TISSUES
LECTURE NOTES
TISSUE – A group of cells that have a similar structure and function. A group of tissues
combines together to form organs.
HISTOLOGY – The study of tissues.
BASIC TISSUE TYPES:
1. EPITHELIAL
2. CONNECTIVE
3. MUSCLE
4. NERVOUS
TISSUE DESCRIPTIONS:
1. Epithelial tissue – Made of cells closely packed together with very little
intercellular material.
2. Connective tissue – Dense tissue made of cells with lots of intercellular
material made of fibers in a matrix or ground substance that may be liquid,
gelatinous or solid.
3. Nerve tissue – Consists of one or more bundles of impulse-carrying fibers that
connect the brain and the spinal cord with other parts of the body. It is the
most highly organized tissue of the body.
4. Muscle tissue – tissue composed of fibers that are able to contract causing and
allowing movement of the parts and organs of the body.
TISSUE FUNCTIONS:
1. Epithelial – 4 functions
a. Protective barrier – temp, environment, microorganisms
b. Absorbs nutrients
c. Secretes hormones, mucus and enzymes
d. Excretes waste like urea and sweat
2. Connective –
a. Binds to other tissue structures to support and organize body
b. Binds to foreign cells to protect the body
c. Binds to molecules to transport materials through body.
3. Nerve – Conducts electrical signals through the body.
4. Muscle – Allows movement of movable body structures.
CHARACTERISTICS OF EPITHELIUM:
1. Covers the body and many of its parts.
2. Lines the body’s serous cavities; blood and lymph vessels, respiratory,
digestive and urinary tracts.
3. Body’s glands consist of epithelial tissue.
4. Cells tightly arranged with little intercellular substance.
5. Always rests on a layer of connective tissue with a basement
membrane between them.
6. No capillaries in epithelium – oxygen and nutrients provided by
connective tissue below through diffusion.
7. Cells undergo constant mitosis – replace outer layers cells lost through
wear and exposure to forces and environment.
KEY TERMS OF EPITHELIAL TISSUE – EPITHELIUM
1. Epithelium – covering of internal organs of body, and lining of vessels, body
cavities and glands.
2. Serous – Epithelial tissue that lines closed body cavities and covers the organs
in that cavity.
3. Membrane – A thin layer of tissue that covers a surface, lines a cavity or
divides a space.
4. Basement membrane – The fragile, noncellular layer of tissue that secures the
overlying layers of stratified epithelium.
5. Diffusion – The process of a substance moving from an area of high
concentration to an area of lower concentration.
CLASSIFICATIONS OF EPITHELIAL TISSUE:
1. By shape – 3 types
2. By tissue layer arrangement - 2
BY SHAPE:
1. Squamous – Flat cells, scalelike
i. Lines blood vessels and alveoli
ii. Tissue thinness allows gas and chemical passage
2. Cuboidal – Cube-like box cells – equal height, width, depth
i. Lines glands such as thyroid and salivary glands
ii. Tissue shape promotes secretion of gland chemicals
3. Columnar – Rectangular box cells with one longer side
i. Lines the stomach and intestines
ii. Secretes gastric juices and enzymes
iii. Cilia sweep substances along – fallopian tubes
BY TISSUE LAYER ARRANGEMENT:
1. Simple tissue – Single cell layer
a. Lines the capillaries, thyroid and stomach
b. Tissue thinness allows gas/substances passage in/out
Example – Oxygen flows through the capillary walls to the cells, while
carbon dioxide flows from the cells into the capillaries.
2. Stratified tissue – More than one cell layer
a. Outer layer of skin, lining of esophagus and vagina
b. Tissue thickness and its secretions help protect body against
pathogens.
c. Squamous cells only
KEY TERM: Alveolus/alveoli – Small sacs within the lungs in which the exchange of
gasses take place, absorbing oxygen and releasing carbon dioxide.
TYPES OF CONNECTIVE TISSUE AND THEIR FUNCTIONS:
1. Loose connective tissue – Fills space between and penetrates into organs.
2. Dense connective tissue – Regularly and irregularly arranged, embedded
fibers.
3. Specialized connective tissue – Connective tissue with specialized functions.
THREE TYPES OF LOOSE CONNECTIVE TISSUE:
1. Reticular – Located in spleen, lymph nodes and bone marrow.
- Filters harmful substances from blood and lymph.
2. Areolar – Located in loose accumulations between tissues and organs.
- Most widely distributed
- Connects tissues
- Three cell types –
1. Fibroblasts – repair
2. Macrophages – Phagocytosis
3. Mast cells – Produce anticoagulant heparin and
histamines, an inflammatory substance.
3. Adipose – Located under skin
- Provides padding
- Provides insulation
- Provides a place for fat storage
DENSE CONNECTIVE TISSUE:
Fibrous – Provides strong, flexible connections and the formation of scars.
1. Regular arrangements – tendons, ligaments, aponeuroses
2. Irregular arrangements – muscle sheaths, joint capsules and fascia.
KEY TERMS:
1. Tendon – a fibrous connective tissue that connects muscle to bones
2. Ligament – a fibrous connective tissue that joins bone to bone
3. Deep fascia – band of connective tissue that covers or binds together body
structures within cavities
4. Dermis – connective tissue that makes up the inner layer of skin.
SPECIALIZED CONNECTIVE TISSUE:
1. BONE – located in skeleton
a. Forms bones to support body
b. Protect organs and tissues
2. CARTILAGE – located in the nose, ears, trachea, Eustachian tubes
and at bone joints
Provides firm, but not rigid structure and padding between bones
3. BLOOD – located throughout blood system
a. transports materials including oxygen through body
b. Combats foreign organisms and cells
4. LYMPHATIC – located in lymph nodes, spleen, tonsils and thymus
a. Forms certain types of white blood cells
5. MYELOID – located in bone marrow
a. forms red and white blood cells and platelets
6. ELASTIC – located along walls of large arteries and alveoli
a. helps in maintaining blood pressure in blood system
b. helps in exhalation of breath in the lungs
CONNECTIVE TISSUE FUNCTIONS:
1. SUPPORT – Bones support body tissues
2. NOURISHMENT – Blood carries nutrients and synovial membranes nourish
cartilage
3. TRANSPORTATION – Blood transports gases, enzymes and hormones to
cells
4. CONNECTION – Tendons connect muscles to bone and Ligaments connect
bone to bone
5. PROTECTION – Bones protect vital organs and Blood cells protect us from
microbes
6. MOVEMENT – Muscles pull on our bones and bone move us through our
environment
7. INSULATION – Adipose tissue insulates, pads
8. STORAGE – Bone stores mineral salts, calcium and phosphorous. Adipose
stores energy
9. ATTACHMENT & SEPARATION – Attaches skin to underlying muscle.
Layers around and between organs.