12.2&3 MALE REPRODUCTION - SPERM PRODUCTION, EJACULATION, TESTOSTERONE Flashcards
3 TIERS of REPRODUCTIVE AXIS in MALES
HYPOTHALAMUS
PITUITARY (ANTERIOR)
- LH, FSH
TESTIS
-TESTOSTERONE and production spermatozoa
in HPT AXIS what is the role of the HYPOTHALAMUS
RELEASE GnRH (GONADOTROPHIN RELEASING HORMONE)
into hypothalamohypophysial shunt (portal system of blood vessels)
to PITUITARY
in HPT AXIS what is the role of the ANTERIOR PITUITARY GLAND
GONADOTROPES SECRETE LH and FSH
in response to GnRH (hypothalamus)
in HPT AXIS what is the role of the LEYDIG CELLS
in INTERSTITIUM of TESTIS
- STIMULATED by LH to produce TESTOSTERONE
in HPT AXIS what is the role of the SERTOLI CELLS
STIMULATED by FSH to SUPPORT SPERMATOGENESIS in the seminiferous epithelium (surround spermatogonia)
what is STIMULATED by LH in males
TESTOSTERONE PRODUCTION in LEYDIG CELLS (has LH RECEPTORS)
what is STIMULATED by FSH in males
SUPPORT of SPERMATOGENESIS by SERTOLI CELLS
and synthesise ABP (protein)
when LH BINDS to LH RECEPTORS on LEYDIG CELLS what is STIMULATED in order to produce Testosterone
ADENYLATE-CYCLASE
- activates cAMP
- protein kinases
- cholesterol esterases
- free cholesterol
(pregnenolone)
testosterone
ORIGINS of TESTOSTERONE
95% from TESTIS
5% from other sources including:
- ADRENAL CORTEX
- ADIPOSE TISSUE
- SKIN
- BRAIN
- MUSCLE
FUNCTIONS of TESTOSTERONE in FOETAL LIFE
- SEX DIFFERENTIATION
- DEVELOPMENT of ACCESSORY SEX ORGANS
- DESCENT of TESTIS
(foetal leydig cells regress after birth)
FUNCTIONS of TESTOSTERONE in PUBERTY
- DEVELOPMENT of SECONDARY SEXUAL CHARACTERISTICS including:
change in BRAIN, VOICE
Increase HEIGHT, MUSCLE mass, FACIAL hair
Production of SPERM and SEXUAL FUNCTION
97% of TESTOSTERONE is…
PROTEIN-BOUND
MAJORITY of TESTOSTERONE is BOUND to
SEX HORMONE-BINDING GLOBULIN (SHBG)
- strongly
- INACTIVE
some bound to ALBUMIN (less strongly, some activity)
which TESTOSTERONE is the MOST ACTIVE but difficult to measure
FREE TESTOSTERONE (not protein-bound)
TESTOSTERONE bound to SHBG are
INACTIVE
how to MEASURE BIOAVAILABLE TESTOSTERONE
- measure FREE fraction and those BOUND to ALBUMIN
- using VERMEULEN EQUATION, can be estimated from testosterone, SHBG and albumin concs
ACTIVTY of TESTOSTERONE is mostly due to its ACTIVE FORM called
DIHYDROTESTOSTERONE (DHT)
what is TESTOSTERONE CONVERTED to
DIHYDROTESTOSTERONE (DHT)
- ACTIVE FORM
how is TESTOSTERONE CONVERTED to DHT (using what)
ENZYME 5-ALPHA-REDUCTASE
5-ALPHA-REDUCTASE may be
- Deficient - leading to lack of masculinisation
- Target for drugs in BPH (Benign Prostatic Hyperplasia)
where does SPERMATOGENESIS happen
SEMINIFEROUS TUBULES of TESTES
SPERMATOGENESIS is STIMULATED by
ANTERIOR PITUITARY GONADOTROPHIC hormones:
- LH and FSH
SPERMATOGENESIS occurs at average age
13
SEMINIFEROUS TUBULES SUPPORTING cells:
- SUSTENTACULAR CELLS of the basement membrane
- SERTOLI CELLS
GERMINAL ELEMENTS of SEMINIFEROUS TUBULES comprise of EPITHELIAL CELLS including:
- Slowly dividing PRIMITIVE STEM CELL population
- Rapidly proliferating SPERMATOGONIA
- SPERMATOCYTES undergoing Meiosis
- metamorphosing SPERMATIDS
INNERMOST LAYER of SEMINIFEROUS TUBULE consists of 2 CELLS
- SPERMATOGONIA (primitive germ cells)
- SERTOLI CELLS (Surround germ cells, offering STRUCTURAL SUPPORT)
through the FORMATION and BREAKDOWN of GAP JUNCTIONS, SERTOLI CELLS…
GUIDE GERM SPERM CELLS TOWARDS LUMEN
the availability of NUTRIENTS TO GERM CELLS is CONTROLLED by the SERTOLI CELLS through these GAP JUNCTIONS
through restriction of substances and the blockage of paracellular diffusion
the FORMATION of TIGHT JUNCTIONS serves as the PHYSICAL BASIS for the…
BLOOD-TESTIS BARRIER
- creating microenvironment that is SPECIALISED and IMMUNOLOGICALLY SAFE
Blood-Testis Barrier: formed by the tight junctions between Sertoli cells - creates a barrier, allows environment (microenvironment) to be safe for sperm.
Prevents escape of membrane antigens of differentiating sperm into blood which would activate immune system.
Prevents entry of toxins into seminiferous tubules
Helps maintain unique chemical composition of s.f fluid
which RECEPTORS do SERTOLI CELLS EXPRESS
- ANDROGEN RECEPTORS for RECOGNITION of TESTOSTERONE (essential in progression of spermatogenesis)
- FSH RECEPTORS for RECOGNITION of FSH (essential for maximal sperm production)
during EMBRYOGENESIS PRIMORDIAL GERM CELLS MIGRATE into..
TESTES
become IMMATURE germ cells - SPERMATOGONIA
what happens to SPERMATOGONIA from PUBERTY
undergo MITOSIS and continually proliferate and differentiate and develop to form SPERM
steps in SPERMATOGENESIS
- SPERMATOGONIA MIGRATE among SERTOLI CELLS TOWARDS CENTRAL LUMEN of SEMINIFEROUS TUBULE
- SPERMATOGONIA progressively modified and ENLARGED (MITOSIS) to form Large PRIMARY SPERMATOCYTES
- Primary Spermatocytes undergo MEIOSIS I to form 2 SECONDARY SPERMATOCYTES
- secondary spermatocytes DIVIDE (MEIOSIS II) to form SPERMATIDS
- modified to become SPERMATOZOA
Approx how long does SPERMATOGENESIS take
64 days
what is SPERMATOGENESIS
PRODUCTION of MATURE SPERMATOZOA
what is SPERMIOGENESIS
CONVERSION of SPERMATIDS INTO SPERMATOZOA
what is SPERMIATION
RELEASE of SPERMATOZOA INTO LUMEN
what is CAPACITATION
FINAL MATURATION of SPERMATOZOA in FEMALE GENITAL TRACT
(conditioning process to liberate acrosome)
what is the CONVERSION of SPERMATIDS into SPERMATOZOA called
SPERMIOGENESIS
what is the RELEASE of SPERMATOZOA into the LUMEN called
SPERMIATION
before DIFFERENTIATING and ELONGATING into Spermatozoa, SPERMATIDS still have usual CHARACTERISTICS of
EPITHELIOID CELLS
on the outside of the ANTERIOR TWO THIRDS of the HEAD of the SPERMATOZOON what is there
THICK CAP - ACROSOME
ACROSOME of SPERMATOZOA HEAD is mainly FORMED from the..
GOLGI APPARATUS
what does ACROSOME of SPERMATOZOA HEAD contain
ENZYMES
- help sperm to enter ovum
(eg Hyaluronidase and tubal mucosal enzymes for corona radiata,
acrosin (proteolytic) esterases and neuraminidase for zona pellucida)
both TESTES produce up to how much sperm a day
120 MILLION per DAY
where is MOST of the SPERM STORED
VAS DEFERENS
(small amount in epididymis)
normal MOTILE, FERTILE SPERM are capable of FLAGELLATED MOVEMENT through the fluid liquid medium at what VELOCITY
1-4 mm/min
POST ejaculate MAXIMAL LIFE SPAM of SPERM is
24-48 HOURS at body temperature
(although can live for many weeks in male genital ducts)
role of TESTOSTERONE in SPERMATOGENESIS
GROWTH and DIVISION of GERM CELLS
role of LH in SPERMATOGENESIS
STIMULATES LEYDIG CELLS to SECRETE TESTOSTERONE
role of FSH in SPERMATOGENESIS
STIMULATES SERTOLI CELLS necessary for the CONVERSION of SPERMATIDS to SPERMATOZOA (SPERMIOGENESIS)
how are OESTROGENS FORMED and what are they ESSENTIAL for in SPERMATOGENESIS
- formed FROM TESTOSTERONE by SERTOLI CELLS when stimulated by FSH
(FSH -> SCs -> Testosterone
-> Oestrogens) - essential for SPERMIOGENESIS (SPERMATIDS TO SPERMATOZOA)
Role of GROWTH HORMONE in SPERMATOGENESIS
- CONTROLS BACKGROUND METABOLIC FUNCTIONS of the TESTES
- PROMOTES EARLY DIVISION of SPERMATOGONIA
what controls background METABOLIC FUNCTIONS of the TESTES and promotes EARLY DIVISION of the SPERMATOGONIA
GROWTH HORMONE
what INHIBITS SPERMATOGENESIS
INCREASE in TEMPERATURE
(internal temp of scrotal sac is 2-3 degrees lower than body temp)
how is REGULATION of SCROTAL TESTES TEMPERATURE brought about
CONTRACTION or RELAXATION of DARTOS and CREMASTER MUSCLES of the scrotum
what can cause DEGENERATION of the SEMINIFEROUS TUBULES
INFECTIONS such as MUMPS
Where does SEMINAL FLUID come from
ACCESSORY SEX GLANDS,
PROSTATE (nutrients, enzymes, PSA)
SEMINAL VESICLES (mucoid material - fructose, citric acid, nutrients, prostaglandins, fibrinogens)
BULBOURETHRAL glands (mucus)
average VOLUME of EJACULATE and what does it contain
3 mL
- SPERMATOZOA
(less than 1%) (100 million/mL) - SEMINAL FLUID
SEMINAL FLUID is unusual because of its HIGH CONCENTRATIONS of
- POTASSIUM
- ZINC
- CITRIC ACID
-FRUCTOSE - PHOSPHORYLCHOLINE
- SPERMINE
- FREE AMINO ACIDS
- PROSTAGLANDINS
- ENZYMES (acid phosphatase, diamine oxidase, beta-glucuronidase, lactate dehydrogenase, alpha-amylase, PSA, seminal proteinase)
process of SEXUAL AROUSAL
- sexual arousal
LIBIDO (requires TESTOSERONE) - ERECTION
increased blood flow into penile corpus cavernosa - EMISSION
deposition of sperm into proximal part of urethra - EJACULATION
forceful discharge of semen through urethra - DETUMESCENCE / RELAXATIN
reflex reaction of EJACULATION is TRIGGERED by
EMISSION
- entry of SEMEN from the prostatic urethra into the BULBOUS URETHRA
EJACULATION is dependent on what REFLEX
SPINAL CORD REFLEX
- with CEREBRAL CONTROL
AFFERENT (sensory)
- SACRAL SPINAL CORD S2-S4
EFFECT (somatic motor neurons)
- via PUDENDAL NERVE
AFFERENT (sensory) reflex of EJACULATION is from which SPINAL CORDS
S2-S4 (SACRAL)
EFFERENT (somatic motor neurons) reflex of EJACULATION is via which NERVE
PUDENDAL NERVE
what MUSCLE CONTRACTIONS propel the semen via the urethra through the external meatus (EJACULATION)
- RHYTHMIC CONTRACTIONS of the STRIATED MUSCLES of the PERINEAL AREA:
Muscles of PELVIC FLOOR, ISCHIOCAVERNOSUS, BULBOSPONGIOSUS muscles - SPASMODIC CONTRACTIONS of the muscles of the HIPS and ANAL SPHINCTER
(spasm, sudden involuntary)
