Reproductive System/ Human Embryology

Germ cell vs gametes

diploid (form gametes) vs haploid (sex cells)

Gonads

reproductive structures responsible for producing gametes and sex hormones, ovaries in females and testes in males

Ovary

two structures that produce eggs

Oviduct

aka fallopian/uterine tube, where fertilization occurs, allows for eggs to move from ovary to uterus (one oviduct for each ovary)

Uterus

muscular chamber where embryo develops until birth, zygote attaches to inside of uterine wall after fertilization

Cervix

connects uterus to vagina, where the baby moves through due to dilation during birth

Vagina

muscular tube-like structure where intercourse takes place and the final area of birth canal before baby emerges

Fimbriae

fingerlike projections at entrance of fallopian tube that sweep eggs into the fallopian tube from the ovary (through gap space)

Testes

main male reproductive organ that produces sperm and male sex hormones, found in scrotum

Scrotum

external cavity that houses testes, provides optimal temperature for sperm production (pull closer to body when it’s cold and drop when it’s hot)

Seminiferous tubules

coiled tubules in the testes that produce sperm, containing spermatogonia, sertoli cells, and leydig cells

Spermatogonia

germ cells in the seminiferous tubules that undergo meiosis to create sperm gametes

Sertoli cells

surround spermatogonia in seminiferous tubules that nurture developing sperm, stimulated by FSH

Leydig cells

Surround seminiferous tubules and begin producing testosterone + androgens at puberty, stimulated by LH

Epididymis

coiled tubes that sit in back of seminiferous tubules (one attached to each teste), site for final maturation and storage of sperm where glycoprotein coat is added

Vas deferens

muscular tube that undergoes peristalsis, transferring sperm from epididymis to ejaculatory duct

Ejaculatory duct

formed by merging of vas deferens and seminal vesicle duct that passes through prostate gland and eventually merges with urethra

Urethra

a duct that allows for passage of semen and urine

Penis

transports semen into vagina

Path of sperm

SEVEn UP: Seminiferous tubules, Epididymis, Vas deferens, Ejaculatory duct, nothing, Urethra, Penis

Seminal vesicles

pair of glands that secrete seminal fluid into seminal vesicle duct, containing mucous, fructose, and prostaglandins

Mucous

provides liquid for sperm

Fructose

provides energy for sperm

Prostaglandins

stimulates uterine contractions that help sperm move into uterus

Prostate gland

produces slightly alkaline fluid that mixes with sperm and substances from other glands to make up semen, helps neutralize the acidic environment of the female reproductive tract

Cowper’s glands

AKA bulbourethral glands, produce fluid to lubricate the urethra and neutralize any acidity from residual urine

Steps in oogenesis before birth (embryonic development)

1. Primordial germ cells move to ovaries and eventually differentiate into oogonia (precursor egg cells)

2. Oogonia undergo mitosis to become primary oocytes

3. Primary oocytes remain in prophase I until puberty

What are the follicles doing during embryonic development oogenesis?

composed of granulosa cells surrounding primary oocytes, relatively inactive

Steps in oogenesis during puberty

1. primary oocyte triggered to finish meiosis I by LH surge

2. secondary oocyte (most of cell contents) and polar body are produced

3. Secondary oocyte enters meiosis II and remains at metaphase II until fertilization

Steps of follicular development during puberty

1. a few follicles are selected to continue development, with one becoming dormant, granulosa cells grow larger and become more active to become primary follicles

2. Layer of theca cells forms outside granulosa cells and produces estrogen (in response to hormones, now secondary follicle)

3. Fluid filled space in follicle between granulosa cells called antrum forms, increasing follicle size

4. Follicle reaches mature state

5. Only the biggest, strongest, healthiest follicle stays and the rest degenerate

End of oogenesis if fertilization occurs

1. Secondary oocyte finishes meiosis II

2. Fertilized egg (ovum) is produced and a second smaller polar body

3. Diploid zygote forms

Follicle

structure made of cells that surrounds and supports the development of the egg by providing nutrients, regulating meiosis, and produces estrogen from ovary

Zona pellucida

Outer layer secreted by primary oocyte that sits in between oocyte and primary follicle, plays a role in sperm binding

Mature follicle

AKA tertiary or graafian follicle, final form

Corona radiata

a few layers of granulosa cells surrounding oocyte once follicle reaches maturity

LH surge

triggered by increasing levels of estrogen from the follicle, causing ovulation (eject oocyte from follicle into fallopian tube) and primary oocyte to continue meiosis

Ovulation

release of secondary oocyte from ovary into fallopian tube

Corpus luteum

developed from remaining follicle after egg is released into fallopian tube, secretes estrogen and progesterone to maintain uterine lining during pregnancy (if egg is fertilized), degenerates into corpus albicans if no fertilization

Corpus albicans

degenerated form of corpus luteum in absence of fertilization that later disintegrates (essentially scar tissue)

steps in Spermatogenesis

1. spermatogonium undergo mitosis

2. spermatogonia differentiate into primary spermatocytes

3. primary spermatocytes undergo meiosis I and form 2 secondary haploid spermatocytes

4. Secondary spermatocytes undergo meiosis II and form 4 spermatids

5. spermatids continue development (including flagellum) into spermatozoa

6. Spermatozoa released from walls of seminiferous tubules

7. Swept into epididymis for final maturation (full mobility)

major sections of spermatozoa (mature sperm) from posterior to anterior

tail (flagellum), midpiece (mitochondria for energy), sperm nucleus (haploid), acrosome (penetrates egg, filled with hydrolytic enzymes)

Capacitation

last functional maturation step of sperm in female reproductive tract, stabilizing lipids and proteins are lost causing sperm to become more motile, allowing for egg penetration

Most important parts of capacitation

glycoprotein coat removal, destabilization of apical plasma membrane (exposes acrosome), and hyperactivation (extreme motility)

Effects of exogenous testosterone injection

increases muscle mass and estrogen, decreases spermatogenesis, endogenous testosterone production, and size of testes (all result of negative feedback)

Three phases of ovarian cycle

Follicular phase, ovulation, luteal phase

Progesterone

steroid hormone that prepares and maintains uterine tissues needed to support growth/development of embryo

Follicular phase

first ~13 days of cycle, consists of development of egg and secretion of estrogen from follicle

Steps of the follicular phase

1. Hypothalamus and anterior pituitary monitor estrogen and progesterone in blood

2. Low levels stimulate hypothalamus to release GnRH in pulses

3. Anterior pituitary is stimulated to release FSH and LH (mostly FSH)

4. Follicle is stimulated to secrete estrogen, initiating buildup of uterine lining, and LH levels begin to rise gradually

Ovulation

lasts about a day; midcycle release of egg

Steps of the ovulatory phase (ovulation)

1. Estrogen levels peak, triggering rapid frequency GnRH release

2. GnRH stimulates a spiked increase of FSH and LH

3. “LH surge” triggers ovulation (release of egg from ovary) and increased progesterone production (builds up uterine lining)

4. Empty follicle turns into corpus luteum, ramping up progesterone production (and some estrogen), suppressing LH and FSH release

Luteal phase

days 15-28, secretion of estrogen + progesterone from corpus luteum after ovulating

Steps of Luteal phase (absence of fertilization)

1. corpus luteum continues producing estrogen and progesterone (peak day 21 ish)

2. Endometrium develops in response (thickens uterus)

3. negative feedback of high estrogen + progesterone decreases GnRH from hypothalamus, terminating production of FSH/LH from anterior pituitary

4. Decreased LH causes corpus luteum to disintegrate into corpus albicans

5. Decreased estrogen+progesterone causes endometrium shedding during menstrual phase

6. FSH begins to rise and cycle repeats

Steps of Luteal phase (PRESENCE of fertilization)

1. corpus luteum continues producing estrogen and progesterone

2. Endometrium develops in response (thickens uterus)

3. implantation occurs and placenta forms

4. placenta secretes hCG to maintain corpus luteum (and endometrium)

5. hCG is eventually replaced by progesterone from placenta

human chorionic gonadotropin (hCG)

peptide hormone produced by placenta to maintain corpus luteum for estrogen and progesterone production (maintains endometrium), detected in pregnancy tests (passes from blood to urine)

Three phases of menstrual/uterine cycle

Menses (menstrual), proliferative, secretory

Steps of menstrual/uterine cycle

1. body sheds thickens uterine lining build up from last reproductive cycle due to degeneration of corpus luteum and decreased estrogen + progesterone (bleeding as top layer is removed from body, menses/menstrual phase, days 1-5)

2. secretion of estrogen from growing follicle causes thickening of endometrium (proliferative phase, days 6-14)

3. estrogen and progesterone released from corpus luteum cause increased growth and development of endometrium (secretory phase, days 15-28, coincides with luteal phase of ovarian cycle)

How does female hormonal contraception work?

estrogen and/or progesterone are spiked artificially high, causing a negative feedback that suppresses LH and FSH preventing the LH surge that makes ovulation occur, preventing fertilization

Male reproductive cycle

hypothalamus releases GnRH, triggering anterior pituitary to release FSH and LH. FSH causes Sertoli cells to promote sperm development and LH causes Leydig cells to release testosterone (supports/maintains spermatogenesis)

ovum

egg after it has been ovulated from ovary

oocyte

egg prior to ovulation (in ovary)

perivitelline space

space between zona pellucida and plasma membrane of egg

Fertilization

haploid egg and sperm fuze to become diploid zygote

Zona pellucida sperm binding receptors

sperm bind to signify animals are same species; ZP1, ZP2, ZP3, ZP4

ZP3

most important ZP receptor, triggers acrosome reaction (acrosin release) when sperm bind

Acrosin

proteolytic enzyme on sperm head that breaks through zona pellicula

Polar body

result of unequal division of cytoplasm in mitotic cell division (egg gets most of stuff)

Polyspermy

multiple sperm fuzing with the ovum

Two methods to prevent polyspermy

fast block and slow block

Fast block

when the sperm binds to the egg’s plasma membrane, instantaneously sodium channels open and depolarize the plasma membrane (Na+ floods in) to +20mV, preventing other sperm from binding, only lasting a few minutes (slow lasting)

Slow block

After the fast block, Ca2+ are released from ER into cytoplasm of egg, causing cortical reaction (ectocytosis with cortical grannuoles), enlarging perivitelline space, detaching it from plasma membrane (forming fertilization envelope), simultaneously inactivating ZP receptors (locking sperm out from fertilizing)

Cleavage

rapid cell division without any cell growth, split into holoblastic and meroblastic, determinant and indeterminant, and spiral and radial

Holoblastic cleavage

cleavage furrow separates cell into equal sized blastomeres, low amount of yolk and done in placental mammals

Meroblastic cleavage

partial and uneven cleavage, resulting in different sized blastomeres, high amounts of dense yolk and done in birds/reptiles

Determinant cleavage

cell divides into two blastomeres that have decided what cell they are going to become

Indeterminant cleavage

cell divides into two resulting blastomeres that have not decided what cell they are going to be come yet

Spiral cleavage

cleavage furrow has no pattern of alignment (random in regards to polar axis), creating disorganized appearance (unequal cell division with macromeres and micromeres)

Radial cleavage

cleavage furrow is perfectly parallel or perpendicular to original polar axis, creating very organized structure of blastomeres

Animal pole vs Vegetol pole

different sides of the egg with less yolk (where animal grows and lots of division occurs) vs more yolk (less division), creating polar axis (line splitting two sides apart)

All protostomes undergo what types of cleavage?

Determinant spiral

All deuterostomes undergo what types of cleavage?

indeterminant radial

Morula

solid ball of cells with 16-32 blastomeres

Blastulation

transformation of morula into blastula

Blastula/blastocyst

hollow, fluid filled ball of hundreds of cells

Blastocoel

inner hollow part of the blastula/blastocyst

Gastulation

transformation of blastula/blastocyst into gastrula (invagination/folding motion)

Blastopore

folded in part of a gastrula that either becomes mouth or anus (protostome or deuterostome)

Gastrula

phase of embryo development where germ layers have developed

Archenteron

cavity that links first opening to second in gastrula (primitive digestive tract)

Germ layer

one of three cell types that forms from gastulation (most primitive type of differentiated cell line): ectoderm, mesoderm, endoderm

Trophoblast

outer layer of cells on exterior of blastula, later forming placenta (chorion), responsible for implantation and produces hCG (human chorionic gonadotropin)

Inner cell mass (embryoblast)

inner layer of cells of blastula that gives rise to embryo, amnion, yolk sac, and allantois, made up of epiblast (top layer) and hypoblast (bottom layer)

Zona hatching

process where embryo breaks free from zona pellucida

Bilaminar disc

epiblast and hypoblast stacked together like pancakes

Trilaminar

ectoderm, mesoderm, and endoderm stacked together like pancakes

Amnion

innermost membrane that encloses embryo filled with amnioc fluid acting as a cushion formed by epiblast

Primitive streak

thickened epiblast layer consisting of two bumps and a groove in the middle (primitive groove) extending from head to tail of embryo

mesenchyme/mesanchymal cells

cells that are undifferentiated and migratory (go in between epiblast and hypoblast)