Chapter 12: Animal Reproduction and Development Flashcards
female reproduction anatomy
a. Ovary: ova, or eggs, are produced. Each female has two ovaries.
b. Oviduct: eggs move from ovary to uterus through oviduct (Fallopian/uterine tube); one for each ovary; swept by fimbrae
c. Uterus: fertilized ovum implants (attaches) on the inside wall, endometrium, of uterus. Development of embryo
occurs here until birth.
d. Vagina: at birth, fetus passes through cervix (opening in the uterus), through and out of body
male reproduction anatomy
path of sperm is SEVEnUP
a. Testis: each consists of seminiferous tubules for production of sperm and interstitial cells (Leydig cells)
produces male sex hormones (testosterone = androgen) secreted in the presence of LH; sertoli cells stimulated by FSH
surround and nurture sperm (also secrete peptide hormone inhibin, acts on PitGl to inhibit FSH release); testis contained in
scrotum-about 2oC lower than body temp for sperm production.
b. Epididymis: coiled tube, one attached to each testis; site for final maturation and storage of sperm.
c. Vas deferens: transfer sperms from one epididymis to urethra.
d. Seminal vesicles: Two glands, during ejaculation secrete into vas deferens: provide mucus (liquid for sperm),
fructose as ATP, and prostaglandins (stimulate uterine contractions that help sperm move into uterus).
e. Prostate gland: secretes milky alkaline fluid into urethra; neutralizes acidity of urine that may still be in urethra,
also vagina acidity. Also neutralizes seminal fluid (too acidic from metabolic waste of sperm)
f. Bulbourethral glands (aka Cowper’s): secrete small amount of fluid of unknown function into urethra.
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g. Penis: transport semen (fluid containing sperm and secretions) into vagina.
3. Sperm: compact packages of DNA specialized for effective male genome delivery.
a. Sperm head: haploid (23 chromosomes); at tip is acrosome (a lysosome
containing enzymes [hyaluronidase] which are used to penetrate egg-originates from
Golgi body vesicles that fused together). Only nuclear portion of sperm enters the egg.
b. Midpiece: flagellum (9 + 2 microtubule array), lots of mitochondria.
c. Tail: remainder of flagellum; sperm is propelled by whiplike motion of tail
and midpiece.
SEVEnUP: seminiferous tubules epidydmis vas deferens ejaculatory duct urethra penis
gametogenesis in humans
- It is the meiotic cell divisions that produce eggs (oogenesis) and sperm
(spermatogenesis). Egg contains most of the cytoplasm, RNA, organelles, and nutrients
needed by developing embryo.
1. Oogenesis: being during embryonic development; oogonia (fetal cells) (mitosis) primary oocytes (meiosis) and
remain at Prophase I until puberty (one primary oocyte during each menstrual cycle-28days, stim’d by FSH) continue its
development through remainder of meiosis I within follicle (protects and nourishes oocyte) (completion of Meiosis I)
secondary oocyte (most of cytoplasm) + polar body (small cytoplasm; may or may not divide but products disintegrate)
formed; now arrested at metaphase of meiosis II until ovulation
2. Ovulation: releases secondary oocyte from vesicular follicle (caused by LH surge). If fertilized by sperm (finishes
meiosis II) ovum/egg (diploid once completely fertilized) + polar body (degenerate)
3. Spermatogenesis: begins at puberty within seminiferous tubules of testes. Spermatogonia cells (mitosis) primary
spermatocytes (meiosis) 2 secondary spermatocytes (meiosis II) 4 spermatids. - Sertoli cells: in seminiferous tubules provide nourishment to spermatids as they differentiate into mature spermatozoa
(sperm). They complete maturation (gain motility and are stored) in the epididymis.
Capacitation – penultimate step in maturation of the spermatozoa while in the vagina, allows for egg penetration
hormonal control of human reproduction: Female
Female Reproductive Cycle: ovarian cycle (ovary) + menstrual cycle (uterus).
a. Menstrual Cycle – divided into follicular, ovulation, luteal, menstruation (proliferative/secretory/menstruation)
Hypothalamus and anterior pituitary initiate: monitor estrogen and progesterone in blood;
Low level hypothalamus GnRH FSH and LH (via anterior pituitary-negative feedback)
Follicle develops FSH stimulate follicle to secrete estrogen lots of estrogen (positive feedback on AP)
LH Surge Ovulation (follicle is now corpus luteum-maintained by LH [which along w/ estrogen begins to
decrease after ovulation], secretes estrogen + progesterone)
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Development of endometrium (thickens in prepn
for implantation of fertilized egg)
NO IMPLANTATION:
(negative-feedback on AP from ↑e+p) terminates production of FSH + LH (due to ↓GnRH from hypothalamus)
Corpus luteum (no longer maintained by LH) disintegrates corpus albicans, no estrogen + progesterone
endometrium shed during menstruation’s flow phase.
IMPLANTATION:
If implantation occurs embryo (placenta) secretes
chorionic gonadotropin (HCG) maintain corpus luteum
Production of e + p remain high endometrium stays HCG is
later replaced by progesterone from placenta.
b. Ovarian Cycle
1. Follicular phase: development of egg and secretion of
estrogen from follicle.
2. Ovulation: midcycle release of egg.
3. Luteal phase: secretion of estrogen and progesterone from corpus luteum after ovulation.
Estrogen – thicken endometrium
Progesterone – development and maintenance of endometrial wall
male reproductive cycle
- Male Reproductive Cycle:
- GnRH FSH + LH (also called ICSH, interstitial cell stimulating hormone testosterone and androgens from testis).
- FSH and testosterone influence Sertoli cells to promote development of sperms (nourish sperm during
development-spermatogenesis). Hormone and gamete production are constant unlike female.
embryonic development
D. Embryonic Development
- Four stages in growth and development of animal: gametogenesis (sperm/egg formation), embryonic development
(fertilization of egg until birth), reproductive maturity (puberty), aging process to death.
- In mammals, development is two stages—embryonic followed by fetal development. Fetus is an embryo that resembles
the infant form.
1. Stages of Embryonic Development (sea urchin-echinoderm):
a. Fertilization: sperm penetrate plasma membrane of 2nd oocyte.
1. Recognition: before penetration, sperm secretes proteins that bind with receptor that reside on glycoprotein
layer (vitelline layer-zone pellucida in human) surrounding plasma membrane of oocyte ensures same species fertilization
Zona Pellucida – !! Glycoprotein membrane surrounding plasma membrane of an oocyte. External but essential to the oocyte. First
appears in unilaminar oocytes; secreted by both the oocyte and follicular cells (at puberty FSH stimulates growth of granulosa cells around
primary oocyte that secrete the viscous zona pellucoda). It binds sperm, and is required to initiate the acrosome reaction (sperm releases
contents of acrosome as it approaches egg; contributes to charge based fast block of polyspermy). 5 days after fertilization,
blastocyst performs zone hatching (zona pellucida degenerates + replaced by underlying layer of trophoblastic cells so it can implant
in the uterus).
2. Penetration: plasma membranes of sperm and oocyte fuse, sperm nucleus enter oocyte.
3. Formation of fertilization membrane: vitelline layer forms fertilization membrane blocks additional sperm (due
to cortical reaction: exocytosis of enzymes produced by cortical granules in egg cytoplasm during fertilization – slow block
when seen in mammals)
4. Completion of meiosis II in 2nd oocyte: sperm penetration triggers meiosis 2; ovum + polar body (discharged
through plasma membrane) produced.
5. Fusion of nuclei and replication of DNA: sperm and ovum nuclei fuse zygote (diploid-23 pairs in human).
b. Cleavage: rapid cell divisions without cell growth; each cell = blastomere (less cytoplasm than original zygote)
1. Embryo polarity: egg has upper, animal pole and lower, vegetal pole (contain more yolk material which is
denser than cytoplasm, settles at bottom; differentiates into extraembryonic membranes that protect+nourish embryo).
Animal cell can divide through mitosis at a faster rate. (?)
2. Polar and equatorial cleavages: early cleavages are polar, dividing egg into segments that stretch from pole to
pole (segments of orange); others are parallel with equator.
3. Radial and spiral cleavages: radial in deuterostomes forming (indeterminate) cells at animal and vegetal poles
that are aligned together, top cells directly above bottom cells. In protostomes (spiral-determinate), cells formed on top are
shifted relative to those below.
4. Indeterminate and determinate cleavages: indeterminate (blastomeres can individually complete normal
development if separated). Determinate cannot develop into complete embryo if separated; each is differentiated into part of
the embryo.
Note: fertilization takes place in the oviduct; cleavage while swept; embryo at blastula stage by the time it reaches the uterus for implantation (img)
c. Morula: successive cleavage results in solid ball of cells (~8+ cells stage) (first 8 cells are totipotent)
d. Blastula: cell division continues; liquid fills morula and pushes cells out to form circular cavity surrounded by
single layer of cells. Blastocoel is the cavity. (~128 cells stage). (get a good picture for this and make sure it distinguishes
how the mammalian blastocyst has an inner cell mass)
-In humans the blastula is called the blastocyst and implants into the endometrium (development here)
e. Gastrula(tion): invagination into blastula, forming two-layered embryo with an opening from outside into center
cavity.
1. Three germ layers: ectoderm, mesoderm, and endoderm (3rd layer is formed between outer and inner layer of
invaginated embryo). Give rise to all subsequent tissues.
a. Endoderm – epithelial lining of digestive & respiratory, parts of liver, pancreas, thyroid, and urinary bladder lining
b. Mesoderm – musculoskeletal, circulatory system, excretory system, gonads, connective tissue, portions of digestive & respiratory, notochord
c. Ectoderm – Nervous system (brain and spinal cord), integument (epidermis & hair / epithelium of nose, mouth, anal canal), sense structures
(lens of eye, retina), teeth, neural tube
Note: some primitive animals (e.g. sponges, cnidarian) will develop mesoglea, a noncellular layer, instead of mesoderm
2. Archenteron: center cavity formed by gastrulation.
3. Blastopore: opening into archenteron, becomes mouth (protostomes) or the anus (deuterostomes)
embryonic membrane development
- Chorion: outer membrane. Birds and reptiles: membrane for gas exchange. Mammals: chorion implants into
endometrium, and later, the chorion and maternal tissue form the placenta (a blend of maternal and embryonic tissues
across which gases, nutrients, and wastes are exchanged) - Allantois: Sac that buds off from archenteron (cavity of gastrula forming primitive gut) that eventually
encircles the embryo, forming layer below chorion. Birds + reptiles: initially stores waste products as uric acid. Later fuses
w/ chorion membrane for gas exchange w/ blood vessels below. Mammals: allantois transports waste products to
placenta; eventually forms umbilical cord between embryo and placenta: transporting gases, nutrients, and wastes. Becomes
urinary bladder in adults. - Amnion: encloses amniotic cavity, a fluid-filled cavity that cushions the developing embryo, much like the
coelom cushions internal organs in coelomates
61 - Yolk sac: In birds and reptiles,
organogenesis
g. Organogenesis: cells continue to divide after gastrulation differentiate develop into specific tissues and
organs. In chordates:
1. Notochord: cells along dorsal surface of mesoderm layer form notochord, a stiff rod that provides support in
lower chordates. Vertebrae of higher chordates are formed from nearby cells in mesoderm.
2. Neural tube: In ectoderm layer directly above notochord, layer of cells forms neural plate. Plate indents,
forming neural groove, then rolls up into a cylinder, the neural tube. This develops into the CNS. Additional cells roll off
top of neural tube and form neural crest (which form teeth, bones, muscles of skull, pigment cells in skin, and nerve tissue)
exceptions to general embryonic development patterns
- Frog: amphibian
a. Gray crescent: sperm penetrates frog egg reorganization of cytoplasm pigmented cap of animal pole rotates
towards point of penetration while gray, crescent-shaped region forms opposite the point of penetration. Spemann found in early
cleavage, each individual cell could develop into a frog only if it had a small portion of gray crescent.
b. Gastrulation: blastopore forms at border between gray crescent and vegetal pole. During gastrulation, cells
migrate over top edge (dorsal lip-formed from same region previously occupied by
gray crescent) of and into blastopore in process called involution; blastocoel
disappears and replaced by a different cavity (the archenteron). (this is confusing, see
here for in depth explanation). Bottom edge of blastopore ventral lip, side
lateral lip.
c. Yolk: more extensive than sea urchin; cells from vegetal pole rich in yolk
material form yolk plug near dorsal lip. - Bird
a. Blastodisc: yolk of bird egg is very large, not involved in cleavages;
cleavages only occur in blastula that consists of flattened, disk-shaped region that sits
on top of yolk (blastodisc).
b. Primitive streak: when gastrulation begins, invagination occurs along line called primitive streak (rather than a
circle). As cells migrate into here, results in an elongated blastopore rather than circular as in sea urchins and frogs. - Humans and most other mammals:
a. Blastocyst: blastula stage consisting of two parts—outer ring of cells (trophoblast) and inner mass of cells
(embryonic disc).
-Inner cell mass goes on to form the epiblast and hypoblast; epiblast is what gives rise to the endo/epi/mesoderm.
b. Trophoblast: accomplishes implantation by embedding into endometrium; produces human chorionic
gonadotropin (HCG) to maintain e+p production from corpus luteum (which in turn maintains endometrium); it later
forms the chorion (later forms placenta).
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c. Embryonic disc: within cavity created by trophoblast, inner cell mass clusters at one pole and flatten into
embryonic disc (analogous to blastodisc of birds and reptiles). Primitive streak develops gastrulation development of
embryo + extraembryonic membranes (except chorion)
factors that influence development
- Influence of egg cytoplasm: cytoplasmic material distributed unequally in egg, non-uniform distribution of cytoplasm
(think gray crescent in frogs and yolk in bird eggs) results in embryonic axes, such as animal and vegetal poles. When
cleavages divide egg daughter cells have different quality of cytoplasmic substances (cytoplasmic determinants).
Unique substances influence subsequent development of each daughter cell. Sea urchin: slice 8-ball embryo into two halves. Longitudinal
embryo has cells from animal & vegetal pole normal development results. Horizontal embryo only has cells from animal OR vegetal abnormal
development results. Confirms the cytoplasmic determinants affecting development. Spemann confirmed with gray crescent vs none cuts. - Embryonic induction: influence of one cell/group of cells over neighboring cells; organizers (controller cells) secrete
chemicals that diffuse among neighboring cells, influence their development (Dorsal lip [fxning as a primary organizer] of
blastopore induces notochord development in nearby cells); 2nd dorsal lip grafted to embryo two notochords developed. - Homeotic genes: control of development by turning on and off other genes that code for substances that directly affect
development. Mutant homeotic genes in fruit flies wrong body parts in wrong places. Homeobox (unique DNA
segment-180 nts) identifies a particular class of genes that control development (encodes homeodomain of protein that can bind
DNA)
