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152 Cards in this Set

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endocrine system

provides long-term regulation by using chemical messengers to relay information and instructions between cells.

hormones

-the body contains about 30 of these chemical messengers which regulate activities such as sleep, body temperature, hunger, and stress management.


-these are products of the endocrine system and only specialized cells produce the typical kind.


-they are released in one tissue and transported in the bloodstream to alter the activities of specific cells in OTHER tissues.


-typically released where capillaries are abundant and can enter the bloodstream quickly.

Mechanisms of Intercellular communication

direct communication

-two cells of the same type that are adjacent communicate so closely that they function as a single entity.


-via gap junctions.


-coordinate activities by exchanging ions and molecules across gap junctions.

gap junctions

1. coordinate ciliary movement among epithelial cells.


2. coordinate the contraction of cardiac muscle cells.


3. facilitate the propagation of action potentials from one neuron to the next at electrical synapses.

paracrine communication

-cells talking to eachother by releasing chemicals into the extracellular fluid


-telling their neighbors what they are doing at any moment.


-results in the coordination of tissue function at the local level.


-use of chemical messengers to transfer information from cell to cell within a single tissue.

paracrine factors

-also known as local hormones.


-ex. prostaglandins and various growth factors.


-enter the bloodstream, but their concentrations are so low that distant cells and tissues are not affected.

when paracrine factors have secondary effects in other tissues or organs:

they are also acting as hormones.


-by convention, a substance with effects outside its tissue origin is called a hormone if its chemical structure is known... and a factor if that structure remains to be determined.

email and messengers

CV system = email


hormones = messenger


target cells

-each hormone has one


-specific cells that have the receptors needed to bind and "read" the hormonal message when it arrives.

endocrine communication

-the activity of hormones in coordinating cellular activities in tissues in distant portions of the body.

a hormone works by:

-altering operation of target cells by changing the types, quantities, or activities of important enzymes and structural proteins.


-modify the physical structure or biochemical properties of it target cell.


-happens over a long term basis.


a hormone may:

-stimulate the synthesis of an enzyme or a structural protein not already present in the cytoplasm by activating appropriate genes in the cell nucleus


-increase or decrease the rate of synthesis of a particular enzyme or other protein by changing the rate of transcription or translation


-turn an existing enzyme or membrane channel "on" or "off" by changing its shape or structure.

synaptic communication


( the nervous system )

-handles situations requiring split second responses.


-the endocrine system is unable to do this.


-release neurotransmitters at a synapse very close to target cells that have appropriate receptors.


-command travels rapidly as an action potential propagated along axons.

nervous and endocrine similarities

-rely on release of chemicals that bind to targets.


-share some chemical messengers (NE and E)


-regulated by negative feedback mainly.


-goal is to preserve homeostasis by coordinating and regulating the activities of other cells, tissues, organs, and systems.

endocrine cells

glandular secretory cells that release their secretions into the extracellular fluid.


exocrine cells

secrete their products onto the epithelial surfaces, generally by way of two ducts.

Tissues, Organs, and Hormones of the Endocrine System (Upper Body)

Tissues, Organs, and Hormones of the Endocrine System (Lower Body)

Three groups of hormones based on chemical structure

1. amino acid derivatives


2. peptide hormones


3. lipid derivatives

amino acid derivatives


-biogenic amines


-relatively small molecules.


-synthesized from tyrsoine and tryptophan

hormones made from tyrosine

1. thyroid hormones, produced by the thyroid gland.
2. the catecholamines epinephrine(E), norepinephrine(NE), and dopamine .

1. thyroid hormones, produced by the thyroid gland.


2. the catecholamines epinephrine(E), norepinephrine(NE), and dopamine .

peptide hormones

-one group consists of glycoproteins.


-other group consists of short polypeptides and small proteins.

Glycoproteins

-proteins that are more than 200 amino acids long and have carbohydrate side chains.


-includes thyroid-stimulating hormone (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) from the anterior lobe of the pituitary gland, as well as several other hormones produced in other organs.

Short chain polypeptides


-antidiuretic hormone (ADH)


-oxytocin (OCT)


(both are 9 amino acids long)

small proteins

-insulin (51 aa long)


-growth hormone GH (191)


-prolactin PRL (198)


-all hormones secreted by the hypothalamus, heart, thymus, digestive tract, pancreas, and posterior lobe of the pituitary gland, as well as several others produced in other gland.

lipid derivatives

1. Eicosanoids


2. steroid hormones

eicosanoids

-signalling molecules and include;
-leukotrienes,
-prostaglandins
-thromboxanes
-prostacyclins

-signalling molecules and include;


-leukotrienes,


-prostaglandins


-thromboxanes


-prostacyclins

steroid hormones

-lipids structurally similar to cholesterol
-individual hormones differ in the side chains attached to the basic ring structure.
-over time, the liver gradually absorbs these and converts them to a soluble form that can be excreted in the bile or ...

-lipids structurally similar to cholesterol


-individual hormones differ in the side chains attached to the basic ring structure.


-over time, the liver gradually absorbs these and converts them to a soluble form that can be excreted in the bile or urine.

a freely circulating hormone

-remains functional for less than one hour, and sometimes as little as two minutes.


-Inactivated when:


1. it diffuses out of the bloodstream and bind to receptors on target cells


2. it is absorbed and broken down by cells of the liver and kidneys.


3. it is broken down by enzymes in the blood or intestinal fluids.

hormones that travel bound to special carrier proteins

-thyroid and steroid hormones remain in the circulation much longer because when they enter the bloodstream, more than 99% become attached to special transport proteins.

freely circulating and bound hormones

-are in an equilibrium


-as the free hormones are removed and inactivated, bound hormones are released to replace them.


-bloodstream contains a substantial reserve (weeks supply) of bound hormones.

plasma membrane receptors

-receptors for catecholamines, peptide hormones ( hydrophilic/cannot penetrate PM)


-receptors for eicosanoids( hydrophobic/can penetrate PM)


first messenger

hormone that bins to a receptor on the PM surface.

second messenger


intermediary molecule that appears due to a hormone-receptor interaction.


1. cyclic AMP (cAMP), a derivative of ATP.


2. cyclic GMP (cGMP), a derivative of GTP.


3. calcium ions

amplification

when a small number of hormone molecules binds to membrane receptors and thousands of second messengers appear in a cell.


-magnifies the effect of a hormone on a target cell.


(may promote the release of more than one type of second messenger or receptor cascade)

receptor cascade

-production of a linked sequence of enzymatic reactions


-caused by amplification


-hormone can alter many aspects of cell function at the same time because of this.

down-regulation

-process by which the presence of a hormone triggers a decrease in the number of hormone receptors.


-cell becomes less sensitive to high levels of a particular hormone.

up-regulation

-process in which the absence of a hormone triggers an increase in the number of receptors.


-cells become more sensitive to low levels of a particular hormone.

G protein

-the link between the first messenger and the second messenger is usually this.


-an enzyme complex coupled to a membrane receptor.


-these proteins bind GTP.


-80% of prescription drugs target receptors coupled to these.

cyclic AMP and GPCR

phosphodeisterase (PDE)

-enzyme in the cytoplasm that inactivates cAMP by converting it back to AMP.


-this is why cAMP level increase is usually short lived.

calcium ions and GPCR

-phospholipase C (enzyme) triggers a receptor cascade that begins with the producting of diacylglycerol (DAG) and inositol triphosphate (IP3) from membrane phospholipids.


-protein kinase C activation leads to phosphorylation of calcium channel proteins that permits Ca to enter. (positive feedback)


-calmodulin can activate specific cytoplasmic enzymes.

Intracellular receptors

-hydrophobic hormones can diffuse across the PM and bind to these receptors in the cytoplasm or nucleus.


-then specific genes are activated or deactivated.


-alterations in the synthesis of enzymes or structural proteins directly affect both the metabolic activity and the structure of the target cell.

intracellular binding of steroid hormones

-can alter the rate of DNA transcription in the nucleus. 
-this changes the pattern of protein synthesis 

-can alter the rate of DNA transcription in the nucleus.


-this changes the pattern of protein synthesis

intracellular binding of thyroid hormones

-those bound to mitochondria increase the mitochondrial rates of ATP production. 
 

-those bound to mitochondria increase the mitochondrial rates of ATP production.


endocrine reflexes

Triggered by:


1. humoral stimuli (changes in the comp. of the ECF)


2. hormonal stimuli (the arrival or removal of a specific hormone)


3. neural stimuli (the arrival of a neurotransmitters at neuroglandular junctions)

negative feedback controls endocrine reflexes

-a stimulus triggers the production of a hormone, and the direct or indirect effects of the hormone reduce the intensity of the stimuli.

Three Mechanisms of Hypothalamic Control over Endocrine Function

1. secreting regulatory hormones that control endocrine cells in the pituitary gland.


2. endocrine organ (neurons synthesize hormones and transport them along axons to the posterior lobe of the pituitary gland (ADH and OXT)


3. autonomic centers that exert direct neural control over the endocrine cells of the adrenal medullae. (when stimulated release E and NE)


simple endocrine reflex

-hormones are released continuously, but the rate of secretion rises and falls in response to humoral stimuli.


ex. insulin and glucose, the effects of insulin are proportional to its concentration.

relationship between hormone concentration and target cell response

-not always predictable.


-a hormone can have one effect at low concentrations and more exaggerated effects, or even different effects, at high concentrations.

pulses

-several hypothalamic and pituitary hormones are released in these sudden bursts, rather than continuously.


-target cell response can very due to the frequency.

most complicated hormonal instructions from the hypothalamus:

involve changes in the frequency of pulses and in the amount secreted in each pulse.

Anatomy and Orientation of the Pituitary Gland

adenohypophysis

-the anterior lobe of the pituitary gland.


-contains a variety of endocrine cells


-has three regions (pars distalis, pars tuberalis, pars intermedia)


-an extensive capillary network radiates through these regions, giving every endocrine cell immediate access to the bloodstream.

Hypophyseal Portal System and Blood supply to the Pituitary Gland

median eminence

-a swelling near the attachment of the infundibulum where hypothalamic neurons release regulatory factors into the surrounding interstitial fluids.


-secretions enter the bloodstream easily because of fenestrated capillaries.

superior hypophyseal artery

delivers blood to the capillary network in the median eminence

portal vessels

-deliver blood containing regulatory factors to the capillary network within the anterior lobe of the pituitary gland.


(blood vessels that link two capillary beds)

portal systems

efficient means of chemical communication.


-hypophyseal portal system ensures that all the hypothalamic hormones entering the portal vessels reach the target cells in the anterior lobe before being diluted through mixing with the general circulation.


-communication is completely one way however, and any chemicals released "down-stream" must do a complete circuit of the CV system before they reach the capillaries in the portal system.

hypothalamic regulatory hormones

Travel right to the anterior lobe by the hypophyseal portal system.


-releasing hormones


-inhibiting hormones

releasing hormones (RH)

stimulates the synthesis and secretion of one or more hormones at the anterior lobe.

inhibiting hormomes (IH)

prevents the synthesis and secretion of hormones form the anterior lobe.

Typical Pattern of Regulation when Multiple Endocrine Organs are Involved

Variations on the Typical Pattern of Regulation of Endocrine Organs by the Hypothalamus and Anterior Pituitary Lobe

hypothalamic releasing hormones that follow the typical pattern of regulation

Hormones of the Anterior Lobe

also called "tropic hormones", meaning that they turn on endocrine glands or support the functions of other organs:


-Thyroid-stimulating hormone


-adrenocorticotropic hormone


-two gonadotropins called follicle-stimulating hormone, and luteinizing hormone


-prolactin


-growth hormone


-melanocyte-stimulating hormone

Anterior Pituitary Lobe Hormones

Thyroid-Stimulating Hormone (TSH)

"thyrotropin"


targets the thyroid gland and triggers the release of thyroid hormones.


-release in response to thyrotropin-releasing hormone from the hypothalamus.

Adrenocorticotropic Hormone (ACTH)

"corticotropin"


stimulates the release of steroid hormones by the adrenal cortex.


-specifically targets cells that produce glucocorticoids (hormones that affect glucose metabolism)


-release in response to corticotropin-releasing hormone from the hypothalamus.

gonadotropins

hormones that regulate the activities of the gonads (testes or ovaries that produce reproductive cells as well as hormones).


-produced in response to gonadotropin-releasing hormone

hypogonadism

abnormally low production of gonadotropins.


-children do not mature sexually or produce sperm or oocytes.

follicle-stimulating hormone (FSH)

"follitropin"


promotes follicle development in females, and in combo with luteinizing hormone, stimulates secretion of estrogens by ovarian cells.


-also stimulates nurse cells, which are specialized cells in the seminiferous tubules where sperm differentiate.

estradiol

the most important estrogen

nurse cells

specialized cells in the seminiferous tubules where sperm differentiate.


when stimulated by FSH, the promote physical maturation of developing sperm.

inhibin

peptide hormone released by the testes and ovaries that inhibits FSH production.


Luteinizing hormone (LH)

"lutropin"


induces ovulation (production of reproductive cells in females.


promotes ovarian secretion of estrogens and progesterone, which prepare the body for possible pregnancy.

androgens

male sex hormones.


produced by interstitial cells of the testes which are stimulated by interstitial cell-stimulating hormone (ICSH) which is the male version of LH.

testosterone

most important male sex hormone.

Prolactin

works with other hormones to stimulate mammary gland development.


-also stimulates milk production after a baby is born.


-inhibited by dopamine.

prolactin, estrogens, progesterone, glucocorticoids, pancreatic hormones, and hormones produced by the placenta

cooperate in preparing the mammary glands for secretion.

milk ejection

only occurs in response to oxytocin release at the posterior lobe.

Growth Hormone (GH)

"somatotropin"


stimulates cell growth and replication by accelerating the rate of protein synthesis.


-skeletal muscle cells and chondrocytes are paricularly sensitive to this.


-stimulation of growth by this hormone involves two mechanisms.

insulin-like growth factors (IGFs)

"somatomedins"-> indirect effect


stimulate tissue growth by binding receptors on a variety of plasma membranes.


-in skeletal muscle fibers, cartilage cells, and other targets, they increase the uptake of amino acids and their incorporation into new proteins. (stimulates protein synthesis and cell growth)


-these effects develop almost immediately after GH is released.


direct actions of GH

-tend to appear after blood glucose and amino acid concentrations have returned to normal levels:


-in epithelia and connective tissue, GH stimulates cell division and the differentiation of daughter cells.


-in adipose tissues, GH stimulates the breakdown of stored triglycerides by adipocytes which then release fatty acids into the blood. (glucose-sparing effect)


-in the liver, GH stimulates breakdown of glycogen reserves by liver cells, which then release glucose into the bloodstream. (diabetogenic effect)

glucose-sparing effect

as circulating fatty acid levels rise, many tissues stop breaking down glucose to generate ATP and instead start breaking down fatty acids.

diabetogenic effect

-most other tissues are metabolizing fatty acids rather than glucose when they have the chance, so blood glucose concentrations climb to levels significantly higher than normal.


Melanocyte-Stimulating Hormone (MSH)

"melanotropin"


-the pars intermedia may secrete two forms of this


-stimulates the melanocytes of the skin, increasing production of melanin.


-dopamine inhibits the release.


-in humans, this is produced locally within sun-exposed skin.

human pars intermedia

-virtually nonfunctional


-circulating blood normally does not contain MSH.


-exception during fetal development, very young children, pregnant women, and in the course of some diseases.

Hormones of the Posterior Pituitary Lobe

-posterior lobe = neurohypophysis.
-contains the axons of hypothalamic neurons. 

-posterior lobe = neurohypophysis.


-contains the axons of hypothalamic neurons.

antidiuretic hormone

"vasopressin"


-manufactured by the neurons of the supraoptic nuclei of the hypothalamus, travels down to posterior lobe.


-released in response to a variety of stimuli, most notably a rise in the solute concentration in the blood or a fall in the blood volume or pressure.


-osmoreceptors in the hypothalamus stimulate the neurosecretoy neurons that release this.

alcohol

inhibits the release of ADH


"break the seal"

Oxytocin

-stimulates smooth muscle contraction in the wall of the uterus, promoting labor and delivery.


-promotes ejection of milk by stimulating the contraction of myoepithelial cells around the secretory alveoli and the ducts of the mammary glands.


-may also stimulate smooth muscle contraction in walls of the ductus deferens (sperm duct) and prostate gland.

milk-let-down reflex

oxytocin secretion and milk ejection are part this neuroendocrine reflex.


-normally stimulated by the infant suckling on the teet and sensory nerves innervating the nipples.


-any factor affecting the hypothalamus can modify this reflex (anxiety, stress, and others) preventing the flow.

pituitary hormones and their targets

Thyroid gland (anatomy/histology)

thyroglobulin

-globular protein synthesized and secreted by follicle cells into the colloid of the thyroid follicles.


-contains tyrosine, the building block of thyroid hormones.


steps involved in the formation of thyroid hormones

1. I- from diet delivered to gland, actively transported.
2. I- diffuse to apical surface, lost an e-, become I by the enzyme thyroid peroxidase. This reaction also attaches the atoms to tyr portions of thyroglobulin molecule. 
3. tyrosine molecu...

1. I- from diet delivered to gland, actively transported.


2. I- diffuse to apical surface, lost an e-, become I by the enzyme thyroid peroxidase. This reaction also attaches the atoms to tyr portions of thyroglobulin molecule.


3. tyrosine molecules covalently bond, forming thyroid hormone molecules


4. follicle cells remove thyroglobulin by endocytosis.


5. lysosomal enzymes break down thyroglobulin, aa (which become recycled) and thyroid hormones enter the cytoplasm.


6. T3 and T4 diffuse into blood.


7. Most become attached to thyroid-binding globulins. The rest is attached to transthyretin (thyroid-binding prealbumin) or to albumin.

thyroxine

T4 tetraiodothyronine


contains 4 iodide atoms


-each molecule of thyroglobulin contains 4 - 8 of these.

triiodothyronine

T3 containing 3 iodide atoms


-each molecule of thyroglobulin contains 4 - 8 of these.

bound thyroid hormones

-make up a substantial reserve in the blood


-an equilibrium exists between bound and free thyroid hormone in the bloodstream.

Regulation of Thyroid Secretion

Effects of Thyroid Hormones on Peripheral Tissues

calorigenic effect

-thyroid hormones activate genes that code for enzymes involved in glycolysis and ATP production.


-coupled with the direct effect of thyroid hormones on mitochondira, this effect increases the metabolic rate of the cell.


-cell consumes more energy and generates more heat.


(in young children, TSH production increases in cold weather)


C (clear) cells

"parafollicular cells"


produce calcitonin (CT), which helps to regulate [Ca2+] in body fluids.


-control of its secretion is direct endocrine regulation (hypothalamus and pituitary are not involved)


-activated by an elevation of Ca2+ in blood, turn off again when Ca2+ is normal.

calcitonin

1. inhibits osteoclasts, slowing the rate of Ca2+ from bones


2. stimulates Ca2+ excretion by the kidneys.


-in children, it stimulates bone growth and mineral deposition in the skeleton


-also seems to be important in reducing loss of bone mass 1. during prolonged starvation, and 2. in the late stages of pregnancy.

high [Ca2+]

sodium permeability decreases and membranes become less responsive

low [Ca2+]

sodium permeability increases, cells become more excitable.


-convulsions or muscular spasms can result.

parathyroid glands (anatomy/histology)

parathyroid (chief) cells

-produce the parathyroid hormones.


-monitor the circulating [Ca2+]


-when that is low, these secrete parathyroid hormone (PTH) "parathormone"


Parathyroid hormones

1. mobilizes calcium from bone by affecting osteoblast and osteoclast activity. stimulates osteoblasts to secrete growth factor (RANKL). osteoclasts have no PTH receptors, but do have RANKL receptors.


2. enhances resorption of Ca2+ by the kidneys, reducing urinary loss.


3. stimulates the formation and secretion of calcitriol by the kidneys.

RANKL

growth factor that results in an increase in osteoclasts and osteoclast activity.


-causing an increase in rate of mineral turnover and Ca2+ release. bone matrix erodes and blood Ca2+ rises.

calcitriol

effects complement or enhance those of PTH, but also enhances Ca2+ and PO4 absorption by the GI tract.

effects complement or enhance those of PTH, but also enhances Ca2+ and PO4 absorption by the GI tract.

Homeostatic Regulation of increasing [Ca2+]

Homeostatic Regulation of decreasing [Ca2+]

Hormones of the Thyroid Gland and Parathyroid glands

adrenal gland hormones

adrenal cortex

-yellow due to stored lipids, especially cholesterol and various fatty acids.


-produces more than 24 steroid hormones collectively called corticosteroids.


corticosteroids

-in the bloodstream, these are bound to transport proteins called transcortins.


-these are vital, if gone, person would die.


-turn on transcription of certain genes in the nuclei of a target cell and determine their transcription rates.

aldosterone

-stimulates the conservation of Na+ and elimination of K+ by the kidneys, sweat glands, salivary glands, and pancreas.... preventing loss of Na+ in urine, sweat, saliva, and digestive secretions.


-secretion occurs in response to a drop in blood Na+ content, blood volume, or blood pressure, or a rise in blood K+ concentration. Also released in response to angiotensin II.

cortisol

"hydrocortisone"


secreted when ACTH from the anterior lobe stimulates the zona fasciculata.


liver converts some of this that is circulating into cortisone (another active glucocorticoid)

effects of the activation of the adrenal medullae

-in skeletal muscles, E and NE trigger mobilizing glycogen reserves and accelerate breakdown of glucose to provide ATP (muscular strength and endurance increase)


-in adipose tissue, stored fats are broken down into fatty acids, which are released into the blood for other tissues to use for ATP prod.


-in the liver, glycogen molecules are broken down. glucose is released into blood for use by neural tissue (which cant shift to fatty acid metabolism)


-in the heart, stimulate beta-1 receptors to trigger increase in rate and force of cardiac contraction.

pineal gland

-part of the epithalamus


-contains neurons, neuroglia, and special secretory cells (pinealocytes)

pinealocytes

synthesize melatonin from molecules of the neurotransmitter serotonin. 

synthesize melatonin from molecules of the neurotransmitter serotonin.

collaterals from the visual pathways

-enter the pineal gland and affect the rate of melatonin production.


-rate is slowest during daylight hours and highest at night.

melatonin functions

-inhibit reproductive functions


-protecting against damage by free radicals (antioxidant)


-influencing circadian rhythms

panceas (anatomy/histology)

exocrine pancreas

-clusters of gland cells called pancreatic acini (and ducts)


-99% of the pancreatic volume.


-secrete large quantities of an alkaline, enzyme-rich fluid that reached the lumen of the digestive tract through a network of secretory ducts.

endocrine pancreas

-small group of cells (pancreatic islets) scattered among the exocrine cells.


-secretions are vital to survival.


-each islet contains four types of cells (alpha, beta, delta, and F)


Hormones produced by the Pancreatic Islets

alpha cells

produce the hormone glucagon which raises blood glucose levels by increasing the rate of glycogen breakdown and glucose release by the liver.

beta cells

-produce the hormone insulin which lowers blood glucose levels by increasing the rate of glucose uptake and utilization by most body cells, and by increasing glycogen synthesis in skeletal muscles and the liver.


-also secrete amylin, a peptide whose level rises after a meal.


delta cells

-produce a peptide hormone identical to growth hormone-inhibiting hormone, which suppresses the release of glucagon and insulin by other islet cells and slows the rates of food absorption and enzyme secretion along the digestive tract.

F cells

-produce pancreatic polypeptide which inhibits gallbladder contractions and regulates the production of some pancreatic enzymes.


-may also help control rate of nutrient absorption by the digestive tract.

regulation of increase in blood glucose levels

regulation of decrease in blood glucose levels

Diabetes Mellitus

Clinical problems that arise due to untreated diabetes mellitus

also peripheral tissue damage due to reduced blood flow (tissue death, ulceration, infection, and loss of toes)

also peripheral tissue damage due to reduced blood flow (tissue death, ulceration, infection, and loss of toes)

Representative Hormones Produced by Organs of Other Systems

Renin

specialized kidney cells (juxtaglomerular cells) release this in response to:
1. sympathetic stimulation 
2. decrease in renal blood flow. 
starts the RAAS

specialized kidney cells (juxtaglomerular cells) release this in response to:


1. sympathetic stimulation


2. decrease in renal blood flow.


starts the RAAS

hormones of the reproductive system

Clinical Implications of Endocrine Malfunction

leptin

-peptide hormone produced by adipose tissue


-best known as a feedback control of appetite


-binds to hypothalamic neurons involved with emotion and appetite control when we eat.


-satiation (sense of fullness)

leptin must be present for normal levels of GnRH and gonadotropin synthesis to take place

explains:


1. thin girls enter puberty later


2. increase in body fat can improve fertility


3. women stop menstruating when their body fat content becomes very low.

antagonistic effect

-two hormones have an oppose eachother but bind to the same target.


-ex. calcitonin and PTH


-ex. insulin and glucagon

synergistic effect

-two hormones have additive effects, so the net result is greater than the effect each hormone would produce alone


-ex. glucose-sparing action of GH and glucocorticoids.

permissive effect

the first hormone is needed for the second to produce its effect.


-ex. E does not change energy consumption unless the thyroid hormones are also present in normal concentrations.

integrative effects

-hormones produce different but complementary effects, results in specific tissue and organs.


-important in coordinating activities of diverse physiological systems.


-ex. calcitriol and parathyroid hormone on tissues involved in calcium metabolism.

general adaptation syndrome


(response to stress)


Alarm Phase

general adaptation syndrome


(response to stress)


Resistance Phase

general adaptation syndrome


(response to stress)


Exhaustion Phase

Most notable endocrine change with age

-decline in the concentrations of reproductive hormones.


-many others do not change with age (TSH, thyroid hormone, ADH, PTH, prolactin, and glucocorticoids)