Tissue Level of Organization II PDF

TISSUE LEVEL OF ORGANISATION (II) Dr P De Gabriele MD DipWH(ICGP) MMCFD CONNECTIVE TISSUE The most abundant tissue in the body A binding and supporting tissue Highly vascular and thus has a rich blood supply. An exception is cartilage, which is avascular. Connective tissue –...

TISSUE LEVEL OF ORGANISATION (II) Dr P De Gabriele MD DipWH(ICGP) MMCFD CONNECTIVE TISSUE The most abundant tissue in the body A binding and supporting tissue Highly vascular and thus has a rich blood supply. An exception is cartilage, which is avascular. Connective tissue – does not occur on free surfaces such as the surfaces of body cavities or the external surface of the body – contains cells that are widely scattered rather than closely packed – contains considerable intercellular material called matrix. Functions of Connective Tissues Protection Support The binding together of various organs The cells of the Connective Tissue These produce the intercellular substance that largely determines the tissue’s qualities. – It is nonliving. – It may consist of Fluid Semifluid Mucoid Fibrous material They store fat. They ingest bacteria and cell debris. They form anticoagulants. They give rise to antibodies that protect against disease. CONNECTIVE TISSUE EMBRYONIC CONNECTIVE TISSUE – Mesenchyme – Mucous connective tissue ADULT CONNECTIVE TISSUE A. Connective tissue proper 1. Loose (areolar) connective tissue 2. Adipose tissue 3. Dense (collagenous) connective tissue 4. Elastic connective tissue 5. Reticular connective tissue B. Cartilage 1. Hyaline cartilage 2. Fibrocartilage 3. Elastic cartilage C. Osseous (bone) tissue D. Vascular (blood) tissue EMBRYONIC CONNECTIVE TISSUE This is connective tissue that is present primarily in the embryo or foetus. – Embryo refers to a developing human from fertilisation through the first two months of pregnancy. – Foetus refers to a developing human from the third month of pregnancy to birth. Mesenchyme Mucous Connective Tissue (Wharton’s Jelly) Mesenchyme Exclusively found in the embryo The tissue from which all other connective tissues eventually arise It is found – beneath the skin – along the developing bones of the embryo In blood vessels, the mesenchymal cells differentiate into fibroblasts Mesenchyme Consists of highly branched mesenchymal cells Embedded in a fluid substance. Mucous Connective Tissue (Wharton’s jelly) Another kind of embryonic connective tissue Found primarily in the foetus Located in the umbilical cord of the foetus where it supports the wall of the cord. Mucous Connective Tissue (Wharton’s jelly) Consists of flattened or spindle-shaped cells Embedded in a mucus-like substance containing fine collagenous fibres ADULT CONNECTIVE TISSUE Present in the newborn Does not change after birth A. Connective Tissue Proper This is connective tissue that has a more or less fluid intercellular material a fibroblast as the typical cell Connective Tissue Proper There are five types of such tissues: Loose (areolar) connective tissue Adipose tissue Dense (collagenous) connective tissue Elastic connective tissue Reticular connective tissue 1. LOOSE (AREOLAR) Connective Tissue One of the most widely distributed connective tissues in the body It is continuous throughout the body. It is present – in all mucous membranes – around all blood vessels and nerves – around body organs – in the papillary region of the dermis of the skin. Loose (Areolar) Connective Tissue It consists of: loosely woven fibres that are neither abundant nor arranged to prevent stretching several kinds of cells embedded in a semifluid intercellular substance. Fibres in Loose Connective Tissue Collagenous (white) fibres – They consist of the protein collagen. – Usually occur in bundles – Very tough and resistant to a pulling force – Yet somewhat flexible because they are usually wavy – Afford a great deal of strength Elastic (yellow) fibres – They consist of the protein elastin. – Freely branch and rejoin one another – Also provide strength – They have great elasticity Reticular fibres – They consist of collagen plus some glycoprotein. – Very thin fibres that branch extensively – Offer support and strength – form the stroma of many soft organs. Intercellular Substance in Loose Connective Tissue Consists of a viscous material called hyaluronic acid This facilitates the passage of nutrients from the blood vessels of the connective tissue into adjacent cells and tissues. However, its thick consistency may impede the movement of some drugs. Cells in Loose Connective Tissue Fibroblasts Macrophages Plasma cells Mast cells Melanocytes (pigment cells) Adipocytes (fat cells) Leucocytes (white blood cells) Fibroblasts Large flat cells with branching processes. These form collagenous and elastic fibres and viscous ground substance when the tissue is injured. Macrophages Irregular in form Have short branching projections They are derived from white blood cells called monocytes. They are capable of engulfing bacteria and cellular debris by phagocytosis. Plasma cells Small cells Either round or irregular They develop from a type of white blood cell called a lymphocyte (B cell). They give rise to antibodies. They provide a defensive mechanism, through immunity. They are mostly found in connective tissue of the digestive tract and the mammary glands. Mast Cells They develop from another type of white blood cell called a basophil. They form heparin, an anticoagulant that prevents blood from clotting in the vessels. They also produce – Histamine – Serotonin – chemicals that dilate small blood vessels Melanocytes (Pigment Cells) Adipocytes (Fat Cells) Adipocytes are derived from fibroblasts. They have the shape of a ‘signet ring’. The cytoplasm and the nucleus are pushed to the edge of the cell by a large droplet of fat. Leucocytes (White Blood Cells) 2. ADIPOSE TISSUE A form of loose connective tissue that contains adipocytes that specialize in fat storage. Adipose tissue is found – in the subcutaneous layer beneath the skin – around the kidneys – at the base and on the surface of the heart – in the marrow of long bones – as padding around joints – and behind the eyeball in the orbit. 3. DENSE (COLLAGENOUS) CONNECTIVE TISSUE A close packing of fibres – irregularly arranged where tensions are exerted in various directions – regularly arranged where tension is exerted in one direction Less intercellular substance than in loose connective tissue Dense Irregular Connective Tissue most fasciae the reticular dermis of the skin the periosteum of bone the perichondrium of cartilage the membrane capsules around kidneys, liver, testes and lymph nodes  Dense Regular Connective Tissue A predominance of collagenous (white) fibres arranged in bundles Fibroblasts are placed in rows between the bundles. The tissue is silvery white, tough, yet somewhat pliable. The principal component of tendons, many ligaments and aponeuroses 4. ELASTIC CONNECTIVE TISSUE This has a predominance of freely branching elastic fibres. This gives the tissue a yellow colour. This tissue can be stretched and will snap back into shape. It provides stretch and strength, allowing structures to perform their functions efficiently. Elastic connective tissue is a component of – the cartilages of the larynx – the walls of the elastic arteries – the trachea – the bronchial tubes to the lungs – the lungs themselves ELASTIC CONNECTIVE TISSUE Fibroblasts are present only in the spaces between the fibres. 5. RETICULAR CONNECTIVE TISSUE Consists of interlacing reticular fibres. It helps to form a delicate supporting stroma for many organs – the liver – the spleen – lymph nodes B. Cartilage A type of connective tissue that is capable of enduring considerably more stress than the rest of connective tissue types. However, cartilage has no blood vessels (except for the perichondrium) or nerves of its own. Cartilage consists of A dense network of collagenous fibres and elastic fibres – The collagenous fibres offer strength to cartilage. – The elastic fibres offer elasticity. The cells of mature cartilage are called chondrocytes. – They occur singly or in groups within spaces called lacunae in the intercellular substance. The matrix is made up of chondroitin sulphate, a jellylike substance. – This offers resilience that is the ability to assume its original shape after deformation. The surface of the cartilage is surrounded by irregularly arranged connective tissue called perichondrium. Types of Cartilage HYALINE CARTILAGE – The most abundant cartilage in the body. – It affords flexibility and support. FIBROCARTILAGE – It combines strength and rigidity. ELASTIC CARTILAGE – It provides strength and maintains the shape of certain organs.  Hyaline Cartilage It appears as a bluish-white, glossy, homogeneous mass. Collagenous fibres are present. The prominent chondrocytes are found in lacunae. Hyaline Cartilage It is found – at joints over the ends of long bones – at the ventral ends of ribs forming the costal cartilage – the nose, larynx, bronchi and bronchial tubes leading to the lungs Fibrocartilage The chondrocytes are scattered through many bundles of visible collagenous fibres. Fibrocartilage It is found at – the symphysis pubis – in the intervertebral discs between vertebrae – in the menisci of the knee Elastic Cartilage The chondrocytes are located in a threadlike network of elastic fibres. Elastic Cartilage It is found in – the epiglottis of the larynx – the external part of the ear (the pinna) – the auditory (Eustachian) tubes C. OSSEOUS TISSUE (BONE) Osseous tissue, together with cartilage, forms the skeletal system of the body. The basic unit of compact bone is the osteon (Haversian system).  The Osteon Lamellae – concentric rings of hard, intercellular substance Lacunae – small spaces between lamellae that contain osteocytes Canaliculi – radiating minute canals that provide numerous routes so that nutrients can reach the osteocytes and wastes can be removed from them Central (Haversian) canal – contains blood vessels and nerves Bone consists of Widely separated cells – Mature bone cells are called osteocytes. Abundant intercellular substance that consists of – Mineral salts – calcium phosphate and calcium carbonate that offer the hardness to bone Collagenous fibres