Development of Heart of Animals The Heart is a specialized blood vessel with a lumen and thick muscular walls. In mammals, it arises from a cardiogenic plate located in front of the head in the splanchnic mesoderm and beneath the pericardial coelom. Due to a reversal in position, the heart primordium comes to lie above the pericardial […]
Development of Haemopoiesis in animals The first site of blood formation is in the area vasculosa of the wall of the yolk sac. Here between the extraembryonic splanchnic-mesoderm and endoderm the blood islands of Pander develop. These are solid masses of mesenchymal cells united by cellular stands to form a network. As they become differentiated the outer
Development of Cardiovascular system in animals Both the blood vessels and blood cells arise from mesenchyme. The earliest formative tissue of this kind is the angioblast which differentiates in the mesodermal wall of the yolk sac where groups of angioblasts form the blood islands of Pander. Originally solid, these soon hollow out and in this process the
Development of Mammary gland of animals An ectodermal thickening called milk line or mammary ridge extends on either side as longitudinal bands between the bases of limb buds. The primordial band is developed in the pectoral region (Primates, elephants) inguinal region (undulates) or throughout (axilla to groin region) in carnivores and pigs. The primordium of
Development of Genital System in animals The genital organs are undifferentiated when they first appear (indifferent period), either by gross or microscopic appearance and hence during this period the term gonad is applied to them. The gonad appears within a thickening called the genital ridge on the medial aspect the urino-genital ridge. The ventral surface
Development of Adrenal Gland in animals The origin of adrenal gland is of double origin. The gland develops in the intermediate mesoderm at the cranial pole of the mesonephric kidney. The adrenal cortex is derived from the surrounding intermediate mesoderm and he adrenal medulla is ectodermal in origin, being formed by cells derived from the neural crest.
Development of Urinary System in animals The urinary and genital system both arises from the mesoderm. Both drain into a common urogenital sinus and hence these two systems are intimately associated in their origin, development and relation. Development of Urinary organs Nowhere in the development of the individual can be found a better example of
Development of Respiratory System of Animals The epithelium of respiratory tree is derived from endoderm. The primordium of this system is the laryngo-tracheal groove, which runs lengthways in the floor of the foregut just behind the last pair of pharyngeal grooves. On the ventral surface, the endoderm projects as a ridge. This ridge is the primordium
Development of Digestive System of Animals The digestive tube consists of an internal tube of endoderm which is the primary tissue that becomes the epithelial lining and an investing layer of splanchnic mesoderm that specializes into the connective tissue, muscle and peritoneum. The primitive gut is made up of three portions, the foregut, midgut and
Development of Tongue of animals The tongue of animals develops from the ventral ends of the branchial arches. It consists of two parts oral and pharyngeal. The oral part is the body occupying the mouth cavity and arises from the mandibular arches in front of the oral membrane and hence is covered by ectodermal epithelium.
