C h a p t e r

18

The Endocrine System

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

Pages 603-635

Endocrine System Introduction

Composed of glands and tissues that secrete chemical regulators called hormones

Study of endocrine system is endocrinology

What do you call a doctor who specializes in diseases of the endocrine system?

Definitions

Hormones are chemicals regulatorsMost are secreted into the blood and

become circulating hormonesThey affect the functioning of other cells These “other cells” are called targets

Definitions

Hormones are specific for certain targets because hormones bind to specific receptors of target cells

Targets range from specific tissues to widespread tissues

Hormones Regulate

GrowthMetabolismFluid, electrolyte, and acid-base balanceReproductionBlood pressureand other processes such as heart rate,

digestion, etc.

Endocrine Glands and Tissues

Secrete hormones Examples Pituitary gland

(hypophysis) Thyroid gland Parathyroid glands Adrenal glands Pancreas Gonads Endocrine tissues

within other organs

Chemistry of hormones

Compounds that act as hormones are: Amino Acid Derivatives

Thyroid hormones Epinephrine, Norepinephrine and Dopamine

Peptide Hormones Small polypeptides and small proteins Glycoproteins

Chemistry of Hormones

Lipid DerivativesEicosanoids

Leukotrienes and prostaglandins

Steroids Estrogen, testosterone and cortisol

Hormone Secretion

Stimulus (another hormone, changes in blood chemistry or nerve stimuli)

Endocrine Gland

Target cell

Hormone secretion

Actions

Blood

Binds to Receptor------------

----------------Hormone

Regulation of Hormone Secretion

Hormone actions depend on cellular receptorsHormones that cannot enter the cell bind to

cell membrane receptorsHormone acts as “first messenger”Hormone-receptor complex simulates formation

of “second messenger” – usually cyclic-AMPSecond messenger produces hormones action

inside cell

Hormone Actions – Hormone Cannot Enter Cell

ATP

c-AMP – 2nd messenger

Hormone – 1st messenger

Membranes Receptor

Enzyme catalyzedreactions Actions

Most Hormones such as peptides and proteins work this way

Regulation of Hormone Secretion

Some Hormones can enter cellHormone binds to intracellular receptorHormone-receptor complex enters nucleusDNA segments (genes) activatedDNA codes for protein formationProtein produces hormone actions

Steroids and thyroid hormones work this way

Hormone Actions – Hormone Enters Cell

DNA in Nucleus

Protein Actions

Hormone Enters Cell

Intracellular Receptor

Regulation of Hormone Secretion

Hormone Concentration Affects Number of Receptors If hormone level high, receptor numbers decrease –

called down-regulation Cells become less sensitive to hormone

If hormone levels low, receptor numbers increase – called up-regulation

Cells become more sensitive to hormone

Up and down regulation help maintain endocrine homeostasis

Control of Secretion

Negative feed back Actions of Effector (Gland) decrease or inhibit

stimulus Actions are usually hormone secretions Most common control

Attempts to maintain normal levels of secretion Thermostat analogy

Positive feed back Actions of Effector increase or continue stimulus What are two examples?

Negative Feedback

Pituitary Gland (Hypophysis)

Small gland connected to hypothalamus

Two parts Anterior pituitary

(adenohypophysis) Posterior pituitary

(neurohypophysis) Infundibulum – a funnel-

shaped structure connecting the pituitary to the hypothalamus

anterior pituitary--------- -----posterior pituitary

hypothalamus

---------infundibulum

Pituitary Gland (Hypophysis)

Posterior pituitary Hormones produced by

hypothalamus and placed in posterior pituitary for secretion

Secretes two hormones Oxytocin (OT) Antidiuretic hormone (ADH)

Pituitary Gland

Anterior pituitary largest part Produces and secretes most

of the hormones Under indirect control of

hypothalamus Hypothalamus secretes

releasing hormones (RH) and inhibiting hormones (IH)

Reach anterior pituitary through hypophyseal portal circulation

Hormones of Anterior Pituitary

Human Growth Hormone (hGH) Targets most cells especially skeletal and muscle

tissue Actions

↑ rate of cell division for growth ↑ protein synthesis provides structure needed for

growth ↑ use of fat for energy, especially during prolonged

exercise ↑ rate of bone growth

Growth Hormone

Results in growth to adulthood and maintenance of skeleton and muscles in adults

May work directly on tissues, but mostly works indirectly by stimulating formation of insulin-like growth factors (IGF’s) in liver that then target muscle, skeletal and other tissues

Growth Hormone Imbalances

Pituitary dwarfism Caused by hyposecretion in childrenResults in small body

Giantism caused by hypersecretion in infants and children resulting in height of 7 to 8 feet

Acromegaly caused by hypersecretion in adults resulting in distorted features

Giantism

Acromegaly

Hormones of Anterior Pituitary

Thyroid stimulating hormone (TSH)Targets thyroid glandStimulates secretion of most thyroid

hormonesAdrenocorticotropic Hormone (ACTH)

Targets suprarenal (adrenal) cortexStimulates secretion of most steroids from

suprarenal glands

Hormones of Anterior Pituitary

Prolactin (PRL)Targets mammary glands Stimulates milk production in mammary

glands in concert with other hormonesGonadotropins

Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) target the ovaries and testes (gonads) and control female and male reproductive physiology

Hormones of the Posterior Pituitary

Oxytocin (OT) Mostly targets smooth muscles of

reproductive system of both sexes Actions in female

Labor (uterine) contractions Release of milk from mammary glands (milk

letdown)

Actions in male Contraction of smooth muscle in

reproductive tissue

Hormones of Posterior Pituitary

Antidiuretic Hormone (ADH) (vasopressin)Targets kidneys, sweat glands and

arteriolesActions

Causes kidneys and sweat glands to conserve water

Constricts arteriolesDo these actions affect blood pressure?

Summary of Pituitary Hormones

Which of the following hormones causes birth?

1. prolactin

2. oxytocin

3. ADH

4. FSH

Question

Thyroid Gland

Large butterfly-shaped gland in neck below voice box (larynx)

Has Two lobes connected by an isthmus

right lobe

left lobe

isthmus

Histology of Thyroid

Composed of many follicles filled with jelly-like (colloidal) thyroglobulin protein

• Thyroid hormones synthesized by follicle cells and stored in combination with thyroglobulin

Thyroglobulin

Thyroid Follicles

Thyroid Hormones Formation

Thyroglobulin protein made by follicular cells Thyroid hormones formed by addition of iodine

to the thryroglobulin protein 3 or 4 iodine atoms added to thyroglobulin

T3 (triiodothyronine) if 3 iodine atoms added

T4 (tetraiodothyronine or thyroxine) if 4 iodine atoms added

Thyroid Hormone Formation

Synthesis and secretion stimulated by anterior pituitary hormone TSH (thyrotropin)

When secreted, T3 and T4 combine with blood proteins for transport to target cells

Once in target cells, produce metabolic effects to provide energy and stimulate growth

Target Tissues and Actions of T3 & T4

Targets most tissues, but not allActions

ATP production and use of ATP for energy

Normal growthControl by negative feedback

Control of Thyroid Secretion

Iodine is added to __________ to make T3 and T4.1. thyroxine binding globulin2. thyroglobulin3. albumin4. gamma globulin

Question

Imbalances of T3 & T4

Thyroid dwarfism (cretinism)Too little from birthSevere form

Imbalances of T3 & T4

Hyperthyroidism Too much T3 & T4

Grave’s disease most common form Symptoms

metabolic rate (MR) tachycardia body temperature (BT) anxiety & irritability goiter Exophthalmia (exophthalmos) heat intolerance weight loss

Imbalances of T3 & T4

Hypothyroidism Too little T3 & T4

Symptoms metabolic rate (MR) bradycardia body temperature (BT) lethargy goiter weight gain cold intolerance swollen face (Myxedema)

Imbalances of T3 & T4

Endemic goiter and iodine deficiency Insufficient dietary iodine to make T3 & T4

Endemic refers to ____________________

Lack of negative feedback causes overgrowth of thyroid

Goiter results

Thyroid Disorders

Endemic Goiter Exophthalmia

Parathyroid Glands

Thyroid and parathyroid glands contol blood calcium

Four parathyroid glands embedded in

back of thyroid gland

Control of Blood Calcium

Calcitonin (CT) from thyroid lowers blood calcium by adding it to bones

Parathyroid hormone from parathyroid glands increases blood calcium by removing it from bones

Calcium Homeostasis

Suprarenal (adrenal) Glands

Located on top of kidneys Hormones adjust metabolism

and affect use of nutrients ionic balance energy consumption

Help maintain homeostasis against stress

Suprarenal Layers

Capsule Outer CT covering

Cortex – outer layer Threes zones Secretes steroids

Medulla – inner layer Secretes catecholamines

Suprarenal Histology

Cortex Secrete steroid hormones called corticoids Three Zones

Glomerular (outer) zone Cells in globular clusters Secretes mineralocorticoids such as aldosterone

Fascicular (middle) zone Cells form vertical elongated bundles Secrete glucocorticoids such as cortisol

Reticular (inner) zone Cells form irregular, net-like pattern Secrete some sex steroids in both sexes

Suprarenal Layers

Capsule Cortical Zones

Glomerular zone

Fascicular zone

Reticular zone

Medulla

Corticoids

Mineralocorticoids from glomerular zoneAldosterone most importantRegulates blood sodium, potassium

and acid – increases plasma sodium and decreases plasma potassium

Regulation affects fluid & electrolyte homeostasis

Principal one is cortisolActions include:

Mobilizing Body’s Resources to Resist Stress by

Protein breakdown (catabolism) for energy Formation of new glucose from amino

acids, lactic acid, and the glycerol part of fat molecules-gluconeogenesis

Glucocorticoids from Fascicular Zone

Glucocorticoids from Fascicular Zone

Actions include:Mobilizing Body’s Resources to Resist Stress

Conversion of excess glucose to glycogen (glycogenesis) for storage in liver-provides energy reserve

use of fat for energy assures glucose availability for brain

Maintaining bp by making blood vessels sensitive to vasoconstriction

Actions include:Reducing inflammation

Works with epinephrine (adrenaline) to reduce effects of inflammation.

Various steroids including hydrocortisone, cortisone, and synthetic steroids are used medically to reduce inflammation

Excess cortisol causes fat deposition in abdomen and face.

Control is by negative feedback

Glucocorticoids from Fascicular Zone

Imbalances of GlucocorticoidsAddison’s disease

Insufficient glucocorticoidsUsually caused by own antibodies attacking

suprarenal cortexSymptoms

Lack of energyWeight loss Inability to resist stressJohn F. Kennedy had it

Addison’s Disease – President Kennedy

Before Steroid Treatment During Steroid Treatment

Imbalances of Glucocorticoids

Cushing’s DiseaseExcessive glucocorticoid secretion

Usually caused by tumors in adrenals or elsewhere

Muscle wastingSpindly arms & legs

Fat redistributionLarge abdomen with stretch marksRounded faceFatty hump between shoulders

Cushing’s Syndrome

Before After

Which of the following is one of the actions of cortisol?

1. increased blood Calcium

2. blood glucose

3. gluconeogenesis

4. use of fat for energy

5. 2&3

6. 3&4

Question

Hormones of Suprarenal Medulla

Catecholamines - epinephrine (adrenaline) and norepinephrine (noradrenaline) Targets – most cells React quickly to stress by:

heart rate and strength blood flow to skeletal muscles, heart and brain dilation of airways (bronchodilation) fuel for energy-release of glucose from glycogen blood pressure

Suprarenal Medulla

Suprarenal medulla receives direct innervation from sympathetic nervous system develop from same tissue as Autonomic neurons

Hormones are sympathomimetic effects mimic those of sympathetic NS cause fight-flight behavior

Sympathetic stimulation increases hormone secretion by suprarenal medulla

Which hormone increases cell division, protein synthesis and the use of fat for energy?

1. prolactin

2. hGH

3. TSH

4. ACTH

Question

Pancreas

Large leaf-shapedLocated in curve of small intestine and

behind stomachBoth endocrine and exocrine

Endocrine part controls mostly blood sugar

Exocrine part secretes digestive enzymes

Anatomy of Pancreas

Five inches long Consists of head, body

& tail Most of pancreas is

exocrine and secretes digestive enzymes

Endocrine cells produce hormones that control blood sugar and affect metabolism and digestion

Histology of Pancreas

Exocrine acinar cells surround a small duct

Endocrine cells form Pancreatic Islet (Islets ofLangerhans)

1 to 2 million Islets

Contain four types of cells

Cell Types in the Pancreatic Islets

Alpha cells (20%) produce glucagonBeta cells (70%) produce insulinDelta cells (5%) produce somatostatinF cells (5%) produce pancreatic

polypeptideWill stress glucagon and insulin

secretion

Actions of Insulin

Insulin lowers blood glucose by: uptake of glucose into cellssynthesis of liver glycogen for storage-

glycogenesis

Insulin also protein & fat synthesis

Actions of Glucagon

Glucagon increases blood glucose by:Synthesis of glucose from amino acids in

liver-gluconeogenesisbreakdown of liver glycogen into glucose-

glycogenolysis release of glucose from liver into blood

Regulation of Glucagon & Insulin Secretion

High blood glucose after meal stimulates secretion of insulin and inhibition of glucagon

Low blood glucose when fasting stimulates release of glucagon and inhibition of insulin

Which of the following happens after you eat?

1. More glucose released into blood from liver

2. More glucose moves into cells

3. gluconeogenesis

4. breakdown (catabolism) of glycogen

Question

Diabetes Mellitus

Insulin unavailable for uptake of glucose into cells

Blood glucose becomes elevated – hyperglycemia

Diabetes Mellitus

Two Types:Type I (IDDM) or juvenile DM

Beta cells destroyed by own immune system

Insulin levels lowInsulin injections requiredUsually develops in people younger than 20

Diabetes Mellitus

Type II (NIDDM) or maturity onset DMMost common type (90%)Insulin may still be secreted but cells may

be less sensitive to itInsulin injections may not be requiredMostly in people over 35 who are obeseMay be controlled by diet

Three Signs (P’s) of DM

Polyuria

Polydypsia

Polphagia

Complications of DM

Cardiovascular diseaseLoss of visionKidney disease Diabetic ComaMost complications linked to high

glucose and acidosisAcidosis caused by excessive use of fat

for energy instead of glucose