Lecture 6.pdf

Because learning changes everything. ® Chapter 29 Development, Growth, Aging, and Genetics Seeley’s ANATOMY & PHYSIOLOGY Thirteenth Edition Cinnamon Vanputte, Jennifer Regan, Andrew Russo © 2023 McGra...

Because learning changes everything. ® Chapter 29 Development, Growth, Aging, and Genetics Seeley’s ANATOMY & PHYSIOLOGY Thirteenth Edition Cinnamon Vanputte, Jennifer Regan, Andrew Russo © 2023 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill, LLC.  Lecture Outline Prenatal development begins at fertilization. The zygote undergoes a series of cell divisions that results in the development of an embryo, which grows and develops into a fetus. Growth and development continue after birth through the various life stages of the postnatal period. Access the text alternative for slide images. © McGraw Hill, LLC 2  29.1 Prenatal Development From conception to birth: three stages. 1. Germinal period: first 2 weeks of development during formation of primitive germ layers. 2. Embryonic period: weeks 3 to 8, organ systems develop; developing human is called an embryo. 3. Fetal period: last 30 weeks, organ systems grow and mature’ developing human is called a fetus. Clinical age: mother’s last menstrual period (LMP) used to calculate age of unborn child. Postovulatory age: describes timing of developmental events; calculated as 14 days less than clinical age. © McGraw Hill, LLC 3  Postnatal Life Stages Neonatal: birth to 1 month post partum. Infancy: 1 month to 1to 2 years (when child can walk). Childhood: 1 to 2 years to puberty; many emotional characteristics of a person form at this stage. Adolescence: puberty age (11 to 14) to 20 years. Major physical and physiological changes that affect emotions and behavior. Puberty in females: 11 to 13 years. In males, 12 to 14 years. Period of rapid growth at puberty followed by period of slower growth. Adult stature by 17 to 18 in females; 19 to 20 in males. Adult: 20 years to death. Young adult: 20 to 40 years. Middle age: 40 to 65 years. Older adult: 65 to death. © McGraw Hill, LLC 4  Fertilization 1 Prenatal development begins at fertilization. Sperm attaches to secondary oocyte, sperm contents enter oocyte and join with oocyte pronucleus. Secondary oocyte surrounded by corona radiata and zona pellucida. Flagella of sperm propels it through corona radiata. Acrosome of sperm cell binds to receptor on zona pellucida (ZP3); initiates acrosomal reaction where digestive enzymes are activated. First sperm cell through zona pellucida binds to a receptor on oocyte that causes depolarization. This is the fast block to polyspermy: prevents additional sperm from attaching to oocyte. Zona pellucida degenerates; this is the slow block to polyspermy. © McGraw Hill, LLC 5  1. Of the several hundred million Fertilization 2 sperm cells deposited in the vagina during sexual intercourse, only a few dozen reach the vicinity of the secondary oocyte in the ampulla of the uterine tube. Recall from chapter 28 that the secondary oocyte is surrounded by the corona radiata, which is composed of cumulus cells expelled from the follicle with the oocyte during ovulation. The corona radiata acts as a sort of barrier to those sperm cells that reach the oocyte; however, this barrier is not effective at completely blocking the sperm cells but rather slowing them down. The flagella on the sperm cells propel them through the loose matrix between the follicular cells of the corona radiata. Access the text alternative for slide images. © McGraw Hill, LLC 6  2. Between the corona radiata Fertilization 3 and the oocyte is the zona pellucida, an extracellular membrane comprised mostly of glycoproteins. One particular zona pellucida glycoprotein, called ZP3, is a species-specific sperm cell receptor, to which molecules on the acrosomal cap of the sperm cell bind. This binding initiates the acrosomal reaction, which activates digestive enzymes in the acrosome, primarily hyaluronidase. Access the text alternative for slide images. © McGraw Hill, LLC 7  3. The first sperm cell through the zona pellucida attaches to a receptor molecule (integrin α6β1) Fertilization 4 on the surface of the oocyte plasma membrane and causes depolarization of the membrane within 2–3 seconds. This depolarization, called the fast block to polyspermy, prevents additional sperm cells from attaching to the oocyte plasma membrane. Depolarization also stimulates the intracellular release of Ca2 +. This in turn causes the oocyte to release water and other molecules from secretory vesicles, referred to as cortical granules. These granules are located on the inner surface of the oocyte plasma membrane. The released fluid causes the oocyte to shrink and the zona pellucida to denature and expand away from the oocyte. This results in a fluid-filled space between the oocyte plasma membrane and the zona pellucida called the perivitelline space. As the result of denaturation of the zona pellucida, ZP3 is inactivated, and no additional sperm cells can attach. This reaction is referred to as the slow block to polyspermy. Together, the fast block and the slow block ensure that the oocyte is fertilized by only one sperm cell. Access the text alternative for slide images. © McGraw Hill, LLC 8  Fertilization 5 4. The entrance of a sperm cell into the oocyte stimulates the female nucleus to undergo the second meiotic division, and the second polar body is formed. 5. The nucleus that remains after the second meiotic division, called the female pronucleus, moves to the center of the oocyte, where it meets the male pronucleus of the sperm cell. Both the male and female pronuclei are haploid, each having one chromosome of each homologous pair. 6. Fusion of the pronuclei completes the process of fertilization and restores the diploid number of chromosomes. The product of fertilization is a single diploid cell called a zygote. Access the text alternative for slide images. © McGraw Hill, LLC 9  Early Cell Division 1 Zygote divides to form 2 cells about 18 to 36 hours after fertilization. 2 cells divide to form 4, 8, and so on. Cells are totipotent in first few days; can develop into any cell type needed for development. If a totipotent cell separates from the embryo, a monozygotic (identical) twin may be produced. Differentiation occurs, results in pluripotent embryonic cells: ability to develop into wide range of tissues. Morula: solid ball of 12 or more cells. Blastocyst: hollow sphere of cells containing fluid-filled blastocele. Trophoblast: single layer of cells around blastocele, becomes placenta and extraembryonic membranes. Inner cell mass: thickened area of blastocyst, becomes embryo proper. © McGraw Hill, LLC 10  Early Cell Division 2 (a) Dennis Kunkel Microscopy/Science Source; (b, c, d) DR YORGOS NIKAS/Science Source; (e) Petit Format/Science Source Access the text alternative for slide images. © McGraw Hill, LLC 11  Implantation Implantation occurs when blastocyst burrows into uterine wall. Two populations of trophoblast cells develop into embryonic portion of placenta. Cytotrophoblast remains near other embryonic tissues; branches called chorionic villi protrude into lacunae. Syncytiotrophoblast invades endometrium; forms cavities called lacunae filled with maternal blood. Syncytiotrophoblast layer + basement membrane of chorionic villi = the chorion. © McGraw Hill, LLC 12  Implantation of the Blastocyst and Formation of the Placenta 1 1. As the blastocyst invades the uterine wall, two populations of trophoblast cells develop and form the embryonic portion of the placenta, the organ of nutrient and waste exchange between the embryo and the mother. The first proliferating population of individual trophoblast cells is called the cytotrophoblast. The other trophoblast population is a nondividing syncytium, or multinucleated cell, called the syncytiotrophoblast. The cytotrophoblast remains nearer the other embryonic tissues, and the syncytiotrophoblast invades the endometrium of the uterus. The syncytiotrophoblast is nonantigenic, meaning that, as it invades the maternal tissue, no immune reaction is triggered. Access the text alternative for slide images. © McGraw Hill, LLC 13  Implantation of the Blastocyst and Formation of the Placenta 2 2. As the syncytiotrophoblast encounters maternal blood vessels, it surrounds them and digests the vessel wall, forming cavities called lacunae, which contain maternal blood. The lacunae are still connected to intact maternal vessels, so that blood circulates from the maternal vessels through the lacunae. 3. Cords of cytotrophoblast surround the syncytiotrophoblast and lacunae. Embryonic mesoderm and blood vessels grow into these cords. Access the text alternative for slide images. © McGraw Hill, LLC 14  Mature Placenta and Fetus 1 Branches from the cords of cytotrophoblasts sprout into chorionic villi that protrude into the lacunae like fingers. The entire embryonic structure facing the maternal tissues is called the chorion. As the placenta matures, the cytotrophoblast disappears so that the embryonic blood supply is separated from the maternal blood supply by only the embryonic capillary wall, a basement membrane, and a thin layer of syncytiotrophoblast. © McGraw Hill, LLC 15  Mature Placenta and Fetus 2 Access the text alternative for slide images. © McGraw Hill, LLC 16  Growth of the Fetus Fetus: at 60 days embryo becomes a fetus. Fetal period: from day 60 to birth. Rapid growth. (a) Claude Edelmann/Science Source (b) Petit Format/Nestle/Science Source; Lanugo: fine soft hair covering. Vernix caseosa: waxy coat of protection. Access the text alternative for slide images. (c) Tissuepix/Science Source © McGraw Hill, LLC 17  29.2 Parturition Parturition: process by which a baby is born. In mother. Estrogens overcome inhibitory influence of progesterone. Oxytocin is released. In fetus. Adrenal gland is enlarging prior to parturition due to influence of fetal hypothalamus. Labor. First stage: onset of regular uterine contraction until cervix dilates to fetal head diameter. Second stage: from maximum cervical dilation until baby exits vagina. Third stage: expulsion of placenta from uterus. © McGraw Hill, LLC 18  Parturition 1 1. First stage. The first stage of labor, often called the dilation stage, begins with the onset of regular uterine contractions. This stage extends until the cervix has dilated to a diameter about the size of the fetus’s head. This stage of labor commonly lasts 8– 24 hours, but it may be as short as a few minutes, especially in females who have had more than one child. Normally during labor (95% of the time), the head of the fetus is in an inferior position within the female’s pelvis, so that the head acts as a wedge, forcing the cervix and vagina to open as the uterine contractions push against the fetus. During this stage of labor, the amniotic sac ruptures, releasing the amniotic fluid. The central tendon of the perineum is very important in supporting the uterus and vagina. Tearing or stretching of the tendon during childbirth may weaken the inferior support of these organs, and prolapse of the uterus may occur. Prolapse is a “sinking” of the uterus, so that the uterine cervix moves down into the vagina (first degree), moves down near the vaginal orifice (second degree), or protrudes through the vaginal orifice (third degree). Access the text alternative for slide images. © McGraw Hill, LLC 19  Parturition 2 2. Second stage. The second stage of labor, often called the expulsion stage, lasts from the time of maximum cervical dilation until the fetus exits the vagina. This stage may last from a minute to an hour or more. During this stage, contractions of the abdominal muscles assist the uterine contractions. The contractions generate enough pressure to compress blood vessels in the placenta that blood flow to the fetus is stopped. During periods of relaxation, blood flow to the placenta resumes. Occasionally, synthetic oxytocin (pitocin) is administered to mothers during labor to increase the force of the uterine contractions. However, caution must be exercised in using this drug, so that tetanic contractions, which would drastically reduce blood flow through the placenta, do not occur. Access the text alternative for slide images. © McGraw Hill, LLC 20  Parturition 3 3. Third stage. The third stage of labor actually occurs after the birth of the fetus. This stage is often called the placental stage because during this stage the placenta is expelled from the uterus. Uterine contractions cause the placenta to tear away from the wall of the uterus. Some bleeding from the uterine wall occurs as a consequence of the intimate contact between the placenta and the uterus, but the bleeding is normally limited because uterine smooth muscle contractions compress the blood vessels to the placenta. Access the text alternative for slide images. © McGraw Hill, LLC 21  Factors Influencing Parturition 1 1. Before parturition, the progesterone concentration in the maternal blood is at its highest level and is exerting an inhibitory effect on uterine smooth muscle cells. Near the end of pregnancy, however, estrogen levels rapidly increase in the maternal blood, and their excitatory influence overcomes the inhibitory influence of progesterone. 2. Before parturition, the adrenal glands of the fetus are greatly enlarged, and the rate of adrenocorticotropic hormone (ACTH) secretion by the fetus’s anterior pituitary gland increases. The increase in ACTH is due to the stress of the confined space and limited O2 supply created in the uterus by the growing fetus. 3. ACTH causes the fetal adrenal cortex to produce glucocorticoids, which travel to the placenta, where they alter hormone secretion. Access the text alternative for slide images. © McGraw Hill, LLC 22  Factors Influencing Parturition 2 4. Specifically, the glucocorticoids from the fetal adrenal cortex decrease the rate of progesterone secretion and increase the rate of estrogen synthesis. Also, prostaglandin synthesis is initiated, which strongly stimulates uterine contractions. 5. During parturition, stretching of the uterine cervix stimulates the release of oxytocin from the maternal posterior pituitary gland. 6. Oxytocin stimulates uterine contractions, which move the fetus farther into the cervix, causing further stretch. Thus, by a positive- feedback mechanism, stretch stimulates oxytocin release and oxytocin causes further stretch until the time of delivery. After delivery of the fetus, the cervix is no longer stretched and oxytocin secretion decreases. Access the text alternative for slide images. © McGraw Hill, LLC 23  29.3 The Newborn Respiratory System and Cardiovascular System. Foramen ovale closes, two atria separated. Ductus arteriosus closed, blood no longer flows between pulmonary trunk and aorta. Umbilical vein and arteries degenerate. Digestive System. Meconium (anal discharge) is mixture of cells from digestive tract, amniotic fluid, bile, and mucus excreted by newborn. Stomach begins to secrete acid. Liver does not produce adult bilirubin for first two weeks. Lactose can be digested, but other food must be gradually introduced. © McGraw Hill, LLC 24  Congenital Disorders The term congenital means “present at birth,” and congenital disorders are abnormalities commonly referred to as birth defects. Approximately 70% of all congenital disorders are the result of an unknown cause, 15% have a known genetic cause, and the remaining 15% result from environmental factors or a combination of environmental and genetic factors. Environmental factors, referred to as teratogens, damage the fetus during development. An example of a known teratogen is alcohol. Fetal alcohol syndrome results when a pregnant female drinks alcohol, which crosses the placenta and damages the fetus. The baby is born with a smaller-than-normal head, intellectual disability, and possibly other defects. © McGraw Hill, LLC 25  29.4 Lactation Lactation: production of milk by mother’s breasts (mammary glands) following parturition. Breasts develop during pregnancy. Duct system expands, additional adipose deposited. Prolactin responsible for milk production. Suckling by baby stimulates surge of prolactin and stimulate additional milk production. Colostrum produced first few days after birth. High in protein, contains many antibodies. Milk letdown: reflexive response to baby nursing; oxytocin released by mechanical stimulation of breasts causes ejection of milk. © McGraw Hill, LLC 26  Hormonal Control of Lactation 1. During suckling, mechanical stimulation of the breasts initiates nerve impulses that reach the hypothalamus. 2. In response, the hypothalamus stimulates the release of prolactin from the anterior pituitary gland and oxytocin from the posterior pituitary gland. 3. Prolactin stimulates milk production in alveoli of the mammary glands. Oxytocin stimulates smooth muscle cells associated with the alveoli and ducts of the mammary glands to contract. As a result, milk flows from the breast in a process called milk letdown. In addition, higher brain centers can stimulate oxytocin release, and stimuli, such as hearing an infant cry, can result in milk letdown. Access the text alternative for slide images. © McGraw Hill, LLC 27  Aging and Death 2 Atherosclerosis: deposit and hardening of materials in lesions in large and medium-sized arteries. Result in arteriosclerosis which, in turn, can result in a thrombus and/or embolus. Progressive aging of cells due to exposure to toxic substances. Free radicals: atoms or molecules with an unpaired electron. Can react with and alter cells leading to dysfunction, cancer, or cell damage. Poor diet may lead to vitamin deficiency. Decrease in ATP production; may be from mitochondrial DNA mutations. Immune system is less responsive to outside antigens but more responsive to self antigens. Genetic component: longevity. Progeria: genetic trait causing premature aging. Ability to adjust to stress decreases. © McGraw Hill, LLC 28  29.7 Genetics Genetics: study of heredity. Mendelian genetics: study of how genetic traits are passed on to offspring. Genetic approach to diagnosis and management of disease is called genomic medicine. © McGraw Hill, LLC 29  Mendelian Genetics “Heritable factors” passed on to offspring = genes. Genotype: genes an organism has for a given trait. Phenotype: expression of genes as a trait. Dominant and recessive alleles. Alleles are alternate forms of genes. Dominant masks effects of recessive genes. Homozygous: Having two of the same alleles for a trait. Examples: Homozygous dominant: AA. Homozygous recessive: aa. Heterozygous: Having one dominant and one recessive allele for a trait. Example: Aa. © McGraw Hill, LLC 30  Chromosomes 1 DNA: hereditary material of cells and controls cell activities. Found in discrete sections called chromosomes. Autosomal and sex (X or Y) chromosomes. Contain thousands of genes. Diploid: two copies of chromosomes. Haploid: one copy of chromosomes, only in gametes. Karyotype: map of chromosomes. CNRI/SPL/Science Source Access the text alternative for slide images. © McGraw Hill, LLC 31  Chromosomes 2 Homologous: pairs of chromosome where one is from the father and the other is from the mother. Locus: the location of a gene on a chromosome. Allele: different forms of the same gene. Multiple alleles – sometimes alleles come in more than just dominant and recessive forms. Allelic variant – a different form of an allele. Access the text alternative for slide images. © McGraw Hill, LLC 32  Gene Dominance Complete dominance: the dominant allele covers up the recessive allele and is the only allele expressed. Codominance: both alleles are expressed equally at the same time. Incomplete dominance: the dominant allele and the recessive allele both are expressed, with the recessive being at a much lower level. Example – beta-thalassemia © McGraw Hill, LLC 33  Codominance of Blood Types Genotype Phenotype IAIA or IAi Type A blood (A antigen only) IBIB or IBi Type B blood (B antigen only) I AI B Type AB blood (A and B antigens) ii Type O blood (neither A nor B antigen) Type A blood results from the expression of only the I A allele, type B blood from the expression of only the I B allele, and type O blood from the expression of neither the I A allele nor the I B allele. Type AB blood illustrates codominance and results from the expression of both the I A allele and the I B allele at the same time. © McGraw Hill, LLC 34  Polygenic and Sex-Linked Traits Polygenic traits: determined by expression of multiple genes on different chromosomes. Examples: height, eye and skin color, intelligence. Sex-linked traits: affected by areas of the X and Y chromosomes. X-linked traits more often affect males. Y-linked traits only affect males. Example: hemophilia A. © McGraw Hill, LLC 35  Meiosis and the Transmission of Genes 1 Meiosis: DNA replication followed by two cell divisions. Homologous pairs are separated. Resulting gametes (egg, sperm) unite to form a zygote. Homologous pairs are reunited. New pairs are a mixture of DNA from two individuals. Can use Punnett square to determine probability of offspring having a specific genotype. © McGraw Hill, LLC 36  Meiosis and the Transmission of Genes 2 1. A pair of unduplicated homologous chromosomes are shown. On one homolog the normal, dominant allele is indicated with an uppercase A. On the other homolog, the abnormal allele is indicated with a lowercase a. 2. Before meiosis begins, DNA replication occurs, forming replicated chromosomes that each consist of two chromatids. Each replicated chromosome has two identical alleles as a result of DNA replication. 3. As a result of the first meiotic division, each daughter cell receives one replicated member of a homologous pair. 4. No DNA replication takes place between the first and second meiotic divisions. During the second meiotic division, the chromatids of each chromosome separate. 5. As a result of the second meiotic division, each cell receives one chromatid from each chromosome. Two types of haploid gametes have been produced, those carrying the A allele and those carrying the a allele. Access the text alternative for slide images. © McGraw Hill, LLC 37  Inheritance of a Recessive Trait: Albinism Access the text alternative for slide images. © McGraw Hill, LLC 38  Genetic Disorders 1 Genetic disorders: abnormalities in DNA. Mutation. Mutagens: agents that cause mutations. Errors during meiosis may result in mutation as well. Nondisjunction (failure of chromosomes to separate during meiosis) resulting in aneuploidy such as Down syndrome. © McGraw Hill, LLC 39 Because learning changes everything. ® www.mheducation.com © 2023 McGraw Hill, LLC. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill, LLC.