Reproductive Cycle and Patterns

1
Reproductive Cycle and Patterns
2
Terms and Definitions
3
Parthenogenesis

• Can be caused by environmental conditions
• (in aphids, rotifers, and some crustaceans)
• the development of an egg without fertilization

4
Parthenogenesis Cont.

• Daphnia, a freshwater crustacean, will change to
  asexual reproduction relative to the season and
  environment
• Male honey bees (drones)
• undergo parthenogenesis the females
• come from fertilized eggshttp//www.o-matic.com/p
  lay/parth/parth_swf.html

5
Parthenogenesis Cont.

• Some fish, amphibians, and lizards undergo a
  complex form whereby a doubling of chromosomes
  occurs after meiosis to create zygotes which are
  then diploid

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Hermaphroditism

• Occurs when an animal cannot find a member of the
  opposite sex
• Has both functional reproductive parts
• Can self-fertilize
• Each donates and receives sperm, for producing
  two times the offspring

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Hermaphroditism Cont.

• Each donates and receives sperm, for producing
  two times the offspring
• Can be sequential where it reverses its sex where
  it is a female or protogynous first
• Others are protandrous (male first)

8
External Fertilization

• Usually in moist environments
• Does not always need contact between parents
• Environmental cues and pheromones trigger release
  to increase success
• Fish and amphibians exhibit courtship behavior to
  increase success and permit mate selection

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Internal Fertilization

• Requires more sophisticated systems and
  cooperative mating behaviors
• Copulatory organs and receptacles must be present
• Mating behaviors must include signals for
  copulation to occur

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Protection of Embryo
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External Fertilization

• Does not have protective coverings for embryo
• Only protection is the moist conditions
• Only a small portion survive

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Internal Fertilization

• Eggs usually have a layer of protein or calcium
• i.e., reptiles and monotremes, which are
  platypuses and echidnas, that are mammals that
  lay eggs

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Internal Fertilization Cont.

• Other mammals, such as the marsupials, embrace
  development within the uterus then to the
  mothers pouch
• Placental mammals retain the embryo in the uterus

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Internal Fertilization Cont.

• Highly developed parental care such as nesting
• Fewer zygotes, but survival is greater due to
  protection and care of developing offspring

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Invertebrate Reproductive System

• From simple to complex

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Polychaetes

• Have sexes with distinct gonads
• Gametes come from undifferentiated cells lining
  the coelom (cavity with mesoderm cells)
• P. 593, fig. 29.4, and page 594, fig. 29.5

17
Polychaetes Cont.

• Sometimes released through excretory openings
• The parental body splits open as he or she dies
  and releases the egg

18
Insects

• Have separate sexes with complex structures
• P. 942, fig. 42.6
• Sperm develop in a pair of testes, which pass
  through a coiled duct to and also stored in the
  seminal vesicles
• Ejaculated into the females system

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Insects Cont.

• Eggs develop in the ovaries (2) and pass to the
  vagina where they are fertilized
• May have a spermatheca (a hind-ended sac) where
  sperm can be stored for approximately a year

20
Flatworms

• Are hermaphroditic with a complex system
• P. 942, fig. 42.7
• Female includes an ovary, oviduct, seminal
  receptacle, yolk, yolk glands, and uterus
• Male includes testes, vasefferentia, sperm duct,
  seminal vesicle, and a copulatory apparatus

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Vertebrate Reproduction Systems
22
Systems

• All systems are similar with slight differences
• Nonmammalians vertebrates have a common opening
  called the cloaca
• Birds and snakes have only one branch in the
  uterus while most have two
• Nonmammalian vertebrates do not have developed
  penises

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Human Reproductive System
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Anatomy of Human Male

• External gentalia
• Penis is the male copulatory organ.
• Ejaculatroy duct joins the urethra (from the
  excretory system) which opens at the tip of the
  penis

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Anatomy of Human Male Cont.

• Internal organs include the gonads (testes),
  accessory glands, and connected ducts
• Testes develop in
• the abdomen and
• descend into the scrotum
• after birth
• The sperm develop at
• 2 degrees lower than
• the body temperature

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Reproductive Anatomy of the Human Female

• More complicated than the males
• Internal organs are the gonads (ovaries) plus
  ducts and chambers
• External genitalia include the clitoris and two
  sets of labia that surround the clitoris and
  vaginal opening

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Reproductive Anatomy of the Human Female Cont.

• Ovaries are located the abdominal cavity
• They are enclosed in a protective capsule
• A mesentery flanks and attaches each ovary to the
  uterus
• Gray's Anatomy - Fig. 1164 - Yahooligans!
  Reference -

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Females Ovarian Relationships
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Reproductive Anatomy of the Human Female Cont.

• Each ovary contains follicles (one egg cell
  surrounded by follicle cells, which nourish and
  protect)
• Follicle cells produce estrogen
• From puberty to menopause, one follicle matures
  and releases its egg cell during each menstrual
  cycle

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Reproductive Anatomy of the Human Female Cont.

• Ovulation is when the egg is expelled from the
  follicle
• The remaining follicular tissue forms the corpus
  luteum, which secretes progesterone (maintains
  the uterine lining) and some estrogen (fig. 42.10)

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Reproductive Anatomy of the Human Female Cont.

• If the egg is fertilized, the corpus luteum
  degenerates
• The egg is expelled into the abdominal cavity
  near the opening of the oviduct

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Reproductive Anatomy of the Human Female Cont.

• Cilia line the oviduct and convey it to the
  uterus
• The uterus is a muscular organ 7 cm long and 4-5
  cm wide
• The endometrium, or inner uterine lining, is
  supplied with blood vessels

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Reproductive Anatomy of the Human Female Cont.

• Other structures
• Cervix the neck of the uterus which opens into
  the vagina
• Vagina thin walled chamber that is the
  repository for semen during copulation and forms
  the birth canal

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Reproductive Anatomy of the Human Female Cont.

• Vestibule chamberlike area formed by the two
  pairs of skin folds covering the vaginal orifice
  and urethral opening
• Labia minora the slender skin folds bordering
  the vestibule

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Reproductive Anatomy of the Human Female Cont.

• Labia majora a pair of thick, fatty ridges
  enclosing and protecting the labia minora and
  vestibule
• Clitoris bulb of erectile tissue at the front
  edge of the vestibule, which is covered, that
  secretes mucus into the vestibule during sexual
  arousal

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Reproductive Anatomy of the Human Female Cont.

• Mammary glands are not actually considered part
  of the reproductive system
• Consist of small sacs of epithelial tissue that
  secrete milk
• The milk drains into a series of ducts that open
  at the nipple
• If no mammary glands, the tissue is primarily
  composed of adipose tissue (nonlacting)

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Human Sexual Response

• Consists of diversity of stimuli and responses
• Human sexual behavior is based on the sexual
  response cycle
• These sexual responses show similarities and of
  course the differences in males and females

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Human Sexual Response Cont.

• Two types of sexual or physiological reactions
• Vasocongestion or the filling of a tissue with
  blood (penis and clitoris)
• Myotonia is the increased muscle tension with
  both skeletal and smooth muscles show sustained
  or rhythmic contractions

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Human Sexual Response Cont.

• Four phases in sexual response cycle
• Excitement phase
• Vagina and penis prepare for coitus, with the
  vasocongestion of the penis and clitoris with the
  enlargement of testes, labia, and breasts
• Vaginal lubrication and myotonia occur

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Human Sexual Response Cont.

• Plateau Phase
• The outer third of the vagina becomes vasogested
• The inner third expands and the uterus elevates
• The heart and breathing rates increase with the
  stimulation of the autonomic nervous system

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Human Sexual Response Cont.

• Orgasm
• Third and shortest phase
• Involuntary contractions
• In the males the emission, or forcing the semen
  into the urethra, is followed by expulsion
  (ejaculation)
• In the females, the uterus and the outer vagina
  contract

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Human Sexual Response Cont.

• Resolution Phase
• Reverses the earlier phases, or the vascongested
  organs return to normal size and color, plus
  having the muscles relax

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Spermatogenesis and Oogenesis
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Spermatogenesis

• The production of mature sperm cells in adult
  males
• Continuous process resulting in 250 to 400
  million sperm cells per ejaculation
• Occurs in seminiferous tubules of the testes

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Spermatogenesis Cont.

• Begins with the differentiation of primordial
  germ cells into spermatogonia in the embryonic
  testes both are diploid
• The spermatogonia are located near the outer wall
  of the seminiferous tubules
• They increase in numbers through repeated mitosis
  throughout development and early life

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Spermatogenesis Cont.

• When the male matures, spermatogonia begin to
  differentiate into primary spermatocytes which
  are diploid
• Primary spermatocytes pass through several stages
  before giving rise to mature spermatozoa

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Fetus in last trimester
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Sperm having penetrated egg
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Spermatogenesis Cont.

• Stages spermatocytes pass through
• Each primary spermatocyte undergoes meiosis I to
  produce two haploid secondary spermatocytes
• Each 2nd spermatocyte undergoes meiosis II to
  form two spermatids
• Thus, each primary spermatocyte forms four
  haploid spermatids through meiotic division

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Spermatogenesis Cont.

• Each spermatid becomes associated with a large
  Sertoli cell from which it receives nutrients
• All four spermatids, from each primary
  spermatocyte, differentiate into mature
  spermatozoa

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Spermatogenesis Cont.

• In a spermatozoon, the thick head (haploid
  nucleus) is tipped with the acrosome, which
  contains enzymes to aid in egg penetration
• Behind the head, the sperm contain many
  mitochondria that provide ATP for movement of the
  flagellum

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Oogenesis

• The development of ova (mature, unfertilized egg
  cells)
• See fig. 46.11
• Begins in the embryo when primordial germ cells
  undergo mitotic division to produce diploid
  oogonia

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Oogenesis Cont.

• Each oogonium will develop into a primary oocyte
  by the time of birth of the female
• Between birth and puberty, primary oocytes
  enlarge and the follicles grow
• They replicate DNA and enter prophase I remain
  active by hormones

54
Oogenesis Cont.

• After puberty, during each ovarian cycle, FSH
  stimulates a follicle to enlarge and the primary
  oocyte within completes meiosis I to produce a
  haploid 2nd oocyte and the 1st polar body
• Meiosis then stops again

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Oogenesis Cont.

• LH triggers ovulation and 2nd oocyte is released
  from the follicle
• When the sperm penetrates the 2nd oocytes
  membranes, meiosis II occurs and the 2nd polar
  body will separate from the ovum, completing
  oogenesis

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Differences Between Spermatogenesis and Oogenesis

• All 4 products of meiosis I and II become mature
  spermatozoa because of unequal cytokinesis, most
  of the cytoplasm becomes one daughter cell which
  forms the single ovum, the other cells, or polar
  bodies, will degenerate

57
Differences Between Spermatogenesis and Oogenesis
Cont.

• Spermatogenesis is continuous all potential ova
  are in the ovaries at the time of birth
• Spermatogenesis is uninterrupted in oogenesis,
  long resting periods occur

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Complex Interplay of Hormones
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The Male Pattern

• In males, androgens (hormones) are responsible
  for formation of primary sex characteristics
  (organs) and 2nd sex characteristics (deep voice,
  hair, and muscle growth)

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The Male Pattern Cont.

• Androgens steroid hormones which are produced
  by interstitial tissues of the testes
• Testosterone is the most important example
• Androgens are potent determinants of sexual and
  aggressive behaviors

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The Male Pattern Cont.

• GnRH (from the hypothalamus) stimulates the
  pituitary to release LH (stimulates androgen
  production) and FSH (acts on seminiferous tubules
  to increase sperm production)

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The Female Pattern

• Female mammals display two different types of
  cycles estrous cycles and menstrual cycles
• Estrous cycles occur in non-primate mammals

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The Female Pattern Cont.

• Estrous cycle
• Ovulation occurs after the endometrium thickens
  and vascularizes
• If no pregnancy, the endometrium is reabsorbed by
  the uterus
• Seasonal and climatic changes effect the estrous
  cycle more than the menstrual cycle

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The Female Pattern Cont.

• Menstrual cycle (occurs in primates)
• Same pattern for ovulation
• If no pregnancy, the endometrium is shed from the
  uterus during menstruation
• The cycle varies from one woman to another
  usually 28 days, but can be 20 to 40 days
• Some women are regular while some vary from cycle
  to cycle

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The Female Pattern Cont.

• Three phases of the menstrual cycle (Fig. 46.13)
• Menstrual flow phase
• Time during which most of the endometrium is
  being lost from the uterus
• Persists only a few days
• 1st day first day of the cycle

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The Female Pattern Cont.

• Proliferative Phase
• One to two weeks and involves the regeneration
  and thickening of the endometrium

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The Female Pattern Cont.

• Secretory Phase
• About two weeks is a time when the endometrium
  continues to develop
• Endometrium continues to thicken, or vascularize,
  and develops glands which secrete a glycogen
  fluid
• If no embryo implant by the end of this phase, a
  new menstrual flow phase begins

68
The Female Pattern Cont.

• An ovarian cycle parallels the menstrual cycle
• Follicular phase or time during which several
  follicles begin to grow
• Follicle cell becomes multilayered
• One will continue to mature while others
  degenerate
• A fluid-filled cavity develops which shows a
  bulge on the ovary

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The Female Pattern Cont.

• Ovulatory Phase the follicle and adjacent wall
  of the ovary rupture, releasing the egg
• Luteal Phase the corpus luteum forms endocrine
  tissue that secretes female hormones

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The Female Pattern Cont.

• 5 hormones work (by positive and negative
  feedback loops) to coordinate the menstrual and
  ovarian cycles
• These hormones synchronize follicle growth and
  ovulation with preparation of the uterine lining
  for embryo implantation

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The Female Pattern Cont.

• GnRH secreted by the hypothalamus stimulates the
  anterior pituitary to secrete small quantities of
  FHS and LH
• FSH stimulates immature follicles to grow, with
  more estrogen being secreted
• Follicles secrete estrogen

72
The Female Pattern Cont.

• With more estrogen, the hypothalamus increases
  secretion GnRH which with then increases the FSH
  and LH secretion
• LH increases more than FSH because estrogen
  causes the sensitivity of LH-releasing mechanisms
  (in the pituitary) to GnRH
• The follicles have LH receptors and an respond
  directly to the hormone

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The Female Pattern Cont.

• Thus, LH stimulates maturation of the follicle
  and ovulation (within 25 hours)
• The concentration of LH stimulates the follicular
  tissue to transform to the corpus luteum

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The Female Pattern Cont.

• The LH causes the corpus luteum to secrete
  estrogen, but also to secrete increasing amounts
  of progesterone
• gtconcentrations of estrogen and progesterone
  inhibit GnRH secretion by the hypothal.,
  resulting in less FSH and LH

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The Female Pattern Cont.

• With less estrogen and progesterone, the corpus
  luteum begins to atrophy results in big drop in
  estrogen and progesterone

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The Female Pattern Cont.

• With small concs of estrogen and progesterone,
  the hypothal. Begins to secrete less GnRH that
  causes the pituitary to secrete low levels of FSH
  and LH
• A new follicular phase begins at this point

77
The Female Pattern Cont.

• Coordination of the menstrual cycle with the
  ovarian cycle depends primarily on the levels of
  estrogen and progesterone
• With greater amounts of estrogen secreted the
  endometrium lining thickens or prepares for
  embryo
• Coordination of the follicular phase of ovarian
  cycle with proliferative phase of the menstrual
  cycle

78
The Female Pattern Cont.

• After ovulation, the estrogen and progesterone
  secreted by the corpus luteum stimulate continued
  development of the endometrium
• Arteries grow and the endometrial glands that
  supply nourishment to the embryo mature
• Coordination of the luteal phase of the ovarian
  cycle with the secretory phase of the menstrual
  cycle

79
The Female Pattern Cont.

• With less estrogen and progesterone due to the
  disintegration of the corpus luteum reduce blood
  flow to the endometrium
• The endometrium breaks down and passes out with
  the menstrual flow

80
The Female Pattern Cont.

• A new menstrual cycle begins with a new ovarian
  cycle
• Estrogens are responsible for development of the
  female 2nd sex characteristics

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Hormones and Sexual Maturation

• Mammals cannot reproduce until they reach sexual
  maturity
• Puberty is the onset of reproductive ability
• Occurs between the ages of 8 and 14
• The hypothal. Secretes greater amount of GnRH,
  leading to higher FSH and LH levels

82
Hormones and Sexual Maturation Cont.

• These gonadotropins trigger the reproductive
  system and 2nd sex characteristics
• Indication of is the ejaculation of visible sperm
  by males and the 1st menstruation by females

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Embryonic and Fetal Development
84
From Conception to Birth

• Pregnancy or ______ is the condition of carrying
  one or more developing embryos in the uterus
• Preceded by conception and ends with birth

85
From Conception to Birth Cont.

• Averages 266 days
• Duration in other species correlates with body
  size and extent of development

86
Human Gestation

• 3 trimesters, each about 3 months
• First trimester has the most radical changes for
  both baby and mother
• Fertilization in the oviduct and cleavage (cell
  division) begins in 24 hours
• With cleavage, the zygote develops into a ball of
  cells passing down the oviduct to the uterus

87
Human Gestation Cont.

• Embryo reaches the uterus in 3-4 days and
  develops into a hollow ball of cells called a
  blastocyst
• Develops in one week
• The blastocyst will implant into the endometrium
  in the next five days

88
Human Gestation Cont.

• During implantation, the blastocyst bores into
  the endometrium which grows over the blastocyst
• 1st 2-4 weeks of development, nutrients are
  obtained directly from the endometrium

89
Human Gestation Cont.

• Placenta develops which function in respiratory
  gas exchange, nutrient transfer, and waste
  removal for the embryo
• Blood passes through the umbilical arteries to
  the placenta and returns through the umbilical
  vein

90
Human Gestation Cont.

• This is also the main period of organogenesis
  (development of organs)
• After 8 weeks, the fetus stage begins and
  possesses all organs of the adult in rudimentary
  form
• Fetus is about 5 cm in length at the end of the
  1st trimester

91
Human Gestation Cont.

• The embryo secretes hormones that help control
  the mothers reproductive system
• Human chorionic gonadotropin (HCG) is an
  embryonic hormone that maintains the progesterone
  and estrogen secretion by corpus luteum to
  prevent menstruation
• Progesterone stimulates a protective mucous plug
  in the cervix, growth of the placenta, uterus
  enlargement, cessation of ovulation, and
  menstrual cycling

92
Human Gestation Cont.

• Second trimester rapid growth and the fetus is
  very active
• Grows to 30 cm in length
• Mother feels baby move

93
Human Gestation Cont.

• HCG declines, corpus luteum degenerates, hormone
  levels stabilize, and the placenta secretes
  progesterone to maintain pregnancy
• Uterus grows for the pregnancy to continue

94
Human Gestation Cont.

• Third Trimester growth is rapid and fetal
  activity decreases
• Fetus grows to 50 cm and 3 to 3.5 kg in weight
• Maternal organs become compressed and displaced

95
Human Gestation Cont.

• Labor is induced and regulated by estrogen,
  oxytocin, and prostaglandins
• High estrogen triggers formation of oxytocin
  receptors on the uterus
• Oxytocin (from the fetus and posterior pituitary)
  stimulates muscles of the uterus to contract
• Oxytocin also enhances muscle contractions by
  stimulating prostaglandin secretion by the
  placenta

96
Human Gestation Cont.

• Parturition is a series of strong rhythmic
  contractions of the uterus called labor
• 1st stage is the opening and thinning of the
  cervix until completely dilated
• 2nd stage is the expulsion of the baby from the
  uterus
• Continuous uterine contractions
• Last stage is the expulsion of the placenta from
  the uterus

97
Human Gestation Cont.

• Mammals are unique here in that lactation with
  the postnatal care
• Lower levels of progesterone which allows
  prolactin secretion (inhibition from the anterior
  pituitary)