Chapter 27 - The Reproductive System

function of reproductive system

production of offspring

4 processes that allow the production of offspring to happen

1.) Gamete formation**

2.) Copulation**

3.) Fertilization

4.) Gestation and parturition

• 1.) and 2.) are the only ones covered in this chapter

gamete formation

sperm and ova (egg)

copulation

sperm and egg must be brought together

fertilization

combining genetic content of the sperm and the egg

gestation and parturition

development and birth of the fetus

• gestation = pregnancy

• parturition = labor and delivery

2 similarities between male and female reproduction

1.) Meiosis

2.) Hypothalamic-Pituitary-Gonadal (HPG) axis

meiosis

nuclear division that occurs only in the gonads and results in the formation of gametes

2 reasons why meiosis is important

1.) Reduces the number of chromosomes in gametes by one half

2.) Produces genetic variability

why is reduction of number of chromosomes and production of genetic variability important for reproduction?

they are important for species survival - if every human was genetically identical, introducing a pathogen would kill everyone

before meiosis begins, chromosomes in diploid (2n) parent cell do what?

replicate

what do we call the replicate chromosomes?

sister chromatids - they are genetically identical (carry the same set of genes)

diploid (2n)

containing 2 complete sets of chromosomes (e.g. almost all body cells)

• in humans = 46 chromosomes

haploid (n)

containing a single set of unpaired chromosomes (e.g. the sperm and ovum)

• in humans = 23 chromosomes

homologous chromosomes

matched pairs of chromosomes containing identical genetic information

• one chromosome is inherited from mother, the second is inherited from father

• this creates the diploid number

sister chromatids

a pair of identical copies formed from the replication of a single chromosome

4 steps of meiosis I

1.) Homologous chromosomes synapse to form tetrads and crossing over occurs

2.) Tetrads align randomly on spindle plate

3.) Homologous chromosomes separate and move to opposite poles

4.) Cleavage occurs

what is crossing over?

exchange of genetic material and source of genetic variability within our population

step 3 of meiosis: homologous chromosomes separate and move to opposite poles — sister chromatids DO NOT

separate here!

what is the result of meiosis I?

production of 2 daughter cells that have half of the genetic information needed

what is different between meiosis I and meiosis II?

no chromosome replication and no crossing over in meiosis II like there is in meiosis I

4 steps of meiosis II

1.) Formation of new spindle

2.) Chromosomes line up at equator

3.) Sister chromatids separate and move to opposite poles

4.) Cleavage occurs

what is the result of meiosis II?

4 daughter cells, all of which are haploid (n)

1 round of meiosis results in the production of how many gametes?

4 gametes

Hypothalamic-Pituitary-Gonadal (HPG) axis

the interaction of hormones released by the hypothalamus, anterior pituitary, and gonads

what is the function of the HPG axis?

to regulate hormonal release by the gonads

• by regulating hormonal release, you also regulate gamete formation and other features of the body such as reproductive organ function

3 important structures and their role in the HPG axis

1.) Hypothalamus → releases gonadotropin-releasing hormone (GnRH)

2.) Anterior pituitary gland → releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in response to GnRH presence

3.) Gonads → release sex hormones and produce gametes in response to LH and FSH

male gonads

testes

scrotum

encloses and protects the testes, composed of skin and superficial fascia

importance of the scrotum

allows testes to be ~3º lower than internal body temp

why is it necessary that testes be ~3º lower than internal body temp?

sperm production optimally occurs at slightly lower temps, so if the temp of the testes is too high, it slows down spermatogenesis or creates irregular sperm

what 2 muscles of the scrotum allow the testes to maintain optimal temperature?

1.) Dartos muscle

2.) Cremaster muscle

dartos muscle

changes surface area of scrotal tissue → when it contracts, it reduces surface area, which reduces heat loss

cremaster muscle

changes position of testes → when it contracts, it elevates the testes, pulling them closer to the abdominopelvic cavity, increasing temp

vasculature of the testes

• testicular arteries supply each testis

• testicular veins drain testes (helps prevent testes from becoming too warm)

innervation of testes

sympathetic and parasympathetic divisions serve each testis

• sympathetic = slight decrease in sperm production

• parasympathetic = slight increase in sperm production

spermatic cord

formed from nerve fibers, blood vessels, ductus deferens, and lymphatics - travels from the testes where it eventually enters the body wall via the inguinal canal

seminiferous tubules function

location of sperm production - sperm are produced IN THE WALLS of the tubules (not in the open space)

seminiferous tubules - immature sperm move through

rete testis to epididymis

testicular cancer

formation of malignant tumor in one or both testes - can be seminoma or non-seminoma

seminoma testicular cancer

slightly more frequently seen, least threatening, cancerous cells are less aggressive and don’t grow as quickly

non-seminoma testicular cancer

more dangerous, cancerous cells are more aggressive and divide faster

symptoms of testicular cancer

painless lump or swelling of testis, dull pain in lower pelvis and/or lower back

testicular cancer is caused by

genetics and family history, Klinefelter syndrome, persistent/chronic inflammation

Klinefelter syndrome

XXY, develop male reproductive organs but because of the extra X, it complicates hormonal balances and reproductive organ function

treatment for testicular cancer

chemotherapy and radiation, surgery - it is one of the most easily manageable cancers

3 accessory ducts to testes

1.) Epididymis

2.) Ductus deferens (vas deferens)

3.) Urethra

epididymis

temporarily stores immature sperm

as sperm travel through the epididymis, they develop the ability to

swim, but they don’t start swimming yet

how long can sperm remain in the epididymis?

months

what happens to sperm that do not leave the epididymis?

they can’t fertilize an egg like they should, so they will be phagocytized and destroyed

ductus deferens (vas deferens)

transports sperm out of epididymis during ejaculation

the ductus deferens ends at

ampulla, which ends at ejaculatory duct, which empties into the urethra

vasectomy

• the ductus deferens can be cut or cauterized (burned)

• has no effect on the testes - still produce sperm, they just can’t leave the body

• reversible procedure

urethra

terminal portion of male duct system

urethra - for males, it is both

a urinary structure and a reproductive structure

3 divisions of the urethra

1.) Prostatic urethra

2.) Intermediate part

3.) Spongy urethra

prostatic urethra

portion surrounded by prostate gland

intermediate part of urethra

connects prostatic urethra to spongy urethra, passes through body wall structures

spongy urethra

runs through penis and opens to exterior of body

function of penis

deliver sperm to female reproductive tract during copulation

penis ends in

glans

glans is surrounded by

prepuce (foreskin)

erectile tissue

contains connective tissue, smooth muscle, and vascular space

vascular space of erectile tissue

fills with blood during arousal

2 erectile bodies

1.) Corpus spongiosum

2.) Corpora cavernosa

corpus spongiosum

immediately surrounds urethra, distal portion forms glans, helps keep urethra open (only 1)

corpora cavernosa

paired structures that make up most of penile tissue (2 - left and right)

3 accessory glands of male reproductive system

1.) Seminal glands

2.) Prostate

3.) Bulbo-urethral glands

seminal glands

empty into ejaculatory duct

secretions produced by seminal glands

fructose, prostaglandins, proteins

prostate

composed of 20-30 glands, smooth muscle walls contract during ejaculation to release contents

substances produced by the prostate

citrate, prostate-specific antigen (PSA), and substances that help activate sperm

prostate-specific antigen (PSA)

makes it easier to transfer semen from male to female

prostate cancer likeliness

1 in 6 men will develop prostate cancer - usually develops later in life (age 50+)

prostate ranges from

slow-growing to highly aggressive - men usually die with it, not because of it

symptoms of prostate cancer

difficulty urinating, blood in urine and/or semen, erectile dysfunction, etc. - usually symptomless in early stages

benign prostatic hyperplasia

benign growth of prostate (too many normal cells) - constricts prostatic urethra, making urination difficult and painful

bulbo-urethral glands

produces alkaline mucus

why is it important that bulbo-urethral glands produce alkaline mucus?

sperm are sensitive to acidic conditions of male urethra and female vagina, so the alkaline mucus neutralizes these acidic conditions

semen

the combination of sperm with accessory gland secretions

6 components of seminal secretions

1.) Prostaglandins

2.) Relaxin (and other enzymes)

3.) Fructose

4.) Antibiotic components

5.) Clotting factors

6.) Other

function of prostaglandins

decrease viscosity of mucus in female cervix, stimulate reverse peristalsis in uterus (pushes sperm closer to where it needs to go to fertilize an egg)

function of relaxin (and other enzymes)

promote and enhance sperm motility

function of fructose

catabolized for sperm ATP synthesis

function of antibiotic components

destroy bacteria that could harm sperm

function of clotting factors

coagulate sperm after ejaculation

function of other components of seminal secretions

suppression of female immune system

spermatogenesis

production of male gametes (sperm)

where does spermatogenesis occur?

in the walls of the seminiferous tubules

4 important cell types of seminiferous tubules

1.) Sustenocytes

2.) Spermatogenic cells

3.) Myoid cells

4.) Interstitial endocrine cells

sustenocytes

surround, support, and nourish developing sperm - make up the bulk of the 4 cell types

adjacent sustenocytes are joined by

tight junctions, which prevents sperm from “escaping”

spermatogenic cells

sperm-forming cells, also called spermatogonia - diploid cells that undergo mitosis

myoid cells

contract to move immature sperm from tubules to epididymis - not actual muscle cells but have contractile abilities - produce peristaltic-like wave

interstitial endocrine cells

secrete testosterone (with small amount of estrogen)

why is testosterone important?

because spermatogenesis is dependent on it - it has to be around the spermatogenic cells in order for them to start the process of gamete production

spermatogonia divide via

mitosis (NOT meiosis)

before puberty, all spermatogonia become

more spermatogonia - interstitial cells are inactive and therefore not producing testosterone

after puberty, spermatogonia become either

Type A daughter cells or Type B daughter cells