Chapter 17 - Reproductive System

Question 1

What is reproduction?

Answer 1

Complex process involving formation and fertilization of gametes and regulation of these processes by both parents

Question 2

What occurs after fertilization?

Answer 2

Once fertilization occurs, an embryo is formed and that embryo matures into a fetus through rapid division and differentiation

Question 3

What is sexual reproduction? How does it occur?

Answer 3

Genetic material of two organisms combines and results in a genetically unique offspring
- Occurs via fusion of 2 gametes, specialized sex cells produced by each parent

Question 4

What does sexual reproduction require?

Answer 4

1) Production of functional sex cells or gametes by adult organisms
2) Union of these cells (fertilization) to form a zygote
3) Development of the zygotes into another adult, completing the cycle

Question 5

What are gonads? Where are the gonads produced in males vs. females? What about hermaphrodite species?

Answer 5

Gonads: Production of gametes within this specialized organ

Males: Testes; product sperm in tightly coiled seminiferous tubules

Females: Ovaries; produce oocytes

Hermaphrodite: Possess both functional male/female gonads
- Ex. Earthworm and hydra

Question 6

What is gametogenesis?

- Males vs. females?

Answer 6

The production of functional sex cells

• Males: Spermatogenesis; occurs in the seminiferous tubules of the testes
• Females: Oogensis; occurs in the ovaries

Question 7

What is fertilization?

Answer 7

The union of the egg and the sperm nuclei to form a zygote with a diploid number of chromosomes

Question 8

What is internal fertilization?

• What does this increase?
• Do females usually produce more or less eggs?

Answer 8

Practices by terrestrial vertebrates and provides a direct route for sperm to reach the egg cell

• Increases chance of fertilization success
• Females produce fewer eggs

Question 9

What factors effect egg production in females?

Answer 9

• If early development of offspring occurs outside mothers body, more eggs will be produced to increase change of offspring survival
• Parental care after birth (care for young = fewer eggs)

Question 10

Describe the male reproductive system:

• Testes
• Scrotum
• Vas deferens
• Ejaculatory duct
• Urethra
• Penis
• Glans
• Testosterone

Answer 10

• Testes are located in the scrotum; an external pouch that maintains testes temperature at 2-4C (essential for sperm survival)
• Sperm pass from testes through vas deferents to ejaculatory duct then urethra
• Urethra passes through penis until terminates at external opening at glans of the penis
• Testes are also sight of production for testosterone which regulates secondary male sex characteristics including facial and pubic hair, and voice changes

Question 11

Where does spermatogenesis occur? How does it occurs?

Answer 11

Occurs in the seminiferous tubules

• Diploid cells (spermatogonia) differentiate into diploid cells (primary spermatocytes) which undergo meiotic diction to yield 2 haploid secondary spermatocytes of equal size; a second division produces 4 haploids (spermatids) of equal size
• After meiosis, the spermatids undergo final series of changes to increase mobility resulting in mature sperm (spermatozoa)

Question 12

What does mature sperm look like?

Answer 12

Elongated cell with a head, neck, body, and tail

• Head consists of nucleus
• Tail propels the sperm
• Neck and body possess mitochondria to provide energy for locomotion

Question 13

What does the acrosome do and where is it located?

Answer 13

On head of sperm

- Contains enzymes needed to penetrate tough outer coating of ovum

Question 14

How much sperm does a mature male produce a day?

Answer 14

3 million

Question 15

Describe the female reproductive system:

• Ovaries
• Follicle
• Oviduct
• Fallopian tube
• Uterus
• Cervix

Answer 15

• Ovaries are found in abdominal cavity below digestive system; consist of thousands of follicles
• Follicles are multilayered sac of cells that contain, nourish, and protect immature ovum; also produces estrogen
• Once a month mature ovum is released from ovary and drawn by cilia into the nearby oviduct (fallopian tube) which open into the uterus where fetal development occurs
• Lower end of uterus is the cervix which connects with the vaginal canal; site of sperm deposition during intercourse and passageway where baby is expelled during childbirth

Question 16

Where does oogenesis occur?

- Describe the process

Answer 16

Ovarian follicles

• At birth, immature ovum (primary oocytes) are all that a female will have during her lifetime; they form by mitosis in the ovary
• After menarche (first menstruation), one primary oocyte per month completes meiosis I to yield 2 daughter cells of unequal size (secondary oocyte and polar body)
• Secondary oocyte is expelled from follicle during ovulation
• Meiosis II does not occur until fertilization; when the 2 layers of the oocyte are penetrated during fertilization, 2 haploid cells are formed (mature ovum and polar body)
• Mature ovum is large containing organelles, RNA, cytoplasm, nutrients needs for developing embryo; polar bodies lack resources and degenerate

Question 17

What is the oocyte membrane surrounded by?

Answer 17

Two Layers:

• Inner zona pellucide
• Corona radiata

Question 18

What are the female sex hormones?

- Describe each

Answer 18

Ovaries synthesize and secrete female sex hormones which include estrogen and progesterone - the secretion of both these hormones are regulated by luteinizing hormone (LH) and follicle stimulating hormone (FSH) which in turn are regulated by gonadotropin-releasing hormone (GnRH)

1) Estrogen: Steroid hormone necessary for female maturation; stimulate development of female reproductive tract, development of secondary sexual characteristics, and influence libido; thicken endometrium; secreted by ovarian follicle and corpus luteum
2) Progesterone: Steroid hormone secreted by corpus lute during luteal phase of menstrual cycle; stimulates development/maintenance of endometrium in preparation for implantation

Question 19

What is the menstrual cycle? Describe the 4 stages:

Answer 19

Hormonal secretions of ovaries, hypothalamus, and anterior pituitary play important roles in female reproductive cycle; interaction between hormones result in menstrual cycle (4 phases):

1) Follicular Phase: Cessation of menstrual flow from previous cycle; FSH from ant. pituitary promotes development of follicle which grows and secretes estrogen

2) Ovulation: Midway through the cycle, ovulation occurs where a mature ovarian follicle bursts and releases an ovum; causes by a surge in LH that is preceded, and in part, caused by a peak in estrogen levels
- Once every four weeks until menopause (45-50)
- Menopause = ovaries less sensitive to hormones that stimulate follicle development (LH and FSH) and eventually atrophy
- Remaining follicles disappear, estrogen/progesterone decline, ad ovulation stops

3) Luteal Phase: After ovulation, LH maintains remnant of ruptured follicle (corpus luteum) which secretes estrogen/progesterone
- Progesterone causes glands of endometrium to mature and produce secretions that prepare for implantation of embryo

4) Menstruation: If ovum not fertilized, corpus lute atrophies which results in a drop of progesterone/estrogen labels and the endometrium sloughs off giving rise to menses
- If fertilization occurs, development of placenta and hCG maintaining corpus lute and supply of estrogen/progesterone to maintain the uterus; eventually placenta takes of over production of hormones

Question 20

What occurs during fertilization?

Answer 20

Egg can be fertilized during 12-24h after ovulation and often occurs in lateral, widest part of fallopian tube

• Sperm must travel through vaginal canal, cervix, uterus, and fallopian tubes to reach the ovum
• Sperm remains viable for 1-2 days after intercourse
• Sperm must penetrate corona radiate (acrosome) then forms a tubelike structure (acrosomal process) which extends and penetrates the cell membrane to fuse with the ovum
• Sperm nucleus enters and meets ovums nucleus (meiosis II)
• Acrosomal reaction triggers cortical reaction in the ovum causing Ca to be released into the cytoplasm which initiates a series of reactions the result in formation of fertilization membrane which prevents multiple fertilizations
• Release of Ca also stimulates metabolic changes of ovum to increase metabolic rate which is followed by fusion of sperm nucleus with ovum nucleus to form diploid zygote
• First mitosis division soon follows

Question 21

What are the 2 types of multiple births - explain each:

Answer 21

1) Monozygotic (Identical) Twins: When a single zygotes splits into two embryos
- Genetically identical - sae sex, blood type, etc.
- Splitting at 2 cell stage = separate chorions and placentas
- Splitting at blastula stage = one chorionic sac and share placenta and possible amnion
- If division is incomplete = shames twins

2) Dizygotic (Fraternal) Twins: When two ova are released in one ovarian cycle and are fertilized by two different sperm
- Both impact in uterine wall individually and develop their own placenta, amnion, chorion
- Share no more characteristics than siblings because come from two distinct zygotes