The Male Reproductive System

Reproductive System

Chapter 25 BIO 100

The male reproductive system

• Male genital tract

– Includes the following structures

– Sperm produced by seminiferous tubules of testes

– Undergo maturation in the epididymis

– Sperm pass through vas deferens where products are secreted by glands that contribute to semen

• Prostate

• Bulbourethral glands

• Seminal vesicles

– Semen is alkaline and contains fructose and prostaglandins

• Male gonads, the testes

– Seminiferous tubules

• Site of spermatogenesis - newly formed cells that undergo meiosis

• Sperm structure (fig. 25.10)

• Sertoli cells- nourish developing sperm

– Interstitial cells- between tubules, secrete testosterone

• Hormonal regulation in males

– Gonadotropin releasing hormone - pituitary releases FSH & LH

• FSH stimulates sperm production

• LH stimulates interstitial cells to produce testosterone

• The Epididymis leads to the Vas Deferens

• Millions of sperms are produced each day and stored in the Epididymis and the Vas Deferens

• The Vas Deferens joins the Urethra

• Urethra conducts both urine and semen

• The sperm (in semen) is conducted out of the body during ejaculation – a reflex that occurs as a result of sexual stimulation.

• Orgasm in males

– Penis is the organ of sexual intercourse

• Glans is covered by prepuce (foreskin)

– Circumcision removes foreskin

– Erection - arteries leading into erectile tissue relax, venous drainage is compressed & the erectile tissue fills with blood

– Erectile dysfunction - erectile tissue fails to fill enough to compress venous drainage

» Drugs like Viagra increase penile blood flow

• Orgasm in males

Height of excitation- increased heart rate and respiratory rate, smooth muscle contractions propel semen through urethra

• Males have refractory period after orgasm

• The Male gonads, (testes)

– Develop in the abdomen, migrate to scrotum

• Crypt orchidism-failure of testes to migrate-infertility

– Extra-abdominal location allows thermoregulation

• Spermatogenesis requires lower temperatures

• 7° cooler than core body temperature.

Male reproductive organs

Female reproductive system

• The genital tract

– Ovaries are within the abdominal cavity

• Eggs- ovulated from the surface of the ovary

– Oviducts extend from the ovaries to the uterus

• Egg migrates along oviduct propelled by cilia

– If not fertilized, only is viable for 24 hours

– Fertilization occurs midway through oviduct

• Zygote enters the uterus, implants in the endometrium

– Uterus is a thick-walled muscular organ

• Neck of the uterus (cervix) leads into the vagina

• External genitals

– Collectively called the vulva

• Labia majora- outer skin folds

• Labia minora- inner skin folds

• Glans clitoris- erectile tissue like the penis

– Cleft between labia minora contains the urethra and vestibule of the vagina

• Vagina may be partially closed by the hymen

• Note that in the female the reproductive and urinary systems are entirely separate, unlike males

• Orgasm in females

– Labia minora, vaginal walls,clitoris become engorged

– Erection of nipples

– Secretion of vaginal fluids, mucus for lubrication

– Vagina is the intercourse organ, and the clitoris plays an important role in excitation and orgasm

– Height of excitation- increased heart rate, blood pressure, and smooth muscle contractions

– Females have no refractory period following orgasm

Female hormone levels

• The ovarian cycle

– Many follicles in the cortex of ovary - each contains an oocyte

– A female is born with about 2 million follicles, but they decrease in number to about 400,000 by puberty

• Only about 400 mature throughout life, 1 per month during reproductive years

Female Reproductive System

– Oogenesis - the formation of an egg, is initiated as follicle matures

– Precursor egg cell – oogonia

– End of 1st trimester – no oogonia remain

– Oogonia have divided by mitosis and developed into primary oocytes

– Each oocyte is surrounded a follicle.

• As fetal development continues, Meiosis begins on all primary ooytes – stops at prophase of meiosis I

Female Reproductive System

– After puberty, oocytes mature into eggs – only when uterus is prepared to receive and nourish a fertilized egg.

– Primary oocyte - divides producing one haploid secondary oocyte and one polar body

• If fertilized in the oviduct, the secondary oocyte then undergoes meiosis II

– One egg and a polar body are produced

– The fertilized egg contains the diploid number of chromosomes

• If no fertilization occurs, it degenerates in 10 days and menstrual cycle begins

Ovarian cycle: Ovulation

• As the follicles develop and mature – the primary oocyte complete meiosis I

• Oocyte divides into a secondary oocyte and a polar body

• Hormones are secreted and the follicles mature until it ruptures to release the secondary oocyte – ovulation

• The secondary oocyte egg travles through the oviduct (uterine tube)

• Corpus luteum releases estrogen & progesteron

• These hormones stimulate growth of the uterine lining

• If egg is not fertilized, the corpus luteum breaks down and the uterine lining is shed - menstruation

Female hormone levels:Menstrual Cycle Control

• The uterine cycle-based on an average 28 day cycle

– Days 1-5 menstrual phase

• Drop in progesterone which causes the endometrium to break down and slough off as menstrual flow

– Days 6-13 proliferative phase

• Increase in estrogen production by maturing follicle

• Causes thickening of the endometrium

– Day 14- ovulation occurs

– Day 15-28 secretory phase

• brings about the menstrual phase

• During Pregnancy

– In summary- a source of progesterone is needed to keep the uterus in secretory phase

• Earliest source is Coropus Luteum (CL)

• To maintain the CL the embryo produces HCG (human chorionic gonadotropin) to give the placenta time to develop

• Once the placenta is functional, HCG decreases and the CL degenerates

• The placenta is now the source of progesterone

– Keeps uterus in secretory phase

– Suppresses the anterior pituitary so no new follicles form

Fetal Development

• Fertilization and pregnancy

– Zygote begins cell divisions while still in the oviduct

– Zygote develops into a hallow ball of cells - blastocyst

– Implantation occurs when embryo migrates into uterus

• Embryo at this stage consists of a ball of cells

– Embryo begins to produce human chorionic gonadotropin (HCG)

• maintain progesterone supply

– Trophoblast cells of embryo begin development of the placenta

• supplies fetus with oxygen and nutrients

• Placenta will produce progesterone and estrogen

Implantation

• After implantation, the blastocyst grwos

• Forms 2 fluid-filled sacs:

– Amnion – amniotic cavity

– Yolk sac – which develops into the embryo.

Ø Human yolk sac contains no yolk

• Body structures forms during 3rd – 6th week

• Embryo is recognizable after 2 months – usually shows Visible gonads

• Fetus responds to stimuli @ 3 months

Female hormone levels

• Estrogen and progesterone- have other effects than those in the ovarian and uterine cycles

– Estrogen

• Maintains female secondary sex characteristics

– Breast development, axillary and pubic hair, subcutaneous fat deposition

– Wider pelvis

– Progesterone - Also needed for breast development

• Menopause

– Generally occurs between the ages of 44 - 55

– Ovaries become nonresponsive to GnRH

– Perimenopause - time when cycles become irregular

• Can last 10 years

• Hot flashes, dizziness, headaches, insomnia

• Most women experience only mild symptoms or none at all

– Hormone replacement therapy

• New information suggests that disadvantages outweigh advantages

Control of reproduction

• Birth control methods

– Abstinence is the most effective!

– Oral contraceptives-contain estrogen and progesterone

• Shut down LH and FSH so no ovulation

– Intrauterine device- (known as IUDs)

• Alters the uterine environment so implantation does not occur

– Barrier methods

• Diaphragm- covers the cervix; must be used with spermicide

• Condom-also protects against STD’s; male and female versions available

– implants and injections - progesterone or combinations of estrogen and progesterone

• Function like oral contraceptives but more long term

Natural family planning

• Effectiveness depends upon education and compliance

• Less than 70% effective

• Refrain from intercourse about 3 days before to 3 days after ovulation (ovulation is difficult to predict)

• Morning - after pills

– Emergency contraception

– Taken with 72 hrs. after intercourse

– Two types, both disrupt uterine environment

• Preven- series of progesterone pills; disrupts normal cycle making implantation difficult

• RU-486- mifepristone; blocks progesterone receptors in the uterus so that the endometrium is sloughed off

• Infertility - failure to conceive after 1 year of unprotected intercourse

– 15% of couples are infertile

• 40% male, 40% female, 20% both

– Causes

• Low sperm count or sperm abnormalities

– Contribution to sedentary life style - smoking, alcohol consumption all contribute

• Body weight in women – obesity: ovulation failure

• Pelvic inflammatory disease in women blocks oviducts

• Endometriosis - uterine tissues outside the uterus; can block oviducts

Sexually transmitted diseases

• AIDS-acquired immunodeficiency syndrome

– Caused by HIV (human immunodeficiency virus)

– Infects helper T lymphocytes

– Transmitted by sexual contact including vaginal & anal intercourse and oral-genital contact

– Sharing of hypodermic needles

– Intrauterine transmission is also possible, as well as infection through breast-feeding

– Homosexual males are the largest population affected, with heterosexual females showing the greatest rate of increase

• Genital herpes- caused by herpes simplex

– Type 1 generally causes cold sores while type 2 is associated with genital lesions

– Begins as a tingling or itching sensation

• Development of blisters, swollen lymph nodes, fever, painful urination

• When blister rupture, painful ulcers develop

– After blisters heal the virus becomes dormant

• Stress, menstruation, sunlight, intercourse all may reactivate the virus

– Babies born during an outbreak may be infected

• Genital warts- human papilloma virus

– Transvaginal infection possible at birth

– Flat, raised warts on genitals

– Implicated in cancer of the cervix, vulva, vagina, anus, and penis

– No cure

– Treatment is by topical therapies or surgery

• Hepatitis infections

– Hepatitis B is an STD

• Hepatitis A is transmitted by contaminated water

• Hepatitis C by exposure to infected person’s blood

– Hepatitis B is highly contagious

• Only 50% of infected people have symptoms

• Fever, headache, nausea, muscle aches, abdominal pain, jaundice

• Can lead to liver failure

– Vaccination with HBV vaccine can prevent infection

• Chlamydia - bacterium Chlamydia trachomitis

– More new chlamydial cases diagnosed than any other STD

• 5 times as many women as men are diagnosed

– Mild lower urinary tract symptoms - painful urination, burning, mucus discharge

• Can spread to prostate in men

• Can lead to pelvic inflammatory disease in women-infertility

• Babies born to infected women may develop pneumonia and ocular infections

– Treatment- antibiotics

• Gonorrhea

– Caused by bacterium Neisseria gonorrheoae

– Males- painful urinations, greenish-yellow discharge

– Females-often no symptoms until pelvic inflammatory disease develops

– Babies born to infected mothers may develop severe eye infections leading to blindness

• All babies delivered vaginally receive prophylactic treatment with ocular anitbiotics or silver nitrate

– Treatment for gonorrhea is antibiotic therapy

• Syphilis

– Caused by the bacterium Treponema pallidum

– 3 stages of disease

• Primary stage- hard chancre sores indicates point of infection

• Secondary stage- non-itchy rash, hair loss, gray patches on mucous membranes

• Teriery stage- aneurysms, psychological disturbances, large ulcers on skin

– Congenital syphilis- crosses placenta and causes fetal blindness and malformations

– Treatment for syphilis is penicillin