2025 Physiology Exam 1 Flashcards
Lectures 1-5: Intro/Cell/Membrane, Membrane Transport/Protein Synthesis, Vision/Hearing/Balance, Pulmonary Phys 1, Pulmonary Phys 2
Physiology
The science that is concerned with the function of the living organism and its parts, and of the physical and chemical processes involved.
Pathophysiology
The study of disordered body function (i.e., disease)
The basis for clinical medicine
Homeostasis
The maintenance of a stable
“milieu interieur”
Claude Bernard (1813–1878)
Feedback Control Types
Negative feedback: promotes stability
Feed-forward: anticipates change
Positive feedback: promotes a change in one direction, instability, disease
Negative Feedback Control of Arterial Pressure to Promote Stability
Baroreceptor Reflex: Negative Feedback System to Promote Stability
Cardiopulmonary Reflexes: Feed-Forward Control of Blood Pressure to Anticipate a Change
Feedback Gain
Gain = Correction/Error
A measure of the effectiveness of a feedback system
Hemorrhagic Shock: Positive Feedback
Action Potential: Positive Feedback
Active Transport of Na+ and K +
Remember: sodium is pumped out of the cell, potassium is pumped in …
Simple Diffusion of Na+ and K+
Through leaky channels
Membrane Potential (Vm)
Charge difference across the membrane
Simplest Case Scenario for K+
The Potassium Nernst Potential
AKA = the equilibrium potential
Simplest Case Scenario for Na+
The Sodium Nernst Potential
The Goldman-Hodgkin-Katz Equation
Take home message…
The resting membrane potential is closest to the equilibrium potential for the ion with the highest permeability!
Resting Vm for Various Cell Types
Net Driving Force on Ions
Action Potential Terms
High plasma potassium (hyperkalemia) causes the threshold potential to become less negative, essentially bringing it closer to the resting membrane potential, making it easier to initiate an action potential and thus increasing excitability, while low plasma potassium (hypokalemia) does the opposite, making the threshold potential more negative and decreasing excitability by hyperpolarizing the cell membrane
High plasma potassium levels (hyperkalemia) cause a depolarization of the cell membrane, making the resting membrane potential less negative, while low plasma potassium levels (hypokalemia) result in hyperpolarization, making the resting membrane potential more negative;
The Action Potential
An action potential:
is a regenerating depolarization of membrane potential that propagates along an excitable membrane.
Propagates: conducted without decrement (an “active” membrane event)
Excitable: capable of generating action potentials
Action potential basics:
All-or-none event (need to reach threshold)
Constant amplitude (do not summate)
Initiated by depolarization
Involve changes in permeability
Rely on voltage-gated ion channels
Functions of Action Potentials
Deliver sensory information to CNS
APs in sensory nerves are blocked by local anesthetics. This usually produces analgesia without paralysis. Why no paralysis? LAs are more effective against small diameter neurons with a large surface area to volume ratio.
Hence, small C-fibers that conduct pain sensations are affected more than large, alpha-motorneurons.
Information encoding
The frequency of APs encodes information (amplitude of AP is constant).
Rapid transmission over distance (nerve cell APs)
The speed of transmission depends on fiber size and whether it is myelinated. Information of lesser importance is carried by slowly conducting unmyelinated fibers (nonmyelinated c-fibers conduct pain sensations).
In non-nervous tissues, APs initiate various cellular responses.
muscle contraction
secretion (e.g., Epinephrine from chromaffin cells of medulla)
Membrane Permeability during Action Potential
Ion Channels
Permeability of axon membrane to ions is determined by the:
number of open channels.
Ion channels are usually selectively permeable
permeable to specific ions:
some pass only Na ions and are generally called “Na channels”
some pass only K ions = “K channels”
some pass only Ca ions = “Ca channels” (important in synaptic transmission)
some pass only Cl ions = “Cl channels”
permeable to classes of ion:
Some channels are selective only for cations (Na, K and Ca) over anions (e.g., Cl-)
These are called ‘non-selective cation channels’
Ion channel gating (using voltage-gated as example)
Most voltage-gated channels open in response to depolarization.
The terms “gate” and “gating” refer to transitions between different states.
These “different states” reflect different conformational states of the channel protein
Has minimum of two gating transitions.
activation = opening of channel when membrane is depolarized
deactivation = closure of channel when membrane repolarizes
Refractory Periods
Propagation of Action Potentials
Signal Transmission
Myelination
Schwann cells surround the nerve axon forming a myelin sheath.
Sphingomyelin decreases membrane capacitance and ion flow 5000-fold.
Sheath is interrupted every 1–3 mm by a node of Ranvier.
Nonmyelinated vs Myelinated
MS is an immune-mediated inflammatory DEMYLINATING disease of the CNS
Synapses
Point of communication between neurones
Most synapses involve transmitter substances.
Synapses can be:
- Excitatory
- Inhibitory
Neurons communicate with specialized structures - synapses.
An action potential in the presynaptic cell causes transmitter to be released.
In fast synapses, transmitter substances bind to receptors on postsynaptic cell to directly open ion channels (ligand-gated)
The permeability of this region of the “postsynaptic” membrane to ions is increased.
The selectivity of the channels for particular ions determines whether the membrane is hyperpolarized or depolarized.
The membrane potential will move towards the equilibrium potential for the permeant ion(s)
Excitatory transmitters depolarize the membrane.
Synaptic responses that reach threshold initiate an action potential.
Subthreshold responses can summate with others.
Subthreshold Potential Charge vs Action Potential
Subthreshold potential change (electrotonic)
proportional to stimulus strength (graded)
not propagated but decremental with distance
exhibits summation
Action potential
independent of stimulus strength (all or none)
propagated unchanged in magnitude
summation not possible
Synaptic Response: Excitatory
Examples—nAChR, Glutamate
Permeable to cations (Na+, K+, and Ca2+)
Equilibrium potential ~ 0 mV
Depolarizes postsynaptic cell
Enhances excitability
Synaptic Response - Inhibitory
Examples—GABA, Glycine
Permeable to anions (Cl-)
Equilibrium potential ~ -90 mV
Hyperpolarizes post-synaptic cell
Depresses excitability
Ligands
Ventricular Action Potential
Sinoatrial Node Action Potential
SA Node Action Potential: Parasympathetic
SA Node Action Potential: Sympathetic
Transport of O2 and CO2 into Blood and Tissue Definitions
Partial pressure
Depends on percentage of gas
Driving force for diffusion
Saturation
% Hb that has oxygen bound (note: no units)
Content
Absolute quantity (mL O2/100 mL blood)
Anemia
Decreased ability for the body to carry O2 in the body
Uptake of O2 in Lungs
External Respiration happening in the lungs
***Internal Respiration is within the tissue
Blood O2 Content Throughout Circulation
Greatest amount of O2 PICKED UP in Pulmonary Capillaries
Greatest amount of O2 LOST in the Systemic Capillaries
Moves via Diffusion
Alveolar and Blood Gases
O2 wants to join onto the Hb (hemoglobin) as it moves through Pulmonary Capillaries
Alveolar and Blood Gases Even With No Red Cells
Even with no Hb the O2 will still diffuse across
Blood and Tissue PO2
Balance Between Blood Flow and Tissue PO2
Exercising increases O2 consumption… body needs O2 diffusion increases
Tissue PO2 is determined by balance of delivery and usage
What Happens to Tissue PO2 With Normal Metabolism and Increased Flow?
What Happens to Tissue PO2 With Increased Metabolism and Normal Flow?
Diffusion of CO2
Cellular CO2 is higher than Capillary… diffuse in to be removed
Tissue PCO2 Is Balance between Tissue Metabolism and Blood Flow
Diffusion of CO2
Oxygen Transport (How is it Transported)
Partial pressure (mm Hg) driving force for diffusion
Percent saturation (no units)
HbO2/(Hb+HbO2) (DONT NEED TO KNOW FORMULA)
Content (mL O2/100 mL blood) absolute quantity of oxygen in blood
Transport of O2 in Blood
Dissolved Oxygen
Solubility 0.003 mL O2/100 mL blood mm Hg
Normal blood 0.3 mL O2/100 mL blood
Normal oxygen consumption 250 mL O2/min
Would require 831/min blood flow
*** Very low amount
Hemoglobin
97% transported by Hb
O2 + HB ~= HBO2
1.34 mL O2/g Hb
Normal
15 g Hb/100 mL blood
20 mL O2/100 mL blood
Anemic
10 g Hb/100 mL blood
13 mL O2/100 mL blood
Hemoglobin-Oxygen Dissociation
Curve
Hemoglobin-Oxygen Dissociation
Curve
Hemoglobin-Oxygen Dissociation
Curve
Alveoli
Over wide range hemoglobin will be highly saturated
example: PO2 of 60 saturation is 89%.
Tissue
Normal: 5 mL O2/100 mL blood (20 mm Hg)
Exercise: 15 O2/100 mL blood (40 mm Hg)
Exercise and Uptake of O2
Increased cardiac output
Decreased transit time
Increased diffusing capacity
Opening up of additional capillaries
Better ventilation/perfusion match
Equilibration even with shorter time (previous graph)
Shift of O2 Dissociation Curve
Right shift at tissue
increased carbon dioxide in blood (associate with increased H+)
decreased affinity for oxygen… enter into tissue
maintain partial pressure gradient
Left shift at lungs
loss of carbon dioxide at lungs
increased affinity of oxygen
V/Q Mismatch
Regional V/Q ratios vary throughout lung.
Pathologic conditions include asthma, emphysema, and atelectasis.
Low V/Q regions contribute to hypoxemia (KNOW THIS)
Hypoxemia responsive to increasing FIO2
Regions with V/Q > 1.0 do not contribute to hypoxemia
Transport of CO2
Dissolved
solubility 20× oxygen
venous blood: 2.7 mL/100 mL blood
arterial blood: 2.4 mL/100 mL blood
transported : 0.3 mL/100 mL blood
7% total in the plasma (KNOW THIS)
Most CO2
Enters RBC
Joins with H2O… goes into process shown in picture
HCO3- can serve as a Ph buffer… leaves RBC into plasma
Cl- enters RBC to maintain neutrality (Cl shift)
H+ joins with Hgb to form HHgb (deoxygenated or met hemoglobin)
3 Ways CO2 Transported
Directly in Plasma = 7%
Directly to Hgb = 23%
Process to HHgb = 70%
Transport of Carbon Dioxide at Lung
Hgb has a greater affinity for O2 than H+.
So when O2 comes in it kicks the H+ off and joins to O2
The process goes in reverse than at the tissue
Regulation of Respiration “Factors”
Sensors
gather information
Central controller
integrate signals
Effectors
muscles
Neural Regulation of Respiration
Peripheral Chemoreceptors = Arterial Chemoreceptors (monitor O2 and CO2)
Central chemoreceptors = Medulla Oblongata
Brain Stem
Know the Fourth Ventricle
Pneumotaxic center:
limit inspiration
increase respiratory rate
modulate respiratory system
The apneustic center is a group of nerve cells in the brain that controls the depth and intensity of breathing
Vagus and Glossopharyngeal bringing information from the chemoreceptors to the brain
Respiratory motor pathways control breathing muscles
Dorsal respiratory group
Inspiration
Intrinsic nerve activity
Ventral respiratory group
Inactive during quiet respiration
Active respiration
Projections from the dorsal respiratory group
Lung Receptors
Stretch receptors
Located in smooth muscle of large and small airways
Minimize work of breathing by inhibiting large tidal volumes
Hering–Breuer reflex
Irritant receptors (KNOW THESE)
Nasal mucosa, upper airways, possibly alveoli
Bronchoconstriction
Cough, sneeze
J receptors
Located in the capillary wall, interstitium
Lung disease and edema (pulmonary congestion)
Rapid shallow breathing (tachypnea)
Other Reflexes
Arterial chemoreceptors
Hyperpnea, increased blood pressure
Arterial baroreceptors
Stimulation by elevated blood pressure results in brief apnea and bronchodilation.
Muscles and tendons
Muscles of respiration as well as skeletal muscles, joints, and tendons.
Adjust ventilation to elevated workloads.
Chemical Control of Respiration (Sensors)
Carbon dioxide
central
Most sensitive chemical to create respiration change
Hydrogen ions
central
Oxygen
peripheral (specifically in the Carotid Sinus)
They are “sensing” these chemicals for pass of information to regulate respiration
Chemosensitive Area of the Respiratory Center
In the brain, the result of too much CO2 ultimately means too much H+.
The high H+ in brain stimulates the chemoreceptors to stimulate the efferent motor neurons to increase breathing to blow off CO2
Peripheral Chemoreceptors
How Do Peripheral Chemoreceptors Work
Summary of Chemoreceptors
Carbon dioxide is major stimulus for increased respiration… more than O2
Acts on chemosensitive area through pH
Chemoreceptors are mainly affected by oxygen.
If PCO2 is constant low oxygen can be important.
Questions:
Why is oxygen’s effect on respiration blunted?
Explain ventilatory drive during severe lung disease.
Other Factors that Influence Respiration
Voluntary control
Activity from vasomotor center
Body temperature
increased production of carbon dioxide has direct effect on respiratory center
Irritants
Anesthesia
Cell Composition
Water: 70–85% of cell mass
Ions: 1%
Proteins: 10–20%
Lipids: 2–95%
Carbohydrates: 1–6%
Membrane Components
Proteins on Membrane
Provide “specificity” to a membrane
Defined by mode of association with the lipid bilayer
Integral: channels, pores, carriers, enzymes, etc.
Peripheral: enzymes, intracellular signal mediators
Cell Organelles
Endoplasmic Reticulum
Network of tubular and flat vesicular structures
Membrane is similar to (and contiguous with) the plasma membrane.
Space inside the tubules is called the endoplasmic matrix.
Rough or Granular ER
Outer membrane surface covered with ribosomes
Newly synthesized proteins are extruded into the ER matrix
Proteins are “processed” inside the matrix:
crosslinked
folded
glycosylated (N-linked)
cleaved
Smooth ER
Site of lipid synthesis
Phospholipids
cholesterol
Growing ER membrane buds continuously forming transport vesicles, most of which migrate to the Golgi apparatus
Golgi Apparatus
Membrane composition similar to that of the smooth ER and plasma membrane
Composed of four or more stacked layers of flat vesicular structures
Receives transport vesicles from smooth ER
Substances formed in the ER are:
“processed”
phosphorylated
glycosylated
Substances are concentrated, sorted, and packaged for secretion.
Exocytosis
Secretory vesicles diffuse through the cytosol and fuse to the plasma membrane
Secretory vesicles containing proteins synthesized in the RER bud from the Golgi apparatus
Fuse with plasma membrane to release contents
constitutive secretion—happens randomly
stimulated secretion—requires trigger
Lysosomes fuse with internal endocytotic vesicles.
Vesicular organelle formed from budding Golgi
Contain hydrolytic enzymes (acid hydrolases)
phosphatases
nucleases
proteases
lipid-degrading enzymes
lysozymes digest bacteria
Fuse with pinocytotic or phagocytotic vesicles to form digestive vesicles
Mitochondria
Primary function: extraction of energy from nutrients
“Power house of the cell”
The Nucleus
The double nuclear membrane and matrix are
contiguous with the endoplasmic reticulum
Receptor-Mediated Endocytosis
Molecules attach to cell-surface receptors concentrated in clathrin-coated pits
Receptor binding induces invagination
Also ATP-dependent and involves recruitment of actin and myosin
Digestion of Substances in
Pinocytotic or Phagocytic Vesicles
ATP Production
Step 1
Carbohydrates are converted into glucose.
Proteins are converted into amino acids.
Fats are converted into fatty acids.
Step 2
Glucose, AA, and FA are
processed into Acetyl-CoA.
Step 3
Acetyl-CoA reacts with O2 to
produce ATP.
A maximum of 38 molecules of ATP are formed per molecule of glucose degraded.
Ameboid Locomotion
Continual endocytosis at the “tail” and exocytosis at the leading edge of the pseudopodium
Attachment of the pseudopodium is facilitated by receptor proteins carried by vesicles
Forward movement results through interaction of actin and myosin (ATP-dependent)
Cell Movement Is Influenced by Chemical Substances …
Molecular Gradients Across Cell Membrane
Transport Across the Cell Membrane
Passive diffusion: molecules dissolve in phospholipid bilayer.
Sometimes transport through a channel protein is considered facilitated diffusion (see The Cell: A molecular approach).
Facilitated diffusion allows movement of both polar and nonpolar molecules to move through membrane: ions, carbohydrates, amino acids, nucleosides.
Channel proteins (porins) allow movement of ions and other small polar molecules to move through membrane in bacteria.
Aquaporins are protein channels that allow movement of water through membrane.
Ion Channels
Ungated channels
Transport is determined by size, shape, and charge of channel and ion.
Gated channels
Voltage (e.g., voltage-gated Na+ channels)
Chemical (e.g., nicotinic acetylcholine receptor channels)
Facilitated Diffusion
Also called carrier-mediated diffusion
Factors That Affect the Net Rate of Diffusion
Concentration Difference
Electrical Potential
Hydrostatic Pressure Difference
Active Transport
Primary Active Transport
Molecules are “pumped” against an electrochemical gradient at the expense of energy (ATP).
direct use of energy
Secondary Active Transport
Transport is driven by the energy stored in the electrochemical gradient of another molecule (usually Na+).
indirect use of energy
Primary Active Transport: Na+-K+ ATPase
Na+-K+ ATPase
Located on the plasma membrane of all animal cells
Pumps sodium ions out of cells and pumps potassium ions into cells against electrochemical gradients
Plays a critical role in regulating osmotic balance by maintaining Na+ and K+ balance (inhibition of pump by ouabain causes cell to swell and burst!)
Pump is activated by an increase in cell volume.
Requires about 1/5 of typical cell’s energy and up to 2/3 of neuron’s energy.
Primary Active Transport: Ca2+ ATPase and H+ ATPase
Ca2+ ATPase
Present on the cell membrane and the sarcoplasmic reticulum in muscle fibers
Maintains a low cytosolic Ca2+ concentration
H+ ATPase
Found in parietal cells of gastric glands (HCl secretion) and intercalated cells of renal tubules (controls blood pH)
Concentrates H+ ions up to 1 million-fold
Secondary Active Transport: Symporters
Involves the use of an electrochemical gradient (usually for sodium).
Protein cotransporters are classified as symporters or antiporters.
Transport substance in same direction as a “driver” ion like Na+.
Secondary Active Transport: Antiporters
Transport substance in opposite direction of a “driver” ion like Na+
Mechanism of Active Transport Across Cell Membrane
Osmosis
Osmosis occurs from pure water toward a water/salt solution.
Water moves down its concentration gradient.
Osmotic Pressure
The amount of pressure required to counter osmosis
Osmotic pressure is attributed to the osmolarity of a solution.
Permeant and Impermeant Molecules
Tonicity vs Osmolarity
The tonicity of any solution used to bathe tissue is totally dependent on its effective osmotic pressure. If the effective osmotic pressure of the bathing solution is the same as that of the tissue, there will be no net movement of fluid.
The tonicity (also called effective osmotic pressure) depends on the properties of both the membrane and the solute.
Osmolarity is merely another way of expressing the concentration of a solution.
Genetic Control of Cell Function
Transcription
Step 1. RNA polymerase binds to the promoter sequence.
Step 2. The RNA polymerase temporarily “unwinds” the DNA double helix.
Step 3. The polymerase “reads” the DNA strand and adds complementary RNA molecules to the DNA template.
Step 4. “Activated” RNA molecules react with the growing end of the RNA strand and are added (3′ end).
Step 5. Transcription ends when the RNA polymerase reaches a chain terminating sequence, releasing both the polymerase and the RNA strand.
Messenger RNA and Translation
Complementary in sequence to the DNA coding strand
100s to 1000s of nucleotides per strand
Organized in codons - triplet bases
each codon “codes” for one amino acid (AA)
each AA—except met—is coded for by multiple codons
start codon: AUG (specific for met)
stop codons: UAA, UAG, UGA
Transfer RNA
Acts as a carrier molecule during protein synthesis
Each transfer RNA (tRNA) combines with one AA.
Each tRNA recognizes a specific codon by way of a complementary anticodon on the tRNA molecule.
Polyribosomes
Polyribosomes: multiple ribosomes can simultaneously translate a single mRNA
Control of Gene Function
Genomics
Genomics—the large-scale study of the genome
Recent estimates suggest ~ 30,000 genes.
Humans are 99.8% identical at the genome level, 99.999% identical in the coding regions.
DNA Replication
DNA Repair, Proofreading, and Mutations
Following replication and prior to mitosis, DNA polymerase “proofreads” the “new” DNA, and cuts out mismatches.
DNA ligase replaces the mismatches with complementary nucleotides.
A “mistake” during transcription results in a mutation causing the formation of an abnormal protein.
Approximately 10 DNA mutations are passed to the next generation; however, two copies of each chromosome almost always ensures the presence of a functional gene.
Cell Differentiation
Different from reproduction…
Changes in physical and functional properties of cells as they proliferate
Results not from the loss of genes but from the selective repression/expression of specific genes.
Development occurs in large part as a result of “inductions,” one part of the body affecting another.
Refractive Index
Light speed decreases when it passes through a transparent substance.
The refractive index is the ratio of speed in air to speed in the substance.
Light rays bend when passing through an angulated interface with a different refractive index.
These light rays are eventually focused on retina.
Convex Lens Effect
Convex lens focuses light rays.
Concave Lens Effect
Concave lens diverges light rays.
Refractive Principles
Note that a point source of light has a longer focal length compared to light from a distant source; this is why an object comes into focus as it moves closer to the eye in a person with myopia (nearsightedness, long eyeball).
Dipoter
Lens has less refractive power, but it’s adjustable.
a diopter is a measure of the power of a lens.
1 diopter is the ability to focus parallel light rays at a distance of 1 meter.
the retina is considered to be 17 mm behind refractive center of eye.
hence, the eye has a total refractive power of 59 diopters (1000/17).
Accommodation
Refractive power of lens is 20 diopters.
Refractive power can be increased to 34 diopters by making lens thicker.
This is called accommodation.
Accommodation is necessary to focus image on retina.
Contraction of ciliary muscle attached to ligament pulls ligament forward causing lens to become thicker (which increases refractive power of lens).
Under control of parasympathetic nervous system.
Errors of Refraction
Hyperopia and Myopia
Fluid System of the Eye
Intraocular fluid keeps eyeball round and distended.
2 fluid chambers.
aqueous humor, in front of lens. (freely flowing fluid).
vitreous humor, behind lens (gelatinous mass with little fluid flow).
Produced by ciliary body at rate of 2–3 microliters/min. (~3–4 mL/day)
Intraocular Pressure
Normally 15 mm Hg (range: 2–20 mm Hg).
Level of pressure is determined by resistance to outflow of aqueous humor in canal of schlemm.
Rate of production of aqueous humor is constant.
Increased pressure can cause blindness due to compression of axons of optic nerve as well as blood vessels.
Retina
Light sensitive portion of eye
Contains cones for color vision.
Contains rods for night vision.
Contains neural architecture.
The Fovea
It is a small area at center of retina ~1 mm2.
Center of fovea, called “central fovea” or “fovea centralis” contains only cones.
These cones have special structure.
Aid in detecting detail.
In central fovea, neuronal cells and blood vessels are displaced to each side so light can strike cones with less obstruction.
This is area of greatest visual acuity.
At central fovea: no rods, and ratio of cones to ganglion cells is 1:1.
May explain high degree of visual acuity in central retina.
Rods and Cones
Pigment Layer of Retina
Contains black pigment called melanin.
Prevents light reflection in globe of eye.
Without pigment, light would scatter diffusely; normal contrast between dark and light would be lost.
Photochemistry of Vision
Rods and cones contain chemicals that decompose on exposure to light.
This excites nerve fibers leading from eye.
Membranes of outer segment of rods contain rhodopsin or visual purple.
Vitamin A1 and Vision
Vitamin A1 (aka, all-trans retinal) is converted into 11-cis retinal within the retinal pigment epithelium.
Night blindness (nyctalopia): Lack of vitamin A1 causes a decrease in retinal, which results in decreased production of rhodopsin; and a lower sensitivity of retina to light.
Signal Transmission in Retina
Transmission of signals in retina is by electrotonic conduction.
Allows graded response proportional to light intensity.
Only ganglion cells have action potentials.
Send signals to brain.
Lateral Inhibition
Processing the visual image begins in the retina. One example is lateral inhibition.
Horizontal cells provide inhibitory feedback to rods and cones and bipolar cells.
Output of horizontal cells is always inhibitory.
Prevents lateral spread of light excitation on retina.
Optic Disk
Point where ganglion cell axons (~1 million) exit the eye to form the optic nerve (2nd cranial nerve).
Entry point for retinal blood vessels
Creates a blind spot since there are no rods or cones.
Located 3–4 mm to nasal side of fovea
Size: 1.76 mm (horizontally) × 1.92 mm vertically
Has a central depression called the optic cup.
Amacrine Cells
About 30 different types.
Some involved in the direct pathway from rods to bipolar to amacrine to ganglion cells
Some amacrine cells respond strongly to the onset of the visual signal, some to the extinguishment of the signal.
Some respond to movement of light signal across the retina.
Amacrine cells are a type of interneuron that aid in the beginning of visual signal analysis.
Ganglion Cells
Only ganglion cells have action potentials.
Send signals to brain.
Spontaneously active with continuous action potentials
Visual signals are superimposed on this background.
Many excited by changes in light intensity.
Respond to contrast borders, this is the way the pattern of the scene is transmitted to brain.
Visual Pathways of the Cortex
Function of the Dorsal Lateral Geniculate
Two principle functions:
Relay of information to primary visual cortex
“Gate control” of information to primary visual cortex
Primary Visual Cortex
Primary visual cortex lies in calcarine fissure.
Distribution from eye is shown.
Note large area of representation of macula (which includes fovea).
Fovea has several 100x more representation in cortex compared to peripheral portions of retina.
Secondary visual areas are visual association areas, where the visual image is dissected and analyzed.
Separation of the signals from the two eyes is lost in the primary visual cortex.
Signals from one eye enter every other column, alternating with signals from the other eye.
Allows the cortex to decipher whether the two signals match.
The visual signal in the primary visual cortex is concerned mainly with contrasts in the visual scene.
The greater the sharpness of the contrast, the greater the degree of stimulation.
How the brain perceives a visual image is not understood well.
Movement of Eyes and Cranial Nerves
ANS Innervation of Eye
Parasympathetic preganglionic fibers arise from Edinger-Westphal nucleus and synapse with postganglionic fibers in ciliary ganglion as shown.
The postganglionic fibers send action potentials through ciliary nerves to eyeball to control
1. ciliary muscle (lens focusing).
2. sphincter of iris (constricts pupil).
Parasympathetic nerves excite pupillary sphincter muscle, decreasing pupillary aperture (miosis).
Sympathetic preganglionic fibers originate in intermediolateral horn of 1st thoracic segment of cord and synapse with postganglionic fibers in superior cervical ganglion as shown.
The postganglionic fibers innervate radial fibers of iris (which open pupil), plus several extraocular muscles.
Sympathetic nerves excite radial fibers of iris causing pupillary dilation (mydriasis).
The Tympanic Membrane and Ossicular System
Cochlea
System of three coiled tubes separated by membranes into the scala tympani, scala media, scala vestibuli.
Sound waves cause back and forth movement of the tympanic membrane which moves the stapes back and forth.
This causes displacement of fluid in the cochlea and induces vibration in the basilar membrane.
Organ of Corti lies on surface of basilar membrane; contains hair cells which are electromechanically sensitive.
Muscles of the Ossicles
Two muscles attach to the ossicles:
Stapedius (stapes)
Tensor tympani (malleus)
Attenuation reflex: a loud noise initiates reflex contraction, causing ossicular system to develop rigidity. Both muscles involved.
Structure of the Cochlea
Organ of Corti
Receptor organ that generates nerve impulses
Contains rows of hair cells that have stereocilia
Stereocilia, when bent in one direction cause hair cells to depolarize; when bent in opposite direction hyperpolarize.
This is what begins neural transduction of auditory signal
Hair cells are the receptor organs that generate APs in response to sound vibrations.
The tectorial membrane lies above the stereocilia of the hair cells.
Movement of the basilar membrane causes the stereocilia of the hair cells to shear back and forth against the tectorial membrane.
Auditory Complex
Arranged by tonotopic maps
High frequency sounds at one end of map
Low frequency sounds at other end
Discrimination of sound patterns is lost when auditory cortex is destroyed.
Purpose of Respiration
Goal of respiratory system is to provide O2 and remove CO2.
Functions which accomplish this goal …
Ventilation
Diffusion
O2/CO2 transport
Regulation of ventilation
Standard Notations
Boyle’s Law
Boyle’s Law: For a given quantity of gas in a chamber, the pressure is inversely proportional to the volume of the container.
P1V1 = P2V2
PV = nRT
P = nRT/V
P = gas pressure (atm)
V = volume in which the gas is contained (L)
N = moles of the gas
R = universal gas constant (Latm/mole K)
T = temperature (K)
Dalton’s Law
In a gas mixture the pressure exerted by each individual gas in a space is independent of the pressure exerted by other gases.
Patm = PH2O+PO2+PN2
Pgas = % total gases * Ptotal
Boyle’s Law with Pa
Cell Types in Alveoli
Capillary endothelial cells
Alveoli epithelial cells
Type 1 cells
Type II cells
Fibroblasts (surfactant)
Macrophages
Mast cells
Control of Bronchiolar Diameter
Nervous
Sympathetics
β2 receptors dilate
Parasympathetics
Acetylcholine constrict
Humoral
Histamine, acetylcholine»_space; Constrict
Adrenergic (β agonists)»_space; Relax
Pressures with Movement of Air in Lungs
Pleural pressures
Resting −5 cm H20
Inspiration −8 cm H20
Alveolar pressure
Resting 0 cm H20
Inspiration −1 cm H20
Expiration 1 cm H20
Compliance
∆V/∆P
200 mL/cm H20
(1 cm H20 ~ 0.7 mm Hg)
Airway Resistance
Flow = ∆P π r4/(8 μL)
Resistance = 8 μL/(πr4)
Upper airways major resistance
Decrease in lung volume results in an increase in resistance.
Pulmonary Surfactant
Lung Volumes
Alveolar Ventilation
Alveolar Ventilation
(Tidal volume − dead space)*respiratory rate
Dead Space
Anatomical
150 mL
Physiological
Depends on ventilation-perfusion ratio
Pulmonary Blood Flow
Fick Principle
VO2=Q(Cao2−Cvo2)
VO2 = Oxygen consumption
Q = Blood flow
Cao2 = Arterial content
Cvo2 = Venous content
Pulmonary Resistance to Flow
Pressure drop of 12 mm Hg
Flow of 5 l/min
Resistance 1/7 systemic circulation
Distribution of Lung Blood Flow
Hydrostatic Effects on Lung Blood Flow (Zones of West)
Pulmonary Capillary Pressure Change with Cardiac Output
Effects of Hypoxia on Blood Flow
Result of Hypoxic Vasoconstriction
Decreased Alveolar PO2 Leads to Vascular Constriction
Pulmonary Capillary Dynamics
Outward forces
Pulmonary capillary pressure 7 mm Hg
Interstitial osmotic pressure 14 mm Hg
Negative interstitial pressure 8 mm Hg
Total 29 mm Hg
Inward forces
Plasma osmotic pressure 28 mm Hg
Net filtration pressure 1 mm Hg
Negative interstitial pressure keeps alveoli dry.
Pulmonary Edema
Pulmonary Edema–fluid accumulation in pulmonary interstitial space
Causes
Increase in pulmonary venous and capillary pressure (left-sided heart failure, mitral valve stenosis) outward force
Increased capillary membrane permeability (damage to associated with infections, noxious gases (chlorine, sulfur dioxide).
Decrease in plasma osmotic pressure (liver failure). inward force
Large decrease in intrapleural pressure (inspiring heavily against a closed airway, i.e., severe laryngeal spasm). Negative pleural pressure is transmitted to interstitial and alveolar spaces, favoring fluid movement out of pulmonary capillaries.
Pulmonary edema safety factor: protection against edema until pulmonary capillary pressure equals capillary osmotic pressure.
Causes of pulmonary edema
Left heart failure
Damage to pulmonary membrane
Safety factor
Negative interstitial pressure
Lymphatic pumping
Decreased interstitial osmotic pressure
Respiratory Unit
Gas Exchange
Diffusion in response to concentration gradient
Pressure proportional to concentration
Gas contributes to total pressure in direct proportion to concentration.
CO2 20 times as soluble as O2
Diffusion depends on partial pressure of gas.
Air is humidified yielding a vapor pressure of 47 mm Hg.
Determinate of Diffusion
Fick’s Law
Composition of Alveolar Air
PO2 of Humidified Air
PO2 = (760 − 47) * 0.21 = 713 * 0.21 = 149
Alveoli PO2
PAO2= PIO2 − (PCO2/R)
PAO2 = 149 − (40/0.8) = 99
R is respiratory exchange ratio ~0.8
Remember in a normal person
alveolar PO2 = arterial PO2, and
alveolar PCO2 = arterial PCO2.
Alveolar and Blood Gases
Hyperventilation vs Hypoventilation on PaCO2
Hyperventilation
Increased ventilation beyond metabolic (O2 demand, CO2 production). Results in drop in arterial CO2.
Hypoventilation
Ventilation below needs. PaCO2 rises.
Partial Pressures Along the Airway
Diffusing Capacity
CO2 diffusing capacity is 20 times the diffusing capacity of O2.
Ventilation/Perfusion
Relationship between adequate flow and adequate ventilation
Defined as V/Q
V/Q = (4 L/min)/ (5 L/min) = 0.8
Va/Q = 8.63 * R * (CAO2 − CVO2)/PACO2
If there is no diffusion impairment then the PO2 and PCO2 between an alveolus and end capillary blood are usually the same.
V/Q Mismatch
Differences in airway and lung expansion produce uneven regional ventilation.
Differences in vascular geometry and hydrostatic pressures produce uneven regional blood flow.
V/Q ratios vary across regions within normal healthy lung.
Pathologies that lead to regional changes in ventilation (e.g., asthma) or changes in perfusion (e.g., pulmonary embolism) will increase V/Q mismatch.
V/Q Ratios
High Miss Test Question: CO2 returning form Tissue to Lungs
CO2 returns from the Tissue to Lungs
~23% directly to HGb
~7% in plasma of Blood
~70% is dissolved (bicarbonate)
High Miss Test Question: Glycocalyx
The glycocalyx is a thin, gel-like layer that covers the surface of many cells, including endothelial cells (lining blood vessels) and epithelial cells (lining organs and body surfaces).
It consists of a complex mixture of molecules, including:
Glycoproteins: Proteins with attached sugar molecules (glycans)
Proteoglycans: Glycoproteins with long chains of sugar molecules (glycosaminoglycans)
Glycolipids: Lipids with attached sugar molecules
High Miss Test Question: Neurotransmitters Across Synaptic Cleft
Calcium is needed to release neurotransmitters
High Miss Test Question: Lung Volumes
Do I have char with more of them???
High Miss Test Question: Hydrogen Ions directly effect respiratory center
CO2 enters brain, but H+ is the direct stimulator of the brain respiratory system
pH homeostasis: 7.35-7.4
0-6 = acidic
7 = neutral
8-14 = basic
