Human Tissues: Histology, Types, Glands & Membranes

What is a tissue?

A group of similar cells and cell products working together to perform a specific role in an organ.

What is histology?

The study of tissues and how they are arranged into organs; also called microscopic anatomy.

What are the four primary categories of tissues?

Epithelial tissue, connective tissue, nervous tissue, and muscular tissue.

What is the matrix in the context of tissues?

The extracellular material outside the cells, composed of fibrous proteins and ground substance.

What are the three primary germ layers in embryonic development?

Ectoderm, endoderm, and mesoderm.

What does the ectoderm give rise to?

The epidermis and nervous system.

What does the endoderm give rise to?

The mucous membrane lining the digestive and respiratory tracts and digestive glands.

What does the mesoderm give rise to?

Gelatinous tissue called mesenchyme, which becomes cartilage, bone, and blood.

What are the main functions of epithelial tissue?

Protection, secretion, excretion, absorption, filtration, and sensation.

What is the structure of epithelial tissue?

A sheet of closely adhering cells, one or more cells thick, with an upper surface exposed.

What is the basement membrane?

A layer between the epithelium and underlying connective tissue that anchors the epithelium.

What is the difference between simple and stratified epithelium?

Simple epithelium has one layer of cells, while stratified epithelium has multiple layers.

What are the three shapes of epithelial cells?

Squamous (thin and flat), cuboidal (square or round), and columnar (tall and narrow).

What is simple squamous epithelium?

A single layer of thin, flat cells that permits rapid diffusion or transport of substances.

Where is simple cuboidal epithelium commonly found?

In the liver, thyroid, mammary and salivary glands, bronchioles, and kidney tubules.

What is the function of ciliated pseudostratified columnar epithelium?

Secretes and propels mucus, found in the respiratory tract and portions of the male urethra.

What is keratinized stratified squamous epithelium?

Multiple layers of cells that resist abrasion and reduce water loss, found in the epidermis.

What is the function of nonkeratinized stratified squamous epithelium?

Resists abrasion and penetration by pathogens, found in the tongue, oral mucosa, and esophagus.

What is the structure of urothelium?

Multilayered epithelium whose surface cells change shape when stretched, allowing the urinary tract to fill.

What is connective tissue?

The most abundant and variable tissue type, characterized by cells occupying less space than the matrix.

What are the functions of connective tissue?

Binding, connecting bones, muscles, and organs, and providing structural support.

What is the vascularity of connective tissue?

Variable; loose connective tissues have many blood vessels, while cartilage has none.

What is the primary function of connective tissue?

To bind, support, protect, and transport substances in the body.

What are the main functions of connective tissue?

Binding, support, physical protection, immune protection, movement, storage, heat production, and transport.

What type of connective tissue connects bones to other bones?

Ligaments.

What is the role of fibroblasts in connective tissue?

They produce the fibers and ground substance of the matrix.

What is the function of macrophages in connective tissue?

They engulf foreign material and activate the immune system.

What type of connective tissue is characterized by conspicuous fibers?

Fibrous connective tissue.

What are collagenous fibers made of?

Collagen.

What is the function of elastic fibers in connective tissue?

They allow tissues to stretch and recoil.

What is ground substance in connective tissue?

The material surrounding connective tissue cells, usually gelatinous or rubbery.

What are glycosaminoglycans (GAGs)?

Long polysaccharides that regulate water and electrolyte balance in tissues.

What are the two broad categories of fibrous connective tissue?

Loose connective tissue and dense connective tissue.

What is areolar tissue?

A type of loose connective tissue with loosely organized fibers and abundant blood vessels.

Where is reticular tissue found?

In lymph nodes, spleen, thymus, and bone marrow.

What is the main function of dense regular connective tissue?

To provide strong attachment between muscles and bones, and hold bones together.

What is adipose tissue primarily composed of?

Adipocytes (fat cells).

What is the main function of white adipose tissue?

Energy storage, insulation, and cushioning.

What distinguishes brown adipose tissue from white adipose tissue?

Brown adipose tissue is involved in heat generation and is found mainly in infants and children.

What is cartilage?

A stiff connective tissue with a flexible, rubbery matrix.

What are chondroblasts?

Cartilage cells that produce the matrix.

What type of cartilage is known for its clear, glassy appearance?

Hyaline cartilage.

What is the function of fibrocartilage?

To resist compression and absorb shock.

What are the two forms of bone tissue?

Spongy bone and compact (dense) bone.

What is the structure of spongy bone?

Made of delicate slivers and plates that give it a spongy appearance.

What are osteons?

Cylindrical structural units of compact bone.

What is the central canal in compact bone?

A passage running lengthwise through the shaft of a bone, containing blood vessels and nerves.

What are concentric lamellae?

Ringlike layers of bone matrix surrounding the central canal.

What are osteocytes?

Mature bone cells located in cavities called lacunae between the lamellae.

What are canaliculi?

Tiny canals radiating from each lacuna to neighboring lacunae, allowing osteocytes to contact one another.

What is the periosteum?

Tough fibrous connective tissue covering the whole bone.

What is blood?

A fluid connective tissue that travels through tubular blood vessels, transporting cells and dissolved matter.

What are erythrocytes?

Red blood cells (RBCs) that transport oxygen (O₂) and carbon dioxide (CO₂).

What are leukocytes?

White blood cells (WBCs) that defend against infection and disease.

What are platelets?

Cell fragments involved in blood clotting.

What is excitability in nervous tissue?

The ability to respond to stimuli by changing membrane potential.

What are neurons?

Nerve cells that detect stimuli, respond quickly, and transmit coded information rapidly to other cells.

What is the function of neuroglia?

Protect and assist neurons, acting as the 'housekeepers' of the nervous system.

What are the parts of a neuron?

Cell body, dendrites, and axon.

What is muscular tissue specialized for?

Contracting when stimulated, exerting physical force on other tissues, organs, or fluids.

What are the three types of muscular tissue?

Skeletal, cardiac, and smooth muscle.

What are tight junctions?

Zipperlike connections between adjacent cells that seal the space between them.

What are desmosomes?

Patchlike connections that hold cells together and prevent them from pulling apart.

What are gap junctions?

Communicating junctions that allow ions, nutrients, and small solutes to pass between cells.

What is a gland?

A cell or organ that secretes substances for use elsewhere in the body or releases them for elimination.

What are exocrine glands?

Glands that maintain contact with the epithelial surface through a duct.

What are endocrine glands?

Glands that release hormones directly into the blood without ducts.

What are unicellular glands?

Individual secretory cells found within an epithelium that is mainly nonsecretory.

What is the capsule in multicellular exocrine glands?

Connective tissue covering the gland.

What is parenchyma in glands?

Cells that perform synthesis and secretion, typically cuboidal or simple columnar epithelium.

What is the difference between simple and compound ducts?

Simple ducts are unbranched, while compound ducts are branched.

What is the shape of tubular secretory portions?

Narrow secretory portion with a uniform diameter.

What is an acinar secretory portion?

Secretory cells that form a dilated sac called an acinus or alveolus.

What is an acinus?

A dilated sac formed by secretory cells.

What are tubuloacinar glands?

Glands that have both tubular and acinar secretory portions.

What do serous glands produce?

Thin, watery secretions such as perspiration, milk, tears, and digestive juices.

What is mucin?

A glycoprotein produced by mucous glands that absorbs water to form mucus.

What are goblet cells?

Unicellular mucous glands that secrete mucus.

What is the function of mixed glands?

To produce a mixture of serous and mucous secretions.

What is eccrine (merocrine) secretion?

A mode of secretion that releases products by exocytosis.

What is apocrine secretion?

A mode of secretion where a lipid droplet covered by membrane buds from the cell surface.

What is holocrine secretion?

A mode of secretion where cells accumulate a product and the entire cell disintegrates.

What is a cutaneous membrane?

The skin, consisting of stratified squamous epithelium and connective tissue.

What is a mucous membrane?

A membrane lining passages that open to the external environment, containing epithelium and connective tissue.

What is a serous membrane?

A membrane that lines internal body cavities and produces serous fluid.

What is the matrix in tissue?

Extracellular material surrounding cells.

What does avascular mean?

Without blood vessels.

What is the apical surface?

The surface of an epithelial cell facing away from the basement membrane.

What is simple epithelium?

A type of epithelium with one layer of cells.

What is stratified epithelium?

A type of epithelium with multiple layers of cells.

What distinguishes connective tissue?

Cells surrounded by an extracellular matrix.

What are the three types of muscle tissue?

Skeletal, cardiac, and smooth muscle.

What is the role of neurons?

To transmit signals in the nervous system.

What is the difference between tight junctions and desmosomes?

Tight junctions seal spaces between cells, while desmosomes hold neighboring cells together.

What is the difference between endocrine and exocrine glands?

Endocrine glands release hormones into the blood; exocrine glands release products through ducts.

What is the function of fibroblasts?

To produce connective tissue fibers and ground substance.

What are the three types of cartilage?

Hyaline, elastic, and fibrocartilage.

What is the structural unit of compact bone?

Osteon.

What is the role of adipocytes?

To store fat.