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)

Spermatogonia divide by __

mitosis

Before puberty: spermatogonia become

all spermatogonia become more spermatogonia

After puberty: spermatogonia become

some become Type A daughter cells

others become Type B daughter cells

Spermatogonia: Type B cells become

primary spermatocytes

Spermatogonia: Type A cells become

• maintain the germ cell population

• Undergo self-renewal, remaining as stem cells

Primary spermatocytes undergo

meiosis I → Forms secondary spermatocytes

Secondary spermatocytes undergo

meiosis II → Form spermatids

Spermatids undergo

spermiogenesis → functional (but still immature) sperm

Sperm’s general areas

1. Head

   • acrosome

2. Midpiece

3. Tail

Sperm: Head

holds genetic material, has acrosome

Acrosome

• found in head of sperm

• helmetlike structure that holds hydrolytic enzymes

Sperm: Midpiece

metabolic area—contains mitochondria

Sperm: Tail

locomotor region with flagellum

HPG Axis things specific to males

1. LH stimulates interstitial endocrine cells of testes to secrete testosterone

2. FSH stimulates sustenocytes to release androgen-binding protein (ABP)

in males: LH stimulates __ cells of testes to secrete __

LH stimulates interstitial endocrine cells of testes to secrete testosterone

in males: FSH stimulates __ to release __

FSH stimulates sustenocytes to release androgen-binding protein (ABP)

in males: ABP

ABP keeps local testosterone levels in testes high

in males: HPG axis primarily works _

The HPG axis primarily works after puberty

male Fetus has a surge of _ before birth

gonadotropins and testosterone

• This surge drops quickly, does not appear again until around puberty

Effect of testosterone

Stimulates sperm production in testes

testosterone Secondary sex characteristics

1. Axillary, facial, pubic hair

2. Enhanced hair growth on chest and some body areas

3. Larynx enlargement & deepening of voice

4. Thick, oily skin

5. Increased skeletal muscle size & mass

Secondary sex characteristics

features induced in nonreproductive structures due to influence of sex hormone

Erection: When not aroused

When not aroused → arterioles supplying erectile tissue are constricted

Erection: When aroused

parasympathetic system stimulates release of nitric oxide (NO)

NO vasodilates blood vessels supplying erectile tissue

• Filling of corpora cavernosa compresses drainage vessels → prevents blood from leaving

• Corpus spongiosum also fills, but not as much

erection arousal caused by

touch, erotic sights, sounds, smells, emotional & higher mental activity** (thoughts)

Ejaculation

• propulsion of semen from the duct system

Ejaculation caused by

initiation of spinal reflex

what occurs doing ejaculation

1. Accessory glands contract & release contents to prostatic urethra

2. Internal sphincter of bladder closes

3. Bulbospongiosus muscles of pelvis contract rapidly to propel semen out of the body

Female gonads

Ovaries

Ovaries supported by

Several ligaments

1. ovarian ligament

2. suspensory ligament

3. broad ligament

ovarian ligament

• ligament that supports the ovaries

• anchors ovary to uterus

suspensory ligament

• ligament that supports the ovaries

• anchors ovary to pelvic wall

broad ligament

• ligament that supports the ovaries

• encloses the ovarian ligaments & supports uterine tubes, uterus, vagina

structure of ovaries

Each ovary has an outer cortex and inner medulla

• Cortex is where forming gametes are found

• Medulla contains blood vessels and nerves that serve ovaries

Homeostatic Imbalance of the Ovaries

Polycystic Ovarian Syndrome (PCOS)

Polycystic Ovarian Syndrome (PCOS)

• Homeostatic Imbalance of the Ovaries

• the ovaries & adrenal glands produce and release a higher-than-normal amount of testosterone

• Ovaries usually covered with multiple fluid-filled cysts

• Ovulation does not occur regularly (or at all) → leads to fertility issues

• Many with PCOS have insulin resistance → leads to increased insulin production

  • effects pancreas

PCOS Caused by

• unknown

• probably involves

  • genetics

    • seen in relatives

  • lifestyle

    • smoking

    • stress

    • sleep

    • amount for exercise

    • diet

  • environmental factor

PCOS symptoms

• irregular/light/missing menstrual periods, excess body hair, weight gain, oily skin, thinning hair, infertility, skin discoloration on neck/in armpits/under breasts

  • many secondary sex characteristic like males

PCOS treatment

• There is no cure for PCOS

• Treatment: change in diet & exercise, medications to stimulate ovulation, birth control (usually oral)

  • just symptom management

Accessory Ducts to Ovaries

1. Uterine Tubes (Fallopian tubes)

2. Uterus

3. Endometrium

Uterine Tubes

• Fallopian tubes

• Receive ovulated oocyte from ovary & is site of fertilization

• Supported by mesosalpinx (of broad ligament)

• Walls of tubes have smooth muscle cells, ciliated cells, and non-ciliated cells (supportive, ensure survival)

Regions of Uterine Tubes

1. Infundibulum: “end” of tube closest to the ovary

   • Fimbriae are fingerlike projections at end of each tube

2. Ampulla: middle portion

   • Site of fertilization (typically)

3. Isthmus: connects tube to uterus

Uterus

Receives, retains, and nourishes a fertilized egg

Uterus regions

1. Fundus: most superior dome-shaped region that meets with each uterine tube

2. Body: major portion

3. Cervix: neck of uterus leading into vagina

Glands in the cervix of the uterus _

Glands here secrete mucus to “block off” the uterus from the vagina

Uterine wall layers

1. Perimetrium

2. Myometrium

3. Endometrium

   1. Stratum functionalis

   2. Stratum basalis

Perimetrium

• outermost layer of uterine wall

  • visceral peritoneum

Myometrium

• 2nd layer of uterine wall

• contains smooth muscle

• Contracts during childbirth & without pregnancy (menstrual cramps)