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NOTES: CH 11
The Endocrine System
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HORMONES
HORMONE= a chemical signal secretedinto body fluids (usually blood);communicates regulatory messages within
the body.
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TARGET CELLS= cells equipped torespond to specific hormones
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HOMEOSTASIS
HOMEOSTASIS = maintaining the internalenvironment at a constant level (orbetween narrow limits), including:
-blood pH -oxygen / CO2levels -blood glucose -body temperature
-water balance
**achieved through
negative feedback!
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**both the NERVOUS and ENDOCRINEsystems are involved in maintaining
HOMEOSTASIS!
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ENDOCRINE SYSTEM
- ENDOCRINE GLANDS= hormone-secretingorgans
(ductless glands
they secrete hormones
directly into blood/fluid)
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**there is much overlap with the nervoussystem
- NEUROSECRETORY CELLS: specializednerve cells that secrete hormones
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How do Chemical Signals Work?
each chemical signal has a specific shape;
hormone binds to specific receptor ontarget cell
(cells are unresponsive if they lack theappropriate receptor);
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How do Chemical Signals Work?
-binding of a chemical signal to a receptorprotein triggers chemical events within the
target cell:
1) Binds to receptor on plasma membrane,OR
2) Binds to receptor INSIDE the cell
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Types of Hormones:
Hormones can be:
1) STEROIDS: synthesized
from cholesterol
OR
2) Proteins / peptides /
amines / glycoproteins:syn. from amino acids
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STEROID HORMONES
Are insoluble in water / soluble in lipids
Action once it reaches the target cell:
1) Diffuses through cell membrane;
2) May combine w/a protein (receptor);
3) This hormone-receptor complex binds tospecific regions of target cells DNA;
4) Activates transcription of RNA of that
sequence;5) mRNA is transcribed and target cell
synthesizes proteins (e.g. enzymes,transport)
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NONSTEROID HORMONES
e.g. proteins, peptides, amines, etc. typically combine w/
receptors in the target
cells PLASMA MEMBRANE
the receptor changes shape and asequence of molecular events (enzymesactivated via phosphorylation, etc.) thatresults in the target cell responding to thehormone.
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NONSTEROID HORMONES
Examples of cellular responses to nonsteroidhormones:
-change in membrane permeability
-enzymes activated -promotion of syn. of specific proteins
-cell movement
-secretion of cell products (hormones, enz.) -stimulate/inhibit certain chemical pathways
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LOCAL REGULATORS
LOCAL REGULATORS: affect nearby(local) cells
Growth Factors:
-peptides and proteinsthat function as local
regulators
-stimulate cells to grow,divide & develop normally
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LOCAL REGULATORS
Prostaglandins (PGs):
-modified fatty acids-synthesized just before release (not stored)
-in semen, stimulate contraction of the smoothmuscles of the wall of the uterus; helps sperm
reach the egg-in placenta, stimulates uterus
muscles to contract in labor
-in immune system, help
to induce fever,
inflammation,
intensify pain
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ENDOCRINE SYSTEM
*see fig. 11.1(p. 282): human
endocrine glands
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HYPOTHALAMUS:
-region of lower brain-neurosecretory cells secrete hormones
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PITUITARY GLAND:
-stores secretions from the hypothalamus
-located at base of hypothalamus
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PITUITARY GLAND
POSTERIOR PITUITARY:under direct control of
neurosecretory cells
from the hypothalamus
ANTERIOR PITUITARY: responds to
RELEASING HORMONESfrom thehypothalamus (these travel through theportal veins and to the anterior pituitary)
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Posterior Pituitary Hormones:
1) OXYTOCIN: induces contractions of
uterine muscles; triggers mammaryglands to eject milk
2) ANTIDIURETIC HORMONE (ADH):
causes water retention in the kidneys;decreases urine volume
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Anterior Pituitary Hormones:
1) Growth hormone (GH)2) Prolactin (PRL)
TROPIC HORMONES(stimulate synthesis &release of hormones from OTHER endocrineglands)
3) Thyroid-stimulating hormone (TSH)
4) Adrenicorticotropic hormone (ACTH)
5) Follicle-stimulating hormone (FSH)
6) Luteinizing hormone (LH)
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THYROID GLAND
Just below the larynx on either side and infront of the trachea
Thyroid hormones:
1) Thyroxine (T4)
2) Triiodothyronine (T3)
3) Calcitonin
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Functions of Thyroid Hormones:
"THYROXINEand TRIIODOTHYRONINE:increase rate of energy release fromcarbs; increase rate of protein syn.;
accelerates growth
"CALCITONIN: lowers blood calcium and
phosphate ions
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PARATHYROID GLANDS
on the posterior surface of thethyroid gland
PARATHYROID HORMONE(PTH): increases blood calciumconc. & decreases phosphate ionconc.
**in summary, calcitonin and PTHwork together to maintain stableblood calcium concentration
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ADRENAL GLANDS
ADRENAL GLANDS: adjacent to
the kidneys; made up of 2 parts:
Adrenal cortex (outer
portion): -CORTISOL (glucocorticoid):
glucose metabolism
-ALDOSTERONE(mineralocorticoid):
salt & water balance
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ADRENAL GLANDS
"ADRENAL MEDULLA (inner portion):
"Hormones include:
-epinephrine (adrenalin) -norepinephrine (noradrenalin)
-stimulates the fight or flightresponse to stress
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Fight or Flight Response:
1) Glucose released from liver and muscles;2) Fatty-acid release from fat cells;
3) Increase rate and stroke vol. of heartbeat;
4) Bronchioles of lungs become dilated(increase rate of oxygen delivery to cells);
5) Blood diverted away from skin, digestive
organs and kidneys to the heart, brain &skeletal muscles (increase alertness andreadiness)
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PANCREAS PANCREAS: contains endocrineand
exocrinecells (exocrine cells secretedigestive enz & bicarbonate into ducts)
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PANCREAS
-the endocrine cells are called the ISLETSOF LANGERHANS
-alpha cells: secrete glucagon
-beta cells: secrete insulin
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Feedback cycle to control blood glucose levels:
body cells &
liver cells takeup glucose
blood glucoselevel drops
Blood GlucoseLevel (90 mg/100 mL)
High glucose
level
Beta cellssecreteinsulin
Low glucose
level
blood glucose
level rises
liver cells breakdown glycogen
& release glucose
Alpha cellssecrete glucagon
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Feedback cycle to control blood glucose levels:
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PINEAL GLAND
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PINEAL GLAND
located deep between the
cerebral hemispheres (brain)
secretes the hormone
MELATONIN in response to light conditions
-in the dark, nerve impulses from the retina tothe brain decrease, and melatonin secretionincreases
-works with the brain to regulateCIRCADIAN RHYTHMS
-may help regulate the female menstrual cycle,as well as the onset of puberty
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GONADS
GONADS: (testes in males, ovaries infemales)
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HORMONES PRODUCED BY THE GONADS:
1) Androgens: stimulate
development &maintenance of malereproductive system; (e.g.testosterone)
2) Estrogens: maintenance offemale reproductive
system; (e.g. estradiol)
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HORMONES PRODUCED BY THE GONADS:
3) Progestins: preparing and maintaining uterus
to support growth and development of embryo;(e.g. progesterone)
**all 3 hormones are found in males andfemales, but in different proportions