REPRODUCTIVE SYSTEM


-Sahaj Patel
-Jessie Wong
-Crystal Vinuya

Quick Overview:







Key Concepts:


SECTION 1: Both Asexual and sexual reproduction occur in the animal kingdom
  • Sexual Reproduction: the fusion of haploid gametes forms a diploid cell, the zygote.
      • Animals that develop from zygotes can in turn give rise to gametes by meiosis.
        • Female gamete is called the egg. It is large and does not move
        • Male gamete is called the sperm. It is smaller than the egg and it can move
  • Asexual Reproduction: is the making a new individuals without the fusion of egg and sperm.
    • Most asexual animals rely on mitotic cell division
    • Mechanisms of Asexual Reproduction
      • Many invertebrates can reproduce asexually by fission.
      • Fission: the separation of a parent organism into two individuals of approximately equal size
      • Budding: individuals arise from outgrowths of existing ones
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        Budding
      • 2 Step Process fragmentation and regeneration
        • Fragmentation: breaking the body in several pieces
        • Regeneration: regrowth of lost body parts
    • Parthenogenesis: form of asexual reproduction in which an egg develops without being fertilized
      • Reproduction by parthenogenesis happens in certain species of bees, wasps, and ants.
      • progeny can be either haploid or diploid
      • If it is a haploid, the offspring develop into adults that produce eggs or sperm without meiosis.
    • Sexual Reproduction: An Evolutionary Enigma
      • Sex creates diverse combinations of parental genes made during meiotic recombination and fertilization.
      • Sexual reproduction may enhance the reproductive success of parents when environmental factors change rapidly.
      • Asexual reproduction is most advantageous in favorable environments because it copies the genotypes precisely from one generation to the next.
      • Sexual reproduction can be advantageous because beneficial gene combinations arising through recombination might speed up adaptation.
        • Significant when the rate of beneficial mutations is high and population size is small
    • Reproductive Cycles and Patterns
      • Animals exhibit cycles in reproduction to conserve resources such as reproducing only when sufficient energy sources or stores are available and when environmental conditions favor the survival of offspring.
      • Ovulation: the release of mature eggs, which occurs during the midpoint of each cycle
      • Reproductive cycles are controlled by hormones, which are regulated by environmental cues.
        • Common environmental cues are changes in day length, seasonal temperature, rainfall, and lunar cycles
      • Animals generally reproduce only at certain times of a year.
      • Animals may alternate between asexual and sexual reproduction cycles.
        • In Aphids, rotifers, and water fleas, the females demonstrate both types.
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          Water Flea Daphnia
      • Several genera of fishes, amphibians, and reptiles reproduce exclusively by a complex form of parthenogenesis that involves the doubling of chromosomes after meiosis, producing diploid offspring.
      • Ovulation is more likely to occur if the individual is mounted during the critical time of the hormone cycle
    • Hermaphroditism became the evolutionary solution to sessile animals who are not able to encounter the opposite sex.
      • Hermaphroditism: each individual has both male and female reproductive systems.
      • Any two individuals can mate
      • Some hermaphrodites are capable of self-fertilization
      • Example - earthworms
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    • Another reproductive pattern involves sex reversal, in which an individual changes its sex during its lifetime.
      • Examples - bluehead wrasse and oyster species
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SECTION 2: Fertilization depends on mechanisms that bring together sperm and eggs of the same species

  • What is Fertilization?
    • Fertilization is the union of a sperm and egg.
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      • External Fertilization
        • In external fertilization, the female releases eggs into the environment, where the male fertilizes them.
        • External fertilization requires a moist environment to prevent gametes from drying out and for the sperm to be able to swim to the eggs
        • external image ExternalFertilization.jpg
        • In external fertilization, physical contact not necessary; however timing in crucial to ensure that the gametes from the parents meet
        • Synchronized Release of Gametes
          • Spawning
            • Individuals of a certain species release their gametes into the water at the same time
            • Sometimes, chemical signals trigger certain individuals to release their gametes
          • Changes in day length triggers some animals to release their gametes
        • Unsynchronized Release of Gametes
          • Advantages of unsynchronized release of gametes include: mate selection and release of eggs and sperm at the same time, which result in better survival rates for the offspring
      • Internal Fertilization
        • In internal fertilization, sperm from the male is deposited in or near the female reproductive tract.
        • In internal fertilization, fertilization occurs within the tract
        • Internal fertilization requires compatible reproductive systems and structures
        • Copulation usually occurs along with internal fertilization
          • Male copulatory systems deliver sperm
          • Female reproductive tracts have receptacles to store sperm
            • The female reproductive tracts also deliver sperm to mature eggs
        • Pheromones, like hormones, are signaling molecules that are released into the environment to attract potential mates
  • Ensuring the Survival of Offspring
    • All species tend to produce more offspring than can survive
      • External Fertilization tends to produce more gametes, but only a few zygotes develop
      • Internal Fertilization tends to produce less gametes, and there is greater protection for the embryo such as parental care
    • Animals have special adaptations to protect them when they are in developmental and embryonic stages
      • Some animals remain only in the uterus for a while (For example, some marsupials leave the uterus after a while and attach themselves to a mammary gland and continue fetal development)
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      • Placental animals remain in the uterus throughout fetal development; the mother’s blood supply’s the embryo through a specialized organ—the placenta.
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      • Parental care (Many mammals, including humans, provide parental care. Birds and some reptiles and amphibians also ensure parental care)
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  • Gamete Production and Delivery
    • During embryogenesis, precursor cells are created that remain inactive throughout development. Sexual reproduction relies on these precursor cells for the production of ova and sperm
    • Later, these precursor cells are amplified in number
    • Gonads are the organs that produce gametes
    • In some animals, gametes are derived from undifferentiated cells of the body cavity (coelom)
    • Insect Reproduction
      • Most insects have separate sexes and complex reproductive systems
      • Sperm are stored in seminal vesicles and deposited in female reproductive tracts
      • Eggs are produced in the ovaries and fertilized in the vagina
      • Spermatheca are sperm storing sac carried in females
    • Parasitic worms are hermaphroditic, which means they have both female and male reproductive structures
    • Many vertebrates, with the exception of mammals, have a common opening (cloaca) for excretory waste and reproductive systems.
    • Mammals have separate openings for the excretory and reproductive systems
    • Mechanisms influence the success of fertilization


SECTION 3: Reproductive organs produce and transport gametes


Female Reproductive Anatomy
  • Ovaries
    • Ovaries are female gonads that held by ligaments in the abdominal cavity
    • filled with follicles, which are filled with oocytes, which are partially developed eggs, surrounded by support cells
    • the support cells nourish and protect the cells during oogenesis, the formation and development of an ovum
    • Menstruation/ Ovulation is when 1 follicle is released and expels an egg
    • A primary female sex hormone is Estradiol
    • After ovulation, a tissue called the corpus luteum secretes estradiol with progesterone which helps form the uterine lining during pregnancy
  • Oviducts and Uterus
    • Oviducts (or fallopian tube) connect the ovaries to the uterus and the vagina
    • Cilia on the epithelial lining help when an egg is traveling down the oviduct.
    • The Uterus is the womb!
    • The richly supplied lining full of blood vessels is the endometrium
    • The Cervix is the opening to the vagina
  • Vagina and Vulva
    • The Vagina is the muscular yet elastic chamber used for the insertion of the penis!
    • Vulva is just a collective term for the external female genitals
    • The Labia Majora protects & encloses the vulva
    • The Labia Minora is a cavity surrounded by slender skin folds
    • A thin piece of tissue called the hymen covers the vaginal opening until it is ruptured by physical activity or sex


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AKA POPPING THEM CHERRIES

    • The Clitoris is a short shaft of with a rounded glan (or head) that is covered by a small hood of skin called the prepuce
    • During sexual arousal, the clitoris, vagina, and labia minora all engorge with blood and secrete lubricating mucus, facilitating sex.
  • Mammary Glands
    • Mammary Glands are present in both sexes but produce milk in females.
    • Within the glands, small sacs of epithelial tissue secrete milk, which drain into a series of ducts at the nipple
    • Because of the low level of estradiol in males, male breasts remain small.



Male Reproductive Anatomy
  • Testes
    • Testes are male gonads which are coiled tubes surrounded by connective tissue
    • The tubes are seminiferous tubules where sperm is formed
    • Leydig cells, located in seminiferous tubules, produce testosterone and androgens
    • Sperm is only produced when the testes are cooler than body temperature
    • The scrotum achieves this by maintaining testis temperature about 2˚C below the abdominal cavity
    • Testis within a scrotum = testicle
  • Ducts
    • In the seminiferous tubules, sperm passes into coiled tubes of the epididymis
    • During the passage, the sperm completes their maturation and become motile, but only fertilize when in the female reproductive system
    • During ejaculation sperm is propelled through a muscular duct called the vas deferens
    • Each Vas deferens extends around the urinary bladder, where it joins the seminal vesicle called the ejaculatory duct
    • The Urethra is the outlet tube for excretory and the reproductive system
Accessory Glands
  • Seminal Vesicles
    • There are 2 of them
    • contribute to 60% of semen
    • Semen: Thick, yellowish, and full of alkaline
    • contains mucus, fructose, enzyme, ascorbic acid, and prostaglandins
  • Prostate Gland
        • contains thin fluid made of anticoagulant enzymes and citrate
        • Cause of some of the most common medical problems in men aged 40+
        • Benign cancer occurs in half of the men and enlargement occurs in almost all men over 70+
    • Bulbourethral Glands
      • secrete clear mucus that neutralizes acidic urine remaining in urethra before ejaculation
      • carries sperm
  • Penis
    • Contains the urethra & 3 cylinders of spongy erectile tissue
    • Erections= gorge of blood and sealing of pressure
    • alcohol, drugs, emotional issues, and aging can cause erectile disfunction
    • main shaft of the penis is thick skin
    • glans are mich thinner and sensitive to simulation


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  • Human Sexual Response
      • Sexual response in Males and Females
        • Vasocongestion: filling of tissue with blood
        • Myotonia: increased muscle tension
        • Step One: Excitement
          • Vasocongestion is evident in breasts, penis, labia and mytonia may occur in arms and legs
        • Step Two: Plateau
          • Breathing and heart rate increases, and depression for receiving sperm occurs in the back of the vagina
        • Step Three: Orgasm
          • Emission~ glands and duct contract
          • Ejaculation~ urethra contracts and semen is expelled
          • Orgasms only last 0.8 seconds
        • Step Four: Resolution
          • Vasocongested organs relax
          • Refractory period

SECTION 4: The timing and pattern of meiosis in mammals differ for males and females

    • Gametogenesis is the production of gametes
    • Gametogenesis differs in males and females
      • Spermatogenesis occurs continuously in the testes (within the seminiferous tubules)
        • Spermatogonia are the stem cells that give rise to sperm
        • Sperm are small and motile
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        • Spermatogonia produce spermatocytes that undergo meiosis to produce spermatids (There are four spermatids at the end of meiosis)
        • The head of the sperm consists of a haploid nucleus and acrosome, which contains enzymes that help the sperm penetrate the egg
        • The energy required for the movement of the flagellum, or tail, comes from the ATP provided by the mitochondria
        • external image spermatogenesis.gif
      • Oogenesis occurs in the female embryo.
        • Oogonia are produced from the primordial germ cells
        • Eggs, however, are large and not motile
        • Eggs hold the initial food stores for the embryo
        • external image conception.png
        • These germ cells divide into primary oocytes, which are arrested in prophase I before birth
        • During puberty, FSH stimulates the oocytes to undergo meiosis, and the oocystes are allowed to complete meiosis I. These oocytes are known as secondary oocytes and are arrested in metaphase II
        • In humans, meiosis II is completed only when a sperm penertrates the oocyte
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        • Meiotic cytokinesis is unequal, which produced one large ovum and three smaller haploid polar bodies that disintegrate

SECTION 5: The interplay of tropic and sex hormones regulates mammalian reproduction

    • LH and FSH regulate gametogenesis directly through target tissues in the gonads and indirectly by regulating sex hormones production
    • principal sex hormones are steroid hormones
      • In males, androgens such as testosterone
      • In females, estrogen such as estradiol and progesterone
    • Androgens promote the development of the primary sex male characteristics, such as structures involved in reproduction.
      • causes the voice to deepen, facial and pubic hair to develop, and muscles to grow
      • increases general aggressiveness
    • Estrogens
      • At puberty estradiol stimulates breast and pubic hair
      • induces fat deposition in the breasts and hips, increases water retention, and changes calcium metabolism
    • Hormonal Control of the Male Reproductive System
      • FSH and LH are both required for normal spermatogenesis.
        • FSH promotes the activity of Sertoli cells, which nourish developing sperm
        • LH promotes Leydig cells secrete testosterone in the tubules.
      • Two negative-feedback mechanisms control sex hormone production in males.
        • GnRH, FSH, LH effects on the hypothalamus and pituitary.
        • Inhibin, hormone that is produced by Sertoli cells, acts on the anterior pituitary gland to reduce FSH secretion.
    • The Reproductive Cycles of Females
      • The cyclic shedding of the endometrium from the uterus is called menstruation.
      • Cyclic events that take place in the ovaries is called the ovarian cycle
        • Includes the Follicular phase
          • Growing of the follicle
          • Maturing of the follicle
          • FSH and LH increases until ovulation begins to happen
          • Estradiol is secreted by growing follicle in increasing amounts.
        • Ovulation
        • Luteal phase
          • Development of the corpus luteum
          • Degeneration of the corpus luteum.
          • Progesterone and estradiol is secreted by corpus luteum.
      • Changes that define changes in the uterus is menstrual cycle, also known as uterine cycle.
        • Proliferative phase: endometrium regenerates and thickens.
        • Secretory phase: endmetrium continues to thicken, becomes vascularized, and develops glands that secrete a fluid rich in glycogen.
        • Menstrual flow phase: menstrual bleeding occurs
        • Endometriosis, a disorder in which some cells of the uterine lining migrate to an abdominal location that is abnormal, or ectopic.
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      • Menopause
        • End to ovulation and menstruation
        • Usually around the ages of 46 and 54
        • lose their responsiveness to FSH and LH, resulting in a decline in estradiol production by the ovary.
      • Menstrual Versus Estrous Cycles
        • Only humans and certain primates have menstrual cycles
        • Other mammals have estrous cycles, in the absense of a pregnancy, the uterus reabsorbs the endometrium and no extensive fluid flow occurs.
        • Estrus, a period of sexual activity is the only time a female is receptive to mating.
        • Estrus is also called heat and the female's body temperature increases slightly.
        • Length and frequency of reproductive cycles vary widely among mammals.

SECTION 6: In placement mammals, an embryo develops fully within the mother's uterus.


Conception, Embryonic Development, and Birth
    • 2-5 mL of semen is transferred with 70-130 million sperm in each milliliter.
    • When first ejaculated, semen coagulates and helps the sperm reach the cervix
    • Anticoagulants liquefy the semen and sperm begin swimming though the uterus and oviducts
    • Fertilization- also called conception- occurs when a sperm fuses with an egg in the oviduct
    • The following then occurs...
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    • After the blastocyst is implanted into the endometrium, the embryo secretes a hormone that signal its presence and regulates the mother's reproductive system
    • A hormone is called Human Chorionic Gonadtrophin (hCG)
    • In the absence of hormonal override, the corpus luteum would deteriorate, resulting in menstruation
    • Levels of hCG in maternal blood is so high, some is excreted into urine, a signal of pregnancy, or gestation
    • Human pregnancy averages 266 days from fertilization/ 40 weeks from start of last menstrual cycle
    • Pregnancies are terminated though chromosomal or developmental abnormalities
    • If a fertilized egg is lodged in the oviduct, serious internal bleeding may occur.

    • First Trimester
      • Human fertilization is divided into three trimesters of three months each
      • The embryo's body structures begin to differentiate
      • during the first 2-4 weeks of development, the embryo obtains nutrients from the endometrium
      • The outer layer of the blastocyst, the trophoblast, grows outward and mingles with the endometrium, forming the placenta
      • The placenta is a disk shaped organ made of blood vessels that provides immune protection, exchanges respiratory gases, and disposes metabolic wastes
      • splitting embryo during first month can result in identical twins (monozygotic) or fraternal twins (dizygotic)
      • First Trimester is the main period of organogenesis, the development of body organs
      • most susceptible to damage from radiation or drugs
      • The fetus grows to be about 5 cm long
      • High levels of progesterone initiate changes in the reproductive system
    • Second Trimester
      • Uterus grows enough to be obvious
      • fetus grows to 30 cm
      • fetal movements
      • Corpus luteum deteriorates
      • placenta takes over the production of progesterone
    • Third Trimester
      • fetus grows 3-4 kg in weight and 50 cm in length
      • the mother's organs become compressed and displaced, leading to urination, digestive blockages, and strain in back muscles
      • Prostagladins and hormones induces and regulates labor
      • Uterine contractions bring about birth, or parturition
      • Stage 1: opening and thinning of cervix
      • Stage 2: delivery of baby
      • Stage 3: delivery of placenta
      • Lactation is the postnatal care unique to mammals

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Maternal Immune Tolerance of the Embryo and Fetus
    • Contraception and Abortion
      • Contraception is the deliberate prevention of pregnancy
      • Contraception can be achieved through abstinence
      • temporary abstinence, or the rhythm method / natural family planning depends on refraining from intercourse when conception is likely
      • timing ovulation include factors such as changes in cervical mucus and body temperatures during the menstrual cycle.
      • a 10-20% of pregnancy is reported for couples using natural family planning
      • withdrawal of the penis before ejaculation is unreliable and sperm from previous ejaculations may be transferred
      • Barrier Methods:
        • condoms is one barrier method that leaves pregnancy rates less than 10%
        • a diaphragm is a dome shaped rubber cap inserted into the upper portion of the vagina before intercourse
      • Hormonal contraceptives in the form birth control pills have pregnancy rates of 1% or less
      • the most common birth control pills have a combination of synthetic estrogen and progestin
      • Another hormone based contraceptive contains only progestin which blocks a woman's cervical mucus preventing sperm from reaching the uterus
      • Progestin is administered several ways: time-release, capsules, injections, and tablets
      • Cardiovascular problems, abnormal blood clotting, high blood pressure, stroke, heart attack are all risks
      • however, women on birth control bills have morality rates of half of those of pregnant women.
      • the pill can also reduce ovarian and endometrial cancers
      • sterilization is the permanent prevention of gamete release
      • tubal ligation in women is to tie a section of oviduct, while a vasectomy in men is tying or cutting off the vans deferens
      • Abortion is the termination of a pregnancy in progress

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Modern Reproductive Technologies
    • Detecting Disorders during pregnancy
      • ultrasound can generate images using sound frequencies above the normal hearing range
      • Aminiocentesis and chorionic villus sampling are techniques where a needle is used to obtain fetal cells from fluid or tissue surround the embryo
      • all detectable disorders remain untreatable in the uterus
    • Detecting Diseases and other Disorders
      • Sexually Transmitted Diseases
      • Treating Infertility and Disorders
        • Infertility- an inablility to conceive offspring is common in 1 to 10 couples worldwide
        • reproductive technology can help with fertility problems
        • Hormone therapy can increase sperm/egg production
        • Assisted reproductive technologies involve removing eggs from hormonal stimulation and returns them into the woman's body
        • in in vitro fertilization oocytes are mixed with sperm from culture fishes and are implanted in the woman's uterus
        • intracytoplasmic sperm injection is drawn up into a needle and is injected directly into an oocyte to achieve fertilization

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