Histology - Tissues

Tissues

cells are organized = perform more complex functions

loosely scattered in extracellular matrix (liquid, semisolid, or solid), but some are joined together via junctions

Tight Junctions

adjacent cell membranes are fused to each other, preventing passage of material between cells

found in: tissues that create barriers against the external environment

ex) digestive tract

Desmosomes

adjacent cell membranes are pinned together with a “spot weld” that still allows movement

found in: muscle cells (fibers) & in skin

Gap Junctions

microtubules from tunnels between adjacent cells = flow of cytosol from 1 cell to the next

found in: cardiac muscle to synchronize contractions

Epithelial Tissue

function: protection, secretion, absorption, excretion

location: cover body surface, cover & line internal organs, compose glands

characteristics: lack blood vessels (avascular), cells readily divide, cells are tightly packed = minimal extracellular matrix

polarity: creates an exposed (“apical”) surface & an attached (“basal”) surface for each layer

Basal Surface

attached to a basement membrane

Connective Tissue

function: bind, support, protect, fill spaces, store fat, produce blood cells

location: widely distributed throughout body

characteristics: mostly have good blood supply, cells are farther apart than epithelial cells, with extracellular matrix in between

Muscle Tissue

function: contract to create movement in/of body

location: attached to bones in walls of hollow internal organs, heart

characteristics: lost of fibers but minimal extracellular matrix, highly vascular & innervated, mitotic rates vary

designed to contract/relax & create movement in response to stimulation

Nervous Tissue

electrical communication system of body

works closely with endocrine system

function: conduct impulses for coordination, regulation, integration, & sensory reception, electrical signal conduction to activate muscles & glands to respond to stimuli from internal & external environment

location: brain, spinal cord, nerves

characteristics: cells communicate with each other & other body parts, composed of neurons & neuroglia, avascular, low mitotic rates (if at all)

Cancerous Epithelial Cells

failure to respect basement membrane boundary = they penetrate to invade tissues beneath

Lumen

EP tissue

hollow channel inside tubes in body = “external” surface

Cilia

EP tissue

hair-like cell membrane extensions designed to move material across apical surface of tissue

Microvilli

EP tissue

small cell membrane extensions that increase surface area for better asorption

Goblet Cells

EP tissue

unicellular glands that secrete mucus to trap dirt, dust, & particles & ease passage of material across surface of cell

Number of Cell Layers (EP Tissue)

simple = 1

stratified = layered 2+

Cells Shapes (EP Tissue)

squamous = flat discs

cuboidal = cube-shaped or rounded

columnar = elongated =, rectangular

Simple Squamous ET

single layer of thin, flat cells

substances pass easily through = useful for diffusion & filtration

thin & delicate = easily damaged

makes up walls of air sacs (alveoli) & capillaries (blood vessels) as well as lymphatic vessels

Simple Cuboidal ET

single layer of cube-shaped cells

nucleus = round & centrally situated

more depth makes them good at protection, secretion, & absorption

lines kidney tubules, ducts of some glands

Simple Columnar ET

single layer of elongated cells

nuclei usually elongated & at same level, near basement membrane

sometimes have microvilli, cilia, & goblet cells (secrete mucus)

good at protection, secretion, & abosrption

lines digestive tract (stomach, intestines) & uterus

Pseudostratified Ciliated Columnar ET

single layer, but appears layered

nuclei at 2 or more levels

cells vary in shape, but all reach basement membrane

often has cilia, goblet cells

protection, secretion, absorption, & movement of substance across surface of cell

lines respiratory passageways

Stratified Squamous ET

many layers of flat, thin cells stuck together that create a thick boundary

protection against abrasion

new cells produced in depp layers, push older cell toward free surface

may be keratinized (epidermis) or unkeratinized (ex. linings of oral cavity, vagina, anal canal)

Stratified Cuboidal ET

2-3 layers of cube-shaped cells

more protection than 1 layer

lines ducts of mammary, sweat, &salivary glands, & pancreas

Stratified Columnar ET

several layers of cells

top layer = elongated columnar cells

cube-shaped cells in deeper layers

good for protection as well as secretion

lines part of male urethra, ducts of exocrine glands

Transitional ET

many cell layers

cube-shaped, elongated, & squished cells

changes shape & appearance with increased tension

forms barrier & lining that can expand when stretched

lines urinary bladder, uterus, & part of urethra

Fiber

muscle cell

Striations

visual appearance of stripes = correspond to overlapping microfilaments within muscle fiber

Voluntary Control

conscious regulation of muscle activation

Involuntary Control

unconscious regulation of muscle activation

Skeletal Muscle

attached to bones

striated, parallel fibers

long, cylindrical, multi-nucleated cells

voluntary control (“somatic”)

stimulated by nerve cells

Cardiac Muscle

walls of heart

striated, interwoven (branched) fibers

single nucleus

involuntary control = “autorhythmic”

intercalated discs (specialized intercellular junctions)

Smooth Muscle

walls of hollow organs (“viscera'“) & blood vessels

unstriated, spindle-shaped fibers

single, central nucleus

involuntary control

Neuron

nerve cell

Neuroglia (“Gial Cells”)

“helper cells” surrounding neurons that perform a variety of protective & supportive functions

Connective Tissue Functions

bind structure together

provide support & protection

serve as frameworks

fill spaces

store fat

produce blood cells

protect against infections

help repair tissue damage

Fixed Cells

remain in one place

Wandering Cells

move throughout tissues

ex) macrophages

Fibroblasts

most common in CT

produce fibers

Macrophages

modified WBC that fight infection via phagocytosis

Mast Cells

produce heparin (prevent blood clotting) & histamine (promote inflammation)

Collagen Fibers

collagen protein

thick, flexible strands with great tensile strength

Extracellular Matrix

consists of protein fibers & ground substance

Elastic Fibers

elastin protein

spring-like branched strands with ability to stretch & recoil

Reticular Fibers

thin, highly branched collagen fibers that form scaffolding inside tissues

Ground Substance

non-fibrous protein & other molecules, varying amounts of fluid

fills in spaces around cells & fibers

Loose CT

fewer collagen fibers than dense tissues

types: areolar, adipose, reticular

Dense CT

contain abundant collagen fibers

types: dense regular, dense irregular, elastic

Specialized CT

cartilage, bone, blood

Areolar CT

primarily fibroblasts in gel-like ground substance

collagen & elastic fibers

forms thin, delicate membranes

found everywhere throughout body

ex) subcutaneous layer & beneath most epithelia, where it nourishes nearby epithelial cells

Adipose tissue

adipocyte cells store fat

• psuh theri nuclei to 1 side & crowed out other cell types

cushions, insulates, protects organs

found everywhere throughout body

ex) beneath skin (subcutaneous layer), behind eyeballs, around heart & kidneys, in spaces between muscles

Reticular CT

composed of network of thin reticular fibers

supports walls of internal organs

creates a loose scaffolding for fluid to flow through

found in walls of liver (filter waste form blood), spleen (filters lymphatic fluid)

Dense Regular CT

fibroblasts sandwiched between lots of closely packed collagen fibers

some elastic fibers

very strong, withstands pulling (stretch) in direction of fiber orientation

poor blood supply; slow to heal

blinds body parts together

found in tendons, ligaments

Dense Irregular CT

fibroblasts scattered between randomly organized, thick, interwoven collagenous fibers

very strong, withstands pulling (stretch) in direction of fiber orientation

found in dermis of skin, around skeletal muscles, & makes up joint capsules

Elastic CT

fibroblasts scattered throughout abundant elastic fibers, & some collagen fibers

elastic fibers facilitate stretch & recoil

found in walls of hollow organs = large arteries, airways

Cartilage

support, framework, attachments, protection of underlying tissue, models for developing bone

matrix contains collagen in gel-like ground substance

Chondrocytes (cartilage cells) in lacunae (chambers), surrounds by matrix

lacks blood supply; heals slowly

types: hyaline, elastic, & fibrocartilage

Hyaline Cartilage

most common type

chondrocytes situated in lacunae within gel-like ground substance matrix

fine collagen fibers in matrix

support, protect, create framework for bone

found covering ends of bones at joint surfaces, nose, respiratory passges, embryonic skeleton

Elastic Cartilage

chondrocytes situated in lacunae within gel-like ground substance matrix

some collagen & MANY elastic fibers in matrix

support, protect, create flexible framework

found in external ear & larynx

Fibrocartilage

chondrocytes situated between many collagen fibers in matrix

support, protect, shock absorption

very tough, due to many collagen fibers

found in intervertebral discs (IVDs), menisci of knee & at pubic symphysis

Osteoarthritis

as we age, cartilage tends to calcify or even ossify causing chondrocytes to be poorly nourished & die

Osseous Tissue

most rigid CT

solid matrix composed of minerla salts & collagen

supports & protect vital structures

sites of blood cell production (hematopoiesis)

stores & release minerals

attachment sites for muscles

contain osteocytes (bone cells) in lacunae surrounded by solid matrix

types: compact & spongy

Compact Bone

osteoblasts deposit matrix in lamellae (layers)

lamellae occur in rings around central canals

osteocytes + matrix + central canal form cylindrical units = osteons

osteocytes send out processes into canaliculi, & share blood supply

Osteons

cemented together to form compact bone

central canals contain blood vessels

bone = well-nourished

heals more quickly than cartilage

Spongy Bone

makes up interior part of bone

consists of bony plates containing osteocytes, with space between them for marrow

lighter in weight than compact bone

act as shock absorption to prevent shattering

Blood

formed elements (cells & fragments) suspended in fluid matrix = plasma

types of formed elements: erythrocytes, leukocytes, thrombocytes

transports substances around body via circulatory system

Erythrocytes

red blood cells

transport gases

Leukocytes

white blood cells

defend against infection

Thrombocytes

platelets

help in blood clotting

Membranes

sheets of cells

combination of ET & CT

cover body surfaces & lines cavities

types: serous, mucous, cutaneous

Serous Membrane

“wet membrane”

line ventral body cavities that do not open to outside of body

ex) inner linings of thorax & abdomen; covers organs

simple squamous ET + areolar CT

secrete serous fluid for lubrication, reducing friction

layers: parietal & visceral

Parietal Layer

lines cavity

Visceral Layer

covers individual organ within cavity

Mucous Membrane

“wet membrane”

lines cavities & tubes that pen to outside of body

ex) lining of digestive, respiratory, urinary, & reproductive tracts

ET + areolar CT

goblet cells secrete mucous = important for lubrication, protection, & moisturization

Cutaneous Membrane

“dry membrane”

covers body surface

called skin

Synovial Membranes

composed entirely of CT

line joint cavities