Homeostasis Flashcards
Define homeostasis
maintenance of a constant internal environment
Homeostasis is the property of a system in which variables are regulated so that internal conditions remain stable and relatively constant
What is controlled?
Temperature
Glucose
Blood oxygen
Hydrogen ion
Potassium
Homeostasis model
slide 7
set point
normal range of something
control centre
compares what the level is to what the level should be
Why is communication important in homeostasis?
Cells must communicate with each other to achieve homeostasis
There needs to be a co-ordinated response
Major communication systems include
endocrine (hormones)
nervous (currents and neurotransmitters)
immune (antibodies, cytokines and interleukins)
Autocrine system
Chemical is released from cell into the extracellular fluid and then acts upon the very cell that secreted it
cell sends a isgnal, signal travels to a recpetor on the same cell
Paracrine system
Chemical messengers involved in the communication between cells, released into extracellular fluid - travel short distances, local communication.
-Cell sends a signal, Signal diffuses across gap between cells
-Inactivated locally, so doesn’t enter the blood stream
-Cells then reach a cell a short distance away from the original cell
Examples of Paracrine
Acetylcholine at neuromuscular junction
Interleukins
-Signalling in the immune system
-Mainly between white blood cells
Platelet derived growth factor (PDGF)
-Released from platelets
-Regulates cell growth
Endocrine system (secretion into blood):
Produce and secrete hormones, communication between cells, travel much longer distance, systemic communication, can affect the whole body.
Travel in the blood to then reach the target cell (which is elsewhere in the body relative to the endocrine cell)
Endocrine organs/glands
Hypothalamus (hypothalamic hormones)
include: Dopamine
Pituitary (anterior pituitary hormones)
include: FSH, LH and thyroid stimulating hormone (TSH)
Posterior pituitary hormones
include: oxytocin (released during child birth)
ADH/ vasopressin) (in brain, master endocrine organs)
Master enocrine glands
-Thyroid (front of neck)
-Parathyroid (directly behind neck)
-Adrenals (above kidneys)
-Pancreas
-Ovaries
-Testes
Definition of Hormone
Molecule that act as a chemical messenger
Hormones are classified according to structure
Amino-acid derivatives
Peptide
Steroid
Amino acid hormones
Synthesised from tyrosine
Acts in same way to peptide
Example; adrenaline, thyroid hormones (thyroxine (T4) and triiodothyronine (T3))
Peptide hormones
Made of amino acids
Vary in size from few amino acids to small proteins
Some have carbohydrate side chains (glycoproteins)
Large, hydrophilic charged molecules that cannot diffuse across a membrane.
They bind to receptors on membranes.
Peptide hormone is pre-made and stored in cell, then released and dissolved into blood when needed. Binds to receptor on membrane then chemical reaction produces a quick response from the cell and a 2nd messenger is released in the cell
VERY FAST (minutes) (signal transduction cascade)
Examples; Insulin, growth hormone, thyroid stimulating hormone (TSH) and ADH/vasopressin
Peptide and amino acid hormones similarity
Produce a quick reaction in the body
Peptide Hormones- TSH
In the pituitary cell: Hormone pre-made and stored in cell ready to be released when needed
Hormone dissolved in blood.
Receptor on cell membrane
Chemical reaction produces quick response from cell.
(Signal transduction cascade)
Steroid Hormones
All made from cholesterol
Different enzymes modify molecule to produce a variety of hormones
Hydrophobic- Can’t dissolve in water
Can dissolve in lipids
How steroid hormones work?
Can cross membranes BUT requires transport proteins in blood, targets an intracellular receptor.
Steroid hormone is made by cell and diffuses out once made (not stored), transported in blood bound to transport proteins as it cannot dissolve in water.
Binds to receptor inside cell
RESPONSE (hours/days) since it directly affects DNA- SLOW
Examples; Testosterone, oestrogen and cortisol (long term stress hormone)
Steroid hormones- testosterone
Testosterone made by cell and diffuses out once made in the testes through the phospholipid bilayer
Transported in blood bound to transport protein as can’t dissolve in water (a lot pf hormones have thoer own specific carrier protien)
Receptor is in the target cell
Slow response as directly affects DNA
Positive feedback loop
Amplification of signal.
E.g. clotting cascade & oxytocin release during childbirth
Negative feedback loop
Centre of homeostasis, main way endocrine hormones are controlled.
E.g. blood sugar regulation, temperature regulation, blood pressure regulation, thyroid regulation
- thyroxin, as well as going to target cell, is also sensed by the pituitary, if there is too much thyroxine in the blood then the high thyroxine levels will stimulate the pituitary to stop producing thyroid stimulating hormone (TSH)
Define Exocrine
Secretion into ducts then into organ
Key differences between endocrine and paracrine:
Hormones travel in blood in endocrine whereas in paracrine chemical messengers only travel in extracellular fluid.
Endocrine affects more things and travels further than paracrine
