The Reproductive System

Human reproduction Through the first 6 weeks of devel- opment, human males & females are identical, then the reproduc- tive organs begin to develop. Testes Determining Factor causes the testes to develop, and testo- sterone is needed for the devel- opment of male physical charac- teristics. Estrogen and progesterone produce female characteristics. At puberty, the reproductive system becomes active. Occurs between ages 9 and 15; girls start earlier.

Internal fertilization In internal fertilization, sperm are deposited in or near the female reproductive tract, and fertilization occurs there. Fertilization requires critical timing, often mediated by environ- mental cues, pheromones, and/or courtship behavior.

Internal fertilization Attempts at human fertilization are also affected by environ-mental cues, pheromones, and/or courtship behavior.

Male reproductive system Internal fertilization requires behavioral interactions and compatible copulatory organs. Draw and label. The male reproductive system, including bladder and urethra.

Male reproductive system Another view of the male reproductive system:

The male testis Testis – the male reproductive organ (gonad) in which sperm and testosterone are produced.

The male testis Sperm are produced in the seminiferous tubules.

Spermatozoa Sperm are produced in humans at the rate of ~120 million per day. Development takes ~60 days; the sperm then take a further 10 to 14 days to pass through the ducts of each testicle and the epididymis before they can leave the body in the semen during ejaculation.

Semen production Semen Production Epididymis Seminal Vesicle Semen: the sperm-carrying ejaculate. Semen Production Epididymis Here, sperm become motile and gain the ability to fertilize. Seminal Vesicle Contributes an alkaline fluid to counteract the acidity of the vagina and fructose to nourish the sperm. Prostate gland Contributes an anticoagulant and citrate to nourish the sperm.

Female reproductive system The female reproductive system, including bladder & urethra. Draw and label.

Female reproductive system Another view of the female reproductive system: The endometrium is the inner lining of the uterus, where the embryo will attach. The menstrual cycle influences its thickness.

Female reproductive system The ovary The primary follicle contains an immature oocyte. Girls are born with 500,000 immature oocytes; they mature after puberty. Ovulation! When the egg is mature, the follicle ruptures. This occurs about every 28 days. The ruptured follicle turns into a corpus luteum.

Female reproductive system The fallopian tubes Finger-like projections (fimbriae) receive the oocytes from the ovary, and cilia move the oocytes towards the uterus. The site of fertilization – oocytes live ~24 hours so there is a narrow window for fertilization.

Female reproductive system From the fallopian tube, the fertilized egg travels to the uterus. Endometrium: inner layer of uterus for implantation of a fertilized egg; it sloughs off if no pregnancy occurs (menses).

The menstrual cycle In females, the secretion of hormones and the reproductive events they mediate are cyclic. Humans females have a menstrual cycle and an ovarian cycle. The menstrual cycle refers to changes in the uterus. By convention, the 1st day of the cycle is when bleeding begins.

The menstrual cycle Stages of the menstrual cycle. The menstrual flow phase: loss of endometrial layers (bleeding). The proliferative phase: thinned endometrium regenerates. Secretory phase: endometrium thickens with blood vessels and develops glands that secrete a fluid rich in glycogen. Lasts 2 weeks. If no embryo implants then menstruation starts.

The ovarian cycle The ovarian cycle produces an egg and hormones for its implantation into the endometrium. Follicular phase: follicles of ovary enlarge with developing oocyte. Ovulation: follicle ruptures, releasing oocyte to fallopian tube. Luteal phase: hormones secreted by corpus luteum .

Spermatogenesis vs. oogenesis 1 ovum vs. 4 sperm

Fertilization and Pregnancy

Diagram of a Mature Egg Around the outside are the follicular cells. The zona pellucida surrounds the oocyte and is composed of glyco-proteins. This structure will seal the ovum against multiple fertilizations. The nucleus sits inside the cell with a large volume of cytoplasm (the yolk). The 1st polar body can be seen outside of the plasma membrane. This will degenerate.

Fertilization Pregnancy is the presence of developing offspring in the uterus, an event resulting from fertilization – the fusion of male and female gametes (in the fallopian tube). For this fusion to occur in humans, the sperm needs to penetrate the egg cell, which is surrounded by a zona pellucida and a corona radiata. 2nd meiotic division in fallopian tube

Process of in vitro fertilization Fertilization that is done outside the body (in glass). Outline the steps involved.

Early embryo development After fertilization: the haploid sets of chromosomes from the male and female gametes line up at the equator and prepare for the first mitotic division. This division, within 24 hours after fertilization, is not followed by cell growth, and is, therefore, called a cleavage division. During the first 5 days several cleavage divisions occur within the fallopian tube. Even though cells are dividing, the embryo doesn’t grow. At the 8 cell stage compaction occurs – the cells squish together into a small ball called the morula.

Early embryo development First mitotic divisions

Early embryo development Passage of the fertilized egg through the fallopian tube.

The placenta Structure: Disk-shaped organ, contains embryonic and maternal blood vessels About the size of a dinner plate, and weighing about 1 kg allowing the exchange of materials by diffusion. Two embryonic blood vessels contained within the umbilical cord.

The placenta Function: produces progesterone/estrogen Estrogen maintains endometrium and inhibits menstrual cycle from 2nd trimester onwards Materials are exchanged between the maternal and fetal blood in the placenta. Nutrients: oxygen, glucose, amino acids, vitamins, antibodies. Waste products: carbon dioxide, urea transports glucose, amino acids, lipids, oxygen, carbon dioxide, antibodies, urea

The amnion The fetus is supported and protected by the amniotic sac and amniotic fluid.

The amnion Amniotic sac is an extra-embrionic membrane that extends all the way around the fetus. Provides a cushioning effect Provides thermal stability Provides an environment for free movement of fetus Development of muscles and skeleton of fetus Amniocentesis: sampling the fluid around the baby to check for abnormalities.

Hormones and birth As birth approaches, progesterone levels (which were elevated throughout pregnancy) begin to decline. At this time, oxytocin levels begin to rise. Made by hypothalamus & excreted by pituitary. During parturition, oxytocin is involved in contractions, dilation of the cervix, and minimizing bleeding.

Childbirth When a baby is ready to be delivered, it drops lower in the uterus and puts pressure on the cervix, causing the cervix to stretch.

Childbirth Stretching of the cervix further stimulates the release of the hormone oxytocin, which induces the uterus to contract.