8. Loose and dense Connective Tissue Flashcards
What are the 6 main groups of connective tissue?
- Loose connective tissue
- Dense connective tissue
- Adipose tissue
- Blood
- Bone
- Cartilage
What are the 6 functions of connective tissues?
1) binding and supporting
2) protecting
3) insulating
4) storing reserve fuel and cells
5) transporting substances within the body
6) separation of tissues
What is the function of adipose tissue?
padding and shock absorber, insulation and energy reserve
What is the function of dense connective tissue?
helps attach muscles to bones and link bones together at joints.
What is the general function of loose connective tissue?
holds organs in place and attaches epithelial tissue to other underlying tissues.
What is the function of blood?
transport vehicle for cardiovascular system, carrying nutrients, wastes, respiratory gases and many other substances
What is the function of bone
internally supports body structures, very active tissue, heals much more rapidly than cartilage
What is the function of cartilage
dense, flexible tissue similar to bone tissue
What are the 3 components of connective tissue?
- Cells
- Fibres
- Ground substance
What makes up the extracellular matrix?
Ground substance + fibres
Where is loose connective tissue found?
under epithelial cell layers (e.g. lamina propria) and around glands, surrounds capillaries, nerves and sinusoids
What are the main cells found in loose connective tissue?
Fibroblast, macrophages, other white blood cells, mast cells and adipocytes
What are the two main fibres in loose connective tissue?
Collagen and elastic blood vessel
What is the ground substance in loose connective tissue composed of?
Proteoglycans, hyaluronic acid
What are the specific functions of loose connective tissue?
- Holds vessels that supply fluids
- Permits cell migration
- Involved in inflammation pathways
- Acts as packaging around organs
- Generally hold everything in place
- Cushions and stabilises organs
What are fibroblasts and what is their function?
- Cells that synthesise and secrete the fibres that lie within the ground substance (extracellular matrix).
- cells primarily responsible for the formation of scar tissue
- Myofibroblasts are modified fibroblasts that contain actin and myosin. They are responsible for wound contraction when tissue loss has occurred - pull the wound closed
What are the functions of macrophages?
- phagocytic and can degrade foreign organisms and cell debris
- Macrophages are ‘professional antigen presenting cells’
What are mast cells?
cells filled with basophil granules, found in numbers in connective tissue and releasing histamine and other substances during inflammatory and allergic reactions.
Which granules do mast cells contain?
- Histamine (increases blood vessel wall permeability)
- Heparin (an anticoagulant)
- Cytokines that attract eosinophils and neutrophils
Where are mast cells absent from and why?
Absent from CNS - avoid damaging effects of oedema
What happens to mats cells during an allergic reaction
Mast cells become coated with 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 - degranulation
What are adipose cells generated from?
immature fibroblasts or mesenchymal stem cells
What are the two types of adipose tissue?
- Unilocular - white adipose tissue
2. Multilocular - brown adipose tissue
How many lipid droplets are there in white adipose tissue And what is their size?
single enormous lipid droplet
Where is the nucleus and other organelles in white adipocytes?
nucleus, cytoplasm and organelles all squeezed to one side of the cell
What is the mitochondria number in white adipocytes?
• Normal number of mitochondria
What is the function of white adipose tissue?
padding and shock absorber, insulation and energy reserve
Are white adipose tissue found mainly in adults or children? And why
- In adults, found in large numbers so lipid breakdown is slow and heat only generated after shivering reflex
- Found in small number in neonates because they cannot shiver to generate heat so need brown adipose tissue that have fast lipid breakdown to generate heat
How many lipid droplets are there in brown adipose tissue And what is their size?
Multiple small lipid droplets
Where is the nucleus and other organelles found on brown adipocytes?
nucleus, cytoplasm and organelles all squeezed to the centre of the cell
What is the number of mitochondria in brown adipocytes and why?
Increased number of mitochondria - fast lipid breakdown so need more mitochondria to carry out more respiration to generate more heat
What is the unction of brown adipose tissue?
Provides insulation - by generating more heat- and energy reserve
Are brown adipose tissue found mainly in adults or children? And why
- Very few of these in adults - as they can shiver
- In neonates and young children, lipid breakdown is accelerated, oxidative phosphorylation is uncoupled to generate heat
How do you distinguish between white and brown adipose tissue in histology slide?
If the nucleus is close to the plasmalemma and the central part of the cell is either empty (as in an H&E preparation) or full of triglycerides (as in a Sudan Red preparation), indicating a single large fat droplet, then the adipose tissue is white. If there are numerous fat droplets throughout the cell and nuclei that are more central are obvious, then the adipose tissue is brown.
What are the 3 types of fibres that can be found in connective tissue?
- Collagen
- Reticulin
- Elastin
Describe collagen
Flexible with high tensile strength
What is elastin the primary component of?
elastic fibres
When is elastin laid down?
Elastin is laid down only during fetal development; not replaced in the adult
What produces elastic fibres?
•elastic fibers are produced by fibroblasts or smooth muscle cells within the walls of the vessels.
Where are the sites at which elastic fibres have an important role?
- dermis
- artery walls
- lungs
- sites bearing elastic cartilage
What are reticular fibres composed of?
type III collagen
What is the function of elastin?
allows tissues to recoil after stretch or distension
What is the function of reticulin?
provide a supporting framework
What produces reticulin?
In the lymphatic and hemopoietic tissues, reticular fibers are produced by specialized reticular cells. In most other tissues, reticular fibers are produced by fibroblasts.
What is ground substance composed of ?
Composed of proteoglycans (large macromolecules consisting of a core protein to which glycosaminoglycans are covalently bound)
What are Glycosaminoglycans (GAGs)?
long-chained polysaccharides
What do GAGs do?
- GAGs attract water to form a hydrated gel
* permits rapid diffusion but also resists compression
What is hyaluronic acid?
A unique GAG that is bound to proteoglycans by a link protein to form giant hydrophilic macromolecules- It is present in the ground substance of cartilage
Describe the structure of ground substance
- Hyaluronate is the key
- GAGs (chondroitin sulfate and keratan sulfate) are attached to the core proteins
- In turn these are attached to the hyluronate
- The sugar moieties attract water, but make the ground substance ‘sticky’ and ‘slippery’ at the same time
What are the two types of dense connective tissue?
- Irregular
* Regular
What does irregular and regular dense connective tissue both contain?
Fibroblasts and mostly contain collagen fibres
For irregular dense connective tissue, what direction are the fibres running in and how does it help with its function?
Collagen 1 fibres run in all directions so can resist stress in all direction which help with strength
How many cells are there in irregular dense connective tissue?
Cells are sparse and are typically of a single type, the fibroblast
How much ground substance is in irregular dens connective tissue?
Little ground substance
Where is irregular dens connective tissue found?
- Deep layer of the dermis
2. Submucosa of intestine
How are the fibres arranged in regular dense connective tissue and how does it aid its function?
- fibres are arranged in parallel array and are densely packed to provide maximum strength.
- resists stress in only one direction
Where are regular dense connective tissue found?
- Tendons
- Ligaments
- Aponeuroses
What is the function of tendons?
Connect muscles to bones
How does the myotendinous junction provide strength?
Skeletal muscle fibres connecting
with tendon collagen
bundles at myotendinous junctions
provides tremendous physiological
strength
• The collagen passes from the tendon to the muscle fibres where it interacts with the collagen fibres coating the muscle fibres
• Cross-links between these fibres results in mechanical strength
What is the function of ligaments?
Connect bone to bone
What are collagen bundles in ligaments arranged into?
Fascicles
What are the 3 types of fascia?
- Superficial
- Deep.
- Visceral or parietal
What is fascia made up of
fascia is made up of fibrous connective tissue containing closely packed bundles of collagen fibres oriented in a wavy pattern parallel to the direction of pull
What provides fascia its strength?
Fascia is flexible and able to resist great unidirectional tension forces until the wavy pattern of fibres has been straightened out by the pulling force
What causes scurvy?
Vitamin C is required for the intracellular production of procollagen, where it hydroxylates proline and lysine
• Without vitamin C, collagen formation is disrupted, causing a wide variety of problems throughout the body
• Vitamin C deficiency leads to scurvy, a condition that includes poor wound healing and impaired bone formation
What are the symptoms and signs of scurvy?
- Gum disease
- Bruising of the skin
- Bleeding
- Poor wound healing
How are collagen fibres formed?
- 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
What is the marfan’s syndrome?
•Autosomal dominant disorder in which expression of the fibrillin 1 gene is affected such that elastic tissue is abnormal
What are the symptoms of marfan’s syndrome?
Sufferers are abnormally tall, exhibit arachnodactyly, have frequent joint dislocation and can be at risk of catastrophic aortic rupture (90% mortality rate - aortic aneurysm)
What is Osteogenesis imperfects
• “Brittle bone disease”
• Encompasses a number of different genetic aetiologies (most
are autosomal dominant)
What causes Osteogenesis imperfects?
mutated collagen fibres that do not ‘knit together’ or not enough produced or both
What are the symptoms of Osteogenesis imperfects ?
- Weakened bones (fractures are common)
- Short stature (depends on type)
- Presence of blue sclera
- Hearing loss
- Hypermobility (loose joints) and flat or arched feet
- Poor teeth development
What are the 3 types of capillaries?
- Continuous
- Fenestrated
- Sinusoid
Describe sinusoids
Sinusoids have a discontinuous endothelium and an incomplete basement membrane. Thus permit the free exchange of water and large solutes like plasma proteins
