Chapter 7: Bone Tissue

Question 1

What is the study of bone called?

Answer 1

Osteology

Question 2

What are your most durable remains in bone?

Answer 2

Bones and teeth

Question 3

What are the functions of the skeleton?

Answer 3

• Skeleton is living (it responds to stress in the body)
• Support
• Protection
• Movement
• Electrolyte balance (calcium and phopshate)
  
  • calcium is usually the concern here
• Acid-base balance
  
  • (buffers blood against pH changes by alternating carbonate and phosphate salt levels)
• Blood formation (hemopoiesis)
  
  • makes RBC, WBC, and platelets

Question 4

What is the definition of bone?

Answer 4

Bone (osseous tissue): connective tissue with the matrix hardened by calcium phopshate and other minerals

Question 5

Define mineralization or calcification.

Answer 5

The hardening process of bone.

Question 6

What do individual bones consist of?

Answer 6

Individual bones are organs and they consist of bone tissue, bone marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue.

Question 7

What are the types of bones and some examples?

Answer 7

• Flat bones (sternum, skull bones)
• Long bones: bones that are longer than wide (mostly arms and legs)
• Short bones: length and width are approximately equal (carpals and tarsals)
• Sesamoid bones: bones you develop in a tedon or ligament due to high stress; unnamed (one in carpal, one in foot) (exceptions: patella)
• sutural bones: usually unnamed (e.g. back of head, lamboid formed by small cracks coming together)
• Irregular bones: everything else (e.g. vertebrae)

Question 8

What is the structure of a bone?

Answer 8

Epiphysis: the end of the bone, has proximal end and distal end

Diaphysis: shaft of bone

Epiphyseal Line (aka metaphysis): separates epiphysis from diaphysis

• this called the “growth plate” until growth is dome

Articular cartilage: white, hyaline cartilage at the ends of moveable joints

Spongy bone on the outer layer, compact bone on the inner layer, marrow cavity

Question 9

What are the general features of bone?

Answer 9

• articular cartilage (hyaline)
• nutrient foramina (holes where blood vessels come in)
• Periosteum
• endosteum (thin layer of reticular connective tissue lining marrow cavity)
  
  • contains osteoblasts and osteoclasts
• epiphyseal plate (enables growth in length of bone)
  
  • made of hyaline cartilage
  • when finished, turns into epiphyseal line

Question 10

What are the general features of flat bones?

Answer 10

• Sandwich-like
• two layers of compact bone with a middle layer of spongy bone
• diploe: spongy middle layer
  
  • absorbs shock
  • marrow spaces lined with endosteum
    
    • red, make blood here

Question 11

What are the two layers of periosteum and their general features?

Answer 11

• Outer fibrous layer made of collagen
  
  • some fibers continuous with tendons
  • perforating fibers: penetrate into bone matrix
• Inner osteogenic layer
  
  • important to bone growth and healing of fractures

Question 12

Describe “trabeculae”

Answer 12

Trabaculae (thin plates) is calcified and hard, but it is named for its spongelike appearance. It is covered with endosteum and permeated by spaces filled with bone marrow (where blood is made).

Question 13

What are the 4 types of bone cells and their general features?

Answer 13

• Osteogenic cells
  
  • stem cells that perform mitosis and become osteoblasts
• Osteoblasts: bone forming cells
• Osteocytes: mature bone cells
  
  • found in pockets called lacunae
  • connected to each other by gap junctions and canaliculi (cracks in bone to connect cells)
  • some reabsorb bone matrix and others deposit it (regulates bone modeling)
• Osteoclasts
  
  • the “oddball”; it is not osteogenic
  • derived from fusion of WBC
  • usually multinucleate
  • secretes enzymes and acids for resorption (the break down of bone)

Question 14

What are the main 2 steps involved in the making of bone? How does resorption work?

Answer 14

• Secrete protein (collagen fibers)
  
  • need lots of ATP and amino acids
  • cell needs lots of Rough ER and Golgi
• Deposit calcium salts (from blood)
  
  • process is like making rock candy
• Enzymes dissolve collagen via hydrolysis and acids dissolve salt, which returns to the blood

Question 15

What are the two portions of bone matrix and their general features?

Answer 15

• Organic portion (1/3 of bone)
  
  • Collagen, carbohydrate-protein complexes
  • synthesized by osteoblasts
  • responsible for the flexibility of bone
• Inorganic portion (2/3 of bone)
  
  • 85% hydroxyapatite (calcium phosphate)
  • 10% calcium carbonate
  • 5% other minerals (floride, sodium, etc.)
  • Responsible for the hardness of bone

Question 16

What happens to bone under the following conditions: mineral deficiency and defect in collagen deposition?

Answer 16

Mineral deficiency: soft bones (in adults causes pain, in children causes deformity as seen in Rickets)

Collagen: no flexibility (brittle bone disease), bones snap easily

Question 17

What are the components of a Haversian System or an Osteon?

Answer 17

• Lamella
  
  • columns of the matrix (mainly collagen) that are weight bearing
  • concentric, circumferential, and interstitial lamella
• Central (Haversian) canal)
  
  • contains blood vessels and nerves
• Perforating (Volkmann’s) canals
  
  • channels that connect blood and nerves from periosteum to the central (Haversian) canal

Question 18

What is the structure of spongy bone?

Answer 18

• Lattice of bone covered with endosteum
  
  • trabeculae (thin plates of bone)–develop along the bone’s line of stress
  • spicules (slivers of bone)
  • spaces filled with red bone marrow
  • few osteons, no central canals
• provides strength with minimal weight
  
  • will crush first if depleted calcium (like in osteoperosis)

Question 19

What is the definition of bone marrow, its two types, and their general structures?

Answer 19

Bone marrow: soft tissue in marrow cavities of long bones and small spaces of spongy bone.

• Red marrow (myeloid tissue): contains hemopoetic tissue (makes blood cells)
• Yellow marrow
  
  • only in adults
  • stores triglycerides
  • can transform into red marrow in the event of anemia

Question 20

Where is red marrow (hematopoietic tissue) located in children and in adults?

Answer 20

Children: medullary cavity and all areas of spongy bone (much will be converted to yellow marrow over time)

Adults: head of the femur and the humerus, diploe (spongy bone) of flat bones, some irregular bones (e.g. hip and vertebrae)

Question 21

What is ossification / osteogenesis and its two types?

Answer 21

Ossification is the formation of bone.

• Intramembranous ossification: bone develops within fibrous connective tissue membrane
• Endochondrial ossification: start with mesenchyme, then cartilage, and then bone (bone forms by replacing Hyaline cartilage)

Question 22

How does intramembranous ossification work and what are soem examples of it?

Answer 22

• mesenchymal cells turn to osteoblasts turn to osteocytes, which form spongy bone
• This forms the flat bones of the skull, clavicles, and ossifies the fontanels
• Most of these bones are remodeled (destroyed and reformed) as we grow to adult size

Question 23

How does endochondrial ossification work and what are some examples of it?

Answer 23

• Bone forms by replacing hyaline cartilage
• Forms most of the body below the skull (except the clavicle)
• Mesenchyme turns to chondroblasts, which die and are replaced by osteoblasts turn to spongy bone and finally turn to compact bone

Question 24

What are the two types of endochondrial ossification and how do they work?

Answer 24

• Primary ossification: works on the diaphysis (shaft) of bone
  
  • this is the first part to be destroyed and turned into bone
• Secondary ossification: works on epiphysis (ends of bones)
  
  • this turns cartilage into bone from the center outward
  • cartilage cells undergo mitosis and push the epiphysis away from the diaphysis
  • cartilage cells die and are replaced by bone
  • When plate is finished, no more cartilage plate: now epiphyseal line
    
    • bone can no longer grow in length; plate is closed
• articular cartilage should stay for life

Question 25

What are the two types of dwarfism and how do they work?

Answer 25

* Achondroplastic Dwarfism * long bones stop growing in childhood * Individual has normal torso, but abnormally short arms and legs * growth plates close early (cartilage is not multiplying) * spotaneous mutation produces dominant allele * Pituitary Dwarfism * rare, usually only seen in very poor countries * lack of growth hormone (can be fixed by taking the hormone) * normal proportions with short stature. * lack of hormone messes with CNS

Question 26

\*\*\*\*How does appositional growth (bones widening and thickening) work in the bones?

Answer 26

* Appositional growth occurs at the bones's surface * Continual growth in diameter and thickness * Intramembranous ossification * Osteoblasts of periosteum deposit osteoid tissue * lay down matrix: circumferential lamella * Become trapped as tissue calcifies * Osteoclasts of endosteum enlarge marrow cavity

Question 27

What is the general process of bone remodeling in adults?

Answer 27

* 10% of skeleton is remodeled per year * Remodeled by osteoblasts (bone deposition) and osteoclasts (resportion) * Wolff's law * bone grows or remodels based on the demands placed on it * Exercise promotes bone growth, lack of exercise atrophies bone (and therefore muscle)

Question 28

Desribe the mineral deposition and mineral resorption processes that occur in bone.

Answer 28

* Mineral deposition * osteoblasts produce collagen fibers * fibers become encrusted with minerals * first few crystal act as seed crystals that attract more calcium and phosphate * Abnormal calcification is called a calculus * can form in lung, brain, eye, muscle, tendon, artery * Mineral Resorption * Osteoclasts pump hydrogen to ECF (chloride follows) * Hydrochloric acid (pH 4) dissolves minerals * enzyme (acid phosphatase) digests collagen * Released minerals enter blood

Question 29

What are the two conditions presented in lack of calcium homeostasis and why are they problems?

Answer 29

* Hypocalcemia: low blood calcium * causes overly excitable nervous system and muscle spasms * caused by Vitamin D deficiency, diarrhea, thyroid tumors, underactive parathyroid glands * Pregnancy and lactation increase risk * Test: Chvostek's sign (poke facial nerve, facial nerves will pull unnaturally. * Hypercalcemia: high blood calcium * very rare * nerve and muscles less excitable * Muscle weakness, sluggish reflexes, paralysis * Test: Trousseau's sign (bleed pressure test, fingers curl in)

Question 30

Why is calcium homeostasis important?

Answer 30

* Calcium needed in neuron communication, muscle contraction, blood clotting, and exocytosis * MInerals are deposited into skeleton and withdrawn when they are needed for other purposes * Bone is the bank * Body will sacrifice bone to save pH of blood, which is more critical

Question 31

What factors and hormones can regulate Calcium homeostasis?

Answer 31

* loss: uriary and fecal losses * intake: diet * balance maintained by exchange with osseous tissue * 3 hormones: * calcitrol (Vitamin D absorption, digestive system), calcitonin, parathyroid hormone (both are skeletal system).

Question 32

What calcitrol? How is it made and what does it do?

Answer 32

* Calcitrol is a hormone that regulates calcium homeostasis. * It is the most active form of Vitamin D (Vitamin D3) and it is produced by actions of the skin, liver, and kidneys. * It is a hormonse that raises blood calcium level. * Increases absorption by small intensine, reabsorption by skeleton, less lost in urine * It is necessary for bone deposition * lack of calcitrol results in Rickets for children and ostemalacia for adults

Question 33

What is Calcitonin? What does it do?

Answer 33

* It is a calcium homeostasis hormone * It is produced by the thyroid gland * Its release is trigged by high blood calcium * It will lower blood calcium * inhibits osteoclasts (resorption) * stimulates osteoblasts (grow bone) * Important in children, weak effect in adults except pregnant/lactating woman

Question 34

What is parathyroid hormone and what does it do?

Answer 34

* It is a calcium homeostasis hormone * It is released by the parathyroid glands * It is trigged by low blood calcium * It increases blood calcium * increase number of osteoclasts * promote calcium reabsorption of kidneys (doesn't excrete in urine) * promotes final step of calcitrol synthesis * inhibits collagen synthesis by osteoblasts

Question 35

What is the process of bone development from childhood to early adulthood?

Answer 35

* Infancy and childhood * Epiphyseal plate activity is stimulated by Human Growth Hormone (HGH) * Adolescence: testosterone and estrogens * promote adolescent growth spurts * differentiates the male/female skeleton * induces epiphyseal plate closure * Early Adulthood: bone growth ends 18-21 years * some outliers exist * Adulthood * prevent osteoperosis * build bones up ages 25-40

Question 36

What factors affect bone growth?

Answer 36

* Estrogen * Estrogen has a stronger affect on bone growth than testosterone * Girls grow faster than boys and reach full height earlier * Males grow for a longer time and taller * Anabolic steroids cause growth to stop * epiphyseal plates close prematurely * results in abnormally short adult stature

Question 37

What are bone fractures and their classifications?

Answer 37

* Stress fracture: break caused by abnormal trauma to a bone * Pathological fracture: break in a bone weakened by disease (cancer or osteoperosis) * Classified by structural characteristics * displaced v. nondisplaced * pulled out of normal alignment / not * open v. closed / simple v. compound * Open = open to skin, closed = closed to skin

Question 38

How do fractures heal?

Answer 38

* The fracture in bone creates a hematoma and the bone bleeds a lot * The bone deposits collagen and forms both a soft callus and fibrocartilage * The bone forms a hard callus and spongy bone * The bone remodels into compact bone and is healed

Question 39

What are the treatment types for bone fractures?

Answer 39

* Closed reduction: surgery * Open reduction: no surgery * Casts

Question 40

What is osteoperosis and what problems does it cause?

Answer 40

* Osteoperosis is the most common bone disease * It affects spongy bone the most * (spongy bone is most metabolically active) * Trabiculae get crushed and the bone heals that way * Inhibits resorption of estrogen by osteoclasts * estrogen highly important for bone density * Individuals are subject to fractures of hip, wrist, and vertebral column * Most affected * post menopausal women and underweight, young female athletes * Example: * Widow's hump (deformity of spine due to vertebral bone loss)