Reproductive System PDF

Mr A Sosibo (PhD candidate) [email protected] Presented by Dr M Luvuno Reproduction & Pregnancy  Outline Male reproductive system Female reproductive system Pregnancy  Male Reproductive System Main structures: 1. Testes 2. Reproductive ducts epididymis,...

Mr A Sosibo (PhD candidate) [email protected] Presented by Dr M Luvuno Reproduction & Pregnancy  Outline Male reproductive system Female reproductive system Pregnancy  Male Reproductive System Main structures: 1. Testes 2. Reproductive ducts epididymis, vas deferens, ejaculatory duct, urethra 3. Accessory glands seminal vesicles, prostate gland, bulbourethral glands 4. Supporting structures scrotum, penis, spermatic cords  Male reproduction TESTES (Gonads) Primary male reproductive organs. Oval in shape and are suspended inside a sac (scrotum) by the spermatic cord The spermatic cords 1. Vas (ductus) deferens 2. arteries 3. veins 4. lymphatics 5. Nerves All are bound together by connective tissue.  Testes Produce o sperm (exocrine function): seminiferous tubules o testosterone (endocrine function): interstitial cells descend into scrotum just before birth through inguinal canal Each testis is encapsulated by a tough, white, fibrous tissue called the tunica albuginea.  The interior of the testis is divided into 250 lobules (small lobes). Each lobule contains 1 to 4 highly coiled, convoluted tubules - seminiferous tubules Interstitial cells are found in the connective tissue surrounding the seminiferous tubules The tubules (seminiferous) unite to form a complex network of channels called the rete testis giving rise the epididymis  The rete testis give rise to several ducts that join the epididymis The scrotum is a sac of skin and superficial fascia that hangs outside the abdominal pelvic cavity at the root of the penis and houses the testes Provides an environment three degrees below the core body temperature Responds to temperature changes The seminiferous tubules are involved in sperm cell production - spermatogenesis Spermatogenesis involves 5 stages: Spermatogonia (2n) – mitosis primary spermatocyte (2n) - meiosis I secondary spermatocyte (n) - meiosis II spermatid (n)- connected to each other Spermatozoa (n)-complete single cells In embryonic development germ cells migrate to the testes Spermatogenic stem cells = spermatogonia diploid (2n) = 46 chromosomes outer regions of seminiferous tubules Spermatogonia that undergo meiosis are primary spermatocytes Two cells formed = secondary spermatocytes (1n) (haploid) This is the first meiotic division Secondary spermatocytes undergo meiosis II Two haploid spermatids are produced Each primary spermatocyte produces 4 spermatids The spermatids produced are interconnected To produces separate mature spermatozoa requires the participation of the Sertoli cells This process is called spermiogenesis Sertoli cells secrete factors that regulate spermatogenesis and interconnecte d spermiogenesis Functions of Sertoli Cells Supportive: nutrients, waste materials from spermiogenesis to blood and lymph Phagocytotic: residual bodies shed by spermatids, effete cellular material Secretory: o 8th week – Mullerian inhibitory substance: suppress further development of duct. Prepubertal: prevent meiotic division of germinal epithelial cells Sexually mature: Androgen binding protein (FSH dependent) Protective: Blood-testis barrier- Occluding junctions Each spermatozoon consists of:  Head chromosomes (DNA) acrosome Acrosome has the enzymes necessary for dissolving the ovum membrane and help in fertilization.  Mid Piece: stores mitochondria for energy production  Tail is made of flagella necessary for motility of the sperm.  Sperm production begins at puberty and continues throughout life, Several hundred million sperm are produced each day Once sperm form they move into the epididymis for maturation and storage Stored in epididymis for 3-4 days and later destroyed by macrophages [sperm stored as non-motile within lumen of seminiferous tubules, epididymis, vas deferens] NB!! OVERVIEW  Duct System Epididymis Posterior to the testis First site of sperm maturation consists of a highly coiled tube that provides a place for immature sperm to mature and to be expelled during ejaculation Ductus deferens Extends from the epididymis to the ejaculatory duct Ampulla final enlargement of the duct deferens. Ejaculatory Ducts Start at the junction of the ampulla with the duct of the seminal vesicle Formed by the ductus deferens and seminal ampulla vesicles Ductus deferens and seminal vesicles converge just before they enter the prostate gland Ejaculatory ducts open into the prostatic urethra Its function is to convey sperm cells to the urethra.  Accessory glands Seminal vesicles Produce seminal fluid Secretion forms 70-80% of ejaculate fructose, other sugars, prostaglandins, proteins, amino acids, citric and ascorbic acid Secretion is thick yellow alkaline Fructose gives nourishment and energy Prostaglandins help in muscular contractions to help move sperm in female reproductive tract Contractn of SM propels secretion into ejaculatory duct Prostate Secretes prostatic fluid Fluid contains citric acid, calcium and coagulation proteins, seminal plasmin, proteolytic enzymes Secretions account for nearly 30 percent of the volume of semen The slightly acidic secretions help semen clot following ejaculation and then break down the clot. Clot breakdown involves hydrolytic action of fibrinolysin Bulbourethral glands (Cowper’s glands) pea-sized structures located on the sides of the urethra just below the prostate gland During sexual arousal secretes a clear, slippery secretion – pre-ejaculate Fluid empties into the urethra helps lubricate the urethra for the spermatozoa neutralizes any acidity that may be present due to residual drops of urine in the urethra When ejaculating, seminal vesicle contents are emptied into the ejaculatory ducts. This action greatly increases the volume of fluid that is discharged by the vas deferens. Semen Formed by sperm plus fluid from the accessory glands Urethra Important organ in both urinary and reproductive systems. In reproduction, transports sperm through the penis to outside the body.  Erection Erection, o Accompanied by increase in length and width Emission & of penis Ejaculation o Due to blood flow into erectile tissue of penis o Erectile tissue:  Two paired corpora cavernosa  Unpaired corpus spongiosum o Erection is due to parasympathetic innervation o Vasodilation of arterioles o Neurotransmitter involved is nitric oxide o Venous outflow is partially occluded – aids erection Erection, Emission Movement of semen into the urethra Emission and o Ejaculation Ejaculation o Forcible expulsion of semen from the urethra Both processes are controlled by sympathetic innervation Innervation causes peristaltic contractions of o tubular system o seminal vesicles and prostate o skeletal muscles at the base of the penis Male sexual function requires synergistic action of parasympathetic and sympathetic systems Male reproductive function is regulated by many different hormones  Checkpoint Describe the function of the scrotum Describe the process of spermatogenesis What is meant by spermiogenesis? Describe the functions of epididymis, vas deferens and ejaculatory ducts How do accessory glands contribute to the semen? What are the roles of FSH, LH, testosterone and inhibin in repro..system? MAIN STRUCTURES OF THE FEMALE REPRODUCTIVE SYSTEM Ovaries Paired abdominal organs One ovum produced by one ovary (each reproductive cycle) One ovum breaks through ovarian wall —> enters the abdominal cavity  Fallopian tubes At ovulation: Ovum enters tube (fimbriated end) Travels along tube (facilitated by cilia/smooth muscle) At fertilisation: If sperm present, fertillisation may occure Secretions from tube wall nourish zygote en route to uterus Role of oestrogen and progesterone: Movement of cilia Smooth muscle contraction Secretion of mucus from mucosal glands  Uterus (womb) Structure  continuous with uterine/fallopian tube lumen  pear shaped muscular organ between the bladder and the rectum Layers  Perimetrium: outer connective tissue layer  Myometrium: middle smooth muscle layer  Endometrium: inner epithelial layer Grows cyclically as a result of oestrogen and progesterone stimulation Shed during menstruation  Cervix (neck) Uterus narrows to form a cervix Cervix opens into the vagina Vagina Connects reproductive tract with the external environment  Physical barrier between vagina and uterus is a plug of cervical mucous  Breast (mammary gland) lobes (15- 20) divided by adipose tissue – has nothing to do with ability to nurse subdivided into lobules containing glandular alveoli secrete milk in lactating female milk is secreted into a series of secondary tubules tubules converge to form a series of mammary ducts converge to form lactiferous ducts – drains into tip of nipple lumen expands to form an ampulla (milk accumulation)  development of breasts at puberty Oestrogen - major influence on breast development Prolactin - development of oestrogen receptors Oestrogen responsible for: · increased size / pigmentation of areola · deposition of fat & connective tissue within breasts · growth & branching of ducts Progesterone - acts only on the alveoli for full development of the breasts: oestrogens + progesterone + prolactin together with growth hormone thyroxine insulin cortisol  Hypothalamus During puberty:  secretes gonadotrophin releasing hormone (GnRH) to stimulate anterior pituitary  Anterior pituitary secretes  FSH to stimulate follicle development in the ovary  LH for ovulation. Female reproductive system Ovaries (Gonads)  Primary female reproductive organs Exocrine portion  produce the ova  contain a number of follicles  each follicle encloses an ovum Endocrine portion  produce oestrogen and progesterone  Ovarian cycle The ovary consists of outer cortex and inner medulla Cortex: has developing Ovarian follicles throughout the cortex Medulla: consists of blood and lymphatic vessels along with nerve fibers  Oogenesis Formation and growth of an ovum in an ovary Germ cells migrate into the ovaries during embryonic development Towards the end of gestation, they divide by meiosis forming primary oocytes (2n) At birth there are about 2 million primary oocytes Contained in a hollow ball of cells ovarian (primordial) follicle About 400 000 at puberty 400 ovulate during reproductive life Oogenesis Follicular development Follicles enclose ovum The granulosa cells form a ring around the oocyte= corona radiata Has 2 -3 layers of follicular cells that provide a protein supply to the ovum It is attached to a protective layer of the ovum = zona pellucida Continued growth of one of these follicles results in fusion of the vesicles forming a single fluid filled cavity = antrum Follicle with an antrum = mature (graafian) follicle Summary of oogenesis and follicular development Copyright © 2016 John Wiley & Sons, Inc. All rights reserved. Copyright © 2016 John Wiley & Sons, Inc. All rights reserved.  Hormonal regulation of the female reproductive function Female reproductive cycle Positive feedback in female system allows for ovulation Positive feedback in female system allows for ovulation  Summary: Female reproductive cycle ACTIONS OF OVARIAN STEROIDS ON TARGET TISSUES OESTROGEN function: growth & proliferation Fallopian tubes: affects mucosa proliferation glandular tissue increase ciliated cells / ciliary activity Breasts proliferation of mamm. ducts deposition of fat (puberty) Uterus uterine contractility (pregnancy/ birth) Skeleton increased activity osteoblasts facilitates union epiphyses & diaphyses (limit growth in height) Pelvis broaden "outlet" of pelvis Protein metabolism protein anabolic effect uterus, breasts & skeleton Basal metabolic rate increase BMR slightly Fat deposition fat deposition in breasts, thighs & buttocks Skin increase vascularity & soften texture Water and electrolyte balance some sodium & water retention PROGESTERONE promotes secretory changes Breasts development lobules & alveoli swelling & tenderness (luteal phase) - fluid accumulation Fallopian tubes secretory changes... nutrition of ovum Uterus changes endometrium in preparation for implantation reduces uterine contractility – (pregnancy) Electrolyte balance some sodium & water retention  Checkpont Describe the principal events of oogenesis Which layer of the endometrium sheds off during menstruation Describe major hormonal changes that occur during female reproductive cycle Fertilization ovum is fertilised Fertilisation sperm reach ovary- end oviduct within 5 mins of intercourse (aided by propulsive movements fallopian tube & uterus) millions sperms introduced; only 100 - 1000 reach this point. if viable sperm meets viable ovum in tract, fertilisation likely single sperm penetrates corona radiata (acrosome rxn) makes contact with zona pellucida * Polyspermy (penetration > 1 sperm) prevented by inhibitor (contained in granules within oocyte cytoplasm) Zygote to morula Following fertilization Secondary oocyte completes meiosis II pre-embryo divides mitotically (2, 4, 8 cells etc) passage through oviduct. known as morula (ball of ≥ 8 cells) enters uterus as blastocyst (after 3-4 days) Morula to Blastocyst Blastocyst (fluid-filled ball of cells) chorion (trophoblast cells) single outer layer - develops to placenta inner cell mass below trophoblast - develops into embryo Blastocyst remains free in uterine cavity for 2-3 days Obtains nutrients from uterine gland secretions (slight size increase) Day 6: blastocyst attaches to uterine wall  Implantation Blastocyst embeds itself in endometrium - implantation. Implantation occurs 7-10 days after fertilisation Trophoblast cells secrete proteolytic enzymes These act on the endometrium permitting penetration of blastocyst into endometrial stroma. These cells + maternal cells, form the placenta & membranes of pregnancy.  Chorionic membranes Between day 7 & 12 the blastocyst becomes completely embedded in the endometrium Chorion is two cell thick  Inner cytotrophoblast  Outer syncytiotrophoblast The Inner cell mass also forms three layers  Ectoderm (nervous system and skin)  Mesodem (muscle, bones and some organs  Endoderm (gut and its derivatives) The embryo is separated from the cytotrophoblast by the amniotic cavity Embryonic blood vessels (day 14) Syncytiotrophoblast invades the endometrium It creates numerous blood filled cavities in maternal tissue It then sends projections  chorionic villi Chorionic villi surrounded by maternal blood Maternal blood within placental sinusoids supplied by uterine arteries & drained by uterine veins Embryonic chorionic villi supplied via umbilical arteries & umbilical vein Maternal & foetal circulations are separate, mixing of blood does not occur! The blastocyst secretes human chorionic gonadotropin (hCG) Prolongs the life of the corpus luteum - Identical to LH Mainted secretion of oestrogen and progesterone  no menstruation hCG secretion is essential in the first 5 – 6 weeks when the placenta is immature. hCG declines by the 10th week of pregnancy Home pregnancy tests work by detecting elevated hCG levels in urine  Pregnancy: Endocrine changes Corpus Luteum (persists through 1st trimester & secretes oestrogens & progesterone.) Corpus luteum hormones have important functions:  maintain placenta functionality  development of mammary glands  FSH & LH inhibition by negative feedback Placenta (5th week) secretes oestrogens & progesterone (in response to placental human Chorionic gonadotropin) Oest + Progest concentration increases throughout pregnancy  support development of placenta  mammary glands  inhibit ovulation After 5-6 weeks, endocrine role of corpus luteum taken over by placenta Role of contraceptive pills ?  Formation of placenta and amniotic sac During implantation, the endometrium undergoes changes cellular growth and glycogen accumulation = decidual reaction Maternal cells in contact with the chorion = decidua basalis Decidual basalis + chorion = placenta Cytotrophoblast cells form chorionic villi which invade endometrial spiral arteries  placenta (5th week+), secretes human placental lactogen hormone (hPL)  breast development (also oestrogens & progesterone)  promotes foetal growth foetal adrenals  influence oestriol synthesis in placenta (oestriol dominant oestrogen during pregnancy)  secrete cortisol and diahydroepiandrosterone  affects placental secretion oestrogens / progesterone  may initiate labour  Stages of pregnancy Fertilization to birth ~ 9 months & divided into trimesters Each is about three months long During pregnancy, the zygote undergoes 40 to 44 rounds of mitosis These produce an infant containing trillions of specialized cells organized into tissues and organs.  The First Trimester The three embryonic tissue layers form. Cellular differentiation begins to form organs during the third week After one month the embryo is 5 mm long and composed mostly of paired somite segments During the second month most of the major organ systems form, limb buds develop The embryo becomes a foetus by the seventh week  Beginning the eighth week  the sexually neutral fetus activates gene pathways for sex determination  testes are formed in XY foetuses  ovaries in XX fetuses  External genitalia develop. The Second Trimester The foetus increases in size Bony parts of the skeleton begin to form. Fetal movements can be felt by the mother.  The Last Trimester Stages of pregnancy Foetus increases in size Circulatory and respiratory systems mature in preparation for air breathing Foetal growth uses a large amount of maternal protein and calcium intake Maternal antibodies pass to the foetus during the last month conferring temporary immunity  Labour and Birth Labour = powerful contractions of the uterus that are needed to expel the foetus Two agents stimulate these labour contractions  Oxytocin (produced in the hypothalamus and released in the pituitary), & also produced by the uterus  Prostaglandins (PG2α and PG2) Labour can also be introduced artificially by injecting oxytocin or insertion of PG into the vagina as a suppository Activation of foetal adrenal cortex initiates labour: Oestrogen is important in labour initiation by promoting uterine sensitivity to oxytocin  The foetal adrenals have a cortex made up of two parts  Outer part – secretes cortisol  Inner part (foetal adrenal zone) – dehydroepiandrosterone sulfate (DHEAS) Foetal DHEAS travels to the placenta and is converted to oestrogen Rising oestrogen levels stimulate the uterus to 1. Produce receptors for oxytocin 2. Produce receptors for prostaglandins 3. Produce gap junctions between myometrial cells in the uterus - synchronise and coordinate uterine contractions (electrical synapses) Increase in PG and oxytocin receptors make the myometrium more sensitive to these agents The placenta secretes CRH which stimulates the ant pituitary to secrete ACTH ACTH stimulates cortisol and DHEAS secretion by the foetal adrenals  Cortisol secretion helps with foetal lung maturation & stimulates CRH secretion by the placenta This results in a positive feeback loop that also results in DHEAS secretion The increased DHEAS is converted to estriol Estriol activates myometrium to be more sensitive to oxytocin and PG Stages of labour Following parturition, oxytocin is important in maintaining muscle tone in the myometrium This reduces haemorrhaging from uterine arteries Promotes reduction in size of the uterus  Lactation Milk production is stimulated by prolactin from ant pituitary Prolactin secretion is controlled by prolactin-inhibiting hormone (PIH) secreted by the hypothalamus Increased oestrogen levels act on the mammary glands to block their stimulation by prolactin During pregnancy high oestrogen levels prepare the breasts for lactation but prevent secretion and action of prolactin  When the placenta is expelled as the afterbirth  oestrogen levels declines  prolactin secretion increases Taking off oestrogen inhibition to prolactin secretion Nursing maintains high prolactin levels via a neuroendocrine reflex Suckling activates sensory endings in the breast that relay impulses to the hypothalumus These inhibit PIH and may cause the secretion of prolactin releasing hormone Suckling also stimulate the reflex secretion of oxytocin Oxytocin stimulates contraction of uterus as well as the mammary glands (milk-ejection reflex) Milk production & milk-ejection reflex Hypothalamus - PIH + PSH Anterior Posterior Pituitary Pituitary Sensory Input Prolactin Oxytocin Milk production Milk ejection Suckling  Final Checkpoint Describe the process of spermatogenesis Describe the secretions from the seminal vesicles and prostate gland Discuss the physiology of male erection and ejaculation Discuss the ovarian cycle Outline functions of estrogen and progesterone How is polyspermy prevented? When, where and how does implantation occur? List hormones produced by the placenta and their functions Which hormones contribute to lactation? What is the function of each? Differentiate between the morula and blastocyst