living control mechanisms Flashcards
define homeostasis
the maintenance of a constant internal environment
is the property of a system in which variables are regulated so that internal conditions remain stable and relatively constant
examples of things that need to be kept at a certain level
temperature
blood pressure
pH, glucose and oxygen concentration
hydrogen ion concentration
potassium levels
how is homeostasis achieved
- have a set point (normal range)
- sensor detects change
- control centre processes
- effectors make a change
- variable is regulated back to normal
does every single thing have the same control centre
no its different for everything
what are the 2 main types of communication system
- nervous system
- endocrine system
what does the nervous system use to communicate
electrical impulses
what does the endocrine system use to communicate
hormones
what is a receptor
the part that receives a signal from a cell
what are the 3 main categories of communication
- autocrine
- paracrine
- endocrine
how does autocrine communication work
Chemical is released from cell into the
extracellular fluid and then acts upon the same cell that secreted it
how does paracrine communication work
Chemical messengers involved in the
communication between cells, released into the extracellular fluid - travel short distances, local communication (the cells are close to each other)
the signal diffuses across gaps between cells and doesn’t enter the bloodstream
what are 2 key differences between paracrine and endocrine
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
how does exocrine communication work
Secretion into ducts then into organ
example of paracrine
interleukins
they signal in the immune system
mainly between white blood cells
how does the endocrine communication work
- endocrine cell releases hormone
- hormone travels in bloodstream
- goes to target cell elsewhere in the body
which organs and glands are involved in the endocrine system (7)
- 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) and ADH/ vasopressin) (in brain, master endocrine organs),
- thyroid (front of neck), parathyroid (directly behind neck),
- adrenals (above kidneys),
- pancreas,
- ovaries
- testes
define hormone
a molecule that acts as a chemical structure
how are hormones sub divided into different types
according to structure
thus they all have different functions
what are the different types of hormones (3)
- amino acid derivatives
- peptide
- steroid
what are the most simple type of hormones
amino acid hormones
example of amino acid hormone
adrenaline
what are amino acid hormones synthesised from
tyrosines
what are peptide hormones made of
several amino acids joined together
vary in size from few amino acids to small proteins
some have carbohydrate side chains (glycoproteins)
hydrophilic
do peptide and amino acid hormones produce a quick or slow reaction in body
a quick reaction
example of peptide hormone
thyroid-stimulating hormone - stimulates the thyroid gland
released from pituary
how do peptide hormones work
- cell makes the hormone
- hormone is stored within the cell ready to be released when required
- hormone is dissolved in blood stream
- goes round blood stream to receptor cell on cell membrane
- hormone binds to receptor
- chemical reaction produces quick response from cell
what are steroid hormones derived from
cholesterol
different enzymes modify molecules to produce a variety of hormones
properties of steroid hormones
cant dissolve in water
cant dissolve in lipids
do steroid hormones produce slow or fast response
slow response
how do steroid hormones work
- made continuously by cell
- diffuse through lipid bilayer into blood stream as they are made (Not stored)
- bind to specific carrier protein
- which carries them throughout blood stream
- hormone dissolves through cell membrane at other end
- receptor is inside target cell
- hormone produces change on DNA
- by affecting DNA replication or transcription
- this is why its slow
what is a positive feeback loop
- signal is amplified
- so cell is stimulated to produce more
examples of positive feedback (2)
clotting cascade
oxytocin release during childbirth
what does negative feedback loop do
main way endocrine hormones are controlled.
which systems use negative feedback
blood sugar regulation, temperature regulation, blood pressure regulation, thyroid regulation
how is thyroid regulated using negative feedback
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)
what are problems with feedback
Can get primary hypothyroidism: that is the thyroid is
producing too little thyroxine to induce negative feedback, meaning TSH levels in the blood keep increasing since pituitary doesn’t think there is enough thyroxine in the blood. Can also get primary hyperthyroidism: whereby the thyroid produces too much thyroxine and keeps producing regardless of the presence of TSH produced by the pituitary, TSH levels fall but thyroxine levels rise. Primary - means the problems is with the endocrine gland e.g. the thyroid. Secondary - means the problem is with the pituitary or hypothalamus e.g secondary hypothyroidism - whereby both TSH and thyroxine levels are low (indicative of secondary hypothyroidism) since the pituitary is not producing enough TSH thus little thyroxine is produced meaning target cells are not being induced.
