EXAM 3 TAMU COHN

What is compact/cortical bone

The dense, outermost layer of all bones

It looks solid at the gross (visible) level

What is the significance of compact/cortical bone not just for long bones, but all bones?

it forms the dense, outermost layer of every bone, not just long bones.

What is the periosteum?

The outer covering of bone

what is its structure of the periosteum?

A connective tissue covering on the outside of bone

What is the physiological significance of the periosteum

Attachment: ligaments and tendons attach here (anchored by Sharpey’s fibers)

Blood supply: blood vessels enter the bone through it

Bone growth: contains osteoblasts and enables appositional growth (widening)

Pain: highly innervated—this is where bone injuries hurt

Describe/define all other components of diaphyseal compact bone mentioned & structure on the last slide of lecture outline 6: Osteon

cylindrical unit that runs parallel to the length of the bone (diaphysis)

basic structural unit

Describe/define all other components of diaphyseal compact bone mentioned & structure on the last slide of lecture outline 6: Central (Haversian) Canal

middle hole in each osteon

Contains: artery, vein, nerve

Describe/define all other components of diaphyseal compact bone mentioned & structure on the last slide of lecture outline 6: Concentric Lamellae

rings of bone around the central canal (like tree rings)

Describe/define all other components of diaphyseal compact bone mentioned & structure on the last slide of lecture outline 6: Lacunae

small spaces between lamellae

Contains: osteocytes

Describe/define all other components of diaphyseal compact bone mentioned & structure on the last slide of lecture outline 6: Canaliculi

tiny channels connecting lacunae

Describe/define all other components of diaphyseal compact bone mentioned & structure on the last slide of lecture outline 6: Types of Lamellae (beyond concentric)

Concentric: inside osteons

Interstitial: between osteons

Circumferential: outermost layers around bone

Describe/define all other components of diaphyseal compact bone mentioned & structure on the last slide of lecture outline 6: Volkmann's (Perforating) Canals

horizontal canals

horizontal (connect osteons)

What is the function of the Osteon

main structural unit of compact bone

What is the function of the Central (Haversian) Canal

carries blood vessels and nerves longitudinally (up/down bone)

What is the function of the Concentric Lamellae

provide strength and organization to bone

What is the function of the Lacunae

house bone cells

What is the function of the Canaliculi

allow:

nutrient exchange

waste removal

cell communication

What is the function of the Types of Lamellae (beyond concentric)

reinforce bone at different structural levels

What is the function of the Volkmann's (Perforating) Canals

connect osteons and bring blood from periosteum

What is the anatomical relationship of the Osteon

made up of central canal + lamellae + lacunae + canaliculi

What is the anatomical relationship of the Central (Haversian) Canal

located at center of osteon, surrounded by concentric lamellae

vertical (within osteons)

What is the anatomical relationship of the Concentric Lamellae

arranged around the central canal within each osteon

What is the anatomical relationship of the Lacunae

positioned between lamellae and connected by canaliculi

What is the anatomical relationship of the Canaliculi

connect osteocytes in lacunae → form a communication network

What is the anatomical relationship of the Types of Lamellae (beyond concentric)

integrate multiple osteons into a solid outer layer

What is the anatomical relationship of the Volkmann's (Perforating) Canals

link central canals → create a grid system with Haversian canals

Know relevant synonymous, singular, and plural terms for these structures mentioned in class: compact bone

Compact bone (singular)

Compact bone (plural)

(cortical bone) — synonym

Know relevant synonymous, singular, and plural terms for these structures mentioned in class: spongy bone

(trabecular / cancellous bone) — synonym

Spongy bone (singular)

trabecula (singular)

Trabeculae (plural)

Know relevant synonymous, singular, and plural terms for these structures mentioned in class: lamella

Lamella (singular) / lamellae (plural)

Know relevant synonymous, singular, and plural terms for these structures mentioned in class: canaliculi

Canaliculus (singular)

canaliculi — plural

 Know relevant synonymous, singular, and plural terms for these structures mentioned in class: central canal / Haversian canal

central canal / Haversian canal (synonym)

central (Haversian) canal — singular

Haversian (central) canals — plural

Know relevant synonymous, singular, and plural terms for these structures mentioned in class: Volkmann's (perforating) canals

Volkmann's (perforating) canals (synonym)

Volkmann's (perforating) canals — plural

Volkmann's (perforating) canal (singular)

What are two other terms for spongy bone?

trabecular bone; cancellous bone

Does all bone contain spongy bone; If so, what is its position with respect to compact bone?

yes

It is positioned on the interior of the bone, situated deep to the dense outer layer of compact bone

What tissue discussed in class exists in between the trabeculae of spongy bone?

Red bone marrow — "interstitial spaces filled w/ marrow (red)"

What are the two other ways of synonymously referring to spongy bone?

trabecular bone; cancellous bone

What is the significance of spongy bone tissue?

"purpose: maximizes strength & resists compression"

"has hematopoietic tissue: produces RBCs, WBCs, platelets"

I can think of at least two functional attributes predicated on spongy bone structure, can you?

oriented along stress lines → maximizes strength & resists compression

interstitial spaces filled w/ red marrow → hematopoietic tissue (produces RBCs, WBCs, platelets)

Trabecula: structure

interconnecting rods (beams or struts)... made up of concentric lamellae, osteocytes in lacunae, canaliculi connect cells

Trabecula: organization

a complex, 3D lattice of interconnected rods and plates (spongy bone) that align along biomechanical stress lines to maximize strength and support while minimizing weight

Trabecula: the arrangement of its lamellae

concentric lamellae

Trabecula: its size and the different bone cell types present

~50–300 µm (much thinner than osteons)

Osteocytes, Osteoblasts, Osteoclasts

Trabecula: location

found inside: epiphyses, flat bone, inner layer of diaphyseal wall

Trabecula: presence/absence of endosteum

covered w/ endosteum (contains osteoblasts + osteoclasts)

Osteon: structure

cylindrical unit... runs parallel to length of bone

Osteon: organization

Center = Haversian (central) canal with blood vessels & nerves

Surrounded by concentric lamellae (rings of bone matrix)

Osteocytes sit in lacunae between lamellae

Canaliculi connect cells for nutrient/waste exchange

Bounded by a cement line

Osteon: the arrangement of its lamellae

"concentric lamellae: ring of bone around canal (like tree rings)"

Osteon: its size and the different bone cell types present

approximately 0.2 mm to 0.35 mm

Osteocytes, Osteoblasts, Osteoclasts

Osteon: location

compact bone "outermost layer of ALL bones"

Osteon: presence/absence of endosteum

Yes, endosteum is present within an osteon.

What is the endosteum?

a thin, vascular membrane of connective tissue that lines the inner surface of bone cavities, specifically the medullary (marrow) cavity and the trabeculae of spongy bone

where would the endosteum be located?

lines medullary cavity + trabeculae + central canals

What is its significance of the endosteum?

Lines internal bone surfaces

Covers trabeculae, medullary cavity, and central canals

Key site of bone remodeling

Contains osteoblasts (build bone) and osteoclasts (resorb bone)

Allows continuous bone turnover and repair

Important for growth & healing

Involved in bone development, fracture repair, and calcium regulation

Metabolic interface

Connects bone to bone marrow, supporting nutrient exchange

To the extent discussed in class, understand how osteoblasts and osteoclasts affect trabeculae structure.

Osteoblasts and osteoclasts are located on the outer surface of trabeculae (near the endosteum)

Osteoblasts “lay down new bone” and form new lamellae → thicken and strengthen trabeculae

Osteoclasts break down bone by removing lamellae → shrink or reshape trabeculae

Their actions are coordinated (construction + destruction) and called bone remodeling

This allows trabeculae to be dynamic structures that can change size and shape

Trabeculae can rearrange along stress lines to better support weight and mechanical demands

How do osteoblasts and osteoclasts cooperate by combining/coordinating their actions to maintain/enforce blood calcium homeostasis while also maintaining the structure of trabeculae?

Osteoblasts and osteoclasts act as a remodeling team, where:

Destruction (osteoclasts) + construction (osteoblasts) are harmonized

This allows bone (especially trabeculae) to be:

Structurally maintained and optimized

Responsive to the body’s calcium needs

Is this a specific example of bone remodeling?

specific example of bone remodeling, because it describes the coordinated action of osteoblasts and osteoclasts on trabeculae, where they “add an extra layer of lamella… but then they can also destroy an extra layer,” and the text explicitly states that “anytime you have this kind of cooperation… this is called bone remodeling.

Define bone remodeling in general.

the cooperation between osteoblasts and osteoclasts working together, where osteoblasts build new bone and osteoclasts destroy old bone in a “harmonized” process of construction and destruction, and “anytime you have this kind of cooperation… this is called bone remodeling.”

What are the participants in bone remodeling?

osteoblasts and osteoclasts, which work together in a coordinated way, described in the text as “builders and destroyers” that cooperate in the remodeling process.

Is there another example of bone remodeling we discussed? (Hint: Changes in the proximal epiphysis/metaphyses of the femur starting during the toddler stage).

when trabeculae rearrange themselves along stress lines in weight-bearing bones, where “these trabeculae can rearrange themselves… to increase their ability to bear weight,” and this rearrangement occurs through the cooperation of osteoblasts and osteoclasts, which is bone remodeling.

How is this spongy bone remodeling of these proximal epiphyses beneficial?

trabeculae can rearrange themselves “to increase their ability to bear weight,” allowing the bone to become stronger as the body grows heavier, and this coordinated action of osteoblasts and osteoclasts helps the bone “rise to the bar” and better support mechanical stress over time.

How is the spongy bone and compact bone proportioned in the epiphyses?

, the epiphyses (like other bone regions described) have a “sandwich-like structure” where there are “slabs of compact bone… on either side” and the inside is spongy bone (trabecular bone), meaning compact bone forms the outer layers while spongy bone makes up the interior.

For a long bone, what is the name of the defining structure that must still be present for the bone to still be classified as juvenile?

epiphyseal plate (growth plate)

Once defining structures that must still be present for the bone to still be classified as juvenile structures disappear, what exists in its place and what is it called?

replaced by bone tissue, forming a structure called the epiphyseal line.

In the most basic terms, what does the epiphyseal growth plate promote that can no longer be promoted in its absence?

promotes lengthwise growth of the bone, and once it is gone, the bone can no longer grow in length.

What is the medullary cavity?

a hollowed out region… a cavity that contains a soft tissue, some type of bone marrow,” located in the central portion (core) of the diaphysis, meaning it is a non-bony space in the center of a long bone that contains bone marrow

What types of bone marrow can be contained within the medullary cavity and what inhabits it fully in the very young?

The medullary cavity can contain red bone marrow or yellow bone marrow

In the very young, it is “completely filled with red bone marrow”

As one ages to over ~20 years of life, one type of marrow recedes in the medullary cavity

red bone marrow

Describe the function of these two types of marrow: the type of marrow recedes in the medullary cavity

what makes all blood cells, not just red blood cells, every blood cell, and every immune cell has its origin in the red bone marrow.

As one ages to over ~20 years of life, a type of marrow proliferates.

yellow bone marrow

Describe the function of these two types of marrow: the type of marrow proliferates

an energy reserve… adipose tissue” that stores fat rather than producing blood cells.

Relatively speaking, What is the proportion of compact bone to spongy bone in the diaphysis and where is the spongy bone located?

In the diaphysis, “almost all of the thickness and the volume… is compact bone”

The spongy bone is only in the very innermost layer of the diaphyseal wall (lining the medullary cavity)

Relatively speaking, What is the proportion of compact bone to spongy bone in the epiphyses and where is the spongy bone located with respect to the compact bone?

In the epiphyses, “the huge vast majority of the volume is actually spongy bone”

The compact bone is a very thin outer layer, meaning the spongy bone is located deep to (inside) the compact bone

Describe the histology of osteoprogenitor cells

They are very thin, elongated, and rectangular cells, described as looking like “sharpie marks… very thin with more length than width”

Describe the physiology of osteoprogenitor cells

They are stem (precursor) cells

They undergo mitosis, producing:

one new osteoprogenitor cell

one cell that becomes an osteoblast

Describe the histology of osteoblasts

Plumper, larger cells than osteoprogenitor cells

Align along the surface of bone, between the periosteum and bone surface

Describe the physiology of osteoblasts

Produce bone matrix (organic + inorganic)

Responsible for bone formation and remodeling

Can become osteocytes when surrounded by matrix

Describe the histology of osteoclasts

Described as large bone cells formed from fused monocytes (multiple nuclei)

Describe the physiology of osteoclasts

Break down (reabsorb) bone matrix

Release calcium

Function in bone remodeling

Describe the histology of osteocytes.

Located inside lacunae within bone matrix

Describe the physiology of osteocytes

Maintain bone matrix

Exchange nutrients via canaliculi

Where are osteoprogenitor cells found

Found in periosteum and endosteum (inner layers)

What actions do osteoprogenitor cells perform?

Stem/precursor cells

Undergo mitosis to become osteoblasts

Where are osteoblasts cells found

Found in periosteum and endosteum along bone surface

What actions do osteoblasts cells perform?

Produce bone matrix (collagen + calcium salts)

Responsible for bone formation and remodeling

Where are osteoclasts cells found

Found in periosteum and endosteum

What actions do osteoclasts cells perform?

Break down bone matrix

Release calcium

Participate in bone remodeling

Where are osteocytes cells found

Found inside lacunae within bone

What actions do osteocytes cells perform?

Maintain bone matrix

Exchange nutrients through canaliculi

Which of these cells is effectively a stem cell?

A. Osteocytes

B. osteoclasts

C. osteoprogenitor cells

D. osteoblasts

C. osteoprogenitor cells

Which is a bone destroyer?

A. Osteocytes

B. osteoclasts

C. osteoprogenitor cells

D. osteoblasts

B. osteoclasts

Which is a bone builder?

A. Osteocytes

B. osteoclasts

C. osteoprogenitor cells

D. osteoblasts

D. osteoblasts

How do these "bone building cells" osteoblasts work and what do they produce?

osteoblasts work by secreting bone matrix onto the surface of existing bone, and they produce both the organic matrix (mainly collagen and glycoproteins) and then contribute to the formation of the inorganic matrix (calcium salts), which together form new bone

Which of the 3 cells are effectively different life history stages of the same cell?

A. Osteocytes

B. osteoclasts

C. osteoprogenitor cells

D. osteoblasts

A, C, and D — osteoprogenitor cells → osteoblasts → osteocytes

These are different life history stages of the same cell lineage (stem cell → bone builder → mature maintenance cell).

Which cells participate in bone remodeling?

A. Osteocytes

B. osteoclasts

C. osteoprogenitor cells

D. osteoblasts

B and D — osteoclasts and osteoblasts

Which cells inhabit lacunae and which create a "Howship's lacuna"?

A. Osteocytes

B. osteoclasts

C. osteoprogenitor cells

D. osteoblasts

Osteocytes (A) inhabit lacunae, and osteoclasts (B) create a “Howship’s lacuna.”

How do osteoclasts work? (hint: what do osteoclasts produce that dissolves bone and how do osteoclasts produce a sealed microenvironment for this dissolution to take place?)

osteoclasts work by secreting substances that break down bone matrix, including acids and enzymes that dissolve the mineral and organic components of bone, and they do this by forming a sealed microenvironment against the bone surface, allowing them to concentrate these substances in a confined space and efficiently resorb the bone.

Describe the function of podosomes at the base of osteoclasts?

to anchor the osteoclast tightly to the bone surface, creating a sealed microenvironment that isolates the area underneath the cell so it can concentrate acids and enzymes to dissolve bone effectively.

Describe the significance of a ruffled border (microvilli) at the base of osteoclasts?

greatly increases the surface area of the cell in contact with bone, allowing the osteoclast to secrete more acids and enzymes into the sealed microenvironment and efficiently break down (resorb) bone.

Describe the process of transcytosis and the role of hydronium ion secretion in osteoclast physiology.

by secreting hydronium ions (acid) into the sealed microenvironment beneath the cell, which dissolves the mineral component of bone, along with enzymes that break down the organic matrix; the degraded materials are then taken into the osteoclast and transported across the cell by transcytosis, where they are released on the opposite side, allowing the cell to continuously remove bone while maintaining the resorption process.

Describe the process of transcytosis and the role of powerful hydrolytic enzyme secretion in osteoclast physiology.

by secreting powerful hydrolytic enzymes that digest the organic components of the bone matrix, and the resulting breakdown products are then taken into the osteoclast and transported across the cell by transcytosis, where they are released on the opposite side, allowing continuous bone resorption.