Endocrinology: Hormones of the Gonads, Oestrus and Menstrual Cycles

These flashcards cover key concepts about the endocrine system, hormone production, the menstrual cycle, and pregnancy based on the lecture notes.

What are the main sex hormones produced by the gonads?

The main sex hormones are androgens in males and oestrogens and progestagens in females.

What is the first step in steroid hormone production?

The first step is the removal of the terminal 6 carbons from cholesterol, converting it into pregnenolone.

What are the three groups of sex steroids based on the number of carbon atoms?

C-21 Steroids, C-19 Steroids, and C-18 Steroids.

What hormones are categorized as C-21 Steroids?

Progestogens, Cortisol, and Aldosterone.

What is testosterone primarily produced by in males?

Testosterone is primarily produced by the Leydig cells of the testis.

At what age does testosterone production peak in males?

Testosterone production peaks at about 20 years of age.

What is the role of FSH in male reproductive physiology?

FSH stimulates Sertoli cells to promote spermatogenesis and induces secretion of androgen binding protein.

What is the function of testosterone in males?

Maintains male ducts, stimulates spermatogenesis, induces secondary sexual characteristics, has anabolic effects, and influences foetal development.

What are the two main groups of hormones produced by the ovaries?

Oestrogens and progestagens.

What is the most active and abundant oestrogen during a woman's reproductive years?

17β-Oestradiol.

How does progesterone function during pregnancy?

Prepares the uterine endometrium for implantation and stimulates growth of secretory alveoli in mammary glands.

What initiates menstruation in the menstrual cycle?

A sharp decrease in blood progesterone and 17β-oestradiol levels triggers menstruation.

What defines oestrous cycles in mammals?

Consecutive series of sexual cycles controlled by the endocrine system, with females being receptive to males during oestrus.

What is the main difference between spontaneous and induced ovulators?

Spontaneous ovulators ovulate as part of the oestrous cycle, while induced ovulators ovulate only after copulation.

What is the average duration of a menstrual cycle?

The average menstrual cycle lasts 28 days.

What are the phases of the menstrual cycle?

The menstrual cycle consists of the follicular phase and luteal phase.

What hormonal changes occur during the follicular phase?

High levels of estrogen under the control of FSH and LH, leading to the maturation of follicles.

What triggers ovulation during the menstrual cycle?

A surge in LH and FSH levels leads to ovulation.

What happens to the corpus luteum if fertilization does not occur?

It regresses and degenerates, leading to a drop in progesterone and oestrogen levels.

What hormone does the blastocyst secrete to maintain the corpus luteum?

Human Chorionic Gonadotrophin (HCG).

What is the primary role of the placenta during pregnancy?

It produces significant quantities of progesterone and oestrogens.

How long does pregnancy typically last?

Pregnancy typically lasts about 280 days, or 9 months.

What effect does oxytocin have during parturition?

Oxytocin induces contractions of the myometrium to expel the foetus and placenta.

What physiological effects does oestrogen have on females?

Maintenance of female ducts, promotion of secondary sexual characteristics, and other physiological functions.

What is the role of inhibin in male reproductive physiology?

Inhibin functions as a negative feedback mechanism on FSH secretion.

What is the significance of cholesterol in the synthesis of steroid hormones?

Cholesterol serves as the precursor for all steroid hormones.

What are the primary effects of progesterone during the menstrual cycle?

Prepares the endometrium for implantation and inhibits uterine contractions.

Which hormone is primarily responsible for the secondary sexual characteristics in males?

Testosterone.

What is the primary function of androgens?

Androgens primarily support the development of male reproductive tissues and secondary sexual characteristics.

What hormone triggers the proliferation of the endometrial lining during the menstrual cycle?

Oestrogen.

How do levels of FSH and LH change at the end of each menstrual cycle?

They decrease due to high levels of estrogen and progesterone from the corpus luteum.

What hormonal changes occur during the luteal phase of the menstrual cycle?

High levels of progesterone and 17β-oestradiol are secreted by the corpus luteum.

What defines a polyoestrous mammal?

Mammals that display a succession of oestrous cycles.

What are the three most significant types of oestrogens?

17β-Oestradiol, Estriol, and Estrone.

What physiological roles does progesterone play during pregnancy?

Prepares the uterus and maintains the endometrium, inhibits lactation, and reduces uterine contractions.

How do androgen levels influence spermatogenesis during puberty?

Increased testosterone levels promote spermatogenesis in the testes.

What hormone initiates the development of secondary follicles in the ovary?

FSH initiates the development of secondary follicles.

What occurs to hormone levels when a pregnancy is achieved?

HCG maintains high levels of progesterone and estrogen, preventing the degeneration of the corpus luteum.

What hormonal measures can trigger the onset of the next menstrual cycle?

Decreasing levels of progesterone and estrogen remove negative inhibition, allowing FSH and LH to rise.

What phenotype characteristics do oestrogens promote in females?

Breast enlargement, deposition of adipose tissue, and secondary sexual traits.

What results from the luteinization of the corpus luteum?

The production of high quantities of progesterone, contributing to the preparation of the endometrium for potential implantation.