Lab 8: Lymphatic and Fetal Circulation

Fetal Circulation

  • How it differs from adult cardiovascular system:

    • Fetal circulation includes specialized structures that bypass certain organs (lungs, liver) to optimize nutrient delivery and waste removal via the placenta.

      • Oxygen and nutrients from the mother's blood are transferred to the fetus through the placenta.

      • Blood enters the fetus through the umbilical vein.

      • Some of the blood bypasses the liver via the ductus venosus.

      • The oxygenated blood is then directed towards the heart. Blood entering the right atrium passes through the foramen ovale into the left atrium, skipping the lungs.

      • Blood from the right ventricle is directed to the ductus arteriosus, which connects the pulmonary artery to the aorta, bypassing the lungs.

      • Oxygenated blood is then delivered to the rest of the body through the aorta.

Lymphatic System Anatomy

  • Key components of the lymphatic system:

    • Thymus: Matures T-lymphocytes.

    • Spleen: Cleans blood and houses white blood cells (WBCs).

    • Tonsils: Part of immune defense.

    • Lymph nodes: Filter lymph and house WBCs; located throughout the body.

    • Lymph vessels: Transport lymph back to the bloodstream.

Functions of the Lymphatic System

  • Immunity: Helps in immune response via WBCs.

  • Lipid absorption: Absorbs fats and fat-soluble vitamins from the GI tract.

  • Fluid recovery:

    • Blood in veins is more viscous than in arteries due to fluid loss in tissues.

    • Lymph vessels recover excess interstitial fluid and return it to subclavian veins, cleaning it in the process.

    • Blockage in lymph drainage leads to edema (swelling).

Elephantiasis

  • Caused by lymphatic obstruction due to parasitic worms, leading to limb and skin swelling (fibrosis).

  • Round worms can enter through breaks in skin or via mosquitoes.

Lymphatic Capillaries

  • Lymph:

    • Extracellular fluid (ECF) collected from tissues; clear, colorless, similar to plasma but with less protein.

    • Contains tissue debris and bacteria if present.

  • Structure:

    • Closed at one end, pressure flaps open to take up lymph.

    • Endothelial cells overlap to create flaps that allow larger particles to enter, resembling valves.

The Fluid Cycle

  • Steps:

    1. Excess ECF picked up by lymph capillaries.

    2. Lymph cleaned by lymph nodes.

    3. Returned to blood circulation via subclavian vein.

Lymphatic Vessels

  • Similar characteristics to veins, but have thinner walls and more valves.

  • Form in the embryo by budding off veins.

Route of Lymph Flow

  • Pathway of lymph:

    • Collecting vessels (from lymph capillaries) → lymph nodes (filtered) → lymph trunks → collecting ducts:

    • Right lymphatic duct: Empties into right subclavian vein (drains right arm, head, thorax).

    • Thoracic duct: Empties into left subclavian vein (drains rest of the body).

Lymphatic Drainage of Mammary and Axillary Regions

  • Nodes in the axillary region may be removed during mastectomy for cancer examination (checking for metastasis).

Immunity Overview

  • Types of Immunity:

    • Active: Body produces its antibodies (long-term).

    • Passive: Acquired antibodies (short-term).

    • Natural: From mother to baby.

    • Artificial: Vaccinations, requiring boosters.

Fetal Circulation

  • Unique structures for fetal circulation:

    • Umbilical vein: Carries oxygen-rich blood from placenta to fetus.

    • Umbilical arteries: Carry waste back to placenta.

    • Ductus venosus: Bypasses fetal liver.

    • Foramen ovale: Connects right and left atria to bypass fetal lungs.

    • Ductus arteriosus: Connects pulmonary trunk to aorta.

Blood Circulation Before & After Birth

  • Structures close at birth, transforming fetal circulation into normal adult pathways:

    • Umbilical arteries and veins become ligaments (e.g., ligamentum teres, fossa ovalis).