Human Anatomy - Embryology Student Notes PDF

HUMAN ANATOMY INTRODUCTION TO EMBRYOLOGY I. FERTILIZATION TO EMBRYO II. COMMON DEVELOPMENTAL PATTERN III. STEM CELLS I. FERTILIZATION TO EMBRYO * Fertilization First event in development (via sexual reproduction) Union of male (sperm) and female (ovum) to form a zygote...

HUMAN ANATOMY INTRODUCTION TO EMBRYOLOGY I. FERTILIZATION TO EMBRYO II. COMMON DEVELOPMENTAL PATTERN III. STEM CELLS I. FERTILIZATION TO EMBRYO * Fertilization First event in development (via sexual reproduction) Union of male (sperm) and female (ovum) to form a zygote 2 accomplishments Recombination (mixing) of paternal & maternal genes n = haploid # of chromosomes (23 in humans) n + n = 2n (diploid number of chromosomes, humans= 46) Activates egg Development begins Process Sperm penetrates outer jelly layer Sperm contacts corona radiata Cells lying around egg Acrosome = tip of sperm - filled with enzymes that bind sperm to corona radiata & act to digest away corona radiata and then the zona pellucida Cortical reaction Thousands of enzyme-rich cortical granules are released into space between egg membrane & zona pellucida Water fills rushes in (via osmosis) - and lifts the zona pellucida away from egg Result = all remaining sperm prohibited from entering Functions to block polyspermy = entrance of more than 1 sperm Egg & sperm nuclei fuse II. COMMON DEVELOPMENTAL PATTERN * Cleavage Zygote (fertilized cell) divides repeatedly into a large ball of cells * Blastulation Stage of cleavage following fertilization Blastula = cluster of cells Blastocoel = fluid-filled central cavity Cells of blastula begin to rearrange into basic adult body plan in discrete steps Basic steps Polarization = setting up the main axis of embryo Main embyro axes  Anteroposterior axis Dorsoventral axis Left-right axis Trophoblast = outer ring of cells surrounding the blastocoel Will form the chorion – one of the extraembryonic membranes Inner cell mass = group of cells on 1 side of blastula Will form the embryo * Implantation Day 7 Blastua implants into wall of uterus Endometrium = surface layer of uterus Trophoblast divides into layers Cytotrophoblast = inner cell layer Syncytiotrophoblast = outer thicker cell layer Will burrow into endometrium Contact made with uterine glands and blood vessels Completion = 2nd week * Formation of extraembryonic membranes Amniotes = organisms having a membranous sac called the amnion Membranes Amnion = protective jacket holding fluid around floating embryo Yolk sac = holds fluid, not yolk - source of cells giving rise to blood, lymphoid cells Allantois = contributes to umbilical cord that links embryo with placenta Chorion = forms most of placenta Placenta = means to nourish embryo Exchange of nutrients, waste & respiratory gases between maternal & fetal bloodstreams Transmission of maternal antibodies to fetus – to immobilize or kill viruses & bacteria Production of hormones (mostly estrogen & progesterone) to maintain endometrium (prevent menses) * Gastrulation ("gut" & "formation") Second major step in establishing the body plan Cells from surface of blastula move inside Common cell movement patterns Epiboly = cells spread across surface as unit Involution = cells spread over an internal surface Invagination = wall of cells indent (or) fold inward Delamination = sheets of cells split into parallel layers  Ingression = individual cells migrate inward germ layers differentiate Endoderm = inner layer – will become stem cells  form organs/tissues 1st location = forms walls of primitive gut Mesoderm = middle layer – will become stem cells  form organs/tissues Form from cells migrating in from outer surface of blastula Once inside - they proliferate to form components of the muscular and reproductive systems Form sheets of cells between endo- & ectoderm Lateral sheets - can be divided into 3 regions Epimere = DORSAL (paraxial) mesoderm Mesomere = intermediate mesoderm Hypomere = VENTRAL (lateral plate) mesoderm Some individual cells join neural crest cells to form mesenchyme Multipluripotential tissue Notochord = forms between sheets of dorsal mesoderm Embryonic coelom = central cavity formed within mesoderm Coelom (body cavity) = forms within the hypomere (lateral plate mesoderm) Ectoderm = outer layer – will become stem cells  form organs/tissues of the integumentary and nervous systems * Neurulation ("nerve" & "formation") Process forming a tube of ectoderm- that will form the nervous system Ectoderm = cells on surface left after others have migrated inward Thickens on dorsal side & anterior-posterior axis of embryo into a neural plate Plate margins grow upward into structures called neural folds which meet & fuse together Neural tube is formed by this fusion Will become the brain & spinal cord Neurocoel – is hollow space within tube At fusion - some neural fold cells separate out from the crowd & become neural crest cells Migrate out on defined routes into the body- and contribute to organ formation !! UNIQUE to vertebrates III. STEM CELLS * Properties of stem cells Can divide and renew themselves for long periods of time Can be used as a repair system Are unspecialized Can divide and become specific specialized cell types of the body - each new cell has the potential to either remain a stem cell or become another type of cell with a more specialized function (i.e. a muscle cell, a red blood cell, a brain cell, etc.) * Common sources Bone marrow Hematopoietic stem cell = forms all the types of blood cells in the body Bone marrow stromal cell (mesenchymal stem cells) = is a mixed cell population that generates bone, cartilage, fat, and fibrous connective tissue Umbilical cord Other tissues Muscle Brain The brain does contain stem cells that are able to generate the brain's three major cell types—astrocytes and oligodendrocytes, which are non-neuronal cells, and neurons, or nerve cells * Stem Cell Research Conducted on both Adult Stem Cells and Embryonic Stem Cells. Adult Stem Cell = an undifferentiated cell found among differentiated cells in a tissue or an organ Can renew themselves and can differentiate themselves to become the major specialized cell types of a tissue or an organ The principal roles of Adult Stem Cells in a living organism are to maintain and repair the tissue in which they are found Embryonic Stem Cells = derived from embryos that develop from eggs that have been fertilized in vitro (in an in vitro fertilization clinic) then donated for research purposes with informed consent of the donors These cells are never derived from eggs fertilized inside of a woman's body The embryos from which Human Embryonic Stem Cells are derived are blastocysts  Research hope = stem cells from one tissue may be able to give rise to cell types of a completely different tissue, a phenomenon known as plasticity or transdifferentiation (i.e. blood cells becoming neurons) What are the similarities and differences between embryonic and adult stem cells? (From http://stemcells.nih.gov/info/basics/basics5.asp) Human embryonic and adult stem cells each have advantages and disadvantages regarding potential use for cell-based regenerative therapies. Of course, adult and embryonic stem cells differ in the number and type of differentiated cells types they can become. Embryonic stem cells can become all cell types of the body because they are pluripotent. Adult stem cells are generally limited to differentiating into different cell types of their tissue of origin. However, some evidence suggests that adult stem cell plasticity may exist, increasing the number of cell types a given adult stem cell can become. Large numbers of embryonic stem cells can be relatively easily grown in culture, while adult stem cells are rare in mature tissues and methods for expanding their numbers in cell culture have not yet been worked out. This is an important distinction, as large numbers of cells are needed for stem cell replacement therapies. A potential advantage of using stem cells from an adult is that the patient's own cells could be expanded in culture and then reintroduced into the patient. The use of the patient's own adult stem cells would mean that the cells would not be rejected by the immune system. This represents a significant advantage as immune rejection is a difficult problem that can only be circumvented with immunosuppressive drugs. Embryonic stem cells from a donor introduced into a patient could cause transplant rejection. However, whether the recipient would reject donor embryonic stem cells has not been determined in human experiments. How are embryonic stem cells grown in the laboratory? (From: http://stemcells.nih.gov/info/basics/basics3.asp) Growing cells in the laboratory is known as cell culture. Human embryonic stem cells are isolated by transferring the inner cell mass into a plastic laboratory culture dish that contains a nutrient broth known as culture medium. The cells divide and spread over the surface of the dish. The inner surface of the culture dish is typically coated with mouse embryonic skin cells that have been treated so they will not divide. This coating layer of cells is called a feeder layer. The reason for having the mouse cells in the bottom of the culture dish is to give the inner cell mass cells a sticky surface to which they can attach. Also, the feeder cells release nutrients into the culture medium. Recently, scientists have begun to devise ways of growing embryonic stem cells without the mouse feeder cells. This is a significant scientific advancement because of the risk that viruses or other macromolecules in the mouse cells may be transmitted to the human cells. Over the course of several days, the cells of the inner cell mass proliferate and begin to crowd the culture dish. When this occurs, they are removed gently and plated into several fresh culture dishes. The process of replating the cells is repeated many times and for many months, and is called subculturing. Each cycle of subculturing the cells is referred to as a passage. After six months or more, the original 30 cells of the inner cell mass yield millions of embryonic stem cells. Embryonic stem cells that have proliferated in cell culture for six or more months without differentiating, are pluripotent, and appear genetically normal are referred to as an embryonic stem cell line. Once cell lines are established, or even before that stage, batches of them can be frozen and shipped to other laboratories for further culture and experimentation.