Cell Physiology Dylan Feist
Two Classes of Cells
Prokaryotic – do not have nuclear membrane or compartmentalization of organelles.
Eukaryotic – have a true, membrane bound nucleus and organelles. These include
plants, animals, unicellular and multicellular fungi, and unicellular protozoans.
Cell Structure and Function
Plasma Membrane – surrounds the cell surface and separates the intracellular fluid
from the extracellular fluid.
Cell organelles – performs specific functions.
Cell interior – consists of the nucleus and the cytoplasm
o Nucleus – contains the genetic material
o Cytoplasm – everything outside the nucleus. Includes the cytosol (gel-like
fluid) and the organelles.
o Physical barrier – maintains difference in fluid composition between ICF and
o Cell-to-cell communication – receptors bind signaling molecules arriving at
the cell surface.
o Structural support – specialized connections exist between the plasma
membranes and the extracellular materials.
o Transport – the movement of ions, waste, and secretory products.
o Double layer of lipid molecules
o Embedded proteins
o Different ratios of lipids and proteins in each membrane
o Carbon and hydrogen
o Carboxylic acid groups with a long chain of hydrogen and carbons.
o Saturated = no double bonds
o Unsaturated = one or more double bonds
o Amphipathic – have a polar head group and a nonpolar fatty acid chain.
o They spontaneously form a bilayer
o They are distributed unequally between both halves of the bilayer.
o Maintains proper membrane fluidity
o Fits between phospholipids
o At low temperatures, it prevents crystallization
o Lipids with a short CHO chain o Found in outer leaflet of plasma membrane and form glycocalyx
o There are two classes of membrane proteins
Partially span the membrane
On either the inner or outer surface of the membrane
o Glycoproteins are proteins with an attached carbohydrate. They are found on
the extracellular surface of the plasma membrane and form glycocalyx. They
have selective properties (what gets into the cell).
Fluid Mosaic Model
o Plasma membrane is a dynamic structure
o Rapid lateral transfer of proteins and lipids
o Transverse diffusion is rare
o Fluidity is influences by temperature, cholesterol, and unsaturated tails
o Double bonds cause more fluidity.
o There are many types of macromolecules (mosaic)
o The membrane is not symmetrical on both sides
o The adhesion of simmilar cells produces tissue
o Three main components
Cell Adhesion Molecules (CAMs)
o Cell Adhesion Molecules are specific integral membrane proteins.
Cell-cell adhesions are done by Cadherins
Cell-matric adhesions are done by Integrins
o Extracellular Matrix
Surrounds the cell
Consists of fibrous proteins embedded in the gel-like substance made
up of CHO’s.
Responsible for stable positioning of cells in tissues
Collagen – tensile strength
Elastin –tissue elasticity
Fibronectin – organizing matrix which links components of the matrix
to proteins (such as Integrins) in the plasma membrane.
o Cell Junctions
Specialized junctions between cells
Three main types
ii. Tight Junctions
iii. Gap Junctions
Anchor the cells together Structural integrity
Plaques – anchoring points for Cadherins
Cadherins – extend into extracellular space
Keratin intermediate filaments – anchor the cytoplasmic
surface (strong connection).
Found in epithelial tissue.
Form impermeable junctions.
No space between cells.
Nutrients move from luminal side to blood side.
Essential for polarized cells.
Occludin = nearly impermeable junction.
Transmembrane channels linking cytoplasm of adjacent cells
Movement of small ions and molecules.
Used for communication.
o High [K]
o High [proteins]
o Signal transduction
Nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes,
Ribosomes and cytoskeleton.
o Control center of the cell – contains the genetic material (DNA).
o Nuclear envelope – double porous membrane.
o Nuclear pores – allow selective movement of molecules.
o Nucleolus – synthesizes ribosomal RNA.
o RBCs have no nucleus, skeletal muscle cells have many.
o Responsible for protein synthesis.
o Translates DNA information into an amino acid based on mRNA instructions.
o Two subunits – a small and large subunit.
o Two main types:
Ribosomes bound to the rough endoplasmic reticulum.
o Large organelle.
o Extensively membrane bound.
o Two components: Rough ER – synthesizes protein with bound functional ribosomes.
Produces soluble proteins to be secreted from the cell, or used in the
lumen of lysosomes, or sent to the Golgi.
Smooth ER – synthesizes lipids, stores calcium, and helps in
detoxification in liver cells. Sarcoplasmic reticulum functions solely in
regulating calcium levels.
o Made of flattened sacs, stacked in layers.
Sort and pack proteins, especially for secretion.
Renews and modifies the plasma protein by adding new lipids and
o Produced at the Golgi.
o Contains digestive enzymes that degrade extracellular and intracellular
o Also plays a role in cellular defense.
o Primary lysosome – only digestive enzymes.
o Secondary lysosome - digestive enzymes and particles to be broken down.
o Use oxygen to remove hydrogen from molecules.
o Produces toxic H2O2.
o Catalase breaks down H2O2 into water and oxygen.
o Lots of peroxisomes in the liver.
o Powerhouse of the cell.
o Double membrane.
o Inside is called the matrix, middle is intermembrane space, and the outside is
o The matrix and cristae (sheets or tubules in inner membrane) produce ATP
via cellular respiration.
o The amount of mitochondria depends on need for a cell. For example,
muscles, heart, and liver cells have lots of mitochondria.
o Mitochondria has its own DNA which codes for proteins.
o Maintains cell shape.
o Maintaines organelle positions.
o Mediates cell and organelle motility.
o Consists of three filaments:
i. Microfilament – smallest filament. It is composed of actin and is
continuously assembled and disassembled. It functions to provide
mechanical strength to the cell, to assist in cell movements (microvilli,
pseudopodia, organelle movement) and it interacts with myosin in
muscle fibers to produce muscle contraction. ii. Intermediate filaments – intermediate size. They are responsible
primarily for the formation and maintenance of the cell shape. They
stabilize the position of the organelles. They play a structural role only
and do not participate in cell movements.
iii. Mictotubules – large hollow tubes composed of tubulin that are
strong and are continuously assembled and disassembled. They
function to strengthen the cytoplasm, the change cell shape, and to
assist in cell movement (cilia and flagella) and to move organelles and
The intracellular transport of membrane bound vesicles and
organelles is called axonal transport and it is propelled by
motor proteins called kinesins and dyneins.
Genes, DNA & Proteins
DNA – encodes the information for the synthesis of the structural and enzymatic
proteins of the cell.
Gene – stretch of DNA that codes for the synthesis of a particular polypeptide.
DNA – (transcription) – mRNA – (translation) – Proteins
o Transcription – a process by which RNA is synthesized using information
contained in DNA. It occurs in the nucleus where mRNA is processed and
o The mRNA binds to a free ribosome.
o Translation – the process by which polypeptides are synthesized using mRNA
as a template.
o The signal sequence on the initial amino acids direct protein to its
o ER Signal Sequence – sends protein the ER to finish translation. This
includes secretory proteins, enzymes for the ER, Golgi, and lysosomes, and
integral plasma membrane proteins.
o Without a sequence, translation continues in the cytoplasm. This includes
protein for nucleus, peroxisomes, mitochondria, or proteins that remain in
o Endocytosis – the uptake of material into the cell via vesicles that pinch off
from the cell membrane.
Phagocytosis – uptake of material into a cell via vesicles that pinch
from the cell membrane. Extensions of the plasma membrane engulf
the phagosome which the fuse with a lysosome.
Pinocytosis – cell drinking; an invagination forms, allowing the
absorption of extracellular fluid.
Receptor-mediated endocytosis – receptors bind to specific particles.
It works in low concentrations and requires a receptor.
Exocytosis – the release of material from the cell via vesicles that fuse with the cell
membrane. Vesicles fuse with the cell membrane and release contents into the extracellular fluid. It functions to add components to the plasma membrane, and to
secrete specific substances out of the cell into the ECF.
Transcytosis – the movement of large macromolecules. It can be either endocytosis
or exocytosis. Eg. Glucose movement across epithelial cell.
Driving Forces for Non-Vesicular Transport
Uses concentration gradients.
Molecules move passively from areas of high concentration to areas of
low concentration. Rate is dependent on the concentration.
Analogous to pressure gradient.
Membrane potential – the difference between cell membrane.
Exists because ions experience attractive and repulsive forces.
It depends both of the direction (the sign of the ion) as well as the
magnitude (the sign of the membrane potential).
o Electrochemical Driving Force
The sum of the electrical and chemical driving forces acting on an ion.
The direction depends on the net direction of electrical and chemical
o The passive movement of molecules through a biological membrane’s lipid
o Depends on lipid solubility and the size of the molecule.
Gases and small uncharged polar molecules can pass through.
Large uncharged molecules, ions, and charged polar molecules cannot
o Does not require energy.
o Moves from high to low concentrations.
o Net Flux – net exchange of molecules across a membrane.
o Factors affecting simple diffusion:
Magnitude of driving force.
Membrane surface area.
Membrane permeability (temperature, thickness, size, shape, and
o Rate is not the same for all cases.
Membrane Transport Proteins
o Mediated transport
o Can either be facilitated transport (no energy, passive transport) or active
transport (requires energy).
o Carrier-Mediated Facilitated Diffusion:
Net Flux from high to low.
Does not require energy.
o Channel-Mediated Facilitated Diffusion
Depends on electrochemical gradient.
Voltage gated – changes in voltage. Ligand gated – binding of signaling molecules.
Mechanically gated – mechanical stimuli, such as cell swelling.
o Transport rates plateau because there are only a limited number of binding
o Active Transport:
Pumps uphill, against the electrochemical gradient.
It uses energy.
Primary Active Transport
Uses ATP as the source of energy.
Example is the Sodium/Potassium Ion Pump
3 Na+ out
2 K+ in
Creates the concentration gradients
Protein constantly pumps sodium out of the cell.
Electrogenic – net movement of charge.
Secondary Active Transport
Uses electrochemical gradient.
Couples the movement.
Symport – two substances transported in the same direction.
Antiport – two substances transported in opposite directions.
Can be electroneutral or electrogenic.
o Water Transport
Osmosis – passive movement of water across a membrane. It goes
from low solute concentration to high solute concentration.
o Epithelial Transport
Functional grouping of cells connected by tight junctions. They
transport materials across the cell.
Paracellular (between cell) movement is limited.
Transcellular (through cell) movement is used.
Intestinal epithelium absorbs nutrients.
Uses the cell polarity to move glucose to the blood.
Uses many types of transporters.
Direct – gap junctions.
Indirect – chemical messengers.
o Chemical messengers bind reversibly to receptors.
o The receptors are highly specific, they can reach saturation, and they are
o Signal transduction – sequence of events between binding and the cellular
o Lipid soluble messengers that include steroid and thyroid hormones.
o Bind in cytosol or nucleus.
o Transcription factors alter the transcription of mRNA. Membrane-Bound Receptors
o Water-soluble messengers that include hormones, neurotransmitters,
o First messenger – binds to extracellular receptor.
o Second messenger – intracellular messenger that is produced as a response to
the first messenger.
o Protein-kinase phosphorylates another protein.
o Receptor is also a ligand gated ion channel.
o First messenger causes ion to cross membrane.
o Eg. Calcium channel.
Calcium as a Second Messenger
o Calcium induces calcium release.
o Binds to calmodulin to form complex, which alters the activity of enzymes
o Interact with enzymes to function as a unit.
o Can also function as enzymes.
G Protein Coupled Reaction
o Bind guanosine nucleotides.
o Transmembrane receptors that sense molecules outside the cell and activate
o Conformational change.
cAMP Second Messenger System
o Example of simulatory G-protein.
o Phosphorylation by protein kinase either activates or inhibits a protein.
o Alpha subunit activates adenylate cyclase, which promotes the formation of
cAMP, which activates protein kinase A to signal a response in the cell.
Signal amplification – small changes in concentration can result in a marked
response. This allows hormones and messengers to be effective at very low
concentrations. Nerve and Muscle Dylan Feist
Afferent – the information is transferred from the periphery toward a central
Interneuron – all of the structures are located within the central nervous system.
Efferent – the information flow is from the CNS toward the periphery.
o Eg. May cause skeletal muscle fibers to contract in response to action
o Protected by bony structures called vertebra.
o Ventral horn – location of motorneurons.
o Dorsal horn – location of sensory integration.
o Grey Matter – consists of neurons, dendrites, synapses, and nerve terminals.
Neurons in the grey matter are neighbored by astro-glial cells.
o White Matter – consists of axons and oligodendrocyte-glia, which electrically
insulate and also functionally support the axons.
o A typical mixed peripheral nerve contains both sensory afferent fibers and
efferent motor axons.
Morphological Structure of a Motorneuron:
o Dendrites originate from the cell body.
o The axon wires neurons to communicate with each other via electrical action
o Axon terminal is the presynaptic part of a synapse.
o Axons can have a length of several meters.
Schwann cells enfold axons of both sensory and mororneuron.
o The intracellular fluid contains the lipid myelin, which electrically insulates
o Typical Schwann cell is 0.1 to 1 mm long.
Saltatory conduction is the most effective action potential propagation.
Oligodendrites cover axons in the CNS.
Bipolar neurons have two elongated processes.
Dorsal root ganglion cells are somatic sensors, sensitive to mechanical stimuli,
temperature, or pain.
o The dendritic branch is functionally an axon.
o The real axon extends from the dorsal root ganglion into the spinal cord.
o First node of Ranvier is closes to the receptor.
o Pacinian corpuscles respond to vibration and pressure.
Electrical processes in neurons and muscle fibers are mediated by highly specialized
o Found in plasma membrane
o CNS neuron soma has diameter of 5-50 micrometers.
o Diameter of transport proteins is 0.01 micrometers.
o Mitochondria are ~1 micrometer in size.
o Cell nucleus is several micrometers in diameter.
Diffusion – passive flux of solute towards a compartment of lower concentration.
Intracellular concentration of a cell have high potassium, low sodium, and low
calcium. The Na/K pump is the most important because it transports sodium out of the cells
in exchange of K.
o ATP hydrolysis powers this through a conformational change.
o Secondary active pumps use this electrochemical gradient to move ions.
Voltage gated Na+ channels are important for sodium action potentials.
Osmolarity – a means to measure the extent to which water is attracted by the
content of solutes.
Intracellular membrane surface is negatively charged.
Extracellular membrane surface is positively charged.
Electrochemical equilibrium – when the chemical driving force driving K+ out of the
cell will be compensated by an electrical potential to do the separation of the negative
charge of the impermeable anion and the positive charge of K+.
The Nerst equation allows us to calculate the equilibrium potential. However,
determining the equilibrium potential is only valid if the membrane is exclusively
permeable to that ion.
Conductance and permeability are often used to express the capability of flux ions
through channels. The terms are proportional rather than equal.
Glial cells have the fewest Na(leak) cells.
Typical neuron has a membrane potential of approximately -70 Mv.
o It is notable less negative than glial cells because there are more (leak) Na+
channels, as well as (leak) K+ channels.
o Overshoot – the reversal of a negative value to a positive value during
An action potential is approximately one millisecond. At the beginning of the
action potential, depolarization occurs and causes an overshoot. Repolarization
occurs immediately after.
o Afterhyperpolarization – undershoot below resting baseline.
o gNa is only greater than gK during depolarization and repolarization.
At rest, both Na+ and K+ channels are closed, while many leak K channels are open.
The threshold must be achieved before an action potential is solicited.
All or none response, meaning that the shape and size of an action potential is the
same regardless of the stimulus.
The length constant is measured in mm.
o Determined at the point on the abscissa where voltage has dropped by 63%.
Capacitance is the current flow delay.
o Time constant has a greater value in neurons that have a high resistance
and/or neurons with a high capacitance.
Continuous conduction is unmyelinated axons have a characteristic electronic
voltage drop due to the intra-axonal leak currents.
o Intra-axonal leak currents.
Saltatory conduction in myelinated axons is much faster, particularily in thicker
axons. This is because myelin insulation prevents current flow through leak channels.
The action potential typically jumps across several nodes of Ranvier.
o Faster because leak channels are only present at the nodes of Ranvier
o Up to 100x faster. o Factors that limit action potential speeds: charge of membrane capacitance,
and conformational change of Na+ channels.
Saltatory action potential is up to 100 times faster than continuous conduction
because the electronic potential drop is less pronounced.
Increasing the current also increases the frequency of the action potentials.
o The magnitude of a receptor potential is encoded into a specific frequency of
o Action potential firing rate increases as depolarizing current increases.
The maximum spike frequency is approximately 600 spikes per second.
Adaptation – the return to a resting potential, despite the stimulus amplitude
Dorsal root ganglion cells are somatic sensors.
Mechano sensitive ion channels respond when the skin is touched because the
membrane can stretch.
Glutamate interacts with postsynaptic ion channels to generate an excitatory
Glutamate is the major excitatory neurotransmitter in the CNS.
o Generates excitatory EPSP
o Stored in synaptic vesicles
o Activates ionotropic glutamate receptor.
o Promotes influx of Na+ into the neuron.
o Depolarization occurs
Acetylcholine (Ach) is the neurotransmitter of the motorneurons. The following
occur at the Motor Endplate:
o Vesicles release Ach in response to increased Ca+
o Diffused to postsynaptic Nicotinic receptors.
o Mediates flux of Na+, Ca2+, and K+
o Endplate potential EPP solicited with amplitude 40-60 mV
Sensory information from a peripheral skin receptor propagates via afferent axons
from dorsal root gangions neurons into the spinal cord, where the incoming action
potentials elicit an EPSP (excitatory post synaptic potential) in an interneuron. This
interneuron excites, also via EPSP, a motorneuron in the ventral horn. The action
potentials propagate along the axon of the motorneuron to the periphery, specifically
to activate a skeletal muscle fiber.
Acetylcholine is a neurotransmitter stored in synaptic vesicles. An influx of calcium
ions causes a release of Ach, which induces the activation of a larger cation pore.
There is a flux of Na, Ca, and K along their gradients. This results in an Endplate
Potential, which has an amplitude of 40-60 mV. It does not overshoot because of the
efflux of K+ which antagonizes the depolarization caused by Na and Ca.
A skeletal muscle consists of muscle fibres that are formed by a fused individual
Tendons – connective tissue.
Muscles contract and need energy such as glucose and oxygen.
Each muscle fibre contains many myofibrils that have characteristic bands.
Muscle fiber contains many myofibrils.
o I band contains actin o A band made of thick myosin filaments.
o Sarcomere is the basic unit of myofibril and is composed of actin and myosin
When muscle contracts, the extend of overlap between filaments increases.
Cross bridges are the part of myosin that bind to actin.
Tropomyosin filaments block cross bridge binding sites on actin.
Binding of Ca2+ causes change in tropomyosin and binding site is revealed.
ATP necessary for cross bridge detachment from actin.
Rigor mortis causes by lack of ATP
Arrival of Na+ Action Potential:
o Enters invagination
o Activates voltage sensor in DHP receptor
o Release of Ca2+ due to conformational change. Ryanodine receptor mediates
the release of calcium ions from the sarcoplasmic reticulum.
Muscle contraction lags behind muscle action by several tens of ms.
Fused tetanus – repetitive stimulation. Muscles cannot relax. Blood Dylan Feist
Introduction to Blood
o Blood is approximately 7-8% of our body weight.
o It is mainly present in blood vessels, but some important components are
found in tissues.
o Blood is thicker than water.
o Transport oxygen, carbon dioxide, nutrients, waste, ions, hormones, and
o Regulates ion and pH balance.
o Provides immune protection.
o Prevents blood loss in Hemostatis.
o The percentage of blood volume occupied by packed red blood cells.
o For men, it is approximately 47%
o For women, it is approximately 42%
o The difference is because males have testosterone, which increased red blood
o A high Hematocrit indicates heavier blood, which moves slower and may
cause stress on the heart.
o A low Hematocrit indicates reduced oxygen delivery.
o Made up of two parts:
i. Interstitial Fluid
ii. Plasma – non cellular part of the blood.
o Mostly water. It also contains electrolytes, as well as substances being
transported, such as CO2 and nutrients/waste.
o Functions in distributing body water, buffering, transport, defense, and
Plasma Proteins and Functions
o Albumins – osmotic pressure and carrier of substances.
o Globulins – clotting factors, enzymes, antibodies, and carriers for substances.
o Fibrinogens – forms fibrin threads essential for blood clotting.
o Transferrin – iron transport.
Blood Cell Types
o Red Blood Cell (RBC)
Also called erythrocytes.
o White Blood Cells (WBC)
Much fewer WBC than RBC
Also called leukocytes.
Neutrophils – phagocyte
Pinched off nucleus
Eosiniphils – defense against parasites
Chromatin is clumpy and smudgy Basophils – inflammation
Big dark granules
Monocytes – phagocyte and immune defense
Lymphocytes – two types. B-Cells are for antibody production
and humoral immunity, while T-cells are for cellular
Fairly standard looking
o Platelets or Thrombocytes – assist in hemostasis.
More platelets than WBC, but more RBC than platelets.
o The formation of blood cells.
o Prenatal, it occurs in the yolk sac, liver, and the spleen.
o After birth, it occurs in the bone marrow.
o It is regulated by cytokines, called hematopoietin.
Erythropoietin for RBCs
Interleukins for WBCs
Thrombopoietin for platelets.
Red Blood Cell
o Have a lifespan on 120 days.
o Function in O2 transport.
o Loses nucleus during maturation.
o Principle carrier of oxygen.
o It is responsible for approximately 99% of O2 transport.
o Binds loose and reversibly.
o Process is called oxygenation, not oxidation.
o Has extremely high affinity for CO and it is essentially irreversible.
RBC Production Factors
Hormonal regulation stimulated by low oxygenation, such as low
blood volume, anemia, low hemoglobin, poor blood flow, and
Major cause of anemia.
Body stores it in hemoglobin and the liver and recirculates it.
Some is bound with Ferritin.
o Folic Acid (leafy vegetables, synthesis in thymine)
o Vitamin B-12
Forms complex with Intrinsic Factor.
Insufficient B-12 is called pernicious anemia.
o Intrinsic Factor – need to be able to absorb B-12.
Fate of RBCs
o The cell is broken down.
o The iron recirculates.
o The globin is broken down into amino acids. o Continuously broken down in spleen, and then in liver and then expelled as
o Decreased oxygen carrying capacity.
o Can be caused from decreased RBC production, RBC destruction, loss of
blood, and abnormal production.
o Causes include lack of iron, lack of B-12 and IF, damage of bone marrow,
chronic kidney disease, abnormal shape, chronic menstration.
o Sickle cell anemia produces hard and non flexible sickle shaped RBC which
causes health implications.
The White Blood Cell Story
o Occurs in the bone marrow.
o T-cells are produced in the Thymus.
o Granulocytes and monocytes are found in blood vessels.
o Lymphocytes recirculate in the blood stream.
o Granulocytes and macrophages enter the tissues and stay there.
o Innate Defense
Intact skin, enzymes in saliva, tear, mucus, etc.
Acidic gastric secretion.
WBC (granulocytes, monoctyes/macrophages).
o Acquired Defence
The body remembers what it encountered previously.
The Immune System
Defense against foreign invaders.
Removal of old, damaged cells.
Allergies: exaggerated response.
Innate Defense (Inflammation)
o Phagocytes involved (Neutrophils and Macrophages)
o Innate response to infection or injury.
o Redness, swelling, heat, pain, loss of function.
o Characterized by increased blood flow, increased permeability of small blood
vessels, and the release of inflammatory mediators.
More blood rushes in; arteriole and venule dilation.
Increased blood causes heat and redness.
Edema expands the cellular matric. Histamine is released – itchy/swelling symptoms.
Cellular events – macrophages trap and kill pathogens, movement of
WBCs into the area, phagocytosis.
o The most important feature is the accumulation of WBC in the affected tissue.
i. Marginalization of WBCs
ii. Tethering and rolling of WBCs in blood vessel
iii. Activation of WBCs
iv. Arrest/firm attachment of WBCs to endothelial cells.
v. Emigration/diapedesis – neutrophil expresses the selecting protein
and the endothelial cell expresses selecting binding site. Called rolling
vi. Chemotaxis of WBCs – the ability to move along a concentration
gradient in response to a chemical. Chemotactic factors include
complement products, bacterial products, and arachidonic acid
vii. Recognition of nonself by WBCs
viii. Phagocytosis of invader WBCs
Phagocytes are any cell that can chew things in its
surroundings. They engulf bacteria by first recognizing, then
attaching to it, then internalizing and finally destroying it.
They recognize bacteria based on Pattern Recognition
Receptors, which are proteins expressed by the cells of the
innate immune system.
Opsonins are added to the surface of bacteria to speed up
phagocytosis. They are binding enhancer for the process of
Opsonization – deposition of opsonins enhances engulfment of
Phagocytosis – the infectious agent is surrounded by pseudopods and
internalized in a membrane bound phagocytic vacuole.
Killing and Degradation – two main types:
i. Oxygen dependent killing – production of oxygen free radicals.
ii. Oxygen independent killing – uses bacterial proteins and
o Inflammation is beneficial for short term fix, but in the long term it causes
o Complement proteins – plasma proteins that are inactive. There are activated
and form a signal. Think OIL
O = Opsonization of pathogens
I = Recruitment of inflammatory and immunocompetent cells
L = Lysis of pathogens.
The primary lymphoid tissue is the bone marrow and thymus. The secondary lymphoid tissue is the lymph nodes, spleen, and
tonsils, where the lymphocytes encounter antigen and become
Must be able to recognize antigens, respond to antigens, and
remember their encounter.
o Antigen – molecule that can bind to an antibody, forming a complex.
o Antibody – has two antigen binding sites and is highly specific. It is the
recognition molecule for B-cells.
o B Cells:
Become short-lived plasma cells that make lots of antibodies and are
secreted into the bloodstream.
Become memory cells that have antibody molecules so that next time,
the immune response is faster.
Humoral immunity is the major defense against bacteria and involves
B-cells. It acts hand-in-hand with the innate system.
o Cellular Immunity
Major defense against viruses, cancer, transplants.
T-cells require antigen presentation
The antigen must be presented on an antigen presenting cell
with a major histocompatibility complex before the T-cell will
Three signals before an immune response is triggered:
i. APC presents antigen on MHC
ii. Expression of co-stimulatory molecules on APC
iii. Cytokine secretion by APC.
MHC (major histocompatibility complex)
Two main types:
MHC I – present on all nucleated cells.
MHC II – present on specialized antigen-presenting cells, such
as macrophages, dendritic cells, and B-cells. Especially
o The body can handle different antigens at the same time.
o Passive Immunity – from mothers milk, eg. Only lasts a few weeks.
Platelets & Hemostatsis
Hemostatis is a process that causes bleeding to stop.
Hemeostasis is the maintenance of a standard state within a system.
Key Features of Hemostasis
o Platelet Plug formation (white thrombus)
o Blood clotting (red thrombus)
Fibrinogen, clotting factors, etc. all come together.
o Come from stem cells, but specifically from pieces of the cytoplasm of
o Do not have a nucleus. o Have alpha granules
Adhesion molecules such as von Willebrand factor.
Some clotting factors
o Have dense granules
ADP and ATP
o Platelet Plug Formation
Adhesion – sticking to damaged walls
Activation – changing shape, express receptors, and secrete various
Aggregation of platelets – stick together and form a plug.
Von Willebrand factors cause platelets to accumulate. Then
they bind to fibrinogen and form networks. Thus, the platelets
Activated platelets have two roles: the first is in vasoconstriction and
the second is in further platelet aggregation in case secondary
thrombus formation is needed.
Expansion does not occur because neighboring cells secrete
prostacyclin or nitric oxide, which prevents platelet aggregation at
healthy endothelial cells.
o Arachidonic Acid
Produces Leukotrienes and Prostaglandins.
o Aspirin blocks COX, causing the inactivation of both Thromboxane (pro-
hemostatic effect) and Prostacyclin (anti-hemostatic effect). Since
Thromboxane is found in platelets, it isn’t replenished. Prostacyclin, by
comparison, is replenished, so the net gain is a anti-hemostatic effect.
o Blood Clotting
The key step is the activation of Thrombin so that it can catabolize the
reaction of fibrinogen to fibrin (which is an insoluble plasma protein).
Calcium is an important plasma clotting factor.
Traditional view saw factor XII as essential for the cascade of
activation that results in blood clotting.
Modern view is that Thrombin influences other pathways and a very