BIOL 101 - GRQ 17: Human Reproduction II

What is the name of the tubules within the testes that sperm develop in?

Seminiferous tubules

How long does sperm formation take?

About 10 weeks

What is the name of the tubules within the testes that sperm develop in?

Seminiferous tubules

How long does sperm formation take?

About 10 weeks

How are both mitosis and meiosis involved in making sperm?

In the process of sperm formation, diploid cells multiply by mitosis and roughly 3 million of them differentiate into primary spermatocytes, which undergo meiosis. Meiosis I produces two secondary spermatocytes. Meiosis II forms fours cells with the haploid number of chromosomes. Then, a sperm cell develops by differentiation of these haploid cells. After entering the seminiferous tubule, the sperm passes to the epididymis, where it matures.

What phase of meiosis are primary oocytes stopped short in at birth?

Prophase of meiosis I

Ovaries typically produce their first secondary oocyte at what age

Ovulation

What stage is the egg at when ovulation occurs?

Metaphase of meiosis II

Summarize Figure 27.5B for yourself: being sure to capture both the anatomical changes and the developing egg.

Figure 27.5B depicts oogenesis and the development of an ovarian follicle. This process occurs in the ovary, for the most part, and begins prior to birth. It begins when a diploid cell in each follicle begins meiosis. At birth, each follicle contains a dormant primary oocyte, which is a diploid cell that is resting in prophase I of meiosis I. In order to develop further, the oocyte has to be hormonally triggered. Between puberty and menopause, FSH stimulates one of the dormant follicles to be developed. After being triggered, the follicle enlarges and begins meiosis II. With the entry of sperm, meiosis II is completed. However, meiosis II is unequal, causing a second polar body and a mature egg. The haploid nucleus of the mature egg can fuse with the haploid nucleus of the sperm, thus producing a zygote.

Compare and contrast oogenesis and spermatogenesis:

Both oogenesis and spermatogenesis both produce haploid gametes. In oogenesis, only one mature egg results from each diploid cell that undergoes meiosis. Whereas in spermatogenesis, all four of the products of meiosis develop into mature gametes. These two processes also contrast in how long they take place. Spermatogenesis lasts from puberty until death, while oogenesis is completed before birth and the production of gametes ends at menopause. Lastly, oogenesis has long resting periods but, spermatogenesis occurs in an uninterrupted sequence.

When a follicle is growing, and a secondary oocyte is developing

Pre-ovulatory phase

After the follicle has become a corpus luteum

Post-ovulatory phase

Describe the hormonal events before ovulation, be sure to include any positive or negative feedback discussed:

1. Releasing hormone from hypothalamus stimulates the anterior pituitary

2. Increases output of FSH and LH

3. FSH stimulates growth of ovarian follicle, starting ovarian cycle

4. Estrogen is released

5. FSH and LH is released by the pituitary in surges

6. Ovulation occurs

Negative feedback - rising, still low level of estrogen; keeps blood levels of FSH and LH low

Positive feedback - ovulation approaches and there is a high level of estrogen; pituitary secretes surges of FSH and LH

Describe the hormonal events at and after ovulation, be sure to include any positive or negative feedback discussed:

1. LH stimulates completion of meiosis I, signals enzymes to rupture follicle, allows ovulation to occur, triggers the development of corpus luteum, promotes secretion of progesterone and estrogen by the corpus luteum

2. FSH and LH levels fall

3. Degeneration of corpus luteum; stops secreting estrogen and progesterone

4. Blood levels of hormones decline; new cycle begins

Negative feedback - high levels of estrogen and progesterone; hypothalamus and pituitary cause falling FSH and LH levels which prevents follicles from developing and ovulation from occurring

Cells that secrete hormone: pituitary gland

Cells that are the target of the hormone: stimulates production of gametes in the gonads

Follicle-stimulating hormone (FSH)

Cells that secrete hormone: pituitary gland

Cells that are the target of hormone: stimulates production of androgen by gonads

Luteinizing hormone (LH)

Cells that secrete hormone: ovaries

Cells that are the target of hormone: follicle

Estrogen

Cells that secrete hormone: corpus luteum

Cells that are the target of hormone: endometrium

Progesterone

It becomes thick, sheds if no embryo implants

Uterus lining

Release an egg during ovulation

Ovaries

Peaks to stimulate follicle to grow

Levels of FSH

Peaks to trigger ovulation

Levels of LH

Low levels of estrogen trigger menstruation, peak causes LH surge, promotes thickening of endometrium

Levels of estrogen

Promotes thickening of endometrium

Levels of progesterone

Examine Figure 27.8 and order these from most effective to least effective at preventing pregnancy: pill - withdrawal - vasectomy - IUD - condom

IUD - vasectomy - pill - condom - withdrawal

Which of these can prevent STIs?

Condoms

Provides movement

Flagellum

Provides ATP

Mitochondria

Helps sperm penetrate the egg

Nucleus

Helps the sperm dissolve the outer surface of an egg and fertilize it

Shape of head

Contains enzymes that help the sperm penetrate the egg

Acrosome

How is it ensured that only one sperm penetrates and fertilizes an egg?

Fusion of the sperm and egg plasma membrane prevent another sperm from entering the egg. After the membranes fuse, the egg plasma membrane becomes impenetrable to other sperm cells.