a&p ch 5

histology

organ

structure with discrete boundaries that is composed of two or more tissue types

histology

microscopic anatomy; study of tissues and how they are arranged into organs

tissue

group of similar cells and cell products working together to perform a specific role in an organ

4 primary tissue types

epithelial, connective, nervous, muscular

* different in: type and function of cells, characteristics of matrix, amount of space occupied by cells vs matrix

matrix

extracellular material; composed of: fibrous proteins, clear gel called *ground substance*

3 primary germ layers (embryonic tissues)

* ectoderm (outer): gives rise to epidermis and nervous system, integumentary system, nervous system derives
* endoderm (inner): gives rise to mucous membrane lining digestive and respiratory tracts, digestive glands, other things
* mesoderm (middle): becomes gelatinous tissue called mesenchyme; wispy collagen fibers and fibroblasts in gel matrix, gives rise to cartilage, bone, blood, muscle

interpreting tissue sections

* histologists preserve, slice, and section tissues
* fixative prevents decay (formalin)
* histological sections: tissue sliced into thin sections 1 or 2 cells thick
* stains: tissue mounted on slides and artificially colored w/ histological stain
* sectioning reduces 3-D structure to 2-D slice
* shape/size of nucleus varies

longitudinal section

tissue cut on its long axis

cross section (or transverse section)

tissue cut perpendicular to long axis of organ

oblique section

tissue cut at angle between cross and longitudinal sections

smear

tissue is rubbed across a slide; use when things can’t be sliced (blood)

spread

some membranes and cobwebby tissues are laid out on a slide; squeeze really hard and the tissues squirt out sides of slide (areolar tissue)

epithelial tissue

* epithelia- sheets of closely adhering cells, 1+ cells thick
* covers body surfaces & lines cavities
* upper surface usually exposed to environment/internal space
* constitutes most glands; avascular, nourished by underlying tissues
* have almost zero extracellular matrix, cells very close together, high rate of mitosis

functions of epithelial tissue

* protect deeper tissues from injury and infection
* produce and release chemical secretions
* excrete wastes (kidneys)
* absorb chemicals, including nutrients
* selectively filter substances
* sense stimuli

basement membrane

layer between an epithelium and underlying connective tissue

* collagen, reticular proteins, glycoproteins, other protein-carb complexes
* anchors epithelium to connective tissue below it

basal surface

surface of epithelial cell facing the basement membrane, rapidly reproduce because right under basement membrane, get most nutrients

apical surface

surface of epithelial cell that faces away from basement membrane, exposed to external environment, have almost no metabolism

simple epithelia

contains one layer of cells, named by shape of cells, all cells touch basement membrane

stratified epithelia

contains more than one layer, named by shape of apical cells, some cells rest on top of others and don’t touch basement membrane

4 types of epithelia with one layer of cells

1. simple squamous: thin, scaly cells
2. simple cuboidal: square/round cells
3. simple columnar: tall, narrow cells
4. pseudostratified columnar: falsely appears stratified, every cell reaches basement membrane, not all reach free surface

goblet cells

wineglass-shaped mucus-secreting cells in simple columnar and pseudostratified epithelia

simple squamous epithelium

single row of thin cells; permits rapid diffusion/transport of substances; secretes serous fluid; in alveoli, glomeruli, endothelium, serosa

simple cuboidal epithelium

single layer of square/round cells; absorption and secretion, mucus production and movement; in liver, thyroid, mammary and salivary glands, bronchioles, kidney tubules

simple columnar epithelium

single row of tall, narrow cells; oval nuclei in basal half of cell; brush border of microvilli, ciliated in some organs, may possess goblet cells; absorption and secretion, secretion of mucus; in lining of GI tract, uterus, kidney, uterine tubes, digestive tract

pseudostratified epithelium

looks multilayered, but all cells touch basement membrane; nuclei at several layers; has cilia and goblet cells; secretes and propels mucus; in respiratory tract, male urethra; has cilia because it is not able to break down mucus

stratified epithelia

2-20 layers of cells; cells rest directly on others, only deepest layers attach to basement; 3 kinds, squamous (most common), cuboidal, columnar (rare); 4th type: transitional

* deepest layers undergo continuous mitosis
* resists frictional forces
* keratin: tough waterproofing protein

keratinized stratified squamous epithelium

multiple cell layers; cells become flat and scaly toward surface; resists abrasion; stops water loss through skin; resists penetration by pathogenic organisms; in epidermis, palms and soles heavily

non-keratinized stratified squamous epithelium

same as keratinized epithelium without surface layer of dead cells; resists abrasion and penetration of pathogens; in tongue, oral mucosa, esophagus, and vagina

stratified cuboidal epithelium

2+ cuboidal epithelium; secretes sweat; produces sperm, produces ovarian hormones; in sweat gland ducts, ovarian follicles and seminiferous tubules

* usually around ducts or places with lumen

transitional epithelium

multilayered epithelium with surface cells that change from round to flat when stretched; allows for filling of urinary tract; in ureter and bladder

* change shape, stretchy, transition to round shape (relaxed) to almost squamous shape

cell junctions

connections between two cells; most cells are anchored to each other or their matrix; cells communicate with each other, resist mechanical stress, and control what moves through the gaps

* chemical communication, release hormones into extracellular matrix, then picked up, physical connection

tight junction

linkage between two adjacent cells by transmembrane cell-adhesion proteins

* in epithelia, they form a zone that completely encircles each cell near its apical pole
* seals off intercellular space, making it difficult for substances to pass

desmosome

patch that holds cells together (like clothing snap)

* keeps cell from pulling apart-resist mechanical stress, flexibility but with more resistance
* hook-like, j-shaped proteins arise from cytoskeleton: anchor cytoskeleton to membrane plaque, transmembrane protein from each cell joined by cell adhesion protein
* hemidesmosomes- half desmosomes that anchor basal cells of an epithelium to underlying basement membrane, epithelium can’t easily peel away from underlying tissues

gap (communicating) junction

formed by ring-like connexons

* connexon consists of 6 transmembrane proteins arranged like segments of an orange around water-filled pore
* ions nutrients, and other small solutes pass between cells
* located in cardiac and smooth muscle, embryonic tissue, lens and cornea
* pore in center, allows cytoplasm to flow right into next cell

gland

cell/organ that secretes substances for use elsewhere in the body/releases them for elimination from the body

* usually composed of epithelial tissue in a connective tissue framework and capsule
* secretion: product useful to body (saliva into mouth)
* excretion: waste product (urination)

endocrine glands

have no ducts; secrete hormones directly into blood

* hormones: chemical messengers that stimulate cells elsewhere in the body (thyroid, adrenal, pituitary)
* secretes hormones (majority) and chemicals straight into bloodstream
* some organs have both endocrine and exocrine functions (liver, gonads, pancreas)

exocrine glands

maintain their contact with surface of epithelium by way of a duct

* surfaces can be external (sweat, tear glands), or internal (pancreas, salivary glands)
* make secretions that leave body, secretes into ducts

unicellular glands

found in epithelium that is predominantly nonsecretory, often goblet cells

* can be exocrine/endocrine
* ex: mucus-secreting goblet cells in trachea or endocrine cells of stomach, secrete leptin (hunger hormone)

capsule (exocrine gland structure)

connective tissue covering of exocrine gland

* septa/trabeculae: extensions of capsule that divide interior of gland into compartments (lobes & lobules)
* stratified squamous layer around tissues (**boundary**)

stroma (exocrine gland structure)

connective tissue framework of the gland

* supports and organizes glandular tissue
* gives shape, structure, and support, make primarily of collagen (**framework**)

parenchyma (exocrine gland structure)

cells that perform the tasks of synthesis and secretion

* typically cuboidal or simple columnar epithelium
* makes the thing of the gland (**secretions**)

classification of glands (exocrine gland structure)

* duct shape: simple (unbranched, 1 tube), compound (branched, more than 1 tube)
* gland shape:
* tubular: narrow secretory portion, just a tube (simple tubular-eccrine glands)
* acinar: secretory cells from dilated sac, rounded dead end of gland that makes secretion (acinus/alveolus)
* tubuloacinar: both tubular and acinar portions

serous glands

produce thin, watery secretions

* perspiration, milk, tears, digestive juices

mucous glands

produce glycoprotein, mucin, which absorbs water to form mucus

* goblet cells: unicellular mucous glands
* mucin: carbohydrate that absorbs water and turns into mucus (different kinds of tears have different levels of mucin)

mixed glands

contain both serous and mucous cell types and produce a mixture of the two types of secretions

apocrine secretion

lipid droplet covered by membrane and cytoplasm buds from cell surface

* budding, pinch off parts of cell membrane and those parts make secretion; elevated lipid content, loose cholesterol
* mode of milk fat secretion by mammary gland cells

merocrine secretion

uses vesicles that release their secretion by exocytosis (used by eccrine glands)

* ex: tear glands, pancreas, gastric glands
* lowest lipid concentration; associated with serous glands, watery, low viscosity glands

holocrine secretions

cells accumulate a product until they disintegrate

* cells will self destruct (autolysis) and those pieces are the secretions
* secrete mixture of cell fragments and synthesized substances
* ex: oil glands of scalp and skin, glands of eyelids

membranes

* membranes can only be epithelial, only connective, or a mix of epithelial, connective, and muscular tissue
* ex of only connective: dura mater, synovial membranes, periosteum
* ex of only epithelium: anterior surface of cornea and lens of eye

cutaneous membrane

the skin, largest membrane in the body

* keratinized stratified squamous epithelium (epidermis) resting on a layer of connective tissue (dermis), a compound membrane
* goal: barrier (epidermis), has gases travel across
* skin is an organ because it has multiple tissue types working together

mucous membrane (mucosa)

lines passaged that open to external environment (digestive tracts); absorptive, secretory, and protective functions; often have mucus producing goblet cells

* sublayers: epithelium, lamina propria (areolar tissue), muscularis mucosa (smooth muscle)
* top layer: simple columnar/pseudostratified on surface, typically have cilia on apical side that moves mucus around
* underlying: areolar tissue deeper, gives little strength, and stretchy, highly vascular

serous membranes (serosa)

internal membrane; double membrane with watery liquid in between; extremely slippery, reduce friction ; around heart and joints

* simple squamous resting on a layer of areolar tissue
* produces serous fluid that arises from blood
* covers organs and lines walls of body cavities; endothelium lines blood vessels & heart; mesothelium lines body cavities such as pericardium, peritoneum, and pleura
* visceral: one membrane lies directly against organ, parietal: layers of membrane against cavity wall

tissue growth

increasing number of cells/size of existing cells

hyperplasia

growth through cell multiplication, adding more cells

hypertrophy

enlargement of preexisting cells

* muscle growth through exercise
* accumulation of body fat

neoplasia

development of a tumor (neoplasm)

* benign or malignant
* composed of abnormal, nonfunctional tissue

differentiation

development of more specialized form and function by unspecialized tissue

* ex: embryonic mesenchyme becoming cartilage and bone

metaplasia

changing from one type of mature tissue to another

* simple cuboidal tissue of vagina before puberty changes to stratified squamous after puberty
* pseudostratified columnar epithelium of bronchi of smokers to stratified squamous epithelium

stem cells

undifferentiated cells that are not yet performing any specialized function

* have potential to differentiate into 1+ types of mature functional cells

developmental plasticity

ability of stem cell to give rise to a diversity of mature cell types (change their type)

totipotent (embryonic stem cells)

have potential to develop into any type of fully differentiated human cell including accessory organs of pregnancy

* source: cells of very early embryo

pluripotent

can develop into any type of cell in the embryo, but not accessory organs of pregnancy (embryonic stem cells)

* source: cells of inner cell mass of embryo (blastocyst)

adult stem cells

undifferentiated cells found in mature organs

* some are multipotent (able to develop into 2+ cell lines), little plasticity; ex. bone marrow
* some are unipotent (produce only one cell type), ex. cells giving rise to sperm

induced pluripotent cell (iPS Cell)

start as a multipotent stem cell, reprogrammed to mimic a pluripotent (mature) stem cell

regeneration

replacement of dead/damaged cells by the same type of cell as before

* restores normal function
* ex) repair of minor skin/liver injuries

fibrosis

replacement of damaged cells with scar tissue (as we age); replace damaged cells with replaced cell types

* scar holds organs together, does not restore function
* ex) repair of severe cuts and burns, scarring of lungs in tuberculosis

stages in healing of a skin wound

* healing of a cut in the skin: severed vessels bleed into cut, mast cells & damaged cells release histamine, which dilates blood vessels & makes capillaries permeable
* blood plasma seeps into the wound carrying: antibodies, clotting protein, carry leukocytes to the area
* blood clot forms: knits edges of cut together, limits spread of pathogens
* forms scab that temporarily seals wound & blocks infection; fibrin mesh made of protein that forms, dries out and makes scab
* macrophages phagocytize & digest tissue debris
* new capillaries sprout from nearby vessels
* deeper portions of clot become infiltrated by capillaries & fibroblasts: transform into soft mass (granulation tissue, temporary, first to grow), macrophages remove clot, fibroblasts deposit new collagen
* vascular genesis: grow new capillaries
* epithelial cells around wound multiply & migrate, tissue regenerates
* underlying connective tissue undergoes fibrosis
* remodeling (maturation) phase begins several weeks after injury
* epithelial cells next to wound don’t have the pressure from surrounding cells so that stimulates reproduction

atrophy

shrinkage of a tissue through loss in cell size or #

* **sensile** atrophy through normal aging (over time)
* **disuse** atrophy from lack of use

necrosis

pathological tissue death due to trauma, toxins, or infection

* root word necro= dead, necrosis= tissue death

infarction

**sudden** death of tissue when blood supply is cut off

* heart attack, stroke, myocardial infarction

gangrene

tissue necrosis due to insufficient blood supply (usually involves infection), develops **over time**

* decubitus ulcer (bed/pressure sore)- form of dry gangrene where continual pressure on skin cuts off blood flow
* dry gangrene: common complication of diabetes
* wet gangrene: liquefaction of internal organs with infection (ebola)
* gas gangrene: usually from infection of soil bacterium that results in hydrogen bubbles in tissues

apoptosis

programmed cell death

* normal death of cell that have completed their function and best serve the body by dying and getting out of the way
* every cell has a built-in “suicide program”: extracellular suicide signal binds receptor protein in plasma membrane called Fas, this activates enzymes, endonuclease chops up DNA and protease destroys proteins

connective tissue

diverse, abundant type of tissue in which cells occupy less space than matrix (most cells aren’t in direct contact with each other)

* supports, connects, and protects organs
* highly variable vascularity, loose connect. have many blood vessels, cartilage has few to no blood vessels
* have lots of extracellular matrix, majority of tissue is nonliving (outside cell)
* stores molecules and nutrients, wide variety of functions

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connective tissue functions

connecting organs (tendons & ligaments), support (bones & cartilage), physical protection (cranium, ribs, sternum), immune protection (WBCs attack foreign invaders), movement (bones provide lever system), storage (fat→ calories, calcium, phosphorus), heat production (metabolism of brown fat in infants), transport (blood)

cells of fibrous connective tissue

fibroblasts, macrophages, leukocytes, plasma cells, mast cells, adipocytes

* ground substance: interstitial fluid (in blood it is plasma)

fibroblasts (fibrous connective tissue)

produce fibers and ground substance of matrix

* blast= to build

macrophages (fibrous connective tissue)

phagocytize foreign material and activate immune system when sense foreign matter (antigens)

* arise from monocytes

leukocytes

aka white blood cells; mast cells are another type of leukocyte

* neutrophils attack bacteria
* lymphocytes react against bacteria, toxins, and other foreign agents

plasma cells

synthesize antibodies (proteins)

* arise from lymphocytes

mast cells

often found alongside blood vessels

* secrete heparin to inhibit clotting
* secrete histamine to dilate blood vessels

adipocytes

store triglycerides (fat molecules)

fibers of fibrous connective tissue

* collagenous, reticular, elastic

collagenous fibers

* collagen is most abundant of body proteins
* tough, flexible, stretch resistant
* tendons, ligaments, and deeper layer of skin are mostly collagen
* less visible in matrix of cartilage and bone
* dense tissue, compact

reticular fibers

* thin collagen fibers coated with glycoprotein
* form framework of spleen and lymph nodes
* filtering fibers, filter debris/junk out of system

elastic fibers

* thinner than collagenous fibers


* branch and rejoin each other
* made of protein called elastin
* allows stretch and recoil

ground substance of fibrous connective tissue

usually has gelatinous to rubbery consistency

* glycosaminoglycans (GAGs): long polysaccharides composed of amino sugars and uronic acid, regulate water and electrolyte balance of tissues, chondroitin sulfate- most abundant GAG (causes stiffness of cartilage), heparin and hyaluronic acid
* present within extracellular matrix
* molecular sponges, absorb water, swell up, once pressure is applies, hydrogen bonds break and water squirts out
* in shock absorbers, allows tissues to be able to swell

loose connective tissue

much gel-like ground substance between cells

* types: areolar, reticular

dense connective tissue

fibers fill spaces between cells

* types vary in fiber orientation: dense regular, dense irregular

areolar tissue

loosely organized fibers, abundant blood vessels, and a lot of seemingly empty space

* the general adhesive that helps hold us together, rubber cement
* possess all 6 cell types
* fibers run in random directions (most collagenous, elastic & reticular present)
* found in tissue sections from almost everywhere (surround blood vessels and nerves)
* nearly every epithelium rests on layer (blood vessels provide nutrition to epithelium & waste removal, ready supply of infection fighting leukocytes that move about freely in this tissue) \\
* easy diffusion of nutrients, high rate of exchange, exchange a lot with avascular types

reticular tissue

* mesh of reticular fibers and fibroblasts
* forms supportive stroma (framework) for **lymphatic** organs
* found in lymph nodes, spleen, thymus, bone marrow
* filter stuff

dense regular connective tissue

* densely packed, parallel collagen fibers
* compressed fibroblast nuclei
* elastic tissue forms wavy sheets in some locations
* tendons attach muscles to bones and ligaments hold bones together
* found in tendons and ligaments
* can resist force very well in one direction and not so well in others

dense irregular connective tissue

* densely packed, randomly arranged, collagen fibers and few visible cells
* withstands unpredictable stresses
* in deeper layer of skin; capsules around organs
* has medium resistance in all directions

adipose tissue

tissue where adipocytes are dominant cell

* space between adipocytes is occupied by areolar tissue, reticular tissue, and blood capillaries
* fat is body’s primary energy reservoir, insulator, and cushion
* fat is recycled continuously
* empty looking cells, nucleus pressed against membrane

white fat

main type if adipose tissue (only fat in adults)

* specimens resemble chicken wire
* provides thermal insulation
* cushions organs (eyeballs and kidneys)
* contributes to body contours (female breast & hips)

brown fat

type of adipose tissue in fetuses, infants, children

* color comes from blood vessels and mitochondrial enzymes
* functions as heat generating tissue
* designed to generate lots of ATP

cartilage

stiff connective tissue with flexible matrix; gives shape to ear, nose, larynx

* no blood vessels (avascular): diffusion brings nutrients & removes waste, heals slowly
* matrix rich in GAGs and contains collagen fibers
* types of cartilage vary with fiber composition (hyaline, fibrocartilage, elastic)

chondroblasts

cartilage cells that produce matrix that will trap them; builds cartilage

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chondrocytes

cartilage cells that are trapped in lacunae (cavities)

* chondroblast traps itself in lacuna, then turns into cell that maintains cartilage (chondrocyte)

hyaline cartilage

eases joint movement, holds airway open, moves vocal cords, growth of juvenile long bones; kind of structural, kind of slipper

* has clear, glassy appearance because of fineness of collagen fibers
* location: articular cartilage, costal cartilage, trachea, larynx, fetal skeleton

elastic cartilage

contains abundance of elastic fibers; provides flexible, elastic support

* covered with perichondrium
* fibers oriented in many different directions, gives very flexible support
* location: external ear, epiglottis