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Chapter 16 Endocrine System
Study Guide for Dr. Johnson A&P II TCC South Campus
96
Anatomy
Undergraduate 1
02/05/2013

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Term
What are the two main classes of hormones?
Definition

1. Amino acid based hormones.

    *Amines, Thyroxine, Peptides, and Proteins.

2. Steroids

    *Snythesized from cholesterol.

    *Gonadal and Adrenocortical hormones.

Term
What effects can hormone have on target cells?
Definition

They can:

1. Alter plasma membrane permeability of membrane potential by opening or closing ion channels

2. Stimulate synthesis of proteins or regulatory molecules

3. Activate or deactivate enzyme systems

4. Induce secretory activity

5. Stimulate mitosis

Term
Describe the Mechanism of Hormone action for a Water-soluble hormones (all amino acid–based hormones except thyroid hormone)
Definition

• Cannot enter the target cells

• Act on plasma membrane receptors

• Coupled by G proteins to intracellular second messengers that mediate the target cell’s response

Term
Describe the mechanism of hormone action for Lipid-soluble hormones (steroid and thyroid hormones)
Definition
• Act on intracellular receptors that directly activate genes
Term
Describe Plasma Membrane Receptors and Second-Messenger Systems
Definition

1. Hormone (first messenger) binds to receptor

2. Receptor activates G protein

3. G protein activates adenylate cyclase

4. Adenylate cyclase converts ATP to cAMP (second messenger)

5. cAMP activates protein kinases 

6. Activated kinases phosphorylate various proteins, activating some and inactivating others 

7. cAMP is rapidly degraded by the enzyme phosphodiesterase 8.Intracellular enzymatic cascades have a huge amplification effect

Term
Describe Intracellular Receptors and Direct Gene Activation of Steroid and Thyroid Hormones.
Definition

Steroid hormones and thyroid hormone

1. Diffuse into their target cells and bind with intracellular receptors

2. Receptor-hormone complex enters the nucleus

3. Receptor-hormone complex binds to a specific region of DNA

4. This prompts DNA transcription to produce mRNA

5. The mRNA directs protein synthesis

Term
What is Target Cell Specificity?
Definition

• Target cells must have specific receptors to which the hormone binds

• ACTH receptors are only found on certain cells of the adrenal cortex

• Thyroxin receptors are found on nearly all cells of the body

Term
Target cell activation depends on what three factors?
Definition

1. Blood levels of the hormone

2. Relative number of receptors on or in the target cell

3. Affinity of binding between receptor and hormone

Term
Can hormones influence the number of their receptors?
Definition

Yes.

• Up-regulation—target cells form more receptors in response to the hormone

• Down-regulation—target cells lose receptors in response to the hormone

Term
Do hormones circulate in the blood, freely or are they bound to other cells?
Definition

Both.

• Steroids and thyroid hormone are attached to plasma proteins

• All others circulate without carriers

Term
Hormones are removed from the blood by:
Definition

• Degrading enzymes

• Kidneys

• Liver

• Half-life—the time required for a hormone’s blood level to decrease by half

Term
The concentration of a circulating hormone reflects what?
Definition

• Rate of release

• Speed of inactivation and removal from the body

Term
What are the 3 ways multiple hormones may interact with each other aa a target cell?
Definition

1. Permissiveness: one hormone cannot exert its effects without another hormone being present

2. Synergism: more than one hormone produces the same effects on a target cell

3. Antagonism: one or more hormones opposes the action of another hormone

Term
Levels of hormones in the blood are controlled how?
Definition

• By negative feedback systems

• Vary only within a narrow desirable range

Term
Hormones are synthesized and released in response to what 3 stimuli?
Definition

1. Humoral stimuli

2. Neural stimuli

3. Hormonal stimuli

Term
What is Humoral Stimuli?
Definition

1. Changing blood levels of ions and nutrients directly stimulates secretion of hormones

• Example: Ca2+ in the blood

 Declining blood Ca2+ concentration stimulates the parathyroid glands to secrete PTH (parathyroid hormone).  PTH causes Ca2+ concentrations to rise and the stimulus is removed

Term
What is Neural Stimuli?
Definition

• Nerve fibers stimulate hormone release

• Sympathetic nervous system fibers stimulate the adrenal medulla to secrete catecholamines

Term
What is Hormonal Stimuli?
Definition

• Hormones stimulate other endocrine organs to release their hormones

• Hypothalamic hormones stimulate the release of most anterior pituitary hormones • Anterior pituitary hormones stimulate targets to secrete still more hormones

• Hypothalamic-pituitary-target endocrine organ feedback loop: hormones from the final target organs inhibit the release of the anterior pituitary hormones

Term
What is Nervous System Modulation?
Definition

 The nervous system modifies the stimulation of endocrine glands and their negative feedback mechanisms

• Example: under severe stress, the hypothalamus and the sympathetic nervous system are activated.  As a result, body glucose levels rise

Term
What are the two lobes of the Pituitary Gland?
Definition

1. Posterior pituitary (lobe):

• Pituicytes (glial-like supporting cells) and nerve fibers

2. Anterior pituitary (lobe) (adenohypophysis)

• Glandular tissue

Term
Describe the physiology and function of the posterior lobe of the pituitary gland.
Definition

• A downgrowth of hypothalamic neural tissue

• Neural connection to the hypothalamus (hypothalamic-hypophyseal tract)

• Nuclei of the hypothalamus synthesize the neurohormones oxytocin and antidiuretic hormone (ADH)

• Neurohormones are transported to the posterior pituitary

Term
Describe the physiology and function of the anterior lobe of the pituitary gland.
Definition

• Originates as an out-pocketing of the oral mucosa

• Hypophyseal portal system

• Primary capillary plexus

• Hypophyseal portal veins

• Secondary capillary plexus

• Carries releasing and inhibiting hormones to the anterior pituitary to regulate hormone secretion

Term
Name the 6 Anterior Pituitary Hormones.
Definition

• Growth hormone (GH)

• Thyroid-stimulating hormone (TSH) or thyrotropin

• Adrenocorticotropic hormone (ACTH)

• Follicle-stimulating hormone (FSH)

• Luteinizing hormone (LH)

• Prolactin (PRL)

Term
Describe the function of the anterior pituitary hormones.
Definition

• All are proteins

• All except GH activate cyclic AMP second-messenger systems at their targets

• TSH, ACTH, FSH, and LH are all tropic hormones (regulate the secretory action of other endocrine glands)

Term
What are Growth Hormone (GH)
Definition

• Produced by somatotrophs

• Stimulates most cells, but targets bone and skeletal muscle

• Promotes protein synthesis and encourages use of fats for fuel

• Most effects are mediated indirectly by insulin-like growth factors (IGFs)

 

Term
What are the actions of Growth Hormone?
Definition

• Stimulates liver, skeletal muscle, bone, and cartilage to produce insulin-like growth factors

• Mobilizes fats, elevates blood glucose by decreasing glucose uptake and encouraging glycogen breakdown (anti-insulin effect of GH)

Term
How are Growth Hormones Regulated?
Definition

GH release is regulated by:

1.Growth hormone–releasing hormone (GHRH)

2.Growth hormone–inhibiting hormone (GHIH) (somatostatin)

Term
What are the Homeostatic Imbalances of Growth Hormone?
Definition

Hypersecretion

1.In children results in Gigantism 

2.In adults results in Acromegaly

Hyposecretion

1.In children results in Pituitary Dwarfism

Term
What are Thyroid-Stimulating Hormones (Thyrotropin)
Definition

• Produced by thyrotrophs of the anterior pituitary

• Stimulates the normal development and secretory activity of the thyroid

• Regulation of TSH release

• Stimulated by thyrotropin-releasing hormone (TRH)

• Inhibited by rising blood levels of thyroid hormones that act on the pituitary and hypothalamus

Term
What are Adrenocorticotropic Hormones (Corticotropin)
Definition

A. Secreted by corticotrophs of the anterior pituitary

  • Stimulates the adrenal cortex to release corticosteroids

B. Regulation of ACTH release

  1. Triggered by hypothalamic corticotropin-releasing hormone (CRH) in a daily rhythm

  2. Internal and external factors such as fever, hypoglycemia, and stressors can alter the release of CRH

Term
What are Gonadotropins?
Definition

• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

• Secreted by gonadotrophs of the anterior pituitary

• FSH stimulates gamete (egg or sperm) production

• LH promotes production of gonadal hormones

• Absent from the blood in prepubertal boys and girls

*** Regulation of gonadotropin release***

1.Triggered by the gonadotropin-releasing hormone (GnRH) during and after puberty

2.Suppressed by gonadal hormones (negative feedback)

Term
What is Prolactin (PRL)?
Definition

• Secreted by lactotrophs of the anterior pituitary

• Stimulates milk production

• Regulation of PRL release

• Primarily controlled by prolactin-inhibiting hormone (PIH) (dopamine)

• Blood levels rise toward the end of pregnancy

• Suckling stimulates PRH release and promotes continued milk production

Term
What is the structure and function of The Posterior Pituitary
Definition

• Contains axons of hypothalamic neurons

• Stores antidiuretic hormone (ADH) and oxytocin

• ADH and oxytocin are released in response to nerve impulses

• Both use PIP-calcium second-messenger mechanism at their targets

Term
Describe the function of Oxytocin
Definition

• Stimulates uterine contractions during childbirth by mobilizing Ca2+ through a PIP2-Ca2+ second-messenger system

• Also triggers milk ejection (“letdown” reflex) in women producing milk

• Plays a role in sexual arousal and orgasm in males and females

Term
Describe the function of Antidiuretic Hormone (ADH)
Definition

A. Hypothalamic osmoreceptors respond to changes in the solute concentration of the blood

B. If solute concentration is high 

   1. Osmoreceptors depolarize and transmit impulses to hypothalamic neurons

   2.ADH is synthesized and released, inhibiting urine formation

C. If solute concentration is low

   1.ADH is not released, allowing water loss

D. Alcohol inhibits ADH release and causes copious urine output

Term
What are the Homeostatic Imbalances of ADH
Definition

1. ADH deficiency—diabetes insipidus; huge output of urine and intense thirst

2.ADH hypersecretion (after neurosurgery, trauma, or secreted by cancer cells)—syndrome of inappropriate ADH secretion (SIADH)

Term
Describe the structure and function of the Thyroid Gland.
Definition

• Consists of two lateral lobes connected by a median mass called the isthmus

• Composed of follicles that produce the glycoprotein thyroglobulin

 • Colloid (thyroglobulin + iodine) fills the lumen of the follicles and is the precursor of thyroid hormone

• Parafollicular cells produce the hormone calcitonin

Term
What is the structure of Thyroid Hormone (TH)?
Definition

Actually two related compounds:

 • T4 (thyroxine) has 2 tyrosine molecules + 4 bound iodine atoms

T3 (triiodothyronine) has 2 tyrosines + 3 bound iodine atoms

Term
What is the function of Thyroid Hormone (TH)?
Definition

Is a Major metabolic hormone

• Increases metabolic rate and heat production (calorigenic effect)

Plays a role in:

  1. Maintenance of blood pressure

  2.Regulation of tissue growth

  3.Development of skeletal and nervous systems

  4.Reproductive capabilities

Term
How is Thyroid Hormone (TH) synthesized?
Definition

Thyroglobulin is synthesized and discharged into the follicle lumen

Iodides (I–) are actively taken into the cell, oxidized to iodine (I2), and released into the lumen

Iodine attaches to tyrosine, mediated by peroxidase enzymes

Iodinated tyrosines link together to form T3 and T4

Colloid is endocytosed and combined with a lysosome

T3 and T4 are cleaved and diffuse into the bloodstream

Term
How is Thyroid Hormone (TH) transported?
Definition

• T4 and T3 are transported by thyroxine-binding globulins (TBGs)

• Both bind to target receptors, but T3 is ten times more active than T4

Term
How is Thyroid Hormone (TH) regulated in the body?
Definition

1. Peripheral tissues convert T4 to T3

2. Negative feedback regulation of TH release

    A. Rising TH levels provide negative feedback inhibition on release of TSH (Thyroid Stimulating Hormone)

    B. Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the negative feedback during pregnancy or exposure to cold

Term
What are the Homeostatic Imbalances of Thyroid Hormone (TH)?
Definition

Hyposecretion in adultsMyxedema; endemic goiter is due to lack of iodine

Hyposecretion in infantsCretinism

HypersecretionGraves’ disease

Term
What is the function of Calcitonin?
Definition

• Produced by parafollicular (C) cells

• Antagonist to parathyroid hormone (PTH)

• Inhibits osteoclast activity and release of Ca2+ from bone matrix

• Stimulates Ca2+ uptake and incorporation into bone matrix

 • Regulated by a humoral (Ca2+ concentration in the blood) negative feedback mechanism

• No important role in humans; removal of thyroid (and its C cells) does not affect Ca2+ homeostasis

Term
What is the function of the Parathyroid Gland?
Definition

• Stimulates osteoclasts to digest bone matrix

• Enhances reabsorption of Ca2+ and secretion of phosphate by the kidneys

• Promotes activation of vitamin D (by the kidneys); increases absorption of Ca2+ by intestinal mucosa

Term
What cells in the Parathyroid Gland secrete parathyroid hormone (PTH)?
Definition
oxyphil cells (function unknown) and chief cells secrete Parathyroid Hormone (PTH) or Parathormone
Term
What are and where are the Parathyroid Glands located?
Definition
Four to eight tiny glands embedded in the posterior aspect of the thyroid
Term
Parathyroid hormone (PTH) is used for what?
Definition
Parathyroid Hormone (PTH) is the most important hormone in Ca2+ homeostasis
Term
Through what mechanisim does the Parathyroid release PTH?
Definition

Negative feedback mechanism:

Rising Ca2+ in the blood inhibits PTH release

Term
What are some of the results of homeostatic imbalances of PTH?
Definition

Hyperparathyroidism due to tumor

• Bones soften and deform

• Elevated Ca2+ depresses the nervous system and contributes to formation of kidney stones

Hypoparathyroidism following gland trauma or removal results in tetany, respiratory paralysis, and death

Term
Where are the Adrenal(Suprarenal) Glands located?
Definition
They are paired, pyramid-shaped organs atop the kidneys
Term
What are the structure and function of the Adrenal (Suprarenal) Glands?
Definition

Structurally and functionally, they are two glands in one

1. Adrenal medullanervous tissue; part of the sympathetic nervous system

2. Adrenal cortexthree layers of glandular tissue that synthesize and secrete corticosteroids

Term
What are the layers of the Adrenal Cortex and the corticosteroids they produce?
Definition

1. Zona glomerulosamineralocorticoids

2. Zona fasciculataglucocorticoids

3. Zona reticularissex hormones, or gonadocorticoids

Term
What is the function of Mineralcorticoids?
Definition

A. Regulate electrolytes (primarily Na+ and K+) in ECF

   1.Importance of Na+: affects ECF volume, blood volume, blood pressure, levels of other ions

   2.Importance of K+: sets RMP of cells

B. Aldosterone is the most potent mineralocorticoid

   1. Stimulates Na+ reabsorption and water retention by the kidneys

Term
Describe the mechanism of Aldosterone secretion.
Definition

1. Renin-angiotensin mechanism: decreased blood pressure stimulates kidneys to release renin, triggers formation of angiotensin II, a potent stimulator of aldosterone release

2. Plasma concentration of K+: Increased K+ directly influences the zona glomerulosa cells to release aldosterone

3. ACTH: causes small increases of aldosterone during stress

4. Atrial natriuretic peptide (ANP): blocks renin and aldosterone secretion, to decrease blood pressure

Term
What is the condition caused by the Homeostatic Imbalances of Aldosterone?
Definition

Aldosteronismhypersecretion due to adrenal tumors *Hypertension and edema due to excessive Na+

* Excretion of K+ leading to abnormal function of neurons and muscle

Term
What is the function of Glucocorticoids (Cortisol)?
Definition

• Keep blood sugar levels relatively constant

• Maintain blood pressure by increasing the action of vasoconstrictors

Term
Why does our body need Glucocorticoids (Cortisol)?
Definition

Cortisol is the most significant glucocorticoid

• Released in response to ACTH, patterns of eating and activity, and stress

• Prime metabolic effect is gluconeogenesis—formation of glucose from fats and proteins

• Promotes rises in blood glucose, fatty acids, and amino acids

Term
What condition is caused by the hypersecretion of Glucocorticoids?
Definition

HypersecretionCushing’s syndrome

• Depresses cartilage and bone formation

• Inhibits inflammation

• Depresses the immune system

• Promotes changes in cardiovascular, neural, and gastrointestinal function

Term
What condition is caused by the hyposecretion of Glucocorticoids?
Definition

HyposecretionAddison’s disease

• Also involves deficits in mineralocorticoids

• Decrease in glucose and Na+ levels

• Weight loss, severe dehydration, and hypotension

Term
Describe the structure of the Gonadocorticoids (Sex Hormones).
Definition
• Most are androgens (male sex hormones) that are converted to testosterone in tissue cells or estrogens in females
Term
What is the function of Gonadocorticoids (Sex Hormone)?
Definition

May contribute to:

• The onset of puberty

• The appearance of secondary sex characteristics

• Sex drive

Term
The Chromaffin cells of the Adrenal Medulla secretes what hormones?
Definition
Epinephrine (80%) and Norepinephrine (20%)
Term
Epinephrine and Norepinephrine cause what metabolic changes in the body?
Definition

These hormones cause:

• Blood glucose levels to rise

• Blood vessels to constrict

• The heart to beat faster

• Blood to be diverted to the brain, heart, and skeletal muscle

• Epinephrine stimulates metabolic activities, bronchial dilation, and blood flow to skeletal muscles and the heart

• Norepinephrine influences peripheral vasoconstriction and blood pressure

Term
Where is the Pineal Gland located?
Definition
Small gland hanging from the roof of the third ventricle of the brain.
Term
What cells of the Pineal Gland secretes Melatonin?
Definition
Pinealocytes secrete melatonin, derived from serotonin
Term
What does melatonin help regulate?
Definition

Melatonin may affect:

• Timing of sexual maturation and puberty

• Day/night cycles

• Physiological processes that show rhythmic variations (body temperature, sleep, appetite)

Term
Describe the Pancrease and its location.
Definition
Triangular gland located behind the stomach.
Term
Is the Pancrease part of the Exocrine or Endocrine system?
Definition

Has both exocrine and endocrine cells:

Acinar cells (exocrine) produce an enzyme-rich juice for digestion

Pancreatic islets (islets of Langerhans) contain endocrine cells

   1.Alpha cells produce glucagon (a hyperglycemic hormone)

  2.Beta cells produce insulin (a hypoglycemic hormone)

Term
What organ does Glucagon target?
Definition

Major target is the liver, where it promotes:

Glycogenolysis—breakdown of glycogen to glucose

Gluconeogenesis—synthesis of glucose from lactic acid and noncarbohydrates

• Release of glucose to the blood

Term
What are the effects of Insulin?
Definition

Effects of insulin:

• Lowers blood glucose levels

• Enhances membrane transport of glucose into fat and muscle cells

• Participates in neuronal development and learning and memory

• Inhibits glycogenolysis and gluconeogenesis

Term
What affect does insulin have on cells?
Definition
• Activates a tyrosine kinase enzyme receptor
• Cascade leads to increased glucose uptake and enzymatic activities that
• Catalyze the oxidation of glucose for ATP production
• Polymerize glucose to form glycogen
• Convert glucose to fat (particularly in adipose tissue)
Term
What is the condition caused by an insulin inbalance?
Definition
• Diabetes mellitus (DM)
• Due to hyposecretion or hypoactivity of insulin
Term
What are 3 signs of Diabetes Mellitus?
Definition
• Polyuria—huge urine output
• Polydipsia—excessive thirst
• Polyphagia—excessive hunger and food consumption
Term
What is Hyperinsulinism?
Definition
• Excessive insulin secretion; results in hypoglycemia, disorientation, unconsciousness
Term
Steroid sex hormone (Testosterone) is produced by what organ in males?
Definition
Gonads / Testes
Term
What hormones are produced by the ovaries in a female?
Definition
Estrogen and Progesterone.
Term
What are Estrogene and Progesterone responsible for in a female?
Definition
• Maturation of female reproductive organs
• Appearance of female secondary sexual characteristics
• Breast development and cyclic changes in the uterine mucosa
Term
What hormones does the placenta secrete?
Definition
estrogens, progesterone, and human chorionic gonadotropin (hCG)
Term
What is Testosterone responsible for in a male?
Definition
• Initiates maturation of male reproductive organs
• Causes appearance of male secondary sexual characteristics and sex drive
• Is necessary for normal sperm production
• Maintains reproductive organs in their functional state
Term
What hormone is secreted by the Heart?
Definition
• Atrial natriuretic peptide (ANP) reduces blood pressure, blood volume, and blood Na+ concentration
Term
What hormone is secreted by the Gastrointestinal Tract enteroendocrine cells?
Definition
• Gastrin stimulates release of HCl
• Secretin stimulates liver and pancreas
• Cholecystokinin stimulates pancreas, gallbladder, and hepatopancreatic sphincter
Term
What hormone is secreted by the Kidneys?
Definition
• Erythropoietin signals production of red blood cells
• Renin initiates the renin-angiotensin mechanism
Term
What hormone is secreted by the Skin?
Definition
• Cholecalciferol, the precursor of vitamin D
Term
What hormone is secreted by the Adipose tissue?
Definition
• Leptin is involved in appetite control, and stimulates increased energy expenditure
Term
What hormone is secreted by the Skeleton (osteoblasts)?
Definition
• Osteocalcin prods pancreatic beta cells to divide and secrete more insulin, improving glucose handling and reducing body fat
Term
What hormone is secreted by the Thymus?
Definition
• Thymulin, thymopoietins, and thymosins are involved in normal the development of the T lymphocytes in the immune response
Term
True or False:
Hormone-producing glands arise from all three germ layers
Definition
True
Term
True or False:
Exposure to pesticides, industrial chemicals, arsenic, dioxin, and soil and water pollutants disrupts hormone function
Definition
True
Term
True or False:
Sex hormones, thyroid hormone, and glucocorticoids are vulnerable to the effects of pollutants
Definition
True
Term
True or False:
Interference with glucocorticoids may help explain high cancer rates in certain areas
Definition
True
Term
True or False:
Ovaries undergo significant changes with age and become unresponsive to gonadotropins; problems associated with estrogen deficiency begin to occur
Definition
True
Term
True or False:
Testosterone also diminishes with age, but effect is not usually seen until very old age
Definition
True
Term
True or False:
GH levels decline with age and this accounts for muscle atrophy with age
Definition
True
Term
True or False:
TH declines with age, contributing to lower basal metabolic rates
Definition
True
Term

True or False:

PTH levels remain fairly constant with age, but lack of estrogen in older women makes them more vulnerable to bone-demineralizing effects of PTH

Definition
True
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