A&P Bones 1

What are the 4 functions of the skeletal system?

Support & Protection, Muscle Attachment, stores Energy & Minerals, Hemopoiesis

What are the primary bone cells?

Osteoblasts, Osteoclasts

What is the ECM made of?

Protein Fibers, Ground Substance

Osseous Tissues

What are Osteoblasts? What do they produce?

Cells that produce osteoid and form new bone tissue (osteoid mineralizes)

What are Osteocytes?

Bone cell that develops from osteoblasts that are trapped in the mineralized matrix that they create

What are Osteoclasts? What is their function?

Break down bone matrix, bone remodeling and changing features in already produced bones

What is the Bone Extracellular Matrix made of?

What are the two types/forms of bone?

Cortical (compact) bone and Cancellous (spongy) bone

What are Osteons?

The unit that makes up of compact bone

How is the Cortical Bone organized?

Osteons layered in concentric lamellae of the ECM, central canal in each concentric lamellae to allow nerves and veins to pass through, parallel to direction of compressive stress

How are lamellaes structured in an osteon? What does it provide?

Alternating collagen fiber orientation. Provides multidirectional strength and resistance to torsion

What is the primary structural unit of Cancellous bone (spongy)?

Trabeculae. Does not have osteons

What bone can contain red bone marrow?

Cancellous Bone.

What is the function of red bone marrow? What’s the process called?

Produces blood cells through a process called hematopoiesis

What is the purpose of Cancellous Bone?

Absorb and transmit forces

What is the layer of dense irregular connective tissue that lines the outsides of our bones?

Periosteum

What is the layer of dense irregular connective tissue that lines the inside of our bones?

Endosteum

What is the function of Endosteum and Periosteum?

Growth and repair processes of bones

When a person breaks a bone, what specific tissue layer is primarily responsible for sending the intense pain signals to the brain, and why?

The periosteum, because it contains a lot of sensory nerves

What are the 5 types of bones?

Long Bones, Short Bones, Flat Bones, Irregular Bones, Sesamoid Bones

How do you identify long bones? Whats its purpose?

Longer than wide. Support and movement

How do you identify Short bones? Whats its purpose?

Cube like shape. Stability and movement

How do you identify Flat bones? Whats its purpose?

Thin, often curved. Protection. EX: cranium, shoulders

How do you identify Irregular bones? Whats its purpose?

Complex shape. Support and protection.

How do you identify Sesamoid bones? Whats its purpose?

Small ball shaped bones formed in tendons in response to movement and tension in the tendons. Movement. EX: Patella

What is the end of the long bone called? What kind of bone makes up the structure?

Epiphyses. Cancellous bone inside, articular Cartilage externally.

What is the shaft of the long bone called? What kind of bone makes up the structure? What is the hollow middle called?

Diaphysis. Cortical Bone. Medullary Cavity (lined by endosteum) yellow bone marrow.

What is ossification?

Bone formation

When does bone formation begin in a human?

Around embryonic week 8

What are 2 types of ossification?

Intramembranous and Endochondral ossification

What are the two bone tissue types?

Primary and Secondary Bone

What bone tissue would be used to repair fractures? Why is this specific one useful?

Primary Bone. Laid down quickly, allowing bone to form faster.

What makes primary bone weaker than secondary bone?

Its collagen fibers are irregularly arranged and it has less inorganic material, making it less durable.

How does secondary bone differ from primary bone?

It forms slower, contains fully formed osteons, parallel collagen fibers, and more inorganic material, making it stronger.

What is yellow bone marrow used for? Where can it be found?

Fat storage (energy storage), adult limbs

Where can red bone marrow be found in children and adults?

Children every bone, adults head and trunk

Where can yellow bone marrow be found?

In adults limbs

Where does longitudinal bone growth occur?

Epiphyseal plates in the long bones

5 Zones of the Epiphyseal Plates? (Real People Have Career Opportunities)

Zone of reserve cartilage, proliferation, hypertrophy, calcification, ossification

Where do chondrocytes divide in long bones?

Zone of proliferation

T or F: Longitudinal bone growth pushes epiphysis away from diaphysis

True

What zone pushes the epiphysis away from diaphysis?

Zone of Proliferation

When does growth and ossification stop?

When zone of proliferation is inactive

When does the proliferation rate slow?

End of adolescence

What happens to the epiphysis when the epiphyseal plate closes?

It gets ossified

What happens to growth when epiphysis closes?

Longitudinal growth stops

What age does the epiphyseal plate close in Males and Females?

21 (M), 18 (F)

What is Achondroplasia?

Failure of cartilage growth in an epiphyseal plate

What caused achondroplasia?

Spontaneous mutation

What genetic mutation causes disproportionately short limbs?

Achondroplasia

What is growth in bone width?

Appositional growth

Where does appositional growth occur?

Periosteal surface

How does appositional growth work?

Periosteal osteoblasts create a new cortical matrix superficially, osteoclasts erode the medullary cavity.

When does appositional growth stop?

Never

How does growth hormone promote lengthwise bone growth?

It increases chondrocyte cell division at the epiphyseal plate.

How does growth hormone affect osteogenic cells?

It increases osteogenic cell activity

What cells does growth hormone stimulate in the periosteum?

Osteoblasts

When is growth hormone most important for bone growth?

During infancy and childhood

What hormone increases appositional bone growth?

Testosterone

How does testosterone promote bone lengthening?

It increases chondrocyte cell division

What happens to bone resorption when estrogen inhibits osteoclasts?

Bone resorption decreases because osteoclast activity is reduced

How does estrogen affect the epiphyseal plate?

It accelerates epiphyseal closure, ending lengthwise growth

Which hormone increases chondrocyte division and osteoblast activity?

Growth Hormone

Which hormones increase chondrocyte cell division?

Growth hormone and testosterone

T or F: Girls epiphyseal plates close faster than males. Why or Why not?

True. Higher estrogen production

What are the main functions of skeletal remodeling?

Reshape bones during growth and in response to use, damage, and release minerals into the blood

What is bone deposition, and which cells perform it?

Osteoblasts secrete osteoid, which contains collagen fibers arranged in a spiral pattern, then it mineralizes.

What is mineralization in bone deposition, and how does it strengthen bone?

Calcium and phosphate crystallize on collagen fibers to form hydroxyapatite which hardens the bone

What is bone resorption?

Osteoclasts break down bone tissue and release minerals into the blood

How do osteoclasts break down bone during resorption?

They secrete Hydrogen ions (acid) and enzymes. The acid lowers pH, and the enzymes break down tissue in the extracellular matrix

How do deposition and resorption work together in skeletal remodeling?

Osteoblasts build bone, while osteoclasts break it down. Together, they allow bones to reshape, repair damage, and release minerals

Why is calcium important in bones and the rest of the body?

It gives bone hardness, and is needed for neuron signaling, muscle contractions, heart contractions, and blood clotting

What is calcium homeostasis?

Maintaining a balance of calcium by regulating intake, excretion, and the exchange of calcium between bones and blood

Which three hormones regulate calcium homeostasis?

Calcitriol (Vitamin D), Calcitonin, and Parathyroid Hormone

What is calcitriol, and how is it produced?

Vitamin D, produced through actions of the skin, liver, and kidneys, starting with UV radiation.

What is the main function of calcitriol?

To raise blood calcium levels, promotes calcium absorption in the small intestines, increases osteoclast cells, increases calcium resorption from skeleton, reduces calcium excretion in kidneys

What releases Calcitonin? Where is it produced?

Hypercalcemia (high blood calcium), produced in thyroids

How does calcitonin lower blood calcium levels?

It stops osteoclasts, reducing bone resorption, and stimulates osteoblasts, promoting bone deposition, which takes calcium out of the blood

What causes the release of Parathyroid Hormone? Where is it produced?

Hypocalcemia (low blood calcium), its released by parathyroid glands

How does Parathyroid Hormone increase blood calcium levels?

Inhibits osteoblast activity, reducing bone deposition, and stimulates osteoclasts, continue bone resorption, so calcium is released into the blood

What is the mechanical stress equation?

Force/area

How does bone respond to mechanical stress, and which cells monitor it?

More bone is deposited under areas of high stress, osteocytes monitor it.

What is Wolff’s law?

Bones remodel in response to the habitual forces and demands placed on them

Why is the compact bone layer thickest in certain areas of a long bone’s shaft?

Those areas experience the highest compressive and tensile forces

Why do larger muscles have larger bone attachment sites?

Larger muscles produce greater forces during contraction, causing larger attachment sites to develop on the bone.

How does exercise affect bone formation?

Exercise increases mechanical stress on bones, stimulating bone formation

What is a stress fracture?

Fracture caused by more trauma to a bone than it can handle

What is a pathological fracture?

Fractures in a bone that were weakened by disease

What are the four stages of fracture healing (in order)?

Inflammatory response → Soft callus formation → Hard callus formation → Remodeling

What happens during the inflammatory response?

A blood clot forms and is invaded by blood vessels, fibroblasts, macrophages, osteoclasts, osteoblasts, and chondrocytes, forming granulation tissue

What is granulation tissue, and which cells contribute to it?

Tissue formed when the blood clot is invaded by repair-related cells and blood vessels.

How is the soft callus formed?

Fibroblasts secrete collagen for support, while chondrocytes produce fibrocartilage around the fracture.

How does the soft callus become a hard callus? How long does it take?

Osteoblasts produce a bony collar around the fracture. Takes around 4–6 weeks.

What happens during the remodeling stage of fracture healing?

Osteoclasts remove bone fragments, osteoblasts lay down cancellous bone, and ossification produces cortical bone

What happens to bone deposition and resorption in children and adolescents?

Deposition > Resorption = rapid bone growth and peak bone mass

What happens to bone deposition and resorption in young adults?

Deposition = Resorption

What happens to bone deposition and resorption in older adults?

Deposition < Resorption = bone mass, mineralization, and healing ability decrease

What causes osteoporosis?

Excessive bone resorption = loss of bone density

Which bones are most vulnerable to osteoporosis, and what fractures are common?

Cancellous bone in the spine and femur. Vertebral and hip fractures are common