Chapter 6 - The Skeletal System: Bone Tissue Flashcards
What is Bone?
Bone is an organ made of different tissues working together
Bone, Cartilage, Dense Connective Tissue, Adipose tissue, and Nervous Tissue
Framework of bones and their cartilages make the Skeletal System
What is the Function of the Skeletal System?
1- Provide support
2- Protects internal organs
3- Assist in body movements (in conjunction with muscles)
4- Mineral Homeostasis - Store/release Calcium and Phosphorus
(Osteoblast dissolve - release calcium)
(Calcitonin removes calcium from blood)
5- Participate in Hemopoiesis (Erythroproteins)
6- Stores triglycerides in adipose cells of Yellow Marrow
7- Hormone production - Bones produce Osteocalcin to regulate insulin secretion and blood glucose levels
What are the parts of a Long Bone?
1- Diaphysis - Bone shaft
2- 2 Epiphyses - Both ends of the bone at joints (Reb Bone Marrow)
3- 2 Metaphyses - Region between Diaphysis and Epiphysis
4- Articular Cartilage - Covering both Epiphyses
5- Periosteum - Connective tissue surrounding Diaphysis)
6- Medullary Cavity - Hollow space within Diaphysis (Yellow Marrow)
7- Endosteum - Thin membrane lining Medullary Cavity
Nutrient Artery in Medullary Cavity
What is the Epiphyseal Line?
Hyaline Cartilage line between Epiphysis and Metaphysis
What does Bone contain?
Bone contains abundant Extracellular Matrix that surrounds widely separated cells
Made of :
15% water
30% Collagen
55% Crystalized mineral salts
What are the 4 Types of Bone Cells?
1- Osteoprogenitor Cells:
Bone stem cells able to differentiate into other types of cells
2- Osteoblasts:
Bone-building cells that secrete matrix
3- Osteocytes:
Mature bone cells, produce bone tissue
4- Osteoclasts:
Remodel bones and cause them to release calcium into blood
Decalcification
Osteoprogenitor cell develops into Osteoblast which forms Extracellular Matrix
Osteoblast develops into Osteocyte which maintains bone tissue
Osteoclast functions in resorption, the breakdown of bone extracellular matrix
What is Compact Bone?
Compact Bone is good at providing protection and support
What is Spongy Bone?
Spongy Bone is lightweight and provides tissue support
What is Compact Bone Composed of?
1- Osteon:
Made of Concentric Lamellae
Osteonic Canal in center
Contains Blood vessels
2- External Circumferential Lamellae:
Lamellae around Osteons
3- Internal Circumferential Lamellae:
Lamellae around Spongy Bone
4- Interstitial Lamellae:
Lamellae between Osteons
5- Periosteum:
Outer fibrous layer around Diaphysis
Inner Osteogenic layer
Held by Perforating fibers (Sharpey’s)
Has Periosteal arteries and veins
6- Interosteonic Canals (Volkmann’s or perforating)
Horizontal between Osteons
7- Lacunae:
Residence of Osteocytes
Canaliculi - Diverging tunnel of Lacunae for Osteocytes’ projections
What is Spongy Bone composed of?
Trabeculae
Space for Red Bone Marrow
What is Trabeculae?
Part of Spongy Bone
Contains:
Osteocytes in Lacunae
Lamellae around Lacunae
Osteoblasts aligned along Trabeculae of new bone
Osteoclast
Canaliculi
What is the Blood and Nerve Supply of Bone?
Periosteal Arteries, Periosteal Veins, and Nerves enter Diaphysis through Volkmann’s Canals
Nutrient Artery enter Diaphysis through Nutrient Foramen
Nutrient Veins exit Diaphysis through Nutrient Foramen
Metaphyses and Epiphyses have their own arteries and veins
Metaphyseal Artery/Veins and Epiphyseal Artery/Veins
What is Bone Formation?
Ossification or Osteogenesis
Process of bone formation
Bones form in 4 situations:
During embryological and fetal development
When bones grow before adulthood
When bones remodel
When fractures heal
2 Forms:
Intramembranous Osteogenesis
Endochondral Osteogenesis
What is Intramembranous Osteogenesis?
Occurs in flat bones (Appendicular Skeleton) when a connective tissue membrane is replaced by bone
Cranial bones and Clavicles, forms mostly flat bones
1- Development of Ossification center:
Osteoblasts secrete organic extracellular matrix
2- Calcification:
Calcium and other mineral salts deposited and extracellular matrix calcifies (hardens)
3- Formation of Trabeculae:
Extracellular matrix develops into trabeculae that fuse to form spongy bone
4- Development of Periosteum:
Mesenchyme at the periphery of the bone develops into the periosteum
What is Endochondral Osteogenesis?
Replaces cartilage with bone in the developing embryo and fetus
All bones below base of skull, except scapulae
1- Development of Cartilage:
Mesenchymal cells develop into chondroblasts which form cartilage
2- Growth of Cartilage:
Growth occurs by cell division of chondrocytes
3- Development of Primary Ossification Center:
In this region of Diaphysis, bone tissue has replaced most of the cartilage
4- Development of Medullary Cavity:
Bone breakdown by osteoclasts forms medullary cavity
5- Development of Secondary Ossification Center:
Occurs in Epiphyses of the bone
6- Formation of Articular Cartilage and Epiphyseal Plate:
Both structures consist of Hyaline cartilage
Endochondral Ossification also occurs in Epiphyseal Plates of long bones as the grow in length
How do Bones Thicken?
Bones thicken due to cooperative action of Osteoblasts and Osteoclasts
1- Ridges in periosteum create groove for blood vessel
2- Periosteal ridges fuse, forming an endosteum-lined tunnel
3- Osteoblasts in endosteum build new concentric lamellae inward towards center of tunnel, forming a new osteon
4- Bone grows outwards as Osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels
Osteoblast deposits bone on outer surface
Osteoclast widens medullary cavity from within
What is Bone Fracture and How is it Repaired?
Fracture is a break in a bone
Many different tyees of fractures may occur
Healing process involves 3 different phases in 4 steps:
1- Reactive Phase:
Early inflammation phase - Fracture Hematoma
Neutrophils go to fracture area to fight infection
2- Reparative Phase:
Includes formation of Fibrocartilaginous Callus first, then Bony Callus
Osteoblasts and macrophages go to fracture area and clean up
Macrophages let Fibroblast lay Fibrocartilaginous cells to cover fracture
Over time osteoblasts form bone again
Chondrocytes lay cartilage again
3- Bone Remodeling Phase:
Bony Callus is remodeled
Osteoclasts come over, decalcify excess bone, remodel it correctly
What are some Types of Bone Fractures?
Closed (Simple)
Open (Compound)
Comminuted
Greenstick
Impacted
Pott
Colles
What is a Closed (Simple) Bone Fracture?
Broken bone doesn’t break skin
What is an Open (Cpompund) Bone Fracture?
Broken ends of bone protrude through skin
What is a Comminuted Bone Fracture?
Bone is splintered, crushed, or broken into pieces at site of impact
Smaller bone fragments lie between 2 main fragments
What is a Greenstick Bone Fracture?
Partial fracture in which one side of bone is broken and other side bends
Occurs only in children whose bones not fully ossified and contain more organic material than inorganic material
What is an Impacted Bone Fracture?
One end of fractured bone is forcefully driven into the interior of the other end
What is a Pott Bone Fracture?
Fracture of distal end of lateral leg bone (Fibula)
With serious injury to distal Tibial articulation
What is a Colles Bone Fracture?
Fracture of distal end of lateral forearm bone (Radius) in which distal fragment is displaced posteriorly
What is Bone’s Role in Calcium Homeostasis?
Bones store 99% of body’ Calcium
Parathyroid Gland secretes Parathyroid Hormone (PTH) when calcium levels drop
Osteoclasts stimulated to increase bone resorption and calcium is released
PTH also stimulates production of Calcitriol by kidneys to increase calcium absorption in intestines
What is the Calcium Homeostasis Negative Feedback Loop?
Blood calcium level drops
Parathyroid Gland cells detect this and increase production of cAMP
Parathyroid Hormone Gene turns on and increase PTH release
PTH makes osteoclasts increase bone resorption
PTH makes kidneys retain Ca2+ in blood and excrete phosphate in urine and produce Calcitriol
In response, blood calcium increased
What are the Factors that Affect Bone Growth?
Calcium and Phosphorus
Magnesium
Fluoride
Manganese
Vitamin A
Vitamin C
Vitamin D
Vitamin K and B12
Growth Hormone (GH)
Insulin-Like Growth Factors (IGFs)
Thyroid Hormones (T3 and T4)
Insulin
Sex Hormones (Estrogens and Testosterone)
PTH
Calcitonin (CT)
Exercise
Aging
How does Calcium and Phosphorus affect Bone Growth?
Calcium and Phosphorus make bone extracellular matrix hard
How does Magnesium affect Bone Growth?
Magnesium helps form bone extracellular matrix
How does Fluoride affect Bone Growth?
Fluoride helps strengthen bone extracellular matrix
How does Manganese affect Bone Growth?
Manganese activates enzymes involved in synthesis of bone extracellular matrix
How does Vitamin A affect Bone Growth?
Vitamin A needed for activity of osteoblasts during remodeling of bones
Deficiency stunts bone growth
Toxic in high doses
How does Vitamin C affect Bone Growth?
Vitamin C needed for synthesis of collagen, the main bone protein
Deficiency leads to decreased collagen production that slows down bone growth and delays repair of fractures
How does Vitamin D affect Bone Growth?
Vitamin D’s active form (Calcitriol) is produced by kidneys
Helps build bone by increasing absorption of calcium from GI tract into blood
Deficiency causes faulty calcification and slows bone growth
May reduce risk of Osteoporosis
Toxic in high doses
How does Vitamin K and B12 affect Bone Growth?
Vitamin K and B12 needed for synthesis of bone proteins
Deficiency leads to abnormal protein production in bone extracellular matrix
Decreased bone density
How does Growth Hormone (GH) affect Bone Growth?
GH secreted by anterior lobe of Pituitary Gland
Promotes general growth of all body tissues by stimulating production of Insulin-like Growth Factors
How does Insulin-like Growth factors (IGFs) affect Bone Growth?
IGFs secreted by liver, bones, and other tissues on stimulation of GH
Promotes normal bone growth by stimulating osteoblasts and increasing synthesis of proteins needed to build bone
How does Thyroid Hormones (T3 and T4) affect Bone Growth?
T3 and T4 secreted by Thyroid Gland
Promote normal bone growth by stimulating osteoblasts
How does Insulin affect Bone Growth?
Insulin secreted by Pancreas
Promotes normal bone growth by increasing synthesis of bone proteins
How does Sex Hormones (Estrogens and Testosterone) affect Bone Growth?
Sex Hormones stimulate osteoblasts
Promote “sudden spurt” at puberty
Shut down growth at epiphyseal plates around 18-21 years old, causing end to lengthwise growth of bones
Contribute to bone remodeling in adulthood by slowing bone resorption by osteoclasts and promoting bone deposition by osteoblasts
How does Parathyroid Hormone (PTH) affect Bone Growth?
PTH secreted by Parathyroid Gland
Promotes bone resorption by osteoclasts
Enhances recovery of calcium ions from urine
Promotes formation of Calcitriol
How does Calcitonin (CT) affect Bone Growth?
Calcitonin secreted by Thyroid Gland
Inhibits bone resorption by osteoclasts
How does Exercise affect Bone Growth?
Weight-bearing activities stimulate osteoblasts
So help build thicker stronger bones
Retard loss of bone mass with age
How does Aging affect Bone Growth?
Levels of sex hormones diminish, especially in women after menopause
Bone resorption by osteoclasts outpaces deposition by osteoblasts
Decrease in bone mass
Increased risk of Osteoporosis
What is Rickets?
Osteomalacia for adults is called Rickets in children
Calcium deficiency
Soft bones, Cartilage bends
What is Osteoporosis?
Calcium deficiency
Lack of proteins
Menopause in women
Vitamin D deficiency
Bone density too low, high risk of fractures
Alendronate: medicine acting like Calcitonin, takes calcium from blood to bone
What is the Axial Skeleton?
Skull
Vertebral Column
Rib Cage
What is the Appendicular Skeleton?
Upper and lower limbs
The Girdles attaching them to Axial Skeleton
