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Chapter 5: The Skeletal System

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1 Chapter 5: The Skeletal System
Anatomy & Physiology Kasprowicz

2 Parts of the Skeletal System
Bones (make up the skeleton) Joints (articulations) Cartilages Ligaments (dense, regular connective tissue connecting bone to bone)

3 Divisions of the Skeleton
Axial Skeleton bones that form the longitudinal axis skull, vertebrae, rib cage Appendicular Skeleton bones of the limbs (appendages) & girdles arms, legs, pelvis


5 Functions of the Skeleton
Support for the body our internal framework Protection of soft organs ex. skull  brain rib cage  lungs & heart vertebrae  spinal cord

6 Functions of the Skeleton
Movement skeletal muscles use the bones as levers to move the body & its parts Storage Bone tissue stores minerals, such as calcium and phosphorus Fat is stored in yellow marrow

7 Functions of the Skeleton
5) Blood Cell Formation Hematopoiesis occurs in red marrow The adult skeleton is composed of 206 bones!

8 Classification of Bones
Bones can be classified based on their SHAPE or HISTOLOGICAL ORGANIZATION (STRUCTURE)

9 Classification of Bones: Shape
Long bones Typically long & slender Shaft with heads at both ends Mostly compact bone Examples: arms, legs, fingers, toes

10 Classification of Bones: Shape
2) Short bones Typically box- or cube-shaped Mostly spongy bone Examples: wrists & ankles

11 Classification of Bones: Shape
3) Flat bones thin, flattened usually curved thin layers of compact bone surrounding spongy bone ribs

12 Classification of Bones: Shape
4) Irregular bones Do not fit in other categories Examples: Vertebrae Hip bones



15 Types of Bone (Osseous) Tissue
All bones contain both types of bone tissue. Their relationship & proportions vary depending on bone shape. Compact Bone dense, smooth & homogenous Spongy Bone open network of struts & plates

16 Gross Anatomy of a Long Bone
diaphysis a) tubular shaft b) compact bone epiphysis a) ends of the bone b) mostly spongy bone

17 Gross Anatomy of a Long Bone


19 Structures of a Long Bone
periosteum a) outside covering of the diaphysis b) fibrous connective tissue membrane Sharpey’s fibers connect periosteum to the underlying bone

20 Structures of a Long Bone
3) Arteries supply the osteocytes w/ nutrients & oxygen Articular Cartilage a) covers the epiphyses b) made of hyaline cartilage c) decreases friction at the joints

21 Structures of a Long Bone
Medullary Cavity a) Cavity of the shaft b) bone marrow consists of loose connective tissue - yellow marrow (fat storage) in adults - Contains red marrow (for blood cell formation) in infants c) endosteum layer of cells lining the cavity


23 Bone Histology Osseous tissue (bone) is a type of connective tissue
Four Characteristics of Bone 1) bone matrix is very dense & contains calcium salts 2) contains bone cells (osteocytes) in pockets called lacunae

24 Let’s take a look at each characteristic…
Bone Histology Four Characteristics of Bone cont… 3) Canaliculi allow for gas exchange and diffusion of nutrients and waste products 4) except at joints, bones are covered by the a periosteum Let’s take a look at each characteristic…

25 Bone Histology: Matrix
2/3 of bone matrix is calcium phosphate, Ca3(PO4)2  w/ calcium hydroxide, forms crystals of hydroxyapatite, which incorporate other calcium salts & minerals into the matrix 1/3 of bone matrix is collagen fibers Only 2% of bone mass comes from cells

26 Bone Histology: Cells There are 4 types of bone cells
osteocytes are the most common Osteocytes sit in a pocket-like structure called a lacuna (lacunae, plural) Lacunae are arranged in concentric rings, or layers of matrix, called lamellae (lamella, singular)

27 Bone Histology: Canaliculi
Canaliculi (tiny canals) Radiate from the central canal (blood vessels) to lacunae Form a transport system between osteocytes and between the central canal & osteocytes

28 Bone Histology

29 Bone Histology: Periosteum
Covers all bones, except parts enclosed in joint capsules 2) It is made up of an: outer, fibrous layer inner, cellular

30 Bone Histology: Periosteum
Functions of periosteum a) Isolate bone from surrounding tissues b) Provide a route for circulatory and nervous supply c) Participate in bone growth and repair

31 Periosteum

32 Compact Bone Osteon (Haversian System)
osteon – the basic unit of compact bone Organization of an Osteon a) Osteocytes are arranged in concentric lamellae around a central (Haversian) canal containing blood vessels

33 Compact Bone Organization of an Osteon cont…
b) Central (Haversian) canal opening in the center of an osteon containing blood vessels and nerves c) Perforating (Volkman’s) canal perpendicular to the central canal also containing blood vessels and nerves

34 Compact Bone

35 Compact Bone osteon

36 Spongy Bone 1) Does not have osteons
A “honeycomb” matrix forms an open network of trabeculae Trabeculae have no blood vessels


38 Spongy Bone

39 Spongy Bone: Yellow Marrow
In some bones, spongy bone holds yellow bone marrow which is used to store fat

40 Spongy Bone: Red Marrow
The space between trabeculae is filled with red bone marrow. Red marrow forms red blood cells and supplies nutrients to osteocytes.

41 Bone Markings Surface features of bones that show…
1) Sites of attachment for muscles, tendons, and ligaments 2) Passages for nerves and blood vessels Categories of bone markings projections or processes – grow out from the bone surface depressions or cavities – indentations

42 Bone Markings

43 Bone Markings

44 Bone Formation, Growth & Remodeling
The structure of bone is specialized for flexibility and tensile strength.

45 Bone Formation In embryos, the skeleton is primarily hyaline cartilage
During fetal development, much of this cartilage is replaced by bone By the end of the toddler years, cartilage remains only in isolated areas: - bridge of the nose - parts of ribs - articular cartilage (in the joints) - epiphyseal plates

46 Bone Formation The process of “bone formation” is called ossification.
1) Unless it is a flat bone, a hyaline cartilage model is covered with bone matrix by osteoblasts. osteoblasts - immature, bone-forming cells Over time, the “cartilage bone” is enclosed in a layer of real bone (kind of like an arm in a cast).

47 Bone Formation The enclosed layer of hyaline cartilage is digested away by osteoclasts. osteoclasts - bone destroying cells; break down bone matrix for remodeling and release of calcium The breakdown of the cartilage “model” leaves a medullary cavity in the bone.

48 Bone Formation

49 Bones must grow in both length and width.

50 Bone Growth allow for growth in the length of long bone during
Epiphyseal plates allow for growth in the length of long bone during childhood & adolescence

51 Bone Growth


53 Bone Growth Appositional growth increases the width of the bone.
Osteoblasts in the periosteum add bone tissue to the surface At the same time… Osteoclasts in the endosteum remove bone matrix from the inner surface.

54 In order for bones to retain normal proportions and strength as the body changes in size and strength, bones must constantly remodel.

55 Bone Remodeling 1) Bones become thicker and form larger projections to increase strength for bulky muscles. When you lift its not just the muscles that have to respond!

56 Bone Remodeling 2) When bones are not subject to normal stress/exercise, they atrophy (shrink, shrivel). Bone degenerates quickly! Up to 1/3 of bone mass can be lost in a few weeks of inactivity!

57 Bone Remodeling osteocytes) and bone recycling (by osteoclasts) must
Bone building (by osteocytes) and bone recycling (by osteoclasts) must balance



60 Hormonal Control of Bone Growth & Remodeling

61 Hormonal Control Calcitriol - is made in the kidneys; synthesis
requires vitamin D3 (cholecalciferol) - helps absorb calcium and phosphorus from digestive tract

62 Hormonal Control 2) Parathyroid Hormone (PTH)
- operates on a negative feedback loop - activates bone resorption (osteoclast activity) & increases calcium levels in the blood


64 Hormonal Control 3) Other Hormones - growth hormone and thyroxine
stimulate bone growth - estrogens and androgens stimulate osteoblasts - calcitonin (w/ PTH and calcitriol) regulate calcium and phosphate levels

65 The Effect of Nutrition on Bones

66 Nutrition & Bone 1) Minerals A dietary source of calcium and phosphate
salts, plus small amounts of Mg, F, Fe and Mn

67 Nutrition & Bone 2) Vitamins - vitamin C needed (collagen synthesis
& osteoblast differentiation) - vitamin A stimulates osteoblast activity - Vitamin K and B12 ( protein synthesis in bone)

68 Nutrition & Bone Questions: 1. A pregnant woman is not getting enough calcium in her diet. How will her body respond? (hormone released, response) 2. Sally has a history of osteoporosis in her family. She includes many calcium-rich foods in her diet and takes a vitamin D supplement. How will her body respond? (hormone released, response)

69 Bone Fractures

70 Bone Fractures Types of bone fractures
Closed (simple) fracture – break that does not penetrate the skin Open (compound) fracture – broken bone penetrates through the skin Bone fractures are treated by reduction (realignment of the bone) and immobilization

71 Bone Fractures

72 Bone Fractures

73 Bone Fractures

74 Bone Fracture Repair Step 1: Bleeding produces a clot
(fracture hematoma) establishes a fibrous network bone cells in the area die

75 Bone Fracture Repair Step 2: Callus Formation
Cells of the endosteum and periosteum divide and migrate into fracture zone fibrocartilage“Calluses” stabilize the break

76 Bone Fracture Repair Step 3: Bone Formation
Osteoblasts and osteoclasts migrate to the area and multiply. Osteoclasts deteriorate the fibrocartilage callus as osteoblasts replace it w/new bone tissue. This is now called a bony callus.

77 Bone Fracture Repair Step 4: Bone Remodeling Osteoblasts and
osteocytes remodel the fracture for up to a year, reducing the bone calluses

78 Bone Fracture Repair

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