GHM L10 Flashcards
Describe the purpose of meiosis
- Cell division in sexually reproducing organisms
-Reduces no. of chromosomes in gametes
-in humans, somatic cells: DIPLOID (2 sets of chromosomes). GAMETES: HAPLOID (1 set of chromosomes)
Why are gametes haploid?
Organisms produced via sexual repdocution need correct number of chromosomes
Descibe the hypothalamic-pituitary-gonadal axis
GnRH secreted in hypothalamus (preoptic area)
In anterior pituitary, GnRH stimulates gonadotropes to release gonadotropins (LH, FSH)
LH, FSH in testes, ovaries,- stimulate testes + ovaries to secrete sex androgens, estrogens, progestins to the target cells
INHIBIN secreted by SERTOLI cells of testis - inhibit release of GnRH in hypothalamus and inhibit gonadotropes in anterior pituitary
Also ANDROGENS are involved in negative feedback and positive feedback
positive feedback (some stages in menstrual cycle)
Give an example of positive feedback in the hypothalamic-pituitary-gonadal axis
Menstrual cycle - hormonal surge
Androgens
Describe embryonic gonads
Precursors to somatic cells
Undifferentiated gonads
Consist of
-germ cells
-supporting cells
-steroidogenic ells
IDENTICAL
UNDERSTANDING:
-precursor to testes / ovaries
-depends on sex of individual
-RECOGNISE OVARY + TESTES on diagram
Describe the process of sex differntiation
FEMALE: (ovarian pathway)
-supporting cells differntiate into GRANULOSA cells (which enclose the oocytes to form follicles)
Steroidogenic cells differentiate into THECA cells
MALE: (testicular pathway)
-supporting cells differntiate into SERTOLI cells (encolose germ cells forming testicular cords
Steroidogenic cells differentiate into Leydic cells
Describe the process of gondal development in a male embryo
- 6th week of pregnancy (4 week embryo): migration of PRIMORDIaL (undifferentiated germ cells)
- Primordial germ cells have XY chromosomes
- XY primordial germ cells migrate to the medulla region of primordial gonad
- After these primordial cells collonise medulla of gonad, they proliferate by mitosis (for 2 weeks)
- PRIMORDIAL GERM CELLS develop into SPERMATOGONIA (immature sperm) - DIPLOID
all occurs before birth
6. Supporting sex cord cells form SERTOLI CELLS
Activation SRY protein locus (position) on Y chromosome - leads to formation of primitive testes (premature)
Describe the phenotrype sex differentiation of the male internal genitalia
Male + female internal genitalia derive from different duct systems
-Wolffian duct: MALE
-Mullerian duct: female
In male, MIS (Mullerian Inhibiting Substance) + AMH (anti-mullerian hormone) release - by SRY
SRY released by supporting cells (later SERTOLI)
Wolfian duct is triggered by testosterone to form Epidydymis, Vas deferens, (sperm duct) seminal vesicles
Mullerian duct - degenerates
Dihydrotestosterone - stimulates development of prostate gland (DHT) - type of androgen
Describe phenotypic sex differentiation of the male external genitlia
DHT needed for this process
early embryonic development: genitalia undifferentiated + form urogenital groove (8 weeks)
- DHT stimulates growth of prostate gland + fusion of genital folds, leads toformation of penis around urethra
- DHT stimulates formation of scrotum (formation of labioscrotal swelling, leading to formation of scrotum)
- Early fetal development, testes develop in abdomen, DHT descends them ABDOMEN -> SCROTUM (process important for normal testicular development + temp regulation for sperm production)
- hCG (human chronionic gonadotropin) produced by placenta - stimulates testosterone production in fetal testes
- Descent of testes from abdomen -> scrotum requires presence of hCG - if this process goes wrong, leads to CRYPTORCHIDISM - WHERE ONE / BOTH TESTES FAIL TO DESCEND PROPERLY INTO THE SCROTUM
- Exposure to DHT from 5th weekof development will lead to development of male external genitilia therefore, male phenotype
if this goes wrong, leads to AIS - Androgen Insensitivy Syndrome - individuals with male sex chromosomes XY, have reduced / abscent response to androgens (including DHT) - therefore, despite the presence of the male XY chromosomes, external genitilia may not develop
Male Reproductive Anatomy
Organs
- Gonads - in males, this is testes - produce gametes, secrete hormones
- Ducts: transport, store gametes - vas deferens - sperm duct
-Accessory sex glands: support gametes (prostate gland)
Testes
State 3 functions of the penis
- Urination
- Erection
- Ejaculation
Describe the function of the scrotum
- Supports testes
-Temp regulation
ANATOMY OF TESTES
TUNICA VAGINALIS - outer capsule layer
TUNICA ALBUGINEA inner capsule layer
SEPTUM
SEMINIFEROUS TUBULE
RETE TESTIS
EFFERENT DUCTULES
HEAD OF EPIDYDYMES
BODY EPIDYDYME
TAIL OF EPIDYDYMIS
VAS DEFERENS
-lies inside tuniva vaginalis together with epididymis
-site of SPERMATOGENESIS + androgen production
State the ducts found in the male reproductive system
- Urethra
-Spermatic cord - blood, autonomic nerves + lymph vessels, vas deferens
-Epididymis - spermatozoa (sperm cells) complete maturation (2 week)
-Vas deferens - fushion of epidydymis, stores mature sperm
-Rete testis -carries sperm from seminiferous tubules to epididymis, fusion of seminiferious tubules
Describe spermatogenesis
Conversion of DIPLOID spermatogonia into haploid spermatozoa
Describe spermiogenesis
Converstion of HAPLOID spermatid -> HAPLOID spematozoa
Describe sertoli cells
SUSTENTACULAR CELLS “nurse cells” - provide physical + nutritional support to sperm cells in maturation process
Found in seminiferous tubules
Activated by FSH (produced by pituitary gland)
Sertoli cells connected to each other via TIGHT JUNCTIONS, forms blood-tesits barrier (separates testicular environment from bloodstream)
SECRETE AMH: Anti-mullerian hormone, inhibin (regulates FSH production), ABP (androgen binding protein - binds to androgens, testosterone)
Oestradiol (directs spermatogenesis)
Describe the location and function of the prostate gland
Location - surrounds + opens into urethra where it leaves the bladder
Secretes: SLIGHTLY ALKALINE FLUID - activates sperm + prevents them from sticking together
PROSTATE - problems are common in males over 40
Describe the location and function of bulbourethral gland
Cowper’s gland
Paired galdns, beneath prostate gland
Exocrine glands (secrete fluids)
Secretes alkaline mucous into urethra
Wash residual urine out of urethra when ejaculating semen, raises pH, neutralises acidity of urine
Describe the process of penile erection
- Physiological response to sexual stimulation
- Dilation of cavernous arteries in erectile tissue
- Mediated by release of NO in response to sexual stimulation
- No activates enzyme guanylate cyclase, increases cGMP, which leads to smooth muscle in erectile tissue to relax, allowing dilation of cavernous arteries - they can fill with blood, leads to erection
Describe the 3 columns of erectile tissue
- 2 x corpora cavernosa
1 x corpous spongiosum
State organs involved in ejaculation
Brain
Spinal cord
Peripheral Genital organs
Desribe the composition of semen
SEMINAL FLUID: thick, yellow, alkaline
-mucus
-fructose
-coagulating enzyme
-prostaglandins
State 3 accessory glands
- Seminal vesicle
-Prostate gland
-Bulbourethral gland
Describe the process of capacitation
SPERM MATURATION
Ejaculated sperm cannot fertilise, sperm undergo CAPACITATION in female reproductive tract
Capacitation destabalises sperm”
-removal of glycoproteins from surface of sperm
-exposes other proteins which bind to zona pellucida (protective layer around egg)
-increase in intracellular calcium in sperm
-activation of membrane lipases + protein kinases - makes sperm more fluid, increase mobility + better penetration of egg
-increase membrane fluidity
Describe the journey the sperm cell undertakes to fertlise the egg
Seminiferous tubules (in testes) to fallopian tubes
Describe the production of testosterone in males
H Y P O T H A L A M U S
GnRh
ANTERIOR P I T U I T A R Y
LH FSH
L E Y D I G CELLS SERTOLI
testosterone inhibin
spematogensis
Describe the production and function of androgens in the body
Androgens produced by adrenal glands, include testosterone, DHEA (weak precursor to testosterone)
Why are the androgens released from adrenals considered as “weak” precursors?
Weaker effects than testosterone
Describe how weaker precursors are converted into more potent androgens
By secondary endocrine glands, gonads - testes, ovaries
DHEA / other weak precursors further metabolised, converted to more potent androgens e.g. testosterone
Where are androgens produced in larger quantities? Adrenals or Gonadal tissues
GONADAL TISSUES
Describe male hormone control
FSH + LH only released during puberty
FSH released by pituitary gland stimulates sertili cells in testes to facilitate spermatogenesis (production of sperm)
RELEASE OF FSH REGULATED BY NEGATIVE FEEDBACK MECHANISM. As spermatogenesis progresses, testosterone levels increase, causing sertoli cells to release INHUBIN - sends negative feedback signal to pituitary gland surpresssing FSH release
LH, released by pituitary gland, stimulates Leydig cells to produce testosterone
State where Leydig cells are found
Testes
Describe characteristics of male puberty
9-14
Puberty initiated by release of GnRH
Stimulates anterior pituitary to release LH, FSH
Stimulates testosterone release
LEPTIN - produced by fat cells, involved
Physical changes:
-Adult body odor, increased sebum
-Testicular enlargement
-Penis growth
-Foreskin retraction
-Pubic hair
-Male pattern musculature
-More frequent erections
-Body, facial hair growth
-Adam’s apple more prominent
-Voice change - due to growth of larynx
Describe precocious puberty
- Incomplete (peripheral) precocious puberty: early activation in gonads (testes boys, ovaries girls) or adrenal glands. Production of sex hormones at early age
- True (complete precocity) precocious puberty: activation of HPG axis, regulates production of sex hormones. In this one, level of gonadotropins (LH, FSH) higher than expected for individual ages
- Isosexual preocity: precocious puberty where development of secondary sexual characteristics is consistent with the individual’s biological sex. Boys develop masculine secondary sexual characteristics prematurely
- Contrasexual (heterosexual) precocity: development of secondary sexual characteristics that are not consistent with individual’s biological sex - girls experience virilization, boys experience femiziation
- Gonadotropin-dependent-precocious puberty: when precocious puberty left untreated. This condition leads to premature closure of growth plates in long bones, resulting in limited height potential and short stature
Describe the treatment of true precocious puberty
This is caused mainly by abnomarlties in CNS
Treated by GnRH blockers
Surpress release of gonadotropins, slowing down / delaying puberty
Describe the causes of precocious puberty
GONADOTROPIN INDEPENDENT cause
Can be endogenous or exogenous
Endogenous: testicular source: Testicular tumor, LH excess: HCG producing tumor
Adrenal source: adrenal tumor
Exogenous: Testosterone cream
Describe Complete AIS, its symptoms and causes
COMPLETE ANDROGEN INSENSITIVITY SYNDROME
- Male has typical male chromosome pattern - 46, XY
- Born phenotypically female - born with external genitalia which appear female - body unable to respond to androgens (male sex hormones), so incomplete masculinisation of external genatalia during fetal development
- Presents at puberty - abscent menarche (menstrual period in female) - individuals have no uterus - other changes including breast development occur at puberty (due to converstion of androgens to estrogens in the periphery)
4.Gonads not ovaries but testes: despite apperance of external female genatalia. Testes in abdomen instead of scrotum
- No uterus, no menstrual cycle, amenorrhea
Describe the causes and symptoms of amenorrhea
Due to complete AIS
Absence of uterus
Therefore, absence of menstrual cycle - amenorrhea
Describe the symptoms and causes of cryptorchidism
Absence of one / both testicls from scrotum
Because testes develop in abdomen during fetal development, fail to descend into scrotum
(most cryptochid testes descend into scrotum without any intervension, within first few months)
if not descended by 6 months ORCHIOPEXY: if testes not descended into scrotum by 6 months, orchiopexy type of surgery
RISKS
-reduced fertility in males with prev orchiopexy
-testicular cancer - men who have history of cryptorchiddism, but testes have descended, are at risk
Describe the causes and symptoms of testicular cancer
Malignant
90% germ cell cancer (90% of testicular cancers are germ cell tumours) - unlike ovarian cancers which are of epithelial origin)
RISK FACTORS:
-cryptochidism
-white european
-maternal DES
