Reproduction + Development Flashcards
Why is sexual reproduction an advantage?
Advantageous over asexual reproduction because promotes genetic variety among members of a species
external fertilization
Aquatic animals- external fertilization- gametes meet outside the body; Many gametes are released to ensure perpetuation of the species
internal fertilization
Terrestrial animals- internal fertilization- male delivers sperm directly into the body of a female; Moist tissues inside female provide medium for movement of sperm
Hermaphrodism-
where single individual produces both egg and sperm
Spermatogenesis-
process of forming sperm- occurs in testes; Takes place in seminiferous tubules;
testes
male gonads
seminiferous tubules
hollow tubes within each testis
process of sperm development
Process- spermatogonia primary spermatocytes secondary spermatocytes spermatids mature sperm cells
Sperm cells
Head- contains nucleus with 23 chromosomes, covered by acrosome- contains enzymes which break through the egg
Midpiece- first part of flagellum that contains mitochondria, providing energy for flagella to swim
Tail- remainder of flagellum, arranged in 9+2 array of microtubules
what part of sperm specifically doesn’t enter zygote?
mitochondria of sperm don’t enter zygote
9 + 2
9 couplets surrounding 2 singlets
Sertoli cells-
large cells that surround the seminiferous tubules; prevent sperm from entering bloodstream; Forms compartments that separate sperm cells in different stages of development
Scrotum-
skin covered sac that contains the testes; Maintains temperature slightly below body temp, which is optimal temp for sperm production
(body is 37, scrotum is 35)
What happens after sperm leave seminiferous tubules?
pass into epididymis
What happens after sperm pass into epididymis?
move into vas deferens
vas deferens
sperm duct that extends from the scrotum into the pelvic cavity
What happens after sperm move into vas deferens?
Empties into short ejaculatory duct, then passes through prostate gland, then enters single urethra and leaves the body
Semen-
sperm cells and secretions from glands
Reproductive glands of male
Seminal vesicles, Prostate gland, Bulbourethral glands
prostate gland purpose in reproduction
produces basic fluid that helps neutralize acidic environment of vagina
Bulbourethral glands
paired, located on either side of urethra- releases mucous during sexual arousal, which helps lubricate the penis
Seminal vesicles-
secrete fluid which provides nutrition (fructose) and energy for the sperm
Penis-
erectile organ that delivers sperm into the female reproductive tract; When male is sexually stimulated, blood fills blood vessels in erectile tissue, causing tissue to swell and erection to occur
Testosterone-
male sex hormone; Produced by interstitial cells in the testes; Produces male primary sex characteristics and Stimulate development of secondary sex characteristics at puberty; FSH and LH secreted by pituitary stimulate production of testosterone and spermatogenesis
Insufficient testosterone
sterility
male primary sex characteristics
growth of reproductive organs and spermatogenesis
male secondary sex characteristics
growth of facial and body hair, muscle development, deepening of voice
Oogenesis-
process of ovum formation; takes place on ovaries
ovaries
the female gonads that lie in the pelvic cavity. Each ovary connects to an oviduct-
process of oogenesis
Process- oogonia primary oocytes secondary oocytes ovum
Follicle-
on ovary, primary oocyte and granulosa cells, which form a protective barrier around the oocyte
Follicle cells secrete estrogen as follicle develops
oviduct/fallopian tube
short tube where egg travels through toward the uterus
Uterus
pear-shaped organ that has thick walls of smooth muscle and an epithelial lining called an endometrium
endometrium thickening
Endometrium thickens each month in preparation for pregnancy; If fertilization does not occur, endometrium is discharged during menstruation
Cervix-
lower part of uterus
Vagina-
elastic, muscular tube that extends from uterus to exterior of body- receives sperm during intercourse and is part of the birth canal
vulva
- female external genitalia
Breast:
Composed of adipose tissue and glandular tissue–mammary gland; Lactation- production of milk
lactation hormones
Prolactin secreted after birth Oxytocin secreted when baby suckles
estradiol
(principal estrogen is estradiol)
estrogen
Responsible for primary sex characteristics-development of the sex organs at birth; Secondary sex characteristics- development of breasts, broadening of pelvis, change in body shape
menstrual cycle
Monthly sequence of events that prepares the body for possible pregnancy
Takes place every month from puberty until menopause (age 50)
Average cycle- 28 days
Follicular stage-
begins w onset of menstruation
GnRH released from hypothalamus stimulates the anterior pituitary to release FSH and LH
These cause a few follicles to begin to develop and follicles release estrogen, which causes endometrium to thicken
When estrogen levels peak, this causes a surge of LH to be released
GnRH
Gonadotropin-releasing hormone
FSH
Follicle Stimulating Hormone
LH
Leutinizing Hormone
Ovulation-
Surge of LH causes the follicle to rupture, releasing the secondary oocyte from the ovary. Cilia lining the oviduct sweep the secondary oocyte in towards the uterus. Cells in the cervix secrete a thin mucus, ideal for sperm to swim in
Luteal phase
Corpus luteum, or empty follicle, forms and releases large amounts of estrogen and progesterone. continues to thicken the uterine lining, Also inhibits GnRH, FSH, and LH- preventing another follicle from maturing; Corpus luteum degenerates if secondary oocyte is not fertilized–estrogen and progesterone decrease
Menstrual phase-
Endometrium disintegrates and is sloughed off during menstruation
Low levels of estrogen and progesterone cause FSH and LH to be secreted once again
Fertilization
fusion of egg and sperm
Sperm stay alive for 24 hr, ovum remains fertile for about 24 hr after ovulation
Intercourse between days 12 and 16 is most likely to result in fertilization
When sperm encounters an egg:
Acrosomes in sperm digest surrounding cells of egg
Upon entering, sperm loses flagella
Sperm entry stimulates secondary oocyte to second meiotic division
Male pronucleus then fuses with female pronucleus, forming a diploid zygote
As embryo moves toward uterus, it slowly develops- implants itself in uterus on about 7th day after fertilization
Membranes that surround the embryo release HCG, which signals mother’s corpus luteum to continue to function
HCG
human chorionic gondatoropin
Pregnancy tests
Pregnancy tests check for presence of HCG in urine
Why do concentrations of estrogen and progesterone remain high throughout the pregnancy?
Membranes that surround the embryo release HCG, which signals mother’s corpus luteum to continue to function remain high throughout the pregnancy
What happens to zygote post fertilization
After fertilization, zygote undergoes cleavage-rapid mitotic division so fast that embryo doesn’t increase in size
Cells are called blastomeres- increasingly smaller w each division
Placenta forms
Zygote division
Zygote 2 cells 4 cells … morula- 32 cell stage blastula- hollow ball of cells with fluid-filled cavity called blastocoel
Placenta
organ of exchange between mother and developing embryo. After about 3 months, corpus luteum deteriorates and placenta takes over in secretion of estrogen and progesterone in addition to being organ of exchange
Gastrulation
Process by which the blastula becomes a three-layered embryo, or gastrula
gastrulation beginning
Begins when a groups of cells at the vegetal pole bend inward, or invaginate Invaginated wall meets opposite wall, and blastocoel disappears
Archenteron-
new center cavity formed by gastrulation- completely surrrounded by endoderm cells
Blastopore-
opening to archenteron
Mouth in protostomes
anus in deuterostomes
Organogenesis
process of organ formation
cytoplasmic localization
Oocytes stockpile mRNA transcripts and enzymes as “messages” to be read even as early as fertilization; These messages are passed on to the cells in the blastula. Different cells receive different maternal messages based on where the cuts are made during cleavage.
helps seal the developmental fate of each cell lineage
effect of cytoplasmic localization
These messages cause selective gene expression to occur from gastrulation on- some cell lineages express different groups of genes than others
This is the start of cell differentiation
What happens once cells start to become differentiated from one another?
morphogenesis occurs
morphogenesis
tissues and organs of specific sizes and shapes form
Cells divide and grow, tissues lengthen, responding to release of chemicals
Apoptosis, or programmed cell death, helps
sculpt body parts
Short range signals
involving cell-to-cell contacts- ex- cells can activate or inhibit genes for adhesion proteins or recognition proteins, causing cells to stick to one another or break free for one another
Long range signals
act on control elements in the DNA of embryonic cells that are far away
Embryonic induction-
developmental fates of embryonic cell lineages change when exposed to signals (gene products) from adjacent tissues. Signals are the basis of pattern formation.
pattern formation
sculpting of tissues and organs from clumps of cells in the proper places and proper order in the embryo
morphogens
Example of long range signal that causes embryonic induction. Degradable molecules that diffuse out of signaling centers, so their concentration weakens with distance. This causes each cell at a given point along the resulting gradient to read different parts of the same genome, which affects how it will differentiate
activate classes of master genes as they diffuse through the tissues.
Homeotic genes
types of master genes that lay the foundation for the basic body plan
Products of homeotic genes and master genes
Products of homeotic genes and master genes interact with control elements in different cells. Different genes are activated and suppressed along the anterior-posterior axis and dorsal- ventral axis
What happens when master genes and their products fail in mapping out the overall body plan,
the body cannot form properly- structure can go in a wrong location
master genes
control the structure of the body. All the millions of species are variations on a few dozen plans of master genes.
Often the gene that governs the formation of similar structures in different organisms is nearly identical even if the structures themselves are very different
Mutations have added variations to structures, but changing an entire body plan is likely to kill the embryo.
Endoderm
- innermost layer of gastrula
organogenesis- tissue that line digestive tract and outgrowths (liver, pancreas, lungs)
Ectoderm
outer layer of gastrula
organogenesis outer layer of skin, nervous system, sense organs
Mesoderm
Mesoderm- middle layer
organogenesis- Skeletal tissue, muscle, circulatory, excretory, and reproductive system
when does embryonic cell start to selectively read its genes
Once locked in a tissue, an embryonic cell starts to selectively read its genes. Often it makes and secretes signaling molecules that affect its neighbors
