Human Reproductive System

Sexual reproduction• Sexual reproduction is the production of offspring

from two parents using gametes. The cells of the offspring have two sets of chromosomes (one from each parent), so are diploid. Sexual reproduction involves two stages:

• Meiosis- the special cell division that makes haploid gametes

• Fertilisation- the fusion of two gametes to form a diploid zygote

Basic lifecycle of sexually reproducing organisms

Male Reproductive System

• Production of sperm cells

• Deposition of these cells within the female reproductive tract

MALE REPRODUCTIVE SYSTEM

External GenitaliaExternal Genitalia1. SCROTUM (SCROTAL SACS)• The scrotum is the loose pouch-like sac of skin

that hangs behind the penis. • It contains the testicles (also called testes), as well

as many nerves and blood vessels. The scrotum has a protective function and acts as a climate control system for the testes.

• Maintains testes at 3°C lower than normal body temperature to protect sperm viability

• Special muscles in the wall of the scrotum allow it to contract and relax, moving the testicles closer to the body for warmth and protection or farther away from the body to cool the temperature.

SCROTUM WITH TESTIS INSIDE

2. PENIS- delivers sperm into the female reproductive tract. Regions of the penis

a. Shaftb. Glans penis (enlarged tip) c. Prepuce (foreskin) - Folded cuff of skin around

proximal end, often removed by circumcisiond. Internally there are three areas of spongy

erectile tissue around the urethra, three columns of erectile tissue that enlarge with blood

3. TESTES• Exocrine GlandsGlands (sperm) • Endocrine GlandsGlands (testosterone)• Each lobule contains one to four

seminiferous tubules (sperm birth!)• Tightly coiled structures• Function as sperm-forming

factories• Empty sperm into the rete testis• Sperm travels through the rete

testis to the epididymis• Interstitial cells produce androgens

such as TESTOSTERONE

4. EPIDIDYMIS

• Comma-shaped, tightly coiled tube

• Found on the superior part of the testis and along the posterior lateral side

• Functions to mature and store sperm cells (at least 20 days)

• Expels sperm with the contraction of muscles in the epididymis walls to the vas deferens

INTERNAL ORGANS

Sperm Duct and Urethra

• Sperm will move through the sperm duct or Vas deferens into the urethra

• The urethra is a tube in which sperm and urine goes through to exit the body.

• Seminal vesicle secretes semen: a liquid used as a transport medium for sperm.

Ducts Deferens (Vas Deferens)Ducts Deferens (Vas Deferens)

• Carries sperm from the epididymis to the ejaculatory duct

• Passes through the inguinal canal and over the bladder

• Moves sperm by peristalsis

• Ends in the ejaculatory duct which unites with the urethra

• URETHRAURETHRA– Extends from the base of the

urinary bladder to the tip of the penis

– Carries both urine and sperm– Sperm enters from the ejaculatory

duct

• SEMINAL VESICLESSEMINAL VESICLES• Located at the base of the bladder• Produces a thick, yellowish

secretion (60% of semen)• Fructose (sugar)• Vitamin C• Other substances that nourish and

activate sperm

Prostate GlandProstate Gland

• Encircles the upper part of the urethra– Secretes a milky fluid

• Helps to activate sperm• Helps neutralize the

acidic environment of vagina During sex

• Enters the urethra through several small ducts

Bulbourethral glands or Cowper’s glands

pea-sized structures located on the sides of the urethra just below the prostate gland. These glands produce a clear, slippery fluid that empties directly into the urethra. This fluid serves to lubricate the urethra and to neutralize any acidity that may be present due to residual drops of urine in the urethra.

SemenSemen

• Mixture of sperm and accessory gland secretions

• Advantages of accessory gland secretions Fructose provides energy for sperm cells• Alkalinity of semen helps neutralize the acidic

environment of vagina• Semen inhibits bacterial multiplication• Elements of semen enhance sperm motility

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Puberty and Testosterone

• PubertyAge at which individualsbecome capable ofsexual reproduction• Before puberty small amounts

of testosterone is LOW• During puberty testosterone

level is HIGH

• Testosterone– Produced by TESTIS– Causes development

of male sex organs in embryo, stimulates descent of testes, causes enlargement of genitals and necessary for sperm cell formation

How does the male reproductive system function?

The entire male reproductive system is dependent on HORMONES.

The primary hormones involved in are: follicle-stimulating hormone (FSH),

luteinizing hormone (LH) testosterone.

• FSH and LH are produced by the Pituitary gland located at the base of the brain.

FSH is necessary for sperm production (spermatogenesis),

LH stimulates the production of testosterone, which is necessary to continue the process of spermatogenesis.

Testosterone also is important in the development of male characteristics, including muscle mass and strength, fat distribution, bone mass and sex drive.

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Male Sexual Behavior andMale Sex Act

• Male sexual behavior– Testosterone required to initiate and maintain

• Male sex act– Complex series of reflexes that result in erection

of penis, secretion of mucus into urethra, emission, ejaculation

– Sensations result in orgasm associated with ejaculation and then resolution

Male secondary characteristics • the first body changes of puberty are the growth of the

testicles, • the appearance of pubic hair at the base of the penis

and armpits (called axillary hair) and, in some males, on the chest. he also develops facial hair

• an enlargement of the penis. • the body grows rapidly in size. The shoulders become

wider than the hips, the chest enlarges, and the muscles in the arms, legs, and shoulders grow stronger and more obvious.

• As the male sex organs grow in size, the larynx (voice box or "Adam's apple") also enlarges. As a result, men generally have a deeper voice than women.

• Control of ErectionControl of Erection• 1. Hypothalamus (conscious control)• 2. Parasympathetic nerves promotes blood flow into

penis neurotransmitter- nitric oxide? - Viagra- promotes

vasodilation• 3. Control of emission and ejaculation - sympathetic

nerves- muscle contraction• 4. Sexual excitement (parasympathetic)• - blood flow to erectile bodies, squeezes veins shut

• Ejaculation Ejaculation • Sympathetic activation• - Peristaltic contraction of smooth muscles in ducts

and glands results in ejaculation.

Female Reproductive System

The Ovaries• Ovaries: paired structures in lower portion of the body

cavity. Produce eggs (ova) in tiny cavities called follicles

• Ovaries produce estrogen and progesterone– Regulate development of secondary sex

characteristics• Mammary glands• Broadening of pelvis• Menstrual cycle

• At birth, all of the females eggs are present but in an immature form

• The ovaries produce a female hormone, called estrogen, and store female sex cells or "ova."

• The female, unlike the male, does not manufacture the sex cells. A girl baby is born with about 60,000 of these cells, which are contained in sac-like depressions in the ovaries. Each of these cells may have the potential to mature for fertilization, but in actuality, only about 400 ripen during the woman's lifetime.

Ovulation

• Release of the egg from the ovary • Egg is transported through an oviduct (fallopian

tube) to the uterus

Uterus• The uterus or "womb" is a hollow, muscular

organ in which a fertilized egg, called the "zygote," becomes embedded and in which the egg is nourished and allowed to develop until birth.

• It lies in the pelvic cavity behind the bladder and in front of the bowel. The uterus has inner lining called endometrium which change during the menstrual cycle.

• During pregnancy, the uterus stretches from 3-4 inches in length to a size which will

accommodate a growing baby.

KNOW Superstition, myth or ignorance have surrounded the menstrual period since the beginning of time. This is largely due to a primitive fear of blood. The word, "taboo," may stem from the Polynesian word for menstruation, but not all legends are negative; a girl's first menses is celebrated in some societies, because it is a sign that she can bear children.

The Cervix

• Lower end of the uterus that separates it from the vagina.

Vagina

Vagina• The vagina is a muscular passage which forms

a part of the female sex organs and which connects the neck of the uterus with the external genitals.

• it is approximately 2.5 - 4 inches long, has muscular walls which are supplied with numerous blood vessels. These walls become erect when a woman is aroused as extra blood is pumped into these vessels.

• The vagina has three functions:

- as a receptacle for the penis during sexual intercourse;

- as a outlet for blood during menstruation; - and as a passageway for the baby to pass

through at birth.

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Female Sexual Behaviorand Sex Act

• Female sexual behavior– Depends on hormones

• Androgens and steroids

– Depends on psychological factors

• Female sex act– Parasympathetic stimulation

• Blood engorgement in clitoris and around vaginal opening

• Erect nipples• Mucouslike fluid extruded into

vagina and through wall– Orgasm not necessary for

fertilization to occur

Female puberty characteristics

• Features: more delicate, face rounder, head smaller, rounder (from top). Neck: shorter, more rounded, larynx smaller.

• Shoulders: more rounded, sloping. Chest: smaller, narrower.

• Body Hair: very light and faint. • Breasts: prominent, also well-developed nipples with

large surrounding rings, • Muscles: largely hidden under layers of fat. • Pubic hair: forming straight line across at top. • Hips: wider, more rounded. •

Continue….

• Hands and feet: smaller and narrower. • Thighs: wider at top and shorter in length• he first MENSTRUATION indicates approaching

sexual maturity. In the beginning, the menstrual cycles are still irregular, and in some of them there may be no ovulation. In other words, for a while a girl may menstruate and still be largely infertile. Indeed, a woman usually gains her full reproductive capacity only one or two years after her first menstruation.

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Menstrual Cycle

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Ovulation and Follicle Fate

• Ovulation– Follicle swells and

ruptures, secondary oocyte is released from ovary

– Second meiotic division completed when secondary oocyte unites with sperm cell to form zygote

• Fate of the follicle– Graafian follicle become

corpus luteum– If fertilization occurs,

corpus luteum persists– If no fertilization,

becomes corpus albicans

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Effects of Aging

• Male– Decrease in size and

weight of testes– Decrease in sperm

production– Prostate gland

enlarges and increase in cancer

– Impotence is age-related

– Decrease in sexual activity

• Female– Menopause– Decrease in size of

uterus and vaginal wall thins

– Age related increase in breast, uterine, ovarian cancer

Fertilisation

Reproductive Process: The Implications of Cooperation Between the Sexes

• The sperm enters the cell wall of the ovum and fertilizes the nucleus, starting the process of mitosis that will lead to the embryo, fetus, and infant (upper left)

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Female Fertility and Pregnancy

• Female fertility– Sperm ejaculated into

vagina during copulation and transported through cervix and uterus

• Pregnancy– Oocyte can be

fertilized up to 24 hours after ovulation

– Sperm cells can be viable for up to 6 days in female tract

– Ectopic pregnancy: Implantation occurs anywhere other than uterine cavity

The Menstrual Cycle