PHT 500 - Histology

epithelial tissue function

Covers surfaces, lines cavities, forms glands.

protection, secretion, absorption, and filtration

connective tissue function

supports and binds other tissues

muscular tissue function

produces movement

nervous tissue function

transmits impulses for coordination and control

epithelial tissue

sheets of cells covering body surfaces and lining cavities

locations of epithelium

external surfaces (skin)

internal cavities and organs (lining of the digestive tract, respiratory system)

glands and ducts (sweat glands, salivary glands)

endothelium (blood and lymph vessels)

mesothelium (abdominal, pericardial, pleural cavities)

characteristics of epithelium

cellularity, polarity, avascularity, and high mitotic rate

Cellularity

cells closely packed in single or multiple layers

Polarity (location)

apical domain (top surface)

basal domain (bottom surface)

lateral domain (lateral surface)

avascularity

no direct blood supply

high mitotic rate

rapid cell turnover and regeneration

simple epithelium

single layer of cells

stratified epithelium

multiple layers of cells

pseudostratified epithelium

appears layers but all cells touch the basement membrane

squamous cell

flat and thin

cuboidal cell

as tall as they are wide (square)

columnar cell

taller than they are wide

cilia

MOTILE, found in respiratory tract, uterine tubes

microvilli

NON-MOTILE, found in small intestine, kidney tubules

stereocilia

NON-MOTILE, found in epididymis, inner ear

longer than microvilli

tight junctions (zonula occludens)

prevent material passage between cells

adhering junctions (zonula adherens)

firm cell adhesion

desmosomes

stability against shearing forces

Hemidesmosomes

attach cells to basement membrane

gap junctions

allow molecule diffusion and cell communication

simple squamous epithelium location

mesothelium (digestive organs, lungs, heart)

endothelium (heart chambers, blood vessels)

simple cuboidal epithelium location

small ducts, kidney tubules

simple columnar epithelium location

digestive tract, uterine tubes

stratified squamous epithelium location

nonkeratinized = mouth, esophagus, vagina, anal canal

keratinized = skin (external surfaces)

stratified cuboidal and columnar epithelium location

rare, found in some glands and ducts

pseudostratified epithelium location

respiratory passages, epididymis, vas deferens

motile cilia = trachea and bronchi

stereocilia = epididymis, vas deferens

connective tissue components

cells, fibers, and ground substance

loose connective tissues characteristics

loose, irregular arrangement of fibers

abundant ground substance

loose connective tissue cells

fibroblasts, fibrocytes, adipose cells, mast cells, plasma cells, macrophages

loose connective tissue fibers

collagen, elastic, reticular

fibroblasts

most common cell type

active, synthesize fibers and ground substance

adipose cells

store fat

macrophages

phagocytic, ingest foreign material

mast cells

contain granules, associated with blood vessels

release histamine, heparin

plasma cells

derived from lymphocytes, produce antibodies

leukocytes

defend against infection

dense connective tissue characteristics

thicker, densely packed fibers

less ground substance and fewer cells

dense irregular connective tissue characteristics

predominantly type 1 collagen

random, irregular orientation

provides strength and support

mainly fibroblasts and fibrocytes

dense irregular connective tissue locations

dermis of skin

capsules of organs

dense regular connective tissue charactertistics

predominantly type 1 collagen

minimal ground substance

uniform, parallel arrangement

provides strong binding

mainly fibroblasts located btw rows of collagen fibers

dense regular connective tissue locations

tendons

ligaments

tendinosis

degenerative disease that occurs within the substance of a tendon

***histological exam of tendinosis reveals...

abnormal fibrotic structure including

- collagen disorganization

- decreased fiber diameter

- increased mucoid ground substance

additional findings in tendinosis include

- collage microtears

- focal hypercellularity

- vascular proliferation

- focal necrosis with calcification

tendinosis is associated with...

age, overexertion, or both

what is the difference between dense irregular and dense regular connective tissue?

dense irregular = random orientation and resists multidirectional stress

dense regular = parallel orientation and resists unidirectional stress

connective tissue fibers key functions

mechanical support

physical properties depend on fiber mixture

orientation of the fibers

collagen fibers characteristics

tough, thick, non-branching

most abundant

collagen fiber function

provide tensile strength and support

type 1 collagen location

dermis, tendons, ligaments, bones

type 1 collagen function

resistance to tensile stress

type 2 collagen location

hyaline and elastic cartilage, vitreous body

type 2 collagen function

pressure resistance

type 3 collagen location

lymph nodes, spleen, bone marrow

type 3 collagen function

supporting meshwork

type 4 collagen location

basal lamina

type 4 collagen function

supportive meshwork

hypertrophic scars

raised scars that remain within the margins of the original wound

keloids

scar tissue that grows beyond the margin of the original wound

reticular fiber composition

mainly type 3 collagen

thin, branching fibers

reticular fiber function

form delicate, supportive frameworks

reticular fiber locations

liver, lymph nodes, spleen, hemopoietic organs

support capillaries, nerves, and muscle cells

elastic fiber characteristics

thin, small, branching

capable of stretching and recoiling

elastic fiber composition

microfibrils and elastin

elastic fiber function

provide elasticity and resilience

elastic fiber location

common = lungs, bladder wall, skin, aorta and pulmonary trunk

elastic fiber special synthesis

smooth muscle cells in large vessels

fibroblasts in other organs

marfan syndrome

autosomal-dominant disorder caused by gene mutation which affects the formation of elastic fibers

ground substance

amorphous, transparent, and colorless extracellular matrix

semifluid gel with high water content

ground substance function

supports, surrounds, and bonds connective tissue cells and fibers

fills space btw fibers and cells

facilitates diffusion of nutrients and waste

main components of ground substance

glycosaminoglycans (GAGs), proteoglycans, and adhesive glycoproteins

glycosaminoglycans

unbranched polysaccharide chains

GAG function

attract water, forming a hydrated gel

facilitate diffusion and provide barrier properties

proteoglycans function

attract water, creating a semifluid consistency

support nutrient and waste diffusion

facilitates movement of oxygen, nutrients, metabolites, and waste

prevents movement of large molecules and pathogens

adhesive glycoproteins functions

bind cells to fibers

connect cells, collagen and proteoglycans

establish structural continuity with cytoskeleton

fibronectin function

binds connective tissue cells, collagen fibers, and proteoglycans

interconnects all three components of connective tissue

integrins functions

bind extracellular collagen fibers to actin filaments in cytoskeleton

establish structural continuity

laminin functions

major component of basement membrane

binds epithelial cells to the basal lamina

has binding cites for integrin, type 4 collagen, and proteoglycans

what is cartilage

special form of connective tissue derived from embryonic mesenchymal cells

what is cartilage composed of?

cells and extracellular matrix

what are the characteristics of cartilage

avascular

hydrated extracellular matrix (facilitates diffusion of nutrients and waste)

provides tensile strength, structural support, flexibility, and compression resistance

what are the cells of the cartilage

chondroblasts, chondrocytes, matrix components (GAGs)

what do chondroblasts do

synthesize extracellular matrix

what are chondrocytes

mature cartilage cells maintaining the matrix

what are the characteristics of hyaline cartilage

most common type

contains type II collagen fibrils

what are the functions of hyaline cartilage

serves as a skeletal model in embryos

provides smooth surfaces for joint movement

where is hyaline cartilage located

articular surfaces, costal cartilage, nose, larynx, trachea, bronchi

why is hyaline cartilage on articular surfaces unqiue?

doesn't have a perichondrium

explain the process of osteoarthritis

in the early stage we see fibrillation of the articular cartilage (which is the breakdown) causing the loss of the smooth surface, leaving the cartilage more brush-like.

as breakdown continues, there is eburnation which when the cartilage has worn off all the way to the subchondral bone

what are the characteristics of elastic cartilage

contains numerous elastic fibers

similar to hyaline cartilage but more flexible

what is the function of elastic cartilage

provides flexible support

what are the locations of elastic cartilage

external ear, auditory tube, epiglottis, part of larynx

what are the characteristics of fibrocartilage

mixture of hyaline cartilage and dense collagen fibers (type i)

alternating layers of cartilage matrix and collagen fibers

what is the function of fibrocartilage

provide tensile strength and absorbs compressive shock

where is fibrocartilage located

intervertebral discs, pubic symphysis, meniscus, labrum