Flashcards in Connective tissue and muscle Deck (20):
What is connective tissue?
The general name given to a family of tissues including cartilage, bone, tendons and ligaments.
What are common features of connective tissue?
- The support cells which maintain the tissue are not attached to one another (i.e. unlike epithelial cells).
- The majority of the volume in most connective tissues is taken up by extracellular matrix.
- Other cells may be present, for example those with immunological functions.
- The tissues are derived from mesenchyme, an embryonic tissue principally associated with the mesoderm layer of the early three layer embryo.
What are the three types of ECM components?
- Fibrillar structures which provide strength against tensile forces applied to the tissue; main protein components are collagen, elastin and fibrillin.
- Viscous liquid component which provides resistance to compressive forces. The main molecular components are complex negatively charged polysaccharides which bind water and Na+ ions and are mainly glycosaminoglycans or proteoglycans. The liquid component also provides a solvent in which oxygen, nutrients, waste products and small signalling molecules can diffuse.
- Other molecules whose main function is in binding to cells via specific cell surface receptors and mediating
their attachment to the ECM. The best known example is fibronectin.
What colour are the epidermis, dermis (dense connective tissue) and loose connective tissue below?
- epidermis is blue
- cells in dermis is pink
- in loose connective tissue you can see the fibres clearly
Cells in dense and loose connective tissue
-The support cells for both dense and loose connective tissue are known as fibroblasts, and they have a spindly shape with correspondingly pointed looking nuclei.
- Other cells are mainly migratory white blood cells such as lymphocytes and neutrophils.
- Two types of cell which are normally resident in loose connective tissue but are related to white blood cells are the macrophages and mast cells.
Dense irregular and regular connective tissue
- The dense connective tissue of skin is known as dense irregular connective tissue because the fibres
are randomly oriented to give the tissue equal strength in all directions.
- In some locations such as tendons and ligaments – strength is required in a single direction, and in this case the collagen and other fibres are aligned in parallel and the tissue is known as dense regular connective tissue.
Fat cell in loose connective tissue
- Part of the loose connective tissue in the skin contains a large number of fat cells or adipocytes.
- These appear white and large – about 10 times the diameter of most other cells.
- The ECM components of the tissue lie between the fat cells.
Low and high magnification of cartilage
- Appear as large purple staining regions easily identified at low magnification.
- At higher magnification look for the support cells, recognising them by their blue staining nuclei.
- The support cells of cartilage are called chondrocytes, and they are well separated from each other.
- They each lie in their individual pale staining regions, called lacunae.
- The remaining space, staining purple, is the ECM of the cartilage.
Fibrocartilage contains thicker collagen fibres oriented to provide tensile strength in a particular direction, for example in the pubic symphysis or the intervertebral discs.
- Elastic cartilage contains additional elastic fibres to provide pliability and resilience (for example in the external ear).
What is unusual about cartilage?
Cartilage is unusual in that it has no blood vessels and substances reach the chondrocytes by simple diffusion through the ECM.
- Hyaline cartilage is translucent cartilage.
- It is found on many joint surfaces.
- Has lots of collagen and is mainly made of chondroitin sulfate
- Bone is a specialised connective tissue where the ECM has become mineralised with calcium phosphate crystals to provide great compressive strength.
- The relatively solid region around the edge of the bone shaft is known as compact bone or dense bone
Osteocytes and cavities and mineral and canaliculi
- Dense bone contains the support cells of bone, called osteocytes, within lacunae (gaps)
-There are also other cavities containing blood vessels.
- The mineral prevents free diffusion, and small channels called canaliculi provide a pathway for diffusion of O2 and nutrients from the blood vessels to the osteocytes.
- In transverse section on that slide it can be seen that bone is arranged in structural units called osteons which have a central canal containing blood vessels, with the ECM of the bone arranged in concentric layers around this central canal.
- The collagen fibres are oriented differently in each layer to provide additional strength.
Structures in the bone and cells
- The central part of a bone has spaces between the bone tissue, and is known as spongy bone or cancellous bone.
- The bony structures here are called trabeculae, and they are usually arranged in the way that best resists the mechanical stresses on the bone.
- Most of the space between the trabeculae is filled with bone marrow, the site of developing blood cells.
- There may also be fat cells.
Bone formation and calcium
- New bone is laid down osteoblasts and bone is reabsorbed osteoclasts .
- Because the mineral component of bone can act as a store for Ca2+ and phosphate, these activities are under hormonal control from calcitonin and parathyroid hormone to maintain the normal blood concentrations of these ions.
What do most bones begin as?
- Ccartilage precursors in the foetus, which then get converted to bone – a process known as endochondrial ossification.
- In long bones, a cartilaginous region persists at the growth plates between the shaft and heads until the bone has reached its adult length.
- Cartilage also lines the bone surface where it forms part of a joint.
- Elsewhere the bone is lined with a layer of dense connective tissue – the periosteum.