1. Reproduction
Keri Muma
Bio 6

2. Functions of the Reproductive System
Secretion of sex hormones – influence growth and development of organs and tissues
Production of gametes – sperm and ova
Male gonads  testes  sperm
Female gonads  ovaries  eggs
Produce offspring
Male – deliver sperm to the female reproductive tract
Female – provide an environment for fetus development

3. The human life cycle In humans: Fertilization
Stem cells within the gonads are diploid 2(n) = Contain two sets of chromosomes
Gametes are haploid (n) = having only one set of chromosomes
Fertilization
Is the fusion of sperm and egg
Creates a zygote (2n), or fertilized egg

4. Sex Determination
Inheritance of X and Y chromosomes
Sex chromosomes

5. Sex Determination
Bipotential stage: during the first 6 weeks of fetal development the internal reproductive organs have the potential to develop into male or female structures.
Bipotential tissues
Gonad
Testis or ovary
Wolffian duct
Male
Mullerian duct
Female

6. Embryonic Development: Males
Role of SRY gene in male development – found on the Y chromosome
Gonad medulla differentiates into testis
Sertoli cells – secrete anti-Mullerian hormone
Leydig cells – secrete testosterone and dihydrotestosterone (DHT)
Figure 26-4

7. Embryonic Development: Females
Do not have the Y chromosome so they lack the SRY gene to produce SRY proteins
Gonadal cortex becomes the ovaries
Wolffian ducts degenerates in absence of testosterone
Mullerian ducts become
Vagina
Uterus
Fallopian tubes

8. Development of Internal Organs
Gonadal cortex becomes
ovary in the absence
of SRY protein.
Absence of testosterone
causes Wolffian duct
to degenerate.
SRY protein in a male
embryo directs the
medulla of the
bipotential gonad
to develop into testis.
FEMALE
MALE
Bipotential
gonad
Müllerian duct
Uterus
(a)
Development of internal organs
Ovary
Vagina
Fallopian tube
(from Müllerian
duct)
Testis
Prostate
Seminal vesicle
Vas deferens
Wolffian
duct
Epididymis
Cloacal
opening
Kidney
Anti-Müllerian hormone
from testis causes the
Müllerian ducts to
degenerate.
Absence of anti-Müllerian
hormone allows the
to become
the fallopian
tube, uterus,
and upper part
of the vagina.
Bipotential stage: 6 weeks of fetal development
The internal reproductive organs have the potential
to develop into male or female structures.
Testosterone from
testis converts Wolffian
duct into seminal
vesicle, vas deferens,
and epididymis. DHT
controls prostate
development.
10 WEEKS
AT BIRTH 1 2 3
Figure 23-3a (6 of 6)

9. Development of External Genitalia
Bipotential stage
(6 week fetus)
FEMALE
MALE
Urethral fold
Urethral
fold
groove
Labioscrotal
swelling
Anus
Genital tubercle
Shaft of penis
Glans penis
Scrotum
Clitoris
Labia
majora
minora
opening
Vaginal
Penis
10 WEEKS
AT BIRTH
DHT causes
development
of male external
genitalia.
The testes descend
from the abdominal
cavity into the
scrotum.
In the absence
of androgens,
the external genitalia
are feminized.
(b)
Development of external genitalia 1 2
Figure 26-3b

10. Sex Determination

11. Chromosome Review Humans have 23 pairs of chromosomes
Each somatic cell has two sets of chromosomes (one maternal, one paternal) and is said to be diploid (2n)
Each pair of homologous chromosomes carry equivalent genes which determine particular traits
There is alternative forms of each gene which are called alleles
Gametes only have 23 chromosomes and are said to be haploid (n)

12. Purpose of Meiosis
Meiosis is a type of cell division that produces gametes (sperm and ova) from stem cells in the reproductive tissue
Reduces the original number of chromosomes in half in preparation for fusing with another gamete
Recombination (scrambling) of parents’ genomes to create a unique set of chromosomes in each gamete

13. Meiosis
In meiosis there is two rounds of division which results in 4 haploid cells
1st round separates duplicated homologous chromosomes
2nd round separates sister chromatids

14. Interphase Occurs prior to Prophase I of meiosis
Homologous chromosomes replicate (same as mitosis)

15. Meiosis I
Prophase I
Duplicated homologous chromosomes pair up (tetrads)
Crossing over occurs: homologous chromosome exchange equivalent segments
Occurs between non-sister chromatids
How are non-sister chromatids different from sister chromatids?

16. Meiosis I
Metaphase I
Homologous chromosomes line up in pairs along the central plane in tetrads
Independent assortment: which side each chromosome lines up on is independently of the other pairs

17. Meiosis I Anaphase I Telophase I and Cytokinesis
Homologous chromosomes are separated and move to opposite poles
Telophase I and Cytokinesis
Two haploid cells are formed

18. Meiosis II
Prophase II
Metaphase II
Sister chromatids line up

19. Meiosis II Anaphase II Telophase II and Cytokinesis
Sister chromatids separate and are pulled towards opposite poles
Telophase II and Cytokinesis
Results in 4 haploid gametes

20. Three factors contributing to genetic recombination
1. Crossing over during prophase and metaphase I
Additional mixing of alleles produces further variation in offspring

21. Three factors contributing to genetic recombination
2. Independent assortment of chromosomes in Metaphase I & II
Total # of chromosome combinations = 2n Humans 223 = 8 million combinations

22. Three factors contributing to genetic recombination
3. Random fertilization - egg is fertilized randomly by one sperm
8 million x 8 million = 64 TRILLION possibilities (not considering crossing over)

23. Gametogenesis Gametogenesis – production of gametes
Begins in utero and resumes during puberty
Mitotic divisions in embryonic gonads increases number of spermatogonia or oogonia
DNA replication (S-phase)  primary gametes with 46 duplicated chromosome
Meiosis I  secondary gametes with 23 duplicated chromosomes
Meiosis II  egg or spermatid with 23 chromosomes
At about 5 months there is 6-7 million oogonia in the prenatal ovaries  some die by apoptosis and newborns have about 2 million oocytes  400,000 by puberty  about 400 are ovulated

24. Gametogenesis Figure 26-5
Second meiotic
division
Secondary gamete divides.
23 chromosomes
(haploid)
Disintegrates
Second polar body
disintegrates.
Zygote
Reproductive adult
(may not
occur)
Egg released
from ovary at
ovulation
One primary oocyte
yields 1 egg.
FERTILIZATION
Unfertilized egg passes
out of body.
FEMALE
MITOSIS
STAGE OF CELL DIVISION
Germ cell proliferation
46 chromosomes
per cell (only two
shown here) 46
(diploid)
Sister
chromatids
MEIOSIS
DNA replicates but
no cell division occurs.
2 sets of 46
chromosomes
First meiotic
Primary gamete divides
into two secondary gametes.
duplicated
Oögonium
Embryo
Oögonia
Primary
oocyte
Secondary
(egg)
First
polar
body
MALE
Spermatogonia
spermatocyte
Spermatogonium
Spermatids
Sperm
One primary spermatocyte
yields 4 sperm.
develop into
In females the secondary oocyte is arrested in Metaphase II until fertilization occurs.
Figure 26-5

25. Spermatogenesis Production of sperm cells
Begins at puberty and continues throughout life
Occurs in the seminiferous tubules

26. Regulation of Spermatogenesis
GnRH  LH  Leydig cells  testosterone  sex characteristics
GnRH  FSH  Sertoli cells  spermatocyte maturation
Inhibin triggers negative feedback loop for FSH secretion
Testosterone triggers negative feedback loop for LH and GnRH secretion

27. Regulation of SpermatogenesisLH
GnRH
Hypothalamus
Anterior
pituitary
Inhibin
Testes
Leydig
cells
Testosterone (T)
To body
for secondary
effects
FSH
Integrating center
Efferent pathway
Effector
Tissue response
Sertoli
cell
Cell
products
Second
messenger
ABP T
Androgen-binding
protein (ABP)
Spermatogonium
Spermatocyte
KEY
Figure 26-11

28. Oogenesis Process in which haploid ova are produced by meiosis
The total supply of primary follicles are present at birth
Ability to release eggs begins at puberty

29. Menstrual Cycle in Females
Ovarian cycle – changes that occur in the ovaries
Follicular phase – follicular growth in ovary, increased sensitivity to FSH and increase in estrogen production
Ovulation – ova released from ovary, triggered by surge in LH
Luteal phase – corpus luteum produces hormones to prepare for pregnancy, estrogen and progesterone

30. The Menstrual and Uterine Cycles
Follicular Phase
Luteal Phase
Phases of the
Uterine Cycle
Primary
follicle
Theca
Ovulation
Corpus
luteum
formation
Mature
corpus
Ovarian Cycle
Basal body
temperature
(˚C)
Uterine
cycle
Ovarian
hormone
levels
Gonadotrophic
MENSES
PROLIFERATIVE
PHASE
SECRETORY PHASE
Inhibin
Estrogen
Antrum
FSH
36.4
36.7
DAYS
28/0 7 14 21
albicans LH
Progesterone
Figure (4 of 4)

31. Oogenesis
Corpus luteum – remnants of the ovulated follicle, produces increasing amounts of progesterone and some estrogen for two weeks
If fertilization does not occur –it degenerates into scar tissue and drop in hormones triggers menstruation
If fertilization occurs – the oocyte secretes human chorionic gonadotropin (hCG) which causes the corpus luteum to persist so the menstrual cycle will not be initiated

32. Menstrual Cycle in Females
Uterine cycle – changes in the endometrial lining of the uterus
Menses- shedding of the lining, triggered by drop in progesterone and estrogen
Proliferation phase – endometrial lining adds new layers, influenced by increase in estrogen
Secretory phase – increased blood flow to endometrium, increased glandular secretions, influenced by increase in progesterone

33. The Menstrual and Uterine Cycles
Follicular Phase
Luteal Phase
Phases of the
Uterine Cycle
Primary
follicle
Theca
Ovulation
Corpus
luteum
formation
Mature
corpus
Ovarian Cycle
Basal body
temperature
(˚C)
Uterine
cycle
Ovarian
hormone
levels
Gonadotrophic
MENSES
PROLIFERATIVE
PHASE
SECRETORY PHASE
Inhibin
Estrogen
Antrum
FSH
36.4
36.7
DAYS
28/0 7 14 21
albicans LH
Progesterone
Figure (4 of 4)

34. Hormonal Control of the Menstrual CycleLH
FSH
GnRH
Androgens
Estrogens
Follicle
Granulosa
cells
Thecal
New follicles
begin to
develop
Corpus
luteum
dies
Tonic secretion
resumes
Corpus luteum
Progesterone
Ovum
Estrogen and
progesterone
Stimulus
Integrating center
Efferent pathway
Tissue response
(from ovulated
follicle)
Estrogen
Inhibin
secretes
Early to mid-follicular phase
Late follicular phase and ovulation
Late luteal phase
Early to mid-luteal
phase
High estrogen
output
Small amount of
KEY
Pituitary
Hypothalamus
(a)
(b)
(d)
(c)
Figure (4 of 4)

35. Fertilization

36. Ovulation, Fertilization, and Implantation
Blastocyst
Inner cell
Days 5-9:
Blastocyst implants.
Ovulation
Day 1:
Fertilization
Days 2-4: Cell
division takes place.
Days 4-5: Blastocyst
reaches uterus.
Zygote
Fallopian
tube
Egg
Uterus
Ovary 3 2 4 1 5
Implantation usually occurs on the 7th day after fertilization
Corpus Luteum produces progesterone until the placenta takes over around 10 weeks gestation.
Inner mass of cells will become the baby and the trophoblast will later become the placenta and umbilical cord. The trophoblast cells produce the hCG.
Figure 26-18, steps 1–5