The physiology or „system of life functions" [1] describes the processes in a human body on a molecular, cellular and organic level. It deals with the aspects of metabolism, growth, movement and recreation.

Differences between the sexes
The physical differences between man and woman aren't always striking. An obvious fact is that women can become pregnant, give birth to children and breastfeed them after birth. Men "only" provide the male gametes (sperm) for recreation. [3]

Additionally, there are some statistic differences: On average, women are 14cm smaller than men, [4] a man's brain has 11% more volume and the bone structure of pelvis and skull shows characteristic differences which is important for anthropologic reasons. [5]

Hormones
Basically, both sexes have the same sexual hormones, only that estrogen and progesterone predominate in women and testosterone in men.

Estrogens
Estrogens are the key term for estradiol, estrone and estriol while estradiol has the strongest effect. They are a modification of the molecule cholesterol and thus belong to the steroid hormones. In women, estrogens are mainly produced in the ovaries. [6] [7] [8]

During puberty, estrogens are responsible for the secondary sex characteristics such as the growth of breasts, pubic hair, maturation of uterus and vagina etc. In a monthly cycle, estrogens help in the maturation of the egg and ovulation as well as the circulation and growth of the endometrial lining of the uterus. [FEMALE CYCLE] During pregnancy the estrogen level in a female body is a lot higher, because the placenta produces additional estrogen. The high level of estrogen is an essential factor for the healthy development of the embryo.

Progesterone
Progesterone, also known as pregnancy hormone, is essential for maintaining pregnancy. Similar to estrogens, it's a derivate of cholesterol and is mainly produced during the second half of the cycle by the yellow body of the uterus. During pregnancy it's produced by the placenta. [10] [11] [12] [FEMALE CYCLE]

Progesterone regulates the rising body temperature during ovulation and prepares the endometrial lining of the uterus for a possible pregnancy. During pregnancy it's responsible for the developing mammary glands. Besides, the influence of progesterone causes a larger water deposit in the tissue. This is the reason for a gain in body weight before menstruation and during pregnancy. [10] [11] [12]

Testosterone
Testosterone plays a leading role in both sexes. It's one of the most important androgens and is made of cholesterol. In men, it's produced in the testicles and is essential for sexual maturity and the development of secondary sex characteristics such as beard and breast hair. In women, testosterone is produced in the ovaries and adrenal cortex. It's responsible for a gain in muscle mass, a higher burning of fat and bone density. [7] [13] [14] [15] Testosterone is also considered as hormone of creativity and female imagination. It's increasingly released in sportive and sexual activities and plays an important role for male and female pleasure. According to a current study, people with a higher testosterone level are more helpful than their colleagues. [7] [14] [16] [17]