General Histology 1 Study Guide PDF

GENERAL HISTOLOGY 1/ PHYSIOTHERAPY [Document subtitle] 2022-2023 PROF. GEHAN KHALAF MSA  General Histology 1/ physiotherapy Lecture 1: Introduction to the cell By the end of this lecture...

GENERAL HISTOLOGY 1/ PHYSIOTHERAPY [Document subtitle] 2022-2023 PROF. GEHAN KHALAF MSA  General Histology 1/ physiotherapy Lecture 1: Introduction to the cell By the end of this lecture, students will be able to : 1. Identify different components of the cell. 2. Describe the fluid mosaic model of membrane structure 3. Outline the roles of phospholipid, cholesterol, protein and CHO. 4. Identify the difference between cell membrane and other membranes in the cell 5. Identify the bulk transport, different types of endocytosis and exocytosis. Dr. Gehan Khalaf Page 1  General Histology 1/ physiotherapy The cell (Eukaryotic): Structural & functional unit of living organism Cytoplasm Nucleus Eukaryotic cell has nuclear membrane &its DNA bound to protein Hyaloplasm (cytosol) Suspended bodies Clear colloid solution Contains 1-enzymes 2- protein 3- nutrients Organelles Inclusions (little organ) Living, organized & essential for the cell Nonliving, non-organized & nonessential Membranous Pigments Stored food Exogenous Glycogen 1. Cell membrane 1. Carbon particles 2. Mitochondria 2. Carotene Endogenous Fat 3. Endoplasmic reticulum 1. Hemoglobin 4. Golgi apparatus 2. Melanin 5. Lysosomes 6. Peroxisomes Cytoskeleton: formed of 1- Microtubules. 2- Micro (thin)filaments. ❖ Non membranous 3- Intermediate filaments. 1. Ribosomes 2. Microtubules 3. Filaments Dr. Gehan Khalaf Page 2  General Histology 1/ physiotherapy I.Inclusions: 1- Pigments Exogenous pigments (come from Endogenous pigments (synthesized inside the outside the body). body). a- Carotene a- Hemoglobin b- Dust and carbon particles b- Melanin 2- Stored food Glycogen (carbohydrates) Fat (lipid) Mainly in liver & muscle cells Mainly in fat cells (adipocytes)& liver cells LM: Stained by PAS.--> purple LM: stained by sudan black or sudan III II. Organelles Cell membrane(Plasma lemma) Definition: The thinnest layer surrounding the cell = 8- 10 nm L.M: Can’t be seen….. Why?..................................... E.M: 1- Trilaminar : Three layered structure outer electron dense, inner electron dense & Trilaminar ? intermediate electron lucent Osmium deposit All membranes of organelles have on hydrophilic head on each side this appearance, SO it is called unit membrane of the lipid bilayer 2- A fuzzy (filamentous) electron dense layer on the outer aspect = cell coat. Dr.Gehan Khalaf Page 1  General Histology 1/ physiotherapy Molecular structure of cell membrane: Features Function 1- Lipid 50% Have hydrophilic head and hydrophobic Act as a barrier between tail extra and intra cellular a.Phospholipids Form lipid bilayer aqueous media. Between the phospholipids long chains Has stabilizing effect and b- Cholesterol in inner and outer half of lipid bilayer increase rigidity of fluid nature of phospholipid in cell membrane 2- Protein 50% Two types: Act as: 1. Integral or intrinsic: Ion transport protein Embedded in lipid bilayer [Carriers-Pump] Channels, And Receptors 2. Peripheral or extrinsic : loosely bound, Part of Cytoskeleton 3- Present on the outer aspect of cell Function as specific receptors Carbohydrates membrane for: Formed of glycoprotein& glycolipid a- Adhesion. Cell coat or glycocalyx Are stained with PAS. b- Recognition. By EM appear as a fuzzy (filamentous) c- Response to hormone. layer on the outer aspect of cell membrane Cell membrane structure is called fluid mosaic model …..Why? ……………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………… Dr.Gehan Khalaf Page 2  General Histology 1/ physiotherapy Function of cell membrane I- Selective barrier for transport between intercellular & extracellular 1- Passive transport ( diffusion): With concentration gradient & no need of energy 2- Active transport: Against concentration gradient – need ATP & pump 3- Bulk (vesicular) transport: ❖ Exocytosis: Fusion of membranous vesicles with cell membrane & release its content to the extra cellular fluid. ❖ Endocytosis: Cell engulf a part of extra cellular compartment & surround it by membrane to form vesicle. There are 3 types: Pinocytosis Phagocytosis Receptor mediated endocytosis Cell Fluid Solid Receptor& its ligands engulf (a molecule with high affinity to a receptor), selective uptake To Pinocytotic vesicles phagocytic vesicles coated vesicles form 150 nm in 250 nm in diameter diameter Dr.Gehan Khalaf Page 3  General Histology 1/ physiotherapy Lecture 2: Cytoplasmic organelles By the end of this lecture, students will be able to : 1. Describe the light and electron microscopic features of organelles. 2. Correlate the function of the organelles with the function of the cell. 3. Interpret the structural changes in cell to understand the underlying cause of different diseases. Dr.Gehan Khalaf Page 4  General Histology 1/ physiotherapy Mitochondria Definition: Membranous organelles. Largest organelles 1 x 10 µm in size L.M: - needs special stains  It appears as rods or spheres purple black in color E.M.: Outer membrane Smooth, permeable Inner membrane - Rough (folds-cristae) to increase surface area. - The space inbeween the 2 membranes is called inter- membranous space. Cristae Contains ATP synthase enzyme. Matrix space Electron dense granules ( ca), (Intercristae) Enzymes of Carbohydrate and lipid metabolism, DNA , RNA + Ribosomes  So it can self divide and Form its own protein Function Energy production The number of mitochondria & its cristae increase in cells with high energy metabolism eg. liver cells & muscle cells Medical application Deficiency of mitochondrial enzymes leads to impairment of tissues with high energy requirements as muscle & nervous tissues Ribosomes Dr.Gehan Khalaf Page 5  General Histology 1/ physiotherapy Def. : Non membranous organelle consists of ribonucleo-protein particles (rRNA+protein) It is formed in nucleolus 2 Types 1- Free ribosomes: 2- Attached ribosomes: L.M: basophilic cytoplasm due to its high content of rRNA. E.M: electron dense granules, 2 subunits ( small – large ) Clusters connected by m.RNA Attached to rough endoplasmic (Polysomes) reticulum RER by its large subunits Function Protein synthesis ( ribosomes translate the code of amino acid sequence on mRNA.) Synthesis of protein which Synthesis of protein which need remains in cytoplasm for use to be segregated into RER such within the cell as : 1- secretory protein 2- lysosomal enzymes 3- Integral protein of e.g embryonic cells, plasma membrane e.g. Protein secreting cells: Dr.Gehan Khalaf Page 6  General Histology 1/ physiotherapy Endoplasmic reticulum (membranous organelle) 2 types Rough endoplasmic reticulum RER Smooth endoplasmic reticulum SER LM basophilic cytoplasm Acidophilic cytoplasm EM: 1. Network flat membranous sacs 1. Network of membranous called a cisternae tubules 2. Parallel & Interconnected 2. Not covered by ribosome 3. Covered by ribosomes 3. continuous with RER 4. Continuous with the outer nuclear membrane. Function: Synthesis of protein which need to be 1. Phospholipid synthesis, for all segregated into RER as: cell membranes. 2. Steroid hormone synthesis, 1- …………………………………… as in cells of adrenal cortex. 2- ……………………………………. 3. Glycogen synthesis, as in liver 3- ……………………………………. &muscle cells Transfer vesicles, bud off RER, 4. Drug detoxification, in liver transport the newly formed cells protein to Golgi complex (cis face) 5. Ca storage & pump, in muscles for further processing. They are very prominent in protein secreting cells Golgi apparatus GA Membranous organelle LM: needs special stain EM: Golgi saccules are formed of: - Saucer shape membranous cisternae - Inter connecting - Have 2 face; 1. Convex, cis, immature face receive the transfer vesicles from RER 2. Concave, trans, mature face from which lysosomes and secretory vesicles are released. Dr.Gehan Khalaf Page 7  General Histology 1/ physiotherapy Function 1- Concentration & Modification of protein 2- Sorting & package different proteins to transport to their sites. Secretory proteins , lysosomes and Integral membrane protein ❖ Lysosomes Def.: Membranous organelle / Abundant in phagocytic cells LM: Cannot be seen, EM: 2 types can be identified - 1 ary Lysosomes Homogenous electron dense vesicles./Newly formed not entered in digestive process ‫ ־‬2ary Lysosomes Heterogeneous electron dense vesicles. / Entered in digestive process Function: Intra-cytoplasmic digestion of any engulfed materials& old organelles Different pathways that deliver material to be digested in lysosomes 1. Extra cellular large solid particle  engulfed by phagocytosis  form hetero-phagosomes  lysosomes [2ary] 2. Intracellular particles eg. Old organelle  surrounded by a membrane derived from SER[Autophagy]-> autophagosomes lysosomes [2ary] The digested particles diffuse lysosomal membrane into cytoplasm to be used by cell. The undigested particles [debris] remain within the vacuole and called residual body Medical application Deficiency of lysosomal enzymes  accumulation of undigested material within the cells which interfere with the normal functions Dr.Gehan Khalaf Page 8  General Histology 1/ physiotherapy Lecture 3: Cytoskeleton and nucleus By the end of this lecture, students will be able to : 1. Identify the components and function of cytoskeleton 2. Describe the structure and function of microtubules 3. Outline the structure and function of centriole, cilia and flagella 4. Identify the types of filaments and its significance 5. Identify structure and function of different components of the nucleus (chromatin, nuclear envelope and nucleolus) 6. Compare between the 2 types of chromatin. 7. Interpret the structural changes in cell to understand the underlying cause of different diseases. Dr.Gehan Khalaf Page 9  General Histology 1/ physiotherapy ❖ Microtubules Non membranous organelle - The wall of the tubules consist of protein subunits called tubulin (heterodimer α & β tubulin). Sites: Medical application 1- Cytoplasm ( as a part of cytoskeleton). Chemotherapeutic drugs  prevent 2- Centrioles formation of microtubules  stop cell 3- Cilia & flagella division 4- Mitotic spindles Movement of chromosomes along mitotic spindles in cell division ❖ Centrioles - Paired structure, close to nucleus called (centrosome) - 2 cylinders, perpendicular - Its wall formed of: 9 triplets of microtubules = 27 microtubules - Function: Formation of mitotic spindle, cilia & flagella ❖ Cilia; Motile processes with microtubules core 1. Shaft - 2 singlets microtubules in the center + 9 doublets microtubules peripheral, having dynein arm with ATPase activity for movement - Covered by a cell membrane 2. Basal body: similar to centriole (9 triplets of MTs) 3. Rootlets microtubules extend from basal bodies to fix in the cytoplasm Function: Help movement of particles in one direction over surface of cell; in Respiratory epithelium Medical application Congenital deficiency of ❖ Flagella is a long single cilium found in sperm dynein arm in cilia  immotile cilia  repeated respiratory tract infection and infertility Dr.Gehan Khalaf Page 10  General Histology 1/ physiotherapy Filaments Non membranous organelle 3 types 1- Thin , microfilaments = 6 nm filaments ,formed of Actin protein. Sites a. Muscle ( help in contraction) b. Cell cortex (under cell membrane as part of cytoskeleton) c. Constriction ring (in cell division - telophase) d. Core of microvilli 2-Thick filament = 16 nm filaments ,formed of Myosin protein. Sites: in muscle, it is actin binding protein 3- Intermediate filaments 10 -12 nm They are stable , & formed of heterogeneous types of protein in different tissues Types a. Keratin……………… Epithelium b. Desmin…………….. Muscle c. Neurofilament……… Neurons d. Lamins…………….. Nuclear membrane Function of cytoskeleton ( Microtubules, microfilaments& intermediate filaments) : 1- Shaping & support of cell 2- Movement of organelles & vesicles inside the cell 3- Movement of entire cell Medical application Identification of intermediate filament proteins by means of immunocytochemical methods is a routine procedure in tumors to reveal the cellular origin of the tumor Dr.Gehan Khalaf Page 11  General Histology 1/ physiotherapy Nucleus Nuclear envelope Thin line surrounds the nucleus LM EM Function Dark basophilic 1. Double unit membrane Provide selective line b. Outer membranous layerCovered pathways between with ribosomes / Continuous with nucleus & cytoplasm RER through nuclear pores. c. Inner membranous layer-> attached to Fibrous lamina & Peripheral heterochromatin 1. Perinuclear cisterna 2. Nuclear pores Chromatin; Coiled strands of DNA bound to basic protein ( histone) Types of Heterochromatin Euchromatin chromatin Coiled & condensed / Inactive / Extended & uncoiled / Active (more DNA Dark stained surface available for transcription) / Light- stained LM Basophilic granules Can’t be seen EM Electron dense granules Thin pale threads a- peripheral chromatin b- Nucleolus associated c- Chromatin islands Nucleolus ;Site of ribosome subunits formation Active cells have euchromatin > heterochromatin The nucleus appears light stained, vesicular or open face nucleus. Inactive cells have heterochromatin > euchromatin. The nucleus appears dark stained or condensed nucleus. Dr.Gehan Khalaf Page 12  General Histology 1/ physiotherapy Lecture 4: Epithelium By the end of this lecture, students will be able to : 1. Describe the general characteristics of the epithelial tissue. 2. List the types of epithelial tissue. 3. Describe the structure and correlated functions of each type of epithelial membranes. 4. List the specializations of the different epithelial cell surfaces. 5. Asses the significance of different types of the cell junctions. Dr.Gehan Khalaf Page 13  General Histology 1/ physiotherapy The human body is composed of four basic tissues: Epithelial, Connective, Muscular and Nervous tissues. Main characters of the epithelial tissue: – Mainly of cells with little intercellular substances. – Covers surfaces (covering epithelium) or lines cavities. – The cells lie on a basement membrane – No blood vessels or lymphatics enter in between the cells (avascular), but nerves do. – Nourishment of epithelial tissue occurs by diffusion of nutrients and oxygen from the blood vessels present in the underlying connective tissue. – Epithelial cells are continuously renewed and replaced. – Epithelial tissue may be derived from ectoderm, mesoderm or endoderm. Classification of Epithelial Tissue Surface epithelium [epithelial membranes] – Covers surfaces or lines cavities Glandular epithelium – It is a special type of epithelium characterized by its secretory function. – Glands originate from epithelial cells that leave the surface and penetrate the underlying connective tissue. Types of glandular epithelium – Exocrine glands: when the cells are connected to the surface by duct. – Endocrine gland:. When the cells lose their connection to the surface. Neuroepithelium It is a special type of epithelium which is modified to receive stimuli of some special sensations and convert them into electrical impulses. Sites: – Taste buds for taste sensation. Dr.Gehan Khalaf Page 14  General Histology 1/ physiotherapy I - Surface epithelium – Covers surfaces or lines cavities – Classified according to the number of cell layers into: A. Simple epithelium: formed of a single layer of epithelial cells. B. Stratified epithelium: formed of several layers. A- Simple epithelium 1-Simple squamous epithelium. One layer of flat cells and a flat nucleus. Sites: – Lining the blood vessels (endothelium). – Lining the serous membranes: pleura, pericardium and peritoneum (mesothelium). – Lining the lung alveoli and Bowman’s capsule of the kidney Functions: This type of epithelium is adapted to form a thin membrane for transport & diffusion, and smooth surface to facilitates movement of the viscera. 2- Simple cuboidal epithelium a single layer of cubical cells and rounded central nucleus. Site: – Lining duct of the glands. Function: covering surfaces. 3- Simple columnar epithelium: a single layer of columnar cells and basal oval nucleus. Types and sites: – Unmodified columnar cells: in ducts of the glands. – Modified columnar cells: (secretory, absorptive or ciliated): 1. Secretory: Lining epithelium of the stomach. 2. Absorptive: Have apical microvilli [brush border] to increase the surface area for absorption e.g. the lining epithelium of the small intestine. 3. Ciliated: the free surface is supplied by cilia e.g. uterus. 4- Pseudostratified columnar epithelium: The cells are overcrowded, but they all rest on the basement membrane. Some cells appear short and not reaching the surface. The nuclei appear at different levels giving a false impression of being a stratified type. Dr.Gehan Khalaf Page 15  General Histology 1/ physiotherapy Types and sites: a. Non-ciliated: Large ducts of salivary glands. b. Ciliated: The surface of the cells is provided by cilia and usually associated with goblet cells e.g. trachea, bronchi [RESPIRATORY EPIHELIUM]. B-Stratified epithelium Formed of more than one layer of cells. Types of stratified epithelium: 1- Stratified squamous epithelium: a. Stratified squamous non-keratinized epithelium: - Basal: one layer of columnar cells, - Intermediate : several layer of polygonal cells - Superficial : thin squamous cells at the surface. Sites: It is found in wet surfaces of all openings leading to the skin such as: oral cavity, tongue, oesophagus, cornea, anal canal and vagina. Function: protection b. Stratified squamous keratinized epithelium It is similar to the stratified squamous non-keratinized epithelium but the flat cells of the top layer are covered by non-living layer of keratin. This type is tough, resists friction and is impermeable to water. Sites: Epidermis of the skin. Function: protection 2- Stratified cuboidal epithelium: The cells in uppermost layer are cubical in shape. 3-Stratified columnar epithelium: The cells in the uppermost layer are columnar cells. 4-Transitional epithelium [Urothelium]: It is highly specialized to withstand a great degree of distension. Sites: In the urinary system: Pelvis of the kidney, ureters, urinary bladder. In the empty state, it is formed of 6-8 layers of cells: In the stretched state:2-3 layers. Dr.Gehan Khalaf Page 16  General Histology 1/ physiotherapy Polarity and Specializations of Epithelial Cell Surfaces - Polarity (structural and functional asymmetry) is a characteristic of epithelial cells. -Each of the different three surfaces show different structures adapted to their functions. Specializations of the Apical Surface of Epithelial Cells A- Cilia -Cilia are hair like motile projections or processes extending from the free surfaces of respiratory epithelial cells. Its core formed of microtubules B- Microvilli – Microvilli are non-motile projections extending from the free surface of intestinal epithelium. Their cores are formed of a bundle of actin microfilaments. – Function: Microvilli increase the surface area for absorption. Specializations of the basal surface Basal lamina / Basment membrane A sheet like extra cellular structure separate connective tissue from epithelium Specializations of the Lateral surface of Epithelial Cells – Lateral surface specializations answer the question (How the cells are linked together?) – Lateral surface specializations include: Cell junctions Types of cell junctions 1.Occludens (tight) Junction: Fusion of outer layer of 2 adjacent cell membranes to Close the inter- celullar space (ICS) to prevent passage of any substances between the cells, so it act as a barrier found in Intestinal epithelium & Endothelium of blood capillaries 2. Adhering Junction [as desmosomes & zonula adherens] Lateral borders of adjacent cells are connected by filaments to form strong adhesion. Found in Intestinal epithelium & Epidermis of the skin 3. Gap junction (Communicating junction ) – Cells have narrow ICS & joined by channels  communication & passage of substances – It is found also in non epithelial tissue: Cardiac muscle fibers, nerve cells, bone cells and smooth muscle fibers. Dr.Gehan Khalaf Page 17  General Histology 1/ physiotherapy Lectures 5: Connective tissue By the end of this lecture, students will be able to : 1- Describe the general structure of the connective tissue. 2- Describe the structure and staining properties of the collagen, elastic and reticular fibers with correlation to function. 3- Describe the structure and correlated functions of the different types of the connective tissue cells. 4- Describe the sites, structure and correlated functions of the different types of the connective tissue proper. Dr.Gehan Khalaf Page 18  General Histology 1/ physiotherapy General characters of the connective tissue: -Connective tissue is mesodermal in origin. -It connects, binds and supports other tissues and organs. -It consists of cells, fibers and intercellular substance. -It is penetrated by blood vessels, lymphatics and nerves. Functions of the connective tissue Supports organs and cells. Medium for exchange of nutrients and wastes between blood and tissues. Protects against microorganisms. Repairs damaged tissues. Types of connective tissue: ▪ Connective tissue proper,loose areolar CT ▪ Special types : Adipose ,Cartilage, Bone & Blood Loose (areolar) Connective Tissue: Cells Extra cellular matrix Fibers Ground substance 1. Collagen fibers are tough and provide tensile strength 2. Elastic fibers allow for stretch Tissue fluid 3. Reticular fibers make networks. Macromolecules Derived from proteoglycans and the blood glycoprotein capillarie Dr.Gehan Khalaf Page 19  General Histology 1/ physiotherapy Connective tissue fibers 1-Collagen fibers type I/ white fibers White in color in fresh state Tough and flexible, resist tension Thick, long & Non-branching fibers Form wavy branched bundles Collagen fibers are synthesized by fibroblasts Medical application Scurvy [ vitamin C DEFICIENCY] Defect in synthesis of collagen patient will suffer from bleeding gum, loose teeth, poor wound healing, poor bone development 2-Reticular fibers o Formed of type III collagen. o Thin branching fibers form networks. o They are synthesized by fibroblasts 3-Elastic fibers o Formed of elastin protein o Elastic fibers are yellow in color in fresh state. o They are stretchable but regain their original length. o Are thin, straight and branching fibers ,not form bundle o Synthesized by fibroblasts Connective tissue cells Cells of the connective tissue are classified according to their shape into: Branched cells Oval or rounded cells UMCs Mast cells Fibroblasts Plasma cells Pericytes Fat cells Macrophages Extravasated leucocytes Pigment cells Dr.Gehan Khalaf Page 20  General Histology 1/ physiotherapy 1. Undifferentiated Mesenchymal Cells (UMCs) Origin: young embryonic mesenchymal tissue. Functions: UMCs can differentiate to other C.T cell. And other structures as blood cells, smooth muscle fibers and endothelial cells. 2. Pericytes Origin: UMC Sites: surround the endothelium of blood capillaries and small venules. They usually lie between the endothelial cells and their basement membrane. Functions: Pericytes are postnatal UMCs, can differentiate into fibroblasts, smooth muscle fibers, endothelial cells and osteogenic cells. Contractile  control the diameter of blood capillaries. 3. Fibroblasts Origin: UMCs, pericytes. Site: most common cell in the C.T. Functions: Synthesis of ECM [connective tissue fibers + Proteoglycans and glycoproteins). Healing and repair of injured C.T. 4. Pigment Cells, melanophore Origin: UMCs, pericytes Sites: iris of the eye, dermis of the skin. Functions: Store melanin pigment to protect the tissues from the harmful effects of ultraviolet rays. 5. Macrophages [histiocytes] Origin: blood monocytes. Functions: Phagocytosis: they phagocytose foreign particles, bacteria and microorganisms. Dr.Gehan Khalaf Page 21  General Histology 1/ physiotherapy 6. Mast Cells Origin: progenitor cells in the bone marrow. Functions: Synthesis, storage and secretion of: heparin, histamine. In allergy: degranulation of mast cells and release of various mediators occur which promotes the allergic reactions known as hypersensitivity reaction 7. Plasma Cells Origin: B-lymphocytes Functions: Synthesis and secretion of antibodies (immunoglobulins). The antigens stimulate B lymphocytes  plasma cells ,(secrete immunoglobulins). 8. Fat Cells (adipose cells) Origin: UMCs. Types: A) Unilocular B) Multilocular A- Unilocular adipose cells Sites: [ in white adipose CT] Subcutaneous tissue, around blood vessels, around kidneys Functions: Synthesis and storage of fat. Heat insulation. Supporting function e.g. fat around the kidney. B-Multilocular adipose cells Sites: [Brown adipose CT] Fetuses and new born. Multilocular adipose cells produce heat and thus protect the newborn against cold. It is greatly reduced in adulthood [ present in interscapular and neck region only]. It is called brown fat due to high content of mitochondria and rich blood vessels Functions: Heat generation. Extravasated Leucocytes Leucocytes (neutrophils, eosinophils, lymphocytes, basophils and monocytes) leave the blood stream to enter the connective tissue to perform immune functions. ❖ Free cells in CT : leucocytes plasma cells mast cells free macrophage Dr.Gehan Khalaf Page 22  General Histology 1/ physiotherapy Special Types of connective tissue proper 1- Dense Collagenous Connective Tissue: Formed mainly of collagen fibers + fibroblast A) Dense irregular collagenous connective tissue Mainly fibroblasts and fibrocytes in between irregular bundles of collagen fibers resists stretch from all directions. Sites -Capsules of organs e.g.the liver and the spleen. -Periosteum and perichondrium B) Dense regular collagenous connective tissue Mainly fibroblasts and fibrocytes in between regular collagen bundles that resist tensile forces. Sites: – Tendons and ligaments 2- Elastic Connective Tissue: Mainly fibroblasts in between elastic fibers. Sites: – Ligamentum nuchae. 3- Reticular Connective Tissue reticular cells and reticular fibers that form mesh-like networks. Sites: stroma of any organs. Dr.Gehan Khalaf Page 23  General Histology 1/ physiotherapy Lectures 6: Cartilage By the end of this lecture, students will be able to : 1- Describe the general structure of cartilage. 2- Identify the nutrition and growth of cartilage 3- Compare between the structure of hyaline cartilage, the elastic cartilage and the white fibrocartilage with correlation to the function. Dr.Gehan Khalaf Page 24  General Histology 1/ physiotherapy Cartilage is a special type of connective tissue. It is mesenchymal in origin. Cartilage is formed of: 4- Cells (chondrocytes). 5- Extracellular matrix(ECM) – The extracellular matrix is avascular, firm, and rubbery. – It consists of fibres and ground substance. There are three type of cartilage according to the type of fibres in the matrix 1- Hyaline cartilage (collagen type II) 2- Elastic cartilage (collagen type II+ elastic fibres) 3- White fibrocartilge (collagen type II+ collagen type I) The perichondrium is a dense connective sheath covered all cartilage except articular cartilage [one site of hyaline cartilage] and white fibrocartilage Hyaline cartilage [hyalo= clear] Hyaline cartilage is the most common type. Sites: 1- Costal cartilage 2- Most of the fetal skeleton 3- Articular cartilage 4- Epiphyseal plate of long bone 5- Wall of large respiratory passages (nose,larynx,trachea and bronchi) Structure : Perichondrium: Perichondrium Outer fibrous layer : ‫־‬ Formed of dense irregular connective tissue and blood Chondroblast vessels ‫־‬ Its function is nutrition of avascular cartilage Inner chondrogenic layer: formed of chondroblasts Chondrocytes Chondroblasts Cell nest ▪ Origin: UMCs & pericytes ▪ Site: In the inner layer of the perichondrium. -Shape: oval. They are NOT present inside lacunae. Function: o Synthesis and secretion of ECM of cartilage o Divide and differentiate to chondrocytes. So, it is responsible for appositional growth (addition new layers on the surface) of cartilage and repair of damage. Dr.Gehan Khalaf Page 25  General Histology 1/ physiotherapy 1- Chondrocytes: ▪ Origin: chondroblasts. ▪ Site: Inside the matrix. - Shape: They are present inside lacunae. At the periphery they are small and oval. Towards the center of the hyaline cartilage, the chondrocytes are large and rounded and usually present in groups (up to 8 cells in one lacuna called cell nests. Function: o Synthesis & secretion of ECM of cartilage o Can divide So, it is responsible for interstitial growth of cartilage (adding new matrix from within) 2- Extracellular matrix [clear, basophilic - pale blue] 1- Ground substance a- Macromolecules: b- Tissue fluid - 75% of matrix weight - To Allow easy diffusion of O2 & nutrients from blood vessels of perichondrium to avascular cartilage 2- Fibers - Fine network of collagen type II. Elastic cartilage Yellow in fresh state More flexible and distensible Ear Pinna Sites: Elastic cartilage 1. Ear pinna 2. External auditory canal 3. Eustachian tube 4. Epiglottis 5. Some cartilage of larynx Structure : - Similar to hyaline cartilage except its matrix contain a network of elastic fiber in addition to collagen type II White fibrocartilage White in fresh state In regions subjected to pulling force Sites: 1. Intervertebral disc Collagen fibers 2. Symphysis pubis 3. Semilunar cartilage of knee 4. Near tendon insertion Rows of chondrocytes Structure: 1- Rows of chondrocytes with cartilage matrix 2- Bundles of collagen fibers type I. 3- No perichondrium ( blood vessels present in between collagen fibers) Dr.Gehan Khalaf Page 26  General Histology 1/ physiotherapy Lectures 7: Bone By the end of this lecture, students will be able to : 1. Describe the general structure of the bone. 2. Describe the structure and correlated functions of the bone cells and the bone matrix. 3. Describe the endosteum and periosteum. 4. Describe the structure of the Haversian system (osteon). 5. List the sites of the compact bone and the cancellous bone 6. Compare between the structure of compact and cancellous bone Dr.Gehan Khalaf Page 27  General Histology 1/ physiotherapy Bone is mesenchymal in origin. It is highly vascular.. It is a specialized connective tissue (CT), formed of: I. Bone cells: osteogenic, osteoblast, osteocytes and osteoclasts. II. Bone matrix (calcified matrix). It is covered on the external surfaces by periosteum and lined on internal surfaces by endosteum I. Bone matrix 1. Organic matrix (Osteoid tissue) Fibers ( 90 %) : - Collagen type I - It is responsible for acidophilic matrix and high resistance of the bone. Gound substances (10%) - Macromolecules: - Tissue fluid: more in young and less in old. 2. Inorganic matrix (minerals) - Mainly Calcium , deposit on collagen fiber to form bone lamellae. II. Bone cells 1. Osteogenic cells Origin: UMC. & pericytes Site : In periosteum & endosteum. Function: - Divides & differentiates into osteoblast. 2. Osteoblast (bone forming cell) Origin: Osteogenic cell Site : In periosteum & endosteum. Function: a. Formation & secretion of organic bone matrix (osteoid tissue) b. Release alkaline phosphatase which help deposition of ca in osteoid tissue. c. Differentiate into osteocytes 3. Osteocytes Origin: Osteoblast. Site: In between bone lamellae, inside lacunae & its processes inside canaliculi. Function: Keep the integrity of bone and it is non dividing cell. Dr.Gehan Khalaf Page 28  General Histology 1/ physiotherapy 4. Osteoclasts Origin: Monocyte Site: In Howship’s lacuna, on bone surfaces where resorption occur (Endosteum & bone cavities). Function a. Bone resorption. b. Phagocytosis. Bone remodeling: - A process which involve partial resorption of bone tissue and simultaneous laying down of new bone. - Cells responsible for bone remodeling are osteoblast and osteoclast. Types of bone according to the structure 1. Compact bone Sites: a. Shaft of long bone b. outer covering of any cancellous bone structure: a. Periosteum - Outer fibrous layer: formed of dense irregular CT and blood vessels - Inner osteogenic layer: formed of osteogenic cells & osteoblasts. - Function 1. Provide blood supply 2. Appositional growth 3. Repair of fracture 4. Site of tendon attachments b. Endosteum: Lines inner surfaces and cavities of bone - Contains osteogenic cells, osteoblasts and osteoclasts - Function: Nutrition & appositional growth. c. Haversian canal (longitudinal canal) & volkmann’s canal ( transverse canal) i. Both are lined with endosteum ii. Both contain blood vessels,lymphatic & nerves iii. Inter connect with each other & with periosteum &endosteum d. Bone lamellae (calcified collagen fiber) i. outer circumferential lamellae; under periosteum. ii. Inner circumferential lamellae; under endosteum. iii. Concentric lamellae; around Haversian canal. iv. Interstitial lamellae; in between Haversian system. e. Osteocytes inside lacuna present between bone lamellae. Dr.Gehan Khalaf Page 29  General Histology 1/ physiotherapy Haversion system (osteon): Structural unit of compact bone, it is formed of : 1- Haversian canal. 2- Concentric bone lamellae. 3- Osteocytes within their lacuna in between lamellae. 2. Cancellous bone ( Spongy bone) Sites: 1- Flat bones. f. Short bones. g. Epiphysis of long bone. Structure : 1. Periosteum 2. Outer thin shell of compact bone. 3. Bone trabeculae: - Branching and anastomosing. - Formed of irregular bone lamellae & osteocytes within lacuna in between. 4. Bone marrow spaces: - Are lined by endosteum. - Contain bone marrow. Dr.Gehan Khalaf Page 30  General Histology 1/ physiotherapy Lecture 8: Blood cells By the end of this lecture, students will be able to : 1. Correlate the structure of erythrocytes (RBCs) with the function. 2. Define some clinical terminology related to erythrocytes 3. Classify leucocytes and state its general properties. 4. Describe structure and correlated functions of each type of blood leucocytes. 5. State the general properties of the blood platelets with correlation to function. Dr.Gehan Khalaf Page 31  General Histology 1/ physiotherapy Blood is a special type of connective tissue. It is formed of blood cells and plasma. Blood cells (forming 45% of total blood volume) are: red blood corpuscles [Erythrocytes], white blood cells [Leucocytes] and blood platelets [Thrombocytes]. Erythrocytes or red blood corpuscles (RBCs) General properties of red blood cells: Normal Abnormal conditions Site never leave the circulatory system Hemorrhage = erythrocytes leave circulatory system Shape - Biconcave - Poikilocytosis: Abnormal shape that disc might occur in certain diseases - Forms rouleaux in slow circulation Size 6-9 μm with a mean of 7.5 μm. Microcyte= less than 6 Macrocyte= more than 9 Anisocytosis = great variations in size Stain - In H&E stained sections; Hypochromic= reduced amount of Hb acidophilic with pale central Hyperchromic = increased amount of Hb area. [why?] - Normochromic = normal content of Hb Number In male: 5 – 5.5 x 106 / mm³, Anemia = decreased number In female: 4.5 – 5 x 106 / mm3 Polycythemia = increased number Life 120 days Old RBCs destroyed in liver-spleen &bone span marrow ❖ Correlation of the structure with the function of RBCs 1. Biconcave  facilitate the gas exchange as it increase surface area for gas exchange 2. No nucleus or organelles More space for Hb 3. Presence of Hb  bind with O2 4. Cytoskeleton under the erythrocyte membrane - Maintain the shape of erythrocytes - Maintain the elasticity & flexibility of the membrane allow RBCs to change its shape when pass inside narrow capillaries without damage. 5. Outer surface is covered by glycocalyx (cell coat) which is responsible for blood grouping (A, B, AB & O). Dr.Gehan Khalaf Page 32  General Histology 1/ physiotherapy Leucocytes or white blood cells (WBCs)  Total leucocytic count is: 6000 – 10,000/mm³. more than 10000= leukocytosis, less than 6000= leucopenia.  They are true cells having nuclei and organelles + lysosomes [non specific granules].  Leucocytes are classified according to presence or absence of specific granules into: 1. Granular leucocytes: including: neutrophils, eosinophils and basophils. 2. Agranular or non-granular leucocytes: including: lymphocytes and monocytes. Granular Leucocytes 1- Neutrophils: (Polymorphnuclear leucocytes) Number: 60 – 75% of total leucocytic count. Shape & size: rounded cells, 10 – 12 μm in diameter. Nucleus: is multilobed, segmented formed of 3 to 5 lobes interconnected by chromatin strands. Cytoplasm: contains usual organelles and lysosomes ❖ Neutrophilic specific granules: contain bacteriostastic enzymes.  Functions: Neutrophils are considered as the first line of defense against invasion of bacteria. ❖ Pathological increase: called neutrophilia, e.g.: acute pyogenic infections (as tonsillitis & appendicitis). 2-Eosinophils  Number: 1-5% of total leucocytic count.  Shape & size: rounded cells, 10-12 µm in diameter.  Nucleus: is bilobed (formed of 2 lobes connected by chromatin thread).  Cytoplasm: contains usual organelles and lysosomes ❖ Acidophilic specific granules: contain major basic protein (MBP) and histaminases enzymes.  Functions: 1) Play an important role in controlling the local response in allergic reaction: They release the contents of their granules (as histaminases) to inactivate histamine. 2) Play a role in the defense against certain types of parasites. They discharge MBP to kill these parasites. ❖ Increase number of eosinophils is named eosinophilia. It occurs in allergy and parasitic infection. Dr.Gehan Khalaf Page 33  General Histology 1/ physiotherapy 3-Basophils Number: 0.5-1% of total leucocytic count. Shape & size: rounded cells, 10-12 µm in diameter. Nucleus: is S- shaped or irregular in shape. Cytoplasm: contains usual organelles and lysosomes ❖ Basophilic specific granules: contain heparin and histamine Functions: Release of histamine, heparin promoting allergic reaction. ❖ Increase number of basophils is named basophilia. It occurs in allergy. Non-Granular Leucocytes Lymphocytes Number: constituting 20 – 25% of total leucocytic count. Shape & Size: rounded cell 1. Small lymphocytes: 6-8 µm 2. Medium-sized lymphocytes: 10-15 µm. Nucleus: large central, rounded and condensed nucleus occupying most of the cell. A thin rim of ic cytoplasm is present around the nucleus. Cytoplasm: contains usual organelles and lysosomes ❖ No specific granules. Functions of lymphocytes: B lymphocyte—>Plasma cells —> Antibodies. Humoral immunity T lymphocytes—>Cytotoxic cells ; Cellular immunity Natural killer cell  non specific kill viral infected cells & cancer cells [innate immunity] ❖ Increase their number is named lymphocytosis. It occurs in viral infection as influenza and chronic diseases as T.B. Monocytes Number: 3-8% of total leucocytic count. Shape & size: large rounded cells, 12-20µm in diameter (the largest leucocytes Nucleus is large and kidney –shaped.  Cytoplasm: contains usual organelles and many lysosomes ❖ No specific granules Functions: 1. Phagocytic and Differentiate into macrophages. Dr.Gehan Khalaf Page 34  General Histology 1/ physiotherapy Blood Platelets (Thrombocytes) Number: 250,000- 400,000/mm3. Increase in number = thrombocytosis Decrease in number = thrombocytopenia Shape & origin: rounded to oval biconvex cell fragments detached from megakaryocytes (cells present in the bone marrow). Size: are 2 – 4 μm in diameter. - Cytoplasm: They lack nuclei and have central granular region that contains Coaggulation factors  blood Coagulation and formation of thrombus Dr.Gehan Khalaf Page 35  General Histology 1/ physiotherapy Lecture 9: Muscular tissue By the end of this lecture, students will be able to : 1- Classify muscle tissue, according to their morphology and according to their functions. 2- Describe the structure, sites and correlated functions of the skeletal muscle fibers. 3- Compare between the skeletal muscle, the cardiac muscle and the smooth muscle Dr.Gehan Khalaf Page 36  General Histology 1/ physiotherapy The muscle tissue is formed of muscle fibers surrounded by connective tissue The muscle fibers are cells but called fibers due to its length. Its cytoplasm called sarcoplasm , cell membrane called sarcolemma Types of muscle fibers: 1. Skeletal muscle fibers. 2. Smooth muscle fibers 3. Cardiac muscle fibers 1-Skeletal muscle fibers Are striated voluntary muscle fibers. LM of skeletal muscle fiber: – Shape: Long cylindrical. – Nucleus: multiple rod shape nuclei – Cytoplasm: acidophilic show cross striations. These striations are due to presence of myofibrils [ Each myofibril shows alternating light bands (I bands) and dark bands (A bands)]. The EM structure of skeletal muscle fiber A. Organoids: Myofibrils, T tubule, sER (sarcoplasmic reticulum), Mitochondria. B. Inclusions: glycogen granules and myoglobin. Myofibrils: - Arranged longitudinally and parallel to each other’s. Each myofibril show alternating dark (A) and light (I) bands. - The dark band is bisected by pale H-zone and the light band is bisected by dark z-line. - Sarcomere is the distance between 2 successive z lines. It is the contractile unit of skeletal muscle. It is formed of one dark band with 2 halves I band on either side. - The myofibril contains: A. Thick myosin filaments: confined to the dark band B. Thin actin filaments: they extend from the Z- line on either side of the sarcomere to the dark band short of reaching the H- zone Dr.Gehan Khalaf Page 37  General Histology 1/ physiotherapy Transverse tubules (T-tubules): – These are invaginations of the sarcolemma at the level of the junction between the A & I bands. Their function is conduction of waves of depolarization to all parts of the sarcoplasmic reticulum. The sarcoplasmic reticulum (SR): – It is the sER. – It is formed of tubules and Terminal cisternae, close to the T-Tubule. The triad: – At the junction between A and I bands, the myofibrils are surrounded by three structures: one T-Tubule and two terminal cisternae Structure of skeletal muscle: - Skeletal muscle is formed of bundles of skeletal muscle fibers. - The individual fiber is surrounded by C.T. called endomysium. - Each bundle is surrounded by C.T called perimysium - Many bundles of skeletal muscle fibers are surrounded by epimysium Repair of muscle after injury: Satellite cells are flattened mononucleated cells present between the sarcolemma and basement membrane.. They act as stem cells responsible for repair of small defect after trauma or disease [large defect heals by fibrosis]. They are also responsible for the growth of muscle fibers in length. 2-Cardiac muscle fibers - Present in the myocardium of the heart. - They are striated & involuntary fibers. - Cardiac muscle fibers are not capable of regeneration (not dividable). The defect healed by fibrosis - Shape: short and branching. dark lines between 2 cells Intercalated disks. - The nucleus: Mononucleated Dr.Gehan Khalaf Page 38  General Histology 1/ physiotherapy - The cytoplasm: acidophilic with less distinct cross striations than that of skeletal muscle fibers [because they are branched so the myofibrils are less regular]. - EM: - Rich in mitochondria. - Transverse tubules and sarcoplasmic reticulum (SR): The T-tubules are present at the level of the Z-line. The SR; the terminal cisternae present only to one side of the T-tubule, forming a diad. The diad is formed only of two structures: 1. One Transverse-Tubule. 2. One terminal cisterna. 3-Smooth muscle fibers Involuntary NON STRIATED muscle fibers Site: 1. The wall of blood vessels. 2. The wall of viscera e.g. GIT, respiratory and genito-urinary systems. LM structure: Shape: The fibers are fusiform or spindle shaped. The nucleus is flat or rod shaped central in position. The cytoplasm is acidophilic non striated. EM structure: - Filaments: There are three types of filaments: actin myosin and intermediate filaments, overlap each other at dense bodies. - Less developed Sarcoplasmic reticulum: with no terminal cisternae. - No transverse tubule. There are Caveolae regulate calcium pump - The junctions: gap junctions are present between the muscle fibers. They allow rapid conduction of impulses between the cells, allowing them to contract together in groups. Growth and regeneration 1- Division of the smooth muscle fibers. 2- Differentiation of pericytes. Dr.Gehan Khalaf Page 39  General Histology 1/ physiotherapy Lectures 10: Nervous tissue By the end of this lecture, students will be able to : 1. Classify types of nerve cells (neurons) morphologically and functionally. 2. Describe the structure and correlated functions of the neuron. 3. Outline the differences between the axon and the dendrites of the neuron. 4. Describe the structure of nerve fibers. 5. Describe the organization of the nerve fibers in a peripheral nerves Dr.Gehan Khalaf Page 40  General Histology 1/ physiotherapy Nervous tissue: It can generate and conduct impulses from one part of the body to another. Anatomically is formed of central nervous system [brain & spinal cord] and peripheral nervous system [ peripheral nerves & ganglia] Histologically nervous tissue is formed of : 1. Neurons excitable cells generate and conduct impulses 2. Glial cells  non-excitable cells that function to support neurons e.g Schwann cells Neuron: It is the structural and functional unit of the nervous tissue. Consists of the nerve cell body, its processes. Neurons are classified according to the number of processes into: 1. Pseudounipolar: has one process. Example: spinal ganglia.(Sensory) 2. Bipolar: has two processes (one axon and one dendrite). Example: special sense organs, Retina, olfactory epithelium. 3. Multipolar: has many processes; one axon & many dendrites. Example: almost all neurons of CNS. A. Nerve cell body contains the nucleus and the cytoplasm containing organelles. B. Processes are formed of : i. Axons: long and responsible for transmitting signals to other cells. ii. Dendrites: numerous short processes that receive information from other neurons. A. Neuron Cell Body (perikaryon): The nucleus : large spherical with a prominent nucleolus The cytoplasm: basophilic granules Nissl bodies. EM : - rER + free ribosomes & polysomes (Nissl’s bodies) neurotransmitter [protein] synthesis. They are present in the cytoplasm of the cell body and dendrites and absent in axon and axon hillock - Golgi apparatus: is present around the nucleus. - Mitochondria: provides energy. - Neurofilaments (intermediate filaments): support cell shape - Neurotubules (microtubules): responsible for transport of molecules within the cell. Dr.Gehan Khalaf Page 41  General Histology 1/ physiotherapy Nerve cell processes include axons and dendrites. Differences between the axon & dendrites: Dendrites Axon Multiple Single Short, irregular, wide base and Long, thin with uniform diameter tapering ends all through its length. Gives extensive branches Branches at terminal end. Cytoplasm contains Nissl’s Its axoplasm (cytoplasm) lacks granules Nissl granules & depends on the cell body for its maintenance. Carries impulses towards cell Carries impulses away from cell body (centripetal) body (centrifugal). Non-myelinated. May be myelinated The nerve fiber in peripheral nervous system It is the individual axons of the nerve. It is covered by myelin sheath and Schwann cell (neurilemma ) It is interrupted along its length by gaps called nodes of Ranvier The neurolemma sheath [Schwann cells] Every internodal segment is covered by one Schwann cell. Function : 1. Formation of myelin sheath [ by rotation and forming many layer of its cell membrane] 2. Regeneration of cut nerve fiber [if the cell body still intact] The myelin sheath: The white covering of an axon It consists of many layers of cell membrane of Schwann cells. So it is formed mainly of lipids In H&E stain it dissolves during preparation leaving empty spaces. It can be stained by osmic acid Myelin increases the speed of transmission of nerve impulses. Dr.Gehan Khalaf Page 42  General Histology 1/ physiotherapy Peripheral nerve [NERVE TRUNK]: a) It is a collection of axons arranged in bundles. b) Every nerve fibre (axon) is surrounded by Schwann cells that form myelin. c) Connective tissue covers the nerve: The whole nerve trunk is surrounded by connective tissue called: epineurium. The bundles are surrounded by connective tissue called: perineurium. Individual nerve fibers are surrounded by connective tissue called: endoneurium. NB: in H & E stained transverse section of a nerve you can see a central pink axon surrounded by an empty space of dissolved myelin, then a thin outer circle of Schwann cells. Dr.Gehan Khalaf Page 43  General Histology 1/ physiotherapy Lecture 11: Vascular system By the end of this lecture, students will be able to : 1. Describe the general properties and microscopic structure of blood vessels. 2. Correlate the structure of different blood vessels to its function 3. Describe the structure of blood capillaries. 4. List the different types of blood capillaries and compare between them 5. Identify the function of lymphatic circulation Dr.Gehan Khalaf Page 44  General Histology 1/ physiotherapy The components of blood vascular system: Large artery [elastic artery eg. Aorta – pulmonary] medium sized artery [muscular artery eg. femoral or radial]  arterioles  capillaries  venules  medium sized vein large vein [eg inferior vena cava] The heart General structure of blood vessels wall Tunica Endothelium (simple squamous epith.) intima Sub-endothelial loose CT Internal elastic lamina [IEL] wavy ,fenestrated elastin sheet to give stretch ability and allow diffusion of nutrients to deep layers of the vessel Tunica Smooth muscle (circularly arranged) which secrete and present between media - collagen fiber III [ reticular fiber] - Elastic fibers. External elastic lamina [EEL] Tunica Loose CT adventitia or vasa vasorum [Small blood vessels supply nutrients to the deep layers of externa blood vessel wall). Vasa vasorum are more frequent in veins [ as venous blood is deoxygenated] and in large and medium sized arteries [ as they are too thick to be nourished by diffusion]. These layers are present in different proportions in different blood vessels Capillaries & post-capillary. venules consist only of endothelium , basal lamina & pericytes Dr.Gehan Khalaf Page 45  General Histology 1/ physiotherapy Specific difference in different blood vessels Medium sized artery Medium sized vein Muscular formed mainly of smooth muscle Distributing control the blood supply to different organs by their contraction [VC] and relaxation [VD] Lumen Narrow & folded Wide & contain valves Wall Thick Thin Tunica Thick Thin intima Endothelium Endothelium Sub-endothelial loose CT Sub-endothelial loose CT Internal elastic lamina [IEL] NO IEL Tunica Thick Thin media Mainly Smooth muscle (circularly Few layers of smooth arranged) up to 40 layers & collagen muscle fibers & collagen fiber III [ reticular fiber] fiber III [ reticular fiber] Many Elastic fibers Very few elastic fiber Prominent external elastic lamina NO EEL [EEL] Tunica Thin Thick adventitia Loose CT contains elastic fibers, collagen Loose CT contains more fibers with few vasa vasorum collagen fibers &Very few elastic fibers with many vasa vasorum Dr.Gehan Khalaf Page 46  General Histology 1/ physiotherapy Aorta Elastic  due to large amount of elastic laminae in its media Conducting because they conduct blood away from the heart Lumen Wide Wall Thick Tunica Thick [20%] intima Endothelium Subendothelial CT with many elastic fibers IEL but indistinct as it merge with elastic laminae in tunica media Tunica Thick [main thickness] media Formed of many fenestrated elastic lamina, concentrically arranged Many smooth muscle fibers Collagen , elastic fibers EEL is present but indistinct Tunica Thin with many elastic fibers, collagen and many vasa vasorum adventitia The fenestrae in the elastic laminae serve as holes through which nutrients can diffuse to nourish cells deeper to the lamina. The several elastic laminae keep a continuous blood flow and maintain the blood pressure as in systole, they are stretched & in diastole, elastic recoil propels the blood column forward. Medical application Aortic aneurysm: Is the permanent dilatation of the aorta due to loss of elastic fibers and collagen fibers. Atherosclerosis: There is infiltration by fatty material in intima of arteries intimal thickening (atheromatous plaques). Dr.Gehan Khalaf Page 47  General Histology 1/ physiotherapy Connections between arteries and veins Blood capillaries Thin walled tubules, narrow diameter 7-9 µm, branching & anastomosing to form network General structure 1. Endothelial cells: 2. Basement membrane 3. Pericytes: - Contain actin, myosin  has contractile function to control blood flow in capillaries - Undifferentiating cells  can differentiate into smooth muscle, endothelium & fibroblast Function of blood capillaries: - Capillaries are responsible for exchange of gases and metabolites between blood and tissues Types of blood capillaries Continuous Fenestrated Sinusoidal capillaries capillaries capillaries Lumen Very small & narrow Specific type with large & wide irregular Endothelium - NO pores - Fenestrated type, - have pores  have pores - Joined by tight - Joined by tight - not joined by tight junction junction& junction (slits in between the cells) Basement Continuous Continuous Discontinuous membrane Associating cells Pericytes Pericytes Macrophage Sites Most of sites: 1. Endocrine gland 1. Liver [for passage of [ passage of macromolecules to blood] skeletal muscles , hormone] 2. Bone marrow [ for passage cerebral 2. Intestine of formed blood element to capillaries, [absorption] blood] connective tissue, 3. Glomerular 3. Spleen [filter the blood] thymus capillaries in kidney (filtration of blood) Dr.Gehan Khalaf Page 48  General histology I Dr Gehan Khalaf Page 49