3-5 Flashcards
Define Homeostasis
The maintenance of relatively constant conditions in the body by physiological processes that act to counter any departure from the normal
Who first used the term homeostasis
Walter Bradford Cannon
Which variables are controlled in mammals
1) core body temperature
2) Osmotic Pressure
3) Arterial blood pressure 4) extracellular fluid volume
5) Blood gas concentrations
6) Concentrations of extracellular solutes like Na+, K+, and protons
What is a conformer
An organism who do not complete active homeostasis as they have the same components as surroundings
- Hag fish
Regulators?
GRAPH
Homeostatic organims
Poikilothermy
An organism that does not regulate it’s own internal temperature—> Naked Mole rat
How is homeostasis usually maintained
Negative feedback loops
Positive feedback examples
x 3
Urination
Parturition
Metamorphosis
How does negative feedback work
- Disturbance affects controlled system
- Sensor picks up difference
- Inverting amplifier
- Response which affects the controlled system
What are the main sensors for negative feedback loops in mammals
x 5
- Thermoreceptors (skin and hypothalamus)
- Osmoreceptors (hypothalamus)
- High pressure baroreceptors (carotid sinus, aortic arch and afferent arteriole of kidney)
- Low pressure baroreceptors (atria, great veins and pulmonary vasculature)
- Chemoreceptors (medulla oblongata and carotid and aortic bodies)
What are neurocrine transmitters
Substances released by neurones in the immediate vicinity of target cells or into the blood—>neurotransmitters are a subset of this group
Endocrine transmitters
Hormones
1) Synthesised by a specific tissue
2) Secreted into the bloodstream
3) Change the activity of that target tissue or organ
Paracrine transmitters
‘local hormones’
Diffuse through extracellular fluid to reach and affect target cells of a different cell type to itself
Histamine and Nitric oxide
Autocrine transmitters
Like paracrine but act on same cell type as those that secrete them
Cytokines
Transmitters released by immune cells
Pheromones
Released by animal into environment to affect physiology or behaviour of another animal of the same species
Water-soluble hormones
explain and 3 types
Stored in vesicles and released by exocytosis—>travel loose in blood and bind to membrane-based receptors
TYPES
1) Peptide/ protein hormones
2) Glycoproteins
3) Catecholamines (derived from tyrosine)
Lipid-soluble hormones
what and 4 types
Diffuse out of cells once made and transported in blood bound to special carrier proteins. Usually intracellular receptors
1) Steroid hormones
2) Thyroid hormones
3) fatty acid derivatives
4) Indolamines (melatonin)
G-protein coupled receptor
GRAPH
How to deactivate g-protein coupled receptor
Upon hydrolysis of GTP to GHDP on α-subunit will cause it to rebind to βγ-subunit and become inactive
- in cell a phosphodiesterase hydrolyses cAMP and terminates cell response
Lipid-soluble hormone receptors
Usually in cells and act directly as transcription factors
Getting rid of chemical messengers and half-lives
Most hormones metabolised by liver or kidneys
Half-lives of hormones in plasma can vary from 1-3 minutes for adrenaline to 7 days for thyroxine (T4)
Blood-brain barrier
Prevents circulating substances which also act as neurotransmitters from acting on the brain
- its formed of endothelial cells being connected by particularly tight junctions
- held there by glial cells foot processes
Where is the blood-brain barrier ‘leaky’
x4
- Posterior pituitary gland
- Median eminence
- Pineal gland
- Circumventricular organs
- fenestrated BBB so release hormones into blood or detect their presence
Where is the hypothalamus
Small region of the forebrain above the pituitary gland
What does the hypothalamus do?
Received input from many sources relating to both internal and external environment
—integrates information and controls physiological response—>homeostatic control centre
The hypothalamus contains multiple intercommunicating nuclei
These are collections of nerve bodies
Leptin example
intro
Protein hormone secreted by white fat cells and detected in arcuate nucleus of hypothalamus.
Use levels to establish body’s nutritional state
What if leptin levels are high?—so well fed
1) Feeding behaviour suppressed
2) Release for TRH
3) activates hypothalamic-pituitary-thyroid axis—>increase metabolic rate
4) other function regulated reproductive axis in women
Posterior pituitary
Downgrowth of the brain made of bundles of axons of nerve cells whose bodies are in the hypothalamus
Anterior pituitary
Originates from Rathke’s pouch and lies outside of the BBB—>produces hormones
ADH
Released from PP
- release at high osmotic pressure and in lower concentrations when there is low blood volume
1) Acts on kidney collecting ducts to increase water permeability
2) at higher concentrations causes vasoconstriction and compensates for loss of blood volume
Oxytocin
released by PP
mainly in reproductive functions like the fergusson reflex
(where stretch of cervix then causes more contractions to push baby out, expanding cervix more)
What is a portal vein
A vein that travels between two capillary beds
Anterior pituitary hormones
Involved mostly in control of endocrine glands elsewhere in the body
1) Glycoproteins
2) Somatomammotropins
3) Pro-opiomelanocortin
Hypothalamic-pituitary-thyroid axis
Hypothalamus send hormones to AP which cause release of another hormone which causes an endocrine gland (like thyroid) to release another hormone
—one of the jobs of this hormone is to inhibit the releasing hormone from hypothalamus=LONG-LOOP FEEDBACK
Short is from AP hormone inhibit hypothalamus and ultrashort is hypo prevents hypo
TPT example
GRAPH
Pulsatility
The releasing of hormones in bursts to prevent receptor down-regulation
Feed-forward control
A mechanim by which to prevent ‘overshooting’ the set point and requiring negative feedback to go the other way
- like in drinking
Prevents oscillating levels
What is dynamic equilibrium
Where there is no net force acting across a membrane as the concentration gradient is equal to the electrical gradient.
Represented by E (subscript of the ion)
Why do we say that concentration stays roughly constant
very few ions move across membrane before dynamic equilibrium
What is the Nernst equation?
at 20 degrees
E (ion) in mV = (58/z) log10(conc ion out/conc ion in)
what does it mean if the membrane potential does not equal the equilibrium potential of one ion
Then the membrane is permeable to more than one ion
Line predicted by the GHK equation fits the resting membrane potential of frog muscle cells than the line predicted by nernst K
What is the GHK equation
Picture
What does P represent in the GHK equation?
goldman-Hodgkin-katz
The relative permeability of the ion
What is ouabain
- toxin
- binds to sodium pump
- stops from working
- small loss of -5mV at first
- then slow to zero
What is the actual name of the sodium pump
- what does it do
Sodium-potassium ATPase
- pumps out 3Na+ with 2K+ into the cell
- requires ATP
role of sodium pump
Maintain the concentration gradients of sodium and potassium over long term and the slow leaking increases the concentration of sodium in the cell
How to change membrane permeabilities to ions
Open more channels specific to that ion
