Transcript Plants and Pollinators

The Endocrine System
Chapter 15
Hormones
• Secreted by endocrine glands,
endocrine cells, and certain neurons
• Travel through the bloodstream to
nonadjacent target cells
Other Signaling Molecules
• Neurotransmitters
• Local signaling molecules
• Pheromones
Discovery of Hormones
• Bayliss and Starling severed nerves to dog’s
intestine; left blood vessels intact
• Pancreas still responded
• Extracts of glandular epithelium also
provoked pancreatic response
• Extracts contained secretin
Hormone Interactions
• Opposing interaction
• Synergistic interaction
• Permissive interaction
Endocrine System
Main Sources
• Pituitary gland
• Adrenal glands
• Thyroid gland
• Parathyroid
glands
• Pineal gland
• Thymus gland
Responses to Hormones Vary
• Different hormones activate different
responses in the same target cell
• Not all types of cells respond to a
particular hormone
Two Main Hormone Types
• Steroid hormones
– Derived from cholesterol
– Estrogens, progestins, androgens (such as
testosterone), cortisol, aldosterone
• Peptide hormones
– Peptides, proteins, or glycoproteins
– Glucagon, ADH, oxytocin, TRH, insulin,
somatotropin, prolactin, FSH, LH, TSH
Steroid
Hormones
hormone
• Most diffuse
across the plasma
membrane and
bind to a receptor
• Hormone-receptor
complex acts in
nucleus to inhibit
or enhance
transcription
receptor
hormone-receptor
complex
gene product
Protein
Hormone
• Hormone binds to
a receptor at cell
surface
• Binding triggers a
change in activity
of enzymes inside
the cell
glucagon
glucagon receptor
cyclic AMP + Pi
ATP
cAMP activates
protein kinase A
Protein kinase A converts phosphorylase
kinase to active form and inhibits an
enzyme required for glucagon synthesis.
The Hypothalamus
• Region in the
forebrain
hypothalamus
• Contains hormonesecreting cells
• Interacts with
pituitary
pituitary gland
Pituitary Gland
• Pea-sized gland at base of hypothalamus
• Two lobes
– Posterior lobe stores and secretes hormones
that were synthesized in the hypothalamus
– Anterior lobe produces and secretes its own
hormones
Posterior Lobe
• Antidiuretic hormone
(ADH)
cell body in
hypothalamus
axons
• Oxytocin (OCT)
to the general
circulation
Anterior
Pituitary
•
•
•
•
•
•
ACTH
TSH
FSH
LH
PRL
STH
Normal Hormone Production
• Generally, the body produces only very
small amounts of hormones
• To isolate 1 milligram of TRH, researchers
dissected 7 metric tons of hypothalamic
tissue
Abnormal Somatotropin
Output
• Gigantism
• Pituitary dwarfism
• Acromegaly
Feedback Mechanisms
• Negative feedback
– An increase in concentration of a hormone
triggers activities that inhibit further secretion
• Positive feedback
– An increase in concentration of a hormone
triggers activities that stimulate further
secretion
Cortisol
• Cortisol secretion
– Inhibits blood glucose uptake by muscle and
other tissues
– Causes breakdown of proteins to amino
acids and conversion to glucose
– Causes degradation of adipose tissue to fatty
acids for use as energy source
Feedback Control of
Cortisol Secretion
• Hypothalamus senses rise in glucose and
secretes less releasing hormone (CRH)
• Anterior pituitary responds by secreting
less ACTH
• Adrenal cortex slows its secretion of
cortisol
Localized Feedback in
Adrenal Medulla
• Norepinephrine secreted by neurons in
the medulla accumulates in the synaptic
gap
• Some molecules bind to receptors on
the axon endings that secreted them
• This prevents further secretion of
norepinephrine by that axon
Thyroid Gland Disorders
• Goiter
• Hyperthyroidism
• Hypothyroidism
Calcium Regulation
• Parathyroid hormone (PTH) is the main
regulator of calcium in the blood
• It is secreted when calcium levels drop
• PTH causes bone cells to digest bone
tissue and release calcium
• PTH also stimulates calcium reabsorption
by the kidneys and absorption by the gut
Control of Glucose
Metabolism
insulin
Glucose
uptake
Glucose
to
glycogen
Glucose falls
Glucose is
absorbed
Cells use
glucose
Glucose rises
Glycogen
to glucose
glucagon
Diabetes Mellitus
• Disease in which excess glucose
accumulates in blood, then urine
• Effects include
– Excessive urination
– Constant thirst
– Weight loss
– Ketone formation and acid-base imbalances
Two Types of Diabetes
• Type 1
• Type 2
• Autoimmune disease
• Target cells don’t
respond
• Usually appears in
childhood
• Treated with insulin
injections
• Usually appears in
adults
• Treated with diet,
drugs
The Pineal Gland
• Photosensitive gland embedded in brain
• In the absence of light, secretes melatonin
• Affects the human biological clock
• May also play a role in human puberty and
in seasonal affective disorder
Local Signaling Molecules
• Prostaglandins
– Produced and secreted in response to local
changes
– Sixteen types with a variety of effects
• Growth factors
– Affect cell division rates in tissues