Endocrine System

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Endocrine System
Hormone Classes
The Hypothalamus
Regulating Thyroid
Responses to Stress
Communication
Chemical Messengers
Modes of Hormone Action
Pituitary Gland
Parathyroid Glands
Gonads
Endocrine Vs. Exocrine Glands
Negative Feedback
Endocrine System Functioning
Pancreas
Pineal Gland
System Components
Positive Feedback
Hypothalamus
Adrenal Medulla
Thymus Gland
Hormone Classes
Lipid-Soluble Hormones
Thyroid Gland
Adrenal Cortex
Endocrine Nervous Systems
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I. The Two Major Systems of Communication and
Their Response Times
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• Nervous System is a major system of internal
  communication
• - high-speed electrical signals sent by
  neurotransmitters
• - they travel across the synaptic cleft in
  order to bind to
  receptors on target cell
• -this process results in a rapid response
• example hand touches hot stove and jerks away

• 2. Endocrine System is the second major system
  of internal communication
• hormones transported in circulatory system
  through blood to target cells
• results in much slower response
• examples responses to stress, dehydration, low
  blood glucose levels

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II. Chemical Messengers
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• Nervous system Neurotransmitters are the
  messengers
• -neurons travel via synaptic cleft
• -act on target cells in muscle and sensory
  organs
• -bind to receptors of target cell

2. Endocrine Hormones are the messengers -releas
ed by endocrine glands and transported through
blood -act on appropriate target cells that may
be anywhere in the body -bind to receptors of
target cells -neurosecretory cells
(neurohormones)- specialized cells that release
hormones into blood -different from classic
hormones released by endocrine glands -they are
located in the hypothalamus
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III. Endocrine Glands Vs. Exocrine Glands
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• Endocrine
• -ductless
• -secrete chemical messengers directly into
• extracellular fluid
• 2. Exocrine
• -have ducts that carry secretions to specific
  locations

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IV. Endocrine System Components
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• 1. Endocrine Glands
• -Secrete the hormone messengers
• 2. Hormones
• -Chemical messengers transported through
  endocrine system via blood
• 3.Target Cells
• -Cells with receptors for hormones to bind to
• 4.Target Cell Receptors
• -Hormones bind to these to elicit a response by
  the target cell
• -the receptors are located on the target cell
• Signal Transduction Pathway
• -is initiated by a hormone binding to its
  receptor
• -it is a series of changes in cellular proteins
  that converts an extracellular chemical signal to
  a specific intracellular response
• -response examples activation of an enzyme
  change in uptake or secretion of specific
  molecules rearrangement of the cytoskeleton

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V. Hormone Classes
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1. Chemical Classes A. Peptide Ex. Parathyroid
Hormone (PTH)- raises blood Ca level and is
regulated by the calcium in the blood released
by parathyroid gland B. Protein Ex. Growth
Hormone (GH)- stimulates growth (especially
bones) and metabolic functions regulated by
hypothalamic hormones released by pituitary
gland C. Glycoprotein Ex. Thyroid Stimulating
Hormone (TSH)- stimulates thyroid gland
regulated by thyroxine in blood and hypothalamic
hormones released by pituitary gland
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VI. Hormone Classes Continued
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D. Amine Ex. Triodothyronine (T3) and thyroxine
(T4)- stimulate and maintain metabolic
processes regulated by TSH released by
thyroid gland E. Steroid Ex. Estrogen- stimulate
uterine lining growth promote development and
maintenance of female secondary sex
characteristics regulated by FSH and LH
released by gonads
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VII. General Modes of Hormone Action

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1. Hormone Action a. Sensors (receptors)- detect
stimulus Ex change in blood calcium level
-sensor sends information to control center
(gland) b. control center- compares information
to a set point (desired value) -Control center
sends out signal (effector) to respond to
stimulus c. in endocrine and neuroendocrine
pathways, the effector is called an efferent
signal d. Efferent signal a hormone or
neurohormone that acts on particular tissues,
eliciting physiological or developmental changes
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VIII. General Modes of Hormone Action Continued
Negative Feedback
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• 1. Feedback Loops
• Negative Feedback- effector response reduces
  initial stimulus until response ceases
• -prevents overreaction by system and wild
  fluctuations in the variable being regulated
• -operates in many endocrine and nervous
  pathways, especially when maintaining
  homeostasis
• -negative feedback is more common than positive
  feedback
• Ex hormonal control of blood calcium and
  glucose levels

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IX. General Modes of Hormone Action Continued
-
Positive Feedback
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B. Positive Feedback- involves a change in some
variable that triggers mechanisms that amplify
rather than reverse the change (Cummings
833). -reinforces stimulus, leading to a greater
response Ex neurohormone pathway that regulates
release of milk by nursing mother Ex during
childbirth when the pressure of the babys head
against receptors near the opening of uterus ,
stimulates uterine contractions, causing greater
pressure against uterine opening, heightening
contractions, causing greater pressureit brings
childbirth to completion
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X. Lipid-Soluble Hormones
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1. Lipid Soluble Classes -The intracellular
receptor activated by a lipid- soluble hormone is
a transcription factor, and the response is a
change in gene expression
2. Type of lipid-soluble hormone -chemical
class Steroid -enter cell and bind to receptors
in cytoplasm -hormone-receptor complex enters
nucleus where it binds with chromatin,
activating certain genes -when genes are active,
protein will be produced
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XI. The Hypothalamus
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• The Hypothalamus
• Location
• -ventral part of the forebrain
• 2. Importance
• -Maintains homeostasis by means of regulating
  internal environment receives information from
  nerves and initiates appropriate endocrine
  signals
• -Hormones secreted by the hypothalamus must
  travel via blood to the anterior lobe to the
  pituitary gland before they can work
• -Neurons and hormones are different than the
  hormones secreted by the hypothalamus because
  they are secreted by endocrine secretory cells
  and travel directly to the target cell

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XII. Pituitary Gland
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• Pituitary Gland
• Location
• - base of hypothalamus
• 2. Posterior Lobe
• -releases hormones that are synthesized by
  neurons in the hypothalamus
• -contains axons of neurons that extend from the
  hypothalamus
• -hormones are stored in and released form axon
  endings in posterior lobe
• Ex oxytocin, ADH
• 3. Anterior Lobe
• - synthesizes the hormones it releases
• -is stimulated to produce these hormones when
  hormones produced by the hypothalamus travel in
  blood vessels to the anterior pituitary
• Ex GH, Prolactin, Melanocyte-Stimulating
  Hormone
• POSTERIOR PITUITARY HORMONES CONTINUED
• ????
• CLICK THIS STRANGE HOUSE

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XIII. Endocrine System Functioning
A. Tropic hormone
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a.  produced in the anterior pituitary b.
regulate function of other endocrine glands,
coordinate endocrine signaling - Follicle
Stimulating Hormone (FSH)- stimulate activity of
gonads - Luteinizing Hormone (LH)- stimulate
activity of gonads - Thyroid- Stimulating
Hormone (TSH)- promote normal development of
thyroid and production of its hormones -
Adrenocorticotropic Hormone (ACTH)- stimulate
production and secretion by adrenal glands
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B. Hypothalamus
(yellow structure)
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• Produces tropic hormones to stimulate Anterior
  Pituitary gland
• Releasing hormones promote stimulatory tropic
  hormone secretion
• Inhibitory hormones stop tropic hormone secretion
  
• b. Hormones in blood give feedback to
  hypothalamus to act on anterior pituitary
• Base of hypothalamus has capillaries to take
  hormones
• Carry to small blood vessels connecting to nearby
  anterior pituitary
• Capillary bed w/in anterior pituitary delivers
  hypothalamus hormones

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C. Thyroid Gland
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• a. Hormones Triiodothyronine (T3) and Thyroxine
  (T4)
• T4 is often converted to T3 b/c T3 is more potent
  
• b. Roles of these hormones in metabolism and
  development
• Reorganize tissues in metamorphosis
• Promote normal function of bone- forming cells
• - Branch nerve cells in embryo
• Maintain normal blood pressure, heart rate,
  muscle tone, digestive and reproductive functions
  
• Increase rate Oxygen consumptionincrease
  cellular metabolism
• c. Also produces hormone Calcitonin to help
  parathyroid regulate Ca homeostasis

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d. Negative Feedback Loop Regulating Thyroid
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• The hypothalamus secretes TSHreleasing hormone
  (TRH)
• Stimulates the anterior pituitary to secrete
  thyroidstimulating hormone (TSH)
• Stimulates the thyroid gland to synthesize and
  release the thyroid hormones T3 and T4
• These hormones exert negative feedback on the
  hypothalamus and anterior pituitary by inhibiting
  release of TRH and TSH

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D. Parathyroid Glands
(yellow structures)
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• Embedded in surface of thyroid to regulate Ca 2
  levels (10mg/100mL)
• Low levels of Ca in blood--- release Parathyroid
  Hormone (PTH)
• Induce osteoclast cells in bone to decompose bone
  mineral matrix and release Ca2 into blood
• Stimulate reabsorbing Ca2 in renal tubes of
  kidneys
• Promote inactive vitamin D from skin and food to
  convert to an active hormone form that promotes
  absorption Ca2 in intestines
• c. High levels Ca in blood--- Thyroid releases
  Calcitonin to stop bone stimulation by PTH

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E. Pancreas
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• Alpha cells produce glucagons and Beta cells
  produce insulin
• Antagonistically regulate blood glucose levels
  (90mg/100mL)
• Too high insulin hormone lowers levels of
  glucose
• Stimulate blood cells to take up glucose
• Slow glycogen breakdown in liver and prevents
  fats from breaking down to glucose
• Liver and muscle store sugars as glycogen
• Adipose tissue convert sugars to fat
• d. Too low glucagons hormone increases levels
  glucose
• Stimulate liver to hydrolysis amino acids and
  glycerol to sugars
• Releases sugars slowly into blood

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F. Adrenal Medulla
(center layer)
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• Hormones epinephrine and norepinephrine (aka
  adrenaline and nor adrenaline)
• Function
• Increase rate of glycogen breakdown to increase
  blood glucose
• Stimulate fatty acid release from fat cells
• Increase heart rate, dilate bronchioles to
  increase Oxygen consumption
• Relax some muscles so others can receive more
  blood
• c. In response to external positive or negative
  stress when nervous system hypothalamus receives
  neural signal to send hormones to posterior
  pituitary
• - Peripheral nerve cells-posterior
  pituitary-spinal chord- adrenal medulla

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G. Adrenal Cortex
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• Hormones and functions
• -glucorticoids
• Promote glucose synthesis from noncarbohydrates
  in muscles
• Transport to kidneys to be released in blood
• Anti-inflammatory (suppress immunity prolonged)
• - mineralocorticoids
• Balance salt and water in body
• Stimulate kidney reuptake sodium ions and water
  to increase blood pressure and volume
• - Sex hormones androgens (m), progestins (f),
  estrogen (f)

b. Respond to endocrine signals - Stimulus
(stress)hypothalamusanterior pituitaryACTH adr
enal cortexnegative feedback
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H. Endocrine Responses to Stress
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Adrenal Glands Short Term Adrenal
Medulla Increase blood glucose,
alertness Increase heart rate, blood pressure,
metabolism Decrease digestion, kidney activity
(change blood flow patterns) Long Term
Adrenal Cortex (prolonged responses) Mineralocor
ticoids increase blood pressure and volume,
kidneys store water and sodium Glucocorticoids
Increase glucose (breakdown fats and proteins),
suppress immunity
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I. Gonads
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(M) testes (F) ovaries both produce
steroids Androgens (ie testosterone)
development maintenance M reproductive
system Estrogen maintain F reproductive
system, develop secondary sex
characteristics Progestins (ie progesterone)
prepare maintain uterus to support embryo
Control synthesis of androgen and estrogen
Hypothalamus gonadotropin- releasing hormone
(Gn- RH) stimulates Anterior pituitarys
gonadotropin hormones (FSH and LH)
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J. Pineal Gland
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near center mammalian brain with light sensitive
cells or nervous connections to eyes regulate
functions related to seasonal day length
(circadian rhythms) hormone Melatonin regulate
sleep and reproductive activity
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K. Thymus Gland
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under top breast bone hormone Thymosin
stimulates maturation of T- lymphocytes (T- Cells
immune system) helps differentiate T Cells to
specialize in specific antibodies
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V. Endocrine and Nervous Systems
Theyre related!
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• Structure
• endocrine glands made of nervous tissues
• Hypothalamus important structure of each
• Chemicals
• - both use same transmitters in different ways
  (ie Norepinephrine as hormone or
  neurotransmitter)
• 3. Function
• both communication systems help body maintain
  homeostasis
• Work in conjunction and exert control over one
  another (Nervous system development controlled by
  endocrine system which is under control of nerve
  cells)

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• Posterior Pituitary hormones
• Antidiuretic Hormone (ADH)
• -acts on kidneys
• -increases water retention
• -decreases urine volume
• -part of mechanism that helps regulate the
  osmolarity of blood
• -illustrates importance of negative feedback in
  maintaining homeostasis
• -shows central role of hypothalamus as a member
  of both endocrine system and nervous system
• 2. Oxytocin
• -stimulates uterine contractions of labor that
  are need to move child through birth canal
• -induces target cells in uterine muscles to
  contract
• -this hormone also stimulates release of milk
  from mammary glands by causing surrounding cells
  to contract
• - is an example of positive feedback