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Reproductive System > Sexual Development > Flashcards

Sexual Development Flashcards

1
Q

Outline the components of internal male genitalia.

A

Gonad = testis

Duct system:

  • epididymis
  • vas deferens
  • urethra

Glands:

  • seminal vesicles
  • prostate gland
  • bulbourethral/Cowper’s glands
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2
Q

Outline the components of internal female genitalia.

A

Gonad = ovary

Duct system:

  • Fallopian/uterine tubes
  • uterus
  • cervix
  • vagina
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3
Q

Outline the components of external male genitalia.

A

Penis

Scrotum

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4
Q

Outline the components of external female genitalia.

A

Vulva (everything that is externally visible):

  • mons pubis (mound of fatty tissue above pubic bone)
  • vestibule (cleft containing vaginal and urethral openings)
  • labia minora (inner folds of skin and erectile tissue)
  • labia majora (large, fatty, outer folds of skin tissue)
  • clitoris (erectile tissue) + prepuce (clitoral hood)

Glands:

  • Skene’s glands
  • Bartholin’s glands

Hymen = thin mucous membrane partially covering vaginal opening

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5
Q

List the male secondary sexual characteristics.

A
  • increased relative body size/height
  • body composition: muscle mass and fat distribution (e.g. muscular pectorals, less fat overall, narrow hips)
  • androgenic hair pattern and skin (inc. male pattern baldness)
  • CNS/behavioural changes
  • body odour
  • deeper voice
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6
Q

List the female secondary sexual characteristics.

A
  • reduced relative body size/height
  • body composition: subcutaneous fat distribution (preparation for gestation and lactation)
  • feminine hair pattern and skin
  • breast development (preparation for lactation)
  • CNS/behavioural changes (mainly due to absence of male steroid hormones but some feminising factors too)
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7
Q

What are the different stages of sexual development and differentiation?

A

INDIFFERENT STAGE (gonad + duct system)

STRUCTURAL DEVELOPMENT (in utero; 3-8 weeks)

FUNCTIONAL DEVELOPMENT (continues after birth) 
& MATURATION (puberty: development of secondary sexual characteristics) 
= time at which the onset of sexual maturity occurs and the reproductive organs become functional
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8
Q

Describe the embryological development of the indifferent gonad.

A
  1. Proliferation of epithelium and condensation of underlying somatic mesenchyme forms gonadal/genital ridges (derived from urogenital ridge - intermediate mesoderm)
  2. Primordial germ cells originate in the epiblast and migrate through the primitive streak towards the genital ridge (in the lower thoracic/high lumbar region):
    - 3rd week: reaching the wall of the yolk sac (close to the allantois)
    - 4th week: moving along the dorsal mesentery of the hindgut (through retroperitoneum)
    - 5th week: arriving at primitive gonads
    - 6th week: invasion of genital ridges

note: halted migration —> extra-gonadal tumours e.g. seminoma
3. Once the primordial germ cells have arrived at the genital ridges, the epithelium of the gonadal/genital ridge proliferates and penetrates the underlying mesenchyme —> forming the primitive sex cords (connecting the indifferent gonads to the surface epithelium)

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9
Q

Describe how the indifferent gonad develops into a testis in the male.

A
  1. Expression of SRY gene on Y chromosome (also known as testis-determining factor gene)
  2. Primitive sex cords continue to proliferate and penetrate the underlying medulla to form the medullary/testis cords:
    - in hilum of gland: testis cords break up into tiny cell strands —> rete testis
    - layer of dense fibrous connective tissue separates testis cords from surface epithelium (tunica albuginea)
3. Paramesonephric tubules (Müllerian ducts) partially degenerate ---> become ductuli efferentes 
Mesonephric ducts (Wolffian ducts) becomes the vas deferens/ductus 
deferens
  1. Onset of puberty causes primitive sex cords to hollow out and become seminiferous tubules
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10
Q

Describe how the indifferent gonad develops into a ovary in the female.

A
  1. Absence of SRY genes (“default pathway”)
  2. Medullary primitive sex cords dissociate into germ cell clusters, which are replaced by a vascular stroma (ovarian medulla)
  3. Surface epithelium of ovary continues to proliferate, forming cortical cords which penetrate the underlying mesenchyme
  4. Cortical cords split into clusters, which continue to proliferate and surround each oogonium with a layer of follicular cells (together form primordial follicles)

Paramesonephric ducts (Müllerian ducts) becomes the Fallopian/uterine tubes, cervix, and upper part of the vagina

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11
Q

Contrast the development of the indifferent gonad into testes or ovaries.

A

Y influence —> testis
Absence of Y influence —> ovary

                        TESTIS                                    OVARY
        Medullary cords develop       Medullary cords degenerate
                 No cortical cords              Cortical cords develop
          Thick tunica albuginea              No tunica albuginea
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12
Q

What factors affect the presence of the mesonephric and paramesonephric ducts? How does this affect the internal genitalia present?

A

Presence of testes:
- secretion of androgens supports the mesonephric (Wolffian) duct —> mesonephric duct remains —> makes opening in urogenital sinus independent of ureteric bud —> forms vas deferens (~45cm in adult), epididymis, seminal vesicles, and prostatic urethra

  • secretion of Müllerian Inhibiting Substance (MIH) —> paramesonephric (Müllerian) duct degenerates —> no uterus formed

Absence of testes:
- no testis-derived testosterone (dihydrotestosterone) —> mesonephric duct degenerates —-> no vas deferens, epididymis, seminal vesicles, or prostatic urethra formed

  • no testis-derived MIH —> paramesonephric duct remains —> forms uterus, cervix, uterine tubes, and upper 1/3 of vagina
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13
Q

Describe the paramesonephric ducts. How do they form a uterus?

A

Invaginations of the epithelium of the urogenital ridge

Run along entire length of embryonic trunk parallel to mesonephric ducts

Cranial: open into the abdominal cavity
Caudal: make contact with most anterior part of the cloaca (urogenital sinus)

Paramesonephric ducts extend into the peritoneal cavity towards the midline (dragging the peritoneal membrane from the posterior abdominal wall) —> fuse in the midline —> uterus formed

note: abnormal development may form septum in the middle of the uterus —> bicornate uterus

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14
Q

What factors affect whether the external genitalia develop to be male or female?

A

9 weeks: indifferent stage (phallus, urethral folds, labioscrotal swelling, urogenital sinus)

12 weeks:
+ presence of testis-derived androgen hormone (dihydrotestosterone):

—> genital tubercle elongates & genital folds fuse (forming spongy urethra) —> penis and scrotum formed

  • absence of testis-derived androgen hormone:

—> no elongation or fusion —> vulva formed (urethra opens into vestibule)

note: labioscrotal swelling = scrotum/labia majora
urethral folds = peno-scrotal raphé/labia minora

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15
Q

Describe the descent of the testes.

A
  1. As trunk elongates, the gubernaculum and caudal genital ligament attached to the testis effectively shortens, moving the testis towards the scrotum.
  2. Testis moves through the processus vaginalis (invagination, but not of their peritoneum) which usually loses its patency.
  3. Regression of the extra-abdominal portion of gubernaculum completes the movement of the testis into the scrotum
  4. Peritoneum which followed the descent of the testis forms part of the tunica vaginalis which encapsulates the testis in the scrotum.

Iliac fossa (3 months) —> inguinal canal (7 months) —> superficial ring (8 months) —> scrotum (9 months)

note: consequences of undescended testes = reduced sperm, unable to check for testicular cancer, testicular torsion

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16
Q

Describe the descent of the ovary.

A

Suspensory ligament attaches ovary superiorly

Gubernaculum attaches ovary inferiorly to the labio-scrotal folds (prevents further mechanical descent)

Ligament of ovary proper becomes the round ligament of uterus in inguinal canal

17
Q

What are the different stages in the formation of gametes?

A
  1. Colonise gonad
  2. Proliferate (mitosis)
  3. Meiosis (haploid cells produced)
  4. Cyto-differentiate (i.e. eggs or sperm)
    note: germ cells kept distinct from somatic cell development (protects from influences arising in the rest of the body which stimulate differentiation)
18
Q

Outline the stages in female gamete formation.

A
  1. Germ cells colonise gonadal CORTEX
  2. Oogonia proliferate by mitosis (max. 7 million produced mid-gestation)
  3. Majority of oogonia die during gestation (selection for oogonia which will last for a long time)
  4. Granulosa cells (surrounding somatic cells of ovarian origin) stimulate meiosis (all remaining 2 million enter meiosis before birth, therefore there is a finite number of gametes available)
  5. Meiosis stops at an early stage, forming primordial follicles (oocytes surrounded by granulosa cells)
  6. Onset of puberty stimulates a small proportion of the primordial follicles to develop further (but only 1-2 gametes complete development each month)
19
Q

Outline the stages in male gamete formation.

A
  1. Germ cells colonise MEDULLA of primitive sex cords
  2. Proliferate by mitosis into spermatogonia
  3. Onset of puberty stimulates the cords to hollow out and become seminiferous tubules
  4. Spermatogonia cluster around the periphery (of the seminiferous tubules?); number maintained by mitosis (enough available for ~70yrs)
20
Q

Outline the stages of spermatogenesis.

A

A1 spermatogonia arise and divide a fixed number of times by mitosis

—> ~64 primary spermatocytes produced per A1 spermatogonium (primary spermatocytes joined by cytoplasm)

—> meiosis I & II —> haploid spermatids move towards lumen —> move through sequential sections of epididymis (~6-12 days) and are modified —> spermatozoa produced

note: spermiogenesis

21
Q

How is semen produced?

A

Composition:

  • sperm (via vas deferens)
  • prostate secretions (~20%)
  • seminal vesicle secretions (~60%)
  • bulbourethral gland secretions

Emission (mixing) stimulated by sympathetic system:

  • vas deferens contract —> semen transported to urethra
  • seminal vesicles and prostate gland contracts —> contents exit

note: erection stimulated by parasympathetic, ejaculation stimulated by sympathetic system (Point & Shoot)

22
Q

What investigations could be undertaken to assign the sex of a child with ambiguous external genitalia?

A

Karyotyping (determine genotype)
Pelvic ultrasound (determine internal genitalia - phenotype)
Endocrine screening (levels of LH, FSH, testosterone)
Androgen receptor levels
Palpation of gonads
Length and diameter of phallus
Position of urethral meatus
Degree of labio-scrotal fold function
Presence of vagina/pouch/urogenital sinus

23
Q

What are the presenting signs of Turner’s syndrome at puberty?

A

45,XO

  • short stature
  • ovarian failure —> primary amenorrhoea & infertility
  • failure of secondary sexual characteristics e.g. poor breast development

note: the diagnosis is made before puberty if there are other signs present e.g. peripheral lymphoedema, webbed necks, congenital heart disease

24
Q

Contrast the features and causes of true and pseudohermaphroditism.

A

True/primary hermaphroditism = both ovarian and testicular tissue is present (sometimes in one gonad), resulting in ambiguous genitalia

e. g. sex chromosome mosaic of XY, XX —> testis present on one side (mesonephric duct remains and paramesonephric duct regresses)
e. g. could be due to translocation of SRY gene to X chromosome

Pseudohermaphroditism = set genotype differs to phenotype

e. g. androgen receptor mutations so testosterone cannot effect cells (Swyer syndrome)
e. g. congenital adrenal hyperplasia (increased production of adrenal testosterone, which has a similar effect to testis-derived testosterone) —> variable masculinisation —> ambiguous genitalia

25
Q

What does the urogenital sinus develop into in the male and the female?

A

Both males & females develop bladder & (prostatic & membranous) urethra from urogenital sinus.

Male: presence of testosterone stimulates:

  • prostate gland
  • bulbourethral glands (Cowper’s glands)

Female:

  • greater vestibular (Bartholin’s glands) & lesser vestibular (Skene’s glands)
  • lower 2/3 of vagina (Müllerian ducts join uterus)
26
Q

List some of the processes of the reproductive system.

A
  • make gametes (haploid to create genetic diversity)
  • allow gametes to meet (movement of gametes through duct system)
  • allow the new individual to develop
  • control the process (gonadotrophins, sex steroid hormones)
27
Q

What is the final site of sperm maturation?

A

Epididymis (stored there for up to several months)

28
Q

What arteries supply the corpora cavernosa?

A

Deep arteries

29
Q

Where do the seminal vesicles and vas deferens drain?

A

Internal and external iliac nodes

30
Q

Are the vas deferens and seminal vesicles palpable?

A

Vas deferens can be felt as a firm, hard cord on the posterior aspect of the spermatic cord as it traverses the scrotum to the superficial inguinal ring

Seminal vesicles are palpable by DRE when enlarged

Reproductive System (15 decks)

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