20110110 03 epithelium notes.txt

From Iusmhistology

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Revision as of 12:39, 12 January 2011

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Contents 1 Intro to visual exam 2 Epithelium lecture 2.1 Objectives 2.2 Introduction 2.3 General characteristics 2.4 Epithelial junctions 2.4.1 Tight jxn 2.5 The belt desomosome 2.6 Maculla adherens 2.7 Hemi-desmosome 2.8 Gap jxn 2.9 Cells specializations 2.10 Epithelial polarity 2.11 Secretion 2.11.1 Protien secretion 2.11.2 Mucous secrtion 2.11.3 Steroid secretion 2.12 Basement membrane 2.12.1 BM fxn 2.13 Epithelium types 3 Laboratory 4: Epithelium 3.1 TYPES OF EPITHELIUM 3.1.1 Simple sguamous epithelium 3.1.1.1 Slides 91 and 88: Bowman's capsule 3.1.2 Simple cuboidal epithelium 3.1.2.1 Slides 91 and 88 3.1.2.2 Slide 87: Thyroid 3.1.3 Simple columnar epithelium 3.1.3.1 Slide 58: jejunum of monkey 3.1.3.2 Slide 63: gallbladder 3.1.4 Pseudostratified (ciliated) columnar epithelium 3.1.4.1 Slide 48: Trachea 3.1.5 Stratified squamous epithelium 3.1.5.1 Slide 48: Esophagus 3.1.5.2 Slide 30: Skin 3.1.6 Stratified cuboidal and columnar epithelium 3.1.7 Transitional epithelium 3.1.7.1 Slide 69: Urinary bladder 3.1.8 Epithelial transitions 3.1.8.1 Slide 81: Cervix 3.2 GLANDS 3.2.1 Unicellular glands 3.2.2 Multicellular glands 3.2.2.1 Exocrine glands 3.2.3 Slide 45: submandibular gland

Intro to visual exam

• They will be in MS326.
• Given via power point.
• Pointer on the slide will indicate what we are supposed to be identifying.
• There will be a multiple choice answer sheet.
• The questions can also be about the object, not just the identity of the object.
• There is about 1 minute per question.
  • There are 50 questions per exam.
• There is a review session before the exam.
  • Wednesday the 2nd of February.

Epithelium lecture

Objectives

• Understand the division oftissues into four classes, describing the characteristics of each.
• List the types ofjunctions found between epithelial cells and their unique characteristics. Which ofthese are also found in other tissue types?
• List the surface specializations of epithelial cells and their unique characteristics. Which of these are also found in other tissue types?
• Describe what is meant by epithelial polarity and how apical and basolateral membranes generally differ. Describe how separation oftransporters on an epithelial cell could enable secretion of a substance from the blood into the lumen of an organ.
• Distinguish among merocrine, apocrine, and holocrine modes of secretion. Which is used by serous cells? by mucous cells? by neuroendocrine cells? Can secretion of steroids be said to result from any ofthe three modes of secretion? Explain.
• Describe myoepithelial cells, their function and location.
• Describe the location, composition, and functions of basement membranes. Why is study of basement membranes so interesting with regard to cancer?
• Be able to draw and label all ofthe kinds of epithelia described in Table 4-2 ofyour text.
• Describe the development and classification of glands, as on pp. 76-80 of your text.

Introduction

• We classify everything in to four basic tissue groups.
  • We've done muscle and nerve.
  • Next week is the connective tissue.
• Epithelium is hard to describes but convers many of the functional tissues of the body.
• Epithelium has two general calsses:
  • Cells that line a fluid filled space with tissue underneath.
  • Chords or ropes of cells
    • have lots of blood associated with their surface

General characteristics

• Closely spaced cells, not much space in between.
• Adhere closely to one another.
• Form sheets that line cavities or surfaces of organs (or the whole body, like skin).
• Sheet cells are involved in transport of material between compartments.
• These sheeted cells (and even those not in sheets) are polar.

Epithelial junctions

• There are terminal bars
  • Composed of two EM structures (tight juxns and zonular adherens).
  • shows up as a dark staining line at the connection between adjacent, connected, epithelial cells.
  • These occur on the basolateral face of the cells.
• The terminal bar is dark between the tight jxns and zonular adheren proteins absorb the stain.

Tight jxn

• Tight jxns = zonula occludins
• Think of the old six-packs with plastic rings and where the ring held the cans (cells) together.
• Recall that these tight jxns are only visible on EM.
• Looks like a quilting in metal-shadowed freez-fracture EM.
• Tight jxns are very complicated.
• These effectively block the passage of fluid between adjacent cells.
• The tight jxns has two functions:
  • as a fence: proteins on the basolateral side of the cell cannot pass onto the apical side and vice versa.
  • as a gate: can allow ions or molecules through,
    • Depends on their selectivity, the signaling state of the epithelium, etc.
    • Epithelium can be signaled to open their tight jxns to certain molecules.
• There are several protein components:
  • ZO1 and ZO2 (zonulin occludin)
  • Claudin
  • Occludin
• These are important in structure and regulation.

The belt desomosome

• Called a desomosome because it looks a bit like a spot desomosome but is really different.
• At the top of the cell, below the zonula occludin.
• The zonula adheren is an important part of connecting the two cells and integrating the cytoskeletons, especially the terminal web.

Maculla adherens

• Not just epithelium but many cells have macula adherens.
• These are like spot welds between cells.
• Macula = spot
  • Immacula = spotless

What's the difference between a macula densa and a desomosome?

• At the desomsoem, there is a plaque of prteoins in either cytoplasm, there are membraneous proteins and there are proteins that bridge between the two cells
  • This is an important part of the strength of the skin surface.

Hemi-desmosome

• Half of a desomsome.
• These occur ont he base of the cells, to connect them to ECM (connective tissue).
• They have a plaque of cells in the cytoplasm, membraneous proteins.

• Intermediate filaments are important for hemi and full desomsoems.
  • These are made of keratin.

• There is a large network of actin filaments called the terminal web.
  • The actin filaments from the network can rup apically to generate the microvilli
  • When we look at cancers, we sometimes look at their intermediate filaments; if they are made of keratins we usually call the tumor a carcinoma.

Gap jxn

• A connection between neighboring cells.
• Not a strong physical connection.
• Important functional connection.
• Membranes are head together with a fixed, narrow gap.
• Freeze fracture will help us see this.
• There are pores between one cell and it's neighbor allowing small molecules to pass through.
• Connexons make up these pores.
• One connexon from each cell alighn their channels to form a pore.
  • There are many of these per gap jxn.
• The pore size is less than 1500 MW so signaling molecules like cAMP can get through but things like proteins cannot.
• Gap jxns are regulated in most cells by cytoplasmic Ca+ levels.
  • If one cell gets injured, the ca+ rises and the neighbors shut their gap jxns so they don't get injured, too.
  • It's the connexons that close.
• The connexon is the name of the structure, the protein is a connexin.

Cells specializations

• Microvilli are found on most cells of the lumen of the gut.
  • They can generate a brush border if long enough and packed close enough.
  • We also called them striated borders.
• The glycocalyx is sugar residues hainging off of glycoproteins and glycolipds of the cells.
  • Can be stained by puriotic reactive sschiff reagent.
  • made by actin
• Microplicae
  • These are ridges that come up off the cell.
  • Only seen via EM.
  • Made by actin
• Steriocilia
  • Made by actin
  • Giatn microvili
  • Called cilia because they can be seen individually with LM.
  • There are steriocilia in the kidney and hair cells.
• Basal foldings
  • "highly amnplified" basolateral surface means that there are lots of foldings to increase the surface area.
• Cilia and flagella
  • Cilia are at the surface of epithelial structures.
  • Flagella are generally singular.
  • These have Microtubules to make up the axonea.
  • This is a complex structure with many proteins.
  • Genetic diseases in any of these proteins can cause defective cilia.
  • We generally are thinking of motile cilia when we think of cilia.
  • There are also primary cilia.
    • These are important for epithelia cilia.
    • These can be important for sensing the throw through the tubule, even, like in the kidney.

Epithelial polarity

• The apex is the part that faces the lumen or outside.
  • AKA lumenal membrane
  • AKA mucosal membrane
• Other side is the basolateral membrane
  • AKA serosal membrane--closest to the serum or blood
  • AKA Abluminal membrane.

Secretion

• Epithelial secretion:
  • This is ambiguous.
  • Often means from the blood side to the lumen; like absorption means from lumen to blood.
  • More general is just release from the cell.
  • In a glandular context: secretion means into lumen or blood, or ... not specific.
• Glandular secretion occurs in three ways:
  • Merocrine: what we usually think of
    • Material iin the cell, in a vesicle, which gets merged with the plasma membrane, material is released.
    • Secretion of a product that is packaged int he cell.
    • Hard to do this with things like fats.
  • Apocrine:
    • Move fat covered in proteoins to the inner membrane then wrap it in a very small amoutn of membrane and dump it into the ECF.
    • This happens in arm pit and groin sweat glands; this gives us our special odor.
  • Holocrine:
    • When the entire epithelial cell is sloughed off to provide the secretion.
• Secretion can be constitutive or regulated.
  • For example albumin is secreted constitutively.

Protien secretion

• There are two types of protein secretion:
  • Serious cells:
    • Cytoplasm stains well with H+E
    • Ex: salivary gland
    • Proteins being released in a watery fluid
    • This is mericrine section.
  • Neuroendocrine cells:
    • Scattered throughout epithelia
    • Have secretory granules on the blood side.
    • This is mericrine section.

Mucous secrtion

• A special type of protein secretion.
• The proteins are covered withs ugars.
• Goblet cells are usually by themselves.
  • CAlled this because the mucins get packaged together at the top (apical) of the cell and make it look like a goblet.
• Mucin is the protein.
  • it has lots of sugars.
  • sugars make it stay hydrated well
• In neuroendocrine cells we can concentrate the proteins in the vesicle into a small bundle.
  • Mucin won't do this because it needs so much water.
• Also, mucin secreting cells won't stain well with H+E.

*Goblet cells have lots of ER

• They assume we know about the txn and txln and packaging of protines for secretion.

Steroid secretion

• STeoird are produced in special epithelial cells.
• Not packaged for secretion because it can pass through membranes.
• They can hardly hold the steroid in; perhaps by protein steric binding.
• These cells have ltos of:
  • sER
  • mt
    • have shelf-like cristae instead of tube like cristae
  • fat droplets (a precursor for many steroids)

Something here to study on our own.

Basement membrane

• The old literature calls basement membrane the basal lamina.
• This is an extra cellular structure.
• Has a lamina densa and one or two lamina rara (lamina lucida)
  • Remnantas of dehydration.
  • Used in pathoglogy to distinguish between disease states, especially in the kidney.
  • Two if both cell layers adjacent to the bm are epithelial.
• Lamina reticularis:
  • Set of fibrilar protins connected to the bm.
  • not officially part of the bm.
• Basement membrane is at the basal surfave of most epithelial cells.
  • Most neurve cells and msucle cells have their own bm.
• BM formed by type 4 collagen.
  • This type does not form fibrils.
  • Produces a felt-like structure in bm.
    • Felt is a fabric that is made by gluing small fibers together, essentially. It is not woven like cotton.
• There are lots of glycoproteins in bm:
  • laminin
    • very large
• proteoglycans, too

**

• These molecules are really big.

BM fxn

• BM is an anchoring substrate for the epithelium.
  • Some blistering disease states are from poor anchoring of skin epithelium to the bm.
• BM is a Signal template for differentiation
  • Interfaces with regenerating cells to tell them what kind of cell to be and when and where to grow.
• BM is a filter for molecules
  • Like in the kidney, removing proteins from filtrate.
• BM is a "filter" for cells
  • it keeps cells where they are supposed to be.
  • Most epithelial cells cannot get up and move (diapedesis), unless they have been altered, like in cancer.

Epithelium types

• We should be able to classify epithelium types and glands.
• Epithelium is named by shape of the cells at the surface:
  • Squamous: flat like fried egg
    • Often so flat that we cannot see cytoplasm in LM.
  • Columnar: tall
  • Cuboidal: like a cube
• Simple: one layer of cells
• Stratified epithelium have more than one layer of cells.
  • Still named by cells at the surface.
  • Most common is stratified squamous epithelium, which have fried eggs at the top but columnar at the bottom.
• Transitional epithelium
  • Lines urinary passages, especially bladder.
  • Armor plated cells at the surface (really acidic urine)
  • Can withstand lots of stretch as a group
  • Has "umbrella" cells at the surface that aren't quite cuboidal.
• Pseudostratified colunnar epithelium

**line ?

• • have a jumble of nuclei
  • All cells touch the bm, so it is falsly stratified.

Laboratory 4: Epithelium

TYPES OF EPITHELIUM

• Epithelial cells that form sheets are best viewed when the section is perpendicular to the plane of the epithelial sheet, so you will have to pay careful attention to the plane of section in each specimen.

Simple sguamous epithelium

• Cytoplasm is very thin and may not be visible.
• The nuclei may be flattened or rounded.

Slides 91 and 88: Bowman's capsule

• The bowman's capsule is a classic example of a squamous epithelium.
• The outer layer of the kidney is the cortex.
• Renal corpuscles are scattered throughout the kidney.
  • The corpuscle looks like an empty space with a hemorrhage of cells filling it.
  • The simple squamous epithelial cells surround the empty space.
• See Wheater, Fig. 16.6-16.17).
• The nuclei of the simple squamous epithelial cells are often close together.
  • Though, often squamous cells are wide and therefore the nuclei are far apart.

• We can also find endothelium in slide 91.
  • This is found lining the blood vessels of the kidney.
  • Often the nucleus will be visible but all the cytoplasm will not.

• The last -elium is the mesothelium which is found on the outside of organs that face a space in the body, like the outside of the small intestine or the liver.
  • We'll see the mesothelium when we look at cardiac tissue.
  • Can be seen on slides 19, 54, and 10.

What is mesothelioma

Simple cuboidal epithelium

Slides 91 and 88

• Simple cuboidal epithelium make up most of the tubes in the kidney.
• These cells are nearly as tall as they are wide.
• The nucleus of simple cuboidal epithelium are slightly flattened or fully round.
• The cytoplasm is generally easily seen.
• These are informally called "high" or "low" if they are slightly tall or slightly wide.

Slide 87: Thyroid

• This slide of the thyroid has lots of cuboidal simple epithelium.
• The thyroid has follicles that are filled with colloid (a mixture with properties between those of a solution and fine suspension per wordnet).
• As colloid accumulates in the follicles, surrounding epithelial cells can be compressed.

Simple columnar epithelium

• Simple columnar epithelium are much taller than they are wide.
• The nuclei often elongate along the long axis in order to fit in the cell.

Slide 58: jejunum of monkey

• Note that the brush border can be seen as a sometimes-fuzzy-sometimes-defined layer on the apical surface of the columnar simple epithelial cells.
  • It sometimes even looks like a cell membrane, with darker areas with a lighter middle--like longitudinal stripes.
  • Compare with electron micrographs in Wheater (Fig. 14.25a&b) and

Basic Histology (Figs. 15-25, 15-28, 15-29).

• Note the goblet cells scattered individually in this epithelium.

Can you see a basement membrane? (probably not)

Slide 63: gallbladder

• Note that there is no goblet cells in the gallbladder as there are in the jejunum.
• Also, there is very little fuzziness or longitudinal striation because the microvilli are much smaller than in the jejunum.
  • Note that mucus adhering to the apical surface of the gallbladder cells can look a bit like microvilli.

Pseudostratified (ciliated) columnar epithelium

Slide 48: Trachea

• This is the trachea.
• There are cilia present here in order to move mucus up the airway with trapped pathogen.
• Note that the mucins of the treacheal goblet cells stain more readily than those of the small intestine.
  • Therefore, instead of appearing as a complete lack of stain, they give a granular, light pink-to-blue color.
• The basement membrane is clearly visible in the trachea as a thick pink band.
• Recall that pseudostratified columnar epithelium is not stratified because all the cells reach the basement membrane.
• Recall that basal cells are those epithelial cells that are the closest to the basement membrane.

Stratified squamous epithelium

• Stratifed squamous epithelium come in two flavors: keratinized and unkeratinized.
• In keratinized cells, the amount of keratinization will generally increase as the cells reach the lumem and this can change the appearance.
  • They become lighter stained, wider, and have fewer and fewer nuclei.
• Note that to correctly identify stratified squamous epithelium, one must clarify wehther it is keratinized or non-keratinized.
  • Keratinization seems to give the cell morphology a very irregular shape, to cause light staining, and to be associated with very few nuclei.
  • The esophagus (non-keratinized) has a much more regular, flat shape, has many nuclei and still stains pretty well.

Slide 48: Esophagus

• The esophagus provides a good example of a non-keratinized stratified squamous cells.

Slide 30: Skin

• Here we see the layers of skin.
• Highly keratinized upper layers may be missing as it is hard to section them because they are so tough.

Stratified cuboidal and columnar epithelium

• We will see examples of cuboidal and columna stratified epithelium later.
• For now, examine these in Fig. 5.8 in Wheater.

Transitional epithelium

Slide 69: Urinary bladder

• The bladder is a good example of transitional epithelium whcih makes sense as it needs to be able to be very compact or very very distended.
  • Transitional epithelium is known for its ability to stretch.
• The surface-lining cells are often called umbrella cells.
• The umbrella shapes give the greatest difference between distended and compact.
  • In the distended state, the cells form a smooth layer with few bumps.
  • In the compact state, the umbrella cells form baking-cookie shapes lying next to one another.
• Another difference in the distended and compact state is the concentratin of nuclei near the bm: lower density in the distended state.

Epithelial transitions

• Where two different types of epithelia meet, the tissue is often weak.
  • This is often the site of lymphocyte accumulation.

Slide 81: Cervix

• The cervix has stratified squamous non-keratinizing (as we saw in the esophagus) and simple columnar cells.
  • Note that there is also the endothelial cells of the blood vessels.
  • Compare to Wheater 19.23.

GLANDS

• We will study glands more closely in each organ system.
• This lab will introduce us to glands.
• We should know the major classifications of glands as described in Basic Histology, Chapter 4, pages 77-79.
  • These classes have, in part, to do with the ductal construction of the gland.
• It is hard to characterize the class of a gland by any single slide, so we will not be expected to classify glands based on their ductal architecture.
• All exocrine glands are considered complex.

• Gland objectives:
  • At the completion of this portion of the lab you should be able to:
    • distinguish between ducts and secretory units,
    • distinguish between tubular and acinar secretory units, and
    • distinguish between serous and mucous secretory cells

Unicellular glands

• Unicellular glands are individual cells scattered throughout a tissue.
• Unicellular glands have no duct at all.
• Examples include goblet cells, ween in slide 58 (small intestine) and slide 48 (epithelium of the trachea).
  • Recall that the small intestine was a simple columnar epithelium and the trachea was a pseudostratified columnar epithelium.

Why does it make sense that the trachea is pseudostratified?
What's the special function of a pseudostratified epithelium?

Multicellular glands

• Multicellular glands have...multiple cells combining to form the gland.
• Only the very simplest multicellular glands lack ducts; most have some sort of epithelium-lined duct.
• There are two categories of multicelluarl glands:
  • Simple: which have a single duct that is unbranched.
  • Compound: which have a branched ductal system.
    • All major exocrine glands have compound duct structures, but this can be hard to see in histological slides.

Exocrine glands

• The secretory unit of exocrine glands can be described as:
  • elongated or tubular
  • rounded or acinar.

Slide 45: submandibular gland

• In this slide we can see both serous and mucous cells.
  • Serous cells are basophilic and therefore stain with eosin and are a deep pink.
  • Mucous cells stain faintly
• Serous cells produce a watery, protein-rich secretion.
• Mucous cells produce glycoprotein-rich secretions.
• The submandibular gland is considerd compound, so it will have branched ducts.
• The gland is also considered tubuloacinar so it demonstrates both elongated ducts and rounded dcuts.

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Note the arrangement of ducts within the gland. Going from small to large, the ducts tend to be composed of simple cuboidal, stratified cuboidal, or stratified columnar epithelium (learning the specific names of these ducts will come later!). This gland is also called a "mixed" gland (mixed-function gland) because it consists of both serous and mucous secretory components. Note the difference in staining with H&E of the cytoplasm of serous (blue/reddish-purple) and mucous (unstained) 22 11/27110 secretory cells. Relate this difference to ultrastructure of the cells and the composition of the secretory products. On demonstration is a slide of the submandibular gland stained with PAS for carbohydrate-containing components. Note that the mucus content of the mucous-secreting cells is deeply stained compared to the contents of other cells. (See also PAS staining of basement membranes, below). Both of the secretory cell types in this gland release their products by a merocrine mechanism. This means that the product is packaged in secretory vesicles, which subsequently fuse with the plasma membrane to release their contents (with no loss of cytoplasm). Be sure to read in your text to distinguish merocrine secretion from apocrine secretion (some loss of apical cytoplasm) and holocrine secretion (entire cell is shed). You cannot tell the mode of secretion of a gland by looking at histologic sections, but you will be expected to know what mode is used by a particular gland. Most glandular cells employ merocrine secretion, but we will see examples of glands that are known to use apocrine or holocrine secretion in later laboratory sessions. b) Endocrine glands release their secretion directly into the blood. Take a quick look at the adrenal gland, slide 89. This organ exhibits a feature characteristic of all endocrine glands-- there are no ducts. Small blood vessels should be visible among the numerous endocrine secretory cells. C. SPECIALIZED EPITHELIAL STRUCTURES. 1. Basement Membrane. Visualization of basement membranes in most epithelia can be enhanced by PAS staining. Study the slide of a submandibular gland stained with PAS (on demonstration). The basement membrane beneath the epithelium of the ducts and the secretory acini, not readily distinguishable with H&E staining, stains a deep magenta (mucous cells also stain heavily, so that the basement membranes of the secretory tubules will not be distinguishable). What chemical substance is responsible for the positive PAS reaction? (glycoproteins) 2. Cell surface specializations. Make certain you can identify - and distinguish between- cilia (e.g. slide 48 trachea) and microvilli (e.g. slides 58 jejunum and 63 gallbladder). Review the structure of microvilli and cilia at the ultrastructural level. 23

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