ANS 331: Growth and Development

I.	Growth and Development

	1.	Growth

		A.	An increase in body weight until mature size is reached

		B.	Increase in cell size and cell numbers with protein deposition

		C.	Usually an increase in structural tissues and organs

		D.	Structural Tissues

			a.	Bone

			b.	Muscle

			c.	Other Connective Tissues (Fat, tendons, etc.)

	2.	Development

		A.	Directive coordination of all diverse processes until maturity 
			is reached

			a.	Growth

			b.	Cellular Differentiation

			c.	Changes in body shape and form

II.	Prenatal Growth and Development

	1.	Tissues arise from three embryonic cell layers

		A.	Endoderm

			--Digestive tract, Lungs, and Bladder

		B.	Mesoderm

			--Skeleton, Skeletal muscle, and Connective tissues

		C.	Ectoderm

			--Skin, Hair, Brain, Spinal Cord

	2.	The nucleus directs the growth and development process by gene expression

		A.	Transcription

			a.	DNA to mRNA

		B.	Translation

			a.	mRNA to Protein

	3.	Order of tissue growth follows a sequential trend determined 
		by physiological importance

		A.	Central Nervous System

		B.	Bones

		C.	Tendons

		D.	Muscles

		E.	Intermuscular Fat

		F.	Subcutaneous Fat

III.	Muscle Growth and Development

	1.	Embryonic Skeletal Muscle Development

		A.	Develop from embryonic masses of mesoderm called somites

			a.	Myotome
				--Portion of somite that differentiates into muscle cells

			b.	Located dorsally along axial skeleton

			c.	Spread between skin and body cavity on left and right sides

			d.	Doesn't include muscles of head and limbs

		B.	Head muscles

			a.	Develop from mesoderm of that region

		C.	Limbs

			a.	Develop from mesoderm that migrates to limb buds

		D.	Myoblasts

			a.	Precursors to muscle cells

			b.	Fibroblast-like

			c.	Fuse to form multi-nucleated muscle fibers

			d.	Myoblast fusion is how cells grow in length

		E.	Fibroblast Growth Factor (FGF)

			a.	Controls Myoblasts

			b.	Stimulate proliferation and inhibit fusion

			c.	Removal stimulates fusion and differentiation

        2.	Prenatal Muscle Growth

		A. 	Hyperplasia

                	a.   	Increase in number of fibers

	             	b. 	First 2 trimesters

		B.	Hypertrophy

                    	a. 	Increase in size of fibers

	     		b.	Last trimester

	3.	Postnatal Muscle Growth and Development

		A.	Total number of fibers (Muscle cells) are obtained prenatally

		B.	Increases in length

			a.	Myoblasts added to ends of multinucleated fibers

		C.	Increase in size of fibers

			a.	Increase in size and number of myofibrils

			b.	Due to Protein synthesis (Gene Expression)

		D.	Muscle Repair

			a.	Dormant myoblasts called satellite cells

			b.	Stimulated by FGF

IV.	Connective Tissue Growth and Development

	1.	Fibroblasts

		A.	Precursor to Connective tissue cells

			a.	Osteocytes (-blasts)

			b.	Adipocytes

			c.	Smooth Muscle cells

			e.	Chondrocytes

		B.	Secrete components of connective tissue

			a.	Fibers

				i.	Collagen Fibers

				ii.	Elastic Fibers

				iii.	Reticular Fibers

			b.	Ground Substance

				i.	Fluid to Gel to Solid

		C.	Stimulated by a number of growth factors

	2.	Adipocytes (Fat Cells)

		A.	Store Fat

			a.	Energy Reserve

		B.	Differentiation

			a.	Lipogenic Enzyme Production (Gene Expression)

			b.	Accumulation of fat droplets

			c.	Coalescence of fat droplets into one large droplet

		C.	Hormonal Control

			a.	Growth hormone

				--Stimulates Differentiation

			b.	Insulin-like Growth Factor (IGF)

				--Stimulates Proliferation

			c.	Insulin

				--Stimulates lipogenesis

			d.	Glucagon

				--Stimulate lipolysis	

	3.	Postnatal Fat Deposition

		A.	Four major deposits of fat

			a.	Subcutaneous fat

				i.	Under the skin

				ii.	Backfat

			b.	Intermuscular fat

				i.	Between muscles

				ii.	Seam fat

			c.	Intramuscular fat

				i.	Within muscles

				ii.	Marbling

			d.	Abdominal Fat

				i.	Mostly around kidneys and in pelvis

		B.	Order of fat deposition

			a.	Abdominal

			b.	Intermuscular

			c.	Subcutaneous

			d.	Intramuscular

 	4.	Growth and Development of Bone

		A.	Early Development of bone

			--Embryonic connective tissue is transformed by two methods

			a.	Intramembranous Ossification

				i.	Skull bones

				ii.	Formation of bone from mesoderm

			b.	Endochondral Ossification

				i.	Most bones in body

				ii.	Formation of bone from hyaline cartilage

		B.	Increase in Bone Length

			a.	Cartilage Cells

				i.	Undergo mitosis

				ii.	Increase size of epiphyseal plate

			b.	Epiphyseal Plate

				i.	Diaphysis side undergoes calcification

				ii.	Increase length of bone

		C.	Hormones that effect bone growth.

			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

V.	Growth Curves


	1.	Bone, muscle, and fat are the tissues of primary concern
		 in the livestock industry

	2.	Curves are sigmoidal in shape

	3.	Order of tissue maturity

		A.	Bone

		B.	Muscle

		C.	Fat

	4.	Factors effecting growth

		A.	Maturation rate

			a.	Late maturing grow more

		B.	Sex

			a.	Intact males heavier and leaner at a given age than 					castrates and females
				--Mature later

			b.	Castrates tend to be heavier and leaner than females
				--Mature slightly later

		C.	Nutrition

			a.	Good nutrition needed for proper growth and development

			b.	Excess Protein or energy feed increase fattening
				in the livestock industry

	2.	Curves are sigmoidal in shape

	3.	Order of tissue maturity

		A.	Bone

		B.	Muscle

		C.	Fat

	4.	Factors effecting growth

		A.	Maturation rate

			a.	Late maturing grow more

		B.	Sex

			a.	Intact males heavier and leaner at a given 
				age than castrates and females

				--Mature later

			b.	Castrates tend to be heavier and leaner 
				than females

				--Mature slightly later

		C.	Nutrition

			a.	Good nutrition needed for proper growth 
				and development

			b.	Excess Protein or energy feed 
				increase fattening