Dr Heba's Male Reproductive System Notes - PDF

## Chapter 2: Male Reproductive System - **Components:** Two testes, genital ducts, accessory glands, penis ### 2 Testes - A compound tubular sex gland has 2 functions: reproductive and hormonal. - Testes develop in the dorsal cavity of the peritoneal cavity. - It suspends in scrotum outside the...

## Chapter 2: Male Reproductive System - **Components:** Two testes, genital ducts, accessory glands, penis ### 2 Testes - A compound tubular sex gland has 2 functions: reproductive and hormonal. - Testes develop in the dorsal cavity of the peritoneal cavity. - It suspends in scrotum outside the abdominal cavity at the end of the spermatic cord. - Enclosed separately by tunica vaginalis: isolated serous membrane derived from the peritoneum. - Scortal sac keepstestes at a lower temperature than the body. - In human: below 36.8°C by 1-2°C to avoid sperms death or damage. - Surrounded by tunica albuginea: thick resistant capsule of collagenous connective tissue. - Becomes thicker at / posterior region. - mediastinum testis: fibrous septa project into the gland and diving it into about 250 pyramidal compartments called testicular lobules. - These septa are incomplete, each one is occupied by 1-4 seminiferous tubules in a web of connective tissue rich in nerves and vessels. - Lined with a complex stratified epithelium. - They are coiled forming network, where individual tubules are either blind-ended or branched. - tubuli recti of each lobule connect seminiferous tubules to rete testis. - Present in connective tissue of mediastinum testis. - Connected to the cephalic portion of epididymis by 10-20 ductuli efferents. ### Each seminiferous tubule consists of: - Fibrous tunica propia - Well-defined basal lamina - Seminiferous epithelium - Fibrous tunica propia enveloping the seminiferous tubule consists of several layers of fibroblasts. - The innermost layer adhering to basal lamina consists of squamous epithelium exhibits smooth muscle characteristics. - Epithelium of seminiferous tubule consists of: - Spermatogonia or stem cells - Sertolicells - Function: - Sperm nutrition - Cleaning after division ### Male duct - Coiled epididymis - Vas deferens in the spermatic cord forming ejaculatory duct - Conducts the male cells into prostatic urethra. ### Accessory glands - **Seminal Vesicles:** Elongated sac which taper where they unite with vas deferens. - Each consists of one coiling tube. - Secretes 60-70% of ejaculate. - Connected lumina insections. - Contains large amount of Fructose. - Secretion contains: - Prostaglandins - Flavins - Several other Proteins & enzymes. - Sperms energy source. - **Prostate gland:** Largest accessory sex gland in men. - Contains 30-50 tubuloalveolar glands. - Which empty into 15-25 independent excretory ducts. - Which open into the urethra. - Size & shaped type: Walnut-sized exocrine gland. - Location: It borders the inferior end of urinary bladder and surrounds the urethra. - Function: Produces large portion of fluid makes semen. - That fluid: - Milky white in color. - Contains enzymes, proteins, other chemicals. - To support and protect sperm during ejaculation. - Contains smooth muscle tissues that can constrict to prevent urine or semen flow. - The secretion is slightly acidophilic and contains: - Citric acid - Fibrindysin enzyme - Acid phosphate - Some enzymes and lipids liquefies the semen. - **Cowper's glands / Bulbourethral glands:** Pair of pea-sized exocrine glands. - Size & shape & type. - Inferior to the prostate anterior to anus, location. - Secrete a thin alkaline fluid into urethra. - Function: That fluid lubricates urethra and neutralizes acid from urine. - Enters urethra during sexual arousal prior to ejaculation. - To prepare urethra for semen flow. - **Semen:** The fluid secreted during sexual intercourse by males. - Contains: - Sperms: Male reproductive gametes. - No. of cell suspend chemicals in a liquid medium. - Chemical composition gives it thick, sticky consistency, slightly alkaline pH. - These help semen to support reproduction by helping sperms remain within vagina after intercourse. - Neutralize the acidic environment of vagina. - In healthy adult males, it contains 100 million sperm cell per mL. - Fertilize oogtes inside female's fallopian tube. ### Spermatogenesis - It takes place in the testes and epididymis of adult make. - Prior to puberty, no spermatogensis because of hormonal triggers lack. - At age 13-15 (puberty), gonadotropic hormones are secreted after anterior pituitary gland stimulation and throughout the remainder of life. - Gonadotropic hormones are: - Follicle-Stimulating hormone (FSH) - Luteinizing hormone (LH) - Controlled by hypothalamus. - Spermatogenesis begins when FSH, LH are produced. - LH: Triggers testosterone production by testes. - Stimulates spermatogonium to undergo in primary spermatocytes development process. - FSH: Triggers maturation of germ cells. - Spermatogenic cells are arranged in 4-8 layers occupy the between basal membrane and lumen. ### Stages of Spermatogenesis: - **Stage of growth and food storage:** - Can be one of 2 types: A or B. - Type B only. - 2N Spermatogonium (stem cells) - 2N Primary spermatocyte - Largest cell because of food storage. - **Stage of meiosis I:** - N Secondary spermatocyte - **Stage of meiosis II:** - N Spermatids - **Stage of spermogenesis / Spermatozoa:** - N Immotile - N Sperms or spermatozoa - Smallest cell because of excess fluids loss. - Motile **Important notes:** - PGCs, at the time of birth, recognized in testis sex cords as large, pale cells surrounded by supporting cells. - Puberty, sex cords become seminiferous tubules, alumen is acquired. - PGCs differentiate into spermatogonia spermatogenic lineage. - Spermatogenesis: - Spermatocytogensis - Spermatidogenesis - Spermiogenesis ### Changes during spermatogenesis: - Spermatogonia type B rise to primary spermatocytes (2N). - Primary spermatocyte meiosis I > Secondary spermatocytes (N). - Secondary spermatocyte meiosis I > spermatid (N). ### Spermatogenesis: #### Golgi phase - Formation is derived from golgi apparatus. - Spermatozoa acrosome. - During this formation, many small granules fuse forming the pro-acrosomal granule. - This acrosomal granule becomes closed to the top of the nucleus. - 2 centrioles are recognized posterior to the nucleus. #### Cap phase - The acrosomal granule spreads over the front of the nucleus and covering it with a cap shape. - Nucleus condenses after losing its fluid RNA. #### Acrosomal phase - A depression is formed in the posterior surface of the nucleus. - Proximal centriole placed proximal to the nucleus. - Distal centriole takes aposition behind the proximal centriole. - Distal centriole give rise to axial filament. #### Maturation phase - Shedding off of cytoplasm remainder containing golgi ER and other organelles from spermatozoon. - Leaving thin film of cytoplasm around the middle piece. - Most protein chromatin materials condense in this nucleus. - **Most mitochondria concentrate around the distal centriole and forward the axial filament** - **Form neck and middle piece** - **In the middle piece, the mitochondria arranges in spiral arrangement** ### Spermatozoa Structure - **Head:** - Contains: - Nucleus: genetic function, has haploid number of chromosomes. - Acrosome: - Includes X or Y chromosome, because of separation of XY during meiosis. - For active fertilization. - Derived from Golgi apparatus. - Contains hydrolytic enzymes that released when reaching sperm the ovum. - These enzymes digest the outer membrane of the egg. - Proteins and complex sugars to allow sperm penetration. - Shape varies in different specialties, may be ovoid offlattened from the both sides in man. - **Midpiece:** - Connects head withineck. - Has 2 centrioles. - They respire sugars in semen to generate ATP to provide energy for tail. - Posterior centriole responsible for microtubule formation in sperm tail. - **Tail:** - Also named Flagellum. - Long. - Contains axial filament covered with this cytoplasmic sheath. - Rhythmic contraction of filaments causes forward movement of sperm against the fluid environment. - **Neck:** - Connects Head with midpiece - **Sperm:** 65 mm - **Head:** 5 mm - **Middle piece:** 5 mm - **Principal piece:** 50 mm - **End piece:** 5 mm ### Sperm Abnormalities - **Morphological:** - Head and tail can be: - Giants - Dwarfs - Joined in head or in tail. - All don't move. - **Numerical:** - **Oligospermia** - Less than 30 million per ejaculation. - **Aspermia** - No sperms in semen. - **Necrospermia** - Dead sperms. - **Multinucleated giant cells:** - **Conjugation of spermatocytes and spermatides** - These conjugated cells called binucleated giant cells. - Two cells. - Three or more cells. - Multinucleated giant cells. ## Chapter 3: Female Reproductive system - **Components:** Two ovaries, uterus, fallopian tubes, vagina. ### 2 Ovaries - They release an ovum, which passes through fallopian tube to the uterus. - **Location:** Located in ovarian fosse, which is a shallow depression one on each side of the uterus, in the lateral walls of the pelvic cavity. - They are held loosely by peritoneal ligaments. ### Structure of ovary - **Germinal epithelium:** The outermost layer. - **Tunica albuginea:** Covers the cortex. - **Ovarian cortex:** Consists of ovarian follicles. - Stroma between follicles. - **Ovarian medulla:** The innermost layer. ### The human ova is Alecithal, Homolecithat ### Oogenesis - Early in fetal development, the primordial germ cells (PGCs) differentiate into Oogonia. - **Oogonia:** - 2N - Has 46 chromosomes. ### In fetal development stage of growth - **Primary Oocyte:** - 2N - Has 46 chromosomes. - It replicates DNA starting meiosis I, but it stops in prophase until puberty. - **Stage of meiosis I:** - Under the effect of FSH, one continues meiosis I. - N: 1st polar body. - Has the rest 23 chromosomes - At puberty: - **Secondary Oocyte:** - N - Has 23 chromosomes. - All cytoplasm and organelles. - **Stage of meiosis II:** Starts the meiosis II but stops in metaphase until fertilization. - N: Has 23 chromosomes. - One strand but all the cytoplasm. - **Fertilized ovum:** - N - Has 23 chromosomes. ### Questions 1. Spermatogenesis and Oogenesis are similar in sequence but differ in the timing and final results. (True) 2. Primary spermatocytes and primary oocytes continue developing all the lifetime. (False) 3. The no. of resulting gametes in male and female of human is equal. (False) 4. The human female's ovary at birth contains primary oocyte. (True) 5. What happen if: the secondary oocyte is not fertilized? - Answer: The meiosis II is never completed and secondary oocyte degenerates. ## Chapter 4: Female Reproductive cycle - At puberty (13-15), under the effect of gonadotropine releasing hormone of hypothalamus, pituitary gland is activated and secretes follicle stimulating hormone (FSH) and luteinizing hormone (LH). ### FSH function: - Stimulate ovarian follicle development. - Production of estrogen by follicle cells. ### LH function: - Serve as a hormone for ovulation. - Production of progesterone by follicular cells and corpus luteum. ### Reproductive Cycle - **Ovarian cycle:** changes in the ovary during the menstrual cycle. - Starts at 13-15 years old until 43-50 years old. - Continue for 30-35 years, stops at pregnancy. - **Uterine cycle:** structural changes in endometrium every 28 days because of estrogen and progesterone levels change. - **Menstrual phase:** 1-4 days bleeding. - **Proliferative phase:** 5-14 days. - Estrogen phase. - **Secretory luteal progestronic phase:** 15-24,26 day. - Follicular phase: 1-13,14 day of bleeding. - Ovulation process: 13 or 14 day of bleeding. - Luteal phase: 15-28 day of bleeding. ### Each stage: - **Follicular phase:** - From day 1: day 13 or 14. - Characterized by: - Primary oocyte growth and differntiation. - Follicular cells proliferation. - Zona pellucida formation. - Graffian Follicle Formation. - It occurs because of secreting large amount of LH from anterior pituitary. - **Ovulation day 13 or 14:** - It occurs because of secreting large amount of LH from anterior pituitary. - Mature Graffian follicle ruptures and liberate the secondary oocyte that is surrounded by Zona pellucida and Corona radiata. - **Proliferative phase:** - From bleeding end: day 19. Ovulation. - It is under the control of estrogen. - Characterized by: - Endometrial epithelium regeneration. - Uterine glands grow up. - Arteries elongates and become spiral. - **Secretory phase:** - From day 14: day 24,26, 10-12 days after ovulation. - Characterized by: - Endometrium's thickness increase. - Spiral arteries become coiled. - Uterine glands full with glycogen and mucin. - Venous network show large lacunae. ## Chapter 5: Types of vertebrates Eggs & Envirument - **Animal Eggs:** - **Yolk amount classification:** - **Micro lecithal:** little yolk. - **Meso lecithal:** moderate yolk. - **Macro lecithal / Poly lecithal:** large yolk. - **Yolk distribution classification:** - *Islolecithal / Homolecithal:* - Regularly distributed. - Centrolecithal: centrally distributed. - *Telolecithal:* - Polarized cytoplasm. - Forms a thin periphral layer around yolk. - Has polarized distribution due to gravity in the vegetal pole. - **Notes:** Macrolecithal eggs are telolecithal and centrolecithal. ### Yolk - The reserved material, which contains proteins and lipids droplets and glycogen and minerals. - **Function:** - Source of energy, lipids and glycogen. - Synthesis of proteins, which are required products for embryonic body development. - It influences the egg size, cleavage pattern, morphogenetic movements of blastomere during gastrulation. ### Egg Membranes Types - They are produced outside the egg's plasma membrane. - They vary in different animal groups. - They classify according to their origin. - **Primary:** - Formed by the egg. - Location: Between egg plasma membrane and follicle cells. - Examples: vitelline membrane. - **Secondary:** - Secreted by a layer of follicle cells. - Location: Outside embryy egg membrane. - Examples: - In amphibian: uniform layers of jelly (albumen are deposited around the egg. - In insects: these envelops hold the egg in masses. - In fishes: in the form of chitinous shell, surrounding the egg. - It has a micropyle for sperm enter and make them unappetizing to predator. - In mammals: zona pellucida. - Female sexhormones secretion especially from follicle cells. - **Tertiary:** - Formed during eggs passage in oviduct. - Examples: - In reptiles and birds: they make egg envelopes external to vitelline membrane are added the albumen, shell membranes, porous calcerous shell. ### Egg Membranes Function: 1. **Protection of egg contents from different ecological hazards, as:** Variable pH, temperature, radiations, pollutions. 2. **Prevent polyspermy:** Fertilization by more than one sperm. 3. **Help in sperm adhesion**. 4. **Maintaining egg cleavage**. ## Chapter 6: Fertilization - Union of haploid gametes to reconstitute a diploid cell, which has potential to become a new individual. - They are a series of steps that begin with sperm and ovum first contact. - Transport of ovum. - Go back to chapter 3. ### Fertlization steps 1. **Sperm Capacitation:** - Freshly ejaculated sperms are unable or poorly able to fertilize. - It is associated with removal of adherent seminal plasma proteins and plasma membrane lipids and proteins reorganization. - It occurs while sperm reside in female reproductive tract. - 2. **Penetration of corona radiata:** - Sperm secretes hyaluronidase, helps in corona radiata penetration of granus cells. 3. **Sperm-zona pellucida binding:** - This binding is a receptor-ligand interaction with a high degree of species specificity. - Carbohydrate groups on zona pellucida glycoproteins function as sperm receptors. 4. **Acrosome reaction:** - This reaction allows the sperm to get through the zona pellucida by a provided enzymatic drill like trypsin. - The zona pellucida protein serves as a sperm receptor, which leads to many area of fusion between plasma membrane and outer acrosomal membrane. - Membrane fusion (exocytosis) and leading to acrosomal enzymes leakage from sperms' head. - Plasma membrane and acrosomal contents are lost as sperm penetrates zona pellucida. 5. **Penetration of Zona Pellicida:** - A tract is formed through the zona pellucida by the constant propulsive force from the sperm tail. - Motility and zona digesting enzymes allow sperm traverse in zona pellucida. 6. **Sperm-Oocyte binding:** - One sperm penetrates and it binds and rises with the oocyte's plasma membrane. - Binding occurs at the posterior region of the sperm head. - It is not sure, but a leading candidate in some species is fertilin (a dimeric sperm glycoprotein), that binds to a protein in oocyte plasma membrane and may induce fusion; the molecular nature of the binding is not resolved. 7. **Egg Activation and Cortical Reaction** - Prior to fertilization, egg was arrested in metaphase of second meiosis. - Upon sperm binding, the egg undergoes egg activation. - Egg activation: no. of metabolic and physical changes. - Completion of secondary meiosis and release the second polar body. - Prominent effects include arise in the intracellular concentration of calcium and cortical reaction. ### Cortical Reaction - Massive exocytosis of cortical granules after sperm-oocyte fusion. - Cortical granules contain a mixture of enzymes (proteases), which diffuse into the zona pellucida, alter its structure, including zona reaction. - These components may also interact with the oocyte plasma membrane. ### Zona reaction - It refers to alternation in structure of zona pellucida catalyzed by proteases from cortical granules. - Its critical importance is representing the major block to polyspermy in most mammals. - It is result of two measurable changes in zona pellucida: - Zona pellucida hardens. - Sperm receptors of zona pellucida destruction. ### After fertilization: - Sperm head is incorporated into egg cytoplasm. - Sperm's nuclear envelope disperses and chromatin undergoes decondensation. - Chromatin from both are soon encapsulated in a nuclear membrane forming pro-nuclei. - Each pronucleus contains a haploid genome, they migrate together; their membranes breakdown; the two genomes condenses into chromosomes, thereby reconstituting a diploid organism (2N). ## Chapter 7: Cleavage - Mitotic divisions of zygote to increase the no. of its cells. - It is the first developmental stage of zygote resulting in blastomeres. ### Function of cleavages - Production of many cells. - Preparing zygote for differentiation and morphogenesis. ### Main characteristics of cleavages 1. Unicellular zygote becomes a multicellular blastula. 2. No growth occurs, the size doesn't increase. 3. General shape doesn't change (except blastoceal). 4. Few qualitative changes in chemical composition of blastomere. 5. Cytoplasmic substances remains in place as zygote. 6. Nuclear and cytoplasmic volume increases. 7. Short cell cycle. 8. All blastomeres divide simultaneously. ### Rate of cleavage - It various between species according to: - The content - Yolk distribution. - In most cases, it remains rapid during early and becomes very slow at end. ### Cleavage Planes - **Meridional:** In direction from a.p to v.p. Center of v.p, a.p axis. - **Vertical:** In direction above or below e.p. Halfway between a.p, v.p in direction above or below e.p. - **Equatorial:** - **Latitudinal / Horizontal:** ### Cleavage Types - **Holoblastic / Total:** - Equal: Amphioxus. - Unequal: Toad. - Rotational: Human. - **Meroblastic / Partial:** - Discoidal: Reptiles, birds. - Superficial: Insects. ### Significance of cleavage 1. Subdivision of embryo prepare for intiation of cell differntation. 2. Presumptive organ form areas of the future embryonic body due to cleavage and blastulation. 3. The blastoceol permits the migration and rearrangment of the presumptive organs during gastrulation. ## Chapter 8: Embryonic Development of Amphioxus - **Amphioxus lanceolatus:** the name of small, fish-like, marine Creatures. - Cephalochordates are found in brackish or saltwater, generally near coast, have referred to many sparies. ### Habits and distribution - Is an expert swimmer when occasion requires. - It spends most of its time burrowing in sand. - At rest, it lies buried with head protruding; mouth wide agape. - Its food consists of microscopic organisms and organic particles drawn into mouth. ### Reproductive system - It can be a male or female, but the external shape of gonads are the same. - **Egg:** At fertilization, its diameter is 120 mm, oligiolecithal, homolecithal egg. - **Fertilization:** Takes place externally in aquatic environment. - Eggs spawn from female and sperm are being inseminated by male, and then they conjugate. ### Cleavage - **Perpendicular on the first** - Cleavage 1: 2 equal blastomeres after 60-90 min of insemination. - Cleavage 2: 4 equal blastomeres after 45 min. - Cleavage 3: 8 unequal blastomeres. - Cleavage 4: 16 unequal blastomeres. - 8 macromeres at vegetal pole. - 8 micromeres at animal pole. - **Succesive mitotic divisions:** - Cleavage 5: 32 unequal blastomeres, 2 horizontal cleavages. - Cleavage 6: 64 unequal blastomeres. - Cleavage 7: 128 unequal blastomeres. - Cleavage 8: 256 blastomeres. - **Blastulation:** Micromeres at the animal pole, blastocoel, macromeres at the vegetal pole. - **Blastula of Amphioxus** - **Gastrulation** - **Organogenesis** ### Blastulation - Cellular, hollowsphere containing blastoceal. It becomes apparent in 8 cells stage. - In early stages, blastomeres are large in size but later reduces. - Animal pole's thickness is four or three cells; the outer ones containing black pigment granules. - Vegital pole composed of various solid mass of non-pigmented yolk cells in sizes and shapes. - The floor of blastoceal is more or less flat, while its roof is formed by the arched layers of animal pole's active, small cells. ### Epiboly (Pregastrulation) - Partly larger yolk cells. - The overgrowing of actively dividing cells of animal pole, this circular region is referred to it as germ ring. - **Gastrulation** - **Organogenesis** ## Chapter 9: Developmental Stages of Frog - Frog is from Amphibians, class of subphylum vertebrata. - It is a well-known animal, lives chiefly in ponds and swamps. - It is chosen because it is more advanced than amphioxus, but still a simple animal. ### Oogensis: - **Smaller Oocyte:** - Evenly distributed little amount of yolk. - Nucleus in center. - **Oocyte in later stages:** - Typical telolecithal egg. - Nucleus at animal pole. - **Animal pole:** Has a black appearance because of progressive accumulation of black pigment granules. - **Vegital pole:** Has a cream-white appearance. - In future development, animal pole produces the anterior end of embryo, vegital pole produces the posterior end of embryo. - The primary axis (antero-posterior axis) of the embryo is established when ovum was still in ovary. - During egg passage in the oviducts' narrow part, they are enveloped by 3 distinct thin & gelatinous membranes (tertiary membranes). ### Fertlization - Male shed sperms that swims towards ova and pass through its membranes and fertilize it (similar to amphioxus in location and environment of fertilization). - The egg's mass increases after fertilization, after it was less than one cubic inch. - Sperm enters ova at any point on a latitudinal ping 35 to 40 from animal pole. - There is an immediate reaction of egg in exudation of fluids into the space between the ovum and the chorion. - In this manner, the egg becomes detached and free to rotate within the perivitelline space. Since vegital pole is heavier (as it is telolecithal egg), it becomes orientated with the black pigment of animal pole and the cream-white pigment of vegital pole is below. - Eggs in inverted position develop abnormally and degenerate eventually. - The complete sperm enters; the tail detaches. - The sperm carries many black pigment granules along with it, Indeed, the entire course of sperm is marked by cloud of dark granules. ### Cleavage - **Perpendicular on the first** - Cleavage 1: Vertical after 2-3 h. - Cleavage 2: Vertical after 30-45. - Cleavage 3: Unequal horizontal. - Cleavage 4: 8 unequal blastomeres: - 4 macro at v.p - 4 micro at a.p. - **Succesive mitotic divisions:** - Cleavage 5: 16 unequal blastomeres. - Cleavage 6: 32 unequal blastomeres. - Cleavage 7: 64 unequal blastomeres. - **Blastulation:** - Micromeres at the animal pole. - Blastocoel. - Macromeres at the vegetal pole. - **Blastula of Amphioxus:** - **Gastrulation** - **Organogenesis** ### Blastulation - **Cellular, hollowsphere containing blastoceal, it becomes apparent in 8 cells stage.** - In early stages, blastomeres are large in size, but later reduces. - Animal pole's thickness is four or three cells; the outer ones containing black pigment granules. - Vegital pole composed of various solid mass of non-pigmented yolk cells in sizes and shapes. - The hoor of blastoceal is more or less flat, while its roof is formed by the arched layers of animal pole's active, small cells. ### Epiboly (Pregastrulation) - Partly larger yolk cells. - The overgrowing of actively dividing cells of animal pole; this circular region is referred to it as germ ring. - **Gastrulation** - **Organogenesis** ## Chapter 10: Early Developmental Stages of Human - One ovum has been ovulated from the graffian follicle monthly. - The ovum has 24 hours to be fertlized. - One sperm fuses with receptor on the surface of secondary oocyte and enters it. - This entry initiates meiosis II in oocyte, fusion of egg and sperm nuclei forming diploid zygote. - Cleavage begins after 24 hours of fertilization. ### Cleavage - Short cell cycle. - During cleavage G1 and G2 are by-passed; cells progress from S to M. - S: DNA synthesis. - M: Mitosis. - Embryo undergoes cleavage while it is surrounded by the zona pellucida. - The unicellular zygote will undergo marked asynchrony of early cell division. - Mammalian blastomere doesn't divide together. - Human embryo increases in odd numbers not exponentially 2-4-8. - Mammals undergo holoblastic rotational cleavage, characterized by slow rate, unique cleavage orientation, lack of divisional synchrony, blastocyst formation - No growth in cleavage, the 8 cells are the same size of the zygote. ### Compaction - The 8 cells of the embryo holoose arrangement with plenty space and compact more, but still separated cells. - Protein (E-cadherin) is the responsible for the more compaction. - Cell adhesion protein oppers at compaction. - At end, morula is formed and blastoceol is formed from cells fluids. ### Blastocyst - Formed when the large blastoceol appears and the cells differentiate into the inner cell mass and trophoblasts layer. ### Hatching Blastocyst - It occurs just before implantation. - It occurs as aresult of protease secretion that digest zona pellucida; it was found in cortical granules. ## Implantation process - The uterine lining enlarges. - The trophoblast cell hang into the uterine wall by their microvili and the inner cell mass face the endometrium. - Normal sites: occuring: Superior, cervical, lateral, posterior at the body wall. ### Ectopic Pregnancy - It happens when the fertilization occurs outside uterus; it could be: - Ovarian pregnancy. - Peritoneal brall or cavity pregnancy. - Gastro-intestinal tract pregnancy. - Tubal pregnancy. ## Gastrulation 1. Inner cell mass will differentiate firstly in two layers: upper bilayer epiblast and lower flattened hypoblast. 2. Bilayer epiblast will form embryo proper tissues. 3. Flattened hypoblast will form the yolk sac. 4. Bilayer epiblast differentiate into 3 main germ layers: - Ectoderm - Mesoderm - Endoderm 5. Trophoblast will form the chorionic sac. ### Three main germ layers - **Ectoderm:** - Derivatives: - Nervous system - Sense organs - Epidermis skin layer. - **Mesoderm:** - Derivatives: - Skeletal system - Muscular system - Urino-genital system - Connective tissue - Circulatory system. - **Endoderm:** - Derivatives: - Digestive system and its derivatives. - Respiratory system. ## Changes of zygote from fertilization to birth This time is usually 9 months. ### During Pregnancy: - The zygote undergoes 40-44 mitosis rounds, producing an infant containing trillions of specialized cells organized into tissues and organs. - This 9 months is divided into 3 trimesters, each of 3 months long. ### First trimester months: 1, 2, 3. - The 3 embryonic tissue layers form. - Organogenesis begins during the third week. - The embryo's long is 5mm after one month. - Composed mostly of paired somite segments. ### During second month: - Most major organ systems form. - Limb buds develop. - The embryo becomes a fetus by week 7. - Beginning of week 8, the sexually neutral fetus activates gene pathways for sex determination. - Forming testes in XY fetuses and ovaries in XX fetuses, external genitalia develop. ### Second trimester months: 4, 5, 6 - The fetus increases in size. - Bony parts of skeleton begin to form. - Its movement can be felt by mother. ### Last trimester months: 7, 8, 9 - The fetus increases in size. - Circulatory and Respiratory Systems are mature for air breathing after birth. - Its growth uses large parts of mother's protein and calcium intake. - Maternal antibodies pass to fetus during last month, conferring temporary immunity. ## Chll Fetal membrane They are a result of extra-embryonic development. Function: protection, nutrition, respiration, excretion: ### Yolk sac - Formed from gut endoderm. - Connected to the midgut by yolk stalk. - Forms the Superior mesenteric circulation. - Sometimes persists as Meckel = S diverticulum of the ileum. - Composed of endoderm and splanchnopleure. ### Amnion - Forms a cavity over the embryonic disc. - Attaches to the ventral body wall due to flexion. - Thin, transparent and non-vascular. - Obliterate the extra-embryonic coelom by filling the chorion during development. - Forms up to 500 ml of fluid; this fluid protects the embryo. - Composed of ectoderm and somatopleure. ### Chorion - Surrounds all other fetal membranes (the outermost membrane). - Tough, opaque and vascular. - Formed by trophoblast initially. - Develops villi on its outer surface, which contribute to placenta formation. - Composed of ectoderm and somatopleure. - Forms a chorio allantoic membrane for respiration. - In species where development occurs in shell. ### Allantois - Diverticulum of the hindgut. - Allantoic vessels > umbilical cord, providing nutrition of embryo. - Depot for uric acid in birds. - Serve as primitive urinary bladder in mammals called urachus. - Form a chorio allantoic membrane in reptiles and birds for respiration. - Composed of endoderm and splanchnopleure. ### Placenta - Its origin in the extraembryonic membranes of amniote egg. - Monotremes are oviparous. - The yolk in moroblastically cleaving eggs is not sufficient for complete development. - In small egg (4.4mm diameter) develops forming rapidly dividing outer cell layer that envelopes the egg: - Ep