Reproduction as we all know is the process by which animals (mammals and non-mammals)/plants give birth to their young ones. This process of giving birth to their new babies is categorized into two processes of which one of the processes is sexual reproduction.
In sexual reproduction sperm and ova( gamete), germ cells are formed in the gonads (testes and ovaries) by a process called reduction division or meiosis.
In this type of cell division, the number of chromosomes in the human cell (46) is halved (23), such that each
sperm and ova receives (23)chromosomes
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(Diagram for meiosis)
The fusion of sperm cell and egg cell in the act of fertilization brings about the retrieval of chromosomes to their original number (46) in the zygote (fertilized eggs). The process by which the zygote grows into an adult member of the next generation occurs by the means of mitotic cell division.
When the individual reaches puberty, meiosis forms mature sperm or ova within the gonads such that the life cycle can be continued.
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Diagram of mitosis division
Experimental embryology and modern genetics make it known that in most species of mammals the multiple differences between the male and the female depend primarily on a single chromosome (the y chromosome) and a single pair of endocrine structures.
Diagram for endocrine structure
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The testes in the male and ovaries in the female. The differentiation of the primitive gonads into testes or ovaries in utero is generically determined in humans, but the formation of male genitalia depends upon the presence of a functional secreting testis; in the absence of testicular tissue, development is female.
There is evidence that male sexual behavior and in some species the male pattern of gonadotropin secretion are due to the action of male hormones on the Brain in early development. After birth, the gonads will be quiescent until adolescence when they will be activated by gonadotropins from the anterior pituitary.
The hormones that are separated by the gonads by this time causes the presence of features especially the adult male or female,
And the onset of the sexual cycle in the female.
In the human female, there are regresses in ovarian after several years and menopause while in males, in Gonadal, there is a slow decline in function as it advances and the capacity to father children persists.
Together, in both sexes, gonads have a dual function that is; production of gametogenesis (germ cells) and the sex hormones secretion. Androgens are the steroid sex hormones that are masculinizing in their action and estrogens are the feminizing sex hormones.
The two hormones are secreted in both sexes. As testes secrete a large number of androgens(testosterone), they also secrete little amount of estrogens.
The ovaries secrete estrogen in large amounts and androgens in a small amount.
In both sexes, androgens are secreted from the adrenal cortex. And some of these Androgens are changed to estrogens in fat and other extra-adrenal and extragonadal tissues.
Diagram for estrogens and androgens
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Secretion of progesterone is also done by the ovaries and progesterone is a steroid that performs a specific function in preparing the uterus for pregnancy.
Partly, during pregnancy the ovaries secrete the polypeptide hormone relaxin, this tends to loosen the ligaments of the public symphysis and softens the cervix, easing delivery of the fetus.
Gonads secrete other polypeptides including inhibiting polypeptide that restrains FSH secretion in both sexes.
Reference
•Collins ON.N/Medical physiology/ISBN:978-8811-89-4