Specialized Connective Tissue PDF

 Connective tissue in which fat-storing cells or adipocytes predominate is called adipose tissue.  There are two major types of adipose tissue with different locations, structures, colors, and functions.  White adipose tissue, the more common type specialized for fat storage, co...

 Connective tissue in which fat-storing cells or adipocytes predominate is called adipose tissue.  There are two major types of adipose tissue with different locations, structures, colors, and functions.  White adipose tissue, the more common type specialized for fat storage, consists of cells each containing one large cytoplasmic droplet of whitish- yellow fat.  Brown adipose tissue contains cells with multiple lipid droplets interspersed among abundant mitochondria, which helps give this tissue a darker appearance. Brown adipocytes release heat and function to warm the blood.  Both types of adipose tissue have a rich blood supply and the adipocytes  adipocytes, are very large cells derived from mesenchyme and specialized for energy storage in lipid droplet(s) with triglycerides.  Adipocytes store lipids from three sources: from dietary fats packaged as chylomicrons in the intestine; from triglycerides produced in the liver and circulating as VLDLs; and from fatty acids synthesized locally.  Specialized for relatively long-term energy storage, adipocytes of white adipose tissue are spherical when isolated but are polyhedral when closely packed in situ contains a single huge droplet of lipid filling almost the entire cell. With the single large droplets of triglycerides, white adipocytes are also called unilocular causing the nucleus and remaining cytoplasm to be pushed against the plasma  White adipose tissue is found in many organs throughout the body, typically forming about 20% of the body weight in adults.  Fatty acids are released from white adipocytes by lipase activity when nutrients are needed and carried throughout the body on plasma proteins such as albumin.  Leptin is a polypeptide hormone with target cells in the hypothalamus that is released from white adipocytes and helps regulate eating behavior.  Brown adipose tissue constitutes 2%-5% of the newborn body weight, located mainly in the back, neck, and shoulders, but it is greatly reduced during childhood and adolescence.  In adults it is found only in scattered areas, especially around the kidneys, adrenal glands, aorta, and mediastinum.  The color of brown fat is due to both the very abundant mitochondria (containing cytochrome pigment) scattered among the lipid droplets of the fat cells and the large number of blood capillaries in this tissue.  Adipocytes of this tissue are typically smaller than those of white fat and contain primarily many small lipid droplets (they are multilocular) in cytoplasm containing many mitochondria and a central nucleus.  Fatty acids released in adipocytes of brown fat are metabolized in mitochondria of these cells for thermogenesis rather than ATP synthesis, using uncoupling protein-1.  Is partly rigid, partly flexible it provides support, frameworks, attachments, serves as template for developing bones, and provides cushioned, low-friction surfaces in joints.  characterized by an extracellular matrix (ECM) with high concentrations of (glycose aminoglycan)GAGs and proteoglycans, interacting with collagen and elastic fibers.  Much intercellular material composed of collagenous fibers embedded in a gel-like ground substance  Chondrocytes are embedded within lacunae surrounded by the ECM.  Cartilage ECM typically includes collagen as well as abundant proteoglycans, notably aggrecan, which bind a large amount of water.  Cartilage always lacks blood vessels, lymphatics, and nerves, but it is usually surrounded by a dense connective tissue perichondrium that is vascularized.  Hyaline Cartilage:  Elastic Cartilage  Fibrocartilage  Most common  Has fine collagenous fibers in matrix  Looks like white plastic  Found on ends of bones in joints, soft part of nose, rings in respiratory passages, in end of ribs  Important in bone formation  The ECM of hyaline cartilage is homogenous and glassy, rich in fibrils of type II collagen and aggrecan complexes with bound water.  The ECM has less collagen and more proteoglycan immediately around the lacunae, producing slight staining differences in this territorial matrix.  Chondrocytes occur singly or in small, mitotically derived isogenous groups.  Perichondrium is usually present, but not at the hyaline cartilage of articular surfaces or the epiphyses of growing long bones.  similar to hyaline cartilage except that it contains an abundant network of elastic fibers in addition to a meshwork of collagen type II fibrils  More flexible than hyaline cartilage  Elastic cartilage generally resembles hyaline cartilage in its chondrocytes and major ECM components, but its matrix includes abundant elastic fibers, visible with special stains, which increase the tissue’s flexibility.  Elastic cartilage provides flexible support for the external ear as well as certain structures of the middle ear and larynx; it is always surrounded by perichondrium.  Contains many collagenous fibers  Fibrocartilage takes various forms in different structures but is essentially resulting from a mixing of hyaline cartilage and dense connective tissue  It is found in intervertebral discs, in attachments of certain ligaments, and in the pubic symphysis ,knees  Fibrocartilage contains varying combinations of hyaline cartilage in small amounts of dense connective tissue.  Histologically it consists of small chondrocytes in a hyaline matrix, usually layered with larger areas of bundled type I collagen with scattered fibroblasts.  Fibrocartilage provides very tough, strong support at tendon insertions and in intervertebral discs and certain other joints.  All forms of cartilage form from embryonic mesenchyme.  Cartilaginous structures grow by mitosis of existing chondroblasts in lacunae (interstitial growth) or formation of new chondroblasts peripherally from progenitor cells in the perichondrium (appositional growth).  Repair or replacement of injured cartilage is very slow and ineffective, due in part to the tissue’s a vascularity and low metabolic rate.  Bone is a specialized connective tissue composed of calcified extracellular material, the bone matrix, and following three major cell types  Osteocytes which are found in cavities (lacunae) between bone matrix layers (lamellae), with cytoplasmic processes in small canaliculi that extend into the matrix  Osteoblasts growing cells which synthesize and secrete the organic components of the matrix  Osteoclasts which are giant, multinucleated cells involved in removing calcified bone matrix and remodeling bone tissue  Matrix is deposited in layers called lamellae around osteonic canals  All bones are lined on their internal and external surfaces by layers of connective tissue containing osteogenic cells— endosteum on the internal surface surrounding the marrow cavity and periosteum on the external surface.  Canaliculi are small tubes through which osteocyte cytoplasm extends  The periosteum is organized much like the perichondrium of cartilage, with an outer fibrous layer of dense connective tissue, containing mostly bundled type I collagen, but also fibroblasts and blood vessels.  Internally the very thin endosteum covers small trabeculae of bony matrix that project into the marrow cavities  The endosteum also contains osteoprogenitor cells, osteoblasts, and bone lining cells, but within a sparse, delicate matrix of collagen fibers.  Dense bone immediately beneath the periosteum is called compact bone; deep to the compact bone are small bony trabeculae or spicules of cancellous (or spongy) bone.  In long bones of the limbs, these two types of mature bone tissue occur in both the knobby, bulbous ends, called epiphyses, and in the intervening shaft or diaphysis.  Immature bone, called woven bone, is formed during osteogenesis or repair and has a calcified matrix with randomly arranged collagen fibers.  By the action of osteoclasts and osteoblasts, woven bone undergoes rapid turnover and is remodeled into lamellar bone with new matrix deposited in distinct layers with parallel collagen bundles; both compact and cancellous bone is lamellar bone.  Most lamellar bone consists of lamellae organized concentrically around small central canals containing blood vessels and nerves; this organization is called an osteon or Haversian system.  Within each osteon osteocytic lacunae occur between the lamellae, with canaliculi radiating through the lamellae, which allow all cells to communicate with the central canal.  Transport  Matrix=plasma  Red blood cells  White blood cells  Platelets  Blood cells float in plasma, formed in bone marrow  is specialized connective tissue, like any connective tissue it  consist of :  1) Cells ( Erythrocyte , leukocyte and platelets )  2) Fibers ( proteins that dissolved in plasma albumin, a- & B- globulin  and fibrinogen )  3) Extracellular Matrix ( Plasma )  terminally differentiated structures  lacking nuclei  completely filled with the O2-carrying protein hemoglobin.  RBCs are the only blood cells whose function does not  require them to leave the vasculature.  suspended in an isotonic medium.  are flexible biconcave discs.  They are approximately 7.5 μm in diameter, 2.6 μm thick at  the rim, but only 0.75 μm thick in the center.  Because of their uniform diameters and their presence in  most tissue sections, RBCs can often be used by histologists  as an internal standard to estimate the size of other cells or  structures.  leave the blood and migrate to the tissues where they  become functional and perform various activities related to  immunity.  According to the type of cytoplasmic granules and their nuclear morphology, leukocytes are divided into two  groups: granulocytes and a granulocytes  Granulocytes possess two major types of cytoplasmic granules:  1- lysosomes (often called azurophilic granules in blood cells)  2- specific granules that bind neutral, basic, or acidic stains and have specific functions.  Granulocytes have polymorphic nuclei with two or more distinct (almost separated) nuclear lobes and include the neutrophils, eosinophils, and basophils.  All granulocytes are terminally differentiated cells with a life span of only a few days. Their Golgi complexes and rough ER are poorly developed. They have few mitochondria and depend largely on glycolysis for their low energy needs.  Granulocytes normally die by apoptosis in the connective tissue and billions of neutrophils alone die by apoptosis each day in the adult human. The resulting cellular debris is removed by macrophages and, like all apoptotic cell death, does not itself elicit an inflammatory response.  A granulocytes do not have specific granules, but they do contain azurophilic granules (lysosomes), with affinity for the basic stain azure A.  The nucleus of a granulocyte is spherical or indented but not lobulated.  A granulocyte includes lymphocytes and monocytes  1- Neutrophils , the most abundant type of leukocyte, have polymorphic multilobed nuclei , and faint pink cytoplasmic granules that contain many factors for highly efficient phago lysosomal killing and removal of bacteria.  2-Eosinophils have bilobed nuclei and eosinophilic specific granules containing factors for destruction of helminthic parasites and for modulating inflammation.  3-Basophils , the rarest type of circulating leukocyte, have irregular bilobed nuclei and resemble mast cells with strongly basophilic specific granules containing factors important in allergies and chronic inflamatory conditions, including histamine , heparin , chemokines, and various hydrolases.  Lymphocytes , agranulocytes with many functions as T- and B-cell subtypes  in the immune system, range widely in size, depending on their activation  state, and have roughly spherical nuclei with little cytoplasm and few organelles.  Monocytes are larger agranulocytes with distinctly indented or C-shaped  nuclei that circulate as precursors of macrophages and other cells of the  mononuclear phagocyte system.  Platelets  Platelets are small (2-4 μm) cell fragments derived from megakaryocytes in bone marrow, with a marginal bundle of actin filaments, alpha granules and delta granules , and an open canalicular system of membranous vesicles; rapid degranulation on contact with collagen triggers blood clotting.  Plasma is an aqueous solution, pH 7.4.  containing substances of low or high molecular weight that  make up 7% of its volume.  The dissolved components are mostly plasma proteins, but  they also include nutrients, respiratory gases, nitrogenous  waste products, hormones, and inorganic ions, collectively  called electrolytes.  Through the capillary walls, the low-molecular-weight  components of plasma are in equilibrium with the  interstitial fl uid of the tissues.  Albumin , the most abundant plasma protein, is made in the liver and serves primarily to maintain the osmotic pressure of the blood. a-Globulins and B-globulins , made by liver and other cells, include transferrin and other transport factors; fi bronectin ; prothrombin and other coagulation factors; lipoproteins and other proteins entering blood from tissues. f-Globulins , which are immunoglobulins (antibodies) secreted by plasma cells in many locations. Fibrinogen , the largest plasma protein, also made in the liver, which, during clotting, polymerizes as insoluble, cross-linked fibers of fibrin that block blood loss from small vessels. Complement proteins , a system of factors important in inflammation and destruction of microorganisms.  There are three major types of muscle: (1) skeletal or striated muscle, (2) cardiac muscle, and (3) smooth or visceral muscle.  Connective tissue present in muscle  1-epimysium  2-Perimysium  3-endomysium  Skeletal muscle cells are very long, multinucleated fibers, cylindrically shaped and with diameters up to 100 μm.  The sarcolemma of each fiber is surrounded by an external lamina and thin connective tissue, endomysium, containing capillaries.  Internally each muscle fiber is filled with myofibrils, composed of thousands of thick myosin filaments and thin actin filaments, highly organized into contractile units called sarcomeres.  Within sarcomeres thick and thin filaments interdigitate; globular myosin heads project from the thick filaments toward the F-actin filaments, which are associated with tropomyosin and troponin.  Skeletal muscles contain fibers that can be physiologically classified as the three main types: (1) slow, oxidative (type I); (2) fast, intermediate oxidative-glycolytic (type IIa); and (3) fast, glycolytic (type IIb).  Cardiac muscle fibers are also striated, but they consist of individual cylindrical cells, each containing one (or two) central nuclei and linked by adherent and gap junctions at prominent intercalated discs  Sarcomeres of carrepresent the interfaces between adjacent cells and consist of many junctional complexes  Transverse regions of these irregular, step like discs are composed of many desmosomes and fascia adherents junctions, which together provide strong intercellular adhesion during the cells’ constant contractile activity. ).  cardiac muscle are organized and function similarly to those of skeletal muscle.  Contraction of cardiac muscle is intrinsic at nodes of impulse-generating pacemaker muscle fibers; autonomic nerves regulate the rate of contraction.  Smooth muscle is specialized for slow, steady contraction under the influence of autonomic nerves and various hormones. This type of muscle is a major component of blood vessels and of the digestive, respiratory, urinary, and reproductive tracts and their associated organs.  Smooth muscle fibers are individual small, fusiform (tapering) cells, linked by numerous gap junctions.  Thin and thick filaments in smooth muscle fibers do not form sarcomeres, and no striations are present.  Thin actin filaments attach to α-actin located in dense bodies that are located throughout the sarcoplasm and near the sarcolemma; contraction causes cells to shorten individually.  Sarcoplasmic reticulum is less well-organized in smooth muscle fibers, and there is no transverse tubule system.  Repair and regeneration can occur in skeletal muscle because of a population of reserve muscle satellite cells that can proliferate, fuse, and form new muscle fibers.  Cardiac muscle lacks satellite cells and has little capacity for regeneration.  Regeneration is rapid in smooth muscle because the cells/fibers are small and relatively less differentiated, which allow renewed mitotic activity after injury.  Receive stimuli from both internal and external environments which are then analyses and integrated to produce appropriate coordinated responses in various effector organs.  The nervous system is composed of highly complex intercommunicating networks of nerve cells that receive and conduct impulses along their neural pathways or axons to the CNS for analysis, integration, interpretation, and response. Ultimately, the appropriate response to a given stimulus from the neurons of the CNS is the activation of muscles (skeletal, smooth, or cardiac) or glands (endocrine or exocrine).  Functionally/physiologically: 1. Somatic nervous system (SNS) 2. Autonomic nervous system (ANS) a-sympathatic b-parasympathatic Anatomically and histologically: 1-a Central nervous system (CNS)(brain and spinal cord) 1-b Peripheral nervous system (PNS)(cranial and spinal nerves with their ganglia )  Dendrites Soma Nucleus Nucleolus Trigger zone: Axon hillock Axon Axon Initial collateral segmen t Direction of signal transmission Intern odes 2- Supporting cells a- Node of Ranvier Myelin Neuroglia (in CNS) sheath Schwan n cell b-Schwann cell(in PNS) Terminal arborization Figure Synaptic ( a 12.4a knobs )  Neuron-Structural & functional unit of nervous system consist of 2 parts 1. Cell body/soma/perikaryon 2. Process/neurite 2 types of neurite- 1. Axon 2. Dendrite (Axon & dendrite) is called nerve fiber. Note: 1. Neurons/nerve cells-Active, non- dividing cell 2. Neuroglia/glial cells-Non-active, dividable cell  Most neurons have three main parts The cell body (also called the perikaryon or soma), which contains the nucleus and most of the cell’s organelles and serves as the synthetic or trophic center for the entire neuron. The dendrites, which are the numerous elongated processes extending from the perikaryon and specialized to receive stimuli from other neurons at unique sites called synapses. The axon which is a single long process ending at synapses specialized to generate and conduct nerve impulses to other cells (eg, nerve, muscle, and gland cells). Axons may also receive information from other neurons, information that mainly modifies the transmission of action potentials to those neurons.  Glial cells of the CNS= Astrocytes Oligodendrocytes…myelination Microglial Ependymal cells 12-8  Glial cells (glia), required to support neurons in many ways, consist of six major types: Oligodendrocytes wrap processes around portions of axons in the CNS, forming myelin sheaths that insulate the axons and facilitate nerve impulses.  Astrocytes, the most numerous cell of the CNS, all produce hundreds of processes to cover and provide regulated microenvironments for neuronal perikarya, synapses, and capillaries.  Ependymal cells are epithelial-like cells, lacking basement membranes, which line the fluid-filled cerebral ventricles and central canal of the spinal cord.  Microglia differs from all other glial cells in originating from blood monocytes, not from neural tissue precursors; they mediate immune defense activity within the CNS.  Schwann cells (neurolemmocytes) enclose all axons in nerves of the PNS, producing myelin sheaths around large-diameter axons, whose impulse conductivity is augmented at the nodes of Ranvier between successive Schwann cells. Satellite cells are located within PNS ganglia, aggregated sensory or autonomic neuronal cell bodies, where they enclose each perikaryon and regulate its microenvironment. These supporting “glial” brace and protect the fragile neuron cells Act as phagocytes Control the chemical environment around the nerve cells.  Multipolar neurons, each with one axon and two or more dendrites, are the most common.  Bipolar neurons, with one dendrite and one axon, comprise the sensory neurons of the retina, the olfactory epithelium, and the inner ear.  Unipolar or pseudounipolar neurons, which include all other sensory neurons, each have a single process that bifurcates close to the perikaryon, with the longer branch extending to a peripheral ending and the other toward the CNS.  Anaxonic neurons, with many dendrites but no true axon, do not produce action potentials, but regulate electrical changes of adjacent CNS neurons.