Physiology Flashcards
What is the maintenance of steady state within our bodies by coordinated physiological mechanisms?
Homeostasis
Where does a lot of physiological control occur?
Cell membrane
What is central to the functionality of nerve and muscle cells?
Changes in membrane potential
What must a control system be able to do to maintain homeostasis?
Sense deviations from normal, integrate this information, make appropriate adjustments
What is intrinsic control?
Local controls within an organ
What is extrinsic control?
Regulatory mechanisms from outside an organ, accomplished by the nervous and endocrine systems
What is feedforward?
Responses made in anticipation of a change
What is responses made after a change has been detected?
Feedback
What is a deviation in a controlled variable detected by?
Sensors
What does a sensor inform?
Appropriate control centre
What do control centres instruct?
Effectors
What is an example of positive feedback?
Contractions during labour
Where are membranes found?
The outer boundary of every cell
How permeable are membranes?
Selectively permeable
What do membranes control entry and exit of?
Entry of nutrients and exit of waste/secretory products
What are the amphipathic parts of lipids?
Hydrophilic head, hydrophobic tail
What do lipids form in aqueous solution?
Fluid, lipid bilayer
What is movement of membrane phospholipids dependent on?
Temperature
What does cholesterol do in the membrane?
Aids stiffening and can flip easily
What is the lipid membrane permeable/impermeable to?
Impermeable- charged molecules and water soluble substances
Permeable- small polar molecules
Where are peripheral membrane proteins?
Not embedded within the membrane and adhere tightly to the cytoplasmic/extracellular surface
What are transmembrane proteins?
Integral proteins which span the membrane
What can integral proteins be linked to?
Membrane lipids or fatty acids
What can integral proteins act as?
Ligand binding receptors, adhesion molecules, transporters, enzymes, intracellular signals
What do pores and channels allow?
Passive transport
What do carrier transporters do?
Facilitate or couple the transport of a molecule
What do transport pumps do?
Use energy from ATP to transport substances against a gradient
What are docking marker acceptors and where are they found?
Inner membrane surface, interact with secretory vesicles leading to exocytosis
What are short chain carbohydrates bound to membrane proteins or lipids known as?
Glycoproteins or glycolipids
What do glycoproteins/lipids form a layer called?
Glycocalyx
What do membrane carbohydrates have a role in?
Self identity markers and tissue growth
What are tight junctions?
Join the lateral edges of epithelial cells near the apical membranes
What are adhering junctions which anchor together cells, especially in tissues subject to stretching?
Desmosomes
What are gap junctions?
Communicating junctions which allow the movement of charge carrying ions and small molecules between 2 adjacent cells
What two properties determine whether a particle can pass through the membrane or not?
Lipid solubility and size
What is required for any transport through membranes?
A driving force- active or passive
What two mechanisms drive unassisted transport?
Diffusion down a concentration gradient or movement along an electrochemical gradient
Increasing what factors increases the rate of diffusion?
Concentration gradient, membrane surface area, lipid solubility
Decreasing what factors increases the rate of diffusion?
Molecular weight and distance
What type of channels are always open, or ligand gated?
Leak channels
What is it known as when electrical and chemical gradients act on an ion at the same time?
Electrochemical gradient
What is the electrochemical gradient involved in setting up?
Resting membrane potential
What is the relative speed of osmosis?
Slow
What is used to help water transport?
Aquaporin channels- passive
What makes different cells have different permeabilities to water?
Different numbers of aquaporins
What is osmolarity?
The concentration of osmotically active particles in a substance
What are two methods for carrying molecules against concentration gradients?
Carrier mediated transport or vesicular transport
What happens when a substance binds to a carrier transporter?
The carrier changes conformation
What 3 characteristics determine the kind and amount of material transferred through carrier mediated transport?
Specificity, saturation, competition
What are the two forms of carrier transport?
Facilitated diffusion or active transport
What is primary active transport?
Energy directly required
What is secondary active transport?
Energy not used directly, uses second hand energy stored in ion concentration gradients
What does Na+/K+ ATPase transport?
3Na+ out for every 2K+ in
What does the Na+/K+ ATPase pump have a role in?
Establishing Na+/K+ gradients, regulates cell volume, energy source for secondary active transport
What ion is usually coupled in secondary active transport?
Sodium
What is symport transport?
Secondary active transport where the solute and sodium move in the same direction
What is antiport transport?
Secondary active transport where the solute and sodium move in different directions (Na+ into)
Does vesicular transport require energy?
Yes
What are examples of vesicular transport?
Exo and endocytosis
What is a membrane potential?
Uneven distribution of charge across a membrane
What does membrane potential refer to?
Differences in charge between layers of ECF and ICF
What type of cells have the ability to produce rapid changes in membrane potential?
Excitable cells e.g. nerve and muscle
What is the resting membrane potential?
-70mV
What will the electrical gradient be towards for Na+ and K+?
Negative side
What is the resting membrane potential more permeable to, K+ or Na+?
K+
What is the concentration gradient for K+?
Outwards
What is the electrical gradient for K+?
Inwards
What is the equilibrium potential for K+?
-90mV
What does the +/- sign on a polarity represent?
The excess charge on the inside of the membrane
What is the concentration gradient for Na+?
Inwards
What happens when more Na+ moves into the cell following its chemical gradient?
Outside becomes more negative and is full of Cl- ions
After an influx of Na+, what is the electrical gradient for Na+?
Outwards
What is the equilibrium potential for Na+?
+60mV
What happens with increasing permeability of the membrane to an ion?
This ion drives the membrane potential towards its own equilibrium potential more strongly
Which of K+ and Na+ has a bigger effect on membrane potential?
K+
What helps maintain K+ and Na+ gradient across the membrane?
Na/K ATPase
What type of current does Na/K ATPase create?
Hyperpolarising
What are examples of what membrane potential changes can cause?
Contraction of muscle or secretion of insulin
What is depolarisation?
Membrane potential becomes less negative
What is hyperpolarisation?
Membrane potential becomes more negative
What are ion channels?
Transmembrane proteins which allow rapid flow of selected ions
What are the three types of gated ion channels?
Membrane voltage (voltage gated), chemical substances (ligand gated), physical stimuli
What ion channels are responsible for the depolarisation (upstroke) of APs?
Voltage gated Na+
What ion channels are responsible for the hyperpolarisation (downstroke) of APs?
Voltage gated K+
When do Na+ ion channels become activated during and AP and what does this cause?
Threshold potential- rapid depolarisation
What do neuron APs allow signalling over?
Long distances
Does the size of the stimulus have an effect on the size of the AP?
No- it happens or it doesn’t
What activates both Na+ and K+ channels?
Membrane depolarisation
Which ion channel responds to membrane depolarisation quicker?
Na+
The activation of which ion channel is self reinforcing and what does this mean?
Na+: the opening of a few channels causes more to open which causes more depolarisation (positive feedback)
The activation of which ion channel is self limiting and what does this mean?
K+: outward movement of K+ causes repolarisation which then turns off the stimulus for opening (negative feedback)
What is the refractory period?
During maintained depolarisation, Na+ channels enter a non-conducting, inactivated state
What is required after the refractory period?
Repolarisation for the channels to enter the closed state
On an AP graph, the area from the start of hyperpolarisation to the lowest point on the graph is known as what?
Absolute refractory period
What does the absolute refractory period mean?
No stimulus, however large can elicit a second AP
What is the state of the Na+ channels in the absolute refractory period?
All inactivated
On an AP graph, what is the area from the end of the absolute refractory period to the area where the next AP begins known as?
Relative refractory period
What does the relative refractory period mean?
A stronger than normal stimuli may elicit a second AP
What is the state of Na+ channels in the refractory period?
Mixed inactivated and closed channels as the membrane is hyperpolarised
What is the maximum number of APs in a second?
1000
Why do passive signals in nerve cells not spread far?
Current loss
What is the potential change of an axon relative to?
The given current
What does membrane potential decrease exponentially with?
Distance
What does the distance over which the current spreads depend on?
Membrane and axial resistance
What is the effect of diameter of the axon on current flow resistance?
Bigger the diameter, lower the resistance
What does greater current spread increase?
AP conduction velocity
Is conduction faster in myelinated or non-myelinated axons?
Myelinated
What are Nodes of Ranvier?
Points between myelin sheaths of axons
What id Saltatory conduction?
APs jumping between Nodes of Ranvier
What are examples of demyelinating conditions?
MS and Guillian-Barre syndrome
What do demyelinating conditions cause?
Slowing or cessation of nerve conduction
What is fuel metabolism regulated by?
Hormones- glucagon, insulin, growth hormone, adrenaline and cortisol
What does thyroid hormone regulate?
Metabolic rate
What can be used instead of glucose in prolonged starvation?
Ketones
What does hypoglycaemia lead to?
Confusion and coma
What does hyperglycaemia lead to?
Damaged blood vessels
What are the two types of glands which the pancreas contains?
Exocrine and endocrine (islets of Langerhans)
What do exocrine pancreatic cells produce?
Secrete digestive enzymes and HCO3- to intestinal lumen
What do alpha cells in the islets of Langerhans produce?
Glucagon
What do beta cells in the islets of Langerhans produce?
Insulin
What do delta cells in the islets of Langerhans produce?
Somatostatin
What do F cells in the islets of Langerhans produce?
Pancreatic polypeptide
What does insulin stimulate?
Anabolism: glucose to glycogen, amino acids to proteins and fatty acids to triglycerides
What is insulin the hormone of?
The fed state
What does glucagon stimulate?
Catabolism: glucagon to glucose, triglycerides to fatty acids
What is glucagon the hormone of?
Hunger state
What does glucagon have no effect on?
Protein metabolism
What are the most abundant cells in the islets of Langerhans and whereabouts are they found?
Beta cells in the centre
Which cells are found around the outsides of islets of Langerhans?
Alpha and delta
What are all the different types of cells of the islets of Langerhans linked by?
Gap and tight junctions
What happens to insulin when glucose in the blood is high?
More is secreted into the blood
During fasting, less insulin is secreted and lipids and amino acids are mobilised. What do these lipids and amino acids do?
Provide fuel for oxidation and act as precursors for hepatic ketogenesis and gluconeogenesis
What effect does sympathetic/parasympathetic stimulation have on insulin secretion?
Sympathetic- inhibits, parasympathetic- stimulates
What effect does exercise have on insulin secretion?
Suppresses it
What 3 incretins (peptides) increase insulin secretion?
CCK, GLP-1 and GIP
Where are incretins released and what do they do?
GI tract cells- feedforward mechanism to prime Beta cells for insulin secretion
What are the three prime targets for insulin?
Liver, skeletal muscle and adipose tissue
Where else can insulin affect but isn’t a prime target?
Cardiac muscle
Where are insulin insensitive cells?
Brain, kidneys and RBCs
What is the glucose storage molecule in liver and skeletal muscle?
Glycogen
What is the glucose storage molecule in adipose tissue?
Triglycerides
How does insulin lower plasma glucose in the liver?
Activating enzymes which convert glucose to glycogen
How does insulin lower plasma glucose in skeletal muscle?
Stimulating uptake of glucose from blood into muscle via GLUT4
Where is the defect in type 1 and 2 diabetes?
Type 1- beta cell function
Type 2- insulin receptor sensitivity
Which type of diabetes is more prone to ketogenesis?
1
How is diabetes diagnosed?
Glucose after a meal higher then 11mmol/l
What are some effects of severe diabetes?
Increased plasma glucose after a meal, glucose in urine, formation of ketone bodies, decreased pH and hyperventilation
What is glucagon secreted in response to?
Ingested proteins
What is the principle target of glucagon?
Liver
Where are adrenaline and cortisol released?
Adrenal gland in response to stress
What do adrenaline and cortisol do to plasma glucose?
Increase it
What do adrenaline and cortisol do to gluconeogenesis?
Stimulate it
What does adrenaline stimulate which cortisol doesn’t?
Glycogenolysis
What does cortisol stimulate which adrenaline doesn’t?
Protein catabolism and lipolysis
When are adrenaline and cortisol released?
Adrenaline- short term emergencies
Cortisol- long term
Where is growth hormone secreted?
Anterior lobe of pituitary gland
What does growth hormone cause in response to starvation?
Decreased glucose uptake by muscles, ,obilises glucose from liver, promotes lipolysis in fat cells
What is core optimum body temperature?
Around 37.8 degrees C
How can body heat be gained?
Metabolic heat (internal), radiation, convection, conduction (external)
How can body heat be lost?
Radiation, convection, conduction, evaporation
What hormones increase heat production through metabolic heat?
Adrenaline, noradrenaline, thyroxine
What external action does increased metabolic heat cause?
Muscle activity and hence shivering
What is conduction?
Transfer of heat from objects in contact- heat moves from warmer to cooler
What is convection?
Transfer of heat by air or water currents which carry heat away from the body
What is an active evaporative heat loss process?
Sweating
What controls sweating?
Sympathetic nervous system
What is body temperature controlled by?
A negative feedback system
Where are central thermoreceptors?
Hypothalamus and abdominal organs
Where are peripheral thermoreceptors?
Skin
Where are the effectors for maintaining body temperature?
Skeletal muscle, skin arterioles, sweat glands, behavioural adaptations
Where is the temperature control centre?
Hypothalamus
What part of the hypothalamus is activated by cold?
Posterior
What part of the hypothalamus is activated by warmth?
Anterior
What adaptations does cold result in?
Vasoconstriction and increased skeletal muscle tone (shivering)
What adaptations does warmth result in?
Vasodilation, evaporation of sweat and decreased skeletal muscle tone
What happens to the temperature setpoint in fever?
Increases
Where are chemicals released from in response to infection/inflammation?
Macrophages
What do macrophages stimulate release of which act on the hypothalamus to change the set point?
Prostaglandins
What response does the hypothalamus have to an increased temperature setpoint?
Elicits the cold response to increase temperature
What classes as hyperthermia?
> 40 degrees
What classes as hypothermia?
< 35 degrees
