Types of Body Tissues 1. Epithelial tissue. 2. Connective tissue. 3. Muscular tissue. 4. Nervous tissue. Epithelial tissue It is present in two forms: 1-Epithelia or epithelial membrane (contiguous cells covering external body surfaces and lines internal cavities). 2-Glands (from invaginated epithelial cells). Functions of epithelial tissue: A-Protection. B-Transcellular transport. C-Secretion of mucus, hormones and enzymes. D-Absorption. E-Detection of sensation as taste buds and retina . F-Selective permeability. Characteristics of epithelium:
1.The cells are tightly bound together by junctional complex. 2.Is avascular (nourishment by diffusion from CT.) 3.Rests on basal lamina (formed by epithelial cells) that separate epithelial cells from underlying CT. 4.Has little intercellular space and little extracellular matrix. 5.Its cells exhibit a high turnover rate and constant cell renewal for a particular epithelium Classification of epithelial membranes
According to the number of cell layers: I. Simple (formed of one layer of cells) II. Stratified (formed of more than one layer of cells) According to the morphology of the cells: 1-Simple squamous epithelium: thin low (flat) profile polygonal cells with central flat nuclei. (Ex. pulmonary alveoli, loop of Henle, endothelium of blood vessels, pleura and peritoneal cavities). Simple squamous epithelium 2-Simple cuboidal epithelium: single layer of cuboidal polygonal cells with central round nuclei (Ex. ducts of many glands, covering of the ovary, follicular cells of thyroid follicles and some kidney tubules). 3-Simple columnar epithelium: single layer of columnar cells with ovoid nuclei located in basal half of cells (Ex. lining of stomach, gall bladderand large ducts of glands) . Or may have cilia as in oviduct, uterus, small bronchi and ductuli efferentes. * Simple columnar epith. may exhibit goblet cells and microvilli as in intestine 4-Stratified squamous ( Non-keratinized) epithelium: Is formed of several layers of cells in which the most basal layer rests on basal lamina and it is cuboidal cells, the intermediate layers are polyhedral or polymorphous. The most superficial layer is formed of flat squamous cells not covered with keratin (Ex.lining of mouth, oral pharynx, esophagus, true vocal cords and vagina). 5-Stratified squamous (Keratinized) epithelium: similar to non keratinized type but the superficial layer is covered with keratin (Ex. epidermis of skin specially in soles and palms) 6-Stratified cuboidal epithelium: is composed of two layers only of cuboidal cells (ex. Ducts of sweat glands). 7-Stratified columnar epithelium: Is formed of more than one layer of cells with superficial columnar cells (ex. conjunctiva of the eye, large excretory ducts and regions of male urethra). 8-Transitional epithalium: is formed of many layers of cells, the basal layer is formed of low columnar or cuboidal cells, while the superficial layer is formed of large dome shaped binucleated cells (in empty bladder). *In full bladder the dome-shaped cells become flattened and the epithelium becomes thinner. Pseudostratified columnar epithelium
It appears to be stratified but it is composed of single layer of cells that all are resting on the basal lamina but only some of cells reach the surface of epithelium. Theses tall cells have narrow base and broad apical surface. Cells not extending to the surface have broad base and narrow apical end. The nuclei are located at different levels (ex. Male urethra, epididymis and large excretory ducts).Ciliated Pseudostratified epithelium with goblet cells, has ciliated tall cells that reach the free border (ex. trachea, primary bronchia and nasal cavity) without goblet ex. auditory tube and lacrimal sac. Pseudo stratified columnar ciliated epithelium with goblet cells. Polarity and cell-surface specializations
Apical domain. As microvilli, cilia, stereocilia and flagella. Basolateral domain. As junctional specializations and intercellular interdigitations. Apical and basolateral domains are separated by tight junctions. Lateral membrane specializations (Junctional complex)
1-Occluding or tight junctions (Zonulae Occludetes): forms impermeable barrier, apically located, form belt-like junction that formed by fusion of transmembrane proteins of adjacent cell membranes. 2-zonulae Adherentes: just basal to tight junction & encircle the cell. The intercellular space betwee joining cells is occupied by the extracellular cadherins that attached to intracellular actin filaments. *fascia adherens is similar to zonula adherens but dosenot around the circumference of the cell. 3-Desmosomes (Maculae Adherents): weld-like junctions appear randomly along the lateral cell membrane. They are formed of attachment plaques on the cytoplasmic aspect of adjoining cells. The intermediate filaments of both cells are inserted in theses plaques forming hairpin turn to disperse the shearing forces on the cell. 4-Gap (nexus or communicating) junctions: are widespread in epithelial tissues, cardiac muscle, smooth muscle and neurons. They are narrow gaps (2nm) to communicate adjacent cells. They are belt by transmembrane proteins that have aqueus pores (connexons). Lateral membrane specializations (Junctional complex) Basal surface specialization
1-Basal lamina. 2- Basal enfolding: They increase the surface area of the basal membrane. The basal cytoplasm and mitochondria form finger like projections (striated appearance).They are involved in ion transport and are found in striated ducts of salivary glands. 3-Hemidesosomes: resemble half desmosomes and attached to the basal cell membrane on the basal lamina. The cytoplasmic aspect of cell membrane contains Attachment plaques in which keratin tonofilaments are inserted. Hemidesmosome Gap junction Glands 1-Exocrine glands: secrete their products via ducts
2-Endocrine glands: are ductless, their products pass into the blood or lymph. * Each gland if formed of stroma (C.T. that support and invade the parenchyma ie.capsule and septa) and parenchyma (secretory units and ducts). Exocrine glands Classifications: 1- according to the number of cells:
unicellular (goblet cells) b. multicellular. 2- According to their mode of secretion: merocrine. b. apocrine. c. holocrine. 3-According to the type of secretion: a. mucous glands b. serous glands c. mixed glands (mucous units have serous demilunes) Modes of Secretion Goblet cell Multicellular Exocrine glands
They consist of clusters of secretory cells and ducts. They classified according to their duct shape into: I- Simple glands if their ducts do not branch. II-Compound glands if their ducts branch. They are classified according to morphology of their secretory unit into: I-Tubular glands. II-Alveolar glands. III-Tubuloalveolar glands Types of Exocrine Glands (according to the shape)
Compound acinar Compound tubuloacinar Exocrine glands Pancreas Submandibular gland Endocrine glands They secrete hormones that pass directly into the blood or lymph with ducts. Their cells are arranged either in cords as in pituitary gland or as follicles as in thyroid glands. Diffuse neuroendocrine system, are widespread throughout the digestive tract and respiratory system. Pituitary Gland Thyroid Gland