Male Reproductive Physiology Flashcards by Sarah Gillen

Describe the Hypothalamic-pituitary-testicular axis in terms of hormones released

Hypothalamus = GnRH

Anterior pituitary = FSH, LH

Testes = testosterone, inhibin

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Describe negative feedback via HPT axis

Testosterone from testes inhibits GnRH and LH from H and AP

Inhibin and estradiol inhibit FSH and GnRH

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What 4 physiological processes are controlled by the hypothalamic-pituitary-testicular axis?

Phenotypic gender (embryogenesis)

Sexual maturation (puberty)

Testosterone production

Sperm production

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What is the difference between genetic sex, gonadal sex, and phenotypic sex?

Genetic sex = XY vs. XX

Gonadal sex = testes vs. ovaries

Phenotypic sex = internal and external genitalia

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What hormones determine phenotypic sex?

Antimullerian hormone and testosterone (presence = male, absence = female)

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80% of the testes composition is _____ ______, which produce sperm

Seminiferous tubules

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What cell types are found in the seminiferous tubules?

Sertoli cells (supportive)

Spermatogonia (stem cells)

Spermatocytes (developing sperm)

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If seminiferous tubules make up 80% of the testes, what makes up the other 20%?

Connective tissue/interstitium

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What cell types are found in the CT/interstitium of the testes?

Leydig cells — produce testosterone

Also mast cells, macrophages, nerves, blood vessels, lymph vessels

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In terms of hormonal control, Leydig cells are stimulated by _____, and sertoli cells are stimulated by ____

LH; FSH

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2 Exocrine functions of the sertoli cells

Secrete aqueous fluid into lumen of seminiferous tubules —> sperm transport from tubules to epididymis

Produce androgen-binding protein —> binds testosterone and concentrates it in seminiferous tubules

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In terms of endocrine function of the sertoli cells, what 3 hormones do they produce?

Antimullerian hormone

Inhibin

Aromatase

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Action of antimullerian hormone produced by sertoli cells

Regression of internal femal genital ducts

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Action of inhibin produced by sertoli cells of testes

Inhibits FSH

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Action of aromatase produced by sertoli cells of the testes

Converts testosterone to estradiol-17B

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What are the supportive functions of sertoli cells of the testes?

Provide nutrients to differentiating sperm (transferrin, Fe, lactate)

Form tight junctions (blood testes barrier)

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Leydig cells synthesize and secrete testosterone. They can make their own ______ de novo, or acquire it from circulation

Cholesterol

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How does GnRH secretion change at puberty? What effects does this have on the rest of the HPT axis?

GnRH from hypothalamus becomes pulsatile —> pulsatile FSH and LH secretion from AP —> sex steroid hormon secretion (e.g., testosterone)

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What are the 3 primary androgens?

Testosterone
Dihydrotestosterone (DHT)
Androstenedione

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Androgens bind androgen receptors in reproductive and non-reproductive tissues with varying affinity. Which androgen has the highest affinity in males?

DHT has the highest, followed by testosterone, then androstenedione

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______ is an active androgen in MOST androgenic target tissues?

Testosterone

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Testosterone is made in Leydig cells. Where does it go from there?

To seminiferous tubules —> peritubular capillaries —> peripheral circulation

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Testosterone binds _____ _____ _____in the seminiferous tubules, which leads to its concentration

Androgen-binding protein (ABP)

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Testosterone binds various proteins in peripheral circulation — what proteins does it primarily bind to and which of these allow it to be biologically active?

60% binds sex hormone binding globulin (SHBG) = inactive

38% binds albumin = weakly active

2% is free T = biologically active!

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Testosterone production begins at 7-8 weeks gestation. What are its initial roles in development?

Stimulates formation of internal male genitalia (epididymis, vas deferens, seminal vesicles), penis, scrotum Also stimulates testicular descent

Testosterone leads to the development of what secondary sex characteristics at puberty?

``` Growth spurt Closure of epiphyseal plates Acne Increased muscle mass Deepening of voice Body hair Baldness Libido Growth of penis and seminal vesicles Increased BMR Increased RBCs ```

What aspect of sperm development is stimulated by testosterone?

Spermatogenesis

What enzyme is responsible for the conversion of testosterone to DHT in target tissues?

5-alpha-reductase

T/F: testosterone is an active androgen in most androgenic target tissues, while DHT is only active in some

True

What role does DHT play during development?

Stimulates development of external male genitalia (penis, scrotum, prostate)

What role does DHT play during puberty?

Sebaceous gland activity | Prostate growth

What hormone is often considered responsible for male pattern baldness?

DHT

The pathogenesis of BPH is poorly understood, but requires androgens, especially ____

DHT

BPH causes enlargement of periurethral prostate lobes, which compress the urethra. This leads to what type of storage and voiding symptoms?

Urinary frequency and urgency, slow stream, dribbling after urination

T/F: BPH often represents a malignant process

False - it is NOT premalignant!

What are 1st and 2nd line tx for BPH?

1st line = alpha-1 antagonists which relax smooth muscle in bladder neck and urethra 2nd line = 5-alpha reductase inhibitors which block conversion of testosterone to DHT (less DHT = less hyperplasia)

Testosterone can be aromatized to estrogens like estradiol in peripheral tissues and sertoli cells. What actions does this have in males?

Bone maturation Growth acceleration Breast growth Role in spermatogenesis

In general, male hypogonadism refers to a decrease in ____ and/or _____ production

Sperm/testosterone

In ______ hypogonadism, or Klinefelter syndrome, the pt is born with ______ chromosome profile, meaning that they have a ____ phenotype

Primary; 47 XXY; male (bc they have Y chromosome)

What effect does primary hypogonadism have on testis function?

Abnormal Leydig cell function — low testosterone production —> high LH —> high estrogen Seminiferous tubule dysgenesis —> infertility, decreased inhibin leads to high levels of FSH

Causes of secondary hypogonadism

Nonfunctioning pituitary tumors Kallmann syndrome

Symptoms of secondary hypogonadism d/t nonfunctioning pituitary tumors

Pituitary compression leads to low LH and FSH production —> low testosterone —> hypogonadism Mass effect = visual symptoms, headache

Pathogenesis of Kallmann syndrome leading to secondary hypogonadism

GnRH neurons fail to migrate into hypothalamus during embryonic development —> low GnRH secretion —> low LH, FSH —> low testosterone

Symptoms of secondary hypogonadism due to Kallmann syndrome

Delayed/absent puberty Infertility Impaired sense of smell (anosmia)

Spermatogenesis occurs in the __________, beginning at _____ and continuing throughout life ______ are the immature germ cells present at birth that will undergo this process

Seminiferous tubules; puberty Spermatogonia

What are the 3 phases of spermatogenesis?

Mitotic division Meiotic division Spermiogenesis

Phase 1 of spermatogenesis = mitotic division This phase starts with _______, the immature germ cells which will undergo mitosis to produce ________

Spermatogonia 2 primary spermatocytes

Phase 2 of spermatogenesis = meiotic divisions This phase starts with ___________ which undergo 2 meiotic divisions. The first division produces ________, each with a _____ number of duplicated chromosomes The second division produces ________, each with a _____ number of unduplicated chromosomes

Primary spermatocytes; 2 secondary spermatocytes; haploid 2 spermatids; haploid

Phase 3 of spermatogenesis = spermiogenesis This phase starts with ________ which undergo nuclear and cytoplasmic changes to produce mature ______

Spermatids; spermatozoa

T/F: the entire process of spermatogenesis takes about 25 days

False; it takes ~74

What are the functional parts of the sperm?

Head = fertilization Tail = motility

What are the components of the head of the sperm

Nucleus Acrosome = thick cap, contains enzymes (hyaluronidase, proteolytic enzymes)

What are the components of the tail/flagellum of the sperm?

Axoneme = central skeleton of microtubules Mitochondria Dynein = ATPase

Sperm live best in a slightly _____ environment Increased temperature _______ the lifespan of sperm, hence the role of the scrotum

Alkaline Decreases

Lifespan of sperm in testes vs. in female genital tract

In testes = 1 month or greater In female genital tract = 1-2 days

What is the role of testosterone in spermatogenesis? What hormone is required for stimulating adequate testosterone secretion?

Growth and division of spermatogonia; LH stimuates testosterone

What role does FSH play in spermatogenesis?

FSH stimulates sertoli cells

What role does growth hormone play in spermatogenesis?

Early division of spermatogonia

What route do sperm take prior to ejaculation?

Seminiferous tubules in testes —> epididymis —> vas deferens —> seminal vesicles and ejaculatory duct of prostate —> urethra via bulbourethral glands

Where are sperm stored in order to mature and gain coordinated motility, as well as undergo decapacitation?

Epididymis

________ = addition of molecules to the membranes to prevent premature acrosomal reaction; occurs in epidydimis

Decapacitation

The vas deferens functions to store sperm in the ______, as well as secretes fluid rich in ____ and _____ to nourish sperm prior to ejaculation

Ampulla; citrate; fructose

The ________ secrete fluid containing fructose, citrate, prostaglandins, and fibrinogen to nourish sperm. What role do these prostaglandins play in fertilization?

Seminal vesicles Prostaglandins thin out cervical mucous as well as cause reverse peristalsis in uterus so that sperm can make it to ovaries

The 2 ejaculatory ducts empty sperm into the ______, where they are stored as ____ until ejaculation

Prostatic urethra; semen

The prostate gland secretes slightly _____ fluid containing citrate, phosphate, calcium, and enzymes. This neutralizes the acidity of other seminal fluids, improves ______ of sperm, and aids in fertilization

Alkaline; motility

The ______ glands secrete clear fluid for lubrication of the urethra prior to ejaculation

Bulbourethral

What characteristics of semen are examined during lab testing?

``` Morphology Motility Total sperm count Vitality Volume ```

During arousal, sensory nerve signals at the glans penis are transmitted via _____ nerve to the sacral spinal cord

Pudendal

There are 3 total erectile bodis in the penis: 2 ______ and 1 _______

Corpora cavernosa; corpus spongiosum

During an erection, ________ tone predominates, with _____, _____, and/or _____ NTs participating

Parasympathetic; ACh; nitric oxide (NO); VIP

What role does nitric oxide play during an erection?

NO activates cGMP —> smooth muscle relaxation Arterial dilation for increased blood flow; increased intercavernosal pressure for cavernosal expansion; veins compressed by engorged tissue leading to reduced venous drainage overall

What are some causes of erectile dysfunction?

Vascular disease (HTN, DM, atherosclerosis) Neurogenic Psychogenic Endocrinologic Medication-induced

Tx for erectile dysfunction

Phosphodiesterase-5 (PDE-5) inhibitors like viagra, which increase cGMP levels in erectile tissue

_______ = movement of semen toward ejaculatory ducts, which is under _____ nervous control

Emission; sympathetic

Emission consists of sequential peristaltic contractions of ________ smooth muscle, causing semen to move into internal urethra, and the ______ sphincter of the bladder closes

Vas deferens; internal

Ejaculation occurs when there is rhythmic contraction of the _____ and _____ muscles around the base of the penis, increasing the pressure in genital ducts and urethra

Bulbospongiosus; ischiocavernosus

________ occurs when mature sperm come in contact with fluids in the female tract

Capacitation

Capacitation involves loss of ________ factors in seminal fluid, loss of _______ on acrosome, which weakens the head of the sperm. There is also increased _____ permeability which leads to improved motility and changes in the cellular membrane allowing for acrosome to release enzymes. The ______ ______ receptors are exposed.

Inhibitory; cholesterol; calcium; zona pellucida

When the sperm and oocyte meet, the ______ membrane dissolves and enzymes escape. Among these enzymes: ______ breaks down the granuloma cell layer surrounding the ovum Proteolytic enzymes breakdown tissue cells adhering to ovum, creating a pathway for sperm to pass through _______ and enter ovum so that the cell membranes can fuse and genetic material combines

Acrosomal Hyaluronidase Zona pellucida

Male Reproductive Physiology Flashcards

(79 cards)