Changes

===Circulatory Changes at Birth===

===Circulatory Changes at Birth===

Important circulatory changes occur at birth due to the replacement of the placenta by the lungs as the organ of respiratory exchange. When an newly born animal takes its first  breath, the lungs and pulmonary vessels expand thereby significantly lowering the resistance to blood flow. This subsequently lowers the pressure in the pulmonary artery and the right side of the heart. On the other hand the removal of the placenta courses an increase in the resistance of the systemic circulation and hence an increase in the pressure of the left side of the heart.

Important circulatory changes occur at birth due to the replacement of the [[Female Reproductive Tract -Placenta - Anatomy & Physiology|placenta]] by the [[Lungs - Anatomy & Physiology|lungs]] as the organ of respiratory exchange. When an newly born animal takes its first  breath, the [[Lungs - Anatomy & Physiology|lungs]] and pulmonary vessels expand thereby significantly lowering the resistance to blood flow. This subsequently lowers the pressure in the pulmonary artery and the right side of the heart. On the other hand the removal of the [[Female Reproductive Tract -Placenta - Anatomy & Physiology|placenta]] causes an increase in the resistance of the systemic circulation and hence an increase in the pressure of the left side of the heart.

The birth of the animal also triggers the closure of the foetal shunts:

The birth of the animal also triggers the closure of the foetal shunts:

====Closure of the Foramen Ovale====

====Closure of the Foramen Ovale====

In the foetus the foramen ovale is kept open by the higher pressure of blood in the right atrium compared to the left atrium. At birth the blood pressure in the right atrium decreases due to termination of blood flow from the placenta, whilst pressure in the left atrium increases due to increased pulmonary flow. As a result, the flap of the septum primum presses against the septum secundum closing the foramen ovale. In most individuals, the foramen ovale closes a few months after birth. A scar remains between the two atria once the foramen ovale has closed and this is termed the fossa ovalis.

In the foetus the foramen ovale is kept open by the higher pressure of blood in the right atrium compared to the left atrium. At birth the blood pressure in the right atrium decreases due to termination of blood flow from the [[Female Reproductive Tract -Placenta - Anatomy & Physiology|placenta]], whilst pressure in the left atrium increases due to increased pulmonary flow. As a result, the flap of the septum primum presses against the septum secundum closing the foramen ovale. In most individuals, the foramen ovale closes a few months after birth. A scar remains between the two atria once the foramen ovale has closed and this is termed the fossa ovalis.

====Closure of the Ductus Arteriosus====

====Closure of the Ductus Arteriosus====

The ductus arteriosus is a muscular artery and immediately after birth, contraction of the musculature closes the shunt. Factors which may contribute to the physiological closure of the ductus arteriosus include the increased oxygen content of the blood passing through it and the production of bradykinin, which causes smooth muscle contraction. This physiological closure causes blood to be directed from the pulmonary arteries to the now functioning lungs.  Anatomical closure takes about two months and occurs by infolding of the endothelium and proliferation of the subintimal connective tissue layer. The residual ligament is termed the ligamentum arteriosum.

The ductus arteriosus is a muscular artery and immediately after birth, contraction of the musculature closes the shunt. Factors which may contribute to the physiological closure of the ductus arteriosus include the increased oxygen content of the blood passing through it and the production of bradykinin, which causes smooth muscle contraction. This physiological closure causes blood to be directed from the pulmonary arteries to the now functioning [[Lungs - Anatomy & Physiology|lungs]].  Anatomical closure takes about two months and occurs by infolding of the endothelium and proliferation of the subintimal connective tissue layer. The residual ligament is termed the ligamentum arteriosum.