UNIT B (REPRODUCTION AND DEVELOPMENT) Flashcards
Testes
The male gonads, or primary reproductive organs; male sex hormones and sperm are produced in the testes.
Scrotum
The sac that contains the testes. The temperature in the scrotum is a few degrees cooler than that of the abdominal cavity. The cooler temperatures are important, since sperm will not develop at body temperature. Should the testes fail to descend into the scrotum, the male will not be able to produce viable sperm. This makes the male sterile.
Vas Deferens
Tube that conducts sperm toward the urethra.
Ejaculatory Duct
A tubule formed at the union of the vasa deferentia
and the seminal vesicle ducts and opening into the urethra.
Semen
A secretion of the male reproductive organs
that is composed of sperm and fluids.
Seminal Fluid
The fluid part of semen, which is secreted by three glands.
What contracts during ejaculation?
The vasa deferentia, seminal vesicles, ejaculatory duct, and prostate gland contract, forcing the semen to the base of the penis.
Seminal Vesicle
Structure that contributes to the seminal fluid (semen), a secretion that contains fructose and prostaglandins. Fructose provides a source of energy for the sperm cell and prostaglandins act as a chemical signal in the female system, triggering the rhythmic contraction of smooth muscle and assisting the movement of sperm cells toward the egg.
Prostate Gland
Structure that contributes to the seminal fluid (semen), a secretion containing alkaline buffers that protect sperm cells from the acidic environment of the vagina.
Cowper’s (bulbourethral glands)
Structure that contributes a mucus rich fluid to the seminal fluid (semen).
Ejaculation Order
Seminiferous tubules
Epidydimus
Vas deferens (ductus deferens)
Ejaculatory duct
Nothing
Urethra
Penis
Spermatogenesis Order
Seminiferous tubules: Immature sperm cells divide and differentiate. The site of spermatogenesis.
Spermatogonia: The seminiferous tubules are lined with sperm-producing cells called spermatogonia.
Spermatogonia divide to form Spermacytes
Spermacytes differentiate into Spermatids (23 chromosomes)
Sertoli Cells (Within Seminiferous Tubules)
Nourish the developing sperm cells until they are mature. Produce FSH.
Epididymis
Where sperm cells mature and are stored.
Sperm Order
From each testis, epididymis, ductus deferens, ejaculatory duct, penis.
Acrosome
Sperm have a reduced amount of cytoplasm to help them move fast. Can also be a problem. The cap found on sperm cells, containing enzymes that permit the sperm cell to move through the outer layers that surround the egg.
Middle Piece
Contains mitochondria, energy for the movement of the tail
Tail
Propels the sperm with lashing movement.
Urethra
Carries semen during ejaculation, carries urine from the bladder to the exterior of the body
Primary Sexual Characteristics
Primary sexual characteristics are directly involved in reproduction and are present at birth.
Secondary Sexual Characteristics
External features of an organism that are indicative of its gender (male or female), but are not the reproductive organs themselves.
Distinguishing features, males
Y Chromosome carries the testis-determining factor (TDF) gene to have male sex hormones (androgens). Testes first develop in abdominal cavity and during the 3rd month begin to descend toward scrotum.
Testosterone
Male sex hormone produced by the interstitial cells of
the testes. Stimulates the maturation of the testes and penis and also spermatogenesis. Facial and body hair; the growth of the larynx, which causes the lowering of the voice, the strengthening of muscles. In addition, testosterone increases the secretion of body oils The increased oil production can also create body odour. Testosterone levels are also associated with sex drive and more aggressive behaviour.
Interstitial Cells (Leydig Cells)
Found between the seminiferous tubules within the testes and secrete testosterone.
Gonadotropin-releasing hormone (GnRH)
Chemical messenger from the hypothalamus that stimulates secretions of FSH and LH from the anterior pituitary and regulates the functions of the testes.
Follicle-Stimulating Hormone (FSH) IN MALES
In males, a hormone that increases sperm production. Occurs in the seminiferous tubules (Sertoli Cells).
Inhibin
A hormone produced by the Sertoli cells that inhibits the production of FSH. When sperm counts are high, the Sertoli cells of the seminiferous tubules produce a hormone called inhibin. Inhibin sends a feedback message to the pituitary that inhibits further production of FSH. It also causes the hypothalamus to reduce its production of GnRH.
Luteinizing Hormone (LH)
In males, a hormone that regulates the production of testosterone. Promotes the production of testosterone by the interstitial cells.
High testosterone levels reduce LH production directly by feedback inhibition of LH release from the pituitary and indirectly by feedback inhibition of GnRH release from the hypothalamus. When high levels of testosterone are detected by the hypothalamus, it releases less GnRH, leading to decreased production of LH. Decreased GnRH output, in turn, slows the production and release of LH, which leads to lower testosterone production. Testosterone levels thus remain in check.
Ovum
Egg Cell
Oocyte
An immature ovum
Fetal Development for women
During fetal development in the female, paired ovaries
form in the same abdominal region as the testes in the male. Like the similarly shaped testes, the ovaries descend, but unlike the testes, which come to lie outside of the abdominal cavity, the ovaries remain in the pelvic region. At birth, oocytes (immature ova) are already present within the ovary.
Uterus/Womb
The hollow, pear-shaped organ located between the bladder and the anus in females. The embryo and fetus develop in the uterus during normal pregnancies.
Endometrium
The glandular inner lining of the uterus.
Fallopian Tube (Oviduct0
One of two tubes that connect the ovaries to the uterus. Carries the ovum from ovary to the uterus, and here the beating cilia create a current moving the ovum towards the uterus.
Fibrium
A fingerlike projection at the end of a Fallopian tube.
Vagina
The muscular canal extending from the cervix to the outer environment; the birth canal. The vagina is acidic, creating a hostile environment for microbes that might enter the female reproductive system.
Cervix
A muscular band that separates the vagina from the uterus.
Ovum Size
MUCH larger than sperm! 100 000 times larger, lots of cytoplasm for nutrients.
Oogenesis
The formation and development of mature ova
Follicle
Structure in the ovary that contains the oocyte. A follicle contains two types of cells: a primary oocyte and cells of the granulosa.
Granulosa
The layer of small cells that forms the wall of a follicle. Provides nutrients for the developing oocytes.
Stages of Oogenesis
Nutrient follicle cells surrounding the primary oocyte begin to divide. As the primary oocyte undergoes cell division, the majority of cytoplasm and nutrients move to one of the end poles and form a secondary oocyte. The secondary oocyte contains 23 chromosomes. The remaining cell, referred to as the first polar body,
receives little cytoplasm and dies.
Eventually, the dominant follicle (secondary oocyte) pushes outward, ballooning the outer wall of the ovary. Constriction of blood vessels weakens the ovarian
wall above the follicle, while enzymes weaken the wall of the follicle from the inside. The outer surface of the ovary wall bursts and the secondary oocyte is released. OVULATION!
When Pregnancy Occurs
After ovulation: surrounding follicle cells remain within the ovary and are transformed into the corpus luteum, which secretes hormones essential for pregnancy. If pregnancy does not occur, the corpus luteum degenerates after about 10 days.
Upon its release from the ovary, the secondary oocyte is swept into the funnel-shaped end of the Fallopian tube by the fimbria. The secondary oocyte is moved along the
Fallopian tube by cilia where, if healthy sperm are present, it will become fertilized. The secondary oocyte will then undergo another unequal division of cytoplasm and nutrients and develop into the fertilized ovum. The cell that retains most of the cytoplasm and nutrients becomes the ovum, and the other cell becomes the second polar body, which deteriorates. If the secondary oocyte is not fertilized, it will deteriorate within 24 hours and die. When this occurs, the woman will undergo a menstrual cycle.
Why is there no corpus luteum in IVF
This is because the follicles are removed from the ovary in the process of obtaining viable eggs. Consequently, IVF pregnancies will not have the support of corpus luteum in preparing the endometrium for pregnancy. This is why patients are supplemented with additional progesterone until the end of the first trimester. At the end of the first trimester, the placenta becomes capable of taking over progesterone production, so there is no further need for either the corpus luteum (in natural pregnancies) or external progesterone supplementation in IVF pregnancies.
Stages of the Ovarian Cycle/Menstrual Cycle
- Flow Phase
- Follicular Stage (Days 6-13)
- Ovulation (Day 14)
- Luteal Phase (Days 15-28)
FSH role (WOMEN)
Stimulates follicles and oocytes to mature, as follicles mature estrogen and SOME progesterone is released from the follicle. Once threshold of estrogen is reached, GnRH and FSH is inhibited and GnRH increases production of LH.
(-) as estrogen grows, FSH is inhibited.
Luteinizing Hormone (LH) (WOMEN)
In females, a gonadotropin that promotes ovulation and the formation of the corpus luteum.
(+) as estrogen grows, more LH produced!
Progesterone
Hormone produced primarily by the corpus luteum, that
induces changes in the endometrium during the menstrual cycle.
Estrogen
Hormone that activates development of female secondary
sex characteristics, and increased thickening of the endometrium during the menstrual cycle.
Flow Phase
The shedding of the endometrium during the menstrual cycle. This is the only phase of the female reproductive
cycle that can be determined externally. For this reason, the flow phase is used to mark the beginning of the menstrual cycle. Approximately five days are required for the uterus to shed the endometrium.
Drop in progesterone and estrogen! The Corpus luteum has degenerated and as the follicle grows, estrogen increases.
Follicular Phase
GnRH is released by the hypothalamus, stimulating AP to release FSH. The development of follicles within the ovary. As follicles develop, the hormone estrogen is secreted, increasing the estrogen concentration in the blood.
Rising levels of estrogen! Endometrium begins thickening.
Ovulation
A surge in estrogen triggers the AP to release LH marking ovulation. A sudden surge in LH causes the ovary to release the egg.
Corpus Luteum
A mass of follicle cells that forms within the ovary
after ovulation; secretes estrogen and progesterone essential for pregnancy.
Luteal Phase
The corpus luteum develops. Phase of the
menstrual cycle characterized by the formation of the corpus luteum following ovulation. Estrogen levels begin to decline when the oocyte leaves the ovary, but are somewhat restored when the corpus luteum forms. The corpus luteum secretes both estrogen and progesterone. Prepares the uterus to receive a fertilized egg.
Should fertilization of an ovum not occur, the concentrations of estrogen and progesterone will decrease, thereby causing uterine contractions. These uterine contractions make the endometrium pull away from the uterine wall. The shedding of the endometrium marks the beginning of the next flow phase, and the female menstrual cycle starts all over again.
Rising levels of progesterone! Thicker and thicker.
Menopause
The termination of the female reproductive years.
Birth Control Pills
Oral contraceptives contain high concentrations of progesterone, which inhibits ovulation and thereby prevents conception.
Sperm Travel in Women’s Reproductive Tract
- 150 to 300 million sperm cells travel to the cervix into the uterus
- only a few hundred actually reach the Fallopian tubes
- several sperm attach to ovulated oocyte but only one sperm cell fuses with it
Fertilization
Joining of male and female gamesters each containing 23 chromosomes to produce a total of 46 chromosomes
Layers of Egg
- Inner layer: zona pellucida (thin, clear, proteins and carbs)
- Outer layer: corona radiata (several jelly-like layers of follicle cells which were a source of nourishment for the egg when it was an ovarian follicle)
Order of Movement of Sperm
- Sperm meet corona radiata
- Enzyme containing acrosome releases contents
- Enzymes digest a path through the corona
- Lashes tail to advance
- Sperm enters egg
- Egg’s plasma membrane depolarizes to stop other sperm from binding and entering
- Within 12h of sperm entering the egg, membrane of both sperm and egg disappear
- 23 + 23 = 46!!
- Fertilization complete, zygote forms!
Order of Movement of Egg
- Egg released from an ovary
- Swept into an oviduct
- Fertilized egg carried toward uterus through muscular contractions, wave-like action of cilia
- 3-5 Days for a fertilized egg to reach the uterus
Length of time required for the fertilized ovum to travel the 10 to 12 cm Fallopian tube to the uterus
3-5 Days
Cleavage
Cell division of a zygote, in which the number of cells increases without any change in the size of the zygote. This is what happens in the 3-5 day range. 0.1mm zygote divides by mitosis for the first time (2 cells) then a second time (4 cells) then a third time (8 cells) then a fourth time (16 cells - morula).
Zygote remains 0.1mm, but is made up of many cells
Morula reaches uterus within 3-5 days of fertilization.
Blastocyst
Consists of an outer sphere of cells, from which the extraembryonic structures develop, and an inner cell mass, from which the embryo develops.
This occurs when the morula fills with fluid diffusing from the uterus.
Made of two cells: trophoblast and embryoblast
Trophoblast
Outer layer, will develop into the chorion to form part of the placenta
Embryoblast
Inner cell mass, develop into the embryo itself. Amnion develops from here and encloses the amniotic cavity.
When do amnion and chorion merge?
2nd trimester
Implantation
Between 5-7 days after fertilization, blastocysts attaches to the endometrium. This is complete by the 10-14 days. Trophoblast begins secreting hCG.
hCG
Detected in pregnancy tests, secreted from the blastocysts chorion layer. Has the same effect as LH: maintain the corpus luteum, estrogen and progesterone stay up, endometrium maintained and menstruation STOPPED.
Stays high for 2 months, decreases after 1st trimester as placenta secretes enough estrogen and progesterone to maintain endometrium.
High levels of progesterone and estrogen have a negative-feedback effect and stop the secretion of GnRH, hCG solves this problem!
Gastrulation
During the 2nd week the two-layered structure develops into a three-layered structure called a gastrula. First only has outer ectoderm and inner endoderm, then mesoderm forms.
Ectoderm
- skin, hair, finger nails, sweat glands
- nervous system, brain, peripheral nerves
- lens, retina, cornea
- inner ear, cochlea, semicircular canals
- teeth, inside lining of mouth
Mesoderm
- muscles (skeletal, cardiac, and smooth)
- blood vessels and blood
- kidneys, reproductive structures
- connective tissue, cartilage, bone
Endoderm
- liver, pancreas, thyroid, parathyroid
- urinary bladder
- lining of digestive system
- lining of respiratory tract
Morphogenesis
Distinct structures on dveloping organisms, embryonic cells become different
Differentiation
Cells develop a particular shape a perform specific functions. The development of 3 layers is very important as cells, tissues and organisms of bodies are derived from the primary germ layers through differentiation.
MOSTLY ASSOCIATED WITH ORGAN DEVELOPMENT!
Neurulation and Organ Formation
Between 3 and 8 weeks, organs form. 3 layer embryo transformed into body with separate organs and by week 8, recognizably human!
First Trimester (WEEKS 1-12)
- rapid development (week 8)
- nervous system
- next 4 weeks growth of body accelerates and head slows
- cartilage hardens to bone
- end of 12th week and into the 2nd trimester, male or female distinguishable
- called a fetus after weeks 8-9
Second Trimester (WEEKS 13-24)
Organs continue to develop and the fetus increases in size. It will move enough to make itself know to the mother and it begins to look more like a human infant.
- fourth month: the heartbeat of the fetus heard by stethoscope
- brain grows rapidly and the nervous system starts to function
- legs grow
- skin more pink
Third Trimester (WEEKS 25 - 38)
Organ systems have been established during the first two trimesters; all that remains is for the body mass to increase and the organs to enlarge and become more developed.
- fetal brain cells form rapidly
- testes of males descend into scrotum
- fat layer developed beneath the skin
- digestive and respiratory systems last to mature
- brain cells develop RAPIDLY!
Chorion
The outer extraembryonic structure of a developing embryo that will contribute to the fetal portion of the placenta.
Amnion
A fluid-filled extraembryonic structure. Grows to enclose the embryo and penetrated only by the umbilical cord, amniotic fluid protects embryo from trauma and temperature fluctuation. Eventually will fuse with the chorion.
hCG
An embryonic hormone that maintains the corpus
luteum.
Amniotic Cavity
The fluid-filled cavity surrounding the developing embryo. Between the amnion and the chorion.
Extraembryonic Coelom
Body cavity between the amnion and the chorion.
Placenta
The site for the exchange of nutrients and wastes between
mother and fetus.
Chorionic Villi
Vascular projections of the chorion ensure that a large number of blood vessels of the fetus are exposed to maternal blood. Supplies the placenta.
Yolk Sac
Formed by the second week. A membranous sac that forms during embryo development of most vertebrates; in humans, it does not contain yolk. Contributes to formation of the digestive tract, produces first blood cells and future egg/sperm cells.
Allantois
Extraembryonic structure that contributes to the blood vessels of the placenta. Provides umbilical blood vessels in the placenta. However, unlike the chorion and amnion, the allantois does not envelop the fetus.
Umbilical Cord
Structure that connects the fetus to the placenta.
Human Sex Determination
The male fetus does not differ from a female fetus until about the sixth or seventh week of pregnancy. The SRY (Sex-determining Region of the Y chromosome) gene is mainly responsible for determining the male
phenotype in humans.
Tetrogens
Any medication, chemical, infectious disease, or environmental agent that might interfere with the normal
development of a fetus or embryo.
Order of birth/parturition/labour
- Dilation
- Expulsion
- Placental Stage
Step 1 of Labor
The cervix thins and begins to dilate. As the amnion is forced into the birth canal, it often bursts, and amniotic fluid lubricates the canal (a process referred to as the breaking of the water). As the cervix dilates, uterine contractions move the baby through the birth canal. Following the birth of the baby, the placenta is also
delivered.
Relaxin
A hormone produced by the placenta prior to labour; causes the ligaments within the pelvis to loosen. Decreased production of progesterone is crucial to the onset of labour.
Oxytocin
Hormone from the pituitary gland, causes strong uterine contractions. Prostaglandins, which are also believed to trigger strong uterine contractions, appear in the mother’s blood prior to labour.
Order of Labour
Positive Feedback Mechanism
- Stretching cervix causes release of oxytocin from PPG
- Uterine contractions, cervix stretches, oxytocin released from PPG, stimulates uterine contractions, fetus downwards, cervix continues to stretch
- Oxytocin stimulates uterine muscles directly through prostaglandins
Lactation
Breast development is stimulated from the onset of puberty by estrogen and progesterone. During pregnancy, elevated levels of estrogen and progesterone prepare the
breasts for milk production. Each breast contains about 20 lobes of glandular tissue, each supplied with a tiny duct that carries fluids toward the nipple.
Prolactin
Anterior pituitary gland and associated with milk production. During pregnancy, elevated levels of estrogen and progesterone prepare the breasts for milk production. Each breast contains about 20 lobes of glandular tissue, each supplied with a tiny duct that carries fluids toward the nipple. SUPPRESSED BY DOPAMINE.
Stimulates glands within the breast to begin producing fluids. Estrogen stimulates the release of
large amounts of prolactin during pregnancy; milk production does not occur before birth, however, because the action of prolactin is inhibited by the high levels of progesterone that are present. The drop in estrogen and progesterone levels after birth results in decreased amounts of prolactin, but an increase in prolactin activity because the progesterone-induced inhibition is relieved.
Colostrum
Colostrum contains milk sugar and milk proteins, but lacks the milk fats found in breast milk. A few days after birth, prolactin stimulates the production of milk. Colostrum and mother’s milk supply the baby with an important source of antibodies.
Milk Production…
In the lobes of the glandular tissue (alveoli within lobules) and forced into ducts leading to the nipple.
Oxytocin (in breast)
Within the breast, oxytocin causes weak contractions of smooth muscle, forcing milk into the ducts.
Suckling order
- Stimulates release of oxytocin
- Nerve endings in the nipple and areola stimulated
- Nerve impulses sent to the hypothalamus, PPG, oxytocin
- Oxytocin causes contractions within mammary lobules
- Contraction within lobules causes milk to flow to ducts, where the infant then suckles
- Suckling inhibits FSH AND LH, preventing ovulation and menstruation
If suckling stops
Milk production stops
Increased suckling
More milk production
Identical Twins
One egg is fertilized, the embryo splits
Fraternal Twins
Fertilization of two seperate eggs with two separate sperm cells
Birth Control Pill (require a prescription)
A daily pill taken before sex to prevent pregnancy by regulating hormones consistently.
Morning After Pill (over the counter)
Emergency contraception taken after unprotected sex to prevent pregnancy. It’s a one-time dose.
Contraceptive Methods
Tubal Ligation: surgeon cuts and then ties off the Fallopian tubes
IUD:
Pap Smear:
Fertility Drugs
Stimulate the action of pituitary hormones. Follicle development within the ovary is enhanced and the release of one or more egg cells becomes more probable. Because fertility drugs increase follicle development within the ovary causing multiple ovulations, the chances of having fraternal twins increases.
IVF
- FSH Injection: FSH (Follicle-Stimulating Hormone) is given to make the ovaries grow multiple eggs instead of just one.
- Egg Monitoring: Doctors check the eggs with ultrasounds to see if they’re growing well.
- Trigger Shot: Another hormone is given to make the eggs ready for collection.
- Egg Collection: Eggs are taken from the ovaries.
Fertilization: Eggs are mixed with sperm in a lab to make embryos. - Embryo Transfer: A healthy embryo is placed in the uterus to start a pregnancy.
Blastocyst is inserted into uterus. NOT a zygote.
May be more that one embryo placed –> chance of twins!
important stages
- cleavage and mitotic divisions to form a zygote
- trophoblast and embryoblast (blastocyst) is formed BEFORE implantation
- blastocyst attaches to endometrium through enzymes and implants, u are now pregnent! HCG!!
how does the corpus luteum degenerate
If the egg does not undergo fertilization it stops secreting progesterone and decays. It also send negative feedback when produced enough progesterone and estrogen to stop the production of LH.
