A&P Fetal Circulation

Circulatory System Overview

  • The circulatory system consists of two main circuits: systemic and pulmonary.

    • Systemic Circulation:

      • Carries oxygenated blood from the left ventricle to all parts of the body and returns deoxygenated blood to the right atrium.

      • Requires greater force of contraction and pressure due to longer distance traveled.

    • Pulmonary Circulation:

      • Transports deoxygenated blood from the right ventricle to the lungs for oxygenation and back to the left atrium.

      • Operates at lower pressure compared to systemic circulation.

Anastomoses Functions

  • Anastomosis: A connection between two blood vessels.

    • Acts as a shunt providing continuous blood supply.

    • Arterial Anastomosis:

      • Connects arteries, allowing blood flow to bypass blockages and maintain oxygenation to tissues.

    • Venous Anastomosis:

      • Connects veins, redirecting blood flow to ensure return to the heart even if one pathway is blocked.

Naming of Systemic Arteries and Veins

  • Typically named based on the bone or organ they are associated with:

    • Bone Proximity: E.g., radial artery travels along the radius bone.

    • Organ Association: E.g., gastric artery is named for its relation to the stomach.

Portal Circulation Advantages

  • Hepatic Portal Circulation:

    • Responsible for transporting blood from the gastrointestinal tract to the liver.

    • Functions: Detoxification and filtration of nutrients before they enter systemic circulation.

Fetal Circulation

  • Fetal circulation involves additional structures for efficient nutrient and gas exchange with the mother:

    • Placenta:

      • Connects mother and fetus, allowing exchange of nutrients and oxygen while removing waste products.

    • Umbilical Vessels:

      • Two umbilical arteries (carry deoxygenated blood from fetus to placenta) and one umbilical vein (returns oxygenated blood from placenta to fetus).

Key Structures in Fetal Circulation

  1. Umbilical Arteries: Carry blood to the placenta (deoxygenated).

  2. Umbilical Vein: Returns oxygenated blood from the placenta to the fetus.

  3. Ductus Venosus: Connects the umbilical vein to the inferior vena cava, bypassing the liver.

  4. Foramen Ovale: A hole in the septum between the right and left atria, allowing blood to bypass the non-functioning lungs.

  5. Ductus Arteriosus: Connects the pulmonary trunk to the aorta, allowing blood to bypass the lungs.

  6. Placenta: Main site of gas and nutrient exchange.

Transition after Birth

  • After birth, fetal structures change:

    • Umbilical cord is cut, leading to the cessation of blood flow through umbilical arteries and veins.

    • Ligaments Formation:

      • Umbilical veins become the round ligament of the liver.

      • Ductus venosus becomes the ligamentum venosum.

      • Ductus arteriosus becomes the ligamentum arteriosum.

      • Foramen ovale closes and becomes the fossa ovalis over time.

Summary of Changes at Birth

  • Following the first breath, changes in circulation occur:

    • The foramen ovale closes, splitting the atria's circulation.

    • Ensures efficient separation of oxygenated and deoxygenated blood after birth.