Male Reproduction I Flashcards
Reproduction
Biological process by which a new individual organisms are produced from their parents = asexual and sexual
Asexual reproduction
Offspring originates from a single organism and inherits the parents’ gene
Gemmation
formation of small buds on the surface of the progenitor which can develop into a new individual
Fragmentation
New organism is growing from fragments of the progenitor
Parthenogenesis
Parthenos = virgin
Genesis = birth
Offspring develops from unfertilised eggs e.g. in arthropods, some fish and amphibians
Asexual reproduction advantages
Very quick - no gamete formation necessary
Small populations in secluded areas
Not very complex, requires less energy compared to sexual reproduction
Survival in a stable environment
Asexual reproduction disadvantages
Offspring is clone of parent
Little genetic diversity
Environment usually not stable = long term want to have diversity to be able to adapt to different environments
Often struggle for existence as well as overcrowding
Sexual reproduction in animals
-Consists of gamete formation, fertilisation and development of the zygote
-Gametes: haploid chromosome set
-Primary sex organs: male testes (production of spermatozoa) and female ovaries (production of ova)
-Secrete sex hormones: males (androgens) and females (oestrogen and progesterone)
Fertilisation: leads to a diploid zygote
Sexual reproduction advantages
Introduces genetic diversity and survival in a changing environment
Sexual reproduction disadvantages
Cost intensive (a lot of energy) Only 50% of the genome contribute to the offspring and few offspring
Penis
- male copulatory organ
- roof, shaft, glans penis, foreskin
- corpus sponglosum surrounds urethra
- corpus cavernosa: paired dorsal erectile bodies
Erection
Avascular, sexual arousal
Nerves in penis release nitric oxide
Vasodilation: increased blood flow to corpora cavernous
Scrotum
Sac of skin and superficial fascia
Hangs outside abdominopelvic cavity
Contains paired testes
Midline septum divides scrotum into two compartments, one for each testis
The testes
- Combined within the scrotum
- each testis is surrounded by two tunics
- Tunica vaginalis: outer layer derived from peritoneum
- tunica albuginea = inner layer fibrous capsule
- Septa divide tests into 250 lobules
- Each lobule contains one to four seminiferous tubules
- produce sperm in seminiferous tubules
- sperm ripens from a spertagonium to mature sperm
- produce hormones in interstitial tissue
Semen
Milky-white of stem and accessory gland secretions
- 2-5mL ejaculated contains 20-150 sperm/mL
- contains fructose for ATP production, protects and activates sperm and facilitates sperm movement
- alkaline fluid neutralises acidity of male urethra and female vagina and enhances mobility
Sperm
- Take 74 days for sperm to mature
- Young men make 300 000 sperm a minute = 400 million/day
- Average sperm count it 50/120 – million sperm/mL
- Sperm count <25 million/mL = infertility
Temperature control in testes
- temp is kept constantly 3 degrees lower than core body temp
- lower temp is necessary for sperm production
- two sets of muscles contract the scrotum and can draw the testes towards the abdominal cavity when the testes are cold
Dartos muscle
Smooth muscle, wrinkles scrotal skin, pulls scrotum close to the body
Cremaster muscles
bands of skeletal muscle that elevate testes
The pampiniform plexus
testicular artery entering the scrotum form the abdomen and the testicular been entering the abdomen from the scrotum lie in the tortuous plexus
Countercurrent heat exchange
- blood entering the scrotum from the abdomen is warmer than blood leaving the testes
- heat exchange from blood in the testicular artery to blood the plexus, decreases the temperature of blood entering the testes
- blood leaving the testes is warmed by contraction
Cryptochidism
- undescended testes
Absences of one or both testes from the scrotum - descend to scrotum at 28 weeks of foetal life
- most common genital problem
3-4% of infant boys born with at least one undescended - production of testosterone is not affected by temperature
- treated when 6 months
if not treated: infertility, testicular torsion, cancers
Spermatogensis
production of viable sperm, is greatly affected by the temperature of the testicle
Ducts of the testes
- sperm delivered to exterior through system of ducts
- epididymis -> vas (ductus deferens) -> ejaculatory duct -> urethra
- seminiferous tubules
- straight tubules
- rete testis
- efferent ductules
- epididymis
- vas deferens
Epididymis
- single highly coiled tube
- about 6m long
- maturation of sperm
- passage of sperm 2-6 days
- microvilli absorb testicular fluid and pass nutrients to stored sperm
Vas deferens
Ductus deferens
- sperm transport: smooth muscle in walls propels sperm from epididymis to urethra
- sperm storage
- palpable
- 45cm long
Vasectomy
cutting and ligating ductus deferens as a form of birth control
Accessory glands (3)
Prostate, seminal vesicles, bulbourethral gland
Prostate
encircles urethra interior to bladder size of a peach pit singe gland contributes 30% of spinal fluid contains enzymes secretes milky, slightly acidic fluid
Seminal vesicles
Paires glands
on posterior bladder surface
contribute to 65% of seminal vesicle
alkaline
prostaglandins, clotting protein and fructose
contains a smooth muscle that contraction during ejaculation
duct of seminal gland joins ductus deferens to form ejaculatory duct
Bulbourethral gland
AKAK cowper's glands pea-sized glands inferior to prostate paired glands contribute 5% of seminal fluid lubricate glans penis neutralises traces of acidic urine in urethra alkaline pre-ejaculatory fluid produce thick, clear mucus during sexual arousal
Other ducts
ejaculatory duct
urethra
