Tissues Introduction Epithelial Tissue Classification Glands

Cell Specialization Multicellularity requires a division of labor Cells look and function differently (specialize) in different parts of the body (ex. bone cell vs. nerve cell) Cells specialize into types of tissues, then form organs.

Histology Study of tissues (groups of cells that are similar in structure and function) 4 Tissue Types

1. Connective Tissue Support Connect layers of tissue to each other Bone, ligaments, fat (we will study these in great detail in class later…)

2. Nervous Tissue Control Brain, nerves, spinal cord Highly specialized cells that generate and conduct nerve impulses

3. Muscular Tissue Movement Highly vascular Contraction involves myosin protein filament and cytoskeleton microfilament, actin 2 categories: Striated muscle tissue (voluntary or partly voluntary control) Smooth muscle tissue (involuntary)

3. Muscular Tissue Striated Muscle Ex. Skeletal Ex. Cardiac Attached to skeletal bones Long, cylindrical multi-nucleated cells Visible striations Voluntary control Ex. Cardiac Also striated, but uni-nucleated Branching cells fit tightly with special junctions called intercalated discs

3. Muscular Tissue Smooth muscle No striations Spindle shaped One central nucleus Involuntary muscle Ex. digestive system

4. Epithelial Tissue Interface tissue that forms boundaries between environments and lines surfaces “epithe-” means “laid on” Coverings and Protection (ex. skin) Excretion & Secretion (ex. glands) Filtration (ex. kidneys) Absorption (ex. digestive system)

Identifying Characteristics of Epithelial Tisues 1. Tight fitting sheets Regardless of cell shape or number of layers

Identifying Characteristics LUMEN 2. Apical-Basal Polarity Apical Surface = top surface that borders an “open” space called LUMEN Basal Surface = bottom surface that borders underlying supportive connective tissue Connective Tissue

Identifying Characteristics LUMEN Apical Surface Often w/ microvilli (brush border) Increases SA in areas that need to absorb or secrete Some with cilia to move substances along lumen Connective Tissue

Identifying Characteristics LUMEN Basal Surface Has adhesive sheet of glyco-proteins secreted by epithelial cells called the basal lamina Connective Tissue beneath secretes collagen, creating the Reticular Lamina. Basal Lamina + Reticular Lamina = Basement Membrane (defines the epithelial boundary) LUMEN Connective Tissue

Identifying Characteristics 3. Avascular (a = without) Lacks blood vessels Nourished by connective tissue But Innervated w/ nerve fibers 4. Regeneration and repair quickly

Classification of Epithelial Tissue: Cell Shape Cross-section Squamous – flat, like a fried egg, or scale-like Cuboidal – cubes, large spherical central nuclei Columnar – columns, long oval nuclei, usually near basal surface

Classification of Epithelial Tissue Cell Layers Stratified (many layers) Thick Protective role, subject to wear and tear Regenerate from basal surface to replace apical surface cells that rub off or die Cells differ in shape at apical and basal surface. (named for apical surface) Simple (one layer) Thin: limited, no protection Sparse cytoplasm Found where rapid diffusion is a priority (ex. kidneys, lungs)

Pseudo-stratified Shapes vary in height false Shapes vary in height Nuclei at different levels – appear stratified, but aren’t. All cells reach basement membrane; only a few reach the surface

Simple Squamous Epithelium One layer Flat Function and Location Areas of high diffusion rates: gasses (ex lungs) nutrients and waste exchange (blood vessels and surrounding cells) filtrates (kidneys) Makes lubricating fluid in lining of body cavities (ex. serous membranes)

Simple Squamous Epithelium (Top View) – cells fit like tiled floor

Simple Squamous Epithelium (side view/cross section) – cells look like fried egg LUMEN Figure 4.2

Kidney LUMEN Nucleus of squamous cell

Simple Cuboidal Epithelium One layer Cubed Function and Location Secretion and Absorption Covers walls of SMALL ducts, glands, kidney tubules, ovaries

Cuboidal Cell Spherical, large nuclei LUMEN Basement membrane Apical surface

Basal surface Spherical, large nuclei LUMEN Apical surface

Simple Columnar Epithelium One layer columns Function and Location Absorption & Secretion (ex. digestive tract) When in open to body cavities – called mucous membranes Special Features Often w/ microvilli on apical surface (brush border) Goblet cells, single cell glands, produce protective mucus.

Basal surface Apical surface LUMEN

Pseudostratified Epithelium Function Absorption Secretion of mucus by goblet cells Cilia (larger than microvilli) sweep mucus Location Respiratory Linings & Reproductive tract

LUMEN

LUMEN Cilia Basement Membrane Multilevel nuclei

Stratified Squamous Epithelium Multi-layer (thick!) Flat (only cells on apical surface) Structure Cells often cuboidal or columnar below apical squamous layer Function and Location Protection Keratin (protein) is accumulated in older cells near the surface – waterproofs and toughens skin Location Skin (keratinized), mouth & throat

Dense-Irregular Connective Tissue keratin Squamous Cuboidal Columnar Basement Membrane Dense-Irregular Connective Tissue

Transitional Epithelium Structure Multi-layer Basal surface cells are cuboidal or columnar Apical surface cells vary: changes shape to accommodate for change in volume due to stretching Function Allows stretching Location Urinary bladder, ureters & urethra

Figure 4.10

Nervous Tissue

Muscular Tissue

Glands Cells that secrete or export a product. Secretion = protein, lipids, hormones, steroids, acids Endocrine glands (internally secreting) No duct, release secretion into blood vessels Often hormones Thyroid, adrenal and pituitary glands Exocrine glands (externally secreting) Contain ducts, empty onto epithelial surface Sweat, Oil glands, Salivary glands, Mammary glands.

Shapes of Exocrine glands Branching Simple – single, unbranched duct Compound – branched. Shape: tubular or alveolar Tubular – shaped like a tube Alveolar – shaped like flasks or sacs Tubuloalveolar – has both tubes and sacs in gland

Modes of Secretion Merocrine Holocrine Released by exocytosis Gland is not altered (Ex: Sweat glands and salivary glands) Holocrine Gland ruptures and releases secretion and dead cells as well. Sebaceous (ex. oil glands on the face)