Comparative Vertebrate Physiology Fertilization and nurturing of the embryo and young

Fertilization Sequence of events Sperm capacitation Acrosomal enzymes weaken oocyte membrane Sperm nucleus and centriole penetrates into the ovum Monospermy is assured by: Entry of extracellular Na+ reversing oocyte membrane polarity Ca++ causes cell to prepare for cell division This cortical reaction destroys sperm receptors on plasma membrane

Reproductive synchrony Development/release of gametes from male and female done simultaneously e.g. development of bird testes Environmental cues (temp., day length)

Hormones Viability of the corpus luteum maintained by hCG Levels of estrogen and progesterone rise due to secretion by the placenta Estrogen and progesterone levels rise in anticipation of birthing and lactation

Birthing Involuntary contractions of uterine smooth muscle (positive feedback)

Birthing Amniotic sac pushes up against cervix wall (“breaking of water”) Birth follows Further uterine contraction expels the placenta

Lactation Rising estrogen and progesterone levels stimulate release of PRH Lactogenesis Colostrum is the first milk Humans: little fat, mostly protein, vitamins, antibodies Marine mammals: 58% fat in seals

Milk let down reflex Positive feedback (galactopoiesis)