Reproductive system Flashcards
Reproduction
Is a biological process through which a new generation of individuals is produced from a existing organism
Asexual reproduction
Asexual reproduction is a mechanism through which new individuals are generated from a single parent without the fusion of egg and sperm.
Sexual reproduction
Sexual reproduction is a mechanism through which a new individual is developed from a diploid zygote as a result of the fusion of two haploid gametes (the sperm and the egg) which are produced by two individuals
Asexual reproduction methods
Budding
Fragmentation and regeneration
Parthenogenesis
Budding
Asexual reproduction in which new individuals arise from outgrowths of the animal
-Hydra
Fragmentation and regeneration
Breaking of the body or part of the body into several pieces followed by the growth of a separate individual from each piece
Some annelid worms, numerous sponges, cnidarians and flatworms
Parthenogenesis
Unusual form of asexual reproduction in which an egg develops into a complete individual without being fertilized. -bees, ants, wasps and aphids
Progeny can be diploid or haploid
In bees males (drones) are haploid organisms developed through parthenogenesis. Females are sterile (workers) or fertile (queen) diploid organisms.
Can be seen very rarely in vertebrates like lizards and fish.
Gametes
Gametes (sperms and eggs) are the vehicles that transmit genes from 1 generation to the next
Fertilisation
Is the union of the egg and the sperm (gametes) culminating in fusion of their nuclei.
External fertilisation (facts required and organism)
A moist habitat is always required to prevent the gametes from drying out and to allow the sperm to swim towards the egg.
Many invertebrates, amphibians, most bony fish
Bisexual organisms
Hermaphrodite
1 individual has both female and male reproductive structures and therefor is able to produce both female and male gametes.
Dioecious organisms
Unisexual organisms
Advantages and disadvantages of asexual reproduction
Rapid multiplication of individuals
No time or energy is needed to be spend in searching mates for reproduction.
Very little genetic variations within a population
External reproductive organ of a male
Scrotum and penis
Testes
Found within the scrotum
Should be maintained 2•C below the core body temperature.
Develop in the abdominal cavity and descend into the scrotum just before birth.
Each testis contains lobules comprising of seminiferous tubules.
Sertoli cells secrete inhibin
Leydig cells (interstitial) secrete testeteron
Epididymis
6m in length
Takes about 3 weeks for sperm to travel the length of this duct
During this time sperms become mature and motile
Matured sperms are stored here until ejaculation
Spermatogenesis
Occurs within seminiferous tubules of the testes
Time taken to produce mature sperm cells from a specific spermatogonia is about 7 weeks
Formation and development of sperms is continuous and inexhaustible
Starts at puberty and occurs throughout life
Main steps in spermatogenesis
Primordial germ cell in embryo(2n) —> Spermatogonial stem cell(2n) —> Spermatogonium(2n) —> Primary spermatocyte(2n) —> 2 Secondary spermatocytes(n) —> 4 spermatids(n) —> 4 spermatozoa(n)
Structure of a sperm
Head contains haploid nucleus carrying parental genetic material.
A special vesicle called the acrosome contains hydrolytic enzymes such as trypsin and hyaluronidase that helps the sperm to penetrate the outer layers of the ovum.
Mid-piece contains mitochondria
Tail contains a long flagellum with 9+2 arrangement of microtubules
Life expectancy of a sperm
48 - 72 hours after ejaculation in the female reproductive tract
Semen and sperm count in an normal ejaculate
2-5 mL of semen and sperm count of 40-100 million/mL
Sperms comprises less than 10% of the final ejaculate
Accessory glands associated with male reproductive system
Seminal vesicles, prostate gland and bulbourethtal gland
Seminal vesicles
They are a pair of two small pouches that produce a thick, yellowish fluid that is expelled during ejaculation. Seminal fluid is alkaline to protect the sperm in the acidic environment of the vagina. It contains mucus, fructose (that provides most of the sperm’s energy), a coagulating enzyme (helps semen coagulates after ejaculation), ascorbic acid and local regulators called prostaglandins.
This fluid contributes to about 60% of the volume of semen.
Prostate gland
Found below the urinary bladder. It secretes a thin, milky fluid directly into the urethra through small ducts. This milky secretion contains coagulants, anticoagulant enzymes and citrate which is a sperm nutrient.
This fluid contributes to about 30% of the volume of semen.
Bulbourethral glands
pair of small glands found along the urethra below the prostate. These glands secrete a clear alkaline mucus that is able to neutralize any acidic urine remaining in the urethra and lubricates the lining of the urethra.
FSH and LH hormones direct spermatogenesis by acting on
· FSH stimulates Sertoli cells to nourish the developing sperm.
· LH causes Leydig cells to produce testosterone and other androgens to promote
spermatogenesis.
Negative feedback mechanisms controlling sex hormone production in males
· Testosterone inhibits GnRH, FSH and LH in blood through its effect on the hypothalamus and anterior pituitary.
· Additionally inhibin produced by Sertoli cells, acts on anterior pituitary gland to reduce FSH secretion.
Oogenesis
In oogenesis, cytokinesis during meiosis is unequal, with almost all the cytoplasm segregated to a single daughter cell. This large cell develops to become the egg. The other products of meiosis, which are smaller cells are known as polar bodies. These polar bodies eventually degenerate.
production of mature gametes ceases at about the age 50 years. Unlike in spermatogenesis, during oogenesis there are also long interruptions.
Ovaries
Found on either side of the uterus and are held in place in the abdominal cavity by ligaments
Outer layer of each ovary is covered by. germinal epithelium
Ovum is discharged at the secondary oocyte stage
Main steps in Oogenesis
Primordial germ cell in embryo(2n) —> Oogonia(2n) —Primary Oocyte(2n) —> 1st Polar body, Secondary Oocyte(n) —> 2nd Polar body and mature ovum
Primary oocyte produced by the mitotic division of Oogonia stops at prophase 1 before birth
Secondary Oocyte present in mature follicle is paused at metaphase 2
Only if a sperm penetrates the secondary oocyte, meiosis 2 completes and the secondary oocyte divides into the mature ovum and 2nd polar body.
At birth ovaries contain how many primary oocytes
1-2 million
Out of theses about 500 fully mature between puberty and menopause
Follicular transformations after fertilization
Ruptured follicle left behind after ovulation develops into the corpus luteum which secreted estradiol and progesterone which help to maintain uterine lining during pregnancy
If the egg is not fertilized, the corpus luteum degenerates and leaves a small, permanent scar of fibrous tissue called corpus albicans on ovary surface
Ovarian cycle
Consists of follicular phase (1-14 days) and luteal phase (15-28) days
Follicular phase is the phase in which the follicle grows and the Oocyte matures. Growing follicles secretes estradiol. High levels of estradiol results in a LH surge. In response to both FSH and peak in LH, the follicle and the adjacent wall of the ovary ruptures releasing the secondary oocyte (ovulation)
Uterine (menstrual) cycle
Consists of proliferative phase, secretory phase and menstrual flow phase
During proliferative phase estradiol secreted by growing follicles stimulate the endometrium to thicken. Follicular phase coordinates with this
During secretary phase estradiol and progesterone secreted from the corpus luteum stimulate the maintenance and further development of the lining of the uterus by enlarging the arteries and growth of endometrial glands Luteal phase coordinates with this phase
During menstrual flow phase cyclic shedding of the blood-rich endometrium from the uterus occurs
Menopause
Cessation of ovulation and menstruation in a women.
Takes place between ages 45-55 years
Time taken from fertilization to birth
38 weeks roughly 9 months
Embryonic period
1st 8 weeks human development, therafter the developing individual is called a fetus.
Fertilization (location, time period)
Takes place in the upper reaches of the oviduct within 12 to 24 hours after ovulation
Blastocyst differentiates into
Inner cell mass and trophoblast
Inner cell mass develops into the embryo and the trophoblast develops into the fetal portion of the placenta (chorion)
Trophoblast after ovulation
Secrete human chorionic gonadotropin (hCG) hormone which has the action similar to LH. The hormone hCG rescues the corpus luteum from degeneration and sustains its secretion of progesterone and estrogen which maintain the uterine lining preventing menstruation.
Placenta
The placenta is a disc shaped organ formed by two parts: embryonic/fetal portion formed by chorionic villi of the chorion and maternal portion formed by the endometrium. The placenta produces hormones (e.g. hCG, progesterone etc.) needed to sustain the pregnancy. Oxygen poor blood from the embryo/fetus travels to the placenta through the two arteries of the umbilical cord.
Pregnancy
The hCG hormone secreted by the embryo, maintains the corpus luteum in the ovary to secrete progesterone and estrogen. The presence of hCG in pregnant mother’s blood and urine can be easily detected and therefore is used as an early pregnancy detection test.Most mothers experience nausea (morning sickness) during the first trimester.
By the second trimester, the level of hCG declines and as a result the corpus luteum deteriorates. But the placenta takes over the production of progesterone and estrogens which helps to maintain the pregnancy. Mother can feel fetal movements.
In the third trimester of pregnancy this may lead to digestive blockage and frequent urination.
Umbilical code
Umbilical cord is a flexible cord-like structure containing blood vessels and attaches embryo/fetus to the placenta during gestation.
Lengths of fetus during each trimester
5-7 cm long - 1st trimester
30 cm long - 2nd trimester
50 cm - 3rd trimester
Major fetal changes during 1st trimester
Rudiments of all major organ systems appear. The heart begins to beat by the 4th week.
Major fetal changes during 2nd trimester
Fetus assumes distinctively human features. Mother may feel fetal movements.
Major fetal changes during 3rd trimester
Rapid fetal growth
Most of the organ systems become fully functional
Weighs about 3-4 kg
Fetal activity decreases as it fills the space within the uterus
Lactation
Secretion and ejection of mother’s milk from the mammary glands
Differences between colostrum and true milk
Colostrum contains less nutrients
Human milk
Is a sterile solution containing lactose, fatty acids, amino acids, minerals, vitamins and water
Contraception
Deliberate prevention of pregnancy
Common birth control methods
Condoms for males
Oral contraceptives for females
IUD loop
Depo-provero injection for females
Surgical sterilization methods
Vasectomy for males
Tubal ligation in females
Abortion
Premature termination of pregnancy
Miscarriages
Spontaneous abortion which occurs naturally
Gonorrhea
Neisseria gonorrhoeae bacterium
Syphilis
Treponema pallidum bacterium
AIDS
Human immunodeficiency virus (HIV)
Genital herpes
Herpes simplex 2 virus
Infertility
Inability to conceive offspring
Implantation
7 days after fertilisation, the blastocyst attaches to the mother’s uterus.
Gestation
Gestation is the period of time between conception (fertilisation) and birth.
Methods of detecting disorders during pregnancy
Ultrasound images
Amniocentesis (withdrawal of amniotic fluid from the amniotic cavity using a needle)
Chorionic villi sampling (A catheter is inserted through vagina and cervix, withdrawing foetal cells from chorionic villi)
Methods of resolving infertility problems
Hormone therapy
Surgery
Assisted reproductive technology
Assisted reproductive technology
IVF (In vitro fertilisation) - 50 and 100 thousands of sperm from the male per one oocyte in order to achieve the fertilization. This is due to the fact that in IVF, acrosome reaction has to take place.
Intra-cytoplasmic sperm injection (ICSI) - Needs only 1 sperm per 1 oocyte
Stages of labor
Thining and opening of the cervix
Delivery of the baby
Delivery if the placenta
