Organogenesis Part 2 ______

Home , Body cavity, Coelom, Endoderm, Lateral plate mesoderm, Mesoderm, Mesonephros

______V. Lateral Plate Mesoderm VI. Endoderm ______VII. Development of the Tetrapod Limb VIII. Sex Determination ______

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V. Lateral Plate Mesoderm ______

______paraxial mesoderm chordamesoderm intermediate mesoderm ______

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lateral plate mesoderm ______

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Lateral Plate Mesoderm ______

Terminology: - Somatopleure: somatic mesoderm plus ectoderm ______- Splanchnopleure: splanchnic mesoderm plus endoderm - Coelom: body cavity forms between them ______

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______Lateral Plate Mesoderm ______

• The Coelom: ______

– eventually left and right cavities fuse into one ______– runs from neck to anus in vertebrates – portioned off by folds of somatic mesoderm ______• pleural cavity: surrounds the thorax and lungs • pericardial cavity: surrounds the heart • peritoneal cavity: surrounds the abdominal organs ______

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Figure 12.1 Mesodermal development in frog and chick embryos (Part 3) ______

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Heart Development ______

______• The heart is the first organ to function in the embryo and the circulatory system is the first functional system. ______

– heartÆarteriesÆcapillariesÆveinsÆheart ______• Before the embryo can get very big it must switch from nutrient diffusion to active ______nutrient transport ______

______Heart Development ______

Anatomical Stages: 1. Tube Formation 2. Looping ______3. Chamber Formation ______

outflow ______

______inflow human timeline ______

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Heart Development: Tube Formation ______

presumptive heart cells are specified outflow forming cells (red) ______but not determined in the epiblast migrate in first, inflow second

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migrate ______through together near node ______

“the heart field” ______

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Heart Development: Tube Formation ______The cardiogenic mesoderm migrates out of the mesodermal layer towards the endoderm to form endocardial tubes on either side. ______

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______At the same time the endoderm is folding inward ______

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______Heart Development: Tube Formation ______

The endoderm continues folding inward until it forms its own tube, which drags the two endocardial primordia close to each other. ______

The endocardial tubes are surrounded by ______myocardial progenitors ______

When the endocardial ______tubes get close enough, they fuse together ______

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Heart Development: Tube Formation ______

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If you mess with endoderm migration ______or signaling, you end up with two hearts ______

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Heart Development: Tube Formation ______

• Heart Tube Cell Biology ______– Splanchnic mesoderm cells express cadherins and form an epithelial sheet for their inward migration - MET

– The presumptive endocardial cells undergo EMT to migrate away from the sheet and another MET to form tubes ______

– The cells in the original mesodermal sheet form the myocardium

– The myocardial epithelium fuses first and the two endocardial ______tubes exist together inside for a while before fusing

– Both the rostral end (outflow) and caudal end (inflow) remain as unfused double tubes ______

– The heart beat starts spontaneously as myocardial cells express the sodium-calcium pump - before fusion is even complete ______

______Heart Development: Looping and Chamber Formation ______

left-right asymmetry is due to Nodal and Pitx2 ______

anterior ______

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posterior right left ______

Looping requires: cytoskeletal rearrangement extracellular matrix remodeling asymmetric cell division ______

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Heart Development: Looping and Chamber Formation ______

______valve formation heart valves keep the blood from flowing back into ______the chamber it was just ejected from ______

The septa separate the two atria and ______the two ventricles septation ______

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Heart Development: Looping and Chamber Formation ______

The truncus arteriosis, or outflow tract, also becomes septated allowing one great ______artery to flow from right ventricle to lungs and the other from left ventricle to the body. ______

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______Heart Development: Looping and Chamber Formation ______

•The tricuspid valve is between the right ______atrium and right ventricle. •The pulmonary or pulmonic valve is between the right ventricle and the ______pulmonary artery. •The mitral valve is between the left atrium ______and left ventricle. •The aortic valve is between the left ______ventricle and the aorta. ______

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Heart Development: Looping and Chamber Formation ______

Steps: 1. Endocardial cushions form and fuse 2. Septa grow towards cushion ______3. Valves form from myocardium

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In utero, the foramen ovale allows right left shunting of blood ______

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Embryonic circulatory systems ______

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All of the blood must circulate outside of the ______embryo for oxygenation ______

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______Redirection of human blood flow at birth ______

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Blood Vessel Development ______

• The vessels form independently of the heart ______

• They form for embryonic needs as much as adult ______– Must get nutrition before there is a GI tract – Must circulate oxygen before there are lungs – Must excrete waste before there are kidneys ______– They do these through links to extraembryonic membranes ______

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Blood Vessel Development ______

• The vessels are constrained by evolution ______– Mammals still extend vessels to empty yolk sac – Birds and mammals also build six aortic arches as if we had gills, eventually settling on a single arch ______

• The vessels adapt to the laws of fluid dynamics ______– Large vessels move fluid with low resistance – Diffusion requires small volumes and slow flow – Highly organized size variance controls volume ______– And superbranching smaller vessels control speed ______

______Embryonic circulatory systems ______

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Blood Vessel Development ______

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Blood Vessel Development ______

______Vasculogenesis is the de novo differentiation ______of mesoderm into endothelium ______

It is followed by the endothelium ______recruiting smooth muscle cell coat ______

______Blood Vessel Development ______

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______Starts in the extraembryonic mesoderm as ______well as in the large embryonic blood vessels ______

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Blood Vessel Development ______

______Angiogenesis is the growth and remodeling ______of the 1st vessels in response to blood flow and ______tissue-derived recruitment signals ______

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______Blood Vessel Development ______

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Blood Vessel Development ______

Secondary Vasculogenesis 1. PEO forms from splanchnic ______mesoderm overlying the liver 2. PEO contacts the ventricle and migrates as epicardium ______

3. Subset of epicardial cells delaminate towards myocardium ______4. These undergo MET to form coronary endothelium ______5. Coronary arteries then plug into the aorta where nerves are ______

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Blood Vessel Development ______

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______Blood Vessel Development ______

______It is a common phenomenon for arteries and nerves ______to form together ______

______Less so for veins.... ______

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Blood Vessel Development ______

• Lymphatic drainage forms from jugular vein ______

– Sprouts as lymphatic sacs by angiogenesis ______

– Continues to form secondary drainage system ______

– Major conduit for immune cells ______

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Where do the hematopoietic stem cells of the adult bone marrow come from? ______

Splanchnic mesoderm of ______aorta-gonad-mesonephros (AGM) region in embryo ______

Hemogenic endothelium ______from sclerotome

Hemogenic ______endothelium from many sites ______

______Wherever they come from.... ______

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WOW! ______

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Development of the Endoderm ______

• The Digestive Tube ______– Anterior endoderm forms anterior intestinal portal – Posterior endoderm forms posterior intestinal portal – Midgut goes through expansion and contraction to yolk ______– Each end has ectodermal cap, then forms an entrance ______• The Derivatives – 4 pharyngeal pouches form head and neck structures – Floor between 4th pair buds out to form respiratory tube ______– Gut tube forms esophagus, stomach, SI, LI, rectum – Gut tube buds out to form liver, gall bladder, pancreas ______

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Development of the Endoderm ______

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Human ______Timeline

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______Development of the Endoderm ______

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The cranial neural crest cells migrate ______through this endoderm and contribute component structures around them ______

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Development of the Endoderm ______

Localized Wnt/B-Catenin and retinoic acid cause budding ______

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Development of the Endoderm ______

Normal-time birth is signaled from the lungs ______

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______Development of the Endoderm ______

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Anterior-Posterior specification of the ______gastrointestinal tract

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Development of the Endoderm ______

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Reciprocal Induction Simultaneous ______Anterior-Posterior specification of both endoderm and mesoderm ______

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Development of the Endoderm ______

Mesoderm also ______induces liver bud ______

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______Development of the Endoderm ______

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Development of the Endoderm ______

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The Extraembryonic Membranes ______

• Adaptation for development on dry land ______– As the body starts to develop epithelium expands to isolate embryo within them ______

• Four sets of extraembryonic membranes ______– Somatopleure forms amnion and chorion – Splanchnopleure forms yolk sac and allantois ______

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______The Extraembryonic Membranes ______

Somatopleure forms amnion and chorion Splanchnopleure forms yolk sac and allantois ______

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The Extraembryonic Membranes ______

The amnion folds up to cover the embryo and keep it from drying out ______

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The cells of the amnion secrete water ______

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The Extraembryonic Membranes ______

The chorion surrounds the entire embryo and controls gas exchange ______

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In birds and reptiles it lines shell In mammals it forms the placenta ______

______The Extraembryonic Membranes ______

The yolk sac expands to surround yolk (even if you don’t have any) ______

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The Extraembryonic Membranes ______

The allantoic membrane creates a space for waste storage ______Bird and reptile eggs gotta’ have it ______

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We don’t use it for waste but it contributes to our umbilical cord ______

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