Animal Reproduction and Development • Organisms must reproduce to survive. • Asexual reproduction - genetically identical copies of organism – less energy; advantage when population needs to grow rapidly - no genetic variation. http://ebiomedia.com/gall/classics/Paramecium/images/para4.jpg • Sexual reproduction increases variability. • Union (fertilization) of haploid cells from 2 different parents - diploid cell (zygote). http://sprott.physics.wisc.edu/pickover/zygote.jpg • Production of sex cells (gametes) allows for various combinations of genes through meiosis. http://www.virtuallaboratory.net/virtuallyGenetics/Mendel/graphics/gametes.jpg Fertilization • Haploid egg meets haploid sperm create zygote - 2n (diploid). • External fertilization, chemicals aid sperm in finding egg of correct species. • Internal fertilization - sperm passes through female reproductive tract to egg. http://departments.bloomu.edu/biology/pics/con2/fern_fertilization1w.jpg • Motility, viability of sperm affected by environment of female. • When sperm meets egg, sperm must penetrate several layers that surround egg. • Humans - layers include layer of follicle cells that surround and support egg, and jellylike layer zona pellucida. • Invertebrates - sperm must penetrate jelly coat and vitelline envelope (similar to zona pellucida). • Enzymes found in acrosome at tip of sperm released when sperm contacts outer layer to digest glycoproteins and polysaccharides found here. http://www.genome.duke.edu/genomelife/glarchive/issue9/snails/gl9p5/inline_image http://www.luc.edu/faculty/wwasser/dev/acrosome.htm • Acrosomal process extends beyond head of sperm to allow sperm to contact next layer. • Recognition of sperm and egg proteins required at this step; if successful, sperm and egg membranes fuse, sperm enters egg. http://www.luc.edu/faculty/wwasser/dev/acrosom1.gif • Seconds after fertilization egg reacts to prevent fertilization by additional sperm, membrane potential changes, release of calcium in egg cytoplasm, change in egg membrane that blocks further entry of sperm. • Increase in calcium in cytoplasm stimulates egg development. http://www.swarthmore.edu/NatSci/sgilber1/DB_lab/Urchin/img_urchin/zygote.jpg • Egg pauses in 2nd meiotic division and completes meiosis after fertilization -polar body is produced. http://www.ucalgary.ca/uofc/eduweb/virtualembryo/PageMill_Images/image145.gif Polar body External Development • External development occurs outside female’s body in water or land. • Eggs of fish, amphibians fertilized externally in water. • Embryo develops inside egg feeding on yolk in egg - given little parental care, mass produced to ensure survival of some. http://mkat.iwf.de/mms/images/02000017360220000000_hi.jpg • Aquatic animals release eggs and sperm into environment where fertilization takes place. • Sessile (nonmotile) species often release large numbers of gametes at specific time of year, leaving chance whether or not they are fertilized. http://www.playaportomari.com/Gallery_underwater/images/spawning.jpg • Large number increases chances of fertilization. • External fertilization cannot occur on land. • Very few sperm reach egg during external fertilization, process requires lot of eggs. • Less care parents provide, more eggs required to guarantee survival of some. http://www.abc.net.au/science/scribblygum/october2002/img/spawning.jpg • External development on land occurs in reptiles, birds, and a few mammals (duck-billed platypus). • Adaptations for embryonic development within eggs and land hard shell for protection, extraembryonic membrane to help provide favorable environment for developing embryo. http://www.reptilia.dk/Opdraetsfaciliteter/vandagameklaek01.jpg • Types of extraembryonic membranes include chorion (lines inside of egg shell) • Membrane moist, allows for gas exchange. • Allantois carries out functions like respiration and excretion; many blood vessels - take in O2 give off CO2, water, salt, nitrogenous wastes. http://de.wikipedia.org/wiki/Allantois Allantois Amnion • Third membrane - amnion - encloses amniotic fluid. • Yolk sac encloses yolk. • Blood vessels in yolk sac transfer food to developing embryo. Fig. 47.14 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Internal development • Internal fertilization and development occur within mother. • Different forms including placenta to sustain embryo. • Nonplacental animals, development occurs inside mother - no placenta. http://content.answers.com/main/content/wp/en-commons/thumb/0/02/250px-Koala_climbing_tree.jpg • No region of exchange of materials between blood of mother and embryo. • Eggs relatively large - yolk supplies developing embryo’s needs. • Marsupials (kangaroos) nonplacental animals - develop inside oviduct, obtain food from yolk of egg, give birth to live young. http://kangaroos.org/kangaroo-joey.jpg • Placenta includes tissues of embryo and mother - where exchange of food, oxygen, waste, water take place. • No direct contact between bloodstreams of mother and embryo. • Transport of materials - diffusion and active transport between 2 circulatory systems. http://embryology.med.unsw.edu.au/Notes/images/placenta/plMembraneW450.jpg • Eggs of placental animals small since embryo requires small amount of yolk for nourishment (until placental connection develops). • Humans have yolk sac. • Umbilical cord attaches embryo to placenta; composed completely of embryonic tissue not maternal tissue. • Umbilical cord contains umbilical artery and vein - carry blood into/out of placenta. • Amnion of placental mammals provides watery environment protects against shock. http://www.udel.edu/Biology/Wags/histopage/colorpage/cfr/cfr.htm Early development • Fertilization to birth - single-celled zygote must divide, grow, differentiate into tissues and organs. • Begins with rapid mitotic division cleavage stage - cell does not grow in size - rapidly divides DNA and protein in egg cytoplasm into smaller cells. http://www.ndpteachers.org/perit/Zygote.JPG • Cell division starts in oviduct within hours after fertilization. • Early stages, mitotic division results in 1 cell producing 2 cells, etc - creates morula (solid ball of cells). • Divides to form blastula (hollow ball of cells). • Central cavity filled with fluid secreted by cells (blastocoel). • Blastula consists of outer layer (trophoblast) - develops into placenta; inner mass develops into embryo. • 1st 5-10 days - dividing embryo travels down oviduct and implants itself into uterine wall. • Uterus responds by increasing blood supply - allows embryo to receive nutrition while placenta develops. http://www-personal.umich.edu/~bradbuck/index_files/image004.jpg • Early embryo – cells totipotent have potential to develop into any tissue. • As development continues, cells become determined (specific fate). • Development and differentiation of cells affected by (partly) environment (other cells that surround them) http://www.nature.com/nm/journal/v7/n4/images/nm0401_393_F1.gif • Induction - process by which 1 cell causes neighboring cell to take specific developmental path. • Further along development - less able cell is to change fate - cell can be taken from 1 area and placed into another - changes fate; only lasts for certain period of time. http://scienceblogs.com/clock/upload/2006/12/a3%20cell_differentiation.gif Gastrulation • Mammals - cells of blastula not developmentally determined as specific tissue. • Gastrulation, cells from blastula form 3 germ layers - eventually give rise to specific type of tissue. • 3 germ layers formed - endoderm, mesoderm, ectoderm. • Rapid division of cells at one end of blastula causes infolding (2-layer gastrula) • 2 germ layers – ectoderm (outside), endoderm (inside ) -first present. • Mesoderm cells move between endoderm and ectoderm to form 3rd layer in middle. http://www.gwu.edu/~darwin/BiSc151/Coelom/COELOM1.GIF • Opening formed at point where endoderm folds inward - blastopore. • Cells of each layer differentiate and specialize to form tissues, organs, organ systems. • Ectoderm - epidermis, nervous system, sweat glands. Fig. 47.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Endoderm - lining of digestive tract, respiratory tract, parts of liver and pancreas, bladder lining. • Mesoderm - muscles, skeleton, circulatory system, excretory system, gonads, inner layer of skin (dermis). http://biology.kenyon.edu/courses/biol114/Chap14/Chapter_14.html • Protostomes (annelids, arthropods, mollusks) - future mouth forms from blastopore (opening in blastula). • Deuterostomes (echinoderms and chordates) - blastopore forms anus of mature organism, mouth forms later. http://www.palaeos.com/Invertebrates/Images/DPComparison2.gif Neurulation • Tissues organize themselves into patterns of organs. • Vertebrates - stage following gastrulation - neurulation – 1st parts of nervous system determined from ectoderm. • Notochord develops from mesoderm along dorsal side of embryo. http://mgs.lami.univ-evry.fr/ImageGallery/EXEMPLES/Neurulation/UCLAneurulation.gif • Notochord induces ectoderm above it along exterior surface of embryo to fold inward, forms neural tube of tissue that will become nervous system (spinal cord and brain). • Neural tube defects (spina bifida) occur when this does not happen properly. Fig. 47.11 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Human male reproductive system • Sperm produced in testes - in scrotum. • Spermatogenesis - seminiferous tubules in testes. • Primary spermatocytes on exterior of tubules produce spermatids become sperm - move into center of tubules as they are produced. http://cellbio.utmb.edu/microanatomy/Male_Reproductive/testis10.jpg • FSH, LH involved in spermatogenesis (part of female reproductive system) • Epididymis on exterior of testes sperm finish maturation and are stored. http://www.embryology.ch/images/cimggametogen/03spermato/c3e_spermatogenese.gif • Vas deferens - duct that carries sperm from testes to urethra (connects bladder to exterior). • Glands along path secrete liquid (semen) - carries and provides nutrients for sperm - include seminal vesicles and prostate gland. • Smooth muscle along ducts propel sperm and secretions together. • Testes produce male hormones like testosterone - involved in secondary sex characteristics (facial hair, deepening of voice) • Increased testosterone production during puberty causes changes. Fig. 46.8 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 46.8 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Human female reproductive system • Ovaries paired structures in lower portion of abdominal cavity. • Eggs produced in ovaries through meiosis. • Ovulation - eggs leave follicle, carried into upper end of oviducts (fallopian tubes) http://www.fertility.com/Images/tube_fertilisation_tcm38-555.jpg • At birth, all eggs female will ovulate during lifetime already present in ovaries - paused in meiotic prophase I. • Eggs develop and ovulate at rate of 1 every 28 days, starting in puberty ending in menopause. • Ovaries produce female sex hormones estrogen and progesterone. http://www.tubal-reversal.net/images/ovulation-ovaries.jpg • Estrogen regulates secondary sex characteristics in females development of mammary glands (milk glands), widening of hips involved in menstrual cycle involves interactions of pituitary gland, ovaries, and uterus. Fig. 46.9 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings The menstrual cycle • Involves hormones secreted by hypothalamus (GnRH: gonadotropinreleasing hormone), pituitary (LH and FSH) and ovary (estrogen and progesterone). • GnRH stimulates FSH and LH stimulate estrogen, progesterone secretion (inhibits GnRH, LH, FSH) http://professionals.epilepsy.com/img/hormone_2_s.gif • 4 stages in menstrual cycle: follicular stage, ovulation, corpus luteum stage, menstruation. • Follicular stage, primary oocytes in ovary along with follicular cells that support oocyte form follicle. • FSH (follicle stimulating hormone) from anterior pituitary stimulates follicle to mature. • As follicle matures, produces estrogen which promotes thickening of uterine lining (in case of embryo) - about 9-10 days long. • When follicle is mature - increase in LH secretion by pituitary causes egg to burst out of follicle and ovary during ovulation. • After ovulation, LH acts on remaining follicular cells in ovary to form corpus luteum - secretes estrogen and progesterone to support uterine thickening and development of secretory tissue in uterine lining. • If fertilization does not occur corpus luteum degrades, uterine lining regresses - menstruation. Fig. 46.15 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • If fertilization does occur - embryo goes through small number of cell divisions in 1st few days as it moves down oviduct into uterus. • After few days embryo is blastocyst (hollow ball of cells) implants in uterine lining to go through embryonic development. Fig. 46.16 Copyright © 2002 Pearson Education, Inc.å, publishing as Benjamin Cummings • hCG (human chorionic gonadotropin) - hormone produced that takes place of LH to maintain corpus luteum. • Corpus luteum continues to secrete progesterone and estrogen to maintain uterine wall. • As pregnancy continues, placenta develops, produces estrogen and progesterone - corpus luteum disappears. http://img.search.com/thumb/9/90/Placenta_fetus.jpg/300pxPlacenta_fetus.jpg • If sperm in oviduct at time of ovulation, fertilization takes place in oviduct. • 2 or more eggs released by ovaries - possible that all will be fertilized because of high number of sperm. • 2 separate eggs fertilized by 2 sperm, dizygotic (fraternal) twins produced http://www.inkycircus.com/jargon/images/fraternal_twins _sxc_nr_1.jpg • Twins related like any other siblings. • Only 1 fertilized egg - identical cells separate during early stages of cleavage into 2+ independent embryos -monozygotic (identical) twins result. • Triplets (and higher) can also occur this way. http://www.samom.com/triplets.jpg • 1st 3 months (1st trimester) embryo goes through organogenesis - majority of body plan formed. • When embryo resembles infant fetus. • 2nd, 3rd trimesters pass fetus grows, major organs develop. http://embryology.med.unsw.edu.au/wwwhuman/Stages/Images/Cst800.jpg • As fetus grows, hormones change in intensity, uterine muscles become more reactive to stretching reflexes. • Oxytocin (hormone that induces labor) and reflexes caused by pressure start labor - smooth muscles in uterine wall contracts against baby to push it downward against cervix. http://www.creationofman.net/chapter3/res/41.jpg • Stretching of cervix allows uterine muscles to push baby through cervix and vagina.