Blood Vessels & Lymphoid Structures Lecture Vocabulary

Vocabulary flashcards covering major structural and functional terms related to blood vessels and associated lymphoid tissues.

Tunica adventitia (externa)

Outermost blood-vessel layer composed mainly of dense connective tissue with collagen; contains vasa vasorum in large vessels.

Tunica intima (interna)

Innermost blood-vessel layer consisting of endothelium (simple squamous epithelium) and a thin subendothelial layer.

Tunica media

Middle vessel layer made of smooth muscle and elastin; thickest in arteries, site of vasoconstriction and vasodilation.

Vasa vasorum

Small blood vessels that supply nutrients to the walls of large blood vessels.

Elastic (conducting) artery

10 mm diameter artery near the heart; rich in elastin, acts as pressure reservoir and shows little vasoconstriction.

Muscular (distributing) artery

3–10 mm diameter artery with the thickest tunica media; delivers blood to specific organs and most named arteries.

Arteriole (resistance artery)

≤3 mm diameter vessel that regulates blood flow into local capillary beds through vasoconstriction or dilation.

Pressure reservoir

Function of elastic arteries (e.g., aorta) where they expand during systole and recoil during diastole to maintain blood flow.

Capillary

Microscopic vessel (~8 µm wide) whose wall is reduced to endothelium and a basement membrane; site of exchange.

Continuous capillary

Most common, least permeable capillary type with uninterrupted endothelium and small intercellular clefts.

Fenestrated capillary

Capillary with pores (fenestrations) that increase permeability to water and small solutes; found in kidneys, small intestine, endocrine glands.

Sinusoidal capillary

Most permeable capillary with large gaps and an incomplete basement membrane; located in liver, spleen, and red bone marrow.

Capillary bed

Network of 10-100 capillaries that forms the microcirculation within a tissue.

Precapillary sphincter

Ring of smooth muscle at the entrance to a capillary that regulates blood flow into the bed.

Venule

Small vein (<100 µm) that receives blood from capillaries; thin wall and little to no elastin.

Vein

100 µm vessel with large lumen, thin wall, valves, and adaptations for low-pressure blood return to the heart.

Skeletal muscle pump

Mechanism where contracting muscles compress veins, propelling blood toward the heart.

Respiratory pump

Blood-return aid produced by diaphragm movement; pressure changes during breathing draw venous blood upward.

Vascular anastomosis

Interconnection of blood vessels providing alternative pathways (collateral channels) for blood flow.

Systemic blood pressure

Force exerted by circulating blood on systemic vessel walls, generated by left ventricular contraction.

Systolic pressure

Higher arterial pressure during ventricular systole.

Diastolic pressure

Lower arterial pressure during ventricular diastole.

Peyer's patches

Aggregates of lymphoid tissue in the small-intestinal wall that sample gut pathogens via specialized M cells.

M (microfold) cell

Epithelial cell in Peyer’s patches that translocates antigens to underlying immune cells.

Vermiform appendix

Blind-ended tube attached to the cecum; houses immune cells and may serve as a reservoir for beneficial gut flora.