Functions of the Estrogens- Their Effects on the Primary and Secondary Female Sex Characteristics
A primary function of the estrogens is to cause cellular proliferation and growth of the tissues of the sex organs and other tissues related to reproduction.
Effect of Estrogens on the Uterus and External Female Sex Organs. During childhood, estrogens are secreted onlyin minute quantities, but at puberty, the quantity secreted in the female under the influence of the pituitary gonadotropic hormones increases 20-fold or more. At this time, the female sex organs change from those of a child to those of an adult. The ovaries, fal-lopian tubes, uterus, and vagina all increase several times in size. Also, the external genitalia enlarge, with deposition of fat in the mons pubis and labia majora and enlargement of the labia minora.
In addition, estrogens change the vaginal epithelium from a cuboidal into a stratified type, which is consid-erably more resistant to trauma and infection than is the prepubertal cuboidal cell epithelium. Vaginal infections in children can often be cured by the admin-istration of estrogens simply because of the resulting increased resistance of the vaginal epithelium.
During the first few years after puberty, the size of the uterus increases twofold to threefold, but more important than the increase in uterus size are the changes that take place in the uterine endometrium under the influence of estrogens. Estrogens cause marked proliferation of the endometrial stroma and greatly increased development of the endometrial glands, which will later aid in providing nutrition to the implanted ovum. These effects are discussed later in connection with the endometrial cycle.
Effect of Estrogens on the Fallopian Tubes. The estrogens’effect on the mucosal lining of the fallopian tubes is similar to that on the uterine endometrium.They causethe glandular tissues of this lining to proliferate; especially important, they cause the number of ciliated epithelial cells that line the fallopian tubes to increase. Also, activity of the cilia is considerably enhanced. These cilia always beat toward the uterus, which helps propel the fertilized ovum in that direction.
Effect of Estrogens on the Breasts. The primordial breastsof females and males are exactly alike. In fact, under the influence of appropriate hormones, the masculine breast during the first 2 decades of life can develop sufficiently to produce milk in the same manner as the female breast.
Estrogens cause (1) development of the stromal tissues of the breasts, (2) growth of an extensive ductile system, and (3) deposition of fat in the breasts. The lobules and alveoli of the breast develop to a slight extent under the influence of estrogens alone, but it is progesterone and prolactin that cause the ultimate determinative growth and function of these structures.
In summary, the estrogens initiate growth of the breasts and of the milk-producing apparatus. They are also responsible for the characteristic growth and external appearance of the mature female breast. However, they do not complete the job of converting the breasts into milk-producing organs.
Effect of Estrogens on the Skeleton. Estrogens inhibitosteoclastic activity in the bones and therefore stimu-late bone growth. At puberty, when the female enters her reproductive years, her growth in height becomes rapid for several years. However, estrogens have another potent effect on skeletal growth: They cause uniting of the epiphyses with the shafts of the long bones. This effect of estrogen in the female is much stronger than the similar effect of testosterone in the male. As a result, growth of the female usually ceases several years earlier than growth of the male. A female eunuch who is devoid of estrogen production usually grows several inches taller than a normal mature female because her epiphyses do not unite at the normal time.
OsteoporosisoftheBonesCausedbyEstrogen Deficiency in Old Age. After menopause, almost noestrogens are secreted by the ovaries. This estrogen deficiency leads to (1) increased osteoclastic activity in the bones, (2) decreased bone matrix, and (3) decreased deposition of bone calcium and phosphate. In some women, this effect is extremely severe, and the resulting condition is osteoporosis. Because this can greatly weaken the bones and lead to bone fracture, especially fracture of the vertebrae, a large share of postmenopausal women are treated prophylactically with estrogen replacement to prevent the osteoporotic effects.
Effect of Estrogens on Protein Deposition. Estrogens causea slight increase in total body protein, which is evi-denced by a slight positive nitrogen balance when estrogens are administered. This mainly results from the growth-promoting effect of estrogen on the sexual organs, the bones, and a few other tissues of the body. The enhanced protein deposition caused by testos-terone is much more general and many times as pow-erful as that caused by estrogens.
Effect of Estrogens on Body Metabolism and Fat Deposition.
Estrogens increase the whole-body metabolic rate slightly, but only about one third as much as the increase caused by the male sex hormone testosterone. They also cause deposition of increased quantities of fat in the subcutaneous tissues. As a result, the per-centage of body fat in the female body is considerably greater than that in the male body, which contains more protein. In addition to deposition of fat in the breasts and subcutaneous tissues, estrogens cause the deposition of fat in the buttocks and thighs, which is characteristic of the feminine figure.
Effect of Estrogens on Hair Distribution. Estrogens do notgreatly affect hair distribution. However, hair does develop in the pubic region and in the axillae after puberty. Androgens formed in increased quantities by the female adrenal glands after puberty are mainly responsible for this.
Effect of Estrogens on the Skin. Estrogens cause the skinto develop a texture that is soft and usually smooth, but even so, the skin of a woman is thicker than that of a child or a castrated female. Also, estrogens cause the skin to become more vascular; this is often associ-ated with increased warmth of the skin and also pro-motes greater bleeding of cut surfaces than is observed in men.
Effect of Estrogens on Electrolyte Balance. The chemicalsimilarity of estrogenic hormones to adrenocortical hormones has been pointed out. Estrogens, like aldos-terone and some other adrenocortical hormones, cause sodium and water retention by the kidney tubules.This effect of estrogens is normally slight and rarely of sig-nificance, but during pregnancy, the tremendous for-mation of estrogens by the placenta may contribute to body fluid retention.
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