YR1 Lecture 1H - Tissues I & II - Dr Morven Cameron 2019 Lecture Notes PDF

Tissues Dr. Morven Cameron [email protected] Learning objectives Appreciate the: Definition, typical forms and roles of epithelia. Basic structure and function of connective tissue. The three types of muscle tissue Basic organisation of a neuron. Variety and function of glial cells in the nervous...

Tissues Dr. Morven Cameron [email protected] Learning objectives Appreciate the: Definition, typical forms and roles of epithelia. Basic structure and function of connective tissue. The three types of muscle tissue Basic organisation of a neuron. Variety and function of glial cells in the nervous system. Textbook – Gartner & Hiatt – Color Textbook of Histology 3rd Ed, Elsevier. Tissue types Tissues are groups of similar cells and extracellular products that carry out a common function. 4 different types of tissue: – Epithelial tissue – Connective tissue – Muscle tissue – Nervous tissue Tissue types Tissues are groups of similar cells and extracellular products that carry out a common function. 4 different types of tissue: – Epithelial tissue – Connective tissue – Muscle tissue – Nervous tissue Functions of Epithelial Tissue Interface with environment, spaces within body Protection Selective transport of molecules into body Secretion (protection and lubrication) Sensory transduction (taste buds, ear hair cells). Epithelial Tissue Lines body surface and body cavities. Forms both the external and internal lining of many organs. Constitutes Composed the majority of glands. of one or more layers of closely packed cells that form a barrier between two compartments having different components. Classification of Epithelia Stratified squamous Simple squamous Stratified squamous keratinized Simple columnar Pseudostratified columnar Stratified cuboidal Transitional epithelium Polarity Polarity Apical surface (free, or top, surface) – cilia, microvilli Attachment The basal surface of an epithelium is bound to a thin basement membrane. Basement membrane Attachment Regeneration Epithelial cells have limited life span (eg cells of small intestine replaced every 4-6 days) Must be constantly replaced Simple epithelia – mature cells divide Stratified epithelia – stem cells in basal layers, cells move upwards and shed at surface Cell-cell junctions Four types: –tight junctions –adherens junctions –desmosomes –gap junctions Cell-cell junctions Four types: –tight junctions –adherens junctions –desmosomes –gap junctions Tight junctions Membrane proteins attached to actin cytoskeleton. Provide occlusion of most substances, even small molecules. Only substances that can cross the plasma membrane on both the apical and basal sides can pass. – Can be tightly controlled. Molecular Biology of the Cell. Fig 19.4 Tight junctions Membrane proteins attached to actin cytoskeleton. Provide occlusion of most substances, even small molecules. Only substances that can cross the plasma membrane on both the apical and basal sides can pass. – Can be tightly controlled. Molecular Biology of the Cell. Fig 19.4 Junctions Cell-cell junctions Four types: –tight junctions –adherens junctions –desmosomes –gap junctions Adherens junctions Form an adhesion “belt”, just below tight junctions. Involve cadherins (glycoproteins) for adhesion, coupled to actin. Stops cells from sliding in relation to each other. Molecular Biology of the Cell. Fig 19.9 Cell-cell junctions Four types: –tight junctions –adherens junctions –desmosomes –gap junctions Desmosomes Form more “permanent” attachments with intermediate fibres – type I & II – keratins. Important in tissues that are subject to mechanical forces. –Keep cells from being pulled apart. Desmosomes/hemidesmosomes Form more “permanent” attachments with intermediate fibres – type I & II – keratins. Important in tissues that are subject to mechanical forces. – Keep cells from being pulled apart. Connected with: – Cadherins – desomosomes – Integrins - hemidesmosome Cell-cell junctions Four types: –tight junctions –adherens junctions –desmosomes –gap junctions Gap junctions Mainly for cell-cell communication. Paired connexon hemichannels. Form a pore between cells, can pass substances < 500Da in size (can vary between subtypes) Tissue types Tissues are groups of similar cells and extracellular products that carry out a common function. 4 different types of tissue: – Epithelial tissue – Connective tissue – Muscle tissue – Nervous tissue Connective Tissue (CT) Most diverse, abundant, widely distributed, and microscopically variable of the tissues. Designed to support, protect, and bind organs. Binds body structures together. Flexible and sometimes elastic. All originates from the mesenchyme. Connective tissue types Basic Components of CT All CT share three basic components: –cells –protein fibres –ground substance Components of CT: Cells Connective tissue proper contains fibroblasts. Fat contains adipocytes. Cartilage contains chondrocytes. Bone contains osteocytes. Blood contains red and white blood cells – erythrocytes/leukocytes many CT’s contain white blood cells such as macrophages, which phagocytize foreign materials. Components of CT: Protein Fibres Most CT contain protein fibres throughout the tissue. Strengthen and support connective tissue. Type and abundance of fibres varies depending on function. Three basic types of protein fibers: collagen fibres (strong and stretch-resistant) elastic fibres (flexible and resilient) reticular fibres (form an interwoven framework) Fibroblasts Collagen fibres Elastic fibres Components of CT: Ground Substance Cells and the protein fibers reside within a material called ground substance. Nonliving material produced by the connective tissue cells. Primarily consists of glycosoaminoglycans (GAGs) and proteoglycans and glycoproteins. May be viscous (blood), semisolid (cartilage), or solid (bone). Glycosoaminoglycans (GAGs) Polysaccharide made of amino sugars – Negatively charged. – Attracts Na+ and K+ and so attracts water. More GAGs attract more water à more turgid structure. GAG concentration can change compressibility of a structure. Ground substance interactions Classification of Connective Tissue The connective tissue types present after birth are classified into three broad categories: – connective tissue proper – supporting connective tissue – fluid connective tissue Categories of CT proper Based on the relative proportions of cells, fibers, and ground substance Loose Areolar connective tissue around blood vessels, glands, forms lamina propria, between skin and muscle – Adipose – Reticular tissue Categories of CT proper Based on the relative proportions of cells, fibers, and ground substance Dense connective tissue – Dense regular – Dense irregular Two Broad Categories of CT proper Based on the relative proportions of cells, fibers, and ground substance Dense connective tissue – Dense regular – Dense irregular – Dense elastic Supporting Connective Tissue Cartilage and bone Form a strong, durable framework that protects and supports the soft body tissues. Extracellular matrix contains many protein fibers and a ground substance that ranges from semisolid to solid. Types of Cartilage The human body has three types of cartilage: –Hyaline cartilage –Elastic cartilage –Fibrocartilage Four Types of Bone Cells – Osteoprogenitor cells – stem cells derived from mesenchyme which produce other stem cells and osteoblasts – Osteoblasts – produce new bone, and become entrapped in the matrix they produce and secrete, they differentiate into osteocytes – Osteocytes – mature bone cells – Osteoclasts – are involved in bone resorption Fluid Connective Tissue Blood is a fluid connective tissue composed of : – erythrocytes (red blood cells) - transport oxygen and carbon dioxide between the lungs and the body tissues – leukocytes (white blood cells) - mount an immune response – platelets - involved with blood clotting Lymph – Plasma from blood – “interstitial fluid” Tissue types Tissues are groups of similar cells and extracellular products that carry out a common function. 4 different types of tissue: – Epithelial tissue – Connective tissue – Muscle tissue – Nervous tissue Muscle Tissue Responds to stimulation from the nervous system causing them to shorten. Produce voluntary and involuntary movement. Skeletal muscle - attached to bones of the skeleton and serve to produce movements or exert forces - used for locomotion, posture, breathing, eating, facial expressions etc. - activated by motorneurons - the complex of one motorneuron and the muscle fibre it innervates is termed a motor unit Cardiac muscle Cardiac muscle contractile response triggered by a rise in intracellular free calcium. shortening occurs by the relative movement of actin and myosin filaments similar to skeletal muscle. force of contraction determined by two forces: 1. initial length of cardiac muscle fibres (Frank-Starling law) 2. cardiac muscle fibres are able to develop increased force for the same initial fibre length in response to circulating adrenaline or increased activity in the sympathetic nervous system. Smooth muscle muscle of internal organs eg. gut, blood vessels, uterus. consists of sheets containing many cells linked together. -no cross striations but does contain actin and myosin filaments. - contractile proteins not arranged in sarcomeres. - each smooth muscle cells has a loose matrix of contractile proteins attached to the membrane at junctional complexes between cells. Smooth muscle smooth muscle of two types: single unit (visceral) – behaves as a syncytium connected by gap junctions. multi unit – little spontaneous activity and activated by impulses in specific nerves. both types are innervated by fibres from the autonomic nervous system. smooth muscle maintains a steady level of tension – tone, which may be increased or decreased by hormones, local factors or autonomic activity. Smooth muscle types - examples Single-unit Multi-unit - Digestive tract - Reproductive tract - Urinary bladder - Iris Cilliary muscles Arrector pili Wall of large blood vessels. - Van deferens Tissue types Tissues are groups of similar cells and extracellular products that carry out a common function. 4 different types of tissue: – Epithelial tissue – Connective tissue – Muscle tissue – Nervous tissue Nervous Tissue Consists of neurons (nerve cells), and glial cells that support, protect, and provide a framework for neurons. 1011 in human central nervous system Responsible for consciousness, self awareness, memory, emotion, planning Control muscle, viscera and glands Provide sensory input Central vs peripheral Central nervous system (CNS) – brain (including the retina), spinal cord. Peripheral nervous system (PNS) – peripheral motor neurons, sensory neurons, and enteric nervous system. Neurons Processes extend from the nerve cell body. –Dendrite –Axon Glia Support cells (glia) per neuron In CNS, astrocytes, oligodendrocytes and microglia Outside CNS (the periphery), Schwann cells and satellite cells Myelination Myelination A glial cell (oligodendrocyte or Schwann cell) wraps around axon and lays down myelin in the glial cell membrane Myelination – conduction velocities Tissue types Questions?