Tissues and Membranes

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Outline of Notes

A. General:
Cells are highly specialized and interdependent on one another. Groups of similar cells performing similar functions are called Tissues The study of tissues is called Histology.
Organs are made of tissues. A detailed understanding of tissues will greatly help your understanding of organs and organ systems later in this course. Tissues are classified into 4 main types:

Epithelial, Connective, Muscular and Nervous.

B.Cell Junctions (fig 4-2, p.109)
There are three specialized junctions between cells. These are important in all tissues, but are most common in epithelial tissues.
1. Tight Junctions: no leakage between cells
2. Gap (Communication) Junctions: Channels connect cytoplasm
3. Adhering Junctions: proteins connect cytoskeleton to external structures -Desmosomes: Cells to Cells
-Hemidesmosomes: Cells to extra-cellular fibers

II.Epithelial Tissues (Linings and Coverings; Glands)

A. General Characteristics of Epithelia:
Function in protection, absorption and secretion.
Consist of closely packed cells with specialized contacts
Have an Apical (free) Surface and a Basal lamina
Innervated but avascular: nutrients must come from underlying tissues.
Capable of Regeneration (high rate of mitosis)

B.Specializations of Epithelia:
-Cilia: Aid in movement of extracellular material
-Microvilli: Increased surface area to increase absorption/secretion

C.Classification: Classified by shape/arrangement.
Types: Function:Common Locations:
Simple SquamousExchangeLungs, Capillaries
Simple CuboidalSecretion/Absorption Kidneys
Simple ColumnarAbsorption/Secretion Digestive Tract
Pseudo-Stratified ColumnarProtection (mucus) Respiratory TractStratified Squamous Protection (layers) Skin, Esophagus Stratified Cuboidal Secretion (glandular) Salivary glands Stratified ColumnarProtection, secretion Male Urethra

TransitionalProtection (flexible) Urinary Bladder

C.Glandular Epithelia: One or more cells that secrete a particular substance

1.Endocrine Glands: “internal spaces”
Ductless glands (empty into blood stream)
Produce Hormones: see chapter 18

2.Exocrine Glands: “external spaces”
Multicellular glands have ducts
Further classified by: Secretion Mode, Secretion Type and Structure
a. Secretion Mode:
Merocrine:small scale exocytosis- most glands
Apocrinelarge scale exocytosis- rare
Holocrinecell rupture- sebaceous glands
b. Secretion Type:
Serous (thin, watery solution) water, enzymes
Mucous (thick, viscous) mucin to mucus
c. Structure:Simple, Compound, (ducts)
Tubular, Alveolar, Branched (secreting portion)

3.Unicellular Exocrine Glands:
Goblet Cells (aka Mucous Cells) produce mucin which becomes mucus Found in columnar epithelium: respiratory and digestive systems

III.Connective Tissues: (Function in Protection, Support, Binding)

A.Common Characteristics
Common Origin: Mesenchyme
Highly vascular: well nourished (except cartillage)
Consist of a specialized cell in a non-living matrix.

B. Structural Elements:
Ground substance: fluid + protein = colloid
Fibers:Elastin (yellow)
Collagen (white)
Reticular (fine collagen)
Cells:--Blasts: Producing cells
--Cytes: Mature cells
Adipocytes (fat cells)
WBCs/macrophages: immunity/ protection
Mast cells: local inflammation response
(and allergies)
Melanocytes: Produce dark pigment

C. Types of Connective Tissues:

Mesenchymemesenchymal cellground substance
AdiposeAdipocyteAdipose(fat):inside cell
Reticular connective ReticulocytesReticular fibers
Areolar connectiveFibroblasts...
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