Anatomy 1.3 Epithelium and Glands(Final)

UERMMMCI College of Medicine SUBJECT: Anatomy

Date: (Friday) June 20, 2014

TITLE: Lecture # 3 – Epithelium and Glands LECTURER: Dr. Imelda D. Rivera, MD, FPSP 1st Semester A.Y. 2014 - 2015

Batch 2018 - A

Transcribers: Baldovino, D., Balgomera, N., Ballesteros, F. (09275457969), Balmaceda, J., Balmaceda, R., Banluta, R. Trans Subject Head: Jacinto, C. (09157536686)

LECTURE OUTLINE I.

EPITHELIUM: FUNCTIONS AND CHARACTERISTICS a. The Four Tissue Types b. Functions c. Characteristics

II. TYPES OF EPITHELIAL CELLS III. POLARITY OF EPITHELIAL CELLS

Molecular Biology (6th ed.) Philadelphia, USA: Lippincott Williams & Wilkins. 3. Young, B., Lowe, J., Stevens, A., Heath, J. (2006). Wheater’s Functional Histology: A Text and Colour Atlas (5th ed.). Philadelphia, USA: Elsevier Churchill Livingston. 4. I.

EPITHELIUM: FUNCTIONS AND CHARACTERISTICS

IV. THE BASEMENT MEMBRANE TISSUE

FUNCTION

V. GLANDS LECTURE OBJECTIVES 1. Give the functions of epithelial tissue. 2. Enumerate the characteristics of epithelial tissue, 3. Define cell polarity. 4. Describe the Apical and Lateral modifications. 5. Differentiate the types of lining and glandular epithelium 6. Differentiate the types of cell junctions. 7. Describe the organization of an exocrine gland. References: 1. Mescher, A. (2013.) Junquiera’s Basic Histology (13th ed.) McGraw-Hill. 2.

Ross, M., Pawlina, W. (2011.) Histology: A Text and Atlas: With Correlated Cell and

CELL MORPHO.

ECM

Nervous

Impulse Transmission

Elongated processes

None

Epithelial

Lining / Secretion

Aggregate, polyhedral

Small amount

Muscle

Movement

Elongated, contractile

Moderate amount

Connective

Support, protection

Various fixed & wandering cells

High amount

Functions of Epithelium 1) Covering and protection, e.g. skin 2) Absorption, e.g. GI tract lining 3) Secretion, e.g. mammary glands, Goblet cells (lubrication) 4) Contractility (due to actin fibers), e.g. myoepithelium of lacrimal glands 5) Receptor via transmembrane proteins

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6) Lubrication via secretion of mucous membranes 7) Transport of materials to and from the blood. Characteristics of Epithelium & Epithelial Cells 1) Polyhedral form – due to masses of adjacent cells packed in dense spaces. 2) Basement membrane – ALL epithelium are connected to the deep layers by the basement membrane. 3) Polarity – Organelles and cell functions are concentrated in different regions of the cell (see Polarity of Epithelial Cells) II.

TYPES OF EPITHELIAL CELLS

Covering Epithelium Classified according to: a) Number of layers 1) Simple – only 1 cell layer • Pseudostratified – 1 layer but nuclei are at different levels; all of the cells are touching the basal membrane but have different height

c) Apical/Free-surface Modification/Specialization 1) Ciliated 2) Non-ciliated 3) Flagellated 4) Microvilli § Brush border – uniform of microvilli § Striated border – uneven length of microvilli Simple Epithelial Tissues a) Simple Squamous epithelium o Surface cell shape: flat and very thin o Function: exchange, gas diffusion, secretion, lubrication in pleural cavity, active transport,** o Ex: pleural and abdominal cavity (mesothelium,*) peritoneum, lining blood vessel walls (endothelium,*) lining of ventricles and atria of heart (endocardium*)

2) Stratified – with 2 or more cell layers b) Cell type/shape 1) Squamous – flat, thin (lateral view); rounded to polygonal (surface view) 2) Cuboidal – height and width roughly similar 3) Columnar – height is greater than width; taller than they are wide 4) Transitional – various/different shapes (i.e. round, ovoid, cuboidal, balloon shape, dome shape); always stratified

Figure 1

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Figure 5 Figure 2

Figure 3

b) Simple cuboidal epithelium o Surface cell shape: square/cuboidal with round nucleus at center o Function: absorption, secretion, conduit, barrier o Ex: lining ducts of most glands, small ducts of exocrine glands, surface of ovary, kidney tubules, thyroid follicles

Figure 6

c) Simple columnar epithelium o Surface cell shape: columnar/tall cells with nuclei at basal part o Function: absorption, secretion, protection, lubrication** o Ex: lining of much of digestive tract, intestine, gall bladder

Figure 7

Figure 4

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o

Ex: lining of respiratory track (nasal cavity, trachea, bronchi)

Figure 8

d) Simple columnar ciliated epithelium o Surface cell shape: columnar/tall and ciliated with nuclei located toward the midzone of the cell o Ex: lining of fallopian tube (ciliated)

Figure 10

Stratified Epithelial Tissues The shape and height of the cells usually vary from layer to layer, but only the shape of the cells that form the surface layer is used in classifying the epithelium. 2

Figure 9

e) Pseudostratified columnar ciliated epithelium o Surface cell shape: all cells rest on basement membrane, but at different levels (only 1 layer) cells that reach the surface are columnar; goblet cells distributed randomly o Function: secretion, protection, transport of particles trapped in mucus out of air passages. 1

a) Stratified squamous epithelium o Non-keratinized (wet/moist) § Surface cell shape: flat with nuclei (top most layer) § Function: lubrication, protection, secretion § Ex: lining of mouth, esophagus, larynx, vagina

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o

Keratinized (dry) § Surface cell shape: flat without nuclei (dead cells;) like “flakes” § Function: prevents water loss or desiccation, barrier § Ex: epidermis of skin (Fig. 13)

Figure 11

Figure 13

b) Stratified cuboidal epithelium o Surface cell shape: several layers of cuboidal cells o Function: protection, secretion, conduit o Ex: lining ducts of sweat glands, large ducts of exocrine glands o Has limited distribution in the body

Figure 14

Figure 12

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c) Stratified columnar epithelium o Surface cell shape: columnar o Function: protection, conduit o Ex: conjunctiva of eye, lining some large excretory ducts o Has limited distribution in the body

Figure 15. Urinary bladder lining XSA

III.

d) Transitional epithelium/Urothelium* (ALWAYS stratified) o Surface cell shape: large dome shaped/umbrella cells (empty;) flattened (distended) o Function: lines organs that are subjected to changes in pressure or distention; has minimum of 2 layers even when distended; specialized to protect underlying tissues from the hypertonic effects of urine o Ex: lining renal calyces, renal pelvis, ureter, urinary bladder

POLARITY OF EPITHELIAL CELLS

Polarity - the position of the nucleus and organelles within a cell 1) Apical domain - facing the surface/ lumen of cavity; where activity of the cell is found; golgi complex is located supranuclear (above nucleus); direction of product release is towards apex. 2) Lateral domain - concerned with cell to cell adhesion through protein attachments. Increase surface area for absorption 3) Basal domain - anchored to basal lamina, possesses receptors for hormones and signaling molecules Apical Domain 1) Cilia Structure: • Elongated, hair-like protrusions • Core of cilium consists of an axoneme (a central mictrotubular pair/doublet surrounded by 13 microtubular pairs/doublets in heliocoidal formation • Attached to basal body, which consists of 9 microtubule triplets in helicoidal configuration • Motor protein, dynein, converts ATP into mechanical energy for movement

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Functions: • Motile cilia propel substances • Important locations: respiratory tract, female reproductive tract

Figure 16. Micrograph (b) show ciliated cells from the Fallopian tube. Cilia are labeled C. Diagram (c) shows the structure of a cilium.

2) Microvilli Structure: • Short finger-like projections • Actin filaments at core which attaches to terminal web • Striated Border – microvilli of same height; Brush Border – microvilli of different heights Functions: • Increases surface area 20x – 30x for absorption • Found lining certain tissues such as the intestines, allowing absorption

Figure 18. Diagram of microvillus. Note actin filament core.

3) Stereocilia Structure: • Actin filament core • Longer than microvilli • Anchored by fibrin and erzin Functions: • No motility but increases surface area for concentrated absorption • Located in epididymis 4) Flagellum Structure: • Similar to cilia but larger and usually limited to single flagellum per cell Function: • Movement in whip-like motion to propel cell • Important locations: sperm cells

Figure 17. Microvilli under microscope.

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The Basement Membrane Basal Domain A sheet-like layer that underlies virtually all epithelia, and isolates them from the subjacent connective tissue (CT)

Lateral Domain (Junctional Complexes) Location where two cells contact or attach to each other laterally

The basement membrane is an acid-Schiff (PAS) positive area underneath epithelial cells. Basal Lamina • A product of the epithelium • Lamina Lucida o an electron-lucent zone; 20-100 nm thick o penetrated by nerve cells, never by blood capillaries • Lamina Densa o an electron-dense layer located next to the basal plasmalemma and the CT. Components o Type IV collagen o Glycoproteins (mainly laminin; also entactin) o Perlecan - large heparan sulfate proteoglycan Reticular Lamina • A product of the CT • Components 1. Type III collagen – delicate and reticular 2. Type I collagen fibers. • is attached to the basal lamina with collagen VII anchoring fibrils and fibrillin microfibrils

Figure 19. Various lateral junctions (TJ - Tight junction; ZA Zonula adherens; CJ - Communicating junction; D – Desmosome; HD – Hemidesmosome)

Cell-to-Cell Junction Zonula Occludens/Tight Junction (TJ) Structure • most superficial to apical surface (right under microvilli) • fuses adjacent membranes by transmembrane proteins, claudin and occluding, arranged in anastomosing (contact via merging, see Figure 18) strands (quilt-like appearance) • reinforced by cadherins (cell adhesion molecules)

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Function: • regulates paracellular transport • restrict flow of substances between cell membranes (reason why it is very present in storage areas, e.g. gall bladder.

•

cadherin (mediated by Ca2+) span the plasma membranes of the cells and bind to identical cadherins on adjacent cell anchoring proteins (catenins, vinculin & alpha-actinin) bind actin filaments to the cytoplasmic tails of the cadherins

Function: • anchorage points for cytoskeletal elements, linking the cytoskeletons of individual cells into a strong transcellular network (mechanical attachment to adjacent cells)

Figure 21. Intracellular connection of Zonula Adherens

Macula Adherens / Desmosome (D)

Figure 20. Tight junction under micrograph

Zonula Adherens (ZA): The "adhesion belt" Structure: • located below Zonula Occludens • intracellular gap between membranes (15-20 nm) • transmembrane linker proteins called

Structure: o 3rd and deepest junction in junctional complex gap between adjacent membranes (30 µm) o dense attachment plaques on cytoplasmic sides (desmoplakin and plakoglobin) o intermediate filaments then attach into the attachment plaque o Cadherins (desmoglein and desmocolin) are the transmembrane

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o

proteins that extend across gap for attachment of the two membranes Desmosome numbers are greatest in stratified squamous epithelia

Function: o provide strong adhesion between cells, e.g. skin and intestinal lining o able to withstand the greatest friction also use cadherins as their transmembrane proteins

Figure 22. Micrograph of a desmosome with intermediate filaments (IF)

o

broad, intercellular junction in the transversal sections of an intercalated disc of cardiac muscle anchoring actin filaments.

Function: o serves to stabilize non-epithelial tissue o similar to the Zonula Adherens of epithelial cells a broad intercellular junction in the transversal sections of an intercalated disc of cardiac muscle anchoring actin filaments o helps to transmit contractile forces

Communicating or Gap Junctions/Nexus (CJ) o Contains numerous transmembrane channels (connexons) that permit the passage of inorganic ions and other small molecules from the cytoplasm of one cell to another. o more numerous in embryonic epithelia, involved in exchange of chemical messengers, cell recognition, differentiation and control of cell position

Fascia Adherens Structure: o mainly found in cardiac muscle Figure 23. Connexons forming a gap junction patch

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Function: o Cell-cell communication (electrically and metabolically) o

thought to be important in the control of growth, development, cell recognition and differentiation Connexon - is made up of six transmembrane proteins known as connexins; may be opened or closed depending on the intracellular concentration of calcium ions, the pH or on extracellular signals

Cell-to-Extracellular Matrix Junctions Hemidesmosome Structure: o half desmosomes that are found at the basal surface of the cell o its transmembrane proteins (integrins) bind to extracellular laminins in the basement membrane o the intracellular component of the integrins binds to the anchor protein, plectin and thus to the intermediate filament keratin

Focal Adhesion • anchors the actin cytoskeleton to the extracellular matrix • function: detects and transduces signals from outside the cell • adhesion process depends on the integrin receptors embedded in the plasma membrane Summary of Junctional Features Junction Type Cell-tocell

Occluding Junction

Classificatio n Zonula Occludens

Major link proteins Occludins, claudins, JAM

Anchoring Junction

Zonula Adherens

E-cadherincatenin complex

Macula Adherens

Cadherins (e.g., desmogleins, desmocolins)

Function: o anchors the epithelial cells to the basement membrane and the adjacent connective tissue

Fascia Adherens

Cell-toextra cellular matrix

Communicating / Gap Junction

Nexus

Connexin

Anchoring Junction

Hemi desmosome

Integrins, collagen XVII

Focal adhesion

Integrins

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IV.

GLANDULAR EPITHELIUM

Glandular Epithelia Epithelial cells specialized to secrete substances in membrane-bound secretory granules (vesicles). Examples of Glandular Epithelia 1) Sebaceous glands (lipid) 2) Pancreatic acini (enzymes) 3) Salivary glands (carbohydrate-protein complex) Classifications of Glandular Epithelia I.

Based on Path of Release 1) ENDOCRINE o Ductless o Releases secretions directly into bloodstream can act on distant tissues o Basement membrane has a network of blood vessels that absorb the secreted hormones (e.g. thyroid)

Two major components: a. Acinus (secretory portion) – contains cells that produce secretion b. Ducts (Conducting portion) – transport the secretion out of the gland • connects to the surface glands • (e.g. sweat glands, salivary glands, mammary glands, and liver.) c. Intercalated duct– joins together with acinus d. Intralobar ducts– drain to main excretory duct e. Interlobular ducts– between lobules f. Lobule – where the acini and intercalated ducts are g. located h. Lobes– contains lobules

Figure 24. Arrangement of secretor structures arround capillary

2) EXOCRINE o releases secretions onto an epithelial surface either directly or via a duct o Have ducts that lead to another organ or body surface

Figure 25. Structure of a typical lobular gland

 

3) PARACRINE o cells whose secretions target the immediate extracellular environment, travels short distances then Endocrine

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4) AUTOCRINE o the target cell is on the secreting cell itself

-

o II.

III.

Based on Number of Cells 1) UNICELLULAR (Single Cell) o Consist of large isolated secretory cells o Classic example is the goblet cell which lines the o respiratory tract and small intestines 2) MULTICELLULAR (More than one Cell) o Most common; have cluster of cells o Have connective tissue in a surrounding capsule and o in septa that divide the gland into lobules

o

Ruptures and releases secretion with bits of cytoplasm and plasma membrane e.g. mammary glands and sweat glands The secretory portions of a mammary gland demonstrate apocrine secretion, characterized by extrusion of the secretion product along with a bit of apical cytoplasm.

Based On Mechanism Of Product Released 1) MEROCRINE/ECCRINE o Most common mode of protein secretion o Involves exocytosis of proteins or glycoproteins from membrane-bound vesicles o Cells remain intact o e.g. Pancreatic acinar cells

Figure 26. Mammary glands with membrane-bound secretory vesicles visualized (see arrows)

3) HOLOCRINE o Whole cell disintegrates when it secretes product o Cell makes and fills with secretion and ultimately burst and releases secretions o suicidal glands o e.g. sebaceous glands of skin 2) APOCRINE o Secretion accumulates at the cell’s apical ends.

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Figure 29. Mucous cells. The lumens (arrows) of mucous tubules are larger than those of serous acini. Much connective tissue surrounds the mucous tubules and ducts (D). Figure 27. Longitudinal section of sebaceous gland with duct (D)

2) Serous (Viscous secretion) o With smaller lumen; cytoplasm is granular; oval nuclei o Excretes proteins, often enzymes o Filled apically with secretory granules in different o Pyramidal-shaped cells lining the acinus o e.g. parotid gland, lacrimal gland

Figure 28. Mechanisms of exocrine gland secretion.

IV.

Based on Type of Secretion 1) Mucus/Mucinous (Watery secretion) o Filled apically with secretory granules containing strongly hydrophilic glycoproteins called mucins o most common mechanism of product release o e.g. goblet cells, sublingual gland

Figure 30. Serous cells duct (D) Abundant RER (R), a Golgi complex (G), apical secretory granules (SG) and the small acinar lumen (L)

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3) Mixed Gland o With both mucinous and serous glands o With both serous acini and mucous tubules capped by groups of serous cells o product is a mixture of digestive enzyme and watery mucus o e.g. submandibular gland

V.

Based on Morphology 1) Simple (Unbranched) –with single duct (e.g. sebaceous glands) 2) Compound – with two or more branches

VI.

Based on Morphology Ducks

Simple Glands 1) Simple Tubular- Elongated secretory portion duct usually short or absent 2) Branched tubular- Several long secretory parts joining to drain 1 duct 3) Coiled Tubular- Secretory portion is very long and coiled 4) Acinar/Alveolar- Rounded, Saclike secretory parts entering the same duct Compound Glands 1) Acinar/Alveolar – Several saclike secretory units with small ducts converge at a larger duct 2) Tubular – Several enlongated, colied secretory units and their ducts converge to form larger ducts 3) Tubuloacinar/Tubuloalveolar - Ducts of both tubular and acinar secretory units converge at larger ducts

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V.

HISTOGENESIS AND THE THREE GERM LAYERS

Germ Layer The primary layer of cells formed during the embryo stage. Differentiated epithelial cells rise from the three layers. 1) ENDODERM (innermost layer) a. Respiratory system epithelium b. Alimentary canal epithelium c. Extramural digestive gland epithelium d. Thyroid, parathyroid, and thymus glands’ epithelial components e. Lining epithelium of the tympanic cavity and f. Eustachian tube 2) MESODERM (middle layer) a. Epithelium of kidney and gonads b. Mesothelium c. Endothelium d. Adrenal cortex e. Seminiferous and genital duct epithelium 3) ECTODERM (outer layer) a. Epidermis b. Cornea, lens epithelia c. Components of the inner ear d. Adenohypophysis EPITHELIAL CELL RENEWAL o Achieved through Mitosis Dependent on epithelial type: Small intestine: 4-6 days; not easily abraded Epidermis: 28 days § Stem cells are located along the walls of the hair follicles Stratified Epithelium Mitosis occurs only in the basal layer in contact with the basal lamina

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