Intro to Endocrinology Flashcards
What is endocrinology?
endocrine glands + their secretions (hormones) + diagnosis and treatment of disorders of endocrine system
What is the most common endocrine disorder?
diabetes mellitus
What are glands?
structures (epithelial tissue derivatives) specialized for secretion
What are the two types of glands?
- exocrine glands
- endocrine glands
What cells (important characteristic) do exocrine glands have?
duct cells – exocrine secretions (from secretory portion of gland) are released into ducts, which deliver them to surface of skin or to one of the cavities in the body
What are some examples of exocrine glands? (4)
exocrine pancreas – source of digestive enzymes
sweat glands
salivary glands
mammary gland
What are 2 important characteristics of endocrine glands?
- disappearance of duct cells
- hormones are secreted into blood capillaries
What are some examples of endocrine glands? (4)
pituitary gland
thyroid gland
adrenal glands
parathyroid glands
What are endocrine tissues and cells responsible for?
producing hormones
What are some examples of endocrine tissues and cells? (5)
- islets of Langerhans within pancreas (source of insulin and glucagon)
- granulosa cells of ovarian follicle (estrogen)
- lining of stomach (gastrin), atrial muscle fibres (atrial natriuretic peptide)
- kidneys (renin)
- Leydig cells of testes (testosterone)
What type of effect do hormones have?
can have stimulatory or inhibitory effect
What do hormones interact with?
specific receptors found on or in target cells
What do hormones do?
help to regulate all major functions of the body, including:
- growth and development
- reproduction
- metabolism
- contraction of cardiac and smooth muscle
- glandular secretions
Can a hormone have affect multiple functions?
yes – ie. thyroid hormones
Can a function be controlled by more than one hormone?
yes – ie. reproduction is controlled by thyroid hormone, LH, FSH, estrogen, testosterone
What are the 4 chemical classes of hormones?
- protein hormones
- steroid hormones
- amines
- eicosanoids
Which is the most common class of hormones?
protein hormones
Are protein hormones hydrophilic or hydrophobic?
water soluble (hydrophilic)
What are the steps in protein hormone synthesis?
- transcription and translation (preprohormone)
- processing and packaging (prohormone; hormone)
- storage in secretory vesicles until specific stimulus-induced release
What are protein hormones synthesized by? (3)
anterior pituitary gland
hypothalamus
endocrine pancreas
Are steroid hormones hydrophilic or hydrophobic?
hydrophobic, lipid soluble
What are steroid hormones synthesized from?
cholesterol
What does synthesis of steroid hormones require?
requires specific enzymes, found only within steroidogenic organs, such as:
- gonads (testis and ovary)
- adrenal glands (cortex)
- placenta (during pregnancy)
What do gonads (testis and ovary) produce?
sex steroid hormones (androgens, estrogens, progesterone)
What do adrenal glands (cortex) produce?
corticosteroids (mineralocorticoids, glucocorticoids, androgens)
What does the placenta (during pregnancy) produce?
multiple placental hormones, including estrogens and progesterone
Are steroid hormones transported or stored immediately following synthesis?
diffuse to extracellular fluid and blood (NOT stored in vesicles)
What are amines?
small molecules derived from one of two amino acids: tyrosine and tryptophan
Where us tyrosine found? (2)
- adrenal medulla (inner portion of adrenal gland)
- thyroid gland
In what form is tyrosine found in adrenal medulla (inner portion of adrenal gland)?
precursor of norepinephrine and epinephrine (catecholamines)
In what form is tyrosine found in thyroid gland?
conjugation of two tyrosine molecules is required for production of thyroid hormones
Where is tryptophan found?
- gut and brain
- brain (pineal gland)
In what form is tryptophan found in the gut and brain?
precursor of serotonin
- gut: serotonin regulates motility, secretions
- brain: serotonin regulates emotions, appetite, sleep
In what form is tryptophan found in the brain (pineal gland)?
serotonin is precursor of melatonin
What is melatonin?
biological clock – integrates sleep-wake cycles
What are eicosanoids synthesized from?
lipids and phospholipids
What are most eicosanoids derived from?
arachidonic acid (component of plasma membrane phospholipids)
What do eicosanoids do?
serve as local chemical mediators with powerful biologic activities
ie. prostaglandins
What do prostaglandins do?
involved in inflammation, initiation of labour, airway constriction, etc.
What is homeostasis?
ability of body to maintain a relatively constant environment in the face of a constantly changing external environment
What is the secretion of hormones regulated by?
negative feedback systems
When is negative feedback initiated?
if a factor becomes excessive or deficient, control system initiates negative feedback to bring that factor back to within normal range
Does positive feedback ever occur?
yes
in rare cases, biological action of hormone may INDUCE additional release of that hormone (positive feedback)
What are consequences of positive feedback of hormone secretion?
- can result in vicious cycle incompatible with homeostasis
- then can lead to disease or death
(there are very few examples of physiological positive feedbacks because they disturb homeostasis)
What are the 5 modes of delivery of hormones to target tissues?
- endocrine (most common)
- neuroendocrine
- paracrine
- autocrine
- intracrine
What is the endocrine mode of delivery of hormones to target tissues?
endocrine cells → blood → target tissue
What is the neuroendocrine mode of delivery of hormones to target tissues?
specialized neurons → blood → target tissue
What is the paracrine mode of delivery of hormones to target tissues?
endocrine cells → extracellular space → target tissue
What type of function does the paracrine mode of hormone delivery have?
local function, often provided by eicosanoids and growth factors
What is the autocrine mode of delivery of hormones to target tissues?
endocrine cells → extracellular space → target tissue
What type of function does the autocrine mode of hormone delivery have?
local function, often provided by eicosanoids and growth factors
What is the intracrine mode of delivery of hormones to target tissues?
hormone acts within the cell of origin
What type of function does the intracrine mode of hormone delivery have?
local function, often provided by eicosanoids and growth factors
What must a hormone do to exert its biological function?
hormone must bind to its receptor on and/or in the target tissue and form a hormone-receptor complex
hormone + receptor → hormone-receptor complex → specific biological response
ie. GnRH + receptor (on anterior pituitary) → GnRHR complex → release of LH and FSH
What are receptors?
large proteins, most are highly specific for a single hormone
Where are receptors located? (3)
- cell membrane
- cell cytoplasm
- cell nucleus
Which receptors are located in the cell membrane?
protein hormone and catecholamine receptors
Which receptors are located in the cell cytoplasm?
some steroid hormone receptors (ie. testosterone)
Which receptors are located in the cell nucleus?
some steroid and thyroid hormone receptors
What generates rapid non-genomic responses?
many steroid hormones (including E and T) and thyroid hormones also interact with specific cell-surface receptors to generate rapid non-genomic responses
