12. Animal Reproduction and Development +

Question 1

Female Reproductive System

Answer 1

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.

Question 2

Male Reproduction System

Answer 2

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 ; 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.

Question 3

Sperm

Answer 3

• compact packages of DNA specialized for effective male genome delivery.
  a. sperm head: haploid (23 chromosomes), at tip is acrosome (lysosome containing enzymes used to penetrate egg, originates from Golgi body vesicles. only nuclear portion of sperm enter egg.
  b. midpiece: flagellus (9+ 2 microtubule array), lots of mitochondria
  c. tail: remainder of flagellum, sperm propelled by wavelike motion of tail and midpiece

Question 4

Sperm Path

Answer 4

• SEVEnUP

- seminiferous tubules -> epidydmis -> vas deferens -> ejaculatory duct -> urethra -> penis

Question 5

Oogenesis

Answer 5

• begins during embryonic development
• oogonia (fetal cells) -> (mitosis) primary oocyte -> (meiosis) remain at prophase I until puberty (one primary oocyte continues development through meiosis I within follicle (protect/nourish oocyte) every menstrual cycle) -> completion of meiosis I, secondary oocyte + polary body (small cytoplasm, disintegrate), arrested at metaphase of meiosis II until -> ovulation

Question 6

Ovulation

Answer 6

• release of secondary oocyte from vesicular follice (caused by LH surge)
• if fertilized by sperm -> finished meiosis II

Question 7

Spermatogenesis

Answer 7

• begins at puberty within seminiferous tubules of testes.
• spermatogonia cells -> (mitosis) primary spermatocytes -> (meiosis) two secondary spermatocytes -> (meiosis II) four spermatids

Question 8

Sertoli Cells

Answer 8

• in seminiferous tubules, provide nourishment to spermatids as they differentiate into mature spermatozoa (sperm)
• complete development and are stored in epididymis

Question 9

Capacitation

Answer 9

• penultimate step in maturation of the spermatozoa while in vagina, allows for egg penetration.

Question 10

Oogenesis

Answer 10

primordial germ cell —mitotic division—> primary oocyte (present at birth, arrested in prophase I of meiosis) —completion of meiosis I, onset of II—-> secondary oocyte, arrested metaphase II—–ovulation, sperm entry—> completion of meiosis II, fertilized egg

Question 11

Hormones and the Female Reproductive Cycle

Menstrual Cycle

Answer 11

1. The hypothalamus and anterior pituitary initiate the reproductive cycle. The hypothalamus monitors the
   levels of estrogen and progesterone in the blood. In a negative feedback fashion, low levels of these hormones stimulate the hypothalamus to secrete GnRH -> anterior pituitary to secrete FSH and LH.
2. The follicle develops. FSH stimulates the development of the follicle and the oocyte.
3. The follicle secretes estrogen. FSH stimulates the secretion of estrogen from the follicle.
4. Ovulation occurs. Positive feedback from rising levels of estrogen stimulate the anterior pituitary (through GnRH
   from the hypothalamus) to produce a sudden midcycle surge of LH. This high level of LH triggers ovulation.
5. The corpus luteum secretes estrogen and progesterone. After ovulation, the follicle, now called the corpus luteum, continues to develop under the influence of LH and secretes both estrogen and progesterone.
6. The endometrium thickens. Estrogen and progesterone stimulate the development of the endometrium, the inside lining of the uterus. It thickens with nutrient-rich tissue and blood vessels in preparation for the implantation of a fertilized egg.
7. The hypothalamus and anterior pituitary terminate the reproductive cycle. Negative feedback from high levels of estrogen and progesterone cause the anterior pituitary (through the hypothalamus) to abate production of FSH and LH.
8. The endometrium disintegrates. In the absence of FSH and LH, the corpus luteum deteriorates. As a result, estrogen and progesterone production stops. Without estrogen and progesterone, growth of the endometrium is no longer supported, and it disintegrates, sloughing off during menstruation (flow phase of the menstrual cycle).
9. The implanted embryo sustains the endometrium. If implantation occurs, the implanted embryo secretes human chorionic gonadotropin (HCG) to sustain the corpus luteum. As a result, the corpus luteum will continue to produce estrogen and progesterone to maintain the endometrium. Without HCG, menstruation would begin and the embryo would abort. (Pregnancy tests check for the presence of HCG in the urine.) Later during development, HCG is replaced by progesterone secreted by the placenta. In this way, the embryo directly maintains the pregnancy.

Question 12

Ovarian Cycle

Answer 12

• events in the ovary
  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

Question 13

Male Reproductive Cycle

Answer 13

• same hormones that regulate female cycle
• GnRh (hypothalamus) –> anterior pituitary secretes FSH and LH (ICSH, interstitial cells stimu. hormone). –> LH stimulates interstitial cells in testes to produe testosterone and other male hormones (androgens) -> under influence of FSH and testosterone, Sertoli cells promote development of sperm
• unlike females, hormone and gamete production are constant during reproductive life of the male.
• in addition to influencing production of sperm and eggs, testosteron and estrogen stimulate development of secondary sex characteristics in males and females, respectively.

Question 14

Embryonic Development

Answer 14

1. Fertilization
2. Cleavage
3. Morula
4. Blastual
5. Gastrula
6. Extraembryonic membrane development
7. Organogenesis

Question 15

1. Fertilization

Answer 15

1. Fertilization - sperm penetrates plasma membrane of secondary oocyte.
   a. Recognition - sperm secretes a protein that binds w/ receptor on a glycoprotein layer surrounding plasma mebrane of oocyte. This vitelline layer (zona pelucida in humans) ensures fert. occurs only between same species.
   b. penetration - plasma mebranes fuse and sperm nucleus enters oocyte
   c. vitelline layer forms fertilization membrane which blocks entrance of additional sperm.
   d. completion of meiosis II
   e. fursion of nuclei and replication of DNA. sperm and ovum nuclei fuse, forming zygoe nucleus w/ 23 pairs of chromosomes.

Question 16

Cleavage

Answer 16

• rapid cell divisions without cell growth, as a result each resulting cell (blastomere) contains less cytoplasm than original zygote.
• embryo polarity - embryo has upper, animal pole and a lower, vegetal pole. cells at vegetal pole contain more yolk, or stored food (denser, settle to bottom of egg)
• early cleavages are polar (from pole to pole, like an organge). other cleavages are prallel w/ equator (perpendicular to polar cleavages).
• deutrostomes -> early cleavages are radial and indeterminate
• protostomes -> early cleavages are spiral and determinate

Question 17

3. Morula

Answer 17

• solid ball of cells

Question 18

4. Blastula

Answer 18

• liquid fills morula and pushes cells out to form circular cavity surrounded by single layer of cells.
• this hollow sphere of cells is called blastula, and the cavity is the blastocoel.

Question 19

5. Gastrula

Answer 19

• group of cells invaginate inward into the blastula, forming two layer embryo w/ opening into central cavity
• 3 germ layers: a third layer forms between outer and inner layers of invaginated embryo. Ectoderm (outside), mesoderm (middle), endoderm (inside) -> primary layers from which all tissues develop.
• archentron: center cavity formed by gastrulation. completely surrounded by endodermal cells.
• blastopore: opening of archentron. becomes mouth (protostomes) or anus (deuterostomes)

Question 20

6. Extraembyronic Membrane Development

Answer 20

• chorion. In birds and reptiles -> membrane for gas exchange. In mammals -> implants into endometrium. later chorion w/ maternal tissue forms the placenta.
• Allantois. sac that buds from archentron. after subsequent development, becomes umbilical cord, transporting gases, nutrients, and wastes between embryo and placenta. becomes urinary bladder in adults
• Amnion. encloses amniotic cavity, a fluid-filled cavity that cushions the developing embryo.
• yolk sac. in birds and reptiles, blood vessels transfer nutrients to embryo. in placental mammals, yolk sac is empty.

Question 21

7. Organogenesis

Answer 21

• development of organs
• cells along dorsal surface of mesoderm form the notochord
• ectoderm cells above notochord form neural plate. plate indents forming neural groove then rolls forming neural tube. neural tube develops in CNS. additional cells roll off neural tube and form the neural crest. these cells form various tissues, including teeth, bones, muscles of skull, pigment cells, as well as nerves and others.

Question 22

Endoderm

Answer 22

• epithelial lining of digestive & respiratory, parts of liver, pancreas, thyroid, and urinary bladder lining

Question 23

Mesoderm

Answer 23

• musculoskeletal, circulatory system, excretory system, gonads, connective tissue, portions of digestive & respiratory, notochord

Question 24

Ectoderm

Answer 24

• Nervous system (brain and spinal cord), integument (epidermis & hair / epithelium of nose, mouth, anal canal), sense structures
  (lens of eye, retina), teeth, neural tube

Question 25

Important Variation in Embryonic development (Frog)

Answer 25

• Gray crescent. when sperm penetrate egg, a reorganization of cytoplasm results in appearance of a gray, crescent shaped region, called gray crescent. Each individual cell could develop into a normal frog only if it contained a portion of the gray crescent.
• during gastrualation, cells migrate over the top edge of the blastopore, the top edge called the dorsal lip, forms from same region occupied earlier by gray crescent.
• the yolk material is much more extensive in the frog than in sea urchin (model). cells from vegetal pole rich in yolk form a yolk plug near dorsal lip.

Question 26

Important Variation in Embryonic development (Bird)

Answer 26

• Blastodisc. yolk is very large. cleavages occur in a blastula that consist of a flattened, disk shaped region that sits on top of the yolk. this kind of blastula is called a blastodisc.
• primitive streak. when gastrulation begins, invagination occurs along a line (rather than a circle) called the primitive streak.

Question 27

Important Variation in Embryonic development (Humans and Most other Mammals)

Answer 27

• Blastocyst. blastula stage consists of two parts-an outer ring of cells, the trophoblast, and an inner mass of cells, the embryonic disc.
• Trophoblast. serves several functions. first, it accomplishes implantation by embedding into the endometrium of the uterus. second, it produces HCG to maintain progesterone production of corpus luteum (maintain endometrium). Later, the trophoblast forms the chorion, the extraembryonic membrane that w/ maternal tissue forms the placenta.
• Embryonic Disc. inner cell mass clusters at one pole and flattens into the embryonic disc. which is analogous to blastodisc of birds and reptiles. -> primitive streak develops -> gastrulation follows -> development of embryo and extraembryonic membranes (except chorion)

Question 28

Mechanisms responsible for influencing cell development and differentiation:

Answer 28

1. Influence of egg cytoplasm. cytoplasm distributed unequally in egg and subsequent daughter cells. nonuniform distribution of cytoplasm results in embryonic axes, such as animal and vegetal poles. when cleavages divide the egg, quality of cytoplasm will vary among cells. substances unique to certain cells may influence their subsequent development.
2. Embryonic Induction. influence of one or group of cells on neighboring cells. Cells that exert the influence are called organizers (secrete chemicals that diffuse among neighboring cells).
3. Homeotic genes. turn on and off other genes that code for substances that directly affect development. mutant homeotic genes -> body parts in wrong places. A unique DNA segment (homebox - 180 nucltids) found in most homoeotic genes in numerous species identify a particular class of genes that control development.
4. Apoptosis.

Question 29

Determined

Answer 29

• fate of cell cannot be changed.

Question 30

By embryonic induction, the dorsal lip of the blastopore stimulates the development of the…..in nearby cells.

Answer 30

notochord