Transcript Human Reproduction Reproduction

Human
Reproduction
Reproduction
Male Reproductive Anatomy
Spermatogenesis and Male Hormones
Male Reproductive Technologies and Birth Control
Female Reproductive Anatomy
Oogenesis and Female Hormones
Uterine and Ovarian Cycles
Development of the Fetus
Parturition and Lactation
Reproductive Technologies
Teratogens and Birth Defects
Reproduction
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Reproduction ensures the survival of a species. Sexual
reproduction produces offspring with new and unique
characteristics that may increase their chance of
survival. In advanced forms of reproduction, there are 2
types of gametes (sex cells). These are sperm,
produced by the male, and eggs (ovum), produced by
the female. Each of these gametes contains one half of
the full complement of DNA required in a complete
individual.
 Human females produce about 400 mature eggs from
around ages 12 to 50. This is a relatively small number
since females have about 400,000 egg cells at birth!
 Males produce up to 1 billion sperm each day from the
ages of about 13 to 80 or 90!
 The average gestational period for a human is 266 days.
Male Reproductive Structures
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The male
reproductive
structures are
responsible for:
 producing
sperm
 storing sperm
 delivering
sperm to the
female
Sperm Producing Structures
Scrotum –holds the testes away from the body to keep
them cool. Sperm production only occurs at
temperatures about 3 degrees below body temperature.
 Testis – are the organs responsible for
spermatogenesis. They develop inside the abdominal
cavity of a male fetus and descend only about 2 months
before birth. The testes hold seminiferous tubule that
produce sperm.
 Epididymis – holds spermatozoa for about 2-4 days
while they mature
 Vas Deferens – stores sperm, and conducts sperm
during ejaculation. When a male has a vasectomy, the
vas deferens if cut and tied off, to prevent conduction of
sperm.
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Semen Producing Structures
Seminal Vesicle – produces a rich nutrient fluid that is
an important component of semen.
 Prostate Gland – produces a white, milky, alkaline fluid
component of semen. This fluid neutralizes the acidity of
urethra and the vagina, allowing sperm to survive.
 Cowper’s Gland – produces a rich alkaline mucous that
becomes part of the seminal fluid. This also neutralizes
any acid sperm might be exposed to.
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Structures for Sperm Delivery
Ejaculatory Duct – is responsible for the movement of
fluid from the seminal vesicle to the vas deferens.
 Urethra – is responsible for conduction of urine and
semen out of the penis. During ejaculation, a sphincter
muscle closes off the bladder, preventing urine from
exiting the urethra.
 Penis – is the male organ for copulation. Beneath the
skin, lies the urethra surrounded by spongy protective
tissue that expands to form the glans penis.
 Prepuce (foreskin) – is a loose sheath of skin covering
the glans penis of uncircumcised males. The foreskin
produces oily secretions
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Spermatogenesis
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Spermatozoa – are the smallest cells in the body. They
have very little cytoplasm in the head, and a large tail
(flagellum).
Production of sperm cells occurs in the testis in the
seminiferous tubules. Up to 1 billion sperm are produced
each day. The entire process takes about 65 days.
 Sperm are produced by meiotic division, which produces
cells with one half the normal number of chromosomes.
 Animations
Key structures during sperm production
include:
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Spermatogonia – undifferentiated germ cells that divide by
meiosis and have 46 chromosomes
Primary Spermatocytes – larger cells that undergo meiosis I
Secondary spermatocytes – cells that undergo meiosis II
Spermatids – cells with 23 chromosomes, that are ready to
mature in the epididymus
Spermatozoa – mature sperm cells
Seminal Fluid
Is produced by three different glands:
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Seminal Vesicles – secrete a fluid high in fructose
that provides energy sperm need to swim
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Prostate Gland – produces a milky white alkaline fluid
that neutralizes the acidity of the vagina
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Cowper’s Gland – secretes a buffered fluid that
cleanses and neutralizes the acidity in the urethra
Regulation of the Male Reproductive
Hormones
Male Reproductive Hormones
GnRH – gonadotropic releasing hormone, stimulates the
anterior pituitary to release LH and FSH
 LH / ICSH – luteinizing hormone, stimulates the
interstitial cells of the testes to produce testosterone
 FSH – follicle stimulating hormone, stimulates production
of sperm in the seminiferous tubules, acts on the sertoli
cells
 Testosterone – responsible for male secondary sex
characteristics, required for sperm production
 Interstitial Cells – surround the seminiferous tubules,
produce testosterone when stimulated by LH
 Sertoli Cells – provide nutrients and support for
developing sperm, affected by inhibin and FSH
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Female Reproductive Structures
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The female
reproductive
structures are
responsible for
- reception of
sperm
- producing an egg
- nourishing and
protecting the fetus
- delivering the
baby
Internal Structures
Vagina – facilitates intercourse by accepting the penis, acts
as the birth canal during labor, pH is generally acidic
 Cervix – Thick muscular tissue that plugs closed with mucous
during pregnancy and prevents material from getting into the
uterus, and holds the baby in
 Uterus (womb) – pear shaped muscular organ (5 cm wide)
that houses the developing fetus during pregnancy (30 cm
wide), strong contractions help push the baby out during birth
 Oviducts / fallopian tubes – responsible for the conduction
of the ovum (egg) from the ovaries to the uterus, this is where
fertilization usually takes place
 Fimbrae – small fingerlike projections at the ends of the
oviducts that sweep to draw the egg into the fallopian tube
 Ovaries – produce the ovum from follicles found in the outer
cortex (most females are born with about 2 million follicles,
and only 300-400,000 will remain at puberty)
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Ovarian Structures
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Follicle –are groups of cells that support and protect the
ovum, secrete estrogen to mature the ovum, and
become a corpus luteum following ovulation.
Ovum – egg cell, viable for about 24 hours after release.
Corpus Luteum – cells remaining after a follicle has
ruptured during ovulation, this scar-like tissue secretes
estrogen and progesterone for about 3 months if
fertilization and pregnancy occurs, or deteriorates after
about 14 days if fertilization does not occur.
Oogenesis
Regulation of the Female Reproductive
Hormones
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GnRH – stimulates the anterior pituitary to produce FSH
and LH
LH – responsible for the development of the corpus
luteum, promotes secretion of progesterone, surges of
LH cause ovulation
FSH – stimulates development of the follicle and the
production of estrogen
Estrogen – secreted by the follicles in the ovaries,
causes maturation of the egg and stimulates growth of
the endometrium
Progesterone – secreted by the corpus luteum, causes
the endometrium to become secretory and inhibits both
FSH and LH to prevent ovulation
The Uterine and Ovarian Cycles
The Ovarian Cycle
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Day 1-13: Follicular Phase
 FSH is secreted by the anterior pituitary and promotes
formation of he follicle. The follicle releases estrogen, which
promotes growth of the endometrium.
 Day 14: Ovulation - The ovum is released causing the
follicle to rupture. This lowers the levels of FSH produced.
 Day 15 – 28: Luteal Phase
 LH is secreted by the anterior pituitary and promotes
formation of the corpus luteum, which produces
progesterone, inhibits GnRH, LH and FSH, preventing
subsequent ovulation.
 No Fertilization  corpus luteum degenerates, estrogen and
progesterone levels drop, and menstruation occurs.
 Fertilization  corpus luteum is maintained by HCG (human
chorionic gonadotropic hormone) secreted by the developing
embryo. GnRH, LH and FSH are inhibited by progesterone,
and ovulation cannot occur during pregnancy. Estrogen
levels also remain high to maintain the endometrium.
The Uterine Cycle
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Day 1-5: Menstruation
All hormone levels are low. The endometrium is sloughed off
and the lining is shed. This is known as menstrual bleeding.
Day 5 – 14: Proliferative Phase
FSH promotes formation of the follicle, which produces
estrogen. The estrogen causes vascularization / thickening of
the endometrium in preparation to receive a fertilized egg.
Day 14: Ovulation - A surge of LH causes the corpus luteum
to form.
Day 15-28: Secretory Phase
The corpus luteum secretes progesterone. If fertilization does
not occur, the corpus luteum will degenerate after about 10
days. When the corpus luteum degenerates, the levels of
estrogen and progesterone drop sharply, and menstruation
begin. If fertilization does occur, the corpus luteum continues
producing estrogen and progesterone, maintaining the uterine
lining.
http://www.msnbc.com/news/wld/graphics/menstrual_cycle_dw
2.swf
Fertilization and Pregnancy
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Fertilization – sperm are deposited into the vagina,
where they travel through the cervix, through the uterus
and up into the fallopian tube. Sperm usually meet the
ovum in the fallopian tube. Only one spermatozoa will
fertilize an egg. Once a sperm has penetrated the egg,
enzymatic changes on the head of the sperm, and the
outer coating of the egg, prevent penetration from other
sperm.
http://www.uchsc.edu/ltc/fert.swf
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Implantation- the fertilized egg (embryo) embeds itself
in the endometrium. The embryo produces HCG
(human chorionic gonadotropic hormone) which
maintains the corpus luteum for about 2-3 months. This
hormone is detected in blood or urine with a pregnancy
test, as early as the first day of a missed period.
Placenta – forms around the fetus. The placenta is
responsible for the exchange of gases, delivery of
nutrients and removal of wastes for the fetus. There is
no blood shared between the mother and the fetus. A
fetus may have a different blood type than the mother.
How old are you?
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Gestational age – the length of pregnancy is 38 to 40
weeks, or 266 days. The gestational age is calculated
from the first day of the mother’s last menstrual period.
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Fertilization age – is the actual age of the fetus. It is
usually estimated to be about two weeks shorter than the
date of the last menstrual period.
To calculate due date: LMP –3 months + 7 days
 hCG Pregnancy Test (ELISA)
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Early Stages of Embryonic Development:
Zygote –fertilized egg, divides by cleavage, mitosis with
no increase in size
 Morula – solid ball of cells the same size as the fertilized
egg
 Blastula – hollow ball of cells filled with fluid, outer layer
forms the chorion, inner layer forms the fetus
 Gastrula – the blastula pushes in (invaginates) and
forms the 3 primary germ layers, the hollow space forms
a primitive gut
 BERP: Overview
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Germ Layers
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Endoderm – forms the lining of the GI tract, trachea,
bronchi, lungs, gallbladder, urethra, liver, pancreas,
thyroid and urinary bladder
Mesoderm – forms the muscles, dermis, connective
tissue, bone, cartilage, blood, blood vessels, kidneys and
reproductive organs
Ectoderm – forms the epidermis of the skin, hair, nails,
nervous system, spinal cord, retina, lens, inner ear, lining
of the nose, mouth, anus and tooth enamel
The first month…
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Neurula – appearance of the nervous system in a neural
tube (21 days)
Somites – blocklike portions of the neurula that give rise
to the segmented muscles and vertebral bones
Coelom – forms the gut cavity
Pharyngeal pouches – primitive gill slits
Stage 1
Extra Embryonic Membranes
Placenta – forms when the
embryo is implanted from the
fetal chorionic tissue and the
maternal uterine tissue, secretes
wastes and supplies nutrients
 Chorion – fetal portion of the
placenta, secretes HCG to
maintain the corpus luteum and
the developing embryo
 Amnion – inner membrane filled
with fluid to provide protection,
maintain temperature,
swallowing, etc.
 Allantois – collects nitrogenous
wastes and forms the umbilical
blood vessels
 Yolk Sac – surround the
remaining yolk, first site of blood
cell formation
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Milestones of Development
1 week – fertilization, cleavage, morula, blastocyst
2 weeks – implantation, chorion secretes HCG, 3 germ layers
form
 3 weeks – nervous system is evident, heart begins to form (2
tubes)
 4-5 weeks – limb buds appear, eyes, ears and nose develop,
umbilical cord is attached to placenta
 6-8 weeks – fetus is recognizable as a human, all organ
system are developed, reflexes begin (size = 1.5”, 0.5 g)
 9-16 weeks – heartbeat is audible with a stethoscope, bone
replaces cartilage, eyelashes, etc formed (size = 6”, 0.5 lb)
 17-28 weeks – movement if felt by mother, lanugo and vernix
caseosa covers the skin, eyelids open (size = 12”, 3lb)
 20-40 weeks – fetus moves to head down position, significant
weight gain, lungs mature after about 32 weeks (size = 21”, 7.5
lbs)
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Virtual Develoment
 Conception
Travelogue
to Birth, Anatomical
Parturition and Lactation
Parturition – birth caused by the release of
prostoglandins that cause the release of oxytocin from
the posterior pituitary of the mother. Parturition takes
place in 3 stages:
 Stage 1 – dilation and effacement of the cervix, mucous
plug dislodges, uterine contractions open the cervix
 Stage 2 – delivery of the baby, cervix is dilated to about
10 cm, intense contractions every 1-2 min push the baby
down the birth canal
 Stage 3 – delivery of the placenta
 UAB Health System | Childbirth
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The average labor lasts about 12 hours, but can range
from 1 hour to 36 hours. Sometimes if the delivery does
not go well, or if the baby or mother is at risk, a
ceasarean section may be required. This involves
removing the baby from an incision in the front of the
abdomen.
Immediately after the baby is born, the mother is
encouraged to nurse the infant. At the end of pregnancy,
prolactin stimulates the glandular tissue in the breasts to
produce fluids, colostrum and milk. Colostrum is a rich
fluid containing mostly sugar and proteins. This first milk
is believed to play a role in early immunity. Regular
suckling stimulates the pituitary gland to release
oxytocin, which causes uterine contractions and the “let
down” of milk. At the peak of production, a woman can
make as much as 1.5 L of milk each day.
Reproductive Technologies
and Health
Pap Smear – a sample of cervical cells are taken and
examined for abnormal growth (cancer)
 Ultrasound – uses sound waves to view the baby in the
womb
 Ultrasound Scan Fetal Video Clips
 Amniocentesis – sampling of the cells from the amniotic
fluid at about 16 weeks to check for genetic
abnormalities
 Chorionic Villus Sampling – sampling of cells from the
chorion at about 5 weeks to check for genetic
abnormalities
 http://www.pbs.org/wgbh/nova/miracle/windows.html
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Fertility Technologies
IVF – in vitro fertilization – fertilizing the egg in a petri
dish, and implanting the embryo 2-4 days later
 Life Changine Science - Program 3: IVF
 AID – artificial insemination by donor
 Egg Screening – testing and selecting eggs to be
fertilized
 TSE – testicular sperm extraction
 ICSI – intracytoplasmic sperm injection
 GIFT – gamete intra-fallopian transfer
 AH – assisted hatching
 Embryo Transfer – implantation of an embryo into the
womb or fallopian tube
 Fertility Drugs – induce ovulation, usually many ova are
produced at one time, often results in multiples
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Teratogens
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chemical substances or infections that cause specific birth
defects