A&P Tissues

Tissue

A group of structurally and functionally related cells working together with their surrounding extracellular matrix (ECM) to perform a specific function, such as protection, support, or movement.Tissues are classified into four main types: epithelial, connective, muscle, and nervous tissue.

Histology

The branch of anatomy that studies the microscopic structure of tissues to understand how their organization relates to function and disease.

Extracellular Matrix (ECM)

A complex network of proteins and ground substance that surrounds and supports tissue cells; provides mechanical strength, guides cell placement, and regulates cell survival, growth, and development.

Glycosaminoglycans (GAGs)

Long, negatively charged polysaccharides (sugars) like hyaluronic acid and chondroitin sulfate that attract positively charged ions and water, making ECM hydrated and resistant to compression.

Proteoglycans

Large molecules made of GAGs attached to a protein core; form gel-like aggregates that increase ECM firmness, resist pressure, and act as diffusion barriers to substances.

Collagen fibers

Tough, rope-like protein fibers (at least 20 types exist) that provide high tensile strength, especially abundant in skin, bones, and tendons; most abundant protein in the body.

Elastic fibers

Composed of elastin and glycoproteins, these fibers can stretch up to 1.5x their length (distensibility) and recoil to original shape (elasticity); found in lungs and blood vessels.

Reticular fibers

Thin, branching collagen fibers that create supportive meshworks in organs like the spleen, liver, and lymph nodes to trap foreign cells and support delicate structures.

Tight junctions

Integral membrane proteins that form impermeable seals between adjacent cells (like a zipper), preventing passage of most substances; found in intestinal and blood-brain barriers.

Desmosomes

Anchoring junctions (like buttons) that connect cells at specific spots using linker proteins and intermediate filaments; allow tissues like the skin and heart to withstand mechanical stress.

Gap junctions

Channels formed by protein pores (connexons) between adjacent cells that allow ions and small molecules to pass directly, enabling electrical and chemical communication in cardiac and smooth muscle.

Simple epithelium

A single layer of cells in direct contact with the basement membrane; allows for rapid exchange (diffusion, absorption, secretion); found in lungs, intestines, kidneys.

Stratified epithelium

Multiple layers of epithelial cells, providing thicker protection in areas exposed to friction or stress (e.g., skin, mouth, esophagus); cells in apical layer determine the type.

Pseudostratified

Appears to be multilayered due to uneven nuclei, but all cells touch the basement membrane; often ciliated and contains goblet cells (mucus); found in respiratory tract.

Squamous cells

Thin, flat cells like floor tiles; adapted for fast diffusion; found in alveoli (lungs) and capillaries.

Cuboidal cells

Box-like cells with a central, round nucleus; involved in secretion and absorption; found in kidney tubules and glands.

Columnar cells

Tall, rectangular cells with nuclei near the base; may have cilia or microvilli; specialized for absorption and secretion in places like the digestive tract and uterine tubes.

What are the four basic tissue types?

Epithelial, Connective, Muscle, and Nervous tissue.

Two main components of the extracellular matrix (ECM)?

Ground substance and protein fibers.

What's found in ground substance?

Water, nutrients, ions, glycosaminoglycans (GAGs), and proteoglycans.

Three types of protein fibers in ECM?

Collagen (strength), Elastic (stretch), Reticular (supportive net).

What are tight junctions?

Seals between cells that prevent substances from passing between them.

What are desmosomes?

Strong connections that anchor cells together and help resist mechanical stress.

What are gap junctions?

Channels between cells that allow ions and small molecules to pass — for communication.

Main functions of epithelial tissue?

Protection, secretion, sensation, barrier control, immune defense.

What is the basement membrane?

ECM layer anchoring epithelial tissue to underlying connective tissue.

How is epithelial tissue classified?

By number of layers (simple, stratified, pseudostratified) and cell shape (squamous, cuboidal, columnar).

Simple squamous epithelium location?

Lungs, blood vessels, serous membranes — for rapid diffusion.

Simple cuboidal epithelium location?

Kidney tubules and glands — for absorption and secretion.

Simple columnar epithelium location?

Digestive tract, uterine tubes — often has microvilli or cilia.

Pseudostratified columnar epithelium location?

Respiratory tract — ciliated, with goblet cells that produce mucus.

Paracellular vs. transcellular transport?

Paracellular = between cells; Transcellular = through cells.

What is a goblet cell?

A mucus-secreting unicellular exocrine gland in respiratory and digestive tracts.

Three methods of exocrine secretion?

Merocrine (exocytosis), Holocrine (cell bursts), Apocrine (cell part pinches off)

Main functions of connective tissue?

Support, protection, transport, connection, storage.

Two major types of connective tissue?

Connective tissue proper and specialized connective tissue.

What are fibroblasts?

Cells that make fibers and ground substance in connective tissue proper.

Loose (areolar) connective tissue function?

Cushions and supports organs — under skin and around organs.

Dense irregular connective tissue function?

Resists tension in multiple directions — found in dermis of skin.

Dense regular connective tissue function?

Resists tension in one direction — found in tendons and ligaments.

Adipose tissue function?

Stores energy, insulates, cushions organs.

Hyaline cartilage location?

Joints, nose, fetal skeleton — smooth and flexible support.

Fibrocartilage location?

Intervertebral discs, menisci — strong and shock-absorbing.

Elastic cartilage location?

Ear, epiglottis, larynx — flexible and resilient.

Three types of bone cells?

Osteoblasts (build), Osteocytes (maintain), Osteoclasts (break down).

Components of blood?

Plasma (fluid), red blood cells, white blood cells, platelets.

Three types of muscle tissue?

Skeletal (voluntary), Cardiac (involuntary), Smooth (involuntary).

What is cilia?

Small hair-like structures on the surface of certain cells that move in waves to push substances like mucus or eggs across the tissue surface.

Where is cilia found?

In the respiratory tract (to move mucus and particles) and in the uterine tubes (to move the egg).

What does keratinized mean?

Refers to epithelium where surface cells are filled with keratin, a tough protein that protects against abrasion and prevents water loss.

Where is keratinized epithelium found?

In the skin (epidermis) — it's dry and protective.

What is non-keratinized epithelium?

Epithelium without surface keratin; cells stay moist and alive. Found in areas like the mouth, esophagus, and vagina.

What are membranes in the body?

Thin sheets of tissue made of epithelial and connective tissue that cover surfaces, line cavities, or form barriers between areas.

What is a serous membrane?

Lines body cavities that do not open to the outside (e.g., chest or abdomen) and secretes watery serous fluid to reduce friction.

What are the two layers of a serous membrane?

• Parietal layer: lines the cavity wall

• Visceral layer: covers the organ

Example: The pleura around the lungs

What is a mucous membrane?

Lines body passages that open to the outside, like the digestive or respiratory tract. Secretes mucus to keep surfaces moist and trap particles.

What tissues make up a mucous membrane?

Epithelium, basement membrane, lamina propria (connective tissue), and sometimes smooth muscle.

What is a synovial membrane?

Found inside joint cavities; it does not have epithelium. It secretes synovial fluid to lubricate joints.

What is the cutaneous membrane?

The skin — a dry membrane made of keratinized stratified squamous epithelium and connective tissue.

What is a true membrane?

A body membrane made of both epithelial tissue and connective tissue, used to line or cover structures and secrete fluids.

What are the two types of true membranes?

Serous membranes and mucous membranes.

What is a non-true membrane?

A membrane made only of connective tissue — no epithelium.

What is the only non-true membrane?

Synovial membrane — lines joint cavities and secretes synovial fluid.

Two types of tissue repair?

Regeneration (same cells), Fibrosis (scar tissue from collagen).

What helps tissue healing?

Mitosis ability, good nutrition (protein, vitamin C), and blood supply.

What are intercalated discs?

Connections in cardiac muscle that help heart cells contract together.

What is endomysium?

ECM layer that surrounds each muscle fiber.

Main nervous tissue cells?

Neurons (signal transmission) and neuroglia (support and protect neurons).

Three parts of a neuron?

Cell body (nucleus), dendrites (receive), axon (send signals).