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Principles of Human Anatomy and Physiology, 11e 1

Chapter 18

The Endocrine System

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Chapter 18

The Endocrine System

• The nervous and endocrine systems act as a coordinated interlocking supersystem, the neuroendocrine system.

• The endocrine system controls body activities by releasing mediator molecules called hormones.

– hormones released into the bloodstream travel throughout the body

– results may take hours, but last longer

• The nervous system controls body actions through nerve impulses.

– certain parts release hormones into blood

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Principles of Human Anatomy and Physiology, 11e 3

NERVOUS and ENDOCRINE SYSTEM

• The nervous system causes muscles to contract or glands to secrete. The endocrine system affects virtually all body tissues by altering metabolism, regulating growth and

development, and influencing reproductive processes.

• Parts of the nervous system stimulate or inhibit the release of hormones.

• Hormones may promote or inhibit the generation of nerve impulses.

(4)

General Functions of Hormones

• Help regulate:

– extracellular fluid – metabolism

– biological clock

– contraction of cardiac & smooth muscle

– glandular secretion

– some immune functions • Growth & development

• Reproduction

• Hormones have powerful effects when present in very low

(5)

Principles of Human Anatomy and Physiology, 11e 5

Endocrine Glands Defined

• Exocrine glands

– secrete products into ducts which empty into body cavities or body surface

– sweat, oil, mucous, & digestive glands • Endocrine glands

– secrete products (hormones) into bloodstream – pituitary, thyroid, parathyroid, adrenal, pineal

– other organs secrete hormones as a 2nd function – hypothalamus, thymus, pancreas,ovaries,testes,

(6)

Hormone Receptors

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Principles of Human Anatomy and Physiology, 11e 7

Hormone Receptors

• Although hormones travel in blood throughout the body, they affect only specific target cells.

– Target cells have specific protein or glycoprotein receptors to which hormones bind.

• Receptors are constantly being synthesized and broken down.

• Synthetic hormones that block the receptors for particular naturally occurring hormones are available as drugs.

(8)

Regulation of Hormone Receptors

• Receptors are constantly being synthesized & broken down

– range of 2000-100,000 receptors / target cell

• Down-regulation

– excess hormone leads to a decrease in number of receptors

• receptors undergo endocytosis and are degraded – decreases sensitivity of target cell to hormone

• Up-regulation

– deficiency of hormone leads to an increase in the number of receptors

(9)

Principles of Human Anatomy and Physiology, 11e 9

Blocking Hormone Receptors

• Synthetic drugs may block receptors for naturally occurring hormones

– Normally, progesterone levels drop once/month leading to menstruation. Progesterone levels are maintained when a woman becomes pregnant. – RU486 (mifepristone) binds to the receptors for

progesterone preventing progesterone from

sustaining the endometrium in a pregnant woman • brings on menstrual cycle

(10)

Circulating and Local Hormones

• Hormones that travel in blood and act on distant target cells are called circulating hormones or endocrines.

• Hormones that act locally without first entering the blood stream are called local hormones.

– Those that act on neighboring cells are called paracrines. – Those that act on the same cell that secreted them are

termed autocrines.

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Principles of Human Anatomy and Physiology, 11e 11

Circulating & Local Hormones

• Circulating hormones

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Chemical Classes of Hormones - Overview

• Table 18.2 provides a summary of the hormones. • Lipid-soluble hormones include the steroids, thyroid

hormones, and nitric oxide, which acts as a local hormone in several tissues.

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Principles of Human Anatomy and Physiology, 11e 13

Lipid-soluble Hormones

• Steroids

– lipids derived from cholesterol on SER

– different functional groups attached to core of structure provide uniqueness

• Thyroid hormones

(14)

Water-soluble Hormones

• Amine, peptide and protein hormones

– modified amino acids or amino acids put together – serotonin, melatonin,

histamine, epinephrine – some glycoproteins

• Eicosanoids

– derived from arachidonic acid (fatty acid)

(15)

Principles of Human Anatomy and Physiology, 11e 15

Hormone Transport in Blood

• Protein hormones circulate in free form in blood

• Steroid (lipid) & thyroid hormones must attach to transport proteins synthesized by liver

– improve transport by making them water-soluble – slow loss of hormone by filtration within kidney – create reserve of hormone

(16)

General Mechanisms of Hormone Action

• Hormone binds to cell surface or receptor inside target cell • Cell may then

– synthesize new molecules

– change permeability of membrane – alter rates of reactions

• Each target cell responds to hormone differently

At liver cells---insulin stimulates glycogen synthesis

(17)

Principles of Human Anatomy and Physiology, 11e 17

Action of Lipid-Soluble Hormone

Lipid-soluble hormones bind to and activate receptors within cells.

– The activated receptors then alter gene expression which results in the formation of new proteins.

– The new proteins alter the cells activity and result in the physiological responses of those hormones.

(18)

Action of Lipid-Soluble Hormones

• Hormone diffuses through

phospholipid bilayer & into cell • Binds to receptor turning on/off

specific genes

• New mRNA is formed & directs synthesis of new proteins

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Principles of Human Anatomy and Physiology, 11e 19

Action of Water-Soluble Hormones

Water-soluble hormones alter cell functions by activating plasma membrane receptors, which set off a cascade of events inside the cell.

– The water-soluble hormone that binds to the cell membrane receptor is the first messenger.

– A second messenger is released inside the cell where hormone stimulated response takes place.

• A typical mechanism of action of a water-soluble hormone using cyclic AMP as the second messenger is seen in

(20)

Action of Water-Soluble Hormones

• The hormone binds to the membrane receptor.

• The activated receptor activates a membrane G-protein

which turns on adenylate cyclase.

• Adenylate cyclase converts ATP into cyclic AMP which activates protein kinases.

Protein kinases phosphorylate enzymes which catalyze reactions that produce the physiological response.

(21)

Principles of Human Anatomy and Physiology, 11e 21

Action of Water-Soluble Hormones

• Can not diffuse through plasma membrane

• Hormone receptors are integral membrane proteins

– act as first messenger • The hormone binds to the

membrane receptor.

• The activated receptor activates a

membrane G-protein which turns on

adenylate cyclase.

• Adenylate cyclase converts ATP into cyclic AMP which activates protein kinases.

Protein kinases phosphorylate

enzymes which catalyze reactions that produce the physiological

(22)

Water-soluble Hormones

• Cyclic AMP is the 2nd messenger

– kinases in the cytosol speed up/slow down physiological

responses

• Phosphodiesterase

inactivates cAMP quickly • Cell response is turned

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Principles of Human Anatomy and Physiology, 11e 23

Second Messengers

• Some hormones exert their influence by increasing the synthesis of cAMP

– ADH, TSH, ACTH, glucagon and epinephrine

• Some exert their influence by decreasing the level of cAMP – growth hormone inhibiting hormone

• Other substances can act as 2nd messengers – calcium ions

– cGMP

(24)

Amplification of Hormone Effects

• Single molecule of hormone binds to receptor • Activates 100 G-proteins

• Each activates an adenylate cyclase molecule which then produces 1000 cAMP

• Each cAMP activates a protein kinase, which may act upon 1000’s of substrate molecules

• One molecule of epinephrine may result in

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Principles of Human Anatomy and Physiology, 11e 25

Cholera Toxin and G Proteins

• Toxin is deadly because it produces massive watery diarrhea and person dies from dehydration

• Toxin of cholera bacteria causes G-protein to lock in activated state in intestinal epithelium

• Cyclic AMP causes intestinal cells to actively transport chloride (Na+ and water follow) into the lumen

(26)

Hormonal Interactions

• The responsiveness of a target cell to a hormone depends on the hormone’s concentration, the abundance of the

target cell’s hormone receptors, and influences exerted by other hormones.

• Three hormonal interactions are the – permissive effect

synergistic effect

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Principles of Human Anatomy and Physiology, 11e 27

Hormonal Interactions

• Permissive effect

– a second hormone, strengthens the effects of the first – thyroid strengthens epinephrine’s effect upon lipolysis • Synergistic effect

– two hormones acting together for greater effect

– estrogen & LH are both needed for oocyte production • Antagonistic effects

– two hormones with opposite effects

(28)

Control of Hormone Secretion

• Regulated by signals from nervous system, chemical changes in the blood or by other hormones

• Negative feedback control (most common)

– decrease/increase in blood level is reversed • Positive feedback control

– the change produced by the hormone causes more hormone to be released

(29)

Principles of Human Anatomy and Physiology, 11e 29

HYPOTHALAMUS AND PITUITARY GLAND

• The hypothalamus is the major integrating link between the nervous and endocrine systems.

– Hypothalamus receives input from cortex, thalamus, limbic system & internal organs

– Hypothalamus controls pituitary gland with 9 different releasing & inhibiting hormones

(30)

• The pituitary gland is located in the sella turcica of the sphenoid

bone and is differentiated into the anterior pituitary

(adenohypophysis), the posterior pituitary (neurohypophysis), and pars intermedia (avascular zone in between (Figures 18.5 and 18.21b).

• Pea-shaped, 1/2 inch gland found in sella turcica of sphenoid – Infundibulum attaches it to brain

• Anterior lobe = 75%

– develops from roof of mouth • Posterior lobe = 25%

– ends of axons of 10,000 neurons found in hypothalamus – neuroglial cells called pituicytes

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Principles of Human Anatomy and Physiology, 11e 31

Anterior Pituitary Gland (Adenohypophysis)

• The blood supply to the anterior pituitary is from the superior hypophyseal arteries.

• Hormones of the anterior pituitary and the cells that produce the:

– Human growth hormone (hGH) is secreted by somatotrophs. – Thyroid-stimulating hormone (TSH) is secreted by thyrotrophs.

– Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are secreted by gonadotrophs.

– Prolactin (PRL) is secreted by lactrotrophs.

(32)

Flow of Blood to

Anterior Pituitary

• Controlling hormones enter blood • Travel through portal veins

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Principles of Human Anatomy and Physiology, 11e 33

(34)

Feedback

• Secretion of anterior pituitary gland hormones is regulated by hypothalamic regulating hormones and by negative

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Principles of Human Anatomy and Physiology, 11e 35

Negative Feedback Systems

• Decrease in blood levels • Receptors in

hypothalamus & thyroid • Cells activated to secrete

more TSH or more T3 & T4

(36)

Positive Feedback

• Oxytocin stimulates uterine contractions • Uterine contractions stimulate oxytocin

(37)

Principles of Human Anatomy and Physiology, 11e 37

Human Growth Hormone and

Insulin-like Growth Factors

Human growth hormone (hGH) is the most plentiful anterior pituitary hormone.

• It acts indirectly on tissues by promoting the synthesis and secretion of small protein hormones called insulin-like

growth factors (IGFs).

– IGFs stimulate general body growth and regulate various aspects of metabolism.

– Various stimuli promote and inhibit hGH production (Figure 18.7).

(38)

Human Growth Hormone

• Produced by somatotrophs

• target cells synthesize insulinlike growth

– common target cells are liver, skeletal muscle, cartilage and bone

– increases cell growth & cell division by increasing their uptake of amino acids & synthesis of

proteins

– stimulate lipolysis in adipose so fatty acids used for ATP

(39)

Principles of Human Anatomy and Physiology, 11e 39

Regulation of hGH

• Low blood sugar stimulates release of GHRH from

hypothalamus

– anterior pituitary releases more hGH, more glycogen broken down into glucose by liver cells • High blood sugar stimulates

release of GHIH from hypothalamus

– less hGH from anterior

(40)

Diabetogenic Effect of Human Growth Hormone

• Excess of growth hormone

– raises blood glucose concentration – pancreas releases insulin continually – beta-cell burnout

• Diabetogenic effect

(41)

Principles of Human Anatomy and Physiology, 11e 41

Thyroid Stimulating Hormone (TSH)

• Hypothalamus regulates thyrotroph cells • Thyrotroph cells produce TSH

(42)

Follicle Stimulating Hormone (FSH)

• Releasing hormone from

hypothalamus controls gonadotrophs

• Gonadotrophs release follicle stimulating hormone

• FSH functions

– initiates the formation of follicles within the ovary – stimulates follicle cells to

secrete estrogen

(43)

Principles of Human Anatomy and Physiology, 11e 43

Luteinizing Hormone (LH)

• Releasing hormones from hypothalamus stimulate gonadotrophs

• Gonadotrophs produce LH • In females, LH stimulates

– secretion of estrogen

– ovulation of 2nd oocyte from ovary – formation of corpus luteum

– secretion of progesterone

(44)

Prolactin (PRL)

Prolactin (PRL), together with other hormones, initiates and maintains milk secretion by the mammary glands.

– Hypothalamus regulates lactotroph cells

– Lactotrophs produce prolactin

– Under right conditions, prolactin causes milk production

• Suckling reduces levels of

(45)

Principles of Human Anatomy and Physiology, 11e 45

Adrenocorticotrophic Hormone

Adrenocorticotrophic hormone

(ACTH) controls the production and secretion of hormones called

glucocorticoids by the cortex of the adrenal gland.

– Hypothalamus releasing hormones stimulate

corticotrophs

– Corticotrophs secrete ACTH & MSH

(46)

Melanocyte-Stimulating Hormone

Melanocyte-stimulating hormone (MSH) increases skin pigmentation although its exact role in humans is

unknown.

– Releasing hormone from hypothalamus increases MSH release from the anterior pituitary

– Secreted by corticotroph cells

(47)

Principles of Human Anatomy and Physiology, 11e 47

Posterior Pituitary Gland (Neurohypophysis)

• Although the posterior pituitary gland does not synthesize hormones, it does store and release two hormones.

– Hormones made by the hypothalamus and stored in the posterior pituitary are oxytocin (OT) and antidiuretic

hormone (ADH).

(48)

Posterior Pituitary Gland (Neurohypophysis)

• Does not synthesize hormones

• Consists of axon terminals of hypothalamic neurons • Neurons release two

neurotransmitters into capillaries

(49)

Principles of Human Anatomy and Physiology, 11e 49

Oxytocin

• Two target tissues both involved in neuroendocrine reflexes

• During delivery

– baby’s head stretches cervix

– hormone release enhances uterine muscle contraction

– baby & placenta are delivered • After delivery

Oxytocin stimulates contraction of the

uterus and ejection (let-down) of milk from the breasts.

• Nursing a baby after delivery

stimulates oxytocin release, promoting uterine contractions and the expulsion of the placenta (Clinical Application). • suckling & hearing baby’s cry

(50)

Oxytocin during Labor

• Stimulation of uterus by baby

• Hormone release from posterior pituitary • Uterine smooth muscle contracts until birth

of baby

• Baby pushed into cervix, increase hormone release

• More muscle contraction occurs

(51)

Principles of Human Anatomy and Physiology, 11e 51

ADH

Antidiuretic hormone stimulates water reabsorption by the kidneys and arteriolar constriction.

• The effect of ADH is to decrease urine volume and conserve body water.

(52)

Antidiuretic Hormone (ADH)

• Known as vasopressin • Functions

– decrease urine production – decrease sweating

(53)

Principles of Human Anatomy and Physiology, 11e 53

Regulation of ADH

• Dehydration

– ADH released • Overhydration

(54)

THYROID GLAND - Overview

• The thyroid gland is located just below the larynx and has right and left lateral lobes (Figure 18.10a).

• Histologically, the thyroid consists of the thyroid follicles composed of follicular cells, which secrete the thyroid hormones thyroxine (T4) and triiodothyronine (T3), and

(55)

Principles of Human Anatomy and Physiology, 11e 55

Thyroid Gland

(56)

Histology of Thyroid Gland

• Follicle = sac of stored

hormone (colloid) surrounded by follicle cells that produced it

– T3 & T4

• Inactive cells are short • In between cells called

parafollicular cells

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Principles of Human Anatomy and Physiology, 11e 57

(58)

Formation, Storage, and Release of Thyroid Hormones

• Thyroid hormones are synthesized from iodine and tyrosine within a large glycoprotein molecule called thyroglobulin

(TGB) and are transported in the blood by plasma proteins, mostly thyroxine-binding globulin (TBG).

• The formation, storage, and release steps include – iodide trapping,

– synthesis of thyroglobulin, – oxidation of iodide,

– iodination of tyrosine, – coupling of T1 and T2,

– pinocytosis and digestion of colloid,

(59)

Principles of Human Anatomy and Physiology, 11e 59

Formation of Thyroid Hormone

• Iodide trapping by follicular cells • Synthesis of thyroglobulin (TGB) • Release of TGB into colloid

• Iodination of tyrosine in colloid

• Formation of T3 & T4 by combining T1 and T2 together

• Uptake & digestion of TGB by follicle cells

(60)

Actions of Hormones from

Thyroid Gland

• T3 & T4

– thyroid hormones responsible for our

metabolic rate, synthesis of protein, breakdown of fats, use of glucose for ATP production

• Calcitonin

– responsible for building of bone & stops reabsorption of bone (lowers blood

(61)

Principles of Human Anatomy and Physiology, 11e 61

Control of T3 & T4 Secretion

• Negative feedback system

• Low blood levels of hormones stimulate hypothalamus

• It stimulates pituitary to release TSH

(62)

PARATHYROID GLANDS

• The parathyroid glands are embedded on the posterior surfaces of the lateral lobes of the thyroid

principal cells produce parathyroid hormone

oxyphil cells … function is unknown (Figure 18.13).

Parathyroid hormone (PTH) regulates the homeostasis of calcium and phosphate

• increase blood calcium level

• decrease blood phosphate level

– increases the number and activity of osteoclasts

– increases the rate of Ca+2 and Mg+2 from reabsorption

from urine and inhibits the reabsorption of HPO4-2 so

more is secreted in the urine

(63)

Principles of Human Anatomy and Physiology, 11e 63

Parathyroid

Glands

(64)

Histology of Parathyroid Gland

• Principal cells produce parathyroid hormone (PTH)

(65)

Principles of Human Anatomy and Physiology, 11e 65

Blood Calcium

• Blood calcium level directly controls the secretion of

calcitonin and parathyroid hormone via negative feedback loops that do not involve the pituitary gland (Figure 18.14). • Table 18.7 summarizes the principal actions and control of

(66)

Regulation of Calcium Blood Levels

(67)

Principles of Human Anatomy and Physiology, 11e 67

Adrenal Glands

• The adrenal glands are located superior to the kidneys (Figure

18.15)

• 3 x 3 x 1 cm in size and weighs 5 grams

• consists of an outer cortex and an inner medulla.

– Cortex produces 3 different types of hormones from 3 zones of cortex

(68)

Adrenal Cortex

• The adrenal cortex is divided into three zones, each of which secretes different hormones (Figure 18.15).

– The zona glomerulosa (outer zone) • secretes mineralocorticoids.

– The zona fasciculata (middle zone) • secretes glucocorticoids.

(69)

Principles of Human Anatomy and Physiology, 11e 69

Histology of

Adrenal

Gland

• Cortex

(70)
(71)

Principles of Human Anatomy and Physiology, 11e 71

Mineralocorticoids

• 95% of hormonal activity due to aldosterone • Functions

– increase reabsorption of Na+ with Cl- , bicarbonate and water following it

– promotes excretion of K+ and H+

• Hypersecretion = tumor producing aldosteronism

(72)
(73)

Principles of Human Anatomy and Physiology, 11e 73

Glucocorticoids

• 95% of hormonal activity is due to cortisol • Functions = help regulate metabolism

– increase rate of protein catabolism & lipolysis – conversion of amino acids to glucose

– stimulate lipolysis

– provide resistance to stress by making nutrients available for ATP production

– raise BP by vasoconstriction

– anti-inflammatory effects reduced (skin cream) • reduce release of histamine from mast cells • decrease capillary permeability

(74)

Regulation of

Glucocorticoids

(75)

Principles of Human Anatomy and Physiology, 11e 75

Androgens from Zona Reticularis

• Small amount of male hormone produced – insignificant in males

– may contribute to sex drive in females

(76)

Adrenal Medulla

• Chromaffin cells receive direct innervation from sympathetic nervous system

– develop from same tissue as postganglionic neurons

• Produce epinephrine & norepinephrine • Hormones are sympathomimetic

– effects mimic those of sympathetic NS – cause fight-flight behavior

(77)

Principles of Human Anatomy and Physiology, 11e 77

PANCREATIC ISLETS

• The pancreas is a flattened organ located posterior and

slightly inferior to the stomach and can be classified as both an endocrine and an exocrine gland (Figure 18.18).

(78)

Anatomy of Pancreas

• Organ (5 inches) consists of head, body & tail • Cells (99%) in acini produce digestive enzymes

(79)

Principles of Human Anatomy and Physiology, 11e 79

Cell Organization in Pancreas

(80)

Histology of the Pancreas

(81)

Principles of Human Anatomy and Physiology, 11e 81

Cell Types in the Pancreatic Islets

• Alpha cells (20%) produce glucagon • Beta cells (70%) produce insulin

(82)

Regulation

• Regulation of glucagon and insulin secretion is via

negative feedback

mechanisms (Figure 18.19). – Low blood glucose

stimulates release of glucagon

– High blood glucose

stimulates secretion of insulin

(83)

Principles of Human Anatomy and Physiology, 11e 83

Ovaries and Testes

• Ovaries

– estrogen, progesterone, relaxin & inhibin

– regulate reproductive cycle, maintain pregnancy & prepare mammary glands for lactation

• Testes

– produce testosterone

– regulate sperm production & 2nd sexual characteristics

(84)

Pineal Gland

• Small gland attached to 3rd ventricle of brain • Consists of pinealocytes & neuroglia

(85)

Principles of Human Anatomy and Physiology, 11e 85

Effect of Light on Pineal Gland

• Melatonin secretion producing sleepiness occurs during

(86)

Seasonal Affective Disorder and Jet Lag

• Depression that occurs during winter months when day length is short

• Due to overproduction of melatonin • Therapy

– exposure to several hours per day of artificial light as bright as sunlight

(87)

Principles of Human Anatomy and Physiology, 11e 87

Thymus Gland

• Important role in maturation of T cells

• Hormones produced by gland promote the proliferation & maturation of T cells

– thymosin

– thymic humoral factor – thymic factor

(88)

OTHER HORMONES and GROWTH FACTORS

• Several body tissues other than those usually classified as endocrine glands also contain endocrine tissue and thus secrete hormones.

(89)

Principles of Human Anatomy and Physiology, 11e 89

Eicosanoids

• Local hormones released by all body cells

• alter the production of second messengers, such as cyclic AMP

– Leukotrienes influence WBCs & inflammation – Prostaglandins alter:

• smooth muscle contraction, glandular secretion, blood flow, platelet function, nerve transmission, metabolism.

• Aspirin and related nonsteroidal anti-inflammatory drugs (NSAIDS), such as ibuprofen and

acetaminophen, inhibit a key enzyme in

(90)

Nonsteroidal Anti-inflammatory Drugs

• Answer to how aspirin or ibuprofen works was discovered in 1971

– inhibit a key enzyme in prostaglandin synthesis without affecting the synthesis of leukotrienes • Treat a variety of inflammatory disorders

– rheumatoid arthritis

(91)

Principles of Human Anatomy and Physiology, 11e 91

Growth Factors

• Substances with mitogenic qualities – cause cell growth from cell division

• Many act locally as autocrines or paracrines • Selected list of growth factors (Table 18.12)

– epidermal growth factor (EGF),

– platelet-derived growth factor (PDGF), – fibroblast growth factor (FGF),

– nerve growth factor (NGF),

– tumor angiogenesis factors (TAFs), – Insulin-like growth factor (IFG),

(92)

STRESS RESPONSE

• The stimuli that produce the general adaptation syndrome are called stressors.

• Stressors include almost any disturbance: heat or cold, surgical operations, poisons, infections, fever, and strong emotional responses.

(93)

Principles of Human Anatomy and Physiology, 11e 93

Stress & General Adaptation Syndrome

• Stress response is set of bodily changes called general adaptation syndrome (GAS)

• Any stimulus that produces a stress response is called a stressor

• Stress resets the body to meet an emergency

– eustress is productive stress & helps us prepare for certain challenges

(94)

General

Adaptation

(95)

Principles of Human Anatomy and Physiology, 11e 95

Alarm Reaction (Fight-or-Flight)

• The alarm reaction is initiated by nerve impulses from the hypothalamus to the sympathetic division of the autonomic nervous system and adrenal medulla

(Figure 18.20a). • Dog attack

– increases circulation

– promote catabolism for energy production – promotes ATP synthesis

(96)

Resistance Reaction

• Initiated by hypothalamic releasing hormones (long-term reaction to stress)

– corticotropin, growth hormone & thyrotropin releasing hormones

• Results

– increased secretion of aldosterone acts to conserve Na+ (increases blood pressure) and eliminate H+

– increased secretion of cortisol so protein catabolism is increased & other sources of glucose are found

– increase thyroid hormone to increase metabolism • Allow body to continue to fight a stressor

(97)

Principles of Human Anatomy and Physiology, 11e 97

Exhaustion

• Exhaustion is caused mainly by loss of potassium, depletion of adrenal glucocorticoids, and weakened organs. If stress is too great, it may lead to death.

– Resources of the body have become depleted – Resistance stage can not be maintained

– Prolonged exposure to resistance reaction hormones

• wasting of muscle

• suppression of immune system • ulceration of the GI tract

(98)

Stress and Disease

• Stress can lead to disease by inhibiting the immune system

– gastritis, ulcerative colitis, irritable bowel

syndrome, peptic ulcers, hypertension, asthma, rheumatoid arthritis, migraine headaches, anxiety, and depression.

• people under stress are at a greater risk of developing chronic disease or of dying prematurely

• Interleukin - 1

– link between stress and immunity

– secreted by macrophages; stimulates secretion of ACTH

(99)

Principles of Human Anatomy and Physiology, 11e 99

DEVELOPMENTAL ANATOMY OF THE

ENDOCRINE SYSTEM

• The pituitary gland originates from two different regions of the ectoderm.

• The anterior pituitary derives from the neurohypophyseal bud, located on the floor of the hypothalamus (Figure

18.21).

• The anterior pituitary is derived from an outgrowth of

ectoderm from the mouth called the hypophyseal (Rathke’s)

pouch.

• The thyroid gland develops as a midventral outgrowth of endoderm, called the thyroid diverticulum, from the floor of the pharynx at the level of the second pair of pharyngeal pouches.

(100)

• Thyroid develops ---floor of pharynx 2nd pouch • Parathyroid & thymus --3 & 4 pharyngeal pouches

(101)

Principles of Human Anatomy and Physiology, 11e 101

Development of Pituitary Gland

(102)

DEVELOPMENTAL ANATOMY OF THE

ENDOCRINE SYSTEM

• The adrenal cortex is derived from intermediate mesoderm from the same region that produces the gonads. The

adrenal medulla is ectodermal in origin and derives from the neural crest, which also gives rise to sympathetic ganglion and other nervous system structures (Figure 14.125b).

• The pancreas develops from the outgrowth of endoderm from the part of the foregut that later becomes the

duodenum (Figure 29.12c).

• The pineal gland arises as an outgrowth between the

thalamus and colliculi from ectoderm associated with the diencephalon (Figure 14.26).

(103)

Principles of Human Anatomy and Physiology, 11e 103

Aging and the Endocrine System

• Production of human growth hormone decreases – muscle atrophy

• Production of TSH increase with age to try and stimulate thyroid

– decrease in metabolic rate, increase in body fat & hypothyroidism • Thymus after puberty is replaced with adipose

• Adrenal glands produce less cortisol & aldosterone • Receptor sensitivity to glucose declines

• Ovaries no longer respond to gonadotropins

(104)
(105)

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Diabetes Insipidus

• dysfunction of the posterior pituitary • Hyposecretion of ADH

(106)

Pituitary Gland Disorders

• Hyposecretion during childhood = pituitary dwarfism (proportional, childlike body)

• Hypersecretion during childhood = giantism – very tall, normal proportions

• Hypersecretion as adult = acromegaly

(107)

Principles of Human Anatomy and Physiology, 11e 107

Thyroid Gland Disorders

• Hyposecretion during infancy results in dwarfism & retardation called cretinism

• Hypothyroidism in adult produces sensitivity to cold, low body temp. weight gain & mental dullness

• Hyperthyroidism (Grave’s disease)

– weight loss, nervousness, tremor & exophthalmos (edema behind eyes)

(108)

Parathyroid Gland Disorders

• Hypoparathyroidism results in muscle tetany.

(109)

Principles of Human Anatomy and Physiology, 11e 109

Adrenal Gland Disorders - Tumor

(110)

Adrenal Gland Disorders - Cushing’s Syndrome

• Hypersecretion of glucocorticoids

(111)

Principles of Human Anatomy and Physiology, 11e 111

Adrenal Gland Disorders - Addison’s disease

• Hypersecretion of glucocorticoids

– hypoglycemia, muscle weakness, low BP, dehydration due to decreased Na+ in blood

(112)

Pancreatic Disorders

• Diabetes Mellitus

– This is a group of disorders caused by an inability to produce or use insulin.

• Type I diabetes or insulin-dependent diabetes mellitus is caused by an absolute deficiency of insulin.

• Type II diabetes or insulin-independent diabetes is caused by a down-regulation of insulin receptors. – excessive urine production (polyuria)

– excessive thirst (polydipsia) – excessive eating (polyphagia)

(113)

Principles of Human Anatomy and Physiology, 11e 113

(114)

Photographs for Review

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Principles of Human Anatomy and Physiology, 11e 115

Adrenal Cortex - Review

• Mineralocorticoids

Mineralocorticoids (e.g., aldosterone) increase sodium and water reabsorption and decrease potassium reabsorption, helping to regulate sodium and potassium levels in the body.

– Secretion is controlled by the renin-angiotensin pathway (Figure 18.16) and the blood level of potassium.

• Glucocorticoids

Glucocorticoids (e.g., cortisol) promote breakdown of proteins,

formation of glucose, lipolysis, resistance to stress, anti-inflammatory effects, and depression of the immune response.

– Secretion is controlled by CRH (corticotropin releasing hormone) and ACTH (adrenocorticotropic hormone) from the anterior pituitary

(Figure 18.17).

Androgens

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Adrenal Medulla - Review

• The adrenal medulla consists of hormone-producing cells, called chromaffin cells, which surround large blood-filled sinuses.

• Medullary secretions are epinephrine and norepinephrine

(NE), which produce effects similar to sympathetic responses.

• They are released under stress by direct innervation from the autonomic nervous system. Like the glucocorticoids of the adrenal cortex, these hormones help the body resist

stress. However, unlike the cortical hormones, the medullary hormones are not essential for life.

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Principles of Human Anatomy and Physiology, 11e 117

Review: Cell Types in the Pancreatic Islets

Alpha cells secrete the hormone glucagon which increases blood glucose levels.

Beta cells secrete the hormone insulin which decreases blood glucose levels.

Delta cells secrete growth hormone inhibiting hormone or

somatostatin, which acts as a paracrine to inhibit the secretion of insulin and glucagon.

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OVARIES AND TESTES - Review

Ovaries are located in the pelvic cavity and produce sex hormones (estrogens and progesterone) related to

development and maintenance of female sexual

characteristics, reproductive cycle, pregnancy, lactation, and normal reproductive functions. The ovaries also produce

inhibin and relaxin.

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Principles of Human Anatomy and Physiology, 11e 119

PINEAL GLAND - Review

• The pineal gland (epiphysis cerebri) is attached to the roof of the third ventricle, inside the brain (Figure 18.1).

• Histologically, it consists of secretory parenchymal cells called pinealocytes, neuroglia cells, and scattered

postganglionic sympathetic fibers. The pineal secrets

melatonin in a diurnal rhythm linked to the dark-light cycle. • Seasonal affective disorder (SAD), a type of depression that

arises during the winter months when day length is short, is thought to be due, in part, to over-production of melatonin. Bright light therapy, repeated doses of several hours

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THYMUS GLAND

• The thymus gland secretes several hormones related to immunity .

Thymosin, thymic humoral-factor, thymic factor, and

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