Test 3 Anatomy Physiology

Skeletal system includes

1)Bones : calcified connective tissue, hard and rigid.

2)Cartilages:  flexible yet strong

3)Other Connective tissue  fibers

Bones

  1)Living bone cells : Osteoblast(matures to osteocytes),osteoclast

       2)organic intercellular matrix: 30 %-collagenous matrix provide tensile strength, secreted by osteoblasts & it gets calcified

       3)Inorganic salt:crystalline hydroxyapatite complex of calcium phosphate- 70 %salts

Organic matrix

90%collagen fibers, the remainder is ground substance

If the bone is treated by acid

Minerals dissolve, Collagen stays which is flexible & can be bent.

If incinerated by heat

Collagens broken, remaining inorganic salts are brittle.

Cartilage

Living cells (chondroblast and chondrocytes) and matrix they produce. Matrix contains mucopolysaccharides and bundles of fibers.

Tendons

Every Muscle is attached to Bone by Tendons.        

Ligaments

Across the joints, Bones connected to Bones

Skeletal system and Muscular system work closely

Muscular -skeletal system

Effects of heat and acid on base

• Bone matrix. Like reinforced concrete. Rebar is collagen fibers, cement is hydroxyapatite

• Organic: collagen and proteoglycans

• Inorganic: hydroxyapatite. CaPO₄ crystals

• If mineral removed, bone is too bendable

• If collagen removed, bone is too brittle

Functions of the skeletal system:

1)Support & protection: Supports and protects underlying organs by its tough bony framework(Brain by cranium, ribs, and vertebrae to thoracic and intraabdominal organs, spinal cord).

-For their weight, Bones are nearly as strong as steel.

2) Movements: Muscles are attached to the bones by tendons.

-When muscles contract, they pull on the bones and bones serve as levers that transmit muscular forces and thus help in movement.

-Ligaments allow some movement between bones but prevent excessive movement.

-Interaction of ribs, sternum, intercostal muscles, and diaphragm make breathing possible.

3)Storage of minerals:

-Bones store and release calcium & phosphate.

-When more calcium is in the blood, it is stored in the bone & when deficient in blood, the bone releases the calcium to maintain the calcium balance and is regulated by hormones                                                                                                       

4)Blood cell production

- Bone marrow within some bones at different stages of life produce

-BRC,  WBC(granulocytes) , platelets

In the embryo, the skeleton is composed of

Predominantly hyaline cartilage, but in adults, most of the cartilage is replaced by rigid bones except a few ones like the external ear, nasal bridge, larynx, trachea, part of ribs, and the joint in growing bones

Bone contains three types of cells

-Osteoblasts
-Osteocytes
-Osteoclasts

Osteoblasts

-Make new bone and help repair damage; secretes collagen proteins and a ground substance called chondroitin sulphate and hyaluronic acid, calcium, and phosphate from blood and deposited in bone and hardened
-immature bone cells that secrete matrix compounds (osteogenesis)

• Osteoid—matrix produced by osteoblasts, but not yet calcified to form bone

• Osteoblasts surrounded by bone become osteocytes

Osteocytes

-Carry nutrients and waste products to and from blood vessels in the bone
-Mature bone cells that maintain the bone matrix
-Live in lacunae
-Are between layers (lamellae) of matrix
-Connect by cytoplasmic extensions through canaliculi in lamellae
-Do not divide

• Functions
  -To maintain protein and mineral content of matrix

  -To help repair damaged bone

Osteoclasts

-Break down bone and help to shape it
-Dissolution of hydroxyapatite crystals and release of calcium and phosphate into blood
-Osteoclasts are very active in kids and teens, working on bone as it is remodeled during growth
-They play an important role in the repair of fractures
-Parathormone stimulates functions of osteoclasts
-Secrete acids and protein-digesting enzymes
-Giant, multinucleate cells
-Dissolve bone matrix and release stored minerals (osteolysis)
-Are derived from stem cells that produce macrophages

Parathormone

Stimulates functions of osteoclasts

Osteoporosis

-Loss of both collagen and calcium phosphate reduces bone mass and density
-This is more common in females after menopause suggesting that estrogen fall is a contributing factor
The most effective drug:
- Bisphosphonates kills osteoclasts
-Raloxifene stimulates estrogen receptors in bones

Bone building continues

Throughout life as a body constantly renews and reshapes the bones living tissue

Growth of bones: 3rd month of embryonic development

Ossification in long bones beginning

Growth of bones: 4th month

Primary ossification centers have appeared in the diaphyses of bone

Growth of bones: Birth to 5 years

Secondary ossification centers appear in the epiphyses

Growth of bones: 5 years to 12 years in females 5 to 14 years in males

Ossification is spreading rapidly from the ossification centers and various bones are becoming ossified.

Growth of bones: 17 to 20 years

Bone of upper limbs and scapulae becoming completely ossified

Growth of bones: 18 to 23 years

The bone of the lower limbs becomes completely ossified

Growth of bones: 23 to 25 years

Bone of the sternum, clavicles, and vertebrae become completely ossified

Growth of bones: By 25 years

Nearly all bones are completely ossified

There are three types of cartilage:

Hyaline
Fibrocartilage
Elastic

Consists of specialized cells that produce matrix

-Chondroblasts: form matrix
-Chondrocytes: surrounded by matrix; are lacunae

Matrix

Collagen fibers for strength, proteoglycans for resiliency

Perichondrium

-Doubled-layered C.T sheath covers cartilage except at articulations
-The inner more delicate has fewer fibers and contains chondroblasts
-Outer blood vessels and nerves penetrate no blood vessels in cartilage itself

Articular cartilage

Covers bones at joints and has no perichondrium
-growth

Appositional

New chondrocytes and new matrix at the periphery

Interstitial

Chondrocytes within the tissue divide and add more matrix between the cells

Bone development

Human bones grow until about age 25

Osteogenesis

Bone formation

Ossification

The process of replacing other tissues with bone and bones are formed

Two types of ossification

-Endochondral
-Intramembranous

Endochondral (also called intracartilaginous)

-Most of the bones in the skeleton, especially the long and short bones develop via endochondral ossification
-This type of ossification involves the replacement of a cartilaginous model by bone
-Ossifies bones that originate as hyaline cartilage
-Most bones originate as hyaline cartilage

Intramembranous

-The clavicle and most of the bones of the skull (flat bones) are formed by the intramembranous type.
-These bones form from non-cartilaginous connective tissue

Events of ossification

-Primary ossification center
-Bone collar
-Periosteal buds
-Secondary ossification centers

Primary ossification center

The first change indicative of beginning ossification takes place about the center of the future bone shaft. Here the cartilage cells hypertrophy and the cartilage matrix becomes calcified. Subsequently, part of the calcified matrix disintegrates, opening cavities that communicate with the connective tissue and vessels at the surface.

Bone collar

-The bone collar forms concurrently with the primary ossification center.                                                                    -Cells of the perichondrium begin to form bone. The bone collar holds together the shaft, which has been weakened by the disintegration of the cartilage. The connective tissue about the bone collar, previously a perichondrium, is now called periosteum.

Periosteal buds

These are connective tissue buds or "sprouts" containing mesenchymal cells (which give rise to osteogenic cells) and blood vessels, which grow from the periosteum to reach the primary ossification center. Osteoblasts attach to spicules of calcified cartilage in the primary ossification center and begin to produce osteoid. Thus, bone is formed and the process continues toward both epiphyses while this is occurring, the cartilage outside the primary ossification center increases in size by interstitial and appositional growth.

Secondary ossification centers

About the time of birth, a secondary ossification center appears in each end (epiphysis) of long bones. Periosteal buds carry mesenchyme and blood vessels in and the process is similar to that occurring in a primary ossification center. The cartilage between the primary and secondary ossification canters is called the epiphyseal plate, and it continues to form new cartilage, which is replaced by bone, a process that results in an increase in length of the bone. Growth continues until the individual is about 21 years old or until the cartilage in the plate is replaced by bone. The point of union of the primary and secondary ossification centers is called the epiphyseal line.

Intramembranous ossification

-The source of most of the flat bones, is so called because it takes place within condensations of mesenchymal tissue and not by replacement of pre-existing piece of hyaline cartilage as the case in endochondral ossification.
-The frontal and parietal bones of the skull, as well as parts of the temporal and occipital bones and the mandible and maxilla, are formed by intra-membranous ossification.
-This process also contributes to the growth of short bones and the thickening ( not the lengthening ) of long bones
when you are in your parent's tummy their calcium builds up your bones

Events that take place in intramembranous bone formation

-Increased vascularity of tissue

- Active proliferation of mesenchymal cells

-Osteoblasts begin to lay down osteoid. 

-Osteoblasts either retreat or become entrapped as osteocytes in the osteoid.

-The osteoid calcifies to form spicules of spongy bone

- Bone remodeling occurs 

Active proliferation of mesenchymal cells

The mesenchymal cells give rise to osteogenic cells, which develop into osteoblasts

Osteoblasts begin to lay down osteoid

Osteoid is the organic part of bone without the inorganic constituent.

The osteoid calcifies to form spicules of spongy bone

The spicules unite to form trabeculae.  The inorganic salts carried in by the blood vessels supposedly bring about calcification. The salts are deposited in an orderly fashion as fine crystals (hydroxyapatite crystals) intimately associated with the collagenous fibers. These crystals are only visible with the electron microscope.

Bone remodeling occurs 

Periosteum and compact bone are formed.

Calcification

The process of depositing calcium salts occurs during bone ossification and in other tissues

Steps of endochondral ossification: Step 1

-As the cartilage enlarges chondrocytes near the center of the shaft increase greatly in size
-The matrix is reduced to a series of small struts that soon begin to calcify
-The enlarged chondrocytes then die and disintegrate leaving cavities within the cartilage

Steps of endochondral ossification: Step 2

-Blood vessels grow around the edges of the cartilage and the cells of the perichondrium convert to osteoblasts
-The shaft of the cartilage then becomes ensheathed in a superficial layer of bone

Steps of endochondral ossification: Step 3

-Blood vessels penetrate the cartilage and invade the central region
-Fibroblasts migrating with the blood vessels differentiate into osteoblasts and begin producing spongy bone at a primary center of ossification
-Bone formation then spreads along the shaft towards both ends

Steps of endochondral ossification: Step 4

-Remodeling occurs as growth continues creating a medullary cavity
-The bone of the shaft becomes thicker, and the cartilage near each epiphysis is replaced by shafts of bone
-Further growth involves increases in length and diameter

Steps of endochondral ossification: Step 5

Capillaries and osteoblasts migrate into the epiphyses creating secondary ossification centers

Steps of endochondral ossification: Step 6

-Soon the epiphyses are filled with spongy bone
-An articular cartilage remains exposed to the joint cavity; over time it will be reduced to a thin superficial layer
-At each metaphysis, an epiphyseal cartilage separates the epiphysis from the diaphysis

Dermal ossification

This is also called intramembranous ossification
-It occurs in the dermis
-Produces dermal bones such as the mandible (lower jaw) and clavicle (collarbone)

Steps of intramembranous ossification: Step 1

-Mesenchymal cells aggregate, differentiate into osteoblasts, and begin the ossification process
-The bone expands as a series of spicules that spread into surrounding tissues

Steps of intramembranous ossification: Step 2

As the spicules interconnect, they trap blood vessels within the bone

Steps of intramembranous ossification: Step 3

-Overtime, the bone assumes the structure of spongy bone
-Areas of spongy bone may later be removed, creating medullary cavities
-Through remodeling spongy bone formed in this way can be converted to compact bone

Factors Affecting Bone Growth

• Size and shape of a bone determined genetically but can be modified and influenced by nutrition and hormones

• Nutrition

• Lack of calcium, protein and other nutrients during growth and development can cause bones to be small

• Vitamin D

• Necessary for absorption of calcium from intestines

• Can be eaten or manufactured in the body

• Rickets: lack of vitamin D during childhood

• Osteomalacia: lack of vitamin D during adulthood leading to softening of bones

• Vitamin C

• Necessary for collagen synthesis by osteoblasts

• Scurvy: deficiency of vitamin C

• Lack of vitamin C also causes wounds not to heal, teeth to fall out

• Hormones

• Growth hormone from anterior pituitary. Stimulates interstitial cartilage growth and appositional bone growth

• Thyroid hormone required for growth of all tissues

• Sex hormones such as estrogen and testosterone

• Cause growth at puberty, but also cause closure of the epiphyseal plates and the cessation of growth

Epiphyseal Lines

-When long bone stops growing, after puberty
-Epiphyseal cartilage disappears

-Is visible on X-rays as an epiphyseal line

Mature Bones

-As long bone matures
-Osteoclasts enlarge medullary (marrow) cavity
-Osteons form around blood vessels in compact bone

Bones are classified by

-Shape
-Internal tissue organization
-Bone markings (surface features; marks)

Depending on the shape and size

-Long bones-upper and lower limbs
-Short bones-carpals and tarsals
-Flat bones-Ribs, sternum, skull, scapulae
-Irregular bones- vertebrae facial
-Sesamoid bones- Are small and flat and develop inside tendons near joints of knees, hands, and feet

Depending on the texture

-Compact: dense and hard
-Spongy: Also called cancellous found within the epiphysis and inner wall of the diaphysis. Spaces within spongy bone us filled with bone marrow (red and yellow). Red marrow produces blood cells, yellow marrow contains fat cells that store fat

Diaphysis

-Shaft
-Compact bone

Epiphysis

-End of the bone
-Spongy bone

Epiphyseal plate

-Growth plate
-Hyaline cartilage; present until growth stops

Epiphyseal line

Bone stops growing in length

Medullary cavity

In children medullary cavity is red marrow, which gradually changes to yellow in limb bones and the skull (except for epiphyses of long bones).  The rest of the skeleton is red.

Bone (osseous) tissue

• Dense, supportive connective tissue

• Contains specialized cells

• Produces solid matrix of calcium salt deposits

• Around collagen fibers

• The Cells of Bone

  • Make up only 2% of bone mass

Osteoprogenitor cells

-Mesenchymal stem cells that divide to produce osteoblasts
-Are located in the endosteum, the inner, cellular layer of the periosteum
-Assist in fracture repair

Homeostasis in bone (osseous) tissue

-Bone building (by osteoblasts) and bone recycling (by osteoclasts) must balance
-More breakdown than building, bones become weak
-Exercise, particularly weight-bearing exercise, causes osteoblasts to build bone

The Structure of Compact Bone

-Osteon is the basic unit
-Osteocytes are arranged in concentric lamellae
-Around a central canal containing blood vessels

Perforating Canals:
-Perpendicular to the central canal
-Carry blood vessels into bone and marrow
-Compact bone is covered with a membrane

Circumferential Lamellae

-Lamellae wrapped around the long bone

-Bind osteons together

The Structure of Spongy Bone

-Does not have osteons

-The matrix forms an open network of trabeculae

-Trabeculae have no blood vessels

-The space between trabeculae is filled with red bone marrow:

• Which has blood vessels

  Forms red blood cells

  And supplies nutrients to osteocytes

  Yellow marrow

  In some bones, spongy bone holds yellow bone marrow

  Is yellow because it stores fat

Periosteum

-On the outside

-Covers all bones except parts enclosed in joint capsules

-Is made up of an outer, fibrous layer and an inner, cellular layer

• Functions of Periosteum
  -Isolates bone from surrounding tissues

  -Provides a route for circulatory and nervous supply

  -Participates in bone growth and repair

Perforating fibers

-Collagen fibers of the periosteum:
-Connect with collagen fibers in bone and with fibers of joint capsules;  attach tendons and ligaments

Endosteum

-On the inside
An incomplete cellular layer:
-Lines the medullary (marrow) cavity
-Covers trabeculae of spongy bone
-lines central canals
-contains osteoblasts, osteoprogenitor cells, and osteoclasts
-is active in bone growth and repair

Appositional growth

Compact bone thickens and strengthens long bone with layers of circumferential lamellae

Three major sets of blood vessels develop

-Nutrient artery and vein
-Metaphyseal vessels
-Periosteal vessels

Nutrient artery and vein

-A single pair of large blood vessels
-Enter the diaphysis through the nutrient foramen
-Femur has more than one pair

Metaphyseal vessels

-Supply the epiphyseal cartilage
-Where bone growth occurs

Periosteal vessels

Provide:

-Blood to superficial osteons
-Secondary ossification centers

Lymph and Nerves

-The periosteum also contains
-Networks of lymphatic vessels
-Sensory nerves

Process of Remodeling

• The adult skeleton

  -Maintains itself

  -Replaces mineral reserves

  -Recycles and renews bone matrix

  -Involves osteocytes, osteoblasts, and osteoclasts

• Bone continually remodels, recycles, and replaces

• Turnover rate varies

  -If deposition is greater than removal, bones get stronger

  -If removal is faster than replacement, bones get weaker

Effects of Exercise on Bone

-Mineral recycling allows bones to adapt to stress

-Heavily stressed bones become thicker and stronger

Bone Degeneration

-Bone degenerates quickly

-Up to one-third of bone mass can be lost in a few weeks of inactivity

Normal bone growth and maintenance require nutritional and hormonal factors

-A dietary source of calcium and phosphate salts

-Plus small amounts of magnesium, fluoride, iron, and manganese

• The hormone calcitriol
  -Is made in the kidneys

  -Helps absorb calcium and phosphorus from the digestive tract

  -Synthesis requires vitamin D₃ (cholecalciferol)

What is required for collagen synthesis and stimulation of osteoblast differentiation

Vitamin C

What stimulates osteoblast activity?

Vitamin A

What helps synthesize bone proteins?

Vitamin K and B12

What stimulates bone growth?

The growth hormone and thyroxine

What stimulates osteoblasts?

Estrogens and androgens

Calcitonin and parathyroid hormone

-Regulate calcium and phosphate levels
-Parathyroid Hormone- parathyroid glands

• Increases calcium ion levels by

  • Stimulating osteoclasts

  • Increasing intestinal absorption of calcium

  • Decreasing calcium excretion in kidneys

• Calcitonin - Secreted by parafollicular cells in thyroid

  • Decreases calcium ion levels by

    • Inhibiting osteoclast activity

    • Increasing calcium excretion in kidneys

The Skeleton as a Calcium Reserve

• Bones store calcium and other minerals

• Calcium is the most abundant mineral in the body

  • Calcium ions are vital to:

    • membranes

    • neurons

    • muscle cells, especially heart cells

    • Calcium ions in body fluids Must be closely regulated

• Homeostasis is maintained

  • By calcitonin and parathyroid hormone

  • Which control storage, absorption, and excretion

Calcitonin and parathyroid hormone control and affect

• Bones-Where calcium is stored

• Digestive tract-Where calcium is absorbed

• Kidneys-Where calcium is excreted