Chapter 46: Animal Reporduction Flashcards

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1
Q

Parthenogenesis

A

The development of a new individual from an unfertilized egg

Mainly observed in invertebrates such as wasps and ants

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2
Q

Hermaphroditism

A

Each individual in a species has male and female reproductive systems

Two hermaphrodites can mate and some hermaphrodites can self-fertilize

Individuals of some species undergo sex reversals

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3
Q

Male reproductive anatomy

A

Internal organs:

  • Gonads which produce sperm and hormones
  • Accessory glands that secrete products needed for sperm movement
  • Ducts that carry sperm and glandular secretions
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4
Q

Testes

A

The testes consist of highly coiled tubes surrounded by connective tissue

Sperm form in these seminiferous tubules

Leydig cells produce hormones and are scattered between the tubules

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5
Q

Male reproductive ducts

A

Sperm pass from the seminiferous tubules of a testis into the coiled duct of the epididymis

During ejaculation sperm are propelled through a muscular duct called the vas deferens which extend up and around the bladder

The vas deferens joins a duct from the seminal vesicle behind the bladder forming a short ejaculatory duct before exiting the penis through the urethra

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6
Q

Male reproductive accessory glands

Semen composition

A

Semen is composed of sperm plus secretions from three sets of accessory glands

The two seminal vesicles contribute about 60% of the total volume of semen

  • Fluid is thick, yellowish, and alkaline
  • Contains mucus, fructose, coagulating enzymes, ascorbic acid, and prostaglandins

The prostate gland secretes its products directly into the urethra through several small ducts

  • Fluid is thin and milky
  • Contains anticoagulant enzymes and citrate

The bulbourethral glands secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra

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7
Q

Penis anatomy

A

Composed of three cylinders of spongy erectile tissue

The head of the penis is called the glans and has a thinner skin covering than the shaft and is more sensitive to stimulation

The glans is surrounded by a fold of skin called the prepuce or foreskin

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8
Q

Female reproductive anatomy

A

External reproductive structures include the clitoris and two sets of labia which surround the clitoris and vaginal opening

The internal organs are a pair of gonads and a system of ducts and chambers that carry gametes and house the embryo and fetus

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9
Q

Ovaries

A

The outter layer of the ovary contains many follicles which consist of a partially developed egg, called an oocyte, surrounded by support cells

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10
Q

Oviducts and uterus

A

The egg cell travels from the ovary to the uterus via an oviduct, or fallopian tube

  • Cilia in the oviduct conveys the egg to the uterus by drawing fluid from the body cavity into the oviduct

The endometrium is the uterine lining and is richly supplied with blood vessels

The uterus is a thick muscular organ that narrows the base and forms the cervix which opens into the vagina

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11
Q

Vagina and vulva

A

The vagina opens to the outside at the vulva, the collective term for the external female genitalia

The vulva consists of the:

  • Labia majora- a pair of thick fatty ridges that enclose and protect the rest of the vulva
  • Labia minora- Internal pair of slender skin folds
  • Hymen- a thin piece of tissue that partly covers the vaginal opening at birth
  • Clitoris- has a head called a glans and is covered by the prepuce, a small hood of skin
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12
Q

Spermatogenesis

A
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13
Q

Oogenesis

A
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14
Q

Hormonal control of the male reproductive system

A

FSH stimulates the activity of Sertoli cells in the seminiferous tubules to nourish developing sperm

LH regulates Leydig cells scattered in the connective tissue between the tubules to produce testosterone and other androgens which in turn promote spermatogenesis

Two negative feedback mechanisms control sex hormone production in males

  1. Testosterone regulates the production of GnRH, FSH, and LH through negative feedback mechanisms
  2. Sertoli cells secrete the hormone inhibin which reduces FSH secretion from the anterior pituitary
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15
Q

The ovarian cycle

Follicular phase

A

Follicular phase (day 0−14)

  1. The hypothalmus secretes GnRH which stimulates the anterior pituitary to secrete a small amount of FSH and LH
  2. FSH stimulates follicle growth aided by LH and the cells of the growing follicle start to make estridiol
  3. As estridiol levels continue to rise they exert positive feedback on the hypothalmus and stimulate increased GnRH secretion and sensitivity
  4. The maturing follicle forms a bulge on the surface of the ovary and ruptures in response to a a peak in LH levels
  5. Ovulation marks the end of the follicular phase
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16
Q

The ovarian cycle

Luteal phase

A

Luteal phase (days 15−28)

  1. LH stimulates the remaining follicular tissue to form the corpus luteum, a glandular structure
  2. LH stimulates the corpus luteum to secrete progesterone and estradiol which exert negative feedback on the hypothalamus and pituitary
  3. Negative feedback greatly reduces LH and FSH secretion which prevents maturation of another egg
  4. If no pregnancy, low GnRH causes the corpus luteum to disintegrate which triggers a sharp decline in estradiol and progesterone, removing negative feedback on hypothalmus and pituitary
  5. The pituitary can then secrete enough FSH to stimulate the growth of new follicles
17
Q

The uterine cycle

Also known as the menstrual cycle

A

Proliferative phase (days 6−14)

  1. Estradiol secreted by the growing follicle signals the endometrium to thicken
  2. Uterine thickening occurs in coordination with the follicular phase

Secretory phase (days 15−28)

  1. Estradiol and progesterone secreted by the corpus luteum after ovulation stimulate maintenance and further development of the uterine lining
  2. Stimulates the enlargement of arteries and growth of endometrial glands that can sustain an early embryo
  3. Occurs in coordination with the luteal phase

Menstrual flow phase (days 1−5)

  1. Once the corpus luteum has disintegrated a rapid drop in ovarian hormone concentration causes arteries in the endometrium to constrict
  2. Deprived of circulation the uterine lining largely disintegrates, shedding endometrial tissue and fluid
  3. A new set of ovarian follicles begins to grow during this phase

By convention the first day of flow is designated as day one of the new uterine and ovarian cycle

18
Q

Sexual response cycle

A

The sexual response cycle has four phases

  1. Excitement
  2. Plateau
  3. Orgasm
  4. Resolution

Direct stimulation of genitalia maintains the plateau phase and prepares the vagina for receipt of sperm

19
Q

Conception and implantation

A
  1. Conception (fertilization) occurs in the oviduct
  2. The resulting zygote begins to divide by mitosis in a process called cleavage about 24 hours after conception
  3. After day 4 gives rise to a sphere of cells surrounding a central cavity called a blastocyst
  4. A few days later the embryo implants into the endometrium of the uterus about seven days after conception
20
Q

The first trimester

A

The implanted embryo secrets human chorionic gonadotropin (hCG) that acts like pituitary LH

  • Maintains secretion of progesterone and estrogens by the corpus luteum through the first few months of pregnancy

The first trimester is the main period of organogenesis

After eight weeks all the major structures of the adult are present an embryo is called a fetus

21
Q

Placental development

A

During the first 2−4 weeks the embryo obtains nutrients directly from the endometrium

Meanwhile, the outer layer of the blastocyst called the trophoblast grows outward

Mingles with the endometrium eventually helping form the placenta

Umbilical arteries- 2 smaller tubes that take blood from the fetus to the placenta

Umbilical vein- single larger tube that takes blood from the placenta to the fetus

22
Q

The second trimester

A

The fetus grows and is very active

The mother may feel fetal movements

The uterus grows enough for the pregnancy to become obvious

The placenta produces progesterone

23
Q

Hormonal regulation of labor

A

Once labor begins local regulators (prostaglandins) and hormones (chiefly estradiol and oxytocin) induce and stimulate further contractions

Uterine contractions create a positive feedback loop that stimulates secretion of oxytocin which in turn stimulates further contractions

24
Q

Stages of labor

A
  1. Dilation
  2. Expulsion
  3. Delivery of the placenta