A&P Chapter 4: Tissue Level of Organization

[Four Main Groups - Overview]

Epithelial Tissue

• Function: Covers body surfaces, lines cavities, forms glands

• Structure → Function: Tightly packed cells arranged in sheets → ideal for protection, absorption, and secretion

[Four Main Groups - Overview]

Connective Tissue

• Function: Binds, supports, protects, and integrates body parts

• Structure → Function: Cells are spread within an extracellular matrix → provides strength, support, and flexibility

[Four Main Groups - Overview]

Muscle Tissue

• Function: Movement through contraction

• Types: Skeletal (voluntary), smooth, cardiac

• Structure → Function: Excitable, contractile cells → generate force and movement

[Four Main Groups - Overview]

Nervous Tissue

• Function: Communication via nerve impulses

• Structure → Function: Excitable cells that transmit electrochemical signals → enable rapid coordination

3 Major Germ Layers/Embryonic Tissues

• Ectoderm (outer): forms nervous tissue and epithelium (skin)

• Mesoderm (middle): forms muscle and connective tissue (skeletal, muscular, and circulatory systems)

• Endoderm (inner): forms internal epithelial linings (digestive/respiratory tracts)

[Tissue Membranes]

Mucous Membrane

• Composed of epithelial tissue.

• Line body cavities that are open to outside (digestive tract, respiratory tract, urogenital tract)

• Wet/moist membranes because they secrete mucous = reduces friction and facilitates absorption/secretion

[Tissue Membranes]

Serous Membrane

• Composed of mesothelium (simple squamous epithelium), supported by areolar tissue

• Lines closed body cavities/organs

• Never exposed/connected to outside

• Secrete serous fluid = reduces friction

1. Types: pleura (lung), pericardium (heart), peritoneum (abdominal organs)

[Tissue Membranes]

Cutaneous Membrane (skin)

• Made of stratified squamos + areolar tissue + supported by dense irregular connective tissue

• Covers body surface

• Dry, relatively thick, and waterproof

[Tissue Membranes]

Synovial Membrane

• Line mobile joint cavities but don’t cover opposing joint surfaces

• Secretes synovial fluid

• Differs from epithelia because: develops within connective tissue, no basal lamina present, gaps between cells, and synovial fluid/capillaries exchange fluids

[Epithelial Tissues]

Functions of Epithelial Tissue

• Provides physical protection from abrasion, dehydration, and destruction

• Controls permeability (substances that enter/leave the body)

• Provides sensation: sensory nerves detect changes in environment

• Absorption/filtration

• Can produce secretions (glands)

[Epithelial Tissues]

Structure of Epithelial Tissue

• Sheets of tightly packed cells with little extracellular space

• Avascular (no blood vessels)

• Show polarity: apical surface (free/exposed) and basal surface (attached to basement membrane)

• Anchored by basement membrane/basal lamina.

  • clear layer/lamina lucida: contains glycoproteins + fine protein filaments

  • dense layer/lamina densa: bundles of coarse protein fibers = strength/filter

[Epithelial Tissues]

Characteristics of Epithelial Tissue

• Rapid regeneration (cells divide frequently)

• Cellularity: they form an effective barrier

  • Occluding junctions: form a barrier that isolates surfaces/deeper tissues from the lumen contents. Tight attachments = prevents passage of water/solutes.

  • Adhesion belt: locks together the webs of cells = strengthens region and prevents distortion/leakage at junctions.

  • Gap junction: permits chemical communication that coordinate cell activity. Two cells are held together by interlocking proteins (connexons) that serve as channels.

  • Desmosomes: provide firm attachments between neighboring cells by interlocking cytoskeletons.

    • Hemidesmosomes: attach basal surface to basement membrane.

  • CAM: cells adhesion molecules; transmembrane proteins that bind to each other/other materials. Present in adhesion belt/desmosomes.

[Epithelial Tissue]

Naming Epithelial Tissues

Arrangement

• simple: one layer thick

• stratified: more than one layer

• pseudostratified: false layers (look like more than one, but isn’t)

Shape

• squamos: thin, flat, irregular. look like fried eggs or pancake with butter (nucleus)

• cuboidal: equally wide and tall. hexagonal boxes with spherical nucleus in the center

• columnar: more tall than wide, resemble rectangles with elongated nuclei crowded into a narrow band near the basal lamina

[Epithelial Tissue]

Simple Squamos Epithelium

• Description: single layer of flattened cells with disc-shaped central nuclei

• Function: diffusion/filtration (can secrete lubricant)

• Locations: air sacs in lungs, kidney, linings of heart/lymphatic system

[Epithelial Tissue]

Stratified Squamos Epithelium

• Description: thick layers of flattened cells (can have keratinized/mitotic layer)

• Function: protection

• Locations: outer layer of skin, covers organs (mouth/female reproductive organs)

[Epithelial Tissue]

Simple Cuboidal Epithelium

• Description: single layer of cube-like cells with large spherical nucleus in center

• Function: absorption/secretion

• Locations: ovaries, kidneys, glands

[Epithelial Tissue]

Stratified Cuboidal Epithelium

• Description: rare in human body

• Locations: sweat glands, mammary glands, exocrine glands

[Epithelial Tissue]

Simple Columnar Epithelium

• Description: single layer of tall cells with round/oval nuclei (some can have cilia, goblet cells, or microvilli)

• Function: absorption, secretion of mucus/enzymes

• Locations:

  • non-ciliated: digestive tract (intestines), gallbladder, glands

  • ciliated: bronchi, uterine tubes, uterus

[Epithelial Tissue]

Stratified Columnar Epithelium

• Description: rare in human body

• Locations: lines large ducts (salivary glands/pancreas)

[Epithelial Tissue]

Pseudostratified Columnar Epithelium

• Description: single layer of cells of differing heights (nuclei at different heights)

• Function: secretion, propulsion by cilia

• Locations:

  • non-ciliated: male reproductive ducts

  • ciliated: respiratory tract

[Epithelial Tissue]

Transitional Epithelium

• Description: resembles both stratified squamos/cuboidal. basal cells are cuboidal/columnar

• Function: stretches readily + permits distension

• Locations: lines uterus, bladder, and urethra

[Glands]

Endocrine Glands

• “ductless” glands that produce hormones

• secret directly into interstitial fluids/bloodstream

  • ex: pituitary gland, adrenal gland, thyroid gland

[Glands]

Exocrine Glands

• have ducts

• secrete their substance either on body surfaces or within ducts

Different modes

• merocrine: most common; secrete products from secretory vesicles by exocytosis (ex: salivary glands)

• holocrine: accumulate products until cell ruptures. destroys the cell and must be replaced by cell division (ex: sebaceous glands of skin)

• apocrine: products accumulate within the cells then pinches off packets that contain the secretion (ex: mammary glands)

Cellular

• unicellular: goblet cells that produce mucin which mixes with water = mucus

• multicellular:

  • simple: single duct, doesn’t branch on its way to secretory cells

  • compound: duct divides one or more times on way to secretory cells