Tissue in the human body:
(1) Epithelial: 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.
Two types of epithelial tissues: (1) Covering & lining epithelia and (2) Glandular Epithelium.
The number of cell layers & the shape of the cells in the top layer can classify epithelium.
Simple Epithelium - one cell layer
Stratified epithelium - two or more cell layers
Pseudostratified Columnar Epithelium - 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: 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 found in small spaces. Cartilage has three subtypes: (A) Hyaline cartilage – Weakest, most abundant type, Found at end of long bones, & structures like the ear and nose, (B) Elastic cartilage- maintains shape, branching elastic fibers distinguish it from hyaline and (C) Fibrous Cartilage - Strongest type, has dense collagen & little matrix, found in pelvis, skull & vertebral discs.
(3) Muscle: 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: (A) Motor Neuron – carry impulses from CNS to muscles & glands, (B) Interneuron - interpret input from sensory neurons & end responses to motor neurons and (C) Sensory Neuron – receive information from environment & 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.
Development: 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.
Cell Junctions:
Tight Junctions - Form a seal between cells, define apical and basal sides of an epithelial cell
Gap Junctions - An open junction between two cells, which allows ions, & small molecules to pass freely between the cells.
Adherens Junctions - Link actin cytoskeletal elements in two cells.
Desmosomes - Link keratin filaments in adjoining cells and resist shearing forces.
Hemidesmosomes - Anchor keratin fibers in epithelial cells to the basement membrane through integrin anchors.
