Chapter #16: Endocrine System Flashcards
The Endocrine System
-Secretes various hormones
-Hormones: long-distance chemical messengers that cause a change in metabolic activity of a cell
-Effects are usually long-lasting
-Endocrine glands secrete hormones directly to blood
-Glands highly vascularized
How are hormones long-distance?
they do not effect the cells that are in the same tissue that it’s in, travels all over the body through the blood
Hormones control
-Reproduction
-Growth and development
-Immune system activation
-Maintenance of various blood components (glucose, electrolytes, water, etc.)
Autocrines and paracrines
-sometimes considered part of the endocrine system
-Both are short-distance chemical messengers
-Autocrine: a chemical message that affects the same cell that produces the message
-Paracrine: a chemical message that is produced by one cell but affects a different cell
-Both cells are in the same tissue
Chemical structure of hormones determines
determines longevity, transport in blood, & receptivity by cell
Two major classification of hormones
1) Amino acid-based hormones
2) Steroid hormones
Amino acid-based hormones
-Molecular size varies: amino acid derivatives, peptides, proteins
-Water-soluble: circulate without carrier
What is a carrier protein?
a specific type of protein that transports a substance from point A to point B
Steroid hormones
-Synthesized from cholesterol
-Gonadal hormones and adrenocortical hormones are only steroid hormones in body
-Lipid-soluble: circulate with carrier
How do hormones act?
-Hormones can only affect target cells with appropriate receptors
-Different cell types can have different receptors that can bind the same hormone
How does the fact that different cell types can have different receptors that bind to the same hormone affect the response of target cells?
if you change the receptor shape, you may alter the effect the hormone has on the cell
Major changes produced by hormone binding
1) Altering plasma membrane permeability or membrane potential
2) Stimulates synthesis of enzymes/proteins inside cell
3) Activates/deactivates enzymes
4) Induces secretory activity
5) Stimulates mitosis
Two mechanisms of hormone action
1) Second messenger-systems
2) Intracellular systems
Second-messenger systems
-use receptors found on surface of plasma membrane
-Receptors are usually coupled to regulatory G-proteins
-G-protein activates intracellular second messenger: causes response in cell
-This system is extremely efficient!!
What class of hormone uses the second-messenger systems?
amino-acid hormones
What is the effector enzyme in the second-messenger-systems? What is the second messenger?
-the effector enzyme is adenylate cyclase
-the second messenger is cAMP
Intracellular systems
-Hormone enters cell, then binds to intracellular receptors
-Receptor-hormone complex binds specific regions of DNA: DNA transcription occurs
-Effect: certain proteins produced in larger numbers
What hormones use intracellular systems?
steroid hormones (must be lipid soluble)
Hormone Release
-Stimulating hormone release
-Hormone synthesis & release is controlled by negative feedback mechanisms
-if not for the negative feedback mechanism, a target cell would be doing too much or too little, so you shut of that second release before it happens
Stimulus mechanisms
1) Humoral stimuli: changing blood levels of critical ions & nutrients
-Ex: monitoring Ca2+ levels by parathyroid gland
2) Neural stimuli: nerve fibers stimulate hormone release
-Infrequent
-Ex: norepinephrine & epinephrine release by sympathetic nervous system
3) Hormonal stimuli: hormone released in response to other hormones
-Ex: hypothalamic hormones stimulate or inhibit anterior pituitary gland
Hormone concentration in blood depends on
1) How fast it is being released by endocrine organ
2) How fast it is broken down
-Most hormones removed by kidneys and/or liver
-Water-soluble hormones have shortest half-life
Cellular Response to Hormones
-Target cells only respond to a hormone if it has a specific receptor protein for that hormone
-One hormone may only be able to interact with a few cell types, while another hormone may be able to interact with every cell type
Activation of cell depends on
1) Blood levels of hormone (more concentration in blood = greater likelihood of binding)
2) Number of receptors for specific hormone on/in cell (more receptors = greater likelihood of binding)
3) Affinity of receptor to the hormone (easier it binds, the easier it can have an effect)
Up-regulation
-increase receptor number in response to low hormone levels
-increase the likelihood it can bind to it
Down-regulation
-decrease receptor number in response to high hormone levels
-decrease the likelihood it can bind to it
2+ hormones binding on the same target cell at the same time may result in
1) Permissiveness: one hormone cannot have full effect without binding of a second specific hormone
-Lack of the second hormone may delay or completely inhibit effects of first
2) Synergism: 2+ hormones with similar effects bind target cellamplification occurs
3) Antagonism: one hormone opposes the effect of another
-Hormones can compete for the same receptor
-Hormones act through different metabolic pathways
-Hormones can down-regulate receptor of another hormone
Duration of hormone effects on target cell
-Hormone effect is not always immediate: effects seen after hours or days
-Some hormones must be activated before binding can occur
-Duration of effect varies
-Effects can disappear as levels drop or can persist for hours after levels drop
-Importance: variation of effects = strict control of hormone release
The Pituitary Gland (Hypophysis)
-Connected to hypothalamus
-Two regions of the gland:
1) Anterior pituitary: manufactures and releases several different hormones
2) Posterior pituitary: composed mostly of neural tissue and nerve fibers
-Stores and releases neurohormones produced by hypothalamus
Release of hormones from the pituitary controlled by hypothalamus in 1 of 2 ways
1) Action potentials from hypothalamus cause hormone release
-controlled by Posterior pituitary
2) Hypothalamic hormones released into hypophyseal portal system: stimulate or inhibit hormone release
-controlled by anterior pituitary
Posterior Pituitary & Hypothalamic Hormones
1) Oxytocin
2) Antiduretic Hormone (ADH)
Oxytocin
-Functions: stimulant for uterine contraction, milk ejection, “cuddle hormone”
-Neurotransmitter in brain: promotes nurturing, couple bonding, trust, affectionate behavior
-Stretching of cervix during childbirth sends afferent impulses to hypothalamus: stimulates posterior pituitary to release oxytocin
-positive feedback mechanism
-Stimulates milk-producing glands to contract during breastfeeding
-Oxytocin is released when blood solute concentration is low
Antidiuretic Hormone (ADH)
-Function: inhibits formation of urine by increasing return of water to blood supply by kidneys
-Importance: ADH will influence how much water leaves the body through urine
-Osmoreceptors in hypothalamus monitor solute concentration
-high blood solute concentration because ADH causes more water ti come in when solute concentration is high to balance it
Anterior Pituitary Hormones
-Four of six hormones are tropins: affect activity of another endocrine gland
1) Growth Hormone (GH) (Anterior Pituitary Hormone)
-Metabolic effects
1) Decreases glucose uptake by cells
2) Mobilizes fat stores: releases fatty acids to blood
3) Increases amino acid uptake by cells
-Growth effects
-Liver, bone, skeletal muscle, etc. produce insulin-like growth factor (IGFs) in presence of GH
-IGFs stimulate growth:
1) Increase nutrient uptake by tissue
2) Formation of collagen and deposition of bone matrix
-Release of GH controlled by growth hormone-releasing hormone (GHRH) or growth hormone-inhibiting hormone (GHIH)
2) Thyroid-Stimulating Hormone (TSH)
(anterior pituitary hormone)
-Function: Stimulates development and secretory activity of thyroid gland
-Thyrotropin-releasing hormone (TRH) stimulates TSH release
3) Adrenocorticotropic Hormone (ACTH)
-Function: stimulates adrenal cortex to release hormones
-Corticotropin-releasing hormone (CRH) stimulates ACTH release
4 & 5) Gonadotropins (anterior pituitary hormone)
-Two hormones: 4) Follicle-stimulating hormone (FSH) and 5) Luteinizing hormone (LH)
-Function: regulate function of gonads
-FSH: stimulates production of gametes
-LH: stimulates production of gonadal hormones (estrogen, progesterone, and testosterone)
-Gonadotropin-releasing hormone (GnRH) stimulates release of FSH and LH
-Rising gonadal hormone blood levels inhibit release of GnRH
-Gonadotropins only released after puberty (not released throughout entire lifetime)
6) Prolactin (PRL) (anterior pituitary hormone)
-Function: stimulates milk production in breast tissue
-In males, also produce and release, but do not know what it does
-PRL release increases toward end of pregnancy
-Levels of PRL rise and fall in tandem with blood estrogens
-Rising estrogen stimulates PRL release
-Release controlled by dopamine: inhibitory hormone
The Thyroid Gland
-Produces, secretes, and stores hormones
Retains ~3 months normal supply of hormone
-Function: produces Thyroid Hormone (TH): major metabolic hormone
-Production of TH depends on presence of iodine
-Affects virtually every body cell:
1) Increases metabolic rate and body heat production
2) Regulates tissue growth/development
3) Maintains blood pressure
The Parathyroid Gland
-Secretes parathyroid hormone (PTH)
-Function: contributes to calcium homeostasis in body
-Falling blood Ca2+ levels stimulate PTH release by:
1) Stimulating osteoclasts to increase bone degradation
2) Enhancing Ca2+ reabsorption by kidneys
3) Activating vitamin Dincreases absorption of Ca2+ from digestive system
The Adrenal Glands
-Function: stress response, electrolyte balance
-Two areas of the gland, each functions as individual unit:
1) Adrenal Cortex
2) Adrenal Medulla
Adrenal Cortex (part of adrenal gland)
-outermost region
-Produces corticosteroids
-Three subdivisions:
A) Zona glomerulosa: produce mineralcorticoids
B) Zona fasciculata: produce glucocorticoids
C) Zona reticularis: produce gonadocorticoids
Mineralcorticoids (part of adrenal cortex)
-regulate electrolyte concentration in ECF: especially Na+ and K+
-Importance:
-Na+ influences water movement: can affect blood volume and blood pressure
-K+ determines resting membrane potential: imbalance affects responsiveness of neurons
Glucocorticoids (part of adrenal cortex)
-influence energy metabolism of cells, provide resistance to stressors
-Specific types: cortisol, cortisone, corticosterone
-Cortisol release stimulated by ACTH
-Negative feedbackrising cortisol prevents ACTH release
-Release usually secretory bursts: increases when we first wake up & during eating
-Stress affects cortisol release: CNS overrides negative feedback mechanism & more cortisol released
Effects of glucocorticoids
-Mobilizes body stores to create more glucose
-Provokes sympathetic nervous system: vasoconstriction
Excessive release of glucocorticoids causes
-Depressed cartilage & bone formation
-Inhibits inflammation
-Depresses immune system
-Disrupts normal cardiovascular, neural, gastrointestinal functions
Gonadocortioids (part of adrenal cortex)
-small amounts of androgens released by adrenal cortex
-Some converted to testosterone, others converted to estrogen
-Amount produced by adrenal cortex is very small compared to what is produced by gonads
-Effects:
-Contribute to axillary and pubic hair development
-Females: contributes to sex drive, produce estrogens post-menopause
Adrenal Medulla (part of adrenal gland)
-innermost region of adrenal gland
-Synthesize epinephrine & norepinephrine
-Unequal amounts stored & released
-80% epinephrine: greater influence on metabolic activity & is a dilator of airways in lungs
-20% norepinephrine: greater influence on blood vessel diameter
-Release is initiated by sympathetic nervous system
-Release is short-lived
-Hormones from adrenal medulla are not essential
-sympathetic division produces enough on its own
The Pineal Gland
-Function: secretes melatonin
-Effect: regulates night-day cycles, sleeping schedule
-Release controlled indirectly by visual pathways: intensity & duration of sunlight
The Pancreas
-Hormones produced in pancreatic islets
-Function: controls blood sugar levels
-Produces & secretes 2 hormones
The Pancreas produces & secretes 2 hormones
1) Glucagon
2) Insulin
Glucagon
-produced by alpha cells
-Hyperglycemic effect
-Effects: Stimulates liver to break down glycogen, convert non-carbohydrate molecules to glucose, release glucose from liver cells -Release controlled by dropping blood glucose levels
Insulin
-produced by beta cells
-Hypoglycemic effect
-Effects: Increases glucose uptake by body cells, inhibits glycogen breakdown, inhibits conversion of non-carbohydrate molecules to glucose
-Release controlled by:
1) Elevated blood glucose
2) Rising blood levels of amino acids & fats
3) Acetylcholine release from parasympathetic
4) Any hyperglycemic hormone
What does “hyperglycemic” mean?
raises blood sugar levels
What does “hypoglycemic” mean?
lowers blood sugar levels
Diabetes mellitus
-inadequate (or absent) release of insulin by pancreas
-Effect: consistently high blood sugar levels
-Normal range (fasting): 99 mg glucose/dl blood (or lower)
-Diabetes (fasting): 126+ mg glucose/dl blood
Two types of diabetes mellitus
-Type 1: autoimmune condition: insulin is not produced by the pancreas
-Several genes contribute to condition
-Treatment: insulin shots before meals or continuous fusion pumps
-If left untreateddevelopment of vascular & neural problems
-Type 2: insulin resistance: insulin released, but cells do not respond
-Correlated more with lifestyle
-Some genetic component, but almost all are overweight and underactive
-Similar complications to type 1 diabetes if not managed/treated
-Can be managed with diet and exercise
Gonads
-Females: ovaries produce estrogens & progesterone
-Estrogen function: maturation of reproductive organs, appearance of secondary sex characteristics
-Progesterone function: breast development, cyclic changes in uterine mucosa
-Males: testes produce testosterone
-Function: maturation and maintenance of reproductive organs, appearance of secondary sex characteristics, sex drive, normal sperm production
Placenta
-temporary endocrine organ
-Produces estrogens, progesterone, human chorionic gonadotropin (hCG)
-Function: maintains pregnancy
