Block 2: Skeletal System - Lecture 2.2 Flashcards
What are some characteristics of the Endosteum?
Location: inner most layer made up of reticular CT that covers compact bone and marrow
a. lines medullary cavity and spongy bone surface
Functions: contains osteogenic cells for growth and remodeling
How would you describe the blood supply of a bone?
Very Vascular; bloody tissue with vessels
Blood Vessel Locations:
a. periosteum to diaphysis through nutrient foramina
b. nutrient artery and vein to medullary cavity
c. metaphysis, epiphysis, and periosteum all have vessel entries
Why does it hurt to break a bone?
Sensory neurons run through the periosteum
a. enter cortex through nutrient foramen to endosteum, medullary cavity, and epiphysis
What is special about the medullary cavity in terms of signaling?
The medullary cavity is able to take information both in and out of a bone
How would you describe osseous tissue?
VERY dynamic!
a. turnover 20% of skeleton per year
b. hormones affect bone density
Connects bone to muscle through supporting CT that contain:
a. specialized cells
b. extracellular protein fibers
c. ground substance/ecm
What are the types of cells in bone?
Osteogenic Cells
Osteoblasts
Osteocytes
Osteoclasts
How would you describe Osteogenic Cells?
“Bone Stem Cells”
Formed from mesenchyme (embryonic CT)
Differentiates into Osteoblasts
How do Osteogenic cells become Osteoblasts?
1 Osteogenic cell –> mitosis –> 2 Daughter Osteogenic cells
a. 1 cell stays as an Osteogenic cell
b. 1 cell differentiates into an Osteoblast
How would you describe an Osteoblast?
“Builders”
Transition stage of immature bone cells that make ECM
a. lots of proteins in the ECM
Initiate calcification
a. removes calcium from blood
b. deposits it into the matrix via exocytosis
How do Osteoblasts become Osteocytes?
Two pathways:
a. Apocytosis: programmed cell death
b. Transition to Osteocyte
How would you describe an Osteocyte?
“Maintenance Crew”
Mature bone cells that maintain matrix in response to bone density needs, and blood calcium and phosphate levels
Dendritic Processes: send signals to Osteoblasts and Osteoclasts, make connections, and have blood access
Strain Sensors: regulate remodeling in response to stimuli and mechanical stress
How would you describe Osteoclasts?
“Destroyers”
Formed from Blood Stem Cells
Has multiple nuclei!!
Resorption Bays:
a. pit in compact bone where osteoclasts dissolve matrix to remodel bond
b. secrete acid and proteolytic enzymes to dissolve matrix and proteins, which are absorbed into the blood
c. contain ruffled borders that increase surface area to allow for more absorption
What is the Osseous Matrix?
Everything in the space between Osteocytes
Contains organic (1/3) and inorganic (2/3) materials
How would you describe the Organic materials of the Osseous Matrix?
1/3 of the matrix’s weight
Produced and secreted by Osteoblasts
Primarily contains ground substance and collagen fibers
What are the substances and functions of Ground Substance?
Contains proteins
Glycosaminoglycans (GAGs)
a. trap water
b. glycoproteins: more protein + less carbohydrates, increase joint protection
c. proteoglycans: less protein + more carbohydrates
What are the substances and functions of Collagen Fibers?
Fibrous protein arranged in a helical form
Functions:
a. resistant to pulling forces
b. flexibility
c. framework for deposition of calcium crystals (inorganic)
What are Type I Collagen Fibers?
Most abundant collagen and protein in the body
Locations: bone and fibrous tissues
Polypeptide Formation:
a. glycine combines with other amino acids
Tropocollagen Formation:
a. three polypeptide strands coil together
What are the levels of organization of collagen in compact bone?
(Smallest unit to Largest unit)
1. Osteoblast
2. Tropocollagen
3. Microfibril
4. Fibril
5. Fiber
6. Lamella
7. Osteon
8. Cortical Bone
9. Bone
How would you describe the Inorganic materials of the Osseous Matrix?
2/3 of the matrix’s weight
Mostly calcium phosphate crystals that are crystallized around collagen fibers with help from Osteoblasts
Contents:
a. 85% Hydroxyapatites: mineral salts, calcium (collected by osteoblasts) phosphate salt
b. 10% Calcium Carbonate
c. 5% Other: Mg, Na, K, Fl, etc.
