Transcript document
Endocrine System
Types of Signaling Molecules
• Hormones
• Local Regulators - reach target cells solely
by diffusion
• Neurotransmitters/Neurohormones - utilize
neurotransmitters
• Pheromones - released into the external
environment
Hormones
• Secreted into extracellular fluid, reach
target cells through bloodstream
• Secreted by endocrine glands
Signaling Pathways
• Endocrine Signaling
– Secreted molecules diffuse into blood stream and
trigger response in cells throughout the body
• Paracrine Signaling (Local Regulators)
– Molecules diffuse locally and trigger response in
nearby cells
• Synaptic Signaling
– Neurotransmitters diffuse across a synapse and
trigger response of target cell tissue
Signaling Pathway Continued
• Autocrine Signaling (Local Regulators)
– Secreted molecules diffuse and trigger a
response in the cells that secrete them
• Neuroendocrine Signaling
– Neurohormones diffuse into bloodstream and
trigger responses in target cells throughout
the body
Chemical Classes of Hormones
• Polypeptides - made up of polypeptide
chains, formed by cleaving longer
proteins, water-soluble
• Steroid - fused lipid, non-polar, lipidsoluble
• Amine - synthesized from a single amino
Cellular Response Pathways
• Receptor location
differs between
water-soluble and
lipid-soluble
• Water-soluble are
secreted by
exocytosis and
bind to cell surface
receptors
• Lipid-soluble
diffuse across the
membrane
Once Inside the Cell
• Water-soluble
hormones attach
to the receptor
which responds
via signal
transduction (G
protein-coupled
receptors,
cAMP, second
messenger)
Lipid-Soluble Hormones
• Intracellular
receptors bind to
the hormone,
creating a
hormone-receptor
complex
• HRC moves into
the nucleus where
it interacts with
the DNA,
stimulating
transcription
Multiple Effects of Hormones
• effects by a certain hormone vary when target
cells differ in the molecules that receive them
•For example epinephrine can:
- trigger glycogen breakdown in liver
- increase blood flow to skeletal muscles
- decrease blood flow to digestive tract
•Tissues vary in their responses due to the different
receptors or signal transduction pathways
- epinephrine receptor of a liver cell is called
a
beta receptor, intestinal blood vessels have
an alpha-type epinephrine receptor
• Lipid soluble hormones have different effects, too
- estrogen in birds stimulates the liver to
synthesize the yolk protein but it also
stimulates the reproductive system to
synthesize proteins that make the egg white.
• Sometimes a hormone has different effects in
different species
- thyroxine regulates metabolism in humans
and other vertebrates (frogs) but it does
extra in frogs: fuels resorption of the
tadpole’s tail when morphing into an adult
Signaling by Local Regulators
• Act similarly to hormones
• Chemical compounds function as local
regulators:
•Cytokines- role in immune responses
•Growth factors- stimulate cell proliferation and
differentiation, ensure normal cell development
• Nitric oxide- both neurotransmitter and local
regulator, allows for male erection
• Prostaglandins- modified fatty acids, help sperm
reach egg and help induce labor by stimulating
smooth muscles of uterus
•In immune system: promote fever and inflammation,
intensify pain sensation
• a loop where the response to stimuli is
reduced
•Prevents excessive pathway activity by
getting rid of hormone signaling
• important in maintaining homeostasis
Some Results from the Hormone
Pathways
• signal transduction within target cells brings
a physiological response
• The response reduces the stimulus and the
pathway will end
• example: low pH in small intestine
(duodenum) triggers endocrine cells to
secrete secretin cells. They enter the
bloodstream, go to pancreas, which releases
bicarbonate therefore raising the pH this is
self limiting because the response to secretin
(bicarbonate) reduces the stimulus (pH)
• blood glucose [ ] controls metabolic rate, it is
critical to keep levels near set point
• Hormones glucagon and insulin regulate [ ] of
glucose in the blood
• both produced in the pancreas
• insulin released to trigger the uptake of glucose
from the blood when blood glucose levels rise
above normal level
• glucagon promotes the release of glucose into
the blood when blood glucose drops below set
point
• insulin lowers blood glucose levels by stimulating all
cells outside of brain to take up glucose from the blood
• also decreases rate of glycogen breakdown in the
liver
• glucagon influences levels b/c of effects on target
cells in the liver
• the liver, skeletal muscles, and adipose tissues store
fuel , liver stores sugar as glycogen (only the liver is
sensitive to glucagon)
• when glucose set point is low, glucagon triggers liver
cells to boost glycogen hydrolysis and convert a.a. and
glycerol to glucose bloodstream back to normal
level (see nest slide)
Coordination of Endocrine and
Nervous Systems
• The hypothalamus receives messages
received from the nervous system and
responds
• Sends excretory messages to posterior
and anterior pituitary glands
Posterior Pituitary
• Grows as extension of the hypothalamus
• Secretes oxytocin and antidiuretic hormone
(ADH)
– Oxytocin stimulates production of milk release
– ADH promotes kidney water retention
• Uses endocrine signaling
Anterior Pituitary
• Hormones released by hypothalomous
regulate anterior pituitary secretions
• Each hormone is either a releasing
hormone or an inhibiting hormone
• Secreted near capillaries at base of
hypothalamus
Tropic Hormones
• Hormones that regulate the function of
endocrine glands or cells
Nontropic Hormones
• Hormones that target nonendocrine
tissues
• Prolactin - stimulates mammary glands
• Melanocyte Stimulating Hormone regulates pigment
Thyroid Gland: Metabolism and
Development
• Thyroid Hormone- pair of similar hormones from amino
acid tyrosine: Triidothyronine (T3) and thyroxine (T4)
– Regulates bioenergetics, helps maintain normal blood pressure,
heart rate, muscle tone, regulates digestive and reproductive
functions
• Thyroid gland- in mammals, two lobes on the ventral
surface of the trachea
• All vertebrates require thyroid hormones for normal
functioning of bone-forming cells and branching of nerve
cells during embryonic development of brain
Parathyroid Glands: Control of
Blood Calcium
• Calcium essential to normal functioning of cells
• Parathyroid glands- four small structures
embedded in posterior surface of the thyroid
– Release PTH (parathyroid hormone) when Ca2+ levels
fall below set point of 10mg/100mL
– PTH raises Ca2+ levels directly and indirectly
– If Ca2+ rises above set point, calcitonin released from
thyroid gland
• Calcitonin is hormone that inhibits bone resorption and
enhances Ca2+ release by kidney
Adrenal Glands: Response to
Stress
•
In mammals, two glands with different cell types, functions, embryonic
origins:
– Adrenal Medulla(central): “fight or flight” response, releases 2
hormones, epinephrine (adrenaline) and norephinephrine
(noradrenaline)
• both increase glycogen breakdown by liver cells and stimulate
release of fatty acids from fat cells- increase available chemical
energy
• Catecholamines-class of amine hormones
• Also increase blood supply to heart, brain, skeletal muscles
– Adrenal Cortex(outer): responds to endocrine signals, stressful stimuli
causes hypothalamus to release that stimulates anterior pituitary gland
to release hormone ACTH
• When ACTH reaches cortex, stimulates endocrine cells to secrete
family of steroids called corticosteroids, 2 types in humans:
– glucocorticoids- glucose metabolism, promote glucose
synthesis from noncarbohydrate sources (ex. Proteins)
– Mineralocorticoids- mainly work in maintaining salt and water
balance
Gonadal Sex Hormones
• Most released from testes of males and ovaries
of females (gonads)
– Produce/secrete 3 major categories of steroid
hormones:
• Androgens- mainly testosterone, main role at puberty,
responsible for development of human male secondary sex
characteristics
• Estrogens- most important is estradiol, maintenance of
female reproductive system and development of female
secondary sex characteristics
• Progestins- include progesterone, mostly prepare and
maintain tissues of the uterus
Pineal Gland: Melatonin
• Pineal Gland- small mass of tissue near
the center of the mammalian brain
– Synthesizes and secretes hormone
melatonin, a modified amino acid
• Primary function relates to biological rhythms
associated with reproduction
• Secreted at night, amount released depends on
length
Diseases
• Hyperthyroidism: excessive secretion of thyroid
hormone, most common form is Graves’ disease
– Autoimmune, immune system produces antibodies
that bind to the receptor for TSH and activate
continued thyroid hormone production
– Often proturding eyes from fluid accumulation behind
eyes
• Hypothyroidism: often weight gain, lethargy,
intolerance to cold in adults
– Congenital: inherited, results in retarded skeletal
growth and poor mental development, can be
prevented, if treated with thyroid hormones early in
life
• Tetany: calcium levels fall, potentially fatal,
skeletal muscles begin to contract convulsively
• a disruption of glucose homeostasis can lead to
serious effects on the heart, blood vessels, eyes,
and kidneys
• Diabetes Mellitus can be a result
-caused by a insulin deficiency or reduced response
to insulin in target tissues
- blood glucose levels rise, but cells unable to take up
enough glucose to meet metabolic requirement
-Fat becomes main substrate for cell resp., can form
acidic metabolites that clump in the blood, lowering
pH and killing Na and K ions life threatening
- too much glucose in blood for kidneys to reabsorb,
the glucose is excreted (way to test if one has it)
• Type 1 Diabetes:
-insulin-dependent
- immune system destroys the beta cells of the
pancreas
-destroys persons ability to make insulin, therefore
it needs to be injected, no cure yet (want to find
replacement beta cells)
• Type 2 Diabetes
- non-insulin-dependent
- insulin is produced but target cells fail to take up
glucose from the blood so the levels remain high
-genetic or if overweight
• Growth Disorder:
-there is growth hormone (GH) which is secreted by the
anterior pituitary gland and it stimulates growth.
-The liver responds to GH by letting go insulin-like
growth factors that directly fuel bone and cartilage
growth
•An absence of GH: skeleton stops growing in immature
animals. In humans, there can be too much GM or too little.
-hypersecretion-too much, leads to gigantism, about 8
- hyposecretion- growth hormone deficiency, too little,
properly proportioned but only about 4 feet tall, grow
slower, pituitary dwarfism, treatment if diagnosed
before puberty
("Endocrine System Diseases: Cushing's Syndrome, Addison's Disease and More.“, 1. )
• Osteoporosis:
-a condition where bones become fragile and are likely
to break very easily
- due to lack of estrogen or testosterone (which
increases bone absorption), malnutrition, but also…
- inadequate intake of calcium and Vitamin D
- not enough calcium from diet results in weak bones
that are brittle
-PTH is made when Ca+ in blood is too low. If too much
PTH produced, bones continue to release calcium into
blood, therefore they have will have too littleweak
-low Vitamin D levels: it helps small intestine absorb
calcium, without it they have a hard time doing so.
(“Parathyroid Function: How Parathyroid Glands Work, HowParathyroids Make Parathyroid Hormone
and Control Calcium in Bones and Blood.“, 1)
• http://www.youtube.com/watch?v=rS7SM4
vzs18
• http://www.youtube.com/watch?v=eyO8Di
m3T3U&NR=1