Functions of male Reproductive System: produce gametes deliver gametes protect and support gametes
Spermatogenesis occurs in the testes after puberty. From the testes they are deposited into the epididymas where they are stored. and then vas deferens to begin swimming and prepare to be deposited into the female. Sperm cells are haploid and are produced in the tubules within the testes.
Spermatogenesis occurs in the seminiferous tubules. Here spermatogonia cells (diploid) start to undergo meiosis. Sertoli cells nourish the developing sperm. Interstitial cells outside the tubules produce the hormone testosterone.
A microscopic image shows the Seminiferous Tubules. Identify the structures that are shown here. A. Spermatogonia C. Interstitial cells E. Sertoli cells B. Sperm D. Center of seminiferous tubules C A E D B
Sperm Millions of sperm are produced in an average male every day. If they are not ejaculated, they are reabsorbed after a couple of weeks by the body and recycled. Sperm are very stream-lined for what they do. They don t have any extraneous gear. No food for the trip and no proteins on their surface. Just DNA with a tail. How did evolution select for this in sperm? Flagellum: propulsion Mitochondria: power Nucleus:DNA Acrosome: a way into the egg (digestive enzymes)
In order to deliver the gametes into the females reproductive tract and to the females gametes, the penis must become erect. Blood flows into the erectile tissue and the build up of blood pressure causes the penis to become rigid. Further stimulation of the nerves on the penis triggers a series of smooth muscle contractions that propel the sperm out of the penis. The sensation of orgasm occurs when the control of the body rapidly switches from one nervous center (the parasympathetic) to another (the sympathetic).
Of the millions of sperm cells ejaculated into a female, only a few will survive to meet the egg a couple of days later. This is because the environment into which the sperm will enter is very harsh and the vast majority die: no energy source very acidic The male body provides these things to the sperm cell to aid it on its journey to find the female gamete (the egg): sugar a basic solution to neutralize the acid Why is the environment so harsh? What does evolution say?
So once sperm are formed and then sped on their way out of the vas deferens by muscular contractions, they are mixed with three solutions on their way, and then ejaculated into the female reproductive tract. Seminal Vesicles: fructose-rich fluid: energy for mitochondria protaglandins: initiate female muscle contractions Prostrate Gland: alkaline (basic) fluid: neutralize the acids in the vagina Bulbourethral Gland: lubrication for penis to enter vagina and for sperm to move more easily through the urethra The resulting mixture is called Semen. an ejaculation releases about 3 ml of semen
At puberty the hypothalamus releases gonadotropin-releasing hormone (GnRH). GnRH stimulates the pituitary to produce luteinizing hormone (LH) and follicle stimulating hormone (FSH) LH causes the interstitial cells to produce testosterone. LH and FSH stimulate spermatogonia in the testes. To much testosterone or INHIBIN triggers a negative feedback loop which stops production of GnRH If FSH was suppressed, but LH continued a man would be infertile but not impotent.
Sperm production starts in boys at puberty. The production of testosterone also triggers other secondary characteristics. Voice deepens Start to grow body hair Muscles start to develop height increases Testes drop
All female structures are analogous to male structures and must perform the similar functions. Produce gametes Deliver gametes Provide environment for organism to develop if fertilization occurs
A female is born with all the egg cells that she will ever have. They are immature primary oocytes and only develop into mature egg cells when the woman enters sexual maturity. From puberty (around age 12) until menopause (around age 50) a female will release 1 egg per 28 days (on average) unless fertilization occurs. Eggs are stored and mature in the ovary. They travel down the fallopian tube (oviduct) to the uterus
Oogenesis: The formation of Eggs This begins in the developing ovaries of the female fetus By the 3rd month of fetal development primary oocytes are formed. They stop at the prophase of meiosis I At birth over 2 million primary oocytes are already in place, no new ones are formed.
Many primary oocytes die each day so that by puberty only about 400,000 remain. This is more than enough to produce 1 egg every month from puberty till menopause How many is that if a woman comes into puberty at 13 and menopause at 50?
Surrounding each oocyte is a layer of smaller cells which secrete female hormones and nourish the developing oocyte. The follicle secretes the hormone estrogen. Once a month pituitary hormones stimulate the development of several follicles. The oocytes and these cells are called the follicle.
Meiosis in the Oocyte The polar bodies are left over chromosomes
The follicle ruptures and releases the secondaary oocyte and the fimbriae move it into the oviduct.
The egg starts to move down the Oviduct (fallopian tube). The follicle remains and turns into the Corpus Luteum. The corpus luteum secretes both estrogen and progestrone. If fertilization does not occur the corpus luteum breaks down
If the egg meets a sperm cell and is fertilized during its 3 day journey down the oviduct, it will plant itself on the uterine lining and begin to gain nutrients from the endometrium of the uterus so that it can grow. If the egg does not meet a sperm, the egg will be discarded along with the nutrient-rich endometrium that is primed for its arrival. This is called menstruation and occurs once every 28 days or so unless the egg is fertilized.
Female Secondary Sex Characteristics From the age of 8 to 12, there is a gradual rise in the level of hormones in the female s body. In the early teens, the level rises sharply The increased level of hormones stimulates the development of secondary sexual characteristics in the female Development of breasts Growth of hair around the genitals and under the arms Widening of the hips Increased body fat
The Menstrual Cycle The reproductive hormones follow a cyclical pattern called the menstrual cycle. This cycle usually lasts around 28 days, but can vary in length from 20 to 45 days. It can also differ in its starting time from month to month. The menstrual cycle is also controlled by the hypothalamus. The hypothalamus releases chemicals which stimulate the anterior pituitary gland to release two hormones FSH and LH. These hormones play a major role in stimulating the release of follicles which are groups of cells that contain the ovum or egg.
Menstrual Cycle Women are born with over 2 million follicles, but will only release around 400 during her reproductive life. The menstrual cycle occurs in four stages 1. Follicular stage 2. Ovulation 3. Luteal stage 4. Menstruation
1. Follicular Stage The initial stage of the menstrual cycle. An increase in the level of FSH stimulates the follicles to release high levels of estrogen into the bloodstream. The estrogen stimulates the endometrium of the uterus to thicken and also causes an increased blood supply to the endometrium in preparation for a possible pregnancy. As estrogen increases it causes a decrease in the amount of FSH being produced from the anterior pituitary gland (negative feedback loop). It also causes the hypothalamus to release large amounts of LH which will trigger a follicle to release of an ovum
2. Ovulation Takes place at the midpoint in the cycle, after about 14 days The ovum is released from the ovary into the oviduct. After the egg is released, the empty follicle changes into a structure called the corpus luteum. The corpus luteum is a group of cells which produce the hormone progesterone.
3. Luteal Stage In this stage, LH stimulates the corpus luteum to produce the hormone progesterone. Progesterone inhibits the development of any other follicles and this makes sure that only one ovum (egg) is released during the menstrual cycle. Progesterone also inhibits the production of LH. Causing LH levels to decrease as progesterone increases Eventually the corpus luteum breaks down and the luteal stage ends
4. Menstruation As the progesterone level decreases, the blood supply to the endometrium of the uterus also decreases. The endometrium breaks down Blood vessels in the endometrium rupture Tissues and blood flow out of the vagina As menstruation begins, the first stage of the menstrual cycle (follicular stage) begins once again
Hormone Control of the Menstrual Cycle Also see figure on page 492 in your book
Female Hormone Treatments As a woman ages there is a decrease in the hormones which are produced in her body. As the hormone level decreases, the female s body stops going through the menstrual cycle, we call this menopause. Both during and after menopause, the female s body goes through a series of changes A rise in cholesterol level A decrease in bone mass Constricting and dilating of blood vessels to produce what we call hot flashes Mood changes Hormone replacement therapy - Doctors will prescribe low levels of estrogen and progesterone hormones to lessen the effect of these changes
Hormone Replacement Therapy There are both positive benefits and negative side-effects of this therapy The positive benefits include: Relief of menopausal symptoms such as hot flashes, night sweats and sleep disturbance Prevention of bone loss (osteoporosis) Improved memory Decrease in urinary infections Decrease in macular degeneration. The negative side-effects include: Irregular vaginal bleeding Stomach upset Severe headaches Formation of blood clots Increased risk of breast cancer Increased risk of uterine cancer Edema (water retention) Increased risk of heart attack Fluctuations of blood sugar level