ANS 331: Skeletal System

I.	Functions of the Skeleton

	1.	Support
		A.	Body Framework
	2.	Movement
		A.	Muscle attachment to skeleton
		B.	Movable Joints
	3.	Protection
		A.	Vital Organs
	4.	Mineral Reservoir
		A.	Storage of Calcium, Phosphorus, Sodium, Potassium
	5.	Hemopoiesis
		A.	Bone Marrow produces blood cells

II.	Classifications of the Skeleton

	1.	Axial Skeleton
		A.	Lie on the long axis or midline of body
			a.	Skull, Vertebrae, Ribs
	2.	Appendicular Skeleton
		A.	Bones of the front (pectoral) 
			and hind (pelvic) limbs
			a.	Arm and leg bones
			b.	Shoulder and pelvic bones

III.	Bone Shapes

	1.	Long Bones
		A.	Have long axis
		B.	Most bones of upper and lower limbs
	2.	Short Bones
		A.	Without long axis
		B.	Carpals, Tarsals
	3.	Flat Bones
		A.	Thin bones
		B.	Ribs, Skull
	4.	Irregular Bones
		A.	Vertebrae, patella
		
IV.	Structure of Bone

	1.	Gross Anatomy
		A.	Diaphysis--Bone Shaft
			a.	Metaphysis--Flared part of bone
			b.	Medullary cavity
				i.	Hollow part of bone 
				ii.	Contains bone marrow
				iii.	Lined by endosteum

		B.	Epiphysis--End of bone
		C.	Epiphyseal Plate (also called physis)
			a.	Separates Diaphysis and Epiphysis 
				in young animals
			b.	Permits increases in bone length
			c.	Made of hyaline cartilage
			d.	Cartilage replaced by bone in adults
				i.	Form epiphyseal lines
		D	Periosteum
			a.	Connective tissue covering of bone
			b.	Contain cells important in bone growth 
				and remodeling
				i.	Osteoblasts and osteoclasts
		E.	Articular cartilage
			a.	Lines end of epiphysis in movable bones
	2.	Inner bone
		A.	Compact components
			a.	Solid
		B.	Spongy components
			a.	Trabeculae (spicules) form sponge appearance
				i.	Mineralized tissue
			b.	Allow spaces in bone
				i.	Fill with marrow
			c.	Also make up scaffold to strengthen bone
				i.	Parallel to points of maximum stress
	3.	Microscopic Anatomy
		A.	Unit of structure
			a.	Haversian system or osteon
			b.	Run parallel to long axis of bone
		B.	Haversian canals 
			a.	Contain blood vessels (Capillaries)
			b.	Fed by blood vessels in Volkmann's canals
				i.	Perpendicular canals
			c.	Surrounded by lamellae
				i.	Concentric layers of bone
		C.	Lacunae
			a.	Spaces between lamellae
			b.	Embedded with Osteocytes (bone cells)
		D.	Canaliculi
			a	Interconnect by Lacunae
			b.	Filled with interstitial fluid 
				from capillaries in Haversian canal
				i.	Fluid moves by contraction 
					of osteocytes
	4.	Composition
		A.	Organic Framework
			a.	Collagenous fibers in ground substance
			b.	Produced by  bone cells
				i.	Osteoblasts
					--Very active in bone production
					--Involved in growth
				ii.	Osteocytes
					--Mature bone cell
					--Maintain bone matrix 
					--Synthesize and remodel
				iii.	Osteoclasts
					--Large and motile
					--Bone-resorbing cells
					--Multinucleated
			b.	Provide tensile strength
		B.	Inorganic Salts
			a.	Calcium and Phosphorus
			b.	Allow bone to withstand compression

	5.      Bone Formation
		A.	Embryonic connective tissue is transformed 
			by two methods
			a.	Intramembranous Ossification
				i.	Skull bones
				ii.	Formation of osteoblast 
					from mesoderm
				iii.	Osteoblasts form networks of bony 
					spicules around collagenous fibers
				iv.	Form Spongy bone
				v.	Osteoclasts reabsorb previously 
					laid-down bone to permit osteoblasts 
					to deposit new bone for growth
			b.	Endochondral Ossification
				i.	Most bones in body
				ii.	Formation of bone from hyaline 
					cartilage
				iii.	Perichondrium develops into 
					periosteum that contains osteoblasts
				iv.	Periosteum produces a collar of bone 
					that covers the surface of 
					the diaphysis
				v.	Cartilage matrix of diaphysis 
					calcifies
				vi.	Osteoblasts form spicules of bone 
					around calcified cartilage spicules
				vii.	Primary ossification center 
					in diaphysis
				viii.	Secondary ossification center 
					in epiphysis

	6.	Increase in Bone Length
		A.	Cartilage Cells
			a.	Undergo mitosis
			b.	Increase size of epiphyseal plate
		B.	Epiphyseal Plate
			a.	Diaphysis side undergoes calcification
			b.	Increase length of bone

	7.	Bone Remodeling
		A.	Growth involves a combination of formation 
			of new bone on the outer surface and resorption 
			of bone at the inner surfaces
			a.	Haversian systems are formed, resorbed, 
				and remodeled
		B.	Resorption and remodeling
			a.  	Osteoclasts resorb bone
			b.	Lead vascularization of new bone
			c.	Osteoblasts and osteocytes form new bone

	8.	Bone Repair

		A.	Fractures
			a.	Separation of bone parts
			b.	Consequences
				i.	Loss of alignment
				ii.	Separation of periosteum 
					and endosteum
				iii.	Torn blood vessels supplying bone
			c.	Clots form and lack of blood supply causes 
				local cell death (necrosis)
				i.	Osteocytes
				ii.	Periosteum
				iii.	Bone Marrow	
			d.	Inflammatory condition
				i.	Phagocytic cell clear clot 
					and dead tissues
			e.	Angiogenesis occurs
				i.	Introduction of new blood vessels
				ii.	New bone formation doesn't occur 
					until after angiogenesis
			f.	Callus formation
				i.	Composed of cartilage or spongy bone
				ii.	Form bridge and/or collar 
					around break
			g.	Bone is formed as described previously 
				described by chondrocytes, osteoblasts, 
				osteocytes, and osteoclasts.
				
	9.	Factors that affect bone development

		A.	Stress
			a.	Increase stress, increase strength of bone
			b.	Formation of additional collagen fibers 
				and inorganic salts
			c.	Salts withdrawn in absence of stress
			d.	Bone normally subjected to gravitational 
				and functional forces
		B.	Hormones
			a.	Parathyroid hormone
				--Bone reabsorption
			b.	Calcitonin
				--Bone formation
			c.	Growth Hormone
				--Bone Growth
			d.	Sex Steroids
				--Cause union of the epiphysis with 
					the diaphysis of long bones, 
					ceasing growth of long bones
			e.	Growth Factors
		C.	Nutrition
			a.	Well balanced diet
				  --Building blocks
			b.	Vitamin D
				--Calcium absorption by gut

V.	Joints and Synovial Fluid

	1.	Joints
		A.	Connections between bones
			a.	Bones are connected by ligaments
		B.	Study of joints=arthrology
		C.	Joint inflammation=arthritis
			a.	Common malady among humans and animals
		D.	Three Types of Joints
			a.	Fibrous
			b.	Cartilaginous
			c.	Synovial
		E.	Fibrous Joints
			a.	Also called Synarthroses
			b.	Immovable Joints
			c.	Examples
				i.	Sutures in skull 
				ii.	Union of Splint bone and Metacarpal/Metatarsals in horses
		F.	Cartilaginous Joints
			a.	Also called Amphiarthroses
			b.	Slightly movable
			c.	Examples
				i.	Intravertabral disks
				ii.	Pelvic Symphyses
		G.	Synovial joints
			a.	Joints that glide against each other
				--Freely movable
			b.	Components
				i.	Articular Cartilage
				ii.	Synovial Fluid
			c.	Enclosed by a joint capsule
				i.	Forms a meniscus for cushioning
			d.	Synovial Membrane
				i.	Secretes synovial fluid
				ii.	Surrounds joint capsule except at articular cartilage
				iii.	Vascular Connective tissue
				iv.	Contains synoviocytes
					1.	Produce synovial fluid
			e.	Functions of synovial fluid
				i.	Lubrication
				ii.	Nourishment of articular cartilage
			f.	Articular Cartilage
				i.	Made of Hyaline Cartilage
				ii.	Functions
					1.	Shock absorber
					2.	Bearing surface
					3.	Growth plate