Fetal Circulation

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Study Notes

Fetal Circulation

Fetal circulation refers to the unique circulatory system present in an unborn baby during pregnancy.
The fetal circulatory system is adapted to allow the exchange of nutrients, oxygen, and waste products between the fetus and the mother while the baby is developing in the womb.
Important structures of fetal circulation:
- Placenta: Acts as a bridge between the mother's blood supply and the fetus, exchanging oxygen and nutrients for waste products.
- Umbilical cord: Connects the fetus to the placenta, carrying deoxygenated blood from the fetus to the placenta and oxygenated blood from the placenta to the fetus.
- Foramen ovale: A small opening in the fetal heart between the two atria, allowing some oxygen-rich blood returning from the placenta to bypass the fetal lungs and flow directly into the left atrium.
- Ductus arteriosus: A blood vessel that connects the pulmonary artery (leading to the lungs) to the aorta (leading to the body's systemic circulation), allowing blood to bypass the lungs.
- Ductus venosus: A vessel that shunts oxygenated blood from the umbilical vein directly into the inferior vena cava, bypassing the liver and supplying oxygen and nutrients to the developing fetal tissues.

Changes after Birth

After birth, several changes occur as the baby begins to breathe air and adapt to life outside the womb:
- First breath: When the baby takes its first breath, the lungs expand, and pulmonary blood flow increases, causing the ductus arteriosus to close.
- Closure of foramen ovale: As blood flows into the lungs, pressure in the left atrium increases, leading to the closure of the foramen ovale.
- Closure of ductus venosus: With the umbilical cord clamped and cut after birth, blood flow through the ductus venosus ceases, and the vessel eventually closes.

Congenital Heart Diseases

Congenital heart diseases (CHDs) are a group of structural or functional abnormalities in the heart that are present at birth.
These conditions can affect the heart's chambers, valves, blood vessels, and electrical conduction system.
Types of congenital heart diseases:
- Acyanotic heart defects: Characterized by increased pulmonary blood flow, including:
  - Atrial Septal Defect (ASD): An opening in the wall between the heart's upper chambers (atria).
  - Ventricular Septal Defect (VSD): A hole in the septum between the heart's lower chambers (ventricles).
  - Atrioventricular Canal Defect: Incomplete fusion of the endocardial cushions, resulting in a large central AV valve that allows blood to flow between all four chambers of the heart.
  - Patent Ductus Arteriosus (PDA): Failure of the fetal ductus arteriosus to close after birth, allowing blood to flow from the aorta to the pulmonary artery.
- Cyanotic heart defects: Characterized by decreased pulmonary blood flow, including:
  - Coarctation of the Aorta: Localized narrowing of the aorta, resulting in increased pressure proximal to the defect and decreased pressure distal to the obstruction.
  - Aortic Stenosis: Narrowing or stricture of the aortic valve, causing resistance to blood flow in the left ventricle and decreased cardiac output.
  - Pulmonic Stenosis: Narrowing at the entrance to the pulmonary artery, causing resistance to blood flow and right ventricular hypertrophy.
- Cyanotic heart defects with mixed defects, including:
  - Tetralogy of Fallot: A combination of four defects, including VSD, PS, overriding aorta, and right ventricular hypertrophy.
  - Tricuspid Atresia: The tricuspid valve fails to develop, resulting in no communication between the right atrium and ventricle.
  - Transposition of the Great Vessels: The pulmonary artery leaves the left ventricle, and the aorta exits from the right ventricle, with no communication between the systemic and pulmonary circulations.

Rheumatic Heart Disease

Rheumatic heart disease (RHD) is a serious condition that can result from untreated or inadequately treated streptococcal throat infections.
Causes: RHD is caused by an autoimmune response to an infection with group A Streptococcus bacteria.
Signs and Symptoms: Shortness of breath, fatigue, chest pain, palpitations, and swollen ankles or legs.
Valve Damage: RHD most commonly affects the heart valves, particularly the mitral valve, causing scarring, thickening, and deformities.
Prevention: Primary prevention involves promptly and adequately treating streptococcal infections to prevent the development of acute rheumatic fever (ARF).
Treatment: Focuses on managing symptoms, preventing further damage, and addressing complications. Medications, surgical interventions, and nursing management are used to manage RHD.