Bio 30- Reproductive System

Role of the Male Reproductive System

To produce sperm and deliver them to the

female.

When a sperm combines with an egg, it contributes half the genetic material of the offspring and, in humans and other mammals, determines its sex.

Scrotum

•pouch of skin to hold testes outside of the body (membrane forms over canal) which prevents the testes from re-entering the abdomen)

• sperm cannot develop at body temperature (testes do not descend? STERILE MALE)

Urethra and Ejaculatory duct

•conducts semen through the penis

• carries urine from the bladder to the exterior of the body

Epididymis

•coiled tube where sperm matures and develops (becomes motile)

Vas Deferens

•conducts sperm from epididymis to urethra via ejaculatory duct

FYI- the van deferens is also known as the ductus deferens

Penis (Glands Penis and Foreskin)

•transfers sperm from male to female reproductive tract

•contains the urethra

Testes (testicles)

•produces sperm and sex hormones (testosterone)

Seminiferous Tubules

•bundles of coiled tubes (total length 500m) leading to the epididymis

•produce immature sperm cells -site of spermatogenesis (formation of sperm cells)

Urinary Bladder

•holds and eliminates urine

Rectum and Anus

•holds and eliminates waste

Glands that contribute fluids to semen

-seminal vesicles

-prostate gland

-cowpers gland

Seminal Vesicles

•contributes fructose, prostaglandins, and fluid to semen

Prostate Gland

•contributes to alkaline and mucous fluids to semen

•protects sperm against the acidic environment of the vagina

Cowper’s Gland

•contributes alkaline and mucous fluids to semen

•secretes a mucus-rich fluid prior to ejaculation

Path of sperm from production to ejaculation

testis (site of production)

→ epididymis (stored)

→ vas deferens (transfer tube)

→ seminal vesicle (adds fructose, prostaglandins)

→ prostate gland (adds alkaline, mucous)

→ Cowper’s gland (adds alkaline, mucous)

→ urethra (now called semen)

→ out!

Sexual Excitement (erection)

•erectile tissue in penis fills with blood

•parasympathetic: arteries leading to penis dilate

•sinuses swell, veins constrict keeping blood in the penis

*impotency (erectile dysfunction)-penis fails to become erect

Seminiferous Tubules and Interstitial

Tissues

-interstitial cell

-spermatogonium

-sperm

-Sertoli cell

Interstitial Cell

•hormone-secreting cells (secrete testosterone) that lie outside of the seminiferous tubules of the testes

Spermatogonium

•a diploid germ cell that at puberty will be stimulated by hormones to become a sperm cell

Sperm

•the male gametes carry 23 chromosomes to fertilize an egg (female also contains 23 chromosomes)

Sertoli Cell

•cells in the seminiferous tubules that support and nourish developing sperm cells

Mature Spermatozoa (sperm)

•produced by a process called spermatogenesis in the testes.

•meiotic division of spermatocytes produces spermatids which then differentiate into mature sperm

Sperm Info

•sperm are quite simple in structure because their sole purpose is to swim to the egg and donate their genetic material.

•they are composed of three regions: headpiece, midpiece, and tail.

•sperm do not live long (only about 48 hours), but they swim quickly and there are so many of them (millions per ejaculation) that some are able to reach the egg tofertilize it

Acrosome

•stores enzymes needed to penetrate the protective layer of the egg

Nucleus

•contains 23 chromosomes (half the genetic information needed for a human being)

Mitochondrion

•provides energy to move the tail (flagellum)

Head

•contains the nucleus (genetic material) and is covered by the acrosome cap

Midpiece

•contains mitochondria for energy

Tail (flagellum)

•propels the sperm with a lashing motion (speed: about 3mm/hr)

Sperm and the Scrotum

Sperm production occurs at ~ 35°C

(which is a few degrees lower than

body temperature) so the scrotum

holds the testes outside of the body

to facilitate sperm development at

this lower temperature

Sex Characteristics

The chromosome

combination that results in an

offspring that is

• genetically male: XY

• genetically female: XX

Male Reproductive Negative Feedback Loop

LH → interstitial cells →

testosterone

FSH → Sertoli cells

(seminiferous tubules) →

sperm

2 hormones that affect spermatogensis

-testosterone and FSH

Andropause

-Occurs around age 40 when testosterone levels begin to decrease

Symptoms: fatigue, depression, loss of muscle/ bone loss, decreased sperm production

Treatment: low doses of testosterone

Prostate Enlargement

FYI: Hormonal changes can lead to the enlargement of the prostate gland as the male ages.

Symptoms: discomfort, urinary difficulties (prostate squeezes on urethra) such as

burning sensation when peeing or frequent urination

Treatment: surgery (if cancerous); antibiotics (to reduce inflammation of prostate =

prostatitis)

Diagnosis: digital rectal exam, PSA (enzyme) test

Ovarian Cycle

•takes place in the ovaries

Uterine Cycle

•takes place in the uterus

Significance of the Menstrual Cycle

•The menstrual cycle ensures that an ovum is released at the same time as the uterus is the most receptive to the fertilized egg.

• Having about one cycle every month also allows humans to reproduce many times in a year (as opposed to some animals that breed/reproduce seasonally) which ensure the continuation of human species.

• The hormone responsible for follicle growth is FSH and for ovulation is LH

Corpus luteum

The principal hormone secreted by the corpus luteum (structure formed after the egg has ruptured from the ovary) is progesterone.

Function of Progesterone

•maintaining the thickening of the uterine lining (causes more blood vessels to develop- “vascularization”- in endometrium)

•prevents uterine contractions and inhibits LH through negative feedback

•maintains the embryo the first 12 weeks of development

•inhibits the development of more follicles

Negative Feedback for Hormonal Control

What Happens When the Ovum is Fertilized

•Ovum implants in the endometrium

•Blood progesterone and estrogen levels remain high (they are stimulated by hCG produced by the embryo)

•High progesterone levels maintain the endometrium to support the developing fetus and high estrogen levels stop the ovarian cycle so no more will follicles will mature

•more estrogen, less FSH= no more development

Luteal Stage

•LH stimulates the follicle to develop into the corpus luteum

•the corpus luteum secretes the progesterone and some estrogen

•as the levels of these hormones rise in the blood, they inhibit FSH and LH (anterior pituitary)

•when the corpus luteum degenerates, estrogen and progesterone levels decrease (results in shedding of endometrium= menstruation)

•this causes the anterior pituitary to increase the secretion of FSH and the cycle begins again!

Pictures of Hormones and Phases

GnRH

•secreted in the hypothalamus

•targets the anterior pituitary gland

•stimulates release of FSH & LH

•triggers puberty

FSH

•secreted in the anterior pituitary gland

•targets the ovaries (follicles)

•stimulates the growth and development of the ovarian follicle and female sex hormones

LH

•site of secretion: anterior pituitary

•targets the ovaries (follicles and corpus luteum)

•stimulates (triggers) ovulation

•stimulates growth and development of corpus luteum

Estrogen

•site of secretion: ovaries-follicles (follicular phase before ovulation) → ovaries-corpus luteum (luteal phase after ovulation)

•targets all body cells

•stimulates the development of the female repro tract and secondary sex characteristics

•at high levels, stimulates LH surge

•initiates the growth of the uterine lining

Progesterone

•site of secretion: ovaries-corpus luteum (luteal phase after ovulation)

•targets the uterus

•maintains the growth of the uterine lining

•inhibits uterine contractions

•maintains embryo in 1st 12 weeks of pregnancy

Ovarian Cycle

A follicle contains an immature ovum. In a single ovarian cycle one follicle matures, releases an ovum (ovulation) and then develops into a “yellow-body” called the corpus luteum.

Divided into 2 stages

Follicular Stage

•begins with the increase of FSH (from the anterior pituitary)

•several follicles develop at once → only one follicle will matures (the Graafian follicle)

•as the follicle matures, it releases estrogen

•the rising levels of estrogen inhibits the release of FSH from the anterior pituitary

•at the same time this triggers the release of GnRH from the hypothalamus→ the results in a sharpe increase in LH production

•LH triggers the follicle to burst open and release the ovum= ovulation

Menstrual Cycle

•female reproductive system follows a cyclical pattern

•usually about 28 days

•cycle begins with menstruation and ends with the start of the next menstrual cycle.

Uterine (Menstrual) Cycle

Day 1-5 “flow phase”

-corpus luteum has degenerated (menstruation)

Day 6-13 “follicular phase”

-estrogen is high to stimulate endometrium to thicken (secretes estrogen)

Day 14 “ovulatory phase”

-LH stimulates mature follicle to rupture and release the ovum from the ovary

Day 15-28 “luteal phase”

-release of progesterone by the CL maintains the thickening of endometrium (thickness doubles or even triples)

LH & FSH

These hormones from the AP have numerous effects

-FSH stimulates development of ovarian follicles resulting in the releasing of estrogen

-Estrogen levels peak stimulating a surge in LH and trigger ovulation

Hormone Levels

-Of the follicles that begin developing in response to FSH usually only one (Graafian Follicle) become dominant

-In the first half of the cycle, estrogen is secreted by developing Graafian follicle

-later, Graafian follicle develops into the CL which secretes large amounts of progesterone.

Ovulation

Occurs in day 14 of the menstrual cycle. LH stimulates the ovum to burst out of the mature follicle in the ovary.

Pituitary LH & FSH

The Female

-The female reproductive system in mammals produces eggs, receives the penis and sperm during sexual intercourse, and houses and nourishes the young.

-Female reproductive in mammals are similar in their basic structure (uterus, ovaries, etc.) but the shape of the uterus and the form of the placenta during pregnancy vary

Uterus (womb)

•houses the developing fetus

Oogenesis

•1 mature gamete produced (plus 3 polar bodies that die off)

•Divison of cytoplasm: unequal: 1 viable egg/ovum and 3 polar bodies

•Is meiosis continuous: NO- eggs remain on meiosis until puberty

•At puberty, ovary contains 300,000 to 400,000 eggs. One egg matured each month.

Spermatogenesis

•number of mature gametes produced: 4= sperm

•divison of cytoplasm: equal divison of cytoplasm

•is meiosis continuous: YES- males produce sperm from puberty until death

•are continuously produced: about 300 to 500 million per day

Endometrium

•lining of the uterus- supplied with blood vessels to provide nutrients for the fetus

Fallopian Tube (oviduct)

•conducts egg from ovary to uterus; location where fertilization occurs

Fimbraie

•fingerlike projections that sweep the ovum into the fallopian tube (oviduct)

Ovary

•produces eggs (process: oogensis) and sex hormones

Follicles

•specialized cells in which an ovum (egg) develops, matures, and ruptures from each month

Cervix

•narrow opening to uterus- sperm enter single file; must dilate to accommodate birth of baby

Vagina

•receives penis during sexual intercourse; birth canal; exit for menstrual flow every month

Labium Minora and Majora (the vulva)

•– two pairs of skin folds (minora: inner fold, majora: outer fold) that protects the vaginal opening

Clitoris

•sensitive apex of the vulva that elicits a sexual response when stimulated causing pleasure due to high concentration of nerve endings

Urinary Bladder and Ureter

•holds and eliminates urines and carries urine from the bladder to the exterior of the body

Rectum and Anus

•holds and eliminates wastes

Menstruation

When the endometrium (uterine lining) disintegrates and its tissues and blood flow out of the vagina – occurs monthly if the ovum is not fertilized

Ovulation and Implantation

Fertilization occurs in the fallopian tube, after which it passes down into the uterus.

Eggs or ova are produced by the ovaries and are released at ovulation.

The unfertilized egg lives only for a day or so. It travels along the fallopian tube, where fertilization may occur if sperm are present.

If the egg is fertilized it will become implanted in the lining of the uterus.

If it is not fertilized the prepared lining is shed, passing out through the vagina in the process called menstruation

Unfertilized Ovum Path from Production to Out of the Body

Follicle in ovary (follicle bursts and ovum is released = ovulation)

→ (fimbriae)

→ Fallopian tube (oviduct)

→ uterus

→ cervix

→ vagina

→ out

Fertilized Ovum Path from Production to Out of the Body

Follicle in ovary (follicle bursts and ovum is released = ovulation)

→ (fimbriae)

→ uterus

→ Fallopian tube (oviduct) where the ovum is fertilized by a sperm

→ implants in endometrium and grows for 9 months

→ exits at birth through the cervix

→ vagina

→ out

Human Egg (Ovum)- diagram

Oogenesis vs Spermatogenesis

Egg

•about 100 nanometers in diameter

•haploid (n) 23 chromosomes

•can only survive for one day using energy from mitochondria

•140,000 mitochondria in cytoplasm

•eggs are not motile

•covered in zona pellucida

•lots of cytoplasm

•FSH

Sperm

•head 5 nanometers, midpiece 5 nanometers, and flagellum is 40 nanometers (smaller than egg)

•haploid (n) 23 Chromosomes

•mitochondria creates energy and processes fructose

•50-100 mitochondria in midpiece

•are motile

•sperm has acrosome cap to digest coating of egg

•little cytoplasm