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 littleweak
-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