Mod9: Obj1&2-Reproductive system: Male Flashcards
The male reproductive system
- Manufactures sperm
- Delivers sperm to female reproductive tract
Male reproductive anatomy
Testis is the site of sperm production (hangs in the scrotum) connected to the epididymis, series of tubes that the
sperm has to travel through during its maturation, from there it travels to the ductus deferens, which is a long thin tube that carries the sperm up through the inguinal canal into the abdominal
cavity, into the ejaculatory duct, within the prostate, and it at this point that there is the connection to the prostatic urethra and the bladder, membranous urethra and spongey urethra carrying the sperm to the external urethral orifice
Accessory glands: Bulbourethral gland, prostatic gland, which contribute to the process of delivering
sperm to female
The penis
- An organ designed to deliver sperm into the female reproductive tract*
- Approximate size: 8-10cm long, 3cm diameter (flaccid); 13-18 cm long, 4 cm diameter (erect)
The penis is made of 3 main parts
- Root: The attached region
- Shaft: The free region
- Glans penis: the enlarged tip (covered by the foreskin-or “prepuce” this is removed in circumcisions)
What’s inside the penis?
3 cylindrical columns of erectile tissue
- Dorsal: 2 x corpus cavernosa
- __Ventral: 1 x corpus spongiosum
What causes an erection?
During sexual excitement, parasympathetic nerves to penile arterioles release nitric oxide (NO)
(NO) relaxes smooth muscle:
- Blood vessels dialate
- Increased blood flow to penis
- Vascular channels (corpus cavernosa and corpus spongiosum) become enlarged with blood
- Erection of penis occurs
- Erecetion can be stimulated by touch or sights, sounds and smells
Erectile dysfunction
An inability to maintain an erection
- Due to a deficient release of nitric oxide
- Treated with vacuum pumps, injection of drugs into the penis, or implanting a device into the penis to make it rigid
- Viagra increases blood flow to the penis, to maintain erectile state (prolonging nitric oxide), however decreases systemic blood pressure
The scrotum
Sac of skin that hangs outside the body and houses the testes in two compartments
- Position of testes increases vulnerability to damage but is essential for production of spermatazoa
- Sperm production is best at 34º (lower than body temperature
Temperature regulation of the scrotum is achieved by two muscles:
- Dartos muscle (smooth muscle): When contracted makes scrotum wrinkled and thick, decreases heat loss
- Cremaster muscle (skeletal muscle): When contracted brings scrotum and testes closer to body
- Both muscles contract in cold and relax in warm temperatures
The testes
Internally divided into about 250 lobules
- Each lobule contains seminiferous tubules (factory of sperm production) surrounded by smooth muscle to help squeeze sperm out of testes and into epididymis
- Contain sustenocytes (sertoli, sustentacular or nurse cells) and interstitial cells (Leydig cells) which produce androgens (testosterone)
Sperm production
Takes place in the testes in the seminiferous tubulues
- spermatogenesis
Sperm travels through a series of tubes to get from the testes to outside of the body
- Epididymis (sperm maturation and storage)
- Ductus/Vas deferens (rapid transport)
- Ejaculatory ducts
- Urethra (urine and semen to the outside)
Along the way (sperm travel), secretions are added to the sperm by the accessory glands
- Seminal vesicles
- Bulbourethral gland
- Prostate
Epididymis
Surrounds the posterior edge of the testes and is a series of coiled tubes which:
- Monitor & adjust composition of testicular fluid produced by the seminiferous tubules
- Stores, nourishes and protects spermatozoa while facilitating functional maturation
- Acts as a recycling centre for damaged sperm
- Ejaculate the sperm into the ductus deferens
Ductus Deferens & Seminal vesicles
sperm ejaculated from the epididymis enter the ductus deferens
- The ductus deferens is a tube that runs from the scrotal sac, through the inguinal canal into the abdominal cavity, descends to the urethra
- Seminal vesicles* attach to the ductus deferens
- These glands release a viscous fluid which makes up 60-70% of semen volume and contains substances that enhance sperm motility and their ability to fertilise (fructose-energy, prostaglandins-smooth muscle contraction and fibrinogen-clot in the vagina)
Ejaculatory duct, urethra & prostate
After the seminal vesicles join the vas deferens, the tube is known as the ejaculatory duct
- Immediately joins the urethra and travels through the prostate gland
- Prostate surrounds the urethra and produces fluid that contains citrate (nutrients), enzymes that breakdown seminal clot (fibrinolysin and PSA (found in the blood used to detect prostate cancer) and seminalplasmin (antibiotic properties))
Urethra & Bulbourethral glands
The urethra descends through the prostate and down to the tip of the penis
- Functions to convey both urine and semen
- The urethra is lined with bulbourethral glands (produces a thick mucus which lubricates the glans penis and neutralizes traces of acidic urine (increase sperm motility) in the urethra prior to ejaculation
Ejaculation (destination)
Propulsion of semen from the male duct system
- SYMPATHETIC RESPONSE
- Bladder sphincter muscle contracts
- Reproductive ducts and accessory gands contract
- Bulbospongiosum muscle of penis contracts to eject semen at the rate of 500 cm/s
The onward journey of sperm
Ejaculation is often followed by the continuation of sperm’s journey through the female reproductive system with the aim of fertilising an ovum
Spermatogenesis
Occurs in the seminiferous tubules
- Produces sperm
- Starts at approx 14 years of age, results in 400 million new sperm per day
- Each sperm takes about 10 weeks to make
Terminology
Most body cells are diploid (2n) and contain
- 2 sets of chromosomes (maternal and paternal)
- 23 pairs of chromosomes (46 in total)
- Gametes* (sperm and oocytes) are haploid (n) and contrain:
- 23 chromosomes (one of each pair)
Meiosis
Is the process living things use to make gametes (sex cells), which are used for sexual reproduction
- Meiosis starts with a cell that has 23 pairs of chromosomes
- Each chromosome makes a copy of itself, creating 46 pairs in the cell
- The cell divides into two, twice
- 1st dividion=23 pairs, 2nd dividion=23 chromosomes
Meiosis: Making gametes
Gamete formation involves meiosis
- Meiosis is the nuclear division in the gonads which the number of chromosomes is halved (from 2n to n)
- Produces daughter cells (each with half the normal number of chromosomes, n)
- When fertilisation occurs, the normal diploid chromosomal number is restored (2n=46)
- Introduces genetic variation through random alignment (swapping of chromosomal sections)
Mitosis vs. Meiosis
Spermatogenesis (producing sperm) steps
Spermatogonia=stem cell
- ) Mitosis of the stem cell produces
* A stem cell (type A) and a future sperm (type B) - ) Meiosis produces
- A primary spermatocyte (two)
- Secondary spermatocyte (two spermatids)
- Spermatid are small, non-motile cells close to the lumen of the tubule
- ) Spermatids lose excess cytoplasm and form a tail (spermatozoa)
- ) Spermatozoa breaks away from sustenocytes into the lumen of the seminiferous tubule
- ) Spermatozoa move into the epididymus
Spermatogenesis diagram
- Spermatogensis process, primary spermatocyte that undergoes two miotic divisions, to produce 2 cells and then 4 cells that have haploid component of chromosomes, each of which goes on to become a sperm
Structure of sperm
- Head: genetic region; nucleus and helmet-like acrosome containing hydrolytic enzymes that enable the sperm to penetrate an egg
- Midpiece: Metabolic region; mitochondria
- Tail: locomotor region; flagellum
Semen
Approximatel 2-5ml of semen is ejaculated (20-150 million sperm/ml): 40-750 million sperm with each ejaculate
- Less than 10 million sperm/ml: considered infertile
Semen consists of
- Seminal vesicle secretions: 60%
- Prostate secretions: 30%
- Bulbourethral secretions: 5%
- Epididymal secretions (sperm): 5%
Regulating male reproductive function
The testes make sperm and hormones
- These activities require interactions with the hypothalamus and anterior pituitary
- HYPOTHALAMIC-PITUITARY-GONADAL (HPG) AXIS
HPG axis
- The hypothalamus releases gonadotropin-releaseing hormone (GnRH)
- GnRH signals the release of follicle stimulating hormone (FSH) & luteinizing hormone (LH) from the anterior pituitary
- FSH stimulates spermatogenisis by sustenocytes produce androgen-binding protein (ABP) which concentrates testosterone
- LH signals to interstitial (Leydig) cells to produce testosterone
- Testosterone drives spermatogenesis
- Increased testosterone levels negatively feeds back to inhibit GnRH and FSH/LH release
-
Inhibin is also produced during spermatogenesis and has negative feedback effects on FSH & GnRH
8.
In the absence of GnRH, LH and FSH
The testes will atrophy and sperm and testosterone production cease
What does testosterone do?
At puberty and thereafter:
- Stimulates spermatogenesis
- Increases growth of reproductive ducts and glands
- Increases size of penis
- Enhances ability to maintain erection and obtain ejaculation (no testosterone: sterile and unable to engage in sexual intercourse-replacement therapy)
- Stimulates male secondary sex characteristics
Male secondary sex characteristics
Male characteristics NOT involved in reproduction
- Induced by male sex hormones (testosterone)
- Pubic, axillary and facial hair
- Enhanced hair growth on chest and other areas
- Deepening of voice
- Increased skeletal muscle mass
