Chapter 4: The Tissue Level of Organization Flashcards
Name the four basic types of tissues that make up the human body and state the characteristics of each.
Epithelial tissue covers body surfaces and lines hollow organs, body cavities, and ducts; it also forms glands. This tissue allows the body to interact with both its internal and external environments.
Connective tissue protects and supports the body and its organs. Various types of connective tissues bind organs together, store energy reserves as fat, and help provide the body with immunity to disease-causing organisms.
Muscular tissue is composed of cells specialized for contraction and generation of force. In the process, muscular tissue generates heat that warms the body.
Nervous tissue detects changes in a variety of conditions inside and outside the body and responds by generating electrical signals called nerve action potentials (nerve impulses) that activate muscular contractions and glandular secretions.
Describe the structure and functions of the five main types of cell junctions.
Cell junctions are contact points between the plasma membranes of tissue cells. Tight junctions form fluid-tight seals between cells; adherens junctions, desmosomes, and hemidesmosomes anchor cells to one another or to the basement membrane; and gap junctions permit electrical and chemical signals to pass between cells.
Identify the five different kinds of cell junctions on a diagram.
Tight Junctions
Tight junctions consist of weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells.
Adherens Junctions
Adherens junctions contain plaque, a dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of the cytoskeleton. Transmembrane glycoproteins called cadherins join the cells. Each cadherin inserts into the plaque from the opposite side of the plasma membrane, partially crosses the intercellular space (the space between the cells), and connects to cadherins of an adjacent cell. In epithelial cells, adherens junctions often form extensive zones called adhesion belts because they encircle the cell similar to the way a belt encircles your waist. Adherens junctions help epithelial surfaces resist separation during various contractile activities, as when food moves through the intestines.
Desmosomes
Like adherens junctions, desmosomes contain plaque and have transmembrane glycoproteins (cadherins) that extend into the intercellular space between adjacent cell membranes and attach cells to one another. However, unlike adherens junctions, the plaque of desmosomes does not attach to microfilaments. Instead, a desmosome plaque attaches to elements of the cytoskeleton known as intermediate filaments, which consist of the protein keratin. The intermediate filaments extend from desmosomes on one side of the cell across the cytosol to desmosomes on the opposite side of the cell. This structural arrangement contributes to the stability of the cells and tissue. These spot weld–like junctions are common among the cells that make up the epidermis (the outermost layer of the skin) and among cardiac muscle cells in the heart. Desmosomes prevent epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction.
Hemidesmosomes
Hemidesmosomes resemble desmosomes, but they do not link adjacent cells. The name arises from the fact that they look like half of a desmosome. The transmembrane glycoproteins in hemidesmosomes are integrins rather than cadherins. On the inside of the plasma membrane, integrins attach to intermediate filaments made of the protein keratin. On the outside of the plasma membrane, the integrins attach to the protein laminin, which is present in the basement membrane (discussed shortly). Thus, hemidesmosomes anchor cells not to each other but to the basement membrane.
Gap Junction
At gap junctions, membrane proteins called connexins form tiny fluid-filled tunnels called connexons that connect neighboring cells. The plasma membranes of gap junctions are not fused together as in tight junctions but are separated by a very narrow intercellular gap (space). Through the connexons, ions and small molecules can diffuse from the cytosol of one cell to another, but the passage of large molecules such as vital intracellular proteins is prevented. Gap junctions allow the cells in a tissue to communicate with one another, and allow for the transfer of nutrients and wastes.
State the main differences between epithelial and connective tissues.
The first obvious difference is the number of cells in relation to the extracellular matrix (the substance between cells). In an epithelial tissue many cells are tightly packed together with little or no extracellular matrix, whereas in a connective tissue a large amount of extracellular material separates cells that are usually widely scattered. The second obvious difference is that an epithelial tissue has no blood vessels, whereas most connective tissues have significant networks of blood vessels. Another key difference is that epithelial tissue almost always forms surface layers and is not covered by another tissue. An exception is the epithelial lining of blood vessels where blood constantly passes over the epithelium. Because epithelial tissue lacks blood vessels and forms surfaces, it is always found immediately adjacent to blood vessel–rich connective tissue, which enables it to make the exchanges with blood necessary for the delivery of oxygen and nutrients and the removal of wastes.
Describe the general features of epithelial tissue.
Epithelial tissue consists of cells arranged in continuous sheets, in either single or multiple layers. The various surfaces of covering and lining epithelial cells often differ in structure and have specialized functions. The apical surface of an epithelial cell faces the body surface, a body cavity, the lumen (interior space) of an internal organ, or a tubular duct that receives cell secretions. The lateral surfaces of an epithelial cell, which face the adjacent cells on either side, may contain tight junctions, adherens junctions, desmosomes, and/or gap junctions. The basal surface of an epithelial cell is opposite the apical surface and adheres to extracellular materials such as the basement membrane. The basement membrane is a thin extracellular layer that commonly consists of two layers, the basal lamina and reticular lamina. Epithelial tissue has many different roles in the body; the most important are protection, filtration, secretion, absorption, and excretion. In addition, epithelial tissue combines with nervous tissue to form special organs for smell, hearing, vision, and touch.
What are the two types of epithelium?
(1) Covering and lining epithelium, also called surface epithelium, forms the outer covering of the skin and some internal organs. It also forms the inner lining of blood vessels, ducts, body cavities, and the interior of the respiratory, digestive, urinary, and reproductive systems.
(2) Glandular epithelium makes up the secreting portion of glands such as the thyroid gland, adrenal glands, sweat glands, and digestive glands.
Types of covering and lining epithelial tissue are classified according to two characteristics: the arrangement of cells into layers and the shapes of the cells. Identify the different kinds of covering and lining epithelial tissue.
1. Arrangement of cells in layers:
a. Simple epithelium is a single layer of cells that functions in diffusion, osmosis, filtration, secretion, or absorption. Secretion is the production and release of substances such as mucus, sweat, or enzymes. Absorption is the intake of fluids or other substances such as digested food from the intestinal tract.
b. Pseudostratified epithelium appears to have multiple layers of cells because the cell nuclei lie at different levels and not all cells reach the apical surface; it is actually a simple epithelium because all its cells rest on the basement membrane. Cells that do extend to the apical surface may contain cilia; others (goblet cells) secrete mucus.
c. Stratified epithelium consists of two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear.
2. Cell shapes:
a. Squamous cells are thin, which allows for the rapid passage of substances through them.
b. Cuboidal cells are as tall as they are wide and are shaped like cubes or hexagons. They may have microvilli at their apical surface and function in either secretion or absorption.
c. Columnar cells are much taller than they are wide, like columns, and protect underlying tissues. Their apical surfaces may have cilia or microvilli, and they often are specialized for secretion and absorption.
d. Transitional cells change shape, from squamous to cuboidal and back, as organs such as the urinary bladder stretch.
When we combine the two characteristics (arrangements of layers and cell shapes), we come up with the following types of epithelial tissues:
I. Simple epithelium
**A. Simple squamous epithelium**
1. Endothelium (lines heart, blood vessels, lymphatic vessels)
2. Mesothelium (forms epithelial layer of serous membranes)
** B. Simple cuboidal epithelium**
**C. Simple columnar epithelium**
1. Nonciliated (lacks cilia)
2. Ciliated (contains cilia)
**D. Pseudostratified columnar epithelium**
1. Nonciliated (lacks cilia)
2. Ciliated (contains cilia)
II. Stratified epithelium
**A. Stratified squamous epithelium**
1. Nonkeratinized (lacks keratin)
2. Keratinized (contains keratin)
**B. Stratified cuboidal epithelium**
**C. Stratified columnar epithelium**
**D. Transitional epithelium or urothelium** (lines most of urinary tract)
Differentiate between endocrine and exocrine glands.
The secretions of endocrine glands, called hormones, enter the interstitial fluid and then diffuse into the bloodstream without flowing through a duct. Endocrine secretions have far-reaching effects because they are distributed throughout the body by the bloodstream.
Exocrine glands secrete their products into ducts that empty onto the surface of a covering and lining epithelium such as the skin surface or the lumen of a hollow organ. The secretions of exocrine glands have limited effects and some of them would be harmful if they entered the bloodstream.
Identify exocrine glands based on their structure.
Identify the three kinds of exocrine glands based on their function.
The functional classification of exocrine glands is based on how their secretions are released.
Secretions of merocrine glands are synthesized on ribosomes attached to rough ER; processed, sorted, and packaged by the Golgi complex; and released from the cell in secretory vesicles via exocytosis.
Apocrine glands accumulate their secretory product at the apical surface of the secreting cell. Then, that portion of the cell pinches off by exocytosis from the rest of the cell to release the secretion.
The cells of holocrine glands accumulate a secretory product in their cytosol. As the secretory cell matures, it ruptures and becomes the secretory product.
Explain the general features of connective tissue.
Connective tissue consists of two basic elements: extracellular matrix and cells. A connective tissue’s extracellular matrix is the material located between its widely spaced cells. The extracellular matrix consists of protein fibres and ground substance.
Unlike epithelial tissue, connective tissue usually is highly vascular; that is, it has a rich blood supply. Exceptions include cartilage, which is avascular, and tendons, with a scanty blood supply. Except for cartilage, connective tissue, like epithelial tissue, is supplied with nerves.
Identify the different types of connective tissue cells.
1. Fibroblasts are large, flat cells with branching processes. They are present in all the general connective tissues, and usually are the most numerous.
2. Macrophages are phagocytes that develop from monocytes, a type of white blood cell. Fixed macrophages reside in a particular tissue; examples include alveolar macrophages in the lungs or splenic macrophages in the spleen. Wandering macrophages have the ability to move throughout the tissue and gather at sites of infection or inflammation to carry on phagocytosis.
3. Plasma cells (plasmocytes) are found in many places in the body, but most plasma cells reside in connective tissue, especially in the gastrointestinal and respiratory tracts.
4. Mast cells (mastocytes) are involved in the inflammatory response, the body’s reaction to injury or infection and can also bind to, ingest, and kill bacteria.
5. Adipocytes are fat cells or adipose cells, connective
tissue cells that store triglycerides (fats). They are found deep to the skin and around organs such as the heart and kidneys.
6. Leukocytes (white blood cells) are not found in significant numbers in normal connective tissue. However, in response to certain conditions they migrate from blood into connective tissue. For example, neutrophils gather at sites of infection, and eosinophils migrate to sites of parasitic invasions and allergic responses.
Identify the two major components of the connective tissue extracellular matrix.
1. Ground Substance is the component of a connective tissue between the cells and fibers. The ground substance may be fluid, semifluid, gelatinous, or calcified. It supports cells, binds them together, stores water, and provides a medium for exchange of substances between the blood and cells.
2. Fibers are embedded in the extracellular matrix between the cells: collagen fibers, elastic fibers, and reticular fibers.
Describe the three types of fibres found in the extracellular matrix of connective tissue.
Collagen fibers are very strong and resist pulling or stretching, but they are not stiff , which allows tissue flexibility. Collagen fibers are found in most types of connective tissues, especially bone, cartilage, tendons (which attach muscle to bone), and ligaments (which attach bone to bone).
Elastic fibers, which are smaller in diameter than collagen fibers, branch and join together to form a fibrous network within a connective tissue. Because of their unique molecular structure, elastic fibers are strong but can be stretched up to 150% of their relaxed length without breaking. Equally important, elastic fibers have the ability to return to their original shape after being stretched, a property called elasticity. Elastic fibers are plentiful in skin, blood vessel walls, and lung tissue.
Reticular fibers, consisting of collagen arranged in fine bundles with a coating of glycoprotein, provide support in the walls of blood vessels and form a network around the cells in some tissues, such as areolar connective tissue, adipose tissue, nerve fibers, and smooth muscle tissue. Like collagen fibers, reticular fibers provide support and strength. Reticular fibers are plentiful in reticular connective tissue, which forms the stroma (supporting framework) of many soft organs, such as the spleen and lymph nodes. These fibers also help form the basement membrane.
Identify the different kinds of connective tissue.
I. Embryonic connective tissue
A. Mesenchyme
B. Mucous (mucoid) connective tissue
II. Mature connective tissue
A. Connective tissue proper
1. Loose connective tissue
a. Areolar connective tissue
b. Adipose tissue
c. Reticular connective tissue
2. Dense connective tissue
a. Dense regular connective tissue
b. Dense irregular connective tissue
c. Elastic connective tissue
B. Supporting connective tissue
1. Cartilage
a. Hyaline cartilage
b. Fibrocartilage
c. Elastic cartilage
2. Bone tissue
a. Compact bone
b. Spongy bone
C. Liquid connective tissue
- Blood
- Lymph
Embryonic connective tissue refers to connective tissue present in an embryo or a fetus. Mature connective tissue refers to connective tissue that is present at birth and persists throughout life. One category of mature connective tissue is connective tissue proper, which is flexible and contains a viscous ground substance with abundant fibers. A second category of mature connective tissue is supporting connective tissue, which protects and supports soft tissues of then body. The third category of mature connective tissue is liquid connective
tissue, which means that the extracellular matrix is liquid.
The basic unit of compact bone is an osteon or haversian system. Describe the four parts of an osteon.
The lamellae are concentric rings of extracellular matrix that consist of mineral salts (mostly calcium and phosphates), which give bone its hardness and compressive strength, and collagen fibers, which give bone its tensile strength.
Lacunae, are small spaces between lamellae that contain mature bone cells called osteocytes.
Projecting from the lacunae are canaliculi, networks of minute canals containing the processes of osteocytes. Canaliculi provide routes for nutrients to reach osteocytes and for wastes to leave them.
A central canal or haversian canal contains blood vessels and nerves.
Define membrane and identify the different kinds of membranes.
Membranes are flat sheets of pliable tissue that cover or line a part of the body. The majority of membranes consist of an epithelial layer and an underlying connective tissue layer and are called epithelial membranes. The principal epithelial membranes of the body are mucous membranes, serous membranes, and the cutaneous membrane, or skin. Another type of membrane, a synovial membrane, lines joints and contains connective tissue but no epithelium.
What are the two kinds of bone tissue and how do they differ?
Compact bone is made of osteons, or haversion systems, with each unit containing lamellae, lacunae, canaliculi, and a central, or haversion, canal.
Spongy bone lacks osteons. Rather, it consists of columns of bone called trabeculae which contain lamellae, lacunae, and canaliculi, but lack a central canal. Spaces between trabeculae are filled with red bone marrow.
Identify the three kinds of formed elements present in blood plasma.
Suspended in the blood plasma are formed elements: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).
Red blood cells transport oxygen to body cells and remove some carbon dioxide from them.
White blood cells are involved in phagocytosis, immunity, and allergic reactions.
Platelets participate in blood clotting.
Identify the two kinds of liquid connective tissue.
Blood has a liquid extracellular matrix called blood plasma and formed elements.
Lymph is the extracellular fluid that flows in lymphatic vessels.
Describe the three kinds of epithelial membranes.
A mucous membrane or mucosa line a body cavity that opens directly to the exterior, such as the entire digestive, respiratory, and reproductive tracts, and much of the urinary tract. They consist of a lining layer of epithelium and an underlying layer of connective tissue. The connective tissue layer of a mucous membrane is areolar connective tissue and is called the lamina propria.
A serous membrane or serosa lines a body cavity that does not open directly to the exterior (thoracic or abdominal cavities), and it covers the organs that are within the cavity. Serous membranes have two layers: The layer attached to and lining the cavity wall is called the parietal layer; the layer that covers and adheres to the organs within the cavity is the visceral layer. The mesothelium of a serous membrane secretes serous fluid, a watery lubricant that allows organs to glide easily over one another or to slide against the walls of cavities.
The cutaneous membrane or skin covers the entire surface of the body and consists of a superficial portion called the epidermis and a deeper portion called the dermis.
List the three types of muscle tissue.
Muscular tissue consists of elongated cells called muscle fibers or myocytes that can use ATP to generate force. As a result, muscular tissue produces body movements, maintains posture, and generates heat. It also provides protection. Based on location and certain structural and functional features, muscular tissue is classified into three types: skeletal, cardiac, and smooth.
Contrast the structure, location, and mode of control of skeletal, cardiac, and smooth muscle tissue.
Skeletal muscle tissue consists of long, cylindrical, striated fibers that range from a few cm to over a foot in length. A skeletal muscle fiber is a roughly cylindrical, multinucleated cell with nuclei at the periphery. Skeletal muscle fibre is usually attached to bones by tendons. It plays a role motion, posture, heat production, and protection. It is considered voluntary because it can be made to contract or relax by conscious control.
Cardiac muscle tissue is located in the heart wall and pumps blood to all parts of the body. It consists of branched, striated fibers with usually only one centrally located nucleus. It is involuntary.
Smooth muscle tissue consists of nonstriated fibers (hence the term smooth). Smooth muscle fiber is a small spindle-shaped cell thickest in middle, tapering at each end, and containing a single, centrally located nucleus. Smooth muscle tissue is usually involuntary and can produce powerful contractions as many muscle fibers contract in unison. contract individually, like skeletal muscle fibers. It is found in the iris of the eyes; the walls of hollow internal structures such as blood vessels, airways to lungs, stomach, intestines, gallbladder, urinary bladder, and uterus. It plays a role in motion (constriction of blood vessels and airways, propulsion of foods through gastrointestinal tract, contraction of urinary bladder and gallbladder).
Describe the structural features and functions of nervous tissue.
Nervous tissue consists of only two principal types of cells: neurons and neuroglia.
Neurons, or nerve cells, are sensitive to various stimuli. They convert stimuli into electrical signals called nerve action potentials (nerve impulses) and conduct these action potentials to other neurons, to muscle tissue, or to glands. Most neurons consist of three basic parts: a cell body and two kinds of cell processes—dendrites and axons. The cell body contains the nucleus and other organelles. Dendrites are tapering, highly branched, and usually short cell processes (extensions). They are the major receiving or input portion of a neuron. The axon of a neuron is a single, thin, cylindrical process that may be very long. It is the output portion of a neuron, conducting nerve impulses toward another neuron or to some other tissue.
Even though neuroglia do not generate or conduct nerve impulses, these cells do have many important supportive functions.
Explain the concept of electrical excitability.
Neurons and muscle fibers are considered excitable cells because they exhibit electrical excitability, the ability to respond to certain stimuli by producing electrical signals such as action potentials. Action potentials can propagate (travel) along the plasma membrane of a neuron or muscle fiber due to the presence of specific voltage-gated ion channels. When an action potential forms in a neuron, the neuron releases chemicals called neurotransmitters, which allow neurons to communicate with other neurons, muscle fibers, or glands. When an action potential occurs in a muscle fiber, the muscle fiber contracts, resulting in activities such as movement of the limbs, propulsion of food through the small intestine, and movement of blood out of the heart and into the blood vessels of the body.
What are the 4 functions of muscular tissue?
Muscular tissue consists of cells called muscle fibers or myocytes that are specialized for contraction. It provides motion, maintenance of posture, heat production, and protection.
What is the function of simple squamous epithelium and what are its two types?
Simple squamous epithelium, a single layer of flat cells, is found in parts of the body where filtration or diffusion is a priority process. Endothelium lines the heart and blood vessels. Mesothelium forms the serous membranes that line the thoracic and abdominopelvic cavities and covers the organs within them.
What is the function of simple cuboidal epithelium and where is it found?
Simple cuboidal epithelium, a single layer of cube-shaped cells that function in secretion and absorption, is found covering the ovaries, in the kidneys and eyes, and lining some glandular ducts.
What is transitional epithelium and where is it found?
Transitional epithelium (urothelium) consists of several layers of cells whose appearance varies with the degree of stretching. It lines the urinary bladder.
What are the two kinds of simple columnar epithelium and where are they found?
Nonciliated simple columnar epithelium, a single layer of nonciliated rectangular cells, lines most of the gastrointestinal tract and contains specialized cells that perform absorption and secrete mucus.
Ciliated simple columnar epithelium, a single layer of ciliated rectangular cells, is found in a few portions of the upper respiratory tract, where it moves foreign particles trapped in mucus out of the respiratory tract.
What are the two kinds of pseudostratified columnar epithelium and where are they found?
Nonciliated pseudostratified columnar epithelium has no goblet cells and lines ducts of many glands, the epididymis, and part of the male urethra. The nonciliated variety functions in absorption and protection.
Ciliated pseudostratified columnar epithelium contains goblet cells and lines most of the upper respiratory tract. The ciliated variety moves mucus in the respiratory tract.
