AP Biology 2005-2006 Animal Reproduction Chapter 46.

AP Biology 2005-2006

Animal Reproduction

Chapter 46


Sexual & asexual reproduction Asexual

offspring all have same genes (clones) no variation

Sexual gametes (sperm & egg) fertilization mixing of genes variation

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Parthenogenesis Development of an unfertilized egg

honey bees drones = males produced through

parthenogenesis haploid workers & queens = females produced from

fertilized eggs diploid

queen worker drone


Different strokes…

parthenogenesis in aphids

sex-change in fish

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Hermaphrodites

flat worm

earthworms mating

Having functional reproductive system of both sexes


Fertilization Joining of egg & sperm

external usually aquatic animals

internal usually land animals


Development External

development in eggs fish & amphibians in water

soft eggs= exchange across membrane birds & reptiles on land

hard-shell amniotic eggs structures for exchange of food, O2 & waste

sharks & some snakes live births from eggs

Internal placenta

exchange food & waste live birth


Adaptive advantages? What is the adaptive value of each

type of sexual reproduction number of eggs? level of parental care habitat?


Human Reproduction: Reproductive hormones Testosterone

from testes Functions

Prenatal development of male genitalia

sperm production 2° sexual characteristics Maintenance of sex

drive Estrogen

from ovaries functions

egg production prepare uterus for

fertilized egg 2° sexual characteristics

LH &FSH

testesor

ovaries


Sex hormone control in males

Hypothalamus

Pituitary

Testes

Body cells

GnRH

FSH & LH

testosterone


Sperm production over 100 million produced per day! ~2.5 million released per drop!

Male reproductive system

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Male reproductive system Testes

produces sperm & hormones Scrotum

sac that holds testicles outside of body Epididymis

where sperm mature Vas deferens

tubes for sperm to travel from testes to penis Prostate, seminal vesicles,

Cowper’s (bulbourethal) glands nutrient rich fluid to feed & protect sperm buffer to counteract acids in vagina


Male reproductive system

Testes & epididymis sperm production &

maturation

Glands seminal vesicles,

prostate, bulbourethal produce seminal fluid =

nutrient-rich

seminiferous tubule

sperm

spermatocytes

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Spermatogenesis Spermatogenesis

occurs within each testis in small tubules called seminiferous tubules

This light micrograph shows a cross section of seminiferous tubules, blood vessels and the

interstitial Leydig cells.Leydig cells are responsible for the production of testosterone.

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Spermatogenesis Mitosis and meiosis

may be taking place at any time in the spermatogonia. Mitosis replenishes numbers of cells, meiosis produces actual sperm (spermatozoa)

Sertoli cells help nourish sperm cells during meiosis


SpermatogenesisEpididymis Testis

Coiledseminiferoustubules

Vas deferens

Cross-section ofseminiferous tubule

Spermatozoa

Spermatids(haploid)

2°spermatocytes

(haploid)

1°spermatocyte

(diploid)

Germ cell (diploid)

MEIOSIS II

MEIOSIS I

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Hormonal control of sperm production

LH (Leutinizing hormone) stimulates Leydig cells to produce testosterone

FSH (follicle-stimulating hormone) and testosterone stimulate meiosis in spermatogonia to produce spermatozoa

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Role of epididymis, seminal vesicles, and prostate in semen production

Sperm cells were produced in seminiferous tubules, carried thru the lumen, and sent to the epididymis. They are stored briefly in the epididymis.

On sexual arousal, millions of sperm cells are moved from the epididymis into the vas deferens.

Seminal vesicles add large volume of fluid which has a high conc. of fructose for energy for the sperm cells to swim (approx. 70% of the fluid in

semen is added by the seminal vesicles.) The prostrate adds more fluid: alkalinewhich helps the sperm survive the acidicenvironment in a female’s vagina.

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Female reproductive system

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Female reproductive system Ovaries

produces eggs & hormones Uterus

nurtures fetus; lining builds up each month Fallopian tubes

tubes for eggs to travel from ovaries to uterus

Cervix opening to uterus, dilates 10cm (4 inches)

for birthing baby Vagina

birth canal for birthing baby

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Female reproductive system

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Menstrual cycle Starting at puberty, human females

begin a hormonal cycle called the menstrual cycle. Each cycle lasts (on average) 28 days.

The purpose is to time the release of an egg (ovum) for possible fertilization and later implantation into the inner lining of the uterus (endometrium)

•The implantation must occur when the endometrium is rich with blood vessels.

•The breakdown of the blood vessels leads to menstrual bleeding (menstruation); a sign that no pregnancy has occurred

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Hormones

Hypothalamus

Pituitary

Ovaries

Endometrium of uterus

GnRH

FSH & LH

estrogen progesterone

regulatory center for the menstrual cycle.

The hypothalamus produces a hormone called GnRH (gonadotrophin-releasing hormone).

The target tissue of GnRH is the anterior pituitary gland, which results in the pituitary producing and secreting 2 hormones into the bloodstream:

FSH and LH.

The target tissues for these 2 hormones are the ovaries

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Effects of FSH and LH on the ovaries To increase the production and secretion of estrogen

by the follicle cells of the ovary Estrogen enters the bloodstream Its target tissue is the endometrium of the uterus Result is growth of lining (increase in blood

vessels) Stimulates egg development in ovaries


Egg maturation in ovary A spike in levels of FSH and

LH leads to ovulation (release of oocyte from the follicle)

The outer ring of follicle cells begin to divide and fill in the ‘wound’ area left by ovulation which forms a corpus luteum. The corpus luteum produces progesterone for 10-12 days after ovulation.

Progesterone (hormone) maintains the thickened endometrium

If no pregnancy, the corpus luteum eventually breaks down = less estrogen and

progesterone

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LH

FSH

egg development ovulation = egg release

corpus luteum

estrogen

progesterone

lining of uterus

days 0 7 14 21 28

Menstrual cycle

… as estrogen and progesterone levels fall, the highly vascular endometrium can no longer be maintained. The capillaries begin to rupture and menstruation begins.

The drop in progesterone and estrogen also signals the hypothalamus to begin secreting GnRH and another menstrual cycle begins.


Oogenesis

Meiosis 2 completedtriggered by fertilization

ovulation

In ovaries, cells called oogonia go thru mitosis repeatedly to build up numbers of cells. Then those oogonia grow into larger cells (primary oocytes) and start meiosis, but the process stops at Prophase I, until puberty.

Then FSH periodically stimulates a follicle to grow and induces its primary oocyte to complete meiosis I and start meiosis II

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Comparison of spermatogenesis and oogenesis

Millions of sperm produced every day

4 gametes for every cell that begins meiosis

Very small Occurs in testis Released during

ejaculation Haploid nuclei Continues throughout all

of life, starting at puberty

One egg is ovulated per menstrual cycle

One gamete is produced for each cell that begins meiosis (plus polar bodies)

Eggs are ‘large’ Occurs in ovaries Released during ovulation Haploid nuclei Ovulation starts at puberty,

occurs with each menstrual cycle, then stops at menopause

Spermatogenesis Oogenesis

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Fertilization


Fertilization Enzymes from acrosome are released at the zona pellucida.

Sperm head enters egg, plasma membranes fuse together. This initiates the cortical reaction.

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Fertilization and the cortical reaction

As soon as the sperm reaches the nucleus, the cortical granules fuse with the cell membrane and release their enzymes to the outside, making it impermeable to any other sperm cells.


Early human embryonic development: Cleavage Fertilization triggers the zygote to start repeated

mitotic divisions as it moves down the Fallopian tube toward the uterus

By the time the embryo reaches the uterus, it is approx. 100 cells and is ready to implant into the endometrium of the uterus. At this point, it’s a hollow ball of cells called a blastocyst.

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A few days later, the embryo imbeds itself in the uterine lining. At this point, a woman's body begins to secrete a pregnancy hormone known as HCG. This hormone maintains production of progesterone from the ovary, a crucial factor in maintaining a pregnancy.

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HCG specifics HCG = Human Chorionic Gonadotrophin. It enters the bloodstream of the mother its target tissue is the corpus luteum. HCG

acts to maintain the secretory functions of this gland beyond the length of time typical of a normal menstrual cycle. The corpus luteum continues to make both estrogen and progesterone and the endometrium is maintained.

Later on in pregnancy, the placenta will take over estrogen and progesterone production.

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OrganogenesisUmbilical blood vessels

Chorion

Amnion

Yolksac

AllantoisFetal blood vessels

Maternal blood vessels

Bird embryo

Mammalian embryo

Placenta


Placenta Materials exchange across membranes

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Role of the PlacentaWhen fully formed, 2 fetal blood

vessels within the umbilical cord carry fetal blood to the placenta. The blood is deoxygenated and carries waste products (CO2, urea, hormones). This fetal blood exchanges materials (not blood) with the maternal bloodstream.

Another fetal blood vessel returns the ‘clean’ blood to the fetus (has oxygen and nutrients, hormones)

At no time do the 2 bloods actually mix

When the corpus luteum stops producing estrogen and progesterone, the placenta starts producing and secreting them.

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Role of the amniotic fluid Amniotic sac extends all the

way around the fetus The fluid within it is called

amniotic fluid Several functions:

Provides cushioning effect if something happens to mom’s abdomen

•Provides safe environment where fetus has free movement and can exercise its developing muscles and skeleton

•Provides temperature stability


Human fetal development

7 weeks4 weeks


Human fetal development10 weeks


Human fetal development

12 weeks 20 weeks


Human fetal development 24 weeks (6 months; 2nd trimester)

fetus is covered with fine, downy hair called lanugo. Its skin is protected by a waxy material called vernix


Human fetal development 30 weeks (7.5 months)

umbilical cord


Getting crowded in there!! 32 weeks (8 months)

The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming

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Birth

Hormone induction

positive feedback


Intestine

Placenta

Umbilicalcord

Wall ofuterus

VaginaCervix

Birth (36 weeks)

Bladder

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The end of the journey!

AP Biology 2005-2006 Animal Reproduction Chapter 46.

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Transcript of AP Biology 2005-2006 Animal Reproduction Chapter 46.