elastic lamellae: increase as you age and with BP
- layers of smooth muscle
- each layer of smooth muscle separated by elastic lamellae
3) Tunica Adventitia:
- fibrous + loose connective tissue
- collagen and elastic fibers
- fibroblasts and macrophages
- Vasa vasorum
Medium/Muscular Arteries
Ex) arteries of upper limb and thorax: axillary artery
- Size: 2-10 mm
- Smooth muscle is the predominant component of the media
- Prominent internal elastic membrane
Layers:
1) Tunica Intima
- endothelium with sparse basal lamina
- internal elastic membrane appears wavy because of smooth muscle contractions
2) Tunica Media
- smooth muscle - maintains BP
3) Tunica Adventitia
- Collagen and elastic fibers
- fibroblasts and macrophages
- external elastic membrane
Arteriole/Small Artery
Small Artery:
- internal elastic membrane (IEM)
- media: 3-8 layers of smooth muscle
- adventitia: thin, few elastic fibers
Arteriole:
- No internal elastic membrane
- Media: 1-2 layers of smooth muscle
- Adventitia: non-discrete connective tissue
Capillaries
- Specialized for nutrient + gas exchange
- single endothelial layer with basal lamina
- Continuous capillaries:
- muscle, lung, and CNS
- pericytes: contractile support cells surrounding the endothelium
- Fenestrated capillaries: digestive tract, kidney
- Sinusoid capillaries: Liver, spleen bone marrow
Pericytes
- Surround capillaries and are enclosed in the same basal lamina as the endothelial cells
- Contractile in nature and may modulate blood flow (specifically in the brain)
- Branching cytoplasm
Continuous capillaries
- Typically found in connective tissue, cardiac, skeletal and smooth muscle, skin, lungs, and the CNS
- Uninterrupted endothelium sitting on continuous basal lamina
Fenestrated Capillaries
- Endothelial cells with characteristic fenestrations (openings or holes in the cytoplasm)
- Endocrine glands, gallbladder, kidney pancreas, intestinal tract
Sinusoidal Capillaries
- Larger in diameter and more irregularly shaped
- Endothelial cells have large openings in their cytoplasm
- Liver, spleen, and bone marrow
Venule
Post-capillary
- endothelium, basal lamina, pericytes
Muscular
- located just past post-capillary
- 1-2 layers of smooth muscle in tunica media
Medium Veins
Ex) basilic vein, cephalic vein
- 1-10 mm
- Contain valves - more prominent in lower limbs: one-way flow
- Tunica Intima: endothelium, basal lamina, thin subendothelial layer with smooth muscle
- Tunica media: much thinner than medium arteries
- Tunica Adventitia: thicker than media
Large Veins
- > 10 mm
- Tunica Intima: endothelium, basal lamina, thin subendothelial layer with smooth muscle
- Tunica Media: relatively thin
- Tunica Adventitia: Thickest layer, longitudinal arranged smooth muscle bundles
