Transcript The Reproductive System

The Reproductive
System
Function Preview
 Ensures continuity of the species
by producing offspring
 In sexual reproduction new individuals
are produced by the fusion of haploid
gametes to form a diploid zygote.
 Sperm are male gametes, ova (ovum
singular) are female gametes.
Function Preview
 Meiosis produces cells that are
genetically distinct from each other;
fertilization is the fusion of two such
distinctive cells that produces a unique
new combination of alleles, thus
increasing variation on which natural
selection can operate.
Function Preview
 Sexual reproduction offers the benefit
of generating genetic variation
among offspring, which enhances the
chances of the population's survival.
Anatomy of the Male
Reproductive System
 Common purpose
 Identify the organs and discuss
the general function of each
 Testes: Exocrine and endocrine
functions
Anatomy of the Male
Reproductive System
 Composition of semen and the
glands that produce it
 Erection, ejaculation and
circumcision
 Meiosis and spermatogenesis
 Sperm structure and how it
relates to its function
Anatomy of the Male
Reproductive System
 FSH and LH: Its effect on testes
functioning
Anatomy of the Female
Reproductive System
 Identify the organs of the female
reproductive system and discuss
the general functions
 Vesicular follicle and corpus
luteum of the ovary
 Endometrium, myometrium and
ovulation
Anatomy of the Female
Reproductive System
 Locate the female uterus: cervix,
fundus and body
 What is oogeneis
 What is the influence of FSH and
LH on ovarian function
 Phases and controls of the
menstrual cycle
Anatomy of the Female
Reproductive System
 Function and structure of the
mammary glands
 Fertilization and zygote
 Implantation
 Placenta and its functions
 Three stages of labor
Overview
 Primary sex organs are the gonads
 Testes and ovaries
 Gonads produce sex cells: gametes
 Accessory reproductive organs
 The reproductive role of the male is to
produce sperm, deliver them to the
female
Overview
 Female provide female gametes or
ova
 The joining of a sperm and ova
causes a fusion or a fertilized egg
which is the first cell of a new
individual
Overview
 After fertilization the female uterus
provides a protective environment for
the embryo, later called the fetus,
which develops until birth
Overview
 Human reproduction employs internal
fertilization, and depends on the
integrated action of hormones,the
nervous system, and the reproductive
system. Gonads are sex organs that
produce gametes. Male gonads are the
testes, which produce sperm and male sex
hormones. Female gonads are the ovaries,
which produce eggs (ova) and female sex
hormones.
Anatomy of the male
Reproductive System
 Testes are suspended outside the
abdominal cavity by the scrotum, a
pouch of skin that keeps the testes
close or far from the body at an
optimal temperature for sperm
development.
Anatomy of the male
Reproductive System
 Seminiferous tubules are inside each
testis, and are where sperm are produced
by meiosis. About 250 meters (850 feet)
of tubules are packed into each testis.
Spermatocytes inside the tubules divide
by meiosis to produce spermatids that in
turn develop into mature sperm.
The male reproductive system. Images from Purves et al., Life: The Science of Biology, 4th Edition,
by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with
permission.
Testes
 Fibrous connective
tissue capsule: Tunica
albuginea
 Septa or extensions
form this capsule
divides the testes into
lobules.
 Within the lobules are
the sperm- forming
factories- seminferous
tubules
Testes
 The sperm empty into
the rete testis and
travel to the
epididymis
 Surrounding the
seminiferous tubules
are interstitial cells,
functionally distinct
cells that produce
androgens- most
important is
testosterone
Testes
 In the male spermproducing and
hormone producing
function of the testes
are carried out by two
completely different
cell populations
Accessory Organs
 Epididymis
 Ductus deferens, vas deferens
 Urethra
Accessory Organs
 Epididymis
Epididymis
 First part of the male duct
system
 Provides a temporary storage
site for immature sperm
 It takes 20 days to get here
and the sperm mature gaining
the ability to swim
 Sexual stimulation causes the
walls to contract and expel the
sperm into the ductus deferens
Ductus Deferens
 This is a low power image of the
Ductus Deferens or Vas
Deferens. Notice the Stellate
shaped lumen that is a
characteristic of the duct (red
arrow), along with the very thick
smooth muscle walls indicated by
the blue arrows.
 Red arrow - Stellate Shaped
Lumen Of Vas Deferens
 Blue arrow - Thick Muscular wall
of Vas Deferens
Ductus Deferens
 Runs upward from the epididymis
through the inguinal canal into the
pelvic cavity
 It is enclosed along with blood
vessels and nerves in a connective
tissue sheath: spermatic cord
Ductus Deferens
 The end of the ductus deferens empties
into the ejaculatory duct, which passes
through the prostate gland and merges
with the urethra
 Main function is to propel live sperm from
the epididymis (storage space) and the
distal part of the ductus deferens into the
urethra
Physical prevention (most effective) include vasectomy. Vasectomy: the vas
deferens connecting the testes with the urethra is cut and sealed to prevent the
transport of sperm.
Urethra
 Terminal part of the male duct system
 Three named regions
 Prostatic urethra- prostrate gland
 Membranous urethra
 Spongy urethra- running within the
length of the penis
Accessory Gland and Semen
 Paired seminal vesicles
 Prostrate gland
 Bulbourethral glands (Cowper’s
gland)
 These glands produce the bulk of the
semen
Seminal Vesicles
 Produce about 60% of semen fluid
 Fructose, Vitamin C. prostoglandins
and other substances which nourish
and activate the sperm passing
through the tract
 Sperm and seminal fluid enter the
urethra together during ejaculation
Prostate Gland
 Produce a milky secretion that plays a
role in activating sperm
 Prostrate cancer is the third most
prevalent cancer in men
 Hypertrophy of the prostrate strangles
the urethra: Cystitis and kidney
damage
Bulbourethral Glands
 Produce a thick, clear mucus that
drains into the penile urethra
 This secretion is the first to pass
down the urethra when a man
becomes sexually excited
 Cleanses traces of acidic urine and
serves as a lubricant during
intercourse
Semen
 Milky white, sticky mixture of sperm
and accessory gland secretions
 Provides a transport medium
 Contains nutrients and chemicals that
protect the sperm and aid its
movement
 Fructose provides the energy
 Alkalinity of semen (ph 7.2-7.6)
Semen
 Neutralizes the acid environment of
vagina (pH 3.5 - 4)
 Contains seminal plasmin ( inhibits
bacterial multiplication)
 Hormone relaxin and enzymes that
enhance sperm mobility
Spermatogenisis
 Sperm production
begins at puberty at
continues throughout
life, with several
hundred million sperm
being produced each
day. Once sperm form
they move into the
Human Sperm (SEM x5,785). This image is
epididymis, where
copyright Dennis Kunkel at www.DennisKunkel.com,
they mature and are used with permission.
stored.
Spermatogenesis
 Begins in seminiferous tubules:
Spermatogonia
 FSH- at puberty causes the
production of stem cell (daughter cell
A) and daughter cell B
 Type B- Primary spermatocyte and
undergoes meiosis to form four
spermatids (gametes)
Spermiogeneis
 Head contains: DNA
 Midpiece: Centrioles that form
filaments of the tail
 Tail: Mitochondria are wrapped tightly
around filaments to provide ATP
 The entire process of
spermatogenesis takes 64-72 days
Male Sex Hormones
 The anterior pituitary produces folliclestimulating hormone (FSH) and
luteinizing hormone (LH) or interstitial
cell- stimulating hormone (ICSH).
 Action of LH is controlled by the
gonadotropin-releasing hormone
(GnRH).
Male Sex Hormones
 LH stimulates cells in the seminiferous
tubules to secrete testosterone, which has
a role in sperm production and
developing male secondary sex
characteristics.
 FSH acts on cells to help in sperm
maturation.
 Negative feedback by testosterone
controls the actions of GnRH.
Secondary Sex
Characteristics
 Deepening of the voice due to the
enlargement of the larynx
 Increases hair growth all over the
body
 Enlargement of skeletal muscles to
produce heavier muscle mass
 Increased heaviness of the skeleton
due to thickening of the bones
Anatomy of the Female
Reproductive System
 More complex
 Produces female gametes (ova)
 Nurture and protect the developing fetus
 Ovaries are the primary reproductive
organs
 Ovaries produce both an exocrine product
(ova) and endocrine products ( estrogens
and progesterone)
www.gynaesurgeon.co.uk/anatomy/anatomy6.htm
Ovaries
 Paired and contain saclike structures
called ovarian follicles
 Each follicle consists of an immature
egg (oocyte) surrounded by follicle
cells
 As follicle matures it enlarges and
develops a fluid-filled center: antrum
Ovaries
 The follicle is now called a vesicular
or Graafian follicle: the developing
egg is ready for ovulation
 After ovulation the ruptured follicle is
transformed into the corpus luteum
which eventually degenerates
 Ovulation generally occurs every 28
days
Duct System
 Uterine tubes
 Uterus
 Vagina
The female reproductive tract
Duct System
 The reproductive system of a women is
entirely internal.
 The vagina is the passage that leads from
the outside of the body to the cervix, which
is the opening to the uterus.
 The uterus is the muscular organ where a
fertilized egg attaches and develops. It is
about the size and shape of a pear, and is
lined with a rich and nourishing mucous
membrane called the endometrium.
Fallopian Tubes
 Forms the initial part of the duct
system
 Receives the ovulated oocyte
 Provides a site where fertilization can
occur
 Enclosed and supported by a broad
ligament
Fallopian Tubes
 Unlike the male duct system, no
actual contact between the uterine
tubes and the ovaries
 Distal end expands into infundibulum
which has finger-like projections(
fimbriae)
 Fimbriae create fluid currents to carry
the oocyte into the uterine tube
Fallopian Tubes
 Oocyte is carried to the uterus by
peristalsis and rhytmic beating of cilia
 Takes 3-4 days to get to the uterus
 Oocyte is viable up to 24 hours after
ovulation
 Usual site for fertilization is the
uterine tube
www.2womenshealth.co.uk/Figure02-01.htm
Uterus
 Womb
 Located in the pelvis between the
urinary bladder and the rectum
 Receives, retains and nourishes the
fertilized egg
 The major portion is the body
Uterus
 Superior rounded region above the
entrance of the uterine tubes is the
fundus
 Narrow outlet that protrudes into the
vagina beow is the cervix
Duct System
 From the top of the uterus extend the
fallopian tubes, which lead backward and
downward to the ovaries.
www.afraidtoask.com/STD/stdanatomy.html
sprojects.mmi.mcgill.ca/gynecology/anatute.html
www.gynaesurgeon.co.uk/anatomy/anatomy6.htm
Uterus
 Three layers
 Inner layer or mucosa is the endometrium
 if fertization ocurs, the fertilized egg implants
into the endometrium
 Myometrium is the bulky middle layer
 Composed of smooth muscle
 Active role during the delivery of the baby
Uterus
 Three layers
 Perimetrium or viseceral peritoneum
 Outer serous layer
Menses
 When not pregnant the endometral
lining sloughs off periodically
 Usually every 28 days
 Responds to the levels of the ovarian
hormones
Vagina
 Birth canal
 Provides a passageway for the
delivery of the baby
 Provides a oassageway for menstrual
flow to leave the body
 Receives the penis and semen
 Female organ of copulation
Vagina
 Distal end is partially closed by the
hymen
 Very vascular and tends to bleed if
ruptured
 If too tough it is surgically ruptured to allow for
intercourse
External Genitalia
 Called the Vulva collectively
 Mons pubis
 Labia
 Clitoris
 Urethral and vaginal orifices
 Greater vestibular glands
A: Prepuce (Hood) of
Clitoris
B: Clitoris
C: Opening of Urethra
(urinary tract)
D: Labia minora
E: Labia majora
F: Opening of Vagina
G: Vestibule
H: Hyman tissue
(residual)
I: Opening of Anus
Vulva
 The MONS, a name that comes from the
Latin mons veneris means mound of
Venus, the Roman goddess of love, is the
area of fatty tissue that forms a soft
mound over the pubic bone. The mons is
covered by skin and pubic hair.
Vulva
 The LABIA MAJORA, or OUTER LIPS,
extend from the mons to the anus. They cover
the urinary and vaginal openings and are in
turn covered by pubic hair.
 The LABIA MINORA, or INNER LIPS, are
delicate folds of moist skin that lie inside the
outer lips, although they can protrude beyond
them. They extend from just above the clitoris
to below the vaginal opening. They vary in
size and form in each woman.
Vulva
 The CLITORIS is an exquisitely sensitive
organ that lies just under the mons. It is
covered by the inner lips which can be gently
pushed back to reveal the tip (the head or
glans). The rest of the clitoris can be seen
because it extends inside the body. The clitoris
is extremely sensitive to stimulation and when
stimulated it becomes erect. Although direct
stimulation of the tip of the clitoris is
pleasurable for some women it is
uncomfortable and even painful for others.
Vulva
 The URINARY OPENING is just under the
clitoris. It is the outer part of the urethra, the
tube from the bladder.
 The VAGINAL OPENING is located behind the
urinary opening.
 During sexual stimulation erectile tissue on both
sides of the vagina become engorged with blood.
The whole area becomes moist. The pelvic muscles
contract and relax during orgasm. One- to two-thirds
of the vaginal opening is covered with the HYMEN
until this is broken by intercourse or penetration or
another object or even bicycle or horseback riding.
Vulva
 The VAGINA lies between the urethra and the
rectum.
 Unless a woman is sexually stimulated the
walls of the vagina touch each other.
 When a woman is sexually aroused a slippery
liquid is produced and the vagina opens, or
enlarges. ( Greater Vestibular Glands)
 The vagina can open as much as to facilitate
the passage of a baby, therefore there is no
such thing as a penis too large for a woman's
vagina
.
www.2womenshealth.co.uk/Figure02-02.htm
Female Reproductive
Functions and Cycles
 Oogenesis: Meiosis to produce female
gametes
 The ovary contains many follicles composed
of a developing egg surrounded by an outer
layer of follicle cells.
 Each egg begins oogenesis as a primary
oocyte.
 At birth each female carries a lifetime supply
of developing oocytes, each of which is in
Prophase I.
Female Reproductive
Functions and Cycles
 A developing egg (secondary oocyte) is
released each month from puberty until
menopause, a total of 400-500 eggs.
Oogenesis
 In the female fetus: oogonia or the
female stem cells
 Rapidly multiply
 Daughter cells, the primary oocytes,
push into the ovary connective tissue
 Surrounded by a single layer of cells
and form the primary follicles
Oogenesis
 By birth the oogenia are no longer
exist and a lifetime supply of primary
oocytes exists; arrested in prophase I
 During puberty, the anterior pituitary
secretes FSH
 Stimulates a small number of follicles to
grow and mature
 Ovulation occurs
Oogenesis. The above image is from http://www.grad.ttuhsc.edu/courses/histo/notes/female.html.
Ovarian Cycle
 Cyclic changes that occur monthly
 At puberty, 400,000 oocytes remain
 Small number activated each month
 Follicle prodded by FSH grows it
accumulates fluid in the center: antrum
 Primary oocyte undergoes first meiotic
division
 Produces:
Ovarian Cycle
 Secondary oocyte
 Polar body
 The vesicular follicle contains a secondary
oocyte
 14 days
 Ovualation of secondary oocyte occurs in
response to LH
 Ovulated secondary oocyte still surrounded
by capsule now called the corona radiata
Ovarian Cycle
 LH stimulus causes rupture and release of oocyte
into peritoneal cavity
 Vesicular follicles that do not ovulate overripe and
deteriorate
 LH causes the ruptured follicle to change into
corpus luteum
 Secondary oocyte if penetrated by sperm its nucleus
undergoes the second meiotic division that produces
another polar body and the ovum nucleus
 Meiosis in females yields only one
functional ovum and three tiny polar bodies
Ovarian Cycles
 After puberty the ovary
cycles between a
follicular phase
(maturing follicles) and
a luteal phase (presence
of the corpus luteum).
 These cyclic phases are
interrupted only by
pregnancy and continue
until menopause, when
reproductive capability
ends.
Ovarian Cycles
 During the first phase, the
oocyte matures within a
follicle.
 At midpoint of the cycle, the
oocyte is released from the
ovary in a process known as
ovulation.
 Following ovulation the
follicle forms a corpus
luteum which synthesizes
and prepares hormones to
prepare the uterus for
pregnancy.
Ovarian Cycle
 If secondary oocyte is not penetrated
it deteriorates
Ovarian Cycle
 The ovarian cycle is
http://www.emc.maricopa.
edu/faculty/farabee/BIOB
K/BioBookREPROD.html
hormonally regulated in
two phases.
 The follicle secretes
estrogen before
ovulation
 The corpus luteum
secretes both estrogen
and progesterone after
ovulation.
Ovarian Cycle
 The ovarian cycle
covers events in the
ovary
 The menstrual cycle
occurs in the uterus.
Menstrual Cycle
 Menstrual cycles vary from between 15
and 31 days.
 Menses Days 1-5
 The first day of the cycle is the first day of
blood flow (day 0) known as menstruation.
 During menstruation the uterine lining is
broken down and shed as menstrual flow.
 FSH and LH are secreted on day 0,
beginning both the menstrual cycle and the
ovarian cycle.
Menstrual Cycle
 Menstrual cycles vary from between 15
and 31 days.
 Menses Days 1-5
 Both FSH and LH stimulate the maturation
of a single follicle in one of the ovaries and
the secretion of estrogen.
Menstrual Cycle
 Menstrual cycles vary from between 15 and 31
days.
 Proliferative stage Days 6-14
 Rising levels of estrogen in the blood trigger
secretion of LH
 Basal layer of endometrium regenerates
 stimulates follicle maturation and ovulation
 LH stimulates the remaining follicle cells to form
the corpus luteum, which produces both estrogen
and progesterone.
Menstrual Cycle
 Menstrual cycles vary from between 15 and 31
days.
 Secretory stage 15-31
 Estrogen and progesterone stimulate the
development of the endometrium and preparation
of the uterine inner lining for implantation of a
zygote.
 If pregnancy does not occur, the drop in FSH and
LH cause the corpus luteum to disintegrate.
 The drop in hormones also causes the sloughing
off of the inner lining of the uterus by a series of
muscle contractions of the uterus.
Secondary Sex
Characteristics
 Caused by estrogens (estradiol,
estrone, estriol)
 Estradiol is the most abundant and
responsible for mediating estrogenic
effects
Secondary Sex
Characteristics
 Enlargement of accesory organs of
the femaale reproductive system
 Uterine tubes
 Uterus
 Vagina
 vulva
 Development of the breasts
Secondary Sex
Characteristics
 Appearance of axillary and pubic hair
 Increased deposits of fat beneath the
skin
 Hips
 Breasts
 Widening and lightening of the pelvis
 Onset of the menstrual cycle
Mammary Glands
 Mammary glands develop from
distinctive mammary ridges running
along both sides of the trunk of a
mammalian embryo.
 Mammary glands are found in both
sexes, but cease development in males
well before puberty.
Mammary Glands
 Mammary glands are probably highly
modified sweat glands.
 reasonable to suggest that their origin was
correlated with the development of milk teeth
and the pattern of tooth replacement
(diphyodonty) seen in most modern
mammals.
 Milk teeth are probably not as efficient as adult
teeth at chewing, due partly to their small size
and partly to their ever-changing pattern of
occlusion as the young mammal grows.
Mammary Glands
 This lack of efficiency is accommodated
by reliance on a food that doesn't need to
be chewed, milk.
 Mammary glands are made up of a
system of ducts surrounded by glandular
tissue, which secretes milk.
Mammary Glands
 Milk formation is stimulated by the hormones
prolactin and growth hormone
 Secretion of these hormones is in turn
stimulated by the act of suckling.
 Numerous ducts discharge to the surface of a
fleshy protuberance called a nipple.
 Milk contains high percentages of protein, fat,
and sugars (especially lactose), and some
amount of vitamins and salts.
Fertilization
 transmission of genes from both parents
to offspring
 restoration of the diploid number of
chromosomes reduced during meiosis
 initiation of development in offspring
The egg and sperm. Sperm are color enhanced (green) while the egg is color enhanced to
gold. The above image is modified from http://130.102.208.100/FMRes/FMPro?db=images.fp3&key=32931&-img.
Sperm on the surface of a human egg. This image is from http://130.102.208.100/FMRes/FMPro?db=images.fp3&key=32932&-img.
Fertilization Steps
 Contact between sperm and egg
 Entry of sperm into the egg
 Fusion of egg and sperm nuclei
 Activation of development
Embryonic Events
 Cleavage is the first step in development of
multicelled organisms.
 Cleavage converts a single-celled zygote into
a multicelled embryo by mitosis.
 The blastocyst or chorionic vesicle is produced
by mitosis of the zygote, and is a ball of cells
surrounding a fluid-filled cavity (the
blastocoel).
Embryonic Events
 The decreasing size of cells increases their
surface to volume ratio, allowing for more
efficient oxygen exchange between cells and
their environment.
 RNA and information carrying molecules are
distributed to various parts of the blastula, and
this molecular differentiation sets the stage for
the layering of the body
Embryonic Events
 Gastrulation involves a series of cell
migrations to positions where they will
form the three primary cell layers.
 Ectoderm forms the outer layer.
 Endoderm forms the inner layer.
 Mesoderm forms the middle layer.
Embryonic Events
 Mesoderm
 forms structures associated with
movement and support: body muscles,
cartilage, bone, blood, and all other
connective tissues. Reproductive system
organs and kidneys come from
mesoderm.
Embryonic Events
 Endoderm
 forms tissues and organs associated with the
digestive and respiratory systems. Many
endocrine structures, such as the thyroid and
parathyroid glands, are formed by the
endoderm. The liver, pancreas, and gall
bladder arise from endoderm.
Embryonic Events
 Ectoderm
 tissues associated with outer layers: skin,
hair, sweat glands, epithelium. The brain
and nervous system also develop from the
ectoderm.
Implantation
 The uterine lining becomes enlarged and
prepared for implantation of the embryo in the
trophoblast layer.
 Twelve days after fertilization, the trophoblast
has formed a two-layered chorion.
 Human chorionic gonadotropin (hCG) is
secreted by the chorion, and prolongs the life
of the corpus luteum until the placenta begins
to secrete estrogen and progesterone. Home
pregnancy tests work by detecting elevated
hCG levels in the woman's urine.
Implantation
 Your Placenta or Mine?
 Maternal and embryonic structures interlock to form
the placenta, the nourishing boundary between the
mother's and embryo's systems. The umbilical cord
extends from the placenta to the embryo, and
transports food to and wastes from the embryo.
Changes in the zygote from fertilization to implantation. The above image is from
http://www.biosci.uga.edu/almanac/bio_103/notes/apr_15.html.
Stages of Development
 The period of time from fertilization to
birth (usually 9 months) is divided into
trimesters, each about three months long.
During pregnancy the zygote undergoes
40 to 44 rounds of mitosis, producing an
infant containing trillions of specialized
cells organized into tissues and organs.
Stages of Development
 The First Trimester
 The three embryonic tissue layers form.
 Cellular differentiation begins to form
organs during the third week.
 After one month the embryo is 5 mm long
and composed mostly of paired somite
segments.
 During the second month most of the major
organ systems form, limb buds develop.
Stages of Development
 The First Trimester
 The embryo becomes a fetus by the seventh week.
 Beginning the eighth week, the sexually neutral
fetus activates gene pathways for sex
determination, forming testes in XY fetuses and
ovaries in XX fetuses. External genitalia develop.
Stages of Development
 The Second Trimester
 The fetus increases in size during this
trimester, and bony parts of the skeleton
begin to form.
 Fetal movements can be felt by the mother.
Stages of Development
 The Last Trimester
 During this trimester the fetus increases in size.
 Circulatory and respiratory systems mature in
preparation for air breathing.
 Fetal growth during this time uses large parts of its
mother's protein and calcium intake.
 Maternal antibodies pass to the fetus during the
last month, conferring temporary immunity.
Birth
 Birth is a positive feedback hormonal
mechanism. During birth the cervix dilates to
allow passage of the fetus. Uterine
contractions propel the fetus through the birth
canal, usually head first. Hormonal control of
the birth process involves the release of
oxytocin and prostaglandins, which are
stimulated by uterine contractions, which
stimulate more hormones that cause more
contractions....etc.
Birth
 First Stage: Dilation stage
 The first stage of birth lasts from
beginning of contractions to the full (10
cm) dilation of the cervix.
 Membranes of the amniotic fluid
rupture, lubricating the vagina.(
breaking the water)
Birth
 Second Stage: Expulsion stage
 Strong uterine contractions of a minute
in duration separated by two to three
minute intervals propel the fetus down
the birth canal.
 Abdominal muscles relax in synchrony
with the uterine contractions.
 Vertex position: head-first
 Breech: buttocks- first
Birth
 Third Stage: Placental stage
 After delivery of the baby, the umbilical
cord is clipped and cut.
 The placenta (or afterbirth) in expelled
through the vagina.
Birth
 Milk Production
 Nursing mothers have their hormone levels
and uterine size return to normal much faster
than non-nursing mothers. Breasts develop the
capability for milk secretion about the mid
point of pregnancy. Secretion of milk does not
occur until delivery, and the action of
prolactin. Suckling by the infant causes
production of oxytocin to promote release of
milk into the ducts emptying into the nipple.