Human Reproduction, Development & Ageing - Week 8 Lecture Notes

Topic = The Newborn Infant, Development and Lactation

Guiding Questions

  • How does the fetal blood supply change at birth?

  • What are associated developmental disorders?

  • Detailed exploration of lactation including:

    • Breast anatomy & physiology

    • Recent findings highlighting research neglect of female reproduction.

Heart Anatomy

  • Features of the Heart:

    • Brachiocephalic

    • Superior vena cava

    • Right pulmonary arteries

    • Ascending aorta

    • Fossa ovalis

    • Opening of coronary sinus

    • RIGHT ATRIUM: Contains pectinate muscles, Conus arteriosus, cusp of right AV (tricuspid) valve, chordae tendineae, and papillary muscles.

    • RIGHT VENTRICLE: Includes inferior vena cava trunk, aortic arch.

    • LEFT ATRIUM: Features left common carotid artery, left subclavian artery, ligamentum arteriosum.

    • LEFT VENTRICLE: Contains pulmonary trunk, pulmonary valve, left pulmonary arteries, left pulmonary veins, interventricular septum, trabeculae carneae, and moderator band.

    • Visuals: Frontal section through the heart.

Development and Lactation

  • Major changes for the newborn after delivery include:

    • The necessity for the baby to breathe independently.

    • Before birth, highly oxygenated blood flows from the placenta to the fetus via the umbilical vein.

    • Approximately half of this blood directly reaches the inferior vena cava (IVC).

Blood Dynamics

  • Blood Flow Dynamics After Delivery:

    • Half of the blood passes through the liver before entering the inferior vena cava.

    • The other half bypasses the liver through the DUCTUS VENOSUS.

Right Atrium Blood Mixing

  • Blood entering the right atrium mixes with deoxygenated blood from various body regions including the limbs and head.

  • Oxygen saturation in the right atrium is less than in the umbilical vein.

Fetal Circulation Overview

  • Components of Fetal Circulation:

    • Foramen ovale (open)

    • Placenta

    • Liver

    • Umbilical vein

    • Ductus arteriosus (open)

    • Pulmonary trunk

    • Inferior vena cava

    • Ductus venosus

    • Umbilical arteries

    • Umbilical cord

  • Visual representation of the circulation in a full-term fetus.

Blood Passage to Left Atrium

  • Majority of blood in the right atrium passes to the left atrium via the foramen ovale.

  • In the left atrium, blood mixes with deoxygenated blood from the lungs, due to the non-functional state of fetal lungs.

Blood Flow to the Ventricles

  • From the left atrium, blood flows into the left ventricle then into the ascending aorta.

  • This ensures that major arteries to the heart, head, and upper limbs receive properly oxygenated blood.

  • Some blood enters the right ventricle, which experiences moderate oxygenation, contributing to some blood supply to the lungs for nutrient transport.

Bypassing the Lungs

  • Since the fetal lungs are non-functional, most blood bypasses them via the Ductus Arteriosus.

  • About half of this blood returns to the placenta for reoxygenation through the umbilical arteries, while the other half supplies the gut and lower limbs.

Circulation Anomalies

  • Patent Ductus Arteriosus

    • Comparison between normal and abnormal circulation.

Transition at Birth

  • Changes upon birth: All fetal shunts are rendered unnecessary as placental circulation ceases and the lungs are activated for function.

Ductus Venosus Post-Birth

  • The ductus venosus constricts following birth and transforms into the ligamentum venosum, filling with connective tissue, impacting blood pressure in IVC and the right atrium.

Changes in Pulmonary Blood Flow

  • Upon the first breaths, arterial walls in the lungs reduce in thickness due to air influx.

  • This leads to a rapid decline in pulmonary vascular resistance, increasing blood flow to the lungs.

  • The resultant pressure in the left atrium exceeds that in the right atrium, causing closure of the foramen ovale.

Ductus Arteriosus Closure

  • The ductus arteriosus also constricts at birth.

  • Closure occurs typically within 10-15 hours post-delivery and becomes the ligamentum arteriosum.

Changes in Ventricular Walls

  • Prior to birth, the right ventricular wall is thicker due to higher workload.

  • One month post-birth, the left ventricular wall becomes thicker due to increased workload, while the right atrophies with reduced workload.

Circulation Representation

  • Schematic representations illustrating the circulations of the fetus, neonate, and adult.

Fetal to Newborn Transition and Anatomy

  • Overview of major anatomical changes from fetus to newborn including the aorta, ductus arteriosus, and changes in blood oxygenation levels.

Overview of Developmental Disorders

  • Congenital Heart Defects (CHD):

    • Most common birth defect.

    • Can range from asymptomatic to life-threatening.

    • Risk factors include maternal health issues, rubella, alcoholism, and poor nutrition during pregnancy.

Atrial Septal Defect

  • Conditions where the foramen ovale fails to close after birth, allowing oxygenated blood to flow from the left atrium to the right atrium, ultimately overworking the right side of the heart.

Impacts of Atrial Septal Defect

  • The left-to-right shunt causes oxygenated blood to remain in the pulmonary circuit, leading to inefficiency in systemic circulation.

  • More prevalent in females and often requires surgical correction.

Ventricular Septal Defect

  • The most common congenital heart defect (approximately 25%), characterized by a hole between left and right ventricles.

  • Results in overload to the right side of the heart due to higher pressure in the left ventricle.

Septal Defects

  • Description of small and large septal defects; their effects on pressure and oxygenation, and the potential for cyanosis if shunt reverses.

Patent Ductus Arteriosus

  • The ductus arteriosus remains open post-birth, causing backflow of blood into the pulmonary artery, leading to heart overload.

  • Surgical intervention is often required and is more common in females.

Coarctation of the Aorta

  • A condition involving narrowing of the descending aorta causing disparities in blood pressure above and below the constriction.

  • Results in an increase in cardiac workload.

Tetralogy of Fallot

  • A constellation of four heart defects:

    1. Pulmonary valve stenosis

    2. Right ventricular hypertrophy

    3. Ventricular septal defect

    4. Displaced aorta

  • This combination leads to cyanosis in affected infants, referred to as “blue baby” syndrome.

Illustrated Tetralogy of Fallot

  • Diagram detailing the four defects along with normal anatomy for comparison.

Neurological Disorders

  • Description of Cerebral Palsy:

    • May result from reduced oxygen supply during fetal development or during birth.

    • Factors include maternal infections, trauma during birth or infancy.

Cerebral Palsy Details

  • Predominantly affects males and premature infants.

  • Affects motor functions, may accompany seizures, and ulterior deficits.

  • No cure exists; treatment focuses on managing symptoms.

Spina Bifida

  • A congenital defect resulting from incomplete closure of the vertebrae over the spinal cord.

  • Potential for associated complications such as hydrocephalus and varying degrees of nerve involvement.

Risk Factors for Spina Bifida

  • Associated with unknown causes, however, lack of folate during pregnancy is a strong contributory factor.

  • Other risk factors include genetic history and maternal exposure to radiation.

Associated Disorders with Spina Bifida

  • Potentially accompanied by conditions such as hydrocephalus, cleft lip, and clubfoot.

  • Most common form is Spina Bifida Occulta, typically asymptomatic.

Hydrocephalus Overview

  • Definition and implications of hydrocephalus in neural conditions.

Myelomeningocoele

  • A form of spina bifida where parts of the spinal cord and nerves protrude through the vertebrae, potentially leading to severe neurological complications.

  • Surgical interventions may be necessary.

Introduction to Lactation

  • Defined as a unique mammalian process allowing offspring nourishment particularly when food sources are limited.

Benefits of Breastfeeding

  • Infants experience:

    • Improved cognitive development

    • Decreased risk of ear infections

    • Reduced risk of Sudden Infant Death Syndrome (SIDS).

Consequences of Formula Feeding

  • Studies indicate a 1.3-fold increase in infant mortality

  • Associated with high risks of obesity, Type 2 diabetes, and cardiovascular disease (CVD).

Global Perspectives on Breastfeeding

  • Variability in breastfeeding practices across countries affecting durations and rates of amenorrhea.

Global Breastfeeding Trends

  • Median duration of breastfeeding differs across nations (Indonesia, Kenya, Zimbabwe, Mexico, Brazil); some produce breast milk without amenorrhea.

World Breastfeeding Statistics

  • Representation of breastfeeding initiation rates and durations across various countries, highlighting significant trends.

Physiology of Lactation - Five Stages

  1. Mammogenesis: Development of functional breast tissue.

  2. Lactogenesis: Process of synthesizing and secreting milk.

  3. Galactokinesis: Ejection of milk from the nipple.

  4. Galactopoiesis: Maintenance of milk production.

  5. Involution: Regression of breast tissue after lactation.

Breast Anatomy During Lactation

  • Secretory tissues originate from ectodermal structures, developing notably during 30-40 weeks gestation.

  • Lobar structures associated with colostrum appear before and shortly after birth.

Tissue Development Dynamics

  • Ovarian steroids influence glandular mass increase during puberty, particularly due to estrogen effects.

Breast Structure Overview

  • Anatomy of a lactating breast:

    • Lobular structures contain alveoli leading to lactiferous ducts, which connect to the nipple.

    • Notable structures include Cooper's ligaments, retromammary fat, and glandular tissue.

Understanding Lactation Anatomy

  • Changes in anatomical structures and ratios of glandular to fat tissue in lactating women; 65% glandular within 30 mm of the nipple base.

Comparative Breast Anatomy

  • Differences between older conceptual models of breast anatomy and recent findings, highlighting inaccurate assumptions regarding duct structures.

Ultrasonography and Lactation Studies

  • Recent imaging studies show complexities in the lactating breast and the misinterpretations of older anatomical models.

Microscopic Structure of Breast Tissue

  • Farewell to assumptions about large duct reservoirs; structural breakdown at a microscopic level focusing on secretory processes within lobules.

Alveolar and Ductal Structures

  • Description of microscopic arrangement in lactating breast tissue, highlighting myoepithelial cells' roles and secretory function dynamics.

Lactation Growth Dynamics

  • Continued growth and differentiation during lactation, adjusting to milk volume demands.

Composition of Breast Milk

  • Characteristics of breast milk at birth: high protein, low lactose.

  • Composition transitions as lactation progresses, reverting at weaning.

Evolution of Milk Composition

  • Detailed analysis of breast milk composition across different stages of lactation: colostrum and transitional milk to mature milk.

Hormonal Changes and Milk Secretion

  • Hormonal control during pregnancy and postpartum influencing milk secretion mechanics and breast physiology.

Lactation Period Length

  • Duration of breastfeeding can be flexible, with milk composition remaining fairly stable over time; weaning approaches vary from abrupt to gradual.

Prolactin's Role in Lactation

  • Prolactin secretion dynamics: critical for breast tissue development and milk synthesis, with levels fluctuating after breastfeeding.

Oxytocin Functionality in Lactation

  • Role of oxytocin in the milk ejection reflex, including its release mechanism following nipple stimulation.

Neural Pathways in Lactation

  • Explanation of sensory pathways connecting nipple stimulation to oxytocin release, highlighting complex neuroanatomy involved.

Factors Affecting Milk Production

  • Avoidance of factors such as nutrition and stress impacting breast milk supply while maintaining a safeguard on production levels.

Production Adaptability in Lactation

  • Breast milk quantity will adjust according to infant demand, with expressed milk as an option for increasing output.

Advantages of Breast Milk

  • Nutritional superiority compared to alternatives, rich in secretory IgA and antibacterial enzymes, enhancing an infant's immunity.

Closing Remarks on Breastfeeding Research

  • Discussion on existing gaps in research concerning mother's milk in comparison to other subjects, bringing attention to its critical role in infant development.

Conclusion

  • Understanding the complexities of lactation and its implications is vital for both mother and infant health, emphasizing the need for ongoing research.