Lec1 Terms of Embryology Mitosis and Meiosis PDF

# Terms of Embryology: Mitosis & Meiosis ## Dr. Amber Ilyas Associate Professor SMC/JSMU ## Learning Objectives * Explain terms related to embryology * List steps of cell division during mitosis * Explain the significance of mitosis * Define Meiosis * List the steps of meiosis * Differentiate...

# Terms of Embryology: Mitosis & Meiosis ## Dr. Amber Ilyas Associate Professor SMC/JSMU ## Learning Objectives * Explain terms related to embryology * List steps of cell division during mitosis * Explain the significance of mitosis * Define Meiosis * List the steps of meiosis * Differentiate first and second meiotic divisions * State the phases of meiotic divisions * Justify the importance of meiosis in both sexes * Differentiate between mitosis and meiosis ## Definition of Embryology "Human embryology" is the science concerned with the origin and development of a human being from a zygote to birth of an infant. ## Why do we study Embryology? "The one who sees things from the beginning will have the finest view of them." *Aristotle, 384-322 B.C.* ## Importance of Embryology: * The study of prenatal stages of development, especially those occurring during the embryonic period, helps us understand the normal body structure and the cause of congenital anomalies. * It is also concerned with studying various genetic and environmental factors that disturb normal development and produce birth defects. ## Developmental Anatomy * Is the field of embryology concerned with the structural changes of a person from fertilization to adulthood. * It includes embryology, fetology, and postnatal development. ## Developmental Periods | Period | Description | |---|---| | Prenatal Development | Includes the main developmental changes occurring before birth and is divided into 2 periods: | | Embryonic Period | Begins at fertilization and ends with the end of the 8th week. | | Fetal Period | Begins at the beginning of the 9th week and ends at birth. | | Postnatal Development | Includes changes occurring after birth. e.g., teeth and breast. | ### Critical Periods of Human Development: * It is the stage of development of an embryo that is susceptible to an agent, such as a drug or virus, which can lead to congenital abnormalities. * The development of the embryo is most easily disrupted when the tissues and organs are forming during the embryonic period. ## Teratology (Gr. Teratos, monster) * Is the division of embryology and pathology that deals with abnormal development (birth defects). * It is concerned with various genetic/environmental factors that disturb normal development and thus produces birth defects. ## Trimester ### Introduction: * Pregnancy is broken down into weeks, and is divided into three parts called trimesters. * Full term pregnancy is considered 40 weeks, and an infant delivered before the 37th week is considered premature. * The first, second, and third months are the first trimester of pregnancy. ## Embryonic Development ### I Trimester * 1 Month * 2 Months * 3 Months ## Abortion (L. aboriri, to miscarry) * A premature stoppage of development and expulsion of a conceptus from the uterus or expulsion of an embryo or fetus before it is viable - capable of living outside the uterus. ### What is Abortion? Abortion is a procedure of terminating a pregnancy by removing the fetus/embryo. ### *ABORTUS* Is the products of an abortion (i.e. the embryo/fetus and its membranes). ## Infancy, Neonate, Childhood * **INFANCY**: The earliest period of extrauterine life, roughly the first year after birth. * **NEONATE**: An infant aged 1 month or younger is called a newborn or neonate. * **CHILDHOOD**: The period between infancy and puberty. | Stage | Blood & Body | Stomach | Liver | Kidney | Heart | Lungs | |---|---|---|---|---|---|---| | Premature infant | <37 wk gestation | | Low CYP450 content | | | | | Neonate | < 28 days | Lower body fat | | Lower glomerulation (FR) | | | | Infant | < 1 year | Little to no gastric acid | Low CYP450 content | Low GFR | | | | Toddler | 2-3 years | Normal gastric emptying | Normal CYP450 content | Normal GFR | | | | Child/Adolescent | 2-16 years | Normal gastric emptying | Normal CYP450 content | Normal GFR | | | ## Puberty: * A stage of human development when sexual maturation and growth are completed and result in ability to reproduce. * On average, puberty typically begins between 8 and 13 in females and 9 and 14 in males. ## Adolescence, Adulthood * **ADOLESCENCE**: It is the phase of life between childhood and adulthood, from ages 10 to 19. * **ADULTHOOD**: Having attained full size and strength; grown up; mature * A person who is fully grown or developed. * Adulthood is commonly thought of as beginning at age 20 or 21 years. Middle age, commencing at about 40 years, is followed by old age at about 60 years ### Developmental Periods of Adolescence | Age | Stage | |---|---| | 10-13 | Early Adolescence | | 13-15 | Middle Adolescence | | 16-19 | Late Adolescence | | 20-25 | Young Adulthood | ## Difference between Adolescence & Puberty | | Adolescence | Puberty | |---|---|---| | Definition | The period of development between childhood and adulthood. | The process of physical changes that occur during adolescence, including the onset of sexual maturity. | | Typical Age | Typically occurs between ages 10-19. | Typically occurs between ages 8-13 for girls and 9-14 for boys. | | Development | Changes in body shape, voice, hair growth, and muscle development. | Development of primary and secondary sexual characteristics such as breast development in girls and growth of testes and penis in boys. | | Hormonal Changes | Hormonal changes occur, but not necessarily related to sexual development. | Hormonal changes, specifically the release of sex hormones, trigger physical changes related to sexual development. | | Emotional Changes | Adolescents may experience emotional changes related to increased independence, identity formation, and peer relationships. | Puberty can cause emotional changes related to increased sexual feelings, self-image, and social relationships. | ## Descriptive Terms: Directions * **Cranial:** The top of the embryo or the head. * **Cephalic:** Superior or the head. * **Caudal:** Inferior or the tail end. * **Dorsal:** Back of the embryo. * **Ventral:** Anterior or the belly side. * **Medial:** Near to the midline. * **Lateral:** Flank side. ## Proximal and Distal * **Proximal:** Toward the trunk; near the origin. Proximal = Proximity. * **Distal:** Away from the trunk; far from the origin. Distal = Distant. ## Terms * **Oocytes:** Female germ or sex cells produced in the ovaries. Mature = secondary oocytes. * **Sperm:** Male germ cells produced in testis. ## Fertilization --- Definition: The process by which the male and female gametes (sperm and ovum) unite to give rise to zygote. --- Place: In the ampullary region of the fallopian tube. ## Zygote * Results from the union of an oocyte and sperm during fertilization. ## Gestational Age * From presumed first day of the last menstrual period. * 2 weeks longer than fertilization. ## Cleavage * Series of mitotic cell divisions of the zygote that results in the formation of early embryonic cells (blastomeres). * Size of cleaving zygote is unchanged. ## Morula * Solid mass of 12 to 32 blastomeres. * Occurs 3 to 4 days after fertilization just as embryo enters the uterus. ## Blastocyst * Blastocyst cavity develops inside the morula. * Centrally located cells, the inner cell mass (embryoblast), is the embryonic part of the embryo. ## Implantation **Definition:** The process by which the blastocyst is embedded in the endometrium. **Time:** 5th-6th day begin; 11th-12th day complete. ## Gastrula * Trilaminar embryonic disc. * Subsequently differentiates into tissues and organs. ## Neurula * Early embryo during the 3rd and 4th week when the neural tube is developing from the neural plate. * First appearance of the nervous system after the gastrula stage. ## Conceptus * Embryo and its adnexa or associated membranes. ## Primordium * Beginning of the first indication of an organ or structure. ## Fetus * After the embryonic period and until birth. ## Self Quiz **What do the following terms represent?** * W: Sister chromatid * X: Spindle fibre * Y: Centriole * Z: Centromere ## Mitosis & Meiosis * **Mitosis:** Division of somatic (body) cells. * **Meiosis:** Division of gametes (sex cells). ## Terminology * **Diploid:** Two sets of chromosomes (2n), in humans 23 pairs or 46 total. * **Haploid:** One set of chromosomes (n) - gametes or sex cells, in humans 23 chromosomes. ## Mitosis * **P-MAT:** * **Prophase:** Chromosomes condense and become visible. The nuclear membrane begins to break down. * **Metaphase:** The chromosomes line up at the center of the cell. * **Anaphase:** The sister chromatids separate and move to opposite poles. * **Telophase:** The chromosomes reach the poles, the nuclear membrane reforms, and the cytoplasm divides. ### Early Prophase * Chromatids condense becoming chromosomes. * Nucleolus disappears. * Centrioles separate and start moving to opposite ends of the cell. * Spindle begins to form. ### Late Prophase: * The nuclear membrane fragments, and the microtubules invade the nuclear area. * Centrioles have moved to the opposite poles. * The spindle is completely formed. ### Metaphase: * The chromosomes are aligned at the metaphase plate. * Centrioles move at polar ends and project spindle fibers to connect each chromosome. ### Anaphase: * The paired chromosomes (sister chromatids) separate. * Separated chromatids move to opposite poles. * Partial division of the cytoplasm begins. ### Telophase: * Chromosomes are at the poles. * Chromosomes uncoil, turning into chromatin. * Nuclear envelops reform. * Spindle fibres disappear. ### Cytokinesis: * Occurs at the end of mitosis. * Animal cells: A cleavage furrow separates the daughter cells. * Plant cell: A cell plate separates the daughter cells. * Daughter cells are genetically identical. ## What is Meiosis? * A division of the nucleus that reduces the chromosome number by half. * Important in sexual reproduction. * Involves combining the genetic information of one parent with that of the other parent to produce a genetically distinct individual. ## Phases of Meiosis * A diploid cell replicates its chromosomes. * Two stages of meiosis. * Cells divide twice but only replicate their DNA once. ### Synapsis: Pairing of homologous chromosomes forming a tetrad. ### Crossing Over: Chromatids of tetrad exchange parts. ## Meiosis I - Prophase I * Chromosomes condense. * Homologous chromosomes pair with each other. * Each pair contains four sister chromatids (tetrad). * Crossing over occurs. ## Meiosis I - Stages of Prophase I * **Leptotene:** Leptotene is of very short duration, and progressive condensation and coiling of chromosome fibers take place. * **Zygotene:** At this stage, the synapsis (pairing/coming together) of homologous chromosomes takes place. * **Pachytene:** Is the stage when chromosomal crossover (crossing over) occurs. At the sites where exchange happens, chiasmata form. * **Diplotene:** Homologous chromosomes separate from one another a little, forming a tetrad. * **Diakinesis:** Chromosomes condense further during the diakinesis stage. This is the first point in meiosis where the four parts of the tetrads are actually visible. The nucleoli disappear, the nuclear membrane disintegrates into vesicles, and the meiotic spindle begins to form. ## Meiosis I - Metaphase I * Tetrads or homologous chromosomes move to the center of the cell. ## Meiosis I - Anaphase I * Homologous chromosomes pulled to opposite poles. ## Meiosis I - Telophase I * Daughter nuclei formed. * They are haploid (1n). ## Meiosis II - Prophase II * Each dyad (2 chromatids = 1 chromosome pair) are connected by a centromere. * Nuclear envelope disappears. * The centrioles create spindle fibers again. ## Meiosis II - Metaphase II * Kinetochores of the paired chromatids line up across the equator of each cell. ## Meiosis II - Anaphase II * The chromatids of the chromosomes finally separate, becoming chromosomes in their own right, and are pulled to opposite poles. ## Meiosis II - Telophase II * The chromosomes gather into nuclei, and the cells divide. ## Products of Meiosis * Each of the four cells has a nucleus with a haploid number of chromosomes. ## Meiosis II * Daughter cells undergo a second division; much like mitosis. * NO ADDITIONAL REPLICATION OCCURS. ## Importance of Meiosis * Allows for sexual reproduction, which is the basis of genetic variation in offspring. * This variation allows the offspring a diversity that could be the difference between living or dying. * This gives the species as a whole a greater chance of surviving in a changing ecosystem. * Genetic variation is the foundation of evolution by natural selection. ## Mitosis vs. Meiosis | Feature | Mitosis | Meiosis | |---|---|---| | Cell Type | Somatic Cells | Germ Cells | | Nuclear Division | Divides once | Divides twice | | Phases | Prophase, Metaphase, Anaphase, Telophase | Prophase I & II, Metaphase I & II, Anaphase & II, Telophase I & II | | Daughter Cells | Diploid (2n) | Haploid (n) | | Crossing Over | No | Yes | | Daughter Cell Identity | Genetically identical | Genetically different | | Result | 2 daughter cells | 4 daughter cells | | | Involved in healing and growth | Involved in genetic variation | | | Malfunction results in cancer | Malfunction results in genetic disorders such as Down's syndrome, Klinefelter's syndrome, and Turner's syndrome. | ## Mitosis & Meiosis Venn Diagram **Mitosis:** * Occurs in all organisms (except viruses) * Creates all body (somatic) cells like blood cells * Involves one cell division * Produces two diploid (2n) daughter cells * Daughter cells are genetically identical * Creates a human cell with 46 chromosomes **Meiosis:** * Occurs only in plants, animals, and fungi * Creates only sex (germ) cells like sperm cells * Involves two successive cell divisions * Produces four haploid (n) daughter cells * Daughter cells are genetically different * Creates a human cell with 23 chromosomes **Similarities:** * Occurs in plants and animals * Starts with a diploid parent cell * Produces new cells * Cells undergo DNA replication * Same basic steps