endocrine Flashcards
There exists two primary signaling mechanisms
endocrine system
nervous system
Endocrine system signaling style
Signaling by hormones
Chemical signals that travel via circulatory system (blood)
Only cells with specific receptors will respond to hormones
Relatively slow responses
A small number of hormone producing cells can control a large number of response generating cells
Hormone
secreted molecule that circulates throughout the body and stimulates specific cells
Hormones reach all cells in a body but only elicit a response in specific target cells
Nervous system
Signaling by neurons
Nerves make direct contact with target cells
Fewer target response generating cells are signaled than with hormones
Faster signaling than with hormones
Neuroendocrine signaling
Nerve cell doesn’t release neurotransmitters to a postsynaptic neuron, but releases it to a capillary bed that is then taken up by the circulatory system
Neurohormones diffuse into the bloodstream originating from a neurosecretory cell, and trigger responses in target cells anywhere in the body (synaptic signaling meets endocrine signaling)
. One function of endocrine signaling is to maintain homeostasis. How is this done
Hormones regulate properties that include blood pressure and volume, energy metabolism and allocation, and solute concentrations in body fluids
Many types of cells produce and secrete local regulators which are
molecules that act over short distances, reach their target cells solely by diffusion, and act on their target cells within seconds or even milliseconds
examples of this are
Paracrine signaling
Autocrine signaling
Paracrine signaling
Target cells lie near the secreting cell
Secreted molecules diffuse locally and trigger a response in neighboring cells
Autocrine signaling
Secreted molecules diffuse locally and trigger a response in the cells that secrete them
Secreting cells themselves are the target cells
Prostaglandins
Local regulators that are produced throughout the body and have diverse functions
Promote inflammation and the sensation of pain in response to injury for immune system
Synaptic signaling
Neurotransmitters diffuse across synapses and trigger responses in target tissues
Synaptic signaling is central to sensation, memory, cognition, and movement
Synaptic signaling vs neuroendocrine signaling
Synaptic signalling secretes neurotransmitters and neuroendocrine signaling secretes neurohormones which diffuse from nerve cell endings into the bloodstream
What kind of molecules make up hormones? Four main classes
Amino acid derived hormones (amines)
Polypeptide hormones
Eicosanoids
Steroid hormones
Amino acid derived hormones
Amines
Most are chemical derivatives of Tyrosine
Examples
Epinephrine and norepinephrine
Thyroxine
Epinephrine and norepinephrine
Water soluble hormone involved in stress response
Thyroxine
Lipid soluble hormone involved in determining metabolic rate
Polypeptide hormones
They are chains of amino acids
Each are polypeptide chains of diferent lengths and different sequences
Ex: insulin
Eicosanoids
Eicosanoids are signaling molecules synthesized by essential fatty acids
Used to regulate membrane fluidity
Prostaglandins
mediate inflammation
Steroid hormones
All made from cholesterol
Lipid soluble
Cortisol
Estradiol/Testosterone
How do water-soluble hormones work
All polypeptide hormones
Epinephrine and prostaglandins
Bind to a cell surface receptor(receptor in plasma membrane) and then activate something in the cell
Can get a cytoplasmic response if all that is necessary for a response to be carried out is a signal or can get a gene regulation response
can’t enter cell because of lipid bilayer
How do lipid-soluble hormones work
All steroid hormones
Thyroid hormones
Hormone passes through plasma membrane and binds to receptor in the nucleus or cytoplasm
Only activate new gene transcription
Steroid hormones and thyroid hormones function by activating the transcription of specific genes in target cells
an example of this is the estradiol receptor
Estradiol hormone binds to estradiol receptor in the cytoplasm
This hormone receptor complex enters the nucleus and mRNA/RNA for vitellogenin is created
vitellogenin is A gene transcribed by cells associated with making eggs
Brings in RNA polymerase to transcribe the gene
Steroid hormones can bring about long term changes because
They can stimulate transcription of specific mRNAs
Hormone response to stress
Hormonal component to sympathetic response
Rapid response to stress is caused by epinephrine hormone(and norepinephrine)
A slow response to stress is caused by
Cortisol hormone
Epinephrine is made in the
Adrenal medulla
Cortisol hormone made in the
adrenal cortex
Stress response and the adrenal medulla
Epinephrine is the hormone
Comes from adrenal medulla in the adrenal glands that sit right on top of the kidney
Effect:
Glycogen broken down to glucose -> increase blood glucose
Increase breathing rate
Increase metabolic rate
Stress response and the adrenal cortex
Cortisol hormone
Leads to long term breakdown of proteins and fats
Increases blood glucose
The adrenal cortex, the outer layer of the adrenal gland, produces the cortisol
How does epinephrine work
it is a neuroendocrine signal
Nervous response dgoes all the way to adrenal glands
Brain perceives stress
Sends nerve impulses down to secretory neurons in adrenal medulla
The secretory neurons release epinephrine into the blood
Cells with its receptors respond
What cells respond to epinephrine and how
Liver cells
We have glycogen in liver and muscles
Epinephrine binds to G protein-coupled receptor
Activates G protein that activates adenylyl cyclase
Then activates protein called protein kinase A
This protein inhibits glycogen synthesis and promotes glycogen breakdown
Liver sends glucose out the cell, into the extracellular fluod, and into the capillaries to provide energy around the body
Epinephrine can have different responses in different cells
In liver cells
Ep. binds to beta receptor
Glycogen deposits, glucose exits and cells are fed
Epinephrine can have different responses in different cells
in Smooth muscle cells in wall of blood vessel that supplies skeletal muscle
Epinephrine binds to beta receptor, the cell relaxes and the blood vessel dilates, increasing flow to skeletal muscle
Arterials determine blood flow
Blood vessel dilates, increasing flow to skeletal muscle
Epinephrine can have different responses in different cells
in Smooth muscle cell in wall of blood vessel that supplies intestine
Binds to alpha receptor, cell contracts, blood vessel contracts directing flwo to intestines
Long term stress
lead to an increase in the production of the steroid hormone cortisol
Cortisol will lead to the breakdown of fats and proteins to fuel ATP synthesis in order to deal with stress
Cortisol made in adrenal cortex
Cortisol made in adrenal cortex
How does this come about?
Hypothalamus releases hormones
The release triggers the Anterior pituitary and it tells the anterior pituitary to release another hormone
ACTH
ACTH goes into general circulation and your adrenal cortex has receptors for ACTH and it responds by making cortisol
Anterior pituitary makes a number of polypeptide hormones that are controlled by
Different hypothalamic regulatory factors
Hypothalamus can release different hormones that’ll trigger release of different hormones from anterior pituitary, leading to different responses
Trophic hormones
Hormones that make more hormones
Thyroid hormone
Only molecules in our body that use iodine
Works like a steroid hormone
One of its main functions is determining our metabolic rate
Also important for body temperature regulation
Regulates blood pressure, heart rate, and growth and maintenance of muscles
Negative feedback loops keep hormones at set levels
ex: thyroid hormone
Hypothalamus and anterior pituitary is responsive to thyroid hormones
If the thyroid hormone is below a set point it releases more TRH and TSH and if its above then thyroid hormones feedback to release less TRH and TSH
Posterior pituitary
Where hypothalamic neurons meet capillaries and release hormones
ADH and oxytocin
ADH is important in regulating the kidney
Oxytocin stimulates uterine contraction during birth and Release of milk during nursing
neuroendocrine pathways
Ex: milk release during nursing in mammals
When an infant suckles, it stimulates sensory neurons in the nipples that generate nerve impulses leading to the hypothalamus
This input triggers the secretion of the neurohormone oxytocin from the posterior pituitary gland
Oxytocin then causes contraction of mammary gland cells which force milk from reservoirs in the gland
Negative feedback
the response reduces the initial stimulus
Negative feedback dampens a stimulus and positive feedback reinforces a stimulus, driving a process to completion
Hypothalamus
What does it do
receives information from nerves throughout the body and initiates neuroendocrine signaling appropriate to environmental conditions
Signals from the hypothalamus travel to the
Pituitary gland
Located at the bottom of the hypothalamus
Made up of two glands fused together
Posterior pituitary and Anterior pituitary
Posterior pituitary
Extension of the neural tissue of hyp.
Hypothalamic axons that reach into the posterior pituitary secrete neurohormones synthesized in the hypothalamus
Anterior pituitary
An endocrine gland that synthesizes and secretes hormones in response to hormones from the hypothalamus
Neurosecretory cells of the hypothalamus synthesize what two posterior pituitary hormones
Antidiuretic hormone(ADH) and oxytocin
These neurohormones are stored to be released into the bloodstream in response to nerve impulses transmitted by the hypothalamus
Antidiuretic hormone(ADH)/vasopressin
Regulates kidney function
Circulating ADH increases water retention in the kidneys, helping maintain normal blood osmolarity
Anterior pituitary hormones
Hormone cascade
A form of regulation in which multiple endocrine organs and signals act in series
Signals to the brain stimulate the hypothalamus to secrete a hormone that stimulates or inhibits release of a specific anterior pituitary hormone
The anterior pituitary hormone in turn stimulates another endocrine organ to secrete another hormone that affects specific target tissues
Progesterone
Involved in preparing and maintaining tissues of the mammalian uterus required to develop an embryo
