Chapter 4 - Membranes - Definition

Cardiac muscle tissue consists of branched, striated fibers with usually only one centrally located nucleus. The fibers attach end to end by transverse thickenings of the plasma membrane called intercalated discs, which contain desmosomes and gap junctions. It is involuntary and pumps blood to all parts of the body.

An increase in the size of a tissue because its cells enlarge without undergoing cell division.

The cell body contains the nucleus and other organelles.

The replacement of a diseased or injured tissue or organ. The most successful transplants involve use of a person’s own tissues or those from an identical twin.

Aging causes epithelial tissues to get progressively thinner and connective tissues to become more fragile.

Most neurons consist of three basic parts: a cell body and two kinds of cell processes—dendrites and axons.

Synovial membranes line joints.

Cartilage has a limited capacity for cell replenishment because it has a smaller blood supply.

Mucous membranes line body cavities that open to the outside.

A membrane is a flat sheet of pliable tissues that covers or lines a part of the body.

The functions of skeletal muscle tissue include motion, posture, heat production, and protection.

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.

Cardiac muscle tissue is located in the heart wall.

Cardiac muscle tissue lacks satellite cells, and existing cardiac muscle fibers do not undergo mitosis to form new cells.

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.

Skeletal muscle tissue consists of long, cylindrical, striated fibers with alternating light and dark bands visible under a light microscope. It is a roughly cylindrical, multinucleated cell with nuclei at the periphery and is considered voluntary because it can be made to contract or relax by conscious control.

Dendrites are tapering, highly branched, and usually short cell processes. They are the major receiving or input portion of a neuron.

Intercalated discs are transverse thickenings of the plasma membrane in cardiac muscle tissue that contain desmosomes and gap junctions. They strengthen the tissue and hold fibers together during vigorous contractions, and provide a route for quick conduction of electrical signals throughout the heart.

Wound dehiscence is the partial or complete separation of the outer layers of a sutured incision, often caused by surgical error, early suture removal, or deep wound infection.

Lymph is the extracellular fluid that flows in lymphatic vessels. It is a liquid connective tissue that consists of several types of cells in a clear liquid extracellular matrix that is similar to blood plasma but with much less protein.

Fibrosis is the process where fibroblasts synthesize collagen and other extracellular matrix materials that aggregate to form scar tissue, which is not specialized to perform the functions of the parenchymal tissue.

An autoimmune disorder that attacks the synovial membranes of joints.

Nervous tissue exhibits sensitivity to various types of stimuli, converts stimuli into nerve impulses (action potentials), and conducts nerve impulses to other neurons, muscle fibers, or glands.

Muscular tissue is classified into three types based on location and certain structural and functional features: skeletal, cardiac, and smooth.

An epithelial membrane is a membrane that consists of an epithelial layer and an underlying layer of connective tissue.

The types of fibers in the extracellular matrix are collagen fibers (found in bone, tendons, and ligaments), elastic fibers (found in skin, blood vessel walls, and lungs), and reticular fibers (found around fat cells, nerve fibers, and skeletal and smooth muscle cells).

Dense regular connective tissue consists of parallel bundles of collagen fibers and fibroblasts; it forms tendons, most ligaments, and aponeuroses.

Neurons (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.

The function of cardiac muscle tissue is to pump blood to all parts of the body.

An immune response of the body directed at foreign proteins in a transplanted tissue or organ; immunosuppressive drugs, such as cyclosporine, have largely overcome tissue rejection in heart-, kidney-, and liver-transplant patients.

Collagen fibers increase in number and change in quality with aging, affecting the flexibility of arteries as much as the fatty deposits associated with atherosclerosis.

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.

A mucous membrane or mucosa lines a body cavity that opens directly to the exterior. Mucous membranes line 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.

Since epithelial tissue is avascular, it depends on blood vessels in connective tissue for oxygen, nutrients, and waste disposal.

Simple multicellular exocrine glands have a nonbranched duct; compound multicellular exocrine glands have a branched duct.

A tissue is a group of cells, usually with similar embryological origin, specialized for a particular function.

Cell junctions are points of contact between adjacent plasma membranes.

Simple squamous epithelium is found in parts of the body where filtration or diffusion is a priority process. Endothelium lines the heart and blood vessels, and mesothelium forms the serous membranes that line the thoracic and abdominopelvic cavities.

Skin covers the surface of the body.

Neuroglia are cells that do not generate or conduct nerve impulses but have many important supportive functions.

A chronic inflammatory disease of connective tissue occurring mostly in nonwhite women during their childbearing years. It is an autoimmune disease that can cause tissue damage in every body system.

Electrical excitability is the ability of neurons and muscle fibers to respond to certain stimuli by producing electrical signals such as action potentials.

Nervous tissue consists of neurons (nerve cells), which have a cell body and processes extending from the cell body (one to multiple dendrites and a single axon), and neuroglia, which do not generate or conduct nerve impulses but have other important supporting functions.

Muscular tissue consists of elongated cells called muscle fibers or myocytes that can use ATP to generate force. It produces body movements, maintains posture, generates heat, and provides protection.

Fibroblasts secrete fibers and ground substance of extracellular matrix.

Simple cuboidal epithelium functions in secretion and absorption and is found covering the ovaries, in the kidneys and eyes, and lining some glandular ducts.

The extracellular matrix in connective tissue is composed of ground substance and fibers. The ground substance supports and binds cells together, provides a medium for the exchange of materials, stores water, and actively influences cell functions.

Hyaline cartilage consists of a gel-like ground substance and appears bluish white in the body; it is found in the embryonic skeleton, at the ends of bones, in the nose, and in respiratory structures. It is flexible, allows movement, provides support, and is usually surrounded by a perichondrium.

The nervous system is composed of neurons (nerve cells) and neuroglia (protective and supporting cells).

Serous membranes line cavities that do not open directly to the outside.

Skeletal muscle tissue is usually attached to bones by tendons.

A decrease in the size of cells, with a subsequent decrease in the size of the affected tissue or organ.

The replacement of a diseased or injured tissue or organ with cells or tissues from an animal. Porcine (from pigs) and bovine (from cows) heart valves are used for some heart-valve replacement surgeries.

Adhesions are abnormal joining of tissues, often forming in the abdomen around a site of previous inflammation or after surgery, which can decrease tissue flexibility and cause obstruction.

Voltage-gated ion channels allow action potentials to propagate (travel) along the plasma membrane of a neuron or muscle fiber.

The two layers of a serous membrane are the parietal layer, which lines the cavity wall, and the visceral layer, which covers and adheres to the organs within the cavity.

Tissue repair is the replacement of worn-out, damaged, or dead cells. New cells originate by cell division from the stroma, the supporting connective tissue, or from the parenchyma, cells that constitute the functioning part of the tissue or organ.

The basement membrane provides physical support for the epithelial tissue and plays a part in growth and wound healing, restriction of molecular movement between tissues, and blood filtration in the kidneys.

Transitional epithelium (urothelium) consists of several layers of cells whose appearance varies with the degree of stretching. It lines the urinary bladder.

An epithelial membrane consists of an epithelial layer overlying a connective tissue layer. Types include mucous, serous, and cutaneous membranes.

The cutaneous membrane is the skin. It covers the entire body and consists of a superficial epidermis (epithelium) and a deep dermis (connective tissue).

Bone tissue has a continuous capacity for renewal due to its ample blood supply.

Granulation tissue is actively growing connective tissue that forms across a wound or surgical incision to provide a framework that supports the epithelial cells that migrate into the open area and fill it.

Vitamin C affects the normal production and maintenance of matrix materials, especially collagen, and strengthens and promotes the formation of new blood vessels.

Elastin thickens, fragments, and acquires a greater affinity for calcium with age, which may be associated with the development of atherosclerosis.

The principal epithelial membranes of the body are mucous membranes, serous membranes, and the cutaneous membrane, or skin.

Gap junctions allow cellular communication via passage of electrical and chemical signals between adjacent cells.

Epithelial tissue consists mostly of cells with little extracellular material between adjacent plasma membranes. It is avascular but has a nerve supply and a high capacity for renewal.

Reticular connective tissue consists of reticular fibers and reticular cells and is found in the liver, spleen, and lymph nodes.

Lymph is the extracellular fluid that flows in lymphatic vessels; it is a clear fluid similar to blood plasma but with less protein.

Serous membranes line closed cavities (pleura, pericardium, peritoneum) and cover the organs in the cavities. These membranes consist of parietal and visceral layers.

Synovial membranes line joint cavities and consist of areolar connective tissue; they do not have an epithelial layer.

The action of cardiac muscle tissue, which forms most of the heart wall and is striated, is involuntary.

Electrical excitability is the ability to respond to certain stimuli by producing electrical signals such as action potentials.

Satellite cells are stem cells in skeletal muscle tissue that do not divide rapidly enough to replace extensively damaged muscle fibers.

Connective tissue protects, supports, binds organs together, stores energy, and helps provide immunity.

Blood consists of blood plasma and formed elements: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Because the cells are so thin, substances move most rapidly through squamous cells.

Epithelial tissue has many cells tightly packed together and is avascular, while connective tissue has relatively few cells with lots of extracellular material.

Covering and lining epithelium can be simple, pseudostratified, or stratified. The cell shapes may be squamous (flat), cuboidal (cubelike), columnar (rectangular), or transitional (variable).

Ciliated simple columnar epithelium is found in a few portions of the upper respiratory tract, where it moves foreign particles trapped in mucus out of the respiratory tract.

Connective tissue, one of the most abundant body tissues, consists of relatively few cells and an abundant extracellular matrix of ground substance and protein fibers. It usually has a nerve supply and is usually highly vascular.

Loose connective tissue includes areolar connective tissue, adipose tissue, and reticular connective tissue. Areolar connective tissue consists of the three types of fibers (collagen, elastic, and reticular), several types of cells, and a semifluid ground substance.

Skeletal muscle tissue is attached to bones and is striated and voluntary.

Neurons respond to stimuli by converting the stimuli into electrical signals called nerve action potentials (nerve impulses), and conducting nerve impulses to other cells.

Tissue repair is the replacement of worn-out, damaged, or dead cells by healthy ones.

Signs and symptoms include painful joints, low-grade fever, fatigue, mouth ulcers, weight loss, enlarged lymph nodes and spleen, sensitivity to sunlight, rapid loss of large amounts of scalp hair, and anorexia. A distinguishing feature is an eruption across the bridge of the nose and cheeks called a 'butterfly rash.'

The composition of lymph varies from one part of the body to another. For example, lymph leaving lymph nodes includes many lymphocytes, a type of white blood cell, in contrast to lymph from the small intestine, which has a high content of newly absorbed dietary lipids.

Epithelial tissue covers the body, lines various structures, and forms glands.

Muscular tissue contracts and generates force and heat.

Red blood cells transport oxygen and some carbon dioxide; white blood cells carry on phagocytosis and mediate allergic reactions and immune system responses; platelets are essential for blood clotting.

Mature, differentiated cells can undergo cell division to replace lost or damaged cells. Examples include hepatocytes (liver cells) and endothelial cells in blood vessels.

The subtypes of epithelial tissue include covering and lining epithelium (surface epithelium) and glandular epithelium.

A gland is a single cell or a group of epithelial cells adapted for secretion. There are two types of glandular epithelium: endocrine and exocrine.

Brown adipose tissue (BAT) generates heat.

Dense irregular connective tissue usually consists of collagen fibers and a few fibroblasts; it is found in fasciae, the dermis of skin, and membrane capsules around organs.

Blood consists of blood plasma and formed elements—red blood cells, white blood cells, and platelets; its cells transport oxygen and carbon dioxide, carry on phagocytosis, participate in allergic reactions, provide immunity, and bring about blood clotting.

The epithelial layer of a mucous membrane acts as a barrier that microbes and other pathogens have difficulty penetrating. It also secretes mucus to prevent cavities from drying out, traps particles in the respiratory passageways, lubricates food in the gastrointestinal tract, secretes enzymes needed for digestion, and is the site of food and fluid absorption.

The lamina propria is the connective tissue layer of a mucous membrane, consisting of areolar connective tissue. It supports the epithelium, binds it to underlying structures, allows flexibility, provides protection, holds blood vessels in place, and serves as the vascular source for the overlying epithelium.

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.

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. The epidermis is made of keratinized stratified squamous epithelium, while the dermis consists of dense irregular connective tissue and areolar connective tissue.

Sebaceous (oil) glands are holocrine glands, and salivary glands are merocrine glands.

The tissues of the body are classified into four basic types: epithelial, connective, muscular, and nervous.

Nonciliated simple columnar epithelium lines most of the gastrointestinal tract and contains specialized cells that perform absorption and secrete mucus.

The subclasses of connective tissue are embryonic (found in embryo and fetus) and mature (present in the newborn). Mature connective tissue is subdivided into connective tissue proper (loose and dense), supporting connective tissue (cartilage and bone), and liquid connective tissue (blood and lymph).

Bone or osseous tissue is a supporting connective tissue that consists of an extracellular matrix of mineral salts and collagen fibers that contribute to the hardness of bone, and osteocytes that are located in lacunae. It supports and protects the body, provides a surface area for muscle attachment, helps the body move, stores minerals, and houses blood-forming tissue.

Stem cells may divide to replace lost or damaged cells.

A serous membrane, or serosa, lines a body cavity that does not open directly to the exterior and covers the organs within the cavity. It consists of areolar connective tissue covered by mesothelium (simple squamous epithelium) and secretes serous fluid, a watery lubricant that allows organs to glide easily over one another or against cavity walls.

Nervous tissue detects changes in the environment and generates nerve impulses that activate muscular contraction and glandular secretion.

Stem cells are immature, undifferentiated cells that divide to replace lost or damaged cells. They reside in protected locations in the epithelia of the skin and gastrointestinal tract to replenish cells sloughed from the apical layer, and in red bone marrow to continually provide new red and white blood cells and platelets.

Tight junctions form fluid-tight seals between cells.

Stratified squamous epithelium consists of several layers of cells. A nonkeratinized variety lines the mouth, and a keratinized variety forms the epidermis.

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.

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.

Synovial membranes line the cavities of freely movable joints and lack an epithelium, making them non-epithelial membranes. They are composed of synoviocytes and a layer of connective tissue (areolar and adipose) and secrete synovial fluid, which lubricates and nourishes the cartilage at movable joints and contains macrophages to remove microbes and debris.

Fibrocartilage is found in the pubic symphysis, intervertebral discs, and menisci of the knee joint; it contains chondrocytes scattered among clearly visible bundles of collagen fibers.

Cell types in connective tissue proper include fibroblasts (secrete extracellular matrix), macrophages (perform phagocytosis), plasma cells (secrete antibodies), mast cells (produce histamine), adipocytes (store fat), and white blood cells (respond to infections).

Elastic connective tissue consists of branching elastic fibers and fibroblasts and is found in the walls of large arteries, lungs, trachea, and bronchial tubes.

Tissues heal faster and leave less obvious scars in the young than in the aged; surgery performed on fetuses leaves no scars.

Elastic cartilage maintains the shape of organs such as the epiglottis of the larynx, auditory tubes, and external ear; its chondrocytes are located within a threadlike network of elastic fibers, and it has a perichondrium.

Mucous membranes line cavities that open to the exterior, such as the gastrointestinal tract.

Smooth muscle tissue is found in the walls of hollow internal structures (blood vessels and viscera) and is nonstriated and involuntary.