Endocrinology

Question 1

Homeostasis

Answer 1

• Process of maintaining a constant internal environment despite changes in condition
• Homeostasis isn’t equilibrium

Question 2

Feedback Control

Answer 2

• Negative Feedback: Initial Stimulus -> Response -> Stimulus that inhibits initial stimulus from generating response(eg. regulation of cortisol secretion)
• Positive Feedback: Initial Stimulus -> Response -> Stimulus that reinforces response, turned off by outside factors(eg. Oxytocin secretion during birth)

Question 3

Intercellular Communication

Answer 3

• Gap Junctions: Form direct connections between adjacent cells. Small ions and molecules move through gap junctions(eg. cardiac)
• Contact Dependent: Require interaction between membrane molecules of two cells. Membrane protein binds to membrane protein(eg. immune system)
• Autocrine: Autocrine acts on same cell that secreted them. Paracrine are secreted by one cell and diffuse to adjacent cells. Molecules move through interstitial fluid

Question 4

Reflexes

Answer 4

• Simple reflexes mediated by nervous or endocrine system
• Complex reflexes mediated by both systems and go through several integrating systems

Question 5

Why different control systems?

Answer 5

• Specificity: Neural terminates on a single target cell. Endocrine effects most of cell in body
• Nature of signal: Electrical signal passes through neuron, and chemical neurotransmitters carry signal. For endocrine, chemical signals secreted in blood for distribution throughout the body
• Speed: Very rapid for neural. Much slower for endrocrine
• Duration: very short for neural. Endocrine lasts much longer
• Coding for stimulus intensity: Signal identical in strength for neural. Endocrine is correlated with amount of hormone secreted

Question 6

Features of hormones

Answer 6

• Can be made by different places in the body
  -Chemicals made by cells in specific endocrine gland
• Transported in blood to different targets
• Binds to specific receptors
• Alter activity in cells
• Action must be terminated
• Maintain homeostasis

Question 7

Hydrophilic Hormones

Answer 7

• Water soluble
• Not lipid soluble(lipophobic), cannot cross plasma membrane
• Synthesized in advance
• Dissolved in blood
• Peptide hormones, protein hormones, catecholamines

Question 8

Hydrophobic Hormones

Answer 8

• Not water soluble, does not dissolve in plasma
• Synthesized on demand
• Lipid soluble(lipophilic), readily cross plasma membrane
  -Bound to carrier proteins in blood
• Steroid and thyroid hormones

Question 9

Three types of hormones

Answer 9

• Peptide/protein(eg. insulin)
• Steroid(eg. cortisol)
• Amine(single amino acids)(eg. catecholamines)

Question 10

Peptide Hormones

Answer 10

• Linked amino acids
• Made in advance
• Synthesized like secreted proteins
• Stored in vesicles, released by exocytosis upon signal
• Water soluble
• Bind to membrane receptors
• C-peptide cleaved after release(proinsulin example)

Question 11

Steroid Hormones

Answer 11

• Synthesized from cholesterol
• Made on demand
• Not stored in vesicles
• Released by simple diffusion
• Water insoluble
• Long half-life
• Diffuse into target cells
• Cytoplasm or nucleus receptors

Question 12

Synthesis of catecholamines

Answer 12

• Synthesized in adrenal medulla
• Stored in vesicles prior to release
• Released by exocytsosi
• Lipophobic
• Bind to membrane receptors

Question 13

How do stimuli trigger hormone release

Answer 13

• Chane in membrane potential
• Increase free cytosolic Ca++
• Change enzymatic activity
• Alter transcription of genes coding for hormones
• Promote survival of endocrine cell

Question 14

Glucose stimulation of insulin release

Answer 14

• Glucose goes into cell(increase blood sugar)
• ATP inhibits K+ channel
• Depolarizes cell
• Opens voltage gated Ca++ channel
• Triggers exocytosis insulin release

Question 15

Anterior Pituitary

Answer 15

• Hypothalamic releasing and inhibiting hormones
• Does not create hormones

Question 16

Hormone Interactions

Answer 16

• Synergistic: Multiple hormones act together for greater effect
• Permissive effects: One hormone enhances the target organ’s response to a second later hormone
• Antagonistic: One hormone opposes the action of another

Question 17

Calcium Balance

Answer 17

• RANK/RANKL to increase osteoclast differentiation
• OPG blocks RANK/RANKL
• PTH hormone increase RANK/RANKL and decrease OPG to increase calcium levels -> stimulate calcitriol
• Calcitonin activated in high calcium -> used to decrease calcium levels

Question 18

Fluid Balance

Answer 18

• Vasopressin(ADH): used to conserve body water and increase blood volume/pressure -> cAMP release send aquaporin-2 pores to collecting duct lumen -> increase permeability of water -> water flow to bloodstream
• Aldosterone: Na reabsorption(retain water) and K secretion -> stimulated by angiotensin 2(RAAS) -> aldosterone signaling cause transcription/translation of new channels/pumps -> balances Na/K(Na reabsorb and K out) -> Na pump back into bloodstream
• Atrial Natriuretic Peptide(ANP): increase K reabsorption and decrease Na and water reabsorption(lowers blood pressure) -> causes decrease renin and aldosterone

Question 19

Adrenal Medulla

Answer 19

• Cortisol: Secreted by adrenal cortex, mediates long term stress -> CRH in hypothalamus stimulate ACTH to release cortisol
• Addison’s Disease: hyposecretion of adrenal steroid hormones -> hypoglycemia
• Cushing’s Syndrome: Cortisol excess -> hyperglycemia or tumors
• Zona glomerulosa: Aldosterone
• Zona fasciulata: Glycocorticoids
• Zona reticularis: Sex hormones
• Adrenal medulla: catecholamines

Question 20

Growth and Thyroid Hormone

Answer 20

• Hypothalamus stimulate GHRH -> release GH -> acts on liver to secrete IGF-1 -> growth promoting effects on cells on the body -> chondrocyte recruitment. GH inhibited by GHIH(somatostatin)
• Gigantism: too much GH in childhood, Acromegaly: too much GH in adulthood
• Thyroid hormone: TRH stimulate TSH -> make and release T3, T4
• Hyperthyroidism: Too much thyroid hormone, cause goiter, high heart rate(eg. Grave’s disease)
• Hypothyroidism: Thyroid hormone deficiency, slowed heart rate

Question 21

Male reproductive

Answer 21

• Spermiogenesis: Spermatids mature into spermatozoa, lose cytoplasm and gain tail
• Sertoli cells: Sperm development
• Leydig cells: Secrete testosterone
• GnRH stimulates LH and FSH -> FSH stimulates Sertoli cells(sperm development) and LH stimulate Leydig cells(secrete testosterone)
• Hypogonadism: Decreased functional activity of testes -> decreased androgen production

Question 22

Female Reproductive

Answer 22

• Granulosa cells: Support oocyte development
• Theca cells: Secrete steroid hormone precursors
• Menstrual cycle:
  - Ovarian cycle: Follicular phase(oocyte development) and luteal phase(corpus luteum forms)
  - Uterine cycle: Menstrual and Proliferative phase(Days 1-14) and Secretory phase(Days 4-28)
• Early to mid follicular phase: LH stimulates androgen release from theca cells, FSH stimulates conversion to estrogen by granulosa cells, Granulosa cells secrete AMH. Estrogens exert negative feedback
• Late follicular to ovulation: Inhibit inhibits FSH, high estrogen increase frequency of GnRH pulses -> LH surge(completion of meiosis 1 and cause ovulation)
• Early to mid luteal phase: Secretion of inhibin, progesterone and estrogen -> negative feedback to turn off FSH and LH
• Late luteal phase: If no fertilization, corpus luteum undergoes apoptosis

Question 23

Pregnancy

Answer 23

• Human chorionic gonadotropic(hCG) maintains corpus luteum
• Labour triggered by increase in estrogen/oxytocin receptors, fetal cortisol, CRH, prostaglandins
• Estrogen and progesterone inhibit milk production
• Decrease in dopamine cause prolactin and oxytocin increase -> Milk secretion and smooth muscle contraction

Question 24

Sex Determination

Answer 24

• Males have SRY gene that promotes testes development -> SOX9 transcription -> repress female structures via AMH and initiate sertoli cell differentiation
• Beta-catenin suppress SOX9 expression -> female organs