Chapter 27 - The Reproductive System

Function of reproductive system

Production of offspring

Four processes allow reproduction to happen

1. Gamete formation** → sperm and ova (egg)

2. Copulation** → sperm and egg must be brought together

3. Fertilization → combining genetic content of the sperm and the egg

4. Gestation and parturition → development and birth of the fetus

Zygote

• a diploid cell resulting from the fusion of two haploid gametes

  • sometimes called a “single-celled embryo”

Embryo

Stage of development from soon after the fertilization of the ovum to week 8 of development

• no longer single-celled

Fetus

stage of development from week 8 to birth

infant

after birth has occurred

Meiosis

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

• similar in males and females

• Importance:

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

  2. Produces genetic variability

     • required for species survival, if all were exact same 1 disease could kill all

• Before meiosis begins, chromosomes in diploid (2n) parent cell replicate

  • diploid = 2n = 46

  • haploid = n = 23

Sister chromatids

• replicate chromosomes

Meiosis I steps

1. Homologous chromosomes synapse to form tetrads

2. Crossing over occurs

   • exchange of genetic material

   • (1) in pic

3. Tetrads align randomly on spindle plate

   • (2) in pic

4. Homologous chromosomes separate & move to opposite poles

   • Sister chromatids do not separate here!

   • (3) in pic

5. Cleavage occurs

   • (4) in pic

• Result of meiosis I = production of 2 daughter cells

Meiosis II

1. Formation of new spindle

2. Chromosomes line up at equator

3. Sister chromatids separate & move to opposite poles

4. Cleavage occurs

• Result of meiosis II = production of 4 haploid daughter cells

• note: no chromosome replication, no crossover

Hypothalamic-Pituitary-Gonadal (HPG) axis

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

Important structures and their role in the HPG axis

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

   • starts in brain

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

   • named after effect in female

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

   • Male: testostrone

   • Female: Estrogen and Progestrogen

Male gonads

Testes

• Enclosed & protected by scrotum

  • Composed of skin & superficial fascia

Importance of Scrotum

• Scrotum allows testes to be ~3^o lower than internal body temperature

  • sperm production needs lower temperature

  • high temperature slows down sperm production and makes them abnormal

• Musculature allows testes to maintain optimal temperature

  • Dartos muscle: changes surface area of scrotal tissue

    • contracts → decreases area → decreases heat loss

  • Cremaster muscle: changes position of testes

    • elevates → keeps them warmer

    • depress → keeps them cooler

Testes Vasculature

• Testicular arteries supply each testis

• Testicular veins drain testes

  • temperature control too

  • blood absorbs heat from arteries

• Nerve fibers, blood vessels, ductus deferens, & lymphatics form the spermatic cord

Innervation of testes

• Sympathetic and parasympathetic divisions serve each testis

Seminiferous tubules

• Function: location of sperm production

  • in the walls

• Immature sperm move through rete testis to epididymis

rete testis

• small tubes off to the side of the seminiferous tubules

• Immature sperm move through rete testis to epididymis

Testicular Cancer

• Homeostatic Imbalance

• Formation of malignant tumor in one or both testes

  • Can be seminoma or non-seminoma

    • seminoma: slightly more common 55%

    • non-seminoma: more aggressive and fast

  • usually just one testis

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

• Treatment: chemotherapy & radiation, surgery

  • 95% survival

  • surgery more common for non-seminoma

Testicular Cancer Causes

• genetics & family history

  • chromosome 12

• Klinefelter syndrome

  • XXY

• persistent/chronic inflammation

  • all forms of cancer

• bacterial/viral infection of testis

Accessory Ducts to Testes

1. Epididymis

2. Ductus deferens (vas deferens)

3. Urethra

Epididymis

• Accessory Duct to Testes

• stores immature sperm

• As sperm travel through duct → develop ability to swim

• composed of head, body, and tail

Ductus deferens (vas deferens)

• Accessory Duct to Testes

• transports sperm out of epididymis during ejaculation

• Ends at ampulla

  • Ampulla ends at ejaculatory duct

  • Ejaculatory duct empties into urethra

• The ductus deferens can be cut or cauterized → vasectomy

  • is reversible

  • no effect on testes

  • fairly effective but not immediately

Urethra (male)

• Accessory Duct to Testes

• part of urinary and reproductive system

Divisions of male urethra

1. Prostatic urethra: portion surrounded by prostate gland

2. Intermediate part: connects (1) to (3)

   • pass through body wall structures

3. Spongy urethra: runs through penis & opens to exterior of body

Penis

• Function: deliver sperm to female reproductive tract during copulation

• Ends in glans

  • Glans surrounded by prepuce

Male circumcision

• a surgical procedure involving the removal of the prepuce

• cultural

  • US: 80-85%

  • Everywhere else: <20%

• health benefit: decrease likely hood of infection

Internal Anatomy of the Penis

• Erectile tissue

  • Erectile bodies:

    • corpus spongiosum

    • corpora cavernosa

Erectile tissue

• contains connective tissue, smooth muscle, & vascular space

• Vascular spaces fill with blood

• Two erectile bodies

Corpus spongiosum

• erectile body of the penis

• immediately surrounds urethra

  • keeps it open

• Distal portion forms glans

• only 1

Corpora cavernosa

• erectile body of the penis

• paired structures that make up most of penile tissue

• have 2

Accessory Glands of Male Reproductive System

1. seminal glands

2. prostate

3. bulbo-urethral gland

Seminal glands

• Accessory Gland of Male Reproductive System

• Empty into ejaculatory duct

• seminal fluid - fluid part of semen

• Secretions produced: fructose, prostaglandins, proteins

Prostate

• Accessory Gland of Male Reproductive System

• Composed of 20-30 glands

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

  • PSA: makes semen more liquidy

• Smooth muscle walls contract during ejaculation to release contents

Homeostatic Imbalances of the Prostate

Prostate cancer

Benign prostatic hyperplasia

Prostate cancer

• Homeostatic Imbalance of the Prostate

• 1 in 6 men will develop prostate cancer

  • Usually develops later in life→age 50+

• Ranges from slow-growing to highly aggressive

  • Men usually die with it, not because of it

• Symptoms: difficulty urinating, blood in urine and/or semen, erectile dysfunction, etc.

  • Usually symptomless in early stages

Benign prostatic hyperplasia

• Homeostatic Imbalance of the Prostate

• Benign growth of prostate

• Constricts prostatic urethra → makes urination difficult & painful

Bulbo-urethral glands

• Accessory Gland of Male Reproductive System

• Produces alkaline mucus

• keeps sperm alive in the acidic vagina, as sperm are very sensitive to acidic conditions

Semen

combination of sperm with accessory gland secretions

Components of seminal secretion

1. prostaglandins

2. relaxin (and other enzymes)

3. fructose

4. antibiotic components

5. clotting factors

6. other

prostaglandins (function in seminal secretion)

• decrease viscosity of mucus in female cervix, stimulate reverse peristalsis in uterus

• make transport faster and more efficient

relaxin (and other enzymes) (function in seminal secretion)

• promote & enhance sperm motility

• swim faster and harder

Fructose (function in seminal secretion)

• catabolized for sperm ATP synthesis

• needed for sperm to move

Antibiotic components (function in seminal secretion)

• destroy bacteria that could harm sperm

Clotting factors (function in seminal secretion)

• coagulate sperm after ejaculation

• so doesn’t leave female track

Other components (function in seminal secretion)

• suppression of female immune system

Spermatogenesis

production of male gametes

Important cell types of seminiferous tubules

1. Sustenocytes

2. spermatogenic cells

3. Myoid cells

4. interstitial endocrine cells

Sustenocytes

• Important cell type of seminiferous tubules

• surround, support, and nourish developing sperm

• Adjacent sustenocytes joined by tight junctions → prevent sperm from “escaping”

Spermatogenic cells

• Important cell type of seminiferous tubules

• sperm-forming cells

Myoid cells

• Important cell type of seminiferous tubules

• contract to move immature sperm from tubules → epididymis

Interstitial endocrine cells

• Important cell type of seminiferous tubules

• secrete testosterone (with small amount of estrogen)