Fetal Circulation Anatomy

• These notes cover the anatomy review from the pages listed

Fetal Circulation

• Fetal circulation differs from postnatal circulation; the ductus venosus allows blood to flow from the placenta to fetus via the umbilical vein
• The umbilical vein branches within the fetus, with some blood flowing to the fetal liver
• Most blood bypasses the liver through the ductus venosus and enters the inferior vena cava (IVC)
• After birth, the ductus venosus closes and no longer serves a purpose
• Deflated fetal lungs don't require much blood flow, so blood is rerouted through heart modifications
• The foreamen ovale and ductus arteriosus reroute blood away from the fetal lungs
• The ductus arteriosus connects the pulmonary trunk to the descending aorta
• Blood pumped into the pulmonary trunk flows through the ductus arteriosus into the aorta, bypassing the lungs
• Prostaglandins keep the ductus arteriosus open, while drugs like aspirin and indomethacin block prostaglandin synthesis, causing premature closure
• Babies in the womb get oxygen through the umbilical cord
• The ductus venosus closes when babies take their first breath, as the lungs clear, and the ductus arteriosus opens

Vitamin K

• Vitamin K is a clotting factor that babies are born without
• Babies are injected with vitamin K in the left thigh to prevent bleeding

Blood Type Antigens and Antibodies

• A person with type A blood has the A antigen on their RBCs
• A person with type B blood has the B antigen on their RBCs
• A person with type AB blood has both A and B antigens on their RBCs
• A person with type O blood has neither A nor B antigens on their RBCs
• A person with type A blood has anti-B antibodies in the plasma
• A person with type B blood has anti-A antibodies in the plasma
• A person with type AB blood has neither anti-A nor anti-B antibodies in the plasma
• A person with type O blood has both anti-A and anti-B antibodies in the plasma

Agglutination

• Agglutination is the clumping of the antigen-antibody interaction
• Agglutination reactions can cause RBCs to burst or lyse through hemolysis
• Rapid hemolysis can lead to kidney failure and death due to liberated hemoglobin

Rh Classification System

• Blood type is classified according to the Rh factor, an antigen on the RBC membrane
• Rh+ indicates the presence of the Rh factor
• Rh- indicates the absence of the Rh factor

RhoGAM

• Erythroblastosis fetalis is prevented by administering RhoGAM to Rh-negative mothers during pregnancy and within 72 hours after delivery

Steroid Hormones

• Steroid hormones may or may not be lipid soluble, but all pass through the plasma membrane and bind to receptors in the nucleus
• The steroid-receptor complex stimulates protein synthesis, altering cellular function

Lymphatic System

• Blood is made in the bone marrow from stem cells
• Lymphocytes and monocytes originate in the bone marrow; some lymphocytes mature and reproduce in the lymphatic tissue
• Stem cells differentiate into megakaryocytes, which break into platelets or thrombocytes
• Red blood cells (RBCs) in adults range from 4.2 to 6.0 million/μL
• RBCs transport oxygen and carbon dioxide

Blood Cell Differentiation

• Mature cells contain a nucleus and end in "-blast"
• Cells ending in "-phil" are the first line of defense (white blood cells)
• Connective tissue creates blood cells; myoblasts create muscle and bone; lymphocytes create blood cells

Cardiac Valves

• Atrioventricular (AV) valves are responsible for the "lub-dub sound
• The heart has four valves that keep blood flowing in a forward direction
• AV valves are located between the atria and ventricles and allow blood to flow from the atria into the ventricles
• Semilunar valves control blood outflow from the right and left ventricles and act as exit valves
• AV valves have cusps or leaflets
• When ventricles are relaxed, the AV valves are open, allowing blood to flow from the atria
• The first heart sound (S1 or "lubb") is caused by the closure of the AV valves during ventricular contraction and is best heard over the apex of the heart
• The second heart sound (S2 or "dupp") is caused by the closure of the semilunar valves during ventricular relaxation
• The aortic semilunar valve is located between the left ventricle and the aorta
• Semilunar valves close when pressure in the pulmonary trunk and aorta is greater than the pressure in the relaxed ventricles
• There are two AV valves: the tricuspid and bicuspid (mitral) valves
• There are two semilunar valves: the pulmonic and aortic semilunar valves
• The right AV valve (tricuspid) is located between the right atrium and ventricle and has three cusps
• The left AV valve (bicuspid/mitral) is located between the left atrium and ventricle and has two cusps

SA Node

• The SA node is located in the upper posterior wall of the right atrium and electrical signals originate here
• The SA node, our natural pacemaker, fires a cardiac impulse 60 to 100 times per minute
• The cardiac impulse spreads from the SA node through both atria via atrial conducting fibers and to the AV node

AV Node

• The AV node is located in the floor of the right atrium near the interatrial septum
• The AV node acts as a path for cardiac impulses from the atria to the ventricular bundle of His and slows the cardiac impulse
• Slowing the impulse by the AV node delays ventricular activation, allowing the relaxed ventricle time to fill with blood during atrial contraction
• The heart is located left of the midline behind the sternum
• Ventricles have thicker membranes and pump blood to the arteries
• The left ventricle myocardium side is thicker than the right
• Blood is composed of hemoglobin, which contains iron
• Bilirubin is yellowish pigment from RBC breakdown
• Amino acids are the building blocks of proteins

Macrophages

• Macrophages engage in phagocytosis and antigen presentation, necessary for B and T cell activation
• Antibodies (immunoglobulins) bind antigens causing agglutination, facilitating phagocytosis and pathogen death
• The primary and secondary responses refer to antibody secretion by plasma and memory cells in response to antigen stimulation
• The chest cavity contains two lungs; the right lung has three lobes, and the left lung has two lobes
• The spleen is a major producer of red blood cells in the endocrine system

Fetal circulation differs significantly from postnatal circulation, with structures like the ductus venosus, foramen ovale, and ductus arteriosus playing crucial roles. The ductus venosus allows placental blood to bypass the fetal liver. After birth, these structures close as the lungs become functional.