Anatomy & Physiology Flashcards
What is the role of the endocrine system?
To keep body in a state of homeostasis, carries out communication and regulation in response to normal physiological changes in the body or alterations in the external environment
Endocrine System vs Nervous System
Endocrine is slow acting, nervous is fast acting
Endocrine works using hormones, nervous works using electrochemical impulse
Endocrine regulates activities requiring duration rather than speed, nervous regulates activity of muscles and glands
List all the hydrophilic hormones
Anterior pituitary FSH/LH, TSH, ACTH, GH
Posterior pituitary ADH, oxytocin
Thyroid - Calcitonin
Pancreas - Insulin, Glucagon
Parathyroid - PTH
Gonad - Inhibin
Placenta - hCG
Adrenal Medulla – Catecholamines (Epinephrine, Norepinephrine)
List all the hydrophobic hormones.
Adrenal cortex - Aldosterone, Cortisol
Gonad - Testosterone, Progesterone, Estrogen
Kidney - Vitamin D (Calcitriol)
Pineal - Melatonin
Thyroid - T3, T4
List all the protein and peptide hormones.
Anterior pituitary FSH/LH, TSH, ACTH, GH
Posterior pituitary ADH, oxytocin
Thyroid - Calcitonin
Pancreas - Insulin, Glucagon
Parathyroid - PTH
Gonad - Inhibin
Placenta - hCG
List all the steroid hormones.
Adrenal cortex - Aldosterone, Cortisol
Gonad - Testosterone, Progesterone, Estrogen
Kidney - Vitamin D (Calcitriol)
List all the amine hormones.
Adrenal Medulla – Catecholamines (Epinephrine, Norepinephrine)
Pineal - Melatonin
Thyroid - T3, T4
What are the parts of the pituitary gland?
Anterior pituitary
- Pars distalis
- Pars intermedia
- Pars tuberalis
Posterior pituitary (pars nervosa)
List the acidophils of the Pars distalis and what hormones they secrete respectively.
Somatotrophs - Growth Hormone
Mammotrophs - Prolactin
List the basophils of the Pars distalis and what hormones they secrete respectively.
Gonadotrophs– Follicle Stimulating Hormone , Luteinising Hormone (LH)
Corticotrophs– Adrenocorticotropin Hormone (ACTH aka corticotropin)
Thyrotrophs – TSH
What cells in the Pars intermedia secrete hormones? What hormones do they secrete?
Melanotrophs – Melanocyte stimulating hormone(MSH)
What are the cells in the Pars tuberalis?
Undifferentiated gonadotrophs
What are the features of note in the posterior pituitary gland?
Axons of neurosecretory cells in supraopticnucleus (SON)
Paraventricular nucleus (PVN) of hypothalamus
Pituicytes – sheets around nerve bodies
Herring bodies – contains granules storing ADH and oxytocin
List all the pituitary hormones that directly act on non-endocrine tissues
GH, Prolactin, ADH, Oxytocin
List all the pituitary hormones that when secreted, modulate the activity of other endocrine glands
TSH, ACTH, FSH, LH
What are the parts of the follicle
Follicular cells - synthesize thyroglobulin and secrete it into colloid
Colloid - extracellular space surrounded by follicular cells, site of thyroid hormone formation from thyroglobulin and iodine
Parafollicular cells - cells located in between the follicles, secrete calcitonin
Outline the process of thyroid hormone formation.
- follicle cells ER and GA produce thyroglobulin (TG), tyrosine incorporated into TG at the same time - exocytosis of tyrosine containing TG into colloid
- Thyroid caputres iodine from blood and transfers it into colloid via iodide Na K pump
- thyroperoxidase on follicle cell membrane before colloid oxidised the iodine to activate it
- iodine gets attached to the tyrosine to form MIT or DIT, MIT and DIT get coupled to form the thyroid hormones
- follicular cells endocytose from colloidal side to internalise part of the TG-hormone complex, lysosomes attack resulting vesicle to separate the iodinated hormones from TG
- Resulting T3 and T4 diffuse freely through follicular outer membrane to enter blood, quickly bind to plasma proteins due to high lipophilicity
- iodinase removes iodide from MIT and DIT for recycling of iodine
How are T3 and T4 metabolised?
T4 gets metabolised by 5-deiodinase to form T3 or r-T3
T4 (and T3 somewhat) also gets metabolised by conjugation with glucuronic acid in the liver, conjugate is secreted into bile and eliminated in faeces
How is thyroid hormone release controlled?
- low T3 & T4 triggers TSH secretion
- TSH binds to TSH receptor on follicular cells to start signalling, resulting in increased synthesis and secretion of thyroid hormones
- when T3 and T4 are secreted, triggers negative feedback loop to stop TSH and TRH secretion
What are the physiological effects of T3 and T4
- inc basal metabolic rate
- sympathomimetic effect
- cardiovascular effect
- bone growth and maturation
- development of nervous system in childhood
- normal CNS activity in adults
- increased synthesis and degration of proteins lipids and carbohydrates (depending on metabolic state)
How do T3 and T4 increase basal metabolic rate
increase size and number of mitochondria AND
increase number of enzymes regulating oxidative phosphorylation
therefore increases oxygen consumption and energy use under resting conditions
How do T3 and T4 exert sympathomimetic effect?
inc the proliferation of catecholamine (epinephrine & norepinephrine)target-cell receptors to increase target-cell responsiveness to catecholamines
How do T3 and T4 exert cardiovascular effect?
Increase heart’s responsiveness to catecholamines → inc HR and force of contraction → ↑CO
How do T3 and T4 help with bone growth and maturation
Stimulates growth hormone (GH) secretion and increases Insulin Growth Factor 1 (IGF-1) production by the liver
Promotes effects of GH & IGF-1 on synthesis of new structural proteins and skeletal growth
What would be the TH and TSH/TRH levels be like for hypothyroidism from primary failure of thyroid gland?
TH: low
TSH: high
Goiter present
TSH secreted but thyroid responds insufficiently/doesnt respond
What would be the TH and TSH/TRH levels be like for hypothyroidism from hypothalamic or anterior pituitary failure?
TH: low
TSH/TRH: low
Goiter absent
inability to secrete TSH/TRH
What would be the TH and TSH/TRH levels be like for hypothyroidism from lack of dietary iodine?
TH: low
TSH: high
Goiter present
TSH secreted and binds to TSH receptor, but not enough iodine to make TH
What would be the TH and TSH/TRH levels be like for Graves disease?
Hyperthyroidism
TH: high
TSH: low
Goiter present
TSI present
TSI binds to TSH receptor to stimulate TH release, which -ve feedbacks to result in low TSH and TRH, but TH continues to be released
What would be the TH and TSH/TRH levels be like for hyperthyroidism secondary to excess hypothalamic or anterior pituitary secretion?
TH: high
TSH/TRH: high
Goiter present
Excessive TSH/TRH results in overproduction of TH