Human Histology Lecture 4: Cartilage & Bone PDF

Cartilage and Bone Composition of the Extracellular Matrix LECTURER: Dr. Alyn G. Palomo Click for Template! It is crucial in the survival of Chondrocytes. COURSE OUTLINE...

Cartilage and Bone Composition of the Extracellular Matrix LECTURER: Dr. Alyn G. Palomo Click for Template! It is crucial in the survival of Chondrocytes. COURSE OUTLINE There should be a definite GAG or Glycosaminoglycan-Fiber Ration. I. Cartilage and Bone In cartilage, there should be more GAG compared to II. Cartilage the fibers because this will permit the diffusion of III. Types of Cartilage A. Hyaline Cartilage substance between the blood vessels in the B. Elastic Cartilage surrounding connective tissues. C. Fibrocartilage ○ With this specific GAG-Fiber Ration, it will D. Summary of Cartilage Features maintain the viability of your tissue. IV. Types of Cartilage Growth A. Appositional Growth Skeletal Material for Embryo B. Interstitial Growth C. Regenerative Ability When we were embryos in the womb, our skeleton was V. Bone A. Functions made up of cartilage, specifically Hyaline Cartilage. VI. Classification of Bones ○ Because this cartilage will grow rapidly and A. Shape or Form maintain the degree of stiffness as it grows. B. Microscopic Appearance ○ Later on in fetal life, this cartilage will be C. Maturity replaced by bone. VII. Parts of the Bone ○ When we come out of our mother's womb, our A. Components cartilage has already been replaced by bone. B. Microscopic Structure ○ The Axial and Appendicular skeleton material C. Ossification D. Growth of Bones will be made up of this cartilage. E. Zones of the Epiphyseal Growth Plate In postnatal life, these skeletons will VIII. Appendix 2: Some Factors Affecting Ossification become the bones that we have now. I. CARTILAGE AND BONE III. TYPES OF CARTILAGE Both are two specialized connective tissues. Hyaline Cartilage Elastic Cartilage II. CARTILAGE Fibrocartilage Just like any other Connective Tissue, the Cartilage A. HYALINE CARTILAGE has the following components: ○ Cells Function ○ Fibers ○ Ground Substance To provide resilience and pliability. This is where fiber is suspended. Extracellular Matrix is the result Chondrocyte when Fiber is added with the Ground Substance. The cells in the cartilage. Large and Spherical. Characteristics of Cartilage ○ Can be distorted when they are at the Perichondrium. Avascular Perichondrium is the boundary or ○ No innate blood vessels. border of the cartilage. ○ Tissue gets nutrients from neighboring ○ The cell would become squished or flattened tissues. and not spherical anymore. No Lymphatics Cytoplasm staining will vary according to the activity No Innervations of the Chondrocyte. Viscoelasticity ○ If the cartilage is young and there is still ○ Important characteristic of your Connective active replication, the cytoplasm will be Tissue because it is Viscoelastic. basophilic, indicating protein synthesis. ○ Results in a firm and resilient tissue. Due to the meshwork of collagen and proteoglycan in the extracellular matrix. 1  There are numerous Rough ○ Young Cartilage Endoplasmic Reticulum and a lot of Cells occur singly. large Golgi Apparatus which will be seen as clear areas near the ○ Older Cartilage Nucleus. Cells occur in groups ○ If the cartilage is a bit older and less active, 4-8 isogenous groups in hyaline cartilage the Golgi Apparatus will be much smaller, and there will be less basophilia. Function of Chondrocyte: ○ Secretion of matrix collagen, glycosaminoglycans, and proteoglycan. Chondroblast Cells that function in cartilage matrix production. Lacuna Spaces that the chondrocytes will cells lodge-in. The empty structure. Living: Chondrocytes will fill the lacuna completely. Figure 1.2. Hyaline Cartilage Preparation of/Fixed slide: Chondrocytes will shrink. Matrix Young Growing Cartilage Appears homogeneous Chondrocytes are well preserved. ○ You cannot distinguish if there are fibers. Homogenous basophilia of the cytoplasm. ○ Ground Substance Clear areas are the golgi apparatus. Same refractive index as the fibrils. Basophilic Metachromatic Due to the presence of chondroitin sulfate or keratan sulfate. Metachromatic: ability of a tissue to take up stain or take up a color that is not in the stain. Amorphous ○ No definite shape. Stiff, gelatinous ground substance permeated by Figure 1.1. Young Growing Cartilage of Hyaline Cartilage collagenous fibrils ○ Contains fibers but can’t differentiate it since Perichondrium it is homogenous. Stain is not uniform Border ○ Due to the different concentrations of Made up of dense irregular connective tissue sulfated proteoglycans. 2 Layers (especially in the active and growing Chondroitin sulfate cartilage): Keratan sulfate ○ Outer Fibrous Layer ○ More basophilic at the inner regions near the Contains fibroblast border of the cell compared to the outer ○ Inner Chondrogenic Layer regions further from the cell families. Contains undifferentiated cells ○ Less concentration of sulfated proteoglycans Will continually produce at the outer regions. chondroblasts, which later become Colors of the fibers will not be chondrocytes during the growth of masked anymore by the ground this cartilage. substance. Ground substance = basophilic Cell families Fibers = acidophilic If there are more proteoglycans in A group of cells, or chondrocytes, in cartilage the matrix, then the color of the Also called isogenous groups fibers will be masked by the ground substance which makes it become basophilic. 2  Due to its staining, there are 3 regions that have been B. ELASTIC CARTILAGE described in the cartilage: ○ Capsular/Pericellular territory or matrix Chondrocytes Near the capsule. ○ similar to hyaline ○ Territorial matrix Lacuna Found near the isogenous groups. ○ larger than hyaline ○ Interterritorial matrix Cell families are lesser compared to hyaline Far away from the cell families and ○ 2-4 isogenous groups in elastic cartilage. has a pinkish tinge. Presence of the perichondrium indicates the entirety of Proteoglycan decreased in aging. the elastic cartilage Components of Elastic Cartilage Type II collagen ○ Same component as hyaline. Elastic fiber ○ Predominant fiber Elastic sheets Chondrocytes Chondroblasts Function To provide elasticity in addition to resilience and Figure 1.3. Hyaline Cartilage stained with H&E pliability. Types of Hyaline Cartilage Staining Adult Elastic cartilage is not that visible in H&E ○ Found in the following structures: ○ Pale staining and refracted. Trachea Resorcin-fuchsin and Orcein stain Larynx ○ Helps visualize the elastic fibers. Bronchi ○ Will stain the fibers brown. Costal cartilage Nasal cartilage ○ For support Fetal ○ Used as the skeleton of the fetus As it transforms to bone, what will be left is the epiphyseal plate found in growing children. Epiphyseal plate - remnants of the fetal skeleton. Closes if we reach our maximum height. Articular ○ Found in joints and serve as cushion, and Figure 2.1. Elastic Cartilage provide a low friction surface. Area of Fatty Degeneration Looks like adipose tissue Degeneration of the elastic cartilage Enclosed in the perichondrium Figure 1.4. Types of Hyaline Cartilage 3  D. SUMMARY OF CARTILAGE FEATURES HYALINE ELASTIC FIBRO- CARTILAGE CARTILAGE CARTILAGE Occurrence Fetal skeleton Pinna of Intervertebral Epiphyseal external ear discs plates External Pubic symphysis Articular ends acoustic Articular discs of long bones meatus (sternoclavicular Figure 2.2. Areas of Fatty Degeneration circled within a section Costal Eustachian and temporo- of Elastic Cartilage in the Epiglottis cartilages tube mandibular joints) Nasal cavity Epiglottis Menisci of knee C. FIBROCARTILAGE cartilage Corniculate joints Thyroid Cuneiform Rims of some Contains 2 cells: Cricoid sockets ○ Chondrocyte Arytenoids Lining of tendon Similar to hyaline Tracheal rings grooves Sparse Bronchi plates Insertion of some Arranged singly or in rows tendons and Cell that is lodged in the lacuna ligaments ○ Fibroblast Triangular Cells without the lacuna fibrocartilage Spindle-shaped complex of Cell Families wrist joints ○ Possible, but rare Function Components of Fibrocartilage Resists Provides Resist Mixture of connective tissues: compression flexible support deformation under ○ Dense Connective Tissue Provides for soft tissues stress Type 1 Collagen cushioning, Acts as a shock Dominant Collagen smooth & absorber ○ Hyaline Connective Tissue low-friction Type 2 Collagen surface for No perichondrium joints ○ Only elastic and hyaline cartilage have the Provides perichondrium structural Extracellular Matrix support in ○ Scarce due the density of the fibers. respiratory Herringbone appearance system ○ It's like the spine of a fish. Foundation for development of fetal skeleton, endochondral bone formation & bone growth Regressive change Calcification Fatty Calcification Amianthoid or Degeneration Asbestos formation Presence of Perichondrium Figure 3. Fibrocartilage Yes Yes No Cells Chondroblasts Chondroblasts Chondrocytes Chondrocytes Chondrocytes fibroblasts 4  HYALINE ELASTIC FIBRO- V. BONES CARTILAGE CARTILAGE CARTILAGE Matrix A. FUNCTIONS Type 2 collagen Type 2 collagen Type 1 & 2 Protects vital organs fibrils fibrils collagen fibers For internal support Proteoglycans Elastic fibrils Proteoglycans Lodging space of the bone marrow Proteoglycans Storage of calcium and phosphate Attachment of muscles and tendons Table 1. Summary of Cartilage Features VI. CLASSIFICATION OF BONES IV. TYPES OF CARTILAGE GROWTH A. SHAPE OR FORM A. APPOSITIONAL GROWTH Short When new cartilage is added to the surface by chondroblasts Carpal bones ○ From the inner layer of the perichondrium. Tarsal bones ○ The growth is on the chondrocytes of the perichondrium. Irregular The border of cartilage is called the perichondrium Vertebra ○ The outer layer consists of your fibroblast. ○ The inner layer consists of your chondrogenic Flat cells. Skull B. INTERSTITIAL GROWTH Sternum Growth is within the cartilage Sesamoid ○ One chondrocyte will divide to produce a sister chondrocyte. Patella ○ New cartilage is formed within the cartilage by chondrocytes that divide and produce Long additional matrix. Fingers Thumb Arms Legs Figure 4. Appositional and Interstitial Growth of Cartilage C. REGENERATIVE ABILITY Cartilage is very poor in regeneration ○ They are unable to even heal minor injuries. This is due to the cartilage: Figure 5. Types of Bones ○ Being avascular ○ Having immobile chondrocytes ○ Having a limited proliferation of chondrocytes There are only repairs if the perichondrium is involved as there is an inner chondrogenic layer in the perichondrium. 5  B. MICROSCOPIC APPEARANCE Compact External Solid except in microscopic canals Spongy Internal Branching and anastomosing ○ Bars Figure 7.2. Lamellar Bone ○ Plates ○ Tubes of bone trabeculae VI. PARTS OF THE BONE ○ Both end of long bone A. COMPONENTS 5 Cell Types Osteoprogenitor Cells ○ Give rise to osteoblast. Osteoblast Figure 6. Compact and Spongy parts of the Bone ○ Secretes bone matrix, calcifies bone matrix, retains the ability to divide. C. MATURITY ○ Lines the bone matrix because they are depositing the bone matrix. Woven ○ Cuboidal or polygonal in shape. ○ When active, the nucleus is far away from the Found in fetal skeleton matrix. Immature bone ○ When active, it is markedly basophilic. Unorganized ○ Sometimes, they have a large golgi More cells, random arrangement area/apparatus. More ground substance (GS) Large perinuclear halo can be seen. More basophilic matrix staining Located in: ○ Once the osteoblast continues to secrete the ○ Alveolar sockets bone matrix, they will be enveloped by the ○ Areas where tendons insert into bones whole matrix and they will become osteocytes. When the osteoblast is surrounded by the whole matrix, they become osteocytes. Bone Lining Cells ○ Derived from osteoblast Maintenance and nutritional support of osteocytes. Regulate movement of calcium and phosphate. ○ Periosteal cells lines the periosteum. Figure 7.1. Woven Bone ○ Endosteal cells lines the endosteum. Lamellar Osteocyte ○ Involved in mechanotransduction Mature Respond to mechanical forces Composed of osteons applied to the bone. Organized into concentric lamellae ○ Remodeling of pericanalicular and perilacunar Less cells bone matrix Long axis of cells same as lamellae ○ Secretion of matrix metalloproteinases which Less ground substance (GS) degrades the bone when the bone is not Matrix acidophilic stimulated When constantly lying down, the osteocyte will secrete it and degrade the bone. Will strengthen the bone more if you move more. 6  Osteoclast B. MICROSCOPIC STRUCTURES ○ Macrophage of the bone ○ Bone resorption 3 Lamellae in the Microscopic Appearance of a Compact Bone ○ Multinucleated ○ Cytoplasm is acidophilic and sometimes Osteon foamy ○ Also called the Haversian System. ○ They will be seen directly on the bone tissue ○ The unit of structure of the compact bone. where the bone resorption is taking place. ○ There are concentric lamellae around the They will form a structure called Howship vascular channel. lacunae. These are blood vessels in the ○ It is responsive to the histochemical reaction center surrounded by bone lamellae. of your acid phosphatase (ACP) and also to Interstitial Lamellae tartrate-resistant acid phosphatase (TRAP) ○ Seen between Osteons. which is a clinical marker of osteoclastic ○ Remnants of previous osteons when the bone activity. undergoes remodeling frequently. Circumferential Lamellae ○ This will follow the entire inner and outer circumference of the shaft of the long bone. Figure 8.1. Cell Types of the Bone Figure 9.1. Compact Bone Structures of the Compact Bone Figure 8.2. Osteoblasts and Osteocytes Haversian Canal ○ Channel found at the center of the osteon. Osteon is also known as the Haversian System. Haversian Lamellae ○ Bone lamellae arranged concentrically around the Haversian canal. Cementing Line ○ Refractile structure forming boundary of the osteon. Osteocytes ○ Lodged in a lacuna. Canaliculi ○ Minute canals radiating from the lacuna. Figure 8.3. Osteoblasts and Osteoclasts ○ Contains processes of the osteocytes. Matrix Inorganic ○ Made up of calcium and phosphate in the form of Hydroxyapatite crystals. Organic ○ Mainly Type 1 Collagen. ○ Contains noncollagenous substances such as the proteoglycans in the ground substance (GS-Proteoglycans). Figure 9.2. Microscopic Appearance of the Compact Bone 7 Volkmann Canal and Haversian Canal Volkmann Canal ○ Transverse/Oblique channels. ○ Connects haversian canals/osteon to another. ○ Free surface of marrow. ○ Not surrounded by lamellae. Haversian Canal ○ Longitudinal Channels. ○ Center of an Osteon. ○ Contains 1-2 small blood vessels. Figure 10.1. Endochondral Ossification Intramembranous Also has an ossification center. ○ Composed of mesenchymal cells. Usually seen in the development of flat bones. Figure 9.3. Volkmann Canal and Haversian Canal C. OSSIFICATION How the bone will develop. Endochondral Usually begins with a cartilage model from the embryo. Seen in the development of your axial skeleton. Figure 10.2. Intramembranous Ossification ○ Axial skeleton - center part of the body. By the 12th week of gestation (3 months), the cartilage model will be formed. D. GROWTH OF BONES ○ Periosteal/perichondrial collar will form around the diaphysis. Epiphyseal Plate ○ Signals the beginning of ossification, starting from the diaphysis portion. Responsible for the growth in length. ○ Forms the primary ossification center at the proximal end of the bone which will be Appositional Growth invaded by blood vessels. ○ Afterwhich, a secondary ossification center Responsible for the growth in width. will form at the distal end of the bone. Occurs at the surface, going inside. ○ Proceeds until the entire portion of the bone will be ossified except the epiphysis. Interstitial Growth This becomes the epiphyseal plate. Remains until puberty and maximum Not present in bone. height. ○ Due to the rigid matrix in bone. Responsible for one’s lengthening ○ Cartilage matrix can accommodate and growth. expansion unlike the bone. E. ZONES OF THE EPIPHYSEAL GROWTH PLATE Occurs from the epiphysis to the metaphysis. ○ As the cartilage moves towards the metaphysis, it will be calcified thus becoming bone. ○ Results in the lengthening of bones. 8  B. VITAMINS Deficiency of some vitamins may modify genetically determined effects. 1. VITAMIN D In deficiency states of this vitamin, there is faulty absorption of calcium from food leading to defective calcification of cartilage and osteoid tissue. Cartilage cells hypertrophy and persist, so that the epiphyseal disks become thick and irregular. ○ More osteoid tissue is formed. ○ Hence, the growing end of bone appears knobby. Figure 11. Zones in the Epiphyseal Growth Plate ○ Such knobs at the ends of the ribs of a child suffering from vitamin D deficiency are often Zone 1: Proliferating Young Cartilage referred to as "rachitic rosary". In children, vitamin D deficiency leads to rickets. Cartilage cells are arranged in rows, parallel to the long In adults, there is impaired turn over of bone, leading to axis of the specimen. osteomalacia (adult rickets). Zone 2: Maturation Zone 2. VITAMIN C Cells and lacunae enlarge into cuboidal shape. In the deficiency state of this vitamin, there is defective Moves forward towards the metaphysis. production of fibers and ground substance, and of ○ Becomes the calcifying cartilage. phosphatase in bone, and there is interference in osteoblastic activity. Zone 3: Calcifying Cartilage/Zone of Calcification 3. VITAMIN A The matrix darkens. Lacunae are opened up. Deficiency of vitamin A interferes mainly with remodeling of growing bones. Zone 4: Trabeculae of the metaphysis The bones become thick due to lack of compensatory resorption. Location of metaphysis Rate of ossification in general is reduced. ○ Where the bone is usually developed. A lot of osteoblasts will deposit its matrix so that the C. HORMONES bone can be formed. Clue that you are in the metaphysis: Hypersecretion or hyposecretion of some hormones ○ You will see osteoblasts. may also modify genetically determined effects. Forms a single layer that lines the bone matrix. 1. SOMATOTROPHIC (STH) OR GROWTH HORMONE Zone 5: Resorption OF THE PITUITARY GLAND Not a defined area. Its effect on bone is a part of its influence on the body ○ The metaphysis can have both osteoblasts in general. and osteoclasts. It delays the closure of the epiphysis by stimulating The areas of resorption are those where osteoclasts the proliferation of cartilage cells at the epiphyseal are present. disk. This is a direct effect. Hypersecretion in growing individuals lead to gigantism. APPENDIX II: SOME FACTORS AFFECTING OSSIFICATION Hypersecretion after closure of the epiphysis leads to acromegaly A. GENES ○ Bones become thick due to exaggerated periosteal bone formation. Gene is the basic factor in osteogenesis and in Hyposecretion to dwarfism. morphogenesis in general. Gene determines the: ○ Site of osteogenesis and the presence or absence of a cartilage model, ○ The normal timing and the order in which ossification centers appear, and ○ The time of cessation of growth. 9  2. THYROID HORMONE Its effect on bone is due to its controlling role on metabolic rate. ○ It facilitates maturation of bone. Hyposecretion decreases the rate of ossification and delays the appearance of ossification centers. Hypersecretion may alter normal turn over of developed bone, involving primarily the organic matrix. 3. PARATHYROID HORMONE It regulates mobilization of calcium from bones, tending to increase the breakdown of bone involving both organic and inorganic matrix, leading to osteitis fibrosa. In hyposecretion, there is decreased breakdown of bone, as well as low blood calcium level, leading to tetany. 4. SEX HORMONES They advance the appearance of ossification centers and increase the rate of maturation of bones. A latter effect would be the reduction in the rate of epiphyseal cartilage cells and so hasten the closure of the epiphysis. D. NUTRITION The effects are obvious. 10