The Reproductive System
The Reproductive System
The avian reproductive system is nothing like that of mammals. The reproductive system of aves has evolved to cater to the specific needs and challanges of being a bird. One of the biggest problems of being a bird is that you're everyone's dinner guest. Besides the specific anatomy of the reproductive system itself, birds have adapted a characteristic of reproduction that is very unlike most mammals. Most mammals will have few offspring and will spend copious amounts of time devoted to raising them. Birds, with a few exceptions, will do the opposite -choosing instead to raise large quantities of offspring, devote minimal care, if any, and then leave them to figure things out on their own.
The ovary is a cluster of devoloping yolks, called ova (singular ovum), located midway between the neck and tail of the hen. When a female chick hatches her ovary is fully formed albeit very small. The ovary contains 13,000-14,000 ova that only mature into yolks with the addition of a special fluid called 'yolk fluid'. Each ovum starts out surrounded by a membrane called the vitteline membrane. Over time, yolk is added as the ovum develops. When a female chick hatches she is equipped with all of the eggs that she will ever have.
Ovulation is the release of a mature ovum from the ovary. The ovum is released into the oviduct. The ovum, enclosed in a sac, ruptures along the stigma. The release of the ovum occurs 30-75 minutes after the previous egg is laid.
Diagram 8 shows the female reproductive system
The oviduct is a convoluted tube about 25-27 inches long, which is divided into 5 major sections. These sections are the infundibulum, magnum, isthmus, shell gland/uterus, and the vagina.
The first part of the oviduct, the infundibulum, is 3-4 inches long and it engulfs the ovum that is released from the ovary. The ovum then remains in the infundibulum for 15-18 minutes. The infundibulum is the area in which fertilization can take place.
The next section of the oviduct is the magnum which is 13 inches long. The magnum is the largest section of the oviduct. The ovum remains in the magnum for 3 hours. It is here that the albumen is added.
The third section of the oviduct is the isthmus which is 4 inches long. The egg remains here 75 minutes. The isthmus is slightly constricted. The isthmus is where the inner and outer shell membranes are added.
The next section of the oviduct is the shell gland, or uterus. The shell gland is 4-5 inches long and the egg remains here for over 20 hours. As the name implies, the shell is developed here. The hen sources 47% of her calcium from her bones and her diet supplies the rest. The shell gland is also where the pigment is applied.
The last section of the oviduct is the vagina which is 4-5 inches long and does not play a part in egg formation. The vagina's function is to push the egg out of the body. There are glands located in the vagina where sperm is stored. It is these glands which allow a hen to store sperm for extended periods of time. The bloom is added to the egg in the vagina.
Diagram 9 shows the reproductive system of the male chicken alongside the reproductive system of the female chicken
The male reproductive system and how it functions is almost entirely the same as with mammals, but does a few key differences.
Sperm is produced in the seminiferous tubules which are located in the testes. Sperm production occurs best at slightly cooler temperatures. Because of this, spermatogenesis may occur primarily at night when the body temperature of the bird is lower. Sperm are stored at the terminal end of the vas deferens.
Lying cranioventral to the first kidney lobe are the paired testes. The vas deferens emerges medially and passes caudally to the cloaca where it has a common opening with the ureter in the Urodeum. The terminal vas deferens is swollen as a storage organ: the seminal glomus.
Sperm formation is temperature sensitive. Male birds tend to have relatively low extragonadal sperm reserves and sperm are ejaculated soon after production in the testes.
The next page will discuss the circulatory system.
The female reproductive system
The reproductive system of the female chicken is divided into two main parts: the ovaries and the oviduct. In hens, the left ovary is the only functional ovary. Thus, it is the only ovary secreting hormones and, if damaged, female hormone balance can be thrown off track. The right ovary, however, is present in embryos but regresses during devlopment and serves no purpose in adult hens. The ovary is a cluster of devoloping yolks, called ova (singular ovum), located midway between the neck and tail of the hen. When a female chick hatches her ovary is fully formed albeit very small. The ovary contains 13,000-14,000 ova that only mature into yolks with the addition of a special fluid called 'yolk fluid'. Each ovum starts out surrounded by a membrane called the vitteline membrane. Over time, yolk is added as the ovum develops. When a female chick hatches she is equipped with all of the eggs that she will ever have.
Ovulation is the release of a mature ovum from the ovary. The ovum is released into the oviduct. The ovum, enclosed in a sac, ruptures along the stigma. The release of the ovum occurs 30-75 minutes after the previous egg is laid.
Diagram 8 shows the female reproductive system
The oviduct is a convoluted tube about 25-27 inches long, which is divided into 5 major sections. These sections are the infundibulum, magnum, isthmus, shell gland/uterus, and the vagina.
The first part of the oviduct, the infundibulum, is 3-4 inches long and it engulfs the ovum that is released from the ovary. The ovum then remains in the infundibulum for 15-18 minutes. The infundibulum is the area in which fertilization can take place.
The next section of the oviduct is the magnum which is 13 inches long. The magnum is the largest section of the oviduct. The ovum remains in the magnum for 3 hours. It is here that the albumen is added.
The third section of the oviduct is the isthmus which is 4 inches long. The egg remains here 75 minutes. The isthmus is slightly constricted. The isthmus is where the inner and outer shell membranes are added.
The next section of the oviduct is the shell gland, or uterus. The shell gland is 4-5 inches long and the egg remains here for over 20 hours. As the name implies, the shell is developed here. The hen sources 47% of her calcium from her bones and her diet supplies the rest. The shell gland is also where the pigment is applied.
The last section of the oviduct is the vagina which is 4-5 inches long and does not play a part in egg formation. The vagina's function is to push the egg out of the body. There are glands located in the vagina where sperm is stored. It is these glands which allow a hen to store sperm for extended periods of time. The bloom is added to the egg in the vagina.
The male reproductive system
Unlike mammals, the avian male reproductive system is entirely inside of the bird. Near the anterior ends of the kidneys, along the back, the male chicken possesses two testes. They are light yellow in color and elliptical shaped. Each ductus deferens opens into a small bump, or papilla, on the dorsal wall of the cloaca. The papilla serve as the copulation organ. The rudimentary copulatory organ is located on the medial ventral portion of the cloaca. It is this that is used to vent sex young chicks.Diagram 9 shows the reproductive system of the male chicken alongside the reproductive system of the female chicken
The male reproductive system and how it functions is almost entirely the same as with mammals, but does a few key differences.
Sperm is produced in the seminiferous tubules which are located in the testes. Sperm production occurs best at slightly cooler temperatures. Because of this, spermatogenesis may occur primarily at night when the body temperature of the bird is lower. Sperm are stored at the terminal end of the vas deferens.
Lying cranioventral to the first kidney lobe are the paired testes. The vas deferens emerges medially and passes caudally to the cloaca where it has a common opening with the ureter in the Urodeum. The terminal vas deferens is swollen as a storage organ: the seminal glomus.
Sperm formation is temperature sensitive. Male birds tend to have relatively low extragonadal sperm reserves and sperm are ejaculated soon after production in the testes.
The next page will discuss the circulatory system.
- Next page: The Circulatory System
- Previous page: The Muscle System
