Feralis Ch 4 Flashcards
Asexual Reproduction - Fission
separation of an organism into two new cells (amoeba)
Asexual Reproduction - Budding
occurs when a new individual grows from an existing one and then splits off (hydra)
Asexual Reproduction - Fragmentation + Regeneration
when a single parent breaks into parts that regenerate into new individuals (sponge/ planaria/starfish)
Asexual Reproduction - Parthenogenesis
process in which egg develops without fertilization, resulting in an adult that is either haploid or diploid (honeybees, wasps, ants, some lizards, and hammerhead sharks)
Gonads
Gonads describe the reproductive structures responsible for the production of gametes. In males, the gonads are the testis, while in females, the gonads are the ovaries. The gonads are responsible for primary sex characteristics, and are directly involved in reproduction.
Secondary sex characteristics
differ from primary characteristics in that they indicate sexual maturity but are not involved in reproduction, such as breast development or increased body fat in females during puberty.
Testosterone results in the secondary sex characteristics in men, but also closes the epiphyses of long bones
Ovary
ova, or eggs, are produced here, and each female has two ovaries
Oviduct (fallopian tube/uterine tube)
allows for eggs to move from the ovary to the uterus, with one oviduct for each ovary (2)
The ovary isn’t actually directly connected to its adjacent oviduct, so the egg is swept into the oviduct via finger-like fimbrae. Fertilization occurs here!
Uterus
muscular chamber where development of the embryo occurs until birth. A fertilized ovum implants (attaches) on the inside uterine wall, or endometrium, on day 6 after fertilization
Vagina
at birth, the fetus passes through the cervix, an opening in the uterus, and out of the body
Testis
each consists of seminiferous tubules for production of sperm, and interstitial cells (Leydig cells) that produce male sex hormones testosterone and androgens at the beginning of puberty. These hormones are secreted in the presence of LH.
Testis - Sertoli cells
are stimulated by FSH and serve to surround and nurture sperm, as well as secrete peptide hormone inhibin, which acts on the anterior pituitary to inhibit FSH release
Testis - Scrotum
testis are located here; provides an external cavity about 2oC lower than the body temperature for sperm production.
Epididymis
a coiled tube attached to each testis that serves as the site for final maturation and storage of sperm
Vas deferens
transfers sperm from one epididymis to the urethra
Seminal vesicles
two glands that, during ejaculation, secrete into vas deference and provide mucus (liquid for sperm), fructose (energy for sperm), and prostaglandins (stimulate uterine contractions that help sperm move into uterus).
Prostate gland
secretes milky alkaline fluid into urethra and neutralizes acidity of urine that may still be in the urethra, as well as acidity of the vagina. This gland also neutralizes seminal fluid, which is too acidic from metabolic waste of sperm
Bulbourethral (Cowper’s) glands
secrete small amount of thick mucus of unknown function into urethra
Penis
transports semen (fluid containing sperm and secretions) into the vagina
Sperm
are compact packages of DNA specialized for effective male genome delivery.
Sperm - sperm head
Haploid (23 chromosomes); at tip is acrosome, a lysosome-like organelle containing enzymes (hyaluronidase), which are used to penetrate the egg. The acrosome originates from Golgi body vesicles that fuse together, and only the nuclear portion of the sperm enters the egg
Sperm - Mid-piece
flagellum (9+2 microtubule array) arising from one member of centriole pair, and contains lots of mitochondria
Sperm - Tail
remainder of flagellum; sperm is propelled by whiplike motion of tail and mid-piece
mnemonic SEVEn UP
Use the mnemonic SEVEn UP to memorize the path of sperm: Seminiferous tubules —> Epididymis —> Vas deferens —> Ejaculatory duct —> Urethra —> Penis (pause before the V for maturation!)
Gametogenesis in Humans
Gametogenesis describes the meiotic cell divisions that produce eggs (oogenesis) and sperm (spermatogenesis).
Egg vs sperm
The egg contains most of the cytoplasm, RNA, organelles, and nutrients needed by the developing embryo, which explains why the egg is much larger in size than the sperm. The sperm contributes very little cytoplasm during fertilization.
Oogenesis
Oogenesis - begins during the female embryonic development (before birth). Oogonia (fetal cells) undergo mitosis and become primary oocytes. These primary oocytes begin meiosis, but remain in prophase I until puberty. During puberty, one primary oocyte is selected and stimulated via FSH to continue its development through meiosis I during the ~28 day menstrual cycle.
i. This primary oocyte continues its development within a follicle, which is formed via encircling cells that protect and nourish the oocyte.
ii. Within the follicle, the oocyte completes meiosis I and becomes the secondary oocyte, which consists mostly of cytoplasm. The secondary oocyte also contains a polar body, which has much smaller cytoplasm content, and may or may not divide, but its products disintegrate.
iii. The secondary oocyte remains arrested in metaphase II until ovulation occurs.
Ovulation
Releases the secondary oocyte from a vesicular follicle, which is stimulated by an LH surge. If this oocyte is fertilized by a sperm, the oocyte completes meiosis II, and the resulting ovum/egg becomes diploid. The polar body degenerates.
Ovulation - at puberty
At puberty, FSH stimulates the growth of granulosa cells around the primary oocyte, which release a viscous substance that forms the zone pellucida, a jelly like layer around the egg. The structure at this stage is still a primary follicle.
Next, theca cells differentiate from the interstitial tissue and grow around the follicle to form a secondary follicle. Upon stimulation, by LH, theca cells secrete androgen, which is converted to estradiol (a type of estrogen) by the granulosa cells in the presence of FSH and is secreted into the blood.
Typically, estradiol inhibits LH secretion by the anterior pituitary, but just before ovulation, estradiol levels rise rapidly, causing a dramatic increase in LH secretion.
Spermatogenesis
begins at puberty within the seminiferous tubules of testes. This differs from oogenesis, which begins during fetal development.
Spermatogonia cells
undergo mitosis and become primary spermatocytes. These primary spermatocytes undergo meiosis I and form two secondary spermatocytes, which undergo meiosis II to become four spermatids.
Sertoli cells
Are found in seminiferous tubules, provide nourishment, and “nurse” spermatids as they differentiate into mature spermatozoa (sperm). The sperm complete maturation (gain motility and are stored) in the epididymis.
Semen
the combination of spermatozoa and fluids that leave the penis upon ejaculation.
Capacitation
the penultimate step in the maturation of the spermatozoa while in the vagina that allows for egg penetration. This is the final maturation of spermatozoa.
During capacitation, physiological changes occur to the sperm, including changes in intracellular ion concentration, motility, and metabolism.
What do eggs release to help sperm motility
eggs release progesterone which aids in sperm motility and increases the likelihood of fertilization
Spermatogenesis vs oogenesis
spermatogenesis is a continuous process, while oogenesis is discontinuous.
Female reproductive cycle
consists of ovarian cycle (in the ovary) and the menstrual cycle (involves uterus)
Female reproductive cycle - Menstrual cycle
is divided into the proliferative, secretory, and menstruation (menstrual flow) phases. Menstruation begins with the disintegration of the endometrium (menstrual flow phase)
Hypothalamus and anterior pituitary initiate, Follicle develops, LH surge, Development of endometrium, Corpus luteum disintegrates (no longer maintained by LH)
Female reproductive cycle - Menstrual cycle - Hypothalamus and anterior pituitary initiate
Monitor estrogen and progesterone in blood. Low levels of estrogen and progesterone stimulate hypothalamus → secretes GnRH → stimulates anterior pituitary to release FSH and LH →
Female reproductive cycle - Menstrual cycle - Follicle develops
FSH stimulates follicle to secrete estrogen → lots of estrogen (positive feedback on hypothalamus) → produces GnRH → anterior pituitary produces sudden mid cycle surge of LH →
Female reproductive cycle - Menstrual cycle - LH surge
triggers ovulation (follicle is now the corpus luteum, which develops and is maintained by LH, which along with estrogen, begins to decrease after ovulation), secretes estrogen and progesterone, which stimulate → Development of endometrium
Female reproductive cycle - Menstrual cycle - Development of endometrium
thickens in preparation for implantation of fertilized egg. If no implantation occurs, then negative feedback on anterior pituitary from increased estrogen And progesterone terminates production of FSH and LH, due to low GnRH from hypothalamus → Corpus luteum disintegrates
Female reproductive cycle - Menstrual cycle - Corpus luteum disintegrates
Corpus luteum disintegrates (no longer maintained by LH) - becomes corpus albicans; no estrogen and progesterone results in the endometrium shed during the menstruation flow phase!
Female reproductive cycle - implantation
If implantation occurs, then the embryo (placenta) secretes chorionic gonadotropin (HCG), which maintains the corpus luteum.
The production of estrogen and progesterone remains high, so the endometrium is not shed. HCG is later replaced by progesterone from the placenta. Without HCG, menstruation would begin, and the embryo would abort, as the embryo “maintains” pregnancy. This is why pregnancy tests check the presence of HCG in urine to deduce if a female is pregnant or not. If a fertilized egg implants anywhere other than the endometrium of the uterus, it is considered an ectopic pregnancy, and usually spontaneously aborts.
Graafian follicle
The follicle that releases the secondary oocyte is also called the Graafian follicle
Female reproductive cycle - Ovarian cycle - Follicular phase
development of egg and secretion of estrogen from follicle [ends at ovulation]
Female reproductive cycle - Ovarian cycle - Ovulation
mid-cycle release of egg
Female reproductive cycle - Ovarian cycle - Luteal phase
secretion of estrogen and progesterone from corpus luteum after ovulation [shedding of the uterine lining lasting approximately 5 days]
Note that the secretory phase of the menstrual cycle overlaps with the luteal phase of the ovarian cycle
Estrogen vs progesterone
estrogen serves to thicken the endometrium, while progesterone serves to develop and maintain the endometrial wall.
Progesterone also inhibits lactation during pregnancy. The fall in progesterone after delivery allows for milk production.
Male reproductive cycle
GnRH → FSH + LH (also known as
ICSH, interstitial cell stimulating hormone → testosterone and androgens from testes)
Male reproductive cycle - FSH and testosterone
FSH and testosterone → influence Sertoli cells to promote development of sperm (nourish sperm during development, or spermatogenesis). Hormone and gamete production are constant unlike in females.
Male reproductive cycle - LH
LH stimulates Leydig cells (in the interstitium between seminiferous tubules) to release testosterone + androgens that promote spermatogenesis in tubules.
Male reproductive cycle - Sertoli cells
Sertoli cells secrete inhibin that acts on the anterior pituitary to inhibit FSH secretion.
Male contraception
a pill would interfere with LH and FSH to decrease sperm production
Female hormonal contraception
estradiol and/or progesterone are spiked artificially high → negative feedback suppresses LH/FSH surge → no ovulation can occur → no fertilization possible
Animal embryos follow four stages in growth and development
Animal embryos follow four stages in growth and development: gametogenesis (sperm/egg formation), embryonic development (fertilization of egg until birth), reproductive maturity (puberty), and aging process to death
Development in mammals
development occurs in two stages: embryonic development followed by fetal development. A fetus is an embryo that resembles the human infant form, and in humans, an embryo is called a fetus at about 8 weeks.
Stages of embryonic development (sea urchin, echinoderm) - Fertilization
sperm penetrates plasma membrane of secondary oocyte
Stages of embryonic development (sea urchin, echinoderm) - Fertilization - Recognition
before penetrating, the sperm secretes proteins that bind with receptors that reside on a glycoprotein layer surrounding the plasma membrane of the oocyte. In humans, this layer is a vitelline layer (zona pellucida). In both organisms, the layer ensures same species fertilization.
Zona pellucida
external glycoprotein membrane surrounding the plasma membrane (jelly coat) of an oocyte. This first appears in unilaminar oocytes, and is secreted by both the oocyte and follicular cells. At puberty, FSH stimulates growth of granulosa cells around the primary oocyte that secrete the viscous zona pellucida.
Zona pellucida binding sperm
The zona pellucida expresses specific receptor proteins called ZP3, which bind to proteins expressed in the head of the sperm. The binding of ZP3 triggers the acrosome reaction, during which the enzymatic contents of the acrosome are released.
When the zona pellucida binds sperm, the acrosome reaction is initiated.
The sperm releases the contents of its acrosome as it approaches the egg, and contributes to a charge- based ‘fast block’ of polyspermy
5 days after fertilization
blastocyst undergoes zona hatching (zona pellucida degenerates and is replaced by the underlying layer of trophoblastic cells so it can implant in the uterus)
Capacitation
In capacitation, secretions from the uterus wall and uterine tube destabilize the plasma membrane surrounding the head of the sperm (acrosome), making the head more fluid, which helps prepare it for fertilization and makes the sperm hyperactive (faster and wiggle more).
The capacitated sperm moves through the corona radiata (dense layer of granulosa cell surrounding the oocyte) and comes into contact with the zona pellucida.
Acrosome reaction - enzymatic contents of the acrosome
These enzymes help digest a path through the zona pellucida, allowing the sperm to enter the perivitelline space (space between the plasma membrane of the secondary oocyte and the zona pellucida), which then fuses with the oocyte’s plasma membrane.
How to ensure only one sperm penetrates the zona pellucida and fuses with the oocyte membrane
The fusion of sperm to zona pellucida activates a fast block and a slow block to polyspermy
First, during the fast block, which takes place after fusion, the oocyte membrane depolarizes, preventing other sperm from fusing with it. Slow block to polyspermy is then stimulated by this depolarization —
during slow block to polyspermy, a wave of intracellular calcium is released, causing small cortical granules beneath the oocyte membrane to release their contents outward, rendering ZP3 in the zona pellucida inactivate and making it impermeable. Note that intracellular Ca2+ triggers cortical granule release, but the granules themselves don’t contain Ca2+.
Zona pellucida in non-mammals
In non-mammals, the zona pellucida plays an important role in preventing cross-breeding of different species, especially in species where fertilization occurs outside of the body.
Zona pellucida - immunocontraception
The zona pellucida is also commonly used to control wildlife population via immunocontraception. When the zona pellucida of one animal species is injected into the bloodstream of another, sterility of the second animal occurs due to an immune response. Fertilization cannot occur because antibodies have already bound to the zona pellucida, thus preventing sperm from binding
Fertilization - eggs
Fertilization can be external in water (lots of eggs laid since the chance of fertilization is lower - frogs/amphibians) or internal (terrestrial vertebrates). The # of eggs laid is affected by the following factors: internal vs external fertilization, early development, and amount of parental care (less care = more eggs)
Steps after capacitation and the acrosome reaction
Penetration, Formation of fertilization membrane, Completion of meiosis II in secondary oocyte, Fusion of nuclei and replication of DNA
Steps after capacitation and the acrosome reaction - Penetration
plasma membrane of sperm and oocyte fuse, and the sperm nucleus enters the oocyte
Steps after capacitation and the acrosome reaction - Formation of fertilization membrane
the vitelline layer forms a fertilization membrane that blocks additional sperm (remember, this is due to the cortical reaction, which is the exocytosis of enzymes produced by cortical granules in egg cytoplasm during fertilization → called slow block in mammals)
Steps after capacitation and the acrosome reaction - Completion of meiosis II in secondary oocyte
sperm penetration triggers meiosis II to complete. The oocyte was previously arrested in metaphase in humans. The result is an ovum and a second polar body, which is discharged through the plasma membrane
Steps after capacitation and the acrosome reaction - Fusion of nuclei and replication of DNA
sperm and ovum nuclei fuse → diploid zygote forms. This is associated with a sharp increase in protein synthesis and metabolic activity.
Fertilization location
Fertilization takes place in the oviduct (fallopian tubes); cleavage while swept; and the embryo is at the blastula stage by the time it reaches the uterus for implantation
