A&P I Ch. 7 Bone Structure and Function Flashcards
Functions of Bones
- support
- protection
- movement
- mineral storage
-blood cell formation (hematopoiesis)
Compact Bone
dense or cortical bone and 80% of bone mass
Spongy Bone (cancellous or trabecular bone)
-located internal to compact bone
-appears porous
-20% of bone mass
Hyaline Cartilage
-attaches ribs to the sternum
-covers ends of some bones
-within growth plates
-model for bone formation
Fibrocartilage
-weight-bearing cartilage, withstands compression
-included in intervertebral discs, pubic symphysis, and menisci of knee
Ligaments v.s. Tendons
ligaments connect bone to bone and tendons connect muscle to bone
Osseous Tissue
normal bone proper, major structural and supportive connective tissue in the body
Bone Marrow
soft fatty tissue found in cavities of bones (includes red and yellow)
Red Bone Marrow (myeloid tissue)
-site of blood cell production hemopoietic
-immature blood cells and fat
-found in children
-located in spongy bone and medullary cavity of long bones
-in adults located in selective areas of the axial skeleton (cranium, head of humerus, ribs, vertebrae, ox coxae, sacrum, and coccyx)
Yellow Bone Marrow
-a product of red bone marrow degeneration as children mature
-fat storage
-can covert back to red bone marrow (during severe anemia: condition with reduced erythrocytes)
-facilitates the production of additional erythrocytes
What are the 5 general shape classifications of bone and their specifics?
-long (longer than wide)
-short (equally long and wide i.e. cube-shaped)
-flat (thin, broad, and commonly curved; sutural bones)
-sesamoid (small, flat, and oval-shaped, specialized bones found within tendons)
-irregular (bones that do not fit into any other category)
Epiphyseal Lines
Remnants of growth plate
Endosteum
Lines the inner surface of bone tissue
Medullary Cavity
inner cavity of the long bone
Periosteum
Outermost layer enveloping bone or tough sheath covering bone’s outer surface
-allows blood vessels to anchor to tissue
-contains an outer fibrous layer of dense irregular CT
Perforating Fibers
Collagen fibers; anchors
Compact Bone
-“seen in lab”
-dense or cortical bone
-80% of bone mass
Spongy Bone
-Canecellous or Trabecular
-located internal to compact bone
-appears pours
-20% of bone mass
What does the inner cellular layer of the periosteum contain?
-osteoprogenitor cells
-osteoblasts
-osteoclasts
How do bones have a blood supply?
-spongy bone allows them to be highly vascularized
-blood vessels enter from periosteum
-has a nutrient foramen
Nutrient Foramen
-small opening or hole in bone
-artery entrance and vein exit here
Nerves that supply bone
-mainly sensory nerves
-accompany blood vessels through nutrient foramen
-innervate (supply nerves to) bone, periosteum, endosteum, and marrow cavity
Why do bones have an outer fibrous layer of dense irregular CT?
-protects bone from surrounding structures
-anchors blood vessels and nerves to bone surface
-attachment site for ligaments and tendons
What 3 structures are included in the inner cellular layer of bone?
- osteoprogenitor cells
- osteoblasts
- osteoclasts
Microscopic Structure of Compact Bone
Osteons
Osteons
-small tightly-packed units in compact bone
-each containing a central canal for nerves and blood vessels
-connect to each other via perforating canals
What are Osteon Canaliculi?
- tiny interconnecting channels within bone CT
- appear black under microscope
What do osteon canaliculi do?
- connect adjacent lacunae containing osteocytes + secretions
- extend from each lacuna, travel and connect lacunae and the central canal
- house osteocyte cytoplasmic projections (allow intracellular contact and communication)
- allow the exchange of nutrients, minerals, gases (oxygen), and wastes between blood vessels and osteocytes
Two different types of bone
Spongy and Compact
How do osteons connect?
Perforating canal (connect individual osteons to blood vessels)
Osteoprogenitor Cells
- “resident” stem cells
- matures to become an osteoblast
- located in periosteum and endosteum
- their cellular division yields another stem cell and a “committed cell” (asymmetric)
- rationale
–replacement of old or injured bone cells
–release of Ca++ (homeostasis)
Osteoblasts
-“build bone”
-form from osteoprogenitor stem cells
-synthesize and secrete osteoid
-become entrapped within the matrix
-forms bone matrix
-differentiate into osteocytes
Osteoid
-precursor to bone tissue
-contains collagen
-initially semisolid organic form of bone matrix
-osteoid later calcifies
-contributes to bone flexibility
Osteocytes
-mature bone cells derived from osteoblasts
-lack bone-firming abilities
-maintain bone matrix
-detect stress on bone, signal osteoblasts, and trigger new bone formation
Osteoclasts
-large, multinuclear, phagocytic cells (engulf and digest)
-derived from fused bone marrow cells
-display a ruffled border, increases surface area exposed to bone
-located within or adjacent to a depression/ pit on bone surface
-involved in bone resorption
Pit on bone surface
-called a resorption lacuna (dying bone tissue)
Types of bone cells
Marrow Cells, Osteoblasts, Osteoclasts, and Osteocytes
Marrow Cells
-red marrow
-contains hematopoietic stem cells
-yellow marrow
What effect would the over-activity of osteoclasts have on the body?
bone loss, possibly leading to osteoporosis
Bone Formation
-begins with the secretion of osteoid
-calcification
Calcification (mineralization)
-occurs deposition of hydroxyapatite crystals
-calcium and phosphate ions precipitate out, form crystals
Process required for bone formation
-Vitamin D
-Vitamin C
-Calcium and Phosphate
Vitamin D
enhances calcium absorption from GI tract
Vitamin C
required for collagen formation
Calcium and Phosphate
for calcification
Ossification
-begins in the embryo
-continues through childhood and adolescence
-by 8-12th weeks of embryonic development
8-12th week of embryonic development
-skeleton begins forming
- from intramembranous ossification (minor portion of skeleton)
-endochondral ossification
bone growth
via intramembranous and endochondral ossification
Intramembranous Ossification
-bone cells come from mesenchyme stem cells that make many bones of the skull and part of the clavicle
Endochondral Ossification
-produces the majority of skeletal bones
-bone cells deposited in hyaline cartilage
-chondrocytes die and the area is calcified
Appositional Growth
-bones become thicker through the addition of bony tissue at the outer surface
-osteoblasts in the periosteum secrete additional bone matrix
-osteoblasts (build more osteons) differentiate into osteoclasts which break down bone on the inner surface to prevent bones from becoming too heavy
Bone Resorption
-bone matrix destroyed by substances released from osteoclasts
-proteolytic enzymes released from lysosomes (hydrolytic enzymes) within osteoclasts
-calcium and phosphate dissolved by hydrochloric acid
-freed calcium and phosphate ions enter the blood
-occurs when blood calcium levels are low
Proteolytic Enzymes released from lysosomes within osteoclasts
chemically digest organic matrix components
Growth Hormone
-produced by the anterior pituitary gland
-estrogen and testosterone have similar function during puberty
-directly stimulates growth of cartilage in the epiphyseal plate
Anterior Pituitary Gland
-produces growth hormone
-stimulates liver to produce insulin-like growth factor (IGF/ somatomedin)
IGF
-insulin-like growth factor
-directly stimulates growth of cartilage in the epiphyseal plate
Glucocorticoids
-released from adrenal cortex
-regulate blood glucose level
-high amounts increase bone loss
-impairs growth at epiphyseal plate in children
-must monitor if child is receiving high doses of glucocorticoids (ex. in asthma)
Serotonin
-neurotransmitter and hormone
- most bones with serotonin receptors
If levels are too high:
-osteoprogenitor cells are prevented from differentiating into osteoblasts
-no longer make cells responsible for making bone tissue
HIGH plasma calcium levels
-triggers the release of calcitonin (increase activity of osteoblasts) from the thyroid gland
-calcium salts deposited in the bone
LOW plasma calcium levels
-triggers the release of PTH from the parathyroid glands
-calcium is released from the bones by osteoclast activity and resorbed by the kidneys & intestine
Fractures
breaks in bone
Name the types of fractures
-Transverse Fracture
-Stress Fracture
-Oblique Fracture
-Greenstick Fracture
-Comminuted Fracture
-Pathologic Fracture
-Simple Fracture
-Compound Fracture
Transverse Fracture
horizontal break
Stress Fracture
thin break caused by increased physical activity vertical break
Oblique Fracture
diagonal clean break
Greenstick Fracture
from bone bending and cracking (alongside of bone)
Comminuted Fracture
broken in at least two places (multiple bone fracture shards)
Pathologic Fracture
occurs when a bone is weakened by disease (ex. osteoporosis)
Simple Fracture
-broken but not penetrating the skin
-2 to 3 months to heal
Compound Fracture
-one or both ends of the bone pierce overlying skin
-longer than 2-3 months to heal
Steps of Fracture Repair
1) Fracture Hematoma forms from clotted blood
2) Fibrocartilaginous (soft) Callus forms
3) Hard (bony) callus forms
4) Bone is remodeled
2nd Step of Fracture Repair
Fibrocartilaginous (soft) Callus forms by
-Fracture hematoma reorganized into a CT procallus
-Fibroblasts produce collagen fibers
-Procallus becomes fibrocartilaginous (soft) callus
3rd Step of Fracture Repair
Hard (bony) callus forms
-Osteoblasts adjacent to callus produce trabeculae
-Replaces callus
-Forms a hard (bony) callus
-Continues to grow and thicken
4th Step of Fracture Repair
Bone is remodeled
-Final phase of fracture repair
-Osteoclasts remove excess bony
-Compact bone replaces primary bone
-Usually leaves a slight thickening of bone
Causes of Osteoporosis
osteoclast activity outpacing osteoblast activity; associated with loss of estrogen
Symptoms of Osteoporosis
-stooped posture
-increased susceptibility to fractures
Diagnosis and treatment of Osteoporosis
Diagnosis: most common bone disease
-measurement of bone density
Treatment:
-administration of estrogen
-calcitonin
-balanced diet; active lifestyle
Osteitis Deformans
-symptoms: bone deformity and pain
-results from the disruption between osteoclast and osteoblast function
-characterized by excessive bone resorption followed by excess bone deposition
-larger osteoclasts resorb bone at a higher rate
-newly deposited bone poorly formed
-most commonly affects the pelvis, skull, vertebrae, femur, tibia
Rickets
-incidence increasing in urban U.S. children
-symptoms: bowlegged appearance, disturbances in growth, hypocalcemia, and tetany (cramps and twitches)
-disease caused by Vitamin D deficiency in childhood
-characterized by deficient calcification of osteoid tissue
-occurs in some developing nations
Achondroplasia
-a form of Short-limbed Dwarfism
-means to be “without cartilage formation”
-cause: mutations in the FGFR3 gene
-gene provides instruction for synthesizing a protein involved in the development and maintenance of bone
-deficiency in converting cartilage into bone
-failure of chondrocytes in epiphyseal plate to grow and enlarge
-autosomal dominant pattern
Acromegaly and Gigantism
-Hypersecretion of growth hormone and IGF- 1
-Disorder of disproportionate skeletal, tissue and organ growth
-Gigantism: AKA giantism, excess growth prior to the fusion of the epiphyseal growth plates
-Acromegaly: excessive growth after fusion
-Most common cause of hypersecretion: benign anterior pituitary tumour
Epiphysis
Top and bottom ends of long bones
Diaphysis
Shaft of long bones
Lacunae
-found in compact bone
-house bone cells
The periosteum contains an outer fibrous layer of dense irregular connective tissue what is it for?
-protects bone from surrounding structures
-anchors blood vessels and nerves to bone surface
-attachment site for ligaments and tendons
How is the periosteum attached to the bone?
numerous collagen fibers such as perforating fibers
Perforating Canals
connect osteons
