Connective Tissue Flashcards
What is generally meant by the term ‘connective tissue’?
Connective tissue is a form of tissue which forms a large continuum throughout the body, composed of cells, fibres and ground substance, which functions to shape, structure and support other tissues and organs of the body.
Describe the basic components of a connective tissue.
Connective tissue is made up of cells such as fibroblasts, mast cells and macrophages, fibres such as elastin, collagen and collagen, and ground substance which is formed of hyaluronate proteoglycan aggregates.
Describe the composition and properties of the ground substance of connective tissue.
Ground substance consists of hyaluranate proteoglycan aggregates. Here, hyaluronic acid form polymers to which core protein attaches which, in turn, glygosaminoglycans (GAGs) can bind. The ground substance draws in water due to the negative charge of the hyaluronate in order to create a hydrated gel.
Classify the general groups of connective tissue
Embryonic - messenchymal cells (which give rise to osteoblasts, chondroblasts, fibroblasts, lipoblasts and myoblasts.
CT proper - which can be loose or dense (regular and irregular)
Specialised CT - such as blood, adipose, muscle, cartilage, bone.
Describe the structure and functional properties of collagen
Collagen describes a family of fibre types which are an important component of all connective tissue. It consists of a fibre which is made up of a number of fibrils. These fibrils and formed by single units of collagen, formed from procollagen, which itself is made up of a triple helix of alpha chains. Collagen forms a fibre which has very high tensile strength and so is a strong component of connective tissue.
In what cell, and within which organelles, is collagen synthesised?
Collagen can be synthesised by cells such as fibroblasts and smooth muscle cells. The polypeptide alpha chains are processed and constructed into tropocollagen units in the RER and are modified and packaged further in the Golgi body.
Describe the distribution and function of reticulin fibres.
Reticulin is a type III collagen which forms a mesh work of fibres within organs which suspend cells, such as the liver, lymph nodes and spleen. The fibres form a supportive mesh work which can also function as a physical filter to trap cells and pathogens.
Describe the structure, function and properties of elastic fibres.
Elastic fibres are one type of fibre present to varying extents in connective tissue. Due to their distensible nature and recoil, they are abundant in tissues such as elastic cartilage and the tunica media of elastic arteries. Such fibres are made up of elastin, which is folded and closely associated with fibrillin.
What is the cause of Marfan’s Syndrome?
Marfan’s syndrome is a genetic condition which is inherited through an autosomal dominant pattern. It is caused by a mutation in the fibrillin-1 gene, resulting in abnormal deposition of elastin and so abnormally functioning elastic fibres.
What major organs are affected by Marfan’s syndrome and what symptoms will therefore be present?
CVS - because elastin is an important component of the aortic wall, abnormal functioning of elastin here can result in aortic
aneurysms and aortic dissection.
Eye - because elastin is an important component of the ciliary zonules (part of the suspensions ligaments which attach the ciliary body to the lens) its weakening in this condition can result in lens dislocation.
MSK - people with Marfan’s typically are taller than average, with a lean structure and slender limbs. Their joints are hyper-mobile.
Describe the general structure and properties of loose connective tissue relative to dense connective tissue.
Loose connective tissue is a type of connective tissue proper which, like other types, consist of fibres, cells and ground substance. The main difference is the relative proportions of each. In loose connective tissue the amount of ground substance and cells is increased and the density of fibres is reduced. Examples of this type include the lamina propria and submucosa of the gut.
Describe the general structure and properties of dense connective tissue relative to loose connective tissue.
Dense connective tissue is a type of CT proper which consists of fibres, cells and ground substance. In dense connective tissue the fibres are more abundant and can be organised into regular or irregular patterns. Regular patterns give rise to a stronger connective tissue which can form ligaments, tendons and aponeuroses. Irregular patterns have fibres organised in multiple directions and allows some distensibility in such directions, such as in the dermis.
Describe the histological appearance of tendons, ligaments and aponeuroses.
These tissues are all examples of dense regular CT proper and consist of abundant regularly arranged collagen fibres. This conformation allows for a high tensile strength to connect muscles and bones and allow movement during contraction. Within these fibres the flattened nuclei of fibroblasts can be seen. In ligaments the fibres are organised into fascicles.
How might a fibroblast appear on electron microscopy?
A fibroblast is a highly active cell responsible to the synthesis of collagen fibres and ground substance in connective tissue. As a result on microscopy the nucleus would appear with abundant euchromatin and the cytoplasm with large amounts of rough ER. Surrounding the cell would be the collagen which has been secreted.
Macrophages are one of the cellular components of connective tissue. Describe its appearance on electron microscopy and function in tissue.
Macrophages in tissue are derived from monocytes of the blood. They have a number of functions within the tissue, including phagocytosis of antigen, antigen presentation, cell signalling and recruitment, signalling of fibrous repair and signalling of angiogenesis. On microscopy they would appear with cytoplasmic projections called pseudopodia and, due to their active nature, abundant euchromatin. The cytoplasm a would appear with numerous lysosomes and phagosomes due to their function.
