AP Biology Animal Form and Function

1
AP Biology Animal Form and Function

• Reproductive System

2
Reproductive SystemProduction of Eggs and Sperm

• Characteristics that distinguish the sexes
• Primary sex characteristicsstructures directly
  involved in reproduction (ovaries, uterus,
  testis)
• Secondary sex characteristicsnoticeable physical
  characteristics that differ between males and
  females (facial hair,
• deepness of voice, breasts,
• and muscle distribution)

3
Meiosis

• In order for the newly formed organism to have
  the same number of chromosomes as its parents,
  the chromosome number must be halved when the egg
  and sperm are made.
• This is accomplished by a process called meiosis.
  Then, when one sperm successfully fertilizes the
  egg, the diploid chromosome number is restored

Each sperm cell surrounding this egg cell is
trying to enter it and leave its packet of
genetic information in the form of chromosomes
containing DNA. Only one will be successful.
4
Male Reproductive Organs

• Sperm cells are produced in the testis. Males
  have two testes, located in a sac called the
  scrotum.
• A portion of the testis called the seminiferous
  tubules is where the sperm cells are actually
  made.

5
Spermatogenesis

• Sperm cells begin as diploid body cells located
  in the testes called Primary Spermatocytes.
• After dividing in Meiosis I, they are now haploid
  cells called Secondary Spermatocytes
• After dividing again in Meiosis II, they are
  called spermatids.
• They then mature into sperm cells in the
  epididymis

6
Interstitial Cells in Testes

• Most of the cells in the testes are destined to
  become sperm cells by meiosis.
• In between these cells are other cells, called
  Interstitial Cells.
• These are the structures that produce the
  hormones involved in the male reproductive
  system.

7
Epididymis

• After the sperm cells are formed by meiosis, they
  move into the epididymisthe coiled region
  extending from the testes.
• Here, the spermatids mature into sperm cells.

8
The Journey of the Sperm

• From the epididymis, the sperm moves through the
  vas deferens to the urethra
• The urethra is the tube that releases both sperm
  and urine (not at the same time!)

The seminal vesicles dump fluids into the vas
deferens as the sperm cells pass through. This
fluid adds fructose for energy, prostaglandins
(which stimulate uterine contractions) and mucus,
which helps the sperm swim more efficiently.

• The prostate gland adds a basic
• (pH gt7) liquid to the mix to help combat the
  acidity of the vaginal region of the female.

9
Female Reproductive System

• Ovarythe site of egg production
• The egg leaves the ovary before it is fully
  mature and enters a structure called the oviduct
  (aka Fallopian Tube)
• The oviduct carries the egg from the ovary to the
  uterus.

10
Fertilization

• When fertilized by a sperm cell in the oviduct
  (fallopian tube), after several days travelling
  in the tube, the egg will usually attach itself
  to the inner wall of the uterus (called the
  endometrium).

The uterus connects to the vaginal opening via a
narrowed portion called the cervix. The narrow
opening through which the sperm travels up to the
Fallopian tube is the vagina.
11
The Environment Through Which the Sperm Must
Travel

• As the sperm cells enter, they must survive the
  somewhat hostile environment that the female body
  presents
• Its task is to find its way to the fallopian
  tube, where it must meet the egg and penetrate
  its outer surface to achieve successful
  fertilization.

The sperm works its way through the vaginal
region, up through the cervix, through the
uterus, and into the fallopian tube. If the
timing is right, an egg is in the tube and the
sperm can fertilize the egg to produce a diploid
zygote.
12
Oogenesis
Oogenesisthe development of the egg, begins
while the female is still an unborn embryo. Some
of the fetal cells in the ovary of the embryo
begin meiosis and stop at Prophase I. These are
called Primary Oocytes and they stop further
meiosis and development until the female enters
puberty.
13
Oogenesis
After puberty begins, each month, one of the
Primary Ooctyes completes meiosis I. This
produces a polar body and one Secondary Oocyte, a
haploid cell. As the menstrual cycle continues,
ovulation frees the Secondary Oocyte to travel
into the Fallopian Tube.
14
Oogenesis
The Secondary Oocyte travels down the Fallopian
Tube and, if a sperm cell is present, may be
fertilized. If a successful fertilization occurs,
the secondary oocyte enters Meiosis II, again
producing a Polar Body, as well as an egg which
combines with the sperm to form an embryo.
15
Embryonic Development

• Embryonic development begins as soon as the egg
  is fertilized to produce a diploid zygote.
• This zygote then divides by mitosis many times
  without increasing the size of the embryo.
• During these cleavage divisions, cytoplasm is
  distributed unevenly to the daughter cells, but
  genetic information is distributed equally.
• Different cells will play different roles in the
  body of the future embryo.

16
Embryonic Development
By Day 4 after fertilization, the embryo is a
ball of cells called a morula. As it undergoes
the next round of divisions, fluid will fill the
middle and it will form a hollow ball of cells
called a blastula. The blastula has two parts
the inner cell mass which becomes the embryo and
a trophoblast, which becomes the placenta.
17
The Trophoblast

• The trophoblast aids in attaching the embryo to
  the endometrium (the inner wall of the uterus).
• It also produces human chorionic gonadotropin
  (HCG), which maintains the endometrium by
  ensuring the continued production of
  progesterone.

18
Gastrulation

• The next major stage of embryonic development is
  gastrulation.
• During gastrulation, cells separate into three
  primary layers called germ layers, which
  eventually give rise to the different tissues of
  an adult.

19
Endoderm, Mesoderm, Ectoderm

• The three germ layers of the embryo are the
  endoderm, mesoderm and ectoderm.
• Endoderm inner germ layer gives rise to the
  inner lining of the gut and the digestive system,
  liver, thyroid, lungs, and bladder
• Mesoderm intermediate germ layer gives rise to
  muscle, the circulatory system, reproductive
  system, excretory organs, bones, and connective
  tissues
• Ectoderm outer germ layer gives rise to the
  nervous system and skin, hair and nails.

20
How Do Cells Know What to Do?

• Induction the influence of one group of cells on
  the development of another through physical
  contact or chemical signaling.
• Hans Spemann, a German embryologist showed, for
  example, that the cells of the notocord influence
  the development of the neural plate (which
• eventually becomes the nervous system).
• When the notocord was transplanted into
• a different part of an embryo, the neural
• plate grew in the new location.

21
Homeotic Genes

• Homeotic genes regulate or direct the body plan
  of organisms.
• For example, a flys homeotic genes help
  determine how its segments will develop and which
  appendages should grow from each segment.
• Scientists interfering with the development of
  these animals have shown
• that mutations in these
• genes can lead to growth
• of organs where they
• should not be.

22
Homeotic Genes

• These genes regulate the body plan of animals.
• The DNA sequence of a homeotic gene that tells
  the cell where to put things is called the
  homeobox.
• The homeobox is similar in organism to organism
  and has been found to exist in
• a variety of organisms birds,
• humans, fish, and frogs.

23
Reproductive Hormones

• The hormones involved in human reproduction are
  LH, FSH, estrogen, progesterone, and
  testosterone.
• Estrogen and progesterone continually circulate
  in the female bloodstream. The hypothalamus
  monitors these levels to determine when to
  release certain hormones.
• When estrogen and progesterone are low, the
  hypothalamus secretes GnRH (gonadotropin-releasing
  hormone), which travels to the pituitary gland
  to induce the release of FSH and LH.

24
FSH and LH

• FSH Follicle-stimulating hormone (induces the
  development of the follicle that surrounds the
  primary oocyte during its development) it also
  causes the follicle to release estrogen
• LH luteinizing hormone
• (initiates ovulationthe
• release of a secondary
• oocyte from the ovary)

25
Effects of Birth Control Pills
26
Ovulation Caused by LH Surge

• The LH surge causes further release of estrogen
  and progesterone from the follicle (which has now
  become a structure called the corpus luteum).

The corpus luteum induces the thickening of the
endometrium, the site of future egg
attachment. At this point, the levels of estrogen
and progesterone elevate enough so that the
hypothalamus cuts off prodution of GnRH so that
the LH and FSH levels drop back down.
27
If Fertilization Occurs.

• If fertilization has occurred in the fallopian
  tube, and if the embryo attaches successfully to
  the uterine wall, HCG will be secreted, which
  works to keep the corpus luteum alive.
• As a result, estrogen and progesterone will
  remain high and will keep the endometrium intact.

Left Implanted Embryo at 6 days Right
Implanted Embryo at 6 weeks