TISSUE - a group of similar cells that function

together to perform a specialized activity

There are four kinds of tissues:

1. Epithelial tissue = covers body surfaces; lines body cavities, hollow organs (protection), and ducts; and forms glands (secretion).

2. Connective tissue = supports the body and binds its organs; binds organs together, stores energy reserves as fat, and provides immunity.

3. Muscular tissue = for contraction (movement)

4. Nervous tissue = initiates and transmits nerve impulses that

coordinate body activities.

EPITHELIAL TISSUE

General Features:

• consists largely or entirely of closely packed cells with little extracellular material (extracellular matrix) between adjacent cells.

• cells are arranged in continuous sheets, in either single or multiple layer

• cells have a free surface (apical surface) exposed to a body cavity of an internal organ, or the exterior of the body, and a basal surface which is attached to the basement membrane.

• are avascular• with nerve supply

• lies on a connective tissue layer - the basal lamina / basement membrane

• has a high capacity for renewal (high mitotic rate)

• Functions: protection (skin), filtration (kidneys), diffusion (lungs), secretion (glands), absorption (large intestines)

Kinds of Epithelial Tissue:

Based on the shape of the cells.

Squamous – cells are flat; hexagonal; for diffusion

Cuboidal – cube-shaped. Important in secretion and in also in absorption

Columnar – cells are tall and cylindrical

Transitional – cells can readily change

shape esp. when stretch

Based on the number of layers of cells.

Simple epithelium – single layer of cells;

found in areas where diffusion, osmosis, filtration, secretion and absorption occur.

Stratified epithelium – contains two or more layers of cells; protects underlying tissues; found where there is wear and tear.

Pseudostratified epithelium – contains a single layer of a mixture of cell types. Has a stratified appearance, but is a single layer.

These cells are large, but quite thin, and have a prominent, protruding nucleus. Found in linings of the peritoneal, pleural and pericardial cavities. As well as in the glomerulus of the kidney, the walls of

capillaries, and the alveoli of the lungs.

SIMPLE SQUAMOUS EPITHELIUM

These are collecting ducts in the medulla of a mammalian kidney. Each duct is lined by simple cuboidal epithelium, whose nuclei are quite prominent. This type of epithelium is thicker than simple

squamous epithelium

SIMPLE CUBOIDAL EPITHELIUM

A cross section of the small intestine. The tall, vertical cells seen at the top of the tissue are columnar cells (one is shown - red arrow),

which make up simple columnar epithelium (the cells at the bottom of the image are connective tissue). Since columnar cells are quite thick,

they do not readily allow passive diffusion. They have numerous microvilli (seen as a darker pink staining border at their lumenal

edge). The black arrow is indicating a goblet cell.

SIMPLE COLUMNAR EPITHELIUM

Glandular Epithelium-Exocrine

Glandular Epithelium-Exocrine

Glandular Epithelium-Endocrine

Glandular Epithelium-Endocrine

CONNECTIVE TISSUE

General Features:

• do not usually occur on free surfaces • has a nerve supply (except for cartilage)• usually is highly vascular (except cartilage & tendons) • has three basic elements:

– cells – ground substance – fiber The ground substance and the fibers, which are outside the cells, make up the extracellular

matrix.

The matrix may be solid (as in bone), soft (as in

loose connective tissue), or liquid (as in blood)

• the most widespread and abundant type of tissue in the human body

• Function: support, anchor and bind various parts of the body

• also serves for: protection, blood formation, fat storage, filling space

Kinds of Connective Tissue

1) Loose connective tissue Has fibers which are far apart from each other, and

there are many cells.

• Areolar Connective Tissue

found in the lower layers of the skin, mucous

membranes, blood vessels, nerves, and around

body organs. Its function is to provide strength,

• Adipose Tissue

designed to store fat (triglycerides). The cells are

called adipocytes.

• Reticular Connective Tissue contains a network of interlacing reticular fibers.

Its purpose is to form the framework of many organs and bind together smooth muscle tissue cells such as the lymph nodes, spleen and bone marrow

2) Dense Connective Tissue Also called dense fibrous tissue

Has collagen fibers as its main matrix element

They form strong, rope-like structures such as the tendons – attach skeletal muscles to bones ligaments – connect bones to bones at joints

also found in the dermis of the skin

3) Specialized CT:

A. Bone (osseus) tissue

Composed of bone cells (osteocytes) embedded in small spaces called lacunae

Surrounded by concentric rings that consist of mineral salts (calcium)

Small canals (canaliculi) project out of the lacunae and provide a pathway for nutrients and wastes

Has rock-like hardness

B. Cartilage

Composed of cartilage cells chondrocytes found in spaces called lacunae.

Surrounded by a membrane (perichondrium)

No blood vessels or nerves

Cartilage repairs very slowly after it has been injured

Types of cartilage

1) Hyaline cartilage has abundant collagen fibers hidden by a rubbery matrix with a glassy blue-white appearance

ex: ends of long bones, nose, anterior portion of the ribs, and parts of the larynx, trachea, bronchi, fetal skeleton

2) Fibrocartilage

highly compressible

serves as cushion

strongest type

ex: pubic symphysis,

intervertebral discs, and meniscus of the knee. 3) Elastic cartilage

highly elastic

ex: epiglottis of the larynx, tip of nose, external ear, and auditory (Eustachian) tubes.

C. Vascular Tissue (Blood)

Plasma liquid portion of the blood

consists mostly of water along with suspended proteins, and dissolved substances, ions, food molecules, and hormones

Formed Elements solid portions of the blood of three kinds:

1) erythrocytes - oxygen transporter

2) leukocytes – soldiers of the body, has 2 kinds

a. Granulocytes

neutrophils - most abundant of the WBCs; squeeze through the capillary walls and into infected tissue where they kill the invaders and then engulf the remnants by phagocytosis

eosinophils - numbers increase sharply in certain diseases, especially infections by parasitic worms; are cytotoxic, releasing the contents of their granules on the invader

basophils - increases during infection; play an

important part in some allergic responses

b. Agranulocytes lymphocytes – 2 kinds: B and T lymphocytes monocytes - functions in the ingestion of bacteria (macrophage)

3) thrombocytes – important in blood clotting