Endocrine System (Pt. 1) Flashcards
What two systems make up our body’s ‘communication system’?
The nervous system and the endocrine system
What is the “President” of the endocrine system?
The hypothalamus
What is the “Vice-President”
The pituitary gland
What does the endocrine system release to communicate?
Hormones
Define hormones in the context of the endocrine system
Hormones are substances secreted into the bloodstream which stimulate a response in another cell, tissue or organ
How does the nervous system communicate?
Quickly, using nerve impulses and neurotransmitters at synapses
How does the endocrine system communicate?
By releasing hormones that travel through the bloodstream to regulate activities in different body parts
What are the characteristics of hormones?
Released in one part of the body, regulate cells in another, Enter the bloodstream and affect target cells by binding to their receptor
Can some substances act as both neurotransmitters and hormones?
Yes, for example, norepinephrine can act as both
How fast are endocrine responses typically?
Generally slower, taking minutes or more
How fast are nervous system responses typically?
Quick but typically brief
How specific are the targets of the nervous system compared to the endocrine system?
The nervous system targets specific muscles and glands, while the endocrine system influences many body cells
Do the nervous and endocrine systems interact?
Yes, the nervous system can influence hormone release
List the main endocrine glands in the body.
Pituitary, thyroid, parathyroid, adrenal (suprarenal), and pineal glands
Can organs and tissues that are not part of the endocrine system secrete hormones?
Yes, if they contain secreting cells
Name at least 5 organs or tissues that contain hormone-secreting cells but are not primarily endocrine glands.
Any 5 of: hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, placenta
What are exocrine glands?
Glands that secrete products into ducts and deliver secretions to body cavities, organ lumens, or the body’s outer surface
Give examples of exocrine glands.
Sudoriferous (sweat), sebaceous (oil), mucous, and digestive glands
How do endocrine glands secrete hormones?
They secrete hormones directly into interstitial fluid, which then diffuse into blood capillaries
What is a characteristic of endocrine glands related to blood supply?
They are extremely vascular, relying on the cardiovascular system for hormone distribution
What is typically true about hormone levels in circulation?
They are typically low
What is the study of the structure, function, and disorders of endocrine glands called?
Endocrinology
How do most hormones exert their effects?
They circulate in the blood and bind to receptors on target cells.
What determines the specificity of hormone-receptor interaction?
Each hormone has specific receptors; only the correct hormone will “fit” the correct receptor.
How many receptors can a single cell have?
Between 2,000 to 100,000 specific receptors.
What factors influence how a target cell responds to a hormone?
- Hormone concentration in the blood
- Number of hormone receptors on the target cell
- Influences from other hormones (permissive effects)
What is the permissive effect of hormones?
Some hormones require another hormone’s presence for full effectiveness.
Give an example of a synergistic effect among hormones.
Glucagon and epinephrine together increase blood glucose levels more than either hormone alone.
What is an antagonistic effect?
One hormone counteracts the action of another, such as insulin (which promotes glycogen synthesis) vs. glucagon (which stimulates glycogen breakdown).
How does receptor abundance influence hormone response?
More receptors on target cells (up-regulation) enhance sensitivity to the hormone.
What is an example of how certain hormones work together?
Epinephrine’s effect on lipolysis is amplified by the presence of thyroid hormones (T3 and T4).
How does hormone concentration affect cell response?
Higher hormone levels in the blood lead to a stronger response from target cells.
What is the ongoing process for hormone receptors?
Receptors are continually being synthesized and broken down
What is receptor down-regulation?
When receptors become less sensitive (less effect) in the presence of high hormone concentrations
Give an example of receptor down-regulation.
Insulin receptors in type 2 diabetes
What is receptor up-regulation?
When receptors become more sensitive (more effect) in the presence of low hormone concentrations
Give an example of receptor up-regulation.
Testosterone receptors with aging
Give an example of hormone-induced down-regulation.
High levels of luteinizing hormone (LH) can lead to a reduction in LH receptors in certain testicular cells
What happens in up-regulation when there’s a hormone deficiency?
The number of receptors may increase, enhancing the cell’s sensitivity to that hormone
Explain the process of circulating hormones:
endocrine cells release hormones into the bloodstream. These hormones travel through blood capillaries to reach distant target cells, where they bind to specific hormone receptors, triggering a response.
What are hormones that act on nearby cells called?
Paracrines
Give an example of a paracrine hormone and its action
Interleukin-2 (IL-2) produced by T cells, which helps activate other nearby immune cells
What are hormones that act on the same cell that secretes them called?
Autocrines
Provide an example of autocrine signaling.
Interleukin-2 (IL-2) stimulating the T cell that produced it to generate more T cells
How do circulating hormones differ from local hormones?
Circulating hormones enter the bloodstream to affect the whole body, while local hormones act near their origin without entering the blood
What is an example of a local hormone?
Nitric oxide (NO)
What effect does nitric oxide have on blood vessels?
It relaxes nearby muscles, leading to vasodilation (increased vessel diameter), affecting blood pressure and contributing to penile erection
What are the two main categories of hormones based on solubility?
Lipid-soluble hormones and water-soluble hormones
List four types of lipid-soluble hormones.
Hint: S.T.N.E
Steroid hormones, thyroid hormones, nitric oxide, and eicosanoids
What are two main types of water-soluble hormones?
Amine hormones and peptide/protein hormone
How do water-soluble hormones circulate in the blood?
They circulate freely
How do water-soluble hormones interact with target cells?
They must bind to cell-surface receptors on the plasma membrane and need help from ‘messengers’
What are steroid hormones derived from?
Cholesterol
What makes thyroid hormones (T3 and T4) unique among lipid-soluble hormones?
They contain iodine, making them highly lipid-soluble
Name three examples of amine hormones
Catecholamines (epinephrine, norepinephrine, dopamine), histamine, serotonin, and melatonin
What’s the difference between peptide and protein hormones?
Peptide hormones have 3-49 amino acids, while protein hormones have 50-200 amino acids
Give examples of peptide and protein hormones.
Peptide: antidiuretic hormone, oxytocin. Protein: growth hormone, insulin
How do most lipid-soluble hormones circulate in the blood?
Bound to transport proteins made in the liver
List three functions of transport proteins for lipid-soluble hormones.
- Make lipid-soluble hormones temporarily water soluble
- Slow the passage of small hormones to the kidney for excretion
- Provide a reserve for hormones in blood
Note: soluble, passage, reserve
What percentage of lipid-soluble hormones are typically free in the blood?
About 10%
How do free lipid-soluble hormones interact with target cells?
They penetrate the plasma membrane and typically enter the nucleus to cause a reaction
How do lipid-soluble hormones enter target cells?
They diffuse from the blood through the cell’s plasma membrane
Where do lipid-soluble hormones bind in target cells?
To receptors in the cytosol or nucleus
How do lipid-soluble hormones alter gene expression?
The receptor-hormone complex turns specific DNA genes on or off, leading to mRNA creation
What happens after mRNA is created in response to lipid-soluble hormones?
mRNA moves to the cytoplasm, guiding ribosomes to make new proteins
How do the new proteins affect the cell?
They modify the cell’s activity, generating the hormone’s intended response
Do all lipid-soluble hormones bind inside the cell?
No, eicosanoids bind to receptors on the cell’s surface, similar to water-soluble hormones
what percent of hydrophobic (lipid soluble) hormones are free in the blood?
10 %
How does free lipid-soluble hormone move from the blood to the target cell?
It diffuses from the capillary into interstitial fluid, then across the plasma membrane
Where does a lipid-soluble hormone typically bind in the target cell?
With a receptor, often in the nucleus
What is the immediate effect of a lipid-soluble hormone binding to its receptor?
It causes gene expression
What happens to DNA in response to lipid-soluble hormone binding?
DNA is transcribed to mRNA
How does the cell produce new proteins in response to lipid-soluble hormones?
mRNA and ribosomes make new proteins
How does a water-soluble hormone (1st messenger) reach its target cell?
It diffuses from the capillary into interstitial fluid, then to the receptor on the plasma membrane
What happens when a water-soluble hormone binds to its receptor?
It activates G proteins, which then activate adenylyl cyclase
What does adenylyl cyclase do?
It converts ATP to cAMP (2nd messenger)
What is the role of cAMP in the cell?
cAMP activates many protein kinases
What do protein kinases do?
They add phosphate groups to proteins
What is the effect of phosphorylated proteins?
They stimulate many cellular reactions
What enzyme inactivates cAMP?
Phosphodiesterase
Why is it important that cAMP is inactivated?
To get the cell ready for the next response from the hormone
Why can’t water-soluble hormones cross the cell membrane?
They are not lipid-soluble, so they can’t pass through the lipid bilayer
What is the role of G proteins in water-soluble hormone action?
They are activated by the hormone-receptor complex and stimulate adenylyl cyclase
Why is cAMP called a “Second Messenger”?
It transmits the signal from the hormone-receptor binding (first messenger) inside the cell to initiate the cellular response
What is the amplification mechanism in hormone signaling?
A single hormone-receptor interaction can activate numerous G proteins, leading to a cascade effect that massively amplifies the initial signal
What is the result of the amplification mechanism?
It results in a significant cellular response
Name some other examples of second messengers besides cAMP
Calcium ions, cGMP, IP3, and DAG
What determines which second messenger is used in hormone signaling?
It depends on the specific hormone and target cell type
In the context of hormone signaling, what is considered the “first messenger”?
The hormone-receptor binding on the cell surface
How does cAMP contribute to signal amplification?
By activating multiple protein kinases, which can then phosphorylate many proteins, leading to a cascade of cellular reactions
How are hormones typically released?
In short bursts, with secretion increasing when an endocrine gland is stimulated and decreasing in the absence of stimulation
What is the purpose of regulated hormone release?
To ensure balanced hormone levels for maintaining homeostasis
List the three main mechanisms of hormone secretion control.
- Nervous system signals
- Chemical changes in the blood 3. Other hormones
Give an example of nervous system control of hormone release.
Nerve impulses to the adrenal medulla regulate the release of epinephrine
Provide an example of one hormone controlling the release of another.
Adrenocorticotropic hormone (ACTH) from the anterior pituitary stimulates cortisol release from the adrenal cortex
What type of feedback mechanism is most commonly used in hormone regulation?
Negative feedback
Why is negative feedback used in hormone regulation?
To prevent overproduction of hormones
Give an example of a hormone system that uses positive feedback
Oxytocin during childbirth
What is the purpose of positive feedback in hormone regulation?
To enhance the response
What is the primary mechanism for most hormone regulation?
Negative feedback
Why are negative feedback loops important in hormone regulation?
They prevent excessive fluctuations in hormone levels, which can lead to disorders
Give an example of how hormone imbalance can affect health
Too little insulin leads to high blood sugar (diabetes), while too much can cause hypoglycemia (low blood sugar)
What is the main purpose of negative feedback in the body?
To maintain a stable internal environment despite external changes, promoting overall health and function
In a blood pressure regulation example, what detects changes in blood pressure?
Receptors in blood vessels
What acts as the control center in the blood pressure regulation example?
The brain
What are the effectors in the blood pressure regulation example?
The heart and blood vessels
How do effectors respond to high blood pressure in this example?
The heart rate decreases and blood vessels dilate
What is the end result of this negative feedback loop?
A reduction in blood pressure and a return to homeostasis
How does negative feedback contribute to overall bodily function?
It helps maintain homeostasis, or a stable internal environment
How common is positive feedback in hormone regulation?
Only a few hormones operate via positive feedback
What types of processes are positive feedback loops ideal for?
Processes that need to be decisively completed once initiated, often involving rapid and irreversible changes
How does positive feedback differ from negative feedback in terms of system stability?
Unlike negative feedback which maintains stability, positive feedback thrusts the system toward a culmination
In the childbirth example, what initiates the positive feedback loop?
The stretching of the cervix as the baby moves down the birth canal
What detects the cervix stretching during childbirth?
Stretch-sensitive nerve cells in the cervix
What hormone does the brain release in response to cervix stretching?
Oxytocin
What is the target of oxytocin during childbirth?
The muscles of the uterine wall
How does oxytocin affect uterine muscles?
It causes them to contract more forcefully
How do stronger contractions contribute to the positive feedback loop?
They push the baby further down the birth canal, increasing the stretching of the cervix
What interrupts the positive feedback loop in childbirth?
The birth of the baby, which stops the stretching of the cervix and breaks the cycle
What are the three main steps in how negative feedback works?
- Detection of change
- Hormone secretion adjustment
- Return to set point
How does the endocrine system respond to high hormone levels in negative feedback?
The glands reduce hormone output
In the thyroid hormone example, what hormone does the hypothalamus release?
Thyrotropin-releasing hormone (TRH)
What hormone does TSH stimulate the thyroid gland to produce?
Thyroid hormones (T3 and T4)
How do insulin and glucagon work together in blood sugar regulation?
Insulin lowers blood sugar when it’s high, while glucagon raises it when it’s low
What is the main difference between negative and positive feedback?
Positive feedback amplifies changes, while negative feedback reduces them
What are two key characteristics of positive feedback?
Amplification and a self-enhancing cycle
How does oxytocin contribute to positive feedback during childbirth?
It stimulates uterine contractions, which trigger more oxytocin release, intensifying contractions
Give an example of positive feedback in blood clotting.
Platelets adhere to a damaged site and release chemicals attracting more platelets, continuing until a clot forms
Why is positive feedback less common in the body’s regulatory systems?
It’s used only in specific situations where a rapid outcome is needed
