BIO178 Lecture 4 Summer24 PDF

Lecture 4: The Endocrine System Part 3  Announcements Quiz #1 due tomorrow by 11:59pm The key will be posted by the end of Tuesday next week. Quiz #2 PDF will be up on Monday. Discussion #2 today! Annotated Bibliography & Paper discussion...

Lecture 4: The Endocrine System Part 3  Announcements Quiz #1 due tomorrow by 11:59pm The key will be posted by the end of Tuesday next week. Quiz #2 PDF will be up on Monday. Discussion #2 today! Annotated Bibliography & Paper discussion 2  Outline of Today’s Lecture 1. The Hypothalamic-Pituitary-Gonadal Axis a) Testes b) Ovaries 2. Hypothalamic-Pituitary-Gonadal Function Across the Lifespan 3. The Pineal Gland & Melatonin 4. Endocrine Regulation 3  Learning Objectives By the end of today’s lecture, you should be able to… 1. Describe the structure, functions, and biosynthesis of sex hormones and explain how their secretion is regulated by the hypothalamic-pituitary- gonad axis. 2. Describe how the activity of the hypothalamic-pituitary-gonadal axis changes across the lifespan in males and females. 3. Describe the structure, functions, and biosynthesis of melatonin. 4. **Explain the processes by which secretion and activity of hormones can be regulated** 4  The Gonads and the Hypothalamic-Pituitary-Gonadal Axis Hypothalamic & Anterior Pituitary Hormones 6  Testes Spermatogenesis + tonic (baseline) endocrine function 1. Leydig cells (interstitial) Outside seminiferous tubules Controlled by LH from anterior pituitary Secrete androgens (C19 steroids) 7  21 CH3 Androgens 20 C=O (C19 Steroids) 19 Pregnenolone (precursor) HO O OH O Androstenedione O Testosterone 8  Testes Androgens (cont.) Functions: Spermatogenesis Genital tract maintenance Accessory sex organs 2nd-degree sex characteristics Metabolism Cognition Sexual behavior, aggression Mood a. Testosterone Acts as a prohormone for… Dihydrotestosterone (DHT) (via 5-reductase) Estrogen (via aromatase) b. Dihydrotestosterone (DHT) Strong androgen Can’t be aromatized to estrogen c. Androstenedione Weak androgen 9  Testes 2. Sertoli cells Inside seminiferous tubules Controlled by FSH, testosterone Secrete: a. Müllerian inhibiting hormone (protein) Inhibits development of female accessory sex organs early in development b. Inhibin (protein) Inhibits FSH release from anterior pituitary 10 Hypothalamic-Pituitary-Testicular Axis 11  Hypothalamic-Pituitary-Testicular Axis 1. Hypothalamic Hormone: Gonadotropin-Releasing Hormone (GnRH) Binds to receptors on anterior pituitary Stimulates anterior pituitary to synthesize and secrete gonadotropins (LH and FSH) 2a. Anterior Pituitary Hormone: Luteinizing Hormone (LH) Binds to receptors on Leydig cells Stimulates growth of Leydig cells Stimulates synthesis and secretion of androgens 2b. Anterior Pituitary Hormone: Follicle-Stimulating Hormone (FSH) Binds to receptors on Sertoli cells Stimulates growth and activity of Sertoli cells Stimulates synthesis and secretion of inhibin 3a. Testicular Hormones: Androgens (testosterone) Feed back to hypothal. and pit. to GnRH, LH, and FSH secretion Influence development, structure, and activity of body and brain 3b. Testicular Hormone: Inhibin Feeds back to pituitary to FSH secretion 12  Ovaries Oogenesis + cyclical endocrine function 1. Estrogens (C18 steroids; synthesized from androgens) Genital tract maintenance 2nd-degree sex characteristics Water retention Ca++ metabolism Cognition Hello, my Sexual behavior name is Este! Maternal behavior a. 17b-Estradiol (E2) b. Estrone (E1) c. Estriol (E3) 13  21 CH3 Estrogens 20 C=O (C18 Steroids) 19 Pregnenolone (precursor) HO OH O HO HO 17-Estradiol Estrone 14  Ovaries 2. Progesterone (C21 steroid) Pregnancy maintenance in mammals Sexual behavior Maternal behavior 3. Inhibin (protein) Inhibits FSH release from anterior pituitary Progestogens (C21 steroids): Pregnenolone 21 CH3 Progesterone 21 CH3 (precursor) 20 C=O 20 C=O 19 HO O 15  Temporary Organ: Placenta Protein hormones - act as supplementary trophic hormones: 1. Chorionic gonadotropin (CG/hCG) (LH-like) 2. Placental lactogen (PL) (prolactin-like) 3. Chorionic corticotropin (CC) (ACTH-like) 4. Chorionic thyrotropin (CT) (TSH-like) 5. GnRH, prolactin, etc. Steroid hormones: **Fun Fact: Placenta is full of 1. Estrogens nutrients and many animals – 2. Progestogens including some humans – eat it post- 3. Corticosteroids birth. 4. Androgens 16 …And some animals even eat the placenta of OTHER species! https://www.youtube.com/watch?v=63BZipVY74Y 17  Activity of the Hypothalamic- Pituitary-Gonadal Axis Across the Lifespan Hypothalamic-Pituitary-Gonadal Function Across the Lifespan (Primates) Phase of Life Hypothalamic-Pituitary-Gonadal Axis Prenatal period Active Infancy Active Childhood Dormant (prepubertal hiatus) Puberty Becomes active (reawakening) Adulthood Active Old age Declines (reproductive senescence) 19 Hypothalamic-Pituitary-Gonadal Function Across the Lifespan (Primates) Human female 20 Hypothalamic-Pituitary-Gonadal Function Across the Lifespan (Primates) Human male INSL3 – Insulin-like hormone 3: from gonads; might play a role in development of reproductive organs. 21 The Pineal Gland & Melatonin  Pineal Gland Photoreceptive in non-mammalian vertebrates (“third eye”) Endocrine gland in mammals; produces indoleamines (derivatives of tryptophan): 1. Serotonin (hydrophilic) Produced in light 2. Melatonin (hydrophobic) Produced in dark Circadian rhythms Sleep/wake cycle Reproductive effects (seasonal breeding) 23 Pineal Gland 24  Pineal Gland Serotonin in Pineal Melatonin in Pineal Lewczuk et al. 2014 (ducks) 25 Regulation of Endocrine Function  Endocrine Regulation Regulation of hormone secretion by… 1. Neural input Examples: Hypothalamic hormones Posterior pituitary hormones Adrenal medulla 27  Endocrine Regulation Regulation of hormone secretion by… 2. Hormones Examples: Hypothalamic, anterior pituitary, & target organs 3. Physiological end-products Example: Insulin & blood glucose levels: High glucose  insulin secretion from pancreas Insulin →  glucose uptake into cells 28  Endocrine Regulation Regulation of hormone secretion by… 4. Negative Feedback Production of a hormone is decreased in response to itself or its end-product Involved in most endocrine regulation Maintains stability, consistency Silverthorn 2009 29  Endocrine Regulation Regulation of hormone secretion by… 5. Positive Feedback Silverthorn 2009 Production of a hormone is increased in response to its end-product. Accelerates ongoing process; leads to dynamic change Less common Example: Oxytocin  uterine contractions →  oxytocin 30  Endocrine Regulation Regulation of hormone secretion by… 6. Regulation of Hormone Biosynthesis Example Cortisol increases expression of the enzyme that converts norepinephrine to epinephrine in the adrenal medulla 31  Endocrine Regulation Regulation of hormone secretion by… 7. Biological Rhythms a. Circadian Rhythms Endogenous cycle of ~24 hours in hormone secretion (and many other physiological processes) 32  Endocrine Regulation Regulation of hormone secretion by… 7. Biological Rhythms b. Pulsatile (Episodic) Secretion Many hormones are released in bursts (pulses) Frequency of pulses – minutes to hours 33  Endocrine Regulation Regulation of hormone secretion by… 7. Biological Rhythms c. Circannual (Seasonal) Rhythms Some hormones change across the year Caused by temperature, daylength, or other variables Thyroid-stimulating hormone in humans Testosterone in male deer 34  Endocrine Regulation Regulation of hormone secretion by… 7. Biological Rhythms d. Changes Across the Lifespan Secretion of some hormones changes across the lifespan 35  Endocrine Regulation Regulation of hormone bioactivity by… 1. Regulation of Carrier Proteins Examples: Estrogen  corticosteroid-binding globulin levels  bioavailability of cortisol Cortisol  Corticosteroid-binding globulin levels  bioavailability of cortisol 36  Endocrine Regulation Regulation of hormone bioactivity by… 2. Regulation of Receptor Numbers Can be regulated by either the receptor’s ligand or another hormone a. Up-regulation Examples: Prolactin  prolactin receptors Estrogen  progesterone receptors b. Down-regulation Examples: Insulin  insulin receptors Progesterone  estrogen receptors 37  Endocrine Regulation Regulation of hormone bioactivity by… 3. Regulation of Receptor Affinity Affinity = how likely something is to bind/the strength of the binding High affinity = more receptors will be bound with the ligand Specificity = how specific a ligand needs to be to bind to a receptor Low specificity = more than one ligand may bind to the same receptor 38  Endocrine Regulation Regulation of hormone bioactivity by… 4. Permissive Effects One hormone brings about the conditions necessary for a second hormone to act 39 End of Lecture 4 40