Tissues Flashcards
Tissues
collections of specialized cells and their extracellular matrix (non-cellular extracellular substance surrounding them) that perform a relatively limited number of function.
whats the 4 tissues types
epithelial, connective, muscle and nervous
Epithelial tissues
• covers all surfaces and lines all hollow structures
Cellularity of epithelial tissues
composed almost entirely of cells with very little extracellular matrix and closely bound by specialized junctions
Polarity of epithelial tissues
has distinct surfaces
Apical surface
= free surface not attached to any other cells
• faces external environment (atmosphere) or internal environments such as fluid in tubes
• microvilli =
non-motile projections of the cell membrane (containing microfilaments) on most epithelia
• increase surface area for absorption and secretion
• so dense in the first portion of the kidney tubule known as the “brush border”
cilia
motile projections on the apical surface of the cells that can sweep substances such as mucus along the tube – e.g. pseudostratified ciliated columnar epithelium of the trachea
lateral surface
site of specialized attachment to neighbouring cells
basal surface
site of attachment to basal lamina
Basal lamina (attachment)
specialized type of extracellular material secreted by epithelial and connective tissue cells (Fig 3.3)
• important role in tissue repair
avascular (epithelial)
contains no blood vessels therefore relies on diffusion of gases and nutrients from blood vessels located in underlying connective tissue
arrangement (epithelial)
sheets or layers
regeneration (epithelial)
continually replaced by division of stem cells found close to basal lamina
Function of epithelial cells
- protection of underlying structures
- acting as a barrier – prevents certain substances from crossing, barrier to water and limits water loss from body
- allows passage of certain substances– readily exchanges oxygen and carbon dioxide through lung epithelium and others epithelium are more selective – filtering at the kidney
- secretion – mucus glands, sweat glands, and enzyme-secreting portions of the pancreas are all composed of epithelial cells that secrete their products onto surfaces or into ducts
- absorbing substances – contain specialized carrier proteins on their membranes that allow specific components to be transported – e.g. intestinal epithelium
classification of epithelial cells
- most epithelium classified by two names: the first indicates the number of layers and the second indicates the shape of the cell
- others may have other descriptors added based on the presence of specialized features such as microvilli or cilia
simple epithelium
single layer of cells
• relatively thin and fragile
• found where secretion, absorption or filtration occurs
• provides smallest diffusion distance
stratified epithelium
more than one layer of cells
• found in areas subjected to significant mechanical or chemical stresses
stratified epithelium can be classified as :
- nonkeratinized = moist
- keratinized = dry, durable and moisture resistant and found in the skin where the outer most layers are composed of dead cells
transitional epithelium
unique type of stratified epithelium that lines the urinary bladder, ureters, pelvis of the kidney and superior portion of the urethra. Shape of the cells and the apparent number of layers vary with the amount of stretch on the bladder.
o pseudostratified (pseudo = false) columnar epithelium
is actually one layer of cells with all cells attached to the basement membrane but appears to be multilayered because some cells are shorter and do not extend to the free surface
• usually ciliated
• Shape of the Superficial Cells
quamous (Fig 3.4) = flat or pancake like o cuboidal (Fig 3.5) = cube-shaped – as wide as they are tall o columnar (Fig 3.6) = tall and thin – similar to a column
Glandular epithelium - secretory organs
o primarily composed of epithelium with supporting network of connective tissue
exocrine glands
glands that contain ducts (lined with epithelium) – dump their products into ducts that empty onto external surfaces (such as the skin) or into organ lumen (such as the intestine)
o categorized by nature of secretions
serous glands
watery solution usually containing enzymes
muscous glands
secrete glycoprotein mucin
• mixed exocrine glands
more than one type of cell present allows serous and mucous secretions
o most are multicellular
globlet cells
specialized unicellular mucus secreting cells
o multicellular glands classified according to
• structure of ducts:
• tubular, or acinar (alveolar) = sac-like
• complexity:
- simple – does not branch
* compound – branch repeatedly
merocrine
- no cellular material lost – e.g. sweat glands
apocrine
apical fragments of the cell released and gland cells regrow – e.g. mammary glands
halocrine
entire cells with products shed, destroying cells – e.g. sebaceous (oil) glands
• endocrine glands
release secretions into interstitial fluid (fluid surrounding cells)
ex : hormones
HORMONES
products diffuse into blood to be carried to target tissues
connective tissue
• abundant – part of every organ
• 3 basic components (Fig 3.12)
o specialized cells
o extracellular protein fibers
o fluid – known as ground substance
• extracellular matrix = extracellular proteins + ground substance
• cells separated from each other by lots of extracellular matrix
functions of connective tissues
- enclosing and separating other tissues (packing material)
- connecting tissues to one another – tendons (muscle to bone), ligaments (bone to bone)
- supporting and aiding in the movement of the body – bony skeletal, joints between bones
- energy/nutrient storage – adipose tissue stores fat, bones store minerals
- cushioning and insulating – adipose tissue protects the tissue it surrounds and the insulating layer below the skin conserves heat
- transportation – blood
- protection – lymph with cells of the immune system, bones
fixed c ells (c.T)
• fixed cells = stationary
o provide local maintenance, repair and energy storage
o (suffixes) blasts = “build”/ create more matrix
• fibroblasts = most abundant cell in connective tissue proper
• produce all connective tissue fibers
o “-cytes” = normally functioning cells that “maintain” matrix
• fibrocytes
o clasts = “clear”/ remove extracellular matrix – osteoclasts (remove bony matrix)
o adipose (fat) cells = adipocytes – large amounts of lipid stored pushes rest of cell contents to periphery
wandering cells
• wandering cells – number varies depending on local conditions
o involved in defence and repair of damaged tissue
mast cells ( wandering cells)
cells in loose connective tissue. Contain chemicals such as heparin and proteolytic (breakdown proteins) enzymes that are released in response to tissue injury
leukocytes (wandering cells)
immune/defence cells that move from the blood into loose connective tissue and then back to the blood via the lymph system
macrophages
phagocytic (eat large particles and cells) – can be “fixed” (lie in wait and do not wander through the connective tissue), or “wandering” with ameboid-like motions
platelets
fragments of specialized cells that are released into the blood and contain enzymes and special proteins important in the clotting of blood and prevention of blood loss
o mesenchymal stem cells
respond to local injury or infection in connective tissue and have the potential to differentiate into multiple different cells such as macrophages and fibroblasts
extracellular matrix
- contains: protein fibers and ground substance
* protein fibers: (Fig 3.12)
collagen fibers
rope-like” collagen proteins and most abundant protein in the body
• made by fibroblasts and form bundles that provide strength and resist being pulled
reticular fibrer
“net-like” proteins - very short, thin fibers that branch to form a network
• chemically identical to collagen - just very fine fibers that fill spaces between tissues and organs
elastic fibers
can be stretched or compressed and returns to its original shape
• ground substance – appears as shapeless background in microscope but molecules highly structured
hyaluronic acid
= long, un-branched polysaccharide (sugar) chain that gives slippery quality to fluid
• lubricant for joint cavities, major component of vitreous humor of the eye
o mixture of proteoglycans and glycoproteins
protein and polysaccharides that interact to determine consistency
• eg. GAGS - glycosaminoglycans such as chrondroitin sulphate
connective tissue proper
Loose cT
contains many types of cells and extracellular fibers in a syrupy ground substance
• Loose connective tissue (Fig 3.12, 3.14) – relatively few protein fibers forming lacy network with numerous spaces filled with ground substance and fluid
o areolar tissue = loose packing material of most organs and attaches skin to underlying tissues
• least specialized and contains all cells found in connective tissue proper
• fibroblasts, macrophages, lymphocytes and some adipocytes plus a variety of extracellular proteins
• can be distorted without damage
adipose tissue (loose CT)
adipocytes – contain large amount of lipid
• unlike other connective tissues – quite cellular with small amount of extracellular matrix
• acts as insulator, protective tissue and energy storage
reticular tissue
contains fibroblasts that produce and secrete reticular fibers
• in bone marrow and liver, forms framework of lymphatic organ - spleen and lymph nodes
Dense C.T
• Dense connective tissue (Fig 3.15) – fibroblasts and large number of protein fibers that form thick bundles
dense regular C.t
o dense regular connective tissue – fibers in extracellular matrix oriented in predominately one direction
• dense regular collagenous connective tissue = fibers made of collagen – found in tendons, ligaments
• elastic connective tissue = fibers are parallel bundles of collagen plus lots of elastin in walls of blood vessels and respiratory passages
dense irregular c.T
meshwork of fibers in random orientation, or one layer in one direction and next layer at 90o orientation
• form sheets with strength in many directions but less that dense regular which has higher strength in a specific direction
• dense irregular collagenous connective tissue – forms most of the dermis (inner portion of the skin), and connective tissue capsules around organs such as kidney and spleen
Fluid connective tissue
blood and lymph – collections of distinctive cells in a fluid matrix
• Blood – contain erythrocytes (red blood cells), leukocytes (white blood cells) and platelets (cell fragments) and matrix between cells is plasma - mainly water with some proteins
• Lymph = interstitial fluid and lymphocytes = 99% of cells
Supportive C.T
cartilage and bone – provide strong framework that supports rest of body
cartilage (supportive)
composed of chondrocytes (cartilage cells) located in spaces called lacunae surrounded by extensive and relatively rigid gel matrix containing chondroitin sulfates
o has no blood vessels or nerves (except in the perichondrium – dense irregular connective tissue surrounding the cartilage) therefore heals very slowly after injury
divided into hyaline, elastic and fibrocartilage
Hyaline cartilage
most common type
• collagen fibers small and evenly dispersed in extracellular matrix making it look transparent
• strong and has some flexibility
• found in rib cage, trachea, bronchi, covers all articular (joint) surfaces of bones
• forms framework for bony skeleton
elastic cartilage
contains large amount of elastin fibers in extracellular matrix
• provides stretch and flexibility – found in pinna of ear
fibrocartilage
– has thicker bundles of collagen and is only slightly compressible and very tough
• acts as pads and shock absorbers
• found in knee (menisci), vertebral discs, pubis symphysis, temporomandibular joint
bone
composed of osteocytes (bone cells) within lacunae and surrounded by hard bony matrix with organic and inorganic portions
o organic portion of matrix primarily collagen fibers
o inorganic portion = hydroxyapatite = crystals of calcium and phosphate
o has rich supply of blood - repairs well
o canaliculi = passages formed by slender cytoplasmic extensions of osteocytes that communicate with other osteocytes and blood vessels
spongy bone
spaces between trabeculae (beams of bone) – “sponge-like” appearance
• provides strength and support but is lighter than compact bone
• found on inner portion and ends of long bones, vertebrae, sternum, skull and pelvis
compact bone
more solid with almost no space between many thin layers called lamellae
• layer found on surface of all bones – thickness varies from region to region
• osteon = functional unit of compact bone
periosteum
covers bony surfaces– fibrous outer layer and cellular inner layer
