Transcript Chemical Signals in Animals or The Endocrine System

Chemical Signals in Animals or The Endocrine System
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Basic Definitions
1. Hormone: a chemical signal that . . .
2. Target Cells: have receptors such that hormones have a
specific place to cause an effect.
3. Endocrine glands vs. exocrine glands
a) Endo: these are ductless glands because they secrete
their hormones directly into the blood stream
b) Exocrine: secrete chemicals (sweat, mucus, dig.
enzymes) into ducts that then carry the chemical to their
location
4. Neurosecretory cells: special nerve cells that secrete
hormones.
a) Example: hypothalamus and ADH
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Figure 45.1 Feedback Mechanisms
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The Diversity of Cellular Regulators
1. Growth Factors
a) Peptides or proteins
b) Stimulate cell division
c) Examples:
(i) nerve growth factor (although it can stimulate other
types of cells)
(ii) insulinlike growth factor which stimulates bone
growth.
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Growth Factors (cont’d)
2. Nitric Oxide (NO)
a) when secreted by neurons, it acts as a neurotransmitter
b) when secreted by wbc’s, it kills bacteria and cancer cells
c) when released by cells that line blood vessels it causes
vasodilation by causing smooth muscle that lines the vessels
to relax.
-1998 Nobel Prize in Medicine
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Growth Regulators, cont’d
•
Prostaglandins
a) first discovered in semen produced by the prostate gland
b) stimulate uterine contraction which helps get the sperm
cells to the egg.
c) secreted by the placenta and makes uterine contract
during labor
d) intensify the sensation of pain; inhibited by aspirin and
ibuprofen
e) one kind of prostaglandin causes blood vessels in lungs to
relax, while another kind causes vasoconstriction.
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Figure 45.3 Mechanisms of chemical signaling: a review
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Same Chemical Signal. . .
Different Cellular Response
BECAUSE
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Table 45.1 Major Vertebrate Endocrine Glands and Some of Their Hormones
(Hypothalamus–
Parathyroid glands)
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Table 45.1 Major Vertebrate Endocrine Glands and Some of Their Hormones
(Pancreas–Thymus)
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Figure 45.6a Hormones of the hypothalamus and pituitary glands
The posterior pituitary gland
is an extension of the nervous
tissue of the hypothalamus
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Figure 45.6b Hormones of the hypothalamus and pituitary glands
Hypothalamus controls the ant.
pituitary secretions by
substances called “releasing
factors.”
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Figure 45.7 Two thyroid hormones (thyroxine)
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Figure 45.8 Feedback control loops regulating the secretion of thyroid hormones T3
and T4
Thyroid Releasing Hormone or Factor
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Figure 45.9 Thyroid and Parathyroid Glands in Calcium Homeostasis
Know these three effects
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Interaction of PTH and Vitamin D
1. Helps to convert an inactive form of Vit. D to active form in
the liver and kidneys
2. Vit D is a steroid hormone
3. Once the active form of Vit D is made it helps calcium
reabsorption in the intestines
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The Regulation of Blood Glucose Levels
Pancreas
•Both an exocrine (mostly) and an endocrine gland
•Islets of Langerhans are clusters of cells throughout the
pancreas
•these islets produce two hormones: insulin and glucagon
•each islet has two types of cells: alpha and beta
•Alpha Cells: secrete glucagon (peptide hormone)
•Beta Cells: secrete insulin
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Actions of Insulin
1) stimulates all cells except brain to take up glucose; brain
cells take up glucose without insulin.
2) Slows breakdown of glycogen in liver
3) Inhibits conversion of amino acids and fats to sugar
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Actions of Glucagon
Only liver cells are sensitive to glucagon
•
Increases glycogen hydrolysis
•
Converts amino acids to glucose
•
Converts fats (glycerol) to glucose
•
Releases glucose into the bloodstream
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Figure 45.10 Glucose homeostasis maintained by insulin and glucagon
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Diabetes:
excess sugar in the blood stream
appears in the urine
excess thirst hence drinking of lots of water
fats are used in metabolism resulting in a lowering of pH of
blood.
Type I Diabetes Mellitus (insulin-dependent diabetes)
•body is producing insulin but the body attacks its own beta
cells and destroys them.
•occurs at a young age
•treated with insulin injections
•insulin is now made by genetic engineering
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Type II Diabetes Mellitus
•deficiency of insulin or target cells won’t respond
•occurs at the ripe old age of 40
•exercise and diet!!!!
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Stress Related Hormones
Adrenal glands
•Location
•Two Glands in One
•Adrenal medulla: cells of the medulla are derived from
the nervous system so here is another connection between
the NS and endocrine systems
Secretes epinephrine and norepinephrine (different
molecules, same effect.
Short term stress
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•Adrenal cortex and ACTH (adrenocorticotropic
hormone ( steroid hormones)
Secretes mineralocorticoids and glucocorticoids
Long term stress
Mineralocorticoids (aldosterone)
Retention of sodium and water
Increase in blood volume and pressure
Glucocorticoids (cortisol)
Proteins and fats are converted to sugars
Immune system may be suppressed (cortisone
injections will cause this)
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Figure 45.12 The synthesis of catecholamine hormones
•occurs in adrenal medulla
•tyrosine is an amino acid
(Also called adrenaline)
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Figure 45.14 Stress and the adrenal gland
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Figure 45.13 Steroid hormones from the adrenal cortex and gonads
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Figure 45.2 Hormonal regulation of insect development (Layer 3)
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