organogenesis gastrulation sets the stage for organogenesis, the formation of body organs...

OrganogenesisOrganogenesis

Gastrulation sets the stage for organogenesis, Gastrulation sets the stage for organogenesis, the formation of body organsthe formation of body organs

By the 8By the 8thth week all organ systems are week all organ systems are recognizablerecognizable

Specialization of EctodermSpecialization of Ectoderm

Neurulation – the first event of organogenesis Neurulation – the first event of organogenesis gives rise to the brain and spinal cordgives rise to the brain and spinal cord

Ectoderm over the notochord thickens, Ectoderm over the notochord thickens, forming the neural plateforming the neural plate

The neural plate folds inward as a neural The neural plate folds inward as a neural groove with prominent neural foldsgroove with prominent neural folds

Specialization of EctodermSpecialization of Ectoderm

By the 22By the 22ndnd day, neural folds fuse into a neural day, neural folds fuse into a neural tube, which pinches off into the bodytube, which pinches off into the body

The anterior end becomes the brain; the rest The anterior end becomes the brain; the rest becomes the spinal cordbecomes the spinal cord

Associated neural crest cells give rise to Associated neural crest cells give rise to cranial, spinal, and sympathetic gangliacranial, spinal, and sympathetic ganglia

Specialization of EndodermSpecialization of Endoderm

Embryonic folding begins with lateral foldsEmbryonic folding begins with lateral folds Next, head and tail folds appearNext, head and tail folds appear An endoderm tube forms the epithelial lining of An endoderm tube forms the epithelial lining of

the GI tractthe GI tract Organs of the GI tract become apparent, and oral Organs of the GI tract become apparent, and oral

and anal openings perforateand anal openings perforate Endoderm forms epithelium linings of the Endoderm forms epithelium linings of the

hollow organs of the digestive and respiratory hollow organs of the digestive and respiratory tractstracts

Specialization of the MesodermSpecialization of the Mesoderm

First evidence is the appearance of the First evidence is the appearance of the notochord notochord

Three mesoderm aggregates appear lateral to Three mesoderm aggregates appear lateral to the notochordthe notochord Somites, intermediate mesoderm, and double Somites, intermediate mesoderm, and double

sheets of lateral mesodermsheets of lateral mesoderm


The 40 pairs of somites have three functional The 40 pairs of somites have three functional parts: parts: Sclerotome – produce the vertebrae and ribs Sclerotome – produce the vertebrae and ribs Dermatome – help form the dermis of the skin on Dermatome – help form the dermis of the skin on

the dorsal part of the bodythe dorsal part of the body Myotome – form the skeletal muscles of the neck, Myotome – form the skeletal muscles of the neck,

trunk, and limbstrunk, and limbs


Intermediate mesoderm forms the gonads and Intermediate mesoderm forms the gonads and the kidneysthe kidneys

Lateral mesoderm consists of somatic and Lateral mesoderm consists of somatic and splanchnic mesodermsplanchnic mesoderm


Somatic mesoderm forms the:Somatic mesoderm forms the: Dermis of the skin in the ventral regionDermis of the skin in the ventral region Parietal serosa of the ventral body cavityParietal serosa of the ventral body cavity Bones, ligaments, and dermis of the limbsBones, ligaments, and dermis of the limbs

Splanchnic mesoderm forms: Splanchnic mesoderm forms: The heart and blood vessels The heart and blood vessels Most connective tissues of the bodyMost connective tissues of the body

Development of Fetal CirculationDevelopment of Fetal Circulation

By the end of the 3By the end of the 3rdrd week: week: The embryo has a system of paired vesselsThe embryo has a system of paired vessels The vessels forming the heart have fusedThe vessels forming the heart have fused

Development of Fetal CirculationDevelopment of Fetal Circulation

Unique vascular modifications seen in prenatal Unique vascular modifications seen in prenatal development include umbilical arteries and development include umbilical arteries and veins, and three vascular shunts (occluded at veins, and three vascular shunts (occluded at birth)birth) Ductus venosus – venous shunt that bypasses the Ductus venosus – venous shunt that bypasses the

liverliver Foramen ovale – opening in the interatrial septa to Foramen ovale – opening in the interatrial septa to

bypass pulmonary circulationbypass pulmonary circulation Ductus arteriosus – transfers blood from the right Ductus arteriosus – transfers blood from the right

ventricle to the aortaventricle to the aorta

Effects of Pregnancy: Anatomical Effects of Pregnancy: Anatomical ChangesChanges

Chadwick’s sign – the vagina develops a Chadwick’s sign – the vagina develops a purplish huepurplish hue

Breasts enlarge and their areolae darkenBreasts enlarge and their areolae darken The uterus expands, occupying most of the The uterus expands, occupying most of the

abdominal cavityabdominal cavity

Effects of Pregnancy: Anatomical Effects of Pregnancy: Anatomical ChangesChanges

Lordosis is common due to the change of the Lordosis is common due to the change of the body’s center of gravitybody’s center of gravity

Relaxin causes pelvic ligaments and the pubic Relaxin causes pelvic ligaments and the pubic symphysis to relaxsymphysis to relax

Typical weight gain is about 29 poundsTypical weight gain is about 29 pounds

Effects of Pregnancy: Metabolic Effects of Pregnancy: Metabolic ChangesChanges

The placenta secretes human placental The placenta secretes human placental lactogen (hPL), also called human chorionic lactogen (hPL), also called human chorionic somatomammotropin (hCS), which stimulates somatomammotropin (hCS), which stimulates the maturation of the breaststhe maturation of the breasts

hPL promotes growth of the fetus and exerts a hPL promotes growth of the fetus and exerts a maternal glucose-sparing effectmaternal glucose-sparing effect

Human chorionic thyrotropin (hCT) increases Human chorionic thyrotropin (hCT) increases maternal metabolismmaternal metabolism

Parathyroid hormone levels are high, ensuring Parathyroid hormone levels are high, ensuring a positive calcium balance a positive calcium balance

Effects of Pregnancy: Effects of Pregnancy: Physiological ChangesPhysiological Changes

GI tract – morning sickness occurs due to GI tract – morning sickness occurs due to elevated levels of estrogen and progesteroneelevated levels of estrogen and progesterone

Urinary system – urine production increases to Urinary system – urine production increases to handle the additional fetal wasteshandle the additional fetal wastes

Respiratory system – edematous and nasal Respiratory system – edematous and nasal congestion may occurcongestion may occur Dyspnea (difficult breathing) may develop late in Dyspnea (difficult breathing) may develop late in

pregnancypregnancy

Effects of Pregnancy: Effects of Pregnancy: Physiological ChangesPhysiological Changes

Cardiovascular system – blood volume Cardiovascular system – blood volume increases increases 25-40%25-40% Venous pressure from lower limbs is impaired, Venous pressure from lower limbs is impaired,

resulting in varicose veinsresulting in varicose veins

Parturition: Initiation of LaborParturition: Initiation of Labor Estrogen reaches a peak during the last weeks Estrogen reaches a peak during the last weeks

of pregnancy causing myometrial weakness of pregnancy causing myometrial weakness and irritabilityand irritability

Weak Braxton Hicks contractions may take Weak Braxton Hicks contractions may take placeplace

As birth nears, oxytocin and prostaglandins As birth nears, oxytocin and prostaglandins cause uterine contractionscause uterine contractions

Emotional and physical stress: Emotional and physical stress: Activates the hypothalamus Activates the hypothalamus Sets up a positive feedback mechanism, releasing Sets up a positive feedback mechanism, releasing

more oxytocinmore oxytocin

Parturition: Initiation of LaborParturition: Initiation of Labor

Figure 28.16

Stages of Labor: Dilation StageStages of Labor: Dilation Stage

From the onset of labor until the cervix is fully From the onset of labor until the cervix is fully dilated (10 cm)dilated (10 cm)

Initial contractions are 15–30 minutes apart Initial contractions are 15–30 minutes apart and 10–30 seconds in durationand 10–30 seconds in duration

The cervix effaces and dilatesThe cervix effaces and dilates The amnion ruptures, releasing amniotic fluid The amnion ruptures, releasing amniotic fluid

(breaking of the water)(breaking of the water) Engagement occurs as the infant’s head enters Engagement occurs as the infant’s head enters

the true pelvisthe true pelvis

Stages of Labor: Dilation StageStages of Labor: Dilation Stage

Figure 28.17a, b

Stages of Labor: Expulsion StageStages of Labor: Expulsion Stage

From full dilation to delivery of the infantFrom full dilation to delivery of the infant Strong contractions occur every 2–3 minutes Strong contractions occur every 2–3 minutes

and last about 1 minuteand last about 1 minute The urge to push increases in labor without The urge to push increases in labor without

local anesthesialocal anesthesia Crowning occurs when the largest dimension Crowning occurs when the largest dimension

of the head is distending the vulvaof the head is distending the vulva


Figure 28.17c


The delivery of the placenta is accomplished The delivery of the placenta is accomplished within 30 minutes of birthwithin 30 minutes of birth

Afterbirth – the placenta and its attached fetal Afterbirth – the placenta and its attached fetal membranesmembranes

All placenta fragments must be removed to All placenta fragments must be removed to prevent postpartum bleedingprevent postpartum bleeding


Figure 28.17d

Extrauterine LifeExtrauterine Life

At 1-5 minutes after birth, the infant’s physical At 1-5 minutes after birth, the infant’s physical status is assessed based on five signs: heart status is assessed based on five signs: heart rate, respiration, color, muscle tone, and rate, respiration, color, muscle tone, and reflexesreflexes

Each observation is given a score of 0 to 2Each observation is given a score of 0 to 2 Apgar score – the total score of the above Apgar score – the total score of the above

assessmentsassessments 8-10 indicates a healthy baby8-10 indicates a healthy baby Lower scores reveal problems Lower scores reveal problems

First BreathFirst Breath

Once carbon dioxide is no longer removed by Once carbon dioxide is no longer removed by the placenta, central acidosis occursthe placenta, central acidosis occurs

This excites the respiratory centers to trigger This excites the respiratory centers to trigger the first inspirationthe first inspiration

This requires tremendous effort – airways are This requires tremendous effort – airways are tiny and the lungs are collapsedtiny and the lungs are collapsed

Once the lungs inflate, surfactant in alveolar Once the lungs inflate, surfactant in alveolar fluid helps reduce surface tensionfluid helps reduce surface tension

Occlusion of Fetal Blood VesselsOcclusion of Fetal Blood Vessels

Umbilical arteries and vein constrict and become Umbilical arteries and vein constrict and become fibrosedfibrosed

Fates of fetal vesselsFates of fetal vessels Proximal umbilical arteries become superior vesical arteries Proximal umbilical arteries become superior vesical arteries

and distal parts become the medial umbilical ligamentsand distal parts become the medial umbilical ligaments The umbilical vein becomes the ligamentum teresThe umbilical vein becomes the ligamentum teres The ductus venosus becomes the ligamentum venosumThe ductus venosus becomes the ligamentum venosum The foramen ovale becomes the fossa ovalisThe foramen ovale becomes the fossa ovalis The ductus arteriosus becomes the ligamentum arteriosumThe ductus arteriosus becomes the ligamentum arteriosum

Transitional PeriodTransitional Period

Unstable period lasting 6-8 hours after birthUnstable period lasting 6-8 hours after birth The first 30 minutes the baby is alert and The first 30 minutes the baby is alert and

activeactive Heart rate increases (120-160 beats/min.)Heart rate increases (120-160 beats/min.) Respiration is rapid and irregular Respiration is rapid and irregular Temperature fallsTemperature falls

Transitional PeriodTransitional Period

Activity then diminishes and the infant sleeps Activity then diminishes and the infant sleeps about three hoursabout three hours

A second active stage follows in which the A second active stage follows in which the baby regurgitates mucus and debrisbaby regurgitates mucus and debris

After this, the infant sleeps, with waking After this, the infant sleeps, with waking periods occurring every 3-4 hoursperiods occurring every 3-4 hours

LactationLactation

The production of milk by the mammary The production of milk by the mammary glandsglands

Estrogens, progesterone, and lactogen Estrogens, progesterone, and lactogen stimulate the hypothalamus to release stimulate the hypothalamus to release prolactin-releasing hormone (PRH)prolactin-releasing hormone (PRH)

The anterior pituitary responds by releasing The anterior pituitary responds by releasing prolactinprolactin

LactationLactation

ColostrumColostrum Solution rich in vitamin A, protein, minerals, and Solution rich in vitamin A, protein, minerals, and

IgA antibodies IgA antibodies Is released the first 2–3 daysIs released the first 2–3 days Is followed by true milk productionIs followed by true milk production

Lactation and Lactation and Milk Let-down Milk Let-down

ReflexReflex

After birth, After birth, milk milk production is production is stimulated by stimulated by the sucking the sucking infantinfant

Figure 28.18

Breast MilkBreast Milk

Advantages of breast milk for the infantAdvantages of breast milk for the infant Fats and iron are better absorbedFats and iron are better absorbed Its amino acids are metabolized more efficiently than those Its amino acids are metabolized more efficiently than those

of cow’s milkof cow’s milk Beneficial chemicals are present – IgA, other Beneficial chemicals are present – IgA, other

immunoglobulins, complement, lysozyme, interferon, and immunoglobulins, complement, lysozyme, interferon, and lactoperoxidaselactoperoxidase

Interleukins and prostaglandins are present, which prevent Interleukins and prostaglandins are present, which prevent overzealous inflammatory responsesoverzealous inflammatory responses

Its natural laxatives help cleanse the bowels of meconiumIts natural laxatives help cleanse the bowels of meconium

organogenesis gastrulation sets the stage for organogenesis, the formation of body organs...

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