Chapter 46: Animal Reporduction Flashcards
Parthenogenesis
The development of a new individual from an unfertilized egg
Mainly observed in invertebrates such as wasps and ants
Hermaphroditism
Each individual in a species has male and female reproductive systems
Two hermaphrodites can mate and some hermaphrodites can self-fertilize
Individuals of some species undergo sex reversals
Male reproductive anatomy
Internal organs:
- Gonads which produce sperm and hormones
- Accessory glands that secrete products needed for sperm movement
- Ducts that carry sperm and glandular secretions
Testes
The testes consist of highly coiled tubes surrounded by connective tissue
Sperm form in these seminiferous tubules
Leydig cells produce hormones and are scattered between the tubules
Male reproductive ducts
Sperm pass from the seminiferous tubules of a testis into the coiled duct of the epididymis
During ejaculation sperm are propelled through a muscular duct called the vas deferens which extend up and around the bladder
The vas deferens joins a duct from the seminal vesicle behind the bladder forming a short ejaculatory duct before exiting the penis through the urethra
Male reproductive accessory glands
Semen composition
Semen is composed of sperm plus secretions from three sets of accessory glands
The two seminal vesicles contribute about 60% of the total volume of semen
- Fluid is thick, yellowish, and alkaline
- Contains mucus, fructose, coagulating enzymes, ascorbic acid, and prostaglandins
The prostate gland secretes its products directly into the urethra through several small ducts
- Fluid is thin and milky
- Contains anticoagulant enzymes and citrate
The bulbourethral glands secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra
Penis anatomy
Composed of three cylinders of spongy erectile tissue
The head of the penis is called the glans and has a thinner skin covering than the shaft and is more sensitive to stimulation
The glans is surrounded by a fold of skin called the prepuce or foreskin
Female reproductive anatomy
External reproductive structures include the clitoris and two sets of labia which surround the clitoris and vaginal opening
The internal organs are a pair of gonads and a system of ducts and chambers that carry gametes and house the embryo and fetus
Ovaries
The outter layer of the ovary contains many follicles which consist of a partially developed egg, called an oocyte, surrounded by support cells
Oviducts and uterus
The egg cell travels from the ovary to the uterus via an oviduct, or fallopian tube
- Cilia in the oviduct conveys the egg to the uterus by drawing fluid from the body cavity into the oviduct
The endometrium is the uterine lining and is richly supplied with blood vessels
The uterus is a thick muscular organ that narrows the base and forms the cervix which opens into the vagina
Vagina and vulva
The vagina opens to the outside at the vulva, the collective term for the external female genitalia
The vulva consists of the:
- Labia majora- a pair of thick fatty ridges that enclose and protect the rest of the vulva
- Labia minora- Internal pair of slender skin folds
- Hymen- a thin piece of tissue that partly covers the vaginal opening at birth
- Clitoris- has a head called a glans and is covered by the prepuce, a small hood of skin
Spermatogenesis
Oogenesis
Hormonal control of the male reproductive system
FSH stimulates the activity of Sertoli cells in the seminiferous tubules to nourish developing sperm
LH regulates Leydig cells scattered in the connective tissue between the tubules to produce testosterone and other androgens which in turn promote spermatogenesis
Two negative feedback mechanisms control sex hormone production in males
- Testosterone regulates the production of GnRH, FSH, and LH through negative feedback mechanisms
- Sertoli cells secrete the hormone inhibin which reduces FSH secretion from the anterior pituitary
The ovarian cycle
Follicular phase
Follicular phase (day 0−14)
- The hypothalmus secretes GnRH which stimulates the anterior pituitary to secrete a small amount of FSH and LH
- FSH stimulates follicle growth aided by LH and the cells of the growing follicle start to make estridiol
- As estridiol levels continue to rise they exert positive feedback on the hypothalmus and stimulate increased GnRH secretion and sensitivity
- The maturing follicle forms a bulge on the surface of the ovary and ruptures in response to a a peak in LH levels
- Ovulation marks the end of the follicular phase