Connective Tissue Flashcards
What are the 4 basic types of tissue?
Epithelial
Muscle
Nerve
Connective
What e=are some examples of specialised connective tissue?
Adipose Lymphatic Blood Haemopoietic Cartilage Bone
What are the functions of connective tissue?
- Connects cells to form tissues, connects tissues to form organs and connects organs to form the body. Some tissues provide support as well as connecting (cartilage and bone)
- Transportation - provide a medium for diffusion of nutrients and wastes
- Protection - provide a cushion between tissues and organs and
provides insulation (adipose tissue) - Storage (adipose tissue)
- Defence against infection (blood, lymph, fixed and wandering cells)
- Wound healing (macrophages, fibroblasts, myofibroblasts)
What is CT proper?
General connective tissue - loose and dense
What components does CT proper comprise?
Cells
Fibres
Ground substance
What types of fibres are found in connective tissue and what are their properties?
Collagen – Flexible with high tensile strength
Reticular (also collagen) – Provide a supporting framework/sponge
Elastin – Allows tissues to recoil after stretch or distension (elasticity is the ability to recoil to original size)
What is ground substance?
Ground substance is a viscous, clear substance with a slippery feel. It has a high water content. Composed of proteoglycans
What is a proteoglycan?
A proteoglycan is a large macromolecule consisting of a core protein to which glycosaminoglycans are covalently bound
What is a glysaminoglycan?
Glycosaminoglycans (GAGs) are long-chained polysaccharides. GAGs attract water to form a hydrated gel that permits rapid diffusion but also resists compression.
What is hyaluronic acid?
A unique GAG is hyaluronic acid that is
bound to proteoglycans by a link protein to form giant hydrophilic macromolecules. It is present in the ground substance of cartilage.
The swelling pressure or turgor that occurs in cartilage ground
substance allows it to resist compression without inhibiting flexibility
What is the extracellular matrix?
A term used to describe a complex extracellular structural network that consists of ground substance and fibres
Ground substance made of starch and proteins
GAGS on proteoglycans
Fibres support ground substance
What are the differences in loose and dense connective tissue in terms of cells, fibres and ground substance?
Loose – Many cells – Sparse collagen fibres – Abundant ground substance – Viscous, gel-like consistency – Important role in transport (by diffusion)
Dense
– Few cells, nearly all fibroblasts
– Many collagen fibres
– Little ground substance
Where is loose connective tissue found and why?
Located beneath epithelia (to facilitate diffusion)
Associated with epithelium of glands
Located around small blood vessels
All of the above are sites where pathogens, such as bacteria that have breached an epithelial surface, can be challenged and destroyed by the cells of the immune system. During these reactions, loose connective tissue can undergo considerable swelling
What are the 2 types of dense connective tissue?
Regular and irregular
Describe dense regular connective tissue and where it is found
– Collagen fibres are arranged in parallel bundles and are densely packed. Between the bundles are fibroblasts
– Designed to withstand stress in a single direction
– Seen in tendons, ligaments and aponeuroses
Describe dense irregular connective tissue and where it is found
- Collagen fibres are arranged in bundles orientated in various directions. Between the bundles are fibroblasts
– Designed to withstand stress in multiple directions
– Examples are submucosa of intestine and deep layers of dermis
What are tendons?
A cord of strong fibrous collagen tissue which connects muscle to bone
What type of connective tissue composes tendons?
In tendons that connect muscles to bones the collagen bundles lie in a parallel, densely packed formation in line with the tensile force exerted by the muscle.
Define ligament
A short band of tough, flexible fibrous connective tissue which connects bone to bone
Describe the composition of ligaments
The collagen bundles are densely packed in parallel arrangement, but undulate and are arranged in fascicles, separated by loose connective tissue.
What is an aponeurosis?
Means a flat sheet of regular CT with bundles of fibres in one layer often arranged at 900 angle to those in adjacent layers
What is the dermis?
The dermis is a dense irregular connective tissue located deep to the epidermis
Describe the composition of the dermis
The bundles of collagen are densely packed but irregularly arranged, such that they are orientated in multiple directions.
The skin can thus resist forces in multiple directions to prevent tearing.
The elastic fibres allow a degree of stretch and a restoration to the original shape after the skin is bent or folded.
What are the fixed cells in connective tissue?
Fibroblasts Adipocytes Melanocytes Mast cells Macrophages Mesenchymal stem cells
What are the wandering cells of connective tissue?
Basophils Leucocytes Eosinophils Monocytes Plasma cells
What are fibroblasts and what is their function?
Cells which synthesise and secrete both ground substance and the fibres that lie within the ground substance
They are very important in wound healing and are the cells
primarily responsible for the formation of scar tissue
What are myofibroblasts
Modified fibroblasts that contain actin. They
are responsible for wound contraction when tissue loss has occurred
What are macrophages and what are they derived from?
Macrophages are phagocytic and can degrade foreign organisms and cell debris
Macrophages are ‘professional antigen presenting cells’ (i.e. they can present foreign material to the T lymphocytes of the immune system)
Macrophages are derived from blood monocytes which move into loose connective tissue, especially when there is local inflammation
What are mast cells?
Cells filled with granules
These granules contain:
Histamine (increases blood vessel wall permeability)
Heparin (an anticoagulant)
Substances that attract eosinophils and neutrophils
Look like basophils but are not derived from them
When and why are substances released from mast cells?
Mast cells become coated with Immunoglobulin E (IgE), molecules which specifically bind allergens. When an allergen cross-links these surface-bound IgE molecules, the contents of the granules are all rapidly released from the cell.
The secretions of the granules can result in immediate hypersensitivity reactions, allergy and anaphylaxis.
What is the most common protein in the body and how much of the body’s protein content does it constitute?
Collagen, between 1/3 and 1/4
How many types of collagen are there?
At least 28
Describe collagen type I, II, III and IV
Type I: The most widely distributed type (90% of all collagen). Fibrils aggregate into fibres and fibre bundles (e.g. in tendons, capsules of organs and skin dermis)
Type II: Fibrils do not form fibres (present in hyaline and elastic cartilage)
Type III: Fibrils form fibres around muscle and nerve cells and within lymphatic tissues and organs. It is called reticulin
Type IV: Unique form present in basal lamina of basement membrane
Describe collagen fibril production
Fibroblasts secrete procollagen that is converted to collagen molecules outside the cell. The collagen molecules are then aggregated to form the final collagen fibrils
In some tissues fibrils group together to form collagen fibres
Deficiency of (what) leads to scurvy and why?
Vitamin C deficiency leads to scurvy which include poor wound healing and impaired bone formation
Note that Vitamin C is required for the intracellular production of procollagen.
What is osteogenesis imperfecta a result of?
Abnormal type 1 collagen
Describe reticular fibres in a lymph node
Reticular fibres (reticulin) consist of Collagen type III.
Reticular fibres form an irregular anastomosing network throughout the node.
Lymphocytes are densely packed in the spaces between the fibres
Describe elastic fibres
Elastin is the primary component of elastic fibres, but itself enfolds and is surrounded by microfibrils called fibrillin
It occurs in most connective tissues but to widely varying degrees
Amongst the sites at which elastic fibres have an important role are the dermis, artery walls, lungs and those sites bearing elastic cartilage
What is Marfan’s syndrome and what is the cause?
Marfan’s syndrome is an autosomal dominant disorder in which expression of the fibrillin gene is abnormal such that elastic tissue is abnormal. Sufferers are abnormally tall, exhibit arachnodactyly, have frequent joint dislocation and can be at risk of catastrophic aortic rupture.
What are the 3 layers of a blood vessel?
Tunica intima (endothelial cells) Tunica media (elastin lamellae) Tunica adventitia (collagen)
Describe white adipose tissue cells
Most adipose tissue in the body is white fat.
In typical H & E stained, wax-embedded preparations, the cells look empty. They are empty because the toluene and xylene, used in tissue preparation, have dissolved away the lipid.
Adipose tissue contains fat, a fuel reserve, but also has a role in thermal insulation and in shock- absorbtion.
Describe adipose cells
Unilocular adipose cells (fat cells) are almost completely filled by a single fat droplet.
The cytoplasm is displaced to the rim of the cell and the nucleus to one side.
Describe brown adipose tissue cells. Why are the brown in colour?
Brown fat cells (multilocular adipose cells) each contain many lipid droplets and a central nucleus
The brown colour is due to the rich vascular supply and abundant mitochondria. There is thus a high respiratory capacity for the generation of heat
Where are brown adipose cells found?
These cells are found close to the scapula, sternum and axillae, especially in the newborn. They are also present in the upper chest and neck of adults
