Lecture 3 Flashcards
How do the sympathetic and parasympathetic divisions of autonomic nervous system control male genital system?
The testes, epididymas, male accessory glands, and erectile tissue of the penis receive dual innervation from the sympathetic and parasympathetic branches of the autonomic nervous system
Penis also receives both somatic efferent (motor) and afferent (sensory) innervation through the pudendal nerve
What are the 3 major efferent pathways for the regulation of penile erection?
- Parasympathetic (pelvic nerve)
Erection mainly controlled by parasympathetic system (corpora cavernosa and corpus spongiosum coordinate erection)
Parasympathetic postganglionic terminals release ACh and nitric oxide - Sympathetic (right and left hypogastric nerves)
Decrease sympathetic tone allows relaxation of the corpora and contributes to tumescence - Somatic (pudendal nerve)
Slide 3-6
What is the somatic control of an erection?
Innervates striated penile muscles
Contraction of ischiocavernous muscle during final phase of erection increases pressure inside the corpora cavernosa to valves that are even higher than systemic arterial pressure
Contraction of bulbospongiosus muscle increases enlargement of the corpus spongiosum (and the glans penis)
These contribute to ejaculation and seminal expulsion
Slide 7
What is emission and how does it happen?
Emission is when seminal fluid escapes episodically or continuously from the penile urethra
It’s a result of peristaltic contractions of the ampullary portion of the vas deferents, seminal vesicles and prostatic smooth muscle
Complimented by constriction of the internal sphincter of the bladder (SYMPATHETIC control)- prevents retrograde ejaculation of sperm into urinary bladder
What is erectile dysfunction and the 3 drugs used to treat?
Inability to develop or maintain an erect ion during sexual act
Sildenafil (viagra)
Vardenafil (levitra)
Tadalafil (cialis)
These drugs potentiate the relaxation of penile smooth muscle (corpus cavernosum) by preventing degradation of cGMP
Corpus cavernosum is regulated by NO which increases cGMP
What is ejaculatory dysfunction?
Emission usually accompanied by constriction of internal urethra sphincter
Retrograde ejaculation occurs when this sphincter fails to constrict
Causes semen to enter the urinary bladder rather than passing down the urethra
Slides 10-11
How do you treat ejaculatory dysfunction?
Sympathomimetic drugs such as;
Phentolamine- α adrenergic antagonist
Ephedrine- enhances NE release
Imipramine- inhibits norepinephrine re uptake by presynaptic terminal
These all increase tone of vas deferens and internal sphincter
What is the physiology of the ovary in females?
Ovary consists of an inner medulla and an outer zone (cortex)
Cortex contains developing follicles and corpus luteum (follicle released during menstruation when they grow and mature)
Medulla comprises large blood vessels and other supporting tissue
Slide 14
What is the ovarian cycle?
Folliculogenesis, ovulation, corpus luteum formation
Primary oocyte (4N DNA) -> primordial follicle -> primary follicle -> secondary follicle -> early tertiary follicle -> Graafian follicle -> ovulated ovum
For follicles to be produced, folliculogenesis must take place
At puberty by the time you produce graafian molecule
SLIDE 15
What are the patterns of gonadotrophin (LH and FSH) levels throughout life of female?
FSH and LH peak during dlfetal life and again during early infancy, then fall to low levels for rest of childhood
Onset of puberty, LH and FSH levels slowly rise and then begin to oscillate at monthly intervals (period)
At menopause, gonadotrophin levels rise to very high levels
Slide 16
What is the feedback control of gonadotrophins in females?
Estrogens control it
In childhood, very low estrogen levels are sufficient to fully suppress gonadotropin output
In adolescence, higher estrogen levels needed
In adult women, estrogens must be very high to suppress gonadotropin release
Slide 17-19
What is gonadotropin releasing hormones (GnRH) by GnRH neurons?
In rhythmic phases
Released in bursts into portal vessels around once an hour to stim gonadotrophs in anterior pituitary
In early follicular stage of cycle, gonadotrophs aren’t very GnRH sensitive so each burst causes only small rise in LH
In later stages, gonadotrophs much more sensitive, leads to larger release of LH
Slides 21-25
What do LH and FSH stimulate the ovaries to synthesize and secrete?
Estrogens and progestins
Inhibins and activins
Together the ovarian steroids and peptides exert both negative and positive feedback in the hypothalamus and the anterior pituitary
Inhibins and activins act only on anterior pituitary
Estrogens and progestins act on anterior pituitary and hypothalamic neurons as negative feedback to reduce LH and FSH
Estrogens work at low and high conc, progestins effective only at high conc
Slide 23-24
Do the estrogens directly inhibit GnRH neurons in the arcuate nucleus and preoptic area of the hypothalamus?
No
Estrogens stimulate inter neurons that inhibit GnRH neurons
In arcuate nucleus, exert inhibition via opiates
In preoptic area, exert inhibition via GABA
How do estrogens also feed positively to the hypothalamic-pituitary axis?
At a certain threshold (end of follicular phase), the hypothalamic-pituitary axis reverses its sensitivity to estrogens making them positive to the axis (they now increase sensitivity of gonadotrophs in the anterior pituitary to GnRH
Slide 27
