2.7 Parturition and lactation · Part 2

the body organs namely the heart, limbs, lungs, liver and external genital organs are well developed. By the end of the second trimester , the face is well formed with features, eyelids and eyelashes, eyes blink, body is covered with fine hair, muscle tissue develops and bones become harder. The foetus is fully developed and is ready for delivery by the end of nine months ( third trimester ). During pregnancy, the placenta acts as a temporary endocrine gland and produces large quantities of human Chorionic Gonadotropin (hCG), human Chorionic Somatomammotropin (hCS) or human Placental Lactogen (hPL), oestrogens and progesterone which are essential for a normal pregnancy. A hormone called relaxin is also secreted during the later phase of pregnancy which helps in relaxation of the pelvic ligaments at the time of parturition. It should be noted that XII Std Zoology Chapter XII Std Zoology Chapter Human Reproduction Weeks Formation of foregut, midgut and hindgut. Heart starts functioning. Forebrain is most prominent. Upper limbs appears as paddle-shaped buds Weeks Limbs and digits fully formed. Movements start taking place. Neck appears between head and thorax. External genitalia show sex differences Weeks Eyes and ears are well defined. Ossification of long bones are seen Urine formation begins Weeks Lower limbs reach final development. Movements are seen Weeks Length of foetus increases Hair on the head and eyebrows. Skin becomes covered with sebaceous gland Weeks Lungs are well developed Rapid eye movements begin. Foetus starts gaining weight Weeks Immune system starts developing. Central nervous system developed. Retina is well developed Weeks Body weight increases rapidly. Skin is smooth due to deposition of subcutaneous fat Weeks Blood vessels are completely developed. Baby is positioned into the pelvis in head down position