Endocrine System Flashcards
Glands
organs that secrete hormones
Hormones
signaling molecules that are secreted directly into the bloodstream to travel to target tissue
Peptide Hormones
- made up of amino acids
- derived from larger precursor polypeptides that are cleaved during posttranslational modifications
- charged and cannot pass through plasma membrane so must bind to an extracellular receptor
- considered a first messenger b/c it binds to a receptor and triggers the transmission of a second signal/messenger
- effects are rapid but short-lived b/c act through transient second messenger systems
- generally water soluble and can travel freely in bloodstream
Signaling Cascade
the connection between the hormone at the surface and the effect brought about by second messengers within the cell
List common second messengers (3)
- cAMP
- IP3
- calcium
Steroid Hormones
- derived from cholesterol
- produced primarily by the gonads and adrenal cortex
- nonpolar molecules that can easily cross plasma membrane
- receptors are intracellular (in the cytosol) or intranuclear (in the nucleus) and after binding they form a hormone-receptor complex that binds to DNA to alter gene expression
- effects of hormone are slower but last longer
- cause alterations in amount of mRNA and protein present in cell
- not water soluble so carried by proteins in bloodstream
- includes: estrogen, testosterone, aldosterone, cortisol glucocorticoids
Dimerization
pairing of two receptor hormone complexes
Amino-Acid Derivative Hormones
- includes: epinephrine, norepinephrine, triiodothyronine, thyroxine
- catecholamines are a type of these
Catecholamines
- includes: epinephrine, norepinephrine
- bind to G protein coupled receptors
- important in long-term stress responses
Direct Hormones
secreted and then act directly on a target tissue
Tropic Hormones
- require an intermediary to act
- do not cause a direct change in physiology of tissue but do stimulate production of another hormone by another endocrine gland that acts on the target tissue
- originate in the brain and anterior pituitary gland
Hypothalamus
- bridge between nervous and endocrine system
- located in the forebrain directly above pituitary gland and below thalamus
- regulates pituitary gland through tropic hormones via paracrine release of hormones into a portal system that connects the two organs
How does the hypothalamus interact with the anterior pituitary gland?
- secretes compounds into the hypophyseal portal system (blood vessel that directly connects hypothalamus to anterior pituitary)
- hormones can be found in appreciable concentrations in systemic circulation
List of hormones secreted by hypothalamus and response anterior pituitary hormones (4)
- gonadotropin-releasing hormone (GnRH) -> follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
- growth hormone-releasing hormone (GHRH) -> growth hormone (GH)
- thyroid releasing hormone (TRH) -> thyroid stimulating hormone (TSH)
- corticotropin-releasing factor (CRF) -> adrenocorticotropic hormone (ACTH)
What is different about Prolactin?
- almost all other hormones cause an increase in anterior pituitary secretion but this hormone causes a decrease
- prolactin-inhibitory factor (PIF) which is actually dopamine is released by hypothalamus and causes a decrease in prolactin secretion by the anterior pituitary
Posterior Pituitary Gland
- neurons from hypothalamus send their axons down the pituitary stalk directly to this gland
- essentially an extension of the hypothalamus
- hormones released here: oxytocin, antidiuretic hormone/vasopressin
- doesn’t synthesize any hormones itself, just stores them
Oxytocin
- stimulates uterine contractions during labor and milk letdown during lactation
- involved in bonding behavior with baby
- positive feedback loop
- source: hypothalamus (stored in posterior pituitary)
Antidiuretic Hormone (ADH)
- increases reabsorption of water in collecting ducts of kidneys
- secreted in response to increased plasma osmolarity or increased concentration of solutes within the blood
- source: hypothalamus (stored in posterior pituitary)
List the 7 hormones that are synthesized/secreted by the anterior pituitary gland
- FLAT PEG*
- Follicle-stimulating hormone
- Luteinizing hormone
- Adrenocorticotropic hormone
- Thyroid stimulating hormone
- Prolactin
- Endorphins
- Growth hormone
What anterior pituitary hormones are tropic hormones?
- FLAT*
- Follicle-stimulating hormone
- Luteinizing hormone
- Adrenocorticotropic hormone
- Thyroid stimulating hormone
What anterior pituitary hormones are direct hormones?
- PEG*
- Prolactin
- Endorphins
- Growth hormone
Prolactin
- stimulates milk production in the mammary glands
- release of dopamine from hypothalamus decreases its secretion from anterior pituitary
Growth Hormone
- promotes growth of bone and muscle
- prevents glucose uptake in tissues that aren’t growing and stimulates breakdown of fatty acids which increases availability of glucose overall allowing for muscle and bone to use it
Where does bone growth originate?
epiphyseal plates
What is the cause of gigantism?
excess GH release in childhood
What is the cause of dwarfism?
deficit in GH release during childhood
What is acromegaly?
- when there is excess GH production in adults and they develop large hands + feet + head
- occurs because small bones can still be affected by GH later in life whereas long bones cannot
Follicule Stimulating Hormone (FSH)
- stimulates follicle maturation
- stimulates spermatogenesis
- source: anterior pituitary
Luteinizing Hormone (LH)
- stimulates ovulation
- stimulates testosterone synthesis
- source: anterior pituitary
Adrenocorticotropic Hormone (ACTH)
- stimulates adrenal cortex to make and secrete glucocorticoids (anti-inflammatory)
- source: anterior pituitary
Thyroid-Stimulating Hormone (TSH)
- stimulates the thyroid to produce thyroid hormones
- source: anterior pituitary
Endorphins
- inhibits the perception of pain in the brain
- source: anterior pituitary
Thyroid
- located on front surface of trachea
- two major functions: setting basal metabolic rate which is mediated by releasing T3 and T4; calcium homeostasis
Triiodothyronine (T3)
- 3 iodines attached to tyrosine
- produced by iodination of tyrosine in the follicular cells of the thyroid
- stimulates metabolic activity
- source: thyroid
Thyroxine (T4)
- 4 iodines attached to tyrosine
- produced by iodination of tyrosine in the follicular cells of the thyroid
- stimulates metabolic activity
- source: thyroid
What happens when there are high levels of T3 and T4 secretion?
increased cellular respiration which causes greater amount of protein and fatty acid turnover
Hypothyroidism
- deficiency of iodine or inflammation of thyroid
- characterized by lethargy, decreased body temperature, slowed respiration rate and heart rate, cold intolerance, weight gain
Hyperthyroidism
- excess thyroid hormone resulting from tumor or thyroid over stimulation
- characterized by increased activity level, increased body temperature, increased respiration rate and heart rate, heat intolerance, weight loss
Calcitonin
- produced by C-Cells (parafollicular cells) in thyroid
- decreases plasma Ca2+ levels in 3 ways: (1) increase Ca2+ excretion from kidneys (2) decrease Ca2+ absorption from gut (3) increase Ca2+ storage in bone
Parathyroid Glands
- produces parathyroid hormone
- 4 small structures that sit on posterior surface of thyroid
Parathyroid Hormone (PTH)
- produced by parathyroid gland
- antagonist hormone to calcatonin
- increases blood calcium levels by decreasing exrection of Ca2+ by kidneys, increasing absorption of Ca2+ in gut via vitamin D, and increases bone resorption
- increases plasma Ca2+ levels lead to decreased secretion of this hormone
- also affects phosphorous homeostasis by resorbing phosphate from bone and reducing reabsorption of phosphate in kidney (promoting excretion in urine)
What are the important functions of calcium?
- bone structure/strength
- release of NTs from neurons
- regulation of muscle contraction
- cofactor in clotting of blood
- cell movement
- exocytosis of cellular materials
Adrenal Cortex
- located on top of kidneys
- consists of a cortex and medulla
- secrets 3 different classes of corticosteroids: glucocorticoids, mineralcorticoids, cortical sex hormones
Glucocorticoids
- regulate glucose levels
- affects protein metabolism
- increases blood glucose level and decreases protein synthesis
- anti-inflammatory agent
- includes cortisol ad cortisone
Functions of Cortisol and Cortisone
- raise blood glucose by increasing gluconeogenesis and decreasing protein synthesis
- decrease inflammation and immunologic responses
Mineralcorticoids
- used in salt and water homeostasis mostly at kidneys
- includes aldosterone
Aldosterone
- leads to increased Na+ reabsorption in distal convoluted tubule and collecting duct
- water follows Na+ cations into bloodstream which increases blood volume and pressure while keeping plasma osmolarity unchanged
- leads to decreased reabsorption of K+ and H+ ions in distal convoluted tubule and collecting duct which promotes their secretion in urine
- primarily under the control of the renin-angiotensin-aldosterone system
Cortical Sex Hormones
includes androgens and estrogens
Functions of the Corticosteroids
- SALT, SUGAR, SEX – the deeper you go the better it gets*
- SALT: mineralcorticoids
- SUGAR: glucocorticoids
- SEX: cortical sex hormones
Adrenal Medulla
- derivative of the nervous system
- produces the sympathetic hormones epinephrine and norepinephrine which can be directly secreted into the circulatory system
Epinephrine
- increases breakdown of glycogen to glucose (glycogenolysis) in the liver and muscle
- increase basal metabolic rate
Functions of Epinephrine and Norepinephrine
- increased heart rate
- dilate bronchi
- alter blood flow to supply systems used in sympathetic response – vasodilation of blood vessels leading to skeletal muscle + heart + brain + lungs
- increases blood glucose level
Cortisol increases the synthesis of ____
catecholamines
Pancreas
- contains islets of langerhans which contain 3 distinct groups of hormone producing cells – alpha, beta, delta
- secretes 3 hormones: glucagon, insulin, somatostatin
What hormone is secreted by the alpha cells in the pancreas?
glucagon
What hormone is secreted by the beta cells in the pancreas?
insulin
What hormone is secreted by the delta cells in the pancreas?
somatostatin
Glucagon
- secreted during fasting when glucose levels are low
- secretion stimulates degradation of protein and fat, glycogen to glucose in liver, and production of new glucose via gluconeogenesis
- increases blood glucose concentrations
What two GI hormones stimulate alpha cells to release glucagon?
- cholecystokinin
- gastrin
Insulin
- antagonist to glucagon
- secreted when blood glucose levels are high
- induces muscle and liver cells to take up glucose and store it as glycogen
- stimulates anabolic processes like fat and protein synthesis
- decreases blood glucose concentrations
Hypoglycemia
- occurs when insulin is present in excess
- characterized by low blood glucose concentrations in blood
Diabetes Mellitus
- underproduction/insufficient secretion/insensitivity to insulin
- characterized by hyperglycemia (excess glucose in blood)
- individuals with this have increased glucose in filtrate which leads to excess excretion of water and increased urine volume
- have increased frequency of urination (polyuria) and increased thirst (polydipsia)
Type I Diabetes
- insulin-dependent
- caused by autoimmune destruction of beta cells in pancreas so produce little to no insulin
- require regular injections of insulin to permit hyperglycemia and permit entry of glucose into cells
Type II Diabetes
- non-insulin-dependent
- result of receptor-level resistance to effects of insulin
- partially inherited and partially due to environmental factors (high carb diet and obesity)
Somatostatin
- inhibitor of both insulin and glucagon secretion
- stimulated by increased blood glucose and amino acid concentrations
- also produced by hypothalamus where it functions in decreasing growth hormone secretion
Testes (Gonads)
secrete testosterone in response to stimulation by gonadotropins (LH and FSH)
Ovaries (Gonads)
- secrete estrogen and progesterone in response to FSH and LH
- estrogen maintains female secondary sex characteristics
- progesterone promotes growth/maintenance of endometrium
Pineal Gland
- located deep within the brain
- receives projections directly from retina but not involved in vision so is likely responding to light intensity
Melatonin
- secreted by the pineal gland
- involved in circadian rhythms
Erythropoietin
- produced in kidneys
- stimulates bone marrow to increase production of erthrocytes (RBCs)
- secreted when there are low levels of oxygen in blood
Atrial Natriuretic Peptide (ANP)
- released from heart
- involved in osmoregulation and vasodilation
- helps regulate salt and water balance
- released when cells in atria are stretched from excess blood volume
- promotes excretion of Na+ so increases urine volume
- antagonist to aldosterone because it lowers blood volume and pressure while having no effect on blood osmolarity
Thymosin
- released from the thymus (located behind sternum)
- important in proper T Cell development and differentiation
