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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College

C H A P T E R

Copyright © 2010 Pearson Education, Inc.

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Pregnancy and Human Development: Part B


Organogenesis

• Gastrulation sets the stage for organogenesis: formation of body organs and systems

• At eighth week

• All organ systems are recognizable

• End of the embryonic period


Specialization of Ectoderm

• Neurulation

• First major event of organogenesis

• Gives rise to brain and spinal cord

• Ectoderm over the notochord forms the neural plate

• Neural plate folds inward as a neural groove with neural folds


Specialization of Ectoderm

• By the 22nd day, neural folds fuse into a neural tube

• Anterior end brain; the rest spinal cord

• Neural crest cells cranial, spinal, and sympathetic ganglia, and adrenal medulla

Copyright © 2010 Pearson Education, Inc. Figure 28.10a

(a) 17 days. The flat three-layered embryo has completed gastrulation. Notochord and neural plate are present.

AmnionHead

Tail

Left

Cutedge ofamnion

Right

Primitivestreak

Amniotic cavity

Neural plate

Ectoderm

Mesoderm

Notochord

Endoderm

Yolk sac

Copyright © 2010 Pearson Education, Inc. Figure 28.10b

Somite

Intermediatemesoderm

Lateral platemesoderm

Coelom

Neuralcrest

Neural grooveNeuralfold

• Splanchnic mesoderm

• Somatic mesoderm

(b) 20 days. The neural folds form by folding of the neural plate, which then deepens, producing the neural groove. Three mesodermal aggregates form on each side of the notochord (somite, intermediate mesoderm, and lateral plate mesoderm).

Copyright © 2010 Pearson Education, Inc. Figure 28.10c

Neuralcrest

Somite

Surface ectoderm

Neuraltube

Notochord

(c) 22 days. The neural folds have closed, forming the neural tube which has detached from the surface ectoderm and lies between the surface ectoderm and the notochord. Embryonic body is beginning to undercut.

Copyright © 2010 Pearson Education, Inc. Figure 28.10d

Kidney and gonads(intermediate mesoderm)

Gut lining(endoderm)

• Parietal serosa

• Limb bud

Somaticmesoderm

• Dermis

• Visceral serosa

Splanchnicmesoderm

• Smooth muscle of gut

Epidermis (ectoderm)

DermatomeMyotomeSclerotome

Peritoneal cavity(coelom)

Neural tube(ectoderm) Somite

(d) End of week 4. Embryo undercutting is complete. Somites have subdivided into sclerotome, myotome, and dermatome, which form the vertebrae, skeletal muscles, and dermis respectively. Body coelom present.


Specialization of Endoderm

• Embryonic folding begins with lateral folds

• Next, head and tail folds appear

• Endoderm tube forms epithelial lining of the GI tract

• Organs of the GI tract become apparent, and oral and anal openings perforate

• Mucosal lining of respiratory tract forms from pharyngeal endoderm (foregut)


TailAmnion

Head

Yolk sac

Ectoderm Mesoderm Endoderm

Trilaminarembryonic disc

(a)


Lateralfold

Future gut(digestive tube)

(b)


Somites (seenthrough ectoderm)

Yolk sac

Headfold

Tailfold

(c)


Primitive gut

ForegutHindgut

Neural tube

Notochord

Yolk sac

(d)

Copyright © 2010 Pearson Education, Inc. Figure 28.12

Esophagus

Pharynx

Parathyroid glandsand thymus

Thyroid gland

Trachea

Right andleft lungs

Stomach

Liver

Pancreas

Gallbladder

Small intestine

Large intestine

Umbilicalcord

Connectionto yolk sac

Allantois5-week embryo


Specialization of Mesoderm

• First evidence is appearance of the notochord

• Three mesoderm aggregates appear lateral to notochord

• Somites, intermediate mesoderm, and double sheets of lateral plate mesoderm



• Somites (40 pairs) each have three functional parts

1. Sclerotome cells: produce vertebra and rib at each level

2. Dermatome cells: form dermis of the skin on the dorsal part of the body

3. Myotome cells: form skeletal muscles of the neck, trunk, and limbs (via limb buds)



• Intermediate mesoderm forms gonads and kidneys

• Lateral mesoderm consists of somatic and splanchnic mesoderm


Specialization of the Mesoderm

• Somatic mesoderm forms the:

• Dermis of the skin in the ventral region

• Parietal serosa of the ventral body cavity

• Bones, ligaments, and dermis of limbs

• Splanchnic mesoderm forms:

• The heart and blood vessels

• Most connective tissues of the body


(a) 17 days. The flat three-layered embryo has completed gastrulation. Notochord and neural plate are present.

AmnionHead

Tail

Left

Cutedge ofamnion

Right

Primitivestreak

Amniotic cavity

Neural plate

Ectoderm

Mesoderm

Notochord

Endoderm

Yolk sac


Somite

Intermediatemesoderm


Coelom

Neuralcrest

Neural grooveNeuralfold

• Splanchnic mesoderm

• Somatic mesoderm

(b) 20 days. The neural folds form by folding of the neural plate, which then deepens, producing the neural groove. Three mesodermal aggregates form on each side of the notochord (somite, intermediate mesoderm, and lateral plate mesoderm).


Neuralcrest

Somite

Surface ectoderm

Neuraltube

Notochord

(c) 22 days. The neural folds have closed, forming the neural tube which has detached from the surface ectoderm and lies between the surface ectoderm and the notochord. Embryonic body is beginning to undercut.


Kidney and gonads(intermediate mesoderm)

Gut lining(endoderm)

• Parietal serosa

• Limb bud

Somaticmesoderm

• Dermis

• Visceral serosa

Splanchnicmesoderm

• Smooth muscle of gut

Epidermis (ectoderm)

DermatomeMyotomeSclerotome

Peritoneal cavity(coelom)

Neural tube(ectoderm) Somite

(d) End of week 4. Embryo undercutting is complete. Somites have subdivided into sclerotome, myotome, and dermatome, which form the vertebrae, skeletal muscles, and dermis respectively. Body coelom present.


Epiblast

ECTODERM MESODERM ENDODERM

Notochord Somite Intermediatemesoderm


Somaticmesoderm

Splanchnicmesoderm

• Epidermis, hair, nails, glands of skin• Brain and spinal cord• Neural crest and derivatives (sensory nerve cells, pigment cells, bones and blood vessels of the head)

Nucleuspulposusof inter-vertebral

discs

• Sclerotome: vertebrae and ribs• Dermatome: dermis of dorsal body region• Myotome: trunk and limb musculature

• Kidneys• Gonads

• Parietal serosa• Dermis of ventral body region• Connective tissues of limbs (bones, joints, and ligaments)

• Wall of digestive and respiratory tracts (except epithelial lining)• Visceral serosa• Heart• Blood vessels

Epitheliallining and glands of digestive

and respiratory

tracts


Development of Fetal Circulation

• First blood cells arise in the yolk sac

• By the end of the third week

• Embryo has a system of paired vessels

• Vessels forming the heart have fused



• Unique vascular modifications

• Umbilical arteries and umbilical vein

• Three vascular shunts

• All are occluded at birth



• Vascular shunts

• Ductus venosus: bypasses liver (umbilical vein ductus venosus IVC)

• Foramen ovale: opening in interatrial septum; bypasses pulmonary circulation

• Ductus arteriosus: bypasses pulmonary circulation (pulmonary trunk ductus arteriosus aorta)


Aortic archFetusSuperior vena cavaDuctus arteriosus

Ligamentum arteriosum

Lung

Pulmonary arteryPulmonary veins

Heart

Foramen ovale

Fossa ovalis

LiverDuctus venosus

Ligamentum venosum

Ligamentum teres

Umbilical vein

Inferior vena cava

Hepatic portal vein

UmbilicusAbdominal aorta

Common iliac arteryUmbilical arteries

Medial umbilical ligaments

Urinary bladder

Umbilical cord

(a)

Placenta

High oxygenationModerate oxygenationLow oxygenationVery low oxygenation


Aortic arch NewbornSuperior vena cava

Ductus arteriosus

Ligamentum arteriosum

Lung

Pulmonary artery

Pulmonary veinsHeart

Foramen ovale

Fossa ovalis

Liver

Ductus venosus

Ligamentum venosum

Ligamentum teres

Umbilical vein

Inferior vena cava

Hepatic portal vein

Umbilicus

Abdominal aorta

Common iliac artery

Umbilical arteries

Medial umbilical ligaments

Urinary bladder

(b)

High oxygenation

Moderate oxygenationLow oxygenationVery low oxygenation


Events of Fetal Development

• Fetal period: weeks 9 through 38

• Time of rapid growth of body structures established in the embryo


Yolk sac

Cut edgeof chorion

Amniotic sac

(a) Embryo at week 7, about 17 mm long.

Umbilical cord

Umbilical vein

Chorionicvilli


Effects of Pregnancy: Anatomical Changes

• Reproductive organs become engorged with blood

• Chadwick’s sign: the vagina develops a purplish hue

• Breasts enlarge and areolae darken

• Pigmentation of facial skin many increase (chloasma)


Effects of Pregnancy: Anatomical Changes

• The uterus expands, occupying most of the abdominal cavity

• Lordosis occurs with the change in the center of gravity

•Weight gain of ~13 kg (28 lb)

• Relaxin causes pelvic ligaments and the pubic symphysis to relax to ease birth passage


(a) Before conception (Uterus the size of a fist and resides in the pelvis.)

(b) 4 months (Fundus of the uterus is halfway between the pubic symphysis and the umbilicus.)

(c) 7 months (Fundus is well above the umbilicus.)

(d) 9 months (Fundus reaches the xiphoid process.)


Effects of Pregnancy: Metabolic Changes

• Placental hormones

• Human placental lactogen (hPL), or human chorionic somatomammotropin (hCS)

• maturation of the breasts, fetal growth, and glucose sparing in the mother

• Human chorionic thyrotropin (hCT)

• maternal metabolism

• Parathyroid hormone and vitamin D levels are high throughout pregnancy


Effects of Pregnancy: Physiological Changes

• GI tract

• Morning sickness due to elevated levels of estrogen and progesterone

• Heartburn and constipation are common

• Urinary system

• Urine production due to metabolism and fetal wastes

• Stress incontinence may occur as bladder is compressed



• Respiratory system

• Estrogens may cause nasal edema and congestion

• Tidal volume increases

• Dyspnea (difficult breathing) may occur later in pregnancy



• Cardiovascular system

• Blood volume increases 25–40%

• Blood pressure and pulse rise

• Venous return from lower limbs may be impaired, resulting in varicose veins


Parturition

• Parturition giving birth to the baby

• Labor events that expel the infant from the uterus


Initiation of Labor

• During the last few weeks of pregnancy

• Fetal secretion of cortisol stimulates the placenta to secrete more estrogen

• Causes production of oxytocin receptors by myometrium

• Antagonizes calming effects of progesterone, leading to Braxton Hicks contractions in uterus


Initiation of Labor

• Surfactant protein A (SP-A) from fetal lungs causes softening of the cervix

• Fetal oxytocin causes the placenta to produce prostaglandins

• Oxytocin and prostaglandins: powerful uterine muscle stimulants


Initiation of Labor

• Maternal emotional and physical stress

• Activates the hypothalamus, causing oxytocin release from posterior pituitary

• Positive feedback mechanism occurs


Estrogen

fromplacenta

Induces oxytocinreceptors on uterus

Oxytocin

from fetusand mother’s posterior pituitary

Stimulates uterusto contract

Stimulatesplacenta to make

Stimulate morevigorous contractionsof uterus

Prostaglandins

(+)

(+)


Stages of Labor: Dilation Stage

• Longest stage of labor: 6–12 hours or more

• Initial weak contractions:

• 15–30 minutes apart, 10–30 seconds long

• Become more vigorous and rapid

• Cervix effaces and dilates fully to 10 cm

• Amnion ruptures, releasing amniotic fluid

• Engagement occurs: head enters the true pelvis


Umbilicalcord

Uterus

Cervix

Vagina

(a) Dilation (early)

Placenta


Pubicsymphysis

Sacrum

(b) Dilation (late)


Stages of Labor: Expulsion Stage

• Strong contractions every 2–3 minutes, about 1 minute long

• Urge to push increases (in absence of local anesthesia)

• Crowning occurs when the largest dimension of the head distends vulva

• Delivery of infant


Perineum

(c) Expulsion


Stages of Labor: Placental Stage

• Strong contractions continue, causing detachment of the placenta and compression of uterine blood vessels

• Delivery of the afterbirth (placenta and membranes) occurs ~30 minutes after birth

• All placenta fragments must be removed to prevent postpartum bleeding


Uterus

Placenta(detaching)

Umbilicalcord

(d) Placental


Adjustments of the Infant to Extrauterine Life

• Neonatal period: four-week period immediately after birth

• Physical status is assessed 1–5 minutes after birth

• Apgar score: 0–2 points each for

• Score of 8–10: healthy

•Heart rate

•Respiration

•Color

•Muscle tone

•Reflexes


First Breath

• CO2 central acidosis stimulates respiratory control centers to trigger the first inspiration

• Requires tremendous effort: airways are tiny and the lungs are collapsed

• Surfactant in alveolar fluid helps reduce surface tension

• Respiratory rate: ~45 per minute for first two weeks, then declines


Transitional Period

• Unstable period lasting 6–8 hours after birth

• Alternating periods of activity and sleep

• Vital signs may be irregular during activity

• Stabilizes with waking periods occurring every 3–4 hours


Occlusion of Fetal Blood Vessels

• Umbilical arteries and vein constrict and become fibrosed

• Proximal umbilical arteries superior vesical arteries to urinary bladder

• Distal umbilical arteries medial umbilical ligaments


Occlusion of Fetal Blood Vessels

• Umbilical vein becomes the ligamentum teres

• Ductus venosus ligamentum venosum

• Foramen ovale fossa ovalis

• Ductus arteriosus ligamentum arteriosum


Lactation

• Production of milk by the mammary glands

• Toward the end of pregnancy

• Placental estrogens, progesterone, and lactogen stimulate the hypothalamus to release prolactin-releasing factors (PRFs)

• Anterior pituitary releases prolactin


Lactation

• Colostrum

• Yellowish secretion rich in vitamin A, protein, minerals, and IgA antibodies

• Released the first 2–3 days

• Followed by true milk production

• Suckling initiates a positive feedback mechanism

• Oxytocin causes the letdown reflex


Alveolar glandsrespond by

releasing milk through ducts of

nipples.

Hypothalamussends efferent

impulses to the posterior

pituitary where oxytocin is stored.

Anterior pituitarysecretes prolactin

to blood.

Inhibits hypothalamic neurons thatrelease dopamine. Hypothalamus

releases prolactin releasing factors(PRF) to portal circulation.

Oxytocin is released from theposterior pituitary

and stimulatesmyoepithelial cells

of breasts to contract.

Prolactin targetslactiferous glands.

Milk production

Start

Stimulation of mechanoreceptors

in nipples by suckling infant sends afferent impulses to the hypothalamus.


Advantages of Breast Milk

• Fats and iron are easily absorbed; amino acids more easily metabolized, compared with cow’s milk

• Beneficial chemicals: IgA, complement, lysozyme, interferon, and lactoperoxidase

• Interleukins and prostaglandins prevent overzealous inflammatory responses


Advantages of Breast Milk

• Natural laxative effect helps eliminate bile-rich meconium, helping to prevent physiological jaundice

• Encourages bacterial colonization of the large intestine


Assisted Reproductive Technology

• Surgical removal of oocytes following hormone stimulation

• Fertilization of oocytes

• Return of fertilized oocytes to the woman’s body



• In vitro fertilization (IVF)

• Oocytes and sperm are incubated in culture dishes for several days

• Embryos (two-cell to blastocyst stage) are transferred to uterus for possible implantation



• Zygote intrafallopian transfer (ZIFT

• Fertilized oocytes are transferred to the uterine tubes

• Gamete intrafallopian transfer (GIFT)

• Sperm and harvested oocytes are transferred together into the uterine tubes

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