BIOLOGY: 4 Types of Tissues

The Animal Body: Introduction to Structure and Function

Tissue – Can be classified through size, shape, functions, arrangement

Homeostatic mechanism – to achieve homeostasis

4 Major Types of Tissues

I.              EPITHELIAL TISSUE: Covers Body Surfaces and Lines cavities

Functions:

a.    Protection – covers the entire body and protects it from mechanical injury, chemicals, bacteria and fluid loss

b.    Absorption – lining of the digestive tracts absorbs nutrients and water into the body

c.    Secretion – some epithelial cells are organized in to glands that secrete cell products (hormones, enzymes or sweat)
1. Sweat – Sweat Gland
2. Tears – Lacrimal Gland
3. Saliva – Salivary Gland
4. Milk – Mammary Gland
5. Cerumen/Earwax – Sudoriferous Gland
  ****Glands can be classified as exocrine or endocrine

d.    Sensation – specialized as sensory receptors that receives information

Classification:
~SHAPE

·         Squamous – thin, flattened. Shaped like flagstones. (Nasal cavity, cheeks)

·         Cuboidal – short cylinders, cube shaped. (Kidney)

·         Columnar – columns or cylinders (Trachea)

~NUMBER OF LAYERS

·         Simple Epithelium – 1

·         Stratified Epithelium – 2 or more

·         Pseudostratified – falsely appeared to be layered

II.            MUSCULAR TISSUE

- most abundant tissue in the body

- accounts to nearly 2/3 of body weight

- connected to our bones

- long narrow – muscle cells(fiber)

	Skeletal (striated)	Cardiac	Smooth
Location	skeleton	heart	Digestive tract
Control	voluntary	involuntary	Involuntary
Nuclei per fiber	many	2 or 1	1
Position of nuclei	peripheral	center	center
Speed of contraction	most rapid	intermediate	slowest
Resistance to fatigue	least	intermediate	most
Shape	elongated cylindrical blunt ends	elongated cylindrical brunch fuse	elongated spindle pointed ends

III.           CONNECTIVE TISSUE: Joins & supports other body structures

- almost all organs have connective tissues

- cushions internal organs

- consists of fibers(scattered throughout another structure called matrix which is a thin gel composed of polysaccharide)

Examples:

1.    Blood – circulating tissue; distributed oxygenated blood

2.    Bones & Cartilage – supports skeleton

3.    Adipose Tissue – provides cushions for internal organs

3 Types of Fibers
***fibroblasts = cell that produces fiber

1.    Collagen
- found at the skin (dermis), bones, ligaments
- has tensile strength (capacity to be stretched without tearing)

2.    Elastic – can be stretched easily
- lungs & alveoli, walls of arteries

3.    Reticular – very fine and very branched
- will form a network that will eventually support organs
- liver, spleen, lymphnodes

Types of Connective Tissue

1.    Loose Connective Tissue
- support, reservoir of fluid and salts
- dermis of skin
- wrap nerves, blood vessels, muscles

2.    Dense Connective Tissue
- support, transmission of mechanical force
- ligaments, dermis of skin

3.    Adipose Tissue
- food storage, insulation, support of organs (mammary gland)
- found at subcutaneous layer
- pads around internal organs

4.    Cartilage
- flexible support and reduction of friction
- nose, between trachea, end of bones, vertebral column, ears, fontanel

5.    Bone
- reservoir of calcium
- attachment to muscles

6.    Blood
- transport of oxygen, nutrients and others
- within the heart and blood vessels

IV.          NERVOUS TISSUE: Controls Muscles and Glands

- composed of nerve cells/neurons
- consists of glial cells

Parts:

1.    Cell body
- contains the nucleus and 2 types of cytoplasmic extension
a. Dendrites – receives & transmits into cell body
b. Axon – transmits away from the body

2.    Neuroglia

- major cell type in neural tissue
- provides structural integrity to the nervous sys.
3 kinds: astrocyte, oligodendrocyte, microglia