Biology 1A: Lecture #31

Lecture 31:

Reproduction Part II:

Spermatozoa:

100-300 million produced. Head has an acrosome tip on it which has digestive enzymes for fusion in the egg, contains a nucleus within the head (DNA).

This piles into seminerous tubules, then into epididymus, then into the vas Deferins, which is conected to the ejaculatory duct. The glands that feed into this:

• Seminal vesicles
• Prostate gland   =====> Together these 3 provide enzymes, sugar, and certain pH for sperm.
• Bulbourethral gland

Erection:

Erection- vascular process due to arterial dilation (nerve input).

This process is power by a hormone gas called Nitrous oxide which converts GTP to cyclic GMP (broken down by a phosphodiesterase process to 5′ GMP, which is inhibited by Viagra which keeps higher levels of cGMP around).

This entire process is negative feedback, not just to be inhibitive but also to be continuous.

Hypothalamus produces gnRH (Gonadotrophin releasing hormone) which binds to receptors in the anterior pituitary which causes the production of LH (luteinising hormone) and FSH (Follical Stimulating Hormone). Both males and females produce these hormones.

The LH interacts with its receptors in Leydic cells, which stimulates the conversion of cholesterol into testosterone in the Leydic cells.

FSH binds to its receptor in Sertoli cells which converts T into DHT (DHT stimulates growth and proliferation of spermatogenic cells). If T cells get too much, it gets modulated down so there is less FSH and so on, and vice versa.

To shut down spermatogenesis, too much T will cut it down (but will result in side effects)

Female Gamete Production:

Oogenesis: The object of oogenesis is to make an ovum “egg”. Unlike males gametes, women begin their lives with all the eggs they need.

• Long “Resting” period.
• Unequal cytokinesis (splitting the cytoplasm).
• 1 potential ovum every 28 days.

Primordial germ cell (undifferentiated stem cell) which undergoes mitosis during fetal development. This mitosis process produces oogonia. Then, they undergo a meiotic duplication, forming a primary oocyte (46 chromosomes/4c DNA).

Every 28 days, there is a surge in LH, and these cells undergo first meiotic division.  The secondary oocyte (23Chromosomes 2C DNA) and a polar body (nucleus with little cytoplasm) unequal cytokinesis means the most of the cytoplasm goes to secondary oocyte. This undergoes second Meiosis division, and gives an 23 Chromosome  (ovum) and a second polar body. One oocyte gives ONE ovum.

In ovary, primary follicles in ovum are surrounded by granulosa cells (help induce proliferation). The primary oocyte gets surrounded by a membrane called the zona pelusa. One cell layer is the granulosa cells and after is the theca cells. Theca cells convert cholesterol to T. The Granulosa cells convert T to Estrogen. Surrounding the ovum in the ovary is full of a fluid anterum layer. Fluid builds up and creates pressure. This fuels an LH surge and first meiotic division. And then it pops the secondary oocyte, creating a differentiated structure called the corpus luteam (from granulosa and theca), which produces E + P (Progesterone). Goes to fallopian tubes and is fertilised by sperm leading to a zygote (or not).

NOTE:  If you eat little fat you will still make cholesterol, if you eat too much you dampen down your cholesterol biosynthesis.

Menstrual Cycle:

28 days long. Prior to ovulation, follicular phase (development), after ovulation, Luteal phase, 7 day process.

Build up of estrogen, produces a surge of LH which triggers ovulation phase, then progesterone build up.