Reproductive System Lecture Notes

Reproductive System

Overview

• Reproductive Strategies

• Fertilization and Development

• Male Reproductive System

• Female Reproductive System

• Contraception and Infertility treatments

Asexual Reproduction

• Asexual reproduction is a type of reproduction that doesn't involve the fusion of gametes or change in the number of chromosomes. The offspring that arise from asexual reproduction inherit the full set of genes of their single parent.

• Bud formation shown, with a bud growing on a parent organism. G is noted, with a size of 0.5 mm.

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Clonal Reproduction

• The point of clonal reproduction is explored.

• The question of why some organisms evolved asexual reproduction is raised.

Hermaphroditic Organisms

• Hermaphroditic organisms possess both testes and ovaries in one individual.

  • Example: Tapeworms

• Even though they possess both sets of organs, they still require another organism to reproduce.

Sexual Reproduction

• Requires two parents.

• Produces gametes in gonads.

  • Testes produce sperm.

  • Ovaries produce eggs.

• Union of egg and sperm is called a zygote.

Importance of Sexual Reproduction

• The importance of sexual reproduction and why it evolved is questioned.

Reproduction on Land vs. Water

• Differences in reproduction between land and water environments are considered.

• Reference to Figure 29.3, illustrating reproduction on land.

Fertilization

• Two Types:

  • External: Egg and sperm unite outside the body.

  • Internal: Sperm and egg unite inside the female body.

• Copulation: A sexual union to facilitate the reception of sperm by the female.

Internal Fertilization Strategies

• Three main strategies for embryonic development:

  • Oviparity

  • Ovoviviparity

  • Viviparity

Oviparity

• Occurs in aquatic animals, most reptiles, some amphibians, and all birds.

• Eggs are fertilized internally and deposited outside to complete development.

• The evolution of the amniotic egg freed land animals from needing to reproduce in water.

Ovoviviparity

• Occurs in bony fish, cartilaginous fish, and some reptiles.

• Eggs are fertilized internally and retained within the mother to complete their development.

• The embryo obtains all nourishment from the egg yolk, and young are fully developed when hatched.

Viviparity

• Found in almost all mammals.

• Young develop within the mother, and nourishment is taken directly from the mother’s blood.

• Placenta: Structure through where blood and gas exchange occur.

• Has evolved only in mammals.

Human Reproduction

• In humans, the reproductive system is composed of:

  • Gonads that produce gametes and sex hormones.

  • Accessory organs that conduct gametes and, in females, house the embryo/fetus.

Male Reproductive System

• Testes

  • Gonads

  • Paired structure that produces sperm.

  • Housed in scrotum so sperm develop at a cooler temperature than body temperature.

• Epididymis

  • Site of sperm maturation.

• Vas deferens

  • Vasectomy severs or blocks the path of sperm.

• Urethra

  • Part of the urinary and reproductive system.

Penis

• Contains 3 columns of spongy erectile tissue.

• The erection is produced when neurons in the parasympathetic division cause the release of nitric oxide.

• This causes arterioles to dilate and engorge with blood.

• The pressure compresses other veins, not allowing blood to flow out.

Semen (seminal fluid)

• Contains sperm and secretions from 3 glands:

  • Seminal vesicles—secrete a thick, viscous fluid containing nutrients for sperm (about 60% of semen volume).

  • Prostate gland—secretes milky alkaline fluid believed to activate sperm; may become enlarged in older men (contributes to about 30% of semen volume).

  • Bulbourethral gland—mucous secretions with a lubricating effect (10% volume).

The Testes

• Spermatogenesis—meiosis reduces chromosome number from diploid (2n) to haploid (n).

• Sertoli cells support, nourish, and regulate the production of sperm.

Sperm

• Has 3 distinct parts:

  • Head with nucleus capped by acrosome.

  • Middle piece containing mitochondria.

  • Tail—flagellum.

Hormone Regulation in Men

• Hypothalamus has ultimate control of the testes’ sexual function.

• Secretes gonadotropin-releasing hormone (GnRH) that stimulates the anterior pituitary to produce the gonadotropic hormones.

• Both males and females have 2 gonadotropic hormones:

  • Follicle-stimulating hormone (FSH) promotes spermatogenesis in men.

  • Luteinizing hormone (LH) controls the production of testosterone in men.

Female Reproductive System

• Ovaries: Gonads

• Ducts

  • Oviducts

  • Uterus

• Vagina

Oviducts

• Also called uterine tubes or fallopian tubes.

• Extend from ovaries to uterus.

• Not directly connected to ovaries—fimbriae sweep ovaries.

Uterus

• About the size of a pear.

• Narrow end called cervix.

• Embryo embeds in lining (endometrium).

Vagina

• 45° angle with body's vertical axis.

• Mucosal lining lies in fold allowing for expansion.

External Genitalia - Vulva

• Mons pubis

• Labia major and labia minora

• Clitoris—at junction of labia minora

  • Homologous to penis

  • Shaft of erectile tissue

• Hymen—does not indicate virginity

  • Thin membrane obstructing vaginal opening

  • No biological function

  • Often torn by normal activities but may stay intact even through intercourse

Cycles

• Two types of cycles:

  • Ovarian - events in the ovary

  • Menstrual cycle - Events in the uterus

Ovarian Cycle

• Controlled by the two gonadotropic hormones FSH and LH.

• Consists of two phases:

  • Follicular phase

  • Luteal Phase

Follicular phase

• Begins in the first day of menstruation and lasts until 13th day

• One of the egg cells begin to mature into a sac- like structure called the follicle

• The follicle matures

Luteal Phase

• Begins day 15 to day 28

• Egg is released into the fallopian tubes and stays there for 24 hours

• If sperm does NOT fertilize the egg, the egg disintegrates

Menstrual Cycle

• Days 1–5—female sex hormones at low level, endometrium disintegrates, menses (blood, mucus, and degenerating endometrium) shed in menstruation.

• Days 6–13—increased estrogen causes endometrium (inner membrane of uterus) to thicken.

• Ovulation usually occurs on day 14 of a 28-day cycle.

• Days 15–28—increased progesterone causes endometrium to double in thickness and uterine glands to mature and be prepared to receive developing embryo; if no embryo embeds, low levels of hormones begins process over.

Reproduction Control

• Methods to control reproduction.

Male condoms

• Barrier with spermicide

Female Condom

• Condom/barrier that fits into cervix

Diaphragm - Female Contraceptive

• Latex cup that covers the cervix

Abstinence

• Most reliable and prevents STDs

Birth Control Pills

• Oral contraception

• Combination of estrogen and progesterone that shuts down production of LH and FSH

Contraceptive Implants

• Secretes synthetic progesterone and prevents ovulation

Contraceptive Injections

• Injections of estrogen and progesterone

IUD - Intrauterine Device

• Fertilization will not occur, and implantation of sperm cannot take place

Morning after pill

• Disrupts normal menstrual period making it difficult for embryo to implant

• Can also induce the shedding of uterus lining

Sterilization and Vasectomy

• Vas deferens in males is cut and tied

• Uterine tubes cut and tied

Common Birth Control Methods

• Table 29.1 outlines various birth control methods, their procedures, and effectiveness.

  • Includes abstinence, sterilization (vasectomy and tubal ligation), combined estrogen/progesterone methods (pill, injectable, vaginal ring and patch), progesterone-only methods (tube implant and injectable), IUD, cervical cap, male condom, female condom, coitus interruptus, spermicidal products, natural family planning, vaginal sponge and douche.

  • Effectiveness is measured by the percentage of sexually active women per year who will not get pregnant using the method.

Infertility

• Failure of a couple to achieve pregnancy after one year of regular unprotected sex

• Estimated one in six couples are infertile

• Cause can be attributed to the male (40%), female (40%), or both (20%)

• Male infertility is usually due to low sperm count and/or large number of abnormal sperm

• Female infertility is influenced by body weight

Assisted Reproductive Technologies

• Artificial insemination by donor (AID)

  • Harvested sperm are placed in the vagina by a physician

• Intracytoplasmic sperm injection (ICSI)

  • Single sperm injected into an egg

Assisted Reproductive Technologies Continued

• In vitro fertilization (IVF)

  • Immature eggs taken to maturity in lab dish

  • Sperm added for fertilization

  • Embryos transferred to woman in secretory phase of menstrual cycle

  • Excess embryos may be frozen

• Gamete intrafallopian transfer (GIFT)

  • Devised to overcome low success rate of IVF

  • Method the same as IVF except eggs and sperm placed in the oviduct immediately after being brought together

Sexually Transmitted Diseases

• Abstinence is best protection

• Latex condom offers SOME protection

• Viral STDs can be treated but not cured

  • AIDS

• Only bacterial STDs can be cured

  • Chlamydia, gonorrhea, and syphilis

3 Stages of AIDS

• Category A

  • May last about a year

  • Person asymptomatic carrier—no symptoms but may spread virus

  • Person remains well as long as helper T cell count is high enough

  • With drug therapy, patient may remain in this stage indefinitely

• Category B

  • May last 6–8 years

  • Weight loss, fatigue, fever, diarrhea

  • Infections such as thrush and herpes recur

• Category C

  • Nervous disorders, opportunistic infections

  • Without intensive treatment, patient dies 7–9 years after infection

Viral STDs

• Genital warts

  • Caused by human papillomaviruses (HPVs)

  • Most common STD today

  • Associated with cervical cancer and tumors of the vulva, vagina, anus, and penis

• Genital herpes

  • Painful genital blisters that rupture, leaving ulcers

  • After ulcers heal, disease lies latent until it recurs

  • Fever, stress, sunlight, and menstruation can cause recurrences

• Hepatitis

  • Infection of the liver leading to liver failure, liver cancer, and death

  • Hepatitis A—usually infected by drinking sewage-contaminated water but can be passed sexually

  • Hepatitis B—spread in same manner as AIDS, vaccine available

  • Hepatitis C—from contact with blood from infected person

Bacterial STDs

• Chlamydia

  • Infection usually mild or asymptomatic

  • Causes cervical ulcerations, which increases the risk of acquiring AIDS

  • Risk of pelvic inflammatory disease (PID)—can result in sterility or infertility

• Gonorrhea

  • Easier to diagnose in males—thick, greenish-yellow urethral discharge

  • Latent infection leads to PID in men and women

  • Healing tubes may become blocked by scar tissue leading to sterility or infertility

• Syphilis

  • 3 stages separated by latent periods

  • Final stage may affect cardiovascular and/or nervous systems

  • Bacteria can cross placenta causing birth defects or stillbirth

Other types of STDs

• Trichomoniasis

  • Caused by flagellated protozoan Trichomonas vaginalis

  • Most often acquired through sexual intercourse

  • Symptoms only found in females

  • Asymptomatic males are usually reservoir of infection

• Candida albicans

  • Yeast infection

  • Normal organism found in vagina but overgrows in some circumstances

Human Embryonic Development

• All the events that occur from the time of fertilization until the animal is fully formed

Amniotic Egg

• Structure of an amniotic egg, highlighting the embryo, leathery shell, chorion, allantois, and yolk sac.

Fertilization

• Egg and sperm fuse to form a zygote

Early embryonic development

• Embryonic period: first 2 months

• The zygote will develop in the oviduct for 6 days before implanting in the uterus

• Following fertilization:

  • Embryo undergoes cell division without growth resulting in a tight ball of cells called the morula

  • Morula continues to divide and then hollows out to form a blastula

  • The embryo will then implant onto the uterus, placenta will form and secrete human chorionic growth hormone (hCG)

  • Pregnancy tests check for the presence of hCG

  • If males have high hCG, may be a symptom of testicular cancer

Organ Formation

• Human embryo at 5 weeks has limb buds

  • Arms and legs develop from limb buds

  • Head enlarges, and sense organs become more prominent

  • Umbilical cord has developed connecting embryo to placenta

• 6–8th week

  • Remarkable external appearance change

  • Becomes recognizable as human

  • Head distinct from body

  • Reflex reactions—startle response

  • At the end of this period, embryo is 38 mm long

Fetal development 3rd to 9th month

• Marked by an extreme increase in size

  • Weight and length

• Genitalia appear in 3rd month

• Hair, eyebrows, eyelashes, fingernails, and toenails appear

• 5th–7th months—fine, downy hair covers limbs and trunk and later disappears

Fetal heartbeat

• Fetal heartbeat can be heard at 10 weeks.

20- to 28-week fetus

• Skin is growing so fast it wrinkles

• A fetus born at 22 weeks has a chance of surviving, but the likelihood goes up with increasing age

Birth

• When the fetal brain is sufficiently mature, the hypothalamus causes the pituitary to stimulate the adrenal cortex to secrete androgens.

• Stimulates production of oxytocin and prostaglandin

• Causes the uterus to contract and expel the fetus

3 stages of birth

1. Cervix dilates, and amnion bursts

2. Baby is born, and the umbilical cord is cut

3. Placenta delivered