VETA60 - Developmental Anatomy (Embryology) Module 1 & 2 PDF

**MODULE 1** Introduction to Developmental Anatomy **Embryology** \- a branch of biology dealing with the development of the animal embryo, including the development of fertilized egg and embryo and the growth of the fetus \- had undergone several periods under the influence of notable philosoph...

**MODULE 1** Introduction to Developmental Anatomy **Embryology** \- a branch of biology dealing with the development of the animal embryo, including the development of fertilized egg and embryo and the growth of the fetus \- had undergone several periods under the influence of notable philosophers and scientists -- -- **ancient Sankrit and Egyptian hieroglyphics** \- where first evidence of "knowledge" about embryos are based \- made reference to placenta as the seat of the external soul \- did not consider embryo alive until baby was born \- also had knowledge that eggs could be removes from nests and artificially incubated in ovens **Why eat placenta?** -- hormones for maintenance for physiological functions of the body \- mother instinct \- embryo is not alive until born \- once fetus is out, they remove the placenta for the fetus to breathe \- in some cases, when they don't remove the placenta, they get rid of weaklings (even for most animals) \* mothers lick their fetuses to promote circulation to eliminate fluid **Hippocrates (460 bc -- 370BC)** \- believed that the embryo began development by extracting moisture and breath from the mother \- human fetus gained nourishment by sucking blood from the placenta \- described the stages of hatching of chicks during the 20 days of their creation **Plato (427 -- 347 BC)** \- concept of "souls" in his studies of development \- vegetative soul brings about life (plants) \- sensitive soul enables sensation (animals) \- spiritual soul enables thinking (unique to humans) **Aristotle (384 -- 322 BCE)** \- first to conduct systematic observation on embryos \- recorded different stages in the development of chick embryos \- recognized multiple ways that organisms reproduce \- wrote '*Treatise de generation animalium'* (Generation of Animals) \- mentioned that male contributed semen and female portion called catemania laid the foundation of the embryo **Galen (150 AD -- 180 AD)** **-** Galen of Pergamos \- wrote the book 'On the formation of the Fetus' \- believed that the umbilical cord was necessary for respiration \- describes the fetal development and structures that are now named Allantois, Amnion, and Placenta \- navel button **Leonardo da Vinci** \- in the late 1400s and early 1500s \- dissection of the human fetus and quantitative measurement of embryonic growth  ---------------------------------------- Renaissance and Preformationist Period ---------------------------------------- **Volcher Coiter (1514 -- 1576)** \- published a detailed study of chick embryology \- recognized as "Father of embryology" **William Harvey (1578 -- 1657)** \- best known for his work on blood \- contributed significantly to embryology by expanding and correcting Aristotle's work \- coined the term [epigenesis^1^] \- greatest contribution: ["omne vivum ex ovo"^2^] promoting the existence of ova (even in humans) \- used simple lenses to observe chick embryos and made observation on circulation of blood \- determined the position where the embryo arises in an egg (white spot) \- believed that amniotic fluid was absorbed into the blood of the embryo and later, the fetus +-----------------------------------------------------------------------+ | ^1^ epigenesis -- development of a plant or animal from an egg or | | spore through a series of processes in which unorganized cell masses | | differentiate into organs and organ systems | | | | ^2^ "omne vivum ex ovo" -- "every living thing is from an egg" | +-----------------------------------------------------------------------+ **Marcello Malphigi (1628-1694)** \- professor of medicine \- one of the first scientists to study structures such as the lungs, kidneys, spleen, brain, and skin \- first microscopic account of chick development \- concluded that egg contained miniature chick \- responsible for rise of the preformationist doctrine **Preformation theory** -- the organism is preformed as a complete miniature structure in the egg and simply grows larger as it develops **Ovists** -- those who believed that preformed organisms existed in eggs; supported by Jan Swammerdam, Charles Bonnet, Albert von Haller, etc. **Antoni von Leeuwenhoek (1632 -- 1723)** \- discovered "animacules" (microscopic animals) in semen \- argues that a tiny preformed human was already present \- his discovery led to a 'preformationst period' ensuing an argument over which sex produced the [homunculus^3^] \- observed human sperms through an improved version of a microscope and ----------------------------------------------------------------------------------------------------------------------- ^3^ homunculus -- little man, in the theory of preformation; inhabit the germ cell and to produce a mature individual -----------------------------------------------------------------------------------------------------------------------  **Theory of Homunculus** -- suggested that a little human embryo was hidden in the head of every sperm **Spermists** -- supporters of the theory of homunculus: Anton can Leeuwenhoek and Nicholas Hartsoecker **Malpighi and Swamerdam** \- chief ovists- the homunculi should have even smaller homunculi inside them who had even smaller homunculi / ad infinitum **Lazaro Spallanzani (1729 -- 1799)** \- put an end to the idea of preformation \- successfully performed the first artificial [insemination^4^] using frog eggs -- -- -- -- **Caspar Friedrich Wolf (1738 -- 1794)** **Theory of Epigenesis** -- new structures arise by progressing through a number of different stages **Epigeneticists** \- those who believed that development proceeded progressively from unorganized matter \- asked the preformationists: \* embryonic monsters (embryos with severe congenital malformations) e.g: apodia : amelia -- complete absence of the skeletal parts of a limb : hemimelia -- partial absence of leg, mainly distal part \* regeneration of a star fish arm \* series of arguments between Casper Friedrich Wolff (Epigeneticist) and Albert von Haller (Preformationist) -- -- ------------------------------------------------------------------------------- ^6^amniotes -- group of limbed vertebrates including reptiles, birds, mammals ------------------------------------------------------------------------------- ---------------------------------- Ontogeny recapitulates Phylogeny ---------------------------------- --------------------------------------- Synthesis of Embryology with Genetics --------------------------------------- ------------------------------------------------------------------------------------------------------------------------ ^7^meiosis - type of cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes ------------------------------------------------------------------------------------------------------------------------ ------------------------ Discovery of Induction ------------------------ ------------------------- Experimental Embryology ------------------------- **Hans Spemann (1869 -- 1941)** 1. Removed cells from the dorsal lip of an amphibian blastula 2. Transplanted them to the belly region on another blastula RESULT: embryo developed two notochords, a normal dorsal, and a second along its belly RISE OF GENETICS \- the theory of development had to explain why eggs of different species developed in different way \- developmental mechanisms explained by Roux, Driesch, etc. had genetic components, but back then it was just considered embryology \- most embryologists supported Boveri -- Nucleus was the site of hereditary determinants **Thomas Hunt Morgan** \- split between embryology and genetics \- argued that hereditary determinants lay in cytoplasm; collaborated with Driesch -- removal of cytoplasm from uncleaved egg = defective embryos formed \- responded to 1905 E.B. Wilson and student Nettie Stevens discovery that XX chromosome -- female animals and the XO or XY chromosome -- male animals, thus nucleus determining the sex of the individual, by investigating a parthenogenetic species of aphids -- correlating chromosome number and sex. Results: cytoplasm still determined development \- 1910: found mutations in Drosophila -- interpreted as segregating with the X chromosome -- initially resisted this interpretation \- eventually came to the founding of the gene theory **Gene theory** -- genes are physically linked on the ------------------------ Use of Model Organisms ------------------------ \* no model organisms prior to 1900s - Wilhelm Roux (1850-1924) - frogs - Hans Driesch (1867-1941) -- sea urchins, by Roux's theory - Thomas Hunt Morgan (1866-1945) -- fruit flies **Mosaic Theory** \- by Wilhelm Roux (1850-1924) \- explains cell division \- each division actually separates off differential nuclear materials into different daughter cells \- process is rather like producing a mosaic, in which each resulting piece is different bits of nuclear material from the others though it maintains its individuality **Regulative Theory** \- by Hans Driesch in 1892 \- based on experiments in sea urchin \- after first cell division, he shook the cells apart and places them separately \- instead of producing partial embryos, the cells produced normal embryos that were half-sized \- "Totipotency" -- ability to respond to the needs of the whole and to become any part of the whole that the conditions demanded -- -- **Fritz Muller** \- a naturalist and resident of Brazil \- monograph entitled *Fur Darwin* -- detailed a comparative study of the embryology of crustaceans \- described two possible patterns of development: 1\) embryos either diverge in form from one another after traveling a pace on a common developmental path 2\) the evolutionarily more advanced embryos trace the entire developmental path of their ancestors to the adult stage and progress beyond +-----------------------------------------------------------------------+ | **Module 2** | | | | Basic Terminologies in Embryology | | | | Common Morphological Features in Vertebrae Embryos | +-----------------------------------------------------------------------+ \* primary structures during the early stage of animal's development --------------------------- BASIC TERMS IN EMBRYOLOGY --------------------------- **1. Germ Layer** \- sheet of cells that give rise to all tissues and organs of the body \- formed during gastrulation **a. Ectoderm** **b. Endoderm/Entoderm** **c. Mesoderm**  +-----------------------------------------------------------------------+ | ^8^peritoneal cavity -- diaphragm, walls of abdominal and pelvic | | cavities, and abdominal organs | | | | ^9^pleural -- space between pleura, thin membranes that line and | | surround the lungs | | | | ^10^pericardial -- heart and roots of vessels | | | | ^11^pelvic -- sits below abdominal cavity | | | | ^12^visceral organs -- soft interior organs of the body, heart and | | lungs; in the abdomen, liver, pancreas, and intestines | +-----------------------------------------------------------------------+ ---------------------------------------------------- COMMON MORPHOLOGICAL FEATURES IN VERTEBRAE EMBRYOS ---------------------------------------------------- \* All vertebrae develop in a sequential manner after fertilization 3\. **Notochord** \- solid longitudinal rod formed by mesodermal cells, found beneath the neural tube, extends from the midbrain to the tail  4\. **Gut tube** \- hollow tube lying below the neural tube formed by infolding of entoderm \- rostral end will become the future pharynx and give rise to the respiratory tract, middle portion will become the digestive tract, terminal portion as anus **pharyngeal pouches** 5\. **Pharyngeal/branchial arches** **-** paired arched columns that will form structures of the face, ear, and neck \- each arch has a pouch, pharyngeal pouch, membrane, and cleft (pharyngeal cleft)  6\. **Paraxial mesoderm** \- medial most portion of mesoderm found on either side of the neural tube **somite** \- segmented and each segment of paraxial mesoderm \- will give rise to the axial skeleton (vertebra and ribs) 7\. **Intermediate mesoderm** \- small aggregations of mesodermal cells lateral to the paraxial mesoderm \- gives rise to embryonic kidneys (pronephros and mesonephros) and gonads (testis and ovaries)  8\. **Lateral mesoderm** \- layer of mesodermal cells lying parallel to the intermediate mesoderm *lateral mesoderm* \- splits into two layers: outer somatic (parietal) and inner splanchnic (visceral) during development \- space between two layers is called coelom \- splitting occurs throughout the embryo except in the head and tail regions (coelom is absent) \- somatic mesoderm becomes closely associated with the surface mesoderm, splanchnic mesoderm with endoderm 9\. **Heart** \- a single tube formed below the gut tube \- once formed, never ceases to pump blood which carries nutrients needed by other developing tissues in the body \- bending, twisting, and compartmentalization of its interior characterize further development of this organ 10\. **Arteries** \- the early vessels that delivers blood to the developing organs a\. **Ventral aorta** \- single arterial vessel arising from the rostral end of   11\. **Veins** \- vessels responsible for collecting blood from the different parts of the embryo to: a\. **Cranial cardinal veins** \- paired venous vessels originating from the head region and connect with the common cardinals at the level of the heart b\. **Caudal cardinal veins** \- paired vessels originating from the caudal region of the body and connect with the common cardinal at the level of the heart c\. **Common cardinal veins** \- short, paired vessels that connect the cranial and caudal cardinal veins to the caudal end of the heart d\. **Vitelline veins** \- paired vessels that draws blood from the yolk sac into the caudal end of the heart e\. **Allantoic veins** \- paired vessels that drain the allantois of the blood which is directed towards the caudal end of the heart