What are the three main types of blood vessels and their primary functions?
Arteries carry blood away from the heart, capillaries allow exchange between blood and tissues, and veins return blood to the heart.
What are the three tunics (layers) of blood vessel walls?
Tunica intima, tunica media, and tunica externa.
What is the structure and function of the tunica intima?
It is the innermost layer made of simple squamous epithelium (endothelium) and a subendothelial layer of areolar connective tissue; it provides a smooth surface to reduce friction as blood flows.
What is the structure and function of the tunica media?
It is the middle layer composed of circular smooth muscle and elastic fibers; it controls vasoconstriction and vasodilation to regulate blood pressure and blood flow.
What is the structure and function of the tunica externa?
It is the outer connective tissue layer containing collagen and elastic fibers; it anchors the vessel and may contain vasa vasorum in large vessels.
How do arteries differ structurally from veins?
Arteries have a thicker tunica media, more elastic fibers, and a narrower lumen; veins have a thicker tunica externa, larger lumen, less elastic tissue, and can collapse if empty.
Why can veins act as blood reservoirs?
Because they have large lumens and thin walls, allowing them to hold large volumes of blood; about 55% of blood is in systemic veins at rest.
What is the structure of a capillary?
Capillaries contain only tunica intima (endothelium and basement membrane), allowing rapid exchange.
What are the three types of arteries?
Elastic arteries, muscular arteries, and arterioles.
What are elastic arteries and what is their function?
Large arteries with high elastic fiber content that stretch and recoil to maintain blood flow during diastole; examples include the aorta and pulmonary trunk.
What are muscular arteries and what is their function?
Medium-sized arteries that distribute blood to specific body regions and contain internal and external elastic lamina.
What are arterioles and why are they important?
Smallest arteries that regulate systemic blood pressure and control blood flow into capillary beds.
What is an aneurysm?
A localized ballooning of an arterial wall due to weakening, commonly in the aorta or brain arteries, which may rupture and cause fatal bleeding.
What are continuous capillaries?
Capillaries with tightly joined endothelial cells and small intercellular clefts that allow small molecules to pass but block proteins and cells.
Where are continuous capillaries commonly found?
Muscle, skin, lungs, and central nervous system.
What are fenestrated capillaries?
Capillaries with pores (fenestrations) that allow greater fluid and small protein movement.
Where are fenestrated capillaries found?
Kidneys and intestines.
What are sinusoids?
Capillaries with large gaps and incomplete basement membranes that allow large proteins and blood cells to pass.
Where are sinusoids found?
Bone marrow, spleen, and some endocrine glands.
What are venules?
The smallest veins that collect blood from capillaries and merge into larger veins.
What are the three mechanisms of capillary exchange?
Diffusion, vesicular transport, and bulk flow.
How does diffusion work in capillaries?
Substances move from high to low concentration; oxygen and nutrients move to tissues, while carbon dioxide and wastes move into blood.
What is vesicular transport in capillaries?
Endothelial cells use pinocytosis and exocytosis to transport substances across the cell via vesicles.
What is bulk flow?
Movement of large amounts of fluid due to pressure differences across the capillary wall.
