Chapter 18
Endocrine System
Ductless Glands- Cells release
secretions INTO the extracellular fluid
Hormone Interactions- depends on:
1. Hormone’s concentration
2. The abundance of receptors to detect
3. Influence of other hormones
18-1 Homeostasis
1. Cilia in epithelia
2. Cardiac muscle
3. neurons
Talking to neighbors
Ca, K, Na
Local hormones
(prostaglandins)
Effects outside tissue of origin
Ach-muscles
Crisis management-NS
Hormones- chemical messengers
• F(x) Maintains
Homeostasis
• How?
1. Activate genes to
stimulate
synthesis of
enzymes
2.
/
rate of
protein synthesis
3. Turn an existing
enzyme on/off by
changing shape
• How do local hormones become hormones?
– If they have primary effects in their tissues plus
secondary effects in other tissues and/or organs
– *Paracrine > Endocrine Communication
• Similarities of Endocrine & NS?
– Chemical messengers
(hormones/neurotransmitters)
– Negative feedback
– Regulate homeostasis
Classes of Hormones
Class
Made From
Examples
Amino Acid Derivatives
Tyrosine & Tryptophan
Tyrosine= T4,
catecholamines (E, NE,
dopamine)
Tryptophan= melatonin
Peptide Hormones
Chains of AA
Glycoproteins = TSH,LH,FSH
Short chain polypeptides =
ADH, OXT
Lipid Derivatives
Lipids
Cholesterol derivatives
Eicosanoids(signaling)=
leukotrienes (blood
clotting), prostaglandins
(coordinate cellular activity)
Steroids= androgens,
progestins, calcitriol
Secretion & Distribution
• Free (AA or peptides) • Bound (lipids)
– F(x)<1hr because:
• (thyroid/steroid hormones)
1. Diffuses out of
bloodstream & binds to
target
2. Broken down/absorbed
by liver/kidneys
3. Broken down by
enzymes
• Remain in circulation longer
because they are bound to
protein
– Why bound to Protein?
hydrophilic & dissolves in blood
• Reserve supply lasts for
weeks
How are they Received?
• Extracellular
• Intracellular
• Bind to outer surface of
plasma membrane
• Catecholamines & peptidesbc not lipid soluble
• Bind to inner receptors
• Eicosanoids-lipid soluble
(dissolve through phospholipid
bilayer)
• *Protein=not lipid soluble
• Activate/deactivate specific
genes (DNA in nucleus),
change protein synthesis
– Ex: testosterone>muscle gain
– Thyroid hormones > Rate of
enzymes for metabolism
Messengers
• Hormones bound on outside MUST use intermediary
molecule
• First messenger: Hormone
• Second messenger: does the inside work
– cAMP, cGMP, Ca2+
– Uses G proteins to link 1st to 2nd
• Ex: G protein activates adenylate cyclase, which makes
cAMP, which activates enzyme (kinase), which creates
phosphorylation, which opens ion channels Fig 18-3
Endocrine Reflexes
controlled by negative feedback
• Triggered by:
– Humoral Stimuli- changes in extracellular fluid
(CSF, blood)
– Hormonal Stimuli- arrival of specific hormone
– Neural stimuli- arrival of neurotransmitter at a
neuroglandular junction
• Simple vs complex:
– 1 hormone vs multiple steps & hormones
Hypothalamus
• Integration b/w endocrine &
nervous:
– Produces ADH (restricts
water loss) & OXT (uterus,
mammary, prostate),
travel down infundibulum,
released from posterior
pituitary
– Sympathetic control of
adrenal medullae-release
E & NE
– Secretes regulatory
hormones that controls
anterior pituitary, which in
turn controls thyroid,
adrenals, reproductive
organs
• Releases hormones in
response to change in blood
and/or action potentials
<How do these get to Anterior
pituitary without being
diluted?
Hypophyseal Portal System
• *Ensures hypothalamic
hormones entering portal
system reach target cells
before being diluted
• Portal vessels- link 2
capillary networks
1. Bed 1-Fenestrated capillaries at median
eminence supplied by superior hypophyseal
artery
2. Wrap around infundibulum to anterior lobe
3. Form Bed 2-lead to endocrine cells
4. Hypophyseal veins carry hormones to CV
system
• 1 way circuit- has to go to
all circulation before
reaching #1 again
Regulatory Hormones
• Releasing (RH)stimulates anterior
lobe
• Inhibiting (IH)prevents anterior
lobe
Adenohypophysis-7
Tropic hormones-turn something on
1. Human Growth Hormone (HGH) / somatotropin
• secretion of insulinlike growth factors, increase AA into proteins
• Somatomedins- growth of skeletal muscles, maintains bones in adults
• Stimulate stem cells-promotes healing of injuries & tissue repair
• Glucose sparing effect-breakdown of stored fat
• Diabetogenic effect- stimulates breakdown of glycogen by liver
• ↑with sleep & stress, ↓ obesity
2. Thyroid stimulating Hormone (TSH)
• synthesis of 2 thyroid hormones, causes thyroid to secrete
3. Follicle stimulating Hormone (FSH)
• females-development of eggs, help secrete estrogen
• males-stimulates nurse cells in seminiferous tubules to maturate sperm
4. Luteinizing Hormone (LH)
• females-secretion of estrogens & progesterone (prepare for pregnancy),
ovulation
• males-tells testes to secrete testosterone
Adenohypophysis
Tropic hormones-turn something on
5. Prolactin (PRL)
• females-milk secretion by mammary glands
• males-?, may help regulate androgens
6. Adrenocorticotropic Hormone (ACTH)
• regulate glucocorticoids- blood glucose
7. Melanocyte stimulating Hormone (MSH)
• important in animals
• Stimulates melanocytes of skin-pigment
• found in fetus, very young children, pregnant,
disease -Circulating blood of adult humans
does not have MSH- so we produce it locally
from sun
Neurohypophysis
1. Antidiuretic Hormone (ADH) / vasopressin
• Responds to osmoregulation: rise in the solute
concentration in blood or a fall in blood volume/pressure
• Causes kidneys to conserve H2O by decreasing urine,
reduces sweating
• vasoconstriction > ↑blood pressure
• inhibited by alcohol > ↑ urination > hangover
2. Oxytocin (OT)
• Women- enhances contractions during child delivery
• stimulates milk ejection “letdown”
• Men- smooth muscle contraction in ductus deferens &
prostate for emission
Thyroid Gland
• 2 lateral lobes
connected by
isthmus
• Inferior to thyroid
cartilage
• Anterior to larynx
Thyroid Follicles
• Lined by Simple Cuboidal
• Cavity contains Colloid
(dissolved proteins)
Thyroid Gland
•
•
•
•
•
Follicle cells make thyroglobulin protein (contains aa tyrosine)
Synthesis of hormones requires iodine- pump=iodide >iodine
Hormones: tyrosine + iodine
Thyroxine (T4) & Triiodothryronine (T3)
Synthesis & release rate is controlled by TSH
Follicular Hormones T3 & T4
• Affect most cells
• Bind to receptors in/on cells
until inner levels decrease
• F(x): activate genes for
production of enzymes
involved in glycolysis and
ATP production
• Calorigenic Effect: increase
metabolic rate > heat
• Children: TSH increases in
cold, also used for
development of Skeletal,
muscular, NS
Parafollicular- Calcitonin
•
•
•
•
•
calcium in blood= inhibits
osetoclasts
Bone growth
Important during starvation
and pregnancy
Ca = Na permeability =
membranes are less
responsive
Ca = Na = muscle spasms
Parathyroid
• 2 pairs at
posterior Thyroid
• 2 cells:
– Chief Cells: make
Parathyroid
Hormone (PTH)
– Oxyphils:
unknown
function
Stimulates
osteoblasts=increase in
bone=less Ca in blood
Opposites
Stimulates osteoclasts=
breakdown of bone = more
Ca in blood
<Active form of Vit D from kidneys
Adrenals/Suprarenals
Adrenal Cortex
Adrenal Medulla
1. Zona glomerulosa Mineralocorticoids
aldosterone-↑Na, ↓K
-chromafin cells
-part of ANS
-Epinephrine (adrenaline) &
norepinephrine:
• Accelerate glucose breakdown
in muscle > strength
• Break down stored fat
• Break down glycogen in liver
• Increase in HR & BP
-Fight or Flight responses
2. Zona fasciculata- Glucocorticoids
cortisol, cortisone –increase glucose,
protein breakdown, antiinflammatory & resist stress
3. Zona reticularis- Androgens &
some estrogens -male & female
characteristics
Pheochromocytomashypersecretion of
http://learn.genetics.utah.edu/content/cells/cellcom/
Pancreas
• lies b/w stomach and curve of
small intestine
Endocrine- clusters called Islets of
Langerhans:
1. alpha cells – Glucagon
-↑blood glucose
2. beta cells – Insulin
-↓ blood glucose
3. delta cells – Somatostatin
-inhibits secretion of insulin &
glucagon
4. F cells – Pancreatic polypeptid
-inhibits somatostatin
Exocrine- Acini cells- stain darker
enzyme fluid for digestion
Regulation
• Glucagon
– stimulates breakdown of glycogen &
triglycerides
– stimulates production of glucose in liver
• Insulin
– Accelerates glucose uptake
– Accelerates glucose utilization and enhances
ATP production
– Stimulates AA absorption & protein synthesis
– Stimulates Triglyceride formation in adipose
Diabetes mellitus
Type 1- Insulin Dependent
• Genetic
• Inadequate insulin
production by beta cells
Hyperglycemia- increase in blood sugar
Glycosuria- sugar in urine
Polyuria- excess urination
Polydipsia- excessive thirst
Type 2- Non-insulin Dependent
• Most common
• Insulin is produced but
tissues do not respond
• obesity
What can happen?
Nephropathy-kidney failure
Retinal Damage
Heart attacks
Neuropathies- nerves
Tissue damage- feet
Kidneys
• Erythropoietin: stimulates bone marrow > RBCs
• Renin: blood pressure & electrolytes
• Calcitriol: calcium absorption, released in response to PTH
Thymus
• Thymosin: maturation of T cells
Heart (natriuretic peptides)
• ANP(atrial) & BNP(brain)-reduction in blood volume & pressure
Adipose
• Leptin: feedback of appetite, binds to hypothalamic neurons
involved with emotion (fullness)
• Defective gene > obesity
• Thin > late puberty, body fat > fertility, too low body fat > stop
menstruating
Synergistic effect
• some require other hormones in order to work more extensively
• ex: oocytes need FSH & estrogen
Antagonistic effect
• if 2 oppose each other
• ex: insulin (makes glycogen) vs glucagon (breaks down glycogen) or
PTH vs Calcitonin
Permissive effect
• First is needed for second
• Ex: epinephrine needs thyroid hormones to change energy
consumption
Integrative effect
• Different, but complementary
• Ex: calcitriol and PTH
Stress Response- General Adaptation
Syndrome
Eustress- helps you meet challenges
Distress- harmful
Longer than a few hours
After weeks or months
Diseases/Disorders
• Pituitary Dwarfism:
hyposecretion of HGH
• Gigantism/Acromegaly:
Hypersecretion of HGH
Hyperthyroidism
• Goiter- enlarged thyroid,
insufficient iodine
– Weight loss, difficulty
concentrating (hyperactive)
• Graves Disease- autoimmune
disorder, bulging eyes
Hypothyroidism
• Myxedema- weight gain,
swollen & puffy
• Hypoparathyroid
– Low blood Ca, problems with nerves & Muscular
weakness, tetany
• Hyperparathyroid
– Increase blood Ca, kidney stones, porous bones
Glucocorticoids
• Addison’s Disease- hyposecretion
– Muscle atrophy, kidney damage, inability to tolerate
stress
• Cushing’s Syndrome- hypersecretion
– Rounded face & reddish complexion, weight gain,
facial hair in women
– Can be caused by taking too many steroid drugs (treat
arthritis)