Ch. 4. Tissue level of organization

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Define resolution and its quality

Resolution – Ability to distinguish between two separate points

Function and features of epithelial tissue

Functions

Provide physical protection- Protect surfaces from abrasion, dehydration, or destruction by chemical or biological agents

Control permeability- Most epithelia are capable of selective absorption or secretion

Epithelial barrier can be modified in response to stimuli (Example: calluses- a thickened and hardened part of the skin or soft tissue, especially in an area that has been subjected to friction.)

Provide sensation, Specialized epithelial cells detect changes in environment (for example, touch receptors)

Neuroepithelium Sensory epithelium found in special sense organs

Produce specialized secretions • Glandular epithelial cells produce secretions

Features

▪ Surfaces • Apical surface – Faces exterior of body or internal space - Base – Attached to underlying tissues - Basolateral surface o Includes base and sides (lateral surfaces) attached to neighboring cells

▪ Polarity • Refers to structural differences between exposed and attached surfaces

Apical surface features • If lining a tube, apical surface is exposed to space inside the tube, called lumen • Microvilli found on this surface in digestive, urinary, and reproductive tracts • Cilia found on this surface in parts of the respiratory and reproductive tracts

Examples of simple and stratified epithelia (location, function, description)

Squamous • Thin and flat (squama, plate or scale) irregularly shaped cells (like jigsaw puzzle pieces) • Viewed from above, cells look like fried eggs • In sectional view, disc-shaped nucleus found in thickest part of cell

Cuboidal • Cube-shaped • Like little boxes

Columnar • Taller than they are wide • Slender rectangles

▪ Single layer - Simple epithelium ▪ Several layers of cells -Stratified epithelium

Types of intercellular connections

Hemidesmosomes • Attach deepest epithelial cells to basement membrane 1..Basal lamina _Contains glycoproteins and fine protein filaments o _Produced by basal surface of epithelium 2..Reticular lamina _Contains bundles of coarse protein fibers _Gives strength and restricts diffusion

Tight (occluding) junctions • Interlocking membrane proteins bind adjacent plasma membranes together • Prevent passage of water and solutes between cells • Isolate basolateral surfaces and deeper tissues from contents in lumen • Found in intestinal tract

Adhesion belts • Continuous band of membrane proteins • Strengthens apical region of cells – Reinforces tight junctions • Dense proteins attached to microfilaments of the terminal web (part of cytoskeleton) • Belts encircle cells and bind to adjacent cells

Gap junctions • Held together by interlocking transmembrane proteins (connexons) • Assist chemical communication to help coordinate functions such as secretion or beating cilia • Also found in cardiac muscle and smooth muscle tissue to coordinate contraction

Desmosomes • Provide firm attachments by interlocking adjacent cells’ cytoskeletons • Opposing plasma membranes locked together by cell adhesion molecules (CAMs)

Goblet cells

▪ Mucous (goblet) cells • Only unicellular exocrine glands • Independent, scattered secretory cells in epithelium • Secrete mucin

Know 4 types of membranes; their composition, location and function

Mucous membranes • Line passageways open to the exterior of the body – Digestive, respiratory, reproductive, urinary tracts • Must be kept moist to facilitate movement, absorption, or secretion • Lubricated by mucus or bodily fluids • Supported by areolar connective tissue (lamina propria)

Serous membranes • Composed of mesothelium supported by areolar connective tissue • Delicate and never connected to exterior • Secretes watery serous fluid • Three line subdivisions: – Pleura (pleural cavity and lungs) – Pericardium (pericardial cavity and heart) – Peritoneum (peritoneal cavity and visceral organs)

Cutaneous membrane • Covers surface of body (skin) • Composed of: – Stratified squamous keratinized epithelium – Layer of areolar tissue – Underlying dense irregular connective tissue • Relatively thick, waterproof, and usually dry

Synovial membranes • Lines freely movable joint cavities • Lubricates joint cavity with synovial fluid • Provides oxygen and nutrients to cartilage cells • Not true epithelium – Develops within connective tissue – Lacks basement membrane – Contains gaps between cells (up to 1 mm) – Synovial fluid and capillaries continuously exchange fluid and solutes