Introduction to Embryology PDF

General Human Embryology By: Fikre Bayu Study hard Study hard  Introduction Developmental anatomy: – is the field of embryology – concerned with the changes that cells, tissues, organs, and the body as a whole undergo from a germ cell of each...

General Human Embryology By: Fikre Bayu Study hard Study hard  Introduction Developmental anatomy: – is the field of embryology – concerned with the changes that cells, tissues, organs, and the body as a whole undergo from a germ cell of each parent to the resulting adult Embryology is the study of embryos (prenatal development of embryos and fetuses) Teratology: – is division of embryology and pathology – deals with abnormal development (birth defects) Study hard  Embryologic Terminology Oocyte (ovum, egg) – female germ or sex cells, are produced in the ovaries Sperm (sperma, seed) – male germ cell produced in the testes (testicles) Zygote – results from the union of an oocyte and a sperm during fertilization – is the beginning of a new human being Cleavage – is series of mitotic cell divisions of the zygote – result in the formation of early embryonic cells, blastomeres Morula – solid mass of 12-32 blastomeres – occurs 3 to 4 days after fertilization, just as the early embryo enters the uterus Study hard  Blastocyst – is when morula consist fluid filled cavity with in it. Implantation – process during which the blastocyst attaches to the endometrium, – Occurs approximately 6 days after fertilization. Gastrula: three germ layered during 3rd wk.. Neurula: The early embryo during the 3rd-4th weeks when – neural tube is developing from the neural plate. Embryo – its early stages of human development. – extends to the end of the eighth week (56 days). Fetus (unborn offspring) – After the embryonic period (8 weeks) and until birth Conceptus – embryo and its adnexa or associated membranes. Study hard study hard 6  Descriptive terms in embryology In embryology, several terms relating to position and direction are used, and reference is made to various planes of the body All descriptions are based on the assumption that – The body is erect, with the upper limbs by the sides and the palms directed anteriorly … in the anatomical position Anterior and posterior Dorsal and ventral Terms of Superior and inferior relationship Cranial/ rostral and caudal Proximal and distal Median plane Terms Sagittal plane of planes Coronal study hard plane 7 Descriptive terms in embryology study hard 8  OVERVIEW OF MALE AND FEMALE REPRODUCTIVE ORGANS study hard 9  Male Reproductive System Components of male reproductive system includes: Primary sex organ System of ducts Accessory sex glands External genitalia study hard 10 Male reproductive structures Testis Epididymis Ductus/vas deferens Accessory glands study hard 11  Male reproductive structures Testis # = two Is the male sex gland It lies in the scrotum suspended by the spermatic cord It is enclosed by a serous sac, the tunica vaginalis derived from the peritoneum Each testis is divided into 250 compartments (lobules), containing – seminiferous tubules :produce sperms – interstitial cells :produce testosterone study hard 12 Testis Seminiferous tubules study hard 13 Seminiferous tubules contain 2 types of cells Spermatogonia (stem cells) ▪ Give rise to sperm cells through the process of spermatogenesis Sertoli cells (supporting cells) – Support, nutrition, and protection – Produce proteins, which are necessary for spermiogenesis – Phagocytosis: During spermiogenesis, excess cytoplasm shed as residual bodies is phagocytosed and digested by Sertoli cell lysosomes study hard 14 Male reproductive structures … study hard 15 Intratesticular genital ducts They are; Straight tubules (tubuli recti) Rete testis, and Efferent ductules These ducts carry spermatozoa and liquid from the seminiferous tubules to the duct of the epididymis study hard 16  Male excretory genital ducts Epididymis ✓# = two : L = 4–5m Ductus deferens ✓A much coiled tube for storage and maturation of sperms ✓Adding two layers around the sperm (glycoprotein coat and seminal protein coat) study hard 17 Ductus/Vas deferens 45-50cm long Ductus deferens It is a thick muscular tube that conveys mature sperm from the epididymis to the ejaculatory duct ▪ Ejaculatory duct = Union of ampulla of ductus deferens & ducts of the seminal vesicle ❖From there on, the sperm enters the prostate gland and prostatic urethra study hard 18 Male Accessory Sex Glands study hard 19 Accessory male reproductive glands ✓ Seminal vesicles ✓ Prostate ✓ Cowper’s glands They do not involve in the production of sperm cells but release secretions that form the major part of the semen study hard 20 Male reproductive structures … The accessory glands – Seminal vesicle: Secretes 60% of seminal fluid which contain fructose (for nutrition) prostaglandins, as well as enzymes and other proteins – Prostate gland: Secretes 30% of seminal fluid which contain citrate,fibrinolysin. – Cowper’s gland (bulbo- urethral gland): Secretes an alkaline fluid which neutralize the acidity of the urethra study hard 21 Female Reproductive Structures Primary sex organ (ovary) Fallopian tube Uterus Vagina External genitalia study hard 22 Uterus  The uterus is a hollow muscular organ, in which the fertilized ovum is normally embedded, grows and nourished until birth.  The cavity of the uterus and the vagina form the pathway through which the foetus passes at the end of pregnancy.  This pathway is called the birth canal.  In multiparous woman it is thick, muscular and larger in size.  The uterus has a shape of an inverted “pear”. study hard 23  Uterus … Parts - Fundus, body, isthmus and cervix 1.Fundus Is the part lying above the level of openings of the uterine tubes The area where the tubes join the uterus is called cornu (uterine horn) 2. Body Forms 2/3 of the uterus and extends from the tubal openings to a constricted portion 3. Cervix cylindrical inferior one third The most fixed part extends between the isthmus and the vaginal opening of the uterus It is divided into two by the upper wall of the vaginal A.Supravaginal part – part above the vagina B.Vaginal part (portion vaginalis)- communicates study hard 24 Uterus … The walls of the body of the uterus consist of three layers Perimetrium -thin external layer Myometrium- thick smooth muscle layer Endometrium- thin internal layer study hard 25 Uterus … an outer connective tissue layer, Perimetrium which is adventitia in some areas, but largely a serosa. Firmly attached to the myometrium Myometrium The thick highly vascular smooth muscle layer Endometrium A mucosa, the endometrium, lined by simple columnar epithelium Its covering simple columnar epithelium has both ciliated and secretory cells, the latter forming numerous tubular study hard 26 uterine glands Endometrium The endometrium can be subdivided into two zones Basal layer Adjacent to the myometrium Contains highly cellular lamina propria and the deep basal ends of uterine glands has its own blood supply and is not sloughed off during menstruation (remains relatively unchanged) study hard 27  Endometrium Functional layer Contains less cellular lamina propria Richer in ground substance, most of the length of the glands The functional layer undergoes profound changes during the menstrual cycles – Disintegrate and are shed during menstruation and after parturition (delivery of a baby) study hard 28  Endometrium During the luteal phase of the menstrual cycle, two layers of the functional layer can be distinguished microscopically I. A thin, compact layer consisting of densely packed, connective tissue around the necks of the uterine glands II. A thick, spongy layer composed of edematous connective tissue containing the dilated, tortuous uterine glands study hard 29  Uterine tubes /Fallopian tubes/oviduct The uterine tubes transport the oocytes from the ovaries to the uterus and spermatozoa in the opposite direction. It is in the uterine tubes that fertilization takes place and early cleavage starts. These tubes are about 10-12 cm in length, extending from the uterus to uterine ends of the ovaries. It is lined with secretory epithelium for nourishment of ovum Extent – Length = ~10 -12 cm : Diameter = 1-4mm study hard 30 study hard 31  Utrine tubes … ❑Function – Carry oocytes – Sperms (ampulla of the uterine tube ) – Conveys the cleaving zygote to the uterine cavity – The ova are propelled to the uterus along this tube, partly by peristalsis and partly by ciliary action. study hard 32 study hard 33  Uterine tubes … Parts - 4 1. Infundibulum 2. Ampulla 3. Isthmus 4. Intramural (uterine) part Infundibulum Length = 1cm) ᶲ = 3mm Is a funnel-shaped part close to the ovaries It contains the abdominal or pelvic opening surrounded by thin irregular finger like processes, the fimbrae The fimbrae catch a discharged ovum and passes it to the tube study hard 34 Uterine tubes … Ampulla Length = 5cm ᶲ = 4mm Is the thin walled, longest part that has a widest diameter It follows a slightly tortuous course b/n infundibulum & isthmus Isthmus Length = 3cm) ᶲ = 2 mm Is the part between the widest part, ampulla, and the uterus Is narrower and thicker than the ampulla study hard 35 Uterine tubes … Intramural part Length = 1cm ᶲ = 1 mm Is the part with in the wall of the uterus ✓ It is the narrowest part of the tube Its opening into the uterine cavity study hard 36 ovaries: Is the female sex gland It lies in the ovarian fossa in the side wall of the pelvis Its function is production of ova study hard 37  It secretes two hormones: a. Estrogen (sex hormone): responsible for appearing of 2nd female sex characters. This hormone is secreted from Graffian follicle b. Progesterone (pregnancy hormone): responsible for maintenance of pregnancy by increase the thickness and vascularity of uterine endometrium. This hormone is secreted from corpus luteum after ovulation process study hard 38 study hard 39  ovaries … Color and texture Before the first ovulation the surface is smooth and pink After ovulation, become grey because of the scars Dimensions Vertical = ~3cm Transverse = ~1.5cm Thickness = ~ 1cm Weight = ~ 10-15 gms  The size varies with age and the phases of ovarian cycle but generally they become study hard 40 smaller after menopause Female reproductive cycle ▪ Beginning at puberty, females undergo reproductive cycles (sexual cycles), involving activities of the hypothalamus of the brain, pituitary gland, ovaries, uterus, uterine tubes, vagina, and mammary glands. ▪ These monthly cycles prepare the reproductive system for pregnancy. ▪ Ovarian cycle ▪ Uterine cycle study hard 41  The Ovarian Cycle ▪ The monthly series of events associated with the maturation of an egg is called the ovarian cycle ▪ It has two consecutive phases ▪ The follicular phase is the period of follicle growth, lasting from the 1st to the 14th day of the cycle ▪ The luteal phase is the period of corpus luteum activity, days 14-28 study hard 42. study hard 43  The Ovarian Cycle… The typical ovarian cycle repeats at intervals of 28 days, with ovulation occurring midcycle However, cycles as long as 40 days or as short as 21 days are fairly common In such cases, the length of follicular phase and timing of ovulation vary, but the luteal phase remains constant: It is 14 days between the time of ovulation and the end of the cycle study hard 44  The Follicular Phase Maturation of a primordial follicle to the mature state occupies the first half of the cycle and involves several events – Growth and differentiation of primary oocyte – Proliferation of follicular cells – Formation of zona pellucida – Development of the theca folliculi study hard 45  Ovarian Follicles An ovarian follicle consists of an oocyte surrounded by one or more layers of epithelial cells. 1. PRIMORDIAL FOLLICLE The follicles that are formed during fetal life primordial follicles consist of a primary oocyte enveloped by a single layer of the flattened follicular cells. found in the superficial areas of the cortex. study hard 46 2. Primary follicle Unilaminar primary follicle – Beginning in puberty with the release of follicle- stimulating hormone (FSH), a small group of primordial follicles each month begins a process of follicular growth – This involves growth of the oocyte, proliferation and changes in the follicular cells (form a simple cuboidal epithelium) Multilayered primary follicle – The follicular cells continue to proliferate, forming a stratified follicular epithelium, the granulosa – Follicle cells are now termed granulosa cells and the follicle is a multilayered primary follicle – Between the oocyte and granulosa cells, a layer of glycoprotein called the zona pellucida develops. study hard 47 study hard 48 3.Secondary or antral follicles – As the follicles grow the oocyte increases in size and numbers of granulosa cells also increase, – Small spaces develop within the granulosa layer as the cells secrete follicular fluid – This fluid accumulates, the spaces gradually coalesce, and the granulosa cells reorganize themselves around a larger cavity, the antrum – During the reorganization of the granulosa layer to form the antrum, some cells form a small hillock, the cumulus oophorus, surrounding the oocyte and protruding into the antrum study hard 49  … The granulosa cells around the oocyte make up the corona radiata and accompany the oocyte when it leaves the ovary The stromal cells immediately around the follicle differentiate to form the follicular theca – This layer differentiates into two: Theca interna: well-vascularized endocrine tissue Theca externa: more fibrous outer layer containing smooth muscle and fibroblasts study hard 50 study hard 51  … 4. Mature or graafian follicle – During each menstrual cycle, usually one follicle grows much more than the others and becomes the dominant follicle, while many of the other follicles eventually enter atresia – The dominant follicle undergo ovulation – The antrum increases greatly in size by accumulating follicular fluid and the oocyte adheres to the wall of the follicle through the cumulus oophorus of granulosa cells study hard 52 study hard 53 study hard 54  Ovulation At ovulation the large mature secondary oocyte escapes from the ovary and is caught by the dilated end of the uterine tube. Ovulation normally occurs midway through the menstrual cycle, ie, around the fourteenth day of a typical 28-day cycle. In humans usually only one oocyte is liberated during each cycle, but sometimes either no oocyte or two or more simultaneous oocytes may be expelled. In the hours before ovulation the ovarian follicle, under the influence of FSH and LH, undergoes a sudden growth, producing a cystic swelling on the surface of the ovary A small avascular spot, the stigma, soon appears on this swelling study hard 55  1. Fallopian tube 2. Fimbriae 3. Ovary 4. Follicle 5. Stigma Graafian follicle bulge on the ovary surface. The beginning formation of a stigma (whitish region free of study hard blood 56 vessels).  … The ovulated secondary oocyte adheres loosely to the ovary surface and its drawn into the opening of the uterine tube where fertilization may occur. If not fertilized within about 24 hours, the secondary oocyte begins to degenerate. Some women experience a cramp of pain in the lower abdomen when ovulation occurs which is known as middle pain (mittelschmerz) This episode is caused by the intense stretching of the ovarian wall during ovulation study hard 57  The expelled secondary oocyte Relation of fimbriae and ovary. Fimbriae collect the oocyte and sweep it into the uterine tube study hard 58 Corpus luteum study hard 59  Corpus Luteum After ovulation, the granulosa cells and theca interna of the ovulated follicle reorganize to form a larger temporary endocrine gland, the corpus luteum (L., yellowish body), in the ovarian cortex. Once formed, the corpus luteum begins to secrete progesterone and some estrogen study hard 60  … The fate of the corpus luteum depends on whether a pregnancy occurs. Corpus luteum of menstruation If pregnancy does not occur, the corpus luteum starts degenerating in about 10-12 days and its hormonal output ends. The corpus luteum that persists for part of only one menstrual cycle is called a corpus luteum of menstruation. In this case all that ultimately remains is a scar called the corpus albicans (white body) study hard 61  … Corpus luteum of pregnancy If the oocyte is fertilized, degeneration of the corpus luteum is prevented by human chorionic gonadotropin (hCG), a hormone secreted by the trophoblast of the developing embryo. HCG targets the corpus luteum, maintaining it and promoting further growth of this endocrine gland and stimulating secretion of progesterone to maintain the uterine mucosa. This corpus luteum of pregnancy becomes very large and is maintained by HCG for 4–5 months, by which time the placenta itself produces progesterone (and estrogens) at levels adequate to maintain the uterine mucosa. It then degenerates and is replaced by a large corpus albicans. Removal of the corpus luteum of pregnancy before the fourth month usually leads to abortion. study hard 62 Follicle development and changes within the ovary: A diagram of a sectioned ovary shows the different stages of follicle maturation, ovulation, and corpus luteum formation and degeneration study hard 63  Duration of Ovarian Cycle Ovarian cycle persist Throughout the reproductive life of women and terminate at menopause No ovarian cycle During pregnancy At menopause – Menopause, the permanent cessation of menstruation, usually between the ages of 48 and 55. study hard 64 study hard 65  Hormones and the Ovarian Cycle A gonadotropin-releasing hormone (GRH ) is synthesized by neurosecretory cells in the hypothalamus and is carried by the hypophysial portal system to the anterior lobe of the pituitary gland GRH stimulates the release of two hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH) produced by pituitary gland that act on the ovaries. FSH stimulates the development of ovarian follicles and the production of estrogen by the follicular cells LH serves as the "trigger" for ovulation (release of secondary oocyte) and stimulates the follicular cells and corpus luteum to produce progesterone These ovarian hormones also induce growth of the endometrium study hard 66 Hormonal Control of Ovarian Function study hard 67  The Uterine (Menstrual) Cycle The monthly changes in the internal layer of the uterus constitute the endometrial/uterine cycle, commonly referred to as the menstrual cycle or period The endometrium responds in a consistent manner to the fluctuating concentrations of gonadotropic (FSH and LH) and ovarian hormones (estrogen and progestrone) The average menstrual cycle is 28 days (In 90%, +5) study hard 68  The Uterine (Menstrual) Cycle… These endometrial changes are coordinated with the phases of the ovarian cycle. During this menstrual cycle, the uterine endometrium passes through three stages, the follicular or proliferative phase, the secretory or progestational phase, and the menstrual phase. study hard 69 study hard 70  The Uterine (Menstrual) Cycle… Days 1 - 5 Menstrual phase Usually lasts 4-5 day The functional layer of the uterine wall is sloughed off and discarded with the menstrual flow-menses (monthly bleeding) ▪ Blood + part of endometrium After menstruation, the eroded endometrium is thin At the beginning of this stage, gonado- tropins are beginning to rise a bit and ovarian hormones are at their lowest normal levels. Then FSH levels begin to rise study hard 71  The Uterine (Menstrual) Cycle… The detached tissue and blood pass out through the vagina as the menstrual flow By day 5, the growing ovarian follicles are starting to produce more estrogen study hard 72  The Uterine (Menstrual) Cycle… Days 6-14: Proliferative/follicular phase In this phase the endometrium rebuilds itself Under the influence of rising blood levels of estrogen, the basal layer of the endometrium generates a new functional layer study hard 73  The Uterine (Menstrual) Cycle… As the new functional layer thickens, its glands enlarge and its spiral arteries increase in number There is a two- to three fold increase in the thickness of the endometrium study hard 74  The Uterine (Menstrual) Cycle… Normally, the cervical mucus is thick and sticky, but rising estrogen levels cause it to thin and become crystalline, forming channels that facilitate the passage of sperm into the uterus Ovulation occurs in the ovary at the end of this stage (day 14) in response to the sudden release of LH from the anterior pituitary LH converts the follicle to a corpus luteum study hard 75  The Uterine (Menstrual) Cycle… Days 15-28: Secretory /luteal Phase In this phase, the endometrium prepares for implantation of the embryo Rising levels of progesterone from the corpus luteum act on endometrium causing the spiral arteries to elaborate and coil more tightly. study hard 76  The Uterine (Menstrual) Cycle… The uterine glands enlarge, coil, and begin secreting nutritious glycoproteins into the uterine cavity All events of the secretory phase are promoted by progesterone. Increasing progesterone levels also cause the cervical mucus to become viscous again, forming the cervical plug, which blocks sperm entry and plays an important role in keeping the uterus “private” in the event an embryo has begun to implant study hard 77  The Uterine (Menstrual) Cycle… If fertilization has not occurred, Progesterone levels fall, depriving the endometrium of hormonal support, and the spiral arteries kink and go into spasms Fragmentation continues causing the functional layer to slough off The mentrual cycle starts again on this first day of menstrual flow study hard 78  Ischemic Phase- occurs when the oocyte is not fertilized. Ischemia (reduced blood supply) occurs as the spiral arteries constrict, giving the endometrium a pale appearance. Pregnancy Phase- if pregnancy occurs, the menstrual cycles cease and the endometrium passes into a pregnancy phase. With the termination of pregnancy, the ovarian and menstrual cycles resume after a variable period (usually 6 to 10 weeks if the woman is not breast- feeding her baby). If pregnancy does not occur, the reproductive cycles normally continue until menopause. study hard 79 study hard 80  The Uterine (Menstrual) Cycle… Notice that the menstrual and proliferative phases overlap the follicular stage and ovulation in the ovarian cycle study hard 81  The Uterine (Menstrual) Cycle… The uterine secretory phase corresponds to the ovarian luteal phase study hard 82  Anovulatory menstruation & artificial induction of ovulation Some women fail to ovulate because of a low concentration of gonadotropins. In these cases, administration of an agent to stimulate gonadotropin release and hence ovulation can be employed. Although such drugs are effective, they often produce multiple ovulations, so that the risk of multiple pregnancies is 10 times higher in these women than in the general population. study hard 83  The Beginning of Human Development ▪ The development of human being begins with fertilization ▪ Preparation for fertilization/pregnancy involves 2 main programs of events: 1. Gametogenesis → formation of the male and female gametes in the gonads (ovary or testis) 2. Cyclic changes in the female genital tract → ovarian & uterine cycles study hard 85  Gametogenesis Types of body cells A human being is formed of trillions of cells; these cells are of two types: Somatic cells - which are present in the whole tissues of the body Gametes - which are the sperms and ova study hard 86  Chromosomes Human somatic cells contain 23 pairs of chromosomes for a total of 46; 22 pairs of autosomes and one pair of sex chromosomes. Diploid Cells A cell is said to be diploid if it contains 23 pairs of chromosomes. 2N = 46 One chromosome of each pair is derived from the maternal gamete, the oocyte, and one from the paternal gamete, the sperm. Autosomes contain genetic information for most human characteristics. Homologous and pair chromosomes: sex chromosomes determines whether an individual is female (XX) or male (XY). One member of each pair of chromosomes is inherited from each parent. study hard 87  Gametogenesis The process by which gametes (ova & spermatozoa) is formed: Oogenesis: The production of ovum Spermatogenesis: The production of spermatozoa. ▪ Gametogenesis is divided into four phases: 1. Extra-gonadal origin of primordial germ cells (gametes are derived from primordial germ cells ,PGCS) 2. Proliferation of germ cells by mitosis 3. Meiosis 4. Structural and functional maturation of the ova and spermatozoa study hard 88  Gametogenesis … During early embryonic development, primordial germ cells (PGCs) from the dorsal endoderm of the yolk sac migrate along the hindgut to the gonadal ridge. They multiply by mitosis and once they have reached the gonadal ridge they are called gametogonia. Begin meiosis. =Produces secondary oocytes in the female. =Produces sperm in the male. study hard 89 study hard 90  Primordial germ cells Yolk sac Primordial The germ cells cells,later through differentiate amoeboid into movement, mature gametes move towards i.e. the spermatogonia gonads where (male) theyor arrive oogonia at about 5th week (female) study hard 91 - Meiosis:- - is a special type of cell division that involves two meiotic cell divisions. – takes place in the germ cells to generate male and female gametes, – requires requires two cell divisions, meiosis I and meiosis II, Meiosis I: – male and female germ cells (spermatocytes and primary oocytes) at the beginning of replicate their DNA – In contrast to mitosis, however, homologous chromosomes then align themselves in pairs, (synapsis) – Homologous pairs then separate into two daughter cells, – Thereby reducing the chromosome number from diploid to haploid. Study hard Study hard  Meiotic division II Occur without normal interphase (without intervening step of DNA replication) Each chromosome divides and each half, or chromatid is drawn to a different pole, thus the haploid no. of chromosome (23) is retained and each daughter cell formed by meiosis has the reduced haploid no. of chromosomes. Why Meiosis Provides constancy of chromosome no. Allows random assortment of maternal and paternal chromosomes b/n gametes. Provides variability of Human species. Study hard  Polar Bodies Are cells that receive little amount of cytoplasm during meiosis of primary oocyte. As a result one primary oocyte give rise to four daughter cells ( 3polar bodies + 1 mature gamete), each with 22+ 1X. Polar bodies will not develop to mature gamete. Study hard  Chromosomal abnormalities May be numerical or structural. Numerical abnormalities: Euploid: any exact multiple of n (e.g, diploid or triploid) Aneuploid: is when an extra chromosome is present or when one is missing. – May occur during meiotic division. – may rise if separation does not occur (nondisjunction) thus both members of a pair move into one cell. – Resulting one cell with 24 chro. and other with 22 chro. – The incidence increases in women > 35yrs old. Study hard  Nondisjunction occasionally occur during mitosis in an embryonic cell during the earliest cell divisions. Result in mosaicism. Study hard Study hard  Translocation: When chromosomes break and piece of one chromosome attach to another. Are common particularly between chromosomes, 13, 14, 15, 21, and 22. Trisomy 21 (Down syndrome) Is an extra copy of chromosome 21 (trisomy 21). Risk increases with age (1 in 300 at 35 yrs and 1 in 100 > 40yrs). Features: – Growth retardation – Intellectual disabilities, Mental deficiency – Craniofacial abnormalities – Extra skin folds at the medial corners of the eyes, upward slant to palpebral fissures. – Small ears, cardiac defects, and hypotona. – Brachycephaly, flat nasal bridge. – Protruding tongue Study hard Study hard Study hard  Trisomy 18 (Edwards syndrome ) The incidence is approximately 1 in 5000 newborns. Features: – Intellectual disabilities, growth retardation. – Congenital heart defects, short sternum – Low-set ears, prominent occiput – Flexion of fingers and hands. – Renal anomalies, syndactly (fused digits). – Micrognathia (small jaw), hypoplastic nails.. Study hard  Female neonate with trisomy 18. Note: – the growth retardation, – clenched fists with characteristic positioning of the fingers (second and fifth ones overlapping the third and fourth), – short sternum, and narrow pelvis. Study hard  Trisomy 13 (Patau syndrome ) Deafness, bilateral cleft lip and palate Eye defects: micro/anophthalmia, coloboma. Severe CNS malformation Malformed ears Study hard trisomy 13. Note the: bilateral cleft lip, polydactyly (extra digits). A small omphalocele (herniation of viscera into umbilical cord) is also present. Study hard  Klinefelter's syndrome (47, XXY) small testes, hyalinization of seminiferous tubules; aspermatogenesis (sterility); often tall with disproportionately long lower limbs. Intelligence is less than in normal siblings. Approximately 40% of these males have gynecomastia. Study hard  Turner Syndrome (45, X ) 1 in 8000 live births. Approximately 1% of monosomy X female embryos survive. The phenotype is female Secondary sexual characteristics do not develop in 90% of affected girls, is the most common cytogenetic abnormality observed in live-born humans and fetuses that abort spontaneously accounts for approximately 18% of all abortions caused by chromosome abnormalities. is in the paternal gamete (sperm) in approximately 75% of cases. Study hard  A at birth: loose skin at posterior of the neck, short neck, malformed ears, and swelling in the hand. C. Foot by lymphedema D. webbed neck, and widely spaced nipple Study hard  14-year-old girl(figure below). Note the: – short stature, webbed neck, absence of sexual maturation, – widely spaced nipples, and lymphedema of the hands and feet. 47, XYY Male 1:1000, normal in appearance; usually tall; often exhibit aggressive behavior 47, XXX Female 1:1000, normal in appearance; usually fertile; 15%-25% are mildly mentally retarded. Study hard  Structural Chromosomal Abnormalities result from chromosome breakage Result depends on what happens to the broken pieces (deletions, inversion, or translocation). may be induced by various environmental factors, for example, radiation, drugs, chemicals, and viruses. 1. Translocation: – transfer of a piece of one chromosome to a nonhomologous chromosome. 2. Reciprocal translocation: – when two nonhomologous chromosomes exchange pieces. 3. Deletion: When a chromosome breaks, part of it may be lost Study hard  Cri du chat syndrome: partial terminal deletion from the short arm of chromosome 5. Features: – a weak catlike cry, microcephaly (abnormally small head), – severe mental deficiency (retardation), and congenital heart disease. Prader-Willi syndrome (PWS), Is microdeletion of long arm of paternal chromosome 15 Features: – short stature, mild mental retardation, obesity, hyperphagia (overeating), and hypogonadism (inadequate gonadal function). Angelman syndrome (AS), Microdeletion of long arm of maternal chromosome 15 characterized by: – severe mental retardation, microcephaly, – brachycephaly (short and broad head), seizures, and ataxic (jerky) movements of the limbs andStudytrunk. hard AS PWS Study hard A, Reciprocal translocation. B, Terminal deletion. C, Ring chromosome. D, Duplication. E, Paracentric inversion. F, Isochromosome. G, Robertsonian translocation. Study hard  Spermatogenesis A sequence by which spermatogonia is transformed to mature sperms. This process begins at puberty. Spermatogonia ➔primary spermatocyte ➔reduction division of 1st division ➔2ry haploid spermatocytes ➔undergo 2ry division ➔four haploid spermatids. - This spermatids gradually changed to 4 mature sperm by process called spermiogenesis. - When complete, sperms enter the lumina of the seminiferous tubules. - Sartoli cells:- lines seminiferous tubules. - support and nurture the germ cells. - Sperms are transported passively from seminiferous tubules to epididymis, where they become stored and functionally mature. Study hard Study hard Study hard Study hard  Parts of sperm Head:- forms most of the bulk of the sperm and contains the haploid nucleus. Acrosome:- – caplike saccular organelle containing several enzymes. – Covers anterior two thirds of the nucleus – these enzymes facilitate dispersion of the follicular cells of the corona radiata and sperm penetration of the zona pellucida during fertilization. tail of the sperm:- – provides the motility of the sperm that assists its transport to the site of fertilization. – consists of three segments: middle piece, principal piece, and end piece middle piece: contains mitochondria, which provide the adenosine triphosphate necessary for activity. Neck of the sperm is the junction between the head and tail. Study hard  Oogenesis (ovogenesis): is the sequence of events by which oogonia are transformed into mature oocytes. begins before birth and is completed after puberty. continues to menopause. Prenatal Maturation of Oocytes early fetal life➔ oogonia proliferate by mitosis. Oogonia enlarge to form primary oocytes before birth; As a primary oocyte forms➔ connective tissue cells surround it and form a single layer of flattened, follicular epithelial cells (primordial follicle). As the primary oocyte enlarges during puberty, the follicular epithelial cells become cuboidal in shape and then columnar, forming aStudyprimary hard follicle. Study hard  The primary oocyte soon becomes surrounded by a covering of amorphous acellular glycoprotein material, the zona pellucida. Primary oocytes begin the first meiotic division before birth, but completion of prophase does not occur until adolescence. The follicular cells surrounding the primary oocyte are believed to secrete a substance, oocyte maturation inhibitor, which keeps the meiotic process of the oocyte arrested. Study hard  Postnatal Maturation of Oocytes Begins during puberty, usually one follicle matures each month and ovulation occurs. The long duration of the first meiotic division (up to 45 years) may account in part for the relatively high frequency of meiotic errors, such as nondisjunction. No primary oocytes form after birth. As a follicle matures, the primary oocyte increases in size and, shortly before ovulation, completes the first meiotic division to give rise to a secondary oocyte and the first polar body. the division of cytoplasm is unequal. secondary oocyte receives almost all the cytoplasm and the first polar body receives very little. At ovulation, the nucleus of the secondary oocyte begins the second meiotic division, but progresses only to metaphase. If a sperm penetrates the secondary oocyte, the second meiotic division is completed, and most cytoplasm is again retained by one cell, the fertilized oocyte. Study hard  Approximately: – newborn: two million primary oocytes in the ovaries, – Adolescence: no more than 40,000 remain. – Of these, only 400: become secondary oocytes and are expelled at ovulation during the reproductive period. zona pellucida: – surround primary oocyte – Is amorphous acellular glycoprotein material. COMPARISON OF GAMETES Oocytes massive and immotile Sperm surrounded by the zona pellucida and Microscopic and highly a layer of follicular cells (corona radiata) motile has an abundance of cytoplasm two kinds of normal containing yolk granules sperm: 23, X and 23, Y only one kind of normal secondary oocyte: 23, X Study hard Study hard  Capacitation: a period of sperm conditioning – lasting approximately 7 hours. – a glycoprotein coat and seminal proteins are removed from the surface of the sperm's acrosome. – membrane components of the sperms are extensively altered. – no morphologic changes, but they are more active. – occurs in the uterus or uterine tubes by substances secreted by them. Dispermy : – when two sperms participate in fertilization. – resulting in a zygote with an extra set of chromosomes. Triploidy (69 chromosomes): – triploid conceptions account 20% of chromosomally abnormal spontaneous abortions. Study hard  FERTILIZATION usually occurs in the ampulla of the uterine tube begins with contact between a sperm and an oocyte ends with the intermingling of maternal and paternal chromosomes. takes approximately 24 hours. Phases of Fertilization 1. Passage of a sperm through the corona radiata: – Dispersal of the follicular cells of the corona radiata surrounding the oocyte. 2. Penetration of the zona pellucida: – is the important phase in the initiation of fertilization. Study hard  – action of enzymes released from the acrosome forms pathway for sperm. Such as: esterases, acrosin, and neuraminidase➔ cause lysis of the zona pellucida. – zona reaction: begins once the sperm penetrates the zona pellucida a change in the properties of the zona pellucida that makes it impermeable to other sperms. 3. Fusion of plasma membranes of the oocyte and sperm. – break down at the area of fusion. – head and tail of the sperm enter the cytoplasm of the oocyte, – sperm's plasma membraneStudy hard remains behind 4. Completion of the second meiotic division of oocyte: – activated when sperm penetrates the oocyte. Early pregnancy factor: – an immunosuppressant protein, – is secreted by the trophoblastic cells – appears in the maternal serum within 24 to 48 hours after fertilization. – forms the basis of a pregnancy test during the first 10 days of development. Study hard  Fertilization: – Stimulates the penetrated oocyte to complete the second meiotic division. – Restores the normal diploid number of chromosomes (46). – Results in variation of the human species. – Determines chromosomal sex of the embryo. – Causes metabolic activation of the ootid – initiates cleavage (cell division) of the zygote. X and Y sperms (gender selection) using: – differential swimming abilities of the X and Y sperms – Different speeds of migration of sperms in an electric field – Differences in the appearance of X and Y sperms – DNA difference between X and Y sperms Study hard Study hard