HAP Unit 4, Chapter 6 pp121-50

The Skeletal System

Functions of the Skeletal System

Support – like hangers for our clothes Protection – like knights’ armor

Large scale – obvious bones like the cranium

Small scale – tiny channels and tunnels for blood vessels, nerves, lymph vessels, etc.

Movement – levers for muscles to pull against

Storage – fat/energy and minerals/metabolic reaction roles

Hematopoiesis – blood cell formation

Types of bones (your book has 4)

1. Long greater length than width curved for strength like bridges heaviest in the middle (shaft) largest ratio of lamellar/compact

to trabecular/cancellous bone femur, humerus, metacarpals,

metatarsals

Types of bones (your book has 4)

2. Short equal length and width low ratio of lamellar/compact to trabecular/cancellous bone

light weight, not weight-bearing occurring in groups to create great

range of motion carpals, tarsals

Types of bones (your book has 4)

3. Flat 2 parallel plates of lamellar bone

sandwiching a thin layer of trabecular bone

armor-like protection surface area for attachment of

many ligaments, tendons and subcutaneous fascia

skull bones, ribs, scapula

Types of bones (your book has 4)

4. Irregular difficult to categorize and have

characteristics of several types complex shapes and configurations varying ratios of lamellar to

trabecular bone various functions depending on

location facial bones, vertebrae, coxal bones

(hips)

Types of bones (your book has 4)

5. Sesamoid – the one your book doesn’t include small bones buried in tendons and

ligaments of heavy use/abuse areas no direct articulation with any other

bone vary in number per person everyone has 2 – the patellae (plural) “approximately” 206 bones – this is

why

Gross anatomy terms pp123-4

Some terms from histology and some are new: Compact = NOW lamellar Cancellous = NOW trabecular Diaphysis Epiphysis Medullary cavity Articular cartilage Trabeculae (plural)

Gross anatomy terms pp123-4 Periosteum – 2 layers▪ outer – tough, protective, vascular FCT▪ inner – osteoblasts = bone-builders, finer fibers▪ inner - osteoclasts = bone “cutters” reabsorb

mineral matrix for remodeling and cleaning up debris after damage

Endosteum▪ lines medullary cavity of long bones▪ osteoblasts & osteoclasts

Cartilage on articular surfaces

Gross anatomy pp123-4

Histology pp123-4Haversian Systems - Osteons

Central Haversian Canals – blood and lymph vessels, nerves

Concentric lamellae – concentric rings of mineral matrix surrounding central canal

Osteocytes in lacuna between concentric lamellae▪ Osteoblasts/builders, osteoclasts/destroyers, osteocytes/maintenance

Canaliculi for osteocyte extensions (filopodia) to facilitate diffusion of nutrients and wastes from Haversian canal blood vessels and cells farthest away

Canaliculi, lacunae, filopodia

Dried bone above

Diagram of Haversian System section at left

The importance of filopodia and canaliculi

Histology pp123-4

Haversian Systems continued: Volkmann’s Canals – tunnels that run from one

osteon to another with blood, lymph vessels and nerves, also referred to as “perforating canals”

Collagen fibers for reinforcement▪ Circular – running around between concentric

lamellae▪ Longitudinal – running between concentric lamellae

but the length of the Haversian System Interstitial lamellae – the lamellae that have

to fill in the spaces between the circular Haversian systems – like a box of cans, there are irregular spaces leftover

Histology pp123-4

Histology pp123-4

Histology pp123-4

Interstitial lamellae above

Osteon/Haversian system diagram above

Histology pp123-4

Bone Growth-Ossification pp125-7Also called “Osteogenesis”

This is the one the book doesn’t give you: Intramembranous Ossification:

Flat bones of cranium, face, pelvis, ribs, scapulae

Begins as FCT membrane in fetus & mesenchymal cells (stem cells) differentiate into osteoblasts (bone-builders) by hormone signals

Osteoblasts in the FCT secrete more collagen fibers to form the “osteoid” (preliminary bone scaffold)

When trapped in osteoid, the osteoblasts become osteocytes (mature bone cells)

Bone Growth-Ossification pp125-7

Intramembranous Ossification continued: Osteoblasts collect Ca/Ph salts into tiny spicules

(needles) that grow together to form trabeculae Further work is done by osteoblasts and

osteoclasts (bone “cutters”) to remodel trabecular bone on the outer edges to lamellar bone

Small mid-section remains as red marrow Original FCT membrane becomes periosteum on

external surfaces, and more blood vessels form in both the periosteum and bone during formation processes

Intramembranous Ossification

Endochondral Ossification pp125-7Also called “Osteogenesis”

In your book: Endochondral Ossification All other bones – long, short, some irregular All start as hyaline cartilage model, much smaller

and primitively shaped in fetus at 8 weeks gestational age

Hyaline, like many cartilages has low vascularization, though the perichondrium (FCT covering) is quite vascular and innervated (has nerves)

Chrondrocytes in center of diaphysis become activated by hormone signals to hypertrophy (get bigger), they absorb the cartilage matrix and mineral salts collect

Endochondral Ossification pp125-7Also called “Osteogenesis”

In your book: Endochondral Ossification Blood vessels penetrate diaphysis of hyaline

model as chondrocytes begin to die because the bone collar they are forming prevents them from receiving nutrition

This creates PRIMARY center of ossification (PCO) and new mesenchymal cells arrive through the blood to form the first osteoblasts by fetal age of 12 weeks

Trabecular bone is first to be formed, then remodeled into lamellar bone through the action of hormone-signaled osteoblasts and osteoclasts

Endochondral Ossification pp125-7

The PCO expands toward the epiphyses or edges of bone – long and short bones have epiphyses, irregular bones don’t, but several locations will begin to form ossification centers also – SECONDARY co’s (SCO)

A collar of lamellar bone is remodeled from the trabecular bone and formed around the perimeter of the PCO – dense diaphysis of long bones

Osteoclasts remove most of the trabecular bone in the center of the diaphysis, creating a “medullary cavity,” which will serve to store adipose for long-term energy reserves

Endochondral Ossification pp125-7 Blood vessels penetrate epiphyses of hyaline

model, or areas on the edges of irregular bones forming the SECONDARY centers of ossification – usually 2 or more

The same process begins, but outward and in the direction of the PCO

Remaining between the PCO and SCO is a region of remaining hyaline cartilage – Epiphyseal PLATE,

or “growth plate” Bone growth will continue to occur as long as

hyaline cartilage remains in these plates, varies in individuals and genders/genetics/environmental conditions

Endochondral Ossification pp125-7 Epiphyseal plate breaks are bad. The zone of

osteogenesis and the delicate balance of the work of osteoblasts and osteoclasts can permanently affect the ossification processes – and growth

When the plate is fully ossified, it remains as the epiphyseal line, and growth is completed

The original perichondrium becomes the periosteum

SCO’s become red marrow cavities for hemopoiesis

Hyaline cartilage cap remain at articular surfaces providing for frictionless joint movements

Endochondral Ossification

Endochondral Ossification

Endochondral Ossification

Osteogenesis videos – really good

Start with this one – shorter and slower, a good pace to start: https://www.youtube.com/watch?v=NM8

zQLJ1ipQ This one is very good, watch and

stop it while you go back and review the steps written out in this PPT: https://www.youtube.com/watch?v=xXg

Zap0AvL0

Bone Growth-Ossification pp125-7

Growth in density/diameter can continue for life if weight-bearing exercise/activity continues – defeat osteoporosis girls!

A word about pH: CaCO3 and Ca3(PO4)2 are alkaline and will not

collect in an acidic environment Body fluids are slightly alkaline The more acidic and carbonated foods/beverages

you consume, the more difficult calcification and ossification become – sports injuries in youth!!!

Bone Growth-Ossification pp125-7

In boys, longitudinal growth can occur into the mid-20’s

Girls usually stop in early to late teens

Nutrition, environmental stresses and genetics all determine growth

Human growth hormone (HGH), sex hormones (androgens & male), parathyroid hormone and calcitonin (from thyroid) are all involved

Bone Maintenance - supplemental

Osteoblasts mostly in periosteum, collect calcium salts and remodel into lamellar bone

Osteoclasts mostly in endosteum of the medullary cavity, remove calcium matrix and release to extracellular fluid, where it is retrieved by capillaries and supplied to other metabolic processes, including the work of osteoblasts

Osteocytes within lamellae are engaged in simple maintenance within the bone

Maintenance and Requirements Distal end of femur may be replaced in the

young and active every 4 months! Distal end of tibia is still likely to be

completely hyaline cartilage at 2 years of age – early walking may not be such a great thing!

Requirements: Vitamins for coenzymes in metabolic reactions Minerals – obviously Calories for energy Hormones – see previous pH – slightly alkaline

Repair - supplemental 3 phases – Hematoma, Callus, Remodel1. Hematoma:

Bone is very vascular – it works hard! no pun intended

When it breaks, blood vessels usually are torn Blood clots (hematomas) must form to stop the

bleeding Takes 6-8 hours if left undisturbed – usually

doesn’t happen that quickly because a person is transported to medical facilities, etc.

Because vascularization is disrupted, osteocytes, chondrocytes, fibroblasts (all cells in the area) die

Repair - supplemental 3 phases – Hematoma, Callus, Remodel 2. Callus: 3 weeks +

Blood circulation may begin to be re-established several hours to days later (48 hrs maybe)

Cells in perimeter go through mitosis and begin to spread from edges of damage inward to fill damaged areas – like how burns of integument heal

Periosteum must repair first Endosteum must also repair Osteoblasts and osteoclasts re-generated on

these membranes begin work; osteogenesis processes begin

Repair - supplemental 3 phases – Hematoma, Callus, Remodel2. Callus continued:

Osteoblasts form “patch” of trabecular bone to connect broken ends/pieces

Osteoclasts reabsorb broken bits to recycle the valuable mineral salts

Work of osteoblasts and osteoclasts continues to collect calcium salts and remodel

Trabecular model is formed first from endosteum and periosteum to form collar or patch in break area

Marrow cavity must also be repaired if damaged

Repair - supplemental 3 phases – Hematoma, Callus, Remodel3. Remodel: 6 weeks up to years

Lamellar bone slowly replaces trabecular bone, except in marrow cavities

In many cases, the repaired break is stronger than it was previously

Most of the time, the break is not detectable by X-ray when complete, but a slightly thickened area may remain for life

Pretty much a miracle!

Things to know and learn OYO: text, my notes, PPTs, website materials, CWS, etc.

Because I know you can all read and use images to learn on your own:

*Types of breaks – FTI, not test material*Pathological conditions – not in book*Divisions of Skeleton starting on p127 **Axial pp130-5 and my notes **Appendicular pp135-42 and my notes