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Hormones & Endocrine System
M. Faisal Shahid and Humera Waheed, Ph.D.PCMD, ICCBS.University of Karachi
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Long-Distance Regulators
• Bio-chemical signals “Secreated” in circulatory system to modulate regulatory messages in the organ system.
• Activate specifically on equipped target cells i.e. which have receptor.
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• Two systems coordination:
– a) Endocrine (Ductless) system
– b) Nervous system
• Endocrine system secretes hormones that coordinate slower but longer-acting responses – E.g. Reproduction & Development, Energy
metabolism, growth, and behavior
• Nervous system conveys high-speed electrical signals along specialized cells called neurons.
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Classification of Secreted Signaling Molecules
– Hormones: Long Range, Slow acting, Long Lasting (E.g. Insulin)
– Local regulators: Small Range, Swift acting, Long to Medium Lasting. (E.g. TNFα)
– Neurotransmitters: Single Cell Ranged, Highly Focused and Fast Acting (e.g. Acetylcholine)
– Neurohormones: Long Range, Highly Specific (ATCH, FSH)
– Pheromones: Shed in environment, v. long range, for mating processes. (E.g. Chilogttone)
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The Basics
• Endocrine signals travel via the bloodstream
• Endocrine glands are ductless and secrete hormones directly into surrounding fluid
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Signaling Pattern Followed by Hormones
Bloodvessel Response
Response
Response
Response
(a) Endocrine signaling
(b) Paracrine signaling
(c) Autocrine signaling
(d) Synaptic signaling
Neuron
Neurosecretorycell
Figure 1: Signaling Classification
Bloodvessel
Synapse
Response
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Bloodvessel Response
Response
Response
(a) Endocrine signaling
(b) Paracrine signaling
(c) Autocrine signalingFigure 2: Signaling Classification (Generalized)
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Neurotransmitters
• Neurons (nerve cells) contact target cells at synapses (Infinitesimally short distances).
• Neurotransmitters play a role in sensation, memory, cognition, and movement
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Response
(d) Synaptic signaling
Neuron
Neurosecretorycell
Blood vessel
Synapse
ResponseFigure 3: Signaling Classification (Continued)
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• Neurohormones: Hormones that originate from neurons of brain and diffuse through the bloodstream
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Pheromones
• Pheromones are chemical signals that are released from the body and used to communicate with other individuals in the species
• Pheromones mark trails to food sources, warn of predators, and attract potential mates
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Chemical Classes of Hormones• Molecular function of hormones in vertebrates:
– Polypeptides (proteins and peptides)
– Amines derived from amino acids
– Steroid hormones
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• Lipid-soluble: Cross cell membranes ACTS INSIDE CELLS.
• Water-soluble hormones: Act extracellularly
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Figure 4: Hormones according to solubilty
Water-soluble Lipid-soluble
Steroid:Cortisol
Polypeptide:Insulin
Amine:Epinephrine Amine:
Thyroxine
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• The Endocrine Response: 3 Phases
– Reception: Input
– Signal transduction: Processing
– Response: Output
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NUCLEUS
Signalreceptor
(a) (b)
TARGETCELL
Signal receptorTransportprotein
Water-solublehormone
Fat-solublehormone
Figure 5 (a)
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Figure 5 (b)
Signalreceptor
TARGETCELL
Signal receptorTransportprotein
Water-solublehormone
Fat-solublehormone
Generegulation
Cytoplasmicresponse
Generegulation
Cytoplasmicresponse
OR
(a) NUCLEUS (b)
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Signaling
• Binding of a hormone onreceptor initiates a signal transduction.
• It leads to responses in the cytoplasm for either:
– Enzyme activation
– Change in gene expression
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• The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress
• Epinephrine binds to receptors on the plasma membrane of liver cells
• This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream
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Figure 6: Epinephrine Cascade
cAMP Secondmessenger
Adenylylcyclase
G protein-coupledreceptor
ATP
GTP
G protein
Epinephrine
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Figure 6 (b): Epinephrine Cascade
cAMP Secondmessenger
Adenylylcyclase
G protein-coupledreceptor
ATP
GTP
G protein
Epinephrine
Inhibition ofglycogen synthesis
Promotion ofglycogen breakdown
Proteinkinase A
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Lipid-Soluble Hormones
• Usually cause gene expression alteration
• Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus
• Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes
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Figure 7. Steroid Hormones Signaling
Hormone(estradiol)
Hormone-receptorcomplex
Plasmamembrane
Estradiol(estrogen)receptor
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Figure 7 (b): Steroid Hormone Signaling
Hormone(estradiol)
Hormone-receptorcomplex
Plasmamembrane
Estradiol(estrogen)receptor
DNA
VitellogeninmRNA
for vitellogenin
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Multiple Effects of Hormones
• The same hormone may have different effects on target cells that have
– Different receptors for the hormone
– Different signal transduction pathways
– Different proteins for carrying out the response
• A hormone can also have different effects in different species
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Figure 8. Differential Effects of Same Hormone: Epinephrine
Glycogendeposits
receptor
Vesseldilates.
Epinephrine
(a) Liver cell
Epinephrine
receptor
Glycogenbreaks downand glucoseis released.
(b) Skeletal muscle blood vessel
Same receptors but differentintracellular proteins (not shown)
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Glycogendeposits
receptor
Vesseldilates.
Epinephrine
(a) Liver cell
Epinephrine
receptor
Glycogenbreaks downand glucoseis released.
(b) Skeletal muscle blood vessel
Same receptors but differentintracellular proteins (not shown)
Epinephrine
receptor
Different receptors
Epinephrine
receptor
Vesselconstricts.
(c) Intestinal blood vessel
Figure 8 (b). Differential Effects of Same Hormone: Epinephrine
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Localized Signaling: Paracrine
• In paracrine signaling, non-hormonal chemical signals called local regulators elicit responses in nearby target cells
• Types of local regulators:
– Cytokines and growth factors (Interferon etc.)
– Nitric oxide (NO)
– Prostaglandins (The PAIN ALARMS)
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Major endocrine glands:
Adrenalglands
HypothalamusPineal glandPituitary gland
Thyroid glandParathyroid glands
Pancreas
KidneyOvaries
Testes
Organs containingendocrine cells:
ThymusHeart
Liver
Stomach
KidneySmallintestine
Figure 9. Major Hormone Secretion Sites
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Figure 10. The Feed-back Loops
Pathway Example
Stimulus Low pH induodenum
S cells of duodenumsecrete secretin ( )
Endocrinecell
Bloodvessel
PancreasTargetcells
Response Bicarbonate release
Neg
ativ
e fe
edba
ck
–
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• A negative feedback loop inhibits a response by reducing the initial stimulus
• Negative feedback regulates many hormonal pathways involved in homeostasis
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Insulin and Glucagon: Control of Blood Glucose
• Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis
• The pancreas has clusters of endocrine cells called islets of Langerhans with alpha cells that produce glucagon and beta cells that produce insulin
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Figure 11. The Insulin Loop
Homeostasis:Blood glucose level
(about 90 mg/100 mL)
Insulin
Beta cells ofpancreasrelease insulininto the blood.
STIMULUS:Blood glucose level
rises.
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Figure 12. Insulin Loop
Homeostasis:Blood glucose level
(about 90 mg/100 mL)
Insulin
Beta cells ofpancreasrelease insulininto the blood.
STIMULUS:Blood glucose level
rises.
Liver takesup glucoseand stores itas glycogen.
Blood glucoselevel declines.
Body cellstake up moreglucose.
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Figure 13. The Insulin-Glucagon Loop
Homeostasis:Blood glucose level
(about 90 mg/100 mL)
Glucagon
STIMULUS:Blood glucose level
falls.
Alpha cells of pancreasrelease glucagon.
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Figure 14: The Insulin Glucagon Loop
Homeostasis:Blood glucose level
(about 90 mg/100 mL)
Glucagon
STIMULUS:Blood glucose level
falls.
Alpha cells of pancreasrelease glucagon.
Liver breaksdown glycogenand releasesglucose.
Blood glucoselevel rises.
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Target Tissues for Insulin and Glucagon
• Insulin reduces blood glucose levels by
– Promoting the cellular uptake of glucose
– Slowing glycogen breakdown in the liver
– Promoting fat storage
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• Glucagon increases blood glucose levels by
– Stimulating conversion of glycogen to glucose in the liver
– Stimulating breakdown of fat and protein into glucose
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Diabetes Mellitus
• Diabetes mellitus is perhaps the best-known endocrine disorder
• It is caused by a deficiency of insulin or a decreased response to insulin in target tissues
• It is marked by elevated blood glucose levels
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• Type I diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells
• Type II diabetes mellitus (non-insulin-dependent) involves insulin deficiency or reduced response of target cells due to change in insulin receptors
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Coordination of Endocrine and Nervous Systems in Vertebrates
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• The hypothalamus receives information from the nervous system and initiates responses through the endocrine system
• Attached to the hypothalamus is the pituitary gland composed of the posterior pituitary and anterior pituitary
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• The posterior pituitary stores and secretes hormones that are made in the hypothalamus
• The anterior pituitary makes and releases hormones under regulation of the hypothalamus
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Spinal cord
Posteriorpituitary
Cerebellum
Pinealgland
Anteriorpituitary
Hypothalamus
Pituitarygland
Hypothalamus
Thalamus
Cerebrum
Figure 15: The Pituitary Gland
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Figure 16. The Hormonal Index
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Figure 16 (b). The Hormonal Index
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Figure 16 (c) . The Hormonal Index
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Figure 16 (d). The Hormonal Index
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Figure 16(e). The Hormonal Index
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Posterior Pituitary Hormones
• The two hormones released from the posterior pituitary act directly on nonendocrine tissues
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Figure 17. The Posterior Pituitary Hormones
Posteriorpituitary
Anteriorpituitary
Neurosecretorycells of thehypothalamus
Hypothalamus
Axon
HORMONE OxytocinADH
Kidney tubulesTARGET Mammary glands,uterine muscles
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• Oxytocin induces uterine contractions and the release of milk (positive feedback)
• Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys
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Anterior Pituitary Hormones
• Hormone production in the anterior pituitary is controlled by releasing and inhibiting hormones from the hypothalamus
• For example, the production of thyrotropin releasing hormone (TRH) in the hypothalamus stimulates secretion of the thyroid stimulating hormone (TSH) from the anterior pituitary
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Figure 18. Anterior Pituitary Hormones
Hypothalamicreleasing andinhibitinghormones
Neurosecretory cellsof the hypothalamus
HORMONE
TARGET
Posterior pituitary
Portal vessels
Endocrine cells ofthe anterior pituitaryPituitary hormones
Tropic effects only:FSHLHTSHACTH
Nontropic effects only:ProlactinMSH
Nontropic and tropic effects:GH
Testes orovaries
Thyroid
FSH and LH TSH
Adrenalcortex
Mammaryglands
ACTH Prolactin MSH GH
Melanocytes Liver, bones,other tissues
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Hormone Cascade Pathways
• A primary Hormone Targetting another Hormone Secreting Gland is a TROPIC HORMONE.
• Hormone cascade pathways are usually regulated by negative feedback
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Tropic Hormones
• A tropic hormone regulates the function of endocrine cells or glands
• The four strictly tropic hormones are
– Thyroid-stimulating hormone (TSH)
– Follicle-stimulating hormone (FSH)
– Luteinizing hormone (LH)
– Adrenocorticotropic hormone (ACTH)
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Nontropic Hormones
• Nontropic hormones target nonendocrine tissues
• Nontropic hormones produced by the anterior pituitary are
– Prolactin (PRL)
– Melanocyte-stimulating hormone (MSH)
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• Prolactin stimulates lactation in mammals but has diverse effects in different vertebrates
• MSH influences skin pigmentation in some vertebrates and fat metabolism in mammals
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Growth Hormone
• Growth hormone (GH) is secreted by the anterior pituitary gland and has tropic and nontropic actions
• It promotes growth directly and has diverse metabolic effects
• It stimulates production of growth factors
• An excess of GH can cause gigantism, while a lack of GH can cause dwarfism
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Thyroid Hormone: Control of Metabolism and Development
• The thyroid gland consists of two lobes on the ventral surface of the trachea
• It produces two iodine-containing hormones: triiodothyronine (T3) and thyroxine (T4)
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• Thyroid hormones stimulate metabolism and influence development and maturation
• Hyperthyroidism, excessive secretion of thyroid hormones, causes high body temperature, weight loss, irritability, and high blood pressure
• Graves’ disease is a form of hyperthyroidism in humans
• Hypothyroidism, low secretion of thyroid hormones, causes weight gain, lethargy, and intolerance to cold
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Normaliodineuptake
High leveliodineuptake
Figure 19: Iodine 131 Uptake Micrograph
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Parathyroid Hormone and Vitamin D: Control of Blood Calcium
• Two antagonistic hormones regulate the homeostasis of calcium (Ca2+) in the blood of mammals
– Parathyroid hormone (PTH) is released by the parathyroid glands
– Calcitonin is released by the thyroid gland
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Figure 20. Parathyroid Loop
PTH
Parathyroid gland(behind thyroid)
STIMULUS:Falling blood
Ca2+ level
Homeostasis:Blood Ca2+ level
(about 10 mg/100 mL)
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Figure 20 (b). The Parathyroid Loop
PTH
Parathyroid gland(behind thyroid)
STIMULUS:Falling blood
Ca2+ level
Homeostasis:Blood Ca2+ level
(about 10 mg/100 mL)
Blood Ca2+ level rises.
Stimulates Ca2+
uptake in kidneys
Stimulates Ca2+ release from bones
Increases Ca2+ uptake in intestines
Activevitamin D
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• PTH increases the level of blood Ca2+
– It releases Ca2+ from bone and stimulates reabsorption of Ca2+ in the kidneys
– It also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food
• Calcitonin decreases the level of blood Ca2+
– It stimulates Ca2+ deposition in bones and secretion by kidneys
Control of Blood Calcium
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Adrenal Hormones: Response to Stress
• The adrenal glands are adjacent to the kidneys
• Each adrenal gland actually consists of two glands: the adrenal medulla (inner portion) and adrenal cortex (outer portion)
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Catecholamines from the Adrenal Medulla
• The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline)
• These hormones are members of a class of compounds called catecholamines
• They are secreted in response to stress-activated impulses from the nervous system
• They mediate various fight-or-flight responses
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• Epinephrine and norepinephrine– Trigger the release of glucose and fatty acids
into the blood
– Increase oxygen delivery to body cells
– Direct blood toward heart, brain, and skeletal muscles, and away from skin, digestive system, and kidneys
• The release of epinephrine and norepinephrine occurs in response to nerve signals from the hypothalamus
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Figure 21:The Adrenal Hormones LoopStress
Adrenalgland
Nervecell
Nervesignals Releasing
hormone
Hypothalamus
Anterior pituitary
Blood vesselACTH
Adrenal cortex
Spinal cord
Adrenal medulla
Kidney
(a) Short-term stress response (b) Long-term stress response
Effects of epinephrine and norepinephrine:
2. Increased blood pressure3. Increased breathing rate4. Increased metabolic rate
1. Glycogen broken down to glucose; increased blood glucose
5. Change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity
Effects ofmineralocorticoids:
Effects ofglucocorticoids:
1. Retention of sodium ions and water by kidneys
2. Increased blood volume and blood pressure
2. Possible suppression of immune system
1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose
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Figure 21 (b): The Adrenal Hormones Loop
Stress
Adrenalgland
Nervecell
Nervesignals Releasing
hormone
Hypothalamus
Anterior pituitary
Blood vesselACTH
Adrenal cortex
Spinal cord
Adrenal medulla
Kidney
![Page 72: Hormones and Endocrine System](https://reader036.vdocuments.us/reader036/viewer/2022062412/589bade71a28ab1d748b5279/html5/thumbnails/72.jpg)
Figure 21 (c) :The Adrenal Hormones Loop
(a) Short-term stress response
Effects of epinephrine and norepinephrine:
2. Increased blood pressure3. Increased breathing rate4. Increased metabolic rate
1. Glycogen broken down to glucose; increased blood glucose
5. Change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity
Adrenalgland
Adrenal medulla
Kidney
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The Corticoids
• The adrenal cortex releases a family of steroids called corticosteroids in response to stress
• These hormones are triggered by a hormone cascade pathway via the hypothalamus and anterior pituitary
• Humans produce two types of corticosteroids: glucocorticoids and mineralocorticoids
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Figure 22. Adrenal Hormones
(b) Long-term stress response
Effects ofmineralocorticoids:
Effects ofglucocorticoids:
1. Retention of sodium ions and water by kidneys
2. Increased blood volume and blood pressure
2. Possible suppression of immune system
1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose
Adrenalgland
Kidney
Adrenal cortex
![Page 75: Hormones and Endocrine System](https://reader036.vdocuments.us/reader036/viewer/2022062412/589bade71a28ab1d748b5279/html5/thumbnails/75.jpg)
• Glucocorticoids, such as cortisol, influence glucose metabolism and the immune system
• Mineralocorticoids, such as aldosterone, affect salt and water balance
• The adrenal cortex also produces small amounts of steroid hormones that function as sex hormones
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Gonadal Gender Specific Hormones
• The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progestins
• All three sex hormones are found in both males and females, but in different amounts
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• Testes: androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system
• Testosterone causes an increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks
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• Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system and the development of female secondary sex characteristics
• In mammals, progestins, which include progesterone, are primarily involved in preparing and maintaining the uterus
• Synthesis of the sex hormones is controlled by FSH and LH from the anterior pituitary
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Melatonin and Biorhythms
• The pineal gland, located in the brain, secretes melatonin
• Light/dark cycles control release of melatonin
• Primary functions of melatonin appear to relate to biological rhythms associated with reproduction
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Figure 23. Hormonal Process of Milk Production
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Now, One can:
1. Distinguish between the following pairs of terms: hormones and local regulators, paracrine and autocrine signals
2. Describe the evidence that steroid hormones have intracellular receptors, while water-soluble hormones have cell-surface receptors
3. Explain how the antagonistic hormones insulin and glucagon regulate carbohydrate metabolism
4. Distinguish between type 1 and type 2 diabetes
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5. Explain how the hypothalamus and the pituitary glands interact and how they coordinate the endocrine system
6. Explain the role of tropic hormones in coordinating endocrine signaling throughout the body
7. List and describe the functions of hormones released by the following: anterior and posterior pituitary lobes, thyroid glands, parathyroid glands, adrenal medulla, adrenal cortex, gonads, pineal gland
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Thank You
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Questions?