Hormone Regulation - Physiology Flashcards
Hormone Stimulation - Function
Influences the activity of only certain tissue cells: target cell. Increase or decrease normal cellular processes.
What changes do hormonal stimulus typically produce?
- Alters plasma membrane permeability or membrane potential, or both, by opening or closing ion channels.
- Stimulates synthesis of proteins or enzymes.
- Activates or deactivates enzymes.
- Induces secretory activity.
- Stimulates mitosis.
Mechanisms of Hormone Action - Activation of Protein Kinases
- Hormone binds receptor
- Receptor activates G protein
- Active: GTP
- Inactive: GDP - G protein activates adenylate cyclase
- Adenylate cyclase converts ATP to cyclic AMP
- Cyclic AMP activates protein kinase
- Permit responses of target cells.
Mechanisms of Hormone Action - Protein Synthesis
- Hormone binds to intracellular receptor
- Binded receptor-hormone complex
- Hormone receptor binds to DNA
- Transcription of DNA to produce messenger RNA
- mRNA translated on the cytoplasmic ribosomes to produce specific protein molecules
Control of Hormone Release - Humoral Stimulus
Direct response to changing blood levels of certain critical ions and nutrients.
Target cell activated.
Simplest.
F. ex. insulin from pancreas
Control of Hormone Release - Neural Stimulus
Nerve fibers stimulate hormone release.
F. ex. sympathetic nervous system stimulates adrenal gland to release epinephrine during stress.
Control of Hormone Release - Hormonal Stimulus
Release of hormones in response to hormones produced by other endocrine hormones.
Most complicated. Majority of glands work this way.
Cyclic pathway: not working all the time - menstrual cycle, melatonin at night.
Pineal Gland (Epithalamus)
Major secretory product: melatonin, derived from serotonin.
Peak levels at night, make us drowsy. Lowest levels at noon.
Visual input (day vs night) Retina → pineal gland
Anterior Pituitary Gland and Hypothalamus
Indirect control through release of regulatory hormones. Hormones produced by anterior pituitary: - Growth hormone (GH) - Thyroid-stimulating hormone (TSH) - Adrenocorticotropic hormone (ACTH) - Follicle-stimulating hormone (FSH) - Luteinizing hormone (LH) - Prolactin and beta endorphin
Growth Hormone (Somatotropin)
Promotes protein synthesis and tissue building through direct and indirect mechanisms.
Levels controlled by:
- GHRH: growth hormone releasing hormone
- GHIH: growth hormone inhibiting hormone
Growth Hormone - Glucose Sparing Effect
Switch from glucose to fatty acids - Lypolysis
Growth Hormone - Diabetogenic Effect
Liver stimulation to break down glycogen to glucose, which is then deposited into the blood.
Indirect secondary mechanism: produce IGFs(insulin like growth factors), further stimulating growth effect (bones,muscle,nervous s, immune s)
Thyroid Stimulating Hormone (Thyrotropin)
Stimulates normal development and secretory activity of thyroid gland.
Triggered by thyrotropin-releasing hormone (TRH) from hypothalamus.
Negative feedback.
Adrenocorticotropic Hormone (Corticotropin)
Control stress levels.
Secreted by corticotrophs.
Corticotropin-releasing hormone.
Controls waking up, peak levels in the morning, shortly before awakening.
Gonadotropin - Follicle-Stimulating Hormone
Regulate function of gonads (testes and ovaries) prompted by gonadotropin-releasing hormone (GnRH) in hypothalamus. Stimulates gamete (sperm or egg) production.
Gonadotropin - Luteinizing Hormone
Regulate function of gonads (testes and ovaries) prompted by gonadotropin-releasing hormone (GnRH)
in hypothalamus.
Production of gonadal hormones:
- Triggers ovulation and synthesis and release of ovarian hormones.
- Stimulates production of testosterone.
Prolactin
Produced by lactotrophs. Stimulates milk production.
Primarily controlled by prolactin-inhibiting hormone (dopamine).
Estrogen stimulates prolactin release.
Infant’s suckling stimulates release of prolactin-releasing factor.
Posterior Pituitary Gland and Hypothalamus
No production of hormones, storage and secretion of hormones produced by hypothalamus.
Paraventricular nuclei: Production of oxytocin
Supraoptic nuclei: Production of ADH
Oxytocin and ADH almost identical .
Oxytocin
Stretching of uterus and cervix in birth stimulates oxytocin synthesis in hypothalamus and triggers its release from posterior pituitary gland.
PIP2-Ca2+ (messenger that mobilizes Ca2+) allows for stronger contractions.
Triggers milk ejection.
Cuddle hormone.
Antidiuretic Hormone (ADH)
Prevents wide swings in water balance, to avoid dehydration and water overload.
Hypothalamic neurons monitor solute concentration, when solute is too concentrated → synthesis and release ADH. Causes vasoconstriction.
Severe blood loss → massive amounts of ADH → rise in blood pressure.
Thyroid Hormone - Types
Thyroxine T4:
4 bound iodine atoms.
Major hormone secreted by thyroid follic.
Triiodothyronine T3:
3 bound iodine atoms.
Formed at the target tissues by conversion of T4 to T3.
Thyroid Hormone - Basal Metabolic Rate & Temp Regulation
Hyposecretion: low BMR, low body temp and cold intolerance, decrease appetite, weight gain.
Hypersecretion: High BMR, high body temp, heat intolerance, increased appetite, weight loss.
Thyroid Hormone - Carbohydrate / Lipid / Protein Metabolism
Hyposecretion: Low glucose metabolism, high levels of cholesterol/triglyceride, low protein synthesis, edema.
Hypersecretion: High glucose, fat, protein catabolism, weight loss, loss of muscle mass.
Thyroid Hormone - Nervous System
Normal: normal development of nervous system in fetus /infant, normal adult nervous system function.
Hyposecretion: deficient brain development, retardation (infant), depression, memory impairment (adult).
Hypersecretion: Irritability, restlessness, insomnia, personality changes.
Thyroid Hormone - Cardiovascular System
Normal: normal function of heart.
Hyposecretion: Decreased pumping efficiency, low heart rate and blood pressure.
Hypersecretion: Rapid heart rate, palpitations, high blood pressure, heart failure.
Thyroid Hormone - Muscular System
Normal: normal muscular development and function.
Hyposecretion: sluggish muscle action, muscle cramps, pain, soreness.
Hypersecretion: Muscle atrophy and weakness.
Thyroid Hormone - Skeletal System
Normal: normal growth and maturation of skeleton.
Hyposecretion: growth retardation, skeletal stunting (child), joint pain (adult).
Hypersecretion: Excessive skeletal growth, early epiphyseal closure, short stature (child), demineralization of skeleton (adult).
Thyroid Hormone - Gastrointestinal System
Normal: normal GI motility and tone, increase secretion of digestive juices.
Hyposecretion: Depressed GI motility, tone and secretory activity, constipation.
Hypersecretion: Excessive GI motility, diarrhea, loss of appetite.
Thyroid Hormone - Reproductive System
Normal: normal female reproductive ability and lactation.
Hyposecretion: Depressed ovarian function, sterility, depressed lactation.
Hypersecretion: Depressed ovarian function, impotence (male).
Thyroid Hormone - Integumentary System
Normal: normal hydration and secretory activity of skin.
Hypoactivity: pale, dry, thick skin, facial edema, hair coarse and thick.
Hyperactivity: flushed, thin, moist skin. Fine, soft skin. Soft, thin nails.
Thyroid Hormone Regulation
Falling TH levels: release of thyroid-stimulating hormone (TSH) → more TH
Rising TH levels feedback: inhibit hypothalamic-anterior pituitary axis, temporarily shutting off stimulus for TSH release.
Calcitonin
Produced by parafollicular or C-cells, directly from thyroid.
Excessive Ca2+ levels: humoral stimulus for calcitonin release. Declining Ca2+ levels inhibit C cell secretory activity.
Parathyroid Hormone
Controls calcium balance.
Triggered by falling Ca2+, inhibited by rising Ca2+.
Increases Ca2+ by:
1. Stimulating osteoclasts (bone-resorbing cell).
2. Enhances reabsorption of Ca2+ by kidneys.
3. Promotes activation of vitamin D → increasing reabsorption of Ca2+.
Adrenal (Suprarenal) Gland
Formation of different hormones:
- Aldosterone: renal absorption of sodium and water.
- Cortisol: control cardiac activity, glycogen breakdown.
- Epinephrine & Norepinephrine: inflammatory response, release amino acid.
Aldosterone
Stimulated by decreasing blood volume and pressure and rising K+.
4 mechanism:
Direct:
- Renin-angiotensin mechanism
- Plasma concentration of K+ (↑K+ → ↑Aldosterone)
Indirect:
- ACTH (stress: ↑CRH → ↑ACHT→ ↑Aldosterone)
- Atrial natriuretic peptide (ANP) (Inhibits renin-angiotensin mechanism)
Renin-Angiotensin Mechanism
Influences blood volume and pressure by regulating release of aldosterone and Na+ and water reabsorption by kidneys.
- Release of Renin → angiotensinogen triggers formation of angiotensin II → stimulates aldosterone release.
Glucocorticoids
Depends on short or long term stress.
Secretion regulated by negative feedback.
Rising cortisol levels act on hypothalamus, anterior pituitary, preventing CRH release, shutting off ACTH and cortisol secretion.
Pancreas
Two major pancreatic hormones:
- Glucagon-synthesizing: alpha cell, hyperglycemic.
- Insulin-producing: beta cell, hypoglycemic.
Controls sugar in blood levels.
Glucagon
Hyperglycemic agent
Decrease in blood sugar levels activates glucagon pathway.
Breakdown of glycogen to glucose. (glycogenolysis)
+ gluconeogenesis.
Insulin
Activated because of increase in blood sugar levels.
Lowers blood glucose levels.
Pancreas activated to produce insulin.
Enhances transport of glucose into cell.
Inhibit breakdown of glycogen into glucose.
Menstrual Cycle
FSH and LH act on ovaries to develop follicles.
Estrogen and progesterone prepare uterus for pregnancy.
1. Follicular phase
2. Ovulation
3. Luteal phase
4. Mensturation
Follicular Phase - Menstrual Cycle
FSH stimulates growth of ovarian follicle.
Follicle produces estrogen → inhibits FSH, negative feedback, no more follicle growth → thickens endometrial layer.
Ovulation - Menstrual Cycle
Midway. Estrogen stimulates secretion of hormones (positive feedback) → large surge of LH, lesser of FSH → LH causes follicle to rupture and release egg.
Luteal Phase - Menstrual Cycle
Ruptured follicle → corpus luteum.
Estrogen and progesterone thicken endometrial lining, inhibit FSH, LH → no more follicles developing.
Menstruation - Menstrual Cycle
Fertilization: embryo implants in endometrium and release hormone to sustain corpus luteum.
No fertilization: Corpus luteum degenerates.
Estrogen and progesterone levels drop → endometrial layer eliminated (period) → cannot inhibit anterior pituitary → cycle begins again.
Testicles
GnRH secreted from hypothalamus.
LH stimulates Leydig cells to produce testosterone:
Stimulates formation of sperm.
Maintain libido.
Pubic, axillary and facial hair growth.
FSH drives sperm production in Sertoli cells (spermatogenesis).
