Tissues The Living Fabric

Tissue – a group of cells that have similar structure and that function together as a unit Histology – the microscopic study of tissues

Intracellular matrix – a non-living material that fills the spaces between the cells; may contain special substances such as salts and fibers that are unique to a specific tissue and give that tissue distinctive characteristics

Intracellular Junctions Holds groups of cells together to form tissues found in sheets or other continuous masses of cells Three types: Desmosomes Gap junctions Tight junctions

1. Desmosomes – small “spot welds” that hold adjacent cells together; fibers interlock with each other

2. Gap junctions – formed when membrane channels of adjacent plasma membranes adhere to each other They form gaps or “tunnels” that join the cytoplasm of two cells Fuse the two plasma membranes into a single structure (heart) 3. Tight junctions – occur in cells that are joined by “collars” of tightly fused membrane (lining of intestines and other parts of the body, where it is important to control what gets past a sheet of cells)

Categories of Tissues Epithelial Tissue – covering; lining of surfaces (epi- “over” or “outer”) Connective – support; bone, ligaments, fat (connect) Muscle – movement (contract) Nervous – control; brain, nerves, spinal cord

Function of Epithelial Tissue Protection - Skin protects from sunlight & bacteria & physical damage Absorption - Lining of small intestine, absorbing nutrients into blood Filtration - Lining of kidney tubules filtering wastes from blood plasma

Secretion - Different glands produce perspiration, oil, digestive enzymes and mucus Sensory Perception - Sensory nerve endings embedded in epithelial tissue connect the body with outside stimuli

Characteristics of Epithelial Tissue Form continuous sheets (fit like tiles) Apical Surface (free) -surface that can be exposed to the air or to fluid - sometimes has cytoplasmic projections such as cilia or microvilli

Basement Membrane - Underside of all epithelial cells which anchors them to connective tissue Avascular (a= without) - lacks blood vessels - Nourished by connective tissue Regenerate & repair quickly

Classification – two criteria: shape of cells and the number of cell layers Cell height (shape) – the shape of the nucleus corresponds to the cell shape Squamous – flat and nuclei are usually broad and thin; horizontal longer than vertical Cuboidal – horizontal and vertical equal; nuclei are spherical and centrally located

Columnar – vertical greater than horizontal; nuclei are usually in the lower portion of the cell near the basement membrane Cell layers (cell arrangement) Simple – single cell layer Stratified – multiple layers

Simple Squamous Epithelium Structure - single layer of flattened cells – allows for diffusion and osmosis; sparse cytoplasm Function - Absorption , secretion, and filtration - Not effective protection – single layer of cells Location - Walls of capillaries, air sacs in lungs (alveoli) - Form serous membranes in body cavities

Simple Cuboidal Epithelium Structure - Single layer of cube shaped cells Function - Secretion, absorption, and transportation in glands, filtration in kidneys Location - Glands and ducts (pancreas & salivary), kidney tubules, covers ovaries

Simple Columnar Epithelium Structure - Elongated layer of cells with nuclei at same level, close packed cells Function - Absorption, Protection & Secretion - When open to body cavities – called mucous membranes

Special Features - Microvilli, bumpy extension of apical surface, increase surface area and absorption rate - Goblet cells, single cell glands, produce protective mucus - Cilia – moves secretions along surface Location - Linings of entire digestive tract- secretes digestive enzymes and absorbs nutrients

Pseudostratified Epithelium Structure - Single layer - Irregularly shaped cells with nuclei at different levels – appear stratified, but aren’t - all cells reach basement membrane but not all cells reach the free surface

Function - Absorption and Secretion - Goblet cells produce mucus - Cilia (larger than microvilli) sweep mucus Location - Respiratory tract in which mucus traps dust particles & is moved upward by the cilia - Reproductive tract – lines some of the tubes of the male tract where the cilia propels sperm from one region to another

Here, we have pathogens traveling down the pharynx trying to attack the surface cells. How can they be repelled???

The mucosal cells lining the trachea have released a flood of mucus, trapping the pathogens! Now what???

The cilia successfully sweep the pathogens up and away!

Stratified Squamous Epithelium Structure - Many layers (usually cubodial/columnar at bottom and squamous at top) - cells far away from basement membrane die because it is difficult to receive oxygen and nutrients from underlying connective tissues Function - Protection - Keratin (protein) is accumulated in older cells near the surface – waterproofs and toughens skin

Location - Skin (keratinized), extends a short distance into every body opening that is continuous with the skin (mouth, pharynx, esophagus, anal canal and vagina)

Stratified Cuboidal Epithelium Structure - 2 to 3 layers; cube shaped Function - protection Location - largest ducts of sweat, mammary and salivary glands, male urethra

Stratified Columnar Epithelium Structure - multiple layers, column shaped cells Function - secretion and protection Location - largest ducts of salivary glands, uterus, parts of eye, anus, male urethra

Transitional Epithelium Structure - many layers - very specialized – cells at base are cuboidal or columnar, at surface will vary - change between stratified & simple as tissue is stretched out - stretches in response to tension

Function - allows stretching (change size) Location - urinary bladder

Covering and Lining Epithelia Body membranes are thin sheets of tissue that cover the body, line body cavities, cover organs within the cavities, and line the cavities in hollow organs Epithelial membranes – consists of epithelial tissue and connective tissues to which it is attached

4 main types of Epithelial membranes Mucous (Mucosae) – consist of epithelial tissue that is attached to an underlying loose connective tissue - lines body cavities that open to the outside (digestive, respiratory, excretory, and reproductive tracts) - secretes mucus for lubrication and protection

2) Serous (Serosa) – lines body cavities that do not open directly to the outside, and they cover the organs located in those cavities - consists of a thin layer of loose connective tissue covered by a layer of simple squamous epithelium (mesothelium) 2 parts: parietal – lines cavity wall visceral – covers organs in cavity - covered by thin layer of serous fluid- lubricates the membrane and reduces friction and abrasion when organs move against one another or the cavity wall

3) Cutaneous – covers body surfaces that are exposed to the external environment (skin) dry membrane 4) Endothelial- thin layer of cells that line the interior surface of blood vessels - lines entire circulatory system from the heart to the smallest capillary

Glands One or more cells that make and secrete a product Secretion - protein in aqueous solution: hormones, acids, oils Endocrine glands ; Endo = within - no duct, release secretion into blood vessels - often hormones - thyroid, adrenal and pituitary glands

Exocrine glands; Exo = outside crine = secrete - contain ducts, empty onto epithelial surface - sweat, oil glands, salivary glands, mammary glands

Can be multicellular or unicellular. Pancreas, stomach, sweat glands, salivary glands, mammary glands, sebaceous glands, etc. Unicellular: Goblet cells- single cells called goblet cells that produce mucous

Exocrine glands come in a wide variety of shapes:

Exocrine Secretion: Merocrine- hormones released through cell membrane (sweat & salivary glands, mucous producing goblet cells) Apocrine- part of cell containing hormones pinches off (mammary gland- usually associated with a hair follicle; arm pit, groin) Holocrine- cell bursts to secrete products and must be replaced (sebaceous gland)