Developmental Psychology Module 2: Beginnings PDF

Developmental Psychology 27 DEVELOPMENTAL PSYCHOLOGY MODULE 2: BEGINNINGS ___________________________________________________________________________...

Developmental Psychology 27 DEVELOPMENTAL PSYCHOLOGY MODULE 2: BEGINNINGS ___________________________________________________________________________ Man ask God for a miracle but never did he realize that the miracle he is asking is called life. It is fascinating to discover how life begins. Before new life can begin, all sex cells whether male or female must undergo stages of development. For the female sex cell, it has to undergo 3 stages, the male sex cell into 2 stages. LEARNING OBJECTIVES: Upon completion of the all topics and activities presented in this module you are expected to: 1. Describe the Reproductive Cells. 2. Differentiate, draw and label the parts of the male and female reproductive system. 3. Discuss the mechanisms of heredity. 4. Identify and describe the kinds of twins and multiple births. 5. Describe the kinds of environment and explain how heredity and environment work together. LEARNING CONTENT/TOPICS: A. REPRODUCTIVE CELLS Two kinds of cells, the gametes, are involved in human reproduction: the male gamete sperm and the female gamete called the ovum (egg). A sperm cell is minute or it is one of the smallest cells in the body. It consists of an oval head and a whip like tail and a connecting middle piece; or collar. The sperm cell moves by lashing its tail. It has no yolk. A normal adult man’s testes may produce as many as 300 million or more mature sperm each day. Of the millions of sperms entering the vagina, only a few thousand complete the journey and only one succeeds in penetrating the ovum. THE MALE AND FEMALE REPRODUCTIVE CELLS The ovum on the other hand is the largest human cell. Other cells are only one tenth the size of the ovum. A protective membrane surrounds the egg cell. The ova are not self propelled. They contain yolk, the stored food substance that sustains the fetus early in its development. During the woman’s fertile years between puberty and menopause, one ovum matures and is released each month. The female sex hormones are called estrogen (responsible for producing masculine secondary sexual characteristics, including facial and body hairs). Stages of sex cell development: The female sex cell has to undergo 3 stages of sex cell development: maturation, ovulation and fertilization; while the male sex cell only two stages: maturation and fertilization before new life can begin. a. Maturation – sex cell must undergo cell division known as meiosis or cell reduction division wherein the number of chromosomes is halved from 46 it becomes 23.  Developmental Psychology 28 b. Ovulation – the process of escape of one mature ovum from the ovary to the fallopian tube. This is limited to female sex cells since men do not ovulate. c. Fertilization or conception – the process by which sperm and ovum fuse to form a single new cell, the zygote. This is most likely to occur about 14 days after the beginning of a woman’s menstrual period. B. REPRODUCTION The process by which organisms produce more organisms of their own kind. The Process of Fertilization: The female undergoes a period of ovulation about once each menstrual cycle (which most women, is 28 days). During this period, a mature follicle in one ovary ruptures and expels its ovum. The ovum is swept through the fallopian tube by tiny hair cells, called cilia; toward the uterus or womb. The sperm from the male enter the vagina and begin to swim up through the opening of the cervix, the neck of the uterus, they lead into the fallopian tube where the woman’s ovum lies, but only few sperm actually get this far due to their very acidic environment surrounding the ovum. The protective layer around the ovum then needs to be worn down by the sperm. In the end, one and only one sperm will actually be able to penetrate the membrane of the ovum and the process of fertilization thus occurs. FERTILIZATION Fertilization is the process by which sperm and ovum combine to create a single cell called a zygote, which then duplicates itself again and again by cell division to become a baby. At birth, a girl has all the ova, she will have about 400,000. These immature ova are in her two ovaries (see Figure 3.1) each ovum in its own small sac, or follicle. In a sexually mature woman, ovulation occurs about once every 28 days until menopause. The ovum is swept along through the fallopian tube by tiny hair cells called cilia, toward the uterus, or womb. Fertilization normally occurs during the brief time the ovum is passing through the fallopian tube. The sperm from the testes of a mature male (refer to figure 3.2) are produced at a rate of several hundred million a day are ejaculated in the semen at sexual climax. They enter the vagina and try to swim through the cervix.  Developmental Psychology 29 FEMALE REPRODUCTIVE SYSTEM FEMALE REPRODUCTIVE SYSTEM The female reproductive system is illustrated to the right. “Eggs” are produced in the ovaries. Within the ovary, a follicle consists of one precursor egg cell surrounded by special cells to nourish and protect it. A human female typically has about 400,000 follicles/potential eggs, all formed before birth. Only several hundred of these “eggs” will actually ever be released during her reproductive years. Normally, in humans, after the onset of puberty, due to the stimulation of follicle-stimulating hormone (FSH) one “egg” per cycle matures and is released from its ovary. Ovulation is the release of a mature “egg” due to the stimulation of leutenizing hormone (LH), which then stimulates the remaining follicle cells to turn into a corpus luteum which then secretes progesterone to prepare the uterus for possible implantation. If an egg is not fertilized and does not implant, the corpus luteum disintegrates and when it stops producing progesterone, the lining of the uterus breaks down and is shed. Each “egg” is released into the abdominal cavity near the opening of one of the oviducts or Fallopian tubes. Cilia in the oviduct set up currents that draw the egg in. If sperm are present in the oviduct (if the couple has recently had intercourse), the egg will be fertilized near the far end of the Fallopian tube, and the embryo will start to divide and grow as it travels to the uterus. The trip down the Fallopian tube takes about a week as the cilia in the tube propel the unfertilized “egg” or the embryo down to the uterus. At this point, if she had intercourse near the time of ovulation, the woman has no idea whether an unfertilized “egg” or a new baby is travelling down that tube. During this time, progesterone secreted by the corpus luteum has been stimulating the endometrium, the lining of the uterus, to thicken in preparation for possible implantation, and when a growing embryo finally reaches the uterus, it will implant in this nutritious environment and begin to secrete its own hormones to maintain the endometrium. If the “egg” was not fertilized, it dies and disintegrates, and as the corpus luteum also disintegrates, its progesterone production falls, and the unneeded, built-up endometrium is shed. The uterus has thick, muscular walls and is very small. In a nulliparous woman, the uterus is only about 7 cm long by 4 to 5 cm wide, but it can expand to hold a 4 kg baby. The lining of the uterus is called the endometrium, and has a rich capillary supply to bring food to any embryo that might implant there. The bottom end of the uterus is called the cervix. The cervix secretes mucus, the consistency of which varies with the stages in her menstrual cycle. At ovulation, this cervical mucus is clear, runny, and conducive to sperm. Post-ovulation, the mucus gets thick and pasty to block sperm. The vagina is a relatively-thin-walled chamber. It serves as a repository for sperm (it is where the penis is inserted), and also serves as the birth canal. Note that, unlike the male, the female has separate opening for the urinary tract and reproductive system. These openings are covered externally by two sets of skin folds. The thinner, inner folds are the labia minora and the thicker, outer ones are the labia majora. The labia minora contain erectile tissue like that in the penis, thus change shape when the woman is sexually aroused. The opening around the genital area is called the vestibule. There is a membrane called the hymen that partially covers the opening of the vagina. This is torn by the woman’s first sexual intercourse (or sometimes other causes like injury or some kinds of vigorous physical  Developmental Psychology 30 activity). In women, the openings of the vagina and urethra are susceptible to bacterial infections if fecal bacteria are wiped towards them. At the anterior end of the labia, under the pubic bone, is the clitoris, the female equivalent of the penis. This small structure contains erectile tissue and many nerve endings in a sensitive glans within a prepuce which totally encloses the glans. This is the most sensitive point for female sexual stimulation, so sensitive that vigorous, direct stimulation does not feel good. It is better for the man to gently stimulate near the clitoris rather than right on it. THE MALE REPRODUCTIVE SYSTEM MALE REPRODUCTIVE SYSTEM The male reproductive system is illustrated to the right. Sperm are produced in the testes located in the scrotum. From there, sperm are transferred to the epididymis, coiled tubules also found within the scrotum, that store sperm and are the site of their final maturation. In ejaculation, sperm are forced up into the vas deferens (plural = vasa deferentia). From the epididymis, the vas deferens goes up, around the front of, over the top of, and behind the bladder. The ends of the vasa deferentia, behind and slightly under the bladder, are called the ejaculatory ducts. The seminal vesicles are also located behind the bladder. Their secretions are about 60% of the total volume of the semen (= sperm and associated fluid) and contain mucus, amino acids, fructose as the main energy source for the sperm, and prostaglandins to stimulate female uterine contractions to move the semen up into the uterus. The seminal vesicles empty into the ejaculatory ducts. The ejaculatory ducts then empty into the urethra (which, in males, also empties the urinary bladder). The initial segment of the urethra is surrounded by the prostate gland. The prostate is the largest of the accessory glands and puts its secretions directly into the urethra. The bulbourethral glands or Cowper’s glands are the third of the accessory structures. These are a small pair of glands along the urethra below the prostate. Their fluid is secreted just before emission of the semen, thus it is thought that this fluid may serve as a lubricant for inserting the penis into the vagina, but because the volume of these secretions is very small, people are not totally sure of this function. The urethra goes through the penis. In humans, the penis contains three cylinders of spongy, erectile tissue. During arousal, these become filled with blood from the arteries that supply them and the pressure seals off the veins that drain these areas causing an erection, which is necessary for insertion of the penis into the woman’s vagina. In a number of other animals, the penis also has a bone, the baculum, which helps to stiffen it. The head of the penis, the glans penis, is very sensitive to stimulation. In humans, as in other mammals, the glans is covered by the foreskin or prepuce, which may have been removed by circumcision. Medically, circumcision is not a necessity, but rather a cultural “tradition”. Males who have not been circumcised need to keep the area between the glans and the prepuce clean so bacteria and/or yeasts don’t start to grow on accumulated secretions, etc. there. There is some evidence that uncircumcised males who do not keep the glans/prepuce area clean are slightly more prone to penile cancer. MECHANISMS OF HEREDITY  Developmental Psychology 31 The science of genetics is the study of heredity – the inborn factors, inherited from the biological parents, that affect development. When ovum and sperm unite, they endow the baby-to-be with a genetic makeup that influences a wide range of characteristics from the color of the skin, eyes, hair to health, intellect and personality. HEREDITY The transmission of traits from parents to offspring through the genes. The traits most influenced by heredity include physical features, predisposition to certain diseases, intelligence, sensory acuity, mental disorder and other fundamental abilities and other fundamental abilities and capacities. PRINCIPLES OF HEREDITY 1. Principle of Reproduction – states that like produces like. 2. Principle of Variation – states that no two individuals are exactly alike. Sometimes, differences maybe small or sometime very pronounced. 3. Principle f Chance – chance plays an important role in the transmission of hereditary traits. 4. Principle of Dominance and Recessiveness – this principle determines resemblance’s and differences among members of the family. Dominant Gene – gene whose hereditary characteristics are expressed or developed when paired with another gene. Recessive Gene – genes whose hereditary characteristics are not expressed or developed when paired with a dominant one. It is only expressed when paired with another recessive gene. GENES AND CHROMOSOMES DOMINANT TRAITS brown eyes normal skin color curly hair extra finger or toes normal hair dwarfed limbs normal sight normal blood normal vision RECESSIVE TRAITS blue eyes albinism (lack of pigments) straight hair hemophilia (failure of blood to clot) baldness normally proportioned limbs night blindness color blindness The basic unit of heredity is the gene. Genes determine inherited characteristics; they contain all the hereditary material passed from biological parents to children. Each cell in the body contains an estimated 100,000 genes, which are made of the chemical deoxyribonucleic acid (DNA). DNA carries the biomechanical instructions that tell the cells how to make the proteins that enable them to carry out each specific body function. Each gene seems to be located by function in a definite position on a rod shaped structure called the chromosome. The twenty two pairs of chromosomes which determine the different traits of an individual is called autosomes and the last pair which determine the sex is the gonosome.  Developmental Psychology 32 Normally every cell in the body except the mature sex cells, or gametes, has 23 pairs of chromosomes – 46 in all. The sperm and the ovum only have 23 each; through a complex process of cell division called meiosis, the gametes receive only one chromosome from each pair. Thus, when the sperm & the ovum fuse at conception, they produce a zygote with 46 chromosomes, half from the father & half from the mother. Meiotic division is random, producing, except for monozygotic twins, a different combination of genes for each child. At conception, the single celled zygote has all the biological information needed to guide its development into a human baby. This happens through mitosis, a process by which the cells divide in half over and over again. Each division creates a duplicate of the original cell, with the hereditary information. When development is normal, each cell (except the gametes) continues to have 46 chromosomes identical to those in the original zygote. TWINS & MULTIPLE BIRTH There are two possible ways for twins to develop. Twins may result from the division of a fertilized egg, or by the fertilization of two ripe eggs, simultaneously released by the ovary. Identical or Monozygotic Twins - One type of twin is identical or monozygotic twin. Identical twins come from a single egg cell fertilized by a sperm cell. Since only one egg cell is fertilized, the cell is called monozygotic. When the fertilized cell splits into halves, each embryonic structure or fetus that develops is genetically identical to the other. Identical twinning is the only source of human beings with identical genotypes. Identical twins are always of the same sex, and with almost identical genes. Non-identical or Fraternal Twins - Non-identical or fraternal twins are more common than identical twins, they come from two eggs released at the same time and fertilized by two sperms. They may be of the same sex or of different sexes. They are just like ordinary offspring delivered at the same time. Difference between Identical and Fraternal Twins Identical Twins Fraternal Twins Are products of a single sperm & by a Are products of two different eggs single egg fertilized by 2 different sperms Have same genes Have different genes In the early stage, the embryo divides The embryo develops independently completely Having separate placenta & fetal sacs Share the same placenta & fetal sac Maybe of the same or opposite sex Always of the same sex SAMPLE: fraternal twins and identical twins  Developmental Psychology 33 Conjoined Twins (Siamese Twins) - Identical twins are born joined together, generally at the head, chest or hip. Triplets, Quadruplets, etc. Triplets and other forms of multiple birth may be of 3 types: Identical – in that all have come from the same zygote Identical or Non-identical – where one maybe a single tone coupled with identical twins. Quadruplets – composed of a pair of identical and a pair of non-identical twins; or siblings, each having come from a separate fertilized ovum. Determination of Sex: At conception the zygote receives 23 chromosomes, or segments of hereditary materials from the sperm & 23 from the ovum. They align themselves in pairs: 22 pairs are autosomes or non sex chromosomes; while the twenty third pair are sex chromosomes, which determine if the baby will be male or female. When an ovum is fertilized by an X-carrying sperm, the resulting zygote has the pair XX and thus becomes female. When an ovum is fertilized by a Y-carrying sperm, the zygote has the pair XY and so becomes male. The sex of the child, therefore, depends entirely on the sex chromosome carried by the sperm cell from the male CHROMOSOMAL ABNORMALITIES: When a cell divides to form a gamete, a pair of chromosomes may fail to separate, so one of the gametes has one chromosome too many and the other has one chromosome too few. When the sex chromosomes is involved, the fertilized egg may carry either a single female chromosome (XO), an extra female chromosome (XXY), or an extra male chromosome (XYY). The X chromosome is necessary for development; so a zygote with only a male chromosome (OY) never survives.  Developmental Psychology 34 A) Turner’s Syndrome – condition resulting from the absence in girls of one female sex chromosome (XO). The girls are generally short, lack secondary sex characteristics and have retarded spatial skills but normal verbal skills. TURNER’S SYNDROME B) Klinefelter’s Syndrome – condition resulting from the presence in boys of an extra female sex chromosome (XXY). The boys are sterile, have rounded bodies and maybe somewhat retarded. KLINEFELTER’S SYNDROME C) Down’s Syndrome – condition that results when an extra chromosome 21 is present in the zygote or when extra material from chromosome 21 becomes attached to another chromosome, as a result, mentally retarded also called “trisomy 21”. DOWN’S SYNDROME  Developmental Psychology 35 D) XYY – male, tall stature: tendency to have low IQ, especially verbal (no special treatment). E) XXX – female, normal appearance, menstrual irregularities learning disorders, mental retardation F) Fragile X – minor to severe mental retardation; symptoms, which are more severe in males include delayed speech and motor development, speech impairments, and hyperactivity; the most common form of mental retardation. Genetic Counseling – a clinical service that advises couple of their probable risk of having children with hereditary defects. Chromosomes from body tissues maybe analyzed and photographed and the photographs enlarged and arranged according to size and structure called karyotype (a photograph that shows the chromosomes when they are separated and aligned for cell division). KARYOTYPE D. ENVIRONMENT In the development of all new behavior patterns, no amount of stimulation or practice will produce the behavior pattern until a certain level of maturation has been reached. But then, it is not the behavior itself that matures, for behavior implies an interaction between the individual & elements in his environment. To study the broader aspect of human behavior, it is important to consider the fact that heredity does not operate in a vacuum but that it is constantly limited and modified by environment. Environment - includes all the conditions in the world that influence behavior, growth, development or life processes in any way. Prenatal environment – the environment that influences individuals before birth. Internal conditions like the amniotic fluid which surrounds the unborn child, pressure that surrounds the fetus, nutrition, the general condition of the mother, and the birth process should be considered environments of the organism. Postnatal environment – the environment after birth. This environment may be external (air, trees, houses, etc.) and social (includes the other human beings who in any way influence us). HOW HEREDITY AND ENVIRONMENT WORK TOGETHER Researchers and scientists regard heredity and environment as two forces that are fundamentally intertwined and inseparable. Instead of looking at genes and experience as operating  Developmental Psychology 36 directly on an organism, they see both as part of a complex developmental system. From conception, throughout life, a combination of constitutional factors (related to biological and psychological make- up), and social, economic and cultural factors help shape development. (Review Reaction Range and Canalization) Complex behaviors have genetic loading that gives people a propensity for a particular developmental trajectory. However, the actual development requires more: an environment. And that environment is complex just like the mixture of genes we inherit. Environmental influences range from the things we lump together under “nurture” (such as parenting, family dynamics, schooling, and neighborhood quality) to biological encounters (such as viruses, birth complications, and even biological events in cells).