Glossary — Key Terms with NEET Context — Notes

Term	Definition	NEET Context
Basement membrane	Non-cellular layer beneath epithelium, made of collagen IV and glycoproteins	Anchors epithelium; breach = cancer invasion
Chondrocytes	Cartilage cells residing in lacunae	Key cells of all three cartilage types
Chondroitin sulfate	Glycosaminoglycan forming cartilage ground substance	"What is cartilage matrix?" → chondroitin sulfate
Cloaca	Common exit chamber for digestive, urinary, reproductive tracts in frog	Present in frog, reptile, bird — absent in most mammals
Compact bone	Dense outer bone with Haversian systems	Site of the Haversian system
Extracellular matrix (ECM)	Non-cellular material surrounding connective tissue cells	Hallmark of connective tissue; type varies by CT subtype
Fibroblasts	Primary connective tissue cells that produce ECM components	Key cell of areolar CT; also in tendons
Haversian canal	Central canal in compact bone containing blood vessels + nerves	"What does Haversian canal contain?" → blood vessels + nerves
Haversian system (osteon)	Structural unit of compact bone: lamellae + central canal + lacunae + canaliculi	Only found in bone — key identification feature
Intercalated discs	Junctions between cardiac muscle cells containing gap junctions + desmosomes	Exclusive to cardiac muscle; enable synchronized contraction
Lacunae	Small spaces in hard matrix (bone or cartilage) housing cells	Osteocytes (bone) and chondrocytes (cartilage) both in lacunae
Mast cells	Granule-containing cells in areolar CT that release histamine	Source of histamine in inflammation/allergy
Mesonephric kidney	Adult amphibian kidney type	Frog kidney type (not metanephric like mammals)
Neuroglia	Non-excitable support cells of neural tissue	Schwann cells (PNS myelin); oligodendrocytes (CNS myelin); astrocytes; microglia
Osteocytes	Mature bone cells in lacunae	Maintain bone matrix; connected via canaliculi
Plasma	Liquid matrix of blood	"Blood matrix?" → plasma
Sinus venosus	Accessory heart chamber receiving systemic venous blood	Present in frog, absent in mammals
Truncus arteriosus	Arterial vessel distributing blood from frog ventricle	Present in frog, absent in mammals
Ureotelic	Organisms that excrete nitrogen as urea	Frogs are ureotelic; amphibians and mammals