F. REPRODUCTIVE SYSTEM
1. Discuss the development of the gonads.
Genital ridges give rise to gonads (mesoderm: mesomere). Primordial germ cells (endoderm) migrate to genital ridges and become established just internal to peritoneum and this area of genital ridge becomes germinal epithelium. Gonads develop into either ovaries or testes influenced by genes, hormones, temperature, etc. Gonads develop a dorsal mesentary: mesorchium in males or meovarium in females. In males, primary sex cords become seminiferous tubles that produce sperm. In females, primary sex cords regress, new secondary sex cords form and are the source of oocytes.
2. Name the female and male gonad.
3. Review the anatomy of the testes. Discuss the testes position in the adults of vertebrate species.
Testes are paired organs that serve as both endocrine gland and sex organ. Testes produce sperm from germ cell lines. They are encapsulated by tunica albuginea. Seminiferous tubules, coiled tubules lined with germinal epithelium, compose bulk of testis and form sperm in most vertebrates. Some fish, cyclostomes, and urodeles lack seminiferous tubules; sperm are made within cysts. The testes are located in the abdominal cavity of monotremes, elephants, whales, and non-mammals. They descend permanently in ungulates, carnivores, and humans. They are retractile in rabbits and lower primates.
4. Follow the ejaculatory pathway of sperm. Contrast this pathway between nonplacental and placental mammals.
Testes to vasa efferentia to vas deferens to cloaca (nonplacental)/urethra (placental) to copulatory organs
5. Describe various copulatory organs, including claspers, gonopodium, hemipenis, and penis.
When fertilization is internal, the male usually has some intromittent or copulatory organ to introduce sperm into the reproductive tract. The claspers of sharks and chimaeras are a modified portion of the pelvic fin. Some groups of teleosts (e.g., guppies) have a gonopodium, which is a modified portion of the anal fin. All amniotes have internal fertilization, and most have some sort of intromittent organ; the exceptions are the tuatara and most birds. Squamates have a paired copulatory structure called a hemipenis that are sac-like and do not have erectile tissue. Turtles, crocodilians, primitive birds (e.g., ostriches, ducks), and mammals have a penis, which consists of a single or paired masses of erectile tissue called corpora cavernosa (singular,corpus cavernosum), with some sort of urethral groove or tube to carry sperm and urine. In mammals this tube is the corpus spongiosum. The proximal end of the corpus cavernosum is attached to the pelvis by connective tissue.
6. Describe the ovaries and oviducts amongst the vertebrates.
The ovary is unpaired in cyclostomes. In most fishes, the ovaries are compact; in amphibians the ovaries are saclike; those of other tetrapods are more compact, with more connective tissue (stroma). Therian mammals have very compact ovaries. In all of these groups the ova are ovulated into the coelom, and find their way to the oviduct. In teleosts, however, the ovaries are hollow, because part of the coelom has been enclosed by the developing ovary, and eggs are shed into an ovarian cavity (rather than the coelomic cavity) which is continuous with the gonaduct. In female birds the right ovary does not develop, probably to permit production of larger eggs.
7. Discuss the development of oviducts.
In both males and females of gnathostomes, a second duct develops alongside the mesonephric duct, either by splitting of the mesonephric duct, or by a longitudinal folding of the peritoneum, depending on the group. This second duct is the Muellerian duct. Cyclostomes lack an oviduct, and eggs are shed into the coelom, as are the sperm. In males the duct degenerates, but in females it becomes the oviduct.
8. Describe the uterus, cervix and vagina in mammals.
In therians each Muellerian duct differentiates into an oviduct, uterus, and vagina. The uterus is closed by a muscular neck called the cervix. In most marsupials the ducts remain separate, and therefore they have a duplex uterus and paired vaginae. If the uterus is Y-shaped externally and mostly divided it is duplex, as in monotremes, marsupials, and rodents. Slightly more fused conditions are called bipartite, as in carnivores, and bicornuate. A simplex uterus has a single uterine chamber, as in most primates. The vagina, a cloacal derivative, empties into the urogenital sinus in most placental mammals. In rodents and primates, the vagina opens directly to the vulva, exterior genitals.
9. Characterize the cloaca, vent, anus, urorectal fold, coprodeum, urodeum, and proctodeum.
The cloaca is the common cavity into which the intestinal, genital, and urinary tracts open in vertebrates such as fish, reptiles, birds, and some primitive mammals. The cloacal opening, or vent, receives intestine and urogenital structures in all vertebrates except placental mammals. In reptiles, birds, and monotremes, the cloaca is partitioned by the urorectal fold into the coprodeum (which collects digestive waste), urodeum (which collects urine), and the proctodeum (the common undivided terminal cloaca).
10. Discuss the terminal urogenital tract in placental mammals, including that of humans.
The urogenital tract teminates into the urogenital sinus and rectum in placental mammals except primates and rodents. In female humans and rodents, it terminates into the urethra vagina, and rectum.