Human reproduction Biology 30

testes

testes

male gonads that produce sperm and male sex hormone testosterone

seminiferous tubules

long coiled tubes in which spermatogenesis occurs

Sertoli cells

cells that make up the lining of the seminiferous tubules that supports spermatogenesis

Interstitial cells

produces testosterone which promotes development of gametes and secondary sex characteristics

epididymis

site of the final stages of sperm maturation and storage of male gametes

Ductus deferens(or vas deferens)

conducts sperm from epididymis to ejaclatory duct

Seminal vesicles

produces fructose and fluid to semen

• fructose is used as an external energy source

prostate gland

produces mucus(bulk of seminal fluid) and alkaline secretions

Cowper’s gland

produces a pre-ejaculate that neutralizes acids from any urine in the urethra prior to ejaculation

• alkaline buffer provides some protection from acids in female reproductive tract

Urethra

Tube that conducts semen from the penis used for excretory function which conducts urine out of the body

penis

carries semen into the female reproductive tract

spermatogenesis

process of spermatozoa production that occurs in between the sertoli cells of the seminiferous tubules under the influence of FSH

• sertoli cells produce hormone inhibin to regulate pace of sperm production(negative feedback turning down LH and in turn testosterone)

Parts of the spermatozoa

1. Head→has an enzyme cap called acrosome used to penetrate the egg and contains a nucleus with DNA(haploid-23 chromosomes)

2. middle piece→contains large numbers of mitochondria to provide ATP for flagellum

3. tail(flagellum)-used to propel sperm through the female reproductive tract

Semen

a viscous fluid that consists of spermatozoa and secretions from the seminal vesicles, prostate,and cowper’s gland(accessory glands)

Semen functions

1. Produces protective mucus coating on sperm

2. Alkaline buffers to neutralize acids in male urethra(urine) and vagina

3. seminal vesicle produces a fructose rich fluid which nourishes the sperm

Follicle stimulating hormone(FSH) in males

stimulates the development of male sex organs

• promotes spermatogenesis in males

Luteinizing hormone(LH)

stimulates production of testosterone by interstitial cells

• hyper-secretion of testosterone has a negative feedback effects on LH

gametes

Specialized cells involved in sexual reproduction that are haploid

• Gametes include sperm cells in males and egg cells in females

The male reproductive system

consists of the penis, scrotum, testes, an internal duct system, and accessory glands

• the penis is a copulatory organ by which spermatozoa are placed in the female reproductive system

• the scrotum covers and protects the testes and spermatozoic it maintains the testes’ proper temperature for spermatozoa production

effects of Prostrate gland

enlarges slowly after age 40 and can cause difficulties due to enlarged state

• enlarged state squeezes the urethra making urination difficult

testostorone

simulates production of spermatozoa

• elevated levels influence male secondary sex characteristics

Andropause

caused by the decline of testosterone production(around age 40)

• symptoms include: chronic fatigue, depression, loss of bone and muscle mass, and reduced sperm production

• can be treated with hormone therapy

Ovaries

produce eggs and female sex hormones

Follicles

reproductive structure within the ovary where each follicle contains a single ovum surrounded by follicular cells that support ovum development

Fimbriae

finger-like tissues at the ends of the oviducts that sweep egg from ovary into oviduct

fallopian tubes(oviducts)

tube that connects the ovary to uterus also the site of conception

Uterus

shelters the developing embryo/fetus

Endomentrium

the highly vascularized lining of the uterus that provides nutrients for the embryo/fetus

Cervix

ring of muscular tissue that is a opening to the uterus

• prevents developing fetus from entering the birth canal prematurely

vagina

receives the penis during sexual intercourse and serves as the birth canal

Vulva

external genitalia that includes the labia majora and the labia minora

Oogenesis

the process of ova(egg) formation that begins while a woman is still undergoing fetal development

• when a woman is born she already has all the eggs she will release over her reproductive life time

Ovum

Female reproductive cell released during ovulation, capable of being fertilized by sperm to form an embryo

• has a large quantity of cytoplasm that contains nutrients from the first week of development before implantation

• enveloped by successive protective layers sperm must penetrate

Follicle stimulating hormone(FSH) in Women

stimulates follicular growth and development in the ovaries which in turn secrete estrogen

Estrogen

stimulates endometrial growth during the 1st half of the reproductive cycle

• increasing levels have negative feedback effect on FSH

Luteinizing Hormone(LH)

released just prior ovulation(with a burst of FSH) in the middle of the reproductive cycle causing ovulation

• transforms ruptured follicle to become the corpus luteum

• corpus luteum releases estrogen and progesterone which prevents the shedding of the endometrial lining of the uterus

Menopause

marked by a time when a woman no longer menstruates

• usually occurs around 50 years of age

• women who have completed menopause are reproductively infertile

• symptoms-hot flashes, mood swings, increased blood cholesterol, heat disease, etc

• Hormone replacement therapy(HRT) to provie relief

Sexually transmitted infections

Infections transmitted through sexual contact, including HIV, chlamydia, gonorrhea, syphilis, and herpes

• Can be prevented through condom use, regular testing, and vaccination (for HPV and Hepatitis B)

• Symptoms may include genital sores, discharge, pain, and burning during urination.

Chlamydia

symptoms-unusual discharge from penis or vagina, burning sensation while urinating

• effects on fertility/reproductive system:

  women→can cause pelvic inflammatory disease(PID) which scars the oviduct. Increases susceptibility to HIV

• treated with antibiotics

Gonorrhea

symptoms- burning sensation while urinating and thick greenish-yellow discharge

• effects on fertility/reproductive system: lead to PID in women and can spread to the bloodstream

• treated by antibiotics

Syphilis

occurs in 3 stages

1. infectious ulcerate sores(chancres) appear at site of infection

2. appears anywhere on body but mainly palms and soles of feet

3. infection affects cardiovascular and nervous systems. large infectious ulcers called gummas appear

   • treated by antibiotics

   • can infect developing embryos causing defects or stillbirth

genital herpes

symptoms-tingling sensation and blisters in boxer short area

• effects on fertility/reproductive system: high risk of transmission from mother to unborn child. if the infant is infected blindness, neurological disorders, and death can occur

• no cure, individual carries it for life

Human Papilloma Virus(HPV)

symptoms-flat or raised warts in genetial area

• effects on fertility/reproductive system: some forms are linked to cervical cancers tumor formations on vulva, vagina,anus, and penis

HIV/AIDS Infection

symptoms destroy helpers t-cells in the body and make the body susceptible to more infections

• effects on fertility/reproductive system: children born to mothers with this infection have a high likelihood of infection

• shortened as human immune-deficiency virus

• tretament→drug therapy

menstrual cycle

last 28 days in humans and can be divided into two cycles:

1. Ovarian cycle

2. Uterine cycle

Ovarian cycle

describes the events leading to the development and release of the second oocyte

• influences pituitary hormone release and anatomical changes in the ovary’s

• involves follicular stage(days 1-13) and luteal stage(days 15-28)

Follicular stage(day 1-13)

1. follicles begin to grow and mature under the influence of FSH

2. as follicles develop they release estrogen which causes a decrease in FSH secretion

3. day 13 elevated estrogen levels cause a release of GnRH

4. this triggers a spike in LH and FSH that results in the expulsion of the secondary oocyte on day 14(ovulation)

Luteal stage(day 15-28)

1. ruptured follicle becomes the corpus luteum which secretes estrogen and progesterone which halts the growth/maturation of the follicles

2. prevents the shedding of the endometrial lining in uterus to prepare for possible implantation

3. LH begins to decline during days 21-28 which causes the corpus luteum to degenerate

uterine cycle

describe events that take place in the uterus to prepare for potential implantation

1. during days 1-7 the endometrial lining is shed(flow phase)

2. new endometrial lining begins to grow during days 8-14 under the influence of estrogen from follicles in the ovary

3. endometrium thickens and becomes vascularized(grows blood vessels) during days 14-21 due to progesterone and estrogen a fertilized egg can now reach the uterus

4. Days 22-28 endometrium begins to degrade as progesterone and estrogen secretion from corpus luteum declines

fertilization

the fusion of male and female gametes to form a single zygote. Conception typically takes place in the oviducts closest to the ovary

• enzymes in acrosome digest an opening through the protective layers(corona radiate and zona pellucida) to deliver male nucleus to the ovum structure-a zygote

• 12-24 hrs for male and female chromosomes to align before the first mitotic cell division occurs

Steps leading to fertilization

1. the ovum is released from the ovary and swept into the oviducts

• after fertilization the ovum has a viable lifespan of 24 hours

• peristaltic contractions of the oviduct and cilia sweep the ovum towards the uterus which can take 4-7 days for the ovum to meet the uterus

  2. millions of sperm cells exist the male urethra per ejauculation

• most are killed in the acidic environment of the vagina and in the passage through the cervix

• only few make it to the oviduct containing the ovum

  3. structure of the egg including the corona radiata, zona pellucida, and vitelline membrane assist as well

  4. when the sperm meets the egg there is a 12-24 period where maternal and paternal chromosomes align in preparation for the first miotic division

     • this forms a zygote with 43 chromosomes

process of cleavage

after an egg has been fertilized it travels toward the uterus with the goal of implantation

• zygote divides rapidly many times producing smaller cells each time

• at 32 cell stage, the structure is called a morula

• morula reaches the uterus in 3-5 days after conception, then begins to absorb fluid which fills the centre

• cell division without the enlargement of cells is called cleavage which produces daughter cells

process of implantation

the morula reaches the uterus within 3-5 days after fertilization and is now called a blastocyst(the structure that implants in the endometrium)

• between days 5-7 after fertilization, the blastocyst attaches to the endometrium

• trophoblast releases enzymes that digest some of the endometrium allowing it to sink into its lining(causes spotting)

• implantation is completed 10-14 days after conception and the nestling of the blastocyst into the endometrium is called implantation

parts of blastocyst

trophoblast-outer shell of cells

chorion-will form extra-embryonic membranes(formed from trophoblast cells)

• the interior cluster of cells form the inner cell mass which will become the embryo

Human chorionic gonadotropin(hCG)

secreted by the trophoblast to act like LH(which promotes the maintenance of the corpus luteum) and releases progesterone and estrogen

• progesterone and estrogen maintain the endometrium and prevent menstruation

  • hCG stops being released when the placenta is fully formed(3 months) as the placenta produces its own progesterone and estrogen

Corona radiata

the follicular cells that nourished the ovum during development in the ovary

Zona pellucida

specialized layer that can change from flexible jelly-like layer to hard impenetrable barrier once breeched by the sperm

Gastrulation

Process during embryonic development where a blastula transforms into a gastrula

• space forms between the inner cell mass and trophoblast(amniotic cavity) which is surrounded by a membrane called the amnion

• Cells migrate and rearrange to form three germ layers: ectoderm, mesoderm, and endoderm

• makes the beginning of morphogenesis

embryonic development weeks 1-4

2nd week:

• space forms between the inner cell mass and the trophoblast called the amniotic cavity and is filled by amniotic fluid

3rd week:

• mesoderm forms notochord which acts as the framework of backbone and skeleton

• nervous system starts to develop into tube from ectoderm above notochord

• heart starts forming and beating day 18

  4th week:

• blood cells form and fill new formed blood vessels

• lungs,kidney, arm/leg buds, head, eye, ears, nose all began to from and appear

morphogenesis

process by which an organism develops its shape and form during embryonic development

• involves the coordinated movements, differentiations, and growth of cells, tissues, and organs to create the final structure of an organism.

• Morphogens, signaling molecules, and gene expression play crucial roles in morphogenesis.

• Abnormalities in morphogenesis can lead to developmental disorders or birth defects.

three embryonic layers

ectoderm→outer skin including hair, nails, sweat glands, mammary glands, nervous system

Mesoderm→lining of blood vessels, lymphatic vessels, body cavities, connective tissue(blood,bone,muscle)

Endoderm→lining of respiratory system, digestive tract, urinary bladder, most internal organs

Embryonic development weeks 5-8

5th week:

• head has grown and is larger than the rest of the body

• eyes are open but not fully developed

6th week:

• limbs lengthen and move

• gonads produce hormones that influence external genital anatomy

7th-8th week:

• embryo has distinct human features

• organs are formed directed by the CNS

• eyes, nostrils and developed but shut or sealed

  end of 8th week:

• 90% of organs are formed and will continue to enlarge and mature until birth

Amnion

thin transparent membrane that fills iwth amniotic fluid and protects the embryo/fetus from physical trauma

• also allows freedom of movement and prevents limbs from sticking to the body

Yolk sac

contributes to the formation of the digestive tract

• produces embryonic blood cells and future gonads

allantois

forms the umbilical cord(2 arteries 1 vein) and eventually becomes part of the urinary bladder

Placenta

Organ in pregnant mammals that connects the developing fetus to the uterine wall, allowing for nutrient and waste exchange between mother and baby

• made of maternal and fetal tissues(inter-digitated)

• fully formed at 10-12 weeks gestation

• chorionic tissues make up half of the placenta

• transports and stores nutrients(proteins, Fe, Ca) to be released to fetus in the event the mother cannot fully provide

• transports fetal waste to mother’s blood, antibodies from mother to fetus, and gives O2 to baby while also taking Co2 from baby

Parturition(labour)

begins with uterine contractions that start as light 20-30 second long contractions and growing in frequency

• onset labour is strong contractions lasting 40 seconds or longer 15-20 mins apart

• cervical stretching signals release of oxytocin which initiate intensity of contractions

Stages of labour

1. dilation stage:

• uterine contractions/oxytocin cause the cervix to dilate an eventually cause the amniotic sac to break and amniotic fluid to be released(2-20 hrs)

  2. Expulsion stage:

• strong contractions push the baby through the birth canal

• baby’s head rotates allowing the body to pass through the birth canal(30 min-2 hrs)

  3. Placental stage:

  • shortly after the baby is delivered the placenta and umbilical cord are delivered(afterbirth)

Caesarean section

surgical procedure where baby is removed through an incision in the mother’s abdomen

• required if baby is not in correct head down position and cannot be turned, mother has infectious STI, mother has narrow plevis

First trimester

first 8 weeks fall under embryonic development

during the last 4 weeks:

• growth in body length accelerates and growth of head slows

  end of 12th week→cartilage begins to calcify into bone and genitalia can distinguish the sex of the fetus

Second trimester

weeks 13-24 and the physical signs of pregnancy(morning sickness, baby bump) begin to show

• the baby brain grows rapidly and the nervous system starts to fully function

• mother feels fetal movement

• fine soft hair and oily secretions protect and cover the developing skin which appears wrinkled as the fetus has no stored fat

third trimester

weeks 25-38 where fetal brain cells from rapidly

• testes descend into scrotum for males

• layers of subcutaneous fat collects under the skin

• digestive and respiratory systems are the last to mature

Teratogen

agent that causes a structural abnormality due to exposure during pregnancy

• especially significant during the first 9 weeks when the developing embryo/fetus are highly sensitive to environmental factors

  • Cigarettes→smoking or second-hand smoke can cause underweight babies, stillbirths, reduced intellectual ability

  • Alcohol→fetal alcohol syndrome(FAS), decreased weight/height, facial malformations

  • Drugs→eg.thalidomide, causes deformations

  • xrays, pollutants, and large amounts of vitamins(vitamic c) also

Lactation

The production and secretion of milk from the mammary glands, typically occurring in female mammals after giving birth

Prolactin

the hormone needed for milk production that is not secreted during pregnancy due to being suppressed by high levels of estrogen and progesterone

• before birth the breasts secretes colostrum→watery, yellowish fluid similar to milk but contains more protein and less fat. Alos rich in antibodies

Process of breast feeding

• baby suckling stimulates the release of milk from the mother’s breast. baby stimulates nerve endings in nipple and areola sending impulses to hypothalamus, then the posterior pituitary to release oxytocin

• oxytocin causes contracts of mammary lobules that contain alveoli(sacs with milk) which results in the flow of breast milk

• if suckling does not occur milk productions stops

sterile

permanent condition where a person cannot have children

Infertile

condition that causes someone to have very low reproductive potential. sometimes it can be corrected

surrogacy

when a woman is contracted to carry a baby for them

genetic surrogate→mother uses her own eggs(artificial insemination)

gestational surrogate→genetically unrelated to the child(in-vitro fertilization)

Artificial insemination

a reproductive technique used to assist in achieving pregnancy.

• involves the introduction of sperm into a woman's reproductive system, bypassing natural fertilization.

• can be done using fresh or frozen sperm, and it is commonly used in cases of male infertility, single women, or same-sex couples

Superovulation

process that stimulates the release of multiple eggs a sa result of hormone treatment

• often used prior to IVF

Surgical sterilization

surgical form of making someone sterile either a tubal ligation(women) or vasectomy(men)

• Tubal ligation→cutting the oviducts and tying off the ends to prevent egg from reaching the uterus and sperm from reaching the egg

• vasectomy→vas deferens is cut and tied so that semen deos not contain sperm(gametes)

Emergency contraception

Method used to prevent pregnancy after unprotected sex or contraceptive failure

• it contains higher doses of hormones (like progestin) to inhibit ovulation, fertilization, or implantation.

Inhibin

produced by sertoli cells in response to elevated spermatogenesis and reduces the secretion of FSH from anterior pituitary gland

In-vitro fertilization(IVF)

technique in which the ovum is fertilized by the sperm outside of the body. the resulting embryo is reintroduced to the uterus

Steps of IVF

1. stimulation(superovulation)-fertility drugs causes the ovaries to produce more than one egg a month

2. egg retrieval-follicular aspiration, removes eggs from womans body

3. Insemination and fertilization-sperm is placed with best quality eggs an undergoes insemination(mixing sperm to egg) than

4. Embryo culture-fertilized egg divides and becomes an embryo

5. embryo transfer-multiple embryos placed into uterus 3-5 days post egg retrieval and fertilization(may result in multiple pregnancies)