Fertilization and Embryology People, Chickens, Opossums

The Ovary and a Follicle

Fertilization Fusion of haploid (monoploid) sperm and haploid egg. They form a diploid Zygote If the sperm and egg meet outside of the body, it’s called External Fertilization. Fish, frogs, most aquatic animals do this Many eggs are eaten and sperm and eggs can drift apart, so many are produced

Ovulation The egg

The Sperm

Sperm on an egg

External Fertilization: The male fertilizes the eggs as they emerge

Internal Fertilization If the sperm and egg meet inside the body, it’s called Internal Fertilization. Sperm and eggs are confined, and no predators are inside to eat the eggs Few eggs are produced because fertilization per egg is more likely

Stages of Development Early development consists mainly of cell and tissue growth and differentiation

The ENDODERM gives rise to: The lining of the digestive tract The lining of the Respiratory Tract Liver Pancreas

The MESODERM gives rise to: The Muscles The circulatory system The skeleton The excretory system The reproductive systems

The ECTODERM gives rise to: The Nervous System The skin

External Development Occurs outside of mom’s body In water: many organisms have both external development as well as external fertilization. The yolk stored in the egg is the embryo’s food source On land: Birds, many reptiles and a few mammals develop externally after internal fertilization The yolk is the embryo’s food source

Adaptations for external development on land A Shell provides protection Membranes help provide a good environment for embryo development. These include: The amnion: contains amniotic fluid, protects from shock, keeps embryo from sticking to shell Yolk sac surrounds yolk, blood vessels carry nutrients to embryo

More adaptations: Membranes The Allantois works as a respiratory membrane and storage place for uric acid: the nitrogenous waste of the chick The chorion surrounds everything, it lies just inside the shell and helps in gas exchange

The Egg Amniotic Fluid Reptile eggs have leathery shells

Internal Development Growth of the embryo within the body of the female Placental mammals: The embryo develops within the uterus There is little yolk in eggs, so they’re small The Placenta in the uterus forms from embryonic and maternal tissues All transfer of materials from mom to baby and vice versa occurs through the placenta These include nutrients, wastes, and respiratory gases

Placenta There is no direct connection between the bloodstream of mom and fetus Transport is done by diffusion and active transport through the placenta When stretched out, and all wrinkles laid flat, it has the surface area of half of a tennis court!!!!! Most mammals are placental

The placenta and its circulation

The Umbilical Cord It attaches the embryo to the placenta It is full of blood vessels At birth, it contains a wealth of embryonic stem cells, most of which are pumped into the baby during and in the few minutes after birth

Human Development 20 weeks 5 weeks 14 weeks

Ultrasound

Marsupials Mammals without placentas Internal fertilization, and partial internal development without nourishment from mom. The yolk is stored in the egg, and the embryo is born in early development and completes development externally in a pouch with mammary glands found inside The tiny baby has to crawl from the birth canal and find the pouch

Marsupials