Tissues

            Tissues are considered to be one of the very important components of the body. A Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning. 

            The study of tissue is known as histology or, in connection with disease, histopathology.

            The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, and the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of clinical diagnosis and prognosis.

            There are four types of tissues in the human body: Epithelial tissues, connective tissues, muscle tissues and nervous tissues.

       1. Epithelial 

             It is made of cells arranged in a continuous sheet with one or more layers, has apical & basal surfaces. A basement membrane is the attachment between the basal surface of the cell & the underlying connective tissue.

             The number of cell layers & the shape of the cells in the top layer can classify epithelium namely, simple, stratified, pseudostratified columnar, and glandular. 

               

            Simple Epithelium is a one cell layer.

            Stratified epithelium has two or more cell layers.

            Pseudostratified Columnar Epithelium. This is when cells of an epithelial tissue are all anchored to the basement Membrane but not all cells reach the apical surface

            Glandular Epithelium (1) Endocrine: Release hormones directly into the blood stream and (2) Exocrine - Secrete into ducts.

         2. Connective

              It contains many different cell types including: fibroblasts, macrophages, mast cells, and adipocytes. Connective Tissue Matrix is made of two materials: ground substance - proteins and polysaccharides, fiber – reticular, collagen and elastic.

              Classification of Connective Tissue:

Loose Connective - fibers & many cell types in gelatinous matrix, found in skin, & surrounding blood vessels, nerves, and organs.

Dense Connective - Bundles of parallel collagen fibers& fibroblasts, found in tendons& ligaments.

Cartilage - Cartilage is made of collagen & elastin fibers embedded in a matrix glycoprotein & cells called chondrocytes, which was found in small spaces.

Cartilage has three subtypes:

Hyaline cartilage – Weakest, most abundant type, Found at end of long bones, & structures like the ear and nose,

Elastic cartilage- maintains shape, branching elastic fibers distinguish it from hyaline. 

Fibrous Cartilage - Strongest type, has dense collagen & little matrix, found in pelvis, skull & vertebral discs.

             3. Muscle

It is divided into 3 categories, skeletal, cardiac and smooth.

• Skeletal Muscle – voluntary, striated, striations perpendicular to the muscle fibers and it is mainly found attached to bones.

• Cardiac Muscle – involuntary, striated, branched and has intercalated discs

• Smooth Muscle – involuntary, nonstriated, spindle shaped and is found in blood vessels & the GI tract.

         4. Nervous

Consists of only two cell types in the central nervous system (CNS) & peripheral nervous system (PNS):

• Neurons - Cells that convert stimuli into electrical impulses to the brain, and Neuroglia – supportive cells.
• Neurons – are made up of cell body, axon and dendrites. There are 3 types of neurons:
• Motor Neuron –  carry impulses from CNS to muscles and glands,
• Interneuron - interpret input from sensory neurons and end responses to motor neurons
• Sensory Neuron – receive information from environment and transmit to CNS.
• Neuroglia – is made up of astrocytes, oligodendrocytes, ependymal cells and microglia in the CNS, and schwann cells and satellite cells in the PNS.

All tissues of the body develop from the three primary germ cell layers that form the embryo:

• Mesoderm – develops into epithelial tissue, connective tissue and muscle tissue.
• Ectoderm - develops into nervous tissue and epithelial tissue.
• Endoderm – develops into epithelial tissue.

A tissue is like love. A simple idea but somehow complicated. :)