Endocrine Physiology
describe the posterior lobe of the pituitary
(neurohypophysis) Originates from neural tissue Nerve cell bodies are located in the hypothalamic nuclei. Hormones synthesized in the nerve cell bodies Packaged in secretory granules Transported down the axons to posterior pituitary for release into circulation secretes ADH and oxytocin
Progestin
48% bound to albumin 51% bound to corticosteroid binding globulin regulates gonadotropin regulates cyclic changes in the uterus maintains pregnancy development of breasts oral contraceptives blocks ovulatory surge of LH makes cervical mucous repel sperm
Estrogen
48% bound to albumin 51% bound to sex hormone binding globulin (SHBG) excreted by the liver regulates gonadtrophin release influences sexual behavior maintains pregnancy stimulates prolactin release anabolic increases progestin receptors decreases prolactin receptors
5'-iodinase
5'-iodinase converts T4 to T3 by removing one atom of I2 Reverse T3: Inactive form
synthesis, storage, and secretion of amine hormones
Amine hormones (notably epinephrine) are stored as granules in the cytoplasm until needed. (water soluble) Catecholamine hormones - epinephrine, norepinephrine Synthesized from tyrosine in the adrenal medulla Secretes epi > NE (by 4 times!) Stored in secretory granules Secreted similar to peptide hormones Thyroid hormones - thyroxine-T4, triiodothyronine-T3 Synthesized from tyrosine and iodide Transported in blood unbound
what are amine hormones?
Amino acid derivatives not only proteins but have other components Amines are derived from the amino acid tyrosine and are secreted from the thyroid and the adrenal medulla. examples Thyroid hormones Catecholamines (epinephrine, norepinephrine, dopamine)
Pancreas
Both exocrine and endocrine gland Secretes peptide hormones insulin and glucagon into the blood stream
Aldosterone
Conserves sodium Maintains fluid volume Eliminates potassium and hydrogen ions Stimulated by decreased blood volume, decreased sodium, or increased potassium Weakly bound to albumin Half life is 15 min Metabolized in the liver Excess Conn's Syndrome HTN Hypokalemic alkalosis Polyuria Polydipsia
Adrenal glands
Consists of the medulla (inner) and cortex (outer) The medulla secretes epi and norepi The cortex produces and secretes corticosteroid hormones
Hypothalamus
Controls secretion of hormones of anterior and posterior pituitary Portion of the brain (diencephalon) that links the nervous and endocrine systems Intricate network of nuclei (made up of neurons) Some neurons are neurohormonal Synthesize neuropeptides that work as hormones Magnocellular (paraventricular and supraoptic) Oxytocin and ADH Parvocellular Projections to brainstem and spinal cord Release neurohormones that control AP function
Hypothalamic-pituitary axis and the role of thyroid hormone regulation
Controls the synthesis and secretion of thyroid hormones Hypothalamus - Thyroid-releasing hormone (TRH) secreted, which acts on the A pituitary, when then secretes thyroid-stimulating hormone (TSH), which acts on thyroid gland and stimulates synthesis and secretion of T3, T4 TRH -> TSH -> T3, T4 hypothalamus -> anterior pituitary -> thyroid
what decreases ADH release?
Dec. serum osmolarity Ethanol Alpha-agonists ANP
how are large peptide hormones removed and metabolized?
Degraded by kidney Taken into target cells by receptor-mediated endocytosis After binding to receptor on surface of cell, hormone-receptor complex internalized Hormone separated from the receptor and degraded Receptor recycled to the cell membrane surface
describe the difference between Gαs, Gαi, and Gαq
G α s Activates adenylate cyclase Gα i Inhibits adenylate cyclase G α q Activates phospholipase C Gα s activation of adenylate cyclase Increased converstion of ATP to cyclic 3',5'-adenosine monophosphate (cAMP) Increased cAMP activates protein kinase A Proteins are phosphorylated Result in cellular responses Phosphodiesterase breaks down cAMP Gα q activation of phospholipase C Produces diacylglyceral (DAG) and inositol triphosphase (IP3) DAG activates protein kinase C; IP3 increases [Ca++]
actions of thyroid hormones
Growth Bone formation (with GH) Bone maturation (fusion of growth plates) CNS Maturation of CNS in perinatal period Expression of genes for myelination (axonal growth and dev) ANS Like SNS Upregulates beta-receptors in the heart BMR Increased O2 consumption and BMR Increased production of heat Liver Regulates triglyceride and cholesterol metabolism Modulates mitochondrial respiration CV and Respiratory Systems Inc. CO and ventilation rate to ensure adequate O2 to tissues Metabolic effects (catabolic) Increased metabolism, Glucose absorption from GI tract. Increased lipolysis, Protein synthesis and degradation increased
describe negative feedback regulation of hormones
Hormone acts to cause less secretion of hormone Increase [glucose]B → Increase insulin →Decrease [glucose]B → Decrease insulin Decrease [Ca++]B → Increase PTH → Increase [Ca++]B → Decrease PTH
describe positive feedback regulation of hormones
Hormone acts to cause more secretion of the hormone LH before ovulation is a result of positive feedback of estrogen on the AP. LH acts on ovaries and causes more secretion of estrogen
what is the hypothalamic portal system
Hormone rich blood from hypothalamus delivered directly to AP
what hormones are produced in the anterior pituitary?
Hormones produced in the anterior pituitary include growth hormone (GH), prolactin, thyroid-stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and melanocyte-stimulating hormone (MSH).
what hormones are produced in the hypothalamus
Hormones produced in the hypothalamus include thyroid-stimulating hormone (TRH), corticotrophin-releasing hormone (CRH), luteinizing-hormone releasing hormone (LHRH), growth-hormone releasing hormone (GHRH), somatostatin, dopamine, melanocyte inhibiting hormone (MIH), anti-diuretic hormone (ADH) and oxytocin.
what hormones are stored in the posterior pituitary?
Hormones stored in the posterior pituitary include anti-diuretic hormone (ADH) and oxytocin.
what are examples of peptide hormones?
Hypothalamic, A pituitary, P pituitary, pancreatic hormones, ACTH, insulin, glucagon
steps in thyroid hormone synthesis
I- is actively transported from blood into follicular epithelial cells against both chemical and electrical gradients: Low levels of I- stimulate the pump, High levels of I- inhibit the pump I- is oxidized to I2 by thyroid peroxidase I2 combines with tyrosine (which comes from thyroglobulin) to form Monoiodotyrosine (MIT) and Diiodotyrosine (DIT), which remain in follicular lumen until thyroid gland stimulated Two DIT combine to form T4: Occurs quickly, so 10x as much is formed One DIT and one MIT combine to form T3 T3 and T4 are transported across the basal membrane into nearby capillaries to be delivered to the systemic circulation Thyroid hormones circulate in blood Most T4 and T3 circulates bound to thyroxine-binding globulin (TBG) Smaller amounts bind to T4-binding pre-albumin and albumin Even smaller amounts circulate unbound Only free hormones are physiologically active
how are catecholamines removed and metabolized?
Inactivated by enzymes, then excreted in urine MAO - monoamine oxidase COMT - catechol-O-methyl transferase
what increases ADH release?
Inc. serum osmolarity Volume contraction Pain Nausea Hypoglycemia histamine releasing stimuli, beta adrenergic stimulus, PPV, hyperthermia, anxiety, hypoxia, stress and pain
gonadotropin releasing hormone
Increases the release of FSH and LH from the anterior pituitary
what are examples of paracrine agents?
Inflammatory cytokines, leukocyte interleukins
Insulin
Inhibited by Somatostatin, Catecholamines, Alloxan/Streptozocin Lowers blood glucose Lowers free fatty acids Lowers amino acid Lower ketoacids Increases glucose, lipid, and amino acid transport Increases enzymatic action Increases cell growth Increases cell differentiation Increases DNA production Excess will cause hypoglycemia Deficiency will cause hyperglycemia - diabetes mellitus
how is the anterior pituitary linked to the hypothalamus
Linked to hypothalamus by hypothalamic-hypophysial portal system
Cortisol
Operates in negative feedback loop Hypothalamus - CRH - anterior pituitary - ACTH - adrenal cortex - cortisol - liver/organs Made from cholesterol Made in the zona fasciculate/reticularis of the adrenal cortex Bound to corticosteroid binding hormone (75%) and albumin (15%) Half life = 90 min Metabolized in the liver Causes proteolysis, lipolysis, glycolysis, resist stress Excess causes Muscle wasting Decreased wound healing Decreased hair on head Buffalo hump Moon face Hyperglycemia HTN Osteoporosis Cushing Syndrome Deficiency causes Hypoglycemia Hypotension Muscle weakness Adrenal crisis
from what nuclei in the hypothalamus is oxytocin released?
Paraventricular nuclei (hypothalamus)
oxytocin
Paraventricular nuclei (hypothalamus) Release of milk from the breast Suckling is major stimulus for oxytocin secretion Also sight or sound of infant Afferent fibers from nipple to the spinal cord Relays in hypothalamus trigger release of oxytocin from PP Contraction of uterus Used to induce labor Reduce postpartum bleeding
synthesis, storage, and secretion of peptide hormones
Peptide hormones are synthesized as precursor molecules and processed by the endoplasmic reticulum and Golgi where they are stored in secretory granules. When needed, the granules are dumped into the bloodstream. Different hormones can often be made from the same precursor molecule by cleaving it with a different enzyme. (water soluble) Synthesized on rough ER (of endocrine cells) Prehormones to prohormones Prohormones transported to Golgi for packaging Enzymes in secretory vesicles cleave prohormones to hormones Vesicles stored in cytoplasm Vesicles fuse with cell membrane and release hormones into blood stream (exocytosis) Stimulus is increased [Ca++] from depolarization Increased cAMP→ protein kinases → secretion Transported in blood unbound hormone is secreted once the cell is depolarized (stimulus from increased calcium)
what is the hypothalamus?
Portion of the brain (diencephalon) that links the nervous and endocrine systems The hypothalamus contains neurons that control releases from the anterior pituitary. Seven hypothalamic hormones are released into a portal system connecting the hypothalamus and pituitary, and cause targets in the pituitary to release eight hormones. Intricate network of nuclei (made up of neurons) Some neurons are neurohormonal Synthesize neuropeptides that work as hormones Magnocellular (paraventricular and supraoptic) Oxytocin and ADH Parvocellular Projections to brainstem and spinal cord Release neurohormones that control AP function
how are steroid hormones removed and metabolized?
Primarily degraded by liver Conjugated to polar sulfate or glucuronide groups to make steroid water-soluble Conjugated steroids primarily excreted in the urine
what are some examples of autocrine agents?
Prostaglandins, growth factors, interleukin-1
what is a peptide hormone?
Ranging from dipeptide (two amino acids) to large proteins of over 200 amino acids strings of amino acids long string = a protein most common kind of hormone examples Hypothalamic, A pituitary, P pituitary, pancreatic hormones, ACTH, insulin, glucagon
what effects does ADH have? what receptors does it work on?
Regulates serum osmolarity Increases water permeability of the late distal tubules and CDs in kidneys Increases permeability to water (LDT and CD) - V2 receptor Constriction of vascular smooth muscle - V1 receptor
Testes
Release androgens Stimulates sperm production and development and maintenance of male sexual behavior and secondary male characteristics
growth hormone releasing hormone
Released by the Hypothlmus. Promotes synthesis and release of Growth Hormone from AP
corticotropin releasing hormone
Released by the hypothalamus to stimulate the release of adrenocorticotropic hormone
the adrenal medulla secretes (epi/norepi) 4x more than (epi/norpei)?
Secretes epi > NE (by 4 times!)
Ovaries
Secretes estrogen and progesterone Sustains pregnancy and stimulates development and maintenance of female characteristics and sexual behavior
Thyroid
Secretes thyroxine, triodothyronine, and calcitonin Controls metabolic rate and blood calcium levels
synthesis, storage, and secretion of steroid hormones
Steroid hormones are derived from cholesterol by a biochemical reaction series. Defects along this series often lead to hormonal imbalances with serious consequences. Once synthesized, steroid hormones pass into the bloodstream; they are not stored by cells, and the rate of synthesis controls them. Structure similar to cholesterol Synthesized from cholesterol from plasma (and a little from steroid-producing cells) in adrenal cortex gonads placenta Little hormone storage Large store of cholesterol esters available Over 90%, transported in blood by large carrier proteins lipid solubility allows them to cross membrane barriers when the gland is stimulated to release the hormone, it is quickly synthesized from the cholesterol and then released (the hormone is not just sitting there) low protein status = fluid shifts and disturbed hormone regulation
how do intracellular steroid receptors work?
Steroid receptors Hormone-receptor complex binds with DNA Activation or inhibition of gene transcription Binding requires Hydrophobic hormone Ability to cross the plasma membrane Steroids, steroid derivative of Vitamin D The second mechanism involves steroid hormones, which pass through the plasma membrane and act in a two step process. Steroid hormones bind, once inside the cell, to the nuclear membrane receptors, producing an activated hormone-receptor complex. The activated hormone-receptor complex binds to DNA and activates specific genes, increasing production of proteins.
what are steroid hormones?
Steroids are lipids derived from cholesterol. Testosterone is the male sex hormone. Estradiol, similar in structure to testosterone, is responsible for many female sex characteristics. Steroid hormones are secreted by the gonads, adrenal cortex, and placenta. Large family of molecules based on the 17-carbon aromatic cyclopentanophenanthrene nucleus reproductive type of hormones Minor chemical differences are associated with marked differences in biological activity Adrenal cortex (cortisol, aldosterone) Reproductive gland hormones (testosterone, estradiol, progesterone) Vitamin D and metabolites are steroid hormones
what is a paracrine agent?
Substance carried to adjacent target cells over short distances via interstitial fluid
what is an autocrine agent?
Substance that acts back on the cell of origin or adjacent identical cells
what stimulates oxytocin release?
Suckling is major stimulus for oxytocin secretion Contraction of uterus
ADH
Supraoptic > paraventricular nuclei (hypothalamus) Regulates serum osmolarity Increases water permeability of the late distal tubules and CDs in kidneys Increases Inc. serum osmolarity Volume contraction Pain Nausea Hypoglycemia Decreases Dec. serum osmolarity Ethanol Alpha-agonists ANP Increases permeability to water (LDT and CD) - V2 receptor Constriction of vascular smooth muscle - V1 receptor
from what are steroids synthesized from? in what glands?
Synthesized from cholesterol from plasma (and a little from steroid-producing cells) in adrenal cortex gonads placenta
amine hormones (T3/T4) are synthesized from _______
Synthesized from tyrosine and iodide
amine hormones (epi/norpie) are synthesized from _______ in the _______
Synthesized from tyrosine in the adrenal medulla
Glucagon
Synthesized in alpha cells of the pancreas Half life is 5 min Increases blood glucose (from the liver) Glycogenolysis - The catabolism of glycogen to get glucose Gluconeogenesis - The generation of glucose from other organic molecules such as amino acids Lipolysis- The breakdown of fat stored in fat cells Stimulated by Hypoglycemia, Increased amino acids,Prolonged exercise and stress Deficiency causes hypoglycemia Excess causes hyperglycemia
Growth Hormone
Synthesized in the anterior pituitary Promotes growth Increases DNA synthesis Increases the use of fat Decreases the use of carbs Control Hypothalamus - GHRH - anterior pituitary - GH Excess causes Acromegaly Gigantism Deficiency causes Hypoglycemia in adults Dwarfism in children
Calcitonin
Synthesized in the parafollicular cells of the thyroid in response to increased calcium Maintains bones Decreases plasma calcium Operates in negative feedback Stimulated by increased blood calcium levels and gastrin (after a meal) Half life = 60 min Metabolized in the kidneys Deficiency of calcitonin causes osteoporosis
synthesis of thyroid hormones
Synthesized in the thyroid gland Thyroid hormones contain large amounts of iodine (come from diet) Partially intracellular and partially extracellular; completed hormones stored extracellularly in the lumen until the thyroid gland is stimulated to secrete it The least active form is the most abundant form released from the thyroid gland
which thyroid hormone is more active?
T3
which thyroid hormone is more potent?
T3
Which is released in greater quantities, T3 or T4?
T4
which thyroid hormone is more abundant?
T4
what are the hormones released by the anterior pituitary
TSH FSH LH GH Prolactin ACTH (MSH)
target tissues convert T ___ to T ____
Target tissues convert T4 to T3
what are some examples of amine hormones?
Thyroid hormones Catecholamines (epinephrine, norepinephrine, dopamine)
what are receptor protein tyrosine kinases?
Transmembrane proteins with enzymatic activity Phosphorylation of tyrosine Increases kinase activity Can alter transcription of genes The first step is that ligand binding causes receptor dimerization: that is, binding of the ligand brings together two receptors. The receptors, which are tyrosine kinases, can now phosphorylate each other (receptor autophosphorylation). The phosphotyrosine on the phosphorylated receptor is a binding site for an adaptor protein that also binds a guanine-nucleotide exchange factor (GEF protein). Binding to the phosphorylated receptor recruits these proteins to the membrane. The GEF protein activates Ras, a small monomeric G-binding protein by exchanging GTP for GDP (GTP replaces GDP). Ras is one member of a large family of small monomeric G-proteins. G-proteins act as molecular switches: they are activated when they bind GTP. Ras controls cell proliferation, but other monomeric G-proteins are involved in regulating cell shape changes through effects on the cytoskeleton, or involved in membrane trafficking through exocytosis and endocytosis. Activated Ras turns on the first in a cascade of protein kinases, where each protein kinase phosphorylates and activates another protein kinase. The ultimate result is the phosphorylation of transcription factors that enter the nucleus and alter gene expression, turning on genes involved in growth and cellular differentiation. Ras is inactivated when GTP is hydrolyzed to GDP. Like the alpha subunit of a trimeric G-protein, monomeric G-proteins like Ras are GTPases. However, the rate of GTPase activity of Ras is greatly increased by another protein, the GTPase activating protein or GAP protein
what is a neurohormone?
a chemical messenger released by neurosecretory cells A neurohormone is any hormone produced and released by neuroendocrine cells (also called neurosecretory cells) into the blood. By definition of being hormones, they are secreted into the circulation for systemic effect, but they can also have a role of neurotransmitter or other roles such as autocrine (self) or paracrine (local) messenger.
what are ligand gated ion receptors?
a group of transmembrane ion channel proteins which open to allow ions such as Na+, K+, Ca2+, and/or Cl− to pass through the membrane in response to the binding of a chemical messenger (i.e. a ligand), such as a neurotransmitter. When a presynaptic neuron is excited, it releases a neurotransmitter from vesicles into the synaptic cleft. The neurotransmitter then binds to receptors located on the postsynaptic neuron. If these receptors are ligand-gated ion channels, a resulting conformational change opens the ion channels, which leads to a flow of ions across the cell membrane. This, in turn, results in either a depolarization, for an excitatory receptor response, or a hyperpolarization, for an inhibitory response.
what is a neurosecretory cell?
a nerve that is capable of producing granules of a secretory nature Neurosecretion is the storage, synthesis, and release of hormones from neurons. These neurohormones, produced by neurosecretory cells, are normally secreted from nerve cells in the brain that then circulate into the blood. These neurohormones are similar to nonneural endocrine cells and glands in that they also regulate both endocrine and nonendocrine cells. Neurosecretion cells also release their product farther than normal neurons, which only secrete short distances, into the extracellular space some distance from the target cell
How does iodine get into the thyroid gland?
active transport, iodine trapping
special properties of receptors
affinity specificity saturation location - intra or extracellular
what are 3 classes of hormones?
amines, peptides, proteins
what is a hormone?
any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behavior Hormones are used to communicate between organs and tissues for physiological regulation and behavioral activities, such as digestion, metabolism, respiration, tissue function, sensory perception, sleep, excretion, lactation, stress, growth and development, movement, reproduction, and mood 3 classes = amines, peptides, proteins
Where is the thyroid located?
below the larynx, anterior to trachea
what factors effect hormone secretion?
changes in the internal environment (decreased glucose causes increased glucagon, onset of puberty increases FSH and LH) changes in external environment (stress increases epi, cold increases thyroxine)
steroid hormone structure is similar to the structure of ______
cholesterol
What are G protein coupled receptors?
constitute a large protein family of receptors, that detect molecules outside the cell and activate internal signal transduction pathways and, ultimately, cellular responses. Coupling with G proteins, they are called seven-transmembrane receptors because they pass through the cell membrane seven times There are two principal signal transduction pathways involving the G protein-coupled receptors: the cAMP signal pathway and the phosphatidylinositol signal pathway When a ligand binds to the GPCR it causes a conformational change in the GPCR, which allows it to act as a guanine nucleotide exchange factor (GEF). The GPCR can then activate an associated G protein by exchanging the GDP bound to the G protein for a GTP. The G protein's α subunit, together with the bound GTP, can then dissociate from the β and γ subunits to further affect intracellular signaling proteins or target functional proteins directly depending on the α subunit type
how are the peptide prohormones turned into hormones?
enzymes in the secretory vesicles that they are stored in cleave the prohormones to hormones the vesicles are stored in the cytoplasm and are released into the blood stream when needed via exocytosis
true or false - steroids are largely stored in their respective endocrine glands
false - little hormone storage, but large store of cholesterol esterases
what are some examples of neurohormones?
hypothalamic releasing factors, oxytocin, ADH, NE
what glands of the endocrine system are comprised of neurosecretory cells?
hypothalamus, posterior pituitary, adrenal medulla The hypothalamus produces releasing hormones and neurohypophysial hormones in specialized hypothalamic neurons which extend to the median eminence and posterior pituitary. The adrenal medulla produces adrenomedullary hormones in chromaffin cells, cells which are very similar in structure to post-synaptic sympathetic neurons, even though they are not neurons they are derivatives of the neural crest.
where are epinephrine and norepinephrine stored? how are they secreted?
in secretory granules in the adrenal medulla secreted like peptide hormones (exocytosis)
magnocellular versus parvocellular neurons
in the hypothalamus, neuronal bodies are clustered in nuclei w/ projections reaching other brian regions, which allows continuous communication. some of these neurons are neuralhormonal, which means that they synthesize neuropeptides that function as hormones that are released in repsonse to depolarization there are two types of neurons that are important in mediating endocrine functions of the hypothalamus: magnocellular and parvocellular neurons the magnocellular neurons produce large quantities of the neurohormones oxytocin and ADH Parvocellular neurons have Projections to brainstem and spinal cord and Release neurohormones that control AP function Parvocellular neurosecretory cells are small neurons within paraventricular nucleus (PVN) of the hypothalamus. The axons of the parvocellular neurosecretory cells of the PVN project to the median eminence, at the base of the brain, where their neurosecretory nerve terminals release peptides into blood vessels in the hypothalamo-pituitary portal system. The blood vessels carry the peptides to the anterior pituitary gland, where they regulate the secretion of hormones into the systemic circulation.
what is the stimulus for the the peptide hormone to be released from its vesicle via exocytosis?
increased calcium concentration from depolarization increased cAMP activates protein kinases which activates secretion
growth hormone inhibiting hormone (somatostatin)
inhibits growth hormone release
what are the different kinds of receptors?
ligand gated (g protein coupled, receptor protein tyrosine kinase, receptor linked kinase recepter (GH)) intracellular receptors (steroid receptors - complex binds w/ DNA)
thyrotropin releasing hormone
made in the hypothalamus and stimulates thyroid stimulating hormone and prolactin from anterior pituitary to be secreted
ADH causes ________ urine to be produced due to __________
more concentrated urine d/t sodium and water reabsorption into the body
from what nuclei in the hypothalamus is ADH secreted?
paraventricular
what is the most common class of hormone?
peptide
name the glands of the endocrine system
pineal gland, parathyroid gland, hypothalamus, pituitary gland, thyroid, thymus, adrenal gland, pancreas, ovary, testes
where are peptide hormones synthesized?
preprohormones are synthesized on the rough ER of endocrine cells, and then the prohormones transported to golgi for packaging
dopamine
released from hypothalamus and stimulates prolactin
describe the characteristics of endocrine glands
small ductless scattered throughout the body highly vascular (to exert their actions) release hromones directly into blood stream target hormones have hormone specific receptors
what are the mechanisms of the regulation of hormone concentration in the blood?
stimuli and compensatory feedback mechanism Neural input CNS (pancreas receives SNS and PSNS input to regulate insulin and glucagon) Nutrition affects secretion of hormone Control of insulin by plasma glucose levels Control of parathyroid hormone by plasma Ca++ and phosphate levels Hormones Negative feedback is predominant feedback mechanism
What protein is stored with thyroid hormones in colloid?
thyroglobulin
what are the hormones secreted from the hypothalamus?
thyrotropin releasing hormone gonadotropin releasing hormone corticotropin releasing hormone growth hormone rleasing hormone somatostatin (growth hormone inhibiting hormone) dopamine
peptide and amine hormones are transported ______ in blood, while steroid hormones are transported _______ in blood
unbound, bound to carrier proteins
peptide and amine hormones are _________ soluble, while steroid hormones are ________ soluble
water, lipid
