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THE MICROSCOPE

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Ocular lens (Eye piece)

Nose

Objective lens

(4X, 10 or 20 X, and 40X)

Stage

Diaphragm

Condenser

Light source

Base

Stage clip

Head

Arm

Brightness adjustment

Stage adjustment

Fine focus

Coarse focus

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CARE OF THE MICROSCOPE

When transporting microscope, hold in upright position with one hand on the arm and the other supporting the base
Only use lens paper to clean the lens. NEVER USE KIMWIPES.
Always begin the focusing process with the lowest-power objective and change to higher-power lenses as necessary.

Use fine focus only for adjustment

Use coarse adjustment knob only with the lowest power objective lens
Always use a coverslip with temporary preparations

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PUTTING THE MICROSCOPE AWAY

Remove slides from stage and place in appropriate place
Rotate the lowest-power objective lens into position
Move stage to the lowest position
Turn down light brightness
Turn off power
Wipe microscope (not the lens) with Kimwipes or alcohol wipe if needed
Wrap the cord neatly around the base
Lock the cabinet

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TISSUE TYPES

If the students have had 302L (as most of them probably have), then they should already be familiar with the four major types of tissues, the three subtypes of muscle tissue, the basic components of nervous tissue, and the fundamentals of how to operate our compound light microscopes.

This week is all about being able to distinguish the subtypes of ALL the major tissues, and identifying selected structural features. In addition, we’ll be getting into some additional details of compact bone, and the general organization of hollow organs (with the GI tract as our example/model).

Reminder for students: tissues are defined as groups of cells that are similar in structure and function.

Unless otherwise noted, all info for this week comes from Exercise 6A in our lab manual (Exercise 6B is the CD/online Histology Tutorial).

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BODY PLANES AND SECTIONS

3D objects can look very different when viewed in different sections!

Tissues can be cut in cross section, longitudinal section or somewhere in between.

This slide introduces the difficulty of converting 3 dimensional objects into essentially two dimensional pictures. Students should be aware that a slide that says cross section may show a structure not perfectly cut in cross section (it may be slightly off axis), or a complex structure cut many different times.

In the banana figure on this slide, (a) is a cross section, (b) is a longitudinal midsagittal section (cut down the bilaterally symmetrical midline), and (c) shows serial longitudinal coronal (frontal) sections in different planes.

If a student has not had 302L or otherwise has not had a lot of experience with our style of compound light microscopes (or just would like a review), recommend they read Exercise 3 in our lab manual. Some key points: carry with hands on both arm and bas; start at the lowest power objective, focus with the coarse focus knob, then increase objective power and focus with the fine focus knob; don’t use the 100x oil-immersion objective; etc. And remind them to please handle the slides carefully by their edges and to MAKE SURE to put the slide back in its proper slot AND box (etiquette points are again at stake this quarter!). We do have extras of most slides if necessary—but make a list if there are some we should order.

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GENERAL ORGANIZATION OF HOLLOW ORGANS

Mucosa

-epithelium

-lamina propria (areolar CT)

-muscularis mucosae or

elastic lamina (if present)

Submucosa

-well vascularized and

innervated

-dense irregular CT

Muscularis externa

-inner circular layer

-myenteric plexus

-outer longitudinal layer

Serosa

-thinner, located within the

peritoneal cavity

Adventitia

-thicker, located elsewhere

General Organization of Hollow Organs – a preview of a recurring theme this quarter. We won’t test the students on slides of this stuff yet, because we will as we get into the detail of the weeks to come.

Many hollow organs (especially those that make up the GI tract) are divided into four major layers (this figure and info found in Exercise 38—plus a little bit on mucous and serous membranes in Exercise 8—in our lab manual):

-Mucosa: the wet, innermost layer (closest to the lumen), comprised of three sublayers, the mucous epithelium (in most cases, a simple columnar), lamina propria (which is comprised of areolar CT) and the muscularis mucosae (a thin layer of smooth muscle that enables local movements of the mucosa and is a good landmark to distinguish the border between the mucosa and submucosa). In some hollow organs like the larger arteries there is also an elastic lamina present to withstand pressure. Functions: secretion, absorption, protection.

-Submucosa: superficial to the mucosa. It generally has many blood and lymphatic vessels and may also contain exocrine glands and nervous tissue. It is comprised of dense irregular CT. Functions: nutrition, protection.

-Muscularis externa (or simply the “muscularis”): superficial to the submucosa, comprised of smooth muscle. Often it has two layers running in opposite directions (an inner circular layer and an outer longitudinal layer)—although the stomach has three, and some organs have indistinct divisions between the layers. The myenteric plexus runs between the muscle layers and controls the smooth muscle. Function: GI motility (peristalsis, segmentation).

-Serosa/Adventitia: The thin, outer, serous layer covering organs in the peritoneal cavity is called the serosa (or the visceral peritoneum). Function: reduce friction. If the organ resides outside of the peritoneal cavity it is covered by a thicker, nonserous, coarse fibrous sheath known as the adventitia. Function: anchor and protect the surrounded organ. Generally we have allowed the students to memorize that structures above the diaphragm (pharynx and esophagus) and the rectum are covered with adventitia and other organs are covered with serosa. This is a generalization (for instance part of the kidneys are covered with serosa and part with adventitia).

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COMMON HISTOLOGICAL STAINS

Staining techniques preferentially color components in cells.

H&E stains nuclei blue/purple and cytoplasm pink

Mason or Mallory-Azan trichrome are 3-color stains that stain nuclei red, collagen green or blue (respectively) and cytoplasm red.

Silver staining stains certain proteins and DNA brown

Mason

Mallory-Azan

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HISTOLOGY EXPECTATIONS

Know the characteristics of primary tissue types and specific tissue types.

Primary tissue types are epithelial, connective, muscular, and nervous.
Specific tissue types are the subcategories of the primary types.
When identifying a specific tissue type, you must use the full name of the tissue, e.g. simple columnar epithelial tissue, not just simple columnar.

Know at least one location in the body for each specific tissue type.

Be able to identify the specific tissue types from the prepared microscope slides used in the lab.

Images used on the exam are all taken from these slides. The magnification used to obtain the image will be appropriate to distinguish the features of that specific tissue type.

If you include extraneous words in the name of a specific tissue type, points will be deducted.

For example, “skeletal dense regular tissue” does not exist. This is strategy is called “hedging your bets” and it won’t work.

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EPITHELIAL TISSUE

General characteristics

A lot of tightly packed cells; forms continuous sheets
Avascular; relies on diffusion
Free/apical surface
Supported by an adhesive basement membrane

Epithelial tissue is a diverse groups which covers or lines body surfaces, cavities and tubes, and therefore functions as an interface between different biological compartments. As such, they mediate a wide range of activities such as selective diffusion, absorption/secretion, physical protection and containment. Epithelial cells may also specialize and form glands (endocrine and exocrine)

The cells are packed tightly together, form continuous sheets, are avascular and rely on diffusion of oxygen and metabolites from adjoining supporting tissues, have an apical surface (lines free space) and are supported by an adhesive basement membrane.

One important note for the students is they may have to revise their idea of “free space” as “open space” that often is internal, e.g. the inside of a capillary is considered a free space.

There is a blurb of info about epithelial membranes (including mucous and serous membranes) in Exercise 8 in the lab manual.

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EPITHELIUM

Named according to number of layers

Simple: one layer
Stratified: multiple layers (shape of apical cells important diagnostically)

Named according to shape

Squamous: thin and flat (scale-like) cells
Cuboidal: cube-shaped cells
Columnar: column-shaped cells

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EPITHELIUM

Special kinds

Pseudostratified: simple columnar, but cells vary in height and nuclei at different levels; every cell attached to basement membrane, but not all reach the apical surface; often ciliated
Transitional: when not distended, looks like stratified cuboidal, but more layers (4+) and apical cells are domed/rounded

Special conditions

Keratinized: apical surface of stratified squamous may be made up of dead cells and possess a wavy layer of keratin protein

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SIMPLE SQUAMOUS EPITHELIUM

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SIMPLE CUBOIDAL EPITHELIUM

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Simple columnar epithelium

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PSEUDOSTRATIFIED COLUMNAR EPITHELIUM

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STRATIFIED SQUAMOUS EPITHELIUM

Keratinized

Non-keratinized

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STRATIFIED CUBOIDAL EPITHELIUM

Function: protection

Location: largest ducts of sweat, mammary, and salivary glands

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STRATIFIED COLUMNAR EPITHELIUM

Description: several cell layers; basal cells usually cuboidal; superficial cells elongated and columnar

Function: protection, secretion

Location: Rare in the body; small amounts in male urethra and in large ducts of some glands

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TRANSITIONAL EPITHELIUM

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CONNECTIVE TISSUE (CT)

Unlike the many closely packed, uniform cells of epithelial tissues, the varied cells of CT are widely spaced within an extensive extracellular (nonliving) matrix which determines the characteristics of each specific CT.

Extracellular matrix (ECM)

Fibers: Collagen, elastic or reticular

- Loose or dense structure

Ground substance: gel containing water, glycoproteins, polysaccharides etc.

Cells: fibroblasts (secrete fibers) and mast cells (secrete histamine, which triggers the inflammatory response)

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4 CATEGORIES OF CT

CT proper: areolar, dense regular, dense irregular, reticular, adipose
Cartilage: hyaline, elastic, fibrocartilage
Blood
Bone

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CONNECTIVE TISSUE PROPER

Features to ID:

-Fibroblasts

-Mast cells

-Fibers (collagen, elastic and reticular)

-Ground substance

(example shown here: areolar)

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AREOLAR CT

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ADIPOSE CT

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RETICULAR �CT

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DENSE REGULAR �CT

Dense regular CT

Identification: densely packed parallel fibers. Note scattered cells (lack of lacunae distinguish this tissue from cartilages—compare especially to fibrocartilage). Fibroblasts are located in distinct, parallel rows between bundles of collagen fibers, which distinguishes it from smooth muscle where muscle nuclei do not line up perfectly due to the spindle shaped cells. Remember too that most of what you’re seeing here is a lot of collagen fibers (NOT cells)—compared to the many more nuclei and large cells in smooth muscle. In addition, dense regular CT has fewer cells/nuclei than smooth muscle.

Fibers Present: collagen fibers.

Where Located: ligaments and tendons.

Functions: attaches bone to bone or muscle; resists tensile (pulling) forces in single direction.

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DENSE IRREGULAR �CT

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ELASTIC CT

Found in Aorta and other large arteries.

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CONNECTIVE TISSUE: CARTILAGE

Features to ID:

-Perichondrium (not found in fibrocartilage)

-Chondrocytes

-Lacunae

(example shown here: elastic)

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HYALINE CARTILAGE

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ELASTIC CARTILAGE

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FIBRO-CARTILAGE

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BONE

Features to ID:

-Osteon

-Osteocytes

-Lacunae

-Canaliculi

-Haversian canal

-Volkmann’s canal

(page 86)

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BONE

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BLOOD

Features to ID:

-Erythrocytes

-Leukocytes

-Platelets

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SKELETAL MUSCLE

Features to ID:

-Striations

-Multinucleate

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CARDIAC MUSCLE

Features to ID:

-Striations

-Intercalated discs

-Uninucleate

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SMOOTH MUSCLE

Features to ID:

-No striations

-Uninucleate

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NERVOUS TISSUE

Features to ID:

-Neurons

-Neuroglia

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NERVOUS TISSUE: LONGITUDINAL SECTIONS OF NERVES

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NERVOUS TISSUE: CROSS SECTIONS OF NERVES