Endocrine System

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Endocrine System• What is the endocrine system?The endocrine system is comprised of the hormone

producing glands and tissues of the body.

Functioning of the Endocrine SystemThe endocrine system functions along with the

nervous system to help the nervous system to help maintain homeostasis.

Endocrine system functions slower than the nervous system but gives a more sustained effect

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Mechanisms of Hormone Action

• Certain secretory cells release chemical agents (hormones) for the purpose of mediating biologic responses in distant Target Cells.

• Hormones sources– Single amino acid (catecholamines)–Chains amino acids (peptide hormones of

hypothalamus)–Cholesterol (steroids)

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Mechanisms of Hormone Action• Hormones control and integrate many body functions with this

system. • The endocrine system carries out its functions based upon messages

received from the Hypothalamus• The hypothalamus monitors the blood and sends hormones from

glands into the blood when needed• Organs await the arrival of hormones

• In general, hormonal control regulates the metabolic functions of the body, the types of effects that occur inside the cell and determined the character of the cell itself.

• The endocrine system works with the nervous system to regulate: metabolism, water and salt balance, blood pressure, response to stress, and sexual reproduction. 4

Endocrine System

• Endocrine System Hormones/Glands whose functions are solely endocrine include:

• pituitary (hypophysis) • pineal • thyroid • parathyroids • adrenals• pancreas

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Types of Glands

• Endocrine: ductless glands that secrete hormones directly into blood stream

• Exocrine: glands that have ducts and secrete substances such as sweat salvia tears milk or digestive enzymes

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Endocrine Glands• Pituitary Gland• Hypothalamus• Adrenal Cortex• Adrenal medulla• Thyriod• Parathyroid• Pancreas• Thymus• Kidney• Pineal• Ovaries• Testes

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Hormones• These are chemicals that circulate throughout

the blood and exert some measure of control over most every organ and tissue in the body.

Types of HormonesHormones are either Steroidal or Non-steroidal1.Steroid Hormones- hormones manufactured

from fatty substances called cholesterol.2.These substances are fat soluble. Ex. Cortisol

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Steroid Hormones• Steroid hormones are produced

by chemical modification of cholesterol

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•Major classes steroid hormones•glucocorticoids (cortisol)•mineralocorticoids (aldosterone)•androgens (testosterone)•estrogens (estradiol)•Vitamin D metabolites

How steroid Hormones work• These hormones enter a cell and binds to a

protein receptor in the cell. This creates a hormone receptor complex.

• The hormone receptor complex enters the nucleus where it activates a specific gene in the DNA

• Activated gene produces an enzyme(protein) that initiates a chemical reaction within the cell.

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Non Steroid Hormones

• Hormones composed of proteins, peptides or amino acids

• These hormones are not fat soluble. They are unable to enter cells because the are not soluble in the membrane.

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How a Non-Steriod Hormone Works

• A hormone called a first messenger binds to receptors on surfaces of target cells. The binding causes ATP to be changed into cyclic AMP(cAMP).

• Cyclic AMP(second messenger) causes chemical reactions to occur within the cell.

• Ex. Adrenaline, ACTH, LH, FSH, ADH• http://www.youtube.com/watch?

v=SVHXnLgV1fc&safety_mode=true&persist_safety_mode=1&safe=active

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Summary of Steroidal. VS Non Steroidal Hormones

Hormone Solubility in cell membrane

Location of Receptors End Result

Steroidal Within the cell Gene produces a protien

Non-steriodal Surface of cell cAMP causes chain reaction

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Types of Hormones• Antagonistic HormonesThese are hormones that work against each other

or they have opposite effects on the body.Ex. Insulin and GlucagonParathyroid hormone and Calcitonin

Tropic HormonesThese hormones regulate the hormone production

of many other glands.Ex. Thyroid stimulating hormone, HGH 14

Endocrine Hormone Disorders

• Problems with most endocrine glands are either caused by Hyposecretion or Hypersecretion of a hormone.

• Hyposecretion; under secretion of a hormone within the body

• Hypersecretion; A over secretion of a hormone within a body.

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Feedback Mechanisms and Operation of Hormones

• Hormones regulate endocrine function on the basis of feedback mechanisms. There are two types of feedback mechanisms

• 1. Negative feedback loop:• A loop that works to reverse or decrease changes in the

body. When concentration of a hormone rises to above desired levels, a series of steps is taken within the system to cause the concentration to fall. Conversely, steps are taken to increase concentration when the level is too low.

• Ex. Hypothalamus-Pituitary-thyroid feedback mechanism operation

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Positive feedback Mechanism or loopA loop that serves to increase the effect of an

action.Ex. Oxytocin feedback loop• Diagrams pg 424 figure 13.3• Pg. 432 figure 13.13

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Feedback Loops• The release of a hormone is often triggered by a

change in the concentration of some substance in the body fluids.

• Each hormone has a corrective effect, eliminating the stimulus, which then leads to a reduction in hormone secretion.

• This process is called a negative feedback homeostatic control system to keep hormones at normal levels. (if levels increased it would be called positive feedback)

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Hypothalamus and Pituitary• Pituitary has direct

neural and blood connection to the hypothalamus

• Hypothalamus sends releasing factors to anterior pituitary

• Hypothalamus stimulates posterior pituitary via neural pathway

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Hypothalamus• Hypothalamus can synthesize and release hormones

from its axon terminals into the blood circulation. • controls pituitary function and thus has an important,

indirect influence on the other glands of the endocrine system.

• exerts direct control over both the anterior and posterior portions of the pituitary gland.

• regulates pituitary activity through two pathways: a neural pathway and a portal venous pathway.

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Hypothalamus• Neural pathways extend

from the hypothalamus to the posterior pituitary lobe, where the hormones are stored and secreted.

• Portal venous pathways connect the hypothalamus to the anterior pituitary lobe, carry releasing and inhibiting hormones

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Pituitary Gland• Pituitary Gland is located at the base of the skull in an

indentation of the sphenoid bone, and is called the Master Gland.

• Is joined to the hypothalamus by the pituitary stalk and consists of the anterior pituitary and the posterior pituitary.

• Nervous system sends messages to the hypothalamus to exert control over the pituitary

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Anterior pituitary gland• anterior lobe has direct control over the secretion of: • HGH- Somatotropin or human growth hormone• ACTH - adrenocorticotrophic hormone • TTH - thyrotrophic hormone • FSH - follicle stimulating hormone • LH - leutinizing hormone• PRL- prolactin

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Posterior pituitary• Stores and secretes hormones made in the

hypothalamus and contains many nerve fibers. • ADH (Antidiuretic Hormone/Vasopressin), which

controls the rate of water excretion into the urine• Regulates Na+ & K+ reabsorption in the kidneys this

influences blood volume & blood pressure • Oxytocin, which, among other functions, helps

deliver milk from the glands of the breast.

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Adrenal Glands• Located on top of

the kidneys• Adrenal Glands

have an outer cortex and an inner medulla.

• The adrenal cortex and medulla are major factors in the body's response to stress, and are controlled by the hypothalamus

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Adrenal Glands• ACTH - Adrenocorticotrophic Hormone causes adrenal

cortex to release 3 types of hormones: Cortisol (Glucocorticoids), Aldosterone (Mineral corticoids), and sex hormones

• The outer cortex is responsible for the secretion of mineralocorticoids (steroid hormones that regulate fluid and mineral balance) ALDOSTERONE

• glucocorticoids (steroid hormones responsible for controlling the metabolism of glucose) Cortisol

• androgens (sex hormones).

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Adrenal Glands

• Centrally located adrenal medulla is derived from neural tissue and secretes Epinephrine and Norepinephrine

• Epinephrine circulates and acts upon the sympathetic nervous system

• Norepinephrine released from sympathetic nerve endings and from adrenal medulla in small amounts

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Adrenal Mineral Corticoids• ADH - antidiuretic hormone • Regulates Na+ & K+ reabsorption in the kidneys • regulates water retention

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Adrenal Steroids• Testosterone - masculinizing affects, increase lean

body mass • Estrogens - estrodial, estrone, estriol - stimulate

breast development and female pattern fat deposition

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Thyroid Gland

• Located in the throat• Butterfly shaped

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Thyroid Gland

• Thyroid function is regulated by the hypothalamus and pituitary, feedback controls an intrinsic regulator mechanism

• Hormones produced are: • thyroxine (T4) & triiodothyronine (T3), regulate the

metabolic rate of the body and oxygen consumption and increase protein synthesis

• It is released from the thyroid gland when stimulated by TSH from the pituitary. TSH---- Thyroid gland---- release Thyroxin

• TSH and Thyroxin work on a negative feedback loop.32

• calcitonin, has a weak physiologic effect on calcium and phosphorus balance in the body.

• It moves calcium from the blood and into the bones. This lowers the amount of calcium in the blood

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Thyroid Problems• Thyroid gland enlargement may or may not be

associated with abnormal hormone secretion. • An enlarged thyroid gland can be the result of: • iodine deficiency (Goiter)• inflammation, or • benign or malignant tumors

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Hyperthyroidism

• Hyperthyroidism or Grave’s Disease• This disease causes excess production of thyroid

hormones• Weight loss and exopthalmic goiter

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Hypothyroidism

• Caused by a deficiency of thyroxin• Refereed to as Myxedema• Reduced metabolism• Weight gain• Decreased mental capacity

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Thyroid imbalance can cause cretinism, metabolic disorders, and goiter( due to lack

of iodine)

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Parathyroid Glands• There are 4 parathyroid glands

located on the surface of the thyroid. • Parathyroid Glands produce PTH

( parathyroid hormone)• PTH causes bones to release calcium

into the bloodstream• Causes kidneys to reabsorb calcium

from the blood thus increasing amount of calcium in the body

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Pancreas• Located near the small intestine.• Contains specialized endocrine cells called islets

of langerhans• Islets of langerhans is made up of both alpha

and Beta cells. • Secretes insulin, glucagon (regulate blood sugar)

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Diabetes Mellitus• Syndrome when insulin levels are inadequate to keep

blood sugar within normal range. Due to:• Inadequate amount of insulin (Insulin-Dependent

Diabetes Mellitus). Results from severe insulin deficiency secondary to loss of beta cells. Autoimmune process selectively destroys beta cells.

• Inadequate response to normal or high insulin levels (Non-Insulin-Dependent Diabetes Mellitus). More common that IDDM, 90% NIDDM, associated with obesity.

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Type I (insulin-dependent) diabetes

– Autoimmune disease in which pancreatic beta cells are destroyed and thus not enough insulin is produced

– Often develops before age 15

– Patient requires insulin supplement, often by injection

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Type II (non-insulin-dependent) diabetes

– Pancreatic cells function properly and there are sufficient amounts of insulin produced

– Body cells fail to respond to insulin

– Accounts for 90% of diabetes cases in the United States

– Associated with obesity

– Often develops after age 40

– Manageable

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Function of Insulin

• Created by the Beta cells of the islets of langerhans• Causes the conversion of glucose into glycogen that

is stored in the liver• Causes excess glucose to be changed into fat• Helps regulate blood sugar levels. Insulin and

glycogen

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Pancreas( Islets of Langerhans)

• Function of Glucagon(created by the alpha cells of the islets of Langerhans)

• Causes the conversion of Glycogen (Liver) into Glucose that is released into the blood as needed.

• Operation of insulin and Glucagon in sugar(glucose) regulation.

• Insulin and glucagen are antagonistic hormones. They work opposite each other to maintain proper blood sugar levels in a negative feedback loop.

• They work by either increasing or decreasing the amount of glucose (sugar) in the blood. 45

Blood Sugar Control• Insulin and glucagon are produced by small groups of

cells in the pancreas (islets of Langerhans). • Beta cell make insulin (beta cells) and Alpha cells that

make glucagon • Insulin is released when the blood sugar rises too

high. Insulin tells the cells to use sugar. • Glucagon is produced when the blood sugar is falling

too low. Glucagon tells the liver to release sugar that was stored there when the blood sugar was higher.

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Insulin• Insulin promotes glucose entry into cells• Insulin effects enzymes that rule rate of

metabolism of CARBOHYDRATE, FAT, PROTEIN, & ION TRANSPORT

• Carbohydrate metabolism– stimulates glucose utilization, storage & also INHIBITS

glucose formation– Insulin acts on LIVER depending upon plasma glucose

level

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Glucagon• Secreted in response to: decreased blood glucose

levels, increased amino acid levels, or stimulation by growth hormone

• primary function is to increase the circulating blood glucose level: converts stored glucose (primarily in the liver) to circulating glucose.

• promotes glucose formation (from fat and protein when the need for glucose is greater than the amount that can be mobilized from the liver)

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Chronic Diabetic Complications• Retinopathy = due to dilations of retinal vessels from

microaneurysms.• atherosclerotic process that occludes coronary and

other arteries. Leading cause of death in diabetic subjects is coronary heart disease.

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The gonads secrete sex hormones

• The gonads secrete sex hormones– Secretion is controlled by the hypothalamus and the

pituitary

• The steroid hormones are found in both sexes but in different proportions– estrogens– progestins– androgens

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Gonads

• Ovaries- found in females• Produces estrogen and progesterone• Estrogen controls secondary sex characteristics in

females• Prepares the uterus for pregnancy• Progesterone maintains the uterus during

pregnancy• Estrogen and progestins

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• Testes• Found in males• Produces testosterone• Controls secondary sex characteristics in males

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Pineal Gland

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Pineal Gland • Its principal hormone is melatonin.• Synthesis and release of melatonin is stimulated

by darkness and inhibited by light.• Levels of melatonin in the blood rises and falls on

a daily (circadian) cycle with peak levels occurring in the wee hours of the morning.

• Ingesting even modest doses of melatonin raises the melatonin level in the blood. These levels appear: to promote going to sleep and thus help insomnia. Considered to be the biological clock

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Thymus Gland

• Located between the lobes of the lungs in the upper chest. Disappears after puberty

• Produces Thymosin• Function of Thymosin:Causes the production and

maturation of lymphocytes into T-cells

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Growth Hormone Problems

• Gigantism• Dwarfism

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GH - Growth Hormone

• Release of somatomedins from the liver • Uptake of amino acids by tissues • Synthesis of new proteins • Long bone growth • Blunts insulin’s affect on glucose uptake • Induces gluconeogenesis

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Gigantism

• Acromegaly/Gigantism is a very rare disease and syndrome results from a chronic exposure to GH (Growth Hormone) leading to the classic clinical features that the diagnosis seems to be easy

• High exposure to GH produces gigantism in youths prior to epiphyseal fusion and acromegaly in adults.

• In adults, the syndrome is characterized by local overgrowth of bone (skull, mandible). 59

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Dwarfism

• Dwarfism results from growth hormone deficiency. A pituitary dwarf has too little growth hormone. The achondroplastic dwarf has an orthopedic reason for having short limbs and a short spinal column.

• Cause of this is unknown, a tumor or cyst in the pituitary area may cause dwarfism.

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