6 Bones and Skeletal Tissues: Part B.

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Presentation transcript:

6 Bones and Skeletal Tissues: Part B

Bone Development Bones grow and repair throughout life from 2 months into development to death. Stages Formation Growth Remodeling

Two Types of Ossification (bone formation) Intramembranous ossification: during development dense irregular CT start flat bone formation (which bones were these?) Endochondral ossification: during development and during childhood hyaline cartilage CT starts formation of long bones and other bones. (which bones were these?) Why do we care which bones are formed which way?!

One brother has ACHONDROPLASTIC DWARFISM. Which bones are growing normally? Which are not? What does the name of the disorder tell you?

Intramembranous ossification of flat bones How to make a flat bone!

Intramembranous ossification of flat bones CT stem cell Collagen fiber Ossification center Osteoid Osteoblast Early “stem” cells make a collagen sheet, or membrane. Inside this membrane, osteoblasts form from other stem cells Figure 6.8, (1 of 4)

Intramembranous ossification Osteoblast Osteoid Osteocyte Newly calcified bone matrix 3. Osteoblasts secrete osteoid (a mix of gel and collagen fibers) 4. Calcium phosphate adds to the collagen, forming spongy bone. 5. Trapped osteoblasts become osteocytes. Figure 6.8, (2 of 4)

Intramembranous ossification CT stem cells condensing to form the periosteum Spongy bone Blood vessel 6. Blood vessels arrive, and more spongy bone forms 7. Nearby connective tissue becomes the periosteum cover. Figure 6.8, (3 of 4)

Intramembranous ossification Fibrous periosteum Osteoblast Plate of compact bone Spongy bone cavities contain red marrow 8. Osteoblasts change the way they lay down collagen, and form compact bone around the spongy bone, and below the periosteum. 9. Red marrow appears as blood cells are produced in the marrow cavities. Figure 6.8, (4 of 4)

Intramembranous ossification summary The end product is a flat bone! A spongy bone sandwich

Endochondral Ossification Development of long bones (and parts of other bones)

Childhood to adolescence Week 9 Month 3 Birth After conception Month 3 Birth Articular cartilage Secondary ossification center Spongy bone Epiphyseal blood vessel Area of deteriorating cartilage matrix Epiphyseal plate cartilage Hyaline cartilage Medullary cavity Spongy bone formation Bone collar Blood vessel of periosteal bud Primary ossification center 1 A hyaline cartilage “model” of a bone forms. Compact bone collar forms around it Central cartilage area has a planned cell death 2 Blood vessels enter, ostepblasts and minerals arrive and spongy bone forms in diaphyses. 3 4 The epiphyses ossify. Hyaline Cartilage remains only in the epiphyseal plates and articular cartilages. The diaphysis elongates and osteoclasts form the marrow cavity. In the epiphyses, cartilage dies and spongy bone forms. 5 Figure 6.9

Week 9 Hyaline cartilage Bone collar Early “bones” area actually hyaline cartilage “models” 2. The first real bone is compact osseous CT “collar” around the model to give it strength. Bone collar Figure 6.9, step 1

Area of deteriorating cartilage matrix 3. Cartilage in the center of the shaft dies and forms a cavity. Figure 6.9, step 2

Primary ossification center Month 3 4. Blood vessels invade the shaft, bringing minerals. Osteoblasts crawl along the outside of blood vessels into the shaft 5. Osteoblasts form spongy bone inside the shaft in the Primary ossification Center. Spongy bone formation Primary ossification center Blood vessel of periosteal bud Figure 6.9, step 3

The same process occurs in the ends of the bones. Birth Epiphyseal blood vessel Secondary ossification center The same process occurs in the ends of the bones. Medullary cavity Most of the spongy bone is destroyed by osteoclasts to make way for bone marrow. 7. Secondary ossifications centers form at the ends of bone. Figure 6.9, step 4

Spongy bone remains in the ends of bone. The shaft becomes filled with Childhood to adolescence Articular cartilage\ Hyaline cartilage CT Spongy bone remains in the ends of bone. Epiohyseal plate Growth plate Hyaline cartilage connective tissue The only hyaline cartilage CT is now at the ends of the bones and in the epiphyseal plate. The shaft becomes filled with bone marrow Figure 6.9, step 5

Childhood to adolescence Week 9 Month 3 Birth Childhood to adolescence Articular cartilage Secondary ossification center Spongy bone Epiphyseal blood vessel Area of deteriorating cartilage matrix Epiphyseal plate cartilage Hyaline cartilage Medullary cavity Spongy bone formation Bone collar Blood vessel of periosteal bud Primary ossification center 1 Cartilage model Bone grows In diaphyses 2 Blood enters bone 3 Bone grows In epiphyses. Cartilage Dies back throughout bone. 4 Bone tissue continues To grow. Cartilage only At ends of bone and in Growth plates. 5 Figure 6.9

Types of bone GROWTH (length and width) Age birth - 21, bone grows in length. Age 0-100 , bone can grow in width and repair Increases the thickness or density of bone

How does a bone grow in length? The cartilage cells in the epiphyseal plate multiply in spurts, die, and are quickly replaced by bone. There are 5 zones in each epiphyseal plate: Resting zone (cartilage connects to epiphysis) Proliferation zone (multiplication of chondrocytes) 3. Hypertrophic zone (growth of chondrocytes) 4. Calcification zone (invasion of mineral salts) 5. Ossification zone (osteoblasts lay down collagen which combines with mineral salts= osteoid)

Growth in the length of long bones occurs at epiphyseal plate Resting zone Proliferation zone Cartilage cells undergo mitosis. 1 Hypertrophic zone Older cartilage cells enlarge. 2 Calcification zone Matrix becomes calcified; cartilage cells die; matrix begins deteriorating. 3 Calcified cartilage spicule Osteoblast depositing bone matrix Ossification zone New bone formation is occurring. Osseous tissue (bone) covering cartilage spicules 4 Figure 6.10

Hyaline cartilage model of an entire developing long bone, pre-birth

Primary and secondary ossification centers form in the hyaline cartilage model bone epiphysis metaphysis diaphysis Cartilage tissue does NOT turn into bone tissue, it dies and is REPLACED by bone tissue

Chondrocytes in the epiphyseal plate mutlipy, and lengthen the bone. New cartilage grows, lengthening bone Cartilage tissue does NOT turn into bone, it dies and is REPLACED by bone tissue.

To prevent the bone from becoming too wobbly, the cartilage dies, and is replaced by bone. Lengthening is accelerated during puberty by estrogen and testosterone. Older cartilage is Replaced by bone, strengthening bone

The processof of bone lengthening continues until hormone levels rise quite high in the late teens.

By age 21 the increased amounts of estrogen and testosterone STOP bone growth and the growth plate dies and is replace by bone. Growth from birth to the end of puberty In utero birth 18ish 21ish

Growth in the length of long bones occurs at epiphyseal plates Resting zone Proliferation zone Cartilage cells undergo mitosis. 1 Hypertrophic zone Older cartilage cells enlarge. 2 Calcification zone Matrix becomes calcified; cartilage cells die; matrix begins deteriorating. 3 Calcified cartilage spicule Osteoblast depositing bone matrix Ossification zone New bone formation is occurring. Osseous tissue (bone) covering cartilage spicules 4 Figure 6.10

Which x ray is from a child, and which from an adult? Why?

Bones can widen for additional strength and repair throughout life But a diet rich in protein; vitamins C, D, and A; calcium; phosphorus; magnesium; and manganese is necessary.

Bone responds to USE! A bone grows or remodels in response to forces or demands placed upon it We know this because: Handedness (right or left handed) results in bone of one upper limb being thicker and stronger than the other Curved bones are thickest where they are most likely to buckle, and so the body grew extra bone. Large, bony projections grow where heavy, active muscles attach

Load here (body weight) BONE SHAPE depends on the forces placed upon it Figure 6.13

Trabecular patterns in femur

Calcium and Phosphate are stored in bone matrix, but…. Calcium is also necessary for Transmission of nerve impulses Muscle contraction Blood coagulation Calcium? Nerve cells Cell division How does calcium get from the bone matrix to where it is needed?

How does calcium move from bone to blood (resorption)? When calcium and phosphate are needed elsewhere in body.. Osteoclasts digest bone using Lysosomal enzymes (to digest proteins) Acids (to convert calcium salts into soluble forms) Bone minerals and proteins are returned to blood About 1% of minerals flow through blood to other needy tissues. The rest resides in bone. Minerals and protein Back to blood

What processes correct low blood calcium? 1. Falling blood Ca2+ levels 4. Calcium is released from bone into blood Thyroid gland 2. Parathyroid glands release parathyroid hormone into blood. Parathyroid glands 3. PTH stimulates osteoclasts to digest bone. PTH Figure 6.12

Hormonal Control of Blood Ca2+ 1. As blood calcium levels drop 2. Parathyroid glands sense low Ca++, release PTH into blood 3. PTH travels through blood to bone, and stimulates osteoclasts to degrade bone matrix, releasing Ca2+ into the blood 4. SOLUTION! Blood Ca2+ levels raised to normal, and organ receive enough calcium to function

Hypocalcemia: Abnormally low blood calcium Abnormally LOW blood calcium leads to HIGHLY excitable neurons causing skeletal and cardiac muscle spasms

Even excessive sweating can lead to dangerously low blood calcium Even excessive sweating can lead to dangerously low blood calcium. If not corrected quickly it can be fatal.

HYPER calcemia Abnormally HIGH blood calcium -taking antacids (contain calcium carbonate) -release of too much PTH (osteoclasts overwork) -immobility of the patient (calcium leaves bones)

Signs and symptoms of hypercalcemia UNDER excitable neurons and confusion, coma, under performing muscles, heart stops beating.

Common Types of Fractures

Classification of bone fractures Nondisplaced—ends retain normal position Displaced—ends out of normal alignment

Completeness of the break Complete—broken all the way through Incomplete—not broken all the way through

Orientation of the break to the long axis of the bone: Linear—parallel to long axis of the bone Transverse—perpendicular to long axis of the bone

Whether or not the bone ends penetrate the skin: Compound (open)—bone ends penetrate the skin Simple (closed)—bone ends do not penetrate skin skin

Comminuted: Shattered Compression: Crushed Table 6.2

Epiphyseal: cartilage separates from bone Spiral: bone twists Epiphyseal: cartilage separates from bone Table 6.2

Depressed: compacts spongy bone Greenstick: bone does not break all the way through Table 6.2

Stages in the Healing of a Bone Fracture Hemostasis and inflammation Torn blood vessels hemorrhage Hematoma (clot) forms Inflammation causes swollen, painful, red area (as in skin) Hematoma .

Stages in the Healing of a Bone Fracture Fibrocartilage forms Phagocytic cells clear debris Fibroblasts secrete collagen fibers to connect bone ends

Stages in the Healing of a Bone Fracture Bony callus formation Osteoblasts form spongy bone until firm union occurs in ~2 months Compact bone forms on the surface Figure 6.15, step 3

Stages in the Healing of a Bone Fracture Bone remodeling Osteoclasts remodel and smooth the bone approximating the original shape Healed fracture

Bony callus of spongy bone Hematoma External callus Bony callus of spongy bone Internal callus (fibrous tissue and cartilage) New blood vessels Healed fracture Spongy bone trabecula 1 A hematoma forms. 2 Fibrocartilaginous callus forms. 3 Bony callus forms. 4 Bone remodeling occurs. Figure 6.15

Homeostatic Imbalances: Rickets Due to Vitamin D deficiency or insufficient dietary calcium in children leads to bowed and weak bones

Homeostatic Imbalances: Osteporosis In adults, low bone calcium due to lack of estrogen, calcium or vitamin D deficiency, immobility, thyroid disease, and diabetes can cause loss of bone mass

Vertebrae collapse and compress Spongy bone of spine and neck of femur becomes porous and more susceptible to fracture Vertebrae collapse and compress Figure 6.16

Osteoporosis: Treatment and Prevention Diet with sufficient calcium Weight-bearing exercise throughout life