Embryology Final

histology is the study of

tissues

tissue

a group of cells that share a similar structure and function and their extracellular matrix

2 major components of tissues

cells and extracellular matrix

extracellular matrix

a network of molecules and mineral which surround and support the cells within tissues- collagen, elastin, proteoglycans, hydroxyapatite

interstitial fluid functions

transport nutrients to cells, remove waste from cells, transport secretory products from cells

basic tissue types

epithelial tissue, connective tissue, muscle tissue, nervous tissue

epithelial tissue

functions in secretion, absorption, and excretion, forms sheets which line cavities of organs and cover body surface, forms many glands

connective tissue

supports body and holds it together, transports substances through body and protects it from foreign invaders, characterized by cells which produce abundant extracellular matrix

muscle tissue

formed of cells specialized for contraction and movement

nervous tissue

composed of cells with long, fine processes specialized for communication between various body structures and controls/integrates their activities

biopsy

tissue samples removed during medical procedures or surgery, fixed in formalin and studied microscopically

if biopsy results are needed during surgery

biopsy is rapidly frozen using liquid nitrogen and sectioned immediately, decisions can then be made during surgery based on whether or not a sample is malignant or otherwise diseased

epithelial tissue

can arise from all 3 germ layers (ectoderm, mesoderm, endoderm), is subdivided into 2 types (covering/lining epithelium and glandular epithelium)

covering (lining) epithelium

covers the body and lines body cavities, blood and lymphatic vessels, respiratory, digestive, urinary, and reproductive tracts

glandular epithelium

forms secretory part of exocrine and endocrine glands

general functions of epithelial tissues

protection, sensory function, secretion, absorption, excretion

protection of epithelial tissue

the epidermis of skin is a covering epithelium that protects the body from dehydration, injury, and microbial invasion

sensory function of epithelial tissue

specialized epithelial sensory structures are found in the skin, nose, eye, and ear

secretion function of epithelial tissue

glandular epithelium produces many secretory products including digestive enzymes, hormones, mucus, and sweat

absorption function of epithelial tissue

lining epithelium of gut allows absorption of nutrients while that of lungs allows gas exchange, is essential

excretion function of epithelial tissue

epithelium of kidney tubules allows excretion of urine

characteristics of epithelial tissues

a very small amount of extracellular matrix, consist of a sheet of tightly packed cells, avascular, a permeable basement membrane attaching it to underlying ct that oxygen and nutrients diffuse through, a lamina propria that may contain smooth muscle, blood vessels and glands

basement membrane

a thin, noncellular layer which attaches the epithelial tissue to underlying connective tissue, is permeable

lamina propria

layer of connective tissue which lies deep to basement membrane of epithelium lining the respiratory, digestive, and urinary system, may contain smooth muscle, blood vessels, and glands

epithelial tissues are classified by

cell shape and how cells are layered

3 types of epithelium cell shapes and their similarities

squamous epithelium, cuboidal epithelium, columnar epithelium, each eithelial cell has an apical pole and basal pole

apical/basal poles

apical- faces a cavity or space, basal-rests on basement membrane, 2 poles differ in structure and function

simple epithelium

cells are arranged in a single layer

stratified epithelium

cells are arranged in multiple layers

simple squamous epithelium

one layer of squamous cells which readily allow substances to diffuse through them, found in alveoli of lungs, endothelium, mesothelium

endothelium

inner lining of blood and lymph vessels

mesothelium

membranes covering organs and body wall (pleura, pericardium, peritoneum)1

simple cuboidal epithelium

one layer of cuboidal cells resting on a basement membrane, found in glands and ducts, kidney tubules

simple columnar epithelium

one layer of columnar cells which forms the surface of mucous membranes, found in stomach & intestines, uterus & uterine tubules, parts of respiratory system

columnar epithelium may have 1 or more of these specialized structures

goblet cells, microvilli, stereocilia, cilia

goblet cells

contain large secretory vesicles which produce mucus, interspersed among enterocytes in small intestine

microvilli

microscopic fingerlike projections of plasma membrane of columnar cells, greatly increases the surface area of mucosa for absorption, found in intestines

stereocilia

absorptive in function, much longer than microvilli, may branch distally, found in male reproductive system

cilia

long microscopic hairlike processes which move material along a surface

pseudostratified columnar epithelium

a specialized type of columnar epithelium, has only 1 layer of cells, every cell touches basement membrane but some cells don’t reach surface of epithelium, nuclei vary in location of cells creating a false appearance of layering, contains numerous goblet cells

pseudostratified columnar epithelium is found in

respiratory air passages (nasal cavity, bronchi, trachea), male reproductive system

stratified squamous keratinized epithelium

multiple layers of cells with squamous cells forming the outermost layer, contains keratin and is protective in function, found in epidermis, resists mechanical damage and is found in masticatory mucosa covering gingivia and hard palate

keratin

a tough, fibrous protein found in skin, hair, and nails

stratified squamous non-keratinized epithelium

similar to stratified squamous keratinized epithelium but lacks keratin and surface is moist, found in mouth, pharynx, esophagus, vagina, forms lining mucosa covering soft palate, cheeks, floor of mouth, oropharynx and laryngopharynx

stratified cuboidal epithelium

2 or more layers of cuboidal cells arranged over a basement membrane, found in sweat glands, ovarian follicles

stratified columnar epithelium

multiple layers of cells, only those near surface appear columnar, found in male urethra

transitional epithelium

a specialized stratified epithelium present in organs subject to stretch (uterus, urinary bladder), multiple layers of cuboidal cells of varying sizes present, cells assume a squamous shape when organ is stretched, number of observable cell layers decreases with stretch

glandular epithelium

epithelium which is specialized for secretion, secretory portion of glands classified as tubular (short or long/coiled) or acinar (rounded/sac-like)

based on where they secrete their product, glands are classified as

exocrine and endocrine

exocrine glands

secrete their product into ducts which open into a hollow organ or on a surface, found in sweat glands, salivary glands, digestive glands of stomach and pancreas

endocrine glands

secrete their produce directly into bloodstream, includes pituitary, thyroid, parathyroid, and suprarenal glands

functional classifications of exocrine glands

holocrine, apocrine, merocrine

holocrine glands (exocrine)

secretory product collects in the cell which then ruptures to release it, the cell is destroyed in the process, ex-sebaceous glands

apocrine glands (exocrine)

secretory product collects at the apex (tip) of the cell, it’s then pinched off, releasing product into a duct, causes some damage to cell, ex-mammary glands

merocrine glands (exocrine)

secrete their product through the cell membrane without damage to the cell, most secretory cells are this type, ex- salivary glands

types of intercellular junctions

tight (occluding) junctions, adherens junctions, desmosomes, gap junctions, hemidesmosomes

tight (occluding) junctions

forma seal between adjacent cells, most apical of intercellular junctions

adherens junctions

sites of strong cell adhesion found immediately below tight junctions

desmosomes

anchoring junction which forms a single “spot-weld”, does not form a belt around cell

gap junctions

channels for communication between cells

heidesmosomes

attached cells to basal lamina, resemble half a desmosome

connective tissue (CT)

a diverse and widespread tissue type, found in and around every organ in body, consists mainly of extracellular matrix, derived from mesoderm (mesoderm and neural crest cells only)

functions of connective tissue

attachment, support, transport, defense

attachment function of connective tissue

attaches tissues to each other, ex- attaches muscles to bones and bones to bones

support function of connective tissue

forms a supporting framework for body as a whole and for its individual organs

transport function of connective tissue

transports substances between tissues and bloodstream via diffusion through interstitial fluid

defense function of connective tissue

cells of immune system defend against invading pathogens

fibroblasts

most common cells found in connective tissue, develop from mesenchyme, permanent residents (natives) of connective tissue, secrete collage, elastin, and all components of ground substance, also function in tissue repair

adipocytes

fat cells, found in connective tissue of many organs

macrophages

phagocytic cells which are involved in turnover of protein fibers, remove cellular debris, neoplastic cells, bacteria, and other invaders (“big eater”)

mast cells

release mediators of inflammation such as histamine

plasma cells

lymphocyte derived cells which produce antibodies, involved in immune defense

leukocytes (not macrophages or plasma cells)

white blood cells, enter connective tissue from blood vessels (especially during inflammation), not native to connective tissue (unlike fibroblasts), formed in bone marrow and circulate in blood, move into connective tissue through blood vessel walls to perform functions

allergy

a hypersensitivity reaction of tissues to injury via trauma, bacterial infection, etc., release of histamine and other chemicals causes increase in vascular permeability at site of injury, large # of leukocytes pass through blood vessel walls into injured tissue through chemotaxis

chemotaxis

attraction of cells by specific chemicals

clinical signs of inflammation

redness, swelling, heat, and pain

extracellular matrix is made of

fibers and ground substance

major component of fibers found in ECM of CT

the protein collagen

collagen

most abundant protein in body, estimated to contribute over 30% of body’s dry weight, 28 types total but 4 most important

type I collagen

most abundant, found in skin, tendons, and ligaments, resists tension, big fibers

type II collagen

found in cartilage, resists compression

type III collagen

found in muscle, blood vessels, and lymphatic system, maintains structural integrity of expansible organs, forms reticular fibers

type IV collagen

found in basal laminae, supports epithelial cells, functions in filtration

fiber types

collagen fibers, reticular fibers, elastic fibers

collagen fibers

formed from type I collagen budles, tough, inelastic, and provide great tensile strength, found in skin, tendons, and ligaments

reticular fibers

delicate mesh-like fibers formed of type II collagen, occur in networks and support small structures (capillaries), found in stroma of liver, endocrine glands, lymph nodes, and spleen

elastic fibers

formed of elastin protein, allows tissues to stretch and return to original length, found in lungs, walls of large arteries, and external ear

ground substance

a highly hydrated gel-like substance which fills the space between fibers and cells in connective tissue, made of water and macromolecules

functions of ground substance

allows diffusion of molecules, acts as a lubricant, acts as a barrier to infection

macromolecules of ground substance

glycosaminoglycans (GAGs), proteoglycans, multiadhesive glycoproteins

glycosaminoglycans (GAGs)

polysaccharide chains, most abundant is hyaluronan (hyaluronic acid) which binds water and lubricates joints & organs

proteoglycans

larger molecules consisting of a core protein to which varying numbers of GAGs are bonded to

multiadhesive glycoproteins

bind cells to their sunstance

connective tissue proper subdivisions

loose (areolar) CT, dense irregular/regular CT, reticular tissue

loose (areolar) connective tissue

forms lamina propria layer beneath epithelium of many organs, fills spaces between muscle and nerve fibers, surrounds and supports blood vessels and nerves, contains cells, gibers, and ground substance roughly in equal amounts, has a delicate consistency, is flexible and not very resistant to stress, one of most widely distributed tissue types in body

dense connective tissue

consists primarily of densely packed collagen (type I) fibers with fewer cells and less ground substance than loose CT, divided into 2 subtypes- irregular and regular

dense irregular connective tissue

bundles of collagen fibers are randomly interwoven with no definite orientation, can resist stress in any direction, found in dermis of skin, deep fascia, and capsule of organs (kidney, spleen)

dense regular connective tissue

bundles of collagen fibers arranged into parallel rows, great tensile strength, resists stress in 1 direction, found in tendons, aponeuroses, and ligaments, poorly vascularized results in slow repair

reticular tissue

net or mesh-like tissue composed of reticular fibers formed of type III collagen, forms framework of spleen, lymph nodes, and bone marrow, functions as a filter removing worn out RBCs in spleen and pathogens in lymph nodes (which are later phagocytized)

tissue repair

tissue healing depends on activity of fibroblasts (fill gaps caused by injury with CT), in patients who survive heart attacks damaged cardiac juscle is replaced by dense irregular scar tissue by fibroblasts