Testes The testes have 2 important functions: 1) They produce sperm (male gametes). 2) They produce male sex hormones, most importantly testosterone.

Transcription

1 Bilgy 12 Unit 3B The Reprductive System The Male Reprductive System Testes The testes have 2 imprtant functins: 1) They prduce sperm (male gametes). 2) They prduce male sex hrmnes, mst imprtantly teststerne. develpment inside the abdminal cavity but descend int the scrtum during the last tw weeks f fetal develpment. The scrtum is a sac f skin utside the bdy that maintains a temperature 3ºC cler than inside the abdminal cavity due t internal bdy temperature being t high t prduce viable sperm. The scrtum respnds t temperature changes: the testes are pulled clser t the warmth f the bdy wall when cld the scrtal skin is flaccid and lse t increase the surface area fr cling, and the testes hang lwer when warm Hmestatic Imbalance Althugh testicular cancer is relatively rare (affects 1 in every 20,000 males), it is the mst cmmn cancer in yung men aged The mst cmmn sign f testicular cancer is a painless slid mass in the testis, self-examinatin f the testes shuld be practiced by every male. If detected early, the cure rate is impressive. Over 90% f testicular cancers are cured by surgical remval f the cancerus testis fllwed by radiatin therapy and chemtherapy. 1

2 Bilgy 12 Unit 3B Seminiferus Tubules Each testis is cmpsed f cmpartments called lbules that cntain 1-4 tightly ciled seminiferus (sperm prducing) tubules. When males reach puberty spermatgenesis (the prductin f sperm) begins within the seminiferus tubules and cntinues thrughut life. Within the seminiferus tubules there are als specialized cells called Sertli cells that supprt, nurish, and regulate the spermatgenic cells. If sperm grw ld in the epididymis because a male has nt ejaculated, they are eventually phagcytized by epithelial cells f the epididymis. Epididymis site f sperm maturatin which allws them t swim frward and fertilize an egg acts as a temprary strage reserve fr sperm, they can survive there fr several mnths. 2

3 Bilgy 12 Unit 3B Vas deferens prpel mature sperm frm the epididymis int the urethra. At the mment f ejaculatin, thick layers f smth muscle in its walls create strng peristaltic waves that rapidly squeeze sperm frward frm the epididymis, thrugh the vas deferens and int the ejaculatry duct. Once past the prstate gland the ejaculatry duct merges with the urethra Accessry Glands Seminal vesicles pair f seminal vesicles lie at the base f the bladder, secrete seminal fluid int vas deferens seminal fluid, a slightly alkaline slutin (ph 7.5) that mixes with sperm and accunts fr 60% f the ttal vlume f semen and cntains: Fructse an energy surce fr swimming sperm Prstaglandins chemicals that cause the uterus t cntract Prstate gland dughnut shaped gland that surrunds the upper prtin f the urethra just belw the bladder secretes a milky, alkaline fluid that accunts fr 25-30% f the ttal vlume f semen this alkalinity helps neutralize the acidity f the female s vagina, thus it prlngs the life f sperm within the female Bulburethral glands (Cwper s glands) are small pea-sized glands that lie just belw the prstate gland secrete a thick, clear mucus just befre ejaculatin ccurs that neutralizes any traces f acidic urine present in the urethra, s the sperm are nt harmed as they pass thrugh it The Penis a cpulatry rgan, designed t deliver sperm int the female reprductive tract the penis and scrtum are cllectively the external genitalia cnsists f the shaft and ends in an enlarged tip called the glans penis the skin cvering the penis is lse, and slides t frm a cuff f skin called the prepuce r freskin remval f the freskin = circumcisin 3

4 Bilgy 12 Unit 3B internally the penis cntains the urethra and spngy erectile tissue when a man is NOT sexually arused arteriles that supply the erectile tissue with bld are cnstricted and the penis remains flaccid when a man is sexually arused arteriles dilate (relax and widen), erectile tissue becmes engrged with bld and an erectin (enlargement and stiffening f the penis) results an erectin is maintained because the veins that nrmally carry bld away frm the penis get cmpressed Men wh are unable t attain an erectin suffer frm erectile dysfunctin (ED) Sperm Mature sperm have 3 distinct parts: 1) Head Nucleus cntains DNA (23 chrmsmes) that will be dnated t the egg upn fertilizatin. the nucleus is prtected by a helmet called the acrsme, which stres hydrlytic enzymes that allw the sperm t penetrate and enter an egg 2) Midpiece cntains many mitchndria that prvide energy fr mvement f the tail 3) Tail a whip-like flagellum that prpels sperm alng Did Yu Knw? Men can als have their tubes tied as a frm f birth-cntrl? The simple prcedure is called a vasectmy and is usually dne in a dctr s ffice using a lcal anesthetic. In this relatively simple peratin the physician makes a small incisin int the scrtum and then cuts thrugh and ligates (ties ff) the vas deferens. Sperm are still prduced in the testes, but they are unable t leave the male s bdy when he ejaculates. Men wh have undergne this prcedure still ejaculate seminal fluid; hwever, there is n sperm in it. Vasectmy prvides a highly effective frm f birth cntrl (clse t 100%) and it is a prcedure that can ften be reversed if the man s desires. 4

5 Bilgy 12 Unit 3B Orgasm in Males when sexual stimulatin intensifies, sperm enter the urethra frm each vas deferens, accessry glands add secretins t semen, and rhythmic cntractins cause it t be expelled frm the penis in spurts (ejaculatin) during ejaculatin a sphincter clses ff the bladder and prevents urine frm entering the urethra there is up t 400 millin sperm in 2 5 ml f semen that is expelled during ejaculatin - it nly takes ne f them t fertilize an egg Hrmnal Regulatin Teststerne a sterid hrmne prduced by interstitial cells essential fr the nrmal develpment and functining f the male sex rgans, ducts, and glands when the hrmne is deficient r absent reprductive rgans atrphy, semen vlume declines, and erectin and ejaculatin are impaired a man becmes sterile and imptent. respnsible fr male secndary sex characteristics that develp at the time f puberty. E.g. brad shulders, deep vice, nticeable hair n the face, chest, and genitals, muscle develpment, ily skin (acne). Hmestatic Imbalance Accrding t many scientific studies, there has been a gradual and nticeable decline in male fertility ver the last 50 years. Sme scientists believe the main cause is envirnmental txins, PVCs, r ther cmpunds which can mimic the effects f sex hrmnes such as estrgen. These cmpunds have the ability t blck the effects f male sex hrmnes and have been fund t ccur in ur meat and dairy supply as well as in the air we breathe. Cmmn antibitics such as tetracycline may suppress sperm frmatin; and radiatin, lead, certain cmpnents f pesticides, marijuana, lack f selenium in the diet, and excessive alchl can cause abnrmal tw-headed r multiple-tailed sperm t be prduced. 5

6 Bilgy 12 Unit 3B Hrmnal Regulatin f Spermatgenesis and Prductin f Male Sex Hrmnes invlves interactins between the hypthalamus, anterir pituitary gland, and the testes a series f events create a negative feedback lp that maintains a fairly cnstant prductin f sperm and teststerne 1 1) The hypthalamus secretes gnadtrphic-releasing hrmne (GnRH) 2) GnRH stimulates the anterir pituitary t secrete 2 gnadtrphic hrmnes: i) FSH (fllicle stimulating hrmne) ii) LH (leuteinizing hrmne) r (interstitial cell stimulating hrmne) 3) LH stimulates interstitial cells t prduce teststerne. FSH prmtes spermatgenesis in the seminiferus tubules. 2 Negative Feedback: 4) Once sufficient amunts f teststerne have been prduced, its levels in the bld inhibit the hypthalamus frm releasing GnRH. 5) When the sperm cunt is high a hrmne called inhibin is prduced in the testes - it inhibits anterir pituitary release f FSH and the hypthalamic release f GnRH and spermatgenesis is slwed r stpped. When the sperm cunt is lw, the prductin f inhibin is stpped s spermatgenesis can cntinue

7 Bilgy 12 Unit 3B The Female Reprductive System The reprductive rle f the female is far mre cmplex than that f a male. Nt nly des a female prduce egg cells, but her bdy must prepare t nurture a develping embry fr apprximately 40 weeks. Unlike the male reprductive system, the female reprductive system is NOT part f the urinary system the urethra carries nly urine and the vagina nly has reprductive functins. 7

8 Bilgy 12 Unit 3B Ovaries The varies have 2 imprtant functins: Prduce the female gametes (egg cells r va) Prduce sex hrmnes: Estrgen and Prgesterne every wman has 2 varies that are fully develped by birth varian fllicles are fund within the cnnective tissue f each vary Each fllicle cnsists f an immature egg cell, called a primary cyte After puberty, nce a mnth, ne f the fllicles matures int a secndary cyte Once mature, the fllicle ruptures and releases the secndary cyte = vulatin; the empty fllicle is called the crpus luteum Fallpian Tubes (aka Uterine Tubes r Oviducts) The functin f the fallpian tubes: carry the egg frm the vary t the uterus site f fertilizatin superir end f the fallpian tubes have ciliated finger like prjectins called fimbriae that create a current that sweeps the cyte int the fallpian tubes Nte: there is n actual cntact between the varies and the fallpian tubes the cyte is carried thrugh the fallpian tubes, t the uterus, by a cmbinatin f cilia and peristaltic wave-like cntractins an egg lives nly 6-24 hurs unless fertilizatin ccurs, fertilizatin = the fusin f male and female gametes 8

9 Bilgy 12 Unit 3B Uterus The functin f the uterus: prvide prtectin, nutritin and waste remval fr develping embry (weeks 1-8) and fetus (week 9 t delivery) cntractins f the muscular wall during child birth the uterus is a hllw muscular rgan abut the size and shape f an inverted pear The wall f the uterus is cmpsed f 3 layers: 1) Perimetrium utermst layer 2) Mymetrium muscle f the uterus, is the bulky middle layer It is cmpsed f interlacing bundles f smth muscle that cntracts rhythmically during childbirth t expel the baby frm the mther s bdy 3)Endmetrium is the mucsal inner lining f the uterus If fertilizatin ccurs, the embry burrws int the endmetrium (implants) and resides there fr the rest f its develpment, the endmetrium participates in the frmatin f the placenta If implantatin des nt ccur, the endmetrium is shed = menstruatin (apprximately every 28 days) Cervix The cervix lies at the base f the uterus where it meets the vagina. The cervix is a muscular ring r sphincter that hlds the uterus clsed and keeps the fetus in psitin until child birth ccurs. At child birth, the cervix dilates t allw the baby t be brn. glands in the cervix that secrete mucus Cervical mucus has 2 imprtant functins: 1) T blck the entry f sperm, except at mid cycle when it becmes less viscus and allws sperm t pass thrugh 2) The mucus fills the cervical canal t blck the spread f bacteria frm the vagina int the uterus Hmestatic Imbalance Cancer f the cervix is cmmn amng wmen between the ages f 30 and 50. The cancer cells arise frm the epithelium cvering the cervical tip. In a Papaniclau (Pap smear), r cervical smear test, sme f these epithelial cells are scraped away and then examined fr abnrmalities. A Pap smear is the mst effective way t detect this slw-grwing cancer, and wmen are advised t have ne every year. When results are incnclusive, a test fr human papillma virus (HPV) can be dne frm the same Pap sample. 9

10 Bilgy 12 Unit 3B The Vagina The vagina has tw majr functins: Serves as a pathway fr the eliminatin f menstrual fluids and delivery f a baby (ften called the birth canal) Receives the penis (and semen) during sexual intercurse, female rgan f cpulatin an elastic, muscular tube extending between the cervix and vaginal pening, cm lng The ph f a wman s vagina is nrmally quite acidic. This helps keep the vagina healthy and free f infectin, but is it als hstile t sperm. Did Yu Knw? Althugh vaginal fluid in adult females is acidic, it tends t be alkaline in adlescents. Therefre, teenage girls d nt psses an imprtant line f defense against sexually transmitted infectins and they are ften mre likely t transmit these infectins frm their partners. Female External Genetalia The mns pubis muntain n the pubis is a fatty, runded area verlying the pubic symphysis labia majra enclse 2 skin flds called the labia minra Barthlin s glands, 2 pea-sized glands, release mucus int the vestibule and help t keep it mist and lubricated during intercurse clitris is a small prtruding structure cmpsed f erectile tissue richly innervated with sensry nerve endings, sensitive t tuch, it becmes swllen with bld and erect when stimulated during sexual arusal 10

11 Bilgy 12 Unit 3B Physilgy f the Female Reprductive System Ogenesis Frmatin f the Egg In males gamete prductin begins at puberty and cntinues thrughut life, hwever a female is brn with all the eggs she will ever have during her life Female gametes (cytes i.e. eggs) are prduced in a prcess called genesis. Unlike spermatgenesis in males, genesis takes years t cmplete The frmatin f an cyte begins in the varies while a female is still a fetus, but the prcess is suspended until she reaches puberty. Of the 7 millin primary cytes a female is brn with, apprximately 400,000 remain at puberty. Each mnth a single primary cyte will be re-activated s it can cmplete genesis t frm a single vum (egg) 11

12 Bilgy 12 Unit 3B The Ovarian Cycle (28 days) The mnthly series f events assciated with the maturatin f an egg is called the varian cycle A typical varian cycle repeats every 28 days The varian cycle is divided int 3 phases: 1) Fllicular phase perid f fllicle grwth (day 1-14 f the varian cycle). 2) Ovulatin release f an cyte (day 14 f the varian cycle) 3) Luteal phase perid f crpus luteum activity (day f the varian cycle). 12

13 Bilgy 12 Unit 3B Fllicular Phase (Days 1 14) The maturatin f a primary fllicle int a Graafian fllicle Within each vary there are many fllicles that cntain a single primary cyte. Once a mnth, during a female s reprductive years, ne f these fllicles will mature and release an egg (~ 400 in a lifetime) During the fllicular phase the hypthalamus prduces GnRH (gnadtrpin-releasing hrmne) GnRH stimulates the anterir pituitary gland t prduce FSH (fllicle stimulating hrmne) and LH (leuteinizing hrmne) and releases them int the bldstream i. LH causes vulatin ii. FSH stimulates the maturatin f a fllicle which prduces and secretes estrgen and sme prgesterne On the 13 th day f the varian cycle there is a large increase f estrgen in the bld This estrgen spike causes the hypthalamus t release a large amunt f GnRH, leading t a large spike in the prductin f LH These events trigger vulatin Ovulatin (~ Day 14) Ovulatin ccurs when the ballning vary wall ruptures and expels the secndary cyte Once released, the cyte is swept up by fimbriae and transprted int the fallpian (uterine) tube (aka viduct) Luteal Phase (Days 14-28) The luteal phase begins after vulatin After vulatin, LH transfrms the Graafian fllicle int a crpus luteum Crpus luteum is endcrine gland that prduces and secretes prgesterne and sme estrgen int the bldstream rising levels f estrgen and prgesterne prevent (negative feedback cntrl) the anterir pituitary frm releasing LH and FSH and prevents a new fllicle frm frming If pregnancy DOES NOT ccur, the crpus luteum begins t degenerate causing estrgen and prgesterne levels t drp sharply and a wman begins t menstruate If the cyte is fertilized and pregnancy DOES ccur, the crpus luteum cntinues t prduce hrmnes until the placenta takes ver this duty at apprximately 3 mnths int the pregnancy 13

14 Bilgy 12 Unit 3B 14

15 Bilgy 12 Unit 3B The Uterine Cycle (Menstrual Cycle) The female sex hrmnes estrgen and prgesterne secreted by a develping fllicle and the crpus luteum affect the endmetrium, the inner lining f the uterus A wman s uterine cycle is generally repeated every 28 days. Days 1-5 (Menstruatin) Lw levels f estrgen and prgesterne cause the endmetrium t disintegrate and its arteriles and capillaries t weaken and rupture On day ne f the cycle, a flw f bld and tissues, knwn as the menses, passes ut f the vagina during menstruatin (menstrual perid). Menstruatin lasts frm 3-5 days, as the uterus slughs ff the thick lining that tk 3 weeks t build up. 15

16 Bilgy 12 Unit 3B Days 6 13 (Prliferative Phase) Increased prductin f estrgen by a new varian fllicle in the vary causes the endmetrium t thicken and becme vascular and glandular Days (Secretry Phase) Increased prductin f prgesterne by the crpus luteum in the vary causes the endmetrium f the uterus t duble r triple in thickness (frm 1 mm 3 mm). Prgesterne als prmtes the maturatin f uterine glands that secrete a thick mucus-like secretin By this stage f the cycle the endmetrium is ready t receive the develping embry; if this des nt ccur, the crpus luteum in the vary degenerates, and the lw levels f estrgen and prgesterne cause the endmetrium t begin breaking dwn Functins f Estrgen: 1. Prmte the develpment f secndary sex characteristic: breasts, grwth f bdy hair (underarms and pubic area), widening f hips, subcutaneus fat depsits, increases secretins f il and sweat glands 2. High levels f estrgen cause LH t be secreted frm the anterir pituitary t cause vulatin 3. Thickening (prliferative phase) f endmetrium in uterine cycle 4. At the end f pregnancy estrgen causes xytcin receptrs n uterus t becme active Maternal Changes during Pregnancy Pregnancy is the sequence f events that begins with fertilizatin cntinues with implantatin, embrynic develpment (fertilizatin t 3 mnths), fetal develpment (3 mnths t birth) and ends with birth Fertilizatin genetic material frm a sperm cell and a cyte merge int a single diplid (tw cpies f genetic inf) nucleus Sperm cell penetrates the uter glycprtein cat f the cyte, the acrsmal enzymes then digest a path thrugh the cyte t allw the nucleus f the sperm t enter the cyte ccurs hurs after vulatin in the fallpian tubes typically a 3-5 day windw in which pregnancy can ccur due t sperm being able t survive fr up t 5 days in the female; nce vulatin ccurs the cyte is viable fr 24 hurs 16

17 Bilgy 12 Unit 3B Implantatin the attachment f the rapidly dividing embry t the endmetrium; ccurs abut 6 days after fertilizatin Once implanted, the embry secretes human chrinic gnadtrpin (hcg) hcg prevents the crpus luteum frm degeneratin s it will cntinue t secrete prgesterne and estrgens; these hrmnes maintain the uterine lining 17

18 Bilgy 12 Unit 3B Placenta site f exchange f nutrients and wastes between the mther and embry Occurs during the third mnth f pregnancy frmed by the chrin (fetal membrane) f the embry and a prtin f the endmetrium f the mther prtective barrier as mst micrrganisms cannt pass thrugh it almst all drugs, including alchl can pass freely thrugh the placenta frm the third mnth thrugh the remainder f the pregnancy, the placenta prduces prgesterne and estrgen Hmestatic Imbalance Placenta previa is a cmplicatin that can ccur during pregnancy in which the placenta is attached t the uterine wall clse t r cvering the cervix. It can smetimes ccur in the later part f the first trimester, but usually during the secnd r third. The baby cannt be brn vaginally if the placenta is ttally bstructing the pening frm the wmb and must be brn by caesarean. 18

19 Bilgy 12 Unit 3B Labur (giving birth) the prcess by which the fetus is expelled frm the uterus thrugh the vagina The nset f labur is determined by cmplex interactins f placental and fetal hrmnes High levels f estrgen cause uterine muscle fibers t display receptrs fr xytcin Oxytcin is prduced in the hypthalamus and secreted frm the psterir pituitary; it stimulates uterine cntractins Psitive Feedback Cycle f Oxytcin With birth f the infant, the psitive feedback cycle is brken due t cervical distentin ending Lactatin the secretin and ejectin f milk frm the mammary glands Prlactin is secreted frm the anterir pituitary and is the hrmne respnsible fr the prductin f milk suckling f the infant causes the cntinued prductin f prlactin xytcin causes the release f milk int the mammary ducts via the milk ejectin reflex (milk let-dwn) 19

20 Bilgy 12 Unit 3B Pstive Feedback Mechanism f Prlactin and Oxytcin during Breastfeeding 20