MCB244 Tissues

Tissue

group of similar cells and extracellular material/matrix (ECM), generally sharing a common function

Autopsy

examination of organs of a dead body to determine the cause of death or study the changes caused by disease

What are the 4 types of tissues

epithelial, connective, muscle, nervous

What are the functions of epithelial tissue

• physical protection (dehydration, abrasion, destruction)

• selective permeability (allows passage of some substances while preventing passage of others)

• Secretions: some cells are specialized to secrete 

  • sensation: supply info to NS

What are the classifications of epithelial cells by cell layers

simple, straified, and pseudostratified

Simple Epithelium

• one cell later thick; all cells contact basement membrane

• filtration, absorption, or secretion is primary function

Stratified Epithelium

• 2 or more layers of epithelial cells 

• only basal layer in contact with basement membrane

• in areas subjected to mechanical stress

Pseudostratified Epithelium

• appears layered

• all cells contact basement membrane, but may not reach apical surface

What are the classifications of epithelial tissue by cell shape

Squamous, cuboidal, and columnar

Squamous Cells

• flat, wide, irregular in shape

• nucleus flat

Cuboidal Cell

• about as tall as they are wide

• nucleus spherical and in center of cell

Columnar Cells

• slender and taller than they are wide

• nucleus oval; oriented lengthwise in basal region

Transitional Cells

can change shape, depending on the stretch of the epithelium

simple squamous epithelium

• single layer of flat cells with a spherical/oval nucleus

• Function: thinnest barrier that allows rapid diffusion and filtration; secretion in serous membrane

• found in lining of lung air sacs (alveoli), lining of blood and lymph vessel (endothelium), serous membranes of body cavities (mesothelium)

Alveoli

lung air sacs

endothelium

blood and lymph vessel walls

mesothelium

serous membrane of body cavities

Simple Cuboidal Epithelium

• single layer of uniformly shaped cells; about as tall as they are wide

• centrally located spherical nucleus

• Function: absorption and secretion; forms secretory tissue of most glands and small ducts 

Where are simple cuboidal epithelium tissue found

lining of kidney tubules, thyroid gland follicles, surface of ovaries, secretory regions and ducts of most exocrine glands 

Simple Columnar Epithelium

• single later of cells

• taller than they are wide

• oval nucleus, lengthwise in basal region

• ideal for secretory and absorptive functions

  • 2 forms : non-ciliated, ciliated

Non-ciliated Simple Columnar Epithelium

• single layer of non-ciliated cells taller than they are wide

• oval nuclei oriented lengthwise in basal region

• apical surface may contain microvilli/brush border

• may contain unicellular glands called goblet cells that secrete glycoprotein mucin

• functions: absorption and secretion

Where are non-ciliated simple columnar epithelium

lining of most of digestive tract from stomach to anal canal

Ciliated simple columnar epithelium

• single layer of ciliated cells taller than they are wide

• oval nuclei oriented lengthwise in basal region; cilia projecting from apical surface move mucus along

• Goblet cells interspersed

• functions: secretion of mucin and mucus movement; oocyte movement through uterine tube

Where are ciliated simple columnar epithelium found

lining of bronchioles in the lung and uterine tubes

Pseudostratified Columnar Epithelium

• appears in multiple cell layers but not really stratified

• all cells in direct contact with basement membrane

• nuclei scattered at different distances

• not all cells reach apical surface 

• 2 forms

  • ciliated

  • nonciliated

Ciliated Psuedostratified Columnar Epithelium

• single layer of cells; varying heights

• all cells connect to basement membrane but not all cells reach apical surface

• cells have cilia (on apical surface) and goblet cells

• Functions: protection, secretion of mucin, movement of mucus along the epithelial surface by cilia

Where are ciliated pseudostratified columnar epithelium found

large passageways of respiratory system (nasal cavity, parts of pharynx, larynx, trachea, and bronchi)

Non-cilliated pseudostratified columnar epithelium

• single layer of cells with varying heights 

• all cells connect to basement membrane but not all cells reach apical surface 

• cells lack cilia and goblet cells 

• Function: protection

where are non-ciliated pseudostratified columnar epithelium found?

rare- found mainly in male urethre and epididymis

Stratified squamous epithelium

• multiple cell layers; only the deepest layer is in direct contact with basement membrane

• basal layers with cuboidal shape

• apical cells with squamous shape

• function: protects against abrasion and friction

• stem cells in basal layer continuously divide and replace lost cells at surface

• 2 forms: keratinized and non-keratinized

Keratinized Stratified Squamous Epithelium

• multiple cell layers

• basal cells: cuboidal or polyhedral and alive

• apical (superficial cells): squamous and are dead; lack nuclei and organelles but are filled with keratin

• function: protection of underlying tissue from abrasion

Where are keratinized stratified squamous epithelium found

epidermis of the skin

Non-keratinized stratified squamous epithelium

• multiple cell layers

• basal cells: cuboidal or polyhedral; apical (superficial cells)- squamous 

• all cells are alive 

• kept moist with secretions (saliva, mucus)

• cells have organelles and microscopically visible nuclei, but lack keratin

• Function: protection of underlying tissue from abrasion

Where are non-keratinized stratified squamous epithelium found

lining of oral cavity, part of pharynx, esophagus, vagina, anus

Stratified cuboidal epithelium

• 2 or more layers of cells

• superficial cuboidal in shape- as tall as they are wide

• functions: protection and secretion

• forms walls of ducts in most exocrine glands

Where are stratified cuboidal epithelium found

ducts of most exocrine glands and ovarian follicles

Stratified columnar epithelium

• rare

• two or more layers of cells

• columnar cells at apical surface

• functions: protection and secretion

Where are stratified columnar epithelium found

• large ducts of salivary glands, conjunctiva of the eye, parts of male urethra

Transitional epithelium

• in relaxed state, basal cells look cuboidal or polyhedral; apical cells large and rounged

• in stretched state, apical cells flattened

• some cells are binucleated

• function: allows for stretching as bladder fills

Where is transitional epithelium found

limited to urinary tract (bladder, ureters, and parts of urethra)

Glands

individual cells or multicellular organs composed of epithelial tissue

Endocrine glands

lack ducts; secrete hormones into blood

exocrine glands

• invaginated epithelium in connective tissue

• connected with epithelial surface by duct (an epithelium-lined tube for gland secretion)

What are some examples of exocrine glands

sweat glands, mammary glands, salivary glands

Unicellular Exocrine Glands

• do not contain a duct

• located close to epithelium surface

• most common type: goblet cell

Multicellular Exocrine Gland

• numerous cells

• Acini: cell clusters the produce secretions

• ducts transport secretions to epithelial surface

• surrounded by a fibrous capsule, extensions of which may form septa, partitioning a gland into lobes

What are the classifications of glands

simple, compound, tubular, acinar, tubuloacinar

Simple glands

single, unbranched duct

compound gland

branched ducts

tubular glands

secretory portion and duct same diameter

Acinar glands

secretory portion forms expanded sa

tubuloacinar gland

both tubules and acini

Merocrine gland

packaged secretions into vesicles, released by exocytosis

ex: lacrimal and salivary glands

Apocrine Glands

• apical membrane pinches off an becomes secretion

• ex: mammary and ceruminous glands

Holocrine glands

ruptured cell becomes secretion

ex: sebaceous (oil) glands

Connective tissue

most diverse, abundant, and widely distributed of the tissue tupes

What are the components of connective tissue

cells, protein fibers, and ground substance

What is the function of connective tissues

physical protection, support and structural framework, binding of structures, storage, transport, and immune protection

What are the 2 classes of connective tissue cells

wandering cells and resident cells 

Wandering cells

• continuously move through CT

• components of immune system

• repair damaged extracellular matrix

• type of leukocytes (white blood cell)

• protect body from harmful agents

Resident cells

stationary, house in CT, support, maintain, repair extracellular matrix

ex: fibroblasts, adipocytes, macrophages, etc.

Fibroblast 

flat cells with tapered ends 

most abundant resident cells in CT proper 

produce fibers and ground substances of ECM

Adipocytes

appear in small clusters in some types of CT proper

• adipose connective tissue: dominant area of large clusters

Mesenchymal cells

• embryonic stem cell

• divides to replace damaged cells 

  • one replaces mesenchymal cell, other becomes committed cell

Fixed macrophages

• relatively large, irregular-shaped cells

• derived from monocytes (type of leukocyte)

• dispersed throughout matrix

• phagocytize (engulf) damaged cells or pathogens

• released chemicals to stimulate immune system/attract wandering cells

What are the types of protein fibers in connective tissue

collagen, reticular, and elastic 

Collagen Fibers

unbranched, “cable-like” long fibers (white glistening appearance)

numerous in tendons and ligaments

Reticular fibers

• similar to collagen fibers but thinner

• abundant in stroma of some organs

Elastic fibers 

• contain protein elastin (thinner than collagen), usually coated with the glycoprotein fibrillin

• stretch and recoil easily 

• found in skin, walls of arteries 

Ground substance

molecular material produced by CT (connective tissue) cells

• residence for CT cells and protein fibers

• can have viscous, semisolid, or solid consistency

• absorbs compression forces, protects delicate cells from injury

Glycosaminoglycans (GAGs)

large molecule in ground substance (chondroitin sulfate, heparin, hyaluronic acid); charge attracts cations, water follows

Proteoglycans 

formed with GAG linked to a protein; form thick colloids

Glycoproteins

proteins with carbohydrates attached; bond CT cells and fibers to ground substance

Mesenchyma

source of connective tissue cells

• adult CT often has mesenchymal stem cells

Mucous connective tissue

found in umbilical cord only 

Loose Connective Tissue

• fewer cells and protein fibers than dense CT

• protein fibers are sparse and irregularly arranged

• abundant ground substance

• body’s “packing material”, supports structure

• Types: areolar, adipose, and reticular

Areolar CT

• loose organization of collagen and elastic fibers 

• highly vascularized (many blood vessels) 

• predominant cells are fibroblasts within abundant and viscous ground substance 

Function of Areolar CT

protection of tissues and organs; binding skin and some epithelia to deeper tissue; providing space for blood vessels and nerves

Where are areolar ct found?

the papillary layer of dermis, subcutaneous layer, and surrounding organs, nerve and muscle cells, and blood vessels

Adipose CT

• commonly referred to as fat

• composed closely packed adipocytes; nucleus pushed to the edge of the cell by large fat droplet 

• 2 types: white and brown 

• adipose gain/loss due to adipocytes enlarging or shrinking 

White adipose CT

stores energy, acts as insulator, cushions

Brown Adipose CT

found in newborns, generates heat, lost as we age

Function of adipose CT

energy storage; insulation/cushioning and protection

Where is adipose tissue found

subcutaneous layer; covers some organs 

Reticular CT

meshwork of reticular fibers, fibroblasts, leukocytes within a viscous ground substance

Function of Reticular CT

providing structural framework for many lymphatic organs

Where are reticular CT found

spleen, thymus, lymph nodes, and red bone marrow

Dense Connective Tissue

• mostly protein fibers 

• less ground substance than loose CT

• 3 types: regular, irregular, and elastic

Dense Regular CT

• fibroblasts squeezed between densly packed, parallel collagen fibers

• stress typically applied in a single direction 

• few blood vessels; limited ground substance 

• takes long to heat 

Function of Dense Regular CT

attach muscle to bone or bone to bone; resists pressure applied in one direction

Where are dense regular CT found

tendons (attach muscle to bone) and ligaments (attach bone to bone)

Dense Irregular CT

• fibroblasts between densely packed, randomly arranged clumps of collagen fibers

• extensive blood vessels; more ground substance than in dense regular CT

Function of Irregular CT

provides support and resistance to stress in multiple directions; durability

Where is dense irregular CT found

reticular layer of dermis, periosteum of bone, perichondrium of cartiliage, capsules around internal organs; epimysuim of muscle

Elastic CT

• limited fibroblasts between branching and densely packed elastic fibers

Elastic CT Function

allows stretching and recoil

Where is elastic CT found 

walls of large arteries, trachea, vocal cords

What are the 2 types of supporting connective tissue

Cartilage and bone

Cartilage

• firm, semisolid extracellular matrix

• collage and elastic protein fibers

• Chondrocytes": mature cells

• more flexible than bone

• strong and resilient

• occupe small spaces called lacunae

• 3 types: Hyaline Cartilage, Fibrocartilage, and Elastic Cartilage

Hyaline Cartilage 

• most common cartilage 

• irregularly arranged chondrocytes in lacunae, surrounded by ground substance (perichondrium)