The Tissue Level of Organization Flashcards
What is human body tissue?
Collections of cells and cell products that perform specific, limited functions.
Tissues in combination form organs, such as the heart or liver
Four types if tissue
Epithelia
connective
muscle
nervous
Primary germ layers
-Superficial to deep: ectoderm, mesoderm, and endoderm
-formed early in embryonic development
-specialize to form the four primary tissues
-Nerve tissue arises from ectoderm
-Muscle and connective tissues arise from mesoderm
-Epithelial tissues arise from all three germ layers
Epithelia Tissue
-Are sheets of closely adhering cells covering external and internal body surface
-Form most glands-structures that produce secretions
Functions of epithelial tissue
-provide physical protection to deeper tissue
-produce specialized secretions (glandular epithelium)
-absorb chemicals including nutrients
-excrete waste
-provide sensation
Characteristics of epithelia
-Cellularity (cell junctions)
-Polarity (apical and basal surfaces)
-Attachment (basement membrane or basal lamina)
-Avascularity (does not have blood vessels) - usually nourished by underlying connective tissue
-regenration
Apical surfaces
-Microvilli increase absorption or secretion
-Cilia (ciliated epithelium) move substance over the epithelial surfaces
Basolateral surfaces
-Attachment to the basement membrane
-Epithelial maintenance and repair by division of germinative cells (stem cells) near basement membrane
-Intercellular connections (cell junction)
Attachment to the basement membrane
-Basal lamina the closest to the epithelium
-Reticular lamina
-Deeper portion of basement membrane
- provides strength
Epithelial maintenance and repair
-Epithelial cells are replaced by continual division of stem cells located near basement membrane
Intercellular connections
-Large areas of opposing cells membrane interconnected by transmembrane proteins (cell Adhesion Molecules “CAMs”)
-Specialized attachment sites that attach cell to another cell or extracellular material
Types of cell junctions
-Gap junctions
-Tight junction
-Desmosomes
Gap junction
-Allow rapid communication
-Are held together by channel proteins (junctional proteins, connexons)
-Allow ions to pass
-coordinate contraction in hear muscle
Tight junctions
-Between 2 plasma membranes
-Adhesion belt attaches to microfilaments of a terminal web
-Prevents passage of water and solutes
-Isolates waste in the lumen
Desmosomes
-Represent major intercellular adhesive junctions at basolateral membranes
-Mediate direct cell-cell contacts and provide anchorage sites for intermediate filaments important fro the maintenance of tissue architecture
Spot desmosome
Tie cells together an allow bending and twisting
Hemidesmosome
Attach cells to the basement membrane
Squamous
-Thin and flat
Cuboidal
-Square shaped
Columnar
-tall, slender rectangles
Simple epithelium
-Contains single layer of cells
-All cells touch the basement membrane
Stratified epithelium
-Contain several layers of cells
-Some cells rest on top of each other and don’t touch the basement membrane
-Named by shape of apical cells
Simple squamous epithelia
-Single layer of flattened cells with disc shaped central nuclei and sparse cytoplasm
-Mesothelium: Lines body cavities
-Endothelium: Forms inner lining of heart and blood vessels
Function: Reduces friction; controls vessel permeability; performs absorption and secretion
Stratified squamous epithelia
-Composed of several cell layers
- Basal cells are cuboidal or columnar and metabolically active (undergo continuous mitosis)
-daughter cells push towards the surface and become falter a they migrate upward-surface cells are “squamous”
Function: Provides physical protection against abrasion, pathogens, and chemical attack
Two types of stratified squamous epithelia
Keratinized
Non-kertinized
Keratnized
Keratin packed dead cells at the surface (skin)
Non- keratinized
Without surface layer of keratin at the surface (mouth, esophagus….)
Simple Cuboidal Epithelia
-Single layer of cubic like cells with large spherical central nuclei
Locations: Glands; ducts portions of kidney tubules; thyroid gland
Function: Limited protection, secretion, absorption
Stratified cuboidal epithelia
-Typically, two cell layers thick
-Located in ducts of sweat gland and larger ducts of mammary glands
Location: Lining of some ducts (rare)
Function: protection, secretion, absorption
Simple Columnar Epithelia
-Single layer of tall cell with round to oval nuclei
-Cells bear brush border of microvilli or ciliated in some organs
-May contain mucous secreting unicellular glands (goblet cells)
Location: Lining of stomach, intestine, gallbladder, uterine tubes, and collecting ducts of kidneys
Function: protection, secretion, absorption
Stratified columnar epithelia
-Rare type of epithelial tissue
-Composed of column shaped cells arranged in multiple layers.
Locations: Small areas of the pharynx, epiglottis, anus, mammary glands, salivary glands ducts, and urethra
Function: protection
Pseudostratified columnar epithelia
-Looks multilayered, but all cells touch basement membrane (but not all cells reaches the free surface)- falsely appears stratified
-Typically have cilia and goblet cells
-Goblet cells are mucus secreting cells in simple columnar and pseudostratified epithelia
Locations: lining of nasal cavity, trachea, and bronchi; portions of male reproductive tract
Functions: protection, secretion, move mucus with cilia
Transitional epithelia
-Multilayered Epithelium
-Surface cells appearance changes- dome shaped or squamous like depending on the degree of the organ stretch
-Tolerate repeated cycles of stretching without damage
Locations: Urinary bladder; renal pelvis; ureters
Functions: permits repeated cycles of stretching without damage
Glandular Epithelia
-Glands are collections of epithelial cells that produce secretions
Endocrine glands
-release hormones into interstitial fluid
-No ducts (ductless glands)
-Endocrine cells/Endocrine organs
-Exocrine glands produce secretions onto epithelial surfaces through ducts
Gland structure
-unicellular glands
-multicellular glands
Unicellular glands
-Mucous (goblet) cells are unicellular exocrine glands
-Scattered among epithelia
- For example, in intestinal lining
- Secrete mucin, which mixes with water to form mucus
Multicellular exocrine glands
-Structure of the duct
-Simple (undivided_
-Compound (divided)
-Shape of secretory portion of the gland
- Tubular (tube shaped)
- Alveolar or acinar (blind pockets)
-Relationsjip between ducts and glandular areas
-Branched (several secretory areas sharing one duct)
Simple tubular
Ex. Intestinal glands
Simple coiled tubular
Ex. Merocrine sweat glands
Simple branched tublar
Ex. Gastric glands of esophagus
Ex. Mucous glands of esophagus tongue, duodenum
Simple Alveolar (acinar)
Ex. Not found in adult; a stage in development of simple branched glands
Simple branched alveolar
Ex. Sebaceous (oil) glands
Compound Tubular
Ex. Mucous glands (in mouth)
Ex. Bulbo-urethral glands (in male reproductive system)
Ex. Testes (seminiferous tubules)
Compound Alveolar (acinar)
Ex. Mammary glands
Compound tublo-alveolar
Ex. Salivary glands
Ex. Glands of respiratory passages
Ex. Pancreas
Types of secretions
Serous glands, mucous glands, mixed exocrine glands
Serous glands
Watery secretions
Mucous glands
Secrete mucins
Mixed exocrine gland
Both serous and mucous
Modes of secretion
Merocrine secretion, apocrine secretion, holocrine secretion
Merocrine secretion
-The product is released from secretory vesicles at the apical surface of the gland cell by exocytosis
Apocrine secretion
-Involves the loss of apical cytoplasm. Inclusions, secretory vesicles, and other cytoplasmic components are shed in the process. The gland cell the grows and repairs itself before it releases additional secretions
Holocrine secretion
-Occurs as superficial gland cell burst. Continued secretion involves the replacement of these cells through the mitotic divisions of underlying stem cells
Connective tissue
-Diverse abundant type of tissue in which cells are not in direct contact with each others
Connective tissues
-Specialized cells
-Extracellular protein fibers
-Fluid called ground substance
Matrix
-Consists of extracellular components of connective tissue (fibers and ground substance)—accounts for most of the volume of connective tissue
Functions of connective tissues
-establishing a structural framework for the body
-transporting fluids and dissolved materials
-Supporting, surrounding, and interconnecting other types of tissue
-Storing energy reserves, especially triglycerides
-Defending the body from invading microorganisms
Many type of connective tissue based on the number of cells type, the relative properties and proportion of fibers and ground substance
Connective tissue proper
fluid connective tissue
supporting connective tissues
Mesenchyme
-Embryonic connective tissue
-Gives rise to all other connective tissues
-Not found in adults
-Gel-like ground substance with fibers and star-shaped mesenchymal cells
connective tissue proper has
-Varied cell population
-Matrix made up of extracellular fibers and viscous ground substance
Categories of connective tissue proper
-Loose connective tissue has more ground substance, fewer fibers. Ex.: fat (adipose tissue)
-Dense connective tissue has more fibers, less ground substance. Ex. tendone
Fibroblast
The most abundant in all connective tissue proper, secrete proteins and hylauronan