15.21 The concept of stem cells

Vertebrate blood development

• There are two phases of hematopoiesis:

1) Embryonic (“primitive”) phase: transient; provides the embryo with its initial blood cells; associated with the blood islands in the mesoderm; dependent on BMP signaling.

2) Subsequent definitive (“adult”) phase: generates more cell types, and provide the stem cells that will last for the lifetime of the individual (derived from the mesodermal area surrounding the aorta).

15.22 Sources of blood cells to the adult bone marrow (Part 1)

AGM: aorta-gonad-mesonephros region

15.22 Sources of blood cells to the adult bone marrow (Part 2)

15.22 Sources of blood cells to the adult bone marrow (Part 3)

15.23 A model for the origin of mammalian blood and lymphoid cells

15.24 Formation of the human digestive system (Part 1)

15.24 Formation of the human digestive system (Part 2)

15.24 Formation of the human digestive system (Part 3)

15.24 Formation of the human digestive system (Part 4)

15.25 Formation of glandular primordia from the pharyngeal pouches (Part 1)

15.25 Formation of glandular primordia from the pharyngeal pouches (Part 2)

• The respiratory tube sprouts from the pharyngeal floor (between the fourth pair of pharyngeal pouches) to form the lungs.

• The pharynx is where the endoderm meets the ectoderm, and the endoderm plays an important role in determining which pouches develop.

15.26 Regional specification of the gut endoderm and splanchnic mesoderm through reciprocal interactions (Part 1)

15.26 Regional specification of the gut endoderm and splanchnic mesoderm through reciprocal interactions (Part 2)

15.26 Regional specification of the gut endoderm and splanchnic mesoderm through reciprocal interactions (Part 3)

15.27 Pancreatic development in humans (Part 1)

15.27 Pancreatic development in humans (Part 2)

15.30 Partitioning of the foregut into the esophagus and respiratory diverticulum during the third and fourth weeks of human gestation

15.32 The immune system relays a signal from the embryonic lung

15.33 Schematic drawings of the extraembryonic membranes of the chick (Part 1 and 2)

Ectoderm + mesoderm = somatopleure: forms the amnion and chorion

Mesoderm + endoderm = Splanchnopleure: forms the yolk sac and allantois

15.33 Schematic drawings of the extraembryonic membranes of the chick (Part 3)

15.33 Schematic drawings of the extraembryonic membranes of the chick (Part 4)