Endocrine SystemEndocrine System

General FunctionsGeneral Functions

Communication Communication

Integration Integration

ControlControl

Chemical MessengersChemical Messengers

Hormone – substance secreted by an Hormone – substance secreted by an endocrine gland (sometimes from endocrine gland (sometimes from neurosecretory tissues) into the neurosecretory tissues) into the bloodstream that acts on a specific target bloodstream that acts on a specific target tissue to produce a given response. tissue to produce a given response.

Neuroendocrine SystemNeuroendocrine System

Both the nervous and endocrine system Both the nervous and endocrine system function to maintain stability of the internal function to maintain stability of the internal environmentenvironment

Names and Locations of Major Names and Locations of Major Endocrine GlandsEndocrine Glands

Name Name LocationLocation

Hypothalamus Hypothalamus Cranial cavity (brain)Cranial cavity (brain)

Pituitary glandPituitary gland Cranial cavity Cranial cavity

Pineal gland Pineal gland Crainal cavity (brain)Crainal cavity (brain)

Thyroid glandThyroid gland NeckNeck

Parathyroid glandsParathyroid glands NeckNeck

Thymus Thymus Mediastinum Mediastinum

Adrenal glandsAdrenal glands Abdominal cavity Abdominal cavity

Pancreatic IsletsPancreatic Islets Abdominal cavity Abdominal cavity (pancrease)(pancrease)

Ovaries Ovaries Pelvic cavity Pelvic cavity

TestesTestes ScrotumScrotum

PlacentaPlacenta Pregnant uterusPregnant uterus

Classification of HormonesClassification of Hormones

Classification by function:Classification by function: Tropic hormones – hormones that target other Tropic hormones – hormones that target other

endocrine glands and stimulate their growth endocrine glands and stimulate their growth and secretionand secretion

Sex hormones – target reproductive tissuesSex hormones – target reproductive tissues Anabolic hormones Anabolic hormones

Classification by Chemical StructureClassification by Chemical Structure Steroid hormones Steroid hormones Nonsteroid hormonesNonsteroid hormones

Steroid HormonesSteroid Hormones

Steroid hormone molecules are made by Steroid hormone molecules are made by endocrine cells from cholesterol, an important endocrine cells from cholesterol, an important lipidlipid

All have a characteristic chemical group at the All have a characteristic chemical group at the core of each moleculecore of each molecule

Lipid-soluble, thus they can easily pass through Lipid-soluble, thus they can easily pass through the phospholipid plasma membrane of target the phospholipid plasma membrane of target cells. cells.

Examples: cortisol, aldosterone, estrogen, Examples: cortisol, aldosterone, estrogen, progesterone, and testosteroneprogesterone, and testosterone

Steroid Hormone Steroid Hormone StructureStructure

As these examples As these examples show, steroid hormone show, steroid hormone molecules are very molecules are very similar in structure to similar in structure to cholesterol (top), from cholesterol (top), from which they are all which they are all derived.derived.

Nonsteroid HormonesNonsteroid HormonesSynthesized mainly from amino acidsSynthesized mainly from amino acids

Some are proteins (long folded chains of amino Some are proteins (long folded chains of amino acidsacids

Glycoprotein hormones have carbohydrate Glycoprotein hormones have carbohydrate groups attached to their amino acid chainsgroups attached to their amino acid chains

Peptide hormones are smaller than protein Peptide hormones are smaller than protein hormoneshormones

Amino acid derivative hormones are derived Amino acid derivative hormones are derived from a single amino acid moleculefrom a single amino acid molecule

Nonsteroid Hormone StructureNonsteroid Hormone Structure

AA. Protein hormone. Protein hormone

B.B. Peptide hormonePeptide hormone

C.C. Amino acid derivativeAmino acid derivative

How Hormones WorkHow Hormones Work

Hormones signal a cell by binding to Hormones signal a cell by binding to specific receptors on or in the target cell. specific receptors on or in the target cell. (Like a “lock-and-key”)(Like a “lock-and-key”)

Only bind to the receptors Only bind to the receptors that “fit” them exactly.that “fit” them exactly.

Cells can have many different type of Cells can have many different type of receptorsreceptors

Each hormone-receptor interaction Each hormone-receptor interaction produces different regulatory changesproduces different regulatory changes

Target Cell ConceptTarget Cell Concept

Synergism – when hormones work Synergism – when hormones work together to enhance each other’s influence together to enhance each other’s influence on a target cell.on a target cell.

Permissiveness – when a small amount of Permissiveness – when a small amount of one hormone allows a second hormone to one hormone allows a second hormone to have its full effect on a target cell. have its full effect on a target cell.

Antagonism – one hormone produces the Antagonism – one hormone produces the opposite effect of another hormone. opposite effect of another hormone.

Mechanisms of Steroid Hormone Mechanisms of Steroid Hormone Action Action

Can’t travel in plasma because they are lipidsCan’t travel in plasma because they are lipids

Attach to soluble plasma proteinsAttach to soluble plasma proteins

Most steroid receptors are found inside cellsMost steroid receptors are found inside cells

Formation of hormone-receptor complex and Formation of hormone-receptor complex and activates mRNA synthesisactivates mRNA synthesis

Steroid Hormone MechanismSteroid Hormone Mechanism

Mechanisms of Nonsteroid Mechanisms of Nonsteroid Hormone Action Hormone Action

Second messenger hypothesis – theory of Second messenger hypothesis – theory of hormone action in which the hormone hormone action in which the hormone binds to receptors of the target cell, which binds to receptors of the target cell, which then triggers a second molecule within the then triggers a second molecule within the cell to accomplish its function.cell to accomplish its function.

Example of Second Messenger Example of Second Messenger MechanismMechanism

1.1. Hormone-receptor Hormone-receptor complexcomplex

2.2. G-protein reacts with G-protein reacts with GTP GTP

3.3. Activation of adenyl Activation of adenyl cyclasescyclases

4.4. Phosphates removed Phosphates removed from ATP, converting from ATP, converting it to cAMPit to cAMP

5.5. Activates protein Activates protein kinasekinase

6.6. Activation of specific Activation of specific intracellular enzymeintracellular enzyme

7.7. Enzymes influence Enzymes influence specific cellular specific cellular reactionsreactions

Regulation of Hormone Secretion Regulation of Hormone Secretion

Usually part of a negative feedback loopUsually part of a negative feedback loop

Responses that result from the operation Responses that result from the operation of feedback loops within the endocrine of feedback loops within the endocrine system are called endocrine reflexessystem are called endocrine reflexes

Calcium-Calcium-Calmodulin as a Calmodulin as a 22ndnd Messenger Messenger

1.1. 11stst messenger binds messenger binds to a receptor in to a receptor in plasma membraneplasma membrane

2.2. Activation of Activation of membrane bound membrane bound proteins that trigger proteins that trigger the opening of Cathe opening of Ca++++ channelschannels

3.3. CaCa++++-calmoduln -calmoduln complex formed (2complex formed (2ndnd messenger) messenger)

4.4. Activates or Activates or inactivates enzymeinactivates enzyme

Endocrine Endocrine Feedback Feedback

LoopLoop

Prostaglandins (PG’s)Prostaglandins (PG’s)

Unique and diverse group that doesn’t meet the Unique and diverse group that doesn’t meet the usual definition of a hormone. usual definition of a hormone.

Rapidly metabolized soRapidly metabolized so

circulating levels arecirculating levels are

very lowvery low

Produced in a tissue and diffuse a short distance Produced in a tissue and diffuse a short distance to other cells in the tissueto other cells in the tissue

Pituitary Gland Structure Pituitary Gland Structure

Very small, but very important—Very small, but very important—sometimes called the “master gland”sometimes called the “master gland”

Found on the ventral surface of the brainFound on the ventral surface of the brain

Actually two glandsActually two glands Anterior pituitary Anterior pituitary Posterior pituitary Posterior pituitary

Structure and Location of the Structure and Location of the Pituitary GlandPituitary Gland

Anterior Pituitary Anterior Pituitary (Adenohypophysis)(Adenohypophysis)

Composed of several Composed of several cell types that stain cell types that stain differently from one differently from one anotheranother

Hormones include:Hormones include: Growth hormone—Growth hormone—

growth and blood growth and blood glucose levelsglucose levels

Prolactin—milk secretionProlactin—milk secretion Tropic hormones—Tropic hormones—

stimulate other glandsstimulate other glands

Growth Hormone AbnormalitiesGrowth Hormone Abnormalities

Posterior Pituitary Posterior Pituitary (Neurohypophysis)(Neurohypophysis)

Storage and release site for two Storage and release site for two hormones:hormones: Antidiuretic hormone—prevents the formation Antidiuretic hormone—prevents the formation

of large amounts of urineof large amounts of urine Oxytocin—stimulates contraction of uterine Oxytocin—stimulates contraction of uterine

muscles and causes milk ejection from the muscles and causes milk ejection from the breasts (positive feedback mechanisms) breasts (positive feedback mechanisms)

Pineal GlandPineal Gland

Tiny pine cone shaped Tiny pine cone shaped structurestructure

Nervous and endocrine Nervous and endocrine systemsystem

Functions to support the Functions to support the body’s biological clockbody’s biological clock

Melatonin—thought to Melatonin—thought to induce sleepinduce sleep

Thyroid GlandThyroid Gland

Located in the neck Located in the neck

Thyroid hormone (TH) – helps to regulate Thyroid hormone (TH) – helps to regulate metabolic rate as well as cell growth and metabolic rate as well as cell growth and differentiation (general target)differentiation (general target)

Calcitonin – influences tends to decrease Calcitonin – influences tends to decrease blood calcium levels and promote blood calcium levels and promote conservation of bone matrix conservation of bone matrix

Thyroid and Parathyroid GlandsThyroid and Parathyroid Glands

Thyroid Abnormalities Thyroid Abnormalities

Parathyroid Parathyroid

Embeded within the thyroidEmbeded within the thyroid

Secretes Parathyroid Hormone (PTH) – Secretes Parathyroid Hormone (PTH) – acts as an antagonist to calcitonin by acts as an antagonist to calcitonin by increasing release of calcium into the increasing release of calcium into the blood blood

Adrenal Glands Adrenal Glands

Located atop the kidneys Located atop the kidneys Adrenal cortex Adrenal cortex

Aldosterone – sodium homeostasisAldosterone – sodium homeostasis

Cortisol – many functionsCortisol – many functions

Adrenal medulla Adrenal medulla EpinephrineEpinephrine

NorepinephrineNorepinephrine

Adrenal Gland StructureAdrenal Gland Structure

Pancreatic Islets Pancreatic Islets

Edocrine tissue (Islets) account for about Edocrine tissue (Islets) account for about

2% or 3% of the total mass of the 2% or 3% of the total mass of the pancreaspancreas

Important pancreatic hormones:Important pancreatic hormones: Glucagon – increases blood glucose levels by Glucagon – increases blood glucose levels by

converting glycogen to glucoseconverting glycogen to glucose Insulin – promotes movement of glucose out Insulin – promotes movement of glucose out

of the blood into the cellsof the blood into the cells

PancreasPancreas

Regulation of Blood Glucose LevelsRegulation of Blood Glucose Levels

Gonads Gonads Testes produce androgens Testes produce androgens (male sex hormones – mainly (male sex hormones – mainly testosterone which is testosterone which is responsible for male sex responsible for male sex characteristics and sperm characteristics and sperm production production

Ovaries Ovaries Estrogens – female sex Estrogens – female sex

characteristics and reproductive characteristics and reproductive cyclecycle

Progesterone – maintains lining Progesterone – maintains lining of the uterus for pregnancy of the uterus for pregnancy

Placenta Placenta

Interface between the Interface between the circulatory systems of circulatory systems of the mother and the mother and developing fetusdeveloping fetus

Produces human Produces human chorionic chorionic gonadotropin (hCG) gonadotropin (hCG) which serves to signal which serves to signal the retention of the the retention of the uterine lininguterine lining