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The Tissue Level of Organization (Chapter 4) (Epithelial Tissue:…
The Tissue Level of Organization (Chapter 4)
Types of Tissues
Tissue: is used to describe a group of cells found together in the body.
The Four Types of Tissues
Epithelial tissue: refers to the sheets of cells that cover exterior surfaces of the body, line internal cavities and passageways, and form certain glands
Connective tissue: 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: esponding to stimulation and contracting to provide movement, and occurs as three major types: skeletal (voluntary) muscle, smooth muscle, and cardiac muscle in the heart.
Nervous tissue:allowing the propagation of electrochemical signals in the form of nerve impulses that communicate between different regions of the body
Embryonic Origin of Tissues
Totipotent:The first embryonic cells generated have the ability to differentiate into any type of cell in the body
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
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
The mucous membrane: is also a composite of connective and epithelial tissues
Amina propria: The underlying connective tissue l
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
Epithelial Tissue:
Cell junction: Adjoining cells form a specialized intercellular connection between their cell membranes
The epithelial cells exhibit polarity with differences in structure and function between the exposed or apical
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,
Basement membrane: that helps hold it all together.
Generalized Functions of Epithelial Tissue
Epithelial tissues provide the body’s first line of protection from physical, chemical, and biological wear and tear.
The Epithelial Cell
Epithelial cells are typically characterized by the polarized distribution of organelles and membrane-bound proteins between their basal and apical surfaces.
Cell to Cell Junctions
Cells of epithelia are closely connected and are not separated by intracellular material.
Tight junction: which separates the cells into apical and basal compartments.
Classification of Epithelial Tissues
Simple squamous epithelium: have the appearance of thin scales.
Endothelium: is the epithelial tissue that lines vessels of the lymphatic and cardiovascular system, and it is made up of a single layer of squamous cells.
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 Epithelium
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.
Exocrine glands release their contents through a duct that leads to the epithelial surface.
A gland is a structure made up of one or more cells modified to synthesize and secrete chemical substances.
endocrine gland, a ductless gland that releases secretions directly into surrounding tissues and fluids (endo- = “inside”),
exocrine gland whose secretions leave through a duct that opens directly, or indirectly, to the external environment (exo- = “outside”).
Connective Tissue Supports and Protects
Connective tissues perform many functions in the body, but most importantly, they support and connect other tissues
Embryonic Connective Tissue
mesenchyme, the stem cell line from which all connective tissues are later derived.
Classification of Connective Tissues
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.
Connective Tissue Proper
Fibrocytes, adipocytes, and mesenchymal cells are fixed cells, which means they remain within the connective tissue.
Cell Types
The most abundant cell in connective tissue proper is the fibroblast
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.
The mesenchymal cell is a multipotent adult stem cell.
Connective Tissue Fibers and Ground Substance
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
Loose Connective Tissue
Adipose tissue consists mostly of fat storage cells, with little extracellular matrix
Areolar tissue shows little specialization.
Reticular tissue is a mesh-like, supportive framework for soft organs such as lymphatic tissue, the spleen, and the liver
Supportive Connective Tissues
Two major forms of supportive connective tissue, cartilage and bone, allow the body to maintain its posture and protect internal organs.
Cartilage
Embedded within the cartilage matrix are chondrocytes
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.
Muscle Tissue and Motion
Skeletal muscle is attached to bones and its contraction makes possible locomotion, facial expressions, posture, and other voluntary movements of the body.
The muscle cell, or myocyte, develops from myoblasts derived from the mesoderm.
The 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.
Nervous Tissue Mediates Perception and Response
Myelin: A long “tail,” the axon, extends from the neuron body and can be wrapped in an insulating layer
Astrocyte cells, named for their distinctive star shape, are abundant in the central nervous system.
Oligodendrocyte cells produce myelin in the central nervous system
Schwann cell produces myelin in the peripheral nervous system
Tissue Injury and Aging
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, the widening of the blood vessels.
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.
Tissue and Aging
Many tissues, including those in muscles, lose mass through a process called atrophy.