The document discusses the physiology of milk secretion in mammals. It describes the stages of lactation, including mammogenesis, lactogenesis, galactopoiesis, and involution. The key hormones involved in milk production are prolactin and oxytocin. Prolactin stimulates mammary gland growth and milk production, while oxytocin causes the letdown reflex and expulsion of milk from the alveoli. Breast milk contains proteins, carbohydrates, fats, vitamins, minerals, enzymes, hormones, and anti-infective agents that meet the nutritional and immunological needs of infants.