Chpt. 4 Tissue (Midterm)

Glands are classified according to their mode of secretion:

*Merocrine glands (pancreas) - secrete substances as they are produced. *Apocrine glands (mammary glands) - accumulate secretions that are released when a portion of the cell pinches off. *Holocrine glands (sebaceous glands) - accumulate secretions that are released when the cell ruptures & dies.

Goblet Cells:

unicellular glands.

How are glands classified?

Unicellular or multicellular

Glands:

* glands are organs that secrete.

Scar:

A large amount of granulation tissue. Dense irregular collagenous connective tissue. At first a scar is bright red because numerous blood vessels are present. Later the scar becomes white as collagen accumulates and the vascular channels are compressed.

2 Types of bone:

• Spongy bone: has spaces between trabeculae (beams) or plates, of the bone & therefore resemble a sponge. • Compact bone: o More solid, with almost no space between many thin layers or lamellae of bone. Bone is rich in blood supply, due to this bone can repair itself much more readily than can cartilage.

Osteocytes "Bone cells"

• located within holes in the matrix, which are called lacunae & are similar to the lacunae of cartilage.

Epithelial tissue:

1) Epithelium consists of cells with little extracellular matrix. --It covers the surfaces. --Usually has basement membrane --Does not have blood vessels 2) The basement membrane is secreted by the epithelial cells & attached to the underlying tissues.

Fluid CT

1. Blood 2. Hemopoietic tissue

Supporting CT

1. Cartilage 2. Bine

Connective Tissue Proper:

1. Loose connective tissue 2. Dense connective tissue *irregular *regular

Multicellular glands:

o Most exocrine glands are composed of many cells & are called multicellular glands

Endocrine glands

release hormones that are absorbed directly into the blood.

Adhesion Belt

Adhesion belt of glycoproteins is found just below tight junction. It is located between the plasma membranes of adjacent cells & acts as a weak glue that holds cells together. These connections are not as strong as desmosomes.

Goblet Cells:

Are unicellular that secrete mucus. o Mulitcellular glands can be classified according to the structure of their ducts & secretory regions. o Glands that have a single duct are called simple.

Bones

Bone is hard connective tissue (CT) that consists of living cells & mineralized matrix.

Cardiac Muscle:

Cardiac muscle cells are cylindrical but much shorter than skeletal muscle cells. Cardiac muscle cells are striated & usually have one nucleus per cell. They are often branched & connected to one another by intercalated disks (inserted between), which contain specialized gap junctions & are important in coordinating cardiac muscle cell contractions.

Pseudostratified columnar epithelium:

Columnar in shape (taller than they are wide). Although they appear to consist of more than one layer, all the cells rest on the basement membrane.

Smooth Muscle:

Forms walls of hallow organs (except heart). Found in skin & eyes Smooth muscle is responsible for a number of functions, such as moving food through the digestive tract & emptying the urinary bladder. Like cardiac muscle, smooth muscle is controlled involuntarily. Smooth muscle cells are tapered at each end, have a single nucleus & are not striated.

Permanent cells:

Have very limited ability to replicate & if killed are usually replaced by a different type of cell. Some permanent cells, such as neurons, are postmitotic. If damaged, neurons may recover if the cell body is not destroyed; however, if the neuron cell body is destroyed, the remainder of the neuron dies. Some undifferentiated cells of the central nervous system are stem cells that can undergo mitosis & form function neurons in the adult. This has raised hope that damaged areas of the brain may regenerate. Undifferentiated cells of the skeletal & cardiac muscle also have a very limited ability to regenerate in response to injury, although individual skeletal & cardiac muscle cells can repair themselves. In contrast, smooth muscle readily regenerates following injury.

Granulation Tissue:

o Capillaries grow from blood vessels at the edge of the wound & revascularize the area & fibrin in the clot is broken down & removed. The result is the replacement of the clot by granulation tissue. o Granulation Tissue: Delicate, granular-appearing connective tissue that consists of fibroblasts, collagen, & capillaries.

Hyaline Cartilage

o Hyaline Cartilage: Has large amounts of collagen fibers & proteoglycans. Collagen fibers are evenly dispersed throughout the ground substance. Hyaline cartilage in joints & has a very smooth surface. Specimens appear to have a glassy, translucent matrix when viewed on miscroscope. Hyaline cartilage is found where strong support & some flexibility are needed, such as in the rib cage, within trachea & bronchi. Hyaline cartilage covers the surface of bones that move smoothly against each other in joints. Hyaline cartilage forms most of the skeleton before it is replaced by bone, in the embryo & it is involved in growth that increases in length of bones.

Simple squamous epithelium consists of :

one layer of flat or scale like cells that rest on a basement membrane.

o Cells of Connective Tissue

pg. 114

o Protein Fibers of the Matrix

pg. 114

o Proteoglycan aggregate

pg. 115

Eccrine glands

secrete through ducts.

Stratified squamous epithelium consists of:

several layers of cells. Near basement membrane, cells are more cube shape. Near free surface cells are flat or scale like.

Unicellular glands:

some exocrine glands are composed of a single cell & are unicellular glands.

Tight Junctions:

Holds cells together & form a permeability barrier. Tight junctions are formed by plasma membranes of adjacent cells that join one another in a jigsaw fashion to make a tight seal. Near the free surface of simple epithelial cells, the tight junctions form a ring that completely surrounds each cell & binds adjacent cells together to prevent the passage of materials between cells. For example, in the stomsach & urinary bladder chemicals cannot between the cells. Thus, water and other substances must pass through epithelial cells, which can actively regulate which is absorbed & secreted. Found In: areas where a layer of simple epithelium forms a permeability barrier. • For example, water can diffuse through epithelial cells, and active transports, symport, & facilitated diffusion move most nutrients through the epithelial cell of the small intestine.

Desmosomes:

Relatively weak binding is reinforced Disk-shaped structures with very adhesive glycoprotein that binds cells to one another & intermediate filaments that extend into the cytoplasm of cells. Many desmosomes are found in epithelial tissues that are subject to stress, such as stratified squamous epithelium of the skin.

Hemidesmosomes:

Similar to one-half of a desmosome, attach epithelial cells to basement membrane.

Gap Junctions:

Small, special contact region between cells containing protein channels that aid intercellular communication by allowing ions & small molecules to pass from on cell to another. In epithelium, the function of gap junctions is not entirely clear. • Gap junctions between cilated epithelial cells may coordinate the movements of cilia. • In cardiac & smooth muscle tissues, gap junctions are more important in coordinating important functions. • Because ions can pass through gap junctions from on cell to the next, electrical signals can pass from cell to cell to coordinate the contraction of cardiac & smooth muscle cells. • Thus, electrical signals that originate in one cell or the heart can spread from cell to cell & cause the entire heart to contract.

Intercalated disks:

The gap junctions between cardiac muscle cells are found in specialized cell-to-cell connections called intercalated disks. In addition to containing gap junctions, the intercalated disks have desmosomes that help hold adjacent cells in close contact.

Melanosomes:

The goli apparatuses of the melanocytes package melanin into vesicles called melanosomes, which move into the cell processes of the melanocytes. Keratinocytes phagocytize the tips of the melanocyte cell processes, thereby acquiring melanosomes. Although all keratinocytes can contain melanin, only the melanocytes produce it.

Brown Adipose:

Tissue is found in specific areas of the body , such as the axillae (armpits), neck, & near the kidneys. The brown color results from cytochrome pigments in the tissue's numerous mitochondria & its abundant blood supply. It is difficult to distinguish brown adipose from yellow adipose in babies because the color difference is not great. Brown adipose fat is specialized to generate heat as a result of oxidative metabolism of lipid molecules in mitochondria. It can play a significant role in regulating body temperature in newborns & may also play a role in adult metabolism.

Cell connections: p. 110

o Cells have structures that hold them to one another or the basement membrane. o These structures do 3 things: Mechanically bind cells together Help form permeability barrier Provide mechanism for intercellular communication. o Epithelial cells secrete glycoproteins that attach the cells to the basement membrane & to one another.

Epithelial Tissue:

"Epithelium" o Covers & protects surfaces inside & outside body. o Characteristics: Mostly composed of cells. • Made almost entirely of cells with very little extracellular matrix. Covers body surfaces: • Covers body & forms glands that are derived from the surface. Body surface includes the exterior surface, lining of the digestive system & respiratory tracts, heart, blood vessels, and linings of many body cavities. Distinct cell surfaces: • Most epithelial tissues have one free or apical surface, which is not attached to other epithelial cells; and a Basal surface which is attached to a basement membrane. The free surfaces often line the lumen of ducts, vessels, & cavities. Basement Membrane is specialized extracellular material secreted by epithelial & CT cells.

Classification of Epithelial Tissue:

1) Simple - single layer *stratified - 2 or more layers *psuedostratified - single layer appears stratified 2) Squamous - flat, cuboidal, or columnar. *stratified squamous - keratinized / non-keratinized 3) Transitional epithelium - stratified with cells that can change shape from cuboidal to flattened.

Functions of epithelial Tissue:

1) protects underlying structures, acts as barriers, permit some substances to pass through epithelial layers, secrete substances, & absorb substances.

Functional Characteristics:

1) simple epithelium - involved in diffusion, filtration, secretion & absortption. 2) stratified epithelium - serves as a protective role. 3)squamous cells - function in diffusion / filtration 4) Cuboidal / Columnar cells - with a larger cell volume that contains many organelles, secrete or absorb. 5) Transitional epithelium - folded surface that allows the cell to change shape, & the # of cells making up the epithelial layers changes. * a smooth free surface reduces friction (Mesothelium & endothelium). *microvilli increase absorption (intestines). *Cilia move materials across the free surface (respiratory tract & uterine tubes). *cells are bound together mechanically by glycoproteins, desmosomes, & adhesion belts & to the basement membrane by hemidesmosomes. *Tight Junctions: form a permeability barrier. *Gap Junctions: allow intercellular communication.

All 4 of the primary tissue types are derived from...

Each of the 3 germ layers: -Mesoderm -Ectoderm -Endoderm

Bone Matrix has organic & inorganic portions.

• Organic: o Consists of protein fibers, primarily collagen, & other original molecules. • Inorganic: o The mineral portion consists of specialized crystals called hydroxyapatite, which contain calcium & phosphate. The strength & rigidity of the mineralized matrix allows bones to support & protect other tissues & organs.