Important Things to Ask Yourself When Looking at & Studying Tissues
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HUMAN HISTOLOGY
IMPORTANT THINGS TO ASK YOURSELF WHEN LOOKING AT & STUDYING TISSUES
1. What does it look like?
2. What is the name (be specific)
3. Where is it found?
4. What is (are) the name(s) of any special cell(s)?
5. What is (are) the name(s) of any special structure(s)?
6. ALL of the above may not apply to ALL of the tissues studied.
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CONNECTIVE TISSUES
1. Blood
2. Adipose
3. Areolar connective tissue
4. Reticular connective tissue
5. DWFCT (regular & irregular)
6. Cartilage
(hyaline, fibrocartilage. elastic)
7. Compact bone
EPITHELIAL TISSUES
1. Simple squamous epithelium
2. Simple cuboidal epithelium
3. Simple columnar epithelium
4. PSCCE
5. Transitional epithelium
6. Stratified squamous epithelium
a. keratinized (K)
b. nonkeratinized (NK)
MUSCLE
1. Skeletal (teased & diseased)
2. Cardiac
3. Smooth
NERVE
1. Cerebral cortex
2. Giant multipolar neuron
3. Meissner's corpuscle (demo)
4. Pacinian corpuscle (demo)
5. Node of Ranvier (demo)
6. Neuromuscular junction (demo)
MITOSIS
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
SKIN (as an organ)
1. Epidermis
a. stratified squamous epidermis - K
b. stratum corneum
c. stratum basale {also s. germinativum}
2. Dermis
a. dermal papillae
b. DWFCT (main tissue present)
3. Hair Follicle
a. shaft
b. bulb
c. hair papilla
4. Arrector pili muscle
5. Sebaceous gland
6. Eccrine gland
7. Hypodermis
a. adipose
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HISTOLOGY
A tissue consists of a group of cells of similar structure and function, along with the nonliving extracellular substance filling spaces between them. Histologists group all (mature, i.e. not embryonic) human tissues into four major categories: EPITHELIAL, CONNECTIVE, MUSCULAR, and NERVOUS.
You will be expected to accomplish the following: (I) learn to recognize and name the specific types of these four classes of tissues when viewed through a microscope; (ii) name any or all of the structures associated with these tissues; (iii) identify and name the various cells; (iv) name examples of organs or body parts in which these specific tissues may occur; and (v) in some cases describe the function and give the names of specific structures found within the tissue(s).
Following is an outline of the tissues that we will examine through the microscope:
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I. CONNECTIVE TISSUE
A. Areolar
B. Adipose
C. Reticular
D. Dense White Fibrous
1. Regular
2. Irregular
E. Cartilage
1. Hyaline Cartilage
2. Fibrocartilage
3. Elastic Cartilage
F. Vascular (blood)
G. Compact Bone
III. MUSCLE TISSUE
A. Skeletal
B. Cardiac
C. Smooth
II. EPITHELIAL TISSUE
A. Simple Squamous
B. Simple Cuboidal
C. Simple Columnar
D. Pseudostratified ciliated columnar {PSCCE}
E. Transitional
F. Stratified Squamous
1. Keratinized
2. Non-Keratinized
IV. NERVE TISSUE
A. Cerebral Cortex
B. Spinal Cord (Giant Multipolar Neuron)
C. Neuromuscular Junction {NMJ} (demo)
D. Sensory Nerve Endings (demo)
1. Meissner=s Corpuscles
2. Pacinian Corpuscles
E. Nodes of Ranvier (demo)
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I. CONNECTIVE TISSUE
Connective tissue is one of the most abundant and varied of all types of tissues in the body. Most connective tissues share the important feature of being composed mainly of MATRIX (extracellular substance) with relatively few cells, whereas epithelial tissues are composed mainly of densely packed cells with little matrix. In most cases, it is the matrix that characterizes connective tissues.
Connective tissue matrix includes fibers embedded in an amorphous GROUND SUBSTANCE. The ground substance varies from a fluid consistency to a semisolid gel (solid in bone). Fibers are composed of the structural proteins COLLAGEN and ELASTIN. Fibers of elastin are called ELASTIC FIBERS (sometimes yellow fibers). Fibers of collagen are referred to as COLLAGEN FIBERS, RETICULAR FIBERS, or OSSEIN FIBERS, depending on the tissue in which they occur.
Many different types of cells are associated with connective tissues: FIBROBLASTS {that produce the fibers}, CHONDROBLASTS {immature cartilage cells}, CHONDROCYTES {mature cartilage cells}, OSTEOCYTES {bone cells}, ADIPOCYTES {fat cells}, ERYTHROCYTES {red blood cells}, and LEUKOCYTES {white blood cells}. Other specialized types of cells may be found in connective tissues, but these are beyond the scope of this class.
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A. AREOLAR CONNECTIVE TISSUE
Observe on low power a slide labeled AREOLAR TISSUE. This tissue contains long, very thin, threadlike fibers of elastin, a structural protein, called Elastic Fibers. They appear as dark hairlike fibers and provide elasticity to this tissue. Thicker, very pink, nonelastic Collagen Fibers may also be found. Collagen fibers are composed of the most common structural protein in the body ... collagen. Both types of fibers extend in all directions, very much as wind-blown hair appears.
Numerous cells may be seen composed of obvious dark Nuclei surrounded by pale cytoplasm. Fibroblasts are the predominant cell present and actually produce the nonliving matrix of this tissue. Macrophages {monocytes} are also present. Many different types of blood cell may occur transiently in this tissue. We will make no attempt to distinguish these cells. This tissue is found around organs, between muscles, and in subcutaneous skin {hypodermis}. Areolar connective tissue can often be seen as a very slimy, grayish film adhering to the underlying muscle of chicken (or any other vertebrate) when the skin is removed.
B. ADIPOSE
Adipose should be observed on both low and high power. Adipocytes {fat cells} appear as large, rather clear cells with very thin cell membranes and a small dark nucleus. They contain only a tiny amount of cytoplasm. Most of the space within the cell membrane is for the storage of Lipids. Generally, when a person gains weight, the adipocytes do not increase in number, but simply enlarge as more lipid is added within the cell membrane. (Infants, if over-nourished, are an exception to increasing the number of adipocytes.)
Adipose tissue has numerous Collagen Fibers running through it; however, the slides used in this class are not prepared in a manner to make these fibers visible. Adipose is found in the hypodermis, around organs, (e.g., the heart and kidneys), within and between muscles, around nerves, and in other places.
C. RETICULAR CONNECTIVE TISSUE
Reticular connective tissue consists of a network of finely branching fibers of collagen called Reticular Fibers. View these on both low and high power. Fibroblasts are the cells that form the reticular {netlike pattern} fibers. This tissue forms the framework of the liver, lymph nodes, spleen, and bone marrow. It is an important tissue of the Reticuloendothelial System {Tissue Macrophage System}, which is instrumental in the defense against microbial invasion.
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D.DENSE WHITE FIBROUS CONNECTIVE TISSUE {DWFCT}
Dense white fibrous connective tissue {DWFCT} has a shining white appearance when viewed grossly and is very tough when eaten. (There is also a dense yellow fibrous connective tissue that we will not study).
DWFCT differs from areolar (loose) connective tissue in that it has many more Collagen Fibers and fewer cells. Fibroblasts, although few in number, are the most prevalent cell present. Two major types of this tissue are found in the body. They are described as REGULAR DWFCT and IRREGULAR DWFCT; the difference is determined by the arrangement of the collagen fibers.
Regular DWFCT is found in tendons, ligaments, fasciae, aponeuroses (broad, flat sheetlike tendons), periosteum, and the sclera and cornea of the eye.
You should examine a slide of tendon (the slide MAY be labeled white fibrous tissue). Observe in longitudinal section the thick bundles of pink-staining collagen fibers. The fibroblasts are compressed into thin, wavy purple streaks. (Some slides have cross sections also that you are not responsible for.)
Ligaments connect bone to bone across a moveable joint and are similar to tendons except that they contain many more elastic fibers, thereby exhibiting a greater ability to stretch without tearing.
Fasciae and aponeuroses have the bundles of DWFCT arranged in multiple sheets. In the cornea, each sheet of regular DWFCT is at right angles to the next sheet, as in the layers of plywood.
Irregular DWFCT occurs in the Dermis of the skin and sheaths of nerves. Examine a slide labeled scalp. Look at the dermis and observe the bands of collagen fibers. They appear to be short and extend in all directions, hence the term irregular. This tissue has more elastic fibers than regular DWFCT; therefore, the skin is more elastic than tendons.
E. CARTILAGE
Three types of cartilage occur in the human organism: HYALINE, ELASTIC, and FIBROCARTILAGE. They all share similar structures, but there are sufficient differences to make them recognizable.
Cartilage differs from other connective tissues in that it is avascular (no blood supply). It consists of cells called Chondroblasts, Chondrocytes and extracellular fibers embedded in an amorphous, gellike matrix. The cavities within the matrix that contain the chondrocytes are called Lacunae.
1. HYALINE CARTILAGE
This is the most abundant type of cartilage. Costal Cartilages attach ribs to the sternum; Articular Cartilages are found at the end of bones in synovial joints. Tracheal Rings in the trachea ("wind pipe") and the Larynx (voice box or "Adam's apple") are other examples of hyaline cartilage. (The epiglottis, part of the larynx, is elastic cartilage.)
Examine a slide of trachea (may be labeled AHyaline Cartilage@ on both low and high power. The trachea is a complex organ composed of many tissues. The cartilage appears as a dense purple area with many cavities (Lacunae) filled by cells (Chondrocytes).
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Surrounding the cartilage is a layer called the Perichondrium. Note the cells are very small, flattened, and arranged more closely together than the mature part of the cartilage. Some of these Chondroblasts are capable of becoming chondrocytes and will do so when the cartilage grows. The perichondrium has a blood supply, although the major portion of all cartilage is avascular.
2. ELASTIC CARTILAGE
Elastic cartilage is found in the Auricle or pinna, Eustachian Tube and Epiglottis (part of the larynx). The slide you will examine is from the auricle. The cartilage appears (on low power) as a band of tissue running as a wavy strip through the slide. The same structures found in hyaline cartilage may be seen here also: Perichondrium, Lacunae, Chondroblasts. Chondrocytes, and Matrix. Additionally, numerous thin threads of ELASTIC FIBERS are visible. These fibers may appear as very dark, densely packed threads or as very sparse and hard to distinguish fibers depending on the manner in which the slides were stained. They are responsible for giving this cartilage its pliable characteristic.
3. FIBROCARTILAGE:
This tissue occurs in amphiarthrodic (partially moveable) joints of the vertebrae. These pads of cartilage are called intervertebral discs. It is also present in the pubic symphysis and the sacroiliac joints as well as other places.
This cartilage differs from elastic and hyaline: in that it has no perichondrium; the chondrocytes tend to occur in horizontal rows rather randomly placed; and there are numerous dense bundles of collagen fibers between the rows of chondrocytes (rather like the bundles of collagen fibers in regular DWFCT as in tendons).
F. BLOOD
Blood has all the criteria necessary for being classified as a tissue; however, it has the unusual feature of lacking the intercellular cementing substance that causes cells in conventional tissues to adhere to one another. Hence, blood is a "liquid" tissue.
Blood cells are very small and must be viewed on high power. The most predominant cell is the Erythrocyte {red blood cell}. It appears as an enucleated reddish cell that seems to resemble a donut. The cell does not actually have a hole in it. Its shape is a biconcave disc because it loses its nucleus during development. The cell "caves in" much as the cheeks of a person who has had all of their teeth pulled. RBC's contain hemoglobin and are responsible for the transportation of oxygen to the tissues. This blood slide is from a person with Sickle-cell Anemia. The occasional Sickled Cell can be seen among the normal erythrocytes. They look somewhat like a football.
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Leukocytes are the nucleated cells with a colorless cytoplasm that are referred to as "white" blood cells. Actually, they are not white; they are just not red. The nuclei of these cells stain dark blue or purple. There are numerous types of leukocytes; however, at least 1000 power magnification is necessary to positively identify the many different types. All of these types may be classed in two major groups: Granular Leukocytes {GRANULOCYTES} and Agranular leukocytes {AGRANULOCYTES}. The former have numerous granules in the cytoplasm that are difficult to distinguish even at 430x. Granulocytes are large cells with a three to fivelobed nucleus. Agranulocytes have a very large spherical nucleus that occupies most of the cell.
Upon very close inspection, numerous TINY purple dots interspersed among the blood cells may be seen. They are Thrombocytes {blood platelets} and are very important in blood clotting.
G. COMPACT BONE
Bone exists as two main types of tissue: Compact Bone, that is found on the surface of bones; and Cancellous Bone, that may be seen as spongy bone on the inner aspects of bones. Mature compact bone is organized into Haversian Systems {Osteons}, each of which exhibits these structures:
a. Haversian Canal:Canal that extends along the length of a bone containing a blood vessel and a nerve.
b. Lacunae:Spaces between the lamellae (layers of matrix) within which the osteocytes occur (mature bone cells).
c. Osteocytes:Mature bone cells trapped in the matrix and occupying the lacunae.
d. Canaliculi:Cytoplasmic processes of osteocytes appearing as tiny hairlike fibers extending from the cell body.
Obtain a slide labeled GROUND BONE and identify the above structures on low power. Note that numerous Haversian systems are visible on the slide. Occasionally, horizontal canals may be seen connecting two Haversian canals. These are called Volkmann's Canals (Not all slides will have a Volkmann=s canal ... be sure to look at your neighbor=s slide).
Bone matrix consists of Ossein Fibers (composed of collagen) embedded in mineralized (calcium salts) ground substance. The protein fibers are not distinguishable on these slides.
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II. EPITHELIAL TISSUES
Epithelium covers body surfaces and organs and lines cavities. Each of the following is an example of epithelial tissue: lining of vagina, outer surface of eardrum, outer surface of eye, covering of uterus, epidermis, lining of aorta, lining of stomach, etc.
All epithelial tissues share certain characteristics: a free border or edge and a basement membrane. They have numerous cells and very little extracellular matrix. An exception to this is the basement membrane which is actually nonliving ground substance formed by the underlying connective tissue. Most epithelial tissues are attached to a basement membrane of an underlying connective tissue.
Epithelium is classified and often named according to the number of cell layers and the shape of the cells. If the tissue is one cell thick, it is Simple; if it is more than one cell thick, it is Stratified. Squamous epithelial tissues have flat cells that resemble fried eggs. Cuboidal tissues have cells shaped like a peach, and Columnar tissues are shaped like columns (bananas). Hence, a single layer of flattened cells is called Simple Squamous Epithelium. A single layer of column shaped cells is called Simple Columnar Epithelium, etc.
Within each possible classification of epithelium, the cells may or may not have Cilia on their free border. In human tissues these cilia are generally used to move mucus (and consequently anything trapped in the mucus). Cilia are found, for example, lining the respiratory tract, fallopian tubes, and vas deferens.
A. SIMPLE SQUAMOUS EPITHELIUM
This tissue is found in numerous places: Bowman's capsule of the kidney, lining of alveoli in the lungs, capillary walls, etc. We will use the kidney as an example of this tissue. You should refer to chapter 25 in your textbook and learn the BASIC anatomy of the functional unit of the kidney, namely the NEPHRON. The Glomerulus, Bowman's Capsule, and the Renal Tubule must all be recognized and understood FIRST from diagrams, and only then should you attempt to observe them on the microscope. Each of these nephrons (approx. 1,000,000 in each kidney) are all interwoven with each other. Therefore, when a thin slice of kidney is placed on a microscope slide, one cannot expect to see ANYTHING that resembles the diagram.
Place a prepared slide of KIDNEY on low power. The Glomeruli resemble balls of tissue that are surrounded by a thin white space (Bowman's Space). The glomeruli are numerous and more or less randomly distributed in the Cortex of the kidney. Select a glomerulus and switch to high power. Observe across the space (away from the glomerulus) a thin membrane that is one cell thick. This is a Bowman's Capsule. It totally surrounds the glomerulus but is often difficult to see in its entirety. You may have to look at several glomeruli before you find a good example of a Bowman's capsule. The tissue of which Bowman's Capsule is composed is SIMPLE SQUAMOUS EPITHELIUM.
B. SIMPLE CUBOIDAL EPITHELIUM
The Renal Tubule of the kidney is Simple Cuboidal Epithelium through much of its length. Much of the thyroid gland and the outer covering of the ovary are also Simple Cuboidal Epithelium. Most of the tissue on the kidney slide (exclusive of the glomerulus and Bowman's capsule) is simple cuboidal epithelium. Observe on both low and high power the renal tubules cut in both cross & longitudinal sections.
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C. SIMPLE COLUMNAR EPITHELIUM
The lining of the gall bladder, stomach, small intestine, and colon is simple columnar epithelium. In the uterus and oviduct, this same tissue occurs with cilia on the free edge. Notice the nuclei are all in neat rows at the bottom of the cells.