Podcast
Questions and Answers
Growth Hormone (GH) is a ______ amino acid peptide hormone.
Growth Hormone (GH) is a ______ amino acid peptide hormone.
191
GH is produced by ______ in the anterior pituitary gland.
GH is produced by ______ in the anterior pituitary gland.
somatotrophs
Most GH isoforms include all 5 ______ translated to a 191 aa protein.
Most GH isoforms include all 5 ______ translated to a 191 aa protein.
exons
Sertoli cells are also known as ______ cells.
Sertoli cells are also known as ______ cells.
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Leydig cells produce and secrete ______, primarily testosterone.
Leydig cells produce and secrete ______, primarily testosterone.
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The process by which semen is expelled from the penis is called ______.
The process by which semen is expelled from the penis is called ______.
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GH release mostly occurs at ______, particularly associated with deep sleep.
GH release mostly occurs at ______, particularly associated with deep sleep.
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Sustentacular cells provide ______ support for stem cell development.
Sustentacular cells provide ______ support for stem cell development.
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Semen includes secretions from accessory structures such as the ______.
Semen includes secretions from accessory structures such as the ______.
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The ______ is responsible for the transportation of sperm from the epididymis to the ejaculatory duct.
The ______ is responsible for the transportation of sperm from the epididymis to the ejaculatory duct.
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The ______ gland secretes a thick, alkaline mucus-like fluid that helps neutralize acidic urine in the urethra.
The ______ gland secretes a thick, alkaline mucus-like fluid that helps neutralize acidic urine in the urethra.
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The ______ acquires sperm during the process of ejaculation and contains mucus-secreting glands.
The ______ acquires sperm during the process of ejaculation and contains mucus-secreting glands.
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The ______ is where sperm matures and is stored in the male reproductive system.
The ______ is where sperm matures and is stored in the male reproductive system.
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The ejaculatory duct is formed from the junction of the ductus deferens and ______.
The ejaculatory duct is formed from the junction of the ductus deferens and ______.
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Semen contributes to approximately ______% of semen’s total volume.
Semen contributes to approximately ______% of semen’s total volume.
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The ______ supplies blood to the penis via internal pudendal arteries.
The ______ supplies blood to the penis via internal pudendal arteries.
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The internal penis contains ______ bodies surrounded by Buck's fascia.
The internal penis contains ______ bodies surrounded by Buck's fascia.
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The prostate gland produces a milky fluid and makes up ______% of semen volume.
The prostate gland produces a milky fluid and makes up ______% of semen volume.
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Testosterone is secreted by ______ cells.
Testosterone is secreted by ______ cells.
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The SRY gene produces ______ determining factor (TDF).
The SRY gene produces ______ determining factor (TDF).
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Testosterone and INSL3 facilitate testicular ______.
Testosterone and INSL3 facilitate testicular ______.
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The appearance of secondary sexual characteristics begins primarily at ______.
The appearance of secondary sexual characteristics begins primarily at ______.
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Spermatogenesis is regulated by hormones from the ______ and anterior pituitary gland.
Spermatogenesis is regulated by hormones from the ______ and anterior pituitary gland.
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In meiosis, primary spermatocytes produce ______ spermatocytes.
In meiosis, primary spermatocytes produce ______ spermatocytes.
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Spermiogenesis involves changes such as nuclear ______.
Spermiogenesis involves changes such as nuclear ______.
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The process of releasing mature sperm from Sertoli cells is called ______.
The process of releasing mature sperm from Sertoli cells is called ______.
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Testosterone influences male behavior and is the basis for male ______.
Testosterone influences male behavior and is the basis for male ______.
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Puberty typically begins between the ages of ______ and 14.
Puberty typically begins between the ages of ______ and 14.
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Leydig cells are primarily regulated by ______ hormone.
Leydig cells are primarily regulated by ______ hormone.
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Follicle Stimulating Hormone (FSH) chiefly regulates ______ proliferation.
Follicle Stimulating Hormone (FSH) chiefly regulates ______ proliferation.
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Testosterone can be converted to 17𝛽-_______ through aromatase.
Testosterone can be converted to 17𝛽-_______ through aromatase.
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The half-life of Luteinizing Hormone (LH) is approximately ______ minutes.
The half-life of Luteinizing Hormone (LH) is approximately ______ minutes.
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Inhibin B, produced by Sertoli cells, provides primary negative feedback on ______ release.
Inhibin B, produced by Sertoli cells, provides primary negative feedback on ______ release.
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Testes should normally measure between 4.1 cm and 5.2 cm in ______.
Testes should normally measure between 4.1 cm and 5.2 cm in ______.
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GnRH binds to ______ receptors on pituitary cells.
GnRH binds to ______ receptors on pituitary cells.
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Testosterone inhibits GnRH release at the ______ level.
Testosterone inhibits GnRH release at the ______ level.
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The hydrolysis of testosterone by 5𝛼-reductase produces ______.
The hydrolysis of testosterone by 5𝛼-reductase produces ______.
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Androgen-Binding Protein (ABP) is produced by ______ cells.
Androgen-Binding Protein (ABP) is produced by ______ cells.
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Mullerian Inhibitory Factor causes regression of the ______ duct.
Mullerian Inhibitory Factor causes regression of the ______ duct.
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The increase in cytosolic Ca2+ is a result of GnRH's effect on ______.
The increase in cytosolic Ca2+ is a result of GnRH's effect on ______.
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Sex Hormone-Binding Globulin (SHBG) is primarily produced in the ______.
Sex Hormone-Binding Globulin (SHBG) is primarily produced in the ______.
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Study Notes
Growth Hormone (GH)
- GH is a 191 amino acid peptide hormone with a molecular weight of ~22 kDa.
- Its structure is similar to prolactin and chorionic somatomammotropin.
- Two isoforms exist, produced by alternative splicing; most are 191 amino acids, others omit a portion of exon III.
Production and Release of GH
- GH is produced by somatotrophs in the anterior pituitary gland.
- Released in pulsatile bursts throughout the day, with peaks mostly occurring at night (associated with deep sleep).
- GH release increases during exercise and trauma.
- Factors influencing GH release: nutritional status, metabolic conditions, age-related sex steroids, adrenal glucocorticoids, thyroid hormones, renal function, and hepatic function.
Circulation of GH
- Normal circulating levels are approximately 80% bound to proteins.
Male Reproductive System Structure and Function
Testicular Structure and Function
- The testes consist of seminiferous tubules, interstitial connective tissue, and Leydig cells.
- Spermatogonia (sperm-forming cells) reside in the seminiferous tubules.
- Sertoli cells (sustentacular cells) surround the spermatogenic cells to support sperm production.
- Blood-testis barrier prevents immune system recognition of sperm antigens.
Sertoli Cells
- Provide structural support, nutrients, and protection for developing sperm.
- Secrete substances that regulate spermatogenesis (androgen-binding protein, inhibin).
- Phagocytize damaged cells.
Leydig Cells
- Located between seminiferous tubules.
- Produce and secrete testosterone into the interstitial fluid.
- Myoid cells surround tubules, contributing to sperm movement.
Sperm Flow
- Sperm travels from seminiferous tubules to the rete testis and then efferent ductules.
Duct System
- Transports sperm and forms semen.
- Ejaculation expels semen from the penis.
Epididymis
- Coiled tubes that store and mature sperm.
Ductus Deferens (Vas Deferens)
- Transports sperm from the epididymis to the ejaculatory duct.
- Can store sperm for months.
Ejaculatory Duct
- Short duct connecting the vas deferens and seminal vesicles to the prostatic urethra.
Urethra
- Transports both urine and semen.
- Contains mucus-secreting glands that contribute to semen.
- Divided into four parts: intramural, prostatic, membranous, and spongy.
Penis
- Delivers sperm into the female reproductive tract.
- Composed of three erectile bodies (corpora cavernosa and corpus spongiosum).
- Supplied with blood by internal iliac arteries.
- Lymphatic drainage to inguinal lymph nodes.
Accessory Sex Glands
- Produce the liquid portion of semen.
- Seminal vesicles: contribute ~60-70% of semen volume, containing fructose, prostaglandins, and coagulating factors.
- Prostate gland: contributes ~20-30% of semen volume; secretes milky fluid.
- Bulbourethral glands (Cowper's glands): secrete alkaline mucus that neutralizes urine.
Semen
- A sticky, whitish mixture of sperm and fluids from accessory glands.
- Average ejaculate contains 40-750 million sperm cells.
Gonadotropin Regulation of Gonadal Function
Follicle Stimulating Hormone (FSH)
- Short half-life (1-3 hours).
- Stable plasma levels, less variable than LH levels.
- Stimulates Sertoli cell proliferation and regulates seminiferous tubule growth, contributing to testicular size.
- Initiates spermatogenesis at puberty and promotes androgen-binding protein production, blood-testis barrier formation.
Luteinizing Hormone (LH)
- Shorter half-life (30 minutes).
- More variable levels with higher amplitude fluctuations than FSH.
- Regulates testosterone production by Leydig cells.
Control of Gonadotropin Synthesis and Release
- GnRH pulse generator is regulated by stimulatory/inhibitory signals: Norepinephrine, Serotonin, Neuropeptide Y (stimulatory); 𝛽-endorphin, GABA, Dopamine, and Interleukin 1 (inhibitory).
- 17𝛽-estradiol has dual (stimulatory/inhibitory) effects.
- GnRH stimulates phospholipase C, increasing inositol trisphosphate and diacylglycerol, ultimately leading to gonadotropin release.
- GnRH pulse frequency affects FSH (lower frequency = higher FSH) and LH (higher frequency = higher LH) production.
Testosterone Feedback Loop
- Testosterone provides negative feedback on GnRH, pituitary gonadotropin synthesis, and LH pulse amplitude/levels.
- Primarily affects tissues through 17𝛽-estradiol and 5𝛼-dihydrotestosterone.
Inhibin and Activin
- Inhibin B (from Sertoli cells): negative feedback on FSH production, primarily at the pituitary level.
- Activin: stimulates FSH release; antagonizes inhibin B.
Gonadal Hormone Synthesis & Metabolism: Testosterone
- LH stimulates cholesterol mobilization and transport into the steroidogenic pathway.
- Testosterone is primarily bound to SHBG (44%) and albumin (54%).
- Only a small fraction is free.
- Binding proteins regulate hormone action.
Androgen Receptor-Mediated Physiologic Effects
- Testosterone and DHT bind to the androgen receptor, a nuclear receptor influencing transcriptional regulation, DNA binding, and ligand binding.
- Testosterone affects sexual differentiation, libido, pubertal larynx growth, voice deepening, muscle anabolism, RBC production, and spermatogenesis.
- DHT is more potent, and its effects include embryonic external virilization, genitalia development, prostate development, body/facial hair growth, and male pattern baldness (in genetically predisposed).
Functions of Hormones During Fetal Development
- Y chromosome initiates Sertoli cell and spermatogonia development, leading to testis formation.
- Mullerian Inhibitory Factor (MIF): causes Mullerian duct regression.
- Testosterone develops Wolffian duct structures.
- DHT promotes prostate/penis growth.
Testicular Descent
- Two-step process (transabdominal and into scrotal sac) controlled by hormones, particularly testosterone and INSL3.
Effects of Androgens on Other Body Systems
- Puberty (ages 12-14, 4 years), growth hormone increases, and secondary sexual characteristics emerge (body/facial hair, pubic hair, voice change, skin thickening, sebaceous gland secretion, penis enlargement).
- Anabolic effects: increased bone density, muscle mass, and erythrocyte production.
- Affects behavior via libido.
Spermatogenesis
- Continuous process of forming spermatozoa in seminiferous tubules (spermatogonia → primary spermatocytes → secondary spermatocytes → spermatids → spermatozoa).
- Controlled by FSH and LH.
- Takes ~60-70 days.
- Process involves proliferation (mitotic divisions), meiosis, and spermiogenesis (cellular shape changes).
- Spermiation is the release of mature sperm.
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Description
This quiz covers key concepts related to Growth Hormone (GH) including its structure, production, release, and factors influencing its levels. Additionally, it explores the structure and function of the male reproductive system, focusing on testicular components and roles. Test your understanding of these important biological systems!
