Embryology L1 Gametogenesis PDF

INTRODUCTION  7 steps: 1. Gametogenesis 2. Fertilization 3. Cleavage 4. Blastulation 5. Gastrulation 6. Neurulation 7. Organogenesis  The Basics Gametogenesis Gametes are produced during Meiosis...

INTRODUCTION  7 steps: 1. Gametogenesis 2. Fertilization 3. Cleavage 4. Blastulation 5. Gastrulation 6. Neurulation 7. Organogenesis  The Basics Gametogenesis Gametes are produced during Meiosis I & II – Meiosis function = Production of 4 haploid (n) gametes from each diploid oögonium (2n) or spermatogonium (2n) Differences between ♂ (male) and ♀ (female) gamete development ♂ – » continuous development & production of sperm from onset of puberty until….? » stem cells are retained » Sperm are motile and contain very little cytoplasm ♀ – » the entire complement of dictyate primary oocytes are formed during development with 10-20 continuing development during each ovarian cycle » Oocytes are surrounded by follicular cells – forms ovarian follicle » stem cells are exhausted » oocytes are among the largest cells and are non-motile 2.Fertilization: is the process whereby two sex cells (gametes) fuse together to create a new individual with genetic potentials derived from both parents. Have two separate activity: 1. Combining of genes derived from the two parents. 2. Creation of new organisms. Thus The first function is: Transmit genes from parents to offspring. The second is : initiate reactions in the egg cytoplasm that proceed development. Also, Restoration of the diploid number of chromosomes reduced during meiosis.  The Basics Gender Determination Chromosomes determine gender – 23 donated by egg (n) – 23 donated by sperm (n) Syngamy – The fusion of gametes to form a zygote – Consists of plasmogamy – union of cell membranes and cytosol Karyogamy – union of genetic material – Autosomes: 44 or 22 pair – Sex chromosomes: 2 or 1 pair » XX chromosomes = female » XY chromosomes = male  It have 4 major steps: 1. Sperm contacts the egg 2. Sperm or its nucleus enters the egg, and regulation of sperm entry. 3. Sperm and egg nuclei fuse 4. Egg becomes activated and developmental changes begin  Zygote Zygote is a fertilized egg. A fertilized egg becomes an embryo as soon as the first cleavage occurs.  Oviduct Fertilization occurs here  Internal Ferilization Chance of zygote survival is increased greatly  External Fertilization Zygotes chance of survival decreases significantly Structure of sperm Structure of ovum of sea urchin Spermatogenesis Male Reproductive System  Male Reproductive Physiology Basic Functions Function – 1. Produce, maintain & transport viable spermatozoa Testes Epididymis Ductus deferens Accessory glands – Prostate – Seminal vesicles – Bulbourethral glands – 2. Hormone production that develops secondary sexual characteristics Involved in feedback mechanisms relating to spermatogenesis  Male Reproductive Physiology Testes Site of Sperm production – Divided into lobules, each with seminiferous tubules. – Seminiferous tubule functions to Maintain environment for spermatogonia by the basal lamina and the Sertoli cells – Sertoli cells separate the lumen from the basal lamina and create a blood- testis barrier – Creates three compartments » Lumen – low glucose, high K+ & steroid hormones » Basal compartment – the baso- lateral side of the sertoli cells & containing the developing spermatogonia » Interstitial fluid space – below the basal lamina and contains the Leydig cells Produce hormones/paracrines – From Sertoli cells – From Leydig cells  Male Reproductive Physiology Testis Sertoli cells – Produce hormones & paracrines involved with control of hypothalamus-pituitary-gonad axis and the testes directly Anti-Müllerian Hormone (AMH) – Secreted during embryogenesis – Prevents development of the Müllerian ducts Inhibin & activin – Regulate FSH release from anterior pituitary » inhibin decreases FSH release » activin increases LH function & increases FSH release Androgen Binding Protein (ABP) – Binds to testosterone and DHT, reduces the loses due to diffusion resulting in an increase in testicular testosterone levels Estradiols & Aromatase – Support spermatogenesis  Male Reproductive Physiology Testis Sertoli cells, cont… GDNF (glial derived neurotrophic factor) & ERM transcription factor – Maintenance of the stem cell line Leydig cells – Produce androgens testosterone, androstenedione and dehydroepiandrosterone (DHEA) – Increase spermatogenesis – Influence secondary sexual characteristics – Stimulated to produce androgens by luteinizing hormone (LH) FSH increases the response to LH by Leydig cells  Male Reproductive Physiology Accessory Gland Function Job of the accessory glands is to – Secrete seminal fluid (99% of semen volume) Components of seminal fluid – Mucus – Water – Nutrients – Buffers – Enzymes – Prostaglandins – Zinc? – Accessory Glands Prostate Seminal vesicles Bulbourethral glands  Male Reproductive Physiology Accessory Gland Function Seminal Fluid Components, Function and Location (source)  The Basics Spermatogenesis Sperm Production – During development germ cells are produced Remain quiescent until puberty – Actions of hormones from pituitary, sertoli cells and Leydig cells At puberty some spermatogonia will – Undergo mitosis continuously – Enter into meiosis » This ensures a continuous supply of spermatogonia  Spermatogenesis Production of sperm in the testes Produce 4 sperm from one cell Meiosis  The Basics Spermatogenesis Process of sperm production involves three stages 1. Spermatocytogenesis produces secondary spermatocytes from spermatogoium 2. Spermatidogenesis stage where meiosis I & II occur results in spermatid formation 3. Spermiogenesis final stage of sperm development spermatid becomes a motile spermatozoa during spermiation Male Reproductive Phsyiology Testes  The Basics Spermatogenesis Spermiation – The spermatozoa that are formed are initially unable to move. – The flagella must become motile Not used however until ejaculated Prior movement through the male reproductive tract is via peristalsis  Male Reproductive Physiology Testes Spermatogenesis Hormonal Control Flow Chart  Male Reproductive Physiology The sexual response Remember – Function of the reproductive system is to reproduce – Males contribution is Deliver viable sperm into the vagina Requires a complex neural reflexes – Starts with the (1) erection reflex which creates changes in vascular condition within the penile arterioles » Initiated by erotic stimuli (visual, auditory, tactile, cerebral) » the parasympathetic division of the ANS causes vasodilation of the penile arterioles » Erectile tissue fills with blood creating an erection – (2) Emission & Ejaculation during climax » Emission is the movment of sperm from vas deferens into the urethra adding seminal fluid along the way, this is under sympathetic control » Ejaculation is the expulsion of semen due to strong muscular contractions – this is a spinal reflex  Male Reproductive Physiology The sexual response Erection Reflex Pathway  Male Reproductive Physiology The sexual response Emission & Ejaculation during climax – Emission is the movement of sperm from vas deferens into the urethra adding seminal fluid along the way, this is under sympathetic control – Ejaculation is the expulsion of semen due to strong muscular contractions – this is a spinal reflex » Started with the contraction of the bulbospongiosus muscle Disorders – Erectile dysfunction (ED) – Premature ejaculation – Prolonged ejaculation / anorgasmic