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Endocrine System

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Greg Horesovsky

on 13 September 2013

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Transcript of Endocrine System

The Endocrine System The Glands







Figure 10-1 The Endocrine System Target Cells
Are specific cells that possess receptors needed to bind and “read” hormonal messages
Hormones
Stimulate synthesis of enzymes or structural proteins
Increase or decrease rate of synthesis
Turn existing enzyme or membrane channel “on” or “off” The Endocrine System The Endocrine System
Regulates long-term processes:
Growth
Development
Reproduction
Uses chemical messengers to relay information and instructions between cells
Endocrine Communication
Endocrine cells release chemicals (hormones) into the bloodstream
Alters metabolic activities of many tissues and organs simultaneously The Endocrine System Pituitary
Thyroid
Parathyroid
Thymus
Adrenal
Gonads
Pancreas
Pineal Eight Main Endocrine Glands







Figure 10-1 The Endocrine System How
Hormones
Work Steroid hormones are synthesized from cholesterol and fatty acids (eicosanoids)
Therefore can cross cell membrane
Bind to Intracellular Receptors
Alter rate of DNA transcription in nucleus:
Change patterns of protein synthesis
Directly affect metabolic activity and structure of target cell
Includes steroids and thyroid hormones Mechanisms of Hormone Action Hormones and Plasma Membrane Receptors
G Protein:
Enzyme complex coupled to membrane receptor
Involved in link between first messenger and second messenger
Activated when hormone binds to receptor at membrane surface and changes concentration of second messenger cyclic-AMP (cAMP) within cell:
increased cAMP level accelerates metabolic activity within cell Mechanisms of Hormone Action Hormones and Plasma Membrane Receptors:
Catecholamines and peptide hormones:
Are not lipid soluble so they can’t cross the cell membrane
Cannot have direct effect on activities inside target cell
Bind to receptors in plasma membrane
Use intracellular intermediary to exert effects:
First messenger:
leads to second messenger
may act as enzyme activator, inhibitor, or cofactor
results in change in rates of metabolic reactions Mechanisms of Hormone Action Hormones can be divided into three groups
Amino acid derivatives
Peptide hormones
These two classes of hormones can not cross the cell membrane because they are not fat soluble
Lipid derivatives
Can freely cross the cell membrane because they are fat soluble
Hormones circulate freely or are bound to transport proteins The Structure of Hormones Endocrine reflexes can be triggered by
Humoral stimuli:
Changes in composition of extracellular fluid
Hormonal stimuli:
Arrival or removal of specific hormone
Neural stimuli:
Arrival of neurotransmitters at neuroglandular junctions The Control of Endocrine Activity Steroids and Thyroid Hormones Nonsteroidal Hormones Target Cells and Hormones Hormone Receptor
Is a protein molecule to which a particular molecule binds strongly
Different tissues have different combinations of receptors
Presence or absence of specific receptor determines hormonal sensitivity Mechanisms of Hormone Action Hormones Heart
Produces natriuretic peptides (ANP and BNP):
When blood volume becomes excessive
Action opposes angiotensin II (produced by the liver, causes vasoconstriction and raises blood pressure)
Resulting in reduction in blood volume and blood pressure
Thymus
Atrophies in adulthood
Produces thymosins (blend of thymic hormones):
That help develop and maintain normal immune defenses Endocrine Tissues of Other Systems Blood Glucose Levels
When levels rise:
Beta cells secrete insulin, stimulating transport of glucose across plasma membranes
When levels decline:
Alpha cells release glucagon, stimulating glucose release by liver Pancreas Lies in posterior portion of roof of third ventricle (in the brain)
Synthesize hormone melatonin
Inhibiting reproductive functions
Protecting against damage by free radicals
Setting circadian rhythms
Melatonin is important in maintaining wake/sleep patterns Pineal Gland Mineralocorticoids
For example, aldosterone:
Stimulates conservation of sodium ions and elimination of potassium ions (therefore increasing water retention and blood pressure!)
Increases sensitivity of salt receptors in taste buds
Antagonized by Atrial Natriuretic peptide (ANP) produced by the heart
Glucocorticoids
For example, cortisol (hydrocortisone) with corticosterone:
Stimulates glucose production in the liver and glycogen formation
Androgens
Similar to those produced by the testes in males
Primary source of androgens in women Adrenal\Suprarenal Cortex Lies anterior to thyroid cartilage of larynx
Consists of two lobes
Thyroglobulin (Globular Protein)
Used entirely within the thyroid gland to produce T4 and T3
Thyroxine (T4)
Contains four iodide ions
Triiodothyronine (T3)
Contains three iodide ions
More potent than T4 The Thyroid Gland Two Classes of Hypothalamic Regulatory Hormones
Releasing hormones (RH):
Stimulate synthesis and secretion of one or more hormones at anterior lobe
Inhibiting hormones (IH):
Prevent synthesis and secretion of hormones from the anterior lobe
Rate of secretion is controlled by negative feedback Pituitary Gland Adipose Tissue Secretions
Leptin:
Acts on the hypothalamus to reduce appetite
Mutations that “inactivate” leptin cause severe obesity
Controls normal levels of GnRH, gonadotropin synthesis
Resistin:
Reduces insulin sensitivity
Obesity can cause type II diabetus mellitus Endocrine Tissues of Other Systems Ovaries (Gonads)
Produce estrogens:
Principle estrogen is estradiol
After ovulation, follicle cells:
Reorganize into corpus luteum
Release estrogens and progestins, especially progesterone Endocrine Tissues of Other Systems Testes (Gonads)
Produce androgens in interstitial cells:
Testosterone is the most important male hormone
Secrete inhibin in nurse (sustentacular) cells:
Support differentiation and physical maturation of sperm Endocrine Tissues of Other Systems Intestines
Produce hormones important to coordination of digestive activities
Kidneys
Produce the hormones calcitriol and erythropoietin
Produce the enzyme renin

Renin activates the renin-angiotensin system by cleaving angiotensinogen, produced by the liver, to yield angiotensin I, which is further converted into angiotensin II by ACE, the angiotensin-converting enzyme primarily within the capillaries of the lungs. Angiotensin II then constricts blood vessels, increases the secretion of ADH and aldosterone, and stimulates the hypothalamus to activate the thirst reflex, each leading to an increase in blood pressure.

Endocrine Tissues of Other Systems Lies between
Inferior border of stomach
And proximal portion of small intestine
Contains exocrine and endocrine cells
Endocrine Pancreas
Consists of cells that form clusters known as pancreatic islets, or islets of Langerhans:
Alpha cells produce glucagon
Beta cells produce insulin Pancreas Suprarenal Medulla
Contains two types of secretory cells:
One produces epinephrine (adrenaline):
75% to 80% of medullary secretions
The other produces norepinephrine (noradrenaline):
20% to 25% of medullary secretions

Important in “fight or flight” response Adrenal\Suprarenal Medulla Lie along superior border of each kidney
Subdivided into
Superficial suprarenal cortex:
Stores lipids, especially cholesterol and fatty acids
Manufactures steroid hormones: adrenocortical steroids (corticosteroids)
Inner suprarenal medulla:
Secretory activities controlled by sympathetic division of ANS
Produces epinephrine (adrenaline) and norepinephrine
Metabolic changes persist for several minutes Suprarenal (Adrenal) Glands Four Effects of PTH
It stimulates osteoclasts:
Accelerates mineral turnover and releases Ca2+ from bone
It inhibits osteoblasts:
Reduces rate of calcium deposition in bone
It enhances reabsorption of Ca2+ at kidneys, reducing urinary loss
It stimulates formation and secretion of calcitriol at kidneys:
Effects complement or enhance PTH
Enhances Ca2+, PO43- absorption by digestive tract Parathyroid Glands Figure 18–12 Embedded in posterior surface of thyroid gland
Parathyroid hormone (PTH)
Produced by parathyroid chief cells
Secreted in response to low blood concentrations of Ca2+ Parathyroid Glands C (Clear) Cells of the Thyroid Gland
Produce calcitonin (CT):
Helps regulate concentrations of Ca2+ in body fluids The Thyroid Gland Thyroid Hormones T4 and T3:
Enter target cells by transport system
Affect most cells in body
Bind to receptors in:
Cytoplasm
Surfaces of mitochondria
Nucleus
In children, essential to normal development of:
Skeletal, muscular, and nervous systems
Calorigenic Effect
Cell consumes more energy resulting in increased heat generation
Is responsible for strong, immediate, and short-lived increase in rate of cellular metabolism The Thyroid Gland Hypothalamic Control over Endocrine Function Hangs inferior to hypothalamus
Connected by infundibulum The Pituitary Gland Hormones and Stress Growth Hormone (GH)
In children:
Supports muscular and skeletal development
In adults:
Maintains normal blood glucose concentrations
Mobilizes lipid reserves Hormones and Growth Antagonistic (opposing) effects
Synergistic (additive) effects
Permissive effects: one hormone is necessary for another to produce effect
Integrative effects: hormones produce different and complementary results Hormone Interactions Hormones and Stress General Adaptation Syndrome (GAS)
Also called stress response
How body responds to stress-causing factors
Is divided into three phases:
Alarm phase
Resistance phase
Exhaustion phase Hormones and Stress Hormones and Stress Hormones and Stress
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