connective tissue Flashcards
functions of connective tissue:
transport- blood.
defence- immune cells move through blood. also connective tissue provides a medium for immune cells to get inside a tissue or organ too take on an infection.
mechanics- connective tissue confers the mechanical properties a tissue needs to perform. bone- hard, cartilage- softer, adipose- really soft, blood- liquid.
energy store- adipose (fat) is a connective tissue- mechanical resistance and protection + energy store.
connecting/linking- provides joining of anatomical structures together and ensuring they stay where they need to be in the body.
extracellular matrix:
connective tissue is the structural framework which holds tissues together. extracellular matrix keeps tissue in place.
ECM is made of-
proteins- the proteins of ECM provide the scaffolding material and tensile strength.
carbohydrates- large sugar molecules called glycosaminoglycans associate with water and form a gel which resists compressive forces. glycosaminoglycans and proteins often interact in ECM to form large branched structures called proteoglycans.
water- in addition to contributing to the mechanical properties of the tissue provides a soluble signalling medium.
ground substance:
the space occupied by the glycosaminoglycan/proteoglycan/water component of ECM is called ground substance. it appears as transparent space in histological sections as it does not survive the harsh processing of fixation and embedding. its properties can vary depending on the tissue that it is found. for example, blood- completely liquid (in blood the ground substance is plasma). cartilage- spongy, gel like, shock absorbing.
resident or wandering:
cells of connective tissue can either be-
resident- cells which are permanently based inside the connective tissue and generally produce the matrix that forms it eg fibroblasts
wandering/migratory/transient- cells move through connective tissue to fulfil a role within it, or on their way to somewhere else eg neutrophil, lymphocytes.
the fibroblast:
fibroblasts are the ultimate connective tissue cell. secrete a wide range of fibres and ground substance. collagen producing machines, secrete large amounts of tropocollagen. very important in wound healing and tissue regeneration; matrix reconstruction after injury. often spindle shaped/elongated, but due to the dynamic nature of these cells and their roles in different tissues, they can appear a diverse range of shapes.
fibre component:
the fibre component of connective tissue is largely made up of 3 types- collagen fibres, elastic fibres and reticular fibres.
collagen:
the most abundant protein in mammals. 25% of all protein in the body is collagen. it helps resist tensile stress (being pulled apart). fibroblast cells produce collagen. collagen is produced inside cells although secreted before final production is finished. leaves the cell in a precursor form called tropocollagen. the polymerises outside of the cell to form mature collagen fibrils. synthesis in this way prevents cells becoming filled with huge mature collagen molecules.
collagen assembly:
- hydroxylation of pro and lys residues; assembly of triple helix in endoplasmic reticulum.
- packaging in golgi secretion/
- cleavage of N- and C- terminal non helical segments.
- cross linking at lysine and hydroxylysine residues and assembly into fibrils.
- aggregation of fibrils into collagen fibres.
elasticity and flexibility:
collagen fibres give the ECM great tensile strength but are not well suited to elasticity and flexibility by some tissues- lung, heart and arteries.
elastic fibres:
formed in fibroblasts as tropoelastin. once secreted it polymerises, and x links are formed. composed of a fibrillin plus elastin. fibres may be branched (skin, lungs) or form sheets (arteries). elastic fibres are the association between the elastin protein and microfibrils of the protein fibrillin.
reticular fibres:
a type of fine collagen- type III collagen. they form a meshwork structure called reticulin. meshwork structure is random. fibres are around 2um in diameter, which are made up by several fibrils 20-40nm in diameter
types of connective tissue:
connective tissue can be classified into different types based on proportion of cells, ground substance and fibres in addition to the conformation of fibres.
dense connective tissue contains a relatively high proportion of fibres and smaller amounts of ground substance.
loose connective tissue contains a higher proportion of ground substance and smaller proportion of fibres.
dense regular connective tissue fibres are aligned relative to one another. dense connective tissue can be described as dense regular connective tissue. fibres are aligned relative to one another. dense connective tissue can also be described as dense irregular connective tissue- no obvious orientation exists.
loose connective tissue:
loose connective tissue can be further broken down into 3 types- areolar, adipose and reticular connective tissue.
areolar connective tissue:
the most abundant connective tissue in the body. a mixture of fibre types (collagen generally predominates). no easily identifiable structure or conformation. fibroblasts are the predominant cell type. substances can move easily from cell to cell and from the blood vessels. found throughout the body, common beneath epithelial layers and surrounding blood vessels.
adipose connective tissue:
contains a particular type of connective tissue cell called adipocytes (fat stores). may appear fairly homogenous or may be interspersed in other tissue such as muscle. adipose is the bodys main energy store. provides a layer of insulation and acts to protect internal structures within the body from external impacts.
reticular connective tissue:
similar in appearance to areolar connective tissue. made up of short, branched collagen fibres composed of type III collagen. found in lymphoid tissues such as lymph nodes, thymus, tonsils, spleen, bone marrow and liver. difficult to visualise with conventional histological stains, so special techniques are used. the technique is called silver impregnation, which through a series of chemical reactions causes the fibres to interact with silver ions, giving them a black appearance- gomorris technique.
dense regular connective tissue:
extremely strong. most of the tissue is occupied by fibres. fewer cells than loose connective tissue. fewer types of cells, with fibroblasts predominating. the direction of the fibre alignment of collagen fibres is typically parallel to the direction of force which is placed upon it. great at resisting tensile strength in 1 direction. common tendons and ligaments.
dense irregular connective tissue:
also very strong. found where resistance to tensile strength is required but may not be applied from a single direction. like regular dense connective tissue fibroblasts are the predominating cell. contains densely packed collagen fibres that are randomly aligned to form a meshwork. common in the lower layers of skin (dermis).
specialised connective tissue- cartilage:
atypical connective tissue as it is avascular (does not contain any blood vessels). not very good at repairing itself. the resident cells within cartilage are called chondrocytes. typically chondrocytes produce type II collagen. cartilage is often coated in a film of dense irregular connective tissue called perichondrium.
hyaline cartilage:
colourless transparent. often found in joints where it protects from bone on bone friction. when present on articulating surfaces on bone like joints, it is referred to as articular cartilage. found on other places including the trachea, nose, larynx and between the ribs and sternum. chondrocytes produce collagen and ground substance. collagen fibres are thin and have similar optical properties to the ground substance, so are difficult to resolve light microscopy.
chondrocyte cells live in spaces within the cartilage called lacunae.
relatively abundance of glycosaminoglycans in hyaline cartilage matrix gives it its slippery properties.
elastic cartilage:
contains some collagen but also an abundance of elastic fibres. the tissue has the ability to withstand repeated deformation and return to its original shape. like hyaline cartilage, the resident cells are chondrocytes. found in the tissue which forms the lobe of the ear, and also the epiglottis.
fibrocartilage:
toughest types of cartilage. useful at resisting compressive forces. found in the intervertebral disk. contains densely packed collagen fibres which may include type 1. an intermediate between dense connective tissue and cartilage and can be difficult to distinguish. chondrocytes may be spotted in distinct rows, they are also characteristically round and still occur in lacunae. lots of collagen.
bone:
bones themselves are organs containing bone tissue and other structures such as blood vessels, nerves and marrow. there are 2 types of bone tissue. cortical bone tissue- hard, compact exterior of bone. cancellous/trabecular bone tissue- spongy, porous interior of bone.
the cells which produce bones are called osteoblasts.
epiphysis:
the round end section of a long bone is called the epiphysis. the long section between the epiphysis is called the diaphysis. bone is lined on the outside by a layer of dense irregular connective tissue called periosteum. osteoblasts produce type 1 collagen. about 70% of bone by weight is hydroxyapatite. they also produce a calcium phosphate containing mineral called hydroxyapatite. this precipitates onto the collagen matrix to give it its strength.
cortical bone:
also referred to as compact bone. makes up about 75% weight of the skeleton, it is made up of smaller subunits of bone called osteons. an osteon is a series of concentric rings of calcified extracellular matrix containing cells called osteocytes. through the middle of each osteon runs a canal called the haversian canal. the haversian canal contains the bones blood and nerve supply. like cartilage, the pockets in tissue in which the osteocytes live are called lacunae.
trabecular bone:
also referred to as cancellous bone. the lattice work series of rods which form the architecture of this sort of bone called trabeculae. trabeculae give the interior of bone a very high surface area. much greater vascularity than compact bone. houses the bone marrow, which is the main source of blood cell formation in the body. greater porosity than cortical bone (porosity between 50-90%). makes up about 20% of the total bone weight of an adult human.
blood:
blood connects different areas of the body chemically and physically via circulation.
muscle tissue:
3 types- smooth, skeletal, cardiac. the cells of muscle are called myocytes.
skeletal muscle:
voluntary. brings about movement of bones. made up of large cells with multiple nuclei. the cytoplasm (sarcoplasm) of muscle tissue contains 2 important proteins- actin and myosin, which work together in muscle contraction and relaxation. the arrangement of these proteins in skeletal muscle in repeated subunits parallel to the direction of force, gives the muscle a lined appearance (striated). the membrane of skeletal muscle cells has a specialised name too- sarcolemma. skeletal muscle cells are multilinear, nuclei are peripheral.
smooth muscle:
involuntary. under control of the autonomic nervous system. forms inside of the hollow organs such as the bladder, blood vessels and the GI tract. cells are spindle shaped and may be easily mistaken for fibroblasts in some tissue sections. it has no striations as the actin and myosin are arranged less predictably in the cell cytoplasm.
cardiac muscle:
found exclusively in the walls of the heart. striated like skeletal muscles. 1 or 2 nuclei. nuclei are central not peripheral. cells arranged in a branched, tubular structure, held together by areolar connective tissue. the cell junctions in cardiac muscle are referred to as intercalated disks which may be visible in histological sections.
