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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.
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B.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.
C. 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.
D. 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.PSEUDOSTRATIFIED CILIATED COLUMNAR EPITHELIUM (= PSCCE)
Look on the trachea slide (may also be labeled pseudostratified ciliated columnar epithelium) at the edge of the tissue for PSCCE. The Cilia are visible on high power. Goblet Cells may also be seen. The tissue appears stratified because it has nuclei at various levels in the different cells. Although the nuclei appear stratified, each column-shaped cell is attached to the basement membrane; therefore, this is a tissue exhibiting false stratification (hence the name).
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D. STRATIFIED SQUAMOUS EPITHELIUM
This tissue consists of multiple layers of cells. The layer next to the underlying connective tissues is cuboidal cells; however, the outermost layer of cells is squamous (flattened). Stratified tissues are always named by the shape of the cell layer at the free border. Two types of this tissue are common in humans:
1. STRATIFIED SQUAMOUS EPITHELIUM
NONKERATINIZED
Found lining the vagina, esophagus, & oral cavity. The epithelial layer is found at the top of the slide. Notice the cells at the surface are flattened and that distinct nuclei are visible. These cells are continuously shed into the oral cavity. The presence of nuclei is a clear indication that keratinization does not occur in this tissue and is useful in distinguishing from the next tissue you will observe (keratinized stratified squamous epithelium). This lining is much thicker in the mature female than the immature or menopausal adult because of the effect of estrogen.
The thicker layer of tissues below the epithelium consists mainly of connective tissues organized into various structures, glands, blood and lymph vessels, nerves (very few), and two unorganized layers of smooth muscle. Near the vaginal orifice the muscle is skeletal rather then smooth.
2. STRATIFIED SQUAMOUS EPITHELIUM KERATINIZED
The skin is the largest organ in the body and has three layers: epidermis, dermis, and hypodermis. The Epidermis consists entirely of keratinized stratified squamous epithelium over the entire surface of the body with very little difference except on the palms of the hands and soles of the feet where it is much thicker and devoid of hair follicles. Because of this it is often referred to as thick skin or thin skin.
Examine the scalp slide (thin skin) and note the Epidermis, Dermis, and Hypodermis. The epidermis consists of four distinct layers (five on the palms and soles). The bottom-most layer, termed Stratum Basale, consists of a single row of cells next to the dermis. These cells divide (by mitosis), giving rise to the cell layers above. The outer layer of epidermis, the Stratum Corneum, appears somewhat like flaky pie crust near the surface. The cells formed below have all died and been converted into the protein Keratin. They are constantly shed from all of the body surfaces. If excessive shedding occurs from the scalp, it is called dandruff. People allergic to cats, dogs, horses, etc. are actually allergic to the protein in these cells shed by the animal. The stratum corneum is thicker on the palms and soles, especially where a person has a callus or corn.