Lactation

1. Lactation

	A. Final Phase of the reproductive cycle of mammals
	B. Physiological state of mammary gland linked to reproductive
                  state of the animal
	C. Essential Phase of Farm Animal Reproduction

2. Anatomy of the Udder

	A. Teat--Cows, Sheep, Goats, Horses
	   Nipple--Pigs, Humans
	B. Streak Canal
	C. Teat Cistern
	D. Gland Cistern
	E. Milk Ducts & Ductules
	G. Lobes and Lobules
	 	a. Lobule: Contain up to 200 alveoli
	H. Alveoli
		a. Functional Unit 
		   --Where milk is synthesized and released
		b. Alveoli Cells
		   --Secretory epithelial cells
		c. Myoepithelial Cells
		   --Contract in response to Oxytocin
		   --Cause Milk letdown
		d. Capillaries
		   --Bring milk building blocks to 				Alveoli cells
		   --500 to 1000 volumes of blood to 				make one volume of milk.	
			
3. Species Differences

	A. Cattle
		a. 4 mammary glands (quarters)
		b. 4 teats (one per gland)
		c. 1 streak canal per teat
	B. Sheep & Goats
		a. 2 mammary glands
		b. 2 teats
		c. 1 streak canal per teat
	C. Horses
		a. 4 mammary glands
		b. 2 teats
		c. 2 streak canals per teat
	D. Pigs
		a. 4-9 pairs of mammary glands
		b. 8-18 nipples
		c. 2 streak canals per nipple 
		   --drain sectors (simple glands)
		d. 2 sectors per gland
	E. Humans
		a. 2 mammary glands
		b. 2 nipples
		c. 10-20 streak canals per nipple
		d. 10-20 sectors (simple glands)

4. Mammary Growth (Mammogenesis)

	A. Embryonic and Fetal Period
		a. Ectodermal
		b. Milk lines (band, streak, line, crest, hillock)
		   --Divide into nodules
		c. Mammary Buds
		   --Lenticular
		   --Spherical 
		   --Conical
		d. Primary Mammary Cord or Sprout
		   --Sprouts from apex of cone
		   --Becomes Gland & Teat Cisterns
		   --In species with two streak canals 				have two Cords per Bud
		e. Secondary & Tertiary Cords 
		   --Develop into ducts
	
	B. Postnatal Mammary Growth

		a. Before Pregnancy
		   --Puberty
		   --Estrus effect
		b. During Pregnancy
		   --Further duct development
		   --New Alveoli appear later
		   --Hypertrophy

	C. Endocrine Control of Mammary Growth

		a. Gland Ablation Studies (Rodents)
		   --To get full mammary development
			i.   Estrogen
			ii.  Progesterone
			iii. Somatotropin
			iv.  Prolactin
			v.   ACTH (Adrenocorticotropic Hormone)
				--Stimulates Glucocorticoids

		b. Ruminants
			i. Placental Lactogen
			   --May be primary player
			   --has ST & PRL-like effects

		c. Sex Steroid Hormones
			i.  Estrogen
                        	--Involved in lengthening 
					and branching of ducts
                	ii. Progesterone
                        	--Duct and ductule cell multiplication
                                --Enlargement and/or widening
                        	--Actually inhibits mammary growth 
                                	at high levels
                	iii.Progesterone + Estrogen 
				--Causes lobuloalveolar development
                        	--Occurs eventually if animal doesn't 
					become pregnant
                                		
		d. Artificial Induction of Mammary Growth
			i.   Estrogen + Progesterone
			ii.  Never get lactation like natural
			iii. High incidence of ovarian cysts

5. Initiation of Lactation (Lactogenesis)

	A. Hormonal
		a. Ovarian steroids fall (Progesterone inhibits)
		b. Placental Lactogen disappears
		c. Lactogenic Complex
			i.	Prolactin
			ii.	Glucocorticoids
			iii.	Insulin or IGF-I


6. Milk-Ejection Reflex

	A. Up to half of milk secreted is stored in large 
	   ducts and cisterns
	   --Readily available
	B. Remainder need to be ejected
	C. Oxytocin/Neuroendocrine Reflex
		a. Suckling or other teat/udder stimulation
		   causes release of oxytocin from 
		   neurohypophysis	
		b. Oxytocin synthesized in hypothalamus
		c. Released from neurohypophysis or posterior
		   pituitary

7. Maintenance of Lactation (Galactopoesis)

	A. Physical
		a. Animal must be suckled or milked
	B. Hormonal (Galactopoetic Complex)
		a. Prolactin (Not Cattle)
		b. Somatotropin
		c. Insulin
		d. Thyroid Hormone
		e. Glucocorticoids

8. Regression of the Mammary Gland (Involution)

	A. Weaning or Drying-off
		a. Milk pressure on the alveolar cells cause cell death
		b. Alveoli collapse
		c. Alveoli and Lobes disappear
		   --apoptosis (programmed cell death)

	B. Senile involution
		a. Caused by lack of reproductive hormones