Reproductive System Ch 46a

Both asexual and sexual reproduction occur in the animal kingdom Asexual reproduction involves the formation of individuals whose genes all come from one parent. There is no fusion of sperm and egg. Sexual reproduction is the formation of offspring by the fusion of haploid gametes. Ovum: female gamete - usually large and nonmotile. Spermatozooan: male gamete - usually small and motile. Sexual reproduction increases genetic variation among offspring.

Asexual Reproduction Sexual Reproduction

Hermaphroditism versus Gonochorism Sexuality Hermaphroditism versus Gonochorism Hermaphroditism: both sexes in the same individuals Gonochorism: sexes are separate Acropora sp., a hermaphoditic coral Fungia scutaria, a gonochoric coral eggs egg cloud sperm packet

Brooding vs Broadcast Spawning Brooding: eggs develop to planula stage in gastrovascular cavity of parent polyp Broadcast Spawning: eggs and sperm are shed into the water column where fertilization and development occurs D. Gulko released gametes planula in polyp Pocillopora damicornis, a brooder broadcast spawner

Sequential hermaphroditism: an individual reverses its sex during its lifetime. Protogynous: female to male Protandrous: male to female

Parthenogenesis Egg development without fertilization Aphid Daphnia Honeybee Whiptail lizard Komodo Dragon Hammerhead Shark

Internal and external fertilization both depend on mechanisms ensuring that mature sperm encounter fertile eggs of the same species Internal fertilization requires cooperative behavior that leads to copulation.

External fertilization requires a moist habitat that will protect a developing egg from desiccation and heat stress. Specific mating behaviors assure that sperm and egg will be in the same place at the same time. Surinam Toad

Pheromones: chemical signals released by one organism that influence the behavior of other individuals of the same species. Many act as male attractants. female male

Species with internal fertilization usually produce fewer zygotes but provide more parental protection than species with external fertilization Internal fertilization usually results in the production of fewer zygotes than does internal fertilization. However, the survival rate is lower for external fertilization than it is for internal fertilization.

The externally fertilized eggs of fishes and amphibians are surrounded by a gelatinous coat. The internally fertilized amniote eggs of birds, reptiles, and monotremes are protected by calcium and protein shells. In mammals the embryo is retained within the females reproductive tract. Platypus egg New born platypuses and Mom

Parental care of offspring may occur regardless of whether fertilization is external or internal.

Complex reproductive systems have evolved in many animal phyla The least complex reproductive systems lack gonads. Polychaete worms lack gonads. Eggs and sperm develop from undifferentiated cells lining the coelom. Some reproductive systems, such as that seen in parasitic flatworms, can be very complex.

Reproductive anatomy of a parasitic flatworm

Most insects have separate sexes with complex reproductive systems. In many species the female reproductive system includes a spermatheca, a sac in which sperm may be stored for a year or more.

The basic plan of all vertebrate reproductive systems are very similar. However, there are variations. In many non-mammalian vertebrates the digestive, excretory, and reproductive systems share a common opening to the outside, the cloaca. Mammals have separate opening for the digestive and reproductive systems. Female mammals also have separate openings for the excretory and reproductive systems.

Human reproduction involves intricate anatomy and complex behavior Reproductive Anatomy of the Human Male. The scrotum and the penis are the external components of the reproductive system. The internal reproductive organs consist of gonads, accessory sex glands, and ducts.

Male Reproductive System

Male Reproductive System

The sensitive glans penis is covered by thinner skin. External structure of the penis: The shaft of the penis is covered by relatively thick skin. The sensitive glans penis is covered by thinner skin. The glans is covered by the prepuce which may be removed by circumcision. There is no verifiable health benefit to circumcision.

The engorgement of the penis with blood causes an erection. The penis is composed of three layers of spongy erectile tissue. During sexual arousal the erectile tissue fills with blood from arteries. The resultant increased pressure seals off the veins that drain the penis. The engorgement of the penis with blood causes an erection. An erection is essential to the insertion of the penis into the vagina. The penis of some mammals possesses a baculum, a bone that helps stiffen the penis.

Viagra® acts by promoting the action of nitric oxide. Impotence can result from the consumption of alcohol and other drugs, and emotional, nervous system, or circulatory problems. Treatment includes drugs and penile implant devices. Viagra® acts by promoting the action of nitric oxide.

Testes

Testes are the male gonads. Consists of many highly coiled seminiferous tubules surrounded by layers of connective tissue. Sperm form in seminiferous tubules. Leydig cells (interstitial cells), scattered between seminiferous tubules produce androgens (ex. testosterone).

Testes are located in the scrotum, outside the body cavity. This keeps testicular temperature cooler than the body cavity. The testes develop in the body cavity and descend into the scrotum just before birth.

From the seminiferous tubules sperm pass to the coiled tubules of the epididymis. It takes about 20 days for sperm to pass through the tubules of the epididymis. In the epididymis sperm become motile and gain the ability to fertilize.

Semen Seminal fluid is thick, yellowish, and alkaline. It contains mucus, fructose, a coagulating enzyme, ascorbic acid, and prostaglandins. Accessory glands: seminal vesicle prostate gland bulbourethral gland

Seminal vesicle: A pair of glands that secrete a liquid component of semen into the vas deferens. Secretion is alkaline, which neutralizes the acidic condition of the female genital tract. Seminal fluid contains fructose. Seminal Vesicle

Prostate gland: Location- surrounds and opens into the urethra where it leaves the bladder. Secretion- slightly alkaline fluid that activates the sperm and prevents them from sticking together Prostate problems are common in males over 40. Prostate cancer is one of the most common cancers in men. Prostate

Bulbourethral gland (Cowper’s gland): Location- paired glands that lie beneath the prostate Secretion- a thick, clear alkaline mucous that drains into the membranous urethra. Function- It acts to wash residual urine out of the urethra when ejaculating semen-- raises pH; neutralizes acidity of urine. Bulbourethral gland

Ejaculation Ejaculation propels sperm from the epididymis to the vas deferens. The vas deferens run from the scrotum and behind the urinary bladder. Here each vas deferens joins with a duct from the seminal vesicle to form an ejaculatory duct. The ejaculatory ducts open into the urethra. The urethra drains both the excretory and reproductive systems.

Ejaculate A male usually ejaculates about 2 – 5 mL of semen; each milliliter containing about 50 – 130 million sperm. Bulbourethral fluid also carries some sperm released before ejaculation. This is one of the reasons why the withdrawal method of birth control has a high failure rate.

Spermatogenesis

Mature Spermatozoa acrosome head nucleus tail mitochondria

Seminiferous Tubules

Seminiferous Tubules spermatozoa Sertoli cell spermatids spermatogonium 1º spermatocyte 2º spermatocyte spermatids Sertoli cell spermatozoa Seminiferous Tubules

Sperm Maturation & Development (maturation: 62-72 days)

Hormones Involved in Spermatogenesis Gonadotropin Releasing Hormone (GnRH) Follicle Stimulating Hormone (FSH) Interstitial Cell Stimulating Hormone (ICSH), also called LH Testosterone Inhibin

Hormonal Control of Spermatogenesis Hypothalamus GnRH Anterior Pituitary ICSH/LH FSH

Hormonal Control of Spermatogenesis ICSH/LH Interstitial Cells Testosterone

Hormonal Control of Spermatogenesis FSH Testosterone Sertoli Cells Spermatogenesis Inhibin

Hormonal Control of Spermatogenesis Feedback Inhibition Inhibin Acts on anterior pituitary Inhibits FSH production Testosterone Acts on hypothalamus Inhibits GnRH production

Some Other Effects of Testosterone muscle and bone growth facial and pubic hair growth thickening of vocal cords growth of pharyngeal cartilage hair follicle effects stimulates sebaceous glands

Reproductive Anatomy of the Human Female External reproductive structures: labia clitoris vaginal opening Internal reproductive structures: ovaries fallopian tube (uterine tube) cervix uterus vagina fimbrae

Female Reproductive System Biology 100 Human Biology Female Reproductive System uterine tube fimbriae ovary uterus bladder cervix urethra clitoris vagina l. minora l. majora vaginal orifice

Biology 100 Human Biology egg uterine tube ovary ovary uterus perimetrium endometrium myometrium cervix vagina

Oogenesis in the Ovary

Oogenesis Ovary- contains 400,000 oocytes; release about 500 in a lifetime Ovary- under influence of FSH. The follicles mature every 28 days Primary follicle produces estrogens And primary oocyte completes its 1st division produces 2ndary oocyte and polar body

Oogenesis Aprox 1/2 way through the 28 day cycle the follicle reaches the mature Vesticular or Graffian follicle stage. Estrogen levels rise and release LH and FSH and triggers ovulation. The 2ndary oocyte travels down the uterine tube to the uterus. If fertilized by sperm, it will produce a zygote

Oogenesis

Ovum

Hormones Involved in the Female Reproductive Cycle Gonadotropin Releasing Hormone (GnRH) Follicle Stimulating Hormone (FSH) Luteinizing Hormone (LH) Estrogen Progesterone

Female Hormonal Cycle Hypothalamus GnRH Anterior Pituitary LH FSH

Female Hormonal Cycle FSH LH Follicle Cells Estrogen

The Uterine Cycle

Ovarian Cycle

Hormone Fluctuation

Some Other Effects of Estrogen breast development external genitalia growth stimulates bone growth increases HDL and lowers LDL

Menopause: cessation of ovarian and menstrual cycles. Usually occurs between ages 46 and 54. Due to ovaries decreased responsiveness to gonadotropins. Menopause affects: changes in sexual desire triggers mood swings causes debilitating hot flashes may lead to bone and heart problems short-term memory loss insomnia

Milk drains into a series of ducts opening at the nipple. Mammary glands. Are present in both males and females. Are not a component of the reproductive system. Contain epithelial tissue that secrete milk. Milk drains into a series of ducts opening at the nipple.