Post on 16-Jul-2015
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
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