biology 2401 exam 2

tissue

a group of similar cells working together to perform a particular function

4 major groups of tissue

epithelial, connective, muscle, and nervous

histology

the study of tissues

2 most significant ways cells are stuck together

1. via the "sticky" glycocalyx (sugar coats) on the surfaces of the cells

2. via specialized junctions (include desmosomes, tight junctions and gab junctions)

desmosomes

- filamentous connections that not only hold adjacent cells together but also give internal structural support to the cells

- do not prevent materials from passing in between the connected cells

plaque

- each desmosome contains one located on the cytoplasmic surface

- consists of glycoproteins and resembles a tiny button

cadherins

filamentous proteins that radiate out from the plaque and intertwine with cadherin filaments from the adjacent cell

where are desmosomes found?

in tissues that experience stretching, such as skin

tight junctions

- continuous bands of protein that form an almost impenetrable barrier to prevent substances from passing through the intercellular space between the connected cells

- consist of occludins

occludins

extend out from the plasma membrane of adjoining cells and fuse together

where are tight junctions found?

in cells that line the stomach and intestines, and in cells that line blood vessels in the brain

gap junctions

tiny channels that allow materials to pass from the cytoplasm of one cell into the cytoplasm of an adjacent cell

when do gap junctions form?

when transmembrane proteins called connexons in adjacent cells bind to one another

where are gap junctions found?

in cardiac and smooth muscle cells

epithelial tissue (epithelium)

forms thin membranous coverings around and inside various organs and it forms glands

how is epithelial tissue classified?

as either membranous or glandular

glandular epithelium

forms specialized structures called glands that release substances beneficial to the body

secretion

is a noun when it refers to the substance released from the gland, and it is a verb when referring to the process of releasing the substance

endocrine glands

secrete chemicals called hormones into tissue fluid or the bloodstream (secretions of these glands remain inside the body)

hormones

function as chemical messengers sent through the blood from endocrine glands to other organs in the body

exocrine glands

expel secretions into a cavity or tube that has connections with the outside of the body

how are exocrine glands classified?

as either unicellular or multicellular

goblet cell

the only example of a unicellular gland in the body which secretes musus directly onto the surface of certain epithelial membranes

multicellular glands

expel their secretions into a tiny tube called a duct

how are multicellular glands classified?

based on the structure of the gland and the method of secretion (apocrine, holocrine, merocrine)

apocrine glands

make secretions consisting of portions of glandular cells that have broken off (ex. mammary glands that produce milk in the breasts)

holocrine glands

make secretions consisting of entire cells that have disintegrated (ex. sebaceous (oil) gland in the skin)

merocrine glands

make secretions by exocytosis and are the most common type of exocrine gland (include sweat glands, salivary glands and mammary glands)

membranous epithelium

- exists on the free surface of various organs, including the skin where it forms the epidermis

- also covers the outside of visceral organs such as the stomach and intestines, and lines their internal cavities

- are multicellular

how does membranous epithelium function?

in protection, absorption, filtration and secretion

what are the characteristics of membranous epithelium?

tightly packed cells, cells are arranged in layers, avascular, nerve supply, polarity, basement membrane, some house receptors

stratum

each layer of cells

innervated

what we call tissues that contain fibers from the nervous system

apical surface

outermost layer of cells in contact with the "free" surface

apical cells

cells in the apical surface region

basal surface

deepest layer of cells

basal cells

cells in the basal surface region

polarity

anatomical and physiological differences between their cells located at the free surface and their cells in contact with the underlying connective tissues

basement membrane

a thin layer of glycoproteins and collagen fibers

basal lamina

the glycoprotein component of the basement membrane that is secreted from the basal cells of the epithelium

reticular lamina

the collagen protein component of the basement membrane that is secreted from connective tissue cells lying beneath the epithelium; collagen fibers in this region intertwine to form a net-like pattern

receptors

allow the body to detect changes in the internal and external environment

how is membranous epithelium classified?

by cell shape, cell arrangement and location

squamous

cells are flat and resemble scales on a fish (ex. outer part of your skin)

cuboidal

cells are cube shaped (ex. lining of tiny tubes in the kidneys)

columnar

cells are column-shaped; they are taller than they are wide (ex. various glands of the body)

transitional

cells can change shape from cuboidal to squamous and back to cuboidal, depending on the amount of compression exerted on the cells (ex. line the inside of the urinary bladder)

simple

has only one layer of cells

stratified

has two or more layers of cells

pseudostratified

is actually a simple epithelium but it looks stratified

endothelium

simple squamous epithelium that lines the inside of blood vessels and lymph vessels

serous membranes (mesothelium)

simple squamous epithelia that cover visceral organs and line major body cavities that do not have connections with the outside of the body (include the peritoneal, pleural and pericardial membranes)

serous fluid

watery fluid secreted from serous membranes that reduces friction during movement

mucous membranes

can be simple columnar, pseudostratified, or stratified squamous epithelium but all line cavities that have a connection to the outside of the body

mucus

secretion secreted from goblet cells in mucous membranes

mucin

protein that gives mucus its thick viscous nature

simple squamous epithelium

- forms serous membranes, small sacs within the lungs, filtering devices within the kidneys, and endothelium

- protects underlying tissues by reducing friction (in the case of serous membrane) and allows diffusion of gases through the walls of capillaries and tiny sacs in the lungs

stratified squamous epithelium

- exists on the surface of the skin and the inner linings of the mouth, esophagus, and vagina

- provides protection to underlying tissues

simple cuboidal epithelium

- exists in tiny tubes of the kidney and certain glands and on the surface of the ovary

- protects underlying tissues and allows passage of material between the blood and kidney fluid destines to become urine

stratified cuboidal epithelium

- exists in the ducts of certain glands

- primary function is protection of underlying tissues

simple columnar epithelium

- nonciliated type makes up the inner lining of the digestive tract where it allows absorption of digested food molecules

- ciliated type lines the oviducts and the small tubes in the lungs, where it moves mucus that traps dust and other particles

stratified columnar epithelium

- lines the male's urethra and ducts of some glands

- protects underlying tissues

pseudostratified ciliated columnar epithelium

- contains ciliated cells and goblet cells and lines the nasal cavity, trachea, and part of the male's urethra

- protects underlying tissues by secreting and moving mucus

transitional epithelium

- exists in the lining of the urinary bladder, ureters, and part of the urethra

- allows organs to expand

connective tissue

most abundant tissue in the body and serves primarily to bind structures together

what are the functions of connective tissue?

support, protection, insulation, movement, shock absorption, transport of nutrients and metabolites, and storage

mesenchyme

an undifferentiated, embryonic tissue that all connective tissue arises from

what are the major structural characteristics of connective tissue?

vascularization and an extensive matrix

vascularization

supplied with blood vessels (all connective tissue expect cartilage)

2 components of connective tissue matrix

ground substance and extracellular fibers

ground substance

the fluid component of the matrix and contains water, ions, nutrients, metabolities, adhesion proteins and proteoglycans

adhesion proteins

connect cells to extracellular fibers and the ground substance

fibronectin

most common adhesion protein

proteoglycans

central "wire" consists of a filamentous protein while the "bristles" include a variety of polysaccharides

2 common polysaccharides associated with proteoglycans

hyaluronic acid and chondroitin sulfate

hyaluronic acid

makes ground substance very slippery and aids in lubrication, especially in joints

chondroitin sulfate

makes the ground substance more viscous and helps hold the matrix together, especially in cartilage and bone tissue

extracellular fibers

- abundant in most connective tissues and exists throughout the ground substance of the matrix

- provide structural support and strength for the connective tissue

3 major types of protein fibers in various connective tissues

collagenous fibers, reticular fibers and elastic fibers

collagenous fibers

- made of a protein collagen and appear as white fibers in the matrix

- offer the connective tissue a great amount of resistance to tension

reticular fibers

very thin, highly branched collagenous fibers that give the matrix of certain connective tissues a net-like appearance

elastic fibers

- contain elastin protein and appear as yellow fibers

- allows certain connective tissue to recoil after stretching

fibroblasts

produce the matrix of most connective tissues

fibrocytes

what fibroblasts become for the most part

adipocytes

what fibroblasts become in adipose (fat) tissue

chondroblasts

produce the matrix of cartilage and eventually become chondrocytes

osteoblasts

produce the matrix of bone and eventually become osteocytes

hemocytoblasts

cells that give rise to different blood cells but do not produce the liquid matrix, or plasma, of blood

mast cells

congregate around blood vessels and when stimulated by a variety of chemicals release the chemical histamine

histamine

causes the blood vessels to dilate and become "leaky"

macrophages

- specialized white blood cells that once lived in the blood but squeezed out of the blood vessel into the surrounding tissues

- crawl around engulfing foreign particles and dead or damaged body cells

connective tissue proper

includes all connective tissues except bone, cartilage and blood

how is connective tissue proper subdivided?

loose connective tissue and dense connective tissue

loose connective tissue

have loosely packed intercellular fibers and include areolar, adipose and reticular tissue

areolar tissue

has a gel-like matrix and contains collagenous, reticular, and elastic fibers produced by fibroblasts

lamina propria

areolar tissue beneath a mucous membrane

adipose tissue

a loose tissue containing adipocytes

functions of adipose tissue

energy storage, insulation, protection, and heat generation

adipose (fat) tissue consists in what 2 forms?

yellow fat and brown fat

yellow fat

- gets its characteristic yellow color from pigments such as carotene.

- most common fat in adults and is abundant just below the skin of the abdomen, buttocks and thighs