Human Reproduction and Development  <ul><li>Reproductive organs produce and transport gametes: focus on humans </li></ul><...
Female Reproductive Anatomy <ul><li>The female external reproductive structures include </li></ul><ul><ul><li>The clitoris...
Vagina Uterus Cervix Ovaries Oviduct Uterine wall Endometrium Follicles Corpus luteum
Ovaries <ul><li>The female gonads, the ovaries </li></ul><ul><ul><li>Lie in the abdominal cavity </li></ul></ul><ul><li>Ea...
<ul><li>The process of ovulation </li></ul><ul><ul><li>Expels an egg cell from the follicle </li></ul></ul><ul><li>The rem...
Oviducts and Uterus <ul><li>The egg cell is released into the abdominal cavity </li></ul><ul><ul><li>Near the opening of t...
Male Reproductive Anatomy <ul><li>In most mammalian species </li></ul><ul><ul><li>The male’s external reproductive organs ...
<ul><li>Reproductive anatomy of the human male </li></ul>Figure 46.10 Erectile tissue of penis Prostate gland (Urinary bla...
Seminal vesicle (Rectum) Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland (Urinary bladder) (Pubic bone) E...
Testes <ul><li>The male gonads, or testes </li></ul><ul><ul><li>Consist of many highly coiled tubes surrounded by several ...
Ducts <ul><li>From the seminiferous tubules of a testis </li></ul><ul><ul><li>The sperm pass into the coiled tubules of th...
Glands <ul><li>Three sets of accessory glands </li></ul><ul><ul><li>Add secretions to the semen, the fluid that is ejacula...
<ul><li>Oogenesis is the development of mature ova </li></ul>Ovary Primary germ cell in embryo Differentiation Oogonium Oo...
<ul><li>Spermatogenesis is the production of mature sperm </li></ul>Epididymis Seminiferous tubule Testis Cross section of...
<ul><li>Oogenesis differs from spermatogenesis  </li></ul><ul><ul><li>In three major ways </li></ul></ul><ul><li>First, du...
<ul><li>In menstrual cycles </li></ul><ul><ul><li>The endometrium is shed from the uterus in a bleeding called menstruatio...
<ul><li>Cyclic secretion of GnRH from the hypothalamus </li></ul><ul><ul><li>And of FSH and LH from the anterior pituitary...
<ul><li>The reproductive cycle of the human female </li></ul>Figure 46.13a–e Control by hypothalamus Inhibited by combinat...
The Ovarian Cycle <ul><li>In the ovarian cycle </li></ul><ul><ul><li>Hormones stimulate follicle growth, which results in ...
The Uterine (Menstrual) Cycle <ul><li>Cycle after cycle </li></ul><ul><ul><li>The maturation and release of egg cells from...
Menopause <ul><li>After about 450 cycles, human females undergo menopause </li></ul><ul><ul><li>The cessation of ovulation...
Hormonal Control of the Male Reproductive System <ul><li>Testosterone and other androgens </li></ul><ul><ul><li>Are direct...
Conception, Embryonic Development, and Birth <ul><li>In humans and other placental mammals, an embryo grows into a newborn...
<ul><li>Fertilization of an egg by a sperm, conception </li></ul><ul><ul><li>Occurs in the oviduct </li></ul></ul>Figure 4...
<ul><li>After fertilization </li></ul><ul><ul><li>The zygote undergoes cleavage and develops into a blastocyst before impl...
<ul><li>During its first 2 to 4 weeks of development </li></ul><ul><ul><li>The embryo obtains nutrients directly from the ...
<ul><li>Blood from the embryo </li></ul><ul><ul><li>Travels to the placenta through arteries of the umbilical cord and ret...
<ul><li>The first trimester is the main period of organogenesis </li></ul><ul><ul><li>The development of the body organs <...
Second Trimester <ul><li>During the second trimester </li></ul><ul><ul><li>The fetus grows and is very active </li></ul></...
Third Trimester <ul><li>During the third trimester </li></ul><ul><ul><li>The fetus continues to grow and fills the availab...
<ul><li>A complex interplay of local regulators and hormones </li></ul><ul><ul><li>Induces and regulates labor, the proces...
<ul><li>Birth, or parturition </li></ul><ul><ul><li>Is brought about by a series of strong, rhythmic uterine contractions ...
<ul><li>Amniocentesis and chorionic villus sampling </li></ul><ul><ul><li>Are invasive techniques in which amniotic fluid ...
<ul><li>A human embryo at approximately 6–8 weeks after conception </li></ul><ul><ul><li>Shows the development of distinct...
<ul><li>The question of how a zygote becomes an animal </li></ul><ul><ul><li>Has been asked for centuries </li></ul></ul><...
<ul><li>Preformation is the idea that the egg or sperm contains an embryo </li></ul><ul><ul><li>A preformed miniature infa...
<ul><li>An organism’s development </li></ul><ul><ul><li>Is determined by the genome of the zygote and by differences that ...
<ul><li>After fertilization, embryonic development proceeds through cleavage, gastrulation, and organogenesis </li></ul><u...
Fertilization <ul><li>The main function of fertilization </li></ul><ul><ul><li>Is to bring the haploid nuclei of sperm and...
The Acrosomal Reaction <ul><li>The acrosomal reaction </li></ul><ul><ul><li>Is triggered when the sperm meets the egg </li...
<ul><li>The acrosomal reaction </li></ul>Sperm nucleus Sperm plasma membrane Hydrolytic enzymes Cortical granule Cortical ...
<ul><li>Gamete contact and/or fusion </li></ul><ul><ul><li>Depolarizes the egg cell membrane and sets up a fast block to p...
The Cortical Reaction <ul><li>Fusion of egg and sperm also initiates the cortical reaction </li></ul><ul><ul><li>Inducing ...
<ul><li>These changes cause the formation of a fertilization envelope </li></ul><ul><ul><li>That functions as a slow block...
Activation of the Egg <ul><li>Another outcome of the sharp rise in Ca 2+  in the egg’s cytosol </li></ul><ul><ul><li>Is a ...
Fertilization in Mammals  <ul><li>In mammalian fertilization, the cortical reaction  </li></ul><ul><ul><li>Modifies the zo...
Cleavage <ul><li>Fertilization is followed by cleavage </li></ul><ul><ul><li>A period of rapid cell division without growt...
<ul><li>Cleavage partitions the cytoplasm of one large cell </li></ul><ul><ul><li>Into many smaller cells called blastomer...
<ul><li>The eggs and zygotes of many animals, except mammals  </li></ul><ul><ul><li>Have a definite polarity </li></ul></u...
Gastrulation <ul><li>The morphogenetic process called gastrulation </li></ul><ul><ul><li>Rearranges the cells of a blastul...
<ul><li>The three layers produced by gastrulation </li></ul><ul><ul><li>Are called embryonic germ layers </li></ul></ul><u...
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Human reproduction and development

  1. 1. Human Reproduction and Development <ul><li>Reproductive organs produce and transport gametes: focus on humans </li></ul><ul><li>The internal organs are a pair of gonads </li></ul><ul><ul><li>And a system of ducts and chambers that carry gametes and house the embryo and fetus </li></ul></ul>
  2. 2. Female Reproductive Anatomy <ul><li>The female external reproductive structures include </li></ul><ul><ul><li>The clitoris </li></ul></ul><ul><ul><li>Two sets of labia </li></ul></ul>Prepuce (Rectum) Cervix Vagina Bartholin’s gland Vaginal opening Ovary Oviduct Labia majora Labia minora (Urinary bladder) (Pubic bone) Uterus Urethra Shaft Glans Clitoris Figure 46.9
  3. 3. Vagina Uterus Cervix Ovaries Oviduct Uterine wall Endometrium Follicles Corpus luteum
  4. 4. Ovaries <ul><li>The female gonads, the ovaries </li></ul><ul><ul><li>Lie in the abdominal cavity </li></ul></ul><ul><li>Each ovary </li></ul><ul><ul><li>Is enclosed in a tough protective capsule and contains many follicles </li></ul></ul><ul><li>A follicle </li></ul><ul><ul><li>Consists of one egg cell surrounded by one or more layers of follicle cells </li></ul></ul>
  5. 5. <ul><li>The process of ovulation </li></ul><ul><ul><li>Expels an egg cell from the follicle </li></ul></ul><ul><li>The remaining follicular tissue then grows within the ovary </li></ul><ul><ul><li>To form a solid mass called the corpus luteum, which secretes hormones, depending on whether or not pregnancy occurs </li></ul></ul>
  6. 6. Oviducts and Uterus <ul><li>The egg cell is released into the abdominal cavity </li></ul><ul><ul><li>Near the opening of the oviduct, or fallopian tube </li></ul></ul><ul><li>Cilia in the tube </li></ul><ul><ul><li>Convey the egg to the uterus </li></ul></ul><ul><li>The vagina is a thin-walled chamber </li></ul><ul><ul><li>That is the repository for sperm during copulation </li></ul></ul><ul><ul><li>That serves as the birth canal through which a baby is born </li></ul></ul><ul><li>The vagina opens to the outside at the vulva </li></ul><ul><ul><li>Which includes the hymen, vestibule, labia minora, labia majora, and clitoris </li></ul></ul>
  7. 7. Male Reproductive Anatomy <ul><li>In most mammalian species </li></ul><ul><ul><li>The male’s external reproductive organs are the scrotum and penis </li></ul></ul><ul><li>The internal organs </li></ul><ul><ul><li>Consist of the gonads, which produce sperm and hormones, and accessory glands </li></ul></ul>
  8. 8. <ul><li>Reproductive anatomy of the human male </li></ul>Figure 46.10 Erectile tissue of penis Prostate gland (Urinary bladder) Bulbourethral gland Vas deferens Epididymis Testis Seminal vesicle (behind bladder) Urethra Scrotum Glans penis
  9. 9. Seminal vesicle (Rectum) Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland (Urinary bladder) (Pubic bone) Erectile tissue of penis Urethra Glans penis Prepuce Vas deferens Epididymis Testis Scrotum
  10. 10. Testes <ul><li>The male gonads, or testes </li></ul><ul><ul><li>Consist of many highly coiled tubes surrounded by several layers of connective tissue </li></ul></ul><ul><li>The tubes are seminiferous tubules </li></ul><ul><ul><li>Where sperm form </li></ul></ul><ul><li>Production of normal sperm </li></ul><ul><ul><li>Cannot occur at the body temperatures of most mammals </li></ul></ul><ul><li>The testes of humans and many mammals </li></ul><ul><ul><li>Are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity </li></ul></ul>
  11. 11. Ducts <ul><li>From the seminiferous tubules of a testis </li></ul><ul><ul><li>The sperm pass into the coiled tubules of the epididymis </li></ul></ul><ul><li>During ejaculation </li></ul><ul><ul><li>Sperm are propelled through the muscular vas deferens, the ejaculatory duct, and exit the penis through the urethra </li></ul></ul>
  12. 12. Glands <ul><li>Three sets of accessory glands </li></ul><ul><ul><li>Add secretions to the semen, the fluid that is ejaculated </li></ul></ul><ul><ul><li>The prostate gland </li></ul></ul><ul><ul><ul><li>Secretes its products directly into the urethra through several small ducts </li></ul></ul></ul><ul><ul><li>The bulbourethral gland </li></ul></ul><ul><ul><ul><li>Secretes a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra </li></ul></ul></ul><ul><li>A pair of seminal vesicles </li></ul><ul><ul><li>Contributes about 60% of the total volume of semen </li></ul></ul>
  13. 13. <ul><li>Oogenesis is the development of mature ova </li></ul>Ovary Primary germ cell in embryo Differentiation Oogonium Oogonium in ovary Mitotic division Primary oocyte, arrested in prophase of meiosis I (present at birth) Completion of meiosis I and onset of meiosis II Primary oocyte within follicle Secondary oocyte, arrested at meta- phase of meiosis II First polar body Ovulation Entry of sperm triggers completion of meiosis II Ovum Growing follicle Mature follicle Ruptured follicle Ovulated secondary oocyte Corpus luteum Degenerating corpus luteum 2 n 2 n n n n n Figure 46.11
  14. 14. <ul><li>Spermatogenesis is the production of mature sperm </li></ul>Epididymis Seminiferous tubule Testis Cross section of seminiferous tubule Sertoli cell nucleus Lumen of Seminiferous tubule Spermatogonium Primary spermatocyte (in prophase of meiosis I) Secondary spermatocyte Early spermatids Spermatids (at two stages of differentiation) Differentiation (Sertoli cells provide nutrients) Meiosis II Meiosis I completed Mitotic division, producing large numbers of spermatogonia Sperm cells Acrosome Nucleus Mitochondria Neck Tail Plasma membrane Head Midpiece 2 n 2 n n n n n n n n n n n Figure 46.12 Differentiation and onset of meiosis I
  15. 15. <ul><li>Oogenesis differs from spermatogenesis </li></ul><ul><ul><li>In three major ways </li></ul></ul><ul><li>First, during the meiotic divisions of oogenesis </li></ul><ul><ul><li>Cytokinesis is unequal, with almost all the cytoplasm monopolized by a single daughter cell, the secondary oocyte </li></ul></ul><ul><li>Second, sperm are produced continuously throughout a male’s life </li></ul><ul><ul><li>Which is not the case in oogenesis </li></ul></ul><ul><li>Third, oogenesis has long “resting” periods </li></ul><ul><ul><li>While spermatogenesis produces sperm in uninterrupted sequence </li></ul></ul>
  16. 16. <ul><li>In menstrual cycles </li></ul><ul><ul><li>The endometrium is shed from the uterus in a bleeding called menstruation </li></ul></ul><ul><ul><li>Sexual receptivity is not limited to a specific timeframe </li></ul></ul>
  17. 17. <ul><li>Cyclic secretion of GnRH from the hypothalamus </li></ul><ul><ul><li>And of FSH and LH from the anterior pituitary orchestrates the female reproductive cycle </li></ul></ul><ul><li>Five kinds of hormones </li></ul><ul><ul><li>Participate in an elaborate scheme involving both positive and negative feedback </li></ul></ul>
  18. 18. <ul><li>The reproductive cycle of the human female </li></ul>Figure 46.13a–e Control by hypothalamus Inhibited by combination of estrogen and progesterone Stimulated by high levels of estrogen Inhibited by low levels of estrogen Hypothalamus Anterior pituitary GnRH FSH LH Pituitary gonadotropins in blood LH FSH FSH and LH stimulate follicle to grow LH surge triggers ovulation Ovarian cycle Growing follicle Mature follicle Corpus luteum Degenerating corpus luteum Estrogen secreted by growing follicle in increasing amounts Progesterone and estrogen secreted by corpus luteum Follicular phase Luteal phase Ovulation Ovarian hormones in blood Peak causes LH surge Estrogen Progesterone Estrogen level very low Progesterone and estro- gen promote thickening of endometrium Uterine (menstrual) cycle <ul><ul><li>Endometrium </li></ul></ul>Menstrual flow phase Proliferative phase Secretory phase 0 5 10 14 15 20 25 28 Days 1 (a) (b) (c) (d) (e) 3 6 7 8 4 5 2 10 9
  19. 19. The Ovarian Cycle <ul><li>In the ovarian cycle </li></ul><ul><ul><li>Hormones stimulate follicle growth, which results in ovulation </li></ul></ul><ul><li>Following ovulation </li></ul><ul><ul><li>The follicular tissue left behind transforms into the corpus luteum </li></ul></ul>
  20. 20. The Uterine (Menstrual) Cycle <ul><li>Cycle after cycle </li></ul><ul><ul><li>The maturation and release of egg cells from the ovary are integrated with changes in the uterus </li></ul></ul><ul><li>If an embryo has not implanted in the endometrium by the end of the secretory phase </li></ul><ul><ul><li>A new menstrual flow commences </li></ul></ul>
  21. 21. Menopause <ul><li>After about 450 cycles, human females undergo menopause </li></ul><ul><ul><li>The cessation of ovulation and menstruation </li></ul></ul>
  22. 22. Hormonal Control of the Male Reproductive System <ul><li>Testosterone and other androgens </li></ul><ul><ul><li>Are directly responsible for the primary and secondary sex characteristics of the male </li></ul></ul>
  23. 23. Conception, Embryonic Development, and Birth <ul><li>In humans and other placental mammals, an embryo grows into a newborn in the mother’s uterus </li></ul><ul><li>In humans and most other placental mammals </li></ul><ul><ul><li>Pregnancy, or gestation, is the condition of carrying one or more embryos in the uterus </li></ul></ul>
  24. 24. <ul><li>Fertilization of an egg by a sperm, conception </li></ul><ul><ul><li>Occurs in the oviduct </li></ul></ul>Figure 46.15a, b Ovary Uterus Endometrium From ovulation to implantation Endometrium Inner cell mass Cavity Blastocyst Trophoblast (a) Implantation of blastocyst (b) Ovulation releases a secondary oocyte, which enters the oviduct. 1 Fertilization occurs. A sperm enters the oocyte; meiosis of the oocyte finishes; and the nuclei of the ovum and sperm fuse, producing a zygote. 2 Cleavage (cell division) begins in the oviduct as the embryo is moved toward the uterus by peristalsis and the movements of cilia. 3 Cleavage continues. By the time the embryo reaches the uterus, it is a ball of cells. It floats in the uterus for several days, nourished by endometrial secretions. It becomes a blastocyst. 4 The blastocyst implants in the endometrium about 7 days after conception. 5
  25. 25. <ul><li>After fertilization </li></ul><ul><ul><li>The zygote undergoes cleavage and develops into a blastocyst before implantation in the endometrium </li></ul></ul><ul><li>Human gestation </li></ul><ul><ul><li>Can be divided into three trimesters of about three months each </li></ul></ul><ul><li>The first trimester </li></ul><ul><ul><li>Is the time of most radical change for both the mother and the embryo </li></ul></ul>
  26. 26. <ul><li>During its first 2 to 4 weeks of development </li></ul><ul><ul><li>The embryo obtains nutrients directly from the endometrium </li></ul></ul><ul><li>Meanwhile, the outer layer of the blastocyst </li></ul><ul><ul><li>Mingles with the endometrium and eventually forms the placenta </li></ul></ul>
  27. 27. <ul><li>Blood from the embryo </li></ul><ul><ul><li>Travels to the placenta through arteries of the umbilical cord and returns via the umbilical vein </li></ul></ul>Placenta Umbilical cord Chorionic villus containing fetal capillaries Maternal blood pools Uterus Fetal arteriole Fetal venule Umbilical cord Maternal portion of placenta Fetal portion of placenta (chorion) Umbilical arteries Umbilical vein Maternal arteries Maternal veins Figure 46.16
  28. 28. <ul><li>The first trimester is the main period of organogenesis </li></ul><ul><ul><li>The development of the body organs </li></ul></ul>Figure 46.17a–c (a) 5 weeks. Limb buds, eyes, the heart, the liver, and rudiments of all other organs have started to develop in the embryo, which is only about 1 cm long. (b) 14 weeks. Growth and development of the offspring, now called a fetus, continue during the second trimester. This fetus is about 6 cm long. (c) 20 weeks. By the end of the second trimester (at 24 weeks), the fetus grows to about 30 cm in length.
  29. 29. Second Trimester <ul><li>During the second trimester </li></ul><ul><ul><li>The fetus grows and is very active </li></ul></ul><ul><ul><li>The mother may feel fetal movements </li></ul></ul><ul><ul><li>The uterus grows enough for the pregnancy to become obvious </li></ul></ul>
  30. 30. Third Trimester <ul><li>During the third trimester </li></ul><ul><ul><li>The fetus continues to grow and fills the available space within the embryonic membranes </li></ul></ul>
  31. 31. <ul><li>A complex interplay of local regulators and hormones </li></ul><ul><ul><li>Induces and regulates labor, the process by which childbirth occurs </li></ul></ul>Estrogen Oxytocin from ovaries from fetus and mother's posterior pituitary Induces oxytocin receptors on uterus Stimulates uterus to contract Stimulates placenta to make Prostaglandins Stimulate more contractions of uterus Positive feedback Figure 46.18
  32. 32. <ul><li>Birth, or parturition </li></ul><ul><ul><li>Is brought about by a series of strong, rhythmic uterine contractions </li></ul></ul>Figure 46.19 Placenta Umbilical cord Uterus Cervix Dilation of the cervix Expulsion: delivery of the infant Uterus Placenta (detaching) Umbilical cord Delivery of the placenta 1 2 3
  33. 33. <ul><li>Amniocentesis and chorionic villus sampling </li></ul><ul><ul><li>Are invasive techniques in which amniotic fluid or fetal cells are obtained for genetic analysis </li></ul></ul><ul><li>Noninvasive procedures </li></ul><ul><ul><li>Usually use ultrasound imaging to detect fetal condition </li></ul></ul>Figure 46.21 Head Body Head Body
  34. 34. <ul><li>A human embryo at approximately 6–8 weeks after conception </li></ul><ul><ul><li>Shows the development of distinctive features </li></ul></ul>Figure 47.1 1 mm
  35. 35. <ul><li>The question of how a zygote becomes an animal </li></ul><ul><ul><li>Has been asked for centuries </li></ul></ul><ul><li>As recently as the 18th century </li></ul><ul><ul><li>The prevailing theory was a notion called preformation </li></ul></ul>
  36. 36. <ul><li>Preformation is the idea that the egg or sperm contains an embryo </li></ul><ul><ul><li>A preformed miniature infant, or “homunculus,” that simply becomes larger during development </li></ul></ul>Figure 47.2
  37. 37. <ul><li>An organism’s development </li></ul><ul><ul><li>Is determined by the genome of the zygote and by differences that arise between early embryonic cells </li></ul></ul><ul><li>Cell differentiation </li></ul><ul><ul><li>Is the specialization of cells in their structure and function </li></ul></ul><ul><li>Morphogenesis </li></ul><ul><ul><li>Is the process by which an animal takes shape </li></ul></ul>
  38. 38. <ul><li>After fertilization, embryonic development proceeds through cleavage, gastrulation, and organogenesis </li></ul><ul><li>Important events regulating development </li></ul><ul><ul><li>Occur during fertilization and each of the three successive stages that build the animal’s body </li></ul></ul>
  39. 39. Fertilization <ul><li>The main function of fertilization </li></ul><ul><ul><li>Is to bring the haploid nuclei of sperm and egg together to form a diploid zygote </li></ul></ul><ul><li>Contact of the sperm with the egg’s surface </li></ul><ul><ul><li>Initiates metabolic reactions within the egg that trigger the onset of embryonic development </li></ul></ul>
  40. 40. The Acrosomal Reaction <ul><li>The acrosomal reaction </li></ul><ul><ul><li>Is triggered when the sperm meets the egg </li></ul></ul><ul><ul><li>Releases hydrolytic enzymes that digest material surrounding the egg </li></ul></ul>
  41. 41. <ul><li>The acrosomal reaction </li></ul>Sperm nucleus Sperm plasma membrane Hydrolytic enzymes Cortical granule Cortical granule membrane EGG CYTOPLASM Basal body (centriole) Sperm head Acrosomal process Actin Acrosome Jelly coat Egg plasma membrane Vitelline layer Fused plasma membranes Perivitelline space Fertilization envelope Cortical reaction. Fusion of the gamete membranes triggers an increase of Ca 2+ in the egg’s cytosol, causing cortical granules in the egg to fuse with the plasma membrane and discharge their contents. This leads to swelling of the perivitelline space, hardening of the vitelline layer, and clipping of sperm-binding receptors. The resulting fertilization envelope is the slow block to polyspermy. 5 Contact and fusion of sperm and egg membranes. A hole is made in the vitelline layer, allowing contact and fusion of the gamete plasma membranes. The membrane becomes depolarized, resulting in the fast block to polyspermy. 3 Acrosomal reaction. Hydrolytic enzymes released from the acrosome make a hole in the jelly coat, while growing actin filaments form the acrosomal process. This structure protrudes from the sperm head and penetrates the jelly coat, binding to receptors in the egg cell membrane that extend through the vitelline layer. 2 Contact. The sperm cell contacts the egg’s jelly coat, triggering exocytosis from the sperm’s acrosome. 1 Sperm-binding receptors Entry of sperm nucleus. 4 Figure 47.3
  42. 42. <ul><li>Gamete contact and/or fusion </li></ul><ul><ul><li>Depolarizes the egg cell membrane and sets up a fast block to polyspermy </li></ul></ul>
  43. 43. The Cortical Reaction <ul><li>Fusion of egg and sperm also initiates the cortical reaction </li></ul><ul><ul><li>Inducing a rise in Ca 2+ that stimulates cortical granules to release their contents outside the egg </li></ul></ul>Figure 47.4 A fluorescent dye that glows when it binds free Ca 2+ was injected into unfertilized sea urchin eggs. After sea urchin sperm were added, researchers observed the eggs in a fluorescence microscope. EXPERIMENT RESULTS The release of Ca 2+ from the endoplasmic reticulum into the cytosol at the site of sperm entry triggers the release of more and more Ca 2+ in a wave that spreads to the other side of the cell. The entire process takes about 30 seconds. CONCLUSION 30 sec 20 sec 10 sec after fertilization 1 sec before fertilization Point of sperm entry Spreading wave of calcium ions 500 m
  44. 44. <ul><li>These changes cause the formation of a fertilization envelope </li></ul><ul><ul><li>That functions as a slow block to polyspermy </li></ul></ul>
  45. 45. Activation of the Egg <ul><li>Another outcome of the sharp rise in Ca 2+ in the egg’s cytosol </li></ul><ul><ul><li>Is a substantial increase in the rates of cellular respiration and protein synthesis by the egg cell </li></ul></ul><ul><li>With these rapid changes in metabolism </li></ul><ul><ul><li>The egg is said to be activated </li></ul></ul>
  46. 46. Fertilization in Mammals <ul><li>In mammalian fertilization, the cortical reaction </li></ul><ul><ul><li>Modifies the zona pellucida as a slow block to polyspermy </li></ul></ul>Figure 47.6 Sperm nucleus Acrosomal vesicle Egg plasma membrane Zona pellucida Sperm basal body Cortical granules Follicle cell EGG CYTOPLASM The sperm migrates through the coat of follicle cells and binds to receptor molecules in the zona pellucida of the egg. (Receptor molecules are not shown here.) 1 This binding induces the acrosomal reaction, in which the sperm releases hydrolytic enzymes into the zona pellucida. 2 Breakdown of the zona pellucida by these enzymes allows the sperm to reach the plasma membrane of the egg. Membrane proteins of the sperm bind to receptors on the egg membrane, and the two membranes fuse. 3 The nucleus and other components of the sperm cell enter the egg. 4 Enzymes released during the cortical reaction harden the zona pellucida, which now functions as a block to polyspermy. 5
  47. 47. Cleavage <ul><li>Fertilization is followed by cleavage </li></ul><ul><ul><li>A period of rapid cell division without growth </li></ul></ul>
  48. 48. <ul><li>Cleavage partitions the cytoplasm of one large cell </li></ul><ul><ul><li>Into many smaller cells called blastomeres </li></ul></ul>Figure 47.7a–d Fertilized egg. Shown here is the zygote shortly before the first cleavage division, surrounded by the fertilization envelope. The nucleus is visible in the center. (a) Four-cell stage. Remnants of the mitotic spindle can be seen between the two cells that have just completed the second cleavage division. (b) Morula. After further cleavage divisions, the embryo is a multicellular ball that is still surrounded by the fertilization envelope. The blastocoel cavity has begun to form. (c) Blastula. A single layer of cells surrounds a large blastocoel cavity. Although not visible here, the fertilization envelope is still present; the embryo will soon hatch from it and begin swimming. (d)
  49. 49. <ul><li>The eggs and zygotes of many animals, except mammals </li></ul><ul><ul><li>Have a definite polarity </li></ul></ul><ul><li>The polarity is defined by the distribution of yolk </li></ul><ul><ul><li>With the vegetal pole having the most yolk and the animal pole having the least </li></ul></ul>
  50. 50. Gastrulation <ul><li>The morphogenetic process called gastrulation </li></ul><ul><ul><li>Rearranges the cells of a blastula into a three-layered embryo, called a gastrula, that has a primitive gut </li></ul></ul>
  51. 51. <ul><li>The three layers produced by gastrulation </li></ul><ul><ul><li>Are called embryonic germ layers </li></ul></ul><ul><li>The ectoderm </li></ul><ul><ul><li>Forms the outer layer of the gastrula </li></ul></ul><ul><li>The endoderm </li></ul><ul><ul><li>Lines the embryonic digestive tract </li></ul></ul><ul><li>The mesoderm </li></ul><ul><ul><li>Partly fills the space between the endoderm and ectoderm </li></ul></ul>
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