S2) Connective and Adipose Tissues Flashcards
Describe 4 functions of connective tissue
- Connects cells to form tissues, connects tissues to form organs and connects organs to form the body
- Defence against infection (blood, lymph, fixed and wandering cells)
- Wound healing (macrophages, fibroblasts, myofibroblasts)
- Storage (adipose tissue)
What are the 3 components of Connective Tissue Proper?
- Cells
- Fibres
- Ground Substance
Identify and describe the 3 types of fibre in connective tissue
- Collagen – flexible with high tensile strength
- Reticular – provide a supporting framework/sponge
- Elastin – allows tissues to recoil after stretch or distension
Describe the properties of ground substance in connective tissue
- Viscous, clear substance with a high water content
- It is composed of proteoglycans
What is a proteoglycan?
A proteoglycan is a large macromolecule consisting of a core protein to which glycosaminoglycans (GAGs) are covalently bound
What is an extracellular matrix?
The extracellular matrix is the complex extracellular structural network that consists of ground substance and fibres
Distinguish between the structure of loose and dense connective tissue
- Loose:
I. Many cells
II. Sparse collagen fibres
III. Abundant ground substance
- Dense:
I. Few cells, nearly all fibroblasts
II. Many collagen fibres
III. Little ground substance
Where can loose connective tissue be found?
- Located beneath epithelia (to facilitate diffusion)
- Associated with epithelium of glands
- Located around small blood vessels
Describe the strategic location of the connective tissue
It is located at the sites where pathogens that have breached an epithelial surface and can be challenged and destroyed by the cells of the immune system
Identify two examples of loose connective tissue in the body
- Superficial layer of the dermis in the skin
- Submucosa of the colon
Describe the structure and function of dense regular connective tissue
- Structure:
I. Collagen fibres are arranged in parallel bundles and are densely packed
II. Fibroblasts are between the bundles
- Function: designed to withstand stress in a single direction
Where is dense regular connective tissue found?
- Tendons
- Ligaments
- Aponeuroses
Describe the structure and function of dense irregular connective tissue
- Structure:
I. Collagen fibres are arranged in bundles orientated in various directions
II. Fibroblasts are between the bundles
- Function: designed to withstand stress in multiple directions
Where is dense irregular connective tissue found?
- Submucosa of intestine
- Deep layers of dermis
What do tendons do?
Tendons connect muscles to bones
Describe the arrangement of connective tissue in a tendon
The collagen bundles lie in a parallel, densely packed formation in line with the tensile force exerted by the muscle
What do ligaments do?
Ligaments connect bone to bone
Describe the arrangement of connective tissue in ligaments
The collagen bundles are densely packed in parallel arrangement, but undulate and are arranged in fascicles, separated by loose connective tissue
Describe how the structure of dense irregular connective tissue in the dermis is adapted to its function
- Bundles of collagen are densely packed but irregularly arranged, so the skin can 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 (and myofibroblasts)
- Melanocytes
- Mast cells
- Macrophages
- Adipocytes
- Mesenchymal ‘stem cells’
What are the wandering immune cells in connective tissue?
- Leucocytes
- Plasma cells
- Monocytes
- Eosinophils
- Basophils
What is the role of fibroblasts?
- Fibroblasts synthesise and secrete both ground substance and the fibres that lie within the ground substance
- Important in wound healing and are the cells primarily responsible for the formation of scar tissue
What is the role of myofibroblasts?
- Myofibroblasts are modified fibroblasts that contain actin
- They are responsible for wound contraction when tissue loss has occurred.
What are macrophages and what do they do?
- Macrophages are derived from blood monocytes which move into loose connective tissue (especially during local inflammation)
- They are phagocytic and are professional antigen presenting cells
What are mast cells and what do they contain?
- Mast cells look like blood basophils but are not derived from them
- Mast cell cytoplasm contains abundant granules, containing:
I. Histamine
II. Heparin
III. Substances that attracted eosinophils and neutrophils
Describe the role of mast cells
- Mast cells become coated with IgE moleules which specifically bind to allergens and release the contents of its granules
- These secretions result in immediate hypersensitivity reactions, allergy and anaphylaxis
Differentiate between Collagen Type I - IV
- Type I: widely distributed type, fibrils aggregate into fibres and fibre bundles
- Type II: fibrils do not form fibres (hyaline and elastic cartilage)
- Type III: fibrils form fibres around muscle and nerve cells and within lymphatic tissues and organs (reticulin)
- Type IV: present in basal lamina of basement membrane
How is collagen linked to diseases such as scurvy?
- Fibroblasts secrete procollagen that is converted to collagen
- Vitamin C is required for the intracellular production of procollagen
- Vitamin C deficiency, as seen in scurvy, leads to poor wound healing and impaired bone formation
How is collagen linked to diseases such as osteogenesis imperfecta?
- Osteogenesis imperfecta is due to abnormal type 1 collagen
- It manifests as blue sclera and bone malformation
Describe the structure, location and function of elastic fibres
- Structure: primary component of elastic fibres, surrounded by microfibrils called fibrillin
- Location: occurs in most connective tissues to varying degrees
- Function: allows for distension in the dermis, artery walls & lungs
What is Marfan’s Syndrome?
- 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 are at risk of aortic rupture
Most adipose tissue in the body is white fat.
Describe the structure and function of white adipose tissue
- Structure: unilocular, cytoplasm & nucleus displaced to periphery
- Function: a fuel reserve, thermal insulation & shock absorption
Describe the structure, function and location of brown adipose tissue
- Structure: multilocular, central nucleus, rich vascular supply, abundant mitochondria
- Location: found close to the scapula, sternum and axillae
- Function: high respiratory capacity for heat generation
Brown adipose tissue allow for non-shivering thermogenesis.
This is important for which groups of organisms?
- Babies
- Hibernating animals
