Chapter 10 Flashcards
Puberty brings about many changes in the human body.
- Both genders get a growth spurt during puberty, & the 2ndary sex characteristics begin to develop.
- Males= the growth of body and facial hair, deepening of the voice, & the development of the genitals.
- Females= the growth of body hair, the onset of their menstrual cycle, & the development of breasts & broader hips.
- All of these developments r timed & controlled by hormones
A hormone is
a chemical made by cells in one part of the body that regulate the processes of cells in another part of the body
- are prduced by the endocrine system
- act as chemical messengers, enabling 1 part of the body to give instructions to another part
- Some cells even self-regulate, producing chemicals to stimulate their own cellular processes
Local regulators are
chemicals like hormones but act on nearby cells, rather than cells some distance away.
Hormones r secreted by…
the cells, tissues, & organs that compose the endocrine system
The endocrine system does what?
Regulates & coordinates organ functions like growth, development, reproduction, behavior, energy metabolism, & water balance. (like the nervous system)
The nervous system & Endocrine system
- Both systems regulate & coordinate body functions.
- r structurally, chemically, & functionally related, but they control organ & tissue functions in diff ways
–> Nervous system: Sends fast electrical signals for rapid responses to the external environment.
–> Endocrine system: Uses slower, longer-acting hormonal responses to control organ and tissue functions. - Nervous system regulates the release of most hormones, ultimately controlling the endocrine system.
Endocrine glands are
ductless secretory organs that secrete their hormones
directly into the blood or extracellular fluid.
–> (In contrast, exocrine glands, like the sweat & salivary glands, release their secretions into ducts that lead outside the body or into the body cavities)
- Hormones circulate throughout the body in blood & other fluids.–> As a result, most body cells r constantly exposed to a wide variety of hormones but only target cells will respond to a specific hormone cuz only they have receptor proteins that recognize & bind to that type of hormone
- Hormones r cleared from the body at a steady
rate by enzymatic breakdown in their target cells, in the blood, or in organs such as the liver or kidneys. –> The breakdown products are reused or excreted
There are more than ____known hormones and local regulators in humans. How do they compare to hormones and regulators in other animals?
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- Many r identical or very similar in structure & function to the hormones in other animals, tho many animals have hormones not found in humans.
Hormones are identified by their _____________________.
chemical structure
There are 2 main types of Hormones:
- protein hormones, which are water soluble,
- steroid hormones, which are lipid soluble.
- Most hormones fall into one of these two types
A protein hormone is
a hormone composed of chains of amino acids that is water soluble; usually acts on cell membrane receptors
- amino acid chains= 3 amino acids to more than 200
- released into the blood or extracellular fluid by the cells in the endocrine glands where they are made.
- usually hydrophilic: they have an affinity for water & diffuse well through the blood & intercellular fluids
- 1 group of protein hormones= the growth factors, regulates the division & differentiation of many types of cells in the body
A steroid hormone is
a hormone composed of cholesterol that is not very water soluble; usually passes through the cell membrane & acts on receptors inside the cell
- not very soluble in blood but they can pass easily through the lipid bilayer of cellular membranes
–> Combine with hydrophilic carrier proteins to form water-soluble complexes, enabling diffusion into blood & other fluids.
- When it contacts a cell, it is released from its carrier protein.
- passes through the plasma membrane of the target cell & then binds to internal receptors in the nucleus or cytosol.
- Steroid hormones include aldosterone, cortisol, & the sex hormones. –> all natural
Some steroid hormones have very similar structures but produce very diff effects. Give an example
- ex, testosterone & estradiol, 2 major sex hormones that r responsible for the development of male & female characteristics, respectively, differ only in the presence or absence of a single methyl group
Prohormones
- Many hormones r secreted in an inactive or less active form called prohormones
- Prohormones r converted to active forms by target cells or enzymes in blood or tissues.
- Protein hormones are commonly synthesized as prohormones, which r then converted to the active form in the source cell –> some cases, further conversion occurs once the hormone has been secreted
- Ex, Angiotensinogen, secreted by the liver, is an inactive precursor. –> Cleaved by enzyme to an inactive form of angiotensin, which is activated by angiotensin-converting enzyme (ACE) to regulate blood pressure by increasing it. –> ACE inhibitors r used to manage high blood pressure.
Hormones are usually secreted in relatively ________________, but a process of amplification magnifies their effect. Explain
small amounts
- Once a receptor cell activates a few proteins, these
proteins activate other proteins, each of which activates other proteins, and so on.
- This chain reaction amplifies the effect of the small amount of hormone initially received.
Pathways for Water-Soluble Hormones
- Hormones use 2 main mechanisms to control cellular activities.
- The 1st mechanism governs water-soluble protein hormones (protein hormones), which cannot easily cross membranes
- bind to receptor molecules in the cell membrane, causing the receptor molecule to change shape.
- This activates a signal, which passes into the cell
- This signal can lead to internal changes in the cell, such as releasing enzymes that modify proteins by adding or removing phosphate groups.
- The signal may act only in the cytosol or affect the nucleus, as with many protein hormones such as growth factors
- Ex of the surface receptor mechanism is the protein hormone glucagon. –> When glucagon binds to surface receptors on liver cells, it triggers a series of reactions.
–> These reactions lead to the addition of phosphate groups, which activate the enzyme that governs the breakdown of stored glycogen into glucose.
glucagon is
a hormone produced by alpha cells in the pancreas that raises the blood glucose level by promoting the breakdown of glycogen in the liver
Pathways for Lipid-Soluble Hormones
The 2nd main mechanism involves hormones binding to receptors inside a cell –> used by most steroid hormones
- Steroid hormones=lipid based= lipid soluble= they pass easily through the plasma membrane.
- attach to receptors in the cytosol or nucleus of a cell.
- The hormone-receptor complex then binds to a control sequence on a specific gene, turning the gene’s action on or off.
- Activation & deactivation of the gene changes the
amount of protein that it synthesizes, which changes the cellular activity
- Ex,steroid hormone aldosterone.
-Secreted by adrenal glands when bp is low. - Travels through membranes & binds to receptors in kidney, sweat gland, & colon cells.
- The receptor acts as a transcription factor, synthesizing proteins that increase sodium reabsorption.
- Increased sodium leads to water retention, raising blood pressure.
The two mechanisms used by hormones are not mutually exclusive. Explain.
A single target cell may have receptors for several hormones & respond differently to each hormone.
- Ex, the liver cells of vertebrates have receptors for the pancreatic hormones insulin & glucagon.
- Insulin increases the uptake of glucose & its conversion to glycogen, which decreases the blood glucose level.
- Glucagon stimulates the breakdown of glycogen into glucose, which increases the blood glucose level.
particular hormones can interact with diff types of receptors in or on a range of target cells. Elaborate
- Diff responses r then triggered in each target cell
cuz the receptors trigger diff signal pathways. - As well, the response to a hormone may differ among species.
- Ex, melatonin, a protein hormone derived from tryptophan, is important in regulating daily & annual cycles in most animals. –> But, it also plays a role in regulating the salt glands of marine birds.
In summary, the mechanisms by which hormones work have 4 major features:
1) Only the cells that contain surface or internal receptors for the hormones respond to the hormones.
2) Once bound to their receptors, hormones produce a response by turning cellular processes on or off. They do this by altering the proteins that r functioning in or produced by the cell
3) Hormones are effective in very small concentrations cuz of the amplification that occurs in both the surface and internal receptor mechanisms.
4) The response to a hormone differs among target organs and among species.
Hormones as Part of Feedback Mechanisms
- Most hormones r regulated by negative feedback mechanisms.
- In a -ve feedback mechanism, a chemical that is affected at the end of the action pathway of a hormone controls the further action of the hormone by inhibiting an earlier chemical reaction.
- A response in a feedback loop may be the production of a substance or a decrease in the production of a substance
- Ex, hypothalamus releases thyroid-releasing hormone (TRH), which initiates a pair of hormone releases by the pituitary and thyroid glands.
- As the concof the thyroid hormone in the blood increases, it inhibits an earlier step in the pathway, the secretion of thyroid-stimulating hormone (TSH) by the pituitary gland.
Regulation of Body Processes by Hormones
- Some glands make multiple hormones, & many body processes r influenced by multiple hormones simultaneously.
- Glucose, fatty acids, and ions (e.g., Ca²⁺, K⁺, Na⁺) levels r regulated by hormones from different glands.
- Functions such as metabolism, digestion, growth, sexual development, & stress responses rely on multiple hormones.
- many systems= negative feedback loops adjust the level of secretion of hormones that act in opposing ways.–>maintains homeostasis in the body.
–> Consider regulation of fuel molecules, like glucose, fatty acids, &amino acids, in the blood. Between meals, 5 diff hormone systems, involving the digestive
tract, pancreas, nervous system, & pituitary & adrenal glands, all act together in a coordinated fashion to keep the body’s fuel levels in balance.
Many other important hormones are secreted
by other organs, such as…
the heart, liver, kidneys, and intestines, & have diff primary functions.
The hypothalamus is
the region of the brain that releases hormones to control the pituitary gland, which, in turn, controls
other endocrine glands
- It is a region of the brain & thus part of the nervous system.
- Neurons (nerve cells) in the hypothalamus make a special type of hormone= neurohormones.
A neurohormone is
a hormone produced by neurons, such as in the hypothalamus, that controls the production of other
hormones in the pituitary gland
- The neurohormones travel along the length of the nerve cells, diffuse into the bloodstream, & then travel through the blood into the pituitary
-2 types of neurohormones made by hypothalamus: releasing hormones & inhibiting hormones
–> either stimulate or inhibit the release of specific hormones that r made in the anterior pituitary gland.
- The hormones secreted by the endocrine cells inside the anterior pituitary gland r then released into bloodstream to reach their target tissues, where they control many other endocrine glands & some bodily processes directly
The hypothalamus itself is controlled by input from other parts of the nervous system. Elaborate.
- Some neurons connect directly to the hypothalamus from sensory receptors that monitor lood for changes in body chemistry or temp.
- Input to the hypothalamus also comes from numerous connections from control centres elsewhere in the brain.
- -ve feedback systems help to control how the hypothalamus releases its hormones
The pituitary gland is
a two-lobed gland located within the cranium, just below the brain that produces hormones that control the other endocrine glands
- It has 2 major lobes: the anterior lobe & posterior lobe
- Neurohormones travel through a portal vein connecting the capillaries in the hypothalamus to those in the anterior pituitary gland.
- The portal vein=a critical link between the nervous & endocrine system, as most blood entering the anterior pituitary must first pass through the hypothalamus, allowing the neurohormones to go from hypothalumus to anterior pituitary gland
The pituitary gland is referred to as the _______________ because…
- “master gland”
- it produces hormones that control most of the other endocrine glands
- anterior pituitary secretes several major hormones into the bloodstream, some that drive hormone secretion in other glands.
- posterior pituitary gland stores & releases 2 important hormones, 1 of which helps to control
bp.
Anterior pituitary gland overview
- endocrine system= largely controlled by the anterior pituitary hormones, which, in turn, r controlled by the releasing or inhibiting hormones that come from the
hypothalamus. - The anterior pituitary secretes 8 major hormones into the bloodstream: prolactin, growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, melanocyte-stimulating hormone, endorphins
Anterior Pituitary Gland: PRL
- Full form: Prolactin
- influences reproductive activities & parental care in vertebrates.
- In mammals: stimulates the development of the secretory cells of the mammary glands during late pregnancy, & milk synthesis after birth
- Stimulation of the mammary glands & the nipples, which occurs during suckling, leads to the release
of PRL. - In all vertebrates, it has a role in promoting both maternal & paternal behaviour
- found in non-mammalian vertebrates, where it has a variety of functions. –> Ex, In fish, it is one of the hormones that controls H20 balance.
Anterior Pituitary Gland: GH
- Full form: Growth Hormones
- Stimulates cell division, protein synthesis, and bone growth in children & adolescents, causing overall body growth.
- stimulates protein synthesis & cell division in adults.
- GH binds to target tissues like muscle, triggering release of insulin-like growth factor (IGF),a protein hormone that directly stimulates the growth processes
- controls # of major metabolic processes in mammals: conversion of glycogen–>glucose, fats–>fatty acids to regulate their levels in the blood.
-stimulates body cells to take up fatty & amino acids & limits the rate at which muscle cells can take up glucose. –> helps to maintain the availability of glucose & fatty acids to tissues & organs between meals, which is particularly important for the brain.
Growth Hormone defiencies & overproduction
- In humans, deficiencies in GH secretion during childhood produce pituitary dwarfs, who remain
small in stature - Overproduction of GH during childhood or adolescence, usually cuz of tumour of the anterior pituitary, makes pituitary giants, who may grow up to 2.7 m in height
Tropic Hormones
are hormones secreted by the anterior pituitary gland that control endocrine glands elsewhere in the body.
- the tropic hormones secreted by anterior pituitary gland r Thyroid-stimulating hormone (TSH), Adrenocorticotropic hormone (ACTH),
Follicle-stimulating hormone (FSH), Luteinizing hormone (LH)
Anterior Pituitary Gland: TSH
- Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to grow in size & secrete thyroid hormones
Anterior Pituitary Gland: ACTH
- Adrenocorticotropic hormone (ACTH) triggers hormone secretion by cells in the adrenal cortex.
Anterior Pituitary Gland: FSH
Follicle-stimulating hormone (FSH) affects egg development in females and sperm production in males.
- also stimulates the secretion of sex hormones in female mammals.
Anterior Pituitary Gland: LH
Luteinizing hormone (LH) regulates part of the menstrual cycle in human females and the secretion of sex hormones in males.
- FSH & LH r grouped together as gonadotropins cuz they regulate the activities of the gonads
Anterior Pituitary Gland: MSH
Melanocyte-stimulating hormone (MSH) named cuz of effect on melanocytes, skin cells that contain black pigment melanin
- Increased MSH secretion darkens the skin in fish, amphibians, reptiles, & humans–> less noticeably in humans.
- MSH secretion increases in pregnant women –> combined with elevated estrogen levels, increases skin pigmentation –> effects= reversed after child birth
Anterior Pituitary Gland: Endorphins
protein hormones made by hypothalamus & the pituitary gland
- released by the intermediate lobe of the pituitary gland.
- humans= the intermediate lobe isn’t well developed, comprising only a thin layer of cells between the anterior & posterior lobes.
- In the nervous system, endorphins act as
neurotransmitters in pathways that control pain, thereby inhibiting the perception of pain. –> Hence, endorphins are aka “natural painkillers.”
The posterior lobe of the pituitary gland stores and releases 2 important hormones…
antidiuretic hormone & oxytocin, into the bloodstream
- produced in the cells of the hypothalamus
- r transferred to the posterior pituitary gland along nerve cells that reach from the hypothalamus into the posterior pituitary –> stores the hormones & releases them into the bloodstream when appropriate nerves from the hypothalamus r stimulated.
Antidiuretic hormone
- aka ADH
- Stimulates kidney cells to reabsorb more water from urine, increasing blood volume.
- released when hypothalamus sensory receptor cells detect increase in the blood Na+ conc after salty meal or when the body is dehydrated
- also released when severe blood loss or drop in bp.
- Inhibited by: Ethanol & caffeine, causing increased urine volume.
- Stimulated by: Nicotine & emotional stress, causing H20 retention.
- Stress relief & the return to normal ADH secretion often results in increased urination.
- ADH helps maintain bp by reducing H20 loss & causing blood vessels in some tissues to constrict
ADH & Kidneys
- enables the kidneys to maintain a homeostatic balance of extracellular fluid in the body
- about 85% of H20 filtered into nephrons is reabsorbed in the proximal convoluted tubule.
- remainder is absorbed in the distal convoluted tubule only if ADH is present
- ADH causes the upper part of distal convoluted tubule to be permeable to water. The high conc
of NaCl in the interstitial fluid causes water to move, by osmosis, out of the upper part of the distal tubule & the collecting duct into the interstitial fluid. - It is the control of this volume of water (15 %) in the kidneys that balances the conc of the body fluids.
- Hormones like ADH r also secreted in fish, amphibians, reptiles, & birds. –> In amphibians, they increase amount of water that enters the body through skin & from the urinary bladder.
Oxytocin
- stimulates the release of milk from the mammary
glands of a mother. –> stimulation of the nipples in suckling sends neuronal signals to the hypothalamus & leads to the release of oxytocin. - released oxytocin stimulates more oxytocin secretion by a positive feedback mechanism
- causes the smooth muscle cells surrounding the mammary glands to contract, forcibly expelling the milk through the nipples
- entire cycle, from onset of suckling to milk ejection, takes < 1min in mammals.
- also plays a key role in childbirth by stimulating the contraction of the muscles of the uterus
- In males, it’s secreted into the seminal fluid by the testes.
- When seminal fluid is ejaculated into the vagina, oxytocin stimulates contractions of the uterus, which aid the movement of sperm through the female reproductive tract
The Thyroid gland
located in the front of the throat in humans & is shaped like a bow tie.
- secretes the same hormones in all vertebrates
- The thyroid hormones have an extraordinarily wide range of effects
- The primary thyroid hormone, thyroxine, is aka T4 cuz it contains 4 iodine atoms –> A supply of iodine in the diet is needed to make all of these hormones.
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When there is not enough iodine to make thyroxine…
- the negative feedback loop fails and the thyroid is continually stimulated by TSH from the pituitary gland
- The overstimulated thyroid swells and results in a condition called a goiter, which can result in a noticeable swelling on the neck
- To ensure that people get enough iodine in their diet to produce thyroxine & prevent goiter, iodine
is added to table salt in many places in the world, including Canada.
is the thyroid hormone T4 a steroid hormone?
NO, but it is lipid soluble and can pass through the cell membrane.
- Once inside, T4 loses an iodine atom & is converted into T3.
- T3 enters the nucleus & combines with nuclear receptors. –> There, it alters gene expression, bringing about many of its effects –> increases the metabolic rate; essential for normal body growth
Thyroid hormones are vital to… Elaborate.
….growth, development, maturation, & metabolism
in all vertebrates.
-They interact with growth hormone for their effects on growth & development
- also increase the sensitivity of many body cells to
the effects of epinephrine & norepinephrine: hormones released by the adrenal medulla as part of the fight-or-flight response.
- In amphibians, rising conc of thyroid hormones trigger metamorphosis or a change in body form from tadpole to adult .
- also contribute to seasonal moulting, leading to changes in the plumage of birds & the coat colour of mammals.
Calcitonin
A Protein hormone secreted by specialized thyroid cells as the principal source; also made in lungs & intestines.
-discovered in fish by Dr. Harold Copp, a professor
at the University of British Columbia
- lowers the level of Ca2+ in the blood by inhibiting the ongoing release of calcium from bones.
- Stimulated by high blood Ca²⁺ levels & inhibited by low blood Ca²⁺ levels.
The parathyroid glands
- found only in amphibians, reptiles, birds, & mammals.
- Mammals have 4 parathyroid glands, 2 on each side of the posterior surface of the thyroid gland.
- Each parathyroid= spherical structure about pea size.
- The only hormone they make= parathyroid hormone (PTH), is secreted in response to a fall in the Ca2+ level in the blood
- The PTH pathway= negative feedback loop.
- PTH stimulates bone cells to dissolve the mineral matter of bone tissues, releasing both Ca2+ & P3- ions into blood.
- The released Ca2+ is available for enzyme activation, conduction of nerve signals across synapses, muscle contraction, blood clotting, & other uses.
- Although fish do not have a parathyroid gland, they make PTH & have PTH receptors. However, the origin of the hormone & its precise function remain uncertain.
PTH & Kidney
PTH stimulates enzymes in the kidneys to convert vitamin D, a steroid-like molecule, into calcitriol, its fully active form in the body.
- The activated vitamin D increases the absorption of Ca2+ & phosphates from ingested food by promoting
the synthesis of a calcium-binding protein in the intestines.
- It also increases the release of Ca2+ from bones in response to PTH.
PTH underproduction causes the….
the Ca2+ conc in the blood to fall steadily, disturbing nerve and muscle function.
- As a result, the muscles twitch & contract uncontrollably, & convulsions & cramps occur. –> Without treatment, the condition is usually fatal cuz the severe muscular contractions interfere with breathing
Overproduction of PTH results in…
the loss of so much calcium from the bones that
they become thin and fragile.
- This condition is known as osteoporosis. At the same
time, the elevated Ca2+ conc in the blood causes calcium deposits to form in soft tissues, especially in the lungs, arteries, & kidneys (where the deposits
form kidney stones)
The adrenal glands
- ( ad= “near” and renes=“kidneys”)
- mammal adrenal glands of have 2 distinct regions.
- 1) The central region, aka adrenal medulla, contains highly modified neurosecretory neurons.
-2) The tissue surrounding the adrenal medulla, aka the adrenal cortex, contains non-neural endocrine cells. - The 2 regions secrete hormones with entirely diff functions.
The adrenal medulla secretes
- secretes 2 adrenal hormones: epinephrine & norepinephrine
–> r chem that can act as hormones or neurotransmitters (chemicals that transmit nerve signals) –> They bind to receptors in the plasma membrane of their target cells. - Norepinephrine is also released as a neurotransmitter by some neurons of the nervous system
- they are secreted when the body encounters stresses like excitement, danger (fight-or-flight situations), anger, fear, infection, injury, and even anxiety
The adrenal cortex secretes
several hormones, like aldosterone & cortisol
- Aldosterone= main hormone of mineralocorticoids, is involved in osmoregulation & control of bp.
- Cortisol= main hormone of glucocorticoid hormones that help to regulate blood glucose levels & promote
fats & protein breakdown as alternative fuels when the glucose supply is low
Function of Epinephrine
-prepares the body for handling stress or physical activity
- It causes the heart rate to increase and glycogen & fats to break down, releasing glucose & fatty acids into the blood as fuel molecules
- In the heart, skeletal muscles, & lungs, the blood vessels dilate to increase blood flow. –> Elsewhere, the blood vessels constrict.
- This raises bp, reduces blood flow to the intestines & kidneys, & stops smooth muscle contractions, thus reducing water loss & slowing down the digestive system.
- Airways in lungs dilate, increasing air flow.
- The effects of norepinephrine on heart rate, bp, & blood flow to the heart muscle r similar to those of epinephrine.
The effects of epinephrine are what make it a life-saving drug. Elaborate
- life-saving for someone who is experiencing a severe allergic reaction called anaphylaxis.
- A person who has an extreme allergy can go into shock & die from an anaphylactic reaction.
- Epinephrine counters anaphylaxis. –> Its effects are immediate, opening airways and raising bp. People with severe allergies often carry a pen-shaped epinephrine auto-injector that they can use in an emergency
The pineal gland is
an endocrine gland located in or on the brain of vertebrates that secretes the hormone melatonin to
regulate daily biological rhythms
- Melatonin is a neurohormone secreted by the pineal gland, primarily during periods of darkness. –> as light hitting the eyes generates signals that inhibit melatonin secretion.
- Melatonin targets hypothalamus to synchronize the biological clock with daily light-dark cycles, maintaining biorhythms.
- The nightly release of melatonin may help to synchronize the biological clock with daily cycles of light & darkness. –> Jet lag occurs as the biological clock adjusts to a new time zone, reflects time that is required for melatonin secretion to reset a traveller’s daily biological clock to match the period of daylight in a new time zone
- Melatonin is found throughout animal kingdom, as well as in many plants & fungi.
- In invertebrates, it helps control diurnal (daily) rhythms
location of pineal gland
- mammals= near the brain centre
- birds & reptiles= the surface of the brain, just under the skull, & is directly sensitive to light.
- Some of earliest vertebrates had a light-sensitive organ at the top of the head (a third eye), & some lizards retain an eyelike structure in this location.
- In most vertebrates, the third eye became modified into a pineal gland, which may retain some degree of photosensitivity
- In mammals, it is too deeply buried in the brain to be affected directly by light.
- Nonetheless, specialized photoreceptors in the
eyes make connections to the pineal gland.
Overview of the Invertebrate Endocrine System- Insect Growth & Development Hormones: Ecdysone
- A steroid hormone that signals moulting (shedding of the exoskeleton). –> A new exoskeleton (the hard body covering) is laid down beneath the old exoskeleton, which is then shed.
- Secreted by glands responding to a neurohormone produced in the brain.
Overview of the Invertebrate Endocrine System- Insect Growth & Development Hormones: Juvenile hormone
- Controls metamorphosis –> its presence maintains the larval stage.
–> when absence, , the next moult is metamorphic, making a pupa (if applicable) & then an adult. - In adults, it stimulates reproductive processes like egg development.
- Regulated by inhibitory & stimulatory protein hormones from the brain.
Overview of the Invertebrate Endocrine System-Hormones in Crustaceans:
Moult-Inhibiting Hormone:
- Suppresses ecdysone secretion during periods between moults.
- Inhibition of this hormone triggers moulting.
Ecdysone
- Initiates exoskeleton replacement during moulting.
Metamorphosis and Reproduction:
- governed by a hormone
that is different from, but structurally related to, juvenile hormone
Like most processes of the endocrine system, blood sugar level regulation normally occurs _________________
automatically
-Since all of the body’s cells use glucose as fuel, the regulation of the blood glucose level is crucial to maintaining homeostasis.
Many people have a problem with their blood glucose monitoring system, a condition called___________________. Elaborate
diabetes mellitus
- in 2000, there were 2 million diagnosed diabetes cases in Canada, with >60,000 new cases annually.
- Diabetics have abnormally fluctuating blood glucose level, changing their metabolism & leading to some
serious health risks & long-term problems.
- Diabetics face health risks & must monitor & control their blood glucose levels consistently.
- Advances in technology, including electronic glucose monitors and insulin delivery devices (syringes, pens, pumps), assist diabetics in managing their condition.
- Modern medical research has significantly improved treatments for diabetes & other endocrine disorders,
Pancreas Function
- The pancreas makes 2 main blood sugar-regulating hormones: insulin & glucagon, –>made in specialized endocrine cells= the islets of Langerhans.
- most of the pancreas functions as an exocrine gland secreting digestive enzymes
- about 2% of its cells r endocrine cells forming the islets.
Role of Insulin & glucagon: Insulin
Insulin & glucagon regulate the ability of most tissues in the body to metabolize fuel substances.
INSULIN
- secreted by beta cells in the islets in response to a rise in blood glucose, such as after a meal.
- Insulin lowers blood glucose by instructing target cells ( mainly skeletal muscles, liver cells, & adipose tissue) to uptake glucose.
- Insulin prevents the liver from breaking down glycogen into glucose
- also promotes fatty acid uptake & storage in in adipose tissue while inhibiting fat breakdown.
- lowers amino acid levels by promoting protein synthesis from amino acids, while inhibiting the breakdown of proteins into amino acids.
Role of Insulin & glucagon: Glucagon
- secreted by alpha cells in the islets & opposes insulin by raising blood glucose levels
- Stimulates glycogen breakdown into glucose in the liver.
- Promotes fat breakdown into fatty acids & protein breakdown into amino acids.
- Facilitates glucose synthesis from amino acids & non-carbs, particularly during fasting.
Is secretion of insulin & glucagon regulated by insulin & glucagon regulated by + or - feedback mechanisms
negative feedback mech.
- Alpha & beta cells in the pancreas adjust hormone secretion based on glucose concs in their cytosol.
- High Blood Glucose=Beta cells increase insulin production, & alpha cells decrease glucagon production to lower glucose levels.
- Low Blood Glucose= Alpha cells increase glucagon production, & beta cells decrease insulin production to raise glucose levels.
The adrenal glands also play a role in controlling blood sugar. Elaborate
- The adrenal cortex secretes steroid hormones= glucocorticoids
- main glucocorticoid=cortisol
- glucocorticoids help raise blood glucose levels using 3 major mechanisms
1) they stimulate the synthesis of glucose from
non-carb sources, such as fats and proteins
2) they reduce glucose uptake by body cells, except those in central nervous system –> favouring of glucose uptake in the central nervous system keeps the brain well supplied with glucose between meals & during periods of extended fasting
3) they promote the breakdown of fats & proteins, releasing fatty acids & amino acids into the blood as alternative fuels when the glucose supply is low.
The secretion of glucocorticoids is ultimately under the control of the __________________
hypothalamus
- low glucose conc in blood, or elevated level of epinephrine secreted by the adrenal medulla in response to stress, is detected in the hypothalamus.
- This leads to the secretion of adrenocorticotropic hormone (ACTH) by the anterior pituitary.
- ACTH then promotes the secretion of glucocorticoids by the adrenal cortex.
Despite the body’s different mechanisms for maintaining glucose homeostasis, the level of glucose in the blood is not completely constant. Elaborate
- It varies throughout the day, largely due to meals & sleep.
- there is typicaly an overall slow decrease during the night, with spikes bringing the level of glucose up after each meal during the day
- ## conc of insulin in the blood is much lower than the conc of glucose, but, as this graph shows, it rises & falls with the glucose level.
Hyperglycemia
- A blood glucose level that is too high can cause a condition= hyperglycemia
- Symptoms of hyperglycemia include thirst, frequent urination, sugar in urine, vision problems, fatigue, & weight loss.
Hypoglycemia
A blood glucose level that is too low can cause a condition= hypoglycemia
- Symptoms of hypoglycemia include nervousness, shaking, cold sweats, hunger, headaches, & weakness
