Chapter 2 Epithelial tissue Wang yang 1 Cells

Chapter 2. Epithelial tissue Wang yang 1

Cells Tissue Extracellular matrix（non-cell component） (fibers, ground substance, tissue fluid) ◆ Epithelial tissue are composed of closely apposed polyhedral cells with very little extracellular matrix. 2

Key points in this chapter • • 1. Features of epithelium 2. Types of epithelia 3. Classification of covering epithelium 4. Specific structures in epithelium 3

General features of epithelium 1、Contain more cells which tightly aggregate together and very little extracellular matrix. Apical surface Vertical surface 4

2、Polarity: significantly structural and functional differences in cell’s opposite surface. Free surface Lateral surface Basal surface 5

3、Avascularity: no blood vessels 4、Innervation : rich in sensory nerve ending 5、Basement membrane: a layer of intercellular substance at the base of epithelium 6

Types of epithelia Two basic types – Covering epithelia form a continuous layer over all the free surfaces of the body: the outer layer of the skin the inner surface of cavities and vessels; the ducts of the exocrine glands – Glandular epithelia: * with main function for secretion * make up most of the glands Other types: sensory/germinal epithelium/myoepithelium 7

Classification of covering Epithelia Principle: based on the following features o Layers of cells one layer: simple epi. several layers: stratified epi. o Shape of cells on the vertical section squamous epi. --flat/platelike cuboidal epi. --having the shape of a cube columnar epi. --column 10

Classification depends on layer Simple layer Stratify layers 11

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1、Simple squamous epithelium surface shape BM———— CT————— 14

Apical surface Vertical surface Irregular or polygon border: interdigitate nucleus: round flat cytoplasm: very thin nucleus: oblate/oval 15

Simple squamous epithelium • one layer of flat cells (having one flat nucleus). • found in: - alveoli of the lung - kidney glomerulus - heart, blood and lymphatic vessels - body cavities • thinnest of all - gas diffusion, nutrient absorption - exchange of waste & metabolite - keep organ surface smooth/antifriction 16

1. nuclei (one row of flat nuclei, long axis of the nucleus always parallel to the main axis of the cell) 2. lumen 1 1 1 2 17

The entire circulatory system (blood and lymph vessles) is lined by simple squamous epithelium that is called endothelium. Longitudinal section of the capillary 18

The major body cavities (peritoneum, pleura, pericardium) are lined by a mesodermally derived simple squamous epithelium that is called mesothelium. Function To keep surface of vessels or organ smooth, reduce friction, facilitate the blood/lymph flow and movement of viscera. 19

2、Simple cuboidal epithelium --structural features: • one layer of cuboidal cells, with same height and width (in side view) and hexagonal outline in surface view. • round centrally-located nucleus 20

--Distribution: renal tubule, thyroid gland, ovary surface. . . --Main function: absorption, secretion and covering. 21

3、Simple columnar epithelium --structural features: • one layer of columnar cells, with basally located ovoid nucleus and hexagonal outline in surface view. • goblet cell: scattered, secreting granules-mucinogen +H 2 O=mucus: lubricate and protect epi. 22

Vertical section of duodenum Simple columnar epi. Blue nuclei are almost at the same level, near to basal surface, goblet cells scattered among the epi. 23

4、Pseudostratified ciliated columnar epithelium Different types of cells All cells rest on the BM Not all can reach to the free surface Columnar cell-----------Goblet cell ----------------------cilia on the columnar cell Fusiform cell------------Basal cell----------------24

PSEUDOSTRATIFIED • Appears layered but all cells touch the basement membrane Stratified Pseudostratified B. M. 25

1. Nuclei 2. Epithelium 3. Cilia 4. Lumen Pseudostratified ciliated columnar epi. larger respiratory passages 26

5、Stratified Squamous Epithelium * Multi-layer cells * squamous cells in outermost layers * Large/polygonal cells in intermediate regions * deepest (basal) cells: cuboidal / low columnar resting on the BM strong proliferation ability * Basal surface is sinuate not linear: increase the contact area 27

6、Transitional Epithelium Main Feature: • The shape and layers of the epithelium are changeable, and are depend on the contraction or distention of organ. Distribution: Lining of bladder and ureters surface epithelium Basal epithelium 29

Structural feature of Transitional Epithelium u flexible-including the number of layers and shape of cells In the nondistended bladder : there are six to seven layers of cells. In the distended bladder: there are two to three layers of cells. The cells become flattened. u The surface cells are very large, dome-like or cuboidal in shape, covering several deep cells. u Basal surface almostly parallel to the free surface of the whole transitional epi. 30

Specialized Structures of Epithelial Cell 1) specializations of free surface 2) specializations of lateral surface 3) specializations of basal surface 33

EM diagram of columnar cells Free surface— Lateral surface —cilia — microvillus Cell junction —plasma membrane Basal surface infolding ——BM 34

Microvilli —cell membrane —cytoplasm —microfilament —terminal web 35

Definition of microvilli: Delicate finger-liked projections of cell membrane and cytoplasm protruding from the free surface. 36

Function: increase the cell surface area, better absorption Distribution: absorptive cells i. e. small intestine, proximal renal tubule 37

Striated border EM LM 38

Cilia —cell membrane —cytoplasm —microtubule ——basal body 39

Definition of cilia: Elongated, motile projections of cell membrane and cytoplasm protruding from free surface. 40

Function: Produce a forward-moving wave (rippling wheat field) : cilia are motile, move back and forth, cilia movement is coordinated to push the fluid or particulate matter in one direction over the ciliated epithelium. i. e. 1. Remove the inhale granules. 　 2. Propell the ovum/ germ cells toward the uterus in oviduct. Distribution: Respiratory system and oviduct. 41

Cilia SEM LM 42

Difference between microvilli & cilia appearance observation Surface Axes Composition Basal portion Function Microvilli Small and short EM Cell-membrane Cytoplasm Microfilament Terminal web Increase surface area Cilia Big and long LM/EM Cell-membrane Cytoplasm Microtubule Basal body Movement 43

Specializations of the lateral surface Cell junction： Membrane-associated structures contribute to cohesion and communication between cells. Distribution: Present in most tissues: i. e. muscle tissue and nerve tissue Prominent in epithelial tissue 44

• Tight junction or zonula occludens （紧密连接闭锁小带） • Intermediate junction or zonula adherens （中间连接粘着小带） • Desmosome or macula adherens （桥粒粘着斑） • Gap junction or communication junction （缝隙连接通讯连接） 45

Tight junction (zonula occluden) * Located at the most apical of lateral surface * Point-liked membrane fusions between adjacent cells * Arranged in 2 -4 thread-liked structures * Non-fusion space: 10 -15 nm gap * Serves as a barrier, form a seal that prevents flow of materials between cells = impermeable junction 46

Intermediate Junction (Zonula Adherens) * located just below the tight j as a 'belt' * a gap of 15 -20 nm in width with medium electron- density filament * on cytoplasmic surface of junction membrane electron-dense plaques of material inserted with actin filament to form terminal web * Function /adherent /keep the cell shape /transfer cell contract force =adhering junction 47

Desmosome (Macula Adherens) * plate or disk-shaped * a gap of 20 -30 nm, with low electron-density filaments interdigitate to form intermediate line * attachment plaque (made up of 12 proteins): with attached tonofilament(10 nm) intermediate keratin filament * Function firmly adhesion/connection =adhering junction 48

Gap/ Communication Junction * At deep part of the lateral cell surface * the smallest gap of 2 -4 nm * narrow intercellular space spanned by connexon Connexon------- Cell membrane Gap junction 49

connexon: -protein unit/individual unit of gap junction -composed of 6 -subunits of proteins--connexin -hydrophilic pore---1. 5 nm width in the center Function: small molecular exchanges, ions exchanges, transmit electrical impulse, provide a connective pathway between adjacent cells = communicating junction 50

Review of chapter 2 1. Features of epithelium 2. Types of epithelium 3. Classification of covering epithelium 4. Cell junction 51

1. Which of the following specializations of the apical surface of epithelial cells contain microtubules? A. Microvilli B. Cilia C. Stereocilia D. Both B and C are correct 52

2. The portion of the junctional complex primarily responsible for restricting the passage of molecules between adjacent epithelial cells: A. Zonula occludens B. Zonula adherens C. Macula adherens D. Hemidesmosomes 53

E ____ 3. Epithelial type that plays a protective function and is found lining the esophagus. H ____ 4. Epithelial type that is associated with distensible organs such as the urinary bladder. A _______ 5. Epithelial type found lining small capillaries where it modulates diffusion. ____ 6. Epithelial type consisting of a single layer of B square-shaped cells when viewed in tissue sections. A. Simple squamous B. Simple cuboidal C. Simple columnar D. Stratified cuboidal E. Stratified squamous F. Stratified columnar G. Pseudostratified columnar H. Transitional 54

7. Cilia are commonly seen on cells in tissues that A. line the blood vessels. B. line the respiratory tract. C. form the skin. D. move from one place to another. E. All of these are correct. 55

8. The type of cell junction that prevents the contents of the stomach or urinary bladder from leaking into surrounding tissues is the A. B. C. D. E. adherens junction. gap junction. hemidesmosome. tight junction. 56

9. One might expect to see microvilli on epithelial tissues whose principal function is A. protection. B. movement. C. absorption. D. mineral storage. E. transmission of electrical impulses. 57

10. Which of the following statements is NOT true for the epithelium? A. Epithelium is avascular. B. Epithelium contains very little intercellular material C. Epithelial cells lack mitotic activity D. All epithelial cells of a pseudostratified epitheliumlie on a basal lamina. 58

11. Stratified squamous epithelia are characterized by always having: A. A keratinized layer B. Squamous cells in proximity to the basement membrane C. Majority of cells that are squamous in shape D. Squamous cells at the free surface 59

12. Pseudostratified epithelium differs from stratified epithelia because in the pseudostratified epithelium: A. Two or more than two layers of cells are present B. All cells reach the luminal surface but all cells do not lie on the basal lamina C. All cells lie on the basal lamina but all cells do not 60

13. Mesothelium can be defined as: A. A simple squamous epithelium lining the blood vessels B. A simple squamous epithelium lining the body cavities C. A transitional epithelium D. A pseudostratified epithelium E. None of the above is correct 61

14. Cilia can be distinguished from microvili because cilia: A. Are non-motile B. Are located at the basal lamina C. Always occur singly D. Lack 9+2 tubular arrangement E. Are associated with basal bodies 62

15. Which of the following intercellular junctions would you expect to be most prevalent in an epithelium that is subject to much wear and tear? A. Zonula occludens B. Desmosome C. Gap junction D. Tight junction 63

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