What are connective tissues ?
Tissues with cells embedded in an extensive extracellular matrix
What is the function of the connective tissues ?
- mechanical function
- support
- wrapping and binding
- packing and space filling
- wound healing
- infection control
What are the general features of connective tissues ?
- relatively few cells
- lots of extracellular matrix
What is the composition of the extracelular matrix ?
There are fibres embedded in ground substances
The fibres are -
• collagen (high tensile strength - don’t stretch or branch)
• elastic fibres (stretch and then recoil - branched)
The ground substance is glycosaminoglycans and proteoglycans (complex sugars)
What is the function of the complex sugars in the ECM ?
They are highly charged and so attract water into the matrix
- swelling pressure
- forms a jelly
- compression resistance
- diffusion of nutrients
What is the role of connective tissue cells ?
- make the matrix
- sense loading on the matrix
- modify the matrix according to load
What are the types of connective tissue ?
- connective tissue proper
- cartilage
- bone
What are the different types of connective tissue proper ?
There are 5-6 different types -
1) loose connective tissue
2) dense fibrous connective tissue
• regular
• irregular
3) adipose tissue
• white - storage fat
• brown - also storage fat but can’t turn the stored fat into ATP
4) reticular connective tissue
5) pigmented connective tissue - found in sclera of eye
6) blood
What are the different cells of the loose connective tissue ?
Resident cells :
- fibroblasts
- fat cells
- mast cells
- endothelial cells
Immigrant cells :
- monocytes (in blood) > macrophages (outside of blood)
- lymphocytes > plasma cells
Summarise the role of fibroblasts
- make the ECM
- it is not possible to tell the difference between active and inactive fibroblasts
Summarise the role of fat cells
Used for storage, cushioning and space filling
Summarise the role of mast cells
They contain secretory vesicles (granules) which contain histamine and heparin
Describe the dense fibrous connective tissue
The matrix is dominated by collagen fibres
They can highly organised - regular e.g. tendons and ligaments
They can be random - irregular e.g. the dermis
What is the role of reticular connective tissue ?
It is used for the network and organisation of cells
What is cartilage ?
A skeletal connective tissue
It is avascular and aneural
What are the 3 types of cartilage ?
- hyaline cartilage
- fibrocartilage
- elastic cartilage
Summarise hyaline cartilage
- it occurs on the surface of all joints except the TMJ and in the foetal skeleton and tracheal rings
- it has an outer fibrous layer known as perichondrium
- the cells within it are known as chondrocytes and they sit within a hole known as a lacuna
Summarise fibrocartilage
- It is an intermediate between hyaline cartilage and dense fibrous connective tissue
- It has a high glycosaminoglycan content
- The TMJ is made of fibrocartilage
Summarise elastic cartilage
It is similar to the hyaline cartilage but with lots of elastic fibres in the matrix
E.g. pinna of the ear
What is bone ?
- Bone is a type of connective tissue made of osteocytes which are embedded in calcified matrix
- It is used for support, movement and protection
- 2/3 is inorganic and made of calcium hydroxyapatite
- 1/3 is organic and is made up of 90% collagen and 10% other
Describe the different bone cells and their roles
- osteocytes are derived from osteoblasts and they are the cells that make up the bone
- osteoblasts sit on top of the surface of the bone and make new bone
- osteoclasts remove bone
Why does the skin have irregular dense fibrous connective tissue ?
It provides tension resistance
Why do tendons and ligaments have regular dense fibrous connective tissue ?
High tensile strength is needed to transfer muscle contraction force
Describe the structure of bone
- compact on the outside and spongy in the middle
- contains bone marrow
- highly vascular and innervated
