unit 9 endocrine

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Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning

UNIT 9

Endocrine Glands


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Copyright 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Hormones

Can be divided into three groups

Amino acid derivatives

Peptide hormones

Lipid derivatives Circulate freely or bound to transport proteins


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Hormones

Figure 182 A Structural Classification of Hormones


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Introduction to the Endocrine System

Figure 181 Organs and Tissues of the Endocrine System.


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Introduction to the Endocrine System

Figure 181 Organs and Tissues of the Endocrine System.


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Endocrine Reflexes

Figure 185 Three Mechanisms of Hypothalamic Control over EndocrineFunction.


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Pituitary Gland

Figure 187 The Hypophyseal Portal System and the Blood Supply tothe Pituitary Gland.


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Pituitary Gland

Figure 188a Feedback Control of Endocrine Secretion


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Pituitary Gland

Figure 189 Pituitary Hormones and Their Targets.


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Chapter 19 The Peripheral Endocrine GlandsHuman Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning

Peripheral Endocrine Glands

Include

Thyroid glandsAdrenal glands

Endocrine pancreas

Parathyroid glands


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Thyroid Gland

Consists of two lobes of endocrine tissue joined in middle by

narrow portion of gland Follicular cells

Arranged into hollow spheres

Forms functional unit called a follicle

Lumen filled with colloid Serves as extracellular storage site for thyroid hormone

Produce two iodine-containing hormones derived from

amino acid tyrosine

Tetraiodothyronine (T4or thyroxine)

Tri-iodothyronine (T3)

C cells

Secrete peptide hormone calcitonin


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Thyroid Gland


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Thyroid Gland

Synthesis, storage, and secretion of thyroid hormone

Basic ingredients

Tyrosine

Synthesized in sufficient amounts by body

Iodine

Obtained from dietary intake

Synthesis All steps occur on thyroglobulin molecules within colloid

Tyrosine-containing thyroglobulin is exported from follicularcells into colloid by exocytosis

Thyroid captures iodine from blood and transfers it intocolloid by iodine pump

Within colloid, iodine attaches to tyrosine

Coupling process occurs between iodinated tyrosinemolecules to form thyroid hormones


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The Thyroid Gland

Figure 1810b-c The Thyroid Gland.


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The Thyroid Gland

Figure 1811a The Thyroid Follicles: Synthesis, Storage, and Secretion

of Thyroid Hormones.


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The Thyroid Gland

Figure 1811b The Thyroid Follicles: The Regulation of Thyroid Secretion.


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Thyroid Gland

Storage

Thyroid hormones remain in colloid until they are splitoff and secreted

Usually enough thyroid hormone stored to supply

bodys needs for several months

Secretion Follicular cells phagocytize thyroglobulin-laden colloid

Process frees T3and T4to diffuse across plasma

membrane and into blood


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Thyroid Gland

Effects of thyroid hormone

Main determinant of basal metabolic rate Influences synthesis and degradation of

carbohydrate, fat, and protein

Increases target-cell responsiveness to

catecholamines

Increases heart rate and force of contraction

Essential for normal growth

Plays crucial role in normal development ofnervous system


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Thyroid Gland

Secretion

Regulated by negative-feedback system betweenhypothalamic TRH, anterior pituitary TSH, and

thyroid gland T3and T4

Feedback loop maintains thyroid hormones

relatively constant


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Regulation of Thyroid

Hormone Secretion


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Thyroid Gland

Abnormalities

Hypothyroidism Causes

Primary failure of thyroid gland

Secondary to a deficiency of TRH, TSH, or both

Inadequate dietary supply of iodine Cretinism

Results from hypothyroidism from birth

Myxedema

Term often used for myxedema in adults Treatment

Replacement therapy

Dietary iodine


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Thyroid Gland

Abnormalities

Hyperthyroidism Most common cause is Graves disease

Autoimmune disease

Body erroneously produces thyroid-stimulating

immunoglobulins (TSI) Characterized by exopthalmos

Treatment

Surgical removal of a portion of the over-secreting thyroid

Administration of radioactive iodine

Use of antithyroid drugs


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Role of Thyroid-Stimulating Immunoglobulin in

Graves Disease


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Adrenal Glands

Embedded above each kidney in a capsule of fat

Composed of two endocrine organsAdrenal cortex

Outer portion

Secretes steroid hormones

Adrenal medulla

Inner portion

Secretes catecholamines


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Anatomy of the Adrenal Glands


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Adrenal Glands

Adrenal cortex

Consists of three layers or zones

Zona glomerulosaoutermost layer Zona fasciculatamiddle and largest portion

Zona reticularisinnermost zone

Categories of adrenal steroids Mineralocorticoids

Mainly aldosterone Influence mineral balance, specifically Na+and K+balance

Glucocorticoids Primarily cortisol

Major role in glucose metabolism as well as in protein and lipidmetabolism

Sex hormones Identical or similar to those produced by gonads

Most abundant and physiologically important isdehydroepiandosterone (male sex hormone)


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Adrenal Glands

Aldosterone

Principal action site is on distal and collectingtubules of the kidney

Secretion is increased by

Activation of renin-angiotensin-aldosterone system by

factors related to a reduction in Na+and a fall in bloodpressure

Direct stimulation of adrenal cortex by rise in plasma K+

concentration

Regulation of aldosterone secretion is largelyindependent of anterior pituitary control


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Chapter 19 The Peripheral Endocrine Glands


Adrenal Glands

Cortisol

Stimulates hepatic gluconeogenesis

Inhibits glucose uptake and use by many tissues, but notthe brain

Stimulates protein degradation in many tissues, especiallymuscle

Facilitates lipolysis Plays key role in adaptation to stress

At pharmacological levels, can have anti-inflammatory andimmunosuppressive effects

Long-term use can result in unwanted side effects

Displays a characteristic diurnal rhythm Secretion

Regulated by negative-feedback loop involving hypothalamicCRH and pituitary ACTH


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Adrenal Glands

Secretes both male and female sex hormones in

both sexes Dehydroepiandrosterone (DHEA)

Only adrenal sex hormone that has any biological

importance

Overpowered by testicular testosterone in males Physiologically significant in females where it governs

Growth of pubic and axillary hair

Enhancement of pubertal growth spurt

Development and maintenance of female sex drive

Di d f Ad i l F i


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Disorders of Adrenocortical Function

Aldosterone hypersecretion

May be caused by Hypersecreting adrenal tumor made up of aldosterone-

secreting cells

Primary hyperaldosteronism or Conns syndrome

Inappropriately high activity of the renin-angiotensinsystem

Secondary hyperaldosteronism

Symptoms

Excessive Na+

retention and K+

depletion High blood pressure

Di d f Ad ti l F ti


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Cortisol hypersecretion

Cushings syndrome Causes

Overstimulation of adrenal cortex by excessiveamounts of CRH and ACTH

Adrenal tumors that uncontrollably secrete cortisolindependent of ACTH

ACTH-secreting tumors located in places other than thepituitary

Signs and symptoms

Hyperglycemia and glucosuria (adrenal diabetes) Abnormal fat distributions

buffalo hump and moon face

Di d f Ad ti l F ti


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Adrenal androgen hypersecretion

Adrenogenital syndrome Symptoms

Adult females

Hirsutism

Deepening of voice, more muscular arms and legs

Breasts become smaller and menstruation may cease

Newborn females

Have male-type external genitalia

Prepubertal males

Precocious pseudopuberty Adult males

Has no apparent effect

Di d f Ad ti l F ti


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Adrenocortical insufficiency

Primary adrenocortical insufficiency Addisons disease

Autoimmune disease

Aldosterone deficiency

Hyperkalemia and hyponatremia

Cortisol deficiency Poor response to stress

Hypoglycemia

Lack of permissive action for many metabolic activities

Secondary adrenocortical insufficiency

Occurs because of pituitary or hypothalamic abnormality

Only cortisol is deficient


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St R


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Stress Response

All the actions are coordinated by the hypothalamus

Generalized stress responseActivation of sympathetic nervous system

accompanied by epinephrine secretion

Prepares body for fight-or-flight response

Activation of CRH-ACTH-cortisol system

Helps body cope by mobilizing metabolic resources

Elevation of blood glucose and fatty acids

Decreased insulin and increased glucagon secretion

Maintenance of blood volume and blood pressure

Increased activity of renin-angiotensin-aldosterone

system and increased vasopressin secretion

E d i C t l f F l M t b li


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Endocrine Control of Fuel Metabolism

Metabolism

All the chemical reactions that occur within the cells of thebody

Intermediary metabolism or fuel metabolism

Includes reactions involving the degradation, synthesis,

and transformation of proteins, carbohydrates, and fats

Nutrient molecules are broken down through the process of

digestion into smaller absorbable molecules

Proteins amino acids

Carbohydrates monosaccharides (mainly glucose)

Dietary fats (triglycerides) monoglycerides and free fattyacids

A b li d C t b li


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Anabolism and Catabolism

Anabolism

Buildup or synthesis of larger organic macromoleculesfrom small organic subunits

Reactions usually require ATP energy

Reactions result in

Manufacture of materials needed by the cell

Storage of excess ingested nutrients not immediately neededfor energy production or needed as cellular building blocks

Catabolism

Breakdown or degradation of large, energy-rich organicmolecules within cells

Two levels of breakdown Hydrolysis of large cellular molecules into smaller subunits

Oxidation of smaller subunits to yield energy for ATPproduction

Summary of the Major Pathways Involving Organic Nutrient Molecules


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Summary of the Major Pathways Involving Organic Nutrient Molecules

Interconversions Among Organic Molecules


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Interconversions Among Organic Molecules

Most interconversion of organic molecules occurs in liver

Essential nutrients (certain amino acids and vitamins) Food intake is intermittentnutrients must be stored for use

between meals

Excess circulating glucose

Stored in liver and muscle as glycogen

Once liver and muscle stores are filled up, additional

glucose is transformed into fatty acids and glycerol and

stored in adipose tissue

Excess circulating fatty acids

Become incorporated into triglycerides Excess circulating amino acids

Converted to glucose and fatty acids


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Stored Metabolic Fuel in the Body

Metabolic States


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Metabolic States

Absorptive state

Fed state Glucose is plentiful and

serves as major energy

source

Postabsorptive state

Fasting state

Endogenous energy

stores are mobilized to

provide energy


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Pancreatic Hormones


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Pancreatic Hormones

Pancreas

Endocrine cellsIslets of Langerhans (beta) cells Site of insulin synthesis and secretion

(alpha) cells

Produce glucagon

D (delta) cells Pancreatic site of somatostatin synthesis

PP cells

Least common islet cells

Secrete pancreatic polypeptide

Insulin and glucagon

Most important in regulating fuel metabolism

Pancreatic Hormones


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Pancreatic Hormones

Somatostatin

Released from pancreatic D cells in directresponse to increase in blood sugar and blood

amino acids during absorption of a meal

Prevents excessive plasma levels of nutrients

Local presence of somatostatin decreasessecretion of insulin, glucagon, and somatostatin

itself

Physiologic importance has not been determined

Pancreatic Hormones


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Pancreatic Hormones

Insulin

Anabolic hormone Promotes cellular uptake of glucose, fatty acids,

and amino acids and enhances their conversion

into glycogen, triglycerides, and proteins,

respectively Lowers blood concentration of these small organic

molecules

Secretion is increased during absorptive state

Primary stimulus for secretion is increase in bloodglucose concentration

Pancreas


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Pancreas

Figure 1816 The Regulation of Blood Glucose Concentrations

Diabetes Mellitus


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Diabetes Mellitus

Most common of all endocrine disorders

Prominent feature is elevated blood glucose levels Urine acquires sweetness from excess blood

glucose that spills into urine

Two major types

Type I diabetes

Characterized by lack of insulin secretion

Type II diabetes

Characterized by normal or even increased insulinsecretion but reduced sensitivity of insulins target cells

Comparison of Type I and Type II Diabetes


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Comparison of Type I and Type II Diabetes


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Pancreatic Hormones


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Pancreatic Hormones

Glucagon

Mobilizes energy-rich molecules from storagesites during postabsorptive state

Secreted in response to a direct effect of a fall in

blood glucose on pancreatic cells

Generally opposes actions of insulin

No known clinical abnormalities caused by

glucagon deficiency or excess

Excess of glucose can aggravate hyperglycemia of

diabetes mellitus

Endocrine Control of Calcium Metabolism


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Plasma Ca2+must be closely regulated to prevent changes in

neuromuscular excitability

Also plays vital role in a number of essential activities

Excitation-contraction coupling in cardiac and smooth muscle

Stimulus-secretion coupling

Maintenance of tight junctions between cells

Clotting of blood

Hypercalcemia

Reduces excitability

Hypocalcemia

Brings about overexcitability of nerves and muscles Severe overexcitability can cause fatal spastic contractions of

respiratory muscles



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Three hormones regulate plasma concentration of

Ca2+

(and PO43-

) Parathyroid hormone (PTH)

Calcitonin

Vitamin D



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Parathyroid hormone (PTH)

Secreted by parathyroid glands Primary regulator of Ca2+

Raises free plasma Ca2+levels by its effects on bone

kidneys, and intestines

Essential for life Prevents fatal consequences of hypocalcemia

Facilitates activation of Vitamin D

Parathyroid Glands


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Parathyroid Glands

Figure 1812 The Parathyroid Glands.



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Vitamin D

Stimulates Ca2+

and PO43-

absorption fromintestine

Can be synthesized from cholesterol derivative

when exposed to sunlight

Often inadequate source

Amount supplemented by dietary intake

Must be activated first by liver and then by

kidneys before it can exert its effect on intestines



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Calcitonin

Hormone produced by C cells of thyroid gland Negative-feedback fashion

Secreted in response to increase in plasma Ca2+

concentration

Acts to lower plasma Ca2+levels by inhibitingactivity of bone osteoclasts

Unimportant except during hypercalcemia


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Calcium Disorders


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Calcium Disorders

PTH hypersecretion (hyperparathyroidism)

Characterized by hypercalcemia andhypophosphatemia

PTH hyposecretion (hypoparathyroidism)

Characterized by hypocalcemia and

hyperphosphatemia

Vitamin D deficiency

Childrenrickets

Adultsosteomalacia

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