Fetal circulation and somitogenesis.pptx

Glutamate
Glutamate is the most important excitatory transmitter in
the CNS
Glutamate acts on both ionotropic and metabotropic receptors. Clinically, the
receptor characterized in vitro by N-methyl-D-aspartate (NMDA) binding is
particularly important

1. Fetal Circulation

2. Fetal Cardiovascular system is designed: 1-To serve prenatal needs. 2-To permit modifications at birth, which establish the neonatal circulation.

3. Good respiration in the newborn infant is dependent upon normal circulatory changes at birth.

4. FETAL CIRCULATION  Facilitates the exchange of materials between fetus and mother.  The fetus picks up oxygen and nutrients from eliminates carbon dioxide and wastes through the maternal blood supply by means of the placenta.  Blood passes from the fetus to the placenta via: Two umbilical arteries One umbilical vein.   At birth fetal circulation are no longer needed: The ductus arteriosus becomes the ligamentum arteriosum The foramen ovale becomes the fossa ovalis The umbilical vein becomes the ligamentum teres (round ligament).  

5. Three structures are very important in the transitional circulation: 1- Ductus venosus. 2- Ductus arteriosus. 3- Foramen ovale.

6. Flow Chart of Fetal Circulation

7. Blood reaches & leaves the fetus through the umbilical cord. The umbilical cord Contains two arteries and one vein.

8. Highly oxygenated blood passes from the placenta through the umbilical vein . Half of this blood reaches the IVC through the ductus venosus . Ductus venosus

9. The other Half passes to liver sinusoids then to the IVC. Blood of the IVC reaches the right atrium, then left atrium through the Foramen Ovale . Then to the left ventricle to the ascending aorta, and the aortic arch to supply head & neck brain, cardiac muscle and upper limbs.

10. Small amount of highly oxygenated blood in right atrium mixes with venous blood of the SVC passes to right ventricle . Then to the pulmonary artery then to Ductus Arteriosus (between the Pulmonary trunk & Proximal part of the descending aorta) , to the fetal body. Then back to placenta via the umbilical arteries . Ductus arteriosus

11. After Ligation of the umbilical cord Sudden fall of blood pressure in the IVC and the right Atrium . The valve of the ductus venosus constricts. After Aeration of the lungs at birth: 1- Marked increase in the pulmonary blood flow. 2- Dramatic fall in pulmonary vascular resistance. 3- Thinning in the wall of the pulmonary arteries.

12. Changes After Birth 1- Closure of foramen ovale : a. Physiological closure b. Anatomical closure. 2- Constriction of ductus arteriosus: By the end of the first 24 hours 20% of the lumen of the ductus is closed. By the end of 48 hours 82% is closed. By 96 hours 100% of the duct is closed

13. Bradykinin : It is a substance released from fetal lungs during their initial inflation. This substance has a contractile effect on smooth muscles of the ductus arteriosus. The action of this substance appears to be dependant on the high Oxygen saturation of the aortic blood.

14. When oxygen tension reaches 50 mmHg in the ductus arteriosus it causes constriction of its smooth muscles. During intrauterine fetal life the patency of ductus arteriosus (before birth) is controlled by the low contents of oxygen in the blood passing through it. So hypoxia and other ill-defined factors keep the ductus arteriosus patent.

15. Adult derivatives of fetal vascular structures 1- Umbilical vein------Ligamentum teres. 2- Umbilical arteries—medial umbilical ligaments. 3- Ductus venosus-----Ligamentum venosum. 4- Ductus arteriosus---Ligamentum arteriosum 5- Foramen ovale----fossa ovalis.

16. L igamentum arteriosum

17. Somitogenesis Paraxial mesoderm form pairs of somitomeres (pre-somites) Somitogenesis begins w/ 8 th pair of somitomeres (pairs 1-7 don’t develop into somites) Mesoderm (mesenchyme) is transformed back into epithelium –relies on Noggin antagonism of BMP-4 BMP Noggin

18. Separation of Somites FGF signaling from the node drives proliferation ; Retinoic acid from adjacent mesoderm drives differentiation . Because the node is caudal to the forming somites, there is a head-to-tail gradient of differentiation. Proliferating cells express a ligand (called ephrin B1). As cells differentiate, they begin to express an INCOMPATIBLE receptor (called eph A) that causes the differentiating cells to repel the proliferating cells, thus pinching off and forming a new somite. N-cad (click here for QuickTime version)

19. Somites are balls of epithelial cells with a few mesenchymal cells in the core

20. Epithelial somites then transform back into mesenchyme Signaling from ectoderm induces dermomyotome Signaling from notochord and neural tube induces sclerotome

21. Dermamyotome forms dermis and muscle BMP from ectoderm induces dermatome the remaining dorsomedial and ventrolateral cells become myotome . Dorsomedial portion of dermomyotome sees Shh from notochord and Wnt from spinal cord and becomes muscle that can’t migrate very far ( epaxial muscles of the back) Ventrolateral portion of dermomyotome exposed to high levels of BMP from lateral plate mesoderm and becomes migratory muscle (goes into limbs also “ hypaxial ” muscles of the lateral and ventral body wall, e.g. “lats” and “abs”

22. The sclerotome develops into vertebrae, ribs, and meninges Dorsal sclerotome: Dorsal arch & spinous processes of vertebrae* Medial sclerotome: Meninges* Central sclerotome: Pedicles & transverse processes of vertebrae, proximal portions of ribs Ventral sclerotome: Vertebral bodies and annulus fibrosis of intervertebral disks Lateral sclerotome: Distal portions of ribs *failure of these associated w/ spina bifida

23. Somite (Paraxial mesoderm) forms: 1. Sclerotome 2. Dermamyotome Sclerotome forms: Meninges, vertebral bodies & ribs Dermamyotome forms: 1. Dermis (from dermatome) 2. Muscles (from myotome) (click here for QuickTime version)

24. Anterior and posterior portions of each sclerotome fuse to form vertebral bodies. This offsets the vertebral bodies and segmental muscles. i.e., the vertebrae (sclerotome) are out of phase with muscle (myotome) to form intervertebral joints. This allows the contracting segmental muscles to move the vertebral column laterally. The sclerotome breaks into two parts…

25. Anterior portion of one somite fuses with the posterior portion of the next somite; that way The surrounding muscle bridges sequential vertebral bodies. (click here for QuickTime version)

26. Intermediate mesoderm develops into the urogenital system

27. Lateral plate divides into somatic and splanchnic mesoderm Somatic mesoderm: Lines body wall (somatic mesoderm + ectoderm = somatopleure) Splanchnic mesoderm: Covers endoderm (splanchnic mesoderm + endoderm = splanchnopleure) Coelom = body cavity formed by lateral folding of the embryo Lateral plate mesoderm also generates extraembryonic mesoderm of amnion, yolk sac, and placenta.

28. Somatic (aka parietal) mesoderm stays with epidermis Splanchnic (aka visceral) mesoderm stays with endoderm

29. Thank You