Chapter 6: Skeletal Tissues: Bones, Ligaments, Cartilage

1. Chapter 6: Skeletal Tissues: Bones, Ligaments, Cartilage

2. FUNCTIONS OF skeletal tissues SUPPORT: Bones form the FRAMEWORK of the body and contribute to the shape, alignment, and positioning of body parts; LIGAMENTS help hold bones together, CARTILAGE provides cushion and ‘shock-absorption ‘between bones PROTECTION: bony “boxes” protect the delicate structures they enclose (ref; cranium, rib cage, pelvis) MOVEMENT: bones and their joints constitute levers that move as muscles contract, and as sites of attachment for muscles MINERAL STORAGE: bones are the major reservoir for CALCIUM, PHOSPHORUS, and other minerals HEMATOPOIESIS: blood cell formation is carried out by Myeloid tissue, which is located in the bone marrow

4. trabeculae Spaces between trabeculae filled with red or yellow marrow Bones are the ‘organs’ of the skeletal system. All bones have: • outer “dense” layer of compact bone • Inner, honeycombed region of spongy (cancellous) bone

5. TYPES OF BONES Five major types of structural bones Long bones Short bones Flat bones Irregular bones Sesamoid bones develops within a tendon ( ex.: patella) Bones serve various needs, and their size, shape, and appearance vary to meet those needs Bones vary in the proportion of compact and cancellous (spongy) bone; COMPACT BONE is dense and solid in appearance, whereas CANCELLOUS BONE is characterized by open space partially filled with needle-like structures, called spicules, or trabeculae

6. Most of the bones of the skull are ‘flat bones’ short flat Long Irregular sesamoid

7. The 6 ‘long’ bones: Upper extremity Lower extremity Humerus Radius Ulna Femur Tibia Fibula

8. Parts of a long bone DIAPHYSIS Main SHAFT of a long bone Hollow, cylindrical shape and thick compact bone on the perimeter, with marrow in the middle, (MEDULLARY cavity) Function is to provide strong support without cumbersome weight. (like an architechural column) EPIPHYSES Both ends of a long bone; made of CANCELLOUS BONE filled with marrow Bulbous shape Function is to provide attachments for muscles and give stability to joints

9. Articular cartilage covers joint surface Epiphyseal line located between diaphysis and each epiphysis (in young, growing bones, this can be seen as a METAPHYSIS - an ‘area’ of cartilage between the epiphysis and the diaphysis) In a youngster, this is seen as the epiphyseal plate; Once the bone is mature, it is simply an epiphyseal ‘line’ • Long bone • diaphysis – shaft • epiphyses – bone ends

10. Epiphysis Diaphysis Articular cartilage Periosteum Medullary cavity Endosteum Compact bone Cancellous (spongy)bone

11. (Pls. remember this concept: perimysium, perineurium) • Both membranes contain: • osteogenic cells – stem cells; which give rise to osteoblasts & osteoclasts • OSTEOBLASTS– cells that secrete bone matrix • OSTEOCLASTS – cells that break down bone matrix • membranes • periosteum – covers surface of bone (attachment site for tendons & ligaments) • endosteum – lines marrow cavity

12. More on the components of bones Articular cartilage Layer of hyaline cartilage that covers the articular surface of epiphyses Function is to cushion jolts and blows Periosteum Dense, white fibrous membrane that covers bone Attaches tendons firmly to bones Contains cells that form and destroy bone Contains blood vessels important in growth and repair Contains blood vessels that send branches into bone Essential for bone cell survival and bone formation

13. Components of bone Medullary (or marrow) cavity Tubelike, hollow space in the diaphysis Filled with yellow marrow in adults . (Yellow marrow is fatty, can be called upon to become active hematopoietic tissue if needed) Endosteum: thin, fibrous membrane that lines the medullary cavity

14. periosteum covers compact bone • endosteum encloses trabeculae Spongy bone of flat bones is called diploe • Short, irregular & flat bones • do NOT have shaft, epiphyses, or medullary cavity • thin layer of compact bone surrounds spongy bone center (contains red marrow)

15. Frontal sinuses

16. GLOSSARY OF TERMS: SKELETAL SYSTEMTerm: Definition (with one example):analagous to geographic terms such as peak mount hill cape bluff isle cove condyle a rounded process that articulates with another bone eg. occipital condyle crest a narrow, ridge-like projection; eg. iliac crest epicondyle a projection situated above a condyle eg. medial epicondyle of humerus facet a small smooth surface eg. rib facet of a thoracic vertebra foramen an opening for the passage of b.v. &/or nerves eg. foramen magnum fossa a relatively deep pit or depression; eg. olecranonfossa fovea a tiny pit or depression; eg. fovea capitis head an enlargement at the end of a bone; eg. femoral head linea a narrow line-like ridge; eg. lineaaspera of femur meatus a tube-like passageway within a bone eg. external auditory meatus process a prominent projection of a bone eg. mastoid process of temporal bone ramus a branch-like process; eg. ramus of mandible sinus a cavity within a bone; eg. frontal sinus Spine a sharp projection; eg. spine of scapula styloid a pen-like projection; eg. styloid process of ulna suture interlocking junction between cranial bones; eg. coronal suture trochanter a relatively large process; eg. Greater trochanter of femur tubercle a small knob-like process; eg. tubercle of rib tuberosity a knob-like process larger than a tubercle; eg. tibialtuberosity

17. condyle a rounded process that articulates with another bone eg. occipital condyle crest a narrow, ridge-like projection; eg. iliac crest epicondyle a projection situated above a condyle eg. medial epicondyle of humerus facet a small smooth surface eg. rib facet of a thoracic vertebra

18. foramen an opening for the passage of b.v. &/or nerves eg. foramen magnum fossa a relatively deep pit or depression; eg. Olecranonfossa fovea a tiny pit or depression; eg. fovea capitis head an enlargement at the end of a bone; eg. femoral head

19. linea a narrow line-like ridge; eg. lineaaspera of femur meatus a tube-like passageway within a bone eg. external auditory meatus process a prominent projection of a bone eg. mastoid process of temporal bone ramus a branch-like process; eg. ramus of mandible, Pubic ramus sinus a cavity within a bone; eg. frontal sinus spine a sharp projection; eg. spine of scapula

20. styloid a pen-like projection; eg. styloid process of ulna suture interlocking junction between cranial bones; eg. coronal suture TROCHANTER a relatively large process; eg. Greater trochanter of femur TUBERCLE a small knob-like process; eg. tubercle of rib TUBEROSITY a knob-like process larger than a tubercle; eg. tibialtuberosity

21. Important points re: the makeup of BONE TISSUE Bone is Most distinctive form of connective tissue Extracellular components are hard and calcified Rigidity of bone gives it supportive and protective functions Tensile strength nearly equal to that of cast iron at less than one third the weight: It takes: GRIT and GLUE TO MAKE BONE:, MINERAL and MATRIX >>>>>>> see next slide

22. BONE TISSUE , grit and glue, calcium and collagen !!! Composition of bone matrix INORGANIC SALTS Hydroxyapatite: crystals of CALCIUM AND PHOSPHATE contribute to bone hardness Slender, needlelike crystals are oriented to most effectively resist stress and mechanical deformation Magnesium, sodium, sulfate, and fluoride also found in bone ORGANIC MATRIX Composite of COLLAGENOUS fibers and an amorphous mixture of protein and polysaccharides called ground substance Ground substance is secreted by connective tissue cells Adds to overall strength of bone and gives some degree of resilience to bone

23. Bottom line: yagotta have the GRIT and the GLUE ! Collagen provides flexibility & tensile strength (ability to endure stretching forces) Bones break easily if collagen is inadequate Hydroxyapatites (calcium and phosphate) provide compression strength (ability to endure squeezing forces) Inadequate mineralization = “soft bones” ie osteoporosis

24. MICROSCOPIC STRUCTURE OF Compact bone -- OSTEONS Compact bone contains many cylinder-shaped structural units called osteons, or haversian systems Osteons surround central (osteonal or haversian) canals that run lengthwise through bone and are connected by transverse canals Living bone cells are located in these units, which constitute the structural framework of compact bone Osteons permit delivery of nutrients and removal of waste products

25. Osteon 2. Microscopic Anatomy (compact bone)

26. Represents a single osteon (Singular: Lamella) ref.: ‘ laminate ‘ • osteon (Haversian system) – structural unit of compact bone; runs parallel to long axis of bone; consists of: • concentric lamellae - rings of matrix that surround the central canal - like ‘wrappings’

28. osteocytes – mature bone cells; embedded in lacunae (cavities within matrix) • canaliculi – tiny channels; connect osteocytes to central canal

29. Circumferential lamellae surround diaphysis Interstitial lamellae Concentric lamellae

30. Flat bones also have both compact and cancellous bone tissue

31. MICROSCOPIC STRUCTURE OF BONE (cont.) Structures that make up each osteon Lamellae Concentric Lamellae: cylinder-shaped layers of calcified matrix around the central canal Interstitial Lamellae: layers of bone matrix between the osteons; leftover from previous osteons Circumferential Lamellae: few layers of bone matrix that surround all the osteons; run along the outer circumference of a bone and inner circumference (boundary of medullary cavity) of a bone

32. MICROSCOPIC STRUCTURE OF BONE (cont.) Structures that make up each osteon (cont.) Lacunae: small spaces containing tissue fluid in which bone cells are located between hard layers of the lamella Canaliculi: ultra-small canals radiating in all directions from the lacunae and connecting them to each other and to the central canal Central (osteonal or Haversian) canal: extends lengthwise through the center of each osteon; contains blood vessels and lymphatic vessels

33. MICROSCOPIC STRUCTURE OF BONE (cont.) Cancellous bone No osteons in cancellous bone; it has trabeculae instead Nutrients are delivered and waste products removed by diffusion through tiny canaliculi Bony branches (trabeculae) are arranged along lines of stress to enhance the bone’s strength Blood supply Bone cells are metabolically active and need a blood supply, which comes from the bone marrow in the internal medullary cavity of cancellous bone Compact bone, in addition to bone marrow and blood vessels from the periosteum, penetrates the bone and then, by way of transverse (Volkmann) canals, connects with vessels in the central canals of osteons

35. MICROSCOPIC STRUCTURE OF BONE (cont.) Types of bone cells Osteoblasts Bone-forming cells found in all bone surfaces Small cells synthesize and secrete osteoid, an important part of the ground substance Collagen fibrils line up in osteoid and form a framework for the deposition of calcium and phosphate

37. MICROSCOPIC STRUCTURE OF BONE (cont.) Types of bone cells Osteoclasts Giant multinucleated cells Responsible for the active erosion of bone minerals Contain large numbers of mitochondria and lysosomes Osteocytes: mature, nondividingosteoblasts surrounded by matrix and lying within lacunae ((retirees of the bone, - alive, but relativley inactive, except for ‘maintenance’ - they maintain the matrix surrounding them)

39. So,OsteoblastsMAKE bone,OsteoclastsBREAK DOWN bone, and OsteocytesMAINTAIN bone.

40. question:What is a ‘GIGABYTE’? Slide 40

41. Answer:AGGIE FAST FOOD DIET (GIG A BITE) Slide 41

42. More functions of the skeletal system, bone tissue: Blood formation, calcium storage / regulation

43. BONE MARROW Type of soft, diffuse connective tissue; called myeloid tissue (it is the primary HEMATOPOIETIC tissue - producing BLOOD CELLS) Site for the production of blood cells Found in the medullary cavities of long bones and in the spaces of spongy bone

44. BONE MARROW (cont.) Two types of marrow occur during a person’s lifetime RED MARROW Found in virtually all bones in an infant’s or child’s body Produces red blood cells YELLOW MARROW As an individual ages, red marrow is replaced by yellow marrow Marrow cells become saturated with fat and are no longer active in blood cell production

45. BONE MARROW (cont.) The main bones in an adult that still contain red marrow include the ribs, bodies of the vertebrae, humerus, pelvis, and femur Yellow marrow can change to red marrow during times of decreased blood supply, such as anemia, exposure to radiation, and certain diseases

46. REGULATION OF BLOOD CALCIUM LEVELS Skeletal system is a storehouse for about 98% of body calcium reserves Helps maintain constancy of blood calcium levels Calcium is mobilized and moves in and out of blood during bone remodeling During bone formation, OSTEOBLASTS REMOVE CALCIUM from blood and lower circulating levels During breakdown of bone, OSTEOCLASTS RELEASE CALCIUM into blood and increase circulating levels

47. REGULATION OF BLOOD CALCIUM LEVELS (cont.) Homeostasis of calcium ion concentration is essential for the following: Transmission of nerve impulses Blood clotting Bone formation, remodeling, and repair Maintenance of skeletal and cardiac muscle contraction

48. REGULATION OF BLOOD CALCIUM LEVELS (cont.) Mechanisms of calcium homeostasis Parathyroid hormone Primary regulator of calcium homeostasis Stimulates osteoclasts to initiate breakdown of bone matrix and increase blood calcium levels Increases renal absorption of calcium from urine Stimulates vitamin D synthesis

49. REGULATION OF BLOOD CALCIUM LEVELS (cont.) Mechanisms of calcium homeostasis CALCITONIN Protein hormone produced in the thyroid gland Produced in response to high blood calcium levels Stimulates bone deposition by osteoblasts Inhibits osteoclast activity Far less important in homeostasis of blood calcium levels than is parathyroid hormone