HISTOLOGY+MASTER+HANDOUT+%28+FINALS+REVIEW%29.pdf

Outer membrane: contains porins HISTOLOGY FINALS REVIEW I...

Outer membrane: contains porins HISTOLOGY FINALS REVIEW Inner membrane: Formation of ATP Mitochondria long folds (cristae) Involved in OUTLINE Matrix: innermost apoptosis space; contain DNA, The Cell RNA, and ribosomes Epithelial Tissue Small, spherical β-oxidation Connective Tissue Muscle Tissue membrane-bound H2O2 production Peroxisomes Nervous Tissue Contain oxidative and degradation Cartilage enzymes Detoxification Bone RER is prominent in cells that secrete a lot of proteins, like pancreatic Skin acinar cells, fibroblasts, and plasma cells. SER is prominent in cells Lymphoid and Immune System involved in detoxification or steroid synthesis, like hepatocytes or Respiratory System gonadal cells. Circulatory System Digestive System CYTOSKELETON COMPONENTS Accessory Glands of the Digestive Tract COMPONENT STRUCTURE FUNCTION Endocrine Glands G-actin Cell movement and Urinary System Micro- organized into 2 muscle contraction Male Reproductive System filaments intertwined Cytokinesis Female Reproductive System F-actin filaments Cytoplasmic transport Special Sense Organs Tetramers Stabilize cell junctions Intermediate organized into a Maintain nuclear shape THE CELL Filaments cable as nuclear lamina The basic structural and functional unit of life Cell shape and polarity ⍺β-tubulin Chromosome and Microtubules organized into a PLASMA MEMBRANE organelle movement hollow tube Also known as the cell membrane or plasmalemma Cilia and flagella Trilaminar appearance on transmission electron microscopy NUCLEAR COMPONENTS Proteins are major constituents of membranes (~50%): o Integration is mainly the result of hydrophobic interactions COMPONENT KEY CONCEPTS o Most proteins can move laterally (fluid mosaic model) Selectively-permeable barrier o Large enzymes are less mobile and are located on lipid rafts Outer nuclear membrane and perinuclear space: continuous with RER Nuclear CELL MEMBRANE PROTEIN TYPES Inner nuclear membrane: associated with Membrane TYPES LOCATION EXTRACTION nuclear lamina Incorporated directly Extracted using Nuclear pore complexes: regulate Integral movement of macromolecules within lipid bilayer detergents Bound to one of the two Extracted using Chromatin: DNA and associated proteins Peripheral Chromosome: division of chromatin into membrane surfaces salt solutions Chromatin 23 pairs or 46 chromosomes in total Chromatid: division of a chromosome into CYTOPLASMIC ORGANELLES AND STRUCTURES 2 identical chromatin units in cell division Intensely basophilic due to densely CYTOPLASMIC ORGANELLES concentrated rRNA ORGANELLE STRUCTURE FUNCTION Nucleolus Transcribe, process, and assemble rRNA Composed of rRNA into ribosomal subunits and proteins Assemble Polyribosomes: SUPPLEMENT HISTOLOGIC TYPES OF CHROMATIN Ribosomes polypeptides many ribosomes Euchromatin: (translation) bound to one mRNA o EM: finely dispersed granular material Basophilic o LM: lightly stained basophilic areas Endoplasmic Network of channels or cisternae from the o Predominates in active cells (e.g. large neurons) Reticulum nuclear surface throughout the cytoplasm Heterochromatin: Studded with many o EM: coarse, electron-dense material Rough ER polyribosomes Protein synthesis o LM: intensely basophilic clumps (RER) Very basophilic o Predominates in cells with little synthetic activity (e.g. Phospholipid and circulating lymphocytes), gene-poor DNA sequences (e.g. steroid synthesis telomeres) or variably-inactivated genes (e.g. Barr body) Smooth ER Lack polyribosomes Detoxification (SER) Not basophilic Ca2+ release and sequestration CELLULAR ORGANIZATION AND EMBRYOLOGY Smooth saccular Completes post- Tissues: membranes translational o Cells with similar or closely related functions bound together Cis-face: receives modification of Golgi to form a bigger structure and functional unit (e.g. organs) transport vesicles proteins Apparatus o Basic tissue types: epithelial, connective, muscle, nervous Trans-face: Forms secretory Organs can be divided into two tissue types: packages vesicles vesicles and o Parenchyma: responsible for the organ’s specialized function for transport lysosomes o Stroma: supporting role, usually connective tissue Spherical vesicles Embryonic germ layers: with a membrane Intracellular o Ectoderm: divided into surface ectoderm (e.g. epithelium, Heterolysosome: digestion anterior pituitary), neural tube (e.g. CNS, retina, spinal cord), Lysosomes lysosome with a Turnover of neural crest (e.g. enterochromaffin cells, adrenal medulla) fused vesicle cellular o Mesoderm: include muscle, bone, connective tissue, vessels, Residual body: components blood, adrenal cortex, serous cavities, and dermis indigested material o Endoderm: include gut tube epithelium and luminal epithelial Cylinder-shaped Degrade denatured, derivatives (e.g. lungs, liver, pancreas, thyroid) Proteasomes protein complexes non-functional, or with no membrane unneeded proteins  A comprehensive list of germ layer derivatives can be found in the SIMPLE COLUMNAR Appendix section of this handout. I recommend reading that last to Single layer of cells that are taller than wide avoid getting overwhelmed. Important concepts regarding the germ layers will be emphasized throughout the handout. Usually with specializations on apical cell surface Distribution: o Colon (with goblet cells) and small intestines (with microvilli EPITHELIAL TISSUE and goblet cells) Highly cellular, closely-packed, and avascular o Fallopian tubes (with surface cilia) Only basic tissue to be derived from all 3 germ layers o Respiratory tracts (with pseudostratification) Cells exhibit polarity: o Vas deferens (with stereocilia) o Divided into basal, lateral, and apical surfaces Functions: protection, lubrication, absorption, secretion o Surfaces identified by organelles and surface modifications BASEMENT MEMBRANE Extracellular sheet on which the basal surface of epithelia rest Divided into: basal lamina and reticular lamina BASAL LAMINA Right: Renal collecting duct. Electron-dense layer of fine fibrils Functions: STRATIFIED SQUAMOUS o Separates epithelial cells from underlying connective tissue Two or more layers of flattened cells o Envelops muscles, fat, Schwann cells, cells of adrenal medulla Keratinized stratified squamous (dry) Layers: o Superficial cells lose their nucleus and fill with keratin o Lamina rara externa: o Distribution: epidermis § Electron-lucent area related to epithelial cells o Functions: protection, prevents water loss § Contains glycoproteins, including laminin Non-keratinized stratified squamous (moist) o Lamina densa: o Superficial cells still with nucleus § Middle electron-dense area o Distribution: mouth, esophagus, larynx, vagina, anal canal § Contains a network of fine filaments of type IV collagen o Functions: protection, secretion, prevents water loss o Lamina rara interna: thinner and often indistinct RETICULAR LAMINA Thicker, fibrous meshwork of type III collagen Bound to basal lamina by anchoring fibrils of type VII collagen Middle: Keratinized stratified squamous epithelium of epidermis. SURFACE EPITHELIA Right: Non-keratinized stratified squamous epithelium of esophagus. Simple: contain one cell layer Stratified: contain two or more cell layers STRATIFIED CUBOIDAL AND COLUMNAR Squamous: thin cells Fairly rare histologic types of epithelia Cuboidal: cell width and thickness roughly similar Generally for protection and secretion Columnar: cells taller than wide Stratified cuboidal epithelium: excretory ducts of sweat glands, developing ovarian follicles SIMPLE SQUAMOUS Stratified columnar epithelium: conjunctiva Single layer of flattened cells Distribution: UNIQUE TYPES OF EPITHELIA o Endothelium: lines luminal surface of heart and blood vessels Transitional epithelium (urothelium) o Mesothelium: lines serous surfaces (e.g. pericardium, o Lines most of the urinary tract peritoneum, pleura) o Stratified with round, dome-shaped superficial cells called Functions: umbrella cells o Facilitates movement of viscera (mesothelium) o Specialized for distensibility o Secretion of biologically active molecules (mesothelium) o Active transport by pinocytosis (mesothelium, endothelium) Right: Transitional epithelium of the urinary bladder. Right: Epithelium of thin renal loops of Henle. Pseudostratified columnar epithelium SIMPLE CUBOIDAL o Lines the trachea, bronchi, and nasal cavities Single layer of cells that are equally tall as wide o Layers of cells with nuclei at different levels Distribution: o Not all cells reach surface but all adhere to the basal lamina o Covering of the ovaries o Heavily ciliated to transport particles trapped in mucus o Thyroid gland follicles o Some ducts of salivary glands and pancreas o Collecting tubules of kidneys Functions: covering and secretion Right: Pseudostratified columnar epithelium with goblet cells of upper respiratory tract. Right: Renal collecting tubule.  In branched glands, several secretory portions empty directly into a GLANDULAR EPITHELIA single duct. In compound glands, ducts from several secretory Functional component of specialized organs called glands portions merge with other ducts to form one larger duct. If you see the Synthesize, store, and release substances needed by the body words “larger duct”, then it is most likely a compound gland. Glands are divided into exocrine and endocrine glands TYPES OF EXOCRINE GLANDS BY MODE OF SECRETION COMPARISON OF EXOCRINE AND ENDOCRINE GLANDS Merocrine Glands GLAND TYPE STRUCTURE EXAMPLES Secretion by exocytosis from membrane-bound vesicles or Remain connected secretory granules with the surface Sweat glands Most common method of protein or glycoprotein secretion epithelium Mammary glands Most exocrine glands are merocrine (e.g. salivary glands) Exocrine Contain tubular Salivary glands ducts lined with Digestive glands CATEGORIES OF MEROCRINE GLANDS epithelium CATEGORY PRODUCT MORPHOLOGY Deliver secretions Well-developed RER Non-glycosylated (hormone) into and Golgi complexes Pituitary gland Serous proteins (e.g. blood or lymph Stain intensely Endocrine Adrenal gland digestive enzymes) Lacks ducts and E.g. pancreas, parotid Thyroid gland Stain poorly have no connection Heavily to their epithelium because hydrophilic Mucous glycosylated mucous is washed proteins (mucins) TYPES OF EXOCRINE GLANDS BY STRUCTURE E.g. goblet cells Important terms: o Simple: ducts do not branch Holocrine Glands o Compound: ducts from several secretory portions converge Cells accumulate product and enlarge as they differentiate to form larger ducts Secretion by complete cell destruction and release of product o Branched: several secretory portions drain into one duct and cell debris into the lumen o Tubular: elongated secretory portion Example: sebaceous glands of hair follicles o Acinar (or alveolar): sac-like secretory portion Apocrine Glands SIMPLE GLANDS Product accumulates at the apical end of the cell CLASS FEATURES EXAMPLES Secretion by loss of membrane-enclosed apical cytoplasm, Mucous glands of usually containing one or more lipid droplets Elongated secretory Simple colon Examples: mammary glands, ceruminous glands portion Tubular Intestinal glands or Short or absent duct Merocrine glands secrete using membrane-bound vesicles, so no crypts of Lieberkühn part of the cell is lost during this process. Apocrine glands secrete by Several long Branched Uterine glands losing their apical cytoplasm. Holocrine glands secrete by the secretory parts join Tubular Stomach glands destruction of the whole cell. to drain into 1 duct Coiled Secretory portion is Tubular very long and coiled Sweat glands CONNECTIVE TISSUE Acinar or Rounded, sac-like Small mucous glands Basic tissue type that supports and connects other tissues and Alveolar secretory portion along the urethra cells together Multiple sac-like Major constituent is the extracellular matrix (ECM): Branched Sebaceous glands of o Protein fibers (e.g. collagen, elastic fibers) secretory parts Acinar the skin o Ground substance enter the same duct Originate from mesenchyme: o Mesodermal tissue consisting of viscous ground substance with few collagen fibers o Mesenchymal cells: § Undifferentiated, spindle-shaped cells with large nuclei and prominent nucleoli § Migrate from site of origin to developing organs SUMMARY OF CONNECTIVE TISSUE CELLS Diagram of simple gland classes. CELL STRUCTURE FUNCTION Most common cell COMPOUND GLANDS Irregular cytoplasm CLASS FEATURES EXAMPLES Produce ground with abundant RER Several elongated substance and Submucosal Fibroblast and Golgi complex coiled secretory units extracellular mucous glands Prominent nucleolus Tubular and their ducts fibers (of Brunner) in Euchromatic nucleus converge to form the duodenum Fibrocyte: quiescent larger ducts Polyhedral cells Several sac-like Storage of neutral Adipocyte Single huge lipid Acinar or secretory units with Exocrine fats droplet filling the cell Alveolar small ducts converge at pancreas Also called histiocytes a larger duct Phagocytosis and Macrophage Eccentric, kidney- Ducts of both tubular immune functions shaped nucleus and acinar secretory Tubuloacinar Salivary glands With basophilic Release: units converge at larger ducts secretory granules Heparin Metachromasia: Histamine Mast Cell acidity of cell content Serine protease causes basic dyes to Cytokines change color to red Phospholipids Lymphocyte-derived Large, ovoid cell with basophilic cytoplasm Produce Plasma Cell Rich in RER, large antibodies Golgi complex, and Diagram of compound gland classes. spherical nucleus  Four major GAGs found in proteoglycans: FIBERS OF CONNECTIVE TISSUE o Dermatan sulfate: skin, tendon, aorta o Chondroitin sulfate: cartilage, bone, skin, aorta, cornea Elongated structures formed from proteins that polymerize o Keratan sulfate: cartilage, nucleus pulposus, annulus fibrosus after secretion from fibroblasts o Heparan sulfate: aorta, lung, liver, basal laminae COLLAGEN FIBERS PROTEOGLYCANS Family of 28 proteins that are strong and resistant to Protein core attached to several sulfated GAGs shearing and tearing forces Secreted by exocytosis and bound to hyaluronan Most abundant protein in the body (30% of dry weight) Turnover and renewal is slow but continuous: o Stable in most tendons and ligaments MULTIADHESIVE GLYCOPROTEINS o High in periodontal ligaments surrounding the teeth Have branched oligosaccharide chains that stabilize the ECM o Degradation initiated by collagenases Bind to matrix macromolecules and cell surface integrins (integral membrane proteins that bind ECM proteins) TYPES OF COLLAGEN TYPE MAJOR LOCATION MAIN FUNCTION TYPES OF CONNECTIVE TISSUE Fibril-Forming Collagen Connective tissue proper: consists mainly of fibroblasts, I Skin, tendon, bone, dentin Resistance to tension collagen, and ground substance II Cartilage, vitreous body Resistance to pressure Specialized connective tissue: Skin, muscle, vessels Structural maintenance o Bone, cartilage, blood III o Reticular tissue: consists mainly of reticular fibers Frequently with type I in expansible organs Fetal tissue, skin, bone, Participates in type II o Mucoid tissue: gelatinous tissue with abundant hyaluronan V found in the umbilical cord (Wharton’s jelly) placenta, interstitial tissues collagen function Participates in type II XI Cartilage TYPES OF CONNECTIVE TISSUE PROPER collagen function TYPES CHARACTERISTICS EXAMPLES Network-Forming Collagen Basal lamina, external Filtration and support Less collagen, abundant Lamina propria IV cells and ground of GI tract lamina of epithelial cells Loose Hypertrophic cartilage in substance Fills spaces X Increases matrix density (Areolar) endochondral ossification Supports immune cells, between muscle microvasculature, nerves and nerve fibers Linking/Anchoring Collagen Epithelial basement Anchors basal lamina More collagen, less cells VII Dermis of skin membrane to reticular lamina and ground substance Dense Organ capsules Binds proteoglycans; Protects and supports IX Cartilage, vitreous body Irregular Submucosa layer associated with type II organs of digestive tract XII Placenta, skin, tendons Interact with type I Resists tearing Binds type I collagen Filled with collagen Tendons XIV Placenta, bone Dense bundles Aponeuroses fibrils with type V and XII Regular Few fibroblasts Ligaments The must know collagen fiber types are: Resistance to force Corneal stroma Type I (“bONE”): forms collagen fibers in skin, tendon, and bone Mnemonics for types of connective tissue proper Type II: cartilage (“carTWOlage”) and vitreous (“2 eyes”) Dense irregular (“CPR”): capsules, periosteum, perichondrium, Type III: reticulin fibers (“reTHREEculin”) perimysium, perineurium, reticular layer of dermis Type IV: basement membrane (“type FLOOR”) Dense regular (“TALC”): tendons, aponeuroses, ligaments, cornea Type V: fetal tissue and placenta (“VeVe”) Type VII: connects basement membrane to reticular lamina MUSCLE TISSUE RETICULAR FIBERS Basic tissue type optimized for contractility Consists mainly of type III collagen secreted by modified Common features of muscle cells: fibroblasts called reticular cells o Mesodermal origin Staining properties are due to high amount of sugar chains: o Elongated cells individually wrapped by basal lamina o Argyrophilic: stained black with silver salts o Differentiate by a gradual process of cell lengthening o Periodic acid-Schiff (PAS) positive: stains polysaccharides o Abundant synthesis of actin and myosin Found in delicate connective tissues: Important terms in muscle histology: o Reticular lamina of basement membranes o Sarcolemma: cell membrane o Liver and endocrine gland stroma and vasculature o Sarcoplasmic reticulum: smooth endoplasmic reticulum o Stroma of hematopoietic and immune organs o Sacrosomes: mitochondria o Sarcoplasm: cytoplasm ELASTIC FIBERS o T (transverse) tubules: tubular infoldings of sarcolemma Fine fibers that form sparse networks with collagen o Terminal cisternae: expansions of SR adjacent to T-tubules Allow tissue to distend then return to their original shape Abundant in organs subject to stretching (e.g. lungs, vessels) SKELETAL MUSCLE Structural composition: Produce quick, forceful contractions that are usually voluntary o Fibrillin: protein subunit Key characteristics: o Microfibrils: fibrillin and glycoproteins that form a scaffold o Long multinucleated cells in cylindrical fibers o Elastin: protein that is deposited on the microfibril scaffold o With striations o Well-developed sarcoplasmic reticulum GROUND SUBSTANCE o Triad of 2 terminal cisterns per T-tubule Highly hydrated, transparent mixture of macromolecules o Well-organized sarcomeres, SR, and T-tubules Fills the space between cells and fibers in connective tissue Satellite cells Interstitial fluid: water in the ground substance o Myoblast-like stem cell within basal lamina o Allows for a limited capacity for regeneration GLYCOSAMINOGLYCANS (GAGs) Also called mucopolysaccharides ORGANIZATION WITHIN MUSCLE FIBERS Polymers of repeating disaccharide units Myofilament: Hyaluronan (or hyaluronate or hyaluronic acid): o Thick filament: composed of myosin o Largest and most ubiquitous GAG o Thin filament: composed of actin, troponin, tropomyosin o Binds water and allows for lubrication and molecular Sarcomere: smallest repetitive contractile and functional unit diffusion through connective tissue Myofibril:  o Smallest unit seen under light microscopy NERVOUS TISSUE o Long, cylindrical bundles running parallel to long axis of fiber o Made of sarcomeres arranged end-to-end Develops from the ectoderm in the 3rd week of development Muscle fiber: Composition: o Muscle cell with nuclei and myofibrils filling the sarcoplasm o Extracellular material: very small amount o Surrounded by sarcolemma o Cells: neurons, neuroglial cells Muscle bundle / fascicle: formed by several muscle fibers Anatomic divisions of nervous system: ORGANIZATION OF SKELETAL MUSCLE o Central (CNS): brain, spinal cord (SC) o Peripheral (PNS): nerves (cranial, spinal, peripheral) and Endomysium: ganglia (nerve cell aggregates outside the CNS) o Directly overlies sarcolemma of individual muscle fibers o Delicate layer of reticular fibers and scattered fibroblasts o Rich in nerve fibers and capillaries SUPPLEMENT DEVELOPMENT OF NERVE TISSUE Perimysium: Neural plate: forms from the ectoderm on the mid-dorsal o Thin connective tissue surrounding each muscle fascicle side of the embryo o Penetrated by nerves, blood vessels, and lymphatics Neural tube: Epimysium: o Forms when the sides of the neural plate fold upward, o Dense irregular connective tissue around the entire muscle grow toward each other, and fuse o Carries larger nerves, blood vessels, and lymphatics o Derivatives: brain (including posterior pituitary and except microglia), retina, spinal cord Neural crest: o Cells that separate from the neuroepithelium and migrate o Derivatives: PNS ganglia, leptomeninges (arachnoid and pia), Schwann cells, and several others (see Appendix) NEURON Functional unit of the nervous system Terminally differentiated but highly variable in size and shape CELL BODY Also called the perikaryon or soma Synthetic and trophic center of the entire neuron Notable components: o Nucleus: large, euchromatic with a prominent nucleolus o Cytoplasm (neuroplasm): numerous polyribosomes and RER o Nissl bodies: basophilic regions of several ribosomes and RER o Golgi apparatus: extensive in soma but absent in other parts CARDIAC MUSCLE AXON Produce a characteristic wave of contraction in the heart Transmit impulses away from the cell body (“Axon Away”) Key characteristics: Most neurons only have one axon o Branching, mononucleated cells in cylindrical fibers Branch less than dendrites but undergo terminal arborization o With striations but less developed sarcoplasmic reticulum Notable components: o Dyad of 1 terminal cistern per T-tubule o Axon hillock: region of cell body where the axon originates o Highest concentration of mitochondria (40% cell volume) o Terminal bouton: distal dilation that contacts another neuron o Very poor capacity for regeneration o Axolemma: plasma membrane Unique features: o Axoplasm: cytoplasm rich in mitochondria, microtubules, o Intercalated discs: neurofilaments, and transport vesicles § Transverse lines crossing at irregular intervals o Neurilemmal sheath: § Contain desmosomes, fascia adherens, and gap junctions § Seen in all axons but enveloped by basal lamina in PNS only § Anchor fibrils and allow for spread of contractile stimulus § Made of Schwann cells (PNS) and oligodendrocytes (CNS) o Purkinje fibers: o Myelin: compacted layers of cell membrane internal to § Modified, non-contractile cardiac muscles in certain areas neurilemmal sheath § Initiate and conduct electrical impulses o Cardiac skeleton: fibrous masses of perimysium DENDRITE Transmits impulses toward the cell body (“Dendrite Dito”) Rich in Nissl granules, mitochondria, and neurofibrils SMOOTH MUSCLE Extensive arborization or branching: o Each branch is covered with many synapses Produce slow, steady involuntary contractions o Single neuron can receive signals from several other neurons Key characteristics: Dendritic spines: o Single, closely packed cells in fusiform fibers o Dynamic membrane protrusions along CNS dendritic branches o No striations and no T-tubules o Important for neural plasticity o With gap junctions, caveolae, dense bodies o Good capacity for regeneration through muscle cell mitosis Organization: o Endomysium: contains basal lamina and reticular fibers o Perimysium: rich in collagen and surrounds larger bundles TYPES OF NEURONS ACCORDING TO NUMBER OF PROCESSES SUPPLEMENT ADDITIONAL NERVOUS TISSUE CONCEPTS Central Nervous System White matter: o Composed of myelinated axons with oligodendrocytes o Found deep in the brain and peripherally in spinal cord Gray matter: o Composed of neuron cell bodies, glial, and neuropil o Found peripherally in the brain and deep in spinal cord Cerebral nuclei: darker areas deep within the brain with aggregated neuron cell bodies Peripheral Nervous System Endoneurium: o Thin layer around the external lamina of Schwann cells o Consists of reticular fibers, fibroblasts, capillaries Perineurium: o Sleeve of fibrocytes that bundle axons, Schwann cells, and endoneurium into fascicles o Component of the blood-nerve barrier Epineurium: dense outer fibrous coat of the peripheral nerve, fills spaces between fascicles TYPE MORPHOLGY EXAMPLES Single process that CARTILAGE Unipolar Most sensory neurons Special type of dense regular connective tissue bifurcates Vestibular and Consists of chondrocytes embedded in an ECM matrix One axon and one Bipolar cochlear ganglia dendrite Olfactory epithelium HISTOLOGIC ORGANIZATION OF CARTILAGE One axon with two or Acellular with no blood vessels, lymph vessels or nerves Multipolar Most common type more dendrites Abundant matrix or intercellular substance Many dendrites but Cell component (chondrocytes) found in cavities (lacunae) no true axon Some CNS neurons Anaxonic No action potentials Retina (amacrine MATRIX Regulate charges of and horizontal cells) Produce a strong, hydrated, pliable intercellular material adjacent neurons Contains collagen fibers and amorphous ground substance Components: o Water: 70-80% wet weight NEUROGLIAL CELLS o Type II collagen: most common collagen type in cartilage o Proteoglycans: core protein attached to glycosaminoglycan Support neuronal survival and activities o Aggrecan: 5-10-times more abundant than neurons in CNS § Most abundant proteoglycan of hyaline cartilage Neuropil: § Contain side chains of chondroitin sulfate and keratan sulfate o Network of fine cellular processes from neurons and neuroglia o Chondronectin: o Form a fibrous intercellular network of CNS tissue § Glycoprotein that binds to GAGs, collagen, and integrins Germ cell origins: § Mediates adherence of chondrocytes to ECM o Neural tube (ectoderm): astrocytes, oligodendrocytes, ependymal cells TYPES OF CARTILAGE MATRIX o Neural crest (ectoderm): Schwann cells, satellite cells TYPE KEY FEATURES o Bone marrow (mesoderm): microglia Located immediately around each lacuna and chondrocyte with a pericellular capsule SUMMARY OF NEUROGLIAL CELLS Territorial Mostly proteoglycans and sparse collagen CELLS STRUCTURE FUNCTION More basophilic Central Nervous System Inter- Located more distant from lacunae Star-shaped Structural and territorial Richer in collagen and less basophilic Astrocytes Largest and most metabolic support numerous glial cell Repair processes PERICHONDRIUM Forms myelin and Layer of dense connective tissue between cartilage and tissue Condensed nucleus, neurilemmal Harbors blood supply and small neural component Oligo- scanty cytoplasm sheath around Outer fibrous layer: dendrocytes Predominant glia in several axons o Consists of type I collagen and fibroblasts white matter Electric insulation o Blends with surrounding tissue Monocyte origin Inner chondrogenic layer: Defense and Elongated nuclei o Contains mesenchymal stem cells for chondrogenesis Microglia immunity Evenly distributed o Adheres to cartilage Phagocytic throughout CNS Simple cuboidal CHONDROCYTES Ependymal Lines ventricles and CSF production Specialized cells embedded in the matrix and reside in lacunae Cells central canal and movement Synthesize and maintain cartilage matrix components No basal lamina General morphology: Peripheral Nervous System o Cytoplasm: finely granular, basophilic, with several processes Forms myelin and o Nucleus: ovoid, clumps of chromatin, one or more nucleoli Also called Schwann neurilemmal o Inclusions: fat droplets and glycogen granules neurolemmocytes Cells sheath around a o Well-developed RER and Golgi complex but few mitochondria Small, flat cells single axons Also called mantle Structural and Satellite cells / amphicytes metabolic support Cells Wrap neuronal cell of neuronal cell bodies in ganglia bodies COMPARISON OF CHONDROCYTES AND CHONDROBLASTS BONE Specialized connective tissue composed of a calcified ECM and the cells that secrete and remodel it BONE COMPONENTS OSTEOBLASTS Origin: mesenchymal stem cells (mesoderm) Form a single layer of cuboidal cells on the bone surface Histologic features of active protein synthesis and secretion: CELL KEY FEATURES o Intensely basophilic cytoplasm due to abundant RER Mature cell derived from chondroblasts o Extensive Golgi complex seen as a negative Golgi image Chondrocyte Round and large cells embedded in matrix o Single nucleus and several cytoplasmic processes No mitotic capability Secrete organic matrix components and osteoid: Immature cell of mesodermal origin o Layer of newly-formed bone matrix Chondroblast Elliptical and small cells found in periphery o Located between the osteoblasts and the pre-existing bone With mitotic capability Regulate bone mineralization o Secrete growth factors that promote bone growth o Aid osteoclasts in bone resorption (e.g. secrete osteoclast- TYPES OF CARTILAGE stimulating factor in the presence of parathyroid hormone) Hyaline: most abundant type Possible fates once synthetic activity is completed: Elastic: less matrix but highly pliable o Osteocytes: osteoblasts entrapped in cavities (lacunae) Fibrous: o Bone lining cells: flattened osteoblasts on the bone surface o Can withstand more stress than hyaline or elastic cartilage o Apoptosis: fate of the majority of osteoblasts o Transitional between cartilage and dense connective tissue OSTEOCYTES SUMMARY OF CARTILAGE TYPES Entrapped, flat osteoblasts enclosed singly within lacunae TYPE COMPONENTS EXAMPLES Most abundant cells in bone Type II collagen and Histologic features compared to osteoblasts: aggrecan Upper respiratory o Smaller Golgi complexes and less RER Chondrocytes and tract o More condensed nuclear chromatin Hyaline chondroblasts Articular ends and o Several long dendritic processes occupying canaliculi Perichondrium (except epiphyses of bones Functions: epiphyses and Fetal skeleton o Maintain the calcified bone matrix articular cartilage) o Regulate bone remodeling via paracrine and endocrine effects Type II collagen, o Detect stress- or fatigue-induced microdamage External ear and aggrecan, and darker external acoustic elastic fibers OSTEOCLASTS Elastic meatus Chondrocytes and Epiglottis and some Large, motile, multinucleated cells chondroblasts laryngeal cartilages Origin: fusion of bone marrow-derived monocytes Perichondrium Role in matrix resorption for bone growth and remodeling Abundant type I and II Intervertebral discs Key features: collagen fibers Pubic symphysis o Homogenous, foamy cytoplasm with several nuclei Fibrous Chondrocytes and Meniscus and some o Resorption (Howship) lacunae: enzymatically-etched fibroblasts joints cavities in bone matrix where osteoclasts reside No perichondrium Tendon insertions o Sealing border: circular area where the osteoclast membrane binds tightly to the bone matrix SUPPLEMENT CHONDROGENESIS AND PHYSIOLOGY o Ruffled border: Chondrogenesis § Site of bone resorption with several processes enclosed by Mesenchymal cells: the sealing border 1. Arise from mesoderm starting 5th week of development § Contains proton pumps and releases several enzymes 2. Divide and differentiate into chondroblasts Chondroblasts: 3. Secrete ECM and separate from one another 4. Multiply within the matrix to form isogenous aggregates 5. Mature into chondrocytes lodged in lacunae Cartilage Growth, Degeneration, and Regeneration Interstitial (endogenous) growth: o Mitotic division of pre-existing chondroblasts o Increase length of cartilaginous regions of long bones Appositional (exogenous) growth o Differentiation from progenitor cells in perichondrium o More important during postnatal development Degeneration: o Calcification: most common degenerative process o Age-related changes: less translucent and less cellular Repair: Ocl: osteoclast, Oc: osteocyte, B: bone matrix o Poor capacity for repair due to avascularity o Dependent on perichondrium and produces scar tissue BONE MATRIX Inorganic components (50% of dry weight): o Calcium hydroxyapatite: most abundant material o Non-crystalline calcium phosphate o Bicarbonate, citrate, magnesium, potassium, and sodium ions Organic components: o Type I collagen (90%): provides hardness and resistance o Proteoglycans and glycoproteins (e.g. osteonectin) o Calcium-binding proteins (e.g. osteocalcin) and phosphatases: promote matrix calcification PERIOSTEUM AND ENDOSTEUM Connective tissue lining external (periosteum) and internal (endosteum) surfaces of bones Outer periosteum: o Fibrous layer of dense connective tissue o Contains type I collagen, fibroblasts, and blood vessels o Perforating (or Sharpey) fibers: periosteal collagen fibers that penetrate the matrix and bind the periosteum to bone Inner periosteum: o More cellular with osteoblasts and bone limiting cells o Osteoprogenitor cells: CC: central canal, O: osteocytes, C: canaliculi, L: lamellae, I: interstitial § Mesenchymal stem cells also seen in endosteum lamellae § Proliferate extensively and produce many new osteoblasts TYPES OF LAMELLAR BONE Endosteum: TYPE FEATURES LOCATIONS o Very thin layer that covers the trabeculae (bone matrix that Also called cortical bone Outer region projects into the marrow cavities) Compact o Sparse network of collagen with osteoprogenitor cells, Densely-packed osteons of bones Bone osteoblasts, and bone lining cells or parallel lamellae Adjacent to (80%) With interstitial lamellae periosteum Osteoprogenitor cells à osteoblasts Also called trabecular, Inner region Perichondrial fibroblast-like progenitor cells à chondroblasts Cancellous spongy, medullary bone of bones Bone Interconnected thin Adjacent to (20%) spicules or trabeculae marrow TYPES OF BONE covered by endosteum cavity TYPE FEATURES LOCATIONS Also called immature, Newly calcified Please note that compact and cancellous bone refer to subtypes of lamellar bone. Woven bone is a separate type of bone from lamellar primary, or bundle bone bone bone. Most of the bone tissue in a healthy adult is lamellar. If the Woven Lightly calcified Developing and bone being described is newly/lightly calcified with irregular cells, is Bone Irregular and random growing bones from developing bones, or is from a hard callus, then it is woven bone. arrangement of cells Hard callus of and collagen fractures SUMMARY OF BONE PHYSIOLOGY Also called mature or Remodeled secondary bone from woven OSTEOGENESIS OR BONE DEVELOPMENT Lamellar Heavily calcified bone Intramembranous ossification: Bone Parallel layers (lamellae) Normal regions o Osteoblasts differentiate directly from mesenchyme of collagen with of adult bone o Seen in most bones of the skull and jaw, scapula, clavicle regularly-spaced cells o Ossification centers: § Area of osteoprogenitor cells in condensed mesenchyme ORGANIZATION OF LAMELLAR BONE § Forms irregular areas of woven bone that enlarge, fuse, and Describes most bones in the adult are eventually replaced by compact lamellar bone Organized into multiple layers of calcified matrix Endochondral ossification: Key terms: o Osteoblasts invade pre-existing hyaline cartilage o Lamellae: layers of calcified bone matrix, 3-7 µm thick o Forms most bones of the body o Lacunae: cavities between lamellae containing osteocytes o Bone collar: area where osteoblasts differentiate from the o Canaliculi: perichondrium § Canals that radiate from and anastomose with other lacunae o Primary ossification center: area of diaphysis where § Contains cytoplasmic processes of osteocytes capillaries and osteoprogenitor cells invade the cartilage o Secondary ossification center: similar to primary centers HAVERSIAN SYSTEM OR OSTEON but appear in the epiphysis around the time of birth Lamellae are arranged concentrically around osteons Haversian (or central) canal: BONE GROWTH o Longitudinal channels containing blood vessels and nerves Longitudinal growth: occurs by cell proliferation in the o Lined by endosteum epiphyseal growth plate Cement line: Appositional (circumferential) growth: function of o Discrete lines of mineralized matrix and collagen fibers osteoprogenitor cells in the periosteum o Demarcate boundaries of individual osteons Volkmann’s (or perforating) canals: ZONES OF THE EPIPHYSEAL GROWTH PLATE o Transverse vascular channels lined by endosteum ZONE OF: KEY FEATURES o Connect Haversian canals with each other and with Reserve Farthest from the ossification center medullary and periosteal vessels Cartilage Composed by typical hyaline cartilage CATEGORIES OF LAMELLAE IN LONG BONES Cartilage cells secrete type II collagen and Proliferation Interstitial lamellae: organize into columns o Between osteons and not associated with Haversian canals Swollen chondrocytes secrete type X Hypertrophy o May be remnants of osteons that are being resorbed collagen and compress the matrix Circumferential lamellae: Calcified Hydroxyapatite crystals form o Outer: beneath the periosteum and encircle the whole bone Cartilage Apoptotic chondrocytes release osteocalcin o Inner: encircle the medullary cavity Bone tissue, cells, and osteoid first appear Ossification to form woven then lamellar bone  Thin, translucent layer of flat eosinophilic Stratum keratinocytes Lucidum Absent in thin skin (i.e. whole body except (Clear Cell palms and soles) Layer) Cytoplasm consists exclusively of keratin with no nuclei and organelles Stratum Squamous keratinized cells (15-30 layers) Corneum Protects against friction and water loss (Horny Cell Squames: fully keratinized cells Layer) continuously shed at epidermal surface Please note that some references use stratum germinativum to refer exclusively to the stratum basale. However in Junqueira’s, it is defined as the part of the stratum basale and spinosum where cells can divide. BONE REMODELING AND REPAIR Bone remodeling: o Allows the bone to remain plastic and adaptable o Internal remodeling: coordinated activities for bone resorption and formation o External remodeling: changes in bone shape due to external factors (e.g. pull of muscles form a tubercle) Bone repair: o Excellent capacity for repair due to stem cells and vascularity o Steps in fracture repair: § Fracture hematoma: initiates healing process § Soft callus: fibrocartilage invaded by vessels and osteoblasts MELANOCYTES § Hard callus: fibrocartilage replaced by woven bone Specialized cells of the stratum basale and hair follicle § Remodeling: woven bone replaced by lamellar bone Distributed along the basal lamina at 1 per 5-6 keratinocytes Pale cytoplasm with several long processes SKIN Origin: neural crest (ectoderm) Produce melanin from tyrosine and DOPA: Also known as the integument or cutaneous layer o Protects DNA from UV radiation Largest single organ of the body (15-20% total body weight) o Accumulate in vesicles called melanosomes that are Functions: transferred into keratinocytes via phagocytosis o Protective: selectively-permeable barrier, immune cells o Sensory: sensory receptors, mechanoreceptors LANGERHANS CELLS o Thermoregulatory: insulation (e.g. fat), heat loss (e.g. sweat) o Metabolic: vitamin D synthesis, fat storage, sweating Monocyte-derived dendritic antigen-presenting cells o Sexual signaling: pigmentation, hair, sex pheromones Most clearly seen in the stratum spinosum Comprise a major component of the skin’s adaptive immunity Birbeck (or vermiform) granules: tennis racket-shaped EPIDERMIS cytoplasmic granules with unknown function Stratified squamous keratinized epithelium Renewed every 15-30 days MERKEL CELLS Epidermal ridges: Also called epithelial tactile cells o Also called rete pegs or epidermal pegs Modified keratinocytes with small dense-core granules but o Conical projections of epidermis into the dermis few to no melanosomes Abundant in fingertips and the bases of some hair follicles KERATINOCYTES Most abundant cell type (85-95% of cell population) Produce keratin: DERMIS o Cytoskeletal intermediate filaments Layer of connective tissue that supports the epidermis and o Assemble into microscopically visible bundles (tonofibrils) binds it to the hypodermis o Increase in type and amount as keratinocytes move upward Basement membrane: between the dermis and stratum basale Papillary layer: LAYERS OF THE EPIDERMIS o Thin, superficial layer consisting of loose connective tissue LAYER KEY FEATURES o Includes the dermal papillae: Single layer of basophilic columnar or § Projections of the dermis into the epidermis cuboidal cells on the basement membrane § Prominent in skin subject to frequent pressure Stratum o Components: Intense mitotic activity Basale § Fibroblasts, mast cells, dendritic cells, leukocytes Contains keratinocytes, basal stem cells, melanocytes, and Merkel cells § Type I and III collagen § Type VII collagen: bind the dermis into the basal lamina Usually the thickest layer Reticular layer: Polyhedral cells, central nuclei and nucleoli Stratum o Thick, underlying layer of dense irregular connective tissue Actively synthesizes keratins Spinosum o Responsible for the toughness and strength of skin Thicker in thick skin (e.g. palms, soles) o Where sweat glands, hair, arrector pili muscles are embedded (Prickle Cell Layer) Layer with most Langerhans cells o Components: Stratum germinativum: combined zone of § Type I collagen and elastic fibers basale and spinosum where cells may divide § Proteoglycans: rich in dermatan sulfate 3-5 layers of flattened cells undergoing Contains a rich network of blood and lymphatic vessels: keratinization o Subpapillary plexus: between papillary and reticular layers Stratum Keratohyaline granules: basophilic masses o Deep plexus: between dermis and hypodermis Granulosum of filaggrin and proteins linked with keratin o Arteriovenous anastomoses: between both plexuses for Lamellar granules: contain lamellae of thermoregulation lipids and glycolipids to prevent water loss  HYPODERMIS Also called the subcutaneous layer or superficial fascia Loose connective tissue not considered part of the skin Functions: o Binds the skin to subjacent organs o Allows the skin to slide over underlying structures o Has an extensive vascular supply Contains adipocytes: o Except in eyelids, penis, scrotum, nipple, and areola o Panniculus adiposus: adipose tissue of the belly SKIN SENSORY RECEPTORS TYPE FEATURES STIMULI Unencapsulated Receptors Associated with expanded Merkel Sustained light SUPPLEMENT HAIR FORMATION AND GROWTH nerve endings Cell touch, texture Formation of hair: Found in epidermis Free Extend from papillary Temperature, 1. Keratinocytes in the matrix proliferate and keratinize Nerve dermis into lower pain, itch, tactile 2. Melanocytes transfer melanosomes to keratinocytes Ending epidermal layers receptors 3. Cells get pushed up as they differentiate and die Web of sensory fibers on Hair growth cycle: Root Hair Movement of o Anagen: long period of mitotic activity and growth the hair follicle base Plexus hairs o Catagen: arrested growth and regression of the hair bulb Found in reticular dermis o Telogen: final period of inactivity where hair may be shed Encapsulated Receptors Elliptical structure of NAILS sensory axons winding Meissner Light touch, low- Nail plate: hard plate of keratin on the dorsal distal phalanx among flat Schwann cells (Tactile) frequency Nail bed: Numerous in fingertips, Corpuscle vibrations o Epidermis under the nail plate palms, and soles Found in dermal papillae o Contains only basal and spinous layers Onion-like capsule of Nail root: proximal part of the nail covered by skin concentric lamellae of flat Coarse touch, Nail matrix: Pacinian Schwann cells pressure, high- o Area of proliferating, differentiating keratinocytes in the root Corpuscle Found in reticular frequency o Divided into dorsal and ventral nail matrices dermis, hypodermis, wall vibration o Continuous growth of cells pushes the nail plate forward (3 of rectum, urinary bladder mm/month for fingernails, 1 mm/month for toenails) Eponychium (or cuticle): dorsal extension of the epidermal Krause Ovoid with a thin capsule Low-frequency stratum cornea from the nail root End Found in the dermis of the vibrations Hyponychium: distal end of the plate free of the nail bed Bulbs penis and clitoris Collagenous, fusiform Ruffini Stretch and capsules around axons Corpuscle twisting of skin Found in reticular dermis Pacinian corpuscle (“Pac-ONION”): onion-like capsule Merkel cell (think: “MerKel MagKaiba”): only one exclusively located in the epidermis and only unencapsulated “named” receptor APPENDAGES Associated structures in the skin HAIR Elongated keratinized structures present in all skin except the palms, soles, lips, glans penis, clitoris, and labia minor SEBACEOUS GLANDS General anatomy: Embedded in the dermis (except over the palms and soles) o Hair shaft: part of the hair extending beyond the skin surface Pilosebaceous unit: hair follicle plus associated gland o Hair root: part of the hair embedded in skin Branched acinar glands: o Hair follicles: epidermal invaginations where hair forms o In hairy skin: empties into the upper portion of a hair follicle o Hair bulb: terminal dilation of a growing hair follicle o In hairless skin: empties directly onto the epidermal surface o Dermal papilla: Undergo holocrine secretion: § Inserts into the base of the hair bulb o Basal cells proliferate and differentiate into sebocytes § Carries capillaries and is lined with basal keratinocytes o Cells undergo autophagy and release lipids o Arrector pili muscle: § Smooth muscle connecting hair sheath to papillary dermis Sebum: § Contraction pulls the hair shaft erect o Mixture of wax esters, squalene, cholesterol, triglycerides o Helps maintain the stratum corneum and hair shafts Concentric histologic layers: o Weak anti-bacterial and anti-fungal properties o Medulla: large, vacuolated, moderately-keratinized cells in the core of thick hair SWEAT GLANDS o Cortex: thickest layer of heavily-keratinized, densely-packed cells around the medulla Develop as epidermal invaginations embedded in the dermis o Cuticle: thinnest, peripheral layer of heavily-keratinized Both types undergo merocrine secretion squamous cells Eccrine sweat glands: Epithelial root sheath: o Widely distributed and most numerous on soles o Continuous with outermost cells of the hair bulb o Secretory part: pale-staining stratified cuboidal epithelium o Internal root sheath: § Clear cells: produce sweat, located on basal lamina § Surrounds the initial part of the hair root § Dark cells: release bactericidal glycoproteins in granules § Degenerates above the level of the attached sebaceous gland § Myoepithelial cells: contract to move secretion into the duct o External root sheath: o Duct: two layers of acidophilic cells rich with mitochondria § Extends up to the epidermis o Sweat pore: channel spiraling through epidermis to surface § Continuous with the stratum basale and spinosum Apocrine sweat glands: o Confined to the axillary and perineal skin o Development depends on sex hormones o Secretory part: simple cuboidal, eosinophilic cells  o Duct: open into hair follicles at the epidermis Langerhans Antigen processing and Epidermis o Product: viscous, protein-rich, possibly with pheromones Cell presentation Take note of this! Apocrine sweat glands is a misnomer. Both eccrine Lymph node, Antigen processing and Dendritic Cell and apocrine sweat undergo merocine secretion. spleen presentation Osteoclast Bone Bone matrix digestion LYMPHOID AND IMMUNE SYSTEM Multinuclear Pathologic tissue Foreign body digestion Giant Cell Functional divisions: o Innate immunity: non-specific, mediated by granulocytes and other leukocytes PRIMARY LYMPHOID ORGANS o Adaptive immunity: specific, mediated by lymphocytes and Where lymphocytes initially form antigen-presenting cells THYMUS CELLS OF THE IMMUNE SYSTEM Bilobed mediastinal structure where T cells are produced LEUKOCYTES Originates from the 3rd pharyngeal pouches (endoderm) Leave the blood and migrate to the tissues Capsule: vascularized connective tissue that extends septa Spherical in blood plasma, amoeboid and motile after leaving Lobules: divisions of parenchyma formed by septa the blood vessels Cortex: Granulocytes: o Outer darkly basophilic portion of each lobule o Polymorphic nuclei with two or more lobes o Contains T lymphoblasts (or thymocytes) and macrophages o Two types of cytoplasmic granules: o Thymic epithelial cells (TECs): diverse with euchromatic, § Lysosomes or azurophilic granules: large, dense vesicles large nuclei and features of epithelial and reticular cells that contain myeloperoxidase, lysozyme, and defensin Corticomedullary barrier: sheet-like barrier between cortex § Specific granules: small, less dense, pink-staining vesicles and medulla formed by squamous cortical TECs Agranulocytes: Medulla: o Lack specific granules but have some lysosomes o Lightly-stained inner portion of each lobule o Spherical, non-lobulated nucleus o Contains larger, more mature lymphocytes and TECs o Hassall corpuscles: LEUKOCYTES MORPHOLOGY § Core of hyaline material surrounded by large aggregates CELL FEATURES concentrically-arranged TECs § Control the activity of local dendritic cells and development Granulocytes of regulatory T cells Nucleus with 3-5 lobes Neutrophils Light pink granules (50-70%) TYPES OF THYMIC EPITHELIAL CELLS (TECs) Lifespan of 1-4 days TYPE FEATURES FUNCTION Bilobed nucleus Cortex Eosinophils Red/dark pink granules Line the connective tissue of Form the (1-4%) Lifespan of 1-2 weeks Squamous the capsule and septa blood-thymus Acidophilia from major basic proteins Surround microvasculature barrier Bilobed, S-shaped nucleus Contain processes with Act as APCs, Basophils Blue granules obscuring the nucleus keratin tonofilaments secrete (0.5-1%) Lifespan of many months Stellate Form a cytoreticulum cytokines, Basophilia from heparin & sulfated GAGs where macrophages and attachment of Agranulocytes lymphocytes attach other cells Prominent round, basophilic nucleus Other Form first layer of corticomedullary barrier Lymphocytes Lifespan of hours to years Medulla (20-40%) Divided into B or T cells by surface proteins Aggregate together to form Secrete Monocytes Large cells with a kidney-shaped nucleus Squamous Hassall corpuscles cytokines (2-8%) Lifespan of hours to years Stellate Form a cytoreticulum Same as cortex Highest to lowest count (“Never Let Monkeys Eat Bananas”): Others Form second layer of corticomedullary barrier Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils Agranulocyte nuclei: Monocytes = kidney; Lymphocytes = round Bilobed with red granules: EoSinophils = looks like Spiderman Left: Thymus gland divided by septa (S) with a cortex (Co) and medulla (M). Right: Medulla with thymic epithelial cells (E) and Hassall corpuscles (HC). ANTIGEN-PRESENTING CELLS (APC) BONE MARROW Group of cells that mediate adaptive immunity Found in medullary canals of long bones and cavities of “Professional” APCs: cancellous bound o Active endocytotic system Yellow marrow: filled with adipocytes, increase with age o Express MHC class II molecules (present peptide antigens) o Include: monocyte-derived cells, dendritic cells, thymic Red marrow: blood-forming (hematopoietic) portion epithelial cells o Stroma: contains reticular fibers and specialized fibroblasts “Non-professional” APCs: called stromal cells (or reticular/adventitial cells) o Transiently express MHC class II during inflammation o Hematopoietic cords: islands of developing blood cells o Include: fibroblasts, vascular endothelial cells o Sinusoidal capillaries: run between hematopoietic cords MONONUCLEAR PHAGOCYTE SYSTEM CELL LOCATION FUNCTION Precursor of SECONDARY LYMPHOID ORGANS Monocyte Blood macrophages Where lymphocytes undergo activation and proliferation Connective Produce inflammatory Lymphoid tissue surrounded by capsules tissue, lymphoid molecules, antigen Primary lymphoid nodule: Macrophage organs, lung, processing and o B cell aggregates of uniform cell density marrow, cavities presentation o Follicular dendritic cells: Kupffer Cell Liver Same as macrophage § Mesenchymal cells with long filamentous processes Microglial Cell CNS Same as macrophage § Covered in antibody-antigen complexes where B cells attach  Secondary lymphoid nodule: § Open-ended vessels that open directly into the stroma o Gradually disappear after 2-3 weeks of proliferation § Blood cells must re-enter sinusoids between stave cells o Germinal center: § Stiff/swollen RBCs are blocked from re-entering § Lightly-stained area with large lymphoblasts (centroblasts) 4. Red pulp veins: drain splenic sinusoids § Area of rapid B cell growth and “quality control” 5. Trabecular veins: convergence of red pulp veins o Mantle: darkly-stained area around the germinal center with naïve, non-proliferating B cells MUCOSA-ASSOCIATED LYMPHOID TISSUE (MALT) Located in the mucosa or inner lining of genitourinary, digestive, and respiratory tracts Collectively contains up to 70% of the body’s immune cells Contains diffuse collections of lymphocytes and APCs, lymphoid nodules, and IgA-secreting plasma cells RESPIRATORY SYSTEM Functional divisions: o Conducting portion: nasal cavities to terminal bronchioles o Respiratory portion: respiratory bronchioles to alveoli Two secondary nodules with germinal centers (GC) and mantle (M) Respiratory epithelium: o Lines most the nasal cavities and conducting portions LYMPH NODES o Ciliated pseudostratified columnar epithelium Bean-shaped structures along lymphatic vessels o Lamina propria with seromucous glands and lymphoid tissue With a dense connective tissue capsule extending trabeculae Environments for antigen presentation and development of RESPIRATORY EPITHELIUM CELLS antibody-producing plasma cells CELL FEATURES FUNCTION Cortex: Ciliated Cilia clear microbes o Outer region containing lymphoid nodules Most abundant cell Columnar Cells and debris o Subcapsular and cortical sinuses: carry lymph, lined by a Basal nuclei and thin discontinuous endothelium Goblet Cells Secrete mucin