Hormonal Communication Flashcards
(13 cards)
What is the endocrine system and how does it function?
The endocrine system is made up of endocrine glands—organs that synthesise hormones and secrete them directly into the bloodstream. These hormones help coordinate bodily responses to internal and external stimuli.
Name the major endocrine glands and their hormones/functions.
Pituitary gland (base of brain): Produces a range of hormones that control other glands. These include:
Growth hormone (GH) – stimulates growth and cell reproduction.
Anti-diuretic hormone (ADH) – regulates water balance.
Gonadotropins – LH (Luteinising Hormone) and FSH (Follicle-Stimulating Hormone), which control reproductive processes and the function of the ovaries and testes.
Thyroid gland: Produces thyroxine, which regulates the body’s metabolic rate.
Adrenal glands: Produce adrenaline, which triggers the fight or flight response during stress.
Pancreas: Produces insulin and glucagon, regulating blood glucose levels.
Testes (male): Produce testosterone, which promotes male secondary sexual characteristics and plays a key role in sperm production.
Ovaries (female): Produce oestrogen (regulates the menstrual cycle, promotes development of secondary female characteristics) and progesterone (prepares the uterus for pregnancy and maintains pregnancy).
Thymus: Produces thymosin, which stimulates white blood cell production.
Pineal gland: Produces melatonin, which regulates the circadian rhythm (sleep-wake cycle).
What are hormones and what do they do?
Hormones are chemical messengers that transmit information from one part of the body to another.
They are secreted into the blood when a gland is stimulated and act on target cells with specific receptors.
How do steroid hormones cause changes in cells?
Steroid hormone passes through the cell membrane.
Binds to receptor in the cytoplasm or nucleus.
Hormone-receptor complex binds to DNA.
Transcription is initiated, leading to protein synthesis
What are the key differences between hormonal and neural communication?
Hormonal:
- Chemical messengers (hormones)
- Travel via bloodstream
- Slower but longer-lasting effects
Neural:
- Electrical impulses and neurotransmitters
- Fast and targeted
- Short-term responses
How do non-steroid hormones act on target cells?
Non-steroid hormones are water-soluble and made of proteins or peptides, so they cannot pass through the lipid-based cell membrane. This is because the cell membrane is hydrophobic, making it impermeable to large or polar molecules like proteins.
Instead, non-steroid hormones:
Bind to specific receptors on the cell surface.
Trigger an intracellular signaling cascade via second messengers (e.g., cAMP).
This leads to the activation of enzymes or other proteins that cause the desired response in the cell.
These hormones act quickly but their effects are usually short-lived compared to steroid hormones.
What are the key differences between steroid and non-steroid hormones?
Steroid hormones are lipid-soluble and can pass through the cell membrane. They bind to receptors inside the cell, often in the nucleus, and directly influence gene transcription. This process is slower but results in long-lasting effects. Examples include testosterone and oestrogen.
Non-steroid hormones are water-soluble and cannot pass through the cell membrane. They bind to receptors on the cell surface and activate second messenger systems inside the cell, leading to a faster but shorter-lasting response. Examples include adrenaline and insulin.
Where are the adrenal glands located and what is their basic structure?
Humans have two adrenal glands, located above each kidney. Each gland is approximately 5 cm long and 3 cm wide.
Each adrenal gland consists of:
An outer capsule (protective layer)
The adrenal cortex (beneath the capsule)
The adrenal medulla (central region)
Both the cortex and medulla secrete hormones, but differ in function, regulation, and type of hormones produced.
What types of hormones does the adrenal cortex produce and what are their functions?
The adrenal cortex secretes steroid hormones, which fall into three main categories:
Glucocorticoids (e.g., Cortisol and Corticosterone):
- Secreted in response to signals from the hypothalamus and pituitary gland
- Involved in gluconeogenesis: conversion of proteins and fats into glucose
- Increase blood glucose levels for energy
- Help regulate blood pressure
- Work with corticosterone to modulate immune responses and reduce inflammation
Mineralocorticoids (e.g., Aldosterone):
- Secreted in response to kidney signals
- Controls salt (Na⁺) and water balance in the blood
- Regulates blood pressure
Androgens:
- Act as precursors to male and female sex hormones
- Particularly important during menopause in women
- Although main sex hormone production occurs in the testes and ovaries, the adrenal cortex supplements this
What hormones does the adrenal medulla produce and what are their functions?
The adrenal medulla secretes adrenaline and noradrenaline during times of stress (e.g., fight-or-flight response), triggered by the sympathetic nervous system.
Adrenaline:
Stimulates glycogen breakdown in the liver to release glucose into the blood
Increases heart rate and blood flow to the brain and muscles
Noradrenaline:
Also increases heart rate
Dilates airways in the lungs for improved oxygen delivery
Constricts blood vessels in non-essential organs (e.g., digestive system) to raise blood pressure
Dilates pupils to enhance visual awareness
What are the exocrine and endocrine roles of the pancreas?
Exocrine function:
Secretes digestive enzymes via the pancreatic duct into the duodenum
Involves acinar cells grouped in clusters called secretory acini
Enzymes include:
Amylase – breaks down starch into maltose
Trypsin (a protease) – digests proteins into amino acids
Lipase – breaks lipids into glycerol and fatty acids
Endocrine function:
Performed by clusters of cells called Islets of Langerhans
Contain:
Alpha cells (stained red): produce glucagon, secreted when blood glucose is too low
Beta cells (stained green): produce insulin, secreted when blood glucose is too high
These hormones are released directly into the bloodstream
What are acinar cells and what do they produce?
Acinar cells are the main cell type involved in the exocrine function of the pancreas. They are grouped into clusters called secretory acini and surround the branches of the pancreatic duct.
They produce pancreatic juice, an alkaline fluid containing:
Amylase – breaks starch into sugars
Trypsin – breaks proteins into amino acids
Lipase – breaks lipids into fatty acids and glycerol
These enzymes are secreted into the duodenum to support digestion.
What are the Islets of Langerhans and what hormones do they release?
Islets of Langerhans are clusters of endocrine cells scattered throughout the pancreas. Each islet contains:
Alpha cells (larger, more numerous): produce glucagon
Increases blood glucose by stimulating glycogen breakdown
Beta cells: produce insulin
Decreases blood glucose by stimulating glucose uptake and storage
Both hormones are secreted directly into the bloodstream, making this an endocrine function.
LEARN MICROGRAPH OF PANCREAS!!
