5 Dr. Heba Kalbouneh

Transcription

1 5 Dr. Heba Kalbouneh

2 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 glands produce all types of secretion (proteins, lipids and carbohydrates). How are 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 tube like structure - cells in the center of the tube die to form cavity or lumen - These epithelial cells differentiate into secretary cells (able to secrete a product) - The product is secreted into a lumen and pass 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. Pancreatic duct opens into duodenum -Endocrine gland : If the proliferating cells lose their connection with the surface. Mass of epithelial cells that differentiate and secret a product will develop. This mass is surrounded by rich network of capillaries to secret product (hormones) 1 P a g e

3 directly into blood. Hormones are released outside the cells and picked up by these blood vessels for distribution throughout the body 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 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. B) Endocrine glands: Their products are absorbed by the blood circulation. 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. 2 P a g e

4 - 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. Explanation: - In the intestine, mucus protects the underlying cells from the acid produced from stomach. - 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). 3 P a g e

5 2) According to the shape of secretory units A) Acinar (Alveolar) If the cells are arranged into ball like structure (acinus means grape). B) Tubular: If the cells are arranged into tube like structure - Ducts and secretory 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. - 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 : Supporting connective tissue with blood vessels and nerve supply. For example: In glands, epithelium tissue is the parenchymal and the connective tissue is the stroma Another example: The Heart parenchyma: 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. 4 P a g e

6 Ducts - In large glands, as you go away from the secretory unit, the duct becomes larger and the lining epithelium becomes thicker (cuboidal to columnar and simple to stratified) - Excretory ducts: are generally passive conducting tubes - Larger excretory ducts may be lined by stratified cuboidal or columnar epithelium. Myoepithelialcells - Located between the secretory cells and the basement membrane - Rich in actin and myosin (contractile proteins) - When these cells contract, they squeeze the secretory cells and ducts, helping to extrude the contents. Classification according to the type of secretion: 1. Mucous glands: These glands produce a viscid, slimy, carbohydrate-rich secretion which is called mucus, e.g; the goblet cells. 2. Serous glands: These glands produce thin, watery, protein-rich secretions, often high in enzymatic activity e.g; the parotid salivary gland. 3. Mixed (seromucous or mucoserous) glands: These glands produce both mucous and serous secretions. e.g; the sublingual and submandibular salivary glands. Note: the salivary glands that produce saliva inside the oral cavity are: Parotid Sublingual Submandibular 5 P a g e

7 Classification according to the mode of secretion (how these cells release their product): Merocrine glands: The secretory product is delivered in membrane-bounded vesicles (secretory vesicles) to the apical surface of the cell. Here, vesicles fuse with the plasma membrane and extrude their contents by exocytosis e.g; pancreas, salivary glands Apocrine glands: In these glands part of the apical cytoplasm is lost along with the secretory material. e.g; lactating mammary glands, special sweat glands located in axilla and perianal area and the ceruminous glands of the external auditory tube. Holocrine glands: In these glands the entire cells laden with secretory material disintegrate and all of the cellular contents are discharged from the gland as secretions e.g; the sebaceous glands of skin. Connective tissue The differences between epithelial and connective tissue - Epithelial cells are tightly packed (no or minimal spaces between cells) - Connective tissue cells are widely separated, no cell junctions, high amount of ECM - Epithelium originates from the 3 embryonic layers (endoderm : GI tract, ectoderm : skin, mesoderm: blood vessels ) - Connective tissue originates from the mesenchyme (the middle layer of embryo (mesoderm) - Connective tissue is composed of cells and ECM (ground substance and fibers). It is a filing tissue - Connective tissue is is highly vascularized - The Ground substance (water + stabilizing macromolecules to form gel like structure) doesn t have shape - Connective tissue has variable regeneration power. We will study different types of c.t, and each has its own regeneration power 6 P a g e

8 The function of the connective tissue: 1- Support: this support is mechanical support (support epithelial tissue) and nutritional (c.t has blood vessels (capillaries) and by diffusion epithelial cells get their oxygen and nutrients and eliminate their waste products) 2- defense and protection ( contains inflammatory cells ) 3- storage ( like adipose tissue= it stores lipids) 4- transport (it is a medium for transport of small molecules and gases) We have 2 kinds of cells in c.t * Fixed cells: always found in c.t *transient cells: come on demand if we have inflammatory process, they are recruited from the blood and enter the c.t to perform their defense function Fibroblast - Fibroblast:-active cell that synthesizes fibers + ground substances (Extra cellular material), it is the most numerous cell in c.t - Blast in histology means active cell in synthesis - Fibrocyte is the mature/ retired cell that has done its job and it s in a resting state - Originate from undifferentiated MESENCHYMAL cells (from mesenchyme) - Fibroblasts make collagen fibers (the main component of tendons) Fibrocyte can redifferentiate to fibroblast in case of injury, in order to replace the damaged tissue with ECM Fibroblast Active large abundant cytoplasm full with organelles Prominent nucleus and rounded euchromatic nucleus Many Processes Elongated and more rounded cell Growing phase Fibrocyte Inactive Smaller Scant cytoplasm with Little organelles Nucleus dark (heterochromatic) and flattened Fewer processes Spindle-shaped Mature phase 7 P a g e

9 - Rarely undergo cell division: mature cell doesn t undergo division except in the case of injury - Myofibroblast contains a high amount of actin and myosin, these cells produce contraction at the site of skin wound for example, these cells are then capable of speeding wound repair by contracting the edges of the wound. Summary Active fibroblast - Closely associated with collagen bundles. - Elongated, fusiform, and have many processes. - Cytoplasm is acidophilic and difficult to be differentiated from ECM. Note that the ECM is acidophilic. Since we cant see the cell membrane under the light microscope using H&E, you cant outline the cytoplasm of fibroblasts. They appear as naked nuclei - Nucleus is large (ovoid) euchromatic, prominent nucleolus - E.M: prominent Golgi, mitochondria, rer, actin and myosin. Resting fibroblast (fibrocyte) - Smaller and simple shaped - The nucleus is smaller and darker (heterochromatic). - Few processes. - E.M: few rer. - When stimulated, it may revert to fibroblast. Myofibroblast - Has features of both smooth muscles and fibroblasts. - Their contraction is responsible for wound contraction. 8 P a g e