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Sperm contributes approximately ______% of semen’s total volume.
Sperm contributes approximately ______% of semen’s total volume.
10
A typical ejaculate is between ______ and 5 ml in volume.
A typical ejaculate is between ______ and 5 ml in volume.
2.5
Follicle Stimulating Hormone (FSH) is located on ______ cells.
Follicle Stimulating Hormone (FSH) is located on ______ cells.
Sertoli
Luteinizing Hormone (LH) primarily regulates testosterone production by ______ cells.
Luteinizing Hormone (LH) primarily regulates testosterone production by ______ cells.
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Testosterone inhibits GnRH release at the ______ level.
Testosterone inhibits GnRH release at the ______ level.
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Inhibin B, produced by Sertoli cells, provides primary negative feedback at the ______ level.
Inhibin B, produced by Sertoli cells, provides primary negative feedback at the ______ level.
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Activin stimulates ______ release.
Activin stimulates ______ release.
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The ______ feedback loop involves inhibin B controlling FSH release.
The ______ feedback loop involves inhibin B controlling FSH release.
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Cholesterol transport is facilitated by the ______ protein for testosterone biosynthesis.
Cholesterol transport is facilitated by the ______ protein for testosterone biosynthesis.
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Most testosterone effects are mediated by ______ 17β-estradiol.
Most testosterone effects are mediated by ______ 17β-estradiol.
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Descent into scrotal sac is controlled by ______ and INSL3.
Descent into scrotal sac is controlled by ______ and INSL3.
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Spermatogenesis begins at ______ and continues for life.
Spermatogenesis begins at ______ and continues for life.
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Hormones from the hypothalamus and anterior pituitary gland regulate ______.
Hormones from the hypothalamus and anterior pituitary gland regulate ______.
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Testosterone causes an increase in ______ production, which is essential for red blood cell formation.
Testosterone causes an increase in ______ production, which is essential for red blood cell formation.
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The process of sperm maturation is known as ______.
The process of sperm maturation is known as ______.
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Spermatocytogenesis, spermiogenesis, and ______ make up the entire process of sperm production.
Spermatocytogenesis, spermiogenesis, and ______ make up the entire process of sperm production.
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Secondary sexual characteristics include growth of facial hair and ______.
Secondary sexual characteristics include growth of facial hair and ______.
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During spermatogenesis, primary spermatocytes undergo ______ to produce secondary spermatocytes.
During spermatogenesis, primary spermatocytes undergo ______ to produce secondary spermatocytes.
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Growth Hormone (GH) is a peptide hormone made up of ______ amino acids.
Growth Hormone (GH) is a peptide hormone made up of ______ amino acids.
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GH is produced by ______ in the anterior pituitary gland.
GH is produced by ______ in the anterior pituitary gland.
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The release of GH mostly occurs at ______.
The release of GH mostly occurs at ______.
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Sustentacular cells are also known as ______ cells.
Sustentacular cells are also known as ______ cells.
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Leydig cells produce and secrete ______ into the surrounding interstitial fluid.
Leydig cells produce and secrete ______ into the surrounding interstitial fluid.
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Sperm maturation begins in the ______ tubule.
Sperm maturation begins in the ______ tubule.
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The ______ barrier prevents immune system cells from detecting antigens on sperm cells.
The ______ barrier prevents immune system cells from detecting antigens on sperm cells.
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The process of ______ refers to the expulsion of semen from the penis.
The process of ______ refers to the expulsion of semen from the penis.
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The ______ is the site of sperm maturation and storage.
The ______ is the site of sperm maturation and storage.
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The ______ is responsible for transporting sperm to the ejaculatory duct.
The ______ is responsible for transporting sperm to the ejaculatory duct.
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The ______ secretes a fluid that makes up 60-70% of semen volume.
The ______ secretes a fluid that makes up 60-70% of semen volume.
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The ______ gland surrounds the urethra and is influenced by androgens.
The ______ gland surrounds the urethra and is influenced by androgens.
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The ______ secretes a thick, alkaline mucus-like fluid that neutralizes urine.
The ______ secretes a thick, alkaline mucus-like fluid that neutralizes urine.
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The ______ transports both urine and semen and is surrounded by smooth muscle.
The ______ transports both urine and semen and is surrounded by smooth muscle.
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The ______ has regions that include the head, body, and tail.
The ______ has regions that include the head, body, and tail.
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The ______ expands to form the bulb and glans during erection.
The ______ expands to form the bulb and glans during erection.
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The ______ is filled with many long, coiled tubes and is crucial for sperm storage.
The ______ is filled with many long, coiled tubes and is crucial for sperm storage.
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The ______ transports sperm through the pelvis, crossing over the ureter.
The ______ transports sperm through the pelvis, crossing over the ureter.
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Testosterone is primarily bound to ______ and albumin.
Testosterone is primarily bound to ______ and albumin.
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The enzyme ______ converts testosterone into estradiol.
The enzyme ______ converts testosterone into estradiol.
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The primary roles of DHT include embryonic external virilization and ______ growth.
The primary roles of DHT include embryonic external virilization and ______ growth.
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The ______ hormone is secreted by Sertoli cells and causes Mullerian duct regression.
The ______ hormone is secreted by Sertoli cells and causes Mullerian duct regression.
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The ______ protein, produced by Sertoli cells, is involved in transporting testosterone.
The ______ protein, produced by Sertoli cells, is involved in transporting testosterone.
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Genetic sex is determined at ______.
Genetic sex is determined at ______.
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Testosterone acts through both direct effects and metabolic conversion to ______ and DHT.
Testosterone acts through both direct effects and metabolic conversion to ______ and DHT.
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Testicular production accounts for approximately ______% of circulating estrogen in males.
Testicular production accounts for approximately ______% of circulating estrogen in males.
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Both testosterone and DHT bind to the same ______.
Both testosterone and DHT bind to the same ______.
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The two-step process of testicular descent includes transabdominal migration and ______.
The two-step process of testicular descent includes transabdominal migration and ______.
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Study Notes
Growth Hormone (GH)
- 191 amino acid peptide hormone
- Molecular weight ~22 kDa
- Similar structure to prolactin and chorionic somatomammotropin
- Two isoforms, differing by splicing, affecting translation
- Produced by somatotrophs in the anterior pituitary gland
- Released in pulsatile bursts, mostly at night (deep sleep) and during exercise/trauma
- Factors influencing release include nutritional status, metabolic conditions, age, sex steroids, adrenal glucocorticoids, thyroid hormones, renal and hepatic function.
Circulation of Growth Hormone
- Normal circulating level is 80% of testicular mass.
- Blood contains a basement membrane and two cell types: spermatogonia (sperm-forming cells) and sustentacular cells (Sertoli cells).
Sustentacular Cells (Sertoli Cells)
- Surround spermatogenic cells, providing support
- Form the blood-testis barrier, preventing immune cell-sperm interaction.
- Provide structural support, nutrients, and testicular fluid for sperm transport.
- Produce androgen-binding protein (ABP) and inhibin, regulating spermatogenesis.
- Phagocytose damaged cells.
Leydig Cells
- Interstitial cells located between seminiferous tubules.
- Produce and secrete androgens, primarily testosterone.
Sperm Flow
- Begins in the seminiferous tubules.
- Enters single straight tubules, then the rete testis, and finally the efferent ductules.
Duct System
- Transports sperm with associated fluids (e.g., reabsorption).
- Includes epididymis, ductus deferens, ejaculatory duct, and urethra
Epididymis
- Coiled tubes where sperm mature and are stored.
- Phagocytosis occurs, recycling aging sperm
- Filled with long, coiled tubes; includes head, body, and tail sections - sperm flow pathway from efferent ductules → Ductus epididymis → Ductus deferens
Ductus Deferens (Vas Deferens)
- Extends from the epididymis' tail into the pelvic cavity.
- Passes through the spermatic cord, inguinal canal, and eventually joins up with the ejaculatory duct.
- Capable of storing sperm for months.
Ejaculatory Duct
- Short duct formed by the union of the ductus deferens and a seminal vesicle.
- Passes through the prostate.
Urethra
- Shared by reproductive and urinary systems.
- Transports both urine and semen. Consists of 4 parts:
- Intramural (preprostatic) urethra
- Prostatic urethra
- Membranous urethra (intermediate)
- Spongy (cavernous or penile) urethra
Penis
- Designed to deliver sperm into the female reproductive tract.
- External penis features include root, body, and glans penis (prepuce).
- Internal penis consists of three bodies: 2 corpora cavernosa and 1 corpus spongiosum
- It has a complex blood supply, lymphatic drainage.
Accessory Sex Glands
- Exocrine glands producing the liquid portion of semen.
- Seminal vesicles: main component of semen (60-70%), containing fructose (ATP), prostaglandins (muscle contractions), and coagulating proteins/enzymes.
- Prostate gland: milky fluid; surrounds the urethra and ejaculatory ducts (20-30% of semen volume)
- Bulbourethral glands (Cowper's glands): small glands at the base of the penis; secrete mucus-like fluid that neutralizes acidic urine and lubricates the glans.
Semen
- A whitish mixture of sperm and secretions from accessory glands.
- Typical ejaculate volume is 2.5-5 mL, containing 40-750 million sperm
Gonadotropin Regulation of Gonadal Function
-
Follicle Stimulating Hormone (FSH):
- Half-life of 1-3 hours, stable levels.
- Binds to Sertoli cell membrane receptors, stimulating Sertoli cell proliferation, seminiferous tube growth, initiating spermatogenesis at puberty, and promoting ABP production.
- Normal adult testicular dimensions: 4.1-5.2 cm length, 2.5-3.3 cm width.
-
Luteinizing Hormone (LH):
- Half-life of 30 minutes, variable levels.
- Binds to Leydig cell receptors, regulating testosterone production.
Control of Gonadotropin Synthesis and Release
- Regulated by GnRH pulse generator in the hypothalamus, receiving both stimulatory and inhibitory signals (e.g., norepinephrine, serotonin, neuropeptide Y, beta-endorphin, GABA, dopamine, interleukin 1, 17beta-estradiol).
GnRH Signaling Pathway
- GnRH binds to GPCR, activating phospholipase C.
- This increases inositol trisphosphate (IP3), diacylglycerol (DAG), protein kinase C, and cytosolic Ca2+.
- This leads to gonadotropin release.
- Pulse frequency affects hormone production (FSH and LH).
Testosterone Feedback Loop
- Testosterone inhibits GnRH release, gonadotropin beta-subunit synthesis, LH pulse amplitude, and levels.
- Most testosterone effects mediated via 17beta-estradiol.
FSH Feedback Loop
- Inhibin B (from Sertoli cells) provides primary negative feedback at the pituitary level, controlling FSH release.
Inhibin and Activin
- Inhibin B: Member of the TGF-beta superfamily, produced by Sertoli cells, negatively feedbacks on FSH production.
- Activin: TGF-beta family member, stimulates FSH release and antagonizes inhibin B.
Gonadal Hormone Synthesis & Metabolism: Testosterone
- LH stimulates Leydig cells to produce testosterone.
- This process involves cholesterol transport, sequential enzymatic conversions (including androstenedione to testosterone), gene expression, and increased STAR and P450scc activity.
- Primarily bound to SHBG (44%) and albumin (54%), with only a small fraction as "free" hormone.
Sex Hormone-Binding Globulin (SHBG)
- Produced in the liver and involved in non-genomic steroid signaling.
Testosterone Effects
- Two main pathways include direct effect via androgen receptor (AR) and metabolic conversion to 17beta-estradiol (via aromatase) or 5alpha-dihydrotestosterone (DHT). Enzymatic conversion is irreversible
- 5 alpha-reductase catalyzes the conversion of testosterone into DHT, with effects more potent at lower concentrations.
Gonadal Hormone Synthesis: Estradiol
- Converted from testosterone by aromatase enzyme, found in Leydig cells, adipose tissue, brain, and bone.
- Testicular production ~20% of male estrogen.
Androgen Receptor-Mediated Physiologic Effects
-
Androgen receptor (AR): Member of the nuclear receptor superfamily, with functional domains for transcriptional regulation, DNA binding, and ligand binding. Both testosterone and DHT bind to the same receptor, but DHT elicits a more potent effect due to its longer half-life.
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Testosterone Effects: Sexual differentiation, libido, pubertal larynx growth, deepening of the voice, muscle anabolism, RBC production, and spermatogenesis stimulation.
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DHT EFFECTS: More potent androgen receptor activator with longer half-life, important for embryonic virilization, male external genitalia development, prostate growth, facial/body hair, and male pattern baldness (in predisposed individuals).
Functions of Hormones During Fetal Development
- Development of male genitalia (descent of testes), controlled by hormones (MIF, testosterone, DHT).
Sexual Differentiation
- Driven by genetic, gonadal, and phenotypic sex, with the Y chromosome triggering Sertoli and spermatogonia development, testis formation, and Mullerian duct regression.
Testicular Descent
- A two-step (transabdominal migration and scrotal descent) process, controlled by testosterone and INSL3.
Effects of Androgens on Other Body Systems
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Puberty: (age 12-14, 4 years) marked by increased pulsatile GnRH secretion, activating the HPG axis; this leads to increased gonadotropins, testicular enlargement, sex steroid activation of spermatogenesis, and growth of prostate/seminal vesicles/epididymis, developing secondary sexual characteristics (e.g., hair growth, voice changes, and sebaceous gland activity).
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Testosterone anabolic effects: increase bone density, skeletal muscle mass, and erythrocyte production (due to increased erythropoietin secretion)
Spermatogenesis
- Continuous process of germ cell differentiation to produce spermatozoa.
- Regulated by hypothalamus and anterior pituitary gland hormones (GnRH stimulating more FSH than LH, leading to spermatogenesis).
- Occurs in seminiferous tubules, involving spermatogonia proliferation and meiosis, leading to spermatids that go through spermiogenesis before spermiation, a process that last 60-70 days.
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Description
This quiz covers the essential concepts of Growth Hormone, including its structure, release factors, and physiological roles. It also delves into the function of Sertoli cells in supporting spermatogenesis and maintaining the blood-testis barrier. Test your knowledge on these crucial topics in endocrinology and reproductive biology.
