Overview
This lecture covers the anatomy, histology, and main features of blood vessels, focusing primarily on arteries but also discussing veins and capillaries, as well as essential examples of major vessels in the body.
Blood Vessel Structure & Histology
- All blood vessels are lined by simple squamous epithelial cells called endothelial cells.
- The innermost layer, the tunica intima, contains these endothelial cells.
- Blood vessels (except capillaries) have three layers: tunica intima (inner), tunica media (middle, smooth muscle), and tunica adventitia/externa (outer, connective tissue).
- Arteries maintain a round shape due to a thick tunica media and abundant elastic connective tissue (internal and external elastic lamina).
- Veins have thinner tunica media and often appear wobbly or collapsed, with some large/medium veins possessing one-way valves.
- Capillaries consist only of endothelial cells with a basement membrane—no tunica media or tunica externa.
Arteries: Pathways & Major Branches
- The aorta is the largest artery, divided into ascending aorta, aortic arch (with three branches), thoracic aorta, and abdominal aorta.
- Three aortic arch branches: brachiocephalic trunk (right common carotid & right subclavian), left common carotid, and left subclavian artery.
- Common carotids bifurcate into internal (feeds brain and eyes) and external (feeds face and scalp) carotid arteries.
- Vertebral arteries (from subclavians) supply the posterior brain and join to form the basilar artery; both contribute to the Circle of Willis.
- Major arteries of the upper limb: subclavian → axillary → brachial → radial (thumb side) & ulnar (pinky side).
- Abdominal aorta branches: celiac trunk, superior mesenteric, inferior mesenteric, left/right renal and gonadal arteries.
- The abdominal aorta splits into common iliac arteries; each common iliac divides into internal (pelvis) and external (lower limb) iliac arteries.
- External iliac becomes the femoral artery → popliteal (behind knee) → anterior/posterior tibial arteries → dorsalis pedis and plantar arteries.
Veins & Venous Return
- Veins transport blood back to the heart; largest are the superior and inferior vena cava.
- Large/medium veins of limbs contain one-way valves to prevent backflow; movement of skeletal muscles assists venous return.
- The respiratory pump (changes in thoracic pressure) aids blood flow from the vena cavae to the right atrium.
- Pooling of blood and valve failure can lead to varicose veins and risk of deep vein thrombosis (DVT), which may cause pulmonary embolism.
Specialized Circulations
- The Circle of Willis is an arterial ring at the base of the brain, providing collateral circulation.
- Dural venous sinuses (notably the superior sagittal sinus) drain brain blood into the internal jugular veins.
- The hepatic portal system routes GI blood through the liver via the hepatic portal vein before entering systemic circulation; blood exits liver via hepatic veins into the inferior vena cava.
Vascular Pathology (Basic Concepts)
- Atherosclerosis: buildup of plaques in arteries, leading to narrowing or blockage (risk of heart attack or stroke if ruptured).
- Aortic dissection: tear in the aorta wall, creating a false lumen—rapidly fatal if not treated.
- Aneurysm: vessel wall weakening and ballooning, risk of rupture and fatal bleeding if untreated.
Key Terms & Definitions
- Endothelial cells — Simple squamous cells lining blood vessels.
- Tunica intima/media/adventitia — Inner/middle/outer layers of vessel walls.
- Internal/External elastic lamina — Layers of elastic tissue in arteries.
- Capillary — Smallest blood vessel, site of gas/nutrient exchange.
- Circle of Willis — Arterial ring at the brain’s base for collateral flow.
- One-way valve — Prevents backflow in veins.
- Atherosclerosis — Plaque buildup in arterial walls.
- Aneurysm — Ballooned, weakened vessel wall.
- Dural venous sinus — Venous channels draining the brain.
- Hepatic portal vein — Vein carrying blood from GI tract to the liver.
- Deep vein thrombosis (DVT) — Blood clot in deep veins, risk of embolism.
Action Items / Next Steps
- Review and identify major arteries and veins on models/cadavers.
- Memorize the sequence of branches for aorta and upper/lower limb arteries.
- Study the main features distinguishing arteries, veins, and capillaries histologically.
- Prepare for identification of special circulations (Circle of Willis, hepatic portal system) on lab practicals.