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What is basal lamina, reticular fibers, basememnt membrane?
Basal lamina is the layer between the basal surface of epithelial cells and the connective tissue they are attached to. It is made of proteins and acts as a kind of semipermeable membrane allowing some molecules in and preventing others.
Below it are a layer of reticular fibers that are short fibers forming a network that act as a kind of scafold that help hold the basal lamina to the connective tissue below.
Basement membrane is the combination of the basal lamina and the reticular fibers.
What are cilia?
Whip-like extensions at the apical surface of some epithelial cells. They sort of slap downward with a power stroke, moving debri and mucus along with it, with a slow recovery stroke bringing it back to vertical.
They arise from centrioles called basal bodies near the apical surface of epethelial cells. At its core cilium have nine pairs of microtubules forming a circle at cross section and a single pair in the center. The outer pairs have tiny little protein ( dynein ) arms that will grab onto the next pair. In doing this the cilia is made to bend. Surrounding all these microtubules is a plasma membrane.
What are microvilli?
Hair-like extensions of cell membrane on the apical surface of some cells. These extensions increase the surface area of the small intestine to increase the SI's ability to absorb nutrients. They are also present in the kidneys where the increased surface area aids in ion transport.
-4 main classes...
- Connective tissue proper (CTP) (fat tissue, ligaments)
- Bone tissue
- Blood ( really? blood is a connective tissue? )
What is extracellular matrix?
Water, ground substance, fibers...
Extracellular matrix is made of extracellular material, it is the "stuff" that surrounds the tissue cells themselves.
Extra cellular matrix is made of ground substance. Ground substance can be a fluid or gel-like substance in softer tissues or a hard substance like in bone ( this is actually the gel-like substance made firm by calcification ) that has a high water content with a lot of proteoglycans, hyaluronic acid, and GAGs.
Proteoglycans are macromolecules ( really big mollecules ) made of a protein core with glycosaminoglycans ( GAGs ) extending out radially from a core protein in different directions.
Glycosaminoglacans ( GAGs ) are long-chained polysacharides that attach to a core protein. They are anionc, negatively charged and hydrophilic, attract water.
The proteoglycans ( GAGs around a core protein ) are attached to hyaluronic acid, an even bigger mollecule, several of them on an acid, sort of like rows of bottle brushes attached to the acid.
All of this is negatively charged and attracts water, and ground substance is made mostly of proteoglycans and water.
Extracellular matrix also has protein fibers running through it, callogen, reticular, or elastic fibers.
Where does extracellular matrix come from?
Mesenchymal cells ( mesenchymal stem cells / MSCs ) are a primative kind of cell that can become other cells through differentiation. In cartilage they become chondroblasts -> chondroblasts secrete a matrix around themselves ( the territorial matrix ) that *?*overlaps other territorial matrixes, the overlap areas is the interterritorial matrix.*?*
The chondroblast then decreases its activity and becomes a chondrocyte.
Loose connective tissue
-Areolar connective tissue
Underlies most epithelia in the body, surrounds most small nerves and blood vesels, including capillaries.
- Loose areolar connective tissue functions:
- Supports and binds together other tissues ( holds epithelium to basment membrane.
- Holds body fluids.
- Defends body against infection.
- Stores nutrients as fat.
Extracellular matrix of areolar connective tissue has fibers running through it that perform different functions.
Collagen fibers allow connective tissue to withstand pulling forces ( turns out collagen is better than steel at withstanding tension ). Collagen is made of very thin collagen fibrils bound perpendicularly, all bound together to form a collagen fiber.
Reticular fibers connect connective tissue to epithelia. They help hold capillaries to the connective tissue, epithelium to the connective tissue.
Elastic fibers are long, thin fibers that form a vast network in the extracellular matrix. Elastic fibers are made of elastin which is almost rubber like, allowing tissue with elastic fibers to remain stretchy.
What is a fibroblast?
Fibroblasts are the cells that can become collagen, elastic, or renticular fibers. They secrete protein subunits which, upon entering the extracellular matrix, assemble into the fibers themselves.
Fibroblast is the name of the cell when it is actively producing protein subunits. Fibrocyte is what the cell is called when it is inactive.
What is interstitial fluid?
Interstitial fluid is the fluid part of extracellular matrix. Capillaries moving through the matrix expell small molecules ( water, ions ) and diffuse through the interstitial fluid of the extracellular matrix.
Areolar connective tissue contains defense cells...
Microorganisms attacking the body must pass through areolar connective tissue after passing through epithelium. The areolar contains cells that help fight off these mircroorganisms:
Macrophages - large oval cells with pseuodopods covering its surface, they eat pathogens, microorganisms.
Plasma cells - Egg shaped cells that secrete antibodies. Antibodies bind to foreign bodies and microorganisms to mark them for destruction.
Mast cells - oval shaped cells near small blood vessels that contain large secretory granules. Histamine is one of the chemicals in the granules, it increases the permeability of the blood vessels so that more fluid leaves the blood vessel.
Aveolar conective tissue.
The fat cells are called adipose cells or adipocytes. They store energy reserves as fat. The cytoplasm and nuclues of these cells is squashed up against the cell membrane by a giant lipid droplet.
Adipose tissue is fat tissue ( kind of ). It's like loose connective ( areolar ) tissue but most of it is actually fat cells ( adipose cells / adipocytes ) which is a cell that is mostly one big lipid droplet, a bit of cytoplasm, and a nucleus all squished up against the cell membrane.
Adipose tissue has a lot of capillaris and veins running through it which pull fat out of the blood stream and store the fat in cells ( adipocytes ) as energy reserves for use later. A lot of the body's adipose tissue is just below the skin. It is found in other parts of the body though like around the heart, around lymph nodes, as individual fat cells in bone marrow, all places where a lot of work is going on and energy is needed to drive that work.
Reticular connective tissue.
Reticular connective tissue has a lot of reticular fibers running through it, in fact, it is the only kind of fiber that runs through it ( no elastic or collagen fibers ). This tissue is found in bone marrow, lymph nodes, the spleen, kidneys, and liver. The network of reticular fibers in this tissue support free blood cells in these areas.
Reticular connective tissue also contains fibroblasts called reticular cells which manufacture the reticular fibers. The cells themselves lie on / in the stroma, soft skeleton of fibers that are made of the fibers produced by the fibroblasts.
What is stroma?
Stroma ( meaning bed or bed covering ) is kind of a soft skeleton in connective tissue upon which tissue cells can lie. Also sometimes called "soft skeleton".
What is dense connective tissue?
Dense connective tissue / fibrous connective tissue has lots and lots of collagen, more than areolar tissue and because of this it is very strong tissue that can resist pulling stress very well.
Three types of dense connective tissue are:
Dense irregular connective tissue
Similar to areolar tissue but its collagen fibers are much thicker and stronger. Dense irregular connective tissue is present in the dermis of the skin ( the layer below the epidermis, outermost layer ). Collagen fibers run through it at different planes so that it can resist pulling stress from different directions.
The "irregular" part of the name refers to the irregular way the collagen fibers run through the tissue. In fibrous capsules though ( which are dual layer ) they run parallel to each other in one layer and perpendicular to the other layer in which they run parallel to each other.
The tissue also makes up fibrous capsules that surround joints and some organs such as kidneys, lymphy nodes, and bones.
Dense regular connective tissue.
Dense regular connective tissue is also made of collagen fibers that are parallel ( regular ) to each other. In between the fibers are rows of fibroblasts which produce more fibers. There is little ground material in this tissue and does not have many capillaries / vessels running through it.
Dense regular connective tissue make up tendons ( cords of drc that connnect muscle to bone) and ligaments ( which connect bones to each other ). Drc also makes up fascia wich is a fibrous membrane that wraps around muscles, muscle groups, large blood vessels and nerves. It's kind of like plastic wrap that bind structures together and keep them contained.
Elastic connective tissue.
Made up of mostly elastic fibers, located in walls of arteries and ligaments that connect vertabrae to each other. It is important in these structures to help them recoil / recover from stretching, to pull them back into their proper shape.
Cartilage is a connective tissue that is firm but flexible and is able to withstand compression. It has no blood vessels running through it but does have thin collagen fibers and an extra cellular matrix that is mostly water. Since there are no blood vessels in this tissue needed nutrients diffuse the the matrix.
Mesenchymal cells differentiate to chondryblasts which secrete the matrix, grow collagen fibers, and become chondrocytes after they are done growing fibers and producing matrix. The chondrocytes exist in a cavity in the matrix called a lacuna ( lake ), just kind of a little chondrocyte shaped hole.
Bone tissue is made of collagen fibers made from osteoblasts which secrete bone matrix and the collagen fibers themselves. After growth and production the osteoblasts become osteocytes which occupy lacunae in the matrix. The collagen fibers are coated with inorganic calcium salts which give bones their rigidity.