Unit 2

Tissues

histology

the study of tissues

tissue

group of cells with similar structure working together to perform a similar job

muscle cell

contracts & relaxes

neuron

receives and passes impulses

red blood cell

carries oxygen through the blood stream

4 types of tissues

muscle tissue, nervous tissue, epithelial tissue, connective tissue

epithelial tissue

tissue that covers all internal and external body surfaces, lines body cavities, and makes up glands

forms boundaries in the body

ex; outer layer of skin, lining of stomach, lining of urinary bladder

two forms of epithelial tissue

covering & lining epithelium, glandular epithelium

epithelial tissue structure

• two surfaces: apical + basal surface

  • basement membrane

• avascular but innervated

apical surface

not attached to surrounding tissue, and exposed to either the outside of the body or the lining of an organ

basal surface

attached to underlying connective tissue

basement membrane

in between the epithelial and connective tissue

squamous

flat cells

cuboidal

box-like cells

columnar

tall & skinny cells

simple

one layer of cells

stratified

two or more layers of cells

pseudostratified

appears layered but is only one layer

simple squamous

• resembles a tiled floor

• thin to allow for diffusion

• found in the lungs and blood vessels

simple cuboidal

• function: secretion and absorption

• found in the walls of glands and kidney tubules

simple columnar

• tall closely packed cells

• function: absorption & secretion of mucus

• lines the digestive tract

stratified squamous

• many layers of flat cells

• function: protection from abrasion

• location: skin, mouth, vagina, esophagus

stratified cuboidal

• rare

• found in the ducts of sweat glands & mammary glands

stratified columnar

• rare

• found in pharynx & male urethra

transitional tissue

• forms the lining of urinary organs, ureters, urinary bladder, and part of the urethra

• function: stretches easily (to allow urine to stretch bladder)

pseudostratified columnar

• secretes substances such as mucus

• propels particles forward using cilia

• found in trachea and fallopian tubes

connective tissue

most abundant tissue in your body

• CT proper, cartilage, bone, blood

connective tissue function

• binding and supporting

• protecting

• insulating

• storing fuel

• transporting substances

reason 1 why connective tissue are grouped together

they all develop from the same type of embryonic tissue (mesenchyme)

reason 2 why connective tissue are grouped together

they have varying degrees of vascularity (abundance of blood vessels)

• cartilage is avascular

• other types have rich blood supply

reason 3 why connective tissue are grouped together

in addition to cells, all CT have an extracellular matrix

• all other tissues (epithelial, nervous, muscles) are mainly composed of cells, but within CT a non-living substance called matrix fills the spaces between cells

2 ingredients of matrix

ground substance & fibers

ground substance

watery unstructured material that fills the spaces between cells

fibers

proteins; 3 types

• collagen - extremely tough & provides strength

• elastic - stretch and bounce back like rubber bands

• reticular fibers - thinner and shorter collagen fibers; branch to form nets that support your organs

loose connective tissue

many spaces between fibers of the matrix

3 types: areolar, reticular, adipose

areolar

• most common CT

• matrix: gel-like ground substance; has all three fiber types

• function: serves as packing material that wraps and cushions organs

• location: under epithelial tissues and around organs

reticular

• matrix: gel-like ground substance but only have reticular fibers (no collagen/ elastic)

• function: forms a soft skeleton that supports other cells

• location: lymph nodes, spleen, bone marrow

adipose

• matrix: very little matrix; made mainly of tightly packed adipocytes

• function: energy reserves, insulates body heat, cushions organs

• location: under skin, around kidneys & heart

dense connective tissue

few spaces between fibers of the matrix; also called fibrous

3 types; regular, irregular, elastic

regular

• matrix: closely packed, parallel collagen fibers

• strong when pulled in one direction

• location: tendons & ligaments

• function: tendons connect muscles to bones; ligaments connect bones to bones

irregular

• matrix: randomly arranged collagen fibers

• function: strong when pulled in many directions

• location: dermis, fibrous coverings that surround organs and joints

elastic

• matrix: high number of elastic fibers

• function: allows tissue to bounce back after stretching

• location: walls of ovaries, ligaments connecting vertebrae, lungs

cartilage

• stands up against compression and tension very well; avascular, no nerves

• matrix: firm ground substance that causes a rigid, rubber-like matrix

• chondroblasts & chondrocytes

chondroblasts

immature cartilage cells that produce new matrix until skeleton stops growing

chondrocytes

mature cartilage cells; found in lacunae (cavities)

hyaline

most common type of cartilage in the human body

• matrix: contains many collagen fibers, but has a glassy appearance

• advantages: firm w/ slight flexibility

• locations: articular cartilage at the ends of bones, tip of the nose, costal cartilage (ribs to sternum), trachea

elastic

• matrix: contains many elastic fibers

• advantages: strong and very flexible

• location: external ear, epiglottis

fibrocartilage

• matrix: rows of chondrocytes alternating w/ rows of thick collagen

• advantages: resists compression and tension

• location: locations that withstand heavy pressure, such as the intervertebral disks and cartilage of the knee

blood

• only liquid body tissue

• atypical tissue—doesn’t connect things

• matrix: liquid called plasma; no collagen, elastic, or reticular

red blood cell (erythrocyte)

transport O₂ and CO₂

white blood cell (leukocyte)

fights infection

platelet (thrombocyte)

clots blood after injury

bone

• supports, protects, stores calcium, produces blood cells

• matrix: rigid due to abundant collagen fibers and calcium salts

• vascular

osteoblasts

immature bone cells that produce new bone matrix

osteocytes

mature bone cells; found in cavities called lacunae

compact bones

outer layer of bone; rigid

spongy bone

inside the ends; has spaces filled w/ marrow