Embryo Development PDF

Machine Translated by Google 2. Special embryology Anatomy Degree in Physiotherapy Course 2023-2024 Machine Translated by Google Special embryology is a branch of embryology that focuses on the detailed study of the development and differentiation of specific organs and systems in the organism. The...

Machine Translated by Google 2. Special embryology Anatomy Degree in Physiotherapy Course 2023-2024 Machine Translated by Google Special embryology is a branch of embryology that focuses on the detailed study of the development and differentiation of specific organs and systems in the organism. The most important part that we will study is organogenesis or formation of organs from the three germ leaves Unlike general embryology, which addresses the fundamental principles and processes common to many organisms during early development, special embryology focuses on how these structures form and evolve at different stages of embryonic and fetal development. Machine Translated by Google HEART: Its formation begins from two endocardial tubes, of mesodermal origin, which subsequently fuse to create the primitive cardiac tube. Around day 22 the embryonic heart begins to beat By day 23, bulging and/or differentiation of the primitive cardiac tube occurs, which in the direction of flow are: a) Venous sinus (part of the future AD) b) Primitive atrium (future AI and part of the AD) c) Primitive ventricle (future VI) d) Bulbo cardiaco (futuro VD) e) Venous trunk (future ascending aorta and pulmonary trunk) 3 Machine Translated by Google Between the fifth and eighth weeks, the primitive cardiac tube undergoes a process of twisting, remodeling and septation that transforms its only lumen into the four definitive chambers of the heart. 4 Machine Translated by Google The formation of cardiac septa begins around 28 days 5 Machine Translated by Google BLOOD VESSELS AND BLOOD The development of blood cells and vessels begins outside the embryo, in the mesoderm of the wall of the yolk sac and chorion. Soon the formation of vessels begins inside the embryo. Cells and blood vessels develop from it precursor cell, the hemangioblast. The hemangioblast gives rise to a) Angioblasts, which form the vessels b) Pluripotent stem cells, which form blood cells 6 Machine Translated by Google NOTCHORD A set of medial mesodermal cells form the notochord, which will give rise to the future axial skeleton and musculature In addition, the notochord induces a thickening and furrowing of the ectoderm next to the neural plate, primordium of the central nervous system. 7 Machine Translated by Google NERVOUS SYSTEM Its development begins with a widening of a portion of the ectoderm called neural plate This plate folds inward to create the neural groove, longitudinal The edges of the plate are called neural folds The folds end up joining together to form the neural tube A part of the plate detaches and remains between the tube and the skin of the ectoderm, it is the neural crest 8 Machine Translated by Google 9 Machine Translated by Google During early stages of development, the CNS looks like a hollow tube (neural tube). Subsequently, the most cranial portion widens to form three primary brain vesicles. Prosencephalon or anterior brain. This will in turn give rise to vesicles secondary encephalic: Telencephalon: corresponds to the cerebral hemispheres of the adult Diencephalon: includes thalamus, hypothalamus and related structures Mesencephalon or middle brain Hindbrain or hindbrain. It also gives two secondary vesicles: Metencephalon: corresponds to the pons (pons) and adult cerebellum Myelencephalon: corresponds to the adult medulla oblongata (medulla oblongata) 10 Machine Translated by Google 11 Machine Translated by Google EYES and EARS The eyes appear on the lateral wall of the forebrain, initially as optic grooves, which grow later to form the optic vesicles. When the vesicles reach the surface of the ectoderm, they thickens to form crystalline placodes The most distal part of the vesicle invaginates and forms the domes optics Likewise, the placode of the lens also invaginates to form lens vesicles 12 Machine Translated by Google 13 Machine Translated by Google The first portion of the ear to form is the inner ear, like thickening of the ectoderm, called the otic placode, on each side of the hindbrain The placodes invaginate to form the otic pits, which end up protruding into the ectoderm and give rise to the otic vesicles. The middle ear develops from the first and second pharyngeal or gill pouches. The external ear is formed from the first pharyngeal cleft gill 14 Machine Translated by Google 15 Machine Translated by Google ENDOCRINE SYSTEM Pituitary gland: ectodermal origin. The anterior lobe derives from the roof of the mouth (Rathke's pouch) which then ascends to join the posterior lobe Thyroid, parathyroid, pancreas and thymus: endoderm Adrenal cortex: mesoderm. Adrenal medulla: ectoderm (neural crest) Pineal gland: ectoderm 16 Machine Translated by Google DIGESTIVE SYSTEM Comes from a structure called the umbilical vesicle The primitive intestine, initially tubular, has an internal leaf endodermal and an outer mesodermal sheet It undergoes a series of foldings and growths, including the partial horizontalization of the stomach. Differentiates into anterior, middle and posterior intestine Several organs arise as diverticula from the primitive intestine: salivary glands, liver, gallbladder and pancreas The midgut undergoes rapid development, with elongation and generation of intestinal loops. 17 Machine Translated by Google 18 Machine Translated by Google 19 Machine Translated by Google RESPIRATORY SYSTEM It originates as an outpouching or diverticulum of the foregut, in front of the pharynx. The inner lining is of endodermal origin Cartilage, connective tissue and smooth muscle are of mesodermal origin 20 Machine Translated by Google 21 Machine Translated by Google 22 Machine Translated by Google UROGENITAL SYSTEM The definitive kidneys originate from structures mesodermal cells called metanephros. Initially at the sacral level, they subsequently ascend to be at the lumbar level Other structures called pronephros and mesonephros involute or give rise to genital structures 23 Machine Translated by Google The gonads originate from the so-called gonadal ridges, medial bulges of the mesonephros of mesodermal origin. Adjacent to the gonadal crests are the mesonephric or Wolffian ducts, which will become structures of the male reproductive system. A second pair of ducts, the paramesonephric or Müllerian ducts, will become structures of the female reproductive system. 24 Machine Translated by Google 25 Machine Translated by Google An early embryo has the potential to follow both the male and female pattern of development because it has both sets of ducts and primitive gonads, which can give rise to both testes and ovaries. The male differentiation pattern is due to the presence of a gene on the Y chromosome. In the absence of said chromosome, differentiation is female. In the presence of XX chromosomes, the cortex of the gonad differentiates in the ovary and the marrow undergoes regression. In the presence of XY chromosomes, the medulla differentiates into the testis and the cortex involutes. Although the chromosomal sex is determined at the time of fertilization, the male or female phenotype does not begin to manifest in the embryo until the 7th week 26 Machine Translated by Google 27 Machine Translated by Google SKELETAL SYSTEM Most skeletal tissue is derived from mesenchymal cells derived from mesoderm. The skull is divided into neurocranium and viscerocranium, both of which are subdivided into cartilaginous and membranous portions. 28 Machine Translated by Google Blue: cartilaginous Red: membranous 29 Machine Translated by Google Vertebrae, ribs and sternum derive from the sclerotomas of the somites, which come from the paraxial mesoderm. 30 Machine Translated by Google Appendicular skeleton: Bones are formed by condensations of the mesenchyme in the outline of members Towards the sixth week, mesenchymal condensations become be models of hyaline cartilage that undergo an endochondral ossification process to generate future bones 31 Machine Translated by Google EXTREMITIES First, some sketches of the upper limb appear on the sides of the trunk and two days later the sketches of the lower limb appear. The buds of the limbs are made up of mesoderm and ectoderm Towards the sixth week, the buds present a constriction in their middle portion. The distal segments form the hand and foot plates. Initially, the developing limbs are directed caudally; later, they project ventrally, and at the end they show rotation about their longitudinal axes. The upper and lower limbs rotate in opposite directions and with different degrees 32 Machine Translated by Google 33 Machine Translated by Google MUSCLES Skeletal muscles come from mesodermal somites The somite cells differentiate into three regions: a) Myotome, which gives rise to the skeletal muscles of the head, neck and limbs b) Dermatomes, which give rise to connective tissues including the dermis c) Sclerotoma, which gives rise to the vertebrae and ribs Smooth muscle originates from mesodermal cells that migrate toward the developing viscera 34 Machine Translated by Google 35 Machine Translated by Google PHARYNGEAL OR BRANCHIAL ARCHES Simultaneous with the appearance of somites and the development of the neural tube, five pairs of pharyngeal or branchial arches begin to form on each side of the future head and neck, as protrusions on the surface of the embryo. Each arch has an outer layer of ectoderm, an inner layer of endoderm and an intermediate mesoderm The arches are separated externally by slits, which internally they correspond to gill or pharyngeal pouches Each set of arch, bag and slit gives rise to structures specific to the head and neck (bones, muscles, vessels and nerves) There are 4 obvious pharyngeal arches and 2 less visible 36 Machine Translated by Google 37 Machine Translated by Google Fetal growth Fetal period: between the beginning of the third month and the end of life intrauterine Rapid growth of the body and maturation of organic systems occurs. The growth in length is especially noticeable in the second trimester. The growth in weight is more striking in the last two months The placenta develops during the 3rd month of pregnancy. Formed by: a) Structures of the embryo: chorionic villi b) A portion of the maternal endometrium: decidua basalis Vessels originate from the chorionic villi that go towards the cord. umbilical, which joins the fetus to the placenta, with two arteries and one vein 38 Machine Translated by Google 39 Machine Translated by Google Bibliography Torchia & Persaud. Basic clinical embryology. Elsevier, 2022. Carlson. Human embryology and developmental biology. Elsevier, 2020 Sadler. Langman. Medical embryology. Wolters Kluwer, 2019. Patton & Thibodeau. Anatomy and physiology. Elsevier, 2013. Tortora. Anatomy and physiology. Panamericana, 2011. 40