Human Reproduction Flashcards
class 12 (39 cards)
1
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Human Reproduction – Overview
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- Humans are sexually reproducing and viviparous. - Reproductive events include: Gametogenesis → Insemination → Fertilisation → Zygote formation → Blastocyst development → Implantation → Gestation → Parturition. - Sperm formation continues in males throughout life, but ovum formation ceases in females around 50 years.
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Male Reproductive System – Structure
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- Located in the pelvic region, includes: - Testes, accessory ducts, glands, and external genitalia. - Testes are present in a scrotum, which maintains a temperature 2–2.5°C lower than body temperature, essential for spermatogenesis.
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Testes – Internal Structure
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- Each testis is oval, ~4–5 cm long and ~2–3 cm wide. - Covered by a dense layer-tunica albuginea, internally divided into 250 lobules. - Each lobule contains 1–3 seminiferous tubules where sperms are produced.
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Seminiferous Tubules – Cell Types
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- Lined by two types of cells: - Male germ cells (Spermatogonia) – Undergo meiosis to form sperm. - Sertoli cells – Provide nutrition to germ cells.
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Interstitial Spaces – Leydig Cells & Hormones
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- Interstitial spaces (outside seminiferous tubules) contain: - Leydig cells – Secrete testicular hormones (androgens). - Small blood vessels and immune cells.
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Male Accessory Ducts – Path of Sperm Transport
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- Rete testis → Vasa efferentia → Epididymis → Vas deferens → Ejaculatory duct → Urethra → Penis. - Seminiferous tubules open into vasa efferentia via rete testis. - Vasa efferentia → Epididymis (stores sperm) → Vas deferens (ascends into the abdomen). - Vas deferens joins seminal vesicle duct → Ejaculatory duct → Urethra → Penis. - Urethra extends through penis, opening at urethral meatus.
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Q
External Genitalia – Penis
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- Penis is the male external genitalia. - Made of erectile tissue, helps in insemination. - Glans penis (enlarged tip) is covered by foreskin.
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Male Accessory Glands – Role in Seminal Plasma
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- Paired seminal vesicles, prostate gland, and paired bulbourethral glands. - Secretions form seminal plasma, which is rich in fructose, calcium, and enzymes. - Bulbourethral gland secretions aid in penis lubrication.
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Q
Female Reproductive System – Overview
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- Consists of a pair of ovaries, oviducts, uterus, cervix, vagina, and external genitalia located in the pelvic region. - Also includes a pair of mammary glands, which support ovulation, fertilization, pregnancy, birth, and child care.
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Ovaries – Primary Female Sex Organs
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- Produce ova (female gamete) and secrete steroid hormones (ovarian hormones). - Located one on each side of the lower abdomen. - Each ovary is 2–4 cm long, connected to the pelvic wall and uterus by ligaments. - Covered by a thin epithelium, enclosing ovarian stroma. - Ovarian stroma has two zones: Peripheral cortex and Inner medulla.
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Oviducts (Fallopian Tubes) – Pathway for Ovum
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- Each fallopian tube is 10–12 cm long, extending from the ovary to the uterus. - Divided into three parts: - Infundibulum – Funnel-shaped part near the ovary with fimbriae (finger-like projections) that help in ovum collection after ovulation. - Ampulla – Wider, middle part. - Isthmus – Narrow-lumen part, joins the uterus.
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Uterus – Structure and Function
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- Also called womb, inverted pear-shaped, supported by ligaments attached to the pelvic wall. - Opens into vagina through cervix. - Cervical canal + vagina = Birth canal. - Wall of uterus has three layers: - Perimetrium – External thin layer. - Myometrium – Thick, smooth muscle layer, undergoes strong contractions during childbirth. - Endometrium – Inner glandular layer, undergoes cyclical changes during the menstrual cycle.
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External Genitalia – Female Reproductive Organs
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- Mons pubis – Fatty tissue cushion, covered by skin and pubic hair. - Labia majora – Large, fleshy folds extending down from the mons pubis, surrounding the vaginal opening. - Labia minora – Inner paired folds of tissue beneath the labia majora. - Hymen – Membrane partially covering the vaginal opening. - Clitoris – Small, finger-like structure located above the urethral opening at the junction of labia minora. - Hymen can tear due to first coitus, sports (horseback riding, cycling), sudden falls, tampon use, but its presence/absence is not a reliable indicator of virginity.
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Mammary Glands – Role in Lactation
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- Functional mammary glands are present in all female mammals. - Paired structures (breasts) contain glandular tissue and fat. - Glandular tissue is divided into 15–20 mammary lobes, each containing clusters of alveoli (milk-secreting cells). - Milk storage and transport pathway: - Alveoli → Mammary tubules → Mammary ducts → Mammary ampulla(molk stored here temporarily)→ Lactiferous duct (through which milk is sucked out).
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Gametogenesis – Definition
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- The process by which gametes (sperm and ovum) are formed in the testes (male) and ovaries (female). - Includes spermatogenesis (in males) and oogenesis (in females).
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Spermatogenesis – Formation of Sperm
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- Occurs in the seminiferous tubules of testes and begins at puberty. - Process: - Spermatogonia (diploid, 46 chromosomes) undergo mitotic division to increase in number. - Some spermatogonia differentiate into primary spermatocytes (diploid, 46 chromosomes). - First meiotic division: Primary spermatocytes → 2 secondary spermatocytes (haploid, 23 chromosomes). - Second meiotic division: Secondary spermatocytes → 4 haploid spermatids (23 chromosomes each). - Spermiogenesis: Spermatids transform into spermatozoa (sperms). - Spermiation: Mature sperm is released from seminiferous tubules.
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Hormonal Control of Spermatogenesis
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- Initiated at puberty due to an increase in Gonadotropin Releasing Hormone (GnRH) from the hypothalamus. - GnRH stimulates anterior pituitary to release: - Luteinizing Hormone (LH): Acts on Leydig cells, stimulating testosterone (androgen) production. - Follicle Stimulating Hormone (FSH): Acts on Sertoli cells, which produce factors aiding spermiogenesis. - Testosterone promotes sperm production and maintains male reproductive structures.
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Structure of a Sperm
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- Microscopic structure with head, neck, middle piece, and tail. - Head contains haploid nucleus and an acrosome (enzyme-filled cap) to aid fertilization. - Middle piece contains mitochondria for energy. - Tail facilitates sperm motility. - Ejaculation releases 200–300 million sperms; for normal fertility: - 60% must have normal shape & size. - 40% must have vigorous motility.
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Semen – Transport and Composition
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- Sperms are transported through accessory ducts (epididymis, vas deferens, seminal vesicles, prostate). - Seminal plasma + sperms = semen. - Secretions from epididymis, vas deferens, seminal vesicles, and prostate provide nutrients, aid sperm motility and maturation. - Androgens regulate accessory ducts & glands.
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Oogenesis – Formation of Ova
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- Begins during embryonic development and pauses at birth until puberty. - Process: - Oogonia (diploid, 46 chromosomes) multiply in fetal ovary but stop dividing after birth. - Primary oocytes (46 chromosomes) enter prophase I of meiosis and remain arrested in this stage until puberty. - Each primary oocyte is surrounded by granulosa cells, forming primary follicles. - Many primary follicles degenerate; only 60,000–80,000 remain at puberty. - Primary follicles mature into secondary follicles, which develop an outer theca layer. - Tertiary follicle forms, with a fluid-filled antrum and a theca divided into theca interna and theca externa. - First meiotic division occurs: - Unequal division forms haploid secondary oocyte (23 chromosomes, large cytoplasm) and first polar body (tiny, may degenerate or divide further). - Graafian follicle forms, containing zona pellucida around the secondary oocyte. - Ovulation: Graafian follicle ruptures, releasing the secondary oocyte into the oviduct.
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Key Differences Between Spermatogenesis & Oogenesis
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Spermatogenesis: - Starts at puberty and continues throughout life. - Produces millions of sperms daily. - Four spermatids are formed from one spermatogonium. - Equal cytoplasmic division in meiosis. - Sperms are motile. Oogenesis: - Starts before birth; pauses until puberty and ends at menopause. - One ovum is produced per menstrual cycle. - One large ovum and a polar body are formed from one oogonium. - Unequal cytoplasmic division in meiosis. - Ovum is non-motile.
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Menstrual Cycle – Definition & Overview
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- The reproductive cycle in female primates (monkeys, apes, humans). - First menstruation at puberty is called menarche. - Occurs at an average interval of 28–29 days. - Ovulation (release of ovum) happens in the middle of the cycle (~14th day). - If fertilization does not occur, the cycle repeats. - Menstrual cycles cease at ~50 years of age (menopause).
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Phases of the Menstrual Cycle
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The cycle has four main phases: 1. Menstrual Phase (Days 1–5): - Endometrial lining breaks down and sheds (menstruation). - Blood, mucus, and tissue are expelled through the vagina. - Occurs if fertilization does not happen. - Menstrual cramps may be experienced due to uterine contractions. 2. Follicular (Proliferative) Phase (Days 6–14): - Primary follicles grow into a mature Graafian follicle. - Endometrial lining regenerates after menstruation. - FSH and LH levels rise, stimulating estrogen secretion from follicles. - Estrogen helps endometrial thickening. - Ends with a sharp rise in LH (LH surge) on ~14th day, triggering ovulation. 3. Ovulatory Phase (~Day 14): - LH surge causes rupture of the Graafian follicle and release of the ovum into the fallopian tube. - The ovum remains viable for ~24 hours for fertilization. - Marks the most fertile period in the cycle. 4. Luteal (Secretory) Phase (Days 15–28): - Corpus luteum forms from the remnants of the ruptured follicle. - Secretes progesterone, which maintains the thickened endometrium. - If fertilization occurs, progesterone supports pregnancy. - If no fertilization, the corpus luteum degenerates, progesterone drops, and menstruation begins, starting a new cycle.
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Hormonal Regulation of the Menstrual Cycle
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- Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus stimulates the pituitary gland. - FSH (Follicle Stimulating Hormone): Stimulates follicular development & estrogen secretion. - LH (Luteinizing Hormone): Causes ovulation & corpus luteum formation. - Estrogen: Thickens the endometrial lining during the follicular phase. - Progesterone: Maintains the endometrium during the luteal phase. - If pregnancy occurs, progesterone levels remain high. - If no pregnancy, progesterone falls, causing menstruation.
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Significance of the Menstrual Cycle
- Essential for female fertility. - Cyclic menstruation (from menarche to menopause) is an indicator of reproductive health. - Absence of menstruation may indicate pregnancy, stress, or health issues. - Menopause (~50 years of age): Permanent cessation of menstruation due to decline in ovarian function.
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Fertilisation – Definition & Process
- Fertilisation: Fusion of a sperm and an ovum to form a zygote. - Occurs in the ampullary region of the fallopian tube. - Requires simultaneous transport of sperm and ovum to the ampullary region. - Not all copulations result in fertilisation and pregnancy.
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Steps of Fertilisation
1. Insemination: Semen is released into the vagina during copulation (coitus). 2. Sperm Transport: Motile sperms travel through the cervix → uterus → fallopian tube. 3. Ovum Transport: Ovum is released from the ovary and reaches the fallopian tube. 4. Sperm-Ovum Interaction: - Sperm contacts zona pellucida of the ovum. - Membrane changes occur, preventing entry of multiple sperms (ensures monospermy). 5. Sperm Entry & Oocyte Activation: - Acrosomal enzymes help sperm penetrate zona pellucida. - Secondary oocyte completes meiosis II, forming a haploid ovum and second polar body. 6. Nuclear Fusion & Zygote Formation: - Haploid sperm nucleus fuses with haploid ovum nucleus. - Forms a diploid zygote (46 chromosomes). - Sex of the baby is determined at this stage.
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Sex Determination
- Female gametes (ova) contain X chromosome only. - Male gametes (sperms) contain either X or Y chromosome. - If an X-bearing sperm fertilises the ovum → XX (female). - If a Y-bearing sperm fertilises the ovum → XY (male). - Father determines the sex of the baby.
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Cleavage & Morula Formation
- Zygote undergoes mitotic divisions (cleavage) as it moves toward the uterus. - Cleavage forms 2, 4, 8, 16 blastomeres. - Embryo with 8–16 blastomeres is called a morula.
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Blastocyst Formation & Structure
- Morula divides further → forms blastocyst. - Blastocyst consists of: - Trophoblast (outer layer): Helps in implantation. - Inner Cell Mass (ICM): Develops into the embryo.
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Implantation – Process & Significance
- Blastocyst reaches the uterus and attaches to the endometrium. - Uterine cells multiply, covering the blastocyst. - Blastocyst becomes embedded in the endometrial lining (implantation). - Implantation leads to pregnancy.
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Placenta – Structure & Function
- After implantation, finger-like projections called chorionic villi appear on the trophoblast. - These villi interdigitate with maternal uterine tissue, forming the placenta. - Functions of placenta: - Facilitates oxygen and nutrient supply to the embryo. - Removes carbon dioxide and waste materials from the embryo. - Umbilical cord connects the embryo to the placenta, allowing exchange of substances. - Acts as an endocrine gland, secreting hormones vital for pregnancy.
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Hormones Produced During Pregnancy
- Human Chorionic Gonadotropin (hCG) – Maintains the corpus luteum. - Human Placental Lactogen (hPL) – Helps in fetal growth and maternal metabolism. - Estrogens & Progestogens – Support pregnancy and fetal development. - Relaxin – Secreted in later pregnancy to relax pelvic ligaments. - Increased levels of cortisol, prolactin, and thyroxine support maternal metabolism and fetal growth.
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Gastrulation & Germ Layer Formation
- Inner cell mass of the embryo differentiates into three layers: 1. Ectoderm (outer) – Forms skin, nervous system, eyes, ears. 2. Mesoderm (middle) – Forms bones, muscles, heart, blood, kidneys, reproductive organs. 3. Endoderm (inner) – Forms liver, lungs, pancreas, digestive tract lining. - Stem Cells in the inner cell mass have the potential to form any tissue/organ.
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Major Milestones of Embryonic Development
- 1st month: Heart formation, heartbeat can be detected. - 2nd month: Limbs and digits develop. - 12 weeks (1st trimester end): - Major organ systems are formed. - External genitalia become visible. - 5th month: - First fetal movements observed. - Hair begins to appear on the head. - 24 weeks (2nd trimester end): - Body covered with fine hair (lanugo). - Eyelids separate, eyelashes form. - 9th month: - Fetus fully developed and ready for birth.
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Gestation Period in Different Mammals
- Humans – 9 months (approx. 280 days) - Dogs – 2 months (~60 days) - Cats – 2 months (~65 days) - Elephants – 22 months (longest mammalian gestation)
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Parturition – Childbirth Process
- Gestation Period: 9 months in humans. - Parturition: Process of delivering the baby. - Triggered by: Neuroendocrine Mechanism. - Foetal Ejection Reflex: - Signals from fully developed foetus & placenta trigger mild uterine contractions. - This stimulates oxytocin release from the maternal pituitary. - Oxytocin: - Strengthens uterine contractions (positive feedback loop). - Leads to strong contractions that expel the baby via the birth canal. - Placental Expulsion occurs after delivery.
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Lactation – Milk Production & Breastfeeding
- Mammary Glands: Differentiate during pregnancy. - Lactation: Process of milk secretion. - Colostrum (First Milk): - Produced in the first few days after birth. - Rich in antibodies to boost newborn immunity. - Breastfeeding is essential for healthy infant development.
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Summary of Human Reproduction
- Humans are sexually reproducing and viviparous. - Male Reproductive System: - Testes (sperm production). - Leydig cells → produce testosterone. - Sertoli cells → nourish sperm. - Sperm Structure: Head, neck, middle piece, tail. - Female Reproductive System: - Ovaries → produce ovum & ovarian hormones. - Menstrual Cycle: - ~28 days; regulated by hormones (LH, FSH, Estrogen, Progesterone). - Ovulation → release of 1 ovum per cycle. - Fertilization & Pregnancy: - Sperm meets ovum in ampulla → forms zygote. - Zygote undergoes cleavage → blastocyst implants in uterus. - Placenta develops → supports fetus. - Parturition: Childbirth triggered by oxytocin & uterine contractions. - Lactation: Milk production supports newborn immunity & nutrition.
