Endocrinology Flashcards
Endocrine system
hormones are chemical signalling molecules that travel through the blood and reach every part of the body but only target cells have receptors that allow them to respond
Homeostasis
- organisms use homeostasis to maintain a steady state or internal balance regardless of external environment
What is the role of homeostasis mechanisms in the internal environment?
They moderate changes in the internal environment.
What happens when a variable fluctuates above or below the set point?
It serves as a stimulus.
What detects a stimulus in homeostasis?
A sensor.
What is triggered after a sensor detects a stimulus?
A response.
What does the response do in the homeostasis process?
It returns the variable to the set point.
Hormone
A chemical messenger produced and secreted by a specialised endocrine gland that is transported in the bloodstream to a distant target organ/ cell where it elicits a physiological response
What are the three different classes of hormones?
Proteins/Peptides, Cholesterol Derivatives, Modified Amino Acids
Give an example of a hormone from the Proteins/Peptides class.
Growth hormone
Are protein/peptide hormones hydrophilic or hydrophobic?
Hydrophilic
What are the two examples of Cholesterol Derivatives?
Steroids and Vitamin D
Are cholesterol derivative hormones hydrophilic or hydrophobic?
Hydrophobic
Name two hormones that fall under Modified Amino Acids.
Adrenaline and Thyroid hormones
Is adrenaline hydrophilic or hydrophobic?
Hydrophilic
Are thyroid hormones hydrophilic or hydrophobic?
Hydrophobic
Can non lipid-soluble hormones (e.g., protein hormones) diffuse through the phospholipid bilayer?
No, they cannot diffuse through the phospholipid bilayer.
How do non lipid-soluble hormones affect their target cells?
They act indirectly via extracellular receptors.
What happens when a non lipid-soluble hormone binds to an extracellular receptor?
It triggers an intracellular signaling cascade.
What is the name of the intracellular signaling pathway triggered by non lipid-soluble hormones?
The “second messenger system.”
stages of the second messenger model
- the hormone itself is the first messenger
- it binds to specific receptors on the cell-surface membrane of target cells
- forms a hormone-receptor complex
- activates an enzyme within the cell
- production of a chemical that acts as a second messenger
Can lipid-soluble hormones diffuse through the phospholipid bilayer?
Yes, lipid-soluble hormones (e.g., steroid hormones) can diffuse through the phospholipid bilayer.
Where do lipid-soluble hormones bind once inside the cell?
They bind to intracellular receptors.
What is the effect of lipid-soluble hormone binding on the target cell?
It directly activates target molecules, usually by changing gene expression.
hormone actions
- affect growth, development, metabolic activity and function of tissues
- may be stimulatory or inhibitory
- may act on several tissues or just one specific target tissue-major difference between endocrine and nervous system
- responsive tissues must have specific receptors for that hormone
circulating hormone levels influenced by:
- rate of secretion - by endocrine gland
- rate of metabolism - by target tissue, blood, liver, kidney
- serum binding proteins - transport in blood
Regulation of hormone secretion - by physiological changes
- blood glucose regulates insulin and glucagon releases from pancreas
- stress regulates adrenaline release from adrenal medulla
Regulation of hormone secretion - by endogenous rhythms
- ultradian - cycles in minutes eg GnRH pulses (90 - 120 min)
- Circadian - daily cycles eg testosterone (24hr)
- infradian cycles - monthly eg LH in females (28 day menstrual cycle)
Regulation of Hormone Secretion - by feedback mechanisms
- mostly negative - maintains homeostasis
- some positive feedback - less common
main types of endocrine dysfunction
- hypersecretion
- hyposecretion
- ectopic hormone secretion - hormone made outside normal endocrine gland (eg tumour)
Hyposecretion: genetic
Caused by inherited genetic mutations that affect the production of hormones or glandular function.
Hyposecretion: Dietary
Caused by inadequate intake of nutrients, especially vitamins and minerals, which are necessary for hormone production.
Hyposecretion: Immunological (auto-immune disease)
Caused by the immune system attacking the body’s own tissues, including endocrine glands, leading to decreased hormone production.
Hyposecretion: Cancer
Caused by tumours that damage or replace hormone-producing tissues or glands, impairing their ability to secrete hormones.
Hyposecretion: Iatrogenic (= doctor-caused)
Caused by medical treatments, such as surgery, radiation, or medication, that inadvertently damage hormone-producing glands.
Hyposecretion: Idiopathic
The cause is unknown or cannot be determined despite medical investigation.
hyposecretion- treatment
- Hormone Replacement with Steroids: This treatment is straightforward. Steroids are absorbed in the gastrointestinal tract and have a high success rate.
- Protein Hormones: The treatment with protein hormones is more difficult. These hormones must be injected and are species-specific, meaning that the treatment varies depending on the species.
hypersecretion - functional tumour
a functional tumour is one that produces hormones, leading to an overproduction of hormones in the body
hypersecretion: Ectopic Hormone-Secreting Tumour:
This type of tumour occurs when a tumour outside of the endocrine glands secretes hormones, causing hypersecretion.
hypersecretion: Immunological
In some cases, an immunological issue can cause hypersecretion, where the immune system triggers an overproduction of hormones.
hypersecretion: substance abuse
The use of certain substances, such as drugs or alcohol, can interfere with hormone regulation and lead to hypersecretion.
Hypersecretion: treatment
- Surgical removal of the gland that is hyper-secreting (but will then need replacement therapy!)
- Irradiation of Gland – reduce function (but will then need replacement therapy!)
- Drugs that block the actions of the hormone
Hypothalamic-pituitary system
- plays a major tole in coordinating the entire endocrine system
- pituitary gland = conductor of the endocrine orchestra
- a major interface between brain (nervous system and periphery
- organizes appropriate hormonal responses to stimuli from higher centres of brain in response to changes in the external environment and changes in internal environment
