Download The Endocrine System - APBIOSTUDENTS

The Endocrine System
By Joseph Hernandez
Objectives
 Know the general mechanisms by which molecules integrate and
control the various metabolic activities in both vertebrate and
invertebrate animals.
 Understand how the neuroendocrine center controls secretion
rates of other endocrine glands and responses in nerves and
muscles.
 Know the major endocrine glands and their secretions
 Be familiar with other endocrine glands and their role in the body
 Know how sugar levels are regulated by hormones
 Differentiate the modes of action of steroid and nonsteroid
hormones
Basic Terms:
 Glands are organs that release substances onto the
skin, or into a body cavity or the interstitial fluid.
 Two Types of Glands
 Endocrine Glands are glands that do not have ducts. These
glands secrete their product in the interstitial fluid; where
then it diffuses it the blood through capillaries.
 Exocrine Glands are glands that have ducts. They deliver
their secretions onto external or internal surfaces.
 Target Cells are specific cells that respond to different
hormones.
Sebaceous and Sweat Gland
(Exocrine Glands)
Intercellular Signaling
in Animals
 In all animals, cells constantly signal one another in response to
changes in the internal and external environments. Receiving such
signals can influence a cell’s metabolic activity, division, or gene
expression.
 Gap Junctions
 Local Signaling Molecules are chemical signaling molecules
that are secreted into the interstitial fluid.
 Animal Hormones are longer-range communication molecules,
which are secreted to the blood through the capillaries.
 Pheromones diffuse through water or air and bind to target
cells in individuals.
Nervous-Endocrine
Interactions
 Glands and other hormone sources are collectively
referred to as an animal’s Endocrine System.
 Both neurons and endocrine cells are derived from the
ectodermal (outer) layer. Both respond to the hypothalamus
(the command center). Also, most organs respond to both
nervous signals and hormones.
 Hormones influence:
 Development of Brain. (Before and After birth)
 Sleep/Wake Cycles
 Emotion
 Memory
 Lastly, the Nervous system influences the endocrine system
by controlling the amount secreted of a hormone.
Categories
of Hormones
 Cholesterol makes Steroid Hormones.
 Modified amino acids make Amine Hormones.
 Short Chains of Amino Acids make Peptide Hormones.
 Longer Chains make Protein Hormones.
 **Note: Refer to figure 35.1 on page.600, for specific
hormone group.**
The Nature of
Hormone Action
 There are three steps involved in cellular
communication:
 Signal Reception- a signaling molecule binds to the
receptor.
 Signal Transduction- the signal is changed into a form that
affects target cell behavior.
 Cellular Response- the cell makes a response.
Intracellular
Reception
 Since a Steroid hormone is a lipid, it can easily diffuse across the
cells membrane. Once inside the cell, the steroid hormone forms a
hormone-receptor complex by binding to a receptor in the
cytoplasm or nucleus. This triggers the activation of the promoter
(region of the DNA that allows for transcription to occur) where
genes are transcribed to form mRNA and thus be shipped out of
the nucleus to the cytosol. Lastly, the mRNA translates into a
protein that carries out the target cells response to the signal.
Plasma Membrane
Receptors
 Most Amine hormones, and all peptide or protein
hormones, are to polar so they can’t diffuse across a
membrane.
 They bind to receptors on a target cell’s plasma
membrane. This binding activates an enzyme that
converts ATP to cAMP (cyclic adenosine monophosphate)
then functions as a second messenger.
 Second Messenger: is a molecule that forms inside a
cell in response to an external signal and affects that cells
activity.
Receptor Function and Diversity
 A cell can only respond to a hormone for which it has
appropriate receptors.
 Since all hormone receptors are proteins, gene mutations can
make them less efficient. (Could reduce their ability to function)
 Ex. When there is a mutation of the functional receptors for
testosterone or androgen (steroid hormones). Testes will not
descend because the inability for the receptors to read steroid
hormones.
 Variations in receptor structure also affect responses to
hormones. Different tissues often have receptor proteins that
respond in different ways to bonding of the same hormone.
Major Glands
The
Hypothalamus
 The Hypothalamus is the main
center for control of the internal
environment; it also connects to the
pituitary gland.
Pituitary
Gland
 The Pituitary Gland is the vertebrae endocrine gland located
inside the brain; it interacts with the hypothalamus to control
physiological functions, including activity of many other glands. It
posterior lobe stores and secretes hormones from the
hypothalamus; the anterior lobe makes and secretes it’s own
hormones.
Posterior
Pituitary
 Posterior Pituitary Function
 (ADH) and oxytocin are made in the hypothalamus by
secretory neurons (neurons that make hormones rather than
neurotransmitters). These hormones are stored in the axon
terminals of the secretory hormones and are released when
neuron is excited (action potential).
 Antidiuretic Hormone (ADH) affects certain kidney cells.
The hormone causes these cells to reabsorb more water.
 Oxytocin triggers muscle contractions during childbirth.
Helps move milks into the mammary glands, and also effects
social behavior in some species.
Anterior
Pituitary
 The anterior pituitary produces hormones on its own, but
hormones from the hypothalamus control its secretion.
 Adrenocorticotropic hormone (ACTH) stimulates the release
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of hormones by adrenal glands.
Thyroid-Stimulating hormone (TSH) regulates the secretion of
thyroid hormone by the thyroid glands.
Follicle-stimulating hormone (FSH) and luteinizing hormone
(LH) affect sex hormone secretion and production of gametes
by gonads.
Prolactin (PRL) targets the mammary glands, by stimulating
milk production for a nursing mother.
Growth Hormone (GH) has targets in most tissues. Promotes
growth and metabolism.
Growth Hormone Functions
and Disorders
 Gigantism occurs when there is an overproduction of GH
hormone during childhood. These people have proportional bodies
but are large.
 Acromegaly occurs when there is an overproduction of GH during
adulthood. Since bones cannot grow any larger, they thicken;
usually in hands, feet, and facial features.
 Dwarfism occurs when the body produces too little GH or
receptors are not properly responding to the GH. People are
usually short in stature but proportional.
Feedback Mechanisms
 Most hypothalamic hormones that encourage secretion are
called releasers (POSITIVE FEEDBACK); hormones that
influence reduction of secretion of hormones are called
inhibitors. (NEGATIVE FEEDBACK)
 When inhibitors or releasers are secreted by the secretory
neurons located in the hypothalamus, they enter the stalk
that connects the pituitary to the hypothalamus. (The stalk is
the point in which they meet). There the hormones move into
the capillaries in the stalk and are transferred to the pituitary
gland and diffuse out to the specific target cells. After these
specific hormones influence cells there byproduct enters
capillaries.
Thyroid
 The Thyroid Gland is the endocrine gland located at
the base of the neck; its hormones influence growth,
development, and metabolic rate.
 The thyroid gland produces calcitonin, causes
deposition of calcium in bones of growing children.
How the Thyroid Works
 Negative Feedback Loop
 The anterior pituitary gland and hypothalamus regulate
thyroid hormone secretion. When iodine level in blood
declines the hypothalamus secretes a releasing hormone
(TRH or Thyroid Releasing Hormone) to the anterior pituitary.
The releaser causes the pituitary to secrete thyroidstimulating hormone (TSH). TSH thus goes to the thyroid
gland and induces secretion of the Thyroid Hormone. When
thyroid hormone reaches its normal amount the TSH and
TRH molecules slow down.
Parathyroids
 There are four (4) parathyroid glands; they are situated
on the posterior side of the thyroid gland.
 These glands release parathyroid hormone (PTH) in
response to decline in calcium levels. (NOTE: Calcium
ions have roles in neuron signaling, blood clotting, muscle
contraction, and other physiological processes
Pancreas
 The pancreas is an organ that lies in the abdominal cavity,
behind the stomach. And has both exocrine and endocrine
functions.
 Alpha Cells (located in pancreatic islets)
 These cells secrete glucagon.
 Glucagon targets cells in the liver that causes the activation of
enzymes, which break down glycogen into glucose subunits.
 Beta Cells (located in the pancreatic islets):
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These cells secrete insulin.
Main target cells are the liver, fat, and skeletal muscles cells.
Insulin stimulates the uptake of glucose by fat and muscle cells.
Insulin activates enzymes that function in protein and fat synthesis,
and it inhibits the enzymes that catalyze protein and fat breakdown.
Type 1 Diabetes
 Known as Juvenile-onset diabetes.
 White blood cells recognize the beta cells as non-self or
foreign and destroy them.
 Individuals who have this type of diabetes must take in
injections of insulin so the sugar level in blood can lower.
 Since insulin discourages metabolism of fats, when there is
too little insulin in the blood excessive fat and protein
breakdown occur. Results in weightless and accumulation of
ketones on blood and urine. Ketones come from the breaking
down of fats, and when to many are present, ketoacidosis
occurs. The acidity can interfere with brain function; which
may lead to death or a coma.
Type 2 Diabetes
 Most common type.
 Target cells don’t respond to insulin; while insulin levels are
relatively normal.
 Genetics can be factor.
 Need Insulin injection to lower sugar levels in blood.
Adrenal
Glands
 The Adrenal Glands
 There are two adrenal glands; they are both perched above the
kidneys; size of big grape.
 Its outer layer is the adrenal cortex and its inner portion is the adrenal
medulla. The two parts secrete different hormones, and are controlled
by different mechanisms.
 Hormonal Control of the Adrenal Cortex
 The adrenal Cortex secretes three steroid hormones:
 Aldosterone-controls sodium and water reabsorption.
 Small amounts of male and female sex hormones.
 Cortisol- and adrenal hormone that affects metabolism and immunity.
 Cortisol Control:
 A negative feedback loop governs the cortisol level in blood.
 A decrease in cortisol triggers secretion of CRH (corticotrophin-releasing
hormone) by the hypothalamus. CRH then stimulates secretion of ACTH
(adrenocorticotropic hormone) in the anterior pituitary gland. Then CRH
promotes secretion of cortisol in the adrenal cortex.
The Gonads
 The Gonads
 The gonads are the reproductive organs in male and female
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bodies.
They produce gametes and sex hormones.
Male gonads are called the testes, and they produce
testosterone.
Female gonads are called ovaries, and they produce female
sex hormones known as progesterone and estrogen.
These sex hormones are both produced when the
hypothalamus produces GnRH (Gonadotropin-releasing
hormone).GnRH causes the anterior pituitary to secrete
follicle-stimulating hormone (FSH) and luteinizing hormone
(LH). These end products lead to the secretion of sex
hormones
The Pineal Gland
 The pineal gland secretes melatonin.
 Melatonin is a hormone that serves as a part of an
internal timing mechanism, or biological clock.
 Melatonin secretion declines with bright light, and
increases with bright light due to neurons that lower body
temperature; which make us drowsy.
The Thymus
 The thymus lies beneath the breastbone.
 It secretes thymosins, which are hormones that help
WBCs called T-lymphocytes.
 Grows until puberty, then it shrinks due to sex hormones.
 Aids in immune function.