Chapter 5 - Physical Foundations - Bones

Steady-state flows require _ gradients

Linear

Electrical capacitance application

Homeostasis (as it relates to flow)

steady supply of nutrients and removal of wastes

Steady state

no change in temperature, charge, concentration, pressure with time doesn’t usually happen in the body

What drives fluid (including air) flow?

Pressure

Poiseuille’s law governs

steady-state laminar flow in long narrow tubes

Laminar flow

• Based on Reynold’s number

• Flow through body often approximated as laminar

Viscosity

resistance of shear forces

(its the weird n in the equation)

Law of LaPlace

The larger the vessel radius, the larger the wall tension required to withstand a given internal fluid pressure

• e.g: application trachea or food in esophagus

• e.g: blood vessels cylindrical

• e.g: bladder spherical

• sphereical equation greater bc end on hot dogs break first (the sphereical part)

Law of LaPlace Equation break down

Pressure = (2 x Thickness x Tension)/Radius

• Where

  • Pressure = The pressure inside the sphere

  • Thickness = Thickness of the sphere's wall

  • Tension = Tension within the sphere's wall

• At a constant pressure, the tension in a filled sphere can be decreased by increasing the thickness of the wall

• eg: calculating heart failure, wall thickness matters

Electrical forces between charged particles (when they repel vs attract)

Like charges repel, opposite charges attract

• force very dependent on distance

• in pic: q = charge, r = distance

Coulomb’s Law

• Separated charges in a vacuum experience a force on

  one another described by Coulomb’s law

  • Sign depends on the signs of point charges

  • If space is some medium, add dielectric constant, 

• important thing charge and distance

Electric potential

• work necessary to move charge

• Definition: Potential at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.

• Potential surrounding a negative charge is negative, can get energy out of by bringing a positive charge toward it

• Conclusion: A separation of charge produces an electric potential

capacitance

the ability of a system to store electrical charge

• dependent on area of plate and separation of plates

Biological membranes are essentially _

parallel plate capacitors

• hydrocarbon layer important to separate charges and create potential

current

when there’s a net movement of solute and the solute as charge to it

ion channels

• Have narrow, highly selective pores that can open and close

• significantly faster than carrier protein

  • 100 million ions/second can pass through one open channel, 105 times faster than the fastest carrier protein

• Cannot be coupled to an energy source, only ion diffusion down the concentration gradient

• Selective – permit some inorganic ions to pass, but not other; must shed associated water molecule

Selectivity filters

Protein structures in ion channels or aquaporins that allow only specific molecules through

are ion channels continuously open?

no

• gated

type of ion channel gates

• Voltage gated

• Mechanically gated

• Ligand gated: Open in response to binding of a ligand

Mechanically-gated ion channels important facts

• are also sensors for a number of other systems

  • Include touch, hearing and balance

• Example: Mechanotransduction

  • Ion channels (specifically Ca2+) that respond to changes in substrate stiffness

  • Important in cardiovascular regulation/pathogenesis

Membrane potential

Arises when there is a difference in the electrical charge on each side of the membrane

• Result from passive ion diffusion (animal cells)

• In animal cells, Na+ - K+ pumps keep intracellular [Na+] low

  • K+ balances the negatively charged molecules

    • K+ can move freely in or out of cell in K+ leak channels or is pumped in by Na+ - K+ pumps

• Membrane potential can be determined from the steepness of the K+ concentration gradient

what happens when no initial voltage gradient across the plasma

membrane (membrane potential = 0)

1. K+ is high inside of the cell and low outside of the cell

2. K+ will leave the cell through K+ leak channels, driven by concentration gradient

3. As K+ leaves, each ion leaves behind an unbalanced negative charge

4. A membrane potential is created

5. Efflux of K+ stops when the electrical driving force on K+ exactly balances the concentration gradient

6. Electrochemical gradient = 0

Resting membrane potential

equilibrium condition

• Resting potential of animal cells varies between -20 mV and 120 mV

• balance between chemical concentration force and electrical driving force

Use of Nernst equation

• Can be used to calculate the theoretical resting membrane potential if we know the ratio of internal and external ion concentrations

• The actual value is slightly off, cell is permeable to more than K+ and Cl

physiological significance of membrane potiental and ion movement

Skeletal sytem composed of

1. bones

2. cartilages

3. joints

4. ligaments

   • connect bone to bone

skeletal system _% of body mass

20

how many named bones in skeleton

206

Classification of bones (2 groups)

1. Axial skeleton

   • Long axis of body

   • Skull, vertebral column, rib cage

2. Appendicular skeleton

   • Bones of upper and lower limbs

   • Girdles attaching limbs to axial skeleton

The Axial Skeleton

• Consists of 80 bones

• Three major regions

  1. Skull

  2. Vertebral column

  3. Thoracic cage

Skeletal Cartilage

all types of skeletal cartilages contain _

• chondrocytes in lacunae and extracellular matrix

types of skeletal cartilage

1. hyaline cartilage

2. elastic cartilage

3. fibrocartilage

Hyaline cartilage

• Provides support, flexibility, and resilience

  • transfers of stresses

• Most abundant type

  • mainly found at articulated surfaces

• Articular, costal, respiratory, nasal cartilage

Elastic cartilage

• has high concentration of elastane

• Similar to hyaline cartilage, but contains elastic fibers

• External ear and epiglottis

  • much less than the amount of hyaline cartilage

Fibrocartilage

• Thick collagen fibers—has great tensile strength

• Menisci of knee; vertebral discs

  • weight barring areas

Growth of Cartilage

1. Appositional growth

2. Interstitial growth

• can become calcified

Appositional growth

• Cells secrete matrix against external face of existing cartilage

• building outward

Interstitial growth

• Chondrocytes divide and secrete new matrix, expanding cartilage from within - more to come

• growing from center

Calcification of cartilage

• Occurs during normal bone growth

• Hardens, but calcified cartilage is not bone

• not the same absorbance/dissipation of energy

Classification of Bones by Shape

1. Long bones

2. Short bones

3. Flat bones

4. Irregular bones

Long bones

• Longer than they are wide

• Limb, wrist, ankle bones

Short bones

• Cube-shaped bones (in wrist and ankle)

• sesamoid bones (within tendons, e.g., Patella)

• Vary in size and number in different individuals

Flat bones

• Thin, flat, slightly curved

• Sternum, scapulae, ribs, most skull bones

Irregular bones

• Complicated shapes

  • doesn’t fit into other catorgories

• Vertebrae, coxal bones

Functions of Bones

1. Support

2. Protection

3. Movement

4. Mineral and growth factor storage

5. Blood cell formation

6. Triglyceride (fat) storage

7. Hormone production

Bones provide support for _

body and soft organs

Bones provide protection for _

brain, spinal cord, and vital organs

Bones provide movement via _

Levers for muscle action

Mineral and growth factor storage function of bone

• Calcium and phosphorus, and growth factors reservoir

• mineral matrix storage

hematopoiesis takes place in_

red marrow cavities of certain bones

Triglyceride (fat) storage in bone cavities importance

• energy source

Hormone production in bones

• Osteocalcin

  • Regulates bone formation

  • Protects against obesity, glucose intolerance, diabetes mellitus

Bone textures (other way to classify)

1. Compact/Cortical

   • Dense outer layer; smooth and solid

2. Spongy/Trabecular

   • Honeycomb of flat pieces of bon

Structure of Short, Irregular, and Flat Bones

• Thin plates of spongy bone covered by compact bone

  • very very thin is flat bones

• Plates sandwiched between connective tissue membranes

  • Periosteum (outer layer) and endosteum

• No shaft or epiphyses

  • different from long bones

• Bone marrow throughout spongy bone; no marrow cavity

• Hyaline cartilage covers articular surfaces

Structure of typical long bones

1. Diaphysis

   • long shaft section

2. Epiphyses

   • two ends

Diaphysis

• part of long bone

• Tubular shaft forms long axis

• Compact bone surrounding medullary cavity

Epiphyses

• part of long bone

• Bone ends

• External compact bone; internal spongy bone

• Articular cartilage covers articular surfaces

• Between is epiphyseal line

  • Remnant of childhood bone growth at epiphyseal plate

    • growth plate, calcifies when down growing

Red marrow

• Found within trabecular cavities of spongy bone and diploë of flat bones (e.g., sternum)

• Adult long bones have little red marrow

  • found in ends of long bones

  • have tons when born but converts to yellow

• Heads of femur and humerus only

• Red marrow in diploë and some irregular bones is most active

• Yellow marrow can convert to red, if necessary

  • usually in diseased states

differences in Hematopoietic tissues in bones

• Red vs. Yellow marrow

• Main difference:

  • Red bone marrow produces red blood cells, white blood cells, and platelets (color from hemoglobin in red blood cells)

  • Yellow bone marrow produces fat cells, cartilage, and bones (color from fat cells)

  • Both have lots of blood vessels and capillaries

• At birth, all bone marrow is red

• In adults, red marrow is mainly in the flat bones and the proximal ends of the long bones

Major cell types of bone

1. Osteogenic cells

2. Osteoblasts

3. Osteocytes

4. Bone lining cells

5. Osteoclasts

Osteogenic Cells

• Also called osteoprogenitor cells

• Mitotically active stem cells in periosteum and endosteum

• When stimulated differentiate into osteoblasts or bone lining cells

• Some persist as osteogenic cells

• pic

  • pretty small

  • not doing much in tissue, but ready

Osteoblasts

• Bone-forming cells

• Secrete unmineralized bone matrix or osteoid

  • Includes collagen and calcium-binding proteins

    • Collagen = 90% of bone protein

• Osteogenic cells become osteoblasts

• pic

  • much larger than osteogenic cells

  • have lots of proteins

  • able to synthesize

Osteocytes

• Mature bone cells in lacunae

• Monitor and maintain bone matrix

• Act as stress or strain sensors

  • Respond to and communicate mechanical stimuli to osteoblasts and osteoclasts (cells that destroy bone) so bone remodeling can occur

  • lots of mechanically activated sensors

  • Wolf’s law, its there cell that sense the stress to tell osteoblasts to build more

• pics:

  • needs to sense and communicate hence the protrusions

Bone lining cells

• Flat cells on bone surfaces believed to help maintain matrix

• On external bone surface called periosteal cells

• Lining internal surfaces called endosteal cells

• Do not fulling understand, think they help with bone maintenance

Osteoclasts

• Derived from hematopoietic stem cells that become macrophages

  • not from bone percussors

  • relative of macrophage…phagocytosis

• Giant, multinucleate cells for bone resorption

• When active rest in resorption bay and have ruffled border

  • Not constantly active

  • Ruffled border increases surface area for enzyme degradation of bone and seals off area from surrounding matrix

Compact Bone - microscopic anatomy

• Also called lamellar bone

• Osteon or Haversian system

  • Structural unit of compact bone

  • Elongated cylinder parallel to long axis of bone (Diaphysis)

    • concentric

  • Hollow tubes of bone matrix called lamellae

    • Collagen fibers in adjacent rings run in different directions

      • Withstands stress – resist twisting

    • hollow center allows for integration and vascularization

Canaliculi Formation

• Osteoblasts secreting bone matrix maintain contact with each other and osteocytes via gap junctions

• When matrix hardens and cells are trapped the canaliculi form

  • Allows communication

  • Permit nutrients and wastes to be relayed from one osteocyte to another throughout osteon

Lamellae types

• Interstitial lamellae

• Circumferential lamellae

Interstitial lamellae

• Incomplete lamellae not part of complete osteon

• Fill gaps between forming osteons

• Remnants of osteons cut by bone remodeling

Circumferential lamellae

• Just deep to periosteum

• Superficial to endosteum

• Extend around entire surface of diaphysis

• Resist twisting of long bone

Microscopic Anatomy of Bone: Spongy Bone

• Appears poorly organized

• Trabeculae

  • Align along lines of stress to help resist it

  • No osteons

  • Contain irregularly arranged lamellae and osteocytes interconnected by canaliculi

  • Capillaries in endosteum supply nutrients