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Lecture 4

BIOB33 - Lecture 4.doc

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University of Toronto Scarborough
Biological Sciences
Connie Soros

BIOB33 – Lecture 4 Prof’s Speech - Purple Textbook Material - Orange Foundations: Connective Tissues (Chapter 3) NEURULATION - process of nervous system formation from ectoderm Neurulation starts with signals sent out by NOTOCHORD: Notochord – extends down the midline from the mesoderm - Derived from mesoderm - short rod of condensed mesoderm cells right underneath PS, induces (process of induction) cells of the ectoderm to form a hollow nervous system tube - neurulation - signaling device to cells in the ectoderm: releases bone hormones and other hormones that act on cells in the ectoderm which stimulates the area of the ectoderm above the notochord to become the CNS - during third week ectoderm forms thickened layer called NEURAL PLATE (cells proliferate and become columnar and taller) - the ectoderm starts to thicken in its center and buckle into the neural groove - by the end of the third week lateral edges elevate to form NEURAL GROOVE - the neural groove folds approach each other gradually in the middle and fuse to form the NEURAL TUBE - the 2 sides come together eventually at the top, forming the neural tube, the ectodermal layer grows over the tube and completely closes it - eventually the NEURAL TUBE runs the length of the embryo note: Spinabifida is the failure of the tube to close, skin (ectoderm) doesn’t grow over the neural tube and it is exposed to the environment Mesoderm subdivides into: 1. notochord - basis for central body axis and axial skeleton, induction of neural tube 2. paraxial mesoderm - on both sides of neural tube forms SOMITES, block-like masses responsible for formation of most bone, muscle, cartilage, dermis and connective tissues 3. intermediate mesoderm - forms most of urinary and reproductive systems 4. lateral plate mesoderm - cardiovascular system, lining of body cavities and all connective tissue components of limbs 5. head mesenchyme - connective tissue and musculature of face Endoderm - inner-most tissue after embryonic folding - forms lining of digestive, respiratory and urinary tracts, thyroid gland, parathyroid gland, thymus, liver, gallbladder and pancreas Connective Tissues Tissues that connect or form structures Most diverse, abundant, widely distributed and microscopically variable Most abundant in the body All derived from mesoderm Examples: bone, cartilage, blood, connective tissue proper – ligament, tendon, fibrous tissue, loose connective tissue, dense connective tissue, fat, spongy bone, unorganized tissue Functions of Connective Tissue • Physical protection – bones of cranium, sternum, vertebral column, thoracic cavity, fat surrounding organs • Support and structural framework of the body – bones provide framework and support soft tissues; cartilage supports body structures such as trachea, bronchi, nose and ears; sheets of connective tissue form capsules to support such organs as spleen and kidneys • Skeleton = muscle framework  For any movement in the skeleton, muscles have to be moving over a joint to facilitate the movement • Transporting fluid and dissolved materials – blood carries nutrients, gases, hormones, wastes and blood cells between different regions of the body • Connecting other tissues – ligaments bind bone to bone; tendons bind muscle to bone; dense irregular tissue (fascia) binds skin to underlying muscle and bone • Storing energy – fat is major energy reserve in the body, bones are a large reservoir for calcium and phosphorus • Immune protection – much connective tissue contains white blood cells (leukocytes) which protect the body against disease and mount an immune response against foreign material; the viscous nature of the extracellular matrix interferes with the movement and spread of disease causing organisms - Leuco = white - <1% of blood volume is made up of white blood cells - Only white blood cells are involved in immune protection - Half of blood volume is the plasma - Trachea – always open, all the time - The way you chew is as individual as fingerprints - The tongue is very involved in chewing - We subconsciously know when to swallow - The trachea, nose, ears – made of cartilage, which has some elasticity to it Elements of Connective Tissues • Cells spaced far apart (unlike epithelium) • Lots of extracellular matrix (ECM) between cells  Matrix is the collective term for the extracellular component of any connective tissue that is made of protein fibers and the ground substance  ECM is secreted from cells of connective tissue by proteins in fibrous tissues called fibroblasts  ECM – not made up of cells, made of fluid and other components • Most connective tissue is like make jello with fruit inside, + raw spaghetti (fibres) TERMINOLOGY - ______cyte – a generic cell type (eg. osteocyte in bone, adipocyte in fat) -_______blast – produces something,lays down some foundation (eg. osteoblast is a cell that lays down (makes) bone matrix, fibroblasts in connective tissue proper) -______clast – reabsorbs/breaks down something (eg. osteoclast breaks down bone)  ECM composed of: o Ground substances – sugary water and protein and carbohydrate molecules (gelatin-like), proteins help to keep water in o Fibers:  COLLAGEN – for tensile strength and stretch resistant • Strongest and largest, not elastic  ELASTIC –which are flexible and resistant • Finer, not as strong as collagen fibers  RETICULAR – which form an interwoven network • Interwoven network gives it strength Classification of Connective Tissues: based on type of extracellular matrix: • Connective tissue proper - has a matrix of fibers (loose and dense) in a syrupy ground substance (kind of like “jello” with fruit in it • Different types have different numbers of cell types and different relative proportions of fibers and ground substance (examples include: adipose (fat), ligaments, tendons) • Actually connects things • Different types are based on the arrangement of the fibers within • Dense-regular tissue: fibers are lined up in an organized way • (also dense-irregular and irregular elastic) • Fluid connective tissue - has a matrix of watery liquid than contains dissolved proteins (examples are: blood and lymph) • Doesn’t really connect anything • Supporting connective tissue - has a matrix consisting of a gel (densely packed fibers), cartilage or a solid (matrix is calcified of mineral deposits of predominantly calcium) bone are the two types of supporting connective tissue - Bone = strongest, cartilage = not as strong, but elasticity allows for more movement Connective Tissue Proper • In connective tissue proper, there are fixed and wandering cells • Fixed cells stay in one place, wandering cells move around within the tissue • Types with Loose fibers: Areolar tissue,Adipose tissue, Reticular tissue • Types with Dense fibers: Dense regular, Dense irregular, Elastic Different Types of Connective Tissue Proper contain various types of FIXED and WANDERING cells Fixed Cells: Fibroblasts – produce connective tissue fibers Fibrocytes – maintain connective tissue fibers and matrix Fixed macrophages – phagocytize pathogens and damaged cells; gets rid of anything that shouldn’t be there Adipocytes – store lipid reserves Mesenchymal cells – connective tissue stem cells that can differentiate into other cell types Melanocytes – synthesize melanin Wandering Cells: Free Macrophages – mobile/travelling phagocytic cells (derived from monocytes of the blood) - Decomposes anything unusual Mast Cells – stimulate local inflammation Lymphocytes – white blood cells, participate in immune response – can develop into plasmocytes which produce antibodies (proteins involved in defending the body against disease) Neutrophils and Eosinophils (white blood cells) – small phagocytic blood cells that mobilize during infection or tissue injury Loose Connective Tissue – unorganized tissue with a lot of matrix • Areolar Tissue • Most common, usually right beneath the membrane • Location - deep to the dermis, covered by epithelial lining, between muscles, around blood vessels, nerves and around joints • Forms the hypodermis • Function - connects skin to muscle, cushions organs, provides support but with movement • Matrix – abundant collagen fibers, thin irregularly arranged elastic fibers, small fibroblast cells, adipocyte (fat) cells and abundant gel-like ground substance - Collagen fibers make the matrix strong • Adipose Tissue • Fat • Location – hypodermis, buttocks, breasts, around eyes, surrounds organs • Function – provides padding and cushions shocks, insulates and stores energy • Matrix – predominantly adipocytes, inside each cell is drop of fat surrounded by plasma membrane, pushed nucleus and organelles to the side, absence of fibers, little ground substance - Each cell is one big drop of fat • Reticular Tissue • Reticular tissue is strong but not rigid • Tissue is soft and fibrous • Location - liver, spleen, kidney, lymph nodes, tonsils, appendix, bone marrow • Function - supporting framework • Matrix – predominantly reticular fibers and fibrocytes - The matrix is predominantly fibers with some fibrocytes Dense Connective Tissue • Dense Regular Connective Tissue • The collagen fibers are packed tightly and aligned parallel to applied force (like a group of cables), able to withstand stress in ONE direction, almost no ground substance and fibroblast nuclei are squeezed between layers of fibers • Very little matrix is in between • Mostly strong collagen fibers • Fibrocytes are found in between fibers • Strong in the direction that i
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