Compact bone cross section: - each osteon has a ? - central canals are connected via?

- each osteon has a central canal - perforating canals connect central canal to central canal

Bone: Mace Slides 30-46 Flashcards by Sammy B

Compact Bone Tissue:

-is composed of ______?

osteons (Haversian systems)
Concentric lamellae
External circumferential lamellae
internal circumferential lamellae
Interstitial lamellae
Canaliculi

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Compact bone tissue:

Describe osteons

Small cylindrical structures
Basic functional and structural unit of mature compact bone
Oriented parallel to bone diaphysis

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Osteons have a central canal and _______ canals

perforating canals (Volkmann canals)

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Describe the central canal of osteons

Cylindrical channel
Lies at center of osteon and runs parallel to it
Houses blood vessels and nerves

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Describe perforating canals (Volkmann Canals)

house blood vessels and nerves
run **perpendicular to the central canals
help connect multiple central canals within different osteons

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Compact bone tissue:

-describe Concentric lamellae?

rings of matrix surround the central canal

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Compact bone tissue:

-describe external circumferential lamellae

rings of matrix run immediately internal to bone periosteum

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Compact bone tissue:

-describe internal circumferential lamellae

=rings of matrix run internal to the endosteum

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Compact bone tissue:

-describe interstitial lamellae

=rings of matrix between osteons

if there are 2 osteons (the space b/w them is where interstitial lamellae is

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Compact bone tissue:

-describe canaliculi= (list 4 functions)

-tiny interconnecting channels within bone connective tissue
extend from each lacuna, travel through lamellae
-connect to other lacunae and central canal
-house osteocyte projections permitting intercellular contact
-allow travel of nutrients, minerals, gases, and wastes between blood vessels and osteocytes

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“eyelashes”=

canaliculi

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Compact bone tissue: describe the cross section layout

central canal in the middle
around the central canal are the concentric lamellae
canaliculi inbweteen (around each lacuna (with osteocyte)

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Compact bone cross section:

each osteon has a ?
central canals are connected via?

each osteon has a central canal

- perforating canals connect central canal to central canal

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Compact bone (longitudinal section)

Central canals with osteons

- perforating calnals connecting central canals

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Spongy bone tissue:

do they have osteons?
describe this tissue

-No osteon
-Lattice of rods and plates called trabeculae
The space between trabeculae is filled with bone marrow
-form a meshwork of crisscrossing bars that provide great resistance to stresses

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Spongy bone tissue:

-trabeculae contains:

-parallel lamellae, canaliculi connect lacunae, no central canals, no perforating canals

Describe a cross-section of spongy bone tissue

endosteum on outside (with osteoclasts), also osteoblasts aligned along trabeculae of new bone
canaliculi opening at the surface
parallel lamellae(surrounds trabeculae) (=next layer)
Osteocyte in lacuna

Spongy bone:

-contains?

spicule
lacunas with osteocytes
Red bone marrow cavity
endosteum surrounds the red marrow cavity

Bone remodeling= is a continual process of bone _____ and _____

bone deposition and resorption

Describe bone remodeling

Occurs at periosteal and endosteal surfaces of a bone
Occurs at different rates
e. g., distal part of femur replace every 4 to 6 months
e. g., diaphysis of femur not completely replaced over a lifetime

Bone remodeling: about ____% of the adult skeleton is replaced yearly

20%

-Dependent on the coordinated activities of osteoblasts, osteocytes, and osteoclasts
-The relative activity of these cells is influenced by mechanical stress and the hormones the bones receive

Bone remodeling is dependent on 8 factors (list)

mechanical stress
growth hormone
thyroid hormone
calcitonin
parathyroid hormone
Sex hormones (estrogen and testosterone
Glucocorticoids
serotonin

Bone remodeling:

mechanical stress results from?
mech. stress is detected by?

Results from muscle contraction and gravitational forces (e.g., weight bearing exercise)
Detected by osteocytes and communicated to osteoblasts which increase synthesis of osteoid, followed by deposition of mineral salts.

Bone remodeling:

-growth hormone stimulates?

**Stimulates liver to produced another hormone, somatomedin, both stimulating growth of cartilage in epiphyseal plate,

Bone remodeling: | -thyroid hormone stimulates?

metabolic rate of osteoblasts

Bone remodeling: | -calcitonin stimulates?

calcium deposition in bone and inhibits osteoclast activity

Bone remodeling: - Parathyroid hormone causes? - PTH is stimulated to be released by low ____

* *cause bone loss (=bone resorption) by stimulating the osteoclast activity - low blood calcium levels

Bone remodeling: | -Sex hormones (estrogen and testosterone) stimulate?

osteoblast activity, stimulate growth of epiphyseal plate

Bone remodeling: | -Glucocorticoids cause?

Increase bone loss, impair growth at epiphyseal plate in children (kids that are highly stressed can impair their growth)

Bone remodeling: | -Serotonin inhibits?

Inhibits osteoprogenitor cells from differentiate into osteoblasts when there are chronically high levels

Bone formation: - begins with? - Proceeds with - Requires?

- Begins with secretion of osteoid - Proceeds with calcification, when hydroxyapatite crystals deposited-->calcium & phosphate ions precipitating out, forming crystals - Requires Vitamin D (active form=calcitriol) for enhancing calcium absorption from gGI tract - Requires vitamin C is needed for collagen formation - Requires calcium and phosphate for calcification

Bone Resorption (describe)

- Bone matrix destroyed by substances released from osteoclasts - Proteolytic enzymes released from lysosomes within osteoclasts - Calcium and phosphate dissolved by hydrochloric acid - May occur when blood calcium levels low

Vitamin D production: | -steps

slide 42

Ca 2+ Regulation (Vit D, PTH, negative feedback loop) | blood calcium regulation

1. UV light hits cholesterol in skin capillaries and converts it to Cholecalciferol (Inactive, Vit D3) 2. Vitamin D3 can also be taken in via the diet 3. Cholecalciferol goes into blood 4. At liver cholecalciferol is converted to calcidiol (inactive) and is released into the blood 5. At the kidney calcidiol is transformed to calcitriol (active form of Vitamin D) 6. Low blood Calcium stimulates the parathyroid gland to produce parathyroid hormone (PTH) 7. PTH is released into the blood 8. PTH amplifies the transformation of calcidiol to calcitriol at the Kidney. 9. Effectors of PTH and Calcitriol are synergistically stimulated a. Bone – osteoclast activity is increased releasing Ca++ from bone matrix b. Kidney – urine loss of Ca++ is reduced thus conserving blood Calcium 10. Calcitriol in the blood independently stimulates the small intestine to absorb more Ca++ into the blood from food. 11. Ca++ from the bone, small intestine absorption & kidney conservation of Ca++ results in increased blood Ca++ 12. Increased blood Ca++ returns the Ca++ concentration to normal/homeostasis 13. Normal blood Ca++ levels are sensed by receptors in the parathyroid gland (negative feedback mechanism) & PTH production/release is reduced.