BIO+319_Lab+1.pdf

Lab 1 Histology & Integumentary System After completing this laboratory, you should be able to: ⁙ List the characteristics used to classify all four types of tissue found in the human body. Learning Objectives...

Lab 1 Histology & Integumentary System After completing this laboratory, you should be able to: ⁙ List the characteristics used to classify all four types of tissue found in the human body. Learning Objectives ⁙ Identify epithelial tissues by cell shape and number of layers. ⁙ Identify the various types of connective tissue by cell types and composition of the extracellular matrix. ⁙ Identify the three types of muscle tissue by cell shape and organization. ⁙ Identify neurons and glial cells. ⁙ Describe all locations and functions of each type of tissue and identify each type under the micro- scope. ⁙ Identify the tissue subclasses and be able to differentiate between them. ⁙ Describe the histological organization of compact and spongy bone. ⁙ Describe the functions of tissues and the location of the body in which they are found. Introduction In today’s lab, you will examine how the human body is organized at the tissue level. Histology is the study of tissues (a group of similarly structured cells that work together to accomplish a specific function). Tissues are further orga- nized into organs, with most organs containing a percentage of each tissue type. It is vital to understand histology before you learn about organs and organ systems. There are four major tissue categories: epithelial, connective, muscle and nervous. Each category includes special- ized tissues that have specific locations and functions. When you start to look at slides of tissues, it is important to start by scanning each slide at a low magnification because one slide may contain several tissue types. Then you can increase the magnification and observe individual cells of the tissue. Specimens for histology are first fixed (pre- served), then thinly sectioned, and lastly stained to improve contrast. Acid stains have negatively charged dyes and basic stains have positively charged dyes. These dyes bind to the oppositely charged macromolecules of the sectioned tissues. Different dyes are taken up by different tissues or cellular parts. Minor distortions in sectioned tissues that are only present due to the many steps needed to produce a histology slide are termed artifacts and should not be con- fused with the actual structure of the preserved tissue. You will quickly learn to recognize artifacts. ** You will need long pants and closed-toe shoes for this lab. Don’t forget! No cellphones, pictures, or electronic devices in the lab. ** 2 Lab 1: Histology & Integumentary System Epithelial tissue lines and covers organs (as well as their Epithelial Tissues internal passageways), create boundries between different A B environments, and forms glands. This tissue type is made up of sheets of cells, with the cells in a given sheet tightly Squa joined together via strong intercellular connections formed by tight junctions (connections between adjacent cells that prevent fluid from moving between the cells, Simple Cub from say the apical side to the basal side) and desmo- somes (protein containing connections between adjacent cells that allow them to mechanically hold on to each other thus providing mutual reinforcement). Epithelia functions in filtration, absorption, protection, secretion, excretion, and sensory reception. Colu An epithelium always has one surface where the cells are ©Van-Grin exposed to either the external environment or to an inter- nal passageway or cavity; this surface is called the free or Stratified apical surface. These cells obtain nutrients by diffusion Figure 1. of substances from connective tissue that are underlying A. Simple (one layer) and stratified (more than one layer) epithelia. the epithelia. Each epithelium is attached to the body via B. Top illustration is a squamous-shaped cell. Note the appearance of a basal lamina (located between the epithelium and its the nucleus is flattened. Middle illustration is a cuboidal-shaped cell. Note the appearance of the nucleus, which is round. Bottom illustra- connective tissue layer). The basal lamina is not cellular tion is a columnar-shaped cell. Note the appearance of the nucleus is and is formed by glycoprotein secretions from the epithe- oblong-shaped, but you will find the nuclei of columnar-shaped cells lial cells plus collagen fibers. The basal Alamina functions to be round as well. B as a filter at the base of the epithelium and can form a Squamous-shaped scaffold for wound repair. When observing epithelia microscopically, find the free surface and then look at the opposite edge of the cells. The basal lamina is located right under this edge and appears as a dark line betweenSimple Cuboidal-shaped the epithelial cells and the connective tissue. Epithelia are named according to their shape and number of cell layers (Figure 1). Columnar-shaped A. Simple Epithelia Simple epithelium is termed simple because it has only one layer. The main functions of simple epithelia are ©Van-Griner, LLC diffusion, absorption, filtration, and secretion. At the When a stratified epithelium contains more than one free surface, microvilli on the epithelial cell membraneStratified increase surface area available for absorption. To pro- type of epithelial cell, the type at the free surface deter- tect epithelia at the free surface, cells called goblet cells mines the classification of the tissue. Stratified epithelia secrete mucus that coats the cells. Other cells in a simple regenerate from basal cells that divide and then move out epithelial layer have cilia (small motile hair-like projec- to replace older cells near the apical border. Stratified tions from the apical surface that sweep substances squamous is the most common stratified epithelium. across the apical surface). Thus, ciliary action can sweep mucous along the apical surface to remove debris The apical cells in stratified squamous tissues are furthest from the blood supply and thus often atrophy and flatten. B. Stratified Epithelia Stratified cuboidal epithelium is typically two cells thick Stratified epithelia are composed of more than one layer. and found in locations such as the ducts of sweat glands Stratified epithelia are found in areas exposed to abrasion and mammary glands. Stratified columnar epithelium is and friction, such as the body surface and upper digestive found in limited parts of the male urethra, the pharynx tract, and function mostly for protection. (lining of the breathing passageways of the throat and head), and lining some glandular ducts. Lab 1: Histology & Integumentary System 3 4. Supported by connective tissue – The cells are at- Epithelial tached to and supported by an adhesive basement mem- brane, which is an amorphous material secreted partly by excellent Bone Good to Areolar the epithelial cells (basal lamina) and connective tissue Dense irregular connective cells (reticular lamina) that lie adjacent to each other Blood-forming with the reticular lamina deeper to the basal lamina. The basal lamina was discussed above. The reticular lamina Moderate Smooth muscle is mostly made of fine collagen fibers. The basement Dense regular connective membrane helps the epithelia resist tearing and stretch- ing, reinforces structural integrity, and creates a bound- ary. Cancers of epithelial tissues cannot become meta- Skeletal muscle Weak static until they develop a mechanism to break through Cartilage and free of the basement membrane, and thus if the cancer is caught before this occurs, then the prognosis is almost none much better. None to Cardiac muscle Nervous 5. Avascularity – Lining epithelial tissues have no blood supply of their own (avascular), but instead depend on Tissue regeneration capacity diffusion of nutrients from the underlying connective Figure 2. tissue. Glandular epithelia, however, is very vascular. Regenerative capabilities of tissues. This is not a linear scale, Glandular epithelial cells make up any gland within the so differences between these tissues should be taken as general. body (i.e. sebaceous glands of the skin, exocrine glands Ex. Bone tissue has better regeneration than nervous tissue. in the intestinal lining and hormone releasing endocrine glands). The function of glandular epithelia is directly related to their location. We will introduce them now so that you can understand what glands are when you are looking at tissue slides, but we will talk about this further There are several characteristics that distinguish epithe- in Biol 320. lial tissues from other tissue types: 6. Innervated – Meaning supplied by nerve fibers for 1. Regeneration – If well nourished, epithelial cells regulation. can easily regenerate themselves. This is an important characteristic because many epithelia are subjected to a good deal of friction or exposed to caustic or hostile substances. 2. Polarity – The membranes always have one free surface (apical surface), and typically that surface is significantly different from the basal surface. Most api- cal surfaces have microvilli, but some apical surfaces are smooth and slick. Microvilli are finger-like extensions of the plasma membrane that greatly increase surface area. If the microvilli are so dense that they appear fuzzy under the microscope, they are defined as a brush border and are often seen in secretory or absorbing tissues. Some apical surfaces have cilia. 3. Cellularity and specialized contacts – Cells fit closely together to form membranes (sheets of cells) and are bound together by specialized junctions. 4 Lab 1: Histology & Integumentary System Simple squamous epithelium Thin and often permeable, simple squamous flattened cells found where filtration, or the exchange of substances by rapid diffusion, is a priority (Figure 3). Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia Function: Allows passage of materials by Simple squamous diffusion and filtration in sites where epithelium protection is not important; secretes lubricating substances in serosae (tissue lining of a body cavity or outer lining of an organ) Location: Kidney glomeruli; air sacs of Lumen lungs; lining of heart, blood vessels and lymphatic vessels; lining of ventral body cavity ©Van-Griner, LLC Two simple squamous epithelia in the body have special names that reflect their location: Endothelium provides a slick, friction-reduc- ing lining in hollow organs that transmit body fluids (e.g., lymph, blood). Mesothelium is the epithelium found in se- rous membranes lining the ventral body cavity and covering its organs. Draw what you see in the microscope here. Figure 3. Simple squamous epithelial tissue, in the kidney Lab 1: Histology & Integumentary System 5 Simple cuboidal epithelium Simple cuboidal epithelium consists of a single layer of cells as tall as they are wide and a spherical nucleus (Figure 4). Important functions of this tissue are secretion and absorption. This epithelium forms the walls of the smallest ducts of glands and many kidney tubules. Description: Single layer of cube-like cells with large, spherical central nuclei Function: Secretion and absorption Simple cuboidal epithelium Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface Basement membrane Lumen ©Van-Griner, LLC Draw what you see in the microscope here. Figure 4. Simple cuboidal epithelial tissue in the thyroid gland (left). Occasionally this tissue can look like simple squamous tis- sue when the ducts are enlarged and the cells are flattened. Simple cuboidal epithelial tissue in the kidney (right). 6 Lab 1: Histology & Integumentary System Simple columnar epithelium Simple columnar epithelium is a single layer of tall, closely packed cells lining most of the digestive tract, the uterine tubes and the renal collecting ducts (Figure 5). In the small intestine, the wall is folded and covered with simple columnar epithelium to increase the surface area available for digestion and absorption of nutrients. Further- more, these cells usually have microvilli on the apical surface. In the uterine tubes, the cilia transport released eggs to the uterus. Columnar cells are mostly associated with absorption and secretion. Some simple columnar epithelia display cilia on their free surfaces, which help to move substances or cells through an internal passageway. Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells) Simple columnar epithelium Function: Absorption; secretion of mucus, enzymes and other substances; ciliated Basement membrane type propels mucus (or reproductive cells) by ciliary action. Goblet cell Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder and excretory ducts of some Cilia glands; ciliated variety lines small bronchi, uterine tubes and some regions of the uterus ©Van-Griner, LLC The diagram to the right shows how tissue can look, but note that all columnar cells are attached to the basement membrane Draw what you see in the microscope here. Figure 5. Simple columnar epithelial tissue Lab 1: Histology & Integumentary System 7 Stratified squamous epithelium Stratified squamous epithelium forms the superficial region of the skin, called the epidermis (Figure 6). Stem cells produce new cells at the basal lamina and are pushed toward the free surface by the next group of cells. For the stratified squamus epithelial tissue of the epidermis, the cells become keratinized. These new cells manufacture the protein keratin, which toughens the cells as they die. The cells then dehydrate and interlock into a broad sheet, forming a dry protective barrier against abrasion, chemical exposure and friction. Stratified squamous epithelium of the skin is thus said to be keratinized and has a dry surface. Other prominent areas covered with stratified squamus epithelial are not keratinized. Examples of locations of where non-keratinized stratified squamus epithelium are found are the surface of the tongue, mouth, pharynx, esophagus, anus, and vagina. Description: Thick membrane composed Apical surface of several layers; basal cells are cuboidal or columnar and metabolically active; surface Stratified squamous cells are squamous; in the keratinized type, epithelium (non-keratinized) the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers Basement membrane Function: Protects underlying tissues in Connective tissue areas subjected to abrasion Location: Nonkeratinized type forms the moist linings of the esophagus, mouth and Dead epithelial cells vagina; keratinized variety forms the epidermis of the skin, a dry membrane Stratified squamous epithelium (keratinized) Basement membrane Connective tissue ©Van-Griner, LLC Basal surface Figure 6. Stratified squamous epithelial tissue Draw what you see in the microscope here. 8 Lab 1: Histology & Integumentary System Pseudostratified ciliated columnar epithelium Pseudostratified epithelium lines the nasal cavity, trachea, bronchi, and parts of the male reproductive tract (Figure 7). This tissue has columnar cells and smaller stem cells, which replenish the tissue. While it appears stratified, it is not because every cell touches the basal lamina (hence the pseudo- part of the name). Often the columnar cells are cili- ated and the tissue is called pseudostratified ciliated columnar epithelium. Large goblet cells interspersed among the columnar cells secrete mucus onto the epithelial free surface. The mucus traps dust and other particles in the inhaled air. Cilia at the free surface sweep the mucus to the throat, where it is swallowed and disposed of in the digestive tract. Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting cells and bear cilia Cilia Goblet cell Function: Secretion, particularly of mucus; propulsion of mucus by ciliary Pseudostratified action columnar epithelium Basement membrane Location: Nonciliated type in male’s sperm-carrying ducts and ducts of large Connective tissue glands; ciliated variety lines the trachea, most of the upper respiratory tract. ©Van-Griner, LLC Figure 7. Pseudostratified ciliated columnar epithelial tissue Draw what you see in the microscope here. Lab 1: Histology & Integumentary System 9 Transitional epithelium Transitional epithelium lines organs that must stretch and shrink (i.e. urinary bladder; Figure 8). The cells have a variety of shapes and sizes, and not all of them touch the basal lamina. Most transitional tissue slides are prepared from relaxed transitional tissue and thus the tissue appears thick with cells stacked one on top of another. When the organ is stretched, the epithelium gets thinner as the cells change shape thus allowing for distention of the organ. Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamous-like, depending on degree of organ stretch Transitional Function: Stretches readily and permits epithelium (relaxed) distension of certain hollow organs (i.e. bladder) Transitional epithelium (stretched) Location: Lines the ureters, urinary Basement membrane bladder, and part of the urethra Connective tissue and smooth muscle ©Van-Griner, LLC Figure 8. Transitional epithelial tissue Draw what you see in the microscope here. 10 Lab 1: Histology & Integumentary System Common Embryonic Tissue Figure 9. Mesenchyme is the common embryonic tissue for all connective tissue types Cellular Descendants Fibroblast Chondroblast Osteoblast Hematopoietic stem cell Fibrocyte Chondrocyte Osteocyte Blood cells Connective Tissue Class Connective Tissue Cartilage Osseous (bone) Blood Proper 1. Loose connective 1. Hyaline 1. Compact bone Blood cell Connective Tissue Subclass tissue cartilage 2. Spongy formation and -Areolar 2. Fibrocartilage (cancellous) bone differentiation are -Adipose 3. Elastic cartilage quite complex. -Reticular This will be discussed further in 2. Dense connective Biol 320. tissue -Regular -Irregular Lab 1: Histology & Integumentary System 11 Connective Tissues A. Connective tissue proper Connective tissue provides the body with structural sup- Connective tissue proper has a thick liquid matrix, a va- port and a means of joining structural components to one riety of cell types and is further divided into two groups: another. Connective tissue also protects, stores reserve loose and dense. This tissue contains a variety of cell energy, insulates the body, and transports substances types that contribute to the overall function of the tissue. throughout the body. Mesenchyme (an embryonic tissue) Fibroblasts are stationary cells that secrete proteins that gives rise to all connective tissues. Connective tissues join other molecules in the matrix to form fibers. Mac- vary greatly in the degree to which they are vascularized. rophages patrol these tissues and are mobilized during an infection or injury, migrate to the site of disturbance, Connective tissues are mostly non-cellular meaning and phagocytize damaged tissue cells and microbes. Mast they contain cells that are sparsely spread throughout an cells detect foreign microorganisms and initiate immune extracellular matrix. Unlike epithelial cells, cells in the responses against them. connective tissue are widely scattered throughout the tissue. These cells produce and secrete protein fibers and a ground substance, that together form the extracellular matrix. Suspended in the ground substance are collagen fibers, elastic fibers, and reticular fibers. Collagen fibers are 1 Reticular fiber the strongest and are made up of the protein collagen. 2 Capillary A collagen fiber is made of many cross-linked collagen fi- 3 Ground substance brils which is what gives the fibers their strength. Elastic 4 Fat cell fibers are largely made of elastin, a protein which forms 5 Fibroblast a branching network in the extracellular matrix to pro- 6 Macrophage vide stretch and recoil. Connective tissue will 7 Collagen fiber stretch to the limits of the collagen fibers and 8 Neutrophil then recoil back due to elastic fibers. Reticular 9 Elastic fiber fibers are short, fine fibers made also of col- lagen but with a different chemistry and form 10 Lymphocyte than that of the collagen fibers discussed above. 11 Mast cell Reticular fibers form fuzzy nets that, compared to the larger collagen fibers, have more give or play. As we age, cells secrete fewer pro- 1 7 tein fibers into the matrix, which increases the brittleness of bone and the wrinkling of skin. 2 8 Each connective tissue has its own character- istic blast cell and cyte cell. Example of blast 9 cells are fibroblasts (in connective tissue prop- 3 er), osteoblasts (in bone), and chondroblasts (in cartilage). Once the matrix is generated, the 10 blast cells become less active and mature to the 4 cyte cells. 5 11 Connective tissue is divided into three groups based on cellular composition and matrix char- acteristics. 6 ©Van-Griner, LLC Figure 10. Prototype illustration of connective tissue 12 Lab 1: Histology & Integumentary System Mast cells release histamine that causes inflammatory C. Supporting connective tissue response, but also secrete heparin, proteases, and other There are two types of supporting connective tissue enzymes. Adipocytes are fat cells and contain vacuoles (bone and cartilage) that contain a strong matrix of fibers for the storage of lipids. capable of supporting body weight and stress. Bone has a solid matrix that is composed predominantly of calcium I. Loose connective tissue has an open network of phosphate salt, commonly reffered to as hydroxyapatite. protein fibers in a thick, syrupy ground substance and is Bone supports and protects the body. Bones also provide divided into three groups. cavities for synthesis of blood cells and storing fat. Bone is more rigid than cartilage because bone has both more A. Dense connective tissue is made up of two types of collagen fibers and a matrix filled with hydroxyapatite. fibers: protein fibers assembled into thick bundles of Unlike cartilage, bone is highly vascularized and inner- collagen and elastic fibers with widely scattered cells. vated. Cartilage is a rubbery, avascular, non-innervated There are two types of dense connective tissue: dense tissue, with a gelatinous matrix and fibers for structural regular (protein fibers in the matrix are arranged in support. Cartilage can withstand both compression and parallel bands) and dense irregular (fibers are interwo- tension because it is tough but somewhat flexible. The ven). Dense irregular tissue has fibers that run in many membrane that surrounds all supporting connective tissue directions and is found where tension is exerted from in cartilage is called perichondrium and produces chon- many different directions such as in the capsules of some droblasts which secrete fibers and the ground substance organs and joints, the dermis of the skin, and the submu- of cartilage matrix. Cartilage receives nutrients by diffu- cosa of the digestive tract. sion from the perichondrium. Eventually, chondroblasts become trapped in the matrix in small spaces called B. Fluid connective tissue lacunae. These cells are then called chondrocytes and There are two types of fluid connective tissue: blood and function to maintain the mature tissue. There are three lymph. Blood contains red blood cells, scientifically types of cartilage found in the human body: hyaline, termed erythrocytes, and white blood cells, scientifically elastic and fibrocartilage. Because aging cartilage cells termed leukocytes. Leukocytes mediate immune re- become incapable of cell division and cartilage is avascu- sponses and tissue response to injury. lar, damaged cartilage is slow to heal. We will cover bone tissue a little later in this lab. We will describe these tissues further in the next two labs. Lab 1: Histology & Integumentary System 13 Areolar Tissue Areolar tissue is found throughout the body (Figure 11). This tissue fills spaces between structures for support and protection. It is very flexible and permits muscles to move freely without pulling on the skin. Most of the cells in areolar tissue are oval-shaped fibroblasts that usually stain light. Mast cells are small and filled with dark-stained granules of histamine and heparin, both of which cause inflammation. Macrophages are numerous and protect against invading pathogens. Collagen and elastic fibers are clearly visible in the matrix. Description: Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, Collagen fiber mast cells, and some white blood cells Function: Wraps and cushions organs; its macrophages phagocytize bacteria; plays Fibroblast important role in inflammation; holds and conveys tissue fluid Elastic fiber Location: Widely distributed under the skin Mast cell ©Van-Griner, LLC Figure 11. Areolar (loose connective) tissue Draw what you see in the microscope here. 14 Lab 1: Histology & Integumentary System Adipose Tissue Adipose tissue is found throughout the body and is abundant under the skin and in the buttocks, breasts and abdomen (Figure 12). The distinguishing feature of adipose tissue is displacement of the nucleus and cytoplasm due to the storage of lipids. When an adipocyte stores fat, its vacuole expands with lipid and fills most of the cell while pushing the organelles and cytosol to the periphery. Description: Matrix as in areolar, but very sparse; closely packed adipocytes (fat cells), have nucleus pushed to the side by large fat droplet Adipocyte nucleus Function: Provides reserve food fuel; insulates against heat loss; supports and protects organs Vacuole storing fat Location: Under skin in subcutaneous tissue; around kidneys and eyeballs; within abdomen; in breasts ©Van-Griner, LLC Figure 12. Adipose (loose connective) tissue Draw what you see in the microscope here. Lab 1: Histology & Integumentary System 15 Reticular Tissue Reticular tissue forms the internal supporting framework for soft organs, such as the spleen, liver and lymphatic or- gans as well as hematopoietic tissue (red bone marrow; Figure 13). This tissue is composed of an extensive network of reticular fibers interspersed with small, oval reticulocytes. Description: Network of reticular fibers in a typical loose ground substance; reticular cells lie on the network Function: Fibers form a soft internal skeleton (stroma) that supports other cell Reticulocyte types including white blood cells, mast cells, and macrophages Reticular fiber Location: Lymphoid organs (lymph nodes, bone marrow, and spleen) ©Van-Griner, LLC Figure 13. Reticular (loose connective) tissue Draw what you see in the microscope here. 16 Lab 1: Histology & Integumentary System Dense Regular Connective Tissue Dense regular connective tissue consists mostly of collagen (with some elastic fibers) organized into thick bands with fibroblasts widely interspersed in the fibrous matrix and is poorly vascularized (Figure 14). This strong tissue forms tendons (connect muscle to bone) and ligaments (connect bone to bone). Because tendons and ligaments conduct pulling forces mainly from one direction, the protein fibers in dense regular tissues are parallel. Tendons transfer strong pulling forces from muscle to bone and have an abundance of strong bands of collagen fibers in the matrix. Ligaments have more elasticity than tendons and have a larger quantity of elastic fibers in the matrix. Elastic liga- ments support the bones of the vertebral column. Flat layers of dense regular connective tissue called fascia protect and isolate muscles from surrounding structures and allow muscle movement. Description: Primarily parallel collagen fibers; a few elastic fibers; major cell type is the fibroblast Function: Attaches muscles to bones or to muscles; attaches bone to bone; withstands Collagen fiber great tensile stress when pulling force is applied in one direction Fibrocyte nucleus Location: Tendons; most ligaments; aponeuroses ©Van-Griner, LLC Figure 14. Dense regular connective tissue Draw what you see in the microscope here. Lab 1: Histology & Integumentary System 17 Dense Regular Elastic Tissue A few ligaments are very elastic, so much so that the dense regular connective tissue in those structures is referred to more specifically as elastic connective tissue (Figure 15). Description: Dense regular elastic tissue containing a high proportion of elastic fibers. Function: Allows recoil of tissue Collagen fiber following stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following respiration. Fibrocyte nucleus Location: Walls of large arteries; within certain ligaments associated with the Elastic fiber vertebral column; within the walls of the bronchial tubes ©Van-Griner, LLC Figure 15. Dense regular elastic tissue Draw what you see in the microscope here. 18 Lab 1: Histology & Integumentary System Blood Blood is composed mostly of formed elements which are suspended in a liquid ground substance called plasma (Figure 16). Formed elements are grouped into three categories: erythrocytes (transport blood gases), leukocytes (cells of the immune system and protect the body from infection) and thrombocytes (form a plug to reduce bleeding). You will learn more about blood, lymph tissue and their function in BIOL 320. Description: Red and white blood cells in a fluid matrix Function: Transport of respiratory gases, nutrients, wastes, and other substances Red blood cell Location: Contained within blood vessels Platelets White blood cell ©Van-Griner, LLC Figure 16. Blood Draw what you see in the microscope here. Lab 1: Histology & Integumentary System 19 Hyaline Cartilage Hyaline cartilage is the most common cartilage in the body (Figure 17). This tissue is distinguishable from other cartilages by the apparent lack of fibers in the matrix. Hyaline cartilage does contain elastic and collagen fibers, but they do not stain and therefore are not visible. It provides springy absorption of compression at joints. Description: Amorphous but firm matrix; collagen fibers form an imperceptible network; chondroblasts produce the Lacuna matrix and when mature (chondrocytes) lie in lacunae. Function: Supports and reinforces; has resilient cushioning properties; resists Chondrocyte compressive stress Location: Forms most of the embryonic skeleton; covers the ends of long bones in Matrix joint cavities; forms costal cartilages of the ribs; cartilages of the nose, trachea, and larynx ©Van-Griner, LLC Figure 17. Hyaline cartilage Draw what you see in the microscope here. 20 Lab 1: Histology & Integumentary System Elastic Cartilage Elastic cartilage has many elastic fibers that are visible in the matrix and is therefore easily distinguished from hyaline cartilage (Figure 18). The elastic fibers permit considerable bending and twisting of the tissue. Description: Similar to hyaline cartilage, but more elastic fibers in matrix Function: Maintains the shape of a Lacuna structure while allowing great flexibility Location: Supports the external ear (pinna); epiglottis Chondrocyte Elastic fiber ©Van-Griner, LLC Figure 18. Elastic cartilage Draw what you see in the microscope here. Lab 1: Histology & Integumentary System 21 Fibrocartilage Fibrocartilage contains irregular collagen fibers that are visible in the matrix (Figure 19). This cartilage is very strong and durable and its function is to cushion joints and limit bone movement. Description: Matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate Function: Tensile strength with the ability Lacuna to absorb compressive shock Location: Intervertebral discs; pubis Chondrocyte symphysis; discs of knee joint Collagen fiber in matrix ©Van-Griner, LLC Figure 19. Fibrocartilage Draw what you see in the microscope here. 22 Lab 1: Histology & Integumentary System Skeletal Muscle Tissue Skeletal muscle tissue is found in muscles which are attached to bone, are voluntary and allow the body to move about (Figure 20). Skeletal muscle is composed of long cells called muscle fibers. During development, a number of embryonic cells called myoblasts fuse into one large cell that compose the muscle fiber. Because each fiber forms from numerous embryonic cells, it is multinucleated. It is also striated and these striations cause a distinct band pat- tern that results from the organization of intercontractile proteins called myofilaments (actin and myosin). We will discuss skeletal muscle and its function in great detail later this semester. Description: Long, cylindrical, multinucleate cells; obvious striations Function: Voluntary movement; locomotion; manipulation in the environment; facial expression Skeletal muscle nucleus Location: In skeletal muscles attached to bones or occasionally to skin One muscle cell Striations ©Van-Griner, LLC Figure 20. Skeletal muscle tissue Draw what you see in the microscope here. Lab 1: Histology & Integumentary System 23 Cardiac Muscle Tissue Cardiac muscle tissue uniquely forms the walls of the heart (Figure 21). This tissue is striated like skeletal muscle; however, each cardiocyte (cardiac muscle cell) has a single nucleus and is branched. Like skeletal muscle, the heart has connective tissue layers generated by fibroblasts and contains endomysium between individual cells. Cardiocytes are connected to one another via intercalated discs, which coalesce at ends of the cells in dense desmosome rich patches. Intercalated discs are visible at either end of a cell when viewing the cells length-wise. The high density of gap junctions in these intercalated discs allows coupling of electrical conductivity between adjoining cardiac cells so that the cells can synchronize their rhythm of excitation in contraction and relaxation without conscious control. Description: Branching, striated, generally uninucleate cells that interdigitate at specialized junctions (intercalated discs) Function: As it contracts, it propels blood Cardiac muscle into the circulation; involuntary control nucleus Intercalated disc Location: The walls of the heart Striations ©Van-Griner, LLC Figure 21. Cardiac muscle tissue Draw what you see in the microscope here. 24 Lab 1: Histology & Integumentary System Smooth Muscle Tissue The contractile elements of smooth muscle are not visible as striations (Figure 22). Smooth muscle cells have a fusiform (i.e. spindle) shape, are mononucleate and are not under conscious control. Such cells may be connected by gap junctions. Contraction may be induced and influenced by intracellular communication through gap junctions, hormones, mechanical stress and different neurotransmitters. Smooth muscle in the walls of hollow organs functions to increase or decrease the size of the lumen (the hollow space of a hollow organ) and propel its contents in a single direction. Description: Spindle-shaped cells with central nuclei; no striations; cells arranged closely to form sheets Function: Propels substances or objects (food, urine, or a baby) along internal passageways; involuntary control Smooth muscle nucleus Location: Mostly in the walls of hollow organs ©Van-Griner, LLC Figure 22. Smooth muscle tissue Draw what you see in the microscope here. Lab 1: Histology & Integumentary System 25 Nervous Tissue The nervous system is made up of cells called neurons and glial cells (Figure 23). Together these two types of cells are collectively referred to as either nerve tissue or neural tissue. To maintain homeostasis, the body must constantly evaluate internal and external changes. The nervous system processes information from sensory organs and responds with motor instructions to muscles and glands, which are collectively called the body’s effectors. Cells responsible for receiving, interpreting and sending the signals of the nervous system are called neurons. A typical neuron has several distinct regions. A central nucleus is surrounded by a region called either the cell body or the soma, which contains most of the neuron’s organelles. Radiating out from the soma, many fine extensions called dendrites re- ceive signals from other cells and send this information to the soma. Such signals are integrated at the “trigger zone” (roughly the region where the base of an axon fuses to the soma) to determine if an action potential will be initiated or not Description: Neurons are branching cells; cell processes that may be quite long extend from the nucleus-containing cell Dendrite body; also contributing to nervous tissue are the non-irritable supporting cells Axon Function: Transmit electrical signals from sensory receptors and to effectors (muscles Neuron cell body and glands) Location: Brain, spinal cord and nerves Glial Cells ©Van-Griner, LLC Figure 23. Nervous tissue Draw what you see in the microscope here. 26 Lab 1: Histology & Integumentary System Bone Histology Bone supporting tissue is surrounded by a membrane Bone ossifies in two different ways: intramembranous called the periosteum which contains cells called osteo- bone (cranial bones and the clavicle) develop from blasts for bone growth and repair (Figure 24). Like chon- fibrous membranes and endochondral bone. All other droblasts, osteoblasts secrete the organic components of bones develop from hyaline cartilage. the matrix, become trapped in the lacunae, and mature into osteocytes. In the case of the diaphyseal wall of a The structural unit of bone is an osteon or Haversian sys- long bone pictured below, the bulk of the compact bone tem, and each osteon consists of many rings of calcified is composed of repeating structural units called osteons. matrix called concentric lamellae. Between the lamel- These osteons are composed of rings of concentric lamel- lae, in small lacunae, are the osteocytes which maintain lae surrounding a central (haversian) canal that contains the mineral and protein components of the bone ma- blood vessels and nerves. Canaliculi are small channels trix. Bone requires a substantial supply of nutrients and in the lamellae that provide passageways through the oxygen. Nerves, blood vessels, and lymphatic vessels all solid matrix for diffusion of nutrients and wastes. The pierce the periosteum and enter the bone in a perforat- main function of bones is to provide structural support for ing canal (or Volkmann’s canal; perpendicular to the the body, provide points of attachment to osteon). This canal interconnects with the central canal skeletal muscles, and the protection of internal organs. (Haversian canal) at the center of each osteon. Radiating Osteoblasts are bone forming cells. Once an osteoblast outward from each central canal are the smaller canalic- is encased in bone, it then becomes an osteocyte (bone uli that facilitate nutrient, gas, and waste exchange with maintaining cells). However, osteoclasts are bone the blood. destroying cells. Osteoblasts are constantly resynthesiz- ing new bone and osteoclasts are constantly reabsorbing bone. Thus, calcium in bones can be stored and released 1 Osteon as needed. 2 Osteocyte in lacuna 3 Lamella 1 5 Periosteum 6 Sharpey’s fiber 7 Volkmann’s canal 8 Haversian canal 9 Spongy bone 2 3 5 6 7 8 ©Van-Griner, LLC 9 Figure 24. Osteon illustration Lab 1: Histology & Integumentary System 27 This is a low magnification view of a transverse section through a compact bone collar making up the diaphysis of a long bone. Note the arrangement of concentric lamellae making up each osteon along with the interstitial lamellae that fill space between osteons. 1 Osteocyte in lacuna 2 Haversian canal (central canal) 3 Osteon 4 Volkmann’s canal (perforating canal) 5 5 Interstitial lamella 6 Concentric lamella 6 1 2 3 4 Figure 25. Human ground compact bone This is a high magnification view of a transverse section through a compact bone collar making up the diaphysis of a long bone. Note the structure of each osteocyte encased in a lacuna and the canaliculi that connect to neighboring lacunae and exchange extracellular fluid. 1 Osteocyte in lacuna 2 Canaliculus 3 Haversian canal (central canal) 1 2 3 Figure 26. Human diaphyseal compact bone 28 Lab 1: Histology & Integumentary System The Integumentary System The integumentary system comprises the skin and its de- The Epidermis rivatives (sweat and oil glands, hair, and nails). The skin The epidermis consists of keratinized stratified squamous (cutaneous membrane) is in fact an organ-the largest of epithelium that is organized into layers called strata. the body. This system gives the body a protective barrier Most cells in the epidermis are keratinocytes. Kerati- that is flexible yet resistant to everyday abrasions and in- nocytes produce the fibrous, protective protein keratin. discriminant water loss. The integumentary system also Keratinocytes are produced by the basal layer of the functions to regulate body temperature, house sensory epidermis and migrate out. As they move, they fill with receptors, ensure water homeostasis, protect the body keratin and gradually lose other functions until they are from the environment (i.g. bacterial invasion and me- nothing more than keratin packed in a plasma membrane. chanical insult), and manufacture vitamin D3. There are Eventually they slough off after a life span of 25-45 days. two main tissue layers of the integument: the superficial In high friction areas of the body, this rate of acceler- and avascular epidermis and the deep and vascularized ated friction in a particular area can cause the epidermis dermis layer. to abnormally accelerate turnover to produce a callus. Thick or thin skin is not defined by the total thickness of the skin but instead by the thickness of the epidermis. 1 Epidermis The five layers of the epidermis starting from the apical 2 Dermis layer are: stratum corneum, stratum lucidum (found on 3 Subcutaneous layer (hypodermis) thick skin such as the palm of the hand and sole of the 4 Meissner’s corpuscle foot), stratum granulosum, stratum spinosum, and stratum 5 Sebaceous (oil) gland basale. 6 Hair follicle 7 Eccrine sweat gland 8 Hair shaft 9 Stratum corneum 10 Stratum spinosum 8 11 Free nerve ending 9 12 Arrector pili muscle 10 13 Pacinian corpuscle 14 Apocrine sweat gland 1 15 Adipose cells 4 11 16 Nerve fiber 5 12 2 13 6 7 14 15 3 16 ©Van-Griner, LLC Figure 27. Illustration of the integumentary system Lab 1: Histology & Integumentary System 29 1. Stratum corneum (horny layer) – The stratum cor- 3. Stratum granulosum (granular layer) – Found deep neum is the most superficial layer of the epidermis, to the stratum corneum (other than those areas that have contains 20-30 layers of dead (due to a specialized stratum lucidum), the stratum granulosum contains four form of apoptosis in which the organelles including the to six layers of dark cells that synthesize the protein nucleus breakdown but the plasma membrane thickens) keratohyaline which helps form keratin in more superfi- squamous, anucleate cells, that make up about two-thirds cial layers. The cells in this layer also produce lamellar of the epidermis thickness, and contain keratin. Keratin granules which are released into the extracellular space and thick plasma membranes of the cells protects the and contain a water-resistant glycolipid. Keratinization skin against abrasions while glycolipid between the cells occurs in this layer to increase durability and reduce nearly waterproofs skin. water loss from the integument (tight junctions between cells also reduces water loss). The water barrier cre- 2. Stratum lucidum (clear layer) – Found just deep to the ated by this layer, coupled with the long distance from stratum corneum, the stratum lucidum is a thin trans- the capillaries of the dermis, dooms the cells in the more parent layer of cells found almost entirely in thick skin superficial layers to death. areas such as the palm of your hand and the sole of your foot. These areas are subject to abrasion, and the stratum 4. Stratum spinosum (prickly layer) – Found deep to the lucidum protects the underlying strata. Here, and also in stratum granulosum, the stratum spinosum consists of the stratum corneum, the keratohyaline granules, from the five to seven cells that form cell attachments via desmo- stratum granulosum, cling to the keratin filaments within somes. The desmosomes are connected to intracellular the dying cells which causes the filaments to aggregate pre-keratin filaments that form a tension resisting web into big, parallel arrays of filaments termed tonofila- within the cells. The keratinocytes in this layer appear to ments. have spines causing them to have a prickly appearance. However, this prickly appearance when it occurs is an 1 Desmosomes artifact of preparation the cells. When alive, the cells are 2 Langerhanns cell not actually “prickly”. Scattered among these keratino- 3 Melanocyte cytes are melanin granules and dendritic cells. 4 Basement membrane 5 Merkel cell 6 Stratum corneum 7 Stratum granulosum 8 Stratum spinosum 9 Stratum basale 6 10 Dermis 1 7 2 3 8 4 5 9 Figure 28. Illustration of the 10 layers of the epidermis ©Van-Griner, LLC 30 Lab 1: Histology & Integumentary System 5. Stratum basale (basal layer) – The deepest epidermal 1. The papillary layer consists of areolar tissue that con- layer is the stratum basale and it is attached to the der- tains collagen and elastic fibers. Folds in the papillary mis. This stratum is a single layer of stem cells that are layer, called dermal papillae, form large mounds in thick constantly undergoing mitosis (in response to a peptide skin called dermal ridges that make-up our fingerprints signaling molecule produced by many of the cells of the (these ridges together with the ridges created in the epi- body named epidermal growth factor); thus, this layer is dermis are termed friction ridges and increase grip), and very mitotically active. As new cells arise, one daughter often contain Meissner’s corpuscles (touch receptors), cell is pushed into the stratum spinosum while the other free nerve endings, or capillary loops. This layer also daughter cell stays in the stratum basale. As these cells houses many phagocytes that protect us from invaders migrate from one stratum to the next, they take on the such as bacteria. function of that layer. Melanocytes found in the basal layer produce the pigment melanin. During production, 2. Deep to the papillary layer is the thick reticular layer melanin is packaged into melanosomes for secretion at of the dermis that contains thick collagen fibers in dense, the tips of the melanocytes. Melanin is taken up by kera- irregular connective tissue with pockets of adipose cells. tinocytes where the melanin accumulates on the superfi- Hair follicles and glands originate in this layer. A cutane- cial, sun exposed side of the nucleus to protect the DNA ous plexus of blood vessels lays between the dermis and within from damage due to UV light exposure. hypodermis. The Dermis Deep to the epidermis is the dermis; a layer of irregu- larly arranged flexible, but strong, connective tissue that supports and nourishes the epidermis. The dermis has a rich supply of nerve fibers, blood vessels and lymphatic vessels and is divided into two layers: the papillary layer and the reticular layer. Lab 1: Histology & Integumentary System 31 This longitudinal section of the epidermis is shown with the additional presence of the 1 Stratum corneum stratum lucidum inserted between the stratum corneum and the stratum granulosum. 2 Stratum lucidum This stratum provides extra mechanical strength for skin of the hands and feet. 3 Dermis 4 Stratum granulosum 5 Stratum spinosum 6 Stratum basale 1 4 2 5 6 3 Figure 29. Human plantar skin This longitudinal section of human pigmented skin shows a clear view of melanocytes present in the stratum basale. Melanocytes synthesize the pigment (melanin) granules taken up by the newly formed keratinocytes. Pigmented keratinocytes migrate to the stratum spinosum and form a high density of intercellular attachments via desmosomes. As the cells enter the stratum granulosum, they begin to die because they have migrated too far from the dermal blood supply. During their death throes, cells of the stratum granulosum secrete a glycolipid between cells. This “filling” functions as a barrier for water passage. Keratinocytes of the stratum corneum are dead flattened sacks of keratin but are still cemented together via the glycolipid produced in the stratum granulosum. 1 Stratum corneum 2 Epidermis 1 3 Stratum basale 4 Melanocyte 5 Dermis 2 3 4 5 Figure 30. Human pigmented skin 32 Lab 1: Histology & Integumentary System Accessory Structures of the Integument Function of Skin soft keratin, and consists of air spaces and big cells. The Our skin protects our body by providing a chemical, hair cortex consists of many layers of flattened cells filled physical, and biological barrier. Skin also dissipates heat with hard keratin. The cuticle encompasses a single layer from the body to maintain our constant body temperature. of overlapping cells that serve to separate adjacent cells In order to lose body heat, the nervous system causes der- so that the hairs do not mat. The cuticle also strengthens mal blood vessels to dilate (bringing hot blood near the the hair as it is the most heavily laden with hard keratin. skin) and increases sweat gland activity to dissipate the When the cuticle gets worn away, the keratin fibers in the heat as the sweat evaporates. The opposite occurs when cortex and medulla become exposed and can frizz to pro- we go out into a cold environment so that heat will be duce split ends. Melanocytes at the base of the hair fol- retained in the body. Small amounts of sodium chloride, licle produce and transfer hair pigment to the cortical hair ammonia, urea, and uric acid are excreted from the body cells. The proportion of different colored melanin added in sweat, while large volumes of water can be lost from to the hair will determine the color. Red hair contains the the body in the form of sweat on hot days. Skin addition- extra pigment pheomelanin. If melanin production is ally serves as a sensory bed and performs metabolic func- decreased, air bubbles are added instead and the hair will tions. The skin also has many exteroceptors (respond to be gray or white. stimuli from outside the body). Three major types of hair are found in humans: terminal, A smooth muscle called the arrector pili muscle is at- vellus, and intermediate. Terminal hairs are the thick, tached to each hair follicle. In humans, the muscle has no coarse, heavy, dark hairs on the scalp, eyebrows, and eye- known thermoregulatory use because humans do not have lashes. Vellus hairs are lightly pigmented and distributed enough hair to gain an insulation benefit. We do have over much of the skin as fine “peach fuzz.” Vellus hair is arrector pili muscles, though, and they contract when we pale and found all over the bodies of children and adults. are cold or sometimes when we are experiencing height- The hair on the arms and legs is sometimes referred to as ened emotional states, which produces “goose bumps.” intermediate hairs. When the arrector pili muscle contracts, it does move sebum from the hair follicles to the surface of the skin where it serves as a lubricant. Each hair erupts as a shaft out of a hair follicle. The follicle may even run as deep as into the hypodermis. The deep part of the follicle is referred to as the hair root with the deepest portion termed the hair bulb. At the root tip within the bulb is a hair papilla that contains nerves, blood vessels, and the beginning of the hair matrix, which is the living, proliferative part of the hair. Cells in the matrix undergo mitotic divisions that cause the hair to elongate. Above the matrix, when the hair cells keratin- ize, they harden and die. The hair follicle wall (not the hair shaft) is made up of an outermost peripheral connec- tive tissue sheath (of dermal origin), a glassy membrane (a thickened basal lamina), and an innermost epithelial root sheath (of epidermal origin). The epithelial root sheath is further divided into a thick external root sheath and a thin internal root sheath with only a single layer of epithelial cells covering the papilla. The hair shaft contains an outermost cuticle, outer cortex, and an inner medulla. If the shaft is ribbon-like and flat, the hair will be kinky. If the shaft is oval, the hair will be silky and wavy. If the shaft is perfectly round, the hair will be straight. The hair medulla is absent in fine hairs, contains Lab 1: Histology & Integumentary System 33 Longitudinal section through a hair follicle and the hair root contained within it. Sebaceous glands (oil glands) flank the hair follicle into which sebum (oil) is secreted. Sebum functions as a lubricant for the hair root (the body of the hair below the skin surface). Once the hair root extends beyond the skin surface, it is then termed the hair shaft. Se- bum is also secreted onto the outer surface of the stratum corneum, where it serves an antibacterial function and also a lubricant for the surrounding skin. 1 2 3 4 1 Epithelial root sheath 2 Hair root 3 Hair papilla 4 Sebaceous gland Figure 31. Human hair shaft Glandular Epithelia Exocrine glands secrete their substances onto a body surface or into a body cavity and do not release hormones into the circulation. Unicellular exocrine glands release their secretions by exocytosis directly onto the epithelial sur- face while multicellular glands accomplish a similar task except the secretion passes through a duct on its way to the surface. Exocrine glands produce substances such as saliva, oil, sweat, mucus, bile (from the liver), and digestive enzymes from the pancreas to name a few. 34 Lab 1: Histology & Integumentary System A cell is classified as merocrine if the secretions of that cell are excreted via exocytosis from secretory cells into an epithelial-walled duct or ducts and thence onto a bodily surface or into the lumen. Cells which are classified as apocrine bud their secretions off through the plasma membrane producing membrane-bound vesicles in the lumen. Holocrine secretions are produced in the cytoplasm of the cell and released by the rupture of the plasma membrane, which destroys the cell and results in the secretion of the product into the lumen. ©Van-Griner, LLC Merocrine gland Apocrine gland Holocrine gland Intact cells excrete secretions. Membrane-bound vesicles Whole cells rupture and Example: salivary gland bud off into the lumen. release secretions. Example: mammary gland Example: sebaceous gland Figure 32. Types of exocrine glands. Dark orange cells represent the secretory cells of the particular exocrine gland shown. Transverse cross-section of axillary (armpit) skin showing apocrine sweat glands. Apocrine sweat glands are larger and much more restricted in their location (i.e. axillary and pubic regions) than eccrine sweat glands. Apocrine sweat glands are activated commensurate with pubic and axillary hair growth by sex steroids during puberty. Apocrine secretions contain lipids and proteins not found in eccrine sweat gland secretions as well as possibly pheromones (not yet isolated) that may influence sexual behavior. Eccrine sweat glands are ubiquitous throughout the dermis and retard bacterial growth by creating the acid mantle and are vital for thermoregulation (i.e. evaporative cooling). 1 Eccrine sweat gland 2 Apocrine sweat gland 3 Adipose tissue 1 2 3 Figure 33. Human skin axilla region