TOPIC VII: ENDOCRINE SYSTEM Flashcards
What does the endocrine system regulate?
Growth, reproduction, and metabolism (long-term events). Glands and tissues secrete hormones that travel in the blood to target cells
How do hormones affect target cells?
Hormones bind to receptors on target cells and change cell activity. Target cells are cells of an effector tissue/organ that have specific receptors for that hormone.
Where are hormone receptors found?
On the cell membrane or intracellularly (nuclear).
How do water-soluble hormones act on target cells?
They bind to receptors on the cell membrane and act as “1st messengers” in a signaling cascade because they can’t cross the phospholipid bilayer.
Describe the mechanism of action of water-soluble hormones.
a) Hormone binds to cell membrane receptors b) Hormone-receptor complex activates membrane proteins (e.g., G-proteins) c) Membrane proteins activate 2nd messenger systems (e.g., cAMP, Ca2+).
Explain how cAMP acts as a second messenger.
a) Hormone binds to cell-surface receptor and activates a G-protein b) G-protein activates adenylate cyclase c) Adenylate cyclase converts ATP to cAMP d) cAMP activates protein kinases e) protein kinase acts on other proteins (phosphorylates) to alter their activity.
List reasons for using 2nd messenger systems.
a) Hormone can’t enter cell (water soluble) b) rapid acting (enzymes already present - just activate) c) 1 hormone molecule activates many enzyme molecules (cascade), which multiplies the signal d) limited - messenger broken down or removed.
How are lipid-soluble hormones different from water-soluble hormones in their mechanism of action?
Lipid-soluble hormones enter the target cell and bind to intracellular (nuclear) receptors to trigger protein synthesis. This is a slow but long-lasting response.
Describe the mechanism of action of lipid-soluble hormones.
a) Enter target cell and bind to intracellular (nuclear) receptors b) Hormone-receptor complex binds to DNA (activates genes) ⇒ starts gene transcription – produces messenger RNA (mRNA) c) mRNA attaches to ribosomes to produce proteins (translation).
What are the three types of stimuli that regulate hormone secretion?
Humoral, neural, and hormonal stimuli.
What is a humoral stimulus? Give an example.
Stimulus for hormone release is changes in the concentration of an ion or nutrient in the blood. Example: ↑blood glucose causes pancreatic β-cells to release insulin ⇒ ↓blood glucose.
What is a neural stimulus? Give an example.
Heart Rate (HR).
What is a hormonal stimulus? Give an example.
Metabolism.
Define stress and the General Adaptation Syndrome.
Stress is any extreme external or internal stimulus. General Adaptation Syndrome is a set of body changes triggered by stress and coordinated by the hypothalamus.
What are the three phases of the General Adaptation Syndrome?
Alarm reaction, resistance reaction, and exhaustion.
Describe the alarm reaction (fight or flight) phase.
Immediate response coordinated by the nervous system, including increased blood glucose, heart rate, respiration rate, and decreased blood flow to the skin and abdominal viscera.
Describe the resistance reaction phase.
Long-term response coordinated by endocrine system. Hypothalamic hormones cause release of GH and cortisol to permit recovery or respond to longer-term stress.
What are the effects of cortisol release during the resistance reaction?
Increased blood glucose (liver stimulated to produce new glucose), inhibition of insulin release, inhibition of immune system, bone formation, and formation of CT, and release of aldosterone and antidiuretic hormone (ADH).
What are the long-term effects of the resistance reaction?
Decreased weight, increased blood pressure and heart rate, immune suppression, decreased bone density, and increased risk of type 2 diabetes.
Describe the exhaustion phase.
Results from depletion of body resources (lipid reserves), loss of K+, and damage to organs (heart, liver, kidneys).
What are the functions of testosterone?
Development of reproductive organs and secondary sex characteristics, stimulates bone growth at the epiphyseal plate, promotes protein anabolism, and directly stimulates spermatogenesis
What are the functions of FSH (Follicle Stimulating Hormone) in females?
Stimulates primary follicles to become secondary follicles, inhibited by progesterone.
What are the functions of LH (Luteinizing Hormone) in females?
Stimulates estrogen production from theca and granulosa cells of follicle, LH surge causes ovulation and formation of corpus luteum
What are the functions of estrogen in females?
Required for ovulation, development of secondary sex characteristics, stimulates growth and maintains the endometrium, and stimulates bone growth during puberty.
What are the functions of progesterone in females?
Prepares the uterus for pregnancy
Describe the events of the follicular phase (days 1-14) in the ovarian cycle.
FSH stimulates some 1° follicles ⇒ 2° follicles. Follicles secrete E ∴ blood E rises, and one 2° follicle becomes vesicular follicle.
Describe the events of the menstrual and proliferative phases (days 1-14) in the uterine cycle.
Menstrual phase (days 1-5): stratum functionalis shed and denuded areas bleed. Proliferative phase (days 6-14): E ⇒ repair + proliferation of stratum functionalis.
What event occurs on day 14 of the ovarian/uterine cycles? What triggers it?
Ovulation, triggered by the LH surge.
Describe the luteal phase (days 15-28) of the ovarian cycle.
High P from corpus luteum inhibits GnRH (∴ LH + FSH) ∴ no follicles develop
Describe the secretory phase (days 15-28) of the uterine cycle
Progesterone prepares endometrium for implantation and inhibits uterine contractions.
What happens if fertilization occurs?
Placenta secretes human chorionic gonadotropin (hCG) which maintains corpus luteum, corpus luteum ⇒ P, E for about 6 weeks, then placenta takes over, FSH, LH inhibited by high P.
What happens if fertilization does not occur?
Corpus luteum ⇒ corpus albicans, ∴ ⇓ P and E ∴ no longer inhibit LH, FSH ⇒ LH, FSH ⇑, no longer maintain endometrium ⇒ menstruation.
How do oral contraceptives work?
High E + P ⇒ inhibit GnRH secretion ∴ low FSH, LH - no follicle maturation, no ovulation (mimics luteal phase).
What is the physiological role of the placenta?
Exchange site for gases, nutrients/wastes, hormones, antibodies, drugs, and viruses, and it secretes hormones (Estrogen, Progesterone, hCG).
