Answer to Question 1
1. The follicular phase is characterized by menstruation, the discharge of a bloody fluid from the uterus accompanied by a shedding of the endometrium. This cycle averages 4 to 5 days and is considered to be the first to the fifth days of the cycle.
2. The ovulatory phase is characterized by the stimulation of estrogen, the thickening and vascularization of the endometrium, along with the maturing of the ovarian follicle. This phase begins about the fifth day and ends at the time of rupture of the graafian follicle. This phase occurs about 14 days before the onset of menstruation.
3. The luteal or secretory phase follows ovulation. It lasts about 14 days, unless fertilization occurs, and ends just before a menstrual period. If the egg is not fertilized, the corpus luteum degenerates after 14 days, and a new menstrual cycle begins.
Answer to Question 2
1. The kidneys produce urine and help regulate body fluids.
2. The ureters transport urine from the kidneys to the bladder.
3. The urinary bladder serves as a reservoir for urine.
4. The urethra conveys urine to the outside of the body; in the male it conveys both urine and semen.
A parasite life cycle.
Serotonin and the Sleep–Waking Cycle
The cardiac cycle showing systole and diastole.
Life cycle of Obelia, a hydrazoan that has alternating medusa (left) and polyp generations
The cell cycle
The eukaryotic cell cycle.