Ch. 4: Tissues & Membranes

What is a tissue?

A “fabric” or group of cells with similar structure and function.

What are the four primary types of tissues?

Epithelium, connective, muscle, and nervous.

What is histology?

The microscopic study of tissue.

What is a biopsy?

The removal and examination of tissue samples from a living body for diagnostic purposes.

What is an autopsy?

The examination of a dead body to determine the cause of death and study disease.

Why is the microscopic study of tissue important?

It allows for histology, biopsy, and autopsy, which are crucial for understanding tissue structure, diagnosing diseases, and determining causes of death.

Define epithelial tissue.

A sheet of cells that covers all free body surfaces (inside and out), forming an interface or boundary between two environments.

What are the functions of epithelial tissue?

Protection, absorption, filtration, secretion, and sensory reception.

What does absorption refer to in the context of epithelial tissue function?

The intake of molecules and substances.

How does epithelial tissue function in filtration?

Closely fitted cells can form a “strainer” with small holes.

What is secretion in the context of epithelial tissue function?

The release of molecules and substances.

What are the special characteristics of epithelial tissue?

Cellularity, specialized contacts, polarity (apical and basal surfaces), supported by connective tissue, avascular but innervated, and regeneration.

What is cellularity in epithelial tissue?

Epithelial tissue is composed of closely packed cells.

What are specialized contacts in epithelial tissue?

Epithelial cells fit closely together, forming specialized junctions.

What is polarity in epithelial tissue?

Epithelial cells have one free surface (apical) and one bound surface (basal).

What is the apical surface of epithelial tissue?

The free surface.

What is the basal surface of epithelial tissue?

The bound surface.

What type of tissue supports epithelial tissue?

Connective tissue.

Is epithelial tissue vascular or avascular? Is it innervated?

Avascular (contains no blood vessels) but innervated (supplied by nerve fibers).

What is the regenerative capacity of epithelial tissue?

It has the ability to regenerate.

What are some special structural features of the apical surface of epithelial cells?

Microvilli and cilia.

What are microvilli? Where are they found and what is their function?

Fingerlike extensions of epithelial cells lining some parts of the digestive tract or the kidney. They increase surface area, increasing absorption and secretion, and may create adhesion points for secreted mucus.

What are cilia? What is their structure and function?

Microtubules that project from cell membranes as hairs that move uniformly in one direction (wave-like). They can move substances along the surface of a sheet of epithelial cells.

What is a clinical note regarding cilia and nicotine?

Nicotine decreases ciliary action.

What are lateral cell junctions?

Specialized connections between adjacent epithelial cells.

What are desmosomes? What is their function?

Anchoring junctions linking proteins between cells that prevent cells subjected to mechanical stress (such as skin cells) from being pulled apart; they confer strength.

What are tight junctions? What is their function?

Rivets that securely fuse adjacent plasma membranes together into leakproof sheets; they seal the extracellular space.

What are gap junctions? What is their function?

Channels that allow substances to leak between cells.

What is the basal lamina? Where is it located and what is its composition?

A noncellular, adhesive sheet of glycoproteins secreted by epithelial cells toward the neighboring connective tissue layer.

What are the functions of the basal lamina?

Selective filter and scaffold to which epithelial cells can migrate or grow upon.

What does the basal lamina combine with to form the basement membrane?

Fibers from the connective tissue layer.

Where is the basement membrane located?

Just deep to the basal lamina.

What are the functions of the basement membrane?

Reinforces the epithelial sheet and defines the epithelial boundary.

How is epithelium classified?

By two names: the first indicating the number of cell layers and the second indicating the shape of the cells.

What does "simple" mean when classifying epithelium by the number of cell layers?

One layer.

What does "stratified" mean when classifying epithelium by the number of cell layers?

More than one layer.

What does "pseudostratified" mean when classifying epithelium by the number of cell layers?

Looks like more than one layer, but isn't.

What does "squamous" mean when classifying epithelium by cell shape? Describe the nucleus.

Flat, plate-like, or scale-like; nucleus is flat and disc-like.

What does "cuboidal" mean when classifying epithelium by cell shape? Describe the nucleus.

Cube-shaped or box-like; nucleus is large and round (spherical).

What does "columnar" mean when classifying epithelium by cell shape? Describe the nucleus.

Tall and column-shaped; the nucleus is oval and elongated, located in the basal ⅓.

What are glands?

One or more epithelial cells organized to make and secrete (export) a particular product (often an aqueous fluid that contains proteins).

Describe the secretory pathway in glandular epithelium.

RER → Golgi → vesicles → exocytosis.

What are the two major types of glands?

Endocrine glands and exocrine glands.

What are endocrine glands? How do they secrete their products? What are their secretions called?

Ductless glands that secrete their products directly into the bloodstream. Their secretions are chemical messenger molecules called hormones.

What are hormones?

Chemical messenger molecules manufactured to react with a specific “target” organ(s) in some specific way.

Give an example of an endocrine function of an organ.

The pancreas produces the hormone insulin, which affects the energy pathways used by many organs of the body.

What are exocrine glands? How do they secrete their products?

Glands that secrete their products onto a body surface or into body cavities.

What are unicellular exocrine glands? Give an example and its secretion.

Single-celled exocrine glands; an example is the goblet cell, which secretes a protein called mucin.

What does mucin combine with to form mucus?

Water (H₂O).

What are multicellular exocrine glands composed of? Give examples.

A secretory unit and a duct. Examples include sweat and oil glands, salivary glands, liver, and the exocrine portion of the pancreas.

What are the four main classes of connective tissue?

Connective tissue proper, cartilage, osseous tissue (bone), and blood.

What are the functions of connective tissue?

Binding (connection) and support, protection, insulation, and transportation.

What are the structural elements of connective tissue?

Cell type and extracellular matrix (ECM).

What are the primary cell types found in connective tissue?

Fibrocyte, chondrocyte, osteocyte, and red/white blood cells.

What is the extracellular matrix (ECM) composed of?

Ground substance and fibers.

What is ground substance? What is its composition?

A component of the ECM that holds water and ranges from liquid to jelly to firm. Its composition includes water, adhesion proteins, and polysaccharide molecules.

What are the three types of fibers found in connective tissue? What produces them?

Collagen fibers, elastic fibers, and reticular fibers; they are produced by the cells.

Describe collagen fibers.

Extremely tough fibers with high tensile strength.

Describe elastic fibers.

Fibers that can stretch and recoil.

Describe reticular fibers.

Fine collagen fibers that offer more give.

What are the main characteristics and function of muscle tissue?

Highly cellular, well-vascularized tissue that functions to produce movement.

What are muscle cells also called?

Muscle fibers.

What internal structures within muscle cells are responsible for contraction?

Myofilaments (actin and myosin).

What are the three types of muscle tissue?

Skeletal muscle, cardiac muscle, and smooth muscle.

What is the main component of the Nervous System?

Nervous tissue (brain, spinal cord, nerves, etc.).

What are the two major cell types in nervous tissue?

Neuroglia and neurons.

What is the function of neuroglia?

Nerve support cells that protect, insulate, etc.

What are neurons? What are their functions?

Nerve cells; their functions are irritability (respond to stimuli) and conductivity (send impulses to other areas of the body).

What are the common structural components of a neuron?

Dendrites, cell body, axon, and axonal (presynaptic) terminals.

What are the body's main techniques for protecting itself against pathogens and/or injury?

External defenses and internal defenses.

What are the mechanical external defenses?

Intact skin and mucous membranes.

What are the chemical external defenses?

Fatty acids, enzymes (lysozyme & pepsin), stomach acid, vaginal secretions, and urine.

What are the microbiological external defenses?

The presence of normal flora that compete with pathogens.

What are the internal defenses?

Inflammatory response and specific immune response.

Describe the inflammatory response. Is it specific or nonspecific? How quickly does it develop?

A general response to tissue injury or infection; it is nonspecific and develops quickly.

Describe the specific immune response. Is it specific or nonspecific? How quickly does it develop?

A response that targets specific pathogens; it takes longer to develop.

What happens when tissue injury occurs and external barriers are penetrated?

Internal defenses are activated.

What are the two major ways tissue repair occurs?

Regeneration and fibrosis.

What is regeneration in tissue repair?

Replacement of destroyed tissue with the same kind of tissue.

What is fibrosis in tissue repair? What is the resulting tissue called?

Replacement of destroyed tissue with fibrous connective tissue; the resulting tissue is called scar tissue.

What are the three main steps in tissue repair of a wound?

Inflammation sets the stage, organization restores the blood supply, and regeneration and fibrosis affect permanent repair.

Describe what happens during the "inflammation sets the stage" step of tissue repair.

Severed blood vessels bleed, and inflammatory chemicals are released. Local blood vessels become more permeable, allowing white blood cells, fluid, clotting proteins, and other plasma proteins to seep into the injured area. Clotting occurs, and the surface dries to form a scab.

Describe what happens during the "organization restores the blood supply" step of tissue repair. What is granulation tissue?

The clot is replaced by granulation tissue, which restores the vascular supply. Fibroblasts produce collagen fibers that bridge the gap. Macrophages phagocytize cell debris. Surface epithelial cells multiply and migrate over the granulation tissue. Granulation tissue is a delicate pink tissue composed of capillaries, fibroblasts, and some immune cells.

Describe what happens during the "regeneration and fibrosis affect permanent repair" step of tissue repair.

The fibrotic area matures and contracts; the epithelium thickens. A fully regenerated epithelium with an underlying area of scar tissue results.

How does healing occur in simple infections vs. severe (destructive) infections?

In simple infections, healing is usually solely by regeneration without clot formation or scarring. Severe infections often lead to scarring.

Which tissues regenerate extremely well?

Epithelial tissues, bone, areolar connective tissue, and blood-forming tissue.

Which tissues have a moderate capacity for regeneration?

Smooth muscles and dense regular connective tissue.

Which tissues have a weak regenerative capacity?

Skeletal muscle and cartilage.

Which tissues have virtually no functional regenerative capacity and are typically replaced by scar tissue?

Cardiac muscle and nervous tissue in the brain and spinal cord.

What are membranes composed of?

Continuous multicellular sheets composed of epithelial and connective tissue.

How many main types of membranes are there that are composed of epithelial and connective tissue?

Three.

What is another name for the cutaneous membrane?

Skin.

What do mucous membranes cover?

All portals to the inside of the body.

What do mucous membranes produce?

Mucus.

What do serous membranes line and cover?

Closed internal cavities and the outside of organs.

What do serous membranes produce?

Slippery serous fluid.

How are serous membranes typically named?

By their lining location + the cavity word.

What lines the thoracic cavity?

The parietal pleura.

What is the parietal pleura?

The serous membrane lining the thoracic cavity.

What covers the thoracic organs?

The visceral pleura.