Male Reproductive System, Including Spermatogenesis Flashcards
What does the male reproductive organs consist of?
Consist of:
-right and left testis
-epididymis in scrotum
-deferent duct
-spermatic cord
-seminal vesicle
-ejaculatory duct
-prostrate gland
-bulbouretheral gland (Cowpers gland)
-penis
Describe the scrotum
Pouch of pigmented skin, fibrous tissue and muscle dived into 2 compartment containing:
- 1 testis, 1 epididymis and testicular end of spermatic cord
Position and relations:
Anterior to thighs
Posterior to penis
Inferior to symphysis pubis
Describe the testes (testicles)
Male reproductive glands, suspended in the scrotum.
Size 4.5cm x 2.5cm x 3cm
Describe the 3 layers of the testes
Tunica vaginalis- outer covering of membrane formed from peritoneum
Tunica albuginea- fibrous covering, forms septa which divides testes into lobes
Tunica vasculosa- network of capillaries
Outline the internal structure of the testis
200-300 lobules contain:
Seminiferous tubules
Leydig cells
Epididymis
Vas deferens
Spermatic cord
Blood supply
Nerve supply
Describe seminiferous tubules
Convoluted loops of germinal epithelium. Produce spermatozoa
Describe leydig cells
Lie between seminiferous tubules. Produces testosterone after puberty
Describe epididymis
Single highly convoluted tubule forming a mass at upper pole of testis- 6m long
Describe vas deferens
Duct formed from epididymis as it leaves the scrotum in the spermatic cord
Describe spermatic cord
Suspend testes in scrotum - contains: vas deferens, blood and lymph vessels, nerves
Describe the blood and nerve supply in the testis
Blood supply: testicular arteries/ veins
Nerve supply: branch of 10th/11th thoracic nerves- ilioinguinal nerve
Describe the seminal vesicles
2 fibromuscular pouches 5cm long
Lie at posterior base of the bladder
Join vas deferens by small duct to form ejaculatory duct which then joins urethra
Secrete seminal fluid- alkaline fluid
Neutralises acidic environment of female reproductive tract at intercourse
Provides energy for sperm
Assists coagulation of semen after intercourse
Describe the prostrate
Doughnut shaped gland- 4cm x 3cm x 2cm
Inferior to bladder and surrounds urethra
Function: produces milky coloured prostatic fluid composing 30% of volume of semen
Slightly acidic nature helps semen coagulate after intercourse then breaks down this clot
Bulbourethral glands- pea sized glands inferior to prostrate produce alkaline fluid to protect sperm and secrete mucus to lubricate penis prior to intercourse
Describe the penis
External male organ
Passage for ejaculation of semen and excretion of urine
Root and body- root in perineum; body surrounds urethra
Describe the 3 columns of erectile tissue in the penis
- Corpora cavernosa: 2 lateral columns
- Corpus spongiosum: midventral column containing urethra
- Glans penis: expanded triangular distal end covered with retractable foreskin- prepuce
What 2 ligaments support the penis?
Fundiform and suspensory ligaments
Describe the blood and nerve supply in the penis
Blood supply: branches of internal pudendal arteries and veins
Nerve supply: autonomic and somatic nerves
Describe what occurs during sexual intercourse
Erection: caused by parasympathetic stimulus resulting in massive increase of blood to fill the corpus cavernosa and corpus spongiosum (approx. 130mls of blood)
Ejaculation: sympathetic reflex. Bladder sphincter closes. Peristaltic action of vas deferens, seminal vesicle, ejaculatory ducts and prostrate propel semen into the penile urethra.
It has two phases-
In the first phase, the van deferens (the tubes that store and transport sperm from the testes) contract to squeeze the sperm toward the base of the penis and the prostrate gland and seminal vesicles release secretions to make semen. At this stage, the ejaculatory is unstoppable.
In the second phase, muscles at the base of penis contract every 0.8 seconds and force the semen out of the penis in up to 5 spurts
Approx 2-5 mls of ejaculate is produced in total, although this can vary due to age and health
Approx 20-100 million sperm are released during the process
Describe the onset of puberty
Average age of onset is 12-13 years (though influenced by body mass)
Triggered by Gonadotrophin releasing hormone (GnRH) from hypothalamus stimulating release of Follicle stimulating hormone (FSH) & Lutenising hormone (LH)
Causes considerable body change
Outline 7 secondary sexual characteristics which occur during puberty
Development of body hair
Muscle and skeletal growth
Change in body composition
Pigmentation of external genitalia
Increased activity of secretory glands
Enlargement of larynx- deepening of voice
Skin thickening
What is spermatogenesis?
The process of the formation of male gametes in the testes (sperm)
In early foetal development, primordial germ cells differentiate into spermatogonia
Spermatogonia remain dormant until puberty
Describe the stages of spermatogenesis, with reference to spermiogenesis
Primordial germ cell
-Differentiation
Spermatogonium
-Mitosis
Primary spermatocytes
-Meiosis - DNA replication and crossing over
Secondary spermatocytes
-Meiosis - each chromosome has 2 chromatids, 1 goes into each spermatid
Spermatids
-Spermiogenesis
Spermatozoa
Outline the characteristics of sperm
0.017-0.020mm long
20-100 million in 3ml seminal fluid
Swim 30cm/hour (roughly 30mph)
Survival 2-5 days
Outline the composition of sperm
Head:
Acrosome- contains enzymes required for penetration of oocyte
Nucleus- contains chromosomes
Midpiece:
Contains mitochondria which supply energy to the sperm
Tail:
Flagellum to transport sperm
Describe the hormonal control of testes
Uses a negative feedback loop where the brain secretes hormones to control the testes.
Hypothalamus releases GnRH which targets the anterior pituitary which releases LH and FSH which control secretion from the testes.
LH stimulates the interstitial cells to produce testosterone.
LSH stimulates the seminiferous cells to release androgen binding protein (which enhances the spermatogenic cells ability to bind to testosterone, stimulating spermatogenesis.
Describe the process of fertilisation
Generalised acrosomal process
1. Sperm makes contact with egg
2. Acrosome reacts with zona pellucida
3. Acrosome reacts with perivitelline space
4. Plasma membranes of spermatogenesis and egg fuse
5. Sperm nucleus enters egg
6. Cortical granules fuse with egg plasma membrane, which renders the vitelline layer impenetrable to sperm
Describe the stages of fertilisation
Sperm deposition
Capacitation
Penetration of corona radiata- granulosa cells. This occurs by Acrosome reaction.
Penetration of zona pellucida- glycoprotein layer between corona radiata and oocyte membrane
Fusion of sperm cell membrane with oocyte cell membrane
Oocyte (immature ovum) competes meiosis 2- becomes ovum
Gamete fusion- becomes zygote
