Reproduction - Super 7.docx

Reproduction – Super 7 Oogenesis and spermatogenesis: what are they? Review meiosis and clinical implications for heredity/inheritance Oogenesis: the production of eggs, begins in the fetus Oogonia, the diploid stem cells of female gametes, multiply rapidly by mitosis, and are converted to primar...

Reproduction – Super 7 Oogenesis and spermatogenesis: what are they? Review meiosis and clinical implications for heredity/inheritance Oogenesis: the production of eggs, begins in the fetus Oogonia, the diploid stem cells of female gametes, multiply rapidly by mitosis, and are converted to primary oocytes before birth The infant female’s ovaries contain about 2million primary oocytes arrested in prophase of meiosis 1. At puberty, meiosis resumes. Each month, one primary oocyte completes meiosis 1, producing a large secondary oocyte and a tiny first polar body Meiosis 2 of the secondary oocyte produces afunctional ovum and a second polar body, but does not occur unless the secondary oocyte is penetrated by a sperm The ovum contains most of the primary oocyte’s cytoplasm The polar bodies are nonfunctional and degenerate Spermatogenesis: a process of sperm production in these seminiferous tubules of the testes, begins at puberty Sperm precursor cells are called spermatogonia, and at puberty it undergoes mitotic division which can result in 2 distinct daughter cells (Type A and Type B) Spermatogonia divide by mitosis to maintain the germ cell line (Type A). Some of the progeny become primary spermatocytes, which undergo meiosis 1 to produce secondary spermatocytes (Type B). Secondary spermatocytes undergo meiosis 2, each producing a total of 4 haploid (n) spermatids (4 spermatids with 23 chromosomes) Spermatids are nonmotile- they are converted to functional sperm by spermiogenesis, during which superfluous cytoplasm is stripped away and an acrosome and a flagellum (tail) are produced Spermatozoa: highly specialized cells Head contains genetic material Acrosome contains enzymes to assist sperm in penetration of ovum Mitochondria in midpiece provide energy for movement Sustentacular cells form the blood-testis barrier, nourish spermatogenic cells, move them toward the lumen of the tubules and secrete fluid for sperm transport Meiosis, the basis of gamete production, consists of 2 consecutive nuclear divisions without DNA replication in between. Meiosis reduces the chromosomal number by half and introduces genetic variability. Events unique to meiosis include synapsis and crossover of homologous chromosomes. Spermatogenesis – Meiosis, in detail During interphase before Meiosis 1, spermatogonium’s 46single chromosomes are replicated to form 46 pairs of sister chromatids, which then exchange genetic material through synapsis before the first meiotic division In meiosis 2, the two daughter cells go through a second division to yield four cells containing a unique set of 23 single chromosomes that ultimately mature into four sperm cells Oogenesis – Meiosis, in detail Oogenesis involves the formation of haploid cells from an original diploid cell, called a primary oocyte, through meiosis. The female ovaries contain the primary oocytes. There are two major differences between the male and female production of gametes. First of all, oogenesis only leads to the production of one final ovum, or egg cell, from each primary oocyte (in contrast to the four sperm that are generated from every spermatogonium). Of the four daughter cells that are produced when the primary oocyte divides meiotically, three come out much smaller than the fourth. These smaller cells, called polar bodies, eventually disintegrate, leaving only the larger ovum as the final product of oogenesis. The production of one egg cell via oogenesis normally occurs only once a month, from puberty to menopause Characteristics of male and female reproductive system, sex hormones: main characteristics, cellular mechanism of action Primary sex organs (gonads): the testes (in males), the ovaries (in females) What is the function of gonads? Produce sex cells (gametes) and secrete a variety of steroid hormones (sex hormones) Accessory reproductive organs: Ducts, glands, and external genitalia Common purpose of male and female reproductive organs: To produce offspring Gametes: Sex cells- sperm (in males), ova or eggs (in females) Male reproductive role: To manufacture sperm and deliver them to the female reproductive tract, where fertilization can occur Female reproductive role: To produce ova As a result of intercourse, a sperm and egg may fuse to form a fertilized egg, the first cell of the new individual, from which all body cells will arise Male and female reproductive systems are equal partners in events leading up to fertilization Once fertilization has occurred, female’s uterus provides a protective environment in which the embryo develops until birth Sex hormones: androgens (in males), estrogen and progesterone (in females) Play vital roles in both in the development and function of the reproductive organs and in sexual behaviours and drives. Also influences the growth and development of many other organs and development of the body Anatomy of the Male Reproductive System: Scrotum Sac of skin and superficial fascia containing dartos muscle (smooth muscle) that hangs outside the of the body cavity below the penis Contains paired oval testes – It provides a temperature slightly (3°C) lower than that of the body, as required for viable sperm reproduction Responds to temp changes. Cold – becomes shorter and wrinkled to reduce heat loss, testes are pulled closer to body. Warm – becomes flaccid to increase surface area for cooling, testes hang lower away from body Testes Lie within the scrotum Each testis is covered externally by a tunica albuginea that extends internally to divide the testis into many lobules Each lobule contains sperm-producing seminiferous tubules and interstitial cells (Leydig cells) that produce androgens (most importantly testosterone) Myoid cells surround each seminiferous tubule – By contracting, they help to squeeze sperm and testicular fluids through the tubules and out of the testes The seminiferous tubule of each lobule converges to form a tubules rectus, a straight tubule that conveys sperm into the rete testis, a tubular network on the posterior side of the testis. From the rete testes, sperm leaves the testis through the efferent ductulus and enter the epididymis, which hugs the external testis surface Long testicular arteries, which branch from the abdominal aorta superior to the pelvis- supply the testes. Testicular veins, arise from a network called the pampiniform plexus- it aids in keeping the testes at their cool homeostatic temp by absorbing the heat from arterial blood, cooling it before it enters the testes Testes are served by both divisions of the ANS – when testes are hit forcefully, sensory nerve impulses are transmitted that result in pain and nausea. Penis Glans penis (head) covered by foreskin (prepuce) The male copulatory organ, is largely erectile tissue (2 dorsal columns of corpora cavernosa and 1 ventral column surrounding urethra called corpous spongiosum) Engorgement of the erectile tissue with blood causes the penis to become rigid, an event called erection The Male Duct System: Passageways that carry sperm from testes to exterior Pathway: epididymis, ductus (vas) deferens, ejaculatory duct, urethra Epididymis: single coiled tube about 6m in length; lies along the top and being the testis in the scrotum Serves as site for sperm maturation and storage Sperm mature and develop the capacity of motility as they pass through the epididymis Ductus (vas) deferens – extends from the epididymis to the ejaculatory duct It receives sperm from the epididymis and transports them from the scrotal sac through the inguinal canal and into the pelvic cavity Its terminus fuses with the duct of the seminal vesicle (a gland), forming the (short) ejaculatory duct, which empties into the urethra within the prostate Due to its thick muscular layer, it propels sperm into the urethra by peristalsis during ejaculation Urethra – extends from the urinary bladder to the tip of the penis. It conducts semen and urine to the body exterior. There are 3 regions: Prostatic urethra- the portion surrounded by prostate Membranous (or the intermediate part of the) urethra- in the urogenital diaphragm Spongy (penile) urethra- runs through the penis and opens to the outside at the external urethral orifice Accessory sex glands: produce the bulk of the semen, which contains fructose from the seminal vesicles, activating fluid from the prostate and mucus from the bulbourethral glands Seminal Vesicles Pouchlike glands that produce about 60% of the volume of semen Secretion is yellowish, thick, and rich in fructose and prostaglandins to provide energy needed by sperm for motility Prostate Gland Shaped like a doughnut and located below the bladder Urethra passes through the gland Secretion represents 30% of semen volume- is thin and milk-coloured; contains citrate (nutrient source), several enzymes and prostate-specific antigen (PSA) Activates sperm and is needed for ongoing sperm motility Bulbourethral (Cowper’s) glands Resembles peas in size and shape Secrete mucus-like fluid constituting less than 5% of semen volume Drains into the spongy urethra when male is sexually excited and neutralizes traces of acidic urine in the urethra Semen: A mixture of sperm and secretions of accessory sex glands Liquid contains chemicals that protect and activate the sperm and facilitate their movement Important chemicals in semen are nutrients, prostaglandins, and seminalplasmin Fructose provides fuel needed for sperm ATP synthesis Prostaglandins decrease the viscosity of mucus guarding the entry (cervix) of the uterus and stimulate reverse peristalsis in the uterus, facilitating sperm movement in the female reproductive tract Hormone relaxin and enzymes enhance sperm motility Relative alkalinity of semen (pH 7.2-7.6) helps neutralize the acid environment of the male’s urethra and the female’s vagina, thereby protecting the sperm and enhancing its motility (sperm are sluggish in acidic conditions) Seminalplasmin, an antibiotic chemical, suppress the immune response in a female’s reproductive tract and destroys certain bacteria Clotting factors coagulate the sperm after its ejaculation, liquefying the sticky mass and enabling the sperm to swim and begin its journey thru the female duct system An ejaculation contains 2-5mL of semen, with 20-150 million sperm/mL in normal adult males. Male sexual responses: (1) Erection – allowing it to penetrate the vagina, (2) Ejaculation – expels semen into the vagina Erection – Controlled by PNS reflexes Enlargement and stiffening of the penis, which results from engorgement with blood When sexually excited, parasympathetic reflex is triggered that promotes the release of nitric oxide locally, which relaxes vascular smooth muscle causing the arterioles to dilate, filling the erectile bodies with blood Expansion of the corpora cavernosa of the penis compresses the drainage veins, retarding blood outflow and maintaining engorgement Corpus spongiosum also expands to keep urethra open during ejaculation Male is not sexually aroused: Vasoconstriction and flaccid penile state Impotence: the inability to attain erection Ejaculation – Promoted by SNS When impulses provoking erection reach a certain critical level, a spinal reflex is initiated, and a massive discharge of nerve impulses occurs over the sympathetic nerves serving the genital organs (at the level of L1 and L2) Repro ducts and accessory glands contract, emptying contents into urethra Bladder sphincter constricts, preventing urine expulsion or reflux of semen into bladder Bulbospongiosum muscles undergo a rapid series of rhythmic contractions accompanied by intense pleasure and increased HR and BP It is then followed by muscular and physiological relaxation and vasoconstriction of the penile arterioles, which allows the penis to be flaccid once again Latent period: when man is unable to achieve another orgasm, after an ejaculation. Period lengthens with age Production of testosterone Function is carried out by the interstitial cells of the testes At the time of puberty, hypothalamic secretion of GnRH causes the anterior pituitary to secrete increasing amounts of LH, which stimulates the interstitial cells to secrete testosterone Testosterone has 3 functions “Masculinizes” and promotes development of male characteristics (e.g. voice change) Promotes and maintains development of male accessory organs Stimulates protein anabolism and development of muscle strength Anatomy of Female Reproductive System Ovaries Paired glands flank the uterus on each side and held in position by the ovarian and suspensory ligaments and mesovaria Ovarian follicles: saclike structures embedded in the connective tissue of the ovary cortex Each contain an oocyte, which is an immature sex cell(egg) Surrounding cells are called follicle cells (single layer); granulosa cells (if more than 1 layer is present) Within each ovary are follicles at different stages of development and corpus luteum Primordial follicle- 1 layer of squamous-like follicle cells Primary follicle- 2 or more columanar-type granulosa cells Secondary follicle- have a hollow chamber called the antrum (central fluid cavity) Vesicular (Graafian) follicle- mature follicle; at this stage, the follicle bulges from the surface of the ovary and the oocyte sits on a stalk of granulosa cells at one side of the antrum. Each month, one of the ripening follicles ejects its oocyte from the ovary via ovulation Corpus luteum forms after ovulation, which eventually degenerates Female Reproductive Ducts: includes oviducts, uterus, and vagina Fallopian tubes (oviducts): extends from near the ovary to the uterus Receives the ovulated oocyte and are the site where fertilization occurs Its fimbriated and ciliated distal end creates currents that help move an ovulated oocyte into the uterine tube Cilia of the uterine tube mucosa help propel the oocyte toward the uterus Uterus: located in the pelvis, anterior to the rectum and posterosuperior to the bladder Hollow, thick-walled, muscular organ that functions to receive, retain and nourish a fertilized ovum Has the fundus, body and cervical regions (isthmus, cervix, cervical canal) It is supported by the broad, lateral cervical, utereosacral, and round ligaments. They also allow mobility of the uterus- its position changes as the rectum and bladder fill and empty Uterine wall is composed of the outer perimetrium, the myometrium, and the inner endometrium. The endometrium consists of a functional layer (stratum functionalis), which sloughs off periodically unless an embryo has implanted, and an underlying basal layer (stratum basalis) which rebuilds the functional layer Vagina: extends from the cervix of the uterus to the exterior The copulatory organ and allows the passage of menstrual flow and a baby (birth canal) pH is acidic due to the release of glycogen by epithelial cells, which is anaerobically metabolized to lactic acid by resident bacteria. A low pH helps keep vagina healthy and free of infection – but hostile to sperm External Genitalia Vulva includes mons pubis, clitoris, orifice of urethra and vagina, Bartholin’s gland, labia minora and majora, hymen Labia majora houses the mucus-secreting greater vestibular glands – lubricates the vagina (homologous to bulbourethral glands in males) Perineum: area between vagina opening and anus Accessory Sex glands: Mammary glands (Breasts) Role: to produce milk to nourish a newborn baby Surrounded by adipose and fibrous connective tissue Lactiferous (milk) ducts drain at nipple, which is surrounded by pigmented areola Each mammary gland consists of many lobules, which contain milk-producing alveoli Nipple becomes erect through ANS control of smooth muscle in the presence of tactile or sexual stimuli or exposure to cold Size determined by fat quantity more than amount of glandular (milk-secreting) tissue Effects of Estrogen and Progesterone: Estrogen promotes oogenesis. At puberty, it stimulates the growth of the reproductive organs and the growth spurt and promotes the appearance of the secondary sex characteristics Progesterone cooperates with estrogen in breast maturation and regulation of the uterine cycle Female sexual response: Similar to that of males. Orgasm in females is not accompanied by ejaculation and is not necessary for conception Menstrual cycle: from gonadotropins, to ovary to hormones to endometrium Menstrual Cycle: a series of cyclic changes that the uterine endometrium goes through each month as it responds to the waxing and waning of ovarian hormones in the blood. These endometrial changes are coordinated with the phases of the ovarian cycle, which are dictated by gonadotropins released by the anterior pituitary gland. The menstrual cycle is carefully regulated by several hormones: Luteinizing Hormone (LH) Follicle-stimulating Hormone (FSH) Estrogen Progesterone Menstrual phase (Days 1-5) Characterized by the sloughing of bits of endometrium (uterine lining) with bleeding. Detached tissue and blood pass out through the vagina as the menstrual flow At the start of the stage, ovarian hormones are at their lowest normal level and gonadotropins are rising. Then, FSH levels begin to rise. By day 5- increased production of estrogen by growing ovarian follicles Proliferative Phase (Days 6-14) Characterized by the repair of the endometrium, influenced by the rising blood levels of estrogens. As new layer thickens, its glands enlarge and arteries increase in number Estrogen also induces synthesis of progesterone receptors in the endometrial cells, readying them with interaction with progesterone Estrogen also thins the normally thick cervical mucus, which will facilitate the passage of sperm to the uterus (making the uterus receptive to implantation about one week after ovulation) Ovulation occurs at Day 14 in response to the sudden release of LH from the anterior pituitary. LH also converts the ruptured follicle to a corpus luteum Secretory (Postovulatory) Phase (Days 15-28) Characterized by further thickening of the endometrium and nutritious glycogen secretion by its uterine glands in preparation for implantation of fertilized ovum Increasing progesterone levels cause the cervical mucus to become thick again, forming the cervical plug- so that sperm and bacteria are less likely to enter the uterus Combined actions of the anterior pituitary hormones FSH and LH increase- cause ovulation Sudden sharp decrease in estrogens and progesterone bring on menstruation if pregnancy does not occur. Endometrium, dependent on hormonal support, sloughs off and a new menstrual cycle starts again. Fertilization (oocyte to zygote to embryo to fetus) and fetal development (reviewing timelines) Is the joining of a sperm and oocyte chromosome to form a zygote (fertilized egg) Occurs in the fallopian tube Embryo – the term for the conceptus from fertilization until week 8. (This period is called the embryonic period). From week 9 to birth, referred to as a fetus. At birth- called an infant. Fertilization The oocyte is viable for 12 to 24 hours after ovulation Sperm are viable for 12 to 48 hours after ejaculation Sperm cells must make their way to the uterine tube for fertilization to be possible Mechanisms of Fertilization Membrane receptors on an oocyte pulls in the head of the first sperm cell to make contact The membrane of the oocyte does not permit a second sperm head to enter The oocyte then undergoes its second meiotic division Fertilization occurs when the genetic material of a sperm combines with that of an oocyte to form a zygote The Zygote First cell of a new individual The result of the fusion of DNA from sperm and egg The zygote begins rapid mitotic cell divisions The zygote stage is in the uterine tube, moving toward the uterus The Embryo Developmental stage from the start of cleavage until the ninth week The embryo first undergoes division without growth The embryo enters the uterus at the 16-cell state The embryo floats free in the uterus temporarily Uterine secretions are used for nourishment The Blastocyst Ball-like circle of cells Begins at about the 100-cell stage Secretes human chorionic gonadotropin (hCG) to produce the corpus luteum to continue producing hormones The blastocyst implants in the wall of the uterus (by day 14) The Fetus (After 8 Weeks) All organ systems are formed by the end of the eighth week Activities of the fetus are growth and organ specialization A stage of tremendous growth and change in appearance Developmental Events of the Fetal Period Time Changes and Accomplishments 8 weeks (end of embryonic period) Head same size as body, major brain areas present, liver is large – forms blood cells, digits no longer webbed, cardiovascular system fully functional, ossification begun, all body systems present, length (measured crown to rump) 22mm 9-12 weeks (month 3) Body begins to elongate, brain begins to enlarge, retina present, cervical and lumbar enlargements present, skin epidermis and dermis present, facial features present, liver prominent, bile being secreted, palate fusing, endodermal glands forming, blood cells formation begins in marrow, ossification accelerating, sex detectable, length 90mm 13-16 weeks (month 4) Cerebellum prominent, sensory organs differentiated, blinking and sucking motions detectable, body growth starts to outpace head, GI tract glands developed, meconium collected, kidney attain structure, bones and joint structure apparent 17-20 weeks (month 5) Vernix Caseosa (fatty secretion of sebaceous covers body), Lanugo hair covers skin, fetal position assumed, limbs reach final proportions, quickening occurs (spontaneous muscular activity of fetus), approximate length 190mm 21-30 weeks (months 6 & 7) Period of substantial weight increase, hypothalamic temperature and lung surfactant inadequate, but could survive if premature birth, myelination of spinal cord begins, distal limb bones start to ossify, skin read and wrinkled, nails are present, body lean and proportioned, bone marrow becomes sole area of blood cell formation, in males, testes reach scrotum at 7 months, approximate length 280mm 30-40 weeks (months 8 & 9) Skin pigment present, fat laid down into subcutaneous tissues (hypodermis) approximate length 360mm, weight 7lbs Hormonal induction of labour, Lactation and feedback mechanism During last few weeks of pregnancy, estrogen reach their highest levels in the mother’s blood. Rising levels of fetal adrenocortical hormone (especially cortisol) late in pregnancy is believed to stimulate placental release of large quantities of estrogen. Increased production of surfactant protein A by fetal lungs, triggers an inflammatory response in cervix that stimulates its softening for labour preparation. Estrogen Rise Causes the following: Uterus myometrial cells to form abundant oxytocin receptors Formation of gap junctions between uterine and smooth muscle cells Antagonist for progesterone influence on uterine muscle. Thus, the myometrium becomes irritable and irregular Braxton Hicks contractions initiate. As birth draws near, fetal cells produce oxytocin, which causes the placenta to release prostaglandins, creating more gap junctions in uterine smooth muscle. Prostaglandins play a major role in the softening and thinning of the cervix just before and during labour. When this occurs, cervical distention activates mother’s hypothalamus which signals oxytocin release from the mother’s posterior pituitary. At this point, several positive feedback loops are involved Lactation: Production of milk by the hormone prepared mammary gland Increased levels of placental estrogens, progesterone and human placental lactogen at the end of pregnancy, Stimulates the hypothalamus to release Prolactin Releasing Factors (PRF) Anterior pituitary response by secreting prolactin Initially colostrum is produced consisting of more protein, vitamin A, minerals, IgA antibodies (for immunity), and almost no fat Production of milk depends on mechanical stimulation of the nipple. Mechanoreceptors in the nipple send afferent nerve impulses to the hypothalamus secreting PRF. This results in release of prolactin, and stimulation of milk production Same Afferent nerve impulses prompt hypothalamic release of oxytocin from the posterior pituitary (A positive feedback Mechanism) Oxytocin causes let down reflex. Oxytocin binds to myoepithelial cells surrounding the gland, and milk is ejected from both breasts. Genes, chromosomes and heredity A chromosome is a tightly packed DNA Strand. Nuclei of human cells contain 46 chromosomes (diploid number), 23 pairs of homologous chromosomes (one from father and one from mother). In gamete cells, the number of chromosomes is 23, (haploid chromosomal number) 2/46 are chromosomes are sex chromosomes (X and Y), determining one’s sex (M=XY, F=XX) The other 22 pairs are guiding expression of traits and are called autosomes. Each person has two genes from each parent. Matched genes in the same location (locus) on homologous chromosomes are called alleles. When two alleles controlling a trait are the same, they care called homozygous, and when they are different, they are called heterozygous – for that gene. When one allele masks another, it is considered a dominant gene (indicated with a capital letter (Z)), while the one being masked is called the recessive gene (indicated with a lower-case letter (z)) A person’s genetic makeup is known as their genotype, and how it is expressed is their phenotype Heredity: the understanding on how human genes act and interact Carriers/ heterozygotes, which carry a recessive gene, have the potential to pass it on Examples of dominant phenotype/traits, (Zz or ZZ genotype): freckles, ability to roll tongue, dimples in Cheeks, Huntington’s disease, cystic fibrosis, and Tay-Sachs disease. Examples of recessive phenotype/traits, (zz genotype): Straight hair, albinism, absence of dimples Incomplete dominance: Heterozygote genotype produce phenotypic difference than homozygote Dominant (ZZ) or Recessive (zz). Example of this is Sickle cell anemia. Homozygous recessive individuals (zz) have sickle cell anemia, and but individuals heterozygous for the Sickle cell gene (Zz) produce both sickled and normal hemoglobin RBC. Heredity Karyotype – the diploid chromosomal complement, typically shown as homologous chromosome pairs arranged from longest to shortest (X and Y are arranged by size rather than paired) Genotype – a person’s genetic makeup, or genes Phenotype – observational expression of a genotype 2 of the 46 chromosomes are sex chromosomes- XX = female XY = male Homologous Chromosomes – pairs of chromosomes, one from father (sperm), one from mother (egg) Heterozygous – having different allelic genes at a given locus or (by extension) many loci Homozygous – having identical genes are one or more loci Allele – alternative form of genes on chromosomes Inheritance – patterns in the way traits are handed down from parents to offspring. He observed that organisms (pea plants) inherit traits by way of discrete "units of inheritance". Pedigree – a change that occurs in our DNA sequence, either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke Polymorphism – a discontinuous genetic variation resulting in the occurrence of several different forms or types of individuals among the members of a single species. Types of Inheritance Dominant traits – occurs when one allele masks or suppresses the expression of its partner Dominant-Recessive Inheritance – reflects the interaction of dominant and recessive traits Recessive Traits – a trait due to a particular allele that does not manifest itself in the presence of other alleles that generate traits dominant to it; must be present in double dose to be expressed X-Linked – of or relating to a gene on an X chromosome Multi-Factorial/Polygene – results in continuous, or quantitative, phenotypic variation between two extremes and explains many human characteristics Examples include skin colour, height, metabolic rate, and intelligence A gene whose individual effect on a phenotype is too small to be observed, but which can act together with others to produce observable variation Degrees of Relationships First Degree 1/2 – parents, siblings, children Second Degree 1/4 – aunts/uncles, nieces/nephews, grandparents, grandchildren, half-siblings Third Degree 1/8 – first cousins, great-grandparents, great-grandchildren Genetically very different Crossing over Independent assortment when homologous chromosomes line up Random fertilization Autosomal Dominant Freckles Tongue roller Marfan’s Huntington’s Autosomal Recessive CF PKU Sickle Cell There is no question 7