Maternal pregnancy is divided into three stages of growth and development - the first trimester which involves organogenesis via cellular proliferation, differentiation, and morphogenesis; the second trimester which is centred around organ development and functioning as well as foetal expansion and recognisable movement (quickening); and the third trimester during which the foetus undergoes rapid weight gain.
Second Trimester Foetal Development
The second trimester encompasses the foetal weeks 12-24, or clinical gestational weeks 14-26, according to the UCSF Medical Centre and is referred to as the "golden period of pregnancy" since many first trimester discomforts such as nausea, fatigue, breast tenderness, and frequent urination are alleviated as the maternal body adapts to the changing gestational physiology - nevertheless increased placental secretions of progesterone, estrogen, and human placental lactogen, as well as increased abdominal pressure can elicit heartburn, constipation, abdominal pain, and leg cramps. During the second trimester of pregnancy, the organ rudiments formed in the embryo stage expand in size and further differentiate in response to cellular signalling and gene cascades to coordinate specialised physiological functions needed to support the growing foetus. In addition to foetal growth and development, the placenta also increases in size to increase foetal blood supply and secretes hormones to redirect maternal glucose, amino acids, and free fatty acids towards the foetus to satisfy its increasing metabolic demands.
Skin and Musculoskeletal System
During the sec
The primary function of the respiratory system is to facilitate gaseous exchange between the external environment and the bloodstream, through diffusion across the lung alveoli, in order to oxygenate pulmonary blood via inhalation and remove carbon dioxide via exhalation. ':' In the embryonic stage, the endodermal foregut forms a ventral extension called the respiratory diverticulum which bifurcates into the right and left primary bronchial buds; these structures differentiate into the main bronchi in the second trimester.