The Endocrine System Second controlling system of the body
Nervous system is the fast-control system Uses chemical messengers
(hormones) thatare 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 1 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
othercells 2 The Chemistry of Hormones
Hormones are classified chemically as Amino acidbased, which
includes Proteins Peptides Amines Steroidsmade from cholesterol
Prostaglandinsmade from highly active lipids 3 Mechanisms of
Hormone Action
Hormones affect only certain tissues or organs(target cells or
target organs) Target cells must have specific proteinreceptors
Hormone-binding alters cellular activity 4 Effects Caused by
Hormones
Changes in plasma membrane permeability orelectrical state
Synthesis of proteins, such as enzymes Activation or inactivation
of enzymes Stimulation of mitosis Promotion of secretory activity 5
The Chemistry of Hormones
Two mechanisms in which hormones act Direct gene activation
Second-messenger system 6 Direct Gene Activation (Steroid Hormone
Action)
Diffuse through the plasma membrane oftarget cells Enter the
nucleus Bind to a specific protein within the nucleus Bind to
specific sites on the cells DNA Activate genes that result in
synthesis of newproteins 7 Hormone- receptor complex
Cytoplasm Nucleus Steroid hormone Receptor protein 1 2 3 Hormone-
receptor complex 4 DNA mRNA 5 New protein Plasma membrane of target
cell 6 (a)Steroid hormone action Figure 9.1a 8 Cytoplasm Nucleus
Steroid hormone 1 Figure 9.1a, step 1 9 Nucleus Cytoplasm Steroid
hormone Receptor protein 1 2
Figure 9.1a, step 2 10 Hormone- receptor complex
Cytoplasm Nucleus Steroid hormone Receptor protein 1 2 3 Hormone-
receptor complex Figure 9.1a, step 3 11 Hormone- receptor
complex
Cytoplasm Nucleus Steroid hormone Receptor protein 1 2 3 Hormone-
receptor complex 4 DNA Figure 9.1a, step 4 12 Hormone- receptor
complex
Cytoplasm Nucleus Steroid hormone Receptor protein 1 2 3 Hormone-
receptor complex 4 DNA mRNA 5 Figure 9.1a, step 5 13 Hormone-
receptor complex
Cytoplasm Nucleus Steroid hormone Receptor protein 1 2 3 Hormone-
receptor complex 4 DNA mRNA 5 New protein Plasma membrane of target
cell 6 Figure 9.1a, step 6 14 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 anenzyme
Catalyzes a reaction that produces a second- messenger molecule
(such as cAMP) Oversees additional intracellular changes topromote
a specific response 15 Nonsteroid hormone (first messenger)
Cytoplasm
Enzyme ATP 1 3 2 Second messenger cAMP 4 Receptor protein Effect on
cellular function,such as glycogen breakdown Plasmamembrane of
target cell (b)Nonsteroid hormone action Figure 9.1b 16 Nonsteroid
hormone (first messenger) Cytoplasm
1 Receptor protein Figure 9.1b, step 1 17 Nonsteroid hormone (first
messenger) Cytoplasm
Enzyme 1 2 Receptor protein Figure 9.1b, step 2 18 Nonsteroid
hormone (first messenger) Cytoplasm
Enzyme ATP 1 3 2 Second messenger cAMP Receptor protein Figure
9.1b, step 3 19 Nonsteroid hormone (first messenger)
Cytoplasm
Enzyme ATP 1 3 2 Second messenger cAMP 4 Receptor protein Effect on
cellular function,such as glycogen breakdown Plasmamembrane of
target cell Figure 9.1b, step 4 20 Control of Hormone Release
Hormone levels in the blood are mostlymaintained by negative
feedback A stimulus or low hormone levels in the bloodtriggers the
release of more hormone Hormone release stops once an
appropriatelevel in the blood is reached like insulin &thyroid
hormones 21 Hormonal Stimuli of Endocrine Glands
Most common stimuli Endocrine glands are activated by otherhormones
Examples: Anterior pituitary hormones travel to targetglands, such
as the thyroid gland, to prompt therelease of a particular hormone,
such as thyroidhormone 22 (a) Hormonal stimulus 1 The hypothalamus
secretes hormones that
2 stimulate the anterior pituitarygland tosecrete hormones that
Anterior pituitary gland Thyroid gland Adrenal cortex Gonad
(Testis) stimulate other endocrineglands to secrete hormones 3
Figure 9.2a 23 Humoral Stimuli of Endocrine Glands
Changing blood levels of certain ions stimulatehormone release
Humoral indicates various body fluids such asblood and bile
Examples: Parathyroid hormone and calcitonin areproduced in
response to changing levels ofblood calcium levels Insulin is
produced in response to changinglevels of blood glucose levels 24
(b) Humoral stimulus 1 Capillary blood contains low concentration
of Ca2+, which stimulates Capillary (low Ca2+in blood) Thyroid
gland (posterior view) Parathyroid glands Parathyroid glands PTH 2
secretion of parathyroidhormone (PTH) by parathyroid glands Figure
9.2b 25 Neural Stimuli of Endocrine Glands
Nerve impulses stimulate hormone release Most are under the control
of the sympatheticnervous system Examples: The release of
norepinephrine and epinephrineby the adrenal medulla 26 (c) Neural
stimulus 1 Preganglionic sympathetic fiber stimulates adrenal
medullacells CNS (spinal cord) Preganglionic sympathetic fibers
Medulla of adrenal gland Capillary to secrete catecholamines
(epinephrine and norepinephrine) 2 Figure 9.2c 27 Major Endocrine
Organs
Pituitary gland Thyroid gland Parathyroid glands Adrenal glands
Pineal gland Thymus gland Pancreas Gonads (Ovaries and Testes)
Hypothalamus 28 Pineal gland Hypothalamus Pituitary gland Thyroid
gland
Parathyroid glands Thymus Adrenal glands Pancreas Ovary (female)
Testis (male) Figure 9.3 29 Pituitary Gland Size of a pea
Hangs by a stalk from the hypothalamus in thebrain Protected by the
sphenoid bone Has two functional lobes Anterior
pituitaryglandulartissue(adenohypophysis.) Posterior
pituitarynervoustissue(neurohypophysis) Often called the master
endocrine gland 30 Hormones of the Anterior Pituitary
Six anterior pituitary hormones Two affect non-endocrine targets
Growth hormone Prolactin Four stimulate other endocrine glands
(tropichormones) Thyroid-stimulating hormone
(thyrotropichormone)TSH Adrenocorticotropic hormone(ACTH) Two
gonadotropic hormones(FSH, LH) 31 Hormones of the Anterior
Pituitary
Characteristics of all anterior pituitaryhormones Proteins (or
peptides) Act through second-messenger systems Regulated by
hormonal stimuli, mostlynegative feedback 32 Follicle-stimulating
hormone (FSH) and luteinizing hormone (LH)
Releasing hormones secreted into portal circulation Hypothalamus
Hypothalamus Hypothalamus Anterior pituitary Posterior pituitary
Hypophyseal portal system Adrenocorticotropic hormone (ACTH) Growth
hormone (GH) Bones and muscles Prolactin (PRL) Follicle-stimulating
hormone (FSH) and luteinizing hormone (LH) Thyrotropic hormone (TH)
Adrenal cortex Mammary glands Thyroid Testes or ovaries Figure 9.4
33 Hormones of the Anterior Pituitary
Growth hormone General metabolic hormone Major effects are directed
to growth of skeletalmuscles 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 ofenergy 34
Hormones of the Anterior Pituitary
Growth hormone (GH) disorders Pituitary dwarfism results from
hyposecretionof GH during childhood Gigantism results from
hypersecretion of GHduring childhood Acromegaly results from
hypersecretion of GHduring adulthood 35 Pituitary dwarf (left),
Giant (center), Normal height woman (right)
Figure 9.5 36 Hormones of the Anterior Pituitary
Prolactin (PRL) Stimulates and maintains milk productionfollowing
childbirth by increasing # of milk ducts& milk glands, no
realse of milk Adrenocorticotropic hormone (ACTH) Regulates
endocrine activity of the adrenalcortex Thyroid-stimulating hormone
(TSH) Influences growth and activity of the thyroidgland 37
Hormones of the Anterior Pituitary
Gonadotropic hormones Regulate hormonal activity of the gonads
Follicle-stimulating hormone (FSH) Stimulates follicle development
in ovaries, thegrafian follicle that secretes estrogen Stimulates
sperm development in testes Luteinizing hormone (LH) Triggers
ovulation of an egg in females, it actson the corpus lutium to
secrete progestron Stimulates testosterone production in males 38
PituitaryHypothalamus Relationship
Hormonal release is regulated by releasingand inhibiting hormones
produced by thehypothalamus Hypothalamus produces two hormones
These hormones are transported toneurosecretory cells of the
posterior pituitary Oxytocin Antidiuretic hormone The posterior
pituitary is not strictly anendocrine gland, but does release
hormones 39 Hormones of the Posterior Pituitary
Oxytocin Stimulates contractions of the uterus duringlabour, sexual
relations, and breastfeeding Causes milk ejection in a nursing
woman aftersuckling 40 Hormones of the Posterior Pituitary
Antidiuretic hormone (ADH) Inhibits urine production by promoting
waterreabsorption by the kidneys In large amounts, causes
vasoconstrictionleading to increased blood pressure Also known as
vasopressin 41 Hypothalamic neurosecretory cells Optic chiasma
Hypothalamus Axon
terminals Arterial blood supply Posterior lobe Capillary bed Venous
drainage Anterior lobe of the pituitary ADH Oxytocin Kidney tubules
Mammary glands Uterine muscles Figure 9.6 42 Thyroid Gland Found at
the base of the throat
Consists of two lobes and a connectingisthmus Produces two hormones
Thyroid hormone Calcitonin 43 (a) Gross anatomy of the thyroid
gland, anterior view
Thyroid cartilage Epiglottis Common carotid artery Isthmus of
thyroid gland Trachea Left subclavian artery Brachiocephalic artery
Left lobe of thyroid gland Aorta (a) Gross anatomy of the thyroid
gland, anterior view Figure 9.7a 44 Thyroid Gland Thyroid hormone
Major metabolic hormone
Composed of two active iodine-containinghormones Thyroxine
(T4)secreted by thyroid follicles Triiodothyronine (T3)conversion
of T4 attarget tissues 45 (b) Photomicrograph of thyroid gland
follicles (125)
Colloid-filled follicles Follicle cells Parafollicular cell (b)
Photomicrograph of thyroid gland follicles (125) Figure 9.7b 46
Thyroid Gland Thyroid hormone disorders Goiters
Thyroid gland enlarges due to lack of iodine Salt is iodized to
prevent goiters Types:simple nodular, toxic(Graves disease)
&malignant Cretinism Caused by hyposecretion of thyroxine
duringchildhood 47 Figure 9.8 48 Thyroid Gland Thyroid hormone
disorders (continued) Myxedema
Caused by hypothyroidism in adults Results in physical and mental
slugishnesswith rapid increase in weight Graves disease( toxic
goiter) Caused by hyperthyroidism Results in increased metabolism,
heatintolerance, rapid heartbeat, weight loss, andexophthalmos 49
Figure 9.9 50 Thyroid Gland Calcitonin
Decreases blood calcium levels by causing itsdeposition on bone
Antagonistic to parathyroid hormone Produced by parafollicular
cells Parafollicular cells are found between thefollicles 51 (b)
Photomicrograph of thyroid gland follicles (125)
Colloid-filled follicles Follicle cells Parafollicular cell (b)
Photomicrograph of thyroid gland follicles (125) Figure 9.7b 52
Parathyroid Glands Tiny masses on the posterior of the
thyroid
Secrete parathyroid hormone (PTH) Stimulate osteoclasts to remove
calcium frombone Stimulate the kidneys and intestine to absorbmore
calcium Raise calcium levels in the blood 53 Calcium homeostasis of
blood: 911 mg/100 ml
Calcitonin Calcitonin stimulates calcium salt deposit in bone.
Thyroid gland releases calcitonin. Stimulus Rising blood Ca2+
levels IMBALANCE Calcium homeostasis of blood: 911 mg/100 ml
BALANCE BALANCE Stimulus Falling blood Ca2+ levels IMBALANCE
Thyroid gland Osteoclasts degrade bone matrix and release Ca2+ into
blood. Parathyroid glands Parathyroid glands release parathyroid
hormone (PTH). PTH Figure 9.10 54 Adrenal Glands Sit on top of the
kidneys Two regions
Adrenal cortexouter glandular region hasthree layers
Mineralocorticoids secreted by outermostlayer(zona glumerulosa)
Glucocorticoids secreted by middle layer(z.faciculata) Sex hormones
secreted by innermost layer(z.reticularis) Adrenal medullainner
neural tissue region 55 Adrenal gland Capsule Mineralocorticoid-
secreting area Kidney
Glucocorticoid- secreting area Adrenal gland Adrenal cortex Medulla
Cortex Cortex Sex hormone secreting area Kidney Adrenal medulla
Medulla Figure 9.11 56 Hormones of the Adrenal Cortex
Mineralocorticoids (mainly aldosterone) Produced in outer adrenal
cortex Regulate mineral content in blood Regulate water and
electrolyte balance, itkeeps Na &release K Target organ is the
kidney Production stimulated by renin Production inhibited by
atrial natriuretichormon (ANH) 57 Figure 9.12 58 Decreased Na+ or
increased K+ in Stress blood
Hypothalamus Decreased blood volume and/or blood pressure
Corticotropin- releasing hormone Anterior pituitary Increased blood
pressure or blood volume ACTH Kidney Renin Heart Indirect
stimulating effect via angiotensin Atrial natriuretic peptide (ANP)
Angiotensin II Direct stimulating effect Inhibitory effect
Mineralocorticoid- producing part of adrenal cortex Enhanced
secretion of aldosterone targets kidney tubules Increased
absorption of Na+ and water; increased K+ excretion Increased blood
volume and blood pressure Figure 9.12 58 Hormones of the Adrenal
Cortex
Glucocorticoids (including cortisone andcortisol) Produced in the
middle layer of the adrenalcortex Promote normal cell
metabolism(anti- inflammatory)& antiallergic Help resist
long-term stressors(antidepressant) Released in response to
increased bloodlevels of ACTH 59 Corticotropic cells of anterior
pituitary
Short term Stress More prolonged Hypothalamus Releasing hormones
Nerve impulses Spinal cord Corticotropic cells of anterior
pituitary ACTH Adrenal cortex Preganglionic sympathetic fibers
Adrenal medulla Mineralocorticoids Glucocorticoids Short-term
stress response Long-term stress response Catecholamines
(epinephrine and norepinephrine) 1. Increased heart rate 2.
Increased blood pressure 3. Liver converts glycogen to glucose and
releases glucose to blood 4. Dilation of bronchioles 5. Changes in
blood flow patterns, leading to increased alertness and decreased
digestive and kidney activity 6. Increased metabolic rate 1.
Retention of sodium and water by kidneys 2. Increased blood volume
and blood pressure 1. Proteins and fats converted to glucose or
broken down for energy 2. Increased blood sugar 3. Suppression of
immune system Figure 9.13 60 Hormones of the Adrenal Cortex
Sex hormones Produced in the inner layer of the adrenalcortex Small
amounts are made throughout life Mostly androgens (male sex
hormones) aremade but some estrogens (female sexhormones) are also
formed 61 Adrenal Glands Adrenal cortex disorders Addisons
disease
Results from hyposecretion of all adrenal cortexhormones 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 tohigh blood pressure and
edema 62 Adrenal Glands Adrenal cortex disorders Cushings
syndrome
Results from a tumor in the middle cortical area ofthe adrenal
cortex Moon face, buffalo hump on the upper back,high blood
pressure, hyperglycemia, weakening ofbones, depression
Masculinization Results from hypersecretion of sex hormones Beard
and male distribution of hair growth 63 Hormones of the Adrenal
Medulla
Produces two similar hormones(catecholamines) Epinephrine
(adrenaline) Norepinephrine (noradrenaline) These hormones prepare
the body to deal withshort-term stress (fight or flight) by
Increasing heart rate, blood pressure, bloodglucose levels Dilating
small passageways of lungs 64 Adrenal gland Capsule
Mineralocorticoid- secreting area Kidney
Glucocorticoid- secreting area Adrenal gland Adrenal cortex Medulla
Cortex Cortex Sex hormone secreting area Kidney Adrenal medulla
Medulla Figure 9.11 65 Pancreatic Islets The pancreas is a mixed
gland and has bothendocrine and exocrine functions The pancreatic
islets produce hormones Insulinallows glucose to cross
plasmamembranes into cells from beta cells Glucagonallows glucose
to enter the bloodfrom alpha cells These hormones are antagonists
that maintainblood sugar homeostasis 66 Stomach Pancreas (a) Figure
9.14a 67 Exocrine cells of pancreas Pancreatic islets (b) Figure
9.14b 68 Cord of beta () cells secreting insulin into
capillaries
Exocrine cells of pancreas Alpha () cells Capillaries Cord of beta
() cells secreting insulin into capillaries (c) Figure 9.14c 69
BALANCE: Normal blood glucose level (about 90 mg/100 ml)
Uptake of glucose from blood is enhanced in most body cells
Insulin-secreting cells of the pancreas activated; release insulin
into the blood Insulin Tissue cells Pancreas Glucose Glycogen Blood
glucose falls to homeostatic set point; stimulus for insulin
release diminishes Elevated blood sugar level Liver takes up
glucose and stores as glycogen IMBALANCE Stimulus Blood glucose
level (e.g., after eating four jelly doughnuts) BALANCE: Normal
blood glucose level (about 90 mg/100 ml) Stimulus Blood glucose
level (e.g., after skipping a meal) IMBALANCE Blood glucose rises
to homeostatic set point; stimulus for glucagon release diminishes
Low blood sugar level Glucagon-releasing cells of pancreas
activated; release glucagon into blood Liver breaks down glycogen
stores and releases glucose to the blood Glucose Glycogen Liver
Glucagon Figure 9.15 70 Pineal Gland Found on the third ventricle
of the brain
Secretes melatonin Helps establish the bodys wake and sleepcycles
Believed to coordinate the hormones of fertilityin humans 71 Pineal
gland Hypothalamus Pituitary gland Thyroid gland
Parathyroid glands Thymus Adrenal glands Pancreas Ovary (female)
Testis (male) Figure 9.3 72 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 73 Gonads Ovaries Produce eggs Produce two groups of steroid
hormone
Estrogens Progesterone Testes Produce sperm Produce androgens, such
as testosterone 74 Pineal gland Hypothalamus Pituitary gland
Thyroid gland
Parathyroid glands Thymus Adrenal glands Pancreas Ovary (female)
Testis (male) Figure 9.3 75 Hormones of the Ovaries
Estrogens Stimulate the development of secondaryfemale
characteristics Mature female reproductive organs With
progesterone, estrogens also Promote breast development Regulate
menstrual cycle 76 Hormones of the Ovaries
Progesterone Acts with estrogen to bring about themenstrual cycle
Helps in the implantation of an embryo in theuterus Helps prepare
breasts for lactation 77 Hormones of the Testes Produce several
androgens
Testosterone is the most important androgen Responsible for adult
male secondary sexcharacteristics Promotes growth and maturation of
malereproductive system Required for sperm cell production 78 Other
Hormone-Producing Tissues and Organs
Parts of the small intestine Parts of the stomach Kidneys Heart
Many other areas have scattered endocrinecells 79 Endocrine
Function of the Placenta
Produces hormones that maintain thepregnancy Some hormones play a
part in the delivery ofthe baby Produces human chorionic
gonadotropin(hCG) in addition to estrogen, progesterone,and other
hormones 80 Developmental Aspects of the Endocrine System
Most endocrine organs operate smoothly untilold age Menopause is
brought about by lack ofefficiency of the ovaries Problems
associated with reduced estrogenare common Growth hormone
production declines with age Many endocrine glands decrease output
withage 81