BIOH111
o Cell Module
o Tissue Module
o Integumentary system
o Skeletal system
o Muscle system
o Nervous system
o Endocrine system
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TEXTBOOK AND
REQUIRED/RECOMMENDED READINGS
o Principles of anatomy and physiology. Tortora et al; 14th
edition: Chapter 6
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BIOH111 – SKELETAL SYSTEM MODULE
o Session 9 (Lectures 17 and 18) – Bone physiology:
Building of bone organ – cells, tissue, organ and
repair
o Session 10 (Lectures 19 and 20) - The Skeletal
System: Axial and Appendicular Skeleton, Joints
and Movement
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BIOH111
Lectures 17 and 18
Bone physiology: Building of bone organ –
cells, tissue, organ, development and repair
Department of Bioscience
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OBJECTIVES
Lecture 17:
 Bone cells and tissue


Name and describe bone cells and their function in building and function
of bone tissue
Describe structure and function of 2 bone tissue types – compact and
spongy
 Long bone as an example of bone organ

Describe structure and function of long bone sections
Lecture 18:
 Development and growth of bone tissue
 Describe process of intramemranous and endochondial ossification
 Describe process of growth (length and thickness)
 Identify steps in bone remodelling and fracture repair
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BONE FUNCTION
1. Support – structural framework for the body
2. Protection – protects internal organs from injury
3. Assistance in movement – muscles involved in movement
attached to the skeleton
4. Mineral homeostasis – major calcium and phosphorus
reservoir
5. Blood cell production – stem cells for production of WBCs
and RBCs (red bone marrow)
6. Triglyceride storage – adipose tissue; energy reserve
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BONE STRUCTURE
o Bone is made up of several different tissues:
bone, cartilage, dense connective tissue, epithelium, various blood
forming tissues, adipose tissue and nervous tissue
o 1 bone = 1 organ why is this?
o bones + cartilage +ligaments + tendons = skeletal system
o Bone constantly undergoes remodeling
o NOTE: ‘bone’ means both the tissue and the structural unit
of a skeleton
Building bones: cells → tissue → organ
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cells → tissue → organ
BONE CELLS
o Osteogenic cells – undifferentiated, stem cells
• can divide to replace themselves & can become
osteoblasts
• found in inner layer of bones
o Osteoblasts - form matrix & collagen fibers but can’t divide
o Osteocytes - mature cells that no longer secrete matrix and
the principle cells of bone matrix
o Osteoclasts - huge cells from fused monocytes (WBC)
• function in bone resorption
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CELLS OF
BONE
Osteoblasts
Osteocytes
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Osteoclasts
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cells → tissue → organ
BONE (OSSEOUS) TISSUE
o Type of connective tissue as seen by widely spaced bone
cells separated by matrix.
• Matrix - 25% water, 25% collagen fibers & 50% crystallized mineral
salts (hydroxyapatite and some calcium carbonate)
o Calcification or mineralization – process of mineral salts
deposition in a framework of collagen fibers
• Mineral salts confer hardness on bone while collagen fibers give
bone its great tensile strength
o Bone is not completely solid - small spaces for vessels and
red bone marrow
o 2 types: compact and spongy bone
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COMPACT BONE
Structure: solid, hard layer of bone; makes up the shaft of
long bones and the external layer of all bones
Function: resists stresses produced by weight and movement
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COMPACT BONE HISTOLOGY
o Arranged in units called osteons or Haversian systems.
• Osteons contain blood vessels, lymphatic vessels, nerves, osteocytes
and calcified matrix
o Osteons are aligned in the same direction along lines of stress.
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SPONGY BONE
Structure: light of bone; found only on the interior of the
bones; most of the structure of short, flat, and irregular bones
(e.g. ribs), and the ends of the long bones
Function: supports and protects the red bone marrow
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SPONGY BONE HISTOLOGY
o Arranged in trabeculae (latticework of thin plates of bone) that
surround many red marrow filled spaces
o Trabeculae are irregularly arranged.
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cells → tissue → organ
TYPES OF BONES
o 5 basic types of bones classified
by shape:
• Long - compact
• Short - spongy except surface
• Flat - plates of compact
enclosing spongy
• Irregular - variable
• Sesamoid - develop in tendons
or ligaments (patella)
o Sutural bones – classified by
location; in sutures (joints)
between skull bones
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cells → tissue → organ
LONG BONE STRUCTURE
o Diaphysis:
• “growing between”; shaft – long
cylindrical main portion of the bone
o Epiphyses:
• “growing over”; ends of the bone;
distal or proximal
Why the bold letters?
o Metaphyses:
• joins diaphysis and epiphyses;
• epiphyseal plate (<20yo; cartilage)
→ epiphyseal line (>20yo; bone)
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o Articular cartilage:
• hyaline cartilage covering the part of
epiphysis where the bone forms a joint;
reduces friction
o Medullary cavity:
• marrow cavity within the diaphysis;
contains bone marrow
o Endosteum:
• membrane that lines the medullary
cavity; single layer of bone forming
cells and connective tissue
o Periosteum:
• tough sheath of dense irregular
connective tissue that surrounds the
bone surface
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BLOOD SUPPLY OF BONE
o Periosteal arteries
• supply periosteum
o Nutrient arteries
• enter through nutrient foramen
• supplies compact bone of
diaphysis & red marrow
o Metaphyseal & epiphyseal
arteries
• supply red marrow & bone
tissue of epiphyses
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REVISION
Structure
Function
Diaphysis
Epiphyses
Metaphyses
Articular cartilage
Medullary cavity
Endosteum
Periosteum
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OBJECTIVES
Lecture 17:
 Bone cells and tissue


Name and describe bone cells and their function in building and function
of bone tissue
Describe structure and function of 2 bone tissue types – compact and
spongy
 Long bone as an example of bone organ

Describe structure and function of long bone sections
Lecture 18:
 Development and growth of bone tissue
 Describe process of intramemranous and endochondial ossification
 Describe process of growth (length and thickness)
 Identify steps in bone remodelling and fracture repair
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BONE FORMATION AND GROWTH
Bone formation is termed osteogenesis or ossification and
occurs in 4 situations: fetal bone formation, childhood bone growth,
bone remodeling and fracture repair.
o Two types of ossification occur:
1. Intramembranous ossification – bone forms directly from
or within fibrous connective tissue.
2. Endochondral ossification – bone forms from hyaline
cartilage.
o Two types of bone growth occur:
1. Growth in length
2. Growth in thickness
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INTRAMEMBRANOUS OSSIFICATION
Process used in spongy bone formation of the flat bones of the
skull and the mandible and fetal development.
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3A: HYALINE CARTILAGE - REVISION
o Most abundant (e.g. ends of bones), but weakest; found in
joints, the respiratory tract, and the immature skeleton
o Consists of fine collagen fibers embedded in a gel-type matrix
o Affords flexibility and support and at joints, reduces friction
and absorbs shock
o Bluish-shiny white rubbery substance
o No blood vessels or nerves so repair is very slow
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ENDOCHONDRAL OSSIFICATION
Process of replacing cartilage by bone to form most of the
bones of the body.
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GROWTH IN LENGTH
At birth only Articular cartilage and Epiphyseal plate have not
been converted to bone – sites of the bone growth in length.
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GROWTH IN LENGTH –
e.g. EPIPHYSEAL PLATE
o Growth stages:
• cartilage cells are
produced by mitosis on
Epiphysis side of the
plate
• cartilage cells are
destroyed and replaced
by bone on Diaphyseal
side of the plate
o Ages 18 to 25, Epiphyseal
plates close.
• cartilage cells stop
dividing and bone
replaces the cartilage
(Epiphyseal line)
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GROWTH IN LENGTH –
e.g. EPIPHYSEAL PLATE
End result: extension of bone length
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GROWTH IN THICKNESS –
e.g. PERIOSTEUM OF LONG BONE
Bone can grow in thickness or diameter only by
appositional growth.
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What ossification process do bones use for each of the growth phases?
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BONE REMODELING
Remodeling is the ongoing replacement of old bone tissue by
new bone tissue. 2 stages:
1. Bone deposition – construction of new bone by
osteoblasts (name a process you know about already that is
mediated by osteoblasts)
2. Bone resorption – destruction of old bone by
osteoclasts; osteoclasts form leak-proof seal around cell
edges and secrete enzymes (digest collagen) and acids
(dissolve minerals) beneath themselves and release
calcium and phosphorus into interstitial fluid through
process of endocytosis and exocytosis
Why is bone remodelling important?
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FRACTURE AND REPAIR OF BONE
o A fracture is any break in a
bone structure.
o Healing is faster in bone than in
cartilage due to lack of blood
vessels in cartilage.
o Healing of bone is still slow
process due to vessel damage.
o Clinical treatment: closed or
open reduction.
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REPAIR OF BONE FRACTURE
Step 1: Formation of fracture
haematoma
• damaged blood vessels
produce clot in 6-8
hours, bone cells die
• inflammation brings in
phagocytic cells for
clean-up duty
• new capillaries grow into
damaged area
Also see BIOS222/BIOC222
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REPAIR OF BONE FRACTURE
Step 2: Formation of
fibrocartilaginous callus
formation
• fibroblasts invade the
procallus & lay down
collagen fibers
• chondroblasts produce
fibrocartilage to span the
broken ends of the bone
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REPAIR OF BONE FRACTURE
Step 3: Formation of bony
callus
• osteoblasts secrete
spongy bone that joins
2 broken ends of bone
• lasts 3-4 months
Step 4: Bone remodeling
• compact bone replaces
the spongy bone in the
bony callus
• surface is remodeled
back to normal shape
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REGULATION OF BONE
PHYSIOLOGY
o Endocrine regulation – parathyroid hormone levels
regulate release of Ca2+ from stores (skeleton) into the
blood supply to be used by other systems (e.g. Ca2+
regulates nerve and muscle function and blood clothing)
– details of this regulation see BIOH111, session 22
o Exercise (mechanical stress) - within limits bone has the
ability to alter its strength in response to mechanical
stress by increasing deposition of mineral salts and
production of collagen fibers, making the bones stronger
Any other regulation? Think in groups of 2-3 within your own specialisations..
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REGULATION OF CALCIUM BLOOD
LEVELS
o Parathyroid hormone (PTH) is secreted if
Ca+2 levels falls
• PTH gene is turned on & more PTH is
secreted from PT gland
• osteoclast activity increased, kidney
retains Ca+2 and produces calcitriol
o Calcitonin hormone is secreted from
parafollicular cells in thyroid if Ca+2 blood
levels get too high
• inhibits osteoclast activity
• increases bone formation by
osteoblasts
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Clinical application:
DISORDERS OF BONE
OSSIFICATION
o Rickets
– calcium salts are not deposited properly
– bones of growing children are soft
– bowed legs, skull, rib cage, and pelvic deformities result
o Osteomalacia
– new adult bone produced during remodeling fails to
ossify
– hip fractures are common
Also see BIOS222/BIOC222
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SUMMARY AND REVISION
https://www.youtube.com/watch?v=0dV1Bwe2v6c
Regulation of osteoclast activity-cell signalling via RANK
https://www.youtube.com/watch?v=GpMV197xZXc
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For next class: Thinking within your own interests (e.g. nutrition)
think about and then write how you would apply the knowledge
you acquired in cell, tissue and skeletal modules within a
clinic/patient environment where a patient has presented with
osteoporosis. Clearly outline a problem and how it arises and
then how would you approach the problem if you were a
practitioner.
NOTE: this is NOT compulsory and not a right/wrong answer
exercise. It is here to make you think about biology in the scope
of your own interests. Please hand in the paragraph to the
lecturer at the start of the next session. You will receive feedback
on your knowledge of biology, your approach and your writing –
but NO MARKS.
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