Connective Tissues Lecture PDF

CONNECTIVE TISSUES, BONE and CARTILAGE BY: Jonathan A. Tiongson Jr., RMT Learning Objectives: 1. Describe the general features and functions of connective tissue in the body. 2. Identify the key cells in connective tissue proper and explain their roles. 3. Explain the structu...

CONNECTIVE TISSUES, BONE and CARTILAGE BY: Jonathan A. Tiongson Jr., RMT Learning Objectives: 1. Describe the general features and functions of connective tissue in the body. 2. Identify the key cells in connective tissue proper and explain their roles. 3. Explain the structure and function of the extracellular matrix, including fibers (collagen, elastic, reticular) and ground substance. 4. Classify connective tissue proper into loose (areolar, adipose, reticular) and dense (regular, irregular, elastic) types, and describe their characteristics. 5. Explain the functions of connective tissue proper, such as structural support, protection, storage, transport, and immune defense. CONNECTIVE TISSUES o these are supporting tissues which are joining part of the body o is formed primarily of extracellular matrix -cells -fibers -ground substance Functions: - support - medium for exchange - protection - storage of fat CELLS OF CONNECTIVE TISSUE A. Fixed cells - fibroblasts, adipocytes, Macrophages, Mast cells, pericytes B. Transient cells -Plasma cells, lymphocytes, neutrophils, eosinophils, basophils, monocytes, macrophages FIXED CELLS FIBROBLASTS ○ The most common cells in connective tissue, produce and maintain most of the tissues’ extracellular components. ○ Synthesize and secrete collagen and elastin as well as GAG’s, proteoglycans and multiadhesive glycoproteins that comprise the ground substance.  FIBROBLAST VS. FIBROCYTES Fibroblasts Fibrocytes ✔ Active fibroblasts ✔ Smaller than the active ✔ More abundant and irregularly fibroblast branched cytoplasm ✔ Nucleus is large, ovoid, ✔ Spindle-shaped euchromatic and has a ✔ Fewer processes prominent nucleolus ✔ Less RER and contains a ✔ Cytoplasm has much RER and darker , more well developed Golgi heterochromatic nucleus apparatus MYOFIBROBLAST ○ Are modified fibroblast that demonstrate characteristics similar to those of both fibroblasts and smooth muscle cells ○ Activated form of fibroblast that is capable of contraction. ○ Absence of basal lamina ○ Abundant in areas undergoing wound healing PERICYTES ○ Surround endothelial cells of capillaries and small venules and reside outside the connective tissue compartment, because they possess their own basal lamina ADIPOSE CELLS ○ Are fully differentiated cells that function in the synthesis, storage and release of fats White adipose tissue (unilocular fat cells) Single, large lipid droplet Brown adipose tissue (multilocular fat cells) Multiple, small lipid droplets Adipose Tissue MAST CELLS ○ Arise from bone marrow stem cells and function in mediating the inflammatory process and immediate hypersensitivity reactions MACROPHAGES ○ Belong to the mononuclear phagocytic system and are subdivided into two groups of cells: Phagocytes Antigen-presenting cells APC ○ Act both as fixed and transient cell NOMENCLATURE OF DIFFERENT MACROPHAGES ON ITS SPECIFIED TISSUE LOCATION LIVER Kupffer cells Kidney Mesangial cells Brain/Nervous tissue Microglial cells Bone Osteoclasts Lungs Alveolar macrophage/ Dust cells Connective tissue Histiocytes Skin Langerhan cells Spleen Littoral cells Placenta Hofbauer cells Type A cell Synovial macrophage Lymph nodes Dendritic cells PLASMA CELLS ▪ Derived from B lymphocytes ▪ Nucleus is generally spherical but eccentrically located. ▪ Responsible for the synthesis of Immunoglobulin antibodies. LYMPHOID CELLS - accumulate in the Respiratory system, GI tract and in areas of chronic inflammation 3 types: A)T lymphocytes (T cells) initiate the cell – mediated immune response B) B lymphocytes – (B cells) – function in the humoral immune response C) Null cells – has cytotoxic activity against tumor cells EXTRACELLULAR MATRIX COMPONENTS 1. Ground substance ○ Hydrated, amorphous material that is composed of GAG, proteoglycans and glycoproteins 2. Fibers ○ Collagen – most abundant protein in the human body, representing 30% of its dry weight. It is a key element of all CT, as well as epithelial basements and external laminae of muscle and nerve cells Inelastic and possess great tensile strength Types: Type I: in connective tissue proper, bone, dentin, cementum Type II: hyaline and elastic cartilages Type III: Reticular fibers Type IV: lamina densa of the basal lamina Type V: placenta; associated with type I collagen Type VII: attaching the basal lamina to the lamina reticularis TYPES OF COLLAGEN 1.Type I -most abundant. Play an important role in the calcification process - found in tendons, ligaments, skin and bone 2.Type II – found in cartilage, cornea, vitreous humor 3.Type III - forms network that supports the cell of the glands, lymphoid tissue and bone marrow 4.Type IV- Found in the lamina densa of basal lamina 5.Type V – widely distributed 6.Type VI – associated often with elastin 7.Type VII – component of placental membrane 8.Type VIII – product of endothelial cells 9.Type IX – are synthesized by chondrocytes, located in the paralacunar region of the cartilage 10.Type X – found in regions of hypertrophying cartilage cells Local swelling caused by abnormal large amounts of collagen that form in scars of the skin Reticular Fiber Found in delicate connective tissue of many organs Consist mainly of Collagen Type III Forms an extensive network (reticulum) of extremely thin, heavily glycosylated fibers. Seldom visible in H & E preparations but stained BLACK by impregnation with silver salts Argyrophilic (readily stained with silver impregnation techniques) Reticular fibers contain up to 10% carbohydrate as opposed to 1% in most other collagen fibers. Reticular fibers produced by fibroblasts occur in the reticular lamina of basement membranes and typically also surround adipocytes, smooth muscle and nerve fibers, and small blood vessels. Elastic Fiber Composed of elastin (responsible for elasticity) and microfibrils (responsible for stability) ○ Elastic fibers (and lamellae) are a composite of fibrillin (350 kDa), which forms a network of microfibrils, embedded in a larger mass of cross-linked elastin (60 kDa). Thinner than the type I collagen fibers and have rubberlike properties that allow tissue containing these fibers, such as the stroma of the lungs, to be stretched or distended and return to their original shape.  CLASSIFICATION OF CONNECTIVE TISSUES CONNECTIVE SPECIALIZED TISSUE PROPER CONNECTIVE TISSUE SUPPORTIVE VASCULAR LOOSE CT RETICULAR ADIPOSE TISSUE TISSUE DENSE CT AREOLAR CT CT BLOOD CARTILAGE BONE DENSE DENSE DENSE REGULAR ELASTIC IRREGULAR EMBRYONAL TISSUE MUCOUS MESENCHYME CT CT TYPES OF CONNECTIVE TISSUE PROPER: 1. Loose (Areolar) 2. Dense ❑ Irregular ❑ Regular o Collagenous o Elastic 3. Reticular 4. Adipose LOOSE (AREOLAR) CONNECTIVE TISSUE Composed of loose arrangement of fibers and dispersed cells embedded in a gel-like ground substance Abundant ground substance with fixed connective tissue cells (fibroblast, adipose, macrophages, mast cells) Scattered, loosely woven collagen, reticular and elastic fibers Location: ○ Spaces of the body just deep to the skin ○ Lies below mesothelial lining of internal cavity ○ Adventitia of blood vessels ○ Parenchyma of glands Types: A. Loose areolar- characterized by a loosely arranged fibroelastic tissue that serves as a packing material in unused spaces between organs like the lamina propria B. Loose adipose- fat cells are abundant, ex. panniculus adiposus C. Loose reticular – associated with reticular cells, ex. stroma of the thymus D. Mucous connective tissue - transient type of tissue which appears in the normal development and differentiation of connective tissues. It occurs in umbilical cord as Wharton’s jelly -cells are large, stellate fibroblasts DENSE CONNECTIVE TISSUE Greater abundance of fibers and fewer cells than loose connective tissue Dense Irregular ○ Mostly coarse collagen fibers interwoven into meshwork ○ Fibers are packed so tightly that space is limited for ground substance and cells ○ Fibroblasts are the most abundant cells ○ Location: dermis of the skin, the sheaths of nerves, and the capsules of spleen, testes, ovary, kidney, lymph nodes Dense Regular Collagenous ○ Composed of coarse collagen bundles densely packed and oriented in parallel cylinders ○ Location: tendons, ligaments, aponeurosis Dense Regular Elastic o Coarse branching elastic fibers ○ with only few collagen ○ Location: large blood vessels, ligamenta flava of vertebral column and suspensory ligament of the penis RETICULAR CONNECTIVE TISSUE Major fiber component is type III collagen Interspersed with fibroblasts and macrophages Location: liver sinusoids, adipose tissue, bone marrow, lymph nodes, spleen, smooth muscle and islets of langerhans ADIPOSE CONNECTIVE TISSUE WHITE (UNILOCULAR) ADIPOSE TISSUE ○ Single lipid droplet ○ Present in the subcutaneous layers throughout the body ○ Common in adult human than brown adipose BROWN (MULTILOCULAR) ADIPOSE TISSUE ○ Multiple lipid droplet ○ Heavily vascularized thus brown in color EMBRYONIC CONNECTIVE TISSUE 1. Mesenchymal connective tissue ○ Present only in the embryo and consists of mesenchymal cells 2. Mucous connective tissue ○ Loose, amorphous connective tissue exhibiting a jelly-like matrix composed of hyaluronic acid and populated with type I and type III collagen fibers and fibroblasts ○ Location: Wharton’s Jelly of the umbilical cord and subdermal connective tissue of the embryo CARTILAGE CARTILAGE - firm extracellular matrix which contains collagenous elastic or elastic fibers - forms most of the skeleton in early fetal life - avascular - plays a role in the elongation of the bones Types: 1. Hyaline – translucent in fresh state - most basic and fundamental -serves as a temporary skeleton in the fetus until it is replaced with bone - chondrocytes, collagenous fibers (type II), ground substance (chondroitin sulfate) - has perichondrium - seen in a.) fetal skeleton b.) nose c. ) larynx d.)bronchus e.)trachea f.) ventral ends of the ribs g.) external acoustic meatus Chondrocytes Located at the periphery of the cartilage Have an elliptic shape, with the long axis parallel to the surface. Respire under low-oxygen tension Metabolize glucose mainly by anaerobic glycolysis to produce lactic acid GROWTH HORMONE major regulator of hyaline cartilage growth is pituitary derived growth hormone Acts indirectly promoting the endocrine release from the liver of insulin-like growth factors, which directly stimulates proliferation of chondrocytes Perichondrium All hyaline cartilage is covered by a layer of Dense CT Essential for the growth and maintenance of cartilage Consists largely of collagen type 1 fibers and fibroblasts. 2. Elastic – seen in ear auricle, auditory tube, epiglottis - yellow in color due to elastic fibers - modification of hyaline cartilage 3. Fibrocartilage - occurs where tough support is required - seen in intervertebral disk, symphysis pubis and tendon grooves - lacks perichondrium - collagenous fibers (type I) are abundant in relation to the cells present -act as lubricated cushions and shock absorbers preventing adjacent vertebrae from being damaged by abrasive forces or impacts ELASTIC CARTILAGE TISSUE FIBROCARTILAGE TISSUE 2 methods in which cartilage grows: A. Interstitial growth /endogenous –chondrocytes undergo mitosis and lay down new matrix. There is continued deposition of matrix which forms capsule which lead to separation of cells B. Appositional /exogenous- the osteogenic cells in the chondrogenic layer of the perichondrium multiply and differentiate into chondroblast which deposit matrix around them thus, adding or increasing the size of the cartilage. Major Cartilage types Hyaline cartilage Elastic cartilage Fibrocartilage Main features of the Homogenous, with type Type II collagen, Type II collagen and ECM II collagen and aggregan and darker large areas of Dense CT aggregan elastic fiber with type 1 collagen Major cells Chondrocytes, Chondrocytes, Chondrocytes, chondroblasts chondroblasts fibroblasts Presence of YES YES NO Perichondrium LOCATIONS Upper respi, articular External ear, external Intervetebral discs, ends, epiphyseal plates acoustic meatus, pubic symphysis of long bone, fetal auditory tube, epiglottis skeleton Main functions Provides smooth, Flexible shape, support Provides cushioning, low-friction surfaces in of soft tissues tensile strength and joints, structural support resistance to tearing for respi tract and compression BONE BONE - osseous tissue -rigid form of connective tissue that constitutes most of the skeleton of higher vertebrates Functions: ∙ protect vital organs & support fleshy structures ∙ rigid framework of the body ∙ locomotion and movements ∙ stores calcium and phosphorous ∙ lodging place for bone marrow CONNECTIVE TISSUE OF BONES ▪ Periosteum ▪ Endosteum BONE Bone is a specialized connective tissue composed of calcified extracellular material, the bone matrix, and the three bone cell types (osteocytes, osteoclasts, osteoblasts). Harder and stronger than cartilage. The external surface of the bone is covered by periosteum. The inner surface of the bone is covered by endosteum. Osteoprogenitor cells derived from mesenchymal stem cells and can undergo cell division is a resting cell that can differentiate into an osteoblast and secrete bone matrix. Morphologically, they comprise the periosteal cells that form the innermost layer of the periosteum and the endosteal cells that line the marrow cavities: the ○ Osteonal (Haversian) canals; and the ○ Perforating (Volkmann’s) canals. Osteoblast The differentiated bone-forming cell that secretes organic components of the bone matrix ▪ Type I collagen fibers ▪ Proteoglycans ▪ Bone matricellular glycoproteins (i.e. osteonectin) Osteoblast processes communicate with other osteoblasts and with osteocytes by gap junctions. Osteocytes Are almond-shaped mature bone cells derived from osteoblasts that became trapped in lacunae. They are normally the most abundant cells in bone. They are responsible for maintaining the bone matrix. Synthesize new matrix, as well as participate in matrix degradation → maintain calcium homeostasis Arranged with their long axes in the same direction as the lamellae. Osteoclasts Are multinucleated cells originating from granulocyte-macrophage progenitors Play a role in bone resorption Bone-resorbing cells present on bone surfaces where bone is being removed or remodeled ○ a shallow bay called a resorption bay (Howship’s lacuna) can be observed in the bone directly under the osteoclast. BONE CELLS (SUMMARY) 1. Osteoblast – associated with bone formation 2. Osteocytes – or bone cell - osteoblasts which has become imprisoned with in bone matrix - responsible for maintaining the integrity of the bone matrix 3. Osteoclasts – multinucleated cells - bone destroying cells - lodged in cavities called Howship’s canal 4.Osteoprogenitor- can multiply and become osteoblast, chondroblast or osteoclast PERIOSTEUM An outer fibrous sheath of dense regular connective tissue covering of the bone except articular surface. Two layers 1. Outer fibrous layer 2. Inner cellular (osteogenic) layer Well-defined if active bone formation is in progress The relatively few periosteal cells are capable of undergoing division and becoming osteoblasts under appropriate stimulus. Sharpey’s (Perforating) fibers ▪ Collagen fibers from ligaments and tendons extend directly into the bone tissue, where they are continuous with the collagen fibers of the extracellular matrix of the bone tissue. ▪ Binds periosteum to the bone. ENDOSTEUM Covers small trabeculae of bony matrix that project into the marrow cavities. Also contains osteoprogenitor cells, osteoblasts, and bone lining cells, but within a sparse, delicate matrix of collagen fibers  BONE CAVITIES The marrow cavity and the spaces in spongy bone contain bone marrow. ▪ Red bone marrow ✔ normally restricted to the spaces of spongy bone in the adult ▪ Yellow marrow ✔ consists mostly of fat cells ✔ can revert to red marrow e.g. extreme blood loss  Fibers- osteocollagenous fibers/ sharpy’s fiber accounts for the organic components of intercellular substance. These are the fibers that will bolt into the periosteum. Ground Substance – inorganic salts – CaPO4. , organic substances are also present Morphologic Classifications: 1. Short bones- tarsal bones, carpal bones 2. Irregular bones – vertebrae, bones of the skull 3. Long bones- tibia, fibula, humerus, femur, radius and ulna 4. Flat bones – ribs, scapula 2 Types of Bone 1. Spongy/cancellous-not visible to naked eye, composed of empty spaces which are interconnecting between the bony trabeculae or spicules 2. Compact (dense) – solid & external in location has no bone marrow cavities. OSTEON (HAVERSIAN SYSTEM) - functional unit of a compact bone - cylindrical branching tubes which is arranged around the canal, the haversian canal, which contains blood vessels and nerves. The haversian canal is surrounded by a thick tubular layer of lamella, the concentric lamella which are lined with lacuna where the osteocytes are lodged. The osteocytes lining the concentric lamella are closely related to the canaliculi. The haversian canal communicate with the medullary cavity, the periosteum, and communicate with each other by means of the so called Volkmann’s canal.  BONE GROWTH IN LENGTH Zone of reserve cartilage ✔ Chondrocytes randomly distributed throughout the matrix Zone of proliferation ✔ Chondrocytes proliferating, form rows of isogenous cells in parallel direction Zone of maturation and hypertrophy ✔ Chondrocytes mature, hypertrophy and accumulate glycogen Zone of calcification ✔ Lacunae becomes confluent, hypertrophied chondrocytes die and cartilage matrix calcified Zone of ossification ✔ Osteoprogenitor-osteoblast-osteocyte-calcification ✔ Resorption