Chapter 4--Tissues

Student objectives 1-8

Define tissue

Types

• epithelial
• connective
• muscle
• nervous

Types of cell junctions
tight junctions--allow no fluid to pass between cells

Anchoring junctions fasten cells together or to a substrate, but do not form a seal

Gap junctions allow electrochemical signals to pass from one cell to another

Epithelial tissue
Protection, filtration, lube, repro, secretion, digestion, absorption, transportation, etc.

Characteristics:

• cellularity--closely packed cells
• sheet-like tissue
• polarity
• apical surface may have microvilli (brush border), cilia
• basal surface
• secure cell junctions, some are tight
• avascularity-nourished by blood vessels in underlying connective tissues
• basement membrane
• basal lamina secreted by epithelial cells, reticular lamina (conn. tiss.) form basement membrane
• innervated
• regeneration (high mitotic rate)
• Diverse in origin, derived from all 3 embryonic tissue types (explain endoderm, mesoderm, ectoderm)

Types of epithelial tissues: Covering/lining and glandular.

Categorized based on number of cell layers and shapes of cells (all six-sided)

• Simple epithelia--1 layer/absorption-filtration
• Stratified epithelia--multiple layers/abrasion-prone areas
• Pseudostratified
• Squamous--flattened/scalelike
• Cuboidal--equal height/width
• Columnar--tall/skinny
• Transitional--can change shape

These combine to form other types:

• simple squamous, simple cuboidal, simple columnar,
• stratified squamous, strat. cuboidal, strat. columnar, stratified transitional
• pseudostratified columnar

Names based on cells at top of layers.

A quick tour:

• Simple squamous found where rapid exchange by diffusion necessary, kidneys, lungs. Divided into endothelium in lymphatic and blood vessels (slick) and mesothelium in serous membranes of ventral cavities
• Simple cuboidal--secretion and absorption. Kidney tubules, some glands, ducts. ovarian surface.
• Simple columnar--digestive tract, stomach to rectum. Absorption and secretion. Microvilli and goblet cells. simple ciliated col. epith. in uterine tubes and parts of respiratory tract
• Pseudostratified Columnar Epithelium. Nuclei at various levels. secretion/absorption. Pseud. cil. col. ep. in most of respiratory tract.
• Stratified squamous most widespread strat. Protection. skin, external cavities. Keratin.
• Stratified cuboidal 2 layers. Ducts of sweat glands and other large glands
• Strat. columnar rare. Male urethra, some large glands.
• Transitional. Urinary organs. stretches. Cells elongate and slide

Glandular epithelia

• Endocrine glands--no ducts, hormone production.
• Exocrine glands--oil, saliva, bile, digestive enzymes, milk, mucous--ducts
• Unicellular--mucin
• multicellular functional classification
• merocrine (exocytosis) salivary
• holocrine (rupture) sebaceous
• apocrine rupture/repair. mammary glands only possible examples.

Characteristics:

• Common origin (mesoderm/mesenchyme)
• Varying degrees of vascularity
• Extracellular matrix

Structural elements

• Ground substance -- interstitial fluid + proteoglycans. Coil, intertwine, trap water. Fluid to gel-like, form sieve between cells and capillaries
• Fibers
• collagen fibers
• protein collagen
• tough, white
• elastic fibers
• elastin
• coiled, resilient
• reticular fibers
• collagenous, branching. Surround blood vessels, support soft tissue
• Cells
• mature and immature forms. Immature secrete fibers and ground substance. Mature forms are for maintenance. Examples of immature forms: fibroblasts, chondroblasts, osteoblasts. Mature forms may revert

Types of connective tissue:

Determined by cell type, fiber type and proportion of matrix made up of fiber

• Mature Connective tissue
• Loose connective tissue
• areolar tissue--other subclasses of conn. tissue proper are variants of this. Major cell type is fibroblast. Cushions most organs and muscles, holds and transports fluids, includes macrophages, absorbs fluids involved in inflammation. Has loose, fluid matrix.
• adipose tissue--Adipocytes mostly contain oil. Very cellular.
• Reticular tissue--support for other cells, especially in glands
• Dense connective tissue
• Dense regular--fiber predominant. Closely packed collagen fibers. Fibroblasts predominant cell type. Tendons, ligaments examples.
• Dense irregular--Interwoven thicker collagen fibers. Dermis and covering some organs.
• Elastic tissue--regular and irregular. Stretchy. Elastin. Vocal cords, aorta, intervertebral ligaments.
• Cartilage -- Avascular, no nerves. Cartilaginous structures surrounded by membrane of dense irregular tissue (perichondrium).
• Hyaline cartilage--pads on bones, epiphyses. Collagen
• Elastic cartilage--similar to hyaline, but more elastic fibers. Ear.
• Fibrocartilage--thick collagen. Intervertebral disks, disks in knee. Compressible.
• Bone (osseus tissue) -- Collagen, calcium, well vascularized. Will discuss in more detail later.
• Blood (vascular tissue) Fluid tissue plus formed elements -- will discuss in more detail later.

Other tissue types, both to be discussed later:

Muscle-- skeletal, cardiac and smooth

Nervous-- neurons and supporting cells

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