PHS3341 FINAL

homeostasis

maintenance of a dynamic, steady state in the internal environment

4 primary types of tissues

muscle, connective, nervous, epithelial

organ

2+ tissues organized together for a particular function

11 body systems

circulatory
skeletal
muscle
digestive
integumentary
immune
nervous
respiratory
endocrine
reproductive
urinary

stem cells

undifferentiated cells

where do embryo stem cells come from

blastocysts

where do adult stem cells come from

adult tissues

ICF

fluid in all cells

ECF

plasma + interstitial fluid

plasma

fluid portion of the blood

how can homeostatic systems be classified

intrinsic and extrinsic controls
intrinsic controls are inherent within an organ
extrinsic controls are regulatory mechanisms initiated outside of an organ

3 parts of homeostatic control system

sensor/receptor: detects changes in environment
integrator/control center: integrates this info
effector: triggers the needed adjustments

ER

extensive network of fluid-filled tubules and flattened sacs partially studded with ribosomes that forms new cell membrane and other cell components and manufactures products for secretion

golgi complex

modifies, packages, and distributes newly synthesized proteins

lysosomes

digestive components of the cell

centrioles

site of new growth for microtubules

intermediary metabolism (what and where)

set of all reactions in a cell that involve the synthesis, transformation, and degradation of small molecules like amino acids, fatty acids, and simple sugars
in cytoplasm

2 factors for permeability across plasma membrane

relative lipid solubility
size of particle

what can pass through the plasma membrane unassisted

highly lipid soluble molecules
small molecules
uncharged/nonpolar molecules

what cannot pass through plasma membrane unassisted

large molecules
charged/polar molecules
hydrophilic molecules

3 major protein types in ECM

collagen, fibronectin, elastin

what is the ECM mostly secreted by

fibroblasts

diffusion

movement of molecules from an area of high concentration to an area of low concentration due to the random collisions between molecules

concentration gradient

difference in concentration in two adjacent areas

factors affecting diffusion rate

size of molecules
temperature
concentration
medium
surface area

electrochemical gradient

when both electrical gradient and chemical gradient are acting on a molecule

electrical gradient

difference in charge in two adjacent areas

how to calculate concentration

# of solutes/volume of water

what is osmolarity

total number of solutes in a solution

osmosis

net diffusion of water

when does net movement of water stop

when hydrostatic pressure is equal to osmotic pressure

2 mechanisms of assisted transport

carrier-mediated transport
vesicular transport

how do carrier proteins move solutes

via conformational changes that alternatively expose binding sites to ECF and ICF

3 characteristics to determine the kind and amount of solute moved

specificity
saturation
competition

saturation of carrier proteins

# of carrier proteins are limited, until transport maximum (Tm) is reached, transport of solutes is proportional to the concentration, but when Tm is reached, only the maximum amount of solute can be transported

facilitated diffusion

carrier transport of a solute down its concentration gradient

active transport

carrier transport of a molecule against its concentration gradient

Na+/K+ pump activity

has ATPase activity, cleaving a phosphate off of ATP and phosphorylating itself.
phosphorylation of pump increases affinity of Na+ inside the cell, binding it and flipping its conformation
subsequent dephosphorylation decreases affinity for Na+, releasing it outside the cell, and increases affinity for K+, binding it and flipping its conformation back
process goes on, removing 3 sodium ions and taking in 2 potassium ions inside the cell

uses of Na+/K+ ATPase pump

establishes Na+ and K+ concentration gradients in plasma membrane of all cells
regulates cell volume by regulating solute concentrations inside cell
energy used is also used for secondary active transport of glucose and amino acids

Na+/K+ ATPase Pump cotransport of glucose

Na+/K+ pump keeps intracellular Na+ conc. low, so carrier has a higher affinity for Na+ when it is exposed to the outside
binding of Na+ increases carrier affinity for glucose, binding it
binding of both Na+ and glucose flips the conformation
Na+ is released inside the cell because of its low intracellular concentration, and glucose is also released because of its decreased affinity since Na+ has been released

cotransport vs countertransport

cotransport: both ion and solute move across membrane in the same direction
countertransport: ion and solute move in opposite directions

where is Na+/K+ pump found

in plasma membrane of all cells

endocytosis

plasma membrane surrounds substance to be ingested, fuses over the surface and pinches off a membrane-enclosed vesicle so that engulfed material is trapped within the cell

fate of endocytosis

in most cells, lysosomes degrade the membrane releasing the vesicle’s contents inside the cell
in some cells, endocytotic vesicle bypasses the lysosomes and moves to the opposite side of the cell where it will release its contents via exocytosis

pinocytosis

small portion of ECF is internalized

receptor-mediated endocytosis

binding of a protein causes plasma membrane to dip inward then seal off at the surface, trapping protein inside the cell

membrane potential

separation of charges across membrane

Ohm’s Law

V = IR

relative concentrations of K+, Na+, and A- in and out cells

higher K+ concentration inside
higher Na+ concentration outside
higher A- concentration inside

when do we get K+ equilibrium potential

when K+ concentration and electrical gradient are equal

Nernst Equation

E = 61 log (C0/Ci)

EK+ and ENa+

EK+ is -90mV
ENa+ is +60mV

why are nerve and muscle tissues composed of excitable cells

because when excited, they change their resting potential to produce electrical signals

polarization

when potential is not at 0 mV

depolarization

potential gets less negative than at rest

repolarization

potential gets more negative towards the resting potential

hyperpolarization

membrane gets more negative than at rest

what is resting potential

-70 mV

what are changes in membrane permeability due to

interaction of a chemical messenger
change in electrical field in the vicinity
stimulus
imbalances in leak-pump cycle

2 membrane channels

leak channels
gated-channels

four kinds of gated channels

voltage-gated
chemically gated
mechanically gated
thermally gated

graded potentials

short-distance
can be summed
most commonly, sodium channels open causing a slight depolarization which causes a current and depolarization in adjacent areas
bidirectional
strength depends on stimulus strength
magnitude of local current decreases with distance as some current is leaked through plasma membrane

AP outline

trigger causes depolarization, if threshold is met then explosive depolarization follows to +30mV, followed by a repolarization and a hyperpolarization and a depolarization back to resting potential

three conformations of voltage gated sodium channel

closed but can be opened (activation closed, inactivation gate open)
closed and not capable of opening (both gates closed)
open and activated (both gates open)

why is membrane more permeable to potassium at rest

both voltage-gated potassium and sodium channels are closed, but there are more leak channels for potassium

triggering of AP in terms of ions

trigger causes membrane to depolarize and sodium channels open, causing more depolarization
as activation gate opens, inactivation gate closes slowly causing sodium to rush in
at peak of AP, sodium channels close and potassium channels slowly open, causing an efflux of potassium
leads to hyperpolarization
absolute refractory period as membrane gets depolarized back to resting potential

two ways for AP to be conducted

contiguous conduction: AP is propagated along every patch of membrane down axon (slower)
saltatory conduction: impulse jumps from node to node in myelinated nerve

myelin sheat

lipid covering on nerve that conserves energy, prevents current leakage, and increases speed of AP propagation

absolute refractory period

once voltage gated sodium channels open, they can’t be opened again until resting potential is reached
makes APs unidirectional

relative refractory period

membrane is restimulated only with a stronger stimulus

what does speed of AP depend on

diameter of fiber
whether it’s myelinated or not

what are myelin-forming cells

oligodendrocytes in CNS and Schwann cells in PNS

axon regeneration due to damage in CNS and PNS

axons damaged in CNS can’t be regenerated as though the axons can regenerate themselves, the oligodendrocytes synthesize proteins that inhibit axonal growth
in PNS, schwann cells guide the restoration of axon terminals by first phagocytizing the debris and forming a regeneration tube

what can neurons terminate on

muscle
gland
another neuron

synapse

junction between the cell body and dendrites of one neuron and the axon terminals of another

what is at the end of an axon terminal

synaptic knob where neurotransmitters are stored

neurotransmitter release

when AP travels down to axon hillock, local change in potential opens voltage-gated calcium channels
calcium flows into synaptic knob causing release of neurotransmitter by exocytosis
neurotransmitter diffuses across cleft and binds with receptors on postsynaptic membrane
binding of neurotransmitter causes opening of specific ion channels and triggers specific postsynaptic response

excitatory synapse

binding of neurotransmitter results in nonspecific cation channels opening
influx of sodium into the cell (few potassium out) causes slight depolarization
makes membrane more excitable (closer to threshold) resulting in EPSP

inhibitory synapse

binding of neurotransmitter increases permeability of both potassium and chloride
causes hyperpolarization (potassium out, chloride in)
makes membrane less excitable (further from threshold) resulting in IPSP

GPSP

grand postsynaptic potential, summation of all EPSPs and IPSPs occurring simultaneously

inactivation of neurotransmitter

reuptake into axon terminal
diffusion away from cleft
enzymatic inactivation

parts of brain

brainstem (midbrain, pons, medulla)
cerebellum
forebrain - diencephalon (thalamus and hypothalamus) and cerebrum (basal ganglia and cerebral cortex)

cerebral cortex functions

voluntary control of movement
sensory perception
language
personality traits
sophisticated mental events

basal nuclei

inhibition of muscle tone
coordination of slow, sustained movements
suppression of useless patterns of movement

thalamus

relay station for all synaptic input
crude awareness of sensation
some degree of consciousness
involved in motor control

hypothalamus

regulation of many homeostatic functions
involved in emotion and behaviour
role in sleep-wake cycle
link between endocrine and nervous system

cerebellum

enlargement of muscle tone
coordination of complex motor activity
maintenance of balance
proprioception

brainstem 5 functions

origin of majority of peripheral cranial nerves
cardiovascular, respiratory, and digestive control centers
regulation of muscle reflexes involved in equilibrium and posture
arousal and activation of cerebral cortex
role in sleep-wake cycle

four types of glial cells

astrocytes
oligodendrocytes
microglia
ependymal cells

astrocytes 7 functions

form BBB
take up excess potassium
enhance synapse formation
scaffold during fetal brain development
forms neural scar tissue
physical support
take up and degrade neurotransmitter

oligodendrocytes

form myelin sheath in CNS

microglia

immune cells of CNS
release growth factors at rest

ependymal cells

line cavities in brain and spinal cord
help form cerebrospinal fluid
neural stem cells

microglia formation

formed by bone marrow in early embryonic development they move to CNS and activate upon infection or injury

four protective features of CNS

brain suspended in cerebrospinal fluid for cushioning
blood-brain barrier
bony exterior, skull for brain and vertebral column for spinal cord
3 meninges between bony exterior and nervous tissue

3 layers of meninges from outermost to innermost

dura mater, arachnoid mater, pia mater

dura mater

tough inelastic covering with two layers that are either close together or separate to form dural sinuses or venous sinuses (larger cavities)
venous blood drains from the brain into these sinuses to be returned to the heart and CSF also re-enters the blood at one of these sites

arachnoid mater

subarachnoid space is filled with CSF
protrusions of arachnoid tissue (villi) penetrate through gaps in dura mater and project into dural sinuses
CSF is absorbed across surface of villi into blood circulating in the sinuses