A&P 1 Tissue organization TCC SE Sam Yacoub

Tissue

a group of similar cells and extracellular material that share a common function such as providing protection

Histology

the study of tissues

Four types of tissue

epithelial connective muscle and nervous tissue each with varied structure and function

Epithelium (epithelial tissue)

tissue composed of one or more layers of closely packed cells with little to no extracellular matrix that covers body surfaces lines body cavities and forms the majority of glands

Cellularity (epithelial characteristic)

epithelium is composed almost entirely of tightly packed cells with minimal extracellular matrix

Polarity (epithelial characteristic)

epithelial cells have a distinct apical surface exposed to the external environment or an internal body space often with microvilli or cilia and a basal surface attached to connective tissue

Apical surface

the exposed surface of an epithelial cell facing the external environment or an internal body space which may bear microvilli or cilia

Basal surface

the surface of an epithelial cell that attaches to the underlying connective tissue

Basement membrane

structure attaching epithelium to connective tissue composed of three layers (lamina lucida lamina densa and reticular lamina) made of collagen glycoproteins and proteoglycans that forms a barrier between epithelium and connective tissue

Lamina lucida

one of the three layers of the basement membrane (1)

Lamina densa

one of the three layers of the basement membrane (2)

Reticular lamina

one of the three layers of the basement membrane (3)

Avascularity (epithelial characteristic)

epithelium lacks its own blood vessels and obtains nutrients across the apical surface or from the basal surface

Extensive innervation (epithelial characteristic)

epithelium is richly supplied with nerve endings that detect changes in the environment of that region

High regeneration capacity (epithelial characteristic)

epithelium undergoes frequent cell division and regenerates at a high rate due to continual replacement of lost cells through division of stem cells necessitated by environmental exposure

Physical protection (epithelial function)

epithelium protects external and internal surfaces from dehydration abrasion and destruction

Selective permeability (epithelial function)

epithelium is relatively non-permeable to some substances while promoting the passage of other molecules

Secretion (epithelial function)

some epithelial cells are specialized to secrete substances either scattered among other cell types or arranged in small organized clusters

Sensation (epithelial function)

epithelium contains nerve endings that supply information to the nervous system about touch pressure temperature and pain

Neuroepithelium

specialized epithelium that houses cells responsible for sight taste smell hearing and equilibrium

Epithelial classification naming

epithelia are classified by a two part name based on the number of epithelial cell layers and the shape of the cells at the apical surface

Simple epithelium

epithelium one cell layer thick with all cells in direct contact with the basement membrane found in areas where stress is minimal and filtration absorption or secretion is the primary function such as the lining of air sacs of the lungs intestines and blood vessels

Stratified epithelium

epithelium with two or more layers of epithelial cells in which only the basal layer contacts the basement membrane found in areas subjected to mechanical stress such as the skin esophagus and urinary bladder lining with the basal layer continuously regenerating as apical layer cells are lost

Pseudostratified epithelium

simple epithelium that appears layered due to the distribution of cell nuclei at different levels even though all cells attach to the basement membrane and some do not reach the apical surface

Squamous cells

flat wide irregularly shaped epithelial cells arranged like floor tiles with a flat nucleus

Cuboidal cells

epithelial cells about as tall as they are wide with somewhat rounded edges and a spherical nucleus located in the center of the cell

Columnar cells

epithelial cells that are slender and taller than they are wide with an oval nucleus oriented lengthwise in the basal region

Transitional cells

epithelial cells that change shape depending on the stretch of the epithelium being polyhedral when relaxed and more flat when stretched found where the epithelium stretches and relaxes such as the lining of the bladder

Simple squamous epithelium location and function

lines the air sacs of the lungs blood and lymph vessel walls (endothelium) and the serous membrane of cavities (mesothelium)

Simple cuboidal epithelium location and function

ideal for structural components of glands found in the thyroid gland surface of the ovary walls of kidney tubules and secretory regions and ducts of most glands

Simple columnar epithelium location and function

ideal for secretory and absorptive functions; nonciliated form contains microvilli and lines most of the digestive tract while ciliated form moves mucus in the bronchioles

Pseudostratified columnar epithelium location and function

nonciliated form is rare with a protective function found in the male urethra while ciliated form contains cilia on the apical surface and lines large passageways of the respiratory system

Stratified squamous epithelium location and function

contains stem cells in the basal layer that continuously divide; keratinized form has a dead upper layer filled with keratin found in the epidermis while nonkeratinized form has all living cells found in the oral cavity and esophagus

Stratified cuboidal epithelium location and function

functions in protection and secretion forming the walls of ducts in most exocrine glands such as sweat glands and parts of the male urethra

Stratified columnar epithelium location and function

rare epithelium with columnar cells at the apical surface found in large ducts of salivary glands and some segments of the male urethra

Transitional epithelium location and function

limited to the urinary tract with large rounded apical cells in the relaxed state flattened apical cells in the stretched state and binucleated cells

Gland

an individual cell or multicellular organ of epithelial tissue that secretes substances used elsewhere in the body or for elimination such as mucin electrolytes hormones enzymes or urea

Endocrine gland

gland that lacks ducts and secretes hormones (chemical messengers that influence cell activity elsewhere) directly into the blood such as the thyroid and adrenal glands

Exocrine gland

gland formed from epithelium invaginated into connective tissue that remains connected to the epithelial surface by a duct which is an epithelium-lined tube for gland secretion such as sweat mammary and salivary glands

Connective tissue

the most diverse abundant and widely distributed of the tissue types; it supports protects and binds organs and is composed of cells protein fibers and ground substance; examples include tendons ligaments adipose tissue cartilage bone and blood

Resident cells

stationary connective tissue cells that are housed within the connective tissue and support maintain and repair the extracellular matrix

Wandering cells

connective tissue cells that continuously move through the connective tissue as components of the immune system repairing damaged extracellular matrix and protecting the body from harmful agents

Fibroblasts

flat resident connective tissue cells with tapered ends that are the most abundant resident cells in connective tissue proper and produce the fibers and ground substance of the extracellular matrix

Adipocytes

fat cells that appear in small clusters in some types of connective tissue proper and dominate large clusters in adipose connective tissue

Mesenchymal cells

embryonic stem cells that divide so that one daughter cell replaces the mesenchymal cell while the other becomes a committed cell

Fixed macrophages

relatively large irregularly shaped resident connective tissue cells derived from monocytes that are dispersed throughout the matrix phagocytize damaged cells or pathogens and release chemicals that stimulate the immune system and attract wandering cells

Mast cells

small mobile wandering connective tissue cells located close to blood vessels that secrete heparin to inhibit blood clotting and histamine to dilate blood vessels

Plasma cells

wandering connective tissue cells that form when B-lymphocytes are activated upon exposure to foreign material and that produce antibodies which immobilize foreign material

Free macrophages

mobile phagocytic wandering cells that function like fixed macrophages but are able to move

Neutrophils

leukocytes that phagocytize bacteria

T-lymphocytes

leukocytes that attack foreign materials

Collagen fibers

unbranched cable-like protein fibers that are strong (stronger than steel) flexible and resistant to stretching; they appear white in fresh tissue and are numerous in tendons and ligaments

Reticular fibers

protein fibers similar to collagen fibers but thinner that form a branching interwoven framework which is tough but flexible and abundant in the stroma of lymph nodes spleen and liver

Elastic fibers

protein fibers containing the protein elastin that are branching and wavy stretch and recoil easily appear yellow when fresh help structures return to normal shape after stretching and are found in skin arteries and lungs

Ground substance

the noncellular material produced by connective tissue cells that serves as the residence of connective tissue cells and protein fibers with a consistency that can be viscous (blood) semisolid (cartilage) or solid (bone)

Extracellular matrix

the combination of ground substance and protein fibers in connective tissue

Glycosaminoglycans (GAGs)

large molecules in ground substance made of carbohydrate building blocks some with attached amines that are negatively charged and hydrophilic so their charge attracts cations such as sodium and water follows; types include chondroitin sulfate heparin sulfate and hyaluronic acid

Proteoglycans

molecules formed when a GAG is linked to a protein that are about 90 percent carbohydrate in the form of GAGs and form large structures due to negative repelling charges while performing numerous important functions

Adherent glycoproteins

proteins with carbohydrates attached that bond connective tissue cells and fibers to the ground substance including fibronectin fibrillin and laminin

Functions of connective tissue

physical protection (e.g. bones of skull adipose tissue protecting kidneys and eyes) support and structural framework (e.g. bones) binding of structures (ligaments bind bone to bone tendons bind muscle to bone) storage (adipose tissue is the major energy reserve bone stores calcium) transport (blood carries nutrients gases and wastes) and immune protection (leukocytes protect against disease)

Mesenchyme

the first type of connective tissue in the developing embryo dispersed in ground substance with immature protein fibers and a larger proportion of ground substance than mesenchymal cells; it is the source of all other connective tissue cells

Mucous connective tissue

the second type of embryonic connective tissue with more numerous immature protein fibers than mesenchyme found only in the umbilical cord

Classification of adult connective tissue

all connective tissue derives from mesenchyme which differentiates into connective tissue proper (loose and dense) supporting connective tissue (cartilage and bone) and fluid connective tissue (blood)

Loose connective tissue

connective tissue proper with fewer cells and protein fibers than dense connective tissue sparse and irregularly arranged protein fibers and abundant ground substance that serves as the body's packing material and supports structures; the three types are areolar adipose and reticular

Areolar connective tissue

loose connective tissue found in the papillary layer of the dermis that surrounds organs nerve and muscle cells and blood vessels for protection

Adipose connective tissue

loose connective tissue made mainly of adipocytes; white adipose tissue stores energy acts as insulation and cushions while brown adipose tissue is found in newborns and generates heat and is mostly lost with age; adipocyte number remains stable and weight gain or loss occurs through adipocytes enlarging or shrinking

Reticular connective tissue

loose connective tissue that forms the structural framework of many lymphatic organs such as the spleen and lymph nodes

Dense connective tissue

connective tissue proper composed mostly of protein fibers with less ground substance than loose connective tissue and predominating collagen fibers; the three categories are dense regular dense irregular and elastic

Dense regular connective tissue

dense connective tissue with densely packed parallel arrays of collagen fibers fibroblasts squeezed between layers of fibers scarce ground substance and greatly reduced blood supply; it attaches bone to bone as ligament and muscle to bone as tendon resisting stress applied in one direction; found in tendons and ligaments such as the interosseous membrane between the radius and ulna

Dense irregular connective tissue

dense connective tissue with randomly arranged and clumped collagen fibers fibroblasts in spaces among fibers more ground substance than dense regular connective tissue and extensive blood supply; it withstands stresses applied in all directions and is durable; found in most of the dermis of skin the periosteum covering bone the perichondrium covering cartilage and some organ capsules

Elastic connective tissue

dense connective tissue predominantly composed of elastic fibers with fibroblasts occupying some spaces between fibers that allows for stretching and recoil; found in the walls of elastic arteries such as the aorta the trachea and the vocal cords

Cartilage

supporting connective tissue with a firm semisolid extracellular matrix of collagen and elastic protein fibers containing mature cells called chondrocytes that occupy small spaces called lacunae and are surrounded by a dense irregular connective tissue covering called the perichondrium with an outer fibrous layer and inner cellular layer; cartilage is stronger and more resilient than other connective tissue more flexible than bone avascular in its mature state and found where the body needs support that must withstand deformation such as the tip of the nose; the three types are hyaline cartilage fibrocartilage and elastic cartilage

Chondrocytes

mature cartilage cells that occupy small spaces called lacunae

Lacunae (cartilage and bone)

small spaces that house chondrocytes in cartilage or osteocytes in bone

Perichondrium

the dense irregular connective tissue covering of cartilage with an outer fibrous layer and an inner cellular layer

Hyaline cartilage

cartilage with a glassy-appearing matrix and irregularly arranged chondrocytes in lacunae usually covered by perichondrium that provides support and forms most of the fetal skeleton; found at the tip of the nose trachea most of the larynx costal cartilage and the articular ends of long bones

Fibrocartilage

cartilage with readily visible numerous parallel collagen fibers large chondrocytes in lacunae and no perichondrium that resists compression and acts as a shock absorber in some joints; found in intervertebral discs the pubic symphysis and the menisci of the knee joints

Elastic cartilage

cartilage with abundant elastic fibers forming a weblike mesh chondrocytes in lacunae and a perichondrium that maintains shape while permitting extensive flexibility; found in the external ear and the epiglottis of the larynx

Bone

supporting connective tissue more solid than cartilage that provides greater support but less flexibility composed of organic components (collagen and glycoproteins) and inorganic components (calcium salts) with bone cells called osteocytes housed within lacunae; the two types are compact bone and spongy bone

Osteocytes

mature bone cells housed within lacunae in the bone extracellular matrix

Compact bone

bone type perforated by neurovascular canals and organized into cylindrical structures called osteons that display concentric rings of bone connective tissue called lamellae which encircle the central canal that houses blood vessels and nerves

Osteons

cylindrical structures in compact bone displaying concentric rings called lamellae

Lamellae

concentric rings of bone connective tissue in an osteon that encircle the central canal

Spongy bone

bone type located in the interior of bone with a latticework structure that is strong and lightweight

Functions of bone

serves as levers for movement supports tissues protects vital organs stores minerals such as calcium and phosphorus and houses hemopoietic cells which make blood cells

Blood

fluid connective tissue with formed elements including erythrocytes (transport respiratory gases) leukocytes (protect against infectious agents) and platelets (cellular fragments that help clot blood) suspended in a liquid ground substance called plasma that contains dissolved proteins and transports nutrients wastes and hormones

Plasma

the liquid ground substance of blood containing dissolved proteins that transports nutrients wastes and hormones

Lymph

fluid connective tissue derived from blood plasma with no cellular components or fragments that is ultimately returned to the bloodstream

Muscle tissue

tissue whose cells contract when stimulated causing movement such as voluntary motion of body parts contraction of the heart and propulsion of material through the digestive and urinary tracts; the three types are skeletal cardiac and smooth muscle

Skeletal muscle tissue

long cylindrical striated multinucleated fibers arranged parallel and unbranched that are under voluntary control; primarily responsible for moving the skeleton and selected other body components; attaches to bones or sometimes to skin such as facial muscles

Cardiac muscle tissue

short striated typically branching cells with one or two centrally located nuclei and intercalated discs between cells that are under involuntary control; pumps blood through the heart and is found in the heart wall (myocardium)

Smooth muscle tissue

nonstriated short fusiform cells with one centrally located nucleus that are under involuntary control; moves and propels materials through internal organs and controls the size of the lumen; found in the walls of hollow internal organs such as the intestines stomach airways urinary bladder uterus and blood vessels

Intercalated discs

junctions between cardiac muscle cells

Nervous tissue

tissue located in the brain spinal cord and nerves containing cells called neurons that receive transmit and process nerve impulses and a larger number of glial cells that do not transmit nerve impulses but are responsible for protection nourishment and support of neurons

Neurons

nervous tissue cells with a cell body dendrites and an axon that extend from the cell body; they receive send and process nerve impulses; located in the brain spinal cord and nerves

Glial cells

nervous tissue cells that lack the processes seen in neurons and help protect nourish and support neurons

Cell body of neuron

the part of a neuron containing the nucleus from which dendrites and the axon extend

Dendrite

a process extending from a neuron's cell body that receives signals

Axon

a process extending from a neuron's cell body that transmits nerve impulses

Roles of tissue in an organ (stomach example)

in the stomach wall simple columnar epithelium and gastric glands formed from epithelium line the mucosa overlying areolar connective tissue dense irregular connective tissue houses a nerve plexus three layers of smooth muscle (oblique circular and longitudinal) are separated by a nerve plexus between muscle layers and the outer serous membrane is composed of areolar connective tissue covered by mesothelium (simple squamous epithelium)