Chapter 15 Continuance of Human Life
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Title: Chapter 15 (1 of 127)
Section 15.1 The Human Reproductive System
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Human Reproduction Before beginning to cover this chapter, you will have to do some work on your own. Follow the guidelines for notetaking from a text:
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Note Taking Guidelines The ability to take meaning from written text and internalize it is one of the most important skills you should master as you prepare for continuing your education beyond high school.
Following the guidelines below will help you develop this ability. We will be practicing it throughout the semester; completion of assigned readings with appropriate notes will form the bulk of your homework check marks
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To start, read page 484 and the first part of 485, stopping at the subsection titled "The Male Reproductive System" Take notes on these pages to practice going through this process.
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Human Reproduction Humans undergo sexual reproduction, involving the combination of gametes to form a zygote.
What are gametes?
What is a zygote?
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Human Reproduction Some organisms undergo a different form of reproduction, asexual reproduction. What is the difference between sexual and asexual reproduction?
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Human Reproduction Give two examples of asexual reproduction from the reading you just did.
Streptococci bacteria replicate their genetic material and split in two (mitosis) Oak trees selfpollinate and produce acorns
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Human Reproduction What are advantages and disadvantages of each reproductive strategy?
advantages
sexual
asexual
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disadvantages
Human Reproduction A major advantage of sexual reproduction is the variation it produces in the offspring. By combining the genes from two parents, individual offspring will vary in their characteristics. What is the importance of this variation? 1)
Variation means that different offspring will differ in their abilities to survive within their environment.
2)
This variation provides a better chance that at least some will survive if conditions change.
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Human Reproduction Many animals follow a repruductive cycle that is dependent on the seasons, mating and giving birth only at specific times of the year. What reason might be given for following this strategy?
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Human Reproduction Other animals are able to reproduce at any time of year. This includes humans, some wild animals, and most domesticated animals. Thinking of the answer to the previous question, why might domestic animals have been able to develop so that reproduction does not follow an annual cycle?
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Human Reproduction Human reproduction does, however, follow a cyclic pattern. We will be looking at this pattern in detail throughout the chapter.
First, we will study the male reproductive system, then the female system, and finally examine the development of a human from fertilization until birth.
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Human Reproduction In humans, whether an embryo will develop into a male or female is controlled genetically. The sperm cell determines whether a baby will be male or female...the egg plays no role in deciding gender. How many chromosomes / chromosome pairs do most people have? This is because gender is based on the 23rd chromosome pair. Unlike all other chromosome pairs, the sex chromosomes are not homologous; instead, they come in two varieties: X and Y.
X chromosomes are larger, and contain extra genetic information not carried by the Y chromsomes.
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Human Reproduction When an egg is fertilized, half of the chromosomes are donated by the father and half by the mother. In females, both of the sex chromosomes are X; in males, one is an X, and one is a Y. Since only one chromosome from each pair is donated by each parent, there is a 50% chance that the sperm will contain an X chromosome, and a 50% chance that it will contain a Y chromosome. The egg, however, will always contain an X.
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Human Reproduction This gives us four possible combinations, but only two possible results.
X X
oogonium
X Y
X
X X
=
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=
X
X Y
spermatogonium
Y
X
=
=
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Male Reproductive System Homework Read pages 486489, and take your own notes on these pages. Be sure to include definitions for all bolded terms. Explain the interaction of the following pairs of hormones: FSH and Inhibin LH and Testosterone
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Male Reproductive System During development, a fetus formed by a combination of egg and sperm resulting in an XY combination of chromosomes will begin to develop male characteristics at about 8 weeks. During puberty, which generally occurs at around 13 years of age*, the reproductive system becomes functional. Puberty is caused by production and release of reproductive hormones. Unlike the female system, the male reproductive system generally remains functional for the rest of the individual's life. *there is a great deal of individual variation as to the onset of puberty, as well as variation among nationalities. What might be some reasons why puberty tends to begin earlier in North America than in some other areas of the world?
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Male Reproductive System Label the major structures in the male reproductive system.
urinary bladder ureter
seminal vesicle sperm duct
ejaculatory duct prostate gland urethra penis glans foreskin
Cowper's gland anus vas deferens
epididymus testis scrotum
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Male Reproductive System Label the major structures in the male reproductive system.
urinary bladder ureter
seminal vesicle sperm duct
urethra penis glans
foreskin
ejaculatory duct prostate gland Cowper's gland anus vas deferens
epididymus testis
scrotum
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Male Reproductive System Development of sperm cells is called: spermatogenesis This occurs in the seminiferous tubules of the testes, which are surrounded by interstitial cells. Spermatogonia mature during meiosis, forming sperm that are released into the seminiferous tubules, travelling through the epididymus into the vas deferens, and from there into the sperm duct.* Sertoli cells support, nourish, and regulate the developing sperm.
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Male Reproductive System What happens to the sperm cells in the epididymus?
They mature and become motile
Label the parts of a sperm cell: What is the function of the acrosome? When a sperm fertilizes an egg, the acrosome releases enzymes that break down the coating surrounding the egg, and trigger the development of an impenetrable layer. This occurs very quickly, and prevents more than one sperm from fertilizing the egg.
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Male Reproductive System As the sperm enter the ejaculatory duct, the seminal vesicles secrete fluid containing fructose, which the sperm use for energy. The prostate gland and Cowper's gland secrete an alkaline (basic) solution, which acts to neutralize the acids in the female reproductive tract. Why do you think the femal reproductive tract would maintain an acidic environment? This combination of sperm and fluids is called semen. During intercourse, semen travels through the urethra, which is shared by the reproductive and excretory systems. Why are the testes located outside of the body cavity?
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Male Reproductive System Spermatogenesis is stimulated by FSH, which is produced in the anterior pituitary A second hormone, inhibin, is released by the seminiferous tubules along with sperm. This forms a negative feedback loop with FSH. LH, also from the anterior pituitary, stimulates the interstitial cells. These produce the steroid hormone testosterone, which is the major androgen that triggers development of male sex characteristics. LH and testosterone also form a negative feedback loop.
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FSH and Inhibin Control of Spermatogenesis The negative feedback loop created by FSH and Inhibin ensures that the rate of spermatogenesis remains at an appropriate level.
As FSH levels increase, rate of spermatogenesis increases.
FSH levels
Inhibin levels
High levels of FSH stimulate the seminiferous tubules to release the hormone inhibin, which decreases FSH production. As FSH levels fall, the seminiferous tubules slow production of inhibin. This leads to increased FSH production, and completes the negative feedback loop.
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LH and Testosterone The negative feedback loop created by LH and testosterone form a second negative feedback loop, controlling the expression of secondary male sex characteristics.
As LH levels increase, rate of testosterone production by the interstitial cells will also increase.
LH levels
Testosterone levels
As testosterone levels rise, the anterior pituitary is stimulated to decrease production of LH. This leads to a fall in testosterone production, which in turn stimulates the anterior pituitary to increase production of LH...and completes the negative feedback loop.
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Homework Read pages 490493, and take notes on these pages. Be prepared to identify all structures in the female reproductive system, and explain their functions. Complete Questions #16 on page 499, and 1,2, 4, and 5 on page 515. Review the diagrams in this section.
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Homework Page 499 1)
Explain the effects of puberty in males and females. During puberty, the hypothalamus secretes releasing factors which trigger the anterior pituitary to produce reproductive hormones. These hormones stimulate development of secondary sexual characteristics, such as pubic hair, changes in voice and increased muscle mass (males) and development of breasts and widening of the hips (females). It also triggers the development of the reproductive systems, starting the production of sperm in males and ova in females.
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Homework Page 499 2)
Define the term "sex hormone". Sex hormones are those that control the development and functioning of the reproductive system.
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Homework Page 499 3)
Identify the organs that produce sex hormones in males and females. List the hormones produced by each structure. Hypothalamus:
releasing factors (gonatotropin releasing hormone)
Anterior pituitary:LH and FSH Ovaries:
Estrogen and Progesterone
Testes:
Testosterone and Inhibin
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Homework Page 499 4)
Explain the roles of FSH, inhibin, LH, and testosterone in mature males. FSH initiates the development of sperm. Testosterone is needed to maintain the development of mature sperm. AS FSH increases, it causes and increase in release of inhibin, forming a negative feedback loop. This regulates the rate of spermatogenesis. LH stimulates secretion of testosterone, which inhibits release of LH as levels rise, forming another negative feedback loop.
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Homework Page 499 5)
Describe how female sex hormones prepare the reproductive system for a possible pregnancy during a normal menstrual cycle. At the start of the cycle, estrogen and progesterone levels have dropped. This triggers a rise in FSH and LH levels. FSH causes a follicle to develop, which secretes estrogen; this increased estrogen triggers the endometrium to thicken, in preparation for implantation of an embryo. Higher estrogen levels trigger increased LH production, which causes ovulation and stimulates the corpus luteum (following ovulation) to secrete progesterone. Progesterone lowers LH levels, and continues to prepare the endometrium to accept a fertilized ovum. If fertilization does not occur, the corpus luteum breaks down, lowering levels of progesterone, and beginning the cycle again.
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Homework Page 499 6)
When a woman becomes pregnant, menstruation stops for the duration of the pregnancy. Explain how menstruation is prevented if pregnancy occurs. If an embryo implants into the endometrium, the cells secrete human chorionic gonadotropin. This prevents the breakdown of the corpus luteum, which continues to produce progesterone and estrogen. The continued high levels of progesterone and estrogen inhibits secretion of FSH and LH, preventing the development of more follicles and stopping ovulation. The endometrium lining is maintained during pregnancy.
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Homework Page 515 1)
Name the structures within a testis and describe their functions. Seminiferous tubules: tubes in which sperm develop Interstitial cells: surround seminiferous tubules and produce testosterone. Epididymis: coiled tubules in which sperm mature and become motile Vas Deferens: also called the sperm duct, this carries mature sperm out of the testes
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Homework Page 515 2)
Explain the role of testosterone in a mature male, and state where it is produced. Testeosterone is produced in the interstitial cells in the testes. Testosterone is necessary for spermatogenesis.
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Homework Page 515 4)
Outline the path of a sperm from where it forms to where it fertilizes an egg. What glands contribute fluid to semen? Sperm begin in the seminiferous tubules and complete development in the epididymis. Sperm leave the testes through the vas deferens, and enter the ejaculatory duct, then the urethra. During intercourse, sperm enters the vagina, travels through the cervix and into the uterus, then down the oviducts, where fertilization occurs. The seminal vesicles produce a fluid containing fructose, and the prostate and Cowper's glands produce alkaline fluid.
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Female Reproductive System The female reproductive system is completely contained within the body cavity. The female reproductive cell is called the ovum, or egg. Following fertilization, it is called a zygote, and through pregnancy it is sustained and nourished within the mother. Unlike the male reproductive system, in females the excretory and reproductive systems are not combined, with the urethra remaining separate from the vagina.
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Homework Page 515 5)
Explain how the maintenance of high levels of estrogen and progesterone during pregnancy prevents ovulation. High levels of extrogen and progesterone during pregnancy inhibit the release of FSH and LH, which are necessary to trigger the development of a follicle into a mature ovum. So without FSH and LH, ovulation does not occur. During pregnancy, estrogen and progesterone levels remain high because the corpus luteum does not degenerate, due to production of human chorionic gonadotropin from the implanted embryo.
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Female Reproductive System anus cervix clitoris fimbriae
labium majora labium minora ovary oviduct
pubic symphysis rectum ureter urethra urinary bladder uterus vagina vaginal orifice
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Female Reproductive System 1)
2)
4) 3)
cervix
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5) 6)
fimbriae
ovary
oviduct
uterus
vagina
Female Reproductive System ureter
oviduct
fimbriae
ovary uterus urinary bladder cervix
pubic symphysis urethra clitoris
rectum
vagina
anus labium minora labium majora vaginal orifice
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Female Reproductive System 1) oviduct
2)
fimbriae
4) uterus 3)
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ovary
5) cervix 6) vagina
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Class Assignment Complete Investigation 15.A on pages 494495 Be sure to complete all charts, and completely answer all of the questions (#111) on page 495
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Class Assignment
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Female Reproductive Hormones The human reproductive system does not follow a seasonal pattern, but it is cyclical. The release of an ovum is timed so that the uterus is prepared to accept and sustain a zygote.
This pattern is called the menstrual cycle, and is under the control of the hypothalamus.
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Female Reproductive Hormones The ovaries are composed of follicles, each containing a single ovum. During the first stage of the menstrual cycle, the follicular stage, levels of FSH increase.
This stimulates the follicles to produce estrogen, which causes the endometrium (inner lining of the uterus) to thicken and increase its blood supply.
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Female Reproductive Hormones Estrogen forms a negative feedback loop with FSH. What will be the result of the increased estrogen levels on levels of FSH?
Estrogen also stimulates the released of LH, triggering an ovum to be released from one of the developing follicles. This is the second stage, ovulation.
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Female Reproductive Hormones Following ovulation, the follicle changes, becoming a corpus luteum, a group of cells which produces the hormone progesterone, and beginning the next stage of the cycle, the luteal stage.
Progesterone inhibits ovulation from other follicles, and decreases LH production. As LH levels fall, the corpus luteum dgenerates.
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Female Reproductive Hormones Lower progesterone levels result from the breakdown fo the corpus luteum, and decrease blood supply to the endometrium. As the endometrium degenerates, the blood vessels break down, and the excess tissue and blood are removed through the vagina. This is the menstruation stage.
This coincides with the start of the next follicular stage.
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Female Reproductive Hormones If, however, the egg is fertilized, it begins to divide, forming an embryo. When the embryo implants itself into the endometrium, it secretes a chemical called human chorionic gonatotropin (HCG), which prevents the breakdown of the corpus luteum, stopping menstruation and maintaining the blood supply to the endometrium.
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Menopause Males normally continue producing sperm throughout their life, but women stop releasing egg cells during menopause. The age at which this occurs varies greatly, but normally happens sometime after 50 years. Menopause occurs when the ovaries stop releasing ova, because the number of follicles has decreased. Normally only about 400 of the more than two million follicles ever mature and undergo ovulation. Once these follicles have been used, the menstrual cycle will stop.
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Homework Read Pages 496499, and create a chart of the STDs covered in the text. Include: the disease; the cause (viral, bacterial, etc.; how it is transmitted; symptoms; treatment and prognosis.
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Pop Quiz! anus Cowper's gland ejaculatory duct
1
7
epididymus foreskin glans penis
2
prostate gland
3
scrotum seminal vesicle sperm duct vas deferens ureter urethra urinary bladder testis
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8
9 10 11 12
4
5 6
13 14 15
Pop Quiz! In which structure are the sperm cells formed?
epididymus scrotum testis vas deferens
1 2
3 4
Spermatogenesis is triggered by release of
.
In addition to sperm, these release the hormone
,
which forms a
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with the first hormone.
Pop Quiz anus cervix clitoris
11 1
12
2
fimbriae
labium majora labium minora ovary oviduct
pubic symphysis rectum ureter urethra urinary bladder uterus vagina vaginal orifice
3 4
13 5 6
7
16 8
9
10
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14 15
Pop Quiz The four stages of the menstrual cycle are: Follicular stage
Ovulation
Luteal Stage
Menstruation
Increased levels of FSH stimulate the follicles to produce which causes the It also increases the release of
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to thicken. from the anterior pituitary.
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Pop Quiz
Higher LH levels induce the release of an ovum from the
.
After releasing the ovum, this mass of cells becomes the , and begins releasing
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.
Pop Quiz Negative feedback loops: FSH is to estrogen as
If implantation occurs, cells of the
is to progesterone
is released by , preventing the breakdown of the , and inhibiting further ovulation during
pregnancy.
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Pop Quiz Higher LH levels induce the release of an ovum from the
.
After releasing the ovum, this mass of cells becomes the , and begins releasing
.
Negative feedback loops.
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is to inhibin as
is to estrogen.
Section 15.2 Reproductive Control
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Title: 15.2 (67 of 127)
Section 15.3 Development and Differentiation
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Development and Differentiation In this section we will be studying the development of a human from fertilization to birth. *Fertilization and implantation *Differentiation and cell specialization *Stages of embryonic and fetal development *Sustaining the fetus *Stages of childbirth
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Development and Differentiation We already looked at how sperm and egg (ovum) cells are developed and released. These cells are called gametes, and each is haploid. What does this term mean?
When the sperm and egg combine, the result is a zygote. The zygote is diploid, since it combines the genetic material from both the sperm and egg cell.
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Fertilization Fertilization is the first stage in development. It occurs when a sperm cell succesfully combines with an egg cell, forming a zygote. Only a single sperm cell will fertilize an egg. When it connects with the egg, the acrosome releases enzymes that break down the coating around the ovum, changing it so that it becomes acrosome impenetrable to other sperm.
The sperm cell's nucleus will merge with the nucleus of the ovum, resulting in a zygote that has a complete set of chromosomes...in humans, 23 pairs or 46 total.
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Implantation After fertilization, the zygote travels along the oviduct to the uterus. This can take several days. During this period, the zygote begins to divide. However, since it is not taking in any further material, it cannot increase in size. This process of cell division without intermediate growth is called cleavage.
What will happen to the overall size of the individual cells during cleavage?
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Implantation As soon as the zygote begins to divide, normally within 48 hours after fertilization, it is called an embryo. The mass of cells is known as the morula. At this point, all of the cells are still identical.
The embryo continues to divide as it travels down the oviduct. By the time it reaches the uterus, after about 7 days, the morula contains about 100 cells which have formed an almost completely hollow ball, called a blastocyst. The outer layer, called the trophoblast will form the membranes which surround the baby.
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Implantation Implantation takes place once the embryo reaches the uterus. The embryo attaches itself to the inner lining of the uterus. What is the lining of the uterus called? What has previously happened to prepare the endometrium to support the developing embryo?
What prevents the endometrium from breaking down, as it normally would at the end of the menstrual cycle?
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Implantation
Implantation occurs approximately one week after fertilization.
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Class and Homework Assignment Read pages 506509 in Section 15.3, stopping at the subsection titled "Overview of Human Development". Take notes on these pages in your binder. Complete Questions #15 on page 514.
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Question 1, page 514 Describe in detail the events that lead from fertilization to implantation. The zygote continues to be swept down the oviduct by cilia action. It begins to undergo cleavage, forming an embryo. After about a week, the embryo reaches the uterus. By this time, it has formed a hollow ball of about 100 cells, called a blastocyst, composed of an outer layer (trophoblast) with an inner cell mass at one edge. When it reaches the uterus, the embryo attaches to the endometrium...this is implantation.
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Question 2, page 514 Distinguish between a fetus and an embryo. A developing baby is called a zygote from fertilization until it begins to undergo cleavage. At that point, it is called an embryo. Once the embryo begins to form specialized bone cells, at about 8 or 9 weeks after fertilization, it is called a fetus.
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Question 3, page 514 List the primary membranes, and briefly outline their functions in humans. Chorion
Develops from the trophoblast. Attaches the embryo to the endometrium, and together these form the placenta.
Amnion
Membrane surrounding the embryo, providing protection and cushioning. Filled with amniotic fluid.
Yolk sac
In humans, the yolk sac is small, and shrinks during the course of the pregnancy. It is the site of initial blood cell development.
Allantois
Develops into the umbilical chord, providing the connection between the mother and embryo. Blood vessels of the allantois collect nutrients from the mother and remove wastes.
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Question 4, page 514 (A) Developing human embryos do not have a significant amount of yolk as part of their supporting tissues, while chick embryos do. Explain why. In humans, the yolk sac does not need to support the embryo through its development. In the chick, the yolk sac is the only source of nutrients for the embryo until development is complete. (B) Do frog embryos have little yolk for the same reason that human embryos have little yolk? Explain your answer. No, because in frogs, like in chicks, the yolk has to support the embryo until development is complete. However, in frogs, the embryo develops much faster to a point where it leaves the egg and is independent, able to find its own food, so less yolk is needed.
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Question 5, page 514 Explain how the maintenance of high levels of estrogen and progesterone during pregnancy prevents ovulation. Be as specific as possible. High levels of progesterone and estrogen do three things: *They inhibit the production of FSH and LH, which: *Prevents development of follicles in the ovary, stopping ovulation *Maintain the endometrium, stopping menstruation
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Gastrulation Once implantation of the blastocyst has occured, the cells continue to divide. However, now things have changed. Up to this point, the daughter cells have been virtually identical, except that each division resulted in smaller cells. Now, the developing embryo is able to take in nourishment from the endometrium, so it is able to grow. The cells will now also begin to specialize as they divide, starting to form distinct structures. This start of specialization, called gastrulation, begins during the second week after fertilization. The embryo at this stage is called a gastrula.
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Germ Layers As the gastrula continues to undergo cell division, the cells begin to arrange themselves into separate layers, called germ layers. By the end of gastrulation, the embryo has three distinct layers. Each layer eventually specializes to form different parts of the body. Ectoderm: forms skin and nervous system
Mesoderm: forms kidneys, skeleton, muscles, blood vessels, gonads
Endoderm: forms lungs and lining of digestive tract
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Germ Layers
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Primary Membranes The developing embryo is surrounded by various tissues that support, protect, and nourish it throughout development. The outer layer of the blastocyst develops into the chorion, which surrounds the embryo and the other membranes. Inside the chorion is the amnion, which completely surrounds the embryo. It contains amniotic fluid, which provides protection for the developing embryo.
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Connection to the Endometrium Two other membranes, the yolk sac and allantois, develop into the umbilical cord, connecting the embryo to the mother. The yolk sac collects nutrients while the allantois removes wastes.
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Connection to the Endometrium The yolk sac and allantois lead to projections of the chorion, called the chorionic villi, which are the direct connection into the endometrium. Together, the chorion and endometrium form the placenta.
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Nourishment and Waste Removal One important thing to note is that the embryo's blood and the maternal blood never come into direct contact. The umbilical cord is directly connected to the chorionic villi, which extend into the tissue of the placenta.
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Nourishment and Waste Removal Capillaries from the maternal circulatory system also pass through this tissue, however the vessels remain separate. Maternal blood enters the interstitial spaces, and gives up oxygen and nutrients by diffusion. The fluid in the umbilical chord picks up these nutrients and oxygen, while at the same time releasing wastes through diffusion; these wastes are carried away in the maternal blood stream, and removed through excretion.
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Neural Development As the gastrula continues to grow, the cells become increasingly specialized. This process is known as differentiation. One area of the ectoderm begins to fold in, forming a hollow area called the neural tube. These cells will eventually develop into the nervous system. At this stage in development, usually about three weeks after fertilization, the embryo is called a neurula. This stage of development is very similar for all chordates (animals with a spinal chord).
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Overview of Development The total time from implantation to birth is approximately 38 weeks.
This period is divided into three separate trimesters.
Your homework will involve outlining what occurs during each of the three trimesters.
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Homework Read Section 15.3, pages 506514 Make summary notes on these pages Complete Question 7 on page 514 (you don't have to illustrate your flowchart)
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Gastrulation Animation http://www.gastrulation.org/Movie13_1.mov
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Overview of Development The First Trimester: weeks 112
•
Weeks 13 involve development of embryo from a single cell through blastocyst, gastrula, and neurula
•
At four weeks, the limbs, eyes, and spine begin to form
•
Once the first bones cells form, the embryo is called a fetus
•
At 12 weeks, all major organs have started forming
•
Fetus has recognizable head and limbs
•
Total length at this stage is approximately 100 mm (10 cm)
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Overview of Development The Second Trimester: weeks 1324
•
Fetus' heartbeat is audible with a stethoscope
•
Skeleton begins to form
•
Brain grows quickly and nervous sytem begins to function
•
Movement of the fetus can be felt by the mother
•
Organs are formed, but still developing and not fully functional
•
Total length at this stage is approximately 300 mm (30 cm)
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Overview of Development The Third Trimester: weeks 2538
•
Overall size increases rapidly
•
Fetus moves within the uterus frequently
•
Immune system begins to develop
•
The brain grows and develops; eyes are open
•
Nutrition is especially important at this stage, for both mother and the developing fetus, which needs increasing calories
•
Total length at this stage is approximately 525 mm (52.5 cm) and total weight is approximately 3400 g (3.4 kg), although there is a great deal of individual variation
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Class Work Review Section 15.3, pages 506514 Complete Questions 15 on page 514
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Class Work Answers 1)
Describe in detail the series of events leading from fertilization to implantation.
The ovum is fertilized in the oviduct. As the zygote moves along the oviduct, it begins to divide within about 48 hours. As soon as it begins dividing, the zygote is called an embryo. This division is not accompanied by cell growth, so each time the embryo divides, the daughter cells are smaller. This type of division is called cleavage. As the embryo continues dividing, it forms a mass of cells called a morula. By the time it reaches the uterus, at about 7 days after fertilization, the embyro has formed a mostly hollow ball called a blastocyst. This ball will implant into the endometrium, joining with the tissue and beginning to form a connection between the embryo and the mother.
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Class Work Answers 2)
Distinguish between a fetus and an embryo.
When the zygote begins to divide up until the first bone cells begin to form, it is called an embryo. This occurs at approximately eight weeks after fertilization. From this point until birth the developing baby is called a fetus.
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Class Work Answers 3)
List the primary membranes, and briefly outline their functions in humans.
The primary membranes are the chorion, the amnion, and the allantois and yolk sac. These membranes develop from the outer ball of the blasocyst, called the trophoblast. The chorion develops into the placenta when it integrates, through the chorionic villi, into the endometrium. The amnion surrounds the fetus and cushions it with the amniotic fluid. The allantois develops into the blood vessels of the umbilical chord, which connects the fetus to the placenta. The yolk sac joins the allantois in forming the umbilical chord.
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Class Work Answers 4)
A) Developing human embryos do not have a significant amount of yolk as part of their supporting tissues, while chick embryos do. Explain why.
As soon as the umbilical chord develops and attaches to the placenta, a human fetus receives all of its nourishment from the mother's bloodstream. Therefor, there is no more need for the yolk sac to provide these to the fetus. A developing chick embryo, however, is isolated from the mother, encased in the egg shell. The yolk needs to contain a larger amount of nutrients in order to supply these to the developing embryo until it is ready to hatch.
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Class Work Answers 4)
B)
Do frog embryos have little yolk for the same reason that human embryos have little yolk? Explain your answer.
Frog embryos are similar to chick embryos in that they are also isolated from the mother. So unlike humans they require all of the nourishment for their development to be contained in the yolk sac. However, unlike chick embryos, frog embryos go through less development before leaving the egg. A tadpole is in fact not much larger than the original developing embryo, and once it leaves the egg it is able to find its own food, so it doesn't need a large amount of yolk to supply it during development.
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Class Work Answers 5)
Explain how the maintenance of high levels of extrogen and progesterone during pregnancy prevents ovulation. Be as specific as possible.
Implantation triggers the embryo to begin releasing Human Chorionic Gonadotropin (HmCG) which prevents the breakdown of the corpus luteum. This continues to secrete progesterone, and the follicles continue secreting estrogen which maintains the blood supply to the endometrium. Estrogen and progesterone inhibit the release of follicle stimulating hormone (FSH) and leutinizing hormone (LH) from the pituitary gland, and gonadotropin releasing hormone (GnRH) from the hypothalamus. With low levels of FSH and LH, follicles in the ovaries do not mature and ovulation stops.
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Questions?
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Critical Stages of Development What is the term for any substance that can cause an abnormality in fetal development due to exposure during pregnancy?
Give some examples:
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Dilation stage: oxytocin triggers uterine contractions; cervix dilates; amnion breaks Duration: 220 hours
Stages of Childbirth Just before childbirth, levels of these two hormones drop:
This hormone is also involved, but levels will increase:
Expulsion stage: contractions push baby through birth canal; head rotates to ease passage Duration: 0.52 hours
Placental stage: placenta (called afterbirth) and umbilical chord expelled from the uterus Duration: approx. 15 minutes after baby is born
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The hormone named above causes the release of:
These two hormones trigger a reaction in the uterus:
Hormone Activity Oxytocin and one of the prostaglandins stimulate contraction of the uterus during childbirth. This forms a positive feedback loop which culminates after the birth of the child.
What is meant by the term breach birth?
What is a Caesarean section?
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Lactation What is the hormone that stimulates milk production?
Prior to childbirth, high levels of these hormones inhibit production of prolactin:
What is colostrum?
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Lactation Lactation is controlled both by hormones (prolactin and oxytocin) and by physical stimulation.
If the baby stops breastfeeding, production of milk by the mammary glands will stop.
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Twins What are the two possible scenarios that result in the birth of twins? How are twins classified based on what caused the double pregnancy Type of Twins
Cause of double pregnancy
How similar are they?
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Homework Review Section 15.3, and complete the following: Questions #916 on page 516 Join with a partner, and review answers to all questions. Note any areas in which you have difficulty, and any further questions you have. Review answers with the class.
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Homework 9)
Distinguish between identical and fraternal twins. Explain how each type is formed.
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Homework 10) Explain why only one sperm can fertilize an egg. Why is this important?
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Homework 11) At which stage of embryonic development does differentiation begin?
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Homework 12) Describe how the environment in which an embryo develops relates to the amount of yolk it has.
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Homework 13) Describe the significance of each of the following stages of embryonic development: Cleavage: Blastocyst: Gastrulla: Neurula:
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Homework 14) Label the diagram on the right, showing the placement of the primary membranes. Give a function for each structure in humans. a b c d e
f g
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h
Homework 15) Describe the structures and functions of the umbilical cord and the placenta.
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Homework 16) Explain why milk "dries up" if the baby no longer suckles.
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Homework 16) Explain why milk "dries up" if the baby no longer suckles.
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Case Study: Delivered From Death Read the article provided, and answer all questions.
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Homework Review Chapter 15 and note any questions you still have for discussion during Wednesday's class.
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Attachments
Endrocrine Gland Function.wpd codontable2[1]
