Physiology Flashcards
What term describes
“Maintenance of steady states within our bodies by coordinated physiological mechanisms essential for function and survival of cells”?
Homeostasis
What types (2) of cells are influenced by changes to membrane potential?
Muscle and nerve cells
What are the 2 types of physiological controls to maintain homeostasis?
Intrinsic - local and inherent to organ
Extrinsic - accomplished by nervous and endocrine system
What is a response made in ANTICIPATION of change known as? Give an example.
Feedforward.
Exercise.
What is a feedback response?
Response AFTER change has been detected
What are the 2 types of feedback response?
Give an example for each
Positive - AMPLIFIES initial change (E.g. Uterine contraction during labour)
Negative - OPPOSES initial change (E.g. BP, Temp)
What are the 3 components in a feedback response? (Closed-loop)
Sensor - monitors MAGNITUDE
Control centre - COMPARES with a SET POINT
Effector(s) - RESPONSE to bring desired effect
What is the purpose of the baroreceptor reflex?
Short-term moment to moment control of MAP
What is blood pressure?
Outwards hydrostatic pressure exerted on arteries during cardiac contraction (Sytole) or relaxation (Diastole)
What is the cut-off for hypotension?
=/< 90/60mmHg
What is the normal pulse pressure range?
30-50mmHg
Is CO and SV based on both or 1 ventricle?
1 ventricle
What is the normal MAP range?
70-105mmHg
At least how much MAP is needed for vital perfusion?
60mmHg
What are the 3 components in a baroreceptor feedback response for MAP?
Sensor: Baroreceptor (Carotid sinus/ bifurcation via CN IX/ Hering’s nerve) & (Aortic arch via CN X)
Control centre: Medulla oblongata
Effectors: Heart (HR, SV) and Blood vessesls (SVR)
How does MAP affect the firing rate of the afferent neurons of the baroreceptors?
MAP rises - firing rate increases
MAP decreases - firing rate decreases
What is SVR?
Sum of all resistance of all vasculature in the systemic circulation
How much effect does CN X have on ventricular contractility?
Little
Mostly by sympathetic
What are the major resistance vessels? (Biggest change in pressure)
Arterioles
What regulates SVR?
Vascular smooth muscle - changes diameter thus resistance
Why are arterial smooth muscles partially contracted at rest?
Due to vasomotor/ sympathetic tone where there is tonic/continuous discharge and release of noradrenaline by sympathetic nerve
Parasympathetic innervation of arterial smooth muscle can be found in ONLY which body parts?
Penis and clitoris, otherwise no.
What happens when firing rate of afferent baroreceptor neurons decrease?
Reduced cardiac vagal efferent nerve fiber activity
Increased cardiac sympathetic efferent nerve fibre activity
Increased sympathetic vasoconstrictor nerve fibre activity
Sympathetic constrictor tone influences which vessels and what are the outcomes of each?
Veins - influences venous return hence SV
Arteries - influences SVR
What happens to the firing of baroreceptors in CHRONIC high BP?
Firing rate decreases
Only resets and fires again if there is an acute change above the NEW set point
How is MAP controlled in the long-term?
Control of blood volume (E.g. GI, Kidneys) - mainly endocrine
Does SV increase or decrease if cardiac contractility is increased?
Increase
Where does the medulla first synapse and what happens after that?
Nucleus tractus solitarius
Then relays information to other brain regions
Where is the vagal outflow for the heart relayed to in the CNS?
Nucleus ambigus in medulla
And regulation of spinal sympathetic neurons
If the baroreceptor reflex (autonomic nervous system) if an extrinsic control of SV then what governs the intrinsic control?
Frank-starling mechanism.
Direct relation between EDV and SV
How does blood flow in normal arteries? Any sound?
Smooth laminar fashion.
Inaudible.
What sound is heard when BP cuff exceeds SBP?
No sound as flow is blocked
What sound is heard when BP cuff is kept between SBP and DBP? Why?
Korotkoff sound.
Due to turbulent flow when BP intermittently exceeds cuff pressure.
What is the formula for MAP?
DBP + 1/3 (SBP-DBP)
How much longer is diastole compared to systole in a single cardiac cycle?
Twice longer
What is the normal pulse rate?
What else should you note for when taking a pulse? (3)
60-100bpm.
Rhythm, volume, character
What is the normal resp rate?
12-20/min
What is the normal capillary refill time?
<2s
How is consciousness recorded?
AVPU
or GCS
What is the normal O2 sat?
> 95%
At what temperature is the core body maintained at?
37.8
Increased body temp increases cell metabolism.
But what can overheating result in? (4)
Protein denaturation, nerve malfunction, convulsion, death
What can low body temp result in?
Slow down cell reaction and metabolism
What site is good for measuring body temp in hypothermia? (<35)
What is the normal range?
Rectal (more representative of core temp)
36.7 - 37.5
Other than rectal, what other sites can be used to measure body temp?
Tympanic - 35.5 - 37.5
Oral - affected by foods and drinks
Body temp shows slight diurnal variation.
When is body temp lowest?
Early morning
When is body temp higher in menstrual cycle?
2nd half from time of ovulation
What contributes to heat generation in the internal environment (3)?
- Brown fat
- Muscle activity (E.g. Shivering)
- Oxidation of metabolic fuel
What increases BMR?
Hormones such as adrenaline, noradrenaline, thyroxine
What contributes to heat generation from the external environment? (3)
Mostly radiation (50%). Convection, conduction
What contributes to heat loss to the external environment? (4)
Radiation, convection, conduction, evaporation
Is water or air a better conductor of heat?
Water
What is forced air movement across body surface (E.g. by wind or fan)
Carries more heat away in a given period (Wind chill factor)
Convection works with which other process?
Conduction.
E.g. Air warmed via conduction from skin before rising
What is passive evaporation?
Occurs continuously and not subjected to physiological control
What is active evaporation?
E.g. Sweating
Controlled by sympathetic NS
What is one environmental factor that affects evaporation?
Humidity
What is evaporation?
Energy from body required to convert water on skin surface and lining of respiratory airways into vapour
What are the 3 component for the feedback response to regulate temperature?
Sensor: Central thermoreceptors found in hypothalamus, abdominal organs for core temp. Peripheral thermoreceptors found in skin
Control centre: Hypothalamus
Effectors: Skeletal muscle, skin arterioles, sweat glands (and indirectly lead to behavioural changes)
What does the posterior and anterior hypothalamic centre contribute in terms of temperature regulation?
Posterior - cold
Anterior - warmth (A&W)
What are the outcomes of a cold response? (3)
Skin arteriole (SNS): Vasoconstriction restricts blood flow to skin surface to conserve heat
Skeletal muscle: Increased muscle tone, shivering, increased voluntary movement to produce heat/ warm the body
Behavioural changes: Postural change to reduce exposed surface area, warm clothes
What are the outcomes of a warm response? (4)
Skin arteriole (SNS): Vasodilate to promote blood to skin surface to lose heat
Skeletal muscle: Decrease muscle tone, decrease voluntary movement
Sweat glands: Sweat –> evaporation
Behavioural change: Cool clothing
What happens to temp control in infection/ inflammation?
What response is initiated?
Macrophage release endogenous pyrogens which stimulate prostaglandins release in the hypothalamus.
Body temp raised to a higher setpoint –> cold response initiated –> body starts to warm –> Fever (38-40 deg)
When is the setpoint restored back normal from a fever? (2)
What response is initiated?
- Pyrogen release reduced/stopped (E.g. Antibiotics)
- Prostaglandins synthesis reduced (E.g. NSAIDs)
Initiates hot response to cool body –> temp brought down to normal hypothalamic set point `
What can failure of heat regulating mechanism result in?
Hyperthermia (>40 deg)
What is hypothermia?
<35 deg
What component of the phospholipid bilayer have an influence on fluidity?
Cholesterol
What influences the thickness of the phospholipid bilayer?
R groups at the end of the fatty acid tail
How often do phospholipid flip to the other leaflet?
Rarely
What kind of molecules are able to cross the lipid bilayer freely?
Small, uncharged polar molecules
Lipid soluble molecules
What appearance does the cell membrane give off in the electron micrograph?
Laminar appearance with less dense layer in the middle
What are the 3 types of membrane proteins?
Peripherally associated membrane proteins
Integral membrane proteins
Docking-marker acceptors
Are peripheral membrane proteins covalently bonded to integral proteins?
No
What do peripheral membrane proteins adhere tightly to?
Cytoplasmic or extracellular surface of plasma membrane
Not embedded within membrane
How are integral membrane proteins intimately associated with the bilayer? (3)
- Span lipid layer once or several times (a-helical) - transmembrane proteins
- embedded but do not cross bilayer
- linked to lipid component of membrane of fatty acid derivative in the membrane
What are the 5 functions of integral membrane proteins
- Ligand-binding receptors
- Adhesion molecules (E.g. Integrins, Cadherins)
- Transmembrane movement of water soluble substance by acting as pores (passive), carriers (facilitated) or pumps (active)
- Enzymes (E.g. membrane bound carbonic anhydrase)
- Intracellular signalling role (E.g. Kinases and GTP-binding proteins at cytoplasmic surface)
Where are docking-marker acceptors located?
V-SNARE on Inner membrane surface of vesicle coat (coatamer)
What do docking-marker acceptors interact with?
V-SNARE interact with t-SNARE docking marker acceptor of targeted plasma membrane
How are appropriate cargo from the golgi lumen selected for export into vesicles?
Recognition markers in outer membrane of Golgi binds only to the sorting signals of protein molecules to be secreted
What is glycocalyx made of
Glycolipids and glycoproteins
What do membrane carbohydrates serve as?
Self-identify markers for growth, development and interaction
What kind of pump is usually found at the basolateral region of the epithelial cells?
Na+/K+ ATPase
What kind of transport do tight junctions promote and prevent?
Promotes transcellular and prevent/ reduce paracellular
Which part of the lateral edges of epithelial cells do tight junctions join at?
Near apical side
Do desmosomes allow materials to move around in the intercellular space?
Yes
What kind of tissues have desmosomes?
Those subjected to stretching
What is the polarity of the connexins/ channels of gap junctions?
Hydrophilic
*Allows charged ions and small molecules to pass
What are the 2 factors involved in permeability of a particle to pass through a membrane?
- Lipid solubility
2. Size
What are the 2 types of driving force for movement across a membrane?
Passive and active (ATP)
What kind of membrane transport involves molecules and ions that are passively driven across membrane down concentration/ electrical gradient?
*Give 2 examples
Unassisted membrane transport
Simple diffusion, Osmosis
When does simple diffusion stop?
When NET diffusion becomes zero - dynamic equilibrium
*NB there’s still ongoing movement of substance but gradient = 0
What are the 3 directly proportional factors and 2 inversely proportional factors of Fick’s law that affects RATE of NET diffusion across membrane?
Direct: Magnitude of gradient, surface area of membrane, lipid solubility of substance
Inverse: Molecular weight of substance, diffusion distance (bilayer thickness is fairly constant throughout)
Electrical gradient promotes movement of ios towards area of?
Opposite charge
*Like charges repel
What are the 2 types of ion-specific channel proteins?
Leak (always open)
Ligand-gated
What consist of an electrochemical gradient?
Simultaneous electrical and chemical gradient acting on an ion
What channels do water pass through readily in the plasma membrane?
Aquaporins (passive)
Osmosis is the NET diffusion of WATER from an area of higher to lower what?
Solute concentration
What is osmolarity?
Concentration of osmotically active particles in solution
What is the effect of solution on cell volume known as?
Tonicity
What is assisted membrane transport for? (2)
- Poorly lipid soluble molecules
2. Transport against concentration gradient
What are the 4 types of assisted membrane transport?
- Carrier-mediated - depends on carrier specificity and saturation (movement of molecule/time) and substance competition to carrier
- Facilitated - carrier transports down concentration gradient
- Vesicular - requires energy to form vesicles; endocytosis and exocytosis
- Active - Energy required to go against gradient; Primary and secondary. Another flashcard
Other than secreting enzymes and hormones, what else does exocytosis contribute to?
Adding carriers, channels or receptors to plasma membrane.
What is primary active transport?
Give an example of a pump
ATP hydrolysed by carrier protein, Pi binds to carrier and increases affinity for ion
Ion binds, conformation change, affinity reduced, ion and Pi released, shape reverts
Na+/K+ ATPase
What does transport 3 Na OUT and 2 K IN help in? (2)
- Regulate cell volume (solute concentration)
2. Indirectly serves as energy source for secondary active transport
What is secondary active transport?
Uses second-hand energy (indirectly) stored in ion concentration gradient (Na+ will want to go back into cell), acting as driving force to couple with transport solute across plasma membrane
What are the 2 types of secondary active transport?
- Symport - Solute and Na+ in same direction (E.g. GI absorption)
- Antiport - opposite direction (E.g. Na+/H+ to regulate intracellular pH)
What is the ‘separation of opposite charges across membrane to do work’ known as?
Membrane potential
What does the magnitude of membrane potential depend on?
Depends on number of opposing charges separated (concentration gradient and permeability to the ions)
At resting membrane potential, is the membrane more permeable to K+ or Na+
K+, by 100x
Are large negatively charged intracellular proteins permeable?
No
What is the movement of K+ based on concentration and electrical gradient like?
K+ moves out down concentration gradient -> ECF becomes more positive and moves back into cell down electrical gradient due to negatively charged proteins
When both opposing gradients are at equilibrium, net movement = 0
**Same for Na+ but opposite (ECF becomes more negative due to Cl-)
Why is the resting membrane potential slightly more positive than EK+ (Equilibrium potential of K+) in nerve cell?
Resting = -70mV EK+ = -90mV upon net diffusion outwards
More positive due to inward leak of Na+
What does Na+/K+ pump do to the membrane potential?
Hyperpolarises
Why does K+ preferentially move outwards in potassium selective channels?
Outward concentration gradient energy > inward electrical gradient energy
As an ion becomes more permeable, what does it drive the membrane potential towards?
It drives it closer to the ion’s own equilibrium potential
What are the stimuli that regulate gated-ion channels? (3)
- Voltage
- Ligand/ chemical
- Physical (Mechanical/ thermal)
What does action potential do to the polarity of the membrane?
Brief reversal
Generation of action potential follows which principle?
All or None
Activation of Na+ selective channel is?
What is the outcome?
Self-reinforcing
Opening of a few channels will open more (Positive feedback)
What happens to Na+ channels during maintained depolarisation?
What does it contribute to (2)?
Goes from open to non-conducting, inactive state which contributes to repolarisation and refractory period
What happens to Na+ channels during repolarisation?
Becomes closed (ready for depolarisation)
Activation of K+ selective channel is?
What is the outcome?
Self-liming
Repolarisation closes the channel (Negative feedback)
What are the 2 refractory periods? When do they each occur?
- Absolute - during repolarisation (no stimulus can elicit 2nd AP; all Na+ channel inactivated)
- Relative - during hyperpolarisation (stronger than normal stimulus can elicit 2nd AP - mix of inactivated and closed Na+ channels)
Action potential amplitude, magnitude and velocity. Do they fluctuate when propagated along the axon?
No, they stay constant
How to increase passive current spread which increases AP velocity (2)?
- Increase axon diameter
2. Decrease current leak across axon via insulation (Myelin)
How do myelinated and unmyelinated axons conduct AP?
Myelinated - salutatory conduction (jump from node of ranvier to next) –> faster
Unmyelinated - passive current spread
Demyelinating disorders slow nerve conduction.
Give 1 example from the CNS and PNS
CNS: Multiple sclerosis
PNS: Guillain Barre Syndrome
What kind of channels are clustered at the node of ranvier?
Voltage-activated Na+ channel
What microglial cells are responsible for myelin sheath production in the CNS and PNS?
PNS: Schwann cells - many surround a single axon thus multiple myelin layers
CNS: Oligodendrocytes - one cell surround many axons