human reproduction anatomy of the human male main functions: the production of sperm, the male...

Human Reproduction

Anatomy of the human male

Main functions:

The production of sperm, the male gametes;

Spermatogenesis begins at puberty and continues until death;

Delivery of functional sperm to the female reproductive system


Production of Semen (a fluid comprised of):Sperm, which are expelled through the ducts during ejaculation (≈1% of semen volume);Glandular secretions that carry, nourish, and protect the sperm (mostly sugars & buffers)

Testes (plural):Glands that produce sperm; located outside abdominal cavity within the scrotum Scrotum ≡ (saclike pouch ≈ 1-3°C below normal body temperature - sperm can only form at this lower temperature)

How sperm leave the testes

Seminiferous tubules: carries/stores sperm in testes

Epididymis: a series of coiled ducts for maturation & temporary storage of sperm

Vas deferens: tube which carries sperm past connecting lubricating and support glands


Lubricating and support glands:

(a.) Seminal vesicles: secrete sugar-rich fluid that protects & nourishes sperm

(b.) Prostate gland: produces an alkaline fluid that neutralizes both urine in the male urethra and the acidic environment of the vagina

(c.) Bulbourethral glands: secrete fluids that lubricates the male urethra and allows easier coitus (intercourse)


Urethra: tube in the penis that transports semen out of the male’s body; also transports urine from the urinary bladder

Penis: copulatory organ; transient tumescence

Ejaculation: the release of semen through rhythmic contractions of smooth muscle in the Vas deferens

Anatomy of the human female

Main functions:

To produce the female gametes (ova);

To receive sperm;

To provide a suitable environment in which a fertilized ovum might develop during pregnancy


Ovaries:

Contain follicles that nurture ova;

Produces sex hormones;

Functional from puberty to menopause


Oviducts (Fallopian Tubes):

Convey (move) ova towards the uterus;

Muscular contractions & cilia draw ovum (egg) into oviduct;

Location for fertilization to occur


Uterus (womb):Nourishes development of fertilized zygote;Opens into the vagina at cervix

Vagina:Receives the penis during coitus;Forms the birth canal; Multiple layers of expandable smooth muscle;Potential, not defined, space

Puberty

Puberty: when secondary sexual characteristics develop and the potential for sexual reproduction is reached (sperm production or ovulation)

Changes are controlled by hormones that initiate development of secondary sex characteristics;Primary sex characteristics are internal and external reproductive organs (genitalia)

Puberty in males (♂)

Secondary sex characteristics: Primary hormone: testosterone (testes);2° Characteristics: increased hair (body, pubic, & facial), muscle development, deeper voice;Spontaneous ejaculation

Puberty in females (♀)

Secondary sex characteristics: Primary hormone: estrogen (ovaries);2° Characteristics: breast development, broadened pelvis, distribution of body fat; increased hair (body & pubic);Menarche (onset of menstruation)

Testosterone (♂ testes):Sperm production & secondary sexual characteristics

Estrogen (♀ ovaries);Ova production, preparing uterus for fertilized zygote & secondary sexual characteristics

Reproductive hormones

Hormonal control of the testes

Androgens, (testosterone most important), stimulate sperm production

They also maintain homeostasis by a negative feedback mechanism that inhibits the secretion of FSH (follicle-stimulating hormone) and LH (luteinizing hormone)

Stimuli from otherareas in the brain

Hypothalamus

Releasinghormone

Anteriorpituitary

Negative feedback

FSH LH

Testis

Androgenproduction

Spermproduction

Oogenesis: Production of ova

Oogenesis occurs within the ovaries Lifetime supply of primary oocytes is present at

birth that are ‘frozen’ in Prophase I One (maybe more) primary oocyte matures each

menstrual cycle to form a secondary oocyte + polar body

If the secondary oocyte is fertilized, it completes meiosis and becomes a haploid ovum + another polar body

Oogenesis: Production of ova

Ovum maturation in ovary

releasesprogesterone

maintainsuteruslining

produces estrogen

Reproductive Cycle of the Adult Human Female

A cyclical pattern of hormone secretion and reproductive events.

Humans and many other primates have menstrual cycles.

If implantation of a fertilized zygote does not occur, the endometrium (lining of uterus) is shed through the cervix and vagina in the process called menstruation.

The Menstrual Cycle• The series of changes in the female reproductive

system that includes producing an ovum and preparing the uterus for receiving it.

• Once an ovum has been released during ovulation, the part of the follicle that remains in the ovary develops into a structure called the corpus luteum.

• The menstrual cycle begins during puberty and continues for 30 to 40 years, until menopause.

• At menopause, the female stops releasing ova and the secretion of female hormones decreases.

The Menstrual Cycle

• Divided into three phases: the flow phase, the follicular phase, and the luteal phase.

• The timing of each phase of the menstrual cycle correlates with hormone output from the pituitary gland, changes in the ovaries, and changes in the uterus.

LH

FSH

estrogen

progesterone

lining of uterus

egg developmentovulation = egg release

corpus luteum

0 7 14 21 28Days

Menstrual cycle

Controlled by a complex interaction of 4 hormones:

1. follicle stimulating hormone (FSH);

2. luteinizing hormone (LH);

3. estrogen;4. progesterone

Menstrual cycle: Flow phase Day 1 of the menstrual cycle (1st phase) is the day

menstrual flow begins. The shedding of blood, fluid, mucus, and epithelial cells

that make up the endometrium (the internal lining of the uterus) begins.

Contractions of the uterine muscles help expel the uterine lining and can cause discomfort in some females.

The level of FSH in the blood begins to rise, and a follicle in one of the ovaries begins to mature as meiosis of the prophase I cell proceeds.

Menstrual cycle: Follicular phase Follicular (2nd) phase lasts from about day 6 to day

14. As the follicle containing a primary oocyte continues

to develop, it secretes estrogen, which stimulates the repair of the endometrial lining of the uterus.

Day 14 ovulation occurs:Ovulation ≡ follicle enlarges and ruptures ovary

wall; ovum is released to oviduct.Mittelschmerz: ovulation pain

Menstrual cycle: Luteal phase

Luteal (3rd) phase begins after ovulation (≈ day 15). Progesterone increases the blood supply of the

endometrium. These changes correspond to the arrival of a

fertilized ovum (zygote). If the ovum is not fertilized, the rising levels of

progesterone and estrogen from the corpus luteum cause the hypothalamus to inhibit the release of FSH and LH.

Menstrual cycle: Luteal phase Without fertilization, the corpus luteum degenerates

and stops secreting progesterone or estrogen. As hormone levels drop, the thick lining of the uterus

begins to shed. If fertilization occurs the endometrium begins

secreting a fluid rich in nutrients for the embryo.

corpusluteumovary

Female reproductive cycle

pregnancy

maintainsuterus lining

no

yes

Feedbackestrogen

eggmatures &is released(ovulation)

builds up uterus lining

FSH & LH

progesterone

progesterone

fertilized egg(zygote)

HCG

corpus luteum breaks downprogesterone drops

menstruation

corpusluteum

maintainsuterus lining

GnRH

pituitarygland

hypothalamus

Female hormones FSH & LH

released from pituitary gland;

stimulates ova development & hormone release;

peak release = release of ova (ovulation)

Female hormones Estrogen

released from ovary cells around developing ova;

stimulates growth of lining of uterus;

decreasing levels initiate menstruation

Female hormones Progesterone

released from corpus luteum in ovaries

stimulates blood supply to lining of uterus;

decreased levels sustains menstruation

Hormonal coordination of the menstrual and ovarian cycles

FSH (follicle stimulating hormone) produced by pituitary gland stimulates development of follicle

LH (luteinizing hormone) stimulates the development of the corpus luteum; stimulates ovulation

Hormonal coordination of the menstrual and ovarian cycles

Estrogen: secreted by ovaries, stimulates development of uterine lining before implantation

Progesterone: secreted by corpus luteum, maintains uterine lining during pregnancy

Fertilization Fertilization is the union of a sperm and an ovum to

form a diploid zygote. Fertilization results in a zygote and triggers embryonic

development. Occurs normally inside of fallopian tube (oviduct). Fertilization is NOT pregnancy! (PATHWAY) Tens of millions of sperm enter the vagina

cervix uterus oviducts (fertilization)sperm + ovum zygote

23(n) + 23(n) 46(2n)

Fertilization

Only one of the many millions of sperm entering the vagina will penetrate this human ovum to initiate fertilization

Fertilization

The shape of a human sperm cell is adapted to its functionSperm cell is

enzymes, DNA & mitochondria!

Multiple Fertilizations If two (or more) ova are

released in the same cycle and fertilized fraternal siblings (different DNA)

If one ova is fertilized and mitotically divides into two (or more) separate zygotes identical siblings (same DNA)

Fertilization

Implantation Implantation: The fertilized zygote implants into

thickened uterine lining and the embryo starts to secrete the hormone human chorionic gonadotropin (HCG) (the hormone used for pregnancy tests)

HCG keeps the corpus luteum functional and continuing to secrete progesterone.

By the third or fourth month, the placenta takes over for the corpus luteum, secreting enough estrogen and progesterone to maintain the pregnancy.

Implantation = Pregnancy!

Embryonic Development Development: series of orderly, precise steps that

transform a zygote into a multicellular embryoEmbryo ≡ early development stages of a

multicellular organism Includes: 1. cell division (mitotic) 2. cell growth 3. cell differentiation ≡ altering of unspecialized

mitotic embryonic cells into specialized cells, tissues,& organs

Early Embryonic Development Cleavage is the first major

phase of embryonic development It is the rapid succession

of cell divisions (Mitotic) It creates a multicellular

embryo from the zygoteNO growthEmbryonic growth

cannot occur until implantation occurs

ZYGOTE

BLASTULA(hollow ball)

Blastocoel

Cross sectionof blastula

Early Embryonic Development Stages:

1. Morula ≡ solid ball of cells

2. Blastula ≡ single layer of cells surrounding a fluid-filled cavity called the blastocoel

3. NO growth; still dividing original single cell mass

ZYGOTE

BLASTULA(hollow ball)

Blastocoel

Cross sectionof blastula

Embryonic Development

Gastrulation is the second major phase of embryonic developmentThe cells at one end

of the blastula move inward

Embryonic Development

Organs start to form after gastrulation

Embryonic tissue layers begin to differentiate into specific tissues and organ systems

Embryonic Membranes

Amnion ≡ fluid filled sac for protection

Chorion ≡ will form the embryo’s part of the placenta

Yolk sac ≡ produces first blood cells & germ cells

Chorion

Amnion

Yolk sacAllantois

Embryonic Membranes

Allantois ≡ will form the umbilical cord (ropelike structure that attaches embryo to uterus)

Umbilical cord brings nutrients in/wastes out of fetus

Ties into hepatic artery & vein in fetus - bellybutton

Chorion

Amnion

Yolk sac

Allantois

The Placenta

Placenta ≡ A growing fetus exchanges nutrients, oxygen, and wastes with the mother through the placenta

Made of maternal and fetal tissues

Substances pass both ways, but blood does not mix

Placenta Nutrients, wastes, & gasses diffuse across capillaries

Fetal Development

Gestation is pregnancy It begins at implantation and continues until

parturition (birth)● Pregnancy in humans usually lasts about 280 days,

calculated from the first day of the mother’s last menstrual period.

Embryonic development of essential organs occurs in early pregnancy.

The embryo may encounter risks from faults in its genes & from mother’s exposure to environmental factors.

Human fetal development is divided into equal trimesters

First trimester (0 to 3 months)The most rapid changes occur during the first trimester (most developmentally important)10 weekseeks10 weeks

10 weeks

4 weeks 7 weeks 10 weeks


Second trimester (4 to 6 months) Increase in size of fetusGeneral refinement of human features

12 weeks


The fetus spends much of the 2nd & 3rd trimesters just growing…

…and doing flip-turns & kicks inside amniotic sac

Week 20

Human fetal development is divided into equal trimesters24 weeks (6 months; 2nd trimester)

• Fetus is covered with fine, downy hair called lanugo

• Its skin is protected by a waxy material called vernix


Third trimester (7 to 9 months)30 weeks (7.5 months)


32 weeks (8 months)

The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming


Third trimesterGrowth and

preparation for birth

Provides time for maternal body to prepare for birth

Nooo!!! I don’t want to

go to Murdoch’s

class!

Three stages of labor

Dilation of the cervix is the first stage

Cervix starts at less than 1 cm dilation (open) and reaches full dilation at 10 cmLongest stage of

labor (6-12 hours or longer; maybe MUCH longer!)

Three stages of labor Expulsion is the second

stagePeriod from full

dilation of the cervix to delivery of the infant

Uterine contractions occur every 2-3 minutes (positive feedback)

Three stages of labor Expulsion is the second

stageMother feels urge to

push down with her abdominal muscles

Infant is forced down and out of uterus and vagina within a period of about 20 minutes

Three stages of labor

The delivery of the placenta is the final stage of laborUsually occurs

within 15 minutes after the birth of the baby

Some placenta’s are saved and frozen as they are a source of stem cells

Labor & Birth: Positive Feedback

positive feedback

The end of the journey!

And you think 9 months of

Biology is hard!

Lactation: the ‘mam’ in mammal

• Lactation ≡ milk production• Lactation is another positive

feedback system• Suckling stimulates the

hypothalamus pituitary gland to release oxytocin

• Oxytocin stimulates mammary glands to secrete milk

• Continued suckling continues milk production

Yes, males have mammary glands too!

Growth and Aging

Once a baby is born, growth and learning continue.

Human growth varies with age and is somewhat gender dependent.

Females develop earlier

An adult ages

As an adult ages, his or her body undergoes many distinct changes:

-Slower metabolism

-White hair

-Thinner bones

-Vision & hearing diminish

human reproduction anatomy of the human male main functions: the production of sperm, the male...

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