Chapter 4: The Tissue Level of Organization

Nervous tissue

is also excitable, allowing the propagation of electrochemical signals in the form of nerve impulses that communicate between different regions of the body.

Epithelial tissue

also referred to as epithelium, refers to the sheets of cells that cover exterior surfaces of the body, lines internal cavities and passageways, and forms certain glands.

Connective tissue

as its name implies, binds the cells and organs of the body together and functions in the protection, support, and integration of all parts of the body.

Muscle tissue

is excitable, responding to stimulation and contracting to provide movement.

totipotent

meaning each has the capacity to divide, differentiate, and develop into a new organism.

ectoderm

(ecto-= “outer”)

mesoderm

(meso- = “middle”)

endoderm

(endo- = “inner”)

tissue membrane

is a thin layer or sheet of cells that covers the outside of the body (for example, skin), the organs (for example, pericardium), internal passageways that lead to the exterior of the body (for example, abdominal mesenteries), and the lining of the moveable joint cavities.

connective tissue membrane

is formed solely from connective tissue.

synovial membrane

is a type of connective tissue membrane that lines the cavity of a freely movable joint.

epithelial membrane

is composed of epithelium attached to a layer of connective tissue, for example, your skin.

mucous membrane

is also a composite of connective and epithelial tissues.

lamina propria

(literally “own layer”), helps support the fragile epithelial layer.

serous membrane

is an epithelial membrane composed of mesodermally derived epithelium called the mesothelium that is supported by connective tissue.

cutaneous membrane

The skin is an epithelial membrane also called the

cell junction

Adjoining cells form a specialized intercellular connection between their cell membranes called a

basal lamina

a mixture of glycoproteins and collagen, provides an attachment site for the epithelium, separating it from underlying connective tissue.

reticular lamina

which is secreted by the underlying connective tissue, forming a basement membrane that helps hold it all together.

tight junction

which separates the cells into apical and basal compartments.

anchoring junction

includes several types of cell junctions that help stabilize epithelial tissues.

gap junction

forms an intercellular passageway between the membranes of adjacent cells to facilitate the movement of small molecules and ions between the cytoplasm of adjacent cells.

simple squamous epithelium

have the appearance of thin scales.

endothelium

is the epithelial tissue that lines vessels of the lymphatic and cardiovascular

mesothelium

is a simple squamous epithelium that forms the surface layer of the serous membrane that lines body cavities and internal organs.

simple cuboidal epithelium

the nucleus of the box-like cells appears round and is generally located near the center of the cell.

simple columnar epithelium

the nucleus of the tall column-like cells tends to be elongated and located in the basal end of the cells.

Pseudostratified columnar epithelium

is a type of epithelium that appears to be stratified but instead consists of a single layer of irregularly shaped and differently sized columnar cells.

goblet cell

is a mucous-secreting unicellular “gland” interspersed between the columnar epithelial cells of mucous membranes.

Stratified squamous epithelium

is the most common type of stratified epithelium in the human body.

Stratified cuboidal epithelium and stratified columnar epithelium

can also be found in certain glands and ducts, but are uncommon in the human body.

transitional epithelium

so-called because of the gradual changes in the shapes of the apical cells as the bladder fills with urine.

Glandular Epithelium

A gland can be classified as an endocrine gland, a ductless gland that releases secretions directly into surrounding tissues and fluids (endo- = “inside”), or an exocrine gland whose secretions leave through a duct that opens directly, or indirectly, to the external environment (exo- = “outside”).

Merocrine secretion

is the most common type of exocrine secretion.

Apocrine secretion

accumulates near the apical portion of the cell.

holocrine secretion

involves the rupture and destruction of the entire gland cell.

serous gland

produces watery, blood-plasma-like secretions rich in enzymes such as alpha amylase

mucous gland

releases watery to viscous products rich in the glycoprotein mucin.

matrix

Unlike epithelial tissue, which is composed of cells closely packed with little or no extracellular space in between, connective tissue cells are dispersed in a

ground substance

major component of matrix

mesenchyme

the stem cell line from which all connective tissues are later derived.

mucous connective tissue

A second type of embryonic connective tissue forms in the umbilical cord

Connective tissue

proper includes loose connective tissue and dense connective tissue.

Supportive connective tissue

bone and cartilage—provide structure and strength to the body and protect soft tissues.

fluid connective tissue

in other words, lymph and blood, various specialized cells circulate in a watery fluid containing salts, nutrients, and dissolved proteins.

fibroblast

The most abundant cell in connective tissue proper

fibrocyte

a less active form of fibroblast, is the second most common cell type in connective tissue proper.

Adipocytes

are cells that store lipids as droplets that fill most of the cytoplasm.

mesenchymal cell

is a multipotent adult stem cell.

Collagen fiber

is made from fibrous protein subunits linked together to form a long and straight fiber.

Elastic fiber

contains the protein elastin along with lesser amounts of other proteins and glycoproteins

Reticular fiber

is also formed from the same protein subunits as collagen fibers; however, these fibers remain narrow and are arrayed in a branching network.

Adipose tissue

consists mostly of fat storage cells, with little extracellular matrix.

Areolar tissue

It contains all the cell types and fibers previously described and is distributed in a random, web-like fashion.

Reticular tissue

is a mesh-like, supportive framework for soft organs such as lymphatic tissue, the spleen, and the liver.

lacunae (singular = lacuna)

Embedded within the cartilage matrix are chondrocytes, or cartilage cells, and the space they occupy

Hyaline cartilage

the most common type of cartilage in the body, consists of short and dispersed collagen fibers and contains large amounts of proteoglycans.

Fibrocartilage

is tough because it has thick bundles of collagen fibers dispersed through its matrix.

Elastic cartilage

contains elastic fibers as well as collagen and proteoglycans.

Bone

hardest connective tissue

Skeletal muscle

is attached to bones and its contraction makes possible locomotion, facial expressions, posture, and other voluntary movements of the body.

striation

is due to the regular alternation of the contractile proteins actin and myosin, along with the structural proteins that couple the contractile proteins to connective tissues.

Cardiac muscle

forms the contractile walls of the heart.

Smooth muscle

tissue contraction is responsible for involuntary movements in the internal organs.

Neurons

propagate information via electrochemical impulses, called action potentials, which are biochemically linked to the release of chemical signals.

Neuroglia

play an essential role in supporting neurons and modulating their information propagation.

myelin

A long “tail,” the axon, extends from the neuron body and can be wrapped in an insulating layer known as

Astrocyte cells

named for their distinctive star shape, are abundant in the central nervous system.

Oligodendrocyte cells

produce myelin in the central nervous system (brain and spinal cord) while the Schwann cell produces myelin in the peripheral nervous system.

Inflammation

is the standard, initial response of the body to injury.

Necrosis

or accidental cell death, causes inflammation.

Apoptosis

is programmed cell death, a normal step-by-step process that destroys cells no longer needed by the body.

vasodilation

Upon tissue injury, damaged cells release inflammatory chemical signals that evoke local

Clotting

(coagulation) reduces blood loss from damaged blood vessels and forms a network of fibrin proteins that trap blood cells and bind the edges of the wound together.

primary union

describes the healing of a wound where the edges are close together.

secondary union

occurs as the edges of the wound are pulled together by what is called wound contraction.

atrophy

Many tissues, including those in muscles, lose mass through a process

Aging

is also apparent at the cellular level because all cells experience changes with aging.