A&P @ LCC by Dr. Prince

Ch 6 Bone Tissue
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Objectives
  • Know selected key terms
  • Know the three types of cartilage and their locations in the adult skeleton
  • Explain how cartilage grows
  • List the different bone classes and provide examples of each
  • List functions of bones
  • Describe the gross anatomy of a typical long bone
  • Types and locations of bone marrow, cartilage and periosteum
  • Describe the different bone markings
  • Discuss the histology of compact and spongy bone
  • Explain intramembranous and endochondral ossification
  • Describe the process of longitudinal bone growth at the epiphyseal plates
  • List and describe the different types of cells involved in bone growth and remodeling
  • Explain the role of each hormone invloved in bone metabolism and Ca++ homeostasis

 

What are some of the functions of the skeletal system?
 
1.  Support it is a point of attachment for skeletal muscles and supports soft organs
2.  Protection as bones surround major organs
3.  Assists in movement - skeletal muscles attached to bones, provide leverage
4.  Mineral homeostasis - exchange of minerals between bone and blood
5.  Hemopoiesis - red bone marrow produces blood cels
6.  Energy storage - fat in yellow mone marrow
 
What is the difference between compact and spongy bone?
 
Compact bone is arranged in osteons;  concentric lamellae of matrix surrounding a central canal containing blood vessels and nerves, osteocytes in lacunae at edges of lamellae, communicating with central canal via canaliculi and interstitial lamellae between the osteons.  Spngy bone has no osteoons it is made of thin plates of bone called trabeculae and surrounded by spaces containing red bone marrow.  The ostocytes in lacunae get nutrients directly from blood in marrow in spongy bone.
 
How are calcium levels in the blood kept in homeostasis?
 
When calcium leves in the blood decrease (this is the stress) the change would be sended by the thyroid and parathyroid glands.  The thyroid would stop releasing calcitonin, this would stop the osteoblasts from depositing calcium into the bone, and the parathyroids would increase the release of PTH to promote bone resorption by osteoclasts as well as retention and absorption of calcium from kidneys and intestines.  The body does the reverse when calcium levels rise and so negative feedback loops are involved in calcium homeostasis.
 
How does bone grow in length?
 
First you need to understand Endochondral ossification.  During the initial stages of osteogenisis, osteoblasts move away from the primary ossification center in the diaphyses toward the epiphyses.  They invaid the spaces left by the osteoclasts in the medulary cavity.  The osteoblasts do not complete the ossification of the bone immediately because the cartilage of the epiphyses continues to grow.  Cartilage changes from "Resting" to "Proliferating" then to "Hypertrophic" and finaly to the "Calcified" cartilage.  These different stages in the life of cartilage give the different zones of the Epiphyseal plate.  It is the growth of the cartilage in the epiphyseal plate that results in longitudinal bone growth.  It is like two bikers one in front of the other.  As long as they are both going in the same direction and the same speed they can go for miles without colliding with each other.  In this case, the osteoblasts and the epiphysis are both "going away" from the promary center of ossification.  One will never catch the other and so growth would continue.  It is because of the secondary centers of ossification in the epiphysis that longitudinal bone growth stops.  This is like the bikers reaching the dead end of the road, one gets there first then the other and bone growth is over.
 
How does bone increase in diameter?
 
The diameter of a bone enlarges through apposistional growth at the outer surface.  While bone is being added to the outer surface, osteoclasts are removing bone matrix at the inner surface making the marrow cavity larger and larger as the bone increases in diameter.   Appositional bone growth is as follows:
1.  Cells of the inner layer of the periosteum differentiate into osteoblasts and add some mabone matrix to thesurface.
2.  These cells become surrounded by matrix and differentiate into osteocytes and thus lamellae are formed.
3.  As lamellae continue to grow they form osteons around the smaller vessels traping periostium on the inside.  The periostium continues to grow inward forming concentric rings of lamellae and a complete osteon.  This is how bone grows in thickness.
 

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Notes

Bone Tissue

BIOL 2401

LCC

Dr. F. Prince

Objectives chapter 6

The student will be able to describe the functions of the skeletal system.

The student will be able to identify the cell types found in bone and list their major functions.

The student will be able to compare the structure and function of compact and spongy bone.

The student will be able to compare intramembranous and endochondral ossification.

The student will be able to classify bones according to their shape and give examples of each type.

The student will be able to discuss the homeostatic mechanisms of the skeletal system.

Introduction

Bone or osseous tissue forms most of the skeleton

The skeleton is the framework that supports and protects our organs and allows us to move

Objective

The student will be able to describe the functions of the skeletal system.

Bone Physiology

Functions of Bone

Bones provide support of soft tissues and attachment sites for muscles

Protection to internal organs

Movement by providing leverage for muscle contraction

Mineral homeostasis of calcium and phosphorus

Blood cell production in red bone marrow

Storage of energy in yellow bone marrow

Bone Anatomy

Structurally the skeletal system contains four types of connective tissue

Cartilage

bone

bone marrow

periosteum

Bone Structure
Parts of a long bone

diaphysis

epiphyses

metaphysis

articular cartilage

periosteum

medullary cavity

endosteum

Objective

The student will be able to identify the cell types found in bone and list their major functions.

Histology

Bone tissue consists of widely separated cells surrounded by large amounts of matrix

Cell types in bone tissue

osteoprogenitor cells

osteoblasts

osteocytes

osteoclasts

Histology

Bone matrix contains abundant mineral salts primarily hydroxyapatite and some calcium carbonate

Salts are deposited in a framework of collagen fibers a process called calcification or mineralization

Salts confer hardness

Collagen fibers confer tensile strength

Objective

The student will be able to compare the structure and function of compact and spongy bone.

 

Histology Compact Bone

AKA as dense bone tissue consists of osteons or Haversian systems with little space between them

It lies over spongy bone and composes most of the bone tissue of the diaphysis

It protects, supports, and resists stress

Histology Spongy Bone

AKA cancellous bone and does not contain osteons.

It consists of trabeculae

It forms structure of short, flat, and irregular bones and the epiphyses of long bones

It stores red marrow and provides some support

Objective

The student will be able to compare intramembranous and endochondral ossification.

 

Ossification

Ossification or osteogenesis is the process of bone formation

begins when mesenchymal cells become transformed into osteoprogenitor cells that divide giving rise to cells that differentiate into osteoblasts

begins in the 6th or 7th week of life

Intramembranous Ossification

Occurs within fibrous membranes

ossification center forms from mesenchymal cells

the calcifying matrix centers join to form bridges of trabeculae that constitute spongy bone

The periosteum first forms a collar of spongy bone that is then replaced by compact bone

Endochondral Ossification

Bone Growth Length

The epiphyseal plate consists of four zones

Zone of resting cartilage

Zone of proliferating cartilage

Zone of hypertrophic cartilage

Zone of calcified cartilage

Length is increased by interstitial growth

Bone Growth Thickness

Growth is by interstitial and appositonal addition of new bone tissue by osteoblasts

Objective

The student will be able to classify bones according to their shape and give examples of each type.

Illustrative bone shapes - long, short, flat, sesamoid, irregular, sutural

Objective

The student will be able to discuss the homeostatic mechanisms of the skeletal system.

Bone Growth Hormonal Regulation

Before puberty

Human Growth Hormone (hGH)

Insulin like Growth Factor (IGF)

Thyroid hormone

Parathyroid hormone

Calcitonin

At puberty sex hormones stimulate sudden growth and modifications

PTH vs CT

PTH or parathyroid hormone is secreted by the parathyroid glands and it increases blood Ca++ levels

CT or calcitonin is secreted by te thyroid gland and decreases Ca++ levels

See summary of hormones related to homeostasis of bone tissue in your book, OK.

Illustration of the steps in repair of a bone fracture