BIOL 216 Histology

adipocyte

fat-storing cell

adipose tissue

a specialized connective tissue composed mainly of lipid‑rich adipocytes that store fat, provide insulation, cushion organs, and function as an endocrine organ

apical surface

the free, exposed side of an epithelial cell that faces a lumen or the external environment

apocrine

relating to or denoting multicellular glands which release some of their cytoplasm in their secretions (sweat glands)

axon

the long threadlike part of a nerve cell along which impulses are conducted from the cell body to other cells

basal lamina

a thin, specialized layer of extracellular matrix that underlies epithelial and endothelial cells, providing structural support, filtration, and a scaffold for cell signaling

basal surface

bottom edge of a cell or tissue that faces the underlying connective tissue, specifically the basement membrane

basement membrane

a thin, delicate membrane of protein fibers and mucopolysaccharides separating an epithelium from underlying tissue

canaliculi

a small channel or duct

cardiac muscle cells

striated, branched cells with a single central nucleus, interconnected by intercalated discs to enable synchronized heart contractions

chondrocyte

a cell which has secreted the matrix of cartilage and become embedded in it

cilia

microscopic hairs

collagen

the primary structural protein in connective tissues, forming strong, flexible fibers that support bones, skin, cartilage, tendons, and ligaments

columnar cell

an epithelial cell shaped like a column

compact bone

the dense, solid outer layer of bone that provides strength, protection, and structural support

compound gland (compound acinar, compound tubuloacinar)

a type of gland whose secretory units are arranged in multiple branches or lobules rather than a single, unbranched structure

cuboidal cell

cube-shaped cells

cutaneous membrane

a multi-layered epithelial and connective tissue membrane that covers the body’s external surface and serves as a protective barrier

cytosol

water‑based fluid inside cells that contains dissolved ions, proteins, ribosomes, small molecules, and various messenger molecules

dendrite

a branched extension of a neuron that receives and processes signals from other neurons, transmitting them toward the cell body (soma)

dense irregular connective tissue

connective tissue with fibers that are not arranged in parallel bundles

dense regular collagenous connective tissue

connective tissue characterized by tightly packed, parallel bundles of type I collagen fibers, providing high tensile strength along a single axis

dense regular elastic connective tissue

a specialized connective tissue rich in parallel-oriented elastic fibers, providing both strength and elasticity to structures that undergo repeated stretching

desmosome

specialized intercellular junctions that maintain tissue integrity under mechanical stress

ductal epithelium

specialized epithelial lining of ducts in exocrine and some endocrine glands, responsible for transporting, modifying, and regulating secretions

elastic cartilage

a flexible connective tissue rich in elastic fibers, providing both strength and elasticity to specific non-load-bearing structures in the body

elastin

highly elastic protein in connective tissues that allows organs and tissues to stretch and recoil

epithelium

the thin tissue forming the outer layer of a body's surface and lining the alimentary canal and other hollow structures

erythrocytes

red blood cells - essential for transporting oxygen and carbon dioxide in the bloodstream

exocrine

glands that secrete substances through ducts to body surfaces or organ cavities

extracellular fluid

all body fluid located outside the cells, serving as the medium for nutrient delivery, waste removal, and homeostatic regulation

extracellular matrix

non‑cellular network of proteins and polysaccharides that surrounds cells and provides structural support, regulates cell behavior, and helps maintain tissue organization

fibrocartilage

dense, strong connective tissue composed of chondrocytes embedded in a collagen-rich extracellular matrix, specialized to withstand compressive and tensile forces in high-stress areas of the musculoskeletal system

fibrosis

the formation of excess fibrous connective tissue in an organ or tissue (scar tissue)

gap function

allow small substances to move from one cell to another

glial cell

non-neuronal cells that support, protect, and maintain neurons, providing structural, metabolic, and immune functions in the nervous system

glycoprotein

composite molecules consisting of a protein backbone and one or more carbohydrate chains, known as glycans, attached through a process called glycosylation

glycosaminoglycan

long, unbranched polysaccharides composed of repeating disaccharide units

goblet cell

simple columnar epithelial cells that secrete mucus and use merocrine secretion

ground substance

gel-like, non-fibrous material in the extracellular matrix that surrounds and supports cells and fibers

Haversian (osteonic) canal

the longitudinal channel at the core of an osteon

holocrine

the entire secretory cell disintegrates and is secreted through the duct

hyaline cartilage

glassy, translucent connective tissue composed of chondrocytes embedded in a collagen-rich extracellular matrix, providing smooth surfaces for joint movement and structural support

integral protein

membrane-embedded proteins that span or anchor within the lipid bilayer, playing essential roles in transport, signaling, and structural support

intercalated discs

specialized connections between cardiac muscle cells that help them communicate and contract together; contain gap junctions for electrical signals and desmosomes that hold cells together.

keloid

raised overgrowths of scars

keratin

a fibrous protein forming the main structural constituent of hair, feathers, hoofs, claws, horns, etc.

keratinized

living skin cells gradually transform into tough, protein-filled dead cells

lacunae

small spaces or cavities within bone or cartilage that contain cells

lamellae

thin, concentric layers of bone tissue that surround the central canal in an osteon

leukocytes

white blood cells produced in bone marrow

lipid inclusion

a non-living, intracellular storage structure composed primarily of triglycerides (stored lipids) that are not enclosed by a membrane

loose connective tissue

a loose, mesh‑like arrangement of collagen, elastic, and reticular fibers embedded in abundant ground substance, with numerous fibroblasts and immune cells dispersed throughout

membrane-like structure

membranes that have an opening to the outside of the body

merocrine

glandular secretion where cells release their products via exocytosis without damage to the secreting cell

mesothelium

the epithelium that lines the pleurae, peritoneum, and pericardium

mucous membrane

an epithelial tissue which secretes mucus, and lines many body cavities and tubular organs including the gut and respiratory passages

mucus

a slimy substance secreted by the mucous membranes and glands of animals for lubrication, protection, etc.

nervous tissue

primarily composed of neurons (with soma, dendrites, and axons) and neuroglia such as astrocytes, oligodendrocytes, microglial cells, Schwann cells, and satellite cells, forming gray and white matter in the CNS

neurite

any projection extending from the cell body (soma) of a neuron

neuron

a specialized nerve cell that receives, processes, and transmits electrical and chemical signals throughout the nervous system

osteocyte

a mature bone cell that maintains bone tissue, senses mechanical stress, and regulates bone remodeling by coordinating osteoblasts and osteoclasts

osteon

a cylindrical structural unit of compact bone consisting of a central Haversian canal surrounded by concentric lamellae

parietal

relating to or denoting the wall of the body or of a body cavity or hollow structure

plasma

the colourless fluid part of blood, lymph, or milk, in which corpuscles or fat globules are suspended

proteoglycan

large, heavily glycosylated proteins that are a major component of the extracellular matrix (ECM) in connective tissues

proteoglycan aggregate

many molecules + hyaluronic acid

pseudostratified ciliated columnar epithelium

a single-layered epithelial tissue that only appears multilayered, with tall columnar cells bearing cilia that help move mucus and trapped particles—especially in the respiratory tract

pseudostratified epithelium

a single layer of cells that appears multilayered due to nuclei positioned at different levels, with all cells resting on the basement membrane

reticular fiber

a type of loose connective tissue made of thin reticular fibers that form a supportive network for cells, especially in lymph nodes, spleen, and bone marrow

reticular lamina

thin layer of reticular connective tissue fibers that forms part of the basement membrane and helps anchor epithelial tissue to the underlying connective tissue

reticular tissue

a specialized connective tissue that forms a delicate, mesh-like framework (stroma) supporting soft organs and lymphoid structures

secretory epithelium (tubular, acinar, tubuloacinar)

epithelial tissue specialized for producing and releasing secretions

tubular: secretory units shaped like a tube, with a central lumen that transports secretions

acinar: secretory units are spherical or rounded, with a small central lumen (berry-shaped)

tubuloacinar: secretory units combine both tubular and acinar elements within the same gland

simple columnar epithelium

a single layer of tall, column‑shaped cells with basal oval nuclei, specialized for absorption, secretion, protection, and sometimes movement via cilia

simple cuboidal epithelium

a single layer of cube‑shaped cells with centrally located round nuclei, primarily specialized for secretion, absorption, and limited protection, commonly found in kidney tubules, thyroid follicles, ovaries, and glandular ducts

simple epithelium

a single layer of cells that lines internal surfaces and facilitates absorption, secretion, or diffusion depending on its type and location

simple gland (simple tubular, simple acinar)

a type of gland whose duct system is unbranched — meaning it has a single, straight duct that carries secretions from the gland to a target site

simple squamous epithelium

a single layer of flat, polygonal cells with centrally located flattened nuclei, forming thin, smooth linings ideal for diffusion and filtration, found in alveoli, blood vessels (endothelium), and serous membranes (mesothelium)

skeletal muscle cells

long, cylindrical, multinucleated cells specialized for contraction and organized into functional units called sarcomeres

smooth muscle cells

spindle‑shaped, non‑striated, single‑nucleated fibers containing actin–myosin filaments anchored to dense bodies and intermediate filaments, enabling slow, sustained involuntary contraction

soma

bulbous, non-process portion of a neuron or glial cell that contains the cell nucleus

spongy bone

porous, lattice-like bone tissue that provides structural support, reduces skeletal weight, and houses bone marrow for blood cell production

squamous cell

a flat, scale‑like epithelial cell that forms protective layers on your skin, organs, and blood vessels

stratified columnar epithelium

a rare, multi-layered epithelial tissue with columnar cells on the apical surface, primarily serving protective and secretory functions

stratified cuboidal epithelium

a multi-layered epithelial tissue with cube-shaped cells at the apical surface, primarily providing protection and structural support in glandular ducts

stratified epithelium

a type of epithelial tissue composed of multiple layers of cells, primarily designed to protect underlying tissues from mechanical and chemical stress

stratified squamous epithelium

a type of epithelial tissue composed of multiple layers of cells, with the superficial layer being flat (squamous) and the deeper layers typically cuboidal or columnar, providing protection against mechanical and chemical stress

striations

a long, thin streak, ridge, or groove on a surface, often one of many similar parallel marks

synovial

a type of joint or tissue associated with freely movable joints and synovial fluid

thrombocytes

small, anucleated cell fragments derived from bone marrow megakaryocytes that play a crucial role in blood clotting and immune responses (platelets)

tight junctions

help make the spaces between cells impermeable

tissue

a group of structurally and functionally similar cells organized to perform a specific function in the body

trabeculae

thin, beam- or rod-like structures of spongy bone that form a supportive network and help the bone withstand stress

transitional epithelium

a specialized stratified epithelial tissue—also called urothelium—found almost exclusively in the urinary system, where it stretches and changes shape to accommodate fluctuating urine volume

true membrane

membranes that don’t have an opening to the outside of the body

unicellular exocrine gland

single secretory cells, with goblet cells being the most common example, responsible for secreting mucus onto epithelial surfaces

visceral

relating to the viscera

Volkmann’s canals

small, perforating channels in the compact (cortical) bone that connect the Haversian canals (which run the length of the bone) with each other and with the periosteum (the outer tissue covering the bone)

What is the definition of a tissue? Where do tissues sit in the levels of biological organization?

A tissue is a group of similar cells that work together to perform a specific function. They are the third level of organization.

Describe the composition of the extracellular matrix. What is ground substance? Briefly define glycosaminoglycan, proteoglycan, proteoglycan aggregate, glycoprotein, and extracellular fluid. What are the primary protein fibers one could find in the extracellular matrix? What types of tissues would you expect to be highest in extracellular matrix? Lowest?

The ECM is mainly composed of ground substance, protein fibers, and extracellular fluid.

Glycosaminoglycan: Long chains of carbohydrates that attract and hold water, helping make the ground substance gel-like

Proteoglycan: A molecule made of a protein core with GAG chains attached. It helps provide cushioning and hydration

Proteoglycan aggregate: A large complex of many proteoglycans attached to a long molecule of hyaluronic acid. Helps tissues resist compression

Glycoprotein: A protein with carbohydrate groups attached. These help with cell adhesion, movement, and organization of the ECM

Extracellular fluid: Fluid located outside cells that surrounds cells and allows substances such as nutrients, gases, and wastes to move between cells and their environment

Major proteins: collagen, elastic, and reticular fibers

Highest tissue: connective tissue

Lowest tissue: epithelial tissue