The Archetype as Illustrated in Development - Coursework Example

The Archetype as Illustrated in Development Table of Contents I. Introduction ………………………………………………………… 3 II. Comparison between Amphibian and HumanDevelopment ……… 4 a. Frog Egg vs. Female gametes (Ova or egg) ……………… 4 b. Frog Early Cleavage and Human Cleavage ……………... 5 c. Frog Blastula vs. Human Morula ………………………... 7 d. Early Gastrulation: Frog Crescent Blastophore vs. Human Early Blastocyst …………………………………... 8 e. Late Gastrulation: Frog Yolk Plug ……………………….. 10 f. Neural Plate in Neurulation vs. Human Blastocyst ……… 11 g. Neural Tube in Neurulation vs. Human Blastocyst ……… 12 h. Neural Groove in Neurulation vs. Human Blastocyst …… 15 i. Cross Section of a Frog …………………………………… 16 j. Development of Frogs vs. Human Beings ………………... 17 References …………………………………………………………………. 18 Introduction Vertebrates or vertebrata are species that has general characteristics of having a backbone or spinal cord, a brain case, and an internal skeleton while invertebrates are those animals that does not have a backbone. Starfish are invertebrates that are classified under Phylum Echinodermata: Asteroidea.1 Majority of echinoderms has no brain. This makes the starfish entirely the opposite of frog and chick. Vertebrates range from lampreys to Men. Vertebrates with jaws are called ‘gnathostomes’ while vertebrates without jaws are the ‘lampreys’.2 Frogs belong to Tetrapods or four-legged vertebrates and are considered as ectothermic vertebrates.3 Physically, frogs’ skin is smooth, has three-chambered heart, and does not have claws on their toes. Frogs usually lay their eggs in water until it hatches to into tadpole or larva. Tadpoles has to be on the water since they breathes with their gills. Chicks are classified as endothermic vertebrates. 3 Their physiological appearance includes skin covered with feathers, has four-chambered heart, lightweight bones that are hollow, and with wings. Similar to frogs, chicks also lay eggs. In comparison between the eggs produced by chicks and frogs, the egg that comes from chicks has more yolk than the frogs. Since human fertilized egg or the zygote does not contain any yolk, we will take into consideration the frog’s reproduction and development as the best choice in comparison with the human reproduction and development process. Comparison between Human and Amphibian Development Frog Egg vs. Female gametes (Ova or egg) There is a huge difference between a frog egg (mesolecithal egg) and human ova (egg cells). Mesolecithal egg has a moderate amount of yolk being distributed throughout the cytoplasm of the egg with more concentration towards the ‘vegetal pole.’ On the other hand, the human ova do not show traces of yolk. Also, the external portion of the frog egg has a smooth surface while the human ova has an uneven surface. Frog egg is divided into a dark pigmented hemisphere called the animal hemisphere while the lightly pigmented hemisphere is known as the vegetal hemisphere. The gray crescent is the dorsal surface of the embryo that plays a role in establishing the embryonic axis. See figure 1. Human ova, measures around 0.2 mm. in diameter, are enclosed within the egg follicles of the ovaries.5 The cell substance of the ovum i is called oöplasm.10 (in amphibians, oöplasm is equivalent to the yolk) The nucleus is known as the germinal vesicle while the nucleolus is the germinal spot. The ovum is enclosed by a thick transparent envelope called the zona striata or zona pellucida. The outer most layer of the ovum is called the corona radiata or ‘radiating crown.’ 10 See figure 2. Frog Early Cleavage and Human Cleavage Within the first three hours after fertilization of the frog egg, the first cleavage ii furrow occurs and passes from the animal pole to the vegetal pole through the gray crescent. The second furrow occurs at right angles to the first. The third pair of cleavages occurs slightly towards the animal pole because of the presence of the yolk. Starting on its fifth division, the regular pattern of the cleavage becomes irregular. See figure 3. The early stage of embryonic development called cleavageiii occurs 24 hours after the human zygote formation (fertilized egg). A rapid mitotic cell division occurs as the zygote travel its way to the uterine tube. The cell division forms two cells, then four, and so on. Unlike the frog egg, cell division of the zygote follows a regular size pattern. See figure 4. Note: Development stage of human cleavage is until the ninth week in which the zygote divides into two cells called ‘blastomeres’ that subdivide once every 12 to 20 hours as the zygote slowly passes down the fallopian tubes. 10 Frog Blastula vs. Human Morula As the cleavage in frog egg continuous to divide, the blastomeres arrange itself around the outside portion of the blastocoel – a central fluid filled cavity. Frog blastula is formed. Frog blastula occurs 3 hours after frog egg is fertilized. This stage takes 7 hours to finish. See figure 5 In the case of the cleavage of a zygote, blastomeres form tight junctions with one another. This leads to a deformation of their round shape. Instead, a mulberry-shaped mass of cells called morula is formed. There is no sign of blastocoel in the human development. What is formed in the human development is the ‘morula.iv’ A 16-cell morula occurs 3 days after conception. 10 See figure 6 Early Gastrulation: Frog Crescent Blastophore vs. Human Early Blastocyst This stage is where major differences occur. This stage of the frog development involves early and late gastrulation wherein the late gastrulation is not present in the case of the human development. ‘Gastrulation’ in frog is equivalent to the ‘early blastocyst’ in human development. Gastrulation occurs 10 hours after the frog egg is fertilized while the early blastocyst occurs starts on the 5th day of conception.3 It usually last for two days. Gastrulation is the in-folding process that generates the endoderm forming a multilayered embryo from a surface layer of cells in the frog’s blastula. The first sign of gastrulation is the appearance of a small groove on the surface of the blastula. This slit is the starting point of cell formation on the surface of blastula. On the later part of the process, cells begin to move inward over the ventral lip causing a round opening in the blastopore. The movement of cells inward forms the gastrocoele (archenteron). See fig. 7 During the early blastocyst in human development, a cavity starts to appear in the center of the morula which starts to fill with fluid. The grouping of cells is what we call a blastocyst. Note: The inner group of cells is what will develop into fetus later on. It is composed of an outer membrane that nourishes and protects the inner group of cells. Late Gastrulation: Frog Yolk Plug During the end part of gastrulation, most of the cells have already formed a hollow in the center where the yolk will form. At this stage, the gastrocoele and the remnants of the blastocoel is newly formed. The outermost shell or the neural ectoderm is already developed. See figure 9 Note: This stage is not present in the human development. Early and late gastrulation lasts for 8 hours. Neural Plate in Neurulation vs. Human Blastocyst The formation of the neural plate occurs during neutralation stage wherein the neural ectoderm thickens to form the neural plate through a process called induction. It is the gastrula that forms into neurala. This stage occurs approximately 18 hours from the time the frog egg is fertilized. See figure 10 The human blastocyst starts from 7 days after the conception. The late blastocyst is composed of the formation of the trophoblast and the inner cell mass. The trophoblast encloses the large liquid fluid-sphere while the inner call mass refers to the clustering of cells displaced on one side. See figure 11. Neural plate is also present in the human development. It is found overlying the ectodermv. Just like in the frog development, a crease or folds is also present in the neural plate in human development.9 Neural Tube in Neurulation vs. Human Blastocyst In Neurulation, a neural tube or a dorsal hollow nerve tube for the brain is formed. The prosencephalon with optic vesicles, mesencephalon, and rhombencephalon is found in the neural tube.6 See figure 12 & 13. In the late blastocyst, the ectoderm gives rise to the nervous system and the epidermis of the skin is formed. The neural tube in the human development will become the nervous system. The neural tube at the front end is called the anterior neuropore while the rear end is called the posterior neuropore. A successful closure of the neural tube will develop into 3 vesicles for cerebral hemispheres and the brain stem. A total of five vesicles: the cerebral hemispheres, diencephalons, midbrain, pons, and cerebellum & medulla oblongata will form to become the major portion of the central nervous system (CNS) within the skull.7 Neural tube in the human development is already visible between 21 – 22 days. Neural Groove in Neurulation vs. Human Blastocyst Neural groove in neurulation is identified by the depression bordered by a paired neural fold. Other areas found in the neural groove are: notochord, ectoderm, and lateral plate mesoderm which will later on form the muscle layers of the gut and the abdominal wall. See figure 15. Similar to the neural groove found in neurulation, the human development also develops a neural groove – the crease or fold in the neural plate that deepens. Cross-Section of a Frog The six cross sections show the head section wherein the oral suckers develop faster than the other sections. The development of the eyes or the optic vesicles in the head region is already visible. Note: This portion is not comparable with the human being. Cross-section is done only with animals. Dear Client; I would like to inform you that this page, cross-section of a frog, needs to be look upon as I have not done any frog dissection in the past. Kindly focus on this page and delete this red portion after reading. Thanks. Development of Frogs vs. Human Beings Human beings reproduce the same way as other amphibians do. Male and female involvement is vital in the reproductive process of human beings and amphibians. The same is true with other mammals in general. Frog Development Similar to human development, a sperm and egg is required in the frog development. Once the egg is fertilized, it goes through the process of blastulation, gastrulation, and neurulation. After some time, the tailbud of the tadpole becomes visible. Physical development continuous until a tadpole can already swim. Tadpole has a disproportionate large pharynx and gut. As soon as the first hindlimb and forelimb is developed, the body becomes more slender and its proportion is closer to those of frogs. After a few months, the fertilized frog egg is already developed into a full grown frog. See figure A. Human Development7, 10 Human development during the first week begins with fertilization of the egg by sperm. Fertilization of the egg forms the zygote vi. Next development would be the early cell division which forms the blastocyst vii. There are two types of cell division that occurs in human development. These are: mitosis and meiosis.4 Mitosis is a process in which the nucleus divides to produce genetically identical copies of a cell. Meiosis involves the halving of the chromosome number per nucleus in order to introduce genetic variation – egg or sperm / female or male. Starting on the third week, the placenta is already functioning to deliver nutrients and oxygen to and remove wastes from the embryonic blood. Starting on the 2nd month, the placenta is considered as an endocrine organ that produces estrogen, progesterone and other hormones that aids in the maintenance of pregnancy. On the 8th week of the embryonic development, all organ systems is already formed and developed. On the 9th week, the embryo is called as the fetus. During the fetal development period, the developing fetus grows from a crown-to-rump (head-to-toe) wherein the length is about 3cm long weighing approximately 1 gram up to 14 inches weighing approximately 2.7 – 4.1 kg. Between 9 – 12 weeks, the head of the fetus is already dominant with a body that is elongated. The brain continuous to enlarge. On the 12th weeks onwards, the walls of the hollow visceral organs are slowly gaining smooth muscle; the bone marrow begins to produce blood cell formation; the bone formation is accelerating; and the sex is already detectable. On the 4th month, Sensory organs are present. Generally, the face is bigger than the body at this point. Other parts of the body is continuously developing. Starting on the fifth month, vernix caseosa covers the body while the head is covered with lanugo (a silklike hair). Fetal position starts to take up space in the womb. Between 6th to 7th month, myelination of the spinal cord begins and the eyes are already open. The skin is wrinkled and red; fingernails and toenails are present. However, the hypothalamus is still premature to regulate body temperature. Between 8th to 9th month, the bone marrow becomes the sole site of blood cell formation. Skin color becomes pink. At this point, the body is already lean and well proportioned. See figure B. Main Reference: Rudgers, 2007 ‘Early Development of Starfish, Frog and Chick’ Retrieved: February 20, 2007 < http://bio.rutgers.edu/~gb102/lab_7/7i2m-intro.html > References: 1 Knott, E. (2004) ‘Asteroidea: Sea Stars and Starfishes’ Tree of Life Retrieved: February 19, 2007 < http://tolweb.org/ > 2 Janvier, P. (1997) ‘Vertebrata: Animals with Backbones’ Tree of Life Retrieved: February 19, 2007 < http://tolweb.org/ > 3 ‘The Five Classes of Vertebrates’ Cazadero (2004). Retrieved: February 19, 2007 < http://www.davidlnelson.md/ > 4 Hill, M. (2006) ‘UNSW Embryology: An Educational Resource for Learning Concepts in Embryological Development’ The University of New South Wales in Sydney and Australia. Retrieved: February 19, 2007 < http://embryology.med.unsw.edu.au/ > 5 ‘Embryology: The Ovum’ Bartleby.com (2000) Retrieved: February 19, 2007 < http://education.yahoo.com/ > 6 Ackerley, S. (2007) ‘The Frog Neural Tube Stage Embryo’ Developmental Biology Online Retrieved: February 25, 2007 < http://www.uoguelph.ca/ > 7 Scheibel, A. (1997) ‘Embryological Development of the Human Brain’ New Horizons for Learning. SCLinks. Retrieved: February 15, 2007 < http://www.newhorizons.org/ > 8 ‘Baby Development’ Retrieved: February 25, 2007 < http://www.deathroe.com/ > 9 ‘Stages of Development from an Ovum & Spermatozoon to a Newborn’ Religious Tolerance.org Retrieved: February 22, 2007 < http://www.religioustolerance.org/ > 10 Marieb, E. (2004) ‘Essentials of Human Anatomy & Physiology’ 7th Ed. Published by: Pearson Education Inc. pp. 515 – 527 Read More