Chapter 27: Reproduction and Development Flashcards
Asexual vs Sexual Reproduction
Asexual: production of offspring whose genes come from one parent; genetically identical.
Sexual: production of offspring whose genes come from both parents by fertilization.
Ovarian cycle and menstrual cycle
Ovarian cycle: maturation of oocyte in ovaries.
Menstrual cycle: uterus prepares for arrival of fertilized egg.
Types of asexual reproduction (fission, budding, fragmentation, parthenogenesis), examples
Fission: separationg of parent into 2 individuals of equal size. (ex. sea anemone).
Budding: new indvidual splits from existing one (ex. hydra).
Fragmentation/regeneration: breaking of body into several pieces, each developing into adult (ex. starfish).
Pathenogenesis: development of egg without fertilization (komodo dragon).
Advantages of sexual and asexual reproduction
Asexual:
* No need to find a mate.
* Can produce many offspring in a short time.
* Perpetuates successful genotypes (DNA sequences): advantageous in a stable, favorable environment.
Sexual:
* Genetic variability: offspring are genetically diff. from parents, advantageous in fluctuating environments.
Function of female reproductive system: ovary, oviduct, uterus (endometrium, cervix)
See GD for anatomy
Ovary:
* gonads that produce gametes and hormones.
Oviducts:
* Allow oocytes to travel to uterus - fertilization occurs in upper third portion.
Uterus:
* muscular organ where fetus develops.
* Endometrium: uterine lining where embryo implants.
* Cervix: opening beween uterus and vagina.
Function of female reproductive system: vagina, vulva, mammary glands
see GD for identification
Vagina:
* Receives penis during intercourse and serves as birth canal.
Vulva:
* External genitalia (labia majora and minora, clitoris).
Mammary glands:
* Consists of small sacs of glands that secrete milk, which drains into ducts that open at nipple.
Menstrual cycle
Day 1-5: menstruation (low estrogen + progesterone).
Day 6-13: follicle + oocyte mature and releases estrogen → endometrium thickens.
Day 14: ovulation.
Day 15-25: corpus luteum releases estrogen and progesterone to maintain endometrium.
Day 26-28: corpus luteum degenerates → estrogen + progesterone levels fall → endometrium breaks down.
What happens when fertilization happens or doesn’t happen?
If fertilization occurs:
* Embryo produces hormone human chorionic gonadotropin (hCG), preventing corpus luteum from dgenerating.
* Corpus luteum keeps up estrogen and progesterone levels; menstruation doesn’t occur.
No fertilization:
* Corpus luteum eventually degenerates.
* Progesterone and estrogen levels drop, endometrium sheds.
Ovulation
One follicle + oocyte matures every 28 days.
* Mature follicle ruptures and releases egg into oviduct.
Oogenesis
the development of haploid egg cells (oocytes) by meisosis.
* Begins in ovaries before birth.
Difference between diploid and haploid
Diploid have two sets (46 chromosomes, 23 pairs) of chromosomes.
Haploid cells cells contain one set of chromosomes.
* Only human cells that are haploid are sperm and egg.
How do diploid and haploid cells form?
Diploid cells reproduce by mitosis, making daugher cells that are exact replicas.
Haploid cells are result of meiosis, in which diploid cells divide to give rise to haploid cells.
Function of Male Reproductive Organs, scrotum, testis, epididymis, prostate gland
see GD for anatomy
Scrotum: holds testes in an optimal temp. so that sperm can develop.
Testis: gonad that produces sperm cells and testosterone, made of seminiferous tubules.
Epididymis: tubes that store sperm.
Prostate: secretes acidic fluid containing enzymes and zinc into urethra and activates sperm.
Function of Male Reproductive Organs: penis, seminal vesicle, bulbourethral gland
Penis:
* Copulatory organ
* During ejaculation: semen (sperm + seminal fluid) is formed and expelled from the penis
Seminal vesicle:
* Secrete alkaline fluid containing mucus, amino acids, fructose that provide energy for sperm.
* Neutralizes acidic environment of vagina.
Bulbourethral glands:
* Secretes viscous alkaline fluid before ejaculation into urethra to neutralize acidic urine.
Spermatogenesis
the development of haploid sperm cells by meisosis.
* Begins in seminiferous tubules at puberty and continues throughout life.
Structure of sperm
See GD
Head: contains DNA (haploid # of chromosomes).
* Acrosome: contains enzymes to help sperm penetrate egg.
Middle piece: contains mitochondria.
Tail: flagellum.
Phases of embryonic development
- Fertilization
- Cleavage
- Gastrulation
- Organ formation
Embryonic development: fertilization
Union of haploid (23 chromosomes) sperm and egg that forms diploid zygote (46 chromosomes). Occurs in oviduct.
What has to happen in order for sperm to reach egg nucleus? What happens to vitelline layer?
Must pass through:
1. Jelly coat
2. Vitelline layer (contains species-specific receptors)
3. Plasma membrane
After fertilization, vitelline layer pulls away from egg plasma membrane and makes an impenetrable layer between egg and rest of sperm.
Embryonic development: cleavage
See GD
A series of rapid cell divisions that turns unicellular zygote into multicellular embryo. Ultimately results in blastula (hollow ball).
Embryonic development: gastrulation
See GD
Cells continue to divide and migrate to 3 germ layers:
* Ectoderm: outside lyr; becomes skin and nervous system.
* Mesoderm: mid lyr; becomes muscle, bone, and other organs.
* Endoderm: inside lyr; becomes digestive tract.
Embyronic development: organ formation (vertebrae, CNS)
Occurs after gastrulation.
Notochord forms from mesoderm cells; later replaced by vertebral column.
Neural tube develops above (folding of ectoderm) notochord; becomes brain and spinal cord.
Embryonic development: organ development (tissues and organs)
See GD
Develop by changes in:
* Cellular chracteristics e.g. shape.
* Cell migration.
* Apoptosis (programmed cell death).
Name the extraembryonic membranes and explain their function
See GD
- Chorion forms placenta.
- Amnion wraps and holds developing embryo in a fluid-fluid cushion (amniotic fluid).
- Yolk sac site of RBC sythesis; not full of yolk in humans.
- Allantois contributes to the umbilical cord.
What is the placenta?
A collection of tissues that forms ~31 days post-fertilization from chorion and endometrium:
* Separates maternal and fetal blood; permits exchange of nutrients, gases, wastes etc.
Identify the major events in each trimester of human gestation
1st trimester (0 - 13 wks)
* Embryo forms and looks like seahorse.
* Extraembryonic membranes form
* All major organs are established.
* After 9 wks post-fertilization, embryo is called fetus (can move arms and legs, looks human?).
2nd trimester (14 - 26 wks)
* Fetus increases in size
* Human features refined.
3rd trimester (27 wks - birth)
* Circulatory and respiratory systems mature.
* Muscles thicken and skeleton hardens.
* Able to maintain its own body temp.
Labor: hormonal changes
Labor is controlled by a positive feedback mechanism:
* Estrogen released from the ovaries increases sensitivity of uterus to oxytocin.
* Oxytocin is a stimulant for smooth muscles of uterus and
* Also stimulates placenta to make prostaglandins that further stimulate contractions.
Trace the positive
feedback loop that regulates labour
Use GD
Stimulus: Baby’s head stretches cervix.
Receptor: stretch receptors in cervix.
Control: brain that releases oxytocin.
Effector: uterus muscle.
Final physiological effect: uterus contracts and pushes baby out.
The three stages of labor
- Dilation of cervix to 10 cm (6 - 12 hrs).
- Expulsion of fetus: uterine contractions every 2 - 3 min.; assisted by abdominal muscles; fetus pushed thru cervix and out vagina.
- Afterbirth: delivery of placenta that occurs minutes after birth.
List some methods of birth control
Barrier methods physically prevents fertilization (e.g. condoms).
Hormonal birth control prevents ovulation (e.g. birth control pills, vaginal rings, injections).
Other methods provides inhospitable environment for implantation of an embryo (copper intrauterine device (IUD)).
How does hormonal birth control prevent pregnancy
Oral contraceptives contain estrogen and progesterone that exerts negative feedback on brain to prevent hormone secretion:
* No follicular development or ovulation.
* No possible pregnancy.
Surgical sterilization
Vasectomy is removal of portion of vas deferens (sperm still produced, just not ejaculated).
Tubal ligation is closing or cutting of oviducts (sperm can’t reach oocyte).
What are gametes?
Haploid reproductive cells
* COntain half the number of chromosomes as the organism.
What is sperm, egg?
Sperm is male gamete
* Small, has flagellum.
Egg: female gamete
* Larger than sperm, non-motile
What is the difference between zygote and embryo?
Zygote (unicellular): fertilized egg.
Embryo (multicellular): a zygote that’s gone thru at least one cell division.
What do human sexes have in common in terms of reproductive anatomy?
Gonads: produce gametes and secrete hormones
Ducts: transport and store gametes
Structures for copulation
What is the function of the endometrium?
It is the innermost layer of the uterus and is the site of implantation for fertilized egg.
How does egg move down the oviduct to uterus?
Oviduct contain cilliated simple columnar epithelium move egg.
When the endometrium is thick, and estrogen levels are high, what stage of the ovarian cycle is the body in?
Ovulation
What is the corpus luteum? What 2 hormones does it produce?
The follicle tranforms into corpus luteum after ovulation occurs. Produces: estrogen and progesterone.
