Travismulthaupt.com Chapter 46 Animal Reproduction

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Chapter 46Chapter 46

Animal ReproductionAnimal Reproduction

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2 Principle Modes of Reproduction

2 Principle Modes of Reproduction

» 1. Sexual» 2. Asexual

» 1. Sexual» 2. Asexual

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1. Sexual Reproduction1. Sexual Reproduction

» Sexual reproduction is the creation of offspring as a result of the fusion of haploid gametes, the sperm and egg.

» Sexual reproduction is the creation of offspring as a result of the fusion of haploid gametes, the sperm and egg. http://images.google.com/imgres?imgurl=http://www.ccs.k12.in.us/chsBS/kons/kons/images/

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» As a result, a diploid zygote forms and develops into a mature being.

»Most animals reproduce sexually and they are related to changing seasons, hormonal and environmental cues.

» As a result, a diploid zygote forms and develops into a mature being.

»Most animals reproduce sexually and they are related to changing seasons, hormonal and environmental cues.

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» Sexual reproduction can create a problem for individuals who are unable to move or rarely encounter another individual of the same species.

» Sexual reproduction can create a problem for individuals who are unable to move or rarely encounter another individual of the same species.

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2. Asexual Reproduction


» In asexual reproduction, a new individual is created without the fusion of a sperm and/or egg. All genes come from one parent.

» In asexual reproduction, a new individual is created without the fusion of a sperm and/or egg. All genes come from one parent.

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» There are many mechanisms of asexual reproduction:»A. Fission»B. Budding»C. Fragmentation

» There are many mechanisms of asexual reproduction:»A. Fission»B. Budding»C. Fragmentation

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A. FissionA. Fission

» Fission, the separation of a parent into 2 or more individuals of about equal size.

» Fission, the separation of a parent into 2 or more individuals of about equal size.

www.morning-earth.org

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B. BuddingB. Budding

» Budding is where new individuals arise as outgrowths from existing ones. They may detach or remain joined.

» Budding is where new individuals arise as outgrowths from existing ones. They may detach or remain joined.

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C. FragmentationC. Fragmentation» Fragmentation is

the breaking of the body into several pieces--some or all become mature adults (Linckia).

» Fragmentation is accompanied by regeneration so that the new fragments can become new, fully formed adults.

» Fragmentation is the breaking of the body into several pieces--some or all become mature adults (Linckia).

» Fragmentation is accompanied by regeneration so that the new fragments can become new, fully formed adults.

www.vsf.cape.com/

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2. Asexual Reproduction--

Advantages

2. Asexual Reproduction--

Advantages» A. Offspring can be created

without finding mates.» B. Asexual reproduction can

make numerous offspring in a short amount of time.

» A. Offspring can be created without finding mates.

» B. Asexual reproduction can make numerous offspring in a short amount of time.

http://www.swt.edu/~rr33/

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» Theoretically, this is the most advantageous in favorable environments that change little over time.

» Animals can reproduce sexually, asexually, or alternate between the two.

» The ability to switch from sexual to asexual reproduction is often related to season. Asexual reproduction will occur under favorable conditions and sexual reproduction will occur in times of environmental stress.

» Theoretically, this is the most advantageous in favorable environments that change little over time.

» Animals can reproduce sexually, asexually, or alternate between the two.

» The ability to switch from sexual to asexual reproduction is often related to season. Asexual reproduction will occur under favorable conditions and sexual reproduction will occur in times of environmental stress.

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ParthenogenesisParthenogenesis» This is the

development of an egg without being fertilized.

» Some species reproduce by a complex form of parthenogenesis that involves the doubling of chromosomes following meiosis to create a “zygote.”

» This is the development of an egg without being fertilized.

» Some species reproduce by a complex form of parthenogenesis that involves the doubling of chromosomes following meiosis to create a “zygote.”

www.wilsonlab.com/ photos.html

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HermaphroditismHermaphroditism» Hermaphroditism is a

solution to the problem and these individuals have both male and female reproductive parts.

» Some hermaphrodites fertilize themselves, but most mate with other individuals, and when they do they both exchange sperm and eggs.

» Hermaphroditism is a solution to the problem and these individuals have both male and female reproductive parts.

» Some hermaphrodites fertilize themselves, but most mate with other individuals, and when they do they both exchange sperm and eggs.

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HermaphroditismHermaphroditism

» In sequential hermaphroditism, individuals reverse their sex during their lifetime.

» In sequential hermaphroditism, individuals reverse their sex during their lifetime.

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There are 2 Types of Fertilization

There are 2 Types of Fertilization

» 1. Internal» 2. External

» 1. Internal» 2. External

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1. Internal Fertilization1. Internal Fertilization

» Internal fertilization involves the male depositing sperm in or near the female reproductive tract.

» Internal fertilization is an adaptation of terrestrial animals that enables sperm to get to an egg in a dry environment.

» It typically produces a smaller number of offspring and often requires long parental care of young during development.

» Internal fertilization involves the male depositing sperm in or near the female reproductive tract.

» Internal fertilization is an adaptation of terrestrial animals that enables sperm to get to an egg in a dry environment.

» It typically produces a smaller number of offspring and often requires long parental care of young during development.

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2. External Fertilization2. External Fertilization

» External fertilization involves fertilization of eggs that are released by the female into a wet environment and the male then fertilizes them.

» External fertilization involves fertilization of eggs that are released by the female into a wet environment and the male then fertilizes them.

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2. External Fertilization2. External Fertilization

» A moist habitat is typically required for external fertilization, so the sperm can swim to the eggs.

» Typically produces a large number of zygotes, far more than will survive.

» A moist habitat is typically required for external fertilization, so the sperm can swim to the eggs.

» Typically produces a large number of zygotes, far more than will survive.

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Vertebrate Reproductive Systems


» The basic plans of vertebrate reproductive systems are quite similar. There are some variations.

» In non-mammalian vertebrates, the digestive, excretory, and reproductive systems have a common opening to the outside called the cloaca.

» The cloaca was probably present in all vertebrate ancestors.

» The basic plans of vertebrate reproductive systems are quite similar. There are some variations.

» In non-mammalian vertebrates, the digestive, excretory, and reproductive systems have a common opening to the outside called the cloaca.

» The cloaca was probably present in all vertebrate ancestors.

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»Most mammals lack a cloaca and have a separate opening for the digestive tract, excretion, and reproduction.

»Most mammals lack a cloaca and have a separate opening for the digestive tract, excretion, and reproduction.

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Vertebrate Reproductive Systems:

Ovaries


Ovaries» The ovaries are in the abdomen

and contain many follicles.» The ovaries are in the abdomen

and contain many follicles.

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Ovaries


Ovaries» A follicle

consists of an egg surrounded by one or more layers of follicle cells.

» The follicle cells nourish and protect developing eggs.

» A follicle consists of an egg surrounded by one or more layers of follicle cells.

» The follicle cells nourish and protect developing eggs.

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Ovaries


Ovaries» The cells of

follicles produce estrogens which are primary sex hormones.

» Eggs get expelled from follicles during ovulation.

» The cells of follicles produce estrogens which are primary sex hormones.

» Eggs get expelled from follicles during ovulation.

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Ovaries


Ovaries» The follicle cells

which remain grow with the ovary and form the corpus luteum.

» If the egg does not get fertilized, the corpus luteum disintegrates and a new follicle matures during the next cycle.

» The follicle cells which remain grow with the ovary and form the corpus luteum.

» If the egg does not get fertilized, the corpus luteum disintegrates and a new follicle matures during the next cycle.

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Ovaries


Ovaries» The corpus

luteum’s main job is to secrete additional progesterone and estrogen that help to maintain the uterine lining during pregnancy.

» The female reproductive system is not completely closed.

» The corpus luteum’s main job is to secrete additional progesterone and estrogen that help to maintain the uterine lining during pregnancy.

» The female reproductive system is not completely closed.

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Ovaries


Ovaries» The egg cell is released into the

abdominal cavity near the opening of the oviduct (fallopian tube).

» There is a funnel-like opening to the oviduct with cilia that help to draw fluid (and eggs) into them.

» The cilia also beat and move the egg down to the uterus.

» The egg cell is released into the abdominal cavity near the opening of the oviduct (fallopian tube).

» There is a funnel-like opening to the oviduct with cilia that help to draw fluid (and eggs) into them.

» The cilia also beat and move the egg down to the uterus.

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Testes


Testes» The testes

produce semen.» They consist of

highly coiled tubes called seminiferous tubules in which the sperm form.

» The testes produce semen.

» They consist of highly coiled tubes called seminiferous tubules in which the sperm form.

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Testes


Testes» Leydig cells are found in

between the seminiferous tubules and produce testosterone and other androgens.

» Leydig cells are found in between the seminiferous tubules and produce testosterone and other androgens.

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Testes


Testes» Sertoli cells

protect and nurture the developing sperm.

» Males produce sperm continuously at maturation. Females, however, release one or a few eggs on a cyclic basis.

» Sertoli cells protect and nurture the developing sperm.

» Males produce sperm continuously at maturation. Females, however, release one or a few eggs on a cyclic basis.

Instruction.cvhs.okstate.edu

Instruction.cvhs.okstate.edu

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OogenesisOogenesis» Oogenesis begins in

the female embryo when primordial germ cells differentiate into oogonia--ovary specific stem cells.

» An oogonia multiplies by mitosis and then undergoes meiosis and stops at prophase I.

» They are now called primary oocytes.

» Oogenesis begins in the female embryo when primordial germ cells differentiate into oogonia--ovary specific stem cells.

» An oogonia multiplies by mitosis and then undergoes meiosis and stops at prophase I.

» They are now called primary oocytes.

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OogenesisOogenesis» At puberty, the

primary oocytes are stimulated by FSH (anterior pituitary), grow, complete meiosis I and enter meiosis II stopping at metaphase II.

» Ovulation occurs and the secondary oocyte is now released from the follicle.

» At puberty, the primary oocytes are stimulated by FSH (anterior pituitary), grow, complete meiosis I and enter meiosis II stopping at metaphase II.

» Ovulation occurs and the secondary oocyte is now released from the follicle.

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FertilizationFertilization

» When a sperm penetrates the egg, meiosis continues to completion and an ovum is formed. The union of the sperm with the ovum forms a zygote.

» The meiotic divisions of the ovum are uneven and small cells called polar bodies are given off.

» When a sperm penetrates the egg, meiosis continues to completion and an ovum is formed. The union of the sperm with the ovum forms a zygote.

» The meiotic divisions of the ovum are uneven and small cells called polar bodies are given off.

Copyright ©2005 Pearson Education, Inc. Publishing as Pearson Benjamin Cummings. All rights reserved.

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Embryonic Development of Sperm

Embryonic Development of Sperm»During embryonic

development, primordial germ cells of embryonic testes differentiate into spermatogonia which eventually give rise to sperm.

»During embryonic development, primordial germ cells of embryonic testes differentiate into spermatogonia which eventually give rise to sperm.

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Sperm DevelopmentSperm Development

» Spermatogonia differentiate into spermatocytes and then into spermatids.

» While this is happening, meiosis is reducing the chromosome number in half.

» Spermatogonia differentiate into spermatocytes and then into spermatids.

» While this is happening, meiosis is reducing the chromosome number in half.

www.luc.edu/faculty/wwasser/dev/sertoli.gif&imgrefurl

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SpermSperm» Most species have sperm with a

head that contains the nucleus and a tip called a acrosome that has enzymes which exist as entry of the sperm into the egg.

» Behind the head of the sperm is the midpiece that contains a large number of mitochonria which help to power the tail (flagellum).

» Most species have sperm with a head that contains the nucleus and a tip called a acrosome that has enzymes which exist as entry of the sperm into the egg.

» Behind the head of the sperm is the midpiece that contains a large number of mitochonria which help to power the tail (flagellum).


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3 Main Differences Between

Spermatogenesis and Oogenesis



» 1. Meiotic divisions of oogenesis are unequal. A single daughter cell becomes a secondary oocyte and the other products of cell division are called polar bodies and they degenerate.

» 1. Meiotic divisions of oogenesis are unequal. A single daughter cell becomes a secondary oocyte and the other products of cell division are called polar bodies and they degenerate.

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» 2. Most cells from which eggs arise are not thought to be from cells which continuously arise.

» 3. Oogenesis has long resting periods. By contrast, sperm are produced continuously.

» 2. Most cells from which eggs arise are not thought to be from cells which continuously arise.

» 3. Oogenesis has long resting periods. By contrast, sperm are produced continuously.

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Female Mammalian Cycles

Female Mammalian Cycles

» There are two different types of cycles in female mammals.»1. Menstrual Cycles--humans and

other primates.»2. Estrous Cycles--other

mammals.

» There are two different types of cycles in female mammals.»1. Menstrual Cycles--humans and

other primates.»2. Estrous Cycles--other

mammals.

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Differences Between Cycles

Differences Between Cycles

» The difference between the two types of cycles involves the fate of the endometrial lining if pregnancy doesn’t occur.» In menstrual cycles, the uterine

lining (endometrium) gets sloughed off.

» In estrous cycles, the endometrium gets reabsorbed.»Estrus is the period of sexual activity

surrounding the period of ovulation. It is sometimes called “heat.”

» The difference between the two types of cycles involves the fate of the endometrial lining if pregnancy doesn’t occur.» In menstrual cycles, the uterine

lining (endometrium) gets sloughed off.

» In estrous cycles, the endometrium gets reabsorbed.»Estrus is the period of sexual activity

surrounding the period of ovulation. It is sometimes called “heat.”

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Human Female Reproductive Cycle

Human Female Reproductive Cycle

» The human female reproductive cycle is sometimes called the menstrual cycle and can be broken into 2 phases:»The uterine cycle»The ovarian cycle

» The human female reproductive cycle is sometimes called the menstrual cycle and can be broken into 2 phases:»The uterine cycle»The ovarian cycle

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The Ovarian CycleThe Ovarian Cycle» It has 8 stages:» 1. The cycle begins

with a release of GnRH from the hypothalamus.

» 2. GnRH stimulates the anterior pituitary to secrete small amounts of FSH and LH.

» 3. FSH is aided by LH and stimulates follicle growth.

» It has 8 stages:» 1. The cycle begins

with a release of GnRH from the hypothalamus.

» 2. GnRH stimulates the anterior pituitary to secrete small amounts of FSH and LH.

» 3. FSH is aided by LH and stimulates follicle growth.

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The Ovarian CycleThe Ovarian Cycle

» 4. The growing follicles start making estrogen.»The follicular

phase is the part of the cycle where the follicles are growing and oocytes are maturing. Several follicles grow, but only one matures.

» 4. The growing follicles start making estrogen.»The follicular

phase is the part of the cycle where the follicles are growing and oocytes are maturing. Several follicles grow, but only one matures.

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» 5. The estrogen level rises sharply as a result of the growing follicle and this causes the LH and FSH levels to rise as well.

» In a positive feedback mechanism, the high levels of estrogen stimulate the release of GnRH by the hypothalamus.

» 5. The estrogen level rises sharply as a result of the growing follicle and this causes the LH and FSH levels to rise as well.

» In a positive feedback mechanism, the high levels of estrogen stimulate the release of GnRH by the hypothalamus.

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» 6. The positive feedback increases the LH level further and this induces the final maturation of the follicle.

» 6. The positive feedback increases the LH level further and this induces the final maturation of the follicle.

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» 7. The maturing follicle develops an internal fluid filled cavity and a very large bulge. About a day after the LH surge, ovulation occurs and a secondary oocyte is released.

» 7. The maturing follicle develops an internal fluid filled cavity and a very large bulge. About a day after the LH surge, ovulation occurs and a secondary oocyte is released.

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» 8. During the luteal phase, LH stimulates transformation of the follicular tissue left behind to form the corpus luteum--a glandular structure.

» If the corpus luteum is continually stimulated by LH, it will secrete progesterone and estrogen.

» 8. During the luteal phase, LH stimulates transformation of the follicular tissue left behind to form the corpus luteum--a glandular structure.

» If the corpus luteum is continually stimulated by LH, it will secrete progesterone and estrogen.

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» As the combined estrogen and progesterone levels increase, negative feedback occurs on the hypothalamus and pituitary and LH & FSH secretion is inhibited.

» As the combined estrogen and progesterone levels increase, negative feedback occurs on the hypothalamus and pituitary and LH & FSH secretion is inhibited.

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» At the end of the luteal phase, the corpus luteum disintegrates, estrogen and progesterone drop sharply, and the hypothalamus and pituitary are no longer inhibited.

» The cycle can then repeat.

» At the end of the luteal phase, the corpus luteum disintegrates, estrogen and progesterone drop sharply, and the hypothalamus and pituitary are no longer inhibited.

» The cycle can then repeat.

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The Uterine CycleThe Uterine Cycle» Estrogen and

progesterone have a major effect on the uterus.

» Estrogen stimulates the endometrium to thicken.

» In this way, the follicular phase of the ovarian cycle is coordinated with the proliferative phase of the uterine cycle.

» Estrogen and progesterone have a major effect on the uterus.

» Estrogen stimulates the endometrium to thicken.

» In this way, the follicular phase of the ovarian cycle is coordinated with the proliferative phase of the uterine cycle.

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The Uterine CycleThe Uterine Cycle» 9. After ovulation,

the estrogen and progesterone secreted by the corpus luteum stimulate continued development and maintenance of the endometrium.

» There is also an enlargement of arteries and growth of endometrial glands.

» 9. After ovulation, the estrogen and progesterone secreted by the corpus luteum stimulate continued development and maintenance of the endometrium.

» There is also an enlargement of arteries and growth of endometrial glands.

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The Uterine CycleThe Uterine Cycle

» The glands secrete fluid that helps to maintain an embryo before implantation.

» The luteal phase is coordinated with the secretory phase.

» The glands secrete fluid that helps to maintain an embryo before implantation.

» The luteal phase is coordinated with the secretory phase.

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The Uterine CycleThe Uterine Cycle

» 10. The quick drop in ovarian hormone levels triggers the menstrual flow phase.

» The first day of menstruation is the first day of the ovarian cycle.

» During menstruation, the endometrium disintegrates and is sloughed off.

» 10. The quick drop in ovarian hormone levels triggers the menstrual flow phase.

» The first day of menstruation is the first day of the ovarian cycle.

» During menstruation, the endometrium disintegrates and is sloughed off.

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Hormonal Control of the Testes

Hormonal Control of the Testes

» GnRH is released by the hypothalamus.

» This triggers the release of FSH and LH from the anterior pituitary.

» FSH stimultates the Sertoli cells, inducing spermatogenesis.

» LH acts on the Leydig cells stimulating testosterone production.

» GnRH is released by the hypothalamus.

» This triggers the release of FSH and LH from the anterior pituitary.

» FSH stimultates the Sertoli cells, inducing spermatogenesis.

» LH acts on the Leydig cells stimulating testosterone production.

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Sexual CharacteristicsSexual Characteristics

» Testosterone and androgens are responsible for the primary and secondary sex characteristics.

» Androgens are also potent determiners of behavior: sexual behavior, sex drive, singing of frogs, etc.

» Testosterone and androgens are responsible for the primary and secondary sex characteristics.

» Androgens are also potent determiners of behavior: sexual behavior, sex drive, singing of frogs, etc.

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» Primary sex characteristics:» Development of vasa

differentia and other ducts.

» Development of external reproductive structures.

» Sperm production.

» Primary sex characteristics:» Development of vasa

differentia and other ducts.

» Development of external reproductive structures.

» Sperm production.

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» Secondary sex characteristics:»Deepening of voice, facial and

pubic hair.»Muscle growth.

» Secondary sex characteristics:»Deepening of voice, facial and

pubic hair.»Muscle growth.

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Early DevelopmentEarly Development» About 1 week after

conception, cleavage of the developing zygote results in the blastocyst (a sphere of cells with a cavity).

» About 1 week after conception, cleavage of the developing zygote results in the blastocyst (a sphere of cells with a cavity).


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Early DevelopmentEarly Development

» The blastocyst then implants on the endometrial wall.

» HCG is secreted by the developing embryo and signals its presence.



» HCG is secreted by the developing embryo and signals its presence.




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Human GestationHuman Gestation

»Human gestation is divided into three trimesters.

»During the 1st trimester, there is a dramatic change for mom and the embryo.

» The endometrium grows over the blastocyst.

» The embryo begins to differentiate.

»Human gestation is divided into three trimesters.

»During the 1st trimester, there is a dramatic change for mom and the embryo.

» The endometrium grows over the blastocyst.

» The embryo begins to differentiate.

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Human Gestation Trimester 1


» During the 1st 2-4 weeks, the embryo gets its nutrients from the endometrium.

» The outer layer of the blastocyst is called the trophoblast. It mixes with the endometrium and eventually helps to form the placenta.

» The placenta serves as the exchange point between the embryo and mother through which nutrients and wastes travel by diffusion.

» During the 1st 2-4 weeks, the embryo gets its nutrients from the endometrium.

» The outer layer of the blastocyst is called the trophoblast. It mixes with the endometrium and eventually helps to form the placenta.

» The placenta serves as the exchange point between the embryo and mother through which nutrients and wastes travel by diffusion.

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» The first trimester is the main period of organogeneisis.

» The heart begins to beat around week 4.

» At 8 weeks, the embryo is now called the fetus.

» The first trimester is the main period of organogeneisis.

» The heart begins to beat around week 4.

» At 8 weeks, the embryo is now called the fetus.

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» In mom, high levels of progesterone and stimulates formation of the mucous plug, growth of the maternal part of the placenta, enlargement of the uterus, and cessation of ovulation.

» Breast enlargement also occurs.

» In mom, high levels of progesterone and stimulates formation of the mucous plug, growth of the maternal part of the placenta, enlargement of the uterus, and cessation of ovulation.

» Breast enlargement also occurs.

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»During the second trimester, fetal activity increases.

»Hormone levels stabilize.»HCG decreases.» The corpus luteum

deteriorates.» The placenta takes over

production of progesterone. » Pregnancy is now obvious.

»During the second trimester, fetal activity increases.

»Hormone levels stabilize.»HCG decreases.» The corpus luteum

deteriorates.» The placenta takes over

production of progesterone. » Pregnancy is now obvious.

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» Fetal activity decreases.»Mom’s abdominal organs are

displaced.» It ends with labor.» Estrogen is at its highest levels

during the last weeks of pregnancy--it induces the formation of oxytocin receptors.

» Fetal activity decreases.»Mom’s abdominal organs are

displaced.» It ends with labor.» Estrogen is at its highest levels

during the last weeks of pregnancy--it induces the formation of oxytocin receptors.

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LaborLabor

» Positive feedback underlies the process of labor.

» Oxytocin produced by the posterior pituitary stimulates contraction of the smooth muscles of the uterus.

» Additionally, oxytocin stimulates the placenta to release prostaglandins which enhance contractions.

» Positive feedback underlies the process of labor.

» Oxytocin produced by the posterior pituitary stimulates contraction of the smooth muscles of the uterus.

» Additionally, oxytocin stimulates the placenta to release prostaglandins which enhance contractions.

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LaborLabor

» Birth is brought about by a series of strong rhythmic contractions of the uterus.

» This forces the fetus out.

» Birth is brought about by a series of strong rhythmic contractions of the uterus.

» This forces the fetus out.

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LactationLactation

» Lactation is unique to mammals.» After birth, progesterone levels

decrease and the anterior pituitary is freed from the negative feedback and allows for prolactin to be secreted.

» Prolactin stimulates milk production.» The release of milk is controlled by

oxytocin.

» Lactation is unique to mammals.» After birth, progesterone levels

decrease and the anterior pituitary is freed from the negative feedback and allows for prolactin to be secreted.

» Prolactin stimulates milk production.» The release of milk is controlled by

oxytocin.

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Travismulthaupt.com Chapter 46 Animal Reproduction