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Animal Reproduction. 2 forms of reproduction. Asexual Creation of a new individual without the fusion of egg and sperm Sexual The fusion of haploid gametes to form a zygote which is diploid. Asexual Reproduction . Parthenogenesis The egg develops without being fertilized Fragmentation
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2 forms of reproduction • Asexual • Creation of a new individual without the fusion of egg and sperm • Sexual • The fusion of haploid gametes to form a zygote which is diploid
Asexual Reproduction • Parthenogenesis • The egg develops without being fertilized • Fragmentation • Breaking the body into several pieces which develop into complete adults • Budding • New inviduals splitting off from existing ones • Fission • Separation of parents into two or more individuals of approximately equal size
Sexual reproduction • 2 kinds • External fertilization • Internal fertilization
External Reproduction • Eggs are shed by the female and fertilized by the male in the environment • Due to the special environment where an egg can develop, it only takes place in moist environments. • Mostly fish, amphibians • 1 male fertilizing the eggs of one female
Internal Reproduction • Sexual reproduction is the creation of offspring by the fusion of haploid gametes to create a diploid zygote. • The female gamete, the ovum, is a large and none motile cell. • The male gamete, spermatozoon, is a small, motile cell. • Sexual reproduction helps to increase genetic variation by generating a unique combination of genes inherited by both parents.
Reproductive System of a Human Male • External reproductive organs • Scrotum • Contain the testes and held outside the abdominal cavity • Penis • Reproductive structure outside the abdominal cavity responsible for delivering sperm into the female reproductive tract • Internal reproductive organs • Testes • The gonads, responsible for creating sperm • Accessory glands (Ex: Prostate) • Responsible for depositing various things within the urethra and semen to help assist the reproductive process
The Accessory Glands • Seminal vesicles • Contribute about 60% of the total volume of semen • Thick, yellowish, alkaline • Contains Fructose and absorbic acid • Prostate gland • Thin and milky • Anticoagulant enzymes, citrate, slightly acidic • Bulbourethreal glands • Neutralize any acidic urine located within the urethra
Sperm • Spermatogenesis is a continuous and prolific process • Each ejaculation of a human male contains 100 to 650 million sperm cells. • Structure of Sperm: • Head • Contains the haploid nucleus • Acrosome • Tip of the head which helps penetrate eggs • Spiral Mitochondrian • Provides ATP for momvement of the tail
Reproductive Anatomy of a Human Female • External reproductive structures • Clitoris • Labia surrounding the clitoris and vaginal opening • Internal reproductive structures • Ovary • Chambers to conduct the gametes and house the embryo and fetus
The Ovary The ovary lies within the abdominal cavity and attached to the uterus. Each ovary is enclosed in a tough protective capsule and contain many follicles. A follicle is one egg cell surrounded by many layers of follicle cells These are responsible for nourishing and protecting the egg cell.
Internal Reproductive System • Oviduct (fallopian tube) • Funnel-like opening and contains cilia on the inner epithelium lining • Convey the egg cell down the duct to the uterus • Uterus • Thick, muscular organ • Can expand during pregnancy to accommodate a 4-kg fetus • Vagina • The chamber that forms the birth canal through which the baby is born • Repository for sperm during sexual reproduction • Bartholin’s Glands, located near the opening, responsible for lubrication during sexual intercourse • Mammary glands (Not part of the reproductive system but important) • Small sacs of epithelial tissue secrete milk, which drains into ducts emptying into the nipple
External Reproductive System • The vaginal opening and urethral opening are located within a region called the vestibule, bordered by skin folds called the labia minora. • Labia majora • encloses and protects the labia minora and vestibule • Clitoris • Short shaft supporting a rounded glans covered by a small hood of skin (Prepuce) • Erectile tissue with a rich supply of nerve endings
The development of Eggs • Oogenesis is the development of mature, unfertilized egg cells. • The primary oocytes replicate their DNA and enter prophase 1 of meiosis (at birth) waiting to be activated by hormones. • At puberty FSH beings to stimulate a follicle to begin growing again and induces the primary oocyte to complete the first meiotic division. • The second meiotic division completes when the egg is fertilized.
The differences • 1) During the meiotic divisions of oogenesis cytokenesis is unequal because the second oocyte monopolizes the cytoplasm. • 2) While the cells from which sperm development continue to divide by mitosis throughout the male’s life, an ovary already contains all the cells it will ever have that will develop into eggs. • 3) Oogenesis has long down time, while spermatogenesis produces more sperm in an uninterrupted sequence.
Male Hormones • The principal sex hormones are androgens • Testosterone is the most important • Responsible for primary and secondary sex characteristics. • Primary: • Development of reproductive ducts • Development of external reproductive structures • Sperm production • Secondary: • Deepening of the voice • Distribution of facial and pubic hair • Muscle growth
Female Hormones • GnRH – gonadotropin-releasing hormone • Secreted by the hypothalamus • FSH • Follicle stimulating hormone • LH • Luteinizing hormone
Estrous Cycle • Similar to the menstrual cycle, but some key differences. • Estrous • Characterized by specific times in which the vaginal changes permit mating • No shedding of the uterine lining occurs, rather it is reabsorbed by the uterus. • More behavioral changes in the females.
Menstrual Cycle • Menstrual Flow Phase • Menstrual bleeding occurs • Lasts for a few days • Proliferative phase • Thin endometrium regenerates and thickens. • Lasts for 1-2 weeks • Secretory Phase • Endometrium continues to thicken and develops glands tat secrete fluid rich in glycogen. • If an embryo is not implanted in the uterine lining, the cycle starts over
Ovarian Cycle • Another cycle parallel to the menstrual cycle. • Hormonal responses and activity have a large party to do with this cycle. • Divided into 2 phases: • Follicular phase • Luteal phase
Follicular Phase • Follicles in the ovary begin to grow and the egg cell enlarges. • The FSH stimulates follicle growth at this point in time, while the levels of FSH and LH are still relatively low. Follicles have no receptors for LH at this point. • When estrogen begins to rise by the growing follicles, there is a steep increase in the levels of both of these hormones due to a response by the GnRH. • At this point follicles have LH receptors, and ovulation is triggered in response to the large LH concentration. • Ovulation takes place about a day after this surge. • Ovulation is when the follicle and adjacent wall of the ovary rupture and release the oocyte.
Luteal Phase • The follicular tissue left behind in the ovary, form the corpeus lateum, a glandular structure. • Under continued LH during the luteal phase, the corpus luteum secretes estrogen and progesterone. It reaches its maximum development about 8 to 10 days after ovulation. • As these levels rise, hormones exert negative feedback on the hypothalamus inhibiting the secretion of LH and FSH. • The estrogen and progesterone subsequently go down. • The corpus luteum soon disintegrates. • Soon the pituitary gland secretes enough FSH to stimulate the growth of follicles and start the cycle over again.
Conception to Birth • Placental males go through the process of pregnancy (gestation), which is the process of carrying developing individuals in the uterus. • Pregnancy is preceded by conception, the fertilization of the egg by a sperm cell, and continues until the birth of the offspring.
Human pregnancy • It is divided into three trimesters. • The First Trimester is a period of the most radical change for both the mother and the baby.
First Trimester • The egg is fertilized in the oviduct. • After 24 hours, the zygote begins dividing now called a cleavage. • By about a week, it is called a blastocyst, a sphere of cells. • This blastocyst implants itself into the endometrium, which then grows over the blastocyst. • Until tissues grow out from the embryo and interacts with the endometrium to form the placenta, an organ containing the embryonic and maternal blood vessels, the endometrium provides nutrients to the embryo. • This is the main period of organogenesis. • By the 4th week the heart starts beating • By the eigth week all major structures of the adult are present in rudimentary form. • HCG, human chorionic gondaotropin, is released which maintains secretion of progesterone and estrogen by the corpus luteum through the first trimester. Without this, menstruation would occur. • At this point it is known as a fetus.
Second Trimester • The fetus grows rapidly and is extremely active. • Hormone levels stabilize as HCG declines, the corpus luteum detoriorates, and the placenta makes its own progesterone.
Third trimester • Once again the fetus grows rapidly. • During this trimester, Oxytocin receptors in the uterus are formed. • Oxytocin, produced by both the fetus and the mother’s pituitary gland, stimulate powerful contractions by the smooth muscles of the uterus. • It also enhances contractions • The stresses associated with contractions, stimualte the release of more oxytocin and prostagladins, a positive feedack system that underlies the three stages of labor.
Birth • Birth, or parturition, occurs through a series of strong rhytmic uterine contractions. • The second stage is the elivery of the baby. • Strong contractions force the fetus down and out of the uterus and vagina. • The final stage is the delivery of the placenta which follows the baby.
