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Animal Histology BIOL 241 - جامعة نزوى

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2021-10-12 published at Occasions/ Family category

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1.Animal HistologyBIOL 241 Topic 2: Epithelial Tissues Dr. Issa Al-Amri Department of Biological Sciences & Chemistry College of Arts & Sciences
2.Introduction Tissue is a group of similar cells in close contact with each other which function together to perform a specialized activity. Tissues are classified into four categories based on their structure and function: Epithelia Connective Tissue Muscle Nerve
3.Epithelial Tissue An epithelium is a layer or sheet of cells that covers a body surface or lines its internal surface (cavity or duct), or as secretory elements known as glands. It is developed from all three embryonic germ layers: ectoderm, mesoderm, and endoderm. Epithelium is composed mainly of cells with very small amounts of intercellular substance. The cells have strong adhesion due to adhesion molecules, membrane interdigitations and intercellular junctions.
4.Epithelial Tissue The epithelium has a free apical surface which is either exposed to air or fluid, basal surface resting on basement membrane and lateral surface facing the neighbouring cells. Its lower surface is resting on a basement membrane, which rests upon an underlying connective tissue. The basement membrane separate epithelium from connective tissue and blood vessels. Epithelia are avascular (no direct blood supply). It depends on diffusion of molecules (through basal lamina) from the underlying blood supply of the connective tissue for exchange of nutrients, gases and waste products.
5.Epithelial Tissue A. Function: Formation of a protective layer (epidermis). Absorption of water and solutes (intestine). Secretion (intestine, various glands). Excretion (kidney tubules). Selective permeability by tight junctions. Transcellular transportation: molecules transported from epithelial surface to another via: Diffusion (O2 and CO2 across cells of lung alveoli) , Carrier proteins (amino acids in intestine cells), and Vesicles (immunoglobulin A (IgA)).
6.Epithelial Tissue B. Classification: Classification of epithelia based on two criteria: Number of cell layers Cell shape 1. Layers: Simple epithelia are one cell layer thick. Stratified epithelia are two or more cell layers thick. Pseudostratified epithelium is an intermediate type that appears stratified but really is one cell layer thick. Transitional epithelia (lining urinary passage in kidney) line cavities, which may be distended (expanded) or relaxed, and the thickness of the epithelium varies with the degree of distension.
7.Epithelial Tissue Shape: Squamous (flat cells; lining of blood vessels) Cuboidal (cuboidal cells; surface of ovary) Columnar (columnar cells; stomach) Cuboidal and columnar cells form glandular epithelia. Stratified epithelia are classified according to shape of the cells at the free surface.
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9.Epithelial Tissue Classification of Epithelia
10.Classification of Epithelia
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17.Epithelial Tissue C. Basal epithelial surfaces : Basal lamina : Beneath the layer of epithelial cells is an underlying noncellular structure known as the basal lamina which is secreted by the epithelial cells. The basal lamina is associated with an additional layer (reticular lamina) secreted by other cells. Together the basal lamina and the reticular lamina make up the basement membrane. Basal lamina is an extracellular supportive structure 20 – 100 nm thick and made up of collagen type IV.
18.Epithelial Tissue Hemidesmosomes : Specialized junctions resembles half of desmosome. Mediate adhesion of epithelial cells to the underlying extracellular matrix. Present on basal surface of basal cells (e.g. trachea) and myoepithelial cells.
19.Epithelial Tissue
20.Epithelial Tissue Basal plasma membrane infoldings : Common in ion-transporting epithelia (e.g., distal convoluted tubule of the kidney, striated ducts in salivary glands). They form deep invaginations that compartmentalize mitochondria. Function. They increase the surface area and bring ion pumps (Na+–K+ adenosine triphosphatase [ATPase]) in the plasma membrane close to their energy supply (ATP produced in mitochondria).
21.Epithelial Tissue Apical epithelial surfaces : Epithelial surfaces possess microvilli, stereocilia and cilia. Microvilli: Fingerlike projections of epithelia 1 µm long extend into lumen and increase cell surface area. Glycocalyx (sugar coat) present on their surfaces. Microvilli and glycocalyx constitute the brush border of kidney proximal tubule cells and striated border of intestinal absorptive cells. In trachea, they trap dust and germs.
22.Epithelial Tissue Diagram showing intedtinal microvilli
23.Epithelial Tissue TEM image showing microvilli
24.Epithelial Tissue Stereocilia : Very long microvilli in epididymis and vas deferens of male reproductive tract (moving sperm). Cilia : Motile cell processes of 5 – 10 µm long arranged in rows in the apical cell surfaces of certain epithelia (e.g. oviduct epithelium), beating in constant direction in living state, and move substances along their surfaces.
25.Epithelial Tissue
26.Epithelial Tissue Cilia : Axoneme forms the internal structure of cilia, which are surrounded externally by the plasma membrane. Axoneme consists of nine doublet microtubules uniformly spaced around two central microtubules (9+2 configuration). Cilia inserted into basal bodies at the cell apex. A cylindrical structure at base of each cilium consist of nine triplet microtubules arranged radially in shape of pinwheel (9+0), similar to centriole. Inner two triplets of basal body give rise to doublet microtubules of axoneme.
27.Epithelial Tissue
28.Epithelial Tissue
29.Epithelial Tissue Cilium with basal body
30.Epithelial Tissue Motile Cilia and flagellum beating in different directions
31.Epithelial Tissue H&E of Cilia
32. SEM of Cilia and microvilli: structure of oviduct epithelial cells microvilli cilia
33.Epithelial Tissue E. Lateral epithelial surfaces : Cells with junctions that provide adhesion between cells and control movement of materials into and out of lumina. I. Junctional complex: Cell membranes separated by narrow intercellular spaces occupied by proteoglycans and glycoproteins called cell adhesion molecules. Cell to cell adhesion is due to the binding action of the integral membrane glycoproteins and the lateral specialization forming intercellular junctions.
34.Epithelial Tissue I. Junctional complex: Types : Tight junction (zonula occludens): Surround entire apical surface of adjacent cells. Prevent substance movement into intercellular space. Intermediate junction (zona adherens): Surrounds entire length of epithelial cell. 3. Desmosome (macula adherens) Transmembrance glycoproteins link adjacent cells.
35.Epithelial Tissue II. Gap Junctions: Present along the lateral wall of almost all cells except skeletal muscles. Gap junctions have an important role in coordinating the activities of cells such as heart coordinated beats (allow heart pulse to travel from pacemaker along cells so it doesn’t die). III. Interdigitations: Irregular fingerlike projections interlock adjacent epithelial cells
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38.H&E Simple & Pseudostratified : Figure 1 : Squamous (SE) (kidney) Figure 2: Squamous and Cuboidal (CE) (kidney) Figure 3: Columnar with microvilli (MV) (duodenum) - Goblet cells (GC) secret mucus Figure 4: Pseudostratified columnar with cilia (C) (nasal cavity): - terminal web (TW) support cilia which move mucus along epithelial surface - Basal cells (BC)
39.H&E Stratified & Transitional: Figure 1 : Cuboidal (sweat gland) - Epithelium of duct surrounded by basal lamina (BM) Figure 2: Squamous nonkeratinized (lining of oesophagus) - Nourishment to surface cells via diffusion from blood vessels of connective tissue(CT) - cells lie on basement membrane called basal layer (BL) Figure 3: Squamous keratinized (skin) - thick layer of dead cells containing keratin (K) Figure 4: Transitional (bladder) - Relaxed indicated by round, dome-shaped (rC) cells)
40.Figure 1 : TEM: Pseudostratified ciliated columnar epithelium. (trachea) - All cells touch basal lamina (BL) Organelles: rER, mitochondria, Golgi, secretory granules
41.TEM : Epithelial Junctions: Figure 1 : Tight junction. (sweat gland) - Tight junction (arrow) separate lumen of Intercellular canaliculi (IC) from intercellular space Figure 2: Zona occludens (human tissue) - freeze fracture - Junctional elements separated from lumen (arrowheads)
42.Epithelial Tissue: Glands F. Glandular epithelium : This type of epithelial tissue specialized to produce secretion stored in membrane-bound vesicles and secretory granules. Epithelia cells proliferate and penetrate the underlying connective tissue and form secretory units. I. Structure: Gland consists of secretory portion (parenchyma) and ductal epithelial cells, separated by basal lamina from supporting connective tissue (stroma).
43.Epithelial Tissue: Glands Classification: Glands classified into three types on base of site of secretion: Endocrine glands secrete into blood stream. Exocrine glands secrete into a duct or surface. Paracrine glands secrete into local extracellular space.
44.Epithelial Tissue: Glands Endocrine glands: These are ductless (have no ducts), and their secretion (hormones) carried directly to their site of action by the bloodstream. Unicellular (e.g. individual endocrine cells in gastrointestinal and respiratory epithelia). Multicellular (e.g. adrenal gland), secretory material released into capillaries outside the basal lamina of glandular epithelium.
45.Endocirne Glands
46.Epithelial Tissue: Glands Eexocrine glands: These glands composed of secretory units and duct systems. They are classified in different ways: According to number of cells: Unicellular glands like goblet cells , present in large number in the lining epithelia of large intestine and respiratory tract. Multicellular glands which form most of the glands of the body, example salivary glands.
47.Epithelial Tissue: Glands Mode of secretion: Merocrine glands (exocrine part of pancreas), where the secretory products leave the cells by exocytosis with no loss of cellular components. Holocrine glands (sebaceous glands), in which the secretory product is shed with the whole cell, a process which involves destruction of the secretory cell. Apocrine glands (mammary and axillary sweat glands), in which the secretory product is discharged with parts of the apical cytoplasm.
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51.Epithelial Tissue: Glands Type of secretory product : Serous glands composed of serous acini and secrete watery secretion e.g. parotid gland and serous acini of pancreas. Cells are pyramidal or cuboidal, with round nuclei, basal striations, apical secretory granules, and narrow lumen of the acini. Mucous glands composed of mucous acini and secrete viscid mucus secretion (glycoprotein), e.g. sublingual salivary gland. Cells cuboidal to columnar, pale staining cytoplasm, flat basal nuclei and wide lumina of the mucous acini. Seromucous glands (mixed) contain both serous and mucous acini e.g. submandibular salivary glands.
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53.Epithelial Tissue: Glands Shape of ducts transporting secretion : Simple exocrine glands if ducts are unbranched. Compound exocrine glands if the ducts branch repeatedly. Shape of secretory portion contains cells responsible for secretion : Tubular: Simple unbranched: intestinal glands Simple branched: fundic glands of stomach Compound: kidney
54.Epithelial Tissue: Glands Coiled, simple: sweat glands Acinar ( alveolar ): Simple branched: sebaceous glands Compound: mammary glands Tubulo-acinar ( tubulo-alveolar ): Compound: salivary glands and exocrine pancreas
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57.Glands: Figure 1 : Goblet cells (GC) (Ileum) - uncellular exocrine gland - among simple columnar(EC) and pseudostratified cells Figure 2: Goblet cells (GC) (Ileum) - higher mag. of fig.1 - mucin (m), nucleus (rN) - Golgi zone (GZ) Figure 3: Sebaceous gland (Scalp) - associated with hair follicles - surrounded by connective tissue capsule (Ca) Figure 4: Eccrine sweat gland (skin): - simple, unbranched, coiled tubular. - secretory portion (s) - ducts (D), adipose (AD)
58.Glands: Figure 1 : Compound tubuloacinar (alveolar) serous gland (Pancreas) - each acinus appear round with central lumen (L) - zymogen granules (ZG) digestive enzymes - connective tissue (CT) Figure 2: Compound tubuloacinar (alveolar) mucus gland (Soft palate) - acini circular shaped - parenchymal cells (PC) make viscous fluid Figure 3: Compound tubuloacinar (alveolar) mixed gland (Sublingual gland) - mucous acini - serous demilunes (SD) cap mucous units Figure 4: Compound tubuloacinar (alveolar) mixed gland (Submanibular gland): - Serous acini (SA)
59.Epithelial Tissue: Glands Control of glandular activity: Glandular secretion is under neural and endocrine control mediated by chemical messengers. Exocrine secretion of pancreas is stimulated by the hormones secretin and cholecystokinin. Salivary gland secretion is under neural control

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