Human Anatomy and Physiology I Laboratory Histology: Epithelial and Connective Tissue The Histology lab involves study of the appropriate laboratory exercise, completing the Review Sheet for the exercise, and taking the relevant quiz. Look also at the online histology sites mentioned in the introduction. Alternately, your instructor may have you turn in drawings of the tissues in lieu of the Review Sheets. Use the Virtual Microscope or other histology sites for good images of epithelial and connective tissue. Click on the sound icon for the audio file (mp3 format) for each slide. There is also a link to a dowloadable mp4 video which can be played on an ipod. 1
Four Basic Tissue Types: Epithelial lining and secretory tissue Connective supportive and nutritive tissue Muscular contracts to produce movement Nervous integration and control 2 All specific tissues fall into one of the four basic types. In this section we look at epithelial and connective tissues. We will look at nerve and muscle tissues when we cover those topics. 2
Characteristics of Epithelial Tissue Closely packed cells of a mostly uniform type Cells attached to a basement membrane Cells are joined by a junctional complex Tight junctions Desmosomes Gap junctions 3 These are the characteristics common to all epithelial tissues. 3
Epithelium is named according to shape, structure, and arrangement of cells. Shapes of Epithelium squamous - thin and flat cells cuboidal - cube shaped cells columnar - column shaped cells 4 One of the major characteristics of epithelial cells is that they come in somewhat standard shapes, which is the basis for naming them. There are occassional variations, for example a "short columnar" which is shorter than regular columnar and taller than cuboidal. 4
Epithelial Shapes 5 Here are the basic shapes of epithelial cells. Note that the shape and position of the nucleus is a distinguishing characteristic for each shape, and can be diagnostic for epithelial types. 5
Arrangement and Structure of Epithelial Cells simple - single layer of cells stratified - multilayered cells pseudostratified - false stratified transitional - stretchable ciliated - cells possess cilia 6 Arrangement and structural characteristics also distinguish different types of epithelial tissue. 6
Simple vs. Stratified Single Layer Multi-layered 7 Epithelial tissue is called simple if it is one layer thick, stratified if it is multilayered. The apical surface is the free surface in both cases, i.e. the surface toward the lumen of an enclosed tubule or duct, or the surface of the body in the case of the skin. The basal surface is the surface opposite to the apical surface and is attached to a basement membrane. 7
Simple Squamous Epithelium Basement Membrane Tissue wraps to form capillaries, alveoli of lungs, etc. Simple squamous epithelial cells, attached to a basement membrane, wrap around to form tubes and cavities. The basement membrane is on the outside of these tubes (the basal surface), while the apical surface is toward the inside. Capillary walls for instance and the alveoli of the lungs are formed of this very thin tissue. Thinness is the hallmark of simple squamous epithelium, which allows diffusion of substances across the epithelial membrane. 8 8
Functions of Simple Squamous Epithelium The thinnest tissue of the body. Allows transport across membranes in lungs and capillaries. Secretes fluid in serous membranes (e.g. pericardial and pleural membranes, mesenteries). Lines cardiovascular system, covers organs, forms glomerular capsules in kidney. 9 Simple squamous epithelium functions to produce the thinnest membranes of the body such as capillary walls and alveoli of the lungs. This thinness allows for transport of substances across the membranes. Simple squamous epithelium is also secretes serous fluid in mesenteries, and lines the cardiovascular system. 9
Mesothelial Lining of Peritoneal Cavity Plasma membrane cytoplasm nucleus 10 The lining of the peritoneal cavity (roughly the abdominal cavity) is formed of a serous membrane composed primarily of simple squamous epithelium. You are looking at the epithelium from above and can see the cells nuclei and plasma membranes. 10
Bowman s Capsule in the Kidney Nucleus of simple squamous cell Edgewise view of simple squamous cell 11 Cuboidal epithelium also wraps to form tubules and alveoli. These cells are the primary secretory cells in the body's glands. 11
Simple Cuboidal Epithelium Basement membrane Tissue wraps to form tubules and ducts of glands. Forms ducts, tubules and secretory cells in exocrine glands and in organs such as the kidney. 12 Cuboidal epithelium also wraps to form tubules and alveoli. These cells are the primary secretory cells in the body's glands. 12
Convoluted Tubules of the Kidney Nucleus of cuboidal cell Lumen of tubule Cuboidal epithelial cells 13 The secretory cells of most of the body's glands, as well as other organs such as the liver, kidney, and spleen are cuboidal epithelial cells, arranged into tubules, alveoli, or acini. 13
Simple Columnar Epithelium Apical surface may have microvilli or cilia Cell nuclei lie toward basal surface Non-ciliated in the GI tract, e.g. stomach and intestinal lining. Ciliated in portions of the respiratory and genitourinary tracts. 14 Simple columnar epithelium is a lining tissue found where secretion and absorption occur, as in the GI tract, or kidney. They may have microvilli to provide extra surface area, or cilia where mucus movement along their apical surface occurs, such as in the large bronchioles of the respiratory tract. In the GI and respiratory tracts the tissue incorporates goblet cells which secrete mucus. 14
Simple Columnar Epithelium basement membrane Tubule lumen nucleus 15 This is a longitudinal section of a kidney tubule in which the simple columnar epithelial cells are of the "short columnar" variety, with nuclei which are ovoid and more centered in the cell. These tubules reabsorb substances and secrete substances in producing urine. 15
Simple Columnar Epithelium in the Gastrointestinal Tract Goblet cells secrete mucus Basement membrane 16 Goblet cells are specialized epithelial cells which secrete mucus. Mucus helps protect the GI tract lining and traps particulates in the respiratory tract. 16
villus Lining in the Small Intestine Goblet cell simple columnar cells Connective tissue (lamina propria) 17 The lining of the small intestine has several surface modifications to increase its surface area. One is the finger-like villi seen here. The villi are then covered (or lined as you prefer) with columnar epithelial cells. Notice the goblet cells which secrete mucus, so called because of their characteristic goblet shape, narrow at the base and expanded at the apical end. They often give the appearance of holes punched in the lining tissue. 17
Ciliated Simple Columnar Epithelium Ciliated simple columnar is found in large bronchioles of the respiratory tract and in the genitourinary tract. 18 In the respiratory tract the lining is mostly ciliated, with the mucus produced by goblet cells helping to trap particulates. Ciliary action then moves this mucus up the respiratory passages until it reaches the throat where it is swallowed. 18
Ciliated Simple Columnar of Fallopian Tube nucleus cilia lumen Ciliated simple columnar cells connective tissue 19 Ciliated simple columnar epithelium is also found in the fallopian tube, where the cilia help in the movement of an oocyte and zygote down the tube toward the uterus. The center of a tube is known as the lumen. 19
Pseudostratified Ciliated Columnar Epithelium (PCCE) cilia Nuclei at different levels are diagnostic for pseudostratified epithelium. A non-ciliated pseudostratified epithelium is is found in in large glands and parts of male urethra. 20 20
Pseudostratified Ciliated Columnar Epithelium in the Respiratory Tract Cilia Goblet cells secrete mucus Pseudostratified epithelial cells Cilia beat in wave-like fashion to move mucus along the lining surface, carrying dust and particulates up and out of the respiratory tract. 21 21
P.C.C.E. in the Trachea Lumen of Trachea nucleus cilia P.C.C.E. Goblet cell Basal cell As in most all epithelia, basal cells undergo mitosis to produce new cells so that the epithelium constantly exfoliates and is renewed. 22 This shows P.C.C.E. found in the trachea and bronchi of the respiratory tract. In addition to the pseudostratified epithelial cells, there are also goblet cells which secrete mucus, and basal cells which undergo mitosis to replace pseudostratified cells which die. 22
Transitional Epithelium Transitional epithelium lines the urinary tract where it provides stretchability. 4-5 cells non-distended, 3 cells stretched. superficial cells basement membrane 23 Transitional epithelium is found only in the urinary tract, in the urinary bladder and ureter. There it stretches to allow filling of the bladder and to damp the back-pressure in the ureter during micturition (urination) which might otherwise damage the kidney. 23
Transitional Epithelium Wall of the urinary bladder Non-distended transitional epithelium. Distension reduces the number of cell layers. basement membrane Transitional epithelium lines the renal calyces, the ureters, the urinary bladder, and a portion of the urethra. 24 This is transitional epithelium in its unstretched form, when the bladder is empty for example. It is usually 5 layers thick. Imagine as this tissue stretches and the cells slide against one another, the number of layers shrinks to 3 or 4. What junctional structures keep the cells from actually pulling apart? 24
Stratified Squamous old cells exfoliate from surface cells move up from below Basal layer undergoes mitosis Stratified squamous epithelium forms the outer layer or epidermis of the skin. Skin is found as the organ of the integument and also as the lining of mucous membranes in the oral cavity, esophagus, anus and vagina. 25 When an epithelial tissue has more than one layer it is stratified. Stratified squamous epithelium consists of squamous cells in many layers, and is found as the epidermis, or outer layer, of the body's skin. Cells in the epidermis are constantly being replaced as new cells are produced by mitosis in the basal layer and old cells are exfoliated from the apical surface. Humans exfoliate about 90 pounds of cells in the course of a lifetime, and this process keeps the cells of the epidermis constantly renewed. 25
Stratified Squamous in the Epidermis of the Skin Flattened, cornified cells cover the surface as the stratum corneum. epidermis of stratified squamous epithelium dermis Stratum basale cells constantly undergo mitosis. 26 In the outer skin of the body the cells die and become impregnated with keratin and keratohyaline before exfoliating. This produces a protective layer of dead cells called the cornified layer or stratum corneum. 26
Non-keratinized Stratified Squamous Epithelium squamous surface cell Stratified squamous epithelium Section of vaginal wall. Connective submucosa Notice how the cells of the intermediate layers of the stratified squamous epithelium do not flatten and loose their nucleus as they do in keratinized epithelium (previous slide). 27 In the body's internal skin found in the anus, vagina, oral cavity and esophagus, the cells do not become keratinized and exfoliate while still intact. This is the basis for the ability to identify cancerous cells which have exfoliated from the cervix of the uterus using a Pap Smear. 27
Characteristics of Connective Tissues Cells of connective tissues are widely spaced within an intercellular matrix which determines the characteristics of each specific tissue. Intercellular matrix components: fibers - may be collagen (inelastic), elastin (elastic), or reticular. loose or dense structure ground substance - a semisolid gel containing water, glycoproteins, and other substances * Used here the term refers to tissues classified as connective tissue proper as well 28 as cartilage and bone tissue. * Connective tissue has characteristics which are almost the opposite of those of epithelial tissue. It has cells which are widely spaced apart within an intercellular matrix, and the cells may be of several different types. The matrix may have various combinations of ingredients, which determines the type of connective tissue. 28
Cells Found in Connective Tissues fibrocytes, or other generic cell for each tissue: osteocytes for bone, chondrocytes for cartilage, adipocytes for adipose, etc. macrophages and other phagocytic cells. mast cells - like basophils in the blood, these cells secrete histamine and heparin which mediate inflammatory responses. plasma cells - a type of lymphocyte, they secrete antibodies. These cells, along with other white blood cells migrate into connective tissues from the circulation. 29 There will always be one cell type which identifies the specific connective tissue, such as fibrocytes for the fibrous tissues, osteocytes for bone, chondrocytes for chartilage, and adipocytes for adipose tissue. These cells may be called -blasts (e.g. fibroblasts) if they are actively producing new tissue, -clasts if they are breaking down tissue for rebuilding (e.g. osteoclasts), or -cytes (e.g. osteocytes) if they are mature cells. The other cells are defense cells, very similar to white blood cells found in the circulation. 29
Areolar Tissue the Prototype Connective Tissue 30 Areolar tissue is called the prototype connective tissue because it has all the aforementioned components: three types of fibers, all types of cells, in a loose, fluid-filled intercellular matrix. It is the most abundant connective tissue, found associated with most epithelial tissues. 30
Areolar Tissue Elastic fibers Mast cell Collagen fibers Found in in outer dermis of skin, interstitial tissue, mesenteries and serous membranes. Fibroblast Reticular fibers 31 Areolar tissue is found in the outer dermis of the skin beneath the epidermis, in serous membranes of the body, and is the major interstitial tissue, the tissue which binds cells together. Its intercellular matrix contains most of the body's water. 31
Adipose Tissue Low Power Insulation and shock absorption; fatty pads around organs, subcutaneous fat. Connective matrix Adipocytes arteriole 32 Adipose tissue is a tissue which doesn't match the characteristics of other connective tissues. Its cells are close together, and its matrix is sparse. Fat cells (adipocytes) are filled with a lipid vacuole which almost completely occupies their cytoplasm. It is found in fat pads and in subcutaneous fat which function as insulation and shock absorption, as well as nutritional storage. 32
Adipose Tissue high power capillary nucleus of adipocyte venule nucleus of adjacent fibroblast 33 Adipose tissue is found in large amounts beneath the skin (subcutaneous) and in serous membranes throughout the body. It is rich in blood vessels as seen in this highly magnified view. 33
High power Dense Irregular Connective Tissue Low power Nuclei of fibroblasts Collagen fibers Found in in the deep dermis of of the skin and in in the submucosa of of the hollow organs. 34 Dense regular is also known as fibrous connective tissue, or inelastic tissue. It has bundles of inelastic collagen fibers, seen in the high power view above. It is found in the inner dermis of the skin as well as tendons, ligaments, and connective fascia. 34
Dense Regular (Fibrous Connective Tissue) Found in in tendons, ligaments, and fascial coverings. Tendon, l.s. collagen fibers nuclei of fibroblasts 35 Dense regular tissue is found where tensile strength is important, such as tendons and ligaments. There are few fibroblasts and many dense bundles of inelastic collagen fibers. 35
Elastic Connective Tissue The wall of the aorta elastic fibers fibroblasts Found in in the stroma of the lungs and in in the walls of the large arteries. 36 Elastic connective tissue has elastic fibers which are flexible. It is found where flexibility and recoil are important, such as in the walls of arteries (for the expansion and contraction with the pulse) and the stroma or internal support of the lungs (for recoil during expiration). 36
Section of lymph node Reticular Connective Tissue High power Forms the internal stroma of the soft organs such as the spleen and lymph nodes. fibroblast reticular fibers lymphocyte 37 Reticular connective tissue forms the internal support of most of the soft epithelial organs, glands, etc. 37
Lab Protocol 1. Identify characteristics, functions and locations of tissues observed. Suggestion: make a chart showing these things for the major epithelial and connective tissues. 2. Complete the Review Sheet for the Classification of Tissues exercise in the lab manual. 3. Take the Histology online quiz. 38 38