Thyroid hormone
body's major metabolic hormone; composed of 2 hormones containing iodine; binds to intracellular receptors
2 components of thyroid hormone
thyroxine and triiodothyronine
Thyroxine (T4)
major product secreted by thyroid follicles; has 4 iodines
Triiodothyronine (T3)
most will be formed at the target tissue by conversion from T4; has 3 iodines
Thyroid gland
only endocrine gland that stores hormone extracellularly and keeps ~2-3 months of hormone available
synthesis of thyroid hormone
process starts when TSH from anterior pituitary binds to receptors on thyroid follicular cells; as T3 and T4 are released, colloid restocking begins
Metabolism
All of the chemical reactions that occur within an organism
Calcitonin
the "other" thyroid hormone; made by parafollicular cells of the thyroid gland; no well-established physiological role in humans
Calcitonin in non-human animals
released in response to a rise in blood Ca2+, opposing the effects of parathyroid hormone (PTH)
If you have thyroid gland removed
don't need to medically replace calcitonin, but must replace thyroid hormone
Calcitonin as a pharmacological entity
given to treat Paget's Disease and in some circumstances osteoporosis; inhibits osteoclasts????; can stimulate uptake of Ca2+ into bone; in other animals, briefly reduces Ca2+ in blood
Parathyroid glands
small set of jelly bean-shaped glands associated with the thyroid; produce parathyroid hormone
Parathyroid hormone
released when blood calcium is low; increases calcium in the blood
hypocalcemia
low blood calcium
Mechanisms by which parathyroid hormone increases blood calcium
increase osteoclast activity to break down osseous material and release Ca2+; increase Ca2+ reabsorption in kidney tubule; increase activation of vitamin D by kidney --> increase Ca2+ absorption from food in small intestine
adrenal glands (suprarenal glands)
sit on top of the kidneys; adrenal glands are enclosed by a protective fibrous capsule and fat 'cushion'; 2 sections: medulla and cortex both produce hormones
oxyphil cells of parathyroid
we don't know what they do! science is HUMAN
Adrenal medulla
inner-most structures; less like glandular tissue and more like a collection of nervous tissue; part of the sympathetic nervous system
adrenal cortex
outer-most, superior layer; encapsulates the medulla; proper glandular tissue
3 layers of the adrenal cortex (superficial to deep)
zona glomerulosa, zona fasciculata, zona reticularis
Adrenal cortex hormones
produces over 2 dozen known steroid hormones (building block is cholesterol); cortical region of adrenal glands is very lipid-rich
Mineralocorticoids
hormones (ex: aldosterone) that control balance of minerals and H2O
glucocorticoids
metabolic hormones (gluco - sugar), help to keep blood glucose levels fairly constant
gonadocorticoids
adrenal sex hormones
zona glomerulosa, zona fasciculata, zona reticularis
3 layers of cortex, superficial to deep
zona glomerulosa
most superficial layer of cortex beneath capsule, produces mineralocorticoids (e.g. aldosterone)
zona fasciculata
middle layer of cortex, cells are organized into distinctive linear cords, produces glucocorticoids
zona reticularis
innermost layer, sits adjacent to adrenal medulla, produces small amounts of gonadocorticoids
Aldosterone
regulates electrolytes (specifically Na+ and K+) in extracellular fluids, comprises ~95% of all mineralocorticoids
aldosterone effects on Na+
single most abundant cation in ECF; amount of Na+ determines ECF volume; changes in Na+ with change both blood volume and pressure; regulation of Na+ alters levels/activity of other ions (K+, H+, HCO3-, Cl-)
Na+/K+ relative levels
key to resting membrane potential, very carefully controlled levels, related to kidneys
Aldosterone effects on K+
sets resting membrane potential!!; Determines how easily action potentials are generated
CRH
corticotropin releasing hormone
inhibitory effects of aldosterone
blocks the renin/angiotensin pathway - blood pressure drops
aldosterone functions on kidney
cells of juxtaglomerular complex are activated and make renin; renin cleaves a protein (angiotensinogen) to produce angiotensin II
gluconeogenesis
synthesis of glucose from lactic acid and non-carbohydrate sources; making glucose from fats & proteins; energy metabolism
cortisol, corticosterone, cortisone
3 types of glucocorticoids
cortisol
aka hydrocortisone, main glucocorticoid produced in humans
cyclic daily pattern of glucocorticoids
spikes before waking up, drops before and shortly after falling asleep, acute stress disturbs pattern and levels and can drive an increase in blood sugar levels
weak androgens
male sex hormones, converted to testosterone at target tissue cells, small amounts will get converted to estrogen; Amounts made are insignificant compared to what is made by the gonads
androstenedione and dehydroepiandrosterone (DHEA)
two main types of gonadocorticoids
Role of adrenal sex hormones is not clear but in women seems to play a role in
development of axillary (armpit) and pubic hair, sex drive, most of the estrogen made after menopause
Epinephrine and norepinephrine
Two main products of adrenal medulla
Adrenal medulla hormones
Produces two main products (catecholamines made in chromaffin cells), epinephrine & norepinephrine, released during fight-or-flight response but everyday hormones, both molecules has similar effects
epinephrine
~80% of catecholamine release
Pineal gland location
hangs from the roof of the third ventricle in the diencephalon
pineal gland function
secretes melatonin
Pinealocytes
make melatonin
brain sand (pineal sand)
between pinealocytes, dense, Ca2+-containing salts; radiopaque: pineal gland is very obvious on an X-ray of the brain
Pancreas, gonads, placenta
Endocrine Glands that Also Have Other Functions
Adipose Tissue, GI tract, heart, kidneys, skeleton, skin, thymus
Hormone-Secreting Cells in Other Organs
Adipose tissue
can be very metabolically active, not dull or inactive
Pancreas
accessory organ to digestion, has both endocrine and exocrine gland cells
Acinar cells and pancreatic islet cells
endocrine active cell types
Endocrine
dump hormones directly into body fluids (do not have ducts)
exocrine
gland that secretes its products through ducts or channels
Acinar cells
digestive function, make up most of the gland, produce pancreatic juice that is carried to the small intestine via ducts (exocrine)
Pancreatic islet cells (islets of langerhans)
two types: alpha cells and beta cells, together act as sensors to help balance blood sugar levels
alpha cells
glucagon producing, hyperglycemic (increase blood sugar)
beta cells
insulin producing, hypoglycemic (decrease blood sugar)
Glucagon
extremely potent hyperglycemic, one glucagon molecule can lead to the release of 100 million glucose molecules
Major target of glucagon
liver cells
major actions of glucagon
conversion of glycogen -> glucose (glycogenolysis); synthesis of glucose from lactic acid and non-carbohydrate sources (gluconeogenesis); release of glucose to blood
glycogenolysis
breakdown of glycogen to glucose
Insulin regulation and activity
hypoglycemic, two linked amino acid chains, proinsulin: cleaved to produce functional form, also influences metabolism of fats and protein, important roles in brain development (brain is a MAJOR user of sugar)
insulin lowers blood glucose in 3 ways
increases transport of glucose and other sugars into cells
inhibits glycogen -> glucose conversion
inhibits amino acid or fat -> glucose conversion
ovaries
female gonads, release ova and produce estrogens and progesterone
estrogens
maturation of reproductive organs, development of secondary sex characteristics (collection of 3 hormones)
progesterone (working with estrogen)
breast development and changes in uterine mucosa
Testes
male gonads, main hormone: testosterone
testosterone
maturation of the reproductive organs, development of secondary sex characteristics, normal sperm production
Placenta
temporary endocrine organ (short and sweet); Makes estrogen and progesterone and human chorionic gonadotropin
gigantism
excessive height, caused by too much growth hormone in childhood
acromegaly
too much GH after epiphyseal plates have closed, overgrowth of bone in face and extremities
dwarfism
too little GH in childhood; if detected early, can be treated with GH
hypothyroidism (myxedema)
lowers the metabolic rate
hyperthyroidism
Most common form: Grave's Disease; Autoimmune disorder; increases metabolic rate; symptoms: sweating, irregular heartbeat, weight loss, protruding eyes
diabetes
emerging health crisis, becoming more common
Type I diabetes
aka: insulin-dependent, juvenile; generally diagnosed before 15 years of age; autoimmune disease; body attacks its beta cells; several susceptibility genes have been ID'd; molecular mimicry: viral infection looks so similar to beta cells that virus and cells are attacked
Treatment for Type I diabetes
insulin via injection or pump; difficult to control sugar levels; no 'artificial pancreas' exists
Type II diabetes
non-insulin dependent or adult-onset; insulin is produced but insulin receptors can't respond; insulin resistance; incidence increases with age and obesity; ~12 million Type II diabetics in the US
Causes of type II diabetes
Genetics: 25-30% of all cases; lifestyle
Gestational diabetes
high blood sugar levels that develop during pregnancy; pregnancy/placental hormones may interfere with insulin binding to insulin receptor (typically temporary)
Risks of gestational diabetes
pre-eclampsia, depression, baby of large size, underdeveloped newborn lungs
Diabetes statistics
100M people in US are diabetic (~325M people in US), two of every 5 people are expected to develop a form of diabetes in their lifetime