During the 4th week of gestation, limb buds form on the sides of the developing embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week. The tips of these buds condense into the apical ectodermal ridge (AER). The AER continues the elongation Elongation Polymerase Chain Reaction (PCR) of the limb buds and maintains its growth by continuously producing fibroblast growth factor Fibroblast growth factor A family of small polypeptide growth factors that share several common features including a strong affinity for heparin, and a central barrel-shaped core region of 140 amino acids that is highly homologous between family members. Although originally studied as proteins that stimulate the growth of fibroblasts this distinction is no longer a requirement for membership in the fibroblast growth factor family. X-linked Hypophosphatemic Rickets 8 (FGF8). As the AER grows away from the body, tissues differentiate. After the cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. Cartilage: Histology models are formed in the developing limbs, arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology invade central and peripheral areas, giving rise to primary and secondary centers of ossification Ossification The process of bone formation. Histogenesis of bone including ossification. Bones: Development and Ossification. The process of endochondral ossification Ossification The process of bone formation. Histogenesis of bone including ossification. Bones: Development and Ossification is completed when those centers meet and the epiphyseal plate Epiphyseal plate The area between the epiphysis and the diaphysis within which bone growth occurs. Cartilage: Histology is no longer present.
Last updated: Oct 10, 2022
To quickly recall what happens during the 4th week, remember: 4 weeks → 4 limbs, 4 heart chambers
Muscle comes from myotome: ventrolateral cells originating from somites located on either side of neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation that migrate to form muscles. As myotomes migrate, they form:
Positioning, orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment, and growth of limbs in the developing embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week is determined genetically and by the expression of specific timed chemical signals.
Positioning of limbs along the craniocaudal axis is determined by the homeobox (HOX) genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure.
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