Histology 1st Semester PDF

INTRODUCTION TO HISTOLOGY, HISTOLOGICAL TECHNIQUES BY DR KELECHI DURUH DEPT. OF ANATOMY,FBMS COLLEGE OF MEDICINE UNEC 1 OUTLINE Introduction Histological techniques  Biopsy and aspiration  Fixation  Dehydration  Inﬁltration  Embedding or casting 2 OUTLINE contd  Sectioning and Mounting  Staining  Placing the slide on the microscope.  Cryofracture and freeze etching  Microwave method of tissue processing  Tissue culture  Autoradiography  Artifacts 3 INTRODUCTION Histology is the study of the tissues of the body and how these tissues are arranged to constitute organs. Tissues have two components , cells and cellular matrix (ECM) The ECM consists of many kinds of macromolecules e.g. collagen ﬁbrils. ECM is produced by the cells locally by an orderly combination of these tissue s ,organs are formed 4 INTRODUCTION contd ECM supports the cells and is the milieu for supply of nutrients and clearing of waste and secretory products During development, cells and their associated matrix become functionally specialized and give rise to fundamental types of tissue with characteristic structural features. 5 INTRODUCTION contd Cells and tissues could be studied in vitro or in vivo. In vivo histology includes USS, CT,RMI studies of tissues in the living being. In vitro histology consists of the methods used to study tissues outside of the body In vitro studies could be on living cells/tissue or dead cells/tissues 6 HISTOLOGICAL TECHNIQUES These are procedures used in the acquisition , processing and viewing of histologic samples If well carried out, yields quality results 7 BIOPSY AND ASPIRATION Method of acquiring tissue sample for study. Small portion of specimen is excised with sharp blade or f luidy specimen aspirated with aid of needle Fresh tissue specim ens could com e from various sources. They can easily be damaged during removal from patient or experimental animal They should be handled carefully and f ixed as soon as possible after dissection 8 FIXATION Slide preparation begins with f ix ation of tissue specimen. To preserve tissue structure. Its purpose is to prevent tissue autolysis and putrefaction. For best results, biological tissue samples sh o u l d be t ra n sfe r re d i n t o f ix a t i v e immediately after collection. Although there are many types of f ixative, most specimens are f ixed in 10% neutral buffered formalin. Picture of 10% neutral formalin bottle (googleimages) 9 FIXATION contd The optimum formalin-to-specimen volume ratio should be at least 10:1 (e.g., 10ml of formalin per 1cm3 of tissue). This will allow most tissues to become adequately ﬁxed Picture of tissue undergoing ﬁxation process (googleimages) within 6-24 hours 10 DEHYDRATION Water in a specimen must be removed before it can be inﬁltrated with wax. Carried out by immersing specimens in a series of ethanol (alcohol) solutions of increasing concentration. Ethanol is miscible with water and progres s ively replaces the water in the specimen. 11 CLEARING Wax and ethanol are largely immiscible. Solvent miscible with both ethanol and paraf fin wax is used to displace the ethanol in the tissue. Then this in turn will be displaced by molten paraﬃn wax. This stage in the process is called “clearing” and the reagent used is called a “clearing agent”. 12 WAX INFILTRATION The tissue can now be inf il trated with a suitable histological wax A typical wax is liquid at 60°C and can be inﬁltrated into tissue at this temperature. It is actually done in an oven 13 EMBEDDING Process of enclosing tissue in the embedding mould. Mould is ﬁlled with melted wax and specimen is placed on it. Embedding mould. Orient the specimen Slideshare.com well on the mould 14 SECTIONING AND MOUNTING A microtome is used to slice thin tissue sections off the block in the form of a ribbon The microtome can be pre-set to cut different thickness Microtome 15 STAINING Stains are dyes applied to tissue specimen to make them conspicuous and distinguishable from one another. Anionic cell components such as nucleic acid have aﬃnity for basic dyes hence called basophilic Cationic cell components , such as proteins stain with acidic dyes and are termed acidophilic Basic dyes include , hematoxylin,tolidine blue ,alcian and methylene blue Acidic dyes include eosin,orange G and acid fuchsin A combination of stains further distinguishes more tissue components eg H/E In a combination ,the second stain is called a counterstain 16 STAINING Unstained tissue H/E stined tissue 17 STAINING Most cells are transparent, and appear almost colourless when unstained. Haematoxylin and Eosin are used to provide contrast to tissue sections Making tissue structures more visible and easier to evaluate. 18 STAINING contd Following staining, a cover slip is mounted over the tissue specimen on the slide Optical grade glue is used to help protect the specimen. Figure 11: Cover slip 19 PLACING THE SLIDE ON THE LIGHT MICROSCOPE After staining, slide is allowed to dry. Afterwards the slide is ready for viewing on the microscope. The stained slide is placed on the stage of the light microscope and adjusted accurately for viewing. Figure 12: Slide placed on the microscope 20 CRYOFRACTURE AND FREEZE ETCHING This a technique that allow microscopy of cellswithout ﬁxationor embedding Useful in the study of membrane structure Very small tissue specimen is rapidly frozen in liquid nitrogen then cut or fractured The small slice could be viewed under microscope 2 MICROWAVE METHOD OF TISSUE PROCESSING This is a recent technique, in which the microwaves p ossess p enetrativ e p rop erties with shorter processing time (Hegazy et. al., 2015) The size of tissues used must not be more than one cubic cm; otherwise complete and even penetration of microwaves will not occur. Has the advantage of reducing processing time May alter heat labile structures 22 CELLS AND TISSUE CULTURE Live cells and tissues are maintained and studied outside the body in culture. Cell culture allows the direct observation of cellular behavior under the microscope. Sample of culture is mounted on the slide for viewing 2 AUTORADIOGRAPHY Autoradiography is a te c hni q ue that use s photographic f il m to determine where within a c e l l a s p e c i f ic radioactively labeled compound is at the time the c e l l i s f ixe d and sec tioned for microscopy Figure 13: Picture of the autoradiograpy machine (googleimages) 24 ENZYME HISTOCHEMISTRY This is a method for localizing cellular structures using speciﬁc enzymatic activity Examples of enzymes detectable are phosphatases , dehydrogenases and peroxidase 2 ARTIFACTS Artifacts are the result of changes in a tissues structure or the addition of new structure. They include: Swelling and Shrinkage of tissue components a result of poor ﬁxation and/or dehydration techniques. Swelling and shrinkage can sometimes result in rupture of membranes. This sort of damage is particularly evident at the ultrastructure level. 26 ARTIFACTS contd Wrinkles in section, Tear in section, Air bubbles and Dust: Usually the result of poor sectioning technique or poor technique during mounting of sections. Stain precipitate: Can result from use of old stain solutions, use of unf il tered stain solutions. 27 THANK YOU DR SAM CHIME HISTOLOGY OF NERVOUS TISSUE INTRODUCTION Property of irritability and conductivity Respond to various types of stimuli Distributed throughout the body as an integrated network Made up of 2 cell types: (a) Nerve cells (neurons) (b) Glial cells (neuroglia) Nervous system CNS PN NEURON Excitable, independent anatomic and functional units with complex morphological characteristics. Neurons = nerve cells – Cells specialized to transmit messages – Major parts of neuron: Cell body — nucleus and metabolic center of the cell (main part of nerve cell) Processes — ﬁbers that extend from the cell body – can be microscopic or up to 3-4 feet in length NERVE CELL BODY Contains the nucleus and a nucleolus Major biosynthetic center Focal point for the outgrowth of neuronal processes Absence of centrioles (hence its amitotic nature) Prominent basophilic Nissl bodies (rough ER) Contains an axon hillock – cone-shaped area from which axons arise Cytoskeleton of neuron is formed by microtubules & neuroﬁlaments PROCESSES Arm like extensions from the soma Nerve ﬁbre: term used for nerve cell process Two types of processes: axons and dendrites Myelinated axons are called tracts in the CNS and nerves in the PNS DENDRITES Short, tapering processes Branch extensively to form “Dendritic tree” They are the receptive or input regions of the neuron Absence of Golgi complexes AXON Slender processes of uniform diameter arising from the axon hillock Axon hillock lacks RER, ribosomes & Nissl substance Nissl substance is also absent in cytoplasm of axon Usually there is only one unbranched axon per neuron Axon terminals (terminal boutons) Axolemma Axoplasm AXON FUNCTION Generate and transmit action potential Secrete neurotransmitters from the axonal terminals Movement along axons occurs in two ways – Anterograde — toward the axon terminal – Retrograde — toward the cell body Classiﬁcation of neuron Structural: – Multipolar — three or more processes – Bipolar — two processes (axon and dendrite) – Unipolar (pseudounipolar)— single, short process (usually dendrite) – Anaxonic Structural classiﬁcation Classiﬁcation contd - functional Functional: – Sensory (afferent) — transmit impulses toward the CNS – Motor (efferent) — carry impulses toward the body surface – Interneurons (association neurons) — any neurons between a sensory and a motor neuron Synpase Myelin Neuroglia Ependymal cells HISTOLOGY OF CONNECTIVE TISSUE BY DR. MATTHEW AZUBUIKE OKEKE. INTRODUCTION: But as the connective tissue is the glue that holds all other tissues together, it has the important function of ensuring that our body systems work in harmony. CELLS AND FIBRES OF CONNECTIVE TISSUE. CONNECTIVE TISSUE PROPER: CONNECTIVE TISSUE PROPER (CONTD): DENSE CONNECTIVE TISSUE: SPECIALIZED CONNECTIVE TISSUES: (1) RETICULAR CONNECTIVE FIBRES: (2): CARTILAGE TYPES OF CARTILAGE (CONTD): BONES: BONES (CONTD): BLOOD: ADIPOSE TISSUE AND TYPES: ADIPOSE TISSUE AND TYPES (CONTD): EMBRYONIC CONNECTIVE TISSUE: PROTECTIVE AND GLANDULAR EPITHELIUM BY DR KELECHI DURUH DEPARTMENT OF HUMAN ANATOMY FBMS COLLEGE OF MEDICINE UNEC 1 INTRODUCTION Epithelium is a tissue composed of cells tightly bound together structurally and functionally to form a sheet-like or tubular structure with little extracellular matrix. They line cavities of organs and cover body surfaces( internal and external) All substances entering or exiting the body organs must cross the epithelium Functionally grouped as protective, absorptive an secretory or glandular Structurally classiﬁed by shape and density of cells 2 FEATURES OF EPITHELIAL CELLS Size and morphology are dictated by function Size varies from columnar , cuboidal to squamous Nuclear shape may be oval,spherical or ﬂattened corresponding roughly with cell shape Most epithelial tissues posses underlying lamina propia Some epithelial tissues have underlying papillae projections 3 FEATURES OF EPITHELIAL CELLS COLUMNAR EPITHELIUM OVAL NUCLEUS LAMINAR PROPRIA CONNECTIVE TISSUE SCHEMATIC DRAWING OF EPITHLIUM 4 FEATURES OF EPITHELIAL CELLS Epithelial cells exhibit polarity Have basal and apical poles Poles differ in structure and function The basal surface of epithelial cell rest on a basement membrane Epithelial cells adhere strongly to neighboring cells and basal lamina 5 FEATURES OF EPITHELIAL CELLS The apical poles of some epithelial cells exhibit specialization features such as microvilli, stereocilia, cilia Have lateral surface modiﬁcations such as tight junctions,adherens junction,gap junction and desmosomes Have basal surface modiﬁcation, hemidesmosome 6 FEATURES OF EPITHELIAL CELLS EPITHELIAL TISSUE H/E STAIN X400 7 FEATURES OF EPITHELIAL CELLS Basement membrane  Semipermiable ﬁlter for substances reaching the cell from below  Provides structural support for epithelium  Attaches epithelial cells to connective tissue  Helps to organize proteins in the plasma membrane of epithelial cells  Helps to maintain polarity  Aids in signal transduction  Scaffold for rapid epithelial repair and regeneration 8 FEATURES OF EPITHELIAL CELLS 9 FEATURES OF EPITHELIAL CELLS INTERCELLULAR ADHESIONS AND OTHER JUNCTIONS  Tight or occluding junctions– Forms a seal between adjacent cells  Ensures that molecules pass by transcellular paths  Restricts movement of membrane lipids and proteins between apical and lateral surfaces  Adherens junction enhances the function of the tight junction  Aids surface polarization  Gap junction mediate intercellular communication  Desmosomes and hemidesmosomes anchor cell-cell and cell-basement membrane respectively 10 FEATURES OF EPITHELIAL CELLS MICROVILLI TERMINAL WEB CONNECTIVE TIS MICROVILI IN THE INTESTINE. H/E X6500 FEATURES OF EPITHELIAL CELLS  APICAL SURFACE MODIFICATIONS MICROVILLI  Cytoplasmic projections  Numerous in epithelia specialized for absorption  Average size,1microm long and 0.1microm wide  Increases total surface area FEATURES OF EPITHELIAL CELLS STEREOCILIA IN EPIDIDYMIS H/E X400 FEATURES OF EPITHELIAL CELLS STEREOCILIA  Seen in the male reproductive system and inner ear sensory cells  longer, branching and less motile than microvilli  similar functions FEATURES OF EPITHELIAL CELLS LUMEN CILIA COLUMNAR CE GOBLET CELL BASEMENT MEMBRANE BASA LAMINR CILLIATED COLUMNAR EPITHELIUM AND INTERRUPTED NONCILLIATED GOBLET CEL TOLUDINE BLUE X400 FEATURES OF EPITHELIAL CELLS CILIA  Usually larger than micrvilli  About 5-10microm long and 0.2microm wide  Exhibit rapid beating pattern  Moves ﬂuid and suspended matter in one direction along the epithelium TYPES OF EPITHELIA COVERING(LINING) EPITHELIA SECRETORY(GLANDULAR) EPITHELIA COVERING/PROTECTIVE EPITHELIA Cells are organized in one or more layers Classiﬁed according to cell layers and morphology of the outer layer Simple means one layer and stratiﬁed means two or more layers Cell shape may be squamous, cuboidal, columnar, or transitional Squamous cell could be keratinized or non -keratinized PROTECTIVE EPITHELIAL CELLS SCHEMATIC DIAGRAM OF CLASSES OF EPITHELIUM PROTECTIVE EPITHELIAL CELLS SECRETORY/GLANDULAR EPITHELIA Epithelial cells with principal function of producing and secreting various macromolecules. Develop from covering epithelium Exocrine maintains its connection with original epithelium while endocrine does not Exocrine connection with the epithelium is called duct SECRETORY/GLANDULAR EPITHELIA SCHEMATIC DIAGRAM OF FORMATION OF GLAND FROM COVERING EPITHELIUM SECRETORY/GLANDULAR EPITHELIA SCHEMATIC DIAGRAM OF CLASSES OF GLANDS SECRETORY/GLANDULAR EPITHELIA Ducts could be simple or compound Secretory portion may be tubular or acinar Compound glands have branching ducts and multiple types of secretory portions Secretion mechanism could be merocrine, holocrine ,apocrine or a combination SECRETORY/GLANDULAR EPITHELIA MECHANISM OF SECRETION SECRETORY/GLANDULAR EPITHELIA Merocrine secretion could be serous or mucous Serous cells stain intensely with basophillic and acidophillic stains Mucous cells are distinguished by PAS method Some glands are mixed--- seromucous Secretory epithelia usually contain myoepithelial cell TRANSPORT ACROSS EPITHELIUM Mostly by active transport via transcellular paths aided by ion pumps Endocytosis GROWTH OF EPITHELIUM Epithelia is capable of rapid repair and replacement of apoptotic or damaged cells Stem cells population usually situated at the basal layer in contact with the basal lamina undergo mitosis and differentiation CLINICAL CORRELATES Disruption of the tight junction in the G I epithelia by activities of micro-organisms or toxins causes ﬂuid loss also implicated in some gastric ulcers Abnormal desmosome junctions causes blistering diseases Celiac disease is associated with loss of microvili kartagener syndrome is associated with male infertility due to cilia akinesia Metastasia in habitual smokers causes chronic brochitis EXERCISE EXERCISE EXERCISE EXERCISE EXERCISE EXERCISE EXERCISE EXERCISE EXERCISE EXERCISE EXERCISE CHEERS BLOOD AND LYMPHATIC VESSELS BY UMEANO A.V INTRODUCTION The cardiovascular system consists of the heart and blood vessels. The blood vessels that take blood from the heart to various tissues are called arteries. The smallest arteries are called arterioles. Arterioles open into a network of capillaries that pervade the tissues. Exchanges of various substances between the blood and the tissues take place through the walls of capillaries. In some situations, capillaries are replaced by slightly different vessels called sinusoids. Blood from capillaries (or from sinusoids) is collected by small venules that join to form veins. The veins return blood to the heart. Blood vessels deliver nutrients, oxygen and hormones to the cells of the body and remove metabolic base products and carbon dioxide from them. ENDOTHELIUM The inner surfaces of the heart, and of all blood vessels are lined by ﬂattened endothelial cells (also called endotheliocytes). On surface view the cells are polygonal, and elongated along the length of the vessel with sparse cytoplasm. The cytoplasm contains endoplasmic reticulum and mitochondria. Microﬁlaments and intermediate ﬁlaments are also present, and these provide mechanical support to the cell. Many endothelial cells show invaginations of cell membrane (on both internal and external surfaces). Sometimes the inner and outer invaginations meet to form channels passing right across the cell (seen typically in small arterioles). These features are seen in situations where vessels are highly permeable. Adjoining endothelial cells are linked by tight junctions, and also by gap junctions. Externally, they are supported by a basal lamina. FUNCTIONS OF THE ENDOTHELIUM Endothelial cells are sensitive to alterations in blood pressure, blood ﬂow, and in oxygen tension in blood. They secrete various substances that can produce vasodilation by inﬂuencing the tone of muscle in the vessel wall. They produce factors that control coagulation of blood. Under normal conditions clotting is inhibited. When required, coagulation can be facilitated. Under the inﬂuence of adverse stimuli (e.g., by cytokines) endothelial cells undergo changes that facilitate passage of lymphocytes through the vessel wall. In acute inﬂammation, endothelium allows neutrophils to pass from blood into surrounding tissues. Under the inﬂuence of histamine (produced in allergic states) endothelium becomes highly permeable, allowing proteins and ﬂuid to diffuse from blood into tissues. The resultant accumulation of ﬂuid in tissues is called oedema ARTERY The histological structure of an artery varies considerably with its diameter. However, all arteries have some features in common which are as follows: The wall of an artery is made up of three layers The innermost layer is called the tunica intima (tunica = coat). It consists of: i. An endothelial lining ii. A thin layer of glycoprotein which lines the external aspect of the endothelium and is called the basal lamina iii. A delicate layer of subendothelial connective tissue iv. A membrane formed by elastic ﬁbres called the internal elastic lamina ARTERY Outside the tunica intima there is the tunica media or middle layer. The media may consist; i. predominantly of elastic tissue or of smooth muscle. ii. Some connective tissue. iii. On the outside the media is limited by a membrane formed by elastic ﬁbres, this is the external elastic lamina. The outermost layer is called the tunica adventitia. i. This coat consists of connective tissue in which collagen ﬁbres are prominent. ii. This layer prevents undue stretching or distension of the artery. KINDS OF ARTERIES On the basis of the kind of tissue that predominates in the tunica media, arteries are often divided into: I. Elastic arteries (large or conducting arteries) II. Muscular arteries (medium arteries) Elastic arteries include the aorta and the large arteries supplying the head and neck (carotids) and limbs (subclavian, axillary, iliac). The remaining arteries are muscular. Comparison between elastic artery and muscular artery Layers Elastic artery Muscular artery Adventitia. It is relatively thin with greater proportion It consists of thin layer of of elastic ﬁbres. ﬁbroelastic tissue Media Made up mainly of elastic tissue in the Made up mainly of smooth form of fenestrated concentric muscles arranged circularly membranes. There may be as many as ﬁfty layers of elastic membranes. Intima It is made up of endothelium, Intima is well developed, subendothelial connective tissue and specially internal elastic internal elastic lamina. The lamina which stands out subendothelial connective tissue contains prominently more elastic ﬁbres. The internal elastic lamina is not distinct. ARTERY ELASTIC ARTERY MUSCULAR ARTERY ARTERIOLES When traced distally, muscular arteries progressively decrease in calibre till they have a diameter of about 100 µm. They then become continuous with arterioles. The larger or muscular arterioles are 100 to 50 µm in diameter. Arterioles less than 50 µm in diameter are called terminal arterioles. All the three layers, i.e. tunica adventitia, tunica media and tunica intima are thin as compared to arteries. In arterioles, the adventitia is made up of a thin network of collagen ﬁbres. Arterioles are the main regulators of peripheral vascular resistance. Contraction and relaxation of the smooth muscles present in the walls of the arterioles can alter the peripheral vascular resistance (or blood pressure) and the blood ﬂow. Image of an artery and arteriole CAPILLARIES Terminal arterioles are continued into a capillary plexus that pervades the tissue supplied. Capillaries are the smallest blood vessels. The average diameter of a capillary is 8 µm. Exchanges of oxygen, carbon dioxide, ﬂuids and various molecules between blood and tissue take place through the walls of the capillary plexus (and through postcapillary venules). The arrangement of the capillary plexus and its density varies from tissue to tissue, the density being greatest in tissues having high metabolic activity. STRUCTURE OF CAPILLARIES The wall of a capillary is formed essentially by endothelial cells that are lined on the outside by a basal lamina (glycoprotein). Overlying the basal lamina there may be isolated branching perivascular cells (pericytes), and a delicate network of reticular ﬁbres and cells. Pericyte or adventitial cells contain contractile ﬁlaments in the cytoplasm and can transform into other cells. TYPES OF CAPILLARIES There are two types of capillaries: 1.Continuous 2. Fenestrated  Continuous Capillaries Here, the edges of endothelial cells fuse completely with those of adjoining cells to form a continuous wall. In continuous capillaries exchanges of material between blood and tissue take place through the cytoplasm of Structure of continuous endothelial cells capillary. A. Circular section; B. Longitudinal section (Schematic representation) TYPES OF CAPILLARIES  Fenestrated Capillaries In some organs the walls of capillaries appear to have apertures in their endo thelial lining, these are, therefore, called fenestrated capillaries. The ‘apertures’ are, however, always closed by a thin diaphragm (which may represent greatly thinned out cytoplasm of an endothelial cell, or only the basal lamina). Fenestrated capillaries are seen in renal glomeruli, intestinal villi, endocrine glands Structure of fenestrated and pancreas capillary. A. Circular section; B. Longitudinal section (Schematic representation) SINUSOIDS In some tissues the ‘exchange’ network is made up of vessels that are somewhat different from capillaries, and are called sinusoids. Sinusoids are found typically in organs that are made up of cords or plates of cells. These include the liver, the adrenal cortex, the hypophysis cerebri, the parathyroid glands, the spleen, in the bone marrow, and in the carotid body. The wall of a sinusoid consists only of endothelium supported by a thin layer of connective tissue. The wall may be incomplete at places, so that blood may come into direct contact with tissue cells. Deﬁciency in the wall may be in the form of fenestrations (fenestrated sinusoids) or in the form of long slits (discontinuous sinusoids, as in the spleen). At some places the wall of the sinusoid consists of phagocytic cells instead of endothelial cells. Sinusoids have a broader lumen (about 20 µm) than capillaries. These lumen may be irregular and because of this fact blood ﬂow through them is relatively sluggish. SINUSOIDS VEINS  The basic structure of veins is similar to that of arteries. The tunica intima, media and adventitia can be distinguished, specially in large veins.  The structure of veins differs from that of arteries in the following respects: The wall of a vein is distinctly thinner than that of an artery having the same sized lumen. The tunica media contains a much larger quantity of collagen than in arteries. The amount of elastic tissue or of muscle is much less. Because of the differences mentioned above, the wall of a vein is easily compressed. After death veins are usually collapsed. In contrast arteries retain their patency. In arteries the tunica media is usually thicker than the adventitia. In contrast the adventitia of veins is thicker than the media (specially in large veins). In some large veins (e.g., the inferior vena cava) the adventitia contains a considerable amount of elastic and muscle f ibres that run in a predominantly longitudinal direction. These f ibres facilitate elongation and VEINS sh o r t e ni ng o f t h e v e na c a v a w i t h respiration. This is also facilitated by the fact that collagen f ibres in the adventitia form a meshwork that spirals around the vessel. A clear distinction between the tunica intima, media and adventitia cannot be made out in small veins as all these layers consist predominantly of f ibrous tissue. 1. Tunica intima 2. Tunica media Muscle is conspicuous by its complete absence in venous spaces of erectile 3. Tunica adventi ti a tissue, in veins of cancellous bone, dural v e no us si nuse s, re ti nal v e i ns, and Cf. Collagen ﬁbres placental veins. Sm. Smooth muscles VENULES The smallest veins, into which capillaries drain, are called venules. They are 20–30 µm in diameter. Their walls consist of endothelium, basal lamina, and a thin adventitia consisting of longitudinally running collagen ﬁbres. Flattened or branching cells called pericytes may be present outside the basal laminae of small venules (called postcapillary venules), while some muscle may be present in larger vessels (muscular venules). The walls of venules (especially those of postcapillary venules) have considerable permeability and exchanges between blood and surrounding tissues can take place through them. In particular venules are the sites at which lymphocytes and other cells may pass out of (or into) the blood stream Table summary of types of arteries and their features Table summary of types of veins and their features LYMPHATIC VASCULAR SYSTEM The lymphatic vascular system is composed of lymphatic capillaries, lymphatic vessels, and lymphatic ducts, which collect and drain interstitial ﬂuid from the tissue into the large veins. Lymph (ﬂuid in the lymphatic system) contains lymphocytes, immunoglobulins, plasma, foreign antigens, and other substances. Lymphatic vessels carry lymph through the lymph nodes along the lymphatic vessels. Small lymphatic vessels (e.g seen on the hilus of lymph node) have large lumens and very thin walls, which are composed of a layer of endothelium and a little connective tissue with a few smooth muscle cells Large lymphatic vessels have thicker walls than small lymphatic vessels. Large lymphatic vessels are composed of connective tissues and multiple layers of smooth muscle cells LYMPHATIC VASCULAR SYSTEM Contraction of smooth muscle cells helps to move the lymph forward. Large lymphatic vessels are structurally similar to small veins, except they have larger lumens and prominent valves. Valves are present in all sizes of lymphatic vessels. They prevent lymph from f lo wing backward. Lymphatic vessels are often distinguished by lumens that contain clusters of lymphocytes and coagulated plasma. Lymphatic vessels can be found in most of the tissues of the body but not in the central nervous system, the bone marrow, or the hard tissues. LYMPHATIC VASCULAR SYSTEM Small lymphatic vessels, Large lymphatic vessels lymph node Bone and Bone Formation Written by: Dr. Obasi Kosi (PhD) Dept. of Anatomy UNEC. What is a Bone? Bone is a highly vascular tissue which is extensively permeated by blood capillaries that become incorporated during its development. Bone development is known as ossiﬁcation or osteogenesis. All bones are derived from mesenchyme, but by two different processes, depending on which kind of bone they are. Components of Bones : 1. Bone Cells. 2. Calciﬁed Matrix. 3. Periosteum (the outer covering). 4. Endosteum (the inner layer facing the Marrow Cavity). FUNCTIONS OF THE BONE 1. Support 2. Protection 3. Movement –bones and joints – levers 4. Mineral reservoir – Ca++, Phosphorus 5. Hemopoiesis – blood cell formation Types of Bone Cells : 1. Osteoprogenitor cells (Forming) 2. Osteoblasts cells (Immature cells) 3. Osteocytes (Mature cells) 4. Osteoclasts Osteoprogenitor Cells Arise from MESENCHYMAL STEM CELL. - unspecialized stem cells - undergo mitosis and develop into osteoblasts Found in PERIOSTEUM & ENDOSTEUM. Osteoblasts : Derived from OSTEOPROGENITOR cells and can divide. Have CYTOPLASMIC PROCESSES which are extensions of the cytoplasm. Basophilic cells on the surface of the bone (in PERIOSTEUM & ENDOSTEUM). Protein secreting cells. Secrete the ORGANIC PART OF THE BONE MATRIX. Osteocytes After the osteoblasts secrete the bone matrix, it becomes osteocyte in a small space called the LACUNA. Osteocytes are mature bone cells with ﬂattened nucleus and cytoplasmic processes. Can not divide. Maintain Matrix. The lacunae (the plural of lacuna) are connected together by small canals called CANALICULI. Canaliculi contain the cytoplasmic processes of the osteocytes. GAP JUNCTIONS connect the processes of the osteocytes in the canaliculi. Osteoclasts Called BONE RESORBING CELLS Multinucleated, motile, and acidophilic cells in the ENDOSTEUM. Originate by FUSION OF CELLS in the bone marrow. Secrete Enzymes that digest and remove bone m atri x f o rm i ng c av i ti e s and c anal s ( to maintain the Ca++ level in blood). Have cytoplasmic processes called RUFFLED BORDER. Bone Matrix Bone matrix consists of two components: 1. Organic components : Type 1 collagen. Chondroitin sulfate. 2. Inorganic components : Calcium & phosphorus forming HYDROXYAPATITE CRYSTALS. In H&E section, the decalciﬁed bone matrix is acidophilic. It shows the collagen type 1 and the bone cells. The bundles of collagen in the matrix form parallel layers called bone LAMELLAE BONE MATRIX 1. Inorganic salts – APATITE (crystals of calcium and phosphate) gives bone its hardness – oriented to resist stress. 2. Organic m atrix – collagen and ground substance – amorphous mixture of protein and polysaccharides. Bone components: Periosteum It's the outer covering of a bone. It consists of two layers : 1/ outer ﬁbrous layer of dense connective tissue attached to a bone by collagen ﬁbers. 2/ inner cellular layer (Osteogenic layer) of osteoblasts and osteoprogenitor cells. Function : bone formation and repair. Endosteum : it's a layer of cells on the the internal surface of bone facing the marrow cavity. The cells are the osteoprogenitor cells, osteoblasts, and osteoclasts. Function : Bone formation and repair. Types of Bones Bones exist in two forms : COMPACT BONE: forms the outer part of all bones in the body. CANCELLOUS (SPONGY) BONE: forms the inner part of all bones and is more in the epiphysis (the ends of a long bone) than in the diaphysis (the shaft of a long bone). Compact Bone The matrix of a compact bone consists of REGULAR lamellae (layers) of calciﬁed type 1 collagen. The lamellae form parallel cylinders called OSTEONS or HAVERSION SYSTEMS. Osteons are found deeply in the compact bone. Compact Bone The CONCENTRIC lamellae forming the osteons are called OSTEONAL LAMELLAE. Under the periosteum and endosteum, the lamellae do not form osteons and are called CIRCUMFERENTIAL LAMELLAE. Canals in a Compact Bone HARVERSIAN canal in the centre of each osteon contains osteoblasts, osteoclasts, and blood vessels. VOLKMAN'S canals contain blood vessels and connect the harversion canals of adjacent osteons. CANALICULI connect the lacunae with Haversion canals for nutrition of the osteocytes. Cancellous (Spongy) Bones The lamellae of spongy bone do not form osteons. The lamellae form INTERCONNECTED TRABECULAE (Small pieces of bone). The lamellae in each Trabecula are parallel to each other. The Trabeculae are separated by bone marrow spaces lined by endosteum. In Trabeculae, the canaliculi connect lacunae to bone marrow for nutrition of osteocytes. BONE FORMATION The process of bone formation is called ossiﬁcation or Osteogenesis. Bone formation occurs in four situations: 1) Formation of bone in an embryo 2) Growth of bones until adulthood 3) Remodeling of bone 4) Repair of fractures Bones are Formed by 2 Methods : 1. INTRAMEMBRANOUS OSSIFICATION. 2. ENDOCHONDRAL OSSIFICATION (INTRACARTILAGENOUS OSSIFICATION). Formation of Bone in an Embryo cartilage formation and ossiﬁcation occurs during the sixth week of embryonic development two patterns Intramembranous ossiﬁcation Flat bones of the skull and mandible are formed in this way “Soft spots” that help the fetal skull pass through the birth canal later become ossiﬁed forming the skull Endochondral ossiﬁcation The replacement of cartilage by bone Most bones of the body are formed in this way including long bones INTERMEMBRANOUS OSSIFICATION : Bo ne is fo rme d d ire c tly in a me mbrane o f MESENCHYMAL cells without the formation of cartilage. (Ex: Flat bones of the skull) MESENCHYMAL cells d ifferentiate into OSTEOPROGENITOR cells and OSTEOBLASTS which secrete bone matrix and form the PERIOSTEUM. OSTEOBLASTS secrete osteoid (f ib ers, GAGs, trapped osteoblasts become OSTEOCYTES Calcium salts are deposited in the matrix to form bone. OSTEOCLASTS remove part of the bone to form MARROW SPACES (Ex: Frontal bone, Maxilla) INTRAMEMBRANOUS OSSIFICATION ENDOCHONDRAL OSSIFICATION : In this type of ossiﬁcation, Hyaline Cartilage is formed ﬁrst and then replaced by bone (Ex: Long bones) Steps of Endochondral Ossiﬁcation  MESENCHYMAL cells differentiate into chondrocytes and form the cartilage model for bone ‘Hyaline cartilage’.  Chondrocytes near the centre of the cartilage model under HYPERTROPHY and alter the contents of the matrix they secrete enabling mineralization.  Chondrocytes undergo apoptosis due to decreased nutrient availability and degenerates leaving cavities; blood vessels and osteoblasts enter perichondrium which becomes periosteum and secretes BONE COLLAR on surface of cartilage.  Blood vessels and Osteoblasts from periosteum enter the cavities to form the PRIMARY OSSIFICATION CENTRE in the DIAPHYSIS.  OSTEOBLASTS secrete bone matrix.  OSTEOBLASTS mature into OSTEOCYTES  OSTEOCLASTS in the ossif ication centre remove part of the new bone to form the bone marrow cavity. Epiphyseal Growth Plate of Cartilage After ossiﬁcation, a piece of cartilage called EPIPHYSEAL GROWTH PLATE remains between the epiphysis and diaphysis. Ossiﬁcation of the growth plate continues up to the age of 20 years. The growth plate increases the length of bone because its cartilage continues to grow. Ossiﬁcation of Epiphyseal Plate Zones of ossiﬁcation of epiphyseal plate: 1. Zone of cartilage reserve (resting). 2. Zone of proliferation of chondrocytes. 3. Zone of hypertrophy of chondrocytes. 4. Zone of calciﬁcation of cartilage. 5. Zone of ossiﬁcation (formation of bone on the calciﬁed cartilage matrix). 6. Zone of resorption by osteoclasts. Bone Remodeling Is a balance between osteoblast formation and osteoclast degradation. Bone remodeling allows bones to adapt to stresses Heavily stressed bones becomes thicker and stronger Increased muscle growth will result in increased bone growth at the protuberances of bone.  Spongy bone replaced every 3 - 4 years. - compact bone every 10 years. Bone Remodeling Remodeling is usually initiated through osteoclast activation and removal of the bone matrix. Followed by osteoblast production of new bone. BONE REMODELING: FRACTURES  Fractures -blood clot will form around break.  - fracture hematoma  - inﬂammatory process begins - blood capillaries grow into clot - phago c yte s and o ste o c lasts remove damaged tissue.  -procallus forms and is invaded by osteoprogenitor cells and ﬁbroblasts.  -collagen and f ibrocartilage turns procallus to ﬁbrocartilaginous (soft) callus. - broken ends of bone are bridged by callus - osteoprogenitor cells are replaced by osteoblasts and form spongy bone - bony (hard) callus is formed - callus is resorbed by osteoclasts and compact bone replaces spongy bone. Nutritional Requirement Vitamin C promotes proline hydroxylation and is required for collagen formation. Def iciency of Vit. C results in thinning and fragility of the epiphyseal plates predisposing one to fracture. V i tam i ne D: I t p osse ss c al c i trol whi c h promotes the absorption of calcium and phosphate from the gut. Def ic iency of Vit D and sunshine in children results in rickets Ultraviolet Rays/ Sunshine: promotes the production of Vit. D3 from 7- dehydrocholesterol. H o r m o n a l R e g u l a ti o n o f B o n e a n d Resorption Parathyroid hormone (PTH): The blood calcium level is dually regulated through the actions of parathyroid hormone (PTH). The chief consequence of stimulation by PTH is that it promotes bone migration through enlargement of active ruf fled borders on osteoclast. This action is largely an indirect response mediated by osteoblast-derived factors, because PTH induces osteoblasts to secrete a peptide mediator and various cytokines that all enhance resorptive activity in osteoclasts. Hence, PTH induces osteoblasts to promote resorption by osteoclasts, liberating more calcium from bone matrix and consequently raising the blood calcium level. Calcitonin: A key effector cell in bone tissue responses to these two hormones is the osteoclast.. The action of calcitonin on osteoclasts inhibits bone resorption by diminishing the size and activity of the ruf fled borders on osteoclasts. Conversely, calcitonin depresses resorption by osteoclasts, reducing the amount of calcium they liberate from bone matrix and causing the blood calcium level to drop. These and other opposing actions of the two hormones maintain the blood calcium level within closely regulated limits. It should be noted also that an important effect of somatotropin (growth hormone, GH) is to augment bone growth by stimulating proliferation, secretion, and maturation of the chondrocytes in epiphyseal plates. Applied Anatomy Rickets: vitamin D def ic iency which leads to weakening and softening of bones in kids. It is as a result of insuf fic ient calcif ic ation at the growth plate during bone formation. It could result in the failure of apoptosis of the hypotrophied chondrocyte in the growth plate Osteoporosis. Achondroplasia: mutation of the FGFR3 gene which aids in formation of collagen and plays a role in bone ossif ic ation. It prevents adequate bone formation utero leading to shortened stature. Common indication of rickets is Knock Knees/ Bowlegs: Vit. D3 def ic iency. A scarcity of Ca++ and Phosphate delays calciﬁcation of the epiphyseal plates.

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