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Human Reproduction
Anatomy of the human male
Main functions:
The production of sperm, the male gametes;
Spermatogenesis begins at puberty and continues until death;
Delivery of functional sperm to the female reproductive system
Anatomy of the human male
Anatomy of the human male
Production of Semen (a fluid comprised of):Sperm, which are expelled through the ducts during ejaculation (≈1% of semen volume);Glandular secretions that carry, nourish, and protect the sperm (mostly sugars & buffers)
Testes (plural):Glands that produce sperm; located outside abdominal cavity within the scrotum Scrotum ≡ (saclike pouch ≈ 1-3°C below normal body temperature - sperm can only form at this lower temperature)
How sperm leave the testes
Seminiferous tubules: carries/stores sperm in testes
Epididymis: a series of coiled ducts for maturation & temporary storage of sperm
Vas deferens: tube which carries sperm past connecting lubricating and support glands
How sperm leave the testes
Lubricating and support glands:
(a.) Seminal vesicles: secrete sugar-rich fluid that protects & nourishes sperm
(b.) Prostate gland: produces an alkaline fluid that neutralizes both urine in the male urethra and the acidic environment of the vagina
(c.) Bulbourethral glands: secrete fluids that lubricates the male urethra and allows easier coitus (intercourse)
How sperm leave the testes
Urethra: tube in the penis that transports semen out of the male’s body; also transports urine from the urinary bladder
Penis: copulatory organ; transient tumescence
Ejaculation: the release of semen through rhythmic contractions of smooth muscle in the Vas deferens
Anatomy of the human male
Anatomy of the human female
Main functions:
To produce the female gametes (ova);
To receive sperm;
To provide a suitable environment in which a fertilized ovum might develop during pregnancy
Anatomy of the human female
Anatomy of the human female
Ovaries:
Contain follicles that nurture ova;
Produces sex hormones;
Functional from puberty to menopause
Anatomy of the human female
Oviducts (Fallopian Tubes):
Convey (move) ova towards the uterus;
Muscular contractions & cilia draw ovum (egg) into oviduct;
Location for fertilization to occur
Anatomy of the human female
Uterus (womb):Nourishes development of fertilized zygote;Opens into the vagina at cervix
Vagina:Receives the penis during coitus;Forms the birth canal; Multiple layers of expandable smooth muscle;Potential, not defined, space
Anatomy of the human female
Anatomy of the human female
Puberty
Puberty: when secondary sexual characteristics develop and the potential for sexual reproduction is reached (sperm production or ovulation)
Changes are controlled by hormones that initiate development of secondary sex characteristics;Primary sex characteristics are internal and external reproductive organs (genitalia)
Puberty in males (♂)
Secondary sex characteristics: Primary hormone: testosterone (testes);2° Characteristics: increased hair (body, pubic, & facial), muscle development, deeper voice;Spontaneous ejaculation
Puberty in females (♀)
Secondary sex characteristics: Primary hormone: estrogen (ovaries);2° Characteristics: breast development, broadened pelvis, distribution of body fat; increased hair (body & pubic);Menarche (onset of menstruation)
Testosterone (♂ testes):Sperm production & secondary sexual characteristics
Estrogen (♀ ovaries);Ova production, preparing uterus for fertilized zygote & secondary sexual characteristics
Reproductive hormones
Hormonal control of the testes
Androgens, (testosterone most important), stimulate sperm production
They also maintain homeostasis by a negative feedback mechanism that inhibits the secretion of FSH (follicle-stimulating hormone) and LH (luteinizing hormone)
Stimuli from otherareas in the brain
Hypothalamus
Releasinghormone
Anteriorpituitary
Negative feedback
FSH LH
Testis
Androgenproduction
Spermproduction
Oogenesis: Production of ova
Oogenesis occurs within the ovaries Lifetime supply of primary oocytes is present at
birth that are ‘frozen’ in Prophase I One (maybe more) primary oocyte matures each
menstrual cycle to form a secondary oocyte + polar body
If the secondary oocyte is fertilized, it completes meiosis and becomes a haploid ovum + another polar body
Oogenesis: Production of ova
Ovum maturation in ovary
releasesprogesterone
maintainsuteruslining
produces estrogen
Reproductive Cycle of the Adult Human Female
A cyclical pattern of hormone secretion and reproductive events.
Humans and many other primates have menstrual cycles.
If implantation of a fertilized zygote does not occur, the endometrium (lining of uterus) is shed through the cervix and vagina in the process called menstruation.
The Menstrual Cycle• The series of changes in the female reproductive
system that includes producing an ovum and preparing the uterus for receiving it.
• Once an ovum has been released during ovulation, the part of the follicle that remains in the ovary develops into a structure called the corpus luteum.
• The menstrual cycle begins during puberty and continues for 30 to 40 years, until menopause.
• At menopause, the female stops releasing ova and the secretion of female hormones decreases.
The Menstrual Cycle
• Divided into three phases: the flow phase, the follicular phase, and the luteal phase.
• The timing of each phase of the menstrual cycle correlates with hormone output from the pituitary gland, changes in the ovaries, and changes in the uterus.
LH
FSH
estrogen
progesterone
lining of uterus
egg developmentovulation = egg release
corpus luteum
0 7 14 21 28Days
Menstrual cycle
Controlled by a complex interaction of 4 hormones:
1. follicle stimulating hormone (FSH);
2. luteinizing hormone (LH);
3. estrogen;4. progesterone
Menstrual cycle: Flow phase Day 1 of the menstrual cycle (1st phase) is the day
menstrual flow begins. The shedding of blood, fluid, mucus, and epithelial cells
that make up the endometrium (the internal lining of the uterus) begins.
Contractions of the uterine muscles help expel the uterine lining and can cause discomfort in some females.
The level of FSH in the blood begins to rise, and a follicle in one of the ovaries begins to mature as meiosis of the prophase I cell proceeds.
Menstrual cycle: Follicular phase Follicular (2nd) phase lasts from about day 6 to day
14. As the follicle containing a primary oocyte continues
to develop, it secretes estrogen, which stimulates the repair of the endometrial lining of the uterus.
Day 14 ovulation occurs:Ovulation ≡ follicle enlarges and ruptures ovary
wall; ovum is released to oviduct.Mittelschmerz: ovulation pain
Menstrual cycle: Luteal phase
Luteal (3rd) phase begins after ovulation (≈ day 15). Progesterone increases the blood supply of the
endometrium. These changes correspond to the arrival of a
fertilized ovum (zygote). If the ovum is not fertilized, the rising levels of
progesterone and estrogen from the corpus luteum cause the hypothalamus to inhibit the release of FSH and LH.
Menstrual cycle: Luteal phase Without fertilization, the corpus luteum degenerates
and stops secreting progesterone or estrogen. As hormone levels drop, the thick lining of the uterus
begins to shed. If fertilization occurs the endometrium begins
secreting a fluid rich in nutrients for the embryo.
corpusluteumovary
Female reproductive cycle
pregnancy
maintainsuterus lining
no
yes
Feedbackestrogen
eggmatures &is released(ovulation)
builds up uterus lining
FSH & LH
progesterone
progesterone
fertilized egg(zygote)
HCG
corpus luteum breaks downprogesterone drops
menstruation
corpusluteum
maintainsuterus lining
GnRH
pituitarygland
hypothalamus
Female hormones FSH & LH
released from pituitary gland;
stimulates ova development & hormone release;
peak release = release of ova (ovulation)
Female hormones Estrogen
released from ovary cells around developing ova;
stimulates growth of lining of uterus;
decreasing levels initiate menstruation
Female hormones Progesterone
released from corpus luteum in ovaries
stimulates blood supply to lining of uterus;
decreased levels sustains menstruation
Hormonal coordination of the menstrual and ovarian cycles
FSH (follicle stimulating hormone) produced by pituitary gland stimulates development of follicle
LH (luteinizing hormone) stimulates the development of the corpus luteum; stimulates ovulation
Hormonal coordination of the menstrual and ovarian cycles
Estrogen: secreted by ovaries, stimulates development of uterine lining before implantation
Progesterone: secreted by corpus luteum, maintains uterine lining during pregnancy
Fertilization Fertilization is the union of a sperm and an ovum to
form a diploid zygote. Fertilization results in a zygote and triggers embryonic
development. Occurs normally inside of fallopian tube (oviduct). Fertilization is NOT pregnancy! (PATHWAY) Tens of millions of sperm enter the vagina
cervix uterus oviducts (fertilization)sperm + ovum zygote
23(n) + 23(n) 46(2n)
Fertilization
Only one of the many millions of sperm entering the vagina will penetrate this human ovum to initiate fertilization
Fertilization
The shape of a human sperm cell is adapted to its functionSperm cell is
enzymes, DNA & mitochondria!
Multiple Fertilizations If two (or more) ova are
released in the same cycle and fertilized fraternal siblings (different DNA)
If one ova is fertilized and mitotically divides into two (or more) separate zygotes identical siblings (same DNA)
Fertilization
Implantation Implantation: The fertilized zygote implants into
thickened uterine lining and the embryo starts to secrete the hormone human chorionic gonadotropin (HCG) (the hormone used for pregnancy tests)
HCG keeps the corpus luteum functional and continuing to secrete progesterone.
By the third or fourth month, the placenta takes over for the corpus luteum, secreting enough estrogen and progesterone to maintain the pregnancy.
Implantation = Pregnancy!
Embryonic Development Development: series of orderly, precise steps that
transform a zygote into a multicellular embryoEmbryo ≡ early development stages of a
multicellular organism Includes: 1. cell division (mitotic) 2. cell growth 3. cell differentiation ≡ altering of unspecialized
mitotic embryonic cells into specialized cells, tissues,& organs
Early Embryonic Development Cleavage is the first major
phase of embryonic development It is the rapid succession
of cell divisions (Mitotic) It creates a multicellular
embryo from the zygoteNO growthEmbryonic growth
cannot occur until implantation occurs
ZYGOTE
BLASTULA(hollow ball)
Blastocoel
Cross sectionof blastula
Early Embryonic Development Stages:
1. Morula ≡ solid ball of cells
2. Blastula ≡ single layer of cells surrounding a fluid-filled cavity called the blastocoel
3. NO growth; still dividing original single cell mass
ZYGOTE
BLASTULA(hollow ball)
Blastocoel
Cross sectionof blastula
Embryonic Development
Gastrulation is the second major phase of embryonic developmentThe cells at one end
of the blastula move inward
Embryonic Development
Organs start to form after gastrulation
Embryonic tissue layers begin to differentiate into specific tissues and organ systems
Embryonic Membranes
Amnion ≡ fluid filled sac for protection
Chorion ≡ will form the embryo’s part of the placenta
Yolk sac ≡ produces first blood cells & germ cells
Chorion
Amnion
Yolk sacAllantois
Embryonic Membranes
Allantois ≡ will form the umbilical cord (ropelike structure that attaches embryo to uterus)
Umbilical cord brings nutrients in/wastes out of fetus
Ties into hepatic artery & vein in fetus - bellybutton
Chorion
Amnion
Yolk sac
Allantois
The Placenta
Placenta ≡ A growing fetus exchanges nutrients, oxygen, and wastes with the mother through the placenta
Made of maternal and fetal tissues
Substances pass both ways, but blood does not mix
Placenta Nutrients, wastes, & gasses diffuse across capillaries
Fetal Development
Gestation is pregnancy It begins at implantation and continues until
parturition (birth)● Pregnancy in humans usually lasts about 280 days,
calculated from the first day of the mother’s last menstrual period.
Embryonic development of essential organs occurs in early pregnancy.
The embryo may encounter risks from faults in its genes & from mother’s exposure to environmental factors.
Human fetal development is divided into equal trimesters
First trimester (0 to 3 months)The most rapid changes occur during the first trimester (most developmentally important)10 weekseeks10 weeks
10 weeks
4 weeks 7 weeks 10 weeks
Human fetal development is divided into equal trimesters
Second trimester (4 to 6 months) Increase in size of fetusGeneral refinement of human features
12 weeks
Human fetal development is divided into equal trimesters
The fetus spends much of the 2nd & 3rd trimesters just growing…
…and doing flip-turns & kicks inside amniotic sac
Week 20
Human fetal development is divided into equal trimesters24 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 is divided into equal trimesters
Third trimester (7 to 9 months)30 weeks (7.5 months)
Human fetal development is divided into equal trimesters
32 weeks (8 months)
The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming
Human fetal development is divided into equal trimesters
Third trimesterGrowth and
preparation for birth
Provides time for maternal body to prepare for birth
Nooo!!! I don’t want to
go to Murdoch’s
class!
Three stages of labor
Dilation of the cervix is the first stage
Cervix starts at less than 1 cm dilation (open) and reaches full dilation at 10 cmLongest stage of
labor (6-12 hours or longer; maybe MUCH longer!)
Three stages of labor Expulsion is the second
stagePeriod from full
dilation of the cervix to delivery of the infant
Uterine contractions occur every 2-3 minutes (positive feedback)
Three stages of labor Expulsion is the second
stageMother feels urge to
push down with her abdominal muscles
Infant is forced down and out of uterus and vagina within a period of about 20 minutes
Three stages of labor
The delivery of the placenta is the final stage of laborUsually occurs
within 15 minutes after the birth of the baby
Some placenta’s are saved and frozen as they are a source of stem cells
Labor & Birth: Positive Feedback
positive feedback
The end of the journey!
And you think 9 months of
Biology is hard!
Lactation: the ‘mam’ in mammal
• Lactation ≡ milk production• Lactation is another positive
feedback system• Suckling stimulates the
hypothalamus pituitary gland to release oxytocin
• Oxytocin stimulates mammary glands to secrete milk
• Continued suckling continues milk production
Yes, males have mammary glands too!
Growth and Aging
Once a baby is born, growth and learning continue.
Human growth varies with age and is somewhat gender dependent.
Females develop earlier
An adult ages
As an adult ages, his or her body undergoes many distinct changes:
-Slower metabolism
-White hair
-Thinner bones
-Vision & hearing diminish