Dr. Heba Kalbouneh. Dr. Heba Kalbouneh. Dr. Heba Kalbouneh

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1 Dr. Heba Kalbouneh Dr. Heba Kalbouneh Dr. Heba Kalbouneh

2 Basement membrane: What is the basement membrane? - It is a layer of ECM separating the epithelial cells from the underlying connective tissue Basement membrane is a matrix, acellular structure (no cells) and is composed of (proteins, fibers, etc ) Basement membrane is not a membrane but it s a matrix. Basement membrane is a product of epithelial and connective tissue cells. The basement membrane is mainly composed from proteoglycans and glycoproteins, that means it has high amount of sugar (carbohydrates) Under the LM we see basement membrane as a line underneath the epithelial cells. The stain we use called PAS stain (special to stain carbohydrates) Under the EM we see the basement membrane as a two layered structure: Basal lamina: an electron microscopic structure. It has 2 layers: a. Pale layer called lamina lucida (electron lucent).. b. Dark layer called lamina densa (electron dense) -Lamina lucida : composed of integrins and laminins. -Lamina Densa : composed of collagen IV coated with a layer of glycoproteins (more protein) and proteoglycans (more sugar). Reticular lamina:it is composed of fibers called reticular fibers (collagen III). Collagen VII (anchoring protein) anchors collagen III to collagen IV (to help you memorize (3+4=7)): collagen 4 in basal lamina, collagen 3 in reticular lamina and collagen 7 anchors the basal lamina to the reticular lamina (collagen 4 and 3). Both Epithelium and connective tissue cells participate in the formation of basement membrane. The epithelium produces the components of the basal lamina and the connective tissue cells produce the components of the reticular lamina. Is basal lamina exclusive for epithelium? - No, there is basal lamina in other types of tissue like muscle cells for example. Muscle cell is surrounded by a lamina, here it has a different name (external lamina) and it has the same structure. The basement membrane is visible under light microscopy (PAS stain). Electron microscopy shows that the basement membrane consists of

3 overall three layers: the lamina lucida (electron-lucent), lamina densa (electron-dense), and lamina reticularis (electron-lucent) Note that basal lamina is visible only with the electron microscope All three layers seen with the electron microscope represent the single layer seen with the light microscope (basement membrane) - Basement membrane is formed by fusion of two basal laminae, or basal lamina and reticular lamina. E.g.: example of the fusion of two basal laminae: - A capillary is lined by simple Squamous epithelial cells "endothelium". Lung alveolus is also lined by simple Squamous epithelial cells. Each one of them has its own basal lamina. The fusion between these two basal laminae produces a thick basement membrane that is seen under the light microscope. What are the functions of basal lamina? 1. It supports epithelial cells. 2. It acts as a selective barrier (has filtering action) 3. It makes polarity (basal and apical domain) of the epithelial cell. 4. Growth, repair, and regeneration the epithelium -e.g.: the presence of intact basement membrane is necessary as a scaffold for the regeneration of epithelium, ex. burns 5. It effects cell-cell interaction. What is the clinical importance of basal lamina? - Tissue culture (to grow the cells inside dishes, outside the body (invitro)) In cell culture we have to put components of basement membrane molecules in order for epithelial cells to align and form a tissue.

4 - Tumor: its uncontrolled growth of cells. For example, if malignant cells are confined to epithelial tissue and the malignancy does not invade the basement membrane and the underlying connective tissue, the pathologist grades this tumor as grade 1 (Carcinoma in situ) Glandular epithelium Gland: Is a collection of epithelial cells the secrets a certain product, like: proteins, lipids and carbohydrates. Secretion: A certain material that is produced inside the cell and secreted outside the cell to be used within the body. Excretion: When the product is produced in the body and leaves the body (Urine excretion). Epithelial cells can produce 3 types of secretion. Ex: mammary gland produces all types of secretion (proteins, lipids and carbohydrates). How are the glands formed? Glands are epithelial tissue, the covering epithelium or lining epithelium is composed of tightly packed cells set on basement membrane, during fetal development some cells proliferate downward toward the underling connective tissue to form a tube like structure - cells in the center of the tube die to form cavity or lumen - some epithelial cells differentiate into secretary cells (able to secrete a product) - The product is secreted into a lumen and passes through a duct to reach the surface. This type of gland is called exocrine gland - Exocrine gland: if the cells maintain the connection with the surface epithelium, or with a lumen of another organ, ex. Sweat gland duct opens into the surface of the skin, Pancreatic duct opens into duodenum -Endocrine gland : If the proliferating cells lose their connection with the surface. Mass of epithelial cells that differentiates and secrets a product will develop. This mass is surrounded by rich network of capillaries to secret the product (hormone) directly into blood. Hormones are released outside the cells and picked up by these blood vessels for distribution throughout the body

5 1) Exocrine gland: Maintains connection with epithelial surface. So it has a duct. 2) Endocrine gland: does not maintain connection with epithelial surface so it has No duct. Also its secretion goes to blood so it is surrounded by a rich network of capillaries. Classification of the glands: 1) (exo and endo mean where the product goes? ) : A) Exocrine glands: Their products reach the surface of the epithelium or a luminal surface of certain organ. (Exo: outside) B) Endocrine glands: Their products are absorbed by the blood circulation. (Endo: inside) Some glands are mixed exocrine and endocrine glands Like: pancreas (it secrets pancreatic enzymes) Pancreatic enzymes go to the lumen of duodenum (first part of small intestine) through ductal systems. The pancreas also secretes hormones into blood stream (insulin and glucagon) 2) According to the number of cells inside the glands: A) Unicellular glands: Composed only of one cell Like: goblet cell, goblet cells secrete mucus. B) Multicellular glands: Have more than one cell. Like: salivary glands and pancreas. GOBLET CELLS Goblet cells are: 1) Simple columnar epithelial cells. 2) Unicellular glands. - It s named goblet cell because it looks like a wine glass - Wide apically and narrow basally. - The product of this cell is: mucin. - Mucins are glycosylated proteins (glycoproteins, proteoglycans) Once mucins are secreted into the surface, they attract a high amount of water (they become hydrated= mucus). - Goblet cells are found in the intestinal epithelium and the epithelium of respiratory tract. Their mucus secretion is important to protect the cells and lubricate the surface.

6 Explanation: - In the intestine, mucus protects the underlying cells from the acid produced from stomach or the microbes in the ingested food - In the respiratory tract, the mucus layer acts as a sticky layer to clean the inhaled air from dust particles, lubricates and humidifies the inhaled air (The main function of mucus is protection and lubrication) - The goblet cell is highly polarized with the nucleus and other organelles concentrated at the base of the cell (basal domain). The apical domain is occupied by membrane-bound secretory granules containing mucin - Goblet cells are not stained by H and E, they appear white or empty cells. Because goblet cells contain high amount of polysaccharides, they can be stained by PAS stain Multicellular glands: are composed of secretory cells and ductal cells 1) Ducts: Ductal cells line the duct 2) secretory units : The cells specialized for secretion. Classification of multicellular glands is according to two criteria: 1) According to the structure of the duct (branched/unbranched): A) Simple gland: has only one single unbranching duct. B) Compound gland: has more than one duct (branching ducts). 2) According to the shape of the secretory units A) Acinar (Alveolar) If the cells are arranged into a ball like structure (acinus means grape). B) Tubular: If the cells are arranged into a tube like structure - Ducts and secratory units are composed of epithelial cells. - In large multicellular glands, the gland is surrounded by a thick layer of connective tissue (capsule) - The capsule sends septa (divisions) to divide the gland into lobes. - Each lobe is divided into lobules Glands are composed of: - Epithelium tissue and supporting connective tissue containing blood vessels and nerve supply.

7 - The part of the gland that produces its main function (secretion): is the epithelium (secretory units and their ducts) - It is important to know these two terms: Parenchyma: The main tissue producing the main function of the organ. Stroma: The supporting connective tissue, with its blood vessels and nerve supply. For example: In glands, epithelium is the parenchyma and the connective tissue is the stroma In the Heart parenchema : heart muscle cells. They produce contraction of the heart. stroma : connective tissue (with the embedded blood vessels and nerves), supporting these muscle cells Any organ in our body has parenchyma and stroma.