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. Bones are the ‘organs’ of the skeletal system. All bones have:
outer “dense” layer of compact bone
Inner, honeycombed region of spongy (cancellous) bone
Bones are organs because they contain many types of tissues:
Connective tissues – osseous (bone), hyaline cartilage, dense irregular connective tissue of periosteum
Epithelial tissue – simple squamous epithelium that lines blood vessels
Muscle tissue – smooth muscle within blood vessels
Nervous
Trabeculae – thin plates of bone
trabeculae
Spaces between trabeculae filled with red or yellow marrow

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

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

8. DIAPHYSIS EPIPHYSES Parts of a long bone
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. Long bone diaphysis – shaft epiphyses – bone ends
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)
Diaphysis – compact bone surrounds marrow cavity which contains yellow marrow (fat).
Epiphyses – thin layer of compact bone surrounds mass of spongy bone that contains red marrow.
Epiphyseal line is a remnant of the epiphyseal plate – a region of active bone growth during childhood which ossifies during puberty.
In a youngster, this is seen as the epiphyseal plate;
Once the bone is mature, it is simply an epiphyseal ‘line’

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

11. endosteum – lines marrow cavity
(Pls. remember this concept: perimysium, perineurium)
membranes
periosteum – covers surface of bone (attachment site for tendons & ligaments)
endosteum – lines marrow cavity
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

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

15. Frontal sinuses

16. GLOSSARY OF TERMS: SKELETAL SYSTEM Term: 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
linea a narrow line-like ridge; eg. linea aspera of femur
epicondyle a projection situated above a condyle
meatus a tube-like passageway within a bone
eg. medial epicondyle of humerus
eg. external auditory meatus
facet a small smooth surface eg. rib facet of a thoracic vertebra
process a prominent projection of a bone
eg. mastoid process of temporal bone
foramen an opening for the passage of b.v. &/or nerves
ramus a branch-like process; eg. ramus of mandible
eg. foramen magnum
sinus a cavity within a bone; eg. frontal sinus
fossa a relatively deep pit or depression; eg. olecranon fossa
Spine a sharp projection; eg. spine of scapula
fovea a tiny pit or depression; eg. fovea capitis
styloid a pen-like projection; eg. styloid process of ulna
head an enlargement at the end of a bone;
suture interlocking junction between cranial bones;
eg. femoral head
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. tibial tuberosity

17. condyle a rounded process that articulates. with. another bone eg
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. Olecranon fossa
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. linea aspera 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. TROCHANTER a relatively large process;
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. tibial tuberosity

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: ya gotta 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
Bottom line: ya gotta have the GRIT and the GLUE !

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. 2. Microscopic Anatomy (compact bone)
Osteon

26. 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’
Osteocytes maintain bone matrix. If osteocytes die, bone matrix surrounding them is reabsorbed.
Represents a single osteon
(Singular:
Lamella)
ref.:
‘ laminate ‘

28. canaliculi – tiny channels; connect osteocytes to central canal
osteocytes – mature bone cells; embedded in lacunae (cavities within matrix)
canaliculi – tiny channels; connect osteocytes to central canal
Canaliculi (kan”-ah-lik’-u-li)

29. Circumferential lamellae surround diaphysis
Interstitial lamellae
Concentric lamellae
Concentric lamellae – located within the osteon; circle a central canal
Interstitial lamellae – located between osteons
Circumferential lamellae – circle entire diaphysis deep to periosteum & endosteum.

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, nondividing osteoblasts 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, Osteoblasts MAKE bone, Osteoclasts BREAK DOWN bone, and Osteocytes MAINTAIN bone.

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

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

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

43. (it is the primary HEMATOPOIETIC tissue - producing BLOOD CELLS)
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

51. CARTILAGE

52. CARTILAGE Avascular connective tissue
Characteristics
Avascular connective tissue
Fibers of cartilage are embedded in a firm gel
Has the flexibility of firm plastic
No canal system or blood vessels
Chondrocytes receive oxygen and nutrients by diffusion
Perichondrium: fibrous covering of the cartilage
Cartilage types differ because of the amount of matrix present and the amounts of elastic and collagenous fibers

53. CARTILAGE (cont.) HYALINE CARTILAGE Types of cartilage (Figure 7-21)
Most common type
Covers the articular surfaces of bones
Forms the costal cartilages, cartilage rings in the trachea, bronchi of the lungs, and the tip of the nose
Forms from special cells in chondrification centers, which secrete matrix material
Chondrocytes are isolated into lacunae

54. CARTILAGE (cont.) Fibrocartilage Types of cartilage
Elastic cartilage
Forms external ear, epiglottis, and eustachian tubes
Large number of elastic fibers confers elasticity and resiliency
Fibrocartilage
Occurs in pubic symphysis and intervertebral disks, and the meniscii of the knee joints
Small quantities of matrix and abundant fibrous elements
Strong and rigid

55. Functions CARTILAGE (cont.)
Tough, rubberlike nature permits cartilage to sustain great weight or serve as a shock absorber
Strong yet pliable support structure
Permits growth in length of long bones

56. Next few slides are of INTEREST - not to be tested upon, sit back and relax , watch, listen Bone development, fractures and repair:

57. DEVELOPMENT OF BONES
Osteogenesis: development of bone from small cartilage model to adult bone (Figure 7-11)
Intramembranous ossification, (some)
Endochondral ossification (most)
Intramembranous ossification:
Occurs within a connective tissue membrane
Flat bones begin when groups of cells differentiate into osteoblasts
Osteoblasts are clustered together in ossification center
Osteoblasts secrete matrix material and collagenous fibrils

58. 1. Formation of the skeleton
. Bone Development (osteogenesis)
1. Formation of the skeleton
Initial embryonic skeleton made of
fibrous membranes (cranial bones & clavicles) &
hyaline cartilage (all other bones)
Cranial bones – frontal, parietal, temporal & occipital

59. At birth,
osseous
development, (shows
Large
Areas still are cartilagenous)

61. DEVELOPMENT OF BONES (cont.)
Intramembranous ossification
Large amounts of ground substance accumulate around each osteoblast
Collagenous fibers become embedded in the ground substance and constitute the bone matrix
Bone matrix calcifies when calcium salts are deposited
Trabeculae appear and join in a network to form spongy bone
Appositional growth occurs by adding osseous tissue
(like a tree grows in diameter)

62. DEVELOPMENT OF BONES (cont.)
Endochondral ossification
Most bones begin as a cartilage model with bone formation spreading essentially from the center to the ends
Periosteum develops and enlarges to produce a collar of bone
Primary ossification center forms
Blood vessel enters the cartilage model at the midpoint of the diaphysis
Bone grows in length as endochondral ossification progresses from the diaphysis toward each epiphysis
Secondary ossification centers appear in the epiphysis, and bone growth proceeds toward the diaphysis
Epiphyseal plate remains between the diaphysis and each epiphysis until bone growth in length is complete

66. DEVELOPMENT OF BONES (cont.)
Epiphyseal plate is composed of four layers
“Resting” cartilage cells: point of attachment joining the epiphysis to the shaft
Zone of proliferation: cartilage cells undergoing active mitosis, which causes the layer to thicken and the plate to increase in length
Zone of hypertrophy: older, enlarged cells undergoing degenerative changes associated with calcium deposition
Zone of calcification: dead or dying cartilage cells undergoing rapid calcification

69. DEVELOPMENT OF BONES (cont.)
Epiphyseal plate can be a site for bone fractures in young people
Long bones grow in both length and diameter

72. BONE REMODELING Primary osteons develop within early woven bone
Conelike or tubelike space is hollowed out by osteoclasts
Osteoblasts in the endosteum that lines the tube begin forming layers (lamellae) that trap osteocytes between layers
A central canal is left for the blood and lymphatic vessels and nerves
Primary osteons can be replaced later by secondary osteons in a similar manner

73. Mechanical stress, such as physical activity, strengthens bone
Bones grow in length and diameter by the combined action of osteoclasts and osteoblasts
Osteoclasts enlarge the diameter of the medullary cavity
Osteoblasts from the periosteum build new bone around the outside of the bone
Mechanical stress, such as physical activity, strengthens bone

75. Fractures and Repairs

77. REPAIR OF BONE FRACTURES
Fracture: break in the continuity of a bone
Fracture healing
Fracture tears and destroys blood vessels that carry nutrients to osteocytes
Vascular damage initiates repair sequence
Callus: special repair tissue that binds the broken ends of the fracture together
Fracture hematoma: blood clot occurring immediately after the fracture, which is then resorbed and replaced by callus

79. CYCLE OF LIFE: SKELETAL ISSUES
Skeleton fully ossified by mid-20s
Soft tissue may continue to grow; ossifies more slowly
Adults: changes occur from specific conditions
Increased density and strength from exercise
Decreased density and strength from pregnancy, nutritional deficiencies, and illness
Advanced adulthood: apparent degeneration
Hard bone matrix replaced by softer connective tissue
Exercise can counteract degeneration