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.	Starts during Embryonic and Fetal Period
	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. 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

5.	Initiation of Lactation (Lactogenesis)

	A.	Hormonal

		a.	Progesterone falls
			--Inhibits lactogenesis

		b.	Lactogenic Complex
			i.	Prolactin
			ii.	Glucocorticoids
			iii.	Insulin or IGF-I

		d.	Other hormones and growth factors also involved

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 posterior pituitary
		b.  Stimulates myoepithelial cells of alveoli.
	
7.	Maintenance of Lactation (Galactopoesis)

	A.	Physical
		a.	Animal must be suckled or milked

	B.	Hormonal (Galactopoetic Complex)
		a.	Prolactin (Not in cattle)
		b.	Somatotropin
		c.	Insulin
		d.	Thyroid Hormone
		e.	Glucocorticoids

7.	Regression of the Mammary Gland

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

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