Dental Genetics: Inheritance, Genes & Alleles (T Hughes)

Human Biology Revision Weeks 4-6 Dental Genetics 1: Introduction to Inheritance, Genes & Alleles (T Hughes)  Karyotype- collection of all genes/chromosomes in an organism at metaphase  Genetics involves the study of biologically inherited traits, they involve the expression of the...

Human Biology Revision Weeks 4-6 Dental Genetics 1: Introduction to Inheritance, Genes & Alleles (T Hughes)  Karyotype- collection of all genes/chromosomes in an organism at metaphase  Genetics involves the study of biologically inherited traits, they involve the expression of the genotype, impacted by its environment, resulting in a presented phenotype.  The epigenome represented the impact of environment on expression of genes and ultimately expressed phenotypes  Genetics is concerned with information transfer at different levels (cellular individual, populations, generations)  Genes are organised on chromosomes  Each gene is presented in two copies (diploid)  Each copy of a gene is called an allele, one allele is received from the offspring by each parent and is responsible for the coding of proteins.  Nucleus structure: o Enucleate (Red blood cells) with no nucleus, doesn’t need to make protein o Multinucleate (muscular cells), produces significant protein o Nucleoplasm- material within the nucleus o Chromatin- DNA + associated histone proteins o Nucleoli- dark stain (basophilic, negatively charged) and produces ribosome subunits from rRNA that is exported out to the rER via nuclear envelope. Ribosomes are made in the nucleoli  Nucleus staining and appearance: o Dark staining, heterochromatin, large cell, not actively dividing = gap phase/interphase o Lighter staining, euchromatin, appearance of chromatin= actively dividing  Chromosome Structure: o Circular in prokaryotes, linear in eukaryotes o In humans present in homologous chromosomes (2 in each pair received from each parent), also contains sex chromosomes (X-females, Y-males) located on chromosome 23 o Germ cells are haploid and contain half the amount of chromosomes opposed to somatic cells o Homologous chromosomes carry genes at particular o 4 chromatids on a chromosome joined by a protein centromere (site of spindle linkage)  Centromere can be joined at different proximities along the chromosome  Metacentric- centromere in centre of 2 chromosomes  Telocentric- centromere at the end of 2 chromosomes  Acrocentric- centromere in between the end/middle of 2 chromosomes o Chromatin is DNA supercoiled around histones (8 histones make a nucleosome) in preparation for cell division  DNA + RNA Structure: o Purines: adenine + guanine o Pyrimidines: cytosine + thymine + uracil o AT= 2 hydrogen bonds, GC= 3 hydrogen bonds o Nucleotide =3’ sugar, 5’ phosphate, base. Nucleoside: sugar + base  Codons= 3 nucleotides that code for one amino acid o Redundancy arises as 2-3 codons can represent the same amino acid, enables for silent mutations where the amino acid coded for remains unchanged in a base point substitution o Wobble base: third base in codon that can vary but retains the amino acid coded for  Modes of inheritance + Pedigrees o Homozygous-dominant (AA), Homozygous recessive (aa), Heterozygous (Aa) express dominant o There can be incomplete/co-dominance (e.g. AB blood groups ) where both alleles/phenotypes are expressed  o Sex-lined inheritance: A recessive allele on chromosome X with no gene locus for the same trait on Y results in the gene being expressed (dominant) in males as they only need one copy for it to be expressed. o Simple modes of inheritance for pedigree use:  Are the parents (one or both) of affected individuals affected? (determines if its dominant or recessive driven)  If yes, then it is likely to be a dominant disease  What is the male: female ratio among affected individuals? (indicates sex-linked disease)  Are the two parents of affected individuals genetically related? (in-breeding increases the prevalence of recessive genetic disorders as homozygosity is increased)  Are there examples of affected males having affected sons? (indicates sex-linked disease)  Pedigree Symbols:  Male= square  Female= circle o When a trait is determined by more than one gene (polygenic), outcomes are more complex o Pleiotropy: one gene can cause multiple phenotypic traits e.g. Homo-box regulates various expression of genes Dental Genetics 2: The Cell Cycle (T Hughes) Pre lecture summary: The cell cycle is outlined by interphase, mitosis and cytokinesis. Interphase is the longest phase of the cell cycle taking anywhere upwards of 26 hours, mitosis is relatively shorter where the cell spends approximately 2 hours undergoing nuclear division, and cytokinesis is the shortest phase, involving the cleavage of cell cytoplasm to form two identical daughter cells. Interphase is marked by the G1 phase (8-10 hours), S phase (8 hours), and G2 phase (4-6 hours). In the G1 phase the cell in undergoing duplication of infrastructure, this results in cell enlargement and increase in volume as structures such as the mitotic spindle, organelles, cytosolic components and scaffolding is duplicated. At the end of the G1 phase there is the G1 checkpoint, checking that the cell is functional and that infrastructure has been adequately duplicated. In the S phase (s= synthesis), DNA is duplicated, this results in the number of chromosome copies doubling. In the S phase, DNA exists in as euchromatin as DNA replication occurs. In the G2 phase, there is a prominent nucleolus and significant protein/enzyme synthesis activity, the cell volume continues to enlarge as proteins are being synthesised. At the end of G2 phase there is a checkpoint called the S checkpoint to ensure that the DNA has been replicated with high fidelity. The function of mitosis is to separate chromosomes into their respective cells as they undergo nuclear division. Mitosis is characterised by metaphase, anaphase, and telophase and genetic information which is condensed into chromosomes. Replicated chromosomes consist of two sister chromatids held at the centromere. These sister chromatids are separated into different poles of the cell. The number of chromatids is initially double; however the chromosome number does not change. At the end of telophase there is the M checkpoint to ensure that each nucleus contains the correct number of chromosomes. The cell cycle is required for organism maintenance and repair, responsible for growth during developmental stages and repair at mature stages. The cell cycle is also responsible for monitoring the quality of cells, regulating which cells undergo complete division and those which demonstrate pathology/abnormalities. G1= cellular growth through organelle infrastructure duplication (8hours), S= duplication of DNA (8-10hours), G2= continued cell growth and protein synthesis (4-6hours), M= nuclear division, Cytokinesis= cytoplasm division =needed to add in interphase durations + checkpoints   Cell cycle regulation: o Surface-to-volume ratio of cells o Chemical signals such as growth factors/hormones o Contact inhibition (tissue density, lack of space) o Cyclins + cyclin-dependent kinases  G1 Phase (8-10 hours): metabolically active, duplicating infrastructure (organelles + proteins + cytosolic components), increased cell surface area/volume.  S Phase (8 hours): metabolically active as DNA replication occurs with high fidelity  G2 Phase (4-6 hours): metabolically active with high levels of protein synthesis, cell growth observed  Mitosis Phases: o Prophase: formation of mitotic spindle, rupture of nuclear envelope, condensed chromosomes o Metaphase: equatorial plane, nuclear envelope + nucleolus disappears o Anaphase: splitting and aggregation of chromatids at poles o Telophase: nuclear restitution, nuclear envelope reforms, DNA decondenses  Mathematics of Mitosis: o G1: 1 x 2n2c o S: 1 x 2n4c (2 chromosomes but 4 copies of DNA o G2: 1 x 2n4c o M: 2 x 2n2c Dental Genetics 3: Where do proteins come from? (T Hughes)  Genes are coded for through production of mRNA which is made from DNA by transcription (reading of transcribed/template DNA strand) A=T (2 hydrogen bonds) G=C (3 hydrogen bonds) o Phosphate 5’, hydroxyl at 3’ end o Transcript is manufactured 5’ to 3’ o mRNA and coding stand (non-transcribed) are identical, A swapped out for U  Basic requirements for protein synthesis: o Template strand- non-coding strand that is transcribed and complementary to coding strand o RNA polymerase- recruits free nucleotides, adding 5’3’ mRNA o Promoter- promotes gene expression and transcription, acting as the site for RNA polymerase binding  Located upstream (towards 3’ end) o Nucleotides o Helicase- breaks the two h bonds between A=T and the three h bonds between G=C  mRNA function: o Protects DNA from damage o Amplification of gene (multiple mRNA transcripts) o More possibilities for control and regulation (transcription factors, repressors, siRNA, miRNA o Can modify mRNA to introduce further variation (alternative splicing)  Alternative Splicing o Introns (non-coding) are spliced out to form mature mRNA, remaining exons can be rearranged to introduce genetic variation. Different exons cause for the formation of different domains in a protein. o Form of protein diversity and gene regulation o Allows for multiple production of multiple polypeptides from one gene, giving rise to different products o Alternative splicing results in different primary structures  Translation: Translating from nucleotides to amino acids  Requirements for Translation:  o mRNA: RNA script generated from the template (non-coding) strand of DNA that has undergone alternative splicing to generate protein diversity o tRNA: transfer RNA (sugar-phosphate backbone) that carries an anticodon and amino acid attached at the 3’ hydroxy end. Adaptor molecule that transports and positions amino acids to the ribosome o amino acyl tRNA synthetase: enzyme responsible for the addition of amino acids onto the tRNA 3’ OH end via a covalent bond (ATP required). Different synthetases are required for each amino acid o ribosomes: site of polypeptide elongation, 60s and 40s subunit in eukaryotes. Consists of A-site where tRNA binds, P-site where amino acids link to form polypeptide, E-site where tRNA leaves the ribosome to associate with another amino acid. o amino acids  Elongation of polypeptide: mRNA moves through RNA 5’  3’, proteins elongate as tRNA arrives at A-site. Elongation of amino acids and formation of covalent, high energy, peptide bonds = peptidyl transferase Tissues of the Body 1: Introduction Pre-lecture summary: Tissues are comprised of groups of cells with a specialised function, acting in unison to carry out a specific function. Collective activity is permitted through cell-cell communication facilitated by gap junctions and cellular regulation (hormones). The 4 primary types of tissue are connective, muscular, nerve and epithelial. Connective tissue is derived from the ectoderm mesoderm and is classified based on the types of cells, arrangement of fibres and relative proportion of fibres, cells (immune and builder (fibrocytes/chondrocytes/osteocytes) cells) and amorphous ground substance. Muscular tissue is derived from the ectoderm mesoderm and is defined based on its function and characteristics, grouped as either cardiac, smooth or skeletal. Muscular tissue mainly involves the contraction and relaxation of muscle fibres (myofibers). Nervous tissue is derived from the endoderm ectoderm and is involved with signalling, integration and responding via the central and peripheral nervous system. It comprises of neurons and neuroglia (satellite supporting cell). Epithelial tissue lines the internal and external surfaces of the body, surrounding organs acting as a protective barrier/insulator. Epithelial tissue is classified based on the size and layering of cells, it is derived from the ecto, meso and endoderm layers.  Morphological characteristics of: o Epithelium: function is to cover, line, and form glands. Classified based on shape of cells, number of cell layers, specialisation (polarity) at tissue surface o Connective: function is to underlie tissue and provide support. Classified based on the types of cells, arrangement of fibres, relative proportions of cells, fibres, AGS. o Muscle: function is to contract o Nervous: function is to exhibit electrical impulses, receiving, transmitting and integrating pulses  Epithelium: o Highly cellular with little intercellular material, often forms sheets o Tissue has a free surface o Cells attached to and supported by a basal lamina/basement membrane (CT provides nourishment) o Avascular o Dynamic, cells are shed and replaced at high turnover rates o Can be surface or glandular epithelium o Derived from ecto, meso, endoderm  Connective Tissue: o Highly vascular  o Wide range of cell types (blasts, cytes, immune cells) o CDPST functions, connects, compartmentalises, defends, destroys, supports, shapes o Made up of cells, fibres (collagen, elastic, reticular), AGS o Derived from mesoderm  Muscle Tissue: o Capable of contraction (thin actin slides over thick myosin) o Sub categorised into skeletal, cardiac and smooth o Elongated, multinucleated cells o CT provides blood supply o Tissue types separated by basal membrane o Derived from mesoderm (muscle= meso)  Nervous Tissue: o Neurons (axons, cell body, dendrites) + neuroglia (supportive cells in CNS) + Schwann cells (satellite cells in PNS) o Monitors and responds to maintain homeostasis o Excitable, conducive, secretory (neurotransmitters) o Derived from ectoderm (CNS is in head, uppermost organ = uppermost layer = ectoderm)  Tissue membranes: surface epithelium + loose connective tissue (defence cells) that covers surfaces of bodies, cavities or outside of organs. o 1) Cutaneous membrane (skin): stratified squamous with loose CT o 2) Epithelial membranes (mucosa): lines cavities connected to outside (more diverse epithelial cells) o 3) Epithelial membranes (serosa): lines internal body cavities (mesothelium epithelial cells) o 4) Connective tissue membranes: Synovial membrane that lines capsules of synovial joints (e.g. temporomandibular junction TMJ) and produces a lubricating/nutritive fluid Tissues of the Body 2: Epithelial Tissue- Classification Pre lecture summary: Epithelial tissues line the internal and external cavities of the body and are derived from the ectoderm, mesoderm, and endoderm of germ line cells. They are classified based on the shape (squamous, cuboidal, columnar) of the cell present and the number of layers present (simple or stratified). Pseudo- stratified refers to a single layer of cells that have their nuclei in different positions, appearing stratified (located in respiratory tract) all cells touch the basement membrane, transitional epithelium have their surface layer of cells changed in shape (located in urinary tract). Surface epithelia act to protect and form a barrier protecting underlying surfaces, they are always underlined by loose connective tissue to provide support, nourishment and defence cells if surface epithelia are broken. Surface epithelium may contain the following structures, keratin (for barrier purposes), cilia (located in the respiratory tract), microvilli (located in the GIT). Glandular epithelia refer to cells that form secretions, either through exocrine mode where secretions are released into a duct which then deposits on a cellular surface, or through endocrine mode where secretions are released into interstitial space to enter blood vessels and circulate through the body. Examples of exocrine glands include sweat and salivary glands, endocrine glands such as adrenal glands that produce hormones are located in close proximity to blood vessels. The basal lamina refers to the layer of CT that directly adjuncts epithelia cells marking the line between different tissue types. The adhesion between the basal lamina and epithelial cells is facilitated by hemidesmosomes (intermediate filaments, protein plaque) that line the basal surface of epithelial cells.  Characteristics of epithelium: o Highly cellular o Form sheets/layers  o Attached to and supported by basal lamina o Avascular o Dynamic (constantly shed and replaced) o Derived from all three embryonic germ layers o Involved in exchange, absorption, secretion, protection  Surface epithelium: protection, bi-directional exchange of materials, absorption  Glandular epithelium: secretory, form clusters of cells (acini) or line ducts  Epithelial cell biology: o Cell to cell adhesions:  Adhering junctions (adherens are made of actin filaments)  Tight junctions (located apically, made of microfilaments and form an impenetrable seal- zonular occludens)  Communicating junctions (gap junctions located laterally to allow for cell coordination and communication)  Basal lamina= boundary layer at the base of epithelium, demarking ET from CT. Induces polarity as basal lamina controls signals received by cells, resulting in specialisation/differentiation of cell structures and organelles. o 20-100nm thick o Combines with reticular lamina (formed by CT) to form basement membrane o Composed of fibrous proteins + glycans (Type 4 collagen, laminin, nidogen and perlecan secreted by epithelial cells. = Basal lamina made by ET cells o Basal lamina = made by ET o Reticular lamina= made by CT o Functions as a filter and fence  Cell structure + function: o Simple ET: absorption, secretion and transport allowing for fast movement of substances o Stratified ET: protective barrier function o More than one cell type in ET: indicates more than one function, may be secretory and absorbative  Turnover rates of epithelia: greatest turnover in GIT due to eroding/acidic conditions in the stomach, in the skin turnover is slower, and in large glands there is a very slow turnover as there is less environmental stress’  Metaplasia: transformation of one type of epithelium into another type as a result of changes in the environment/response to injury. E.g. cigarette smoke, alcohol, bacteria. Persistent presence of factor results in irreversible dysplasia. o Cigarette smoke results in the loss of cilia in the respiratory tract, transitioning from pseudostratified columnar ciliated to stratified squamous as an opportunity to minimise penetration of toxins into tissue Tissues of the Body 3: Epithelial Tissue- Specialisations  Cell surface domains: o Apical: facing the lumen o Lateral: cell contacts o Basolateral: cell contacts o Basal: attachment to basement membrane  Pathways across epithelia: o Paracellular (between the cells)- this is often inhibited by tight junctions to control selectivity of molecules that pass o Transcellular (through cell cytoplasm)- controlled by microvilli and cell membrane/proteins  Apical surface specialisations:  o Cilia: beat in unison to act as a current, moving substances on surfaces, larger, line respiratory tract alongside goblet cells, made of microtubules, (9+2 arrangement- axoneme) o Microvilli: act for absorption by increasing surface area, located in GIT, shorter and appear as a brushed border. Made of actin filaments o Stereocilia: long branched microvilli for bulk absorption made of actin filaments, appear much longer compared to microvilli and cilia. Line the epididymis (absorb fluid from sperm)  Lateral surface specialisations: Only visible in EM o Tight junctions (zonula occludens)- actin  Fusion of cell membranes, involving transmembrane proteins: Junctional adhesion molecule (JAM), occludins, claudins  Interact with actin filaments of cytoskeleton via zonula occluden proteins  Prevents paracellular movement o Spot desmosomes (macula adherens)- intermediate filaments forming a spot-like weld  Plaque proteins and intermediate filaments are used to hold cells  Lateral localised spot welds  Transmembrane cadherin proteins span intracellular space  Located in ET subjected to mechanical stress and can attach cells strongly to one another  Epidermis, oral cavity, oesophagus o Belt desmosomes (Zonula adherens)- actin o Gap junctions- formed by connexons  Forms pores allowing for movement of molecules and signals  Hydrophillic and small molecules can pass through  Junctional Complexes: ordering of lateral junctions o Tight > Modified desmosomes/zonula adherens> Desmosomes> Gap junctions  Basal surface specialisations: o Hemidesmosomes- intermediate filaments + plaque to attach ET to basement membrane  Structure binds to intermediate filaments (keratins)  Transmembrane integrins proteins bind to laminin molecules in basal lamina Tight junctions are located apically and are also referred to as zonular occludens, they interact with the cytoskeleton and zonula occludens proteins to form a water seal junction. Macula adherens desmosomes use intermediate fibres and a plaque to connect to cadherin proteins. Desmosomes are located lower laterally and use intermediate filaments to connect to cytoskeleton. Gap junctions are located basolaterally and use connexon proteins to facilitate cell communication. Hemidesmosomes use intermediate filaments that bind to the cytoskeleton via integrin proteins, the also bind to the basal lamina. Tissues of the Body 4: Epithelial Tissue- Glandular Epithelium Pre lecture summary: Secretory epithelial glands can release secretions through exocrine or endocrine secretion. Exocrine secretory glands deposit secretions into a duct/tubule that then releases the secretions onto a cell’s surface. During embryonic development, a cluster surface epithelium cells invaginate and reorganise to form a duct, deeper cells further differentiate to form secretory cells. These are classified as acinar/alveolar (round) or tubular (long duct), they can also be simple, compound (acinar + tubules) or branched (having multiple on one duct). Examples of exocrine glands are sweat glands and salivary glands located in the oral cavity. Endocrine glands are often cuboidal in shape and line a blood vessel as they release secretions into the blood stream. In embryonic development surface epithelium invaginate, connecting cells undergo apoptosis, leaving deepest cells to differentiate into secretory cells without a duct, instead secreting into a capillary. Examples include the adrenal gland. Secretions can be released through merocrine (releasing of vesicle), apocrine (releasing of cell membrane bud + cytoplasmic contents) or holocrine (bursting of cell to release contents- e.g. sebaceous gland). The timing of secretions is controlled by myoepithelial cells, these include a muscular component that lies basally to secretory cells and contract when ATP facilitates the binding of thin actin to thick myosin heads, causing a contractile sliding motion. Contraction of myoepithelial cells results in the secretory cells releasing their secretions into the lumen of a duct. Salivary glands are a type of exocrine epithelial cell that have the following cell specialisations: microvilli for absorption, mitochondria to move substances/ions against their concentration gradient, apical vesicles for secretion of salivary enzymes.  Glands are characterised based on their mode of secretion (exocrine or endocrine) they may be associated with goblet cells that aid in secretion and meeting the volume of secretions required.  Development of exocrine glands: o Surface epithelium invaginates and grow down into underlying tissue o Connecting cells deeper continue to form a duct o Even deeper cells develop to become secretory cells o Acinus (secretory cells) form a secretory unit around a duct  Development of endocrine glands: o Surface epithelium invaginates and grow down into underlying tissue o Connecting cells disappear o Deepest cells remain to secrete into capillaries  Secretory Acinus/Alveolus Units: o Pyramidal in shape, broad base close to CT, narrow apex near lumen o May be lined with myoepithelial cells o Can secrete mucous secretions or serous secretions o Basophilic (purple stain) along base location of negatively charged nucleic acids + ribosomes o Acidophilic (pink stain) towards apex, stain of apical secretory granules  Mucous Acini: o Secrete mucous (thick, clear, basophilic) o Well-developed Golgi bodies o Secretory granules are larger and are negatively charged o Pyramidal shape o Pale purple stain  Serous Acini: o Secrete serosa (more granular) o Pyramidal shape o More busy cell components and stain purple o Nucleus more prominent  Secretory tubule units: o Single layer of cuboidal or columnar cells that deposit into a duct  Methods of secretion: o Merocrine/Eccrine: only the secretion is released from the cell into a duct. E.g. pancreas o Apocrine: secretion + some cytoplasm is lost. E.g. sweat glands o Holocrine: cell undergoes degeneration and secretes all contents. E.g. sebaceous glands  Myoepithelial Cells o Epithelia cell with muscle-like contractile properties o Located around the outside of secretory cells and have processes that can extend between individual acinar cells o Control timing of secretion release when stimulated by hormones/nervous system o Located on mammary, sweat glands  Structure of Salivary glands (Compound acinar glands = lobule) o Large quantity of acini that require blood and nerve supply to controls secretion release o Connective tissue supports secretory acini cells and surround lobules. A CT capsule surrounds the gland, CT septum separates lobes of acini Tissues of the Body 5+6: Connective Tissue- Fibres + AGS Pre lecture summary: Connective tissue is derived from the mesoderm and has various functions related to nourishment, support, defence, framework, transportation and structure. The various cells present in CT include white blood cells (leukocytes, neutrophils, macrophages, mast cells) and builder cells (fibroblasts, osteoblasts, chondroblasts). All CT composes of cells, amorphous ground substance (nourish, transport) and fibres (collagen, elastin, reticular), CT is classified based on the presence of cell types and relative proportions of cells, AGS and fibres. CT can be broadly classified into dense, loose, regular, or irregular depending on the function and location of CT. Loose CT = adipose, material underlying ET. Dense regular= tendons/ ligaments. Dense irregular= skin, organ lining, cartilage. Specialised CT= Bone  Structural Cells: Fibroblasts: Secrete all fibres, collagen, elastin, reticular 1. Collagen: provides strength (thickest fibre, appears as parallel bundles). Made of tropocollagen that combines to form collagen fibres (appears banded) 2. Reticular: net-like framework (delicate and thinnest) 3. Elastic: strength, recoiling and elasticity  Storage cells: Adipocytes  Defence cells: Macrophages (phagocytose microorganisms), neutrophils (engulf + recruit), mast cells (release histamine + cytokines to stimulate inflammatory response), plasma cells (secrete antibodies), lymphocytes (B/T-cells)  AGS Matrix: Provides medium for substance exchange, consistency varies between different CT types (plasma in blood, bone, cartilage)  Classification of Connective Tissues: 1. Loose CT: Cells + AGS > Fibres 2. Dense CT: Cells + AGS < Fibres  Dense regular: parallel fibres (unidirectional strength= ligaments, tendons)  Dense irregular: fibres in all directions (strength against shearing, multidirectional forces)  Collagen Synthesis: 1. Synthesis of procollagen in the rER with propeptides on each end 2. Hydroxylation post translational modification (sugar attachments) 3. Triple helix procollagen (soluble) 4. Exporting to golgi body packed into secretory vesicles 5. Exocytosis of procollagen into extracellular space 6. Procollagen peptidase cleaves propeptides forming insoluble tropocollagen 7. Tropocollagen aggregates to form collagen fibrils 8. Fibrils reinforced by covalent cross-links Collagen takes the form (smallest to largest) tropocollagen polymerises to form fibrils< fibre < bundle  Types of collagen: Differ based on amino acid sequence of tropocollagen and polymerisation (fibril formation) o Type 1: forms fibrils, fibres, bundles. Located in most CT, unidirectional properties means its located in dermis, tendons, ligaments, bone as it provides resistance to stress and tension o Type 2: forms fibrils only. Located in cartilage and provides resistance to pressure o Type 3: forms fibrils and fibres. Located in CT, reticular fibres and cellular organs providing a delicate flexible framework o Type 4: forms a network sheet. LoHcated in basal lamina and filters/delicate support  Collagen + Scurvy: o High in proline and lysine that undergo post translational modification into hydroxyproline and hydroxylysine. Vitamin C activates these modifying enzymes, therefore a deficiency results in decreased collagen production, and collagen that is produced is less stable and prone to degradation o Loss of collagen results in loss of PDL (tooth loosening) and osteoporosis  Reticular Fibres: o Composed of collagen type 3 o Form thin, delicate support frameworks for organs   Elastic Fibres: o Elastic, taut, can be branched to form an interconnected network o Found in arteries, skin, lungs as they have stretch/recoil o Composed of amorphous elastin = provides elasticity o Glycoprotein microfibres cross-link elastin molecules o Appears denser in EM  Amorphous Ground Substance o Non fibre component o Fills space and acts as a medium for transport in CT o Carbohydrate and proteins (glycoproteins= laminin, fibronectin + proteoglycans=hyaluronic acid)  Hyaluronic acid (proteoglycan), core proteins with GAG chains attached to a long glycosaminoglycan chain of hyaluronate. o Contains solvation water (attracted by negatively charged core protein + GAG molecules) Tissues of the Body 7: Epithelial Tissue- Connective Tissue Cells Pre-lecture notes Fibroblasts are located in CT and are builder cells responsible for the formation of fibres, collagen for strength, elastic for tensile and recoil, reticular, for support in a mesh network. Collagen is synthesised by fibroblasts where it first begins as procollagen with propeptides which are hydroxylated to form soluble procollagen. Procollagen is exocytosed into extracellular space where it is then cleaved with propeptidases, this results in the formation of insoluble tropocollagen. Tropocollagen proteins polymerise in various combinations to form fibrils which proceed to form different collagen types (T1= fibrils, fibres, bundles- located in unidirectional stressors such as tendons, ligaments, dermis, T2= fibrils only- located in cartilage for force distribution, T3= fibrils and fibres- located in reticular fibres that form the reticular lamina in CT, T4= network sheets that support organs) Reticular fibres are located supporting organs and are the thinnest fibre. Elastic fibres are found in areas that need multidirectional strength and compression. Elastic fibres are made of amorphous elastin molecules that are cross-linked with glycoprotein microfibres to form branched structures. Adipocytes are fat storage cells that appear colourless in LM, they have a thin boundary that marks their edge. All surface epithelia are underlined by loose connective tissue that have defence cells. Macrophages phagocytose pathogens act as antigen presenting cells to B-cells, produce cytokines to activate other cells, plasma cells secrete antibodies, mast cells secrete histamine and heparin to incite an inflammatory response. Mesenchymal cells are those which make up an entire organism’s cells. Pluripotent cells are cells that can differentiate into various cell types in one lineage. Structural cells  Fibroblast: active, produces all fibres and AGS  Fibrocytes: mature, maintenance of environment, less metabolically active. Can revert back to active  Myofibroblasts: form scar tissue that contracts  Adipocytes: fat storage with a thin rim of cytoplasm Defence cells  Macrophages: contains phagosomes and lysosomes to break down pathogens, originate from monocytes. Contain pseudopodia (microfilament processes), abundant in rER and golgi body for production of lysosomes. Antigen presenting that initiate an immune response and produce cytokines.  Plasma cells: produces antibodies, highly basophilic (purple), abundant rER and golgi bodies. Nucleus is off centre  Mast cells: distinct granules (release cytokines and heparin) and increase permeability of capillaries. large dense granules. Increases vasodilation, mucus production and muscle contraction.  Leukocytes: white blood cells - Lymphocytes: small round cell with dark nucleus (immune reactions - Neutrophils: role in bacterial inflammation response  - Eosinophils: two lobes, accumulate in parasitic infections + allergy reactions. red granules Stem cells  Pericytes: Located around capillaries, undifferentiated mesenchymal cell  Mesenchymal cells: cells that can differentiate into multiple cell types Tissues of the Body 8: Cartilage Pre-lecture notes: Cartilage is composed of cells, matrix, and perichondrium, it is classified as loose connective tissue. Cartilage is produced by chondroblasts chondrocytes which secrete cartilage. Chondrocytes are found in lacunae. Cartilage can grow in two dimensions, appositionally (increased diameter) or interstitially (expansion from within the matrix forming isogenous groups). Cartilage is avascular and requires nourishment and support from the surrounding matrix. The perichondrium refers to the thin layer of dense CT that wraps around cartilage (excluding articular cartilage/fibrocartilage). Cartilage can be hyaline (glassy, large liquid component) which is located at bone articulations, the main component of hyaline cartilage is collagen type 2 (fibrils only). It can also be elastic, this cartilage is in the ear as well as the epiglottis/larynx. Fibrocartilage consists of collagen and cartilage to form intervertebral discs, joint capsules (synovial) and ligaments. In bone formation, hyaline cartilage forms the epiphyseal plate at the head of a long bone where bone growth begins. Osteoblasts grow along the epiphyseal plate, receiving support and nourishment from the underlying cartilage as they form the initial template for bone growth. At maturity of the long bone, the epiphyseal plate is lost. Joints are formed when two bones articulate one another, each end of the bone contains hyaline to minimise friction and grinding of bones. Joints are classified based on the level of movement, synarthrosis (immovable), arthrosis, synovial diarthrosis (freely movable), amphiarthrosis (slightly movable). Joints are also classified based on their STRUCTURE (tissues present)- fibrous, cartilaginous, synovial (capsule).  Cartilage (CT= chondrocyte cells, fibres, ground substance) o Perichondrium (CT), Matrix, Chondrocytes in lacunae (groups are referred to as isogenous cartilage) o Glycoproteins, collagens, water o Chondrocytes originate from mesenchymal stem cell (chondrogenic layer beneath fibrous perichondrium layer) and secrete cartilage, lie in lacunae and undergo cell division for appositional growth. o Nourishment is provided by dense CT perichondrium o Collagen Type 2 allows for firm hydrated gel of cartilage o No blood vessels or nerves in cartilage, acts as a medium for nutrients to diffuse through  Proteoglycans in matrix= core protein is GAGs  Hyaluronic acid (solvation water attracted to negative core proteins)  Types of Cartilage: o Hyaline: Important in bone growth, larynx, nose, trachea (Type 2 collagen)  Endochondral ossification (bone growth): Hyaline cartilage grows and then is replaced by bone tissue  Epiphyseal plate: bone growth in length at the plate, cartilage grows and is then replaced by bone  Articular cartilage (no perichondrium): hyaline lines the ends of bones, providing a smooth slippery surface that has shock absorbing function  Limited tissue repair due to avascularity (all nourishment provided by perichondrium CT) + chondrocytes are immobile and cannot proliferate when matured. o Elastic: ear, epiglottis, larynx (type 2 collagen- fibrils only).  Hyaline cartilage + elastic fibres = flexible and strength, resists deformation  o Fibrocartilage: symphysis pubis, intervertebral discs, joint capsules, ligaments (Type 1 AND Type 2 collagen)  Chondrocytes arranged in rows/lines  Resistance to compressive forces, immovable tough tissue  Dense regular CT + Hyaline (T1 + 2 collagen)  Classification of Joints (articulations) o Functional:  Diarthrosis (freely movable)  Amphiarthrosis (slightly movable)  Synarthrosis (immovable): fibrous joints with dense CT  e.g. alveolar bone and tooth o Structural:  Fibrous: joints held by fibrous CT (collagen rich)- no movement in bones  E.g. Gomphoses fibrous joint: Alveolar bone and cementum, CT is the periodontal ligament (Type 1 collagen, fibrils, fibres, bundles) where there is no movement between the bone and tooth= Synarthrosis joint  Cartilaginous: joints connected by hyaline cartilage or fibrocartilage  E.g. Epiphyseal plate or intervertebral discs  Synovial: Joints connected by a synovial cavity – freely movable diarthrosis  Fibrous capsule lined with synovial membrane which houses the synovial fluid (rich in hyaluronic acid + nutrients). Articular hyaline cartilage without perichondrium.  E.g. temporomandibular joint (TMJ), complex synovial joint with two joint spaces (bilateral joint). Consists of dense fibrocartilaginous tissue at the head of the mandibular condyle and temporal bone Tissues of the Body 9: Bone  Bone acts to support/protect the body, act as a calcium/triglyceride storage, and aid blood formation  Consists of organic + inorganic materials calcium hydroxyapatite minerals + Type 1 collagen (fibrils, fibres, bundles)  Bone cells: o Osteoblasts: secrete bone matrix + type 1 collagen, cuboidal shape, unmineralized matrix (osteoid) o Osteocytes: Lie in lacunae (non-secreting), forming concentric lamellae rings centred around a haversian canal. Form cytoplasmic processes in canaliculi via gap junctions o Osteoclasts: facilitate bone resorption, large multinucleated cell (haematopoietic origin), contain many lysosomes for bone degradation by acid secretion, ruffled surface for high SA to degrade bone, stimulated formation by RANKL  Tissue components: o Periosteum: Dense, fibrous CT wrapping around the bone- site of muscle, tendon and ligament attachment. Source of osteoprogenitor cells that give rise to osteoblasts o Endosteum: Dense, fibrous CT lining inside of the bone cavity, covering trabeculae in spongy bone o Red Bone marrow: vascular, fills spaces of spongy bone at epiphyses heads o Yellow Bone marrow: location of fat cells in the diaphysis medullary cavity  Types of bone: o Spongy, trabecular, cancellous: found in heads of bones, affected by compression  Network of connecting trabeculae plates, spaces filled with red bone marrow o Compact, cortical: found in shafts of bones, high mechanical strength.  Haversian System of Cortical Bone The haversian canal forms the centre of an osteon, initially providing vascular and nerve supply, allowing osteoblasts to infiltrate the area. Osteoblasts secrete bone  matrix (calcium mineral + type 1 collagen) in layers called lamellae and when matured, they differentiate into osteocytes that lie in lacunae. Type 1 collagen is lined in parallel fibres in bundle for strength. The osteocytes are able to coordinate action and communicate with one another by extending processes through canaliculi (horizontally placed) and gap junctions. Osteocytes cannot communicate via diffusion as the bone matrix is too mineralised. Volkman’s canals run horizontally to connect different haversian canals for coordination. The remodelling of bone through osteoclast action results in interstitial lamellae that are incomplete circles. o Immature (woven, bundle) bone: First bone laid down which is constantly remodelled, does not form osteons  Bone Cells: o Osteoprogenitor cells: derived from mesenchymal stem cells in bone marrow, osteoblast precursor cells. Found lining periosteum and endosteum. o Lining cells: flattened osteoblasts that cover and protect surface of bone  Mesenchymal stem cells form adipocytes, chondrocytes, osteoblasts, osteocytes  Hematopoietic stem cells form monocytes, macrophages then osteoclasts  Bone turnover: o Resorption: pressure o Formation: tension o Spongy replaced 3-4 years o Compact replaced every 10 years, results in formation of interstitial lamellae as osteons/haversian systems are remodelled o Remodelling more common in adolescents  Regulators of bone metabolism: o RANKL (stimulates osteoclast activity), Cytokines, hormones, drugs Tissues of the Body 10: Muscle  Types of Muscle: o Cardiac:  Wall of the heart  Involuntary  Striated  Branched, multinucleated  Intercalated disks (allow for coordination of muscle contraction and relaxation). Joined by:  Anchoring junctions Fascia adherens(actin connection)  Desmosomes (intermediate filaments)  Gap junctions (communication- connexin proteins)  Type 3 Collagen + Elastin o Smooth:  Walls of hollow organs, blood vessels  Involuntary  Non-striated  Single, centrally located nuclei (fusiform)  Smooth muscle cells are attached to dense bodies/actin plaque that facilitate contraction o Skeletal:  Attachment of bones and skin  Voluntary  Striated, multinucleated  Parallel muscle fibres   Periphery, multinucleated, elongated nuclei  Muscle structure: o Connective tissue, skeletal muscle tissue, blood vessels, nerves o Myocytes contain sarcoplasm (muscle cytoplasm) which is rich in mitochondria and possesses sarcoplasmic reticulum (calcium storage for muscle contraction) o Sarcolemma (muscle cell membrane) invaginates to form T-tubules that penetrate into cells and contain ion channels to propagate action impulses for muscle contraction o Myocytes (muscle fibres) bundle to form protein myofibrils that are wrapped by perimysium CT and confer contractile properties o Myofibrils are bundles of myofilaments (actin- thin & myosin -thick) o Myofibrils join, forming a contractile unit called the sarcomere (region between two Z-lines)  Thin actin slides over thick myosin  A-band: entire length of thick myosin filaments + actin overlap  I-band: contains only thin actin filaments  H-zone: part of A band where there is no overlap  In contraction I-bands become shorter, bringing Z-lines closer to one another, A- band does not change.  Connective tissue wrappings of skeletal muscle: =Fascia- covers the epimysium =Endomysium= around individual muscle fibres =Perimysium= CT that surrounds bundles of muscle fibres (fascicles) =Epimysium= outermost dense irregular CT that wraps the entire muscle, lies underneath the fascia  Skeletal muscle contraction: 1) ATP Hydrolysis- removal of tropomyosin 2) Crossbridge formation between actin + myosin head 3) Power stroke 4) Detachment of myosin head from actin Tissues of the Body 11: Muscle  Myofibrils combine to form a muscle fibre (fascicle) that is wrapped by perimysium. Bungles of muscle fibres combine to form a muscle that is wrapped by epimysium  Mechanism of muscle contraction in Skeletal + Cardiac Muscle (tropomyosin) o Action potential triggers release of acetylcholine o Action potential moves across membrane into myocyte’s T-tubule- stimulates release of Ca2+ from SR o Myofibrils consist of actin that act as myosin binding sites, the actin is bound to tropomyosin- a molecule that blocks the binding of myosin. Troponin complex (troponin-C) refers to tropomyosin, actin & calcium binding protein o Release of Ca2+ via sarcoplasmic reticulum calcium release results in the removal of tropomyosin off the actin via movement of Troponin Complex. o Hydrolysis of ATP, allows for cross-bridging. o Myosin undergoes a conformational change, pulling actin towards the centre of the sarcomere = Power stroke o Another ATP molecule binds to hydrolyse ATP to ADP + Pi to facilitate relaxation and removal of the myosin head o Sarco/endoplasmic reticulum calcium ATPase (SERCA) pumps cytosolic Ca2+ back into SR  Mechanism of muscle contraction in Smooth Muscle (Myosin Light Chain Kinase- NO TROPOMYOSIN) o Calcium enters via T-tubule o Calcium binds to calmodulin o Activation of myosin light chain kinase (MLCK) o Phosphorylation of myosin ATPase o Myosin can bind to actin and cross-bridging occurs + contraction o To stimulate relaxation, calcium is removed from cytosol back into sarcoplasmic reticulum.  Mode of contraction: 1) Action potential (depolarisation of cell + SR release) 2) Contraction (myosin-actin cross-bridging + sliding) 3) Relaxation (removal of cytosolic Ca2+ via SERCA)  Changing the strength of muscle contractions: o Increase fibre number o Increase frequency of stimulation (makes fibres more receptive)  Constant restimulation means less muscle relaxation and maximum sustained contraction can be achieved. o Increase thickness of fibre o Operate muscles at optimum resting length- refers to optimal shortening and stretching of muscle. o Increased cross-bridging capabilities= more force at a faster speed (fast twitch)  Fine motor movements involve few (5-10) muscle fibres for precise, but weaker, forces  ATP Generation for muscle metabolism: 1) Creatine phosphate: short bursts of intense energy (CP donates phosphate to ADP to make ATP) 2) Glycolysis: Anaerobic, fast but inefficient (2ATP/glucose) 3) Oxidative phosphorylation: Aerobic, slow but efficient when glucose is limited (34.5ATP/glucose)  Causes of muscle fatigue: o Insufficient energy (ATP, creatine phosphate, glucose, glycogen) o Central Nervous system fatigue (reduced nerve transmission) o Muscle tears o Reduced sensitivity to calcium/SR calcium release