Reproductive Physiology & Fetal Development

Fetal circulation is similar to adult circulation but modified due to non-functional lungs.
The pulmonary circuit is bypassed to reach the systemic circuit sooner.
Reddish/pinkish colors indicate oxygenated blood, blue indicates carbon dioxide-rich blood; purple indicates mixed blood.
Arteries carry blood away from the heart, veins carry it to the heart.
One umbilical vein carries oxygenated blood from the placenta to the fetus; two umbilical arteries carry deoxygenated blood from the fetus to the placenta.
The umbilical vein goes under the liver and connects to the inferior vena cava.
The inferior vena cava carries deoxygenated blood, so mixing occurs when the umbilical vein joins it.
Blood is shunted from the right to the left side of the heart to bypass the pulmonary circuit.
Umbilical arteries originate from the internal iliac arteries.
After birth, umbilical vessels disintegrate and become adult structures.

Maternal blood high in oxygen and nutrients comes from uterine arteries.
Oxygen and nutrients diffuse through the placental membrane into the umbilical vein due to concentration gradients.
The umbilical vein has the highest oxygen concentration (~80% saturation).
The umbilical vein passes under the liver and connects to the inferior vena cava.
The ductus venosus is a shunt that also connects the umbilical vein to the inferior vena cava, becoming the ligamentum teres in adults (attaches liver to umbilicus).
The inferior vena cava is positioned to direct oxygen-rich blood towards the left atrium.

Blood from the right side of the heart is shunted to the systemic circuit via two routes.
Foramen ovale: A hole between the right and left atria facilitates blood flow from the inferior vena cava directly to the left atrium.
Ductus arteriosus: Connects the pulmonary trunk to the aorta.

Blood from the superior vena cava (deoxygenated) mixes with oxygenated blood from the inferior vena cava in the right atrium.
This mixed blood enters the right ventricle and pulmonary trunk.
Some blood flows to the lungs for development.
Pulmonary veins return blood (now with more carbon dioxide) to the left atrium, mixing with oxygenated blood from the foramen ovale.
The ductus arteriosus shunts blood from the pulmonary trunk to the aorta after the brachiocephalic, left common carotid, and left subclavian arteries to ensure oxygenated blood reaches the head.
Mixing occurs in the inferior vena cava (umbilical vein + deoxygenated blood), right atrium (superior vena cava + inferior vena cava), right ventricle, and after the left subclavian artery (ductus arteriosus).
The highest oxygen concentration is in the umbilical vein; the highest carbon dioxide concentration is in the vena cavae.

Blood travels through the dorsal aorta to the internal iliac arteries, where the umbilical arteries originate.
Umbilical arteries carry carbon dioxide and waste to the placenta for removal.
The mother's system removes carbon dioxide and waste.
Oxygen saturation decreases from the umbilical vein to the umbilical arteries due to mixing.

Primarily involves growth; the foundation is laid in the first trimester.
The mother's body adapts to accommodate the growing fetus, with organs being displaced.
The uterus can reach the xiphoid process, making breathing difficult.

Increased pressure in the abdominal-pelvic cavity.
Swelling in feet and ankles due to pressure on pelvic blood vessels (especially veins).
Hormone relaxin loosens ligaments, including the round ligament and uterosacral ligament, and the pubic symphysis.
Lordosis: Accentuated lumbar curve due to a shift in the center of gravity.

Initiation by the fetus: Adrenal glands release cortisol, stimulating the placenta to increase oxytocin receptors in the myometrium.
Increased estrogen levels from the placenta.
Oxytocin from the mother and fetus stimulates uterine contractions.
Prostaglandins are released from the placenta, causing further uterine contractions and cervical dilation.
Positive feedback loop: Uterine contractions $\rightarrow$ baby's head pushes on cervix $\rightarrow$ more oxytocin release $\rightarrow$ stronger contractions.

Dilation phase: Cervix dilates (up to 10 cm), amniotic sac ruptures.
Expulsion phase: Baby is pushed out of the uterus and vagina (crowning).
Placental stage: Placenta is expelled from the uterus; maternal and fetal blood may mix.
The placenta must be fully removed to prevent infection and hemorrhage.

Making the baby cry helps to make sure that the breathing occurs.
Cutting the umbilical cord and initiating breathing changes fetal circulation to adult circulation.
Foramen ovale closes and becomes the fossa ovalis.
Ductus arteriosus constricts.
Ductus venosus degrades over time.

A secondary circulatory system that complements the cardiovascular system.
Returns fluid to veins, transports lipids, and supports the immune system.
Lymphatic system has three functions:
- Return fluid to our veins.
- Transport lipids.
- Immune system.

Returns fluid to the veins to maintain blood volume.
Transports lipids, including fat-soluble vitamins, via lacteals in the small intestine.

Lymphatic capillaries $\rightarrow$ lymphatic vessels $\rightarrow$ lymph nodes $\rightarrow$ lymphatic trunks $\rightarrow$ lymphatic ducts.
Lymphatic ducts drain into the right and left subclavian areas near the heart.

Collect excess substances around blood capillary beds.
Have a tunica intima but are modified to allow fluid entry but not exit.
End points with finger-like projections.
Epithelial cells overlap, forming mini-valves that open with increased interstitial fluid pressure.
Mini-valves allow large fats, viruses, bacteria, and white blood cells to enter.
Create lymph, which is similar to blood but without erythrocytes.

Lymphatic vessels merge to form lymphatic trunks that drain specific body regions.
Named after the region they drain (e.g., intestinal, lumbar, jugular).

Trunks merge to form two lymphatic ducts: the right lymphatic duct and the thoracic duct.
Location of Lymphatic Ducts:
* The midline.
* Diaphragm.
* Cut the right side from the left side.

Drains the right head and neck, right arm, and right thorax.
Short and empties into the junction of the subclavian and internal jugular veins.

Drains the lower limbs, abdominal-pelvic area, left thorax, left arm, and left head and neck.
Longer and originates at the cisterna chyli.
Travels retroperitoneally along the vertebral bodies and empties into the junction of the internal jugular and subclavian veins on the left side.