Comparative Anatomy - Reproductive System

Editor's Notes

1. Evolutionary survival depends on doing many things successfully: escaping from predators, procuring food, adjusting to the environment, and so on. All of this comes down to reproducing successfully, which is the primary biological role of the genital system. The reproductive system includes the gonads, their products, hormones and gametes, and the ducts that transport gametes. Reproductive hormones facilitate sexual behavior and parental care, prepare the reproductive ducts to receive the gametes, support the zygote, and perform other functions. Main Functions To produce the sex cells (gametes). To ensure fertilization. To provide nourishment of the embryo or fetus until hatching or birth. To release eggs or young from the maternal body.
2. Ovary produces both hormones and mature ova The female gonads, the ovaries, lie in the abdominal cavity Each ovary is enclosed in a tough protective capsule and contains many follicles A follicle consists of one egg surrounded by one or more layers of follicle cells
3. Female Reproductive System Oviducts and Uterus The egg cell is released into the abdominal cavity near the opening of the oviduct or fallopian tube Cilia in the tube convey the egg to the uterus Cervix is the neck of the uterus. Vagina and Vulva The vagina is a thin-walled chamber that is the repository for sperm during copulation and serves as the birth canal.
4. Testes The male gonads, or testes, consist of highly coiled tubes surrounded by connective tissue. Sperm form in these seminiferous tubules. Production of normal sperm cannot occur at the body temperatures of most mammals The testes of many mammals are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity.
5. Male Reproductive System Ducts From the seminiferous tubules of a testis, sperm pass into the coiled tubules of the epididymis where the sperm is temporarily stored. During ejaculation, the sperm are propelled through the muscular vas deferens, the ejaculatory duct, and exit the penis through the urethra. Glands Three accessory sex glands, the seminal vesicle, prostate, and bulbourethral (Cowper’s) gland, respectively, add their secretions as sperm move from the testes to the urethra. This fluid and the sperm it contains constitute seminal fluid, or semen.
6. Indifferent Gonad consist of cortex and medulla The migrating germ cells from the extraembryonic endoderm will travel to the indifferent gonad and takes residence either in the cortex or in the medulla. In the case of females, the migrating germ cells will take residence in the cortex, the cortex expands, primary sex cords degenerates, the secondary sex cords will be produced which functions in housing the follicles. Follicle cells surrounds the ripening egg cells and the theca encloses the follicles. After ovulation the follicles would be converted into corpora lutea (mammals, some elasmobranchs, birds) Blastema becomes the stroma or matrix of the connective tissue in the ovary
7. Pleated- folds/ with folds
8. In amniotes the regressing archinephric duct leaves vestiges like epoophoron and paroophoron (epididymis and paradidymis in male counterpart respectively)
9. In amphibians – the posterior portion of their oviducts provides coat of jelly for the embryo
10. In Teleostei, ovaries fold to enclose pockets of coelom into which eggs rupture.
11. Oviparous chondrichthyes like the catshark (in the picture above) lays eggs which are called Mermaid purse (picture above, lower left) this covering was provided by the nidamental gland (shell gland) in the anterior portion of their oviducts
12. The glandular anterior portion applies albumen to the eggs The part of the tract near the cloaca enlarges because of the ovisac and shell gland The right oviducts of reptiles are larger than the left side The right oviducts of birds is vestigial (lost) because the right ovary regresses in embryos
13. The genital tracts of therian mammals are divided into three regions: oviducts, uterus, and vagina Oviducts of therian mammals are straight and slender because they have relatively small eggs The uterus was lined with endometrium, houses the fetus during pregnancy and provides maternal contribution to the placenta Myometrium is the outer covering of the uterus; it has thick wall and is composed of smooth muscles having circular, longitudinal, and oblique fibers. Cervix closes the uterus
14. Duplex -two cervixes/ uterus Bipartite- Y-shaped externally, nearly divided internally Bicornuate- fusion is nearly complete but does not include anterior end of the organ Simplex- single uterine chamber
15. Distensible means able to stretch or expand
16. (In males, the germ cells that are from the extraembryonic endoderm takes up residence in the medulla and enlarges to become the testis cords that will form the seminiferous tubules.) (In females, the cortex expands, forming secondary sex cords that house the follicles.) Germinal epithelium forms only the peritoneal covering of adult testes. Primary sex cords do NOT degenerate and secondary sex cords are NOT formed. Testes are paired except in cyclostomes ( jawless fishes having large sucking mouth – lampreys and hagfishes) Each is suspended from the dorsal wall of a coelom by a mesentery called the mesorchium. (mesovarium in females) (Testes are usually smoother, firmer, smaller than ovaries of the same species, usually develop earlier.) Testes are paired but may be partially fused as in ELASMOBRANCHS, or completely fused as in ADULT CYCLOSTOMES. (Elasmobranchs –cartilaginous fishes –sharks,rays,skates and other extinct related fishes.)
17. Testes are elongated in CYCLOSTOMES, MOST FISHES, CAECILIANS, and URODELES. Testes are compact and ovoid in some CARTILAGINOUS FISHES, ANURANS, and AMNIOTES. (LABEL- a. Hagfishes (cyclostomes)- single testis that hangs in the dorsal body wall between the kidneys. b. Elasmobranch – partially fused. ) (Spermatogenesis does not occur if temperature is warmer than 36.5oC.) BIRDS- abdominal air sacs; MAMMALS (PRIMATES – MOST CARNIVORES, and MOST UNGULATES) – scrotum; MAMMALS (MONOTREMES, WHALES, ELEPHANTS) – testes are abdominal or pelvic in position if body temperature is relatively low. (birds maintain appropriate temp for spermatogenesis by the abdominal air sacs; scrotum is the cooler pouch of skin where the testis descend at maturity out of the abdominal cavity,- homologous to the large labia in females)
18. Except in CYCLOSTOMES, sperms are released in a closed system of ducts.   (the efferent ducts cross the mesorchium to enter the nephric duct; now called deferent duct when it carries only sperm or both sperm and urine) Deferent ducts carries either the sperm or both sperm and urine. (provide temporary storage and contracts during ejaculation) CHONDRICHTHYANS have paired deferent ducts that convey ONLY SPERM. Several PRIMITIVE RAYFINNED FISHES and SOME DIPNOANS pass sperm into the anterior end of deferent duct which convey both sperm and urine. All AMPHIBIANS have deferent ducts, some species convey ONLY SPERM and in others BOTH sperm and urine. Deferent ducts of AMNIOTES carry ONLY SPERM. (Birds, Reptiles, Mammals)
19. CYCLOSTOMES and MOST BONY FISHES lack copulatory organs. (they lay their eggs in water and male discharges his sperm over them) SOME TELEOST retained their eggs during development or bear live young. Gonopodium- margin of the anal fin as copulatory organ in males. CARTILAGINOUS FISHES also have INTERNAL fertilization. Claspers- pelvic fins as copulatory organ in males. ANURANS have EXTERNAL fertilization. Hence, they don’t have copulatory organs. URODELES have INTERNAL fertilization but LACK copulatory organs. (urodeles include newts and salamanders) Cloacal kiss ( male and female press their cloacas together to transfer sperm)
20. TURTLES and CROCODILES have evolved a grooved penis. (it is located internally on the floor of the cloaca. Small clitoris are present in female turtles and crocodiles) BIRDS copulate by pressing the cloacas together for the transfer of sperm. Primitive birds (OSTRICHES, DUCKS and GEESE) have a small penis. THERIAN MAMMALS have a penis formed from the genital tubercle located anterior to the cloacal opening. (genital tubercle of males becomes the penis, while for the females, it becomes the clitoris, which is the reason why penis is said to be homologous to the clitoris) Glans is variously shaped and is forked in MONOTREMES and MARSUPIALS. (to correspond to the divided vagina of females. Ex. Kangaroo)  
21. Nephric – ureters; Paramesonephric – Mullerian ducts
22. Three compartments of the cloaca : C – as coprodeum U – as urodeum P – as proctodeum
23. Three folds of the cloaca
24. Primitive condition is where the cloaca is the common passageway of the urinary, digestive, and reproductive systems
25. Rectum is independent Urinary and Reproductive ducts fuse and empties through common papilla (Urogenital opening or Genital pore) and exits through the anus