The Endocrine Systemcontents.kocw.or.kr/document/wcu/2012/Anatomy_and... · 2012-06-15 · Hormonal...

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9The Endocrine System

Yong Jeong, MD, PhD

Department of Bio and Brain Engineering

© 2012 Pearson Education, Inc.

The Endocrine System

•Second controlling system of the body•Nervous system is the fast-control system

•Uses chemical messengers (hormones) that are released into the blood

•Hormones control several major processes•Reproduction•Growth and development•Mobilization of body defenses•Maintenance of much of homeostasis•Regulation of metabolism

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Binding of ligands to membrane-spanning receptorsactivates diverse response mechanisms.


Hormone Overview

•Hormones are produced by specialized cells

•Cells secrete hormones into extracellular fluids

•Blood transfers hormones to target sites

•These hormones regulate the activity of other cells

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The Chemistry of Hormones

•Hormones are classified chemically as

•Amino acid–based, which includes

•Proteins

•Peptides

•Amines

•Steroids—made from cholesterol

•Prostaglandins—made from highly active lipids


Mechanisms of Hormone Action

•Hormones affect only certain tissues or organs (target cells or target organs)

•Target cells must have specific protein receptors

•Hormone-binding alters cellular activity

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Effects Caused by Hormones

•Changes in plasma membrane permeability or electrical state

•Synthesis of proteins, such as enzymes

•Activation or inactivation of enzymes

•Stimulation of mitosis

•Promotion of secretory activity


The Chemistry of Hormones

•Two mechanisms in which hormones act

•Direct gene activation

•Second-messenger system

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Direct Gene Activation (Steroid Hormone Action)•Diffuse through the plasma membrane of target cells

•Enter the nucleus

•Bind to a specific protein within the nucleus

•Bind to specific sites on the cell’s DNA

•Activate genes that result in synthesis of new proteins

© 2012 Pearson Education, Inc. Figure 9.1a, step 6

Steroidhormone

Cytoplasm Nucleus

Receptorprotein

Hormone-receptor complex

DNA

mRNA

Newprotein

Plasmamembraneof targetcell

1 2

3

4

5

6

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Second-Messenger System (Nonsteroid Hormone Action)•Hormone binds to a membrane receptor

•Hormone does not enter the cell

•Sets off a series of reactions that activates an enzyme

•Catalyzes a reaction that produces a second-messenger molecule (such as cAMP)

•Oversees additional intracellular changes to promote a specific response

© 2012 Pearson Education, Inc. Figure 9.1b

Nonsteroidhormone (first messenger)

Cytoplasm

Enzyme

Receptorprotein

Plasma membraneof target cell

Secondmessenger

Effect on cellular function, such as glycogenbreakdown

(b) Nonsteroid hormone action

ATP

cAMP

12

3

4

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Control of Hormone Release

•Hormone levels in the blood are mostly maintained by negative feedback

•A stimulus or low hormone levels in the blood triggers the release of more hormone

•Hormone release stops once an appropriate level in the blood is reached


Hormonal Stimuli of Endocrine Glands

•Most common stimuli

•Endocrine glands are activated by other hormones

•Examples:

•Anterior pituitary hormones travel to target glands, such as the thyroid gland, to prompt the release of a particular hormone, such as thyroid hormone

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© 2012 Pearson Education, Inc. Figure 9.2a

(a) Hormonal stimulus

The hypothalamus secretes hormones that…

Hypothalamus

…stimulatethe anteriorpituitary gland to secretehormonesthat…

Anteriorpituitarygland

Thyroidgland

Adrenalcortex

Gonad(Testis)

…stimulate other endocrine glands to secrete hormones

1

2

3


Humoral Stimuli of Endocrine Glands

•Changing blood levels of certain ions stimulate hormone release

•Humoral indicates various body fluids such as blood and bile

•Examples:•Parathyroid hormone and calcitonin are produced in response to changing levels of blood calcium levels

• Insulin is produced in response to changing levels of blood glucose levels

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Capillary blood contains lowconcentration of Ca2+, whichstimulates…

…secretion of parathyroid hormone (PTH) by parathyroidglands

1

(b) Humoral stimulus

Capillary(low Ca2+

in blood)

Parathyroidglands PTH

2

Parathyroidglands

Thyroid gland(posterior view)


Neural Stimuli of Endocrine Glands

•Nerve impulses stimulate hormone release

•Most are under the control of the sympathetic nervous system

•Examples:

•The release of norepinephrine and epinephrine by the adrenal medulla

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© 2012 Pearson Education, Inc. Figure 9.2c

Preganglionic sympatheticfiber stimulates adrenal medulla cells…

…to secrete catecholamines(epinephrine and norepinephrine)

1

(c) Neural stimulus

CNS (spinal cord)

Preganglionicsympathetic fibers

Capillary

Medulla ofadrenalgland

2


Major Endocrine Organs

•Pituitary gland

•Thyroid gland

•Parathyroid glands

•Adrenal glands

•Pineal gland

•Thymus gland

•Pancreas

•Gonads (Ovaries and Testes)

•Hypothalamus

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© 2012 Pearson Education, Inc. Figure 9.3

Pineal gland

HypothalamusPituitary gland

Thyroid gland

Parathyroid glands

Thymus

Adrenal glands

Pancreas

Ovary (female)

Testis (male)


Pituitary Gland

•Size of a pea

•Hangs by a stalk from the hypothalamus in the brain

•Protected by the sphenoid bone

•Has two functional lobes

•Anterior pituitary—glandular tissue

•Posterior pituitary—nervous tissue

•Often called the “master endocrine gland”

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Hormones of the Anterior Pituitary

•Six anterior pituitary hormones

•Two affect non-endocrine targets

•Growth hormone

•Prolactin

•Four stimulate other endocrine glands (tropic hormones)

•Thyroid-stimulating hormone (thyrotropic hormone)

•Adrenocorticotropic hormone

•Two gonadotropic hormones



•Characteristics of all anterior pituitary hormones

•Proteins (or peptides)

•Act through second-messenger systems

•Regulated by hormonal stimuli, mostly negative feedback

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Releasing hormonessecreted into portalcirculation

Anterior pituitary

Hypophysealportal system

Growth hormone (GH)

Bones and muscles Prolactin (PRL)

Mammaryglands

Follicle-stimulatinghormone (FSH)and luteinizinghormone (LH)

Posterior pituitary

Hypothalamus

Adrenocorticotropichormone (ACTH)

Adrenal cortexThyrotropichormone (TH)

Thyroid

Testes or ovaries

HypothalamusHypothalamus



•Growth hormone

•General metabolic hormone

•Major effects are directed to growth of skeletal muscles and long bones

•Plays a role in determining final body size

•Causes amino acids to be built into proteins

•Causes fats to be broken down for a source of energy

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•Growth hormone (GH) disorders

•Pituitary dwarfism results from hyposecretion of GH during childhood

•Gigantism results from hypersecretion of GH during childhood

•Acromegaly results from hypersecretion of GH during adulthood


Pituitary dwarf (left), Giant (center), Normal height woman (right)

Figure 9.5

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•Prolactin (PRL)

•Stimulates and maintains milk production following childbirth

•Function in males is unknown

•Adrenocorticotropic hormone (ACTH)

•Regulates endocrine activity of the adrenal cortex

•Thyroid-stimulating hormone (TSH)

• Influences growth and activity of the thyroid gland



•Gonadotropic hormones

•Regulate hormonal activity of the gonads

•Follicle-stimulating hormone (FSH)

•Stimulates follicle development in ovaries

•Stimulates sperm development in testes

•Luteinizing hormone (LH)

•Triggers ovulation of an egg in females

•Stimulates testosterone production in males

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Pituitary–Hypothalamus Relationship

•Hormonal release is regulated by releasing and inhibiting hormones produced by the hypothalamus

•Hypothalamus produces two hormones•These hormones are transported to neurosecretory cells of the posterior pituitary•Oxytocin•Antidiuretic hormone

•The posterior pituitary is not strictly an endocrine gland, but does release hormones


Hormones of the Posterior Pituitary

•Oxytocin

•Stimulates contractions of the uterus during labor, sexual relations, and breastfeeding

•Causes milk ejection in a nursing woman

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Hormones of the Posterior Pituitary

•Antidiuretic hormone (ADH)

• Inhibits urine production by promoting water reabsorption by the kidneys

• In large amounts, causes vasoconstriction leading to increased blood pressure

•Also known as vasopressin


Opticchiasma

Axon terminals

Anterior lobeof the pituitary

ADH

Kidney tubules

Hypothalamicneurosecretorycells

Hypothalamus

Arterial blood supply

Posterior lobe

Capillary bed

Venous drainage

Oxytocin

Mammary glandsUterine muscles

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Thyroid Gland

•Found at the base of the throat

•Consists of two lobes and a connecting isthmus

•Produces two hormones

•Thyroid hormone

•Calcitonin


Thyroid cartilage

Common carotidartery

Trachea

Brachiocephalic artery

Aorta

(a) Gross anatomy of the thyroid gland, anterior view

Epiglottis

Isthmus ofthyroid gland

Left subclavianarteryLeft lobe of thyroid gland

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Thyroid Gland

•Thyroid hormone

•Major metabolic hormone

•Composed of two active iodine-containing hormones

•Thyroxine (T4)—secreted by thyroid follicles

•Triiodothyronine (T3)—conversion of T4 at target tissues


Colloid-filledfollicles Follicle cells

Parafollicular cell

(b) Photomicrograph of thyroid glandfollicles (125×)

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Thyroid Gland

•Thyroid hormone disorders•Goiters

•Thyroid gland enlarges due to lack of iodine

•Salt is iodized to prevent goiters•Cretinism

•Caused by hyposecretion of thyroxine•Results in dwarfism during childhood


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Thyroid Gland

•Thyroid hormone disorders (continued)

•Myxedema

•Caused by hypothyroidism in adults

•Results in physical and mental slugishness

•Graves’ disease

•Caused by hyperthyroidism

•Results in increased metabolism, heat intolerance, rapid heartbeat, weight loss, and exophthalmos


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Thyroid Gland

•Calcitonin

•Decreases blood calcium levels by causing its deposition on bone

•Antagonistic to parathyroid hormone

•Produced by parafollicular cells

•Parafollicular cells are found between the follicles


Colloid-filledfollicles Follicle cells

Parafollicular cell

(b) Photomicrograph of thyroid glandfollicles (125×)

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Parathyroid Glands

•Tiny masses on the posterior of the thyroid

•Secrete parathyroid hormone (PTH)

•Stimulate osteoclasts to remove calcium from bone

•Stimulate the kidneys and intestine to absorb more calcium

•Raise calcium levels in the blood


Calcitonin

Thyroid glandreleases calcitonin.

StimulusRising bloodCa2+ levels

Calcium homeostasis of blood: 9–11 mg/100 ml

Osteoclastsdegrade bonematrix andrelease Ca2+

into blood.

BALANCE

Calcitoninstimulatescalcium saltdeposit in bone.

StimulusFalling bloodCa2+ levels

BALANCE

Parathyroidglands releaseparathyroidhormone (PTH).

Thyroidgland

Parathyroidglands

PTH

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Adrenal Glands

•Sit on top of the kidneys

•Two regions

•Adrenal cortex—outer glandular region has three layers

•Mineralocorticoids secreted by outermost layer

•Glucocorticoids secreted by middle layer

•Sex hormones secreted by innermost layer

•Adrenal medulla—inner neural tissue region


Adrenal gland

Kidney

Adrenal gland• Medulla

Kidney

Med

ulla

Co

rte

x

CapsuleMineralocorticoid-secreting area

Glucocorticoid-secreting area

Sex hormonesecreting area

Adrenalmedulla

Adrenalcortex

• Cortex

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Hormones of the Adrenal Cortex

•Mineralocorticoids (mainly aldosterone)

•Produced in outer adrenal cortex

•Regulate mineral content in blood

•Regulate water and electrolyte balance

•Target organ is the kidney

•Production stimulated by renin and aldosterone

•Production inhibited by atrial natriuretic peptide (ANP)


Decreased Na+ orincreased K+ in blood

Decreasedblood volumeand/or bloodpressure

Kidney

ReninIndirectstimulatingeffect viaangiotensin

Angiotensin II

Directstimulatingeffect

Increased absorptionof Na+ and water;increased K+ excretion

Increased bloodvolume andblood pressure

Enhanced secretion of aldosterone targets kidney tubules

Mineralocorticoid-producing part of adrenal cortex

Inhibitoryeffect

Atrial natriureticpeptide (ANP)

ACTH

Heart

Increasedblood pressureor blood volume

Anterior pituitary

Corticotropin-releasing hormone

Hypothalamus

Stress

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•Glucocorticoids (including cortisone and cortisol)

•Produced in the middle layer of the adrenal cortex

•Promote normal cell metabolism

•Help resist long-term stressors

•Released in response to increased blood levels of ACTH


Short term

Spinal cord

Catecholamines(epinephrine and norepinephrine)

Adrenalmedulla

1. Increased heart rate2. Increased blood pressure3. Liver converts glycogen

to glucose and releasesglucose to blood

4. Dilation of bronchioles5. Changes in blood flow

patterns, leading toincreased alertness anddecreased digestive andkidney activity

6. Increased metabolic rate

1. Retention of sodium and water by kidneys

2. Increased bloodvolume and bloodpressure

1. Proteins and fatsconverted toglucose or brokendown for energy

2. Increased bloodsugar

3. Suppression of immune system

Short-term stress response Long-term stress response

Preganglionicsympatheticfibers

Nerve impulses

Hypothalamus

More prolongedStress

Releasing hormones

Corticotropic cells ofanterior pituitary

ACTH Adrenalcortex

Mineralocorticoids Glucocorticoids

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•Sex hormones

•Produced in the inner layer of the adrenal cortex

•Small amounts are made throughout life

•Mostly androgens (male sex hormones) are made but some estrogens (female sex hormones) are also formed


Adrenal Glands

•Adrenal cortex disorders

•Addison’s disease

•Results from hyposecretion of all adrenal cortex hormones

•Bronze skin tone, muscles are weak, burnout, susceptibility to infection

•Hyperaldosteronism

•May result from an ACTH-releasing tumor

•Excess water and sodium are retained leading to high blood pressure and edema

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Adrenal Glands

•Adrenal cortex disorders

•Cushing’s syndrome

•Results from a tumor in the middle cortical area of the adrenal cortex

• “Moon face,” “buffalo hump” on the upper back, high blood pressure, hyperglycemia, weakening of bones, depression

•Masculinization

•Results from hypersecretion of sex hormones

•Beard and male distribution of hair growth


Hormones of the Adrenal Medulla

•Produces two similar hormones (catecholamines)

•Epinephrine (adrenaline)

•Norepinephrine (noradrenaline)

•These hormones prepare the body to deal with short-term stress (“fight or flight”) by

• Increasing heart rate, blood pressure, blood glucose levels

•Dilating small passageways of lungs

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Adrenal gland

Kidney

Adrenal gland• Medulla

Kidney

Med

ulla

Co

rte

x

CapsuleMineralocorticoid-secreting area

Glucocorticoid-secreting area

Sex hormonesecreting area

Adrenalmedulla

Adrenalcortex

• Cortex


Pancreatic Islets

•The pancreas is a mixed gland and has both endocrine and exocrine functions

•The pancreatic islets produce hormones

• Insulin—allows glucose to cross plasma membranes into cells from beta cells

•Glucagon—allows glucose to enter the blood from alpha cells

•These hormones are antagonists that maintain blood sugar homeostasis

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Stomach

Pancreas(a)


(b)

Pancreaticislets

Exocrinecells ofpancreas

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© 2012 Pearson Education, Inc. Figure 9.14c

Capillaries

Exocrinecells ofpancreas

Cord of beta (β) cells secretinginsulin into capillaries

Alpha (α)cells

(c)


Uptake of glucosefrom blood isenhanced in mostbody cells

Tissue cells

Glucose GlycogenPancreas

InsulinInsulin-secreting cellsof the pancreasactivated; releaseinsulin into the blood

Elevated bloodsugar level

StimulusBlood

glucose level(e.g., aftereating fourjelly doughnuts)

Blood glucose risesto homeostaticset point; stimulusfor glucagonrelease diminishes

Liver breaksdown glycogenstores andreleasesglucose to theblood

Glucose Glycogen

LiverGlucagon

Glucagon-releasingcells of pancreasactivated; releaseglucagon into blood

Low blood sugar level

StimulusBlood glucose

level (e.g., afterskipping a meal)

Liver takes upglucose and storesas glycogen

Blood glucosefalls to homeostaticset point; stimulusfor insulin releasediminishes

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Pineal Gland

•Found on the third ventricle of the brain

•Secretes melatonin

•Helps establish the body’s wake and sleep cycles

•Believed to coordinate the hormones of fertility in humans


Pineal gland


Thyroid gland

Parathyroid glands

Thymus

Adrenal glands

Pancreas

Ovary (female)

Testis (male)

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Thymus Gland

•Located posterior to the sternum

•Largest in infants and children

•Produces thymosin

•Matures some types of white blood cells

• Important in developing the immune system


Gonads

•Ovaries

•Produce eggs

•Produce two groups of steroid hormone

•Estrogens

•Progesterone

•Testes

•Produce sperm

•Produce androgens, such as testosterone

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Pineal gland


Thyroid gland

Parathyroid glands

Thymus

Adrenal glands

Pancreas

Ovary (female)

Testis (male)


Hormones of the Ovaries

•Estrogens

•Stimulate the development of secondary female characteristics

•Mature female reproductive organs

•With progesterone, estrogens also

•Promote breast development

•Regulate menstrual cycle

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Hormones of the Ovaries

•Progesterone

•Acts with estrogen to bring about the menstrual cycle

•Helps in the implantation of an embryo in the uterus

•Helps prepare breasts for lactation


Menstrual cycle

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Hormones of the Testes

•Produce several androgens

•Testosterone is the most important androgen

•Responsible for adult male secondary sex characteristics

•Promotes growth and maturation of male reproductive system

•Required for sperm cell production


Other Hormone-Producing Tissues and Organs

•Parts of the small intestine

•Parts of the stomach

•Kidneys

•Heart

•Many other areas have scattered endocrine cells

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Endocrine Function of the Placenta

•Produces hormones that maintain the pregnancy

•Some hormones play a part in the delivery of the baby

•Produces human chorionic gonadotropin (hCG) in addition to estrogen, progesterone, and other hormones


•Most endocrine organs operate smoothly until old age•Menopause is brought about by lack of efficiency of the ovaries

•Problems associated with reduced estrogen are common

•Growth hormone production declines with age

•Many endocrine glands decrease output with age

Developmental Aspects of the Endocrine System

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