Uterine (menstrual) cycle,”Menstruation initiated whencorpus luteum degenerates- Other mammals have estrouscycles (uterine cycle withoutbleeding)- Proliferative phase • Endometrium becomesthicker and morevascularized- Secretory phase • Glands develop that secretenutritive substances tosustain embryo for first 2weeks- If embryo does not implant,lining shed- If embryo does implant
pregnancy begins”