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Histology terms & principles 1. Know the basic histology terms and their meanings. (including the common suffixes and prefixes, used in histology) COMMON PREFIXES: TISSUE: CHONDRO – Cartilage HEPATO – Liver Myo – Muscle OSTEO – Bone PNEUMO – Lung LOCATION: EPI – upon/after ENDO – Inner INTER – between INTRA – within JUXTA – beside KARY – nucleus PERI – around COMMON SUFFIXES: -BLAST = Actively dividing cell -CLAST = Break -CYTE = Resting cell -OID = Form -PHAGE = Eat -SOME = Body COMMON TERMS: ADVENTITIA – Vessel or organ covering AFFERENT – To EFFERENT - From CAPSULE – Organ covering CORTEX – Outermost layer HILUS/HILUM – Pit or depression where vessels and nerves enter MEDULLA – Middle MUCOSA – Mucous membrane SEROSA – Support tissue – lines internal cavities SEPTUM – Division STROMA – Support tissue 2. Know the types of epithelial tissues and examples of where they are located. HISTOLOGY – The microscopic study of tissues EPITHELIUM – The protective covering of surfaces both inside and outside the body Characteristics common to most types of epithelium: 1. Epithelium consists almost entirely of cells with very little extracellular material between them 2. Epithelium covers surfaces of the body and forms glands that are derived developmentally from body surfaces. These body surfaces include the outside surface of the body, digestive tract lining, the vessels and linings of many body cavities 3. Most epithelial tissues have o one FREE/APICAL surface not attached to other epithelial cells o a LATERAL SURFACE attached to other epithelial cells o a BASAL SURFACE. This is attached to the BASEMENT MEMBRANE o BASEMENT MEMBRANE – A specialised type of extracellular material that is secreted by epithelial cells and connective tissue cells. It helps attach the epithelial cells to the underlying tissues and plays an important role during tissue repair 4. Specialised cell contacts such as tight junctions and desmosomes, bind adjacent epithelial cells together 5. Blood vessels do not penetrate the basement membrane to reach the epithelium. Therefore all gases and nutrients in the blood reach the epithelium by diffusing across the basement membrane from blood vessels in the underlying connective tissue 6. Epithelial cells retain the ability to undergo mitosis and therefore are able to replace damaged cells with epithelial cells. Undifferentiated cells (stem cells) continuously divide and produce new cells. In the skin and the digestive tract, cells that are lost or die are continuously replace with new cells Functions of the epithelia: Protecting underlying structures – e.g. skin and epithelium of oral cavity Acting as barriers – prevents movement of many substances through the epithelial layer. E.g skin acts as barrier to water and toxic molecules and prevents water loss from the body Permitting the passage of substances – Allows movement of many substances through the epithelial layer. E.g. O2 and CO2 are exchanged between the air and blood through the epithelium in the lungs Secreting substances – E.g sweat glands, mucous glands and enzyme secreting portion of the pancreas Absorbing substances – The cell membrane of certain epithelial tissues contain carrier molecules that regulate absorption of material Classification of Epithelium: Epithelium is classified primarily according to the number or cell layers and the shape of superficial cells. Based on number of cell layers: SIMPLE – 1 layer of cells, each one extending from the basement membrane to the free surface STRATIFIED – >1 one layer of cells, only one is attached to the basement membrane PSUEDOSTRATIFIED COLUMNAR – Appears to be stratified but isn’t. Has 1 layer of cells and ALL are attached to the basement membrane. There appears to be more than one layer of cells bc the cells are tall and reach the free surface. This type of epithelium lines the nasal cavity, trachea and bronchi. They secrete mucus, covering the surface and have cilia on the free surface which moves mucus and debris that accumulates over the surface of the respiratory passages towards the exterior of the body 3 types of epithelium based on the shape: SQUAMOUS – Cells are flat and scale like CUBOIDAL – Cells are cube shaped; as wide as they are tall COLUMNAR – Cells are taller than they are wide Most epithelium are given two names e.g. simple squamous. First one = No. Of layers Second one = Shape of the cells SQUAMOUS: Simple – Mesothelium and endothelium Stratified – Keratinized epithelium: skin Non-keratinized epithelium: Oral cavity, vagina, cornea, oesophagus Stratified squamous epithelium can be broken down according to the condition of their outer most layer: o MOIST – found in mouth, oesophagus, rectum and vagina. Consists of living cells in the deepest and outermost layers. A layer of fluid covers the outermost layer making them moist o KERATINIZED – Found in the skin. Consists of living cells in the deepest layers and outermost layers are composed of dead cells containing the protein keratin. The dead keratinized cells give the tissue a durable, moist-resistant dry character. CUBOIDAL: Simple – Excretory ducts, some kidney tubules, germinal epithelium of ovary Stratified – Rare: Some parts of excretory ducts Pseudostratified – Transitional epithelium of urinary bladder COLUMNAR: Simple – With kinocilia: Uterus, salpinx Without kinocilia: GIT, gallbladder Stratified – Rare: Conjunctival fornix, some parts of male and female urethra Pseudostratified – With kinocilia: respiratory tract Without kinocilia: Rare: some parts of the glandular ducts With stereocilia: Epididymis and vas deferens 3. Briefly outline the key features of the three muscle types. SKELETAL CARDIAC SMOOTH LOCATION Attached to bones Heart Walls of hollow organs, blood vessels, eyes, glands and skin FUNCTION Body movement Contracts to move Movement of food blood through through digestive blood vessels tract, emptying bladder, regulation of blood vessel diameter, change in pupil size, constricts many gland ducts, movement of hair UNIT Fibre Cell Cell UNIT LENGTH Can be up to 50 - 120μm 40 - 200μm. In a several centimetres pregnant uterus upto 500μm UNIT DIAMETER 20 - 100μm 10 -20μm 5 - 10μm NUCLEUS Multinucleated, Single, Single, peripherally located centrally located centrally located NUCLEAR NO. 100’s to 1000’s 1 to 2 1 NUCLEAR Sub-sarcolemmal Central in Central cytoplasm LOCATION perinuclear cytoplasm free of myofibrils NUCLEAR SHAPE Elongated flat Plumpish, Rod shaped or round to ovoid elliptical STRIATIONS Yes Yes No CONTROL Voluntary Involuntary Involuntary SPONTANEOUS No Yes Yes CONTRACTION SPECIAL FEATURES Branching fibres, Gap junctions intercalated disks join the cells to each other (gap junctions)