Human Physiology Midterm 1

4 Major Cell Types

nerve, muscle, epithelial, connective tissue

External/Internal Environments

separated by epithelial membrane, epithelia barrier is continuous

External Environment

source of nutrients/oxygen, repository for wastes, most cells have no direct exchange with it

Examples of External Environment

surroundings external to skin, air in lungs, food in stomach, urine in intestines

Internal Environment

immediate environment of most cells, includes interstitial fluid and plasma

Extracellular Fluid

made of interstitial fluid and plasma

Plasma

fluid around blood cells

Interstitial Fluid

fluid around all other cells

Speed of Action: Endocrine System

slower responses (minutes, hours, longer), diffuse targets (entire tissues and organ systems could be impacted)

Speed of Action: Nervous System

very fast response (milliseconds), often specific target

System used by Endocrine and Nervous System

Negative feedback

Negative Feedback Steps

regulated variable deviates from normal range (stimulus), detection (receptor), inward pathway, integration center (brain), outward pathway, effector, response

Positive Feedback Loops

less common than negative, response reinforces stimulus, require terminating event to break loop

Feedforward control

body starts response in anticipation of change

Feedforward examples

increased saliva production in anticipation of a meal

Plasma Membrane

maintain non-random distribution of molecules across cell membranes, impedes penetration of water-soluble molecules/large polar molecules (glucose)/charged particles (ions)

Hydrophilic, Large, o Charged molecules

cannot cross plasma membrane without assistance,

Hydrophilic signaling molecules such as insulin

usually bind to extracellular receptor and initiates second messenger cascades, fast effect

Hydrophobic molecules

can cross plasma membrane

Hydrophobic molecules bind to

intracellular receptor and alter gene transcription and protein synthesis, slow effect

Increase in Temperature

increases net flux into a cell

increase in size of concentration gradient

increases net flux into cell

increase in surface area of a cell

increases net flux into a cell

increase in thickness of barrier

decreases net flux into a cell

Ways to cross plasma membrane

simple diffusion, facilitated diffusion, active transport, osmosis, vesicular transport

Facilitated diffusion

no energy required, requires transmembrane protein, moves substance down its concentration gradient

Ion Channels (facilitated diffusion)

when ion channels open ions move down concentration gradient

Transport rate across membrane

simple diffusion does not meet a max, substances that require transport will have a max transport rate

Primary Active Transport

requires energy (ATP), requires transmembrane proteins, pumps against concentration gradient

Primary Active Transport Example

Na+/K+ pump, directly uses ATP, 3 Na+ pumped out while 2 K+ pumped in, both against concentration gradients

Secondary Active Transport

pumps against concentration gradient, energy provided by another molecule’s gradient that was previously created by primary active transport, contains cotransport and countertransport

Secondary Active Transport Example (SGLT1 and SGLT2)

Na+ binds to carrier to create a high affinity binding site for glucose in ECF, glucose binding changes carrier conformation so binding sites now face ICF, Na+ released into ICF following concentration gradient

SGLT1 and SGLT2

when Na+ is pumped out of cell, Na+ concentration is low inside which creates gradient for SGLT1 to couple it with glucose entry (against its gradient)

Endocytosis

molecules from the ECF enter the cell through vesicles formed from plasma membrane

Exocytosis

intracellular vesicle fuses with plasma membrane and releases contents into ECF

Proteins

allow for cell to be selectively permeable

Hydrophilic Signaling molecules (noepinephrine)

typically bind to extracellular receptors on external surface of membrane

Hydrophilic signaling molecules can

initiate second messenger cascades and alter ion channel conformations

Hydrophilic signaling molecules have

fast effect and are metabolized/excreted quickly

Hydrophobic signaling molecules (steroid hormones)

bind to intracellular receptors and then alter gene transcription and protein synthesis, slow affect and are excreted slowly

Autocrine Signal Transmission

cell releases chemical messenger that binds to receptors on its own surface, causes response in the same cell

Paracrine Signal Transmission

cell releases chemical messenger to be picked up by a nearby target cell

Neurotransmitter Signal Transmission

cell releases chemical messenger that crosses synapse and picked up at the axon terminal of a neuron

Endocrine Signal Transmission

cell releases chemical messenger into bloodstream to be carried over a long distance to a target cell

Neurohormone Signal Transmission

nerve cells release hormones into bloodstream to regulate distant organs and cells

Signal Transduction

ligand binds its receptor, G protein complex activated, Adenylyl cyclase activated, increased levels of cAMP (second messenger), phosphorylates target proteins around cell

Water crosses most cell membranes

through aquaporins, always passive, always down concentration, osmosis

Osmolarity

total solute concentration of a solution per unit volume, tightly regulated

Roles in Homeostasis

learning, memory, language, intelligence, control system receives info about internal and external environment to integrate and direct cells

CNS

brain and spinal cord

PNS

afferent and efferent divisions

PNS afferent neurons

activity affects what will happen next into CNS

PNS efferent neurons

effect change: movement/secretions, project out of CNS

Cell body

soma, integrates information

Dendrites

receives incoming inputs

Axon hillock

trigger zone, action potential occurs here

90% of cells in nervous system are

glial cells, support functions of neurons

4 types of glial cells

astrocytes, oligodendrocytes, schwann cells, microglia

Astrocytes

helps monitor and regulate ECF of CNS, supply metabolic fuel to neurons, important for blood-brain barrier

Oligodendrocytes

synthesize myelin in CNS

Schwann cells

synthesize myelin in PNS

Microglia

proliferate following neuronal injury, scavengers to remove cell debris, immune function

neurotransmitter chemicals are released by

pre synaotic neurons and act on post synaptic neurons

osmolarity

concentration of total amount of solutes (penetrating and non penetrating)

tonicity

describes behavior, has no units, determined by osmolarity and whether solutes in solution can enter cell

300 mOsm/L

isotonic, no change in cell, isoosmotic

< 300 mOSM/L

hypotonic, cell swells. hypoosomotic

>300 mOSM/L

hypertonic, cell shrinks, hyperosmotic

Always assume intracellular solutes are

non penetrating

Non-penetrating solute

any solute present in ECF that cannot effectively pass through plasma membrane

Non-penetrating solute

Glucose, Na+, Cl-, K+, Mg 2+, Ca 2+, ions in general)

Penetrating solute

urea, ethanol

Why do we care about tonicity?

changes in cell volume can cause drastic changes

movement of water changes cell

volume

movement of solute will impact

how water moves

Hypoosmotic solutions

can be hypotonic, cannot be isotonic or hypertonic

Isosmotic solutions

can be hypotonic and isotonic but not hypertonic

Hyperosomotic solutions

can be hypotonic, isotonic, or hypertonic

Types of membrane potentials

resting membrane, equilibrium, graded/receptor, action

Cell and membrane potential

membranes can be electrically charged, charge influences net flux of charged ions, charge can oppose or increase ion movement

Membrane potential

separation of charges creates electrical potential, separated charges have potential to do work

phospholipid bilayer has

high electrical resistance and acts as a capacitor

Open ion channels in cell membrane

are low-resistance pathway for movement of ions

inside of cell

-70 mV, negative relative to ECF

Electrical driving force

electrical gradient, opposite charges attract, like charges repel

Electrochemical Driving force

combination of both chemical and electrical gradients, describes how both concentration and membrane charge affect ion movement, membrane charge is synonymous with membrane voltage

Compare ion’s

Equilibrium potential (Eion) to the membrane potential (Vm) to determine which way the ion will move

Ions want the membrane potential to be

at their equilibrium potential, move in a direction that brings Vm towards their equilibrium potential

how is resting membrane potential created

Na+/K+ pump

Na+/K+ pump

3 Na+ out, 2 K+ in, losing positive charge (electrogenic), sets up and maintains ICF gradient for Na+ and K+

K+ and Na+ leak channels

K+ (positive charge) is always leaving cell through leak channels, Na+ is always leaking in but much small than K+ leaving

Since K+ is always leaking out compared to Na+ leaking in

that is the reason the cell is always relatively negative compared to ECF

Nernst Potential

for any given concentration gradient of a single ion, the membrane potential that exactly opposes the concentration gradient is known as the equilibrium potential