Topic 1.B

Tissue

A group of cells similar in structure that perform common or related functions.

Four primary tissue types

Epithelial, connective, muscle and nervous tissue.

Why are tissues important for homeostasis?

Specialized cells work together to perform functions that help maintain stable internal conditions.

Epithelial tissue

A sheet of cells covering body surfaces or lining internal cavities.

Covering and lining epithelium

Epithelial tissue that covers external surfaces or lines internal surfaces and cavities.

Glandular epithelium

Epithelial tissue specialized to produce and secrete substances.

Six functions of epithelial tissue

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

Apical surface

The top surface of an epithelial cell

Basal surface

The bottom surface of an epithelial cell

Polarity in epithelial tissue

Epithelial cells have distinct apical and basal surfaces with different roles.

Tight junctions

Cell junctions that seal spaces between cells

Desmosomes

Cell junctions that help hold cells together.

Basement membrane

A supporting layer beneath epithelium, composed of basal and reticular laminae.

Avascular

Lacking blood vessels.

Innervated

Supplied with nerves.

How do epithelial cells receive nutrients if they are avascular?

Nutrients diffuse from blood vessels in the underlying connective tissue.

Why is epithelial tissue's high regeneration capacity useful?

It allows damaged or worn epithelial cells to be replaced.@

Simple epithelium

Epithelium made of one cell layer

Stratified epithelium

Epithelium made of two or more cell layers; provide protection.@

Squamous cells

Flattened, scale-like cells.@

Cuboidal cells

Box-shaped cells.@

Columnar cells

Tall, column-like cells.@

How is stratified epithelium named?

By the shape of the cells at its apical surface.@

Simple squamous epithelium

One layer of flat cells; suited to rapid diffusion, in the lungs and kidneys.@

Endothelium

Simple squamous epithelium lining blood vessels, lymphatic vessels and the heart.@

Mesothelium

Simple squamous epithelium forming serous membranes in the ventral body cavity.@

Simple cuboidal epithelium

One layer of cube-shaped cells

Simple columnar epithelium

One layer of tall cells

Goblet cells

Mucus-secreting cells found in epithelial linings, including the respiratory and intestinal tracts.@

Microvilli on epithelial cells

Increase surface area, improving the capacity for absorption.@

Cilia on epithelial cells

Move material, such as mucus, across the cell surface.@

Pseudostratified columnar epithelium

A single layer of cells of different heights that looks multilayered

Why is pseudostratified epithelium called pseudostratified?

It appears to have several layers, but it is actually a single layer.@

Stratified squamous epithelium

Multiple cell layers with flattened apical cells

Keratinized stratified squamous epithelium

A protective form of stratified squamous epithelium found in the skin.@

Nonkeratinized stratified squamous epithelium

Stratified squamous epithelium lining moist surfaces.@

Transitional epithelium

Epithelium whose cells change shape when stretched

Stratified cuboidal epithelium

Usually two layers of cuboidal cells

Stratified columnar epithelium

A rare epithelial type with column-shaped apical cells

Which epithelium is best suited to rapid diffusion?

Simple squamous epithelium, because its cells are thin

Which epithelium helps the bladder stretch?

Transitional epithelium

Endocrine gland

A ductless gland that releases hormones right into the bloodstream

Exocrine gland

A gland that uses ducts to release substances onto body surfaces or into cavities.

Hormone

A chemical messenger carried through blood or lymph to specific target organs.

Endocrine vs. exocrine glands

Endocrine glands are ductless and release hormones internally; exocrine glands release products through ducts.

Unicellular gland

A gland consisting of one secretory cell, such as a goblet cell.@

Multicellular gland

A gland consisting of many cells, such as a salivary gland.@

Mucin

A sugar-protein substance secreted by mucous cells that dissolves in water to form mucus.

Mucus

A protective and lubricating coating formed when mucin dissolves in water.

Merocrine secretion

Products are released by exocytosis as they are produced

Holocrine secretion

Products accumulate inside cells until the entire cell ruptures

Apocrine secretion

The apical portion of a cell pinches off to release its product

Exocytosis

The release of substances when vesicles fuse with the plasma membrane.@

Endocytosis

The uptake of material into a cell by forming membrane-bound vesicles.@

What is the key difference between merocrine and holocrine secretion?

Merocrine releases products by exocytosis; holocrine releases products when the entire cell ruptures.

Mesenchyme

Embryonic tissue from which connective tissues develop.@

Extracellular matrix (ECM)

Material outside cells, made of ground substance and fibers, that supports connective tissue cells.@

Why does connective tissue vary in firmness?

Its extracellular matrix composition differs among connective tissue types.@

Vascularity

The degree to which a tissue has a blood supply.@

Avascular cartilage

Cartilage lacks blood vessels, so nutrients must diffuse from surrounding tissue.@

Ground substance

The gel-like component of connective tissue matrix through which substances can diffuse.@

Proteoglycans

Molecules with a protein core and attached polysaccharides that contribute to connective tissue ground substance.@

Collagen fibers

Strong fibers that provide high tensile strength and resist pulling forces.@

Elastic fibers

Fibers that allow tissue to stretch and recoil.@

Reticular fibers

Fine, branching fibers that form supportive networks within tissues.@

Blast cells in connective tissue

Immature, active cells that produce fibers and ground substance.@

Cyte cells in connective tissue

Mature cells that primarily maintain existing tissue.@

Fibroblasts

Connective tissue cells that produce fibers and ground substance.@

Chondroblasts

Cells that produce cartilage matrix.@

Chondrocytes

Mature cartilage cells located in spaces called lacunae.@

Osteoblasts

Cells that produce bone matrix.@

Osteocytes

Mature bone cells located in lacunae.@

Lacunae

Small spaces within cartilage or bone matrix that house cells.

Adipose tissue

Fat tissue that stores energy, cushions organs and provides insulation.@

Brown adipose tissue

Fat tissue that uses lipid fuels to produce heat and warm the bloodstream.@

Reticular connective tissue

A meshwork of reticular fibers that supports blood cells in lymph nodes, spleen and bone marrow.@

Dense regular connective tissue

Parallel collagen bundles that resist pulling in one direction

Why are tendons suited to resist pulling in one direction?

Their dense regular connective tissue has collagen fibers arranged in parallel bundles.@

Dense irregular connective tissue

Irregularly arranged collagen bundles that resist tension from many directions

Dense elastic connective tissue

Elastic-fiber-rich tissue that stretches and recoils

Cartilage

A tough but flexible, avascular connective tissue with cells in lacunae and a water-rich matrix.@

Perichondrium

The surrounding connective tissue that supplies nutrients to most cartilage.@

Hyaline cartilage

The most abundant cartilage type

Elastic cartilage

Flexible cartilage found in structures such as the outside of the ear and epiglottis.

Fibrocartilage

Cartilage suited to resist pressure and tension

Bone tissue

Hard connective tissue that supports and protects, stores minerals and provides a site for blood cell formation.@

Compact bone

The dense, smooth outer portion of bone.

Spongy bone

The inner bone tissue organized as a mesh of supporting structures called trabeculae.

Osteoclasts

Cells involved in breaking down bone tissue.@

Why is cartilage less able to repair itself than well-vascularized tissue?

Cartilage is avascular, so nutrients reach its cells by diffusion rather than direct blood supply.@

Blood as connective tissue

Blood transports substances throughout the body, one of the major functions of connective tissue.@

Gland

One or more cells that produce or secrete a fluid

Connective Tissue

The most abundant and widely distributed primary tissue

Characters of Connective Tissue

Supports, binds, protects, insulates, stores fuel, and transports substances

Areolar connective tissue

Loose connective tissue that binds and supports other tissues, fills spaces and holds interstitial fluid