Human Endocrine System

The reproductive cycle of the non primate females is called estrous cycle. The phase when the female is sexually receptive is called as estrus and the phase when the female is not sexually receptive is called as anestrus. When the pineal gland is exposed to light, there is release of the hormone melatonin. The hormone causes stimulation and repression of reproduction in different kind of breeders. This hormone regulated the activity and the release of GnRH (gonadotropin releasing hormone).

Prolactin is secreted by the anterior lobe of pituitary gland. After parturition, secretion and storage of milk in mammary glands is under the influence of this hormone.

Metamorphism is a hormonal effect influenced by hormones. The metamorphism in frogs is under the control of thyroxine which is produced by the thyroid gland. Frogs live in water bodies with rich iodine content to produce thyroxine.The deficiency in iodine would result in a retarded growth.

In frog growth and metamorphosis are controlled by hormones synthesized by endocrine glands near the front of the body. Neurosecretory cells in an insect's brain secrete a hormone, the prothoracicotropic hormone that activates prothoracic glands, which secrete a second hormone, usually ecdysone, that induces ecdysis. PTTH also stimulates the corpora allata, a retrocerebral organ, to produce a juvenile hormone, which prevents the development of adult characteristics during ecdysis.

Prorennin (the precursor to rennin) is produced by the zymogen (chief) cells of the gastric glands in the stomach.

The insulin mRNA is translated as a single chain precursor called preproinsulin, and removal of its signal peptide during insertion into the endoplasmic reticulum generates proinsulin. Insulin and free C peptide are packaged in the Golgi into secretory granules which accumulate in the cytoplasm.

Human insulin is the synthetic insulin which is grown in the laboratories. Human insulin is laboratory created by growing insulin proteins within E.coli bacteria (Escherichia coli). The newly constructed plasmids containing the transplanted genetic material are introduced into a benign E. coli bacterial strain. Once inside the bacteria, the genes are activated by the bacteria to form the protein chains found in insulin

Hormones are the biochemicals which target the cells/organs away from the site of their secretion. Enzymes are the biocatalysts which accelerate the bioreactions by lowering the activation energy of the reaction. Ethylene is a gaseous hormone which is involved in germination, growth, abscission, ripening and stress responses. Thus, option A is correct. 

Estrogens are produced primarily by the ovaries. They are released by the Graafian follicles on the ovaries and are also secreted by the corpus luteum after the egg has been released from the follicle and from the placenta. 

Estrogen is the female sex hormone which is secreted by developing follicles in the ovary. Secretion of gonadotropins during the follicular phase of ovarian cycle stimulate growth and development of follicles. These developing follicles secrete estrogen. Thus, the correct answer is option C.

There are two major female sex hormones: estrogen and progesterone. Both of these are steroid hormones. In women, most estradiol is released from the ovaries and adrenal glands. It is also released by the placenta during pregnancy.

The primary function of oestrogen is the development of the female body and secondary sexual characteristics. These include breasts, endometrium, regulation of the menstrual cycle etc. They are present in significantly higher amounts in women after menarche (onset of menstrual periods at puberty) until menopause (cessation of menstrual periods after completion of reproductive age). Hence, oestrogen is a feminizing hormone.

Oestrogens, in females, are produced primarily by the ovaries, and during pregnancy, the placenta. Follicle-stimulating hormone (FSH) stimulates the ovarian production of oestrogens by the granulosa cells of the ovarian follicles and corpora lutea. Synthesis of oestrogens starts in theca interna cells in the ovary, by the synthesis of androstenedione from cholesterol. 

Ovaries produce and release two groups of sex hormones progesterone and estrogen. 

Relaxin, HCG and placental lactogen are protein hormones having amino acids bonded together in a polypeptide chain. Estradiol is a steroid hormone and has three cyclohexyl rings and one cyclopentyl ring joined into a single structure. Thus, the correct answer is D.