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Try free for 5 days Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer. General histology. Summary Tissues are formed by cells and can be differentiated into four different types: connective tissue , muscle tissue , nerve tissue , and epithelium epithelial tissue.
Overview of the four basic tissue types There are four basic types of tissues in the body: epithelium , connective tissue , nervous tissue, and muscle tissue. Striated muscle Cardiac muscle Skeletal muscle Smooth muscle Epithelium epithelial tissue Surface epithelium Glandular epithelium Epithelium Definition : : The epithelium is one of four basic types of tissues and is present in almost all organs of the human body as lining and glandular tissue.
Classification according to function Surface epithelium Glandular epithelium Distribution : covers all inner and outer surfaces of the body skin and mucous membranes Exception: synovial membrane synovium The synovial membrane is composed of synoviocytes not epithelial cells!
Formation : Different types of epithelia are formed from the three germ layers. Ectoderm : epithelium of skin and skin appendages Mesoderm Epithelium of serous membranes mesothelium : peritoneum , pleural, and pericardial cavities Cells lining the inner surface of blood and lymphatic vessels endothelium Endoderm : epithelium of the respiratory and gastrointestinal tract Surface epithelium Definition : A specialized layer of tissue formed by closely aggregated cells that line the outer surface of organs, blood vessels, the skin , and the inner surface of body cavities.
Divided into squamous, cuboidal, and columnar types. Criteria for classification Layers Simple epithelium : a single layer of epithelial cells with all cells attached to the basement membrane Pseudostratified epithelium : a single layer of cells with the appearance of multiple layers as a result of the nuclei positioned at different levels Stratified epithelium : two or more cell layers with the basal layer attached to the basement membrane Cell shape Explanation : The cell shape of the upper cell layer of a type of epithelium determines the name for the whole epithelium.
Examples: skin , esophagus , cervix , serous membrane e. There are several different basic types of exocrine glands. Click here to find out what types of exocrine glands there are. Glands are dealt with in more detail in the Glandular Tissues topic. Now test your knowledge out with this crossword puzzle.
What do they do? What are their characteristics? There are two major types of epithelia: Covering epithelia and Glandular epithelia Note: epithelia is the plural form of epithelium! Covering Epithelia are important for: Selective diffusion - for example transfer of gases, nutrients and waste products between the blood and surrounding tissues.
Glandular Epithelia: Glands are an organised collection of secretory epithelial cells. Mallory-Azan X These glands are simple tubular glands that open onto the surface of the intestinal lumen. The lining epithelium is simple columnar with brush border and presents many interposed goblet cells. Human small intestine. You can see the villi lined by simple columnar epithelium where we find many goblet cells.
Goblet cells are unicellular exocrine glands that secrete mucus. Human small intestine at higher magnification. The micrograph has been digitally modified to make the goblet cell mucus easily visible light blue. Simple columnar epithelium composed of enterocytes with microvilli in the apical domain and goblet cells. Goblet cells are unicellular, intraepithelial, exocrine glands that excrete mucus in order to lubricate and protect the luminal surface of the hollow organ.
Because of the high content of mucus, that is hydrophobic, the goblet cells are colorless or only slightly stained when conventional staining methods are used. Micrograph at high magnification where you can see the enterocytes interspersed with goblet cells that have an intracellular voluminous amount of colorless mucus.
Simple columnar epithelium consisting of enterocytes and goblet cells stained with alcian blue. This is a selective method for mucins that are stained bright blue. Alcian blu-hematoxylin X Transversal section where you can see many goblet cells. Alcian blue-hematoxylin X Mouse colon. You can see the excreting tubules of the glands. This staining method highlights the mucus of the goblet cells bright blue.
Human seminal vesicles. Seminal vesicles are the simplest form of exocrine multicellular gland, where the whole lining epithelium is made of excreting cells.
In addition, the gastric mucosa and the endometrium of the uterus have this kind of organization. Endometrium of human uterus in the proliferative phase. Another example where the whole lining epithelium is made of excreting cells. Human stomach.
Pyloric region. Rat duodenum. Large excretory duct lined by simple columnar epithelium. Ignesti X Human sublingual gland. Compound tubular exocrine glands that produce a mucous secretion. Human sublingual gland at higher magnification. You can see the stretched secretory portion with an easily visible lumen. The cells have an elongated, flattened nucleus at the base and a colorless cytoplasm. Human soft palate. Selective staining method for mucus that is stained bright blue. Human duodenum.
These glands are exocrine glands located in the submucosa of the duodenum that secrete an alkaline mucus. Figure EA. The easily visible shaded orange gland lumen is typical of the tubular glands and make them distinguishable from acinar glands also in transverse section.
The cytoplasm of the cells of the secreting units is very pale. A flattened nucleus at the base of the cells is a feature that makes glands with a mucous secretion unmistakable. Figure EB. Human penile urethra. Urethral glands. These tubular glands excrete mucus arrows. Human fetal tongue. You can see different types of exocrine glands: tubular glands with a mucous secretion paler and acinar glands with a serous secretion darker.
You can see different types of exocrine glands: tubular glands with a mucous secretion and acinar glands with a serous secretion. Human fetal tongue at higher magnification. You can see the different morphology of the two types of exocrine glands.
You can distinguish the tubular glands with mucous secretion from acinar glands with serous secretion because the first have an elongated secretory unit, an evident lumen, a flattened nucleus located at the base of the cell and a pale cytoplasm, whereas the latter have a hardly visible lumen, a round nucleus located at the center of the cell and a strongly stained cytoplasm.
Compound acinar exocrine gland with serous secretion. Human pancreas. Exocrine component of the pancreas. High magnification of secretory units of a compound acinar exocrine gland with serous secretion. You can notice that the lumen of the acinus is hardly visible, and that the secreting cells have a round nucleus and a brightly stained cytoplasm.
Human parotid gland. The parotid gland is a compound serous exocrine acinar gland. You can see the different morphology of: a the excretory ducts, which have an evident lumen lined by a cuboidal or columnar epithelium; b the secretory units, made of more deeply stained secreting cells with a cytoplasm in which the secretory granules are highly evident.
Simple cuboidal epithelium is found in glandular tissue and in the kidney tubules. Simple columnar epithelium lines the stomach and intestines.
Pseudostratified columnar epithelium lines portions of the respiratory tract and some of the tubes of the male reproductive tract.
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