Human Body Tissues: Characteristics and Types
Tissues: General Characteristics, Histogenesis, and Classification
Tissues are a combination of cells and their products that have the following in common:
- Embryonal origin
- Morphology
- Functions
There are six general types of tissue in our body:
- Epithelial
- Connective
- Muscle
- Nerve
- Blood
- Reproductive
Epithelial Tissue
Epithelial tissue forms the border between the inner and outer environment.
- Covers surfaces in a uni- or multi-stratified manner.
- Almost no extracellular matrix (ECM).
- No blood supply.
- Functions include: Protection, Secretion, Absorption.
- Cell junctions: Desmosomes, nexus, zonula adherens, hemidesmosomes.
- Cells with two poles:
- Apical (with cilia & microvilli)
- Basal (attached to the basal membrane)
Unistratified/Unilayered Epithelium
- Simple squamous epithelium: Blood, Lymph vessels
- Simple cuboidal epithelium: Thyroid gland
- Simple columnar epithelium: Intestine
- Pseudostratified epithelium: Trachea & Bronchi
- Transitional epithelium of Henle: Ureter and urinary bladder
Multistratified Epithelium
- Multistratified squamous keratinizing epithelium:
- Dead cells in the superficial layer
- 5 layers
- Folded basal membrane
- Epidermis of skin
- Multistratified squamous non-keratinizing epithelium:
- Preserved nuclei
- Folded basal membrane
- 4 layers
- Esophagus, vagina, and mouth
- Multistratified squamous non-keratinizing epithelium of the eye:
- Non-folded basal membrane
- No keratinization
- 10 layers
Connective Tissue
- Different structures and functions.
- Great amount of ECM and supplied with blood.
- Mesenchyme origin.
- Fills interstices of body structures and specialized elements, holding them together.
- Functions: Supportive, Trophic, Connective, Defending, Metabolism.
Embryonal Connective Tissue
- Mesenchyme
- Mucoid
Mature Connective Tissues
- Ground substance produced by fibroblasts contains:
- Glycosaminoglycans & Proteoglycans
- Chondroitin sulfate & Heparin sulfate
- Collagen fibers, elastic fibers
- Optically homogenous, retains water, and exhibits Metachromasia
- Fibrous connective tissue with fibrillar intercellular substance:
- Collagenous: collagen fibers made of collagen fibrils
- Elastic: elastic fibers made from elastin, such as in Ligamentum flava
- Reticular: Reticular fibers and reticulum cells
- Pigmentous: melanocytes (producing) & melanophores (storing) melanin
- Connective tissue with solid intercellular substance: Cartilage, Bone, Dental
- Adipose tissue:
- White adipose tissue: unilocular adipocytes, 1 cell + 1 lipid droplet
- Brown adipose tissue: multilocular adipocytes, 1 cell + > 1 droplets
Muscle Tissue
- Highly differentiated cells that facilitate muscle contraction.
- No intercellular substance.
- Muscle cells are elongated cells with myofibrils made of myofilaments.
- Voluntary / Involuntary Muscles.
- Striated / Smooth Muscles.
- Striated Voluntary: skeletal Muscles, symplast type of organization, Mesoblast origin.
- Striated Involuntary: Muscles of the heart, syncytium type of organization, Mesoblast origin.
- Smooth Involuntary: Muscles of the Viscera, cell type of organization, Mesenchyme origin.
Nerve Tissue
Ectoderm origin. Tissue made up of neurons and glial cells. Accepts, modulates, and transports information from the outer environment. Controls homeostasis of the body.
Neurons
(Axon – Body – Dendrites)
- Star-shaped: spinal cord
- Granule-shaped
- Pear-shaped: cerebellum
- Spindle-shaped
- Pyramidal: cortex cerebri
Glial Cells
- Microglial cells
- Ependymal cells
- Schwann cells
- Oligodendrocytes
- Astrocytes
Blood Tissue
- Plasma (55%) + Solid contents (45%)
Plasma
- Non-cellular part of blood tissue.
- Plasma proteins such as globulins and albumins.
- Transport of blood cells, immune response, regulation of temperature, etc.
Solid Contents
- Erythrocytes: Red Blood Cells (RBC)
- Thrombocytes: Blood platelets
- Leukocytes
- Agranulocytes: Lymphocytes, Monocytes
- Granulocytes: Basophil, Eosinophil, Neutrophil