Basic ConceptsBasic Concepts

1

Cellular PhysiologyCellular PhysiologyImportance of cell physiology for health care:- most disorders or pathologies have a cellular etiology- infections may be viral, bacterial or fungal

Genetic disorders:- involving abnormalities in primary  structure or expression of cellular DNA- physiologically critical as genes regulate   cell division, metabolism, cell function, etc.- mutated or altered genes can affect    every system in the body:   - e.g. reproductive, digestive,       musculo-skeletal, sensory, etc.

Metabolism:- encompasses all biochemical reactions carried out by the cell or organism- dependent upon translation of enzymes, availability of nutrients & oxygen, etc.

https://i.pinimg.com/originals/a9/5f/5c/a95f5cb960b4b19288f5c91f31c0b3d7.jpg2

Cellular PhysiologyCellular PhysiologyCritical Elements of Cellular Physiology:- transcription, translation, regulation of protein number & function- regulation of membrane transport (substances entering or leaving cell)- partitioning of the eukaryotic cell interior by membranes & cytoskeleton- regulation of intracellular transport (moving substances from one    region of the cell to another region- extraction & utilization of energy (e.g. conversion of glucose to ATP)- disposal of metabolic wastes (nitrogen balance, removal of toxins, etc.)- regulation of cell division- cellular defense (e.g. autophagy – tagging & removal of    destructive agents)- cellular differentiation and development, growth- cellular pathologies (e.g. abnormalities in organelle function – often   genetic & may involve mitochondria, lysosomes, peroxisomes, etc.)- intercellular adhesion (e.g. enabling cells of the skin to remain    within the skin tissue)- cellular motility (e.g. for macrophages, gametes, etc.)- apoptosis (regulated cell death necessary for development,   differentiation, maintenance, tissue health, etc.)- homeostasis: maintenance of an ‘interior’ environment that differs    from its surroundings (temperature, composition, etc.)

https://media.cellsignal.com/www/images/categories/pathways/akt/mtor.png3

Cellular PhysiologyCellular Physiology

https://upload.wikimedia.org/wikipedia/commons/thumb/8/84/Human_chromosome_diseases_set_en.svg/1024px-Human_chromosome_diseases_set_en.svg.png

Most diseases have a cellular,if not genetic, origin.- e.g. inborn errors of metabolism

4

Cellular AnatomyCellular Anatomy

https://i.pinimg.com/originals/e3/97/fb/e397fb8648a6a9d72bc351fa3d182d1f.jpg

Organelles- membrane-bound functional structures such as:   - nucleus   - mitochondria   - endoplasmic reticulum   - Golgi apparatus   - peroxisome   - lysosome

Not Organelles- structures lacking membrane:   - nucleolus   - free ribosomes   - cytoskeletal structures

Cells may be 'lysed' and fractionated for analysis- lysis may involve rupture or dissolution of the plasma membrane- fractionation of cellular components is often achieved by centrifugation   - low speed: nucleus   - medium speed: mitochondria, lysosomes, peroxisomes   - high speed: free ribosomes, ER- precipitates are termed 'microsomes'

5

Cellular PhysiologyCellular Physiology

https://i.pinimg.com/originals/53/40/48/53404878ebd24693553349c819c8d79c.png

Cells may be injured by:- hypoxia                                         - autoimmune conditions- ischemia                                       - deficient nutrition- physical/chemical trauma         - aging- microbial/viral infection

Such external insults often cause:- an inability of the cell to generate energy (ATP)- generation of damaging free radicals- altered calcium metabolism

Cellular disorders include:- cancer                                    - anemias- Alzheimer disease               - certain metabolic- mitochondrial disorders       disorders

Dysplasia: abnormal division or nuclear regulationMetaplasia: replacement of one cell type by another Anaplasia: de-differentiation

6

Cellular PhysiologyCellular Physiology

http://4.bp.blogspot.com/-XEhFpBkIQiI/Tb28nyJ4dlI/AAAAAAAAAII/J5YajzzuKpw/s1600/fluid.png

ICF: intracellular fluidECF: extracellular fluidISF: interstitial fluid

ICF & ECF are separated by cell membranes.The 2 compartments of ECF are separated by cells.- flow of ECF between plasma & ISF occurs across    the capillary membrane (endothelium)

The cell membrane consists chiefly of lipidsand proteins in approximately equal proportionby mass.- but lipids are usually ~50X more abundant- the exact ratio varies by cell and tissue- organelle membranes are also of variable composition

7

Fluid-Mosaic ModelFluid-Mosaic ModelMost cell membranes consist of:- dynamic bilayer of phospholipids and    interspersed proteins, lipids    - possibly attached to carbohydrates

Phospholipids have a polar hydrophilic‘head’ & two hydrophobic fatty acid ‘tails’: - most PLs are phosphoglycerides- in the bilayer, the fatty acid tails   form the interior- phospholipids are 'amphipathic'

Functional categories ofmembrane protein include:- ion channels   - transporters - receptors        - surface antigens - adhesion molecules

Both membrane proteins and phospholipidsmay have attached carbohydrates: - phospholipids - glycolipids

https://i.pinimg.com/originals/73/a1/6d/73a16dc6a331f91e981c368fe2582025.jpg8

Cell Membrane ProteinsCell Membrane ProteinsMembrane proteins have been categorized by avariety of adjectives:- transmembrane    - extrinsic- peripheral              - integral- anchored

 https://classconnection.s3.amazonaws.com/362/flashcards/2263362/jpg/mosaic-1419F18B7343D4E7B77.jpg    https://i.pinimg.com/originals/73/a1/6d/73a16dc6a331f91e981c368fe2582025.jpg

The plasma membrane may contain>100 different proteins.  Membraneproteins may be attached to thecytoskeleton or form cell junctions.Integral membranes may betransmembrane or embedded.

9

Cell Membrane ProteinsCell Membrane Proteins

http://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-07-08/07_05.jpg10

Cell Membrane ProteinsCell Membrane Proteins

https://swh-826d.kxcdn.com/wp-content/uploads/2015/09/selectively-permeable-membrane.png

In general:- ions and larger, hydrophilic molecules do not    passively diffuse through membranes   - but they may diffuse with the assistance of      a channel or carrier

- some diatomic gases such as O2 & CO2 can  readily diffuse across membranes - movement of water across membranes is    dependent upon large concentration gradients    (osmosis) or the presence of water channels    (aquaporins)

11

MembraneMembraneTransportTransport

12

Characteristics of DiffusionCharacteristics of Diffusion

https://www.youtube.com/watch?v=LUPHohqlPTU

Diffusion is critical for cell nutrition, removalof cellular wastes and general metabolism.Note that particles can diffuse across membranesaccording to concentration, size, solubility, etc.1. Particles move from higher concentration     to lower concentration2. Diffusion occurs spontaneously     - utilizing only the inherent thermodynamic       kinetic energy3. Migration of particles occurs until the     concentration is uniform (equilibrium is achieved)     - although thermal motion of molecules persists 4. Rate of diffusion varies directly with temperature5. Rate of diffusion varies inversely with the size of the molecule 6. Diffusion may occur across a membrane, depending upon the    characteristics of the membrane and particles (permeability) 

https://www.youtube.com/embed/LUPHohqlPTU?enablejsapi=1

13

Characteristics of DiffusionCharacteristics of Diffusion

https://i.pinimg.com/originals/b5/3b/2c/b53b2c4a054750c6132a78021a753e60.jpg

Diffusion coefficient- a term integrating factors such as:   - size of diffusing molecule   - relative solubility of molecule   - temperature   - viscosity of medium, etc.

Diffusion across membranes:- is also affected by the  permeability of the membrane  which is influenced by:   - membrane thickness   - membrane surface area   - membrane solubility   - charge gradient, etc.

14

Fick's Law of DiffusionFick's Law of Diffusion

https://content.openclass.com/eps/pearson-reader/api/item/ab914c98-1923-486b-bdb4-b9187be18b9e/1/file/silverthornHP7-071415-MJ-BO/OPS/img/9812205007.png

Overall, rate of diffusion across a membrane is proportional to:               available surface area X concentration gradient               resistance of membrane X membrane thickness

Membrane resistance varies according to:1. the size of the diffusing molecule2. the solubility of the molecule in lipids3. the composition of the lipid membrane

15

Mechanisms of Passive TransportMechanisms of Passive Transport

https://www.thoughtco.com/thmb/m5HSRVWXvN5lQxAOlFSrFsMobbI=/1500x1001/filters:no_upscale():max_bytes(150000):strip_icc()/facilitated_diffusion-56cdd5033df78cfb37a3460c.jpg

Small molecules that are not able to passively diffuseacross a hydrophobic cell membrane may still diffusethrough the membrane -- provided:1. the concentration gradient is favorable2. a membrane protein is available to facilitate diffusion

Passive membrane transport proteins include:1. ion channel proteins2. carrier proteins

Small molecules conveyed across a membrane againstthe membrane concentration gradient must betransported actively (consuming ATP)

16

Mechanisms ofMechanisms ofPassive TransportPassive Transport

https://www.youtube.com/watch?v=_HBd7RXw880

https://www.youtube.com/embed/_HBd7RXw880?enablejsapi=1

17

Passive Transport: Ion ChannelsPassive Transport: Ion ChannelsMembrane ion channel proteins:- form small hydrophilic pores in the membrane- somewhat selective- allow passage of ions much more rapidly (1000X) than  membrane carrier protein (~ 1 million ions / sec.)- ion channels do not pass ions against their  concentration gradients- are commonly gated and closed, although some 'leak'  channels remain open much of the time- thus, ion flux can be regulated by charge, size, etc.- Na+, K+, Cl-, Ca++, etc. pass through cell membranes   via channels- channels may also be receptors (ligand-gated channels)

https://youtu.be/_icBM60sMOU

https://www.youtube.com/embed/_icBM60sMOU?enablejsapi=1

18

Passive Transport: Ion ChannelsPassive Transport: Ion ChannelsGated ion channels are typically regulated by:- binding of ligand (specific molecule) (c)   - ligand-gated; chemical gating, etc.- mechanical deformation of membrane (b)   - mechanically gated or stretch-gated channel- change in membrane potential (a)   - voltage-gated channel

http://www.macmillanhighered.com/BrainHoney/Resource/6716/digital_first_content/trunk/test/hillis2e/asset/img_ch34/c34_fig05.jpg19

Passive Transport: CarriersPassive Transport: CarriersFacilitated Diffusion - typically moves larger molecules (amino acids, glucose, etc.) - is much slower than transport via ion channels - relatively stereo-specific and subject to inhibition (blocking) - requires that the substrate (molecule to be transported) be   bound by the carrier protein - the carrier protein changes conformation (shape) then    releases the molecule on the opposite side of the     membrane - maximum rate of transport (Vmax) is NOT entirely    concentration-dependent     - as binding of substrate & conformational       shift require time

https://slideplayer.com/slide/13071122/79/images/15/Carrier-Mediated+Transport.jpg20

Primary Active TransportPrimary Active TransportPrimary active transport- membrane protein hydrolyzes ATP in order to transport  molecules across the membrane against their  concentration gradient

ht

Active carriers move solutes across the membraneagainst the electrochemical gradient.Active transport is also coupled to hydrolysis of ATP.

Any substance moved against its concentration gradientmust be transported actively.- by contrast, passive transport implies that the substance   requires a protein intermediary to travel across the   membrane WITH its concentration gradient.

Active transporters are often termed 'pumps'- or ATPases

21

Sodium-Potassium PumpSodium-Potassium PumpThe sodium-potassium pump:- exchanges 2 K ions for 3 Na ions- is critical for cell metabolism

https://youtu.be/_bPFKDdWlCg

https://www.youtube.com/embed/_bPFKDdWlCg?enablejsapi=1

The sodium-potassium pump:- alters cell membrane osmotic balance- and alters the membrane charge gradient

22

Secondary Active TransportSecondary Active TransportIon concentration gradients(usually Na) generated by primaryactive transporters (usually Na-KATPase) are used to movesubstances against theirconcentration gradient- energy from the inward flux of Na  (diffusion) can be used to bring  other molecules across the  membrane- figure shows sodium-dependent  transport of glucose

https://slideplayer.com/slide/15326343/92/images/5/Primary+active+transport.jpg23

Secondary Active TransportSecondary Active TransportCountertransport = antiportCotransport = symport- secondary active transport is  typically sodium dependent  transport- here, the transport of glucose is  secondary to the movement of Na  ions and the actions of the sodium-  potassium pump

https://youtu.be/GhwJzVq-3GY

https://www.youtube.com/embed/GhwJzVq-3GY?enablejsapi=1

24

Secondary Active Transport of GlucoseSecondary Active Transport of Glucose

There are at least 4 class I (passive) glucose transporters- GLUT1: critical for glucose uptake in most cells  - at high concentrations in RBCs- GLUT2: small intestine (apical & basolateral),  pancreatic insulin releasing cells, liver (bidirectional)- GLUT 3: chiefly neuronal- GLUT4: adipose tissue and striated muscle

https://i.ytimg.com/vi/DzN0geHb86I/maxresdefault.jpg

Intestinal uptake of glucose is Na-dependent- secondary active transport

Sodium-dependent transport of glucose utilizes the SGLUT protein

25

Vesicular TransportVesicular Transport

Vesicular transport may be necessary for:- large volumes of material - larger molecules

https://cooper7e.sinauer.com/animation1403.html

Vesicular 'packaging' may also be necessary tomaintain critical osmotic gradients or to regulateintracellular concentrations.

Vesicles are generally formed throughinteraction of the ER, Golgi & perhaps lysosomes.- vesicles fuse with membrane to release contents

Transport of vesicles may occur within the cell or across the cell membrane- intracellular transport of vesicles usually involves  carriage of vesicles along microtubules by motor  proteins- transport across the plasma membrane normally  occurs by exocytosis or endocytosis

In endocytosis the membrane invaginates (rather thanextrudes as in phagocytosis).Endocytosis is constitutive (normal, ongoing) in most cells.

26

Receptor-mediated endocytosisReceptor-mediated endocytosis

https://youtu.be/hLbjLWNA5c0          https://www.thoughtco.com/thmb/UtSHCYERnnGb2ejLmgHDJEo0R9M=/1500x1000/filters:no_upscale():max_bytes(150000):strip_icc()/receptor-mediatedendocytosis-594d62493df78cae81e0b015.jpg

A common form involves clathrin-dependenttransport vesicles (coated by clathrins)- facilitates intercellular communication

https://www.youtube.com/embed/hLbjLWNA5c0?enablejsapi=1

27

PhagocytosisPhagocytosis

https://youtu.be/iZYLeIJwe4w                                 https://upload.wikimedia.org/wikipedia/commons/4/4e/Phagocytosis_--_amoeba.jpg

https://www.youtube.com/embed/iZYLeIJwe4w?enablejsapi=1

28

Vesicular Transport: SecretionVesicular Transport: Secretion

https://www.thoughtco.com/thmb/iFbp1NMrq9HYzkyjDH_NvmNKeAI=/1500x1001/filters:no_upscale():max_bytes(150000):strip_icc()/exocytosis-582df6965f9b58d5b183203f.jpg

Constitutive secretion- occurs in all cells- secreted substances are not stored- substances are secreted soon after  synthesis

Regulated secretion- occurs in response to a chemical   signal- secreted substance is stored prior  to release

29

TransepithelialTransepithelialTransportTransport

https://www.researchgate.net/figure/Transepithelial-transport-routes-and-intercellular-junctions-a-Paracellular-and_fig1_327661992

Typically, transcytosis requiresdifferent types of transporter onthe apical and basal surfaces- transepithelial transport is  important for virtually all tissues   - intestinal epithelium   - renal tubules   - exocrine glands   - gallbladder epithelium   - choroid plexus, etc.

30

TransepithelialTransepithelialTransportTransport

https://www.researchgate.net/profile/Fredrik_Jutfelt/publication/234102737/figure/fig3/AS:669466329378836@1536624619646/Schematic-view-of-intestinal-transepithelial-transport-in-fish-Three-enterocytes-are.ppm

FATP: fatty acid transportprotein

FABP: fatty acid bindingprotein

claudin: essential tight junctionprotein

31

Membrane TransportMembrane Transport

https://content.openclass.com/eps/pearson-reader/api/item/ab914c98-1923-486b-bdb4-b9187be18b9e/1/file/silverthornHP7-071415-MJ-BO/OPS/img/9812205021.png

https://www.youtube.com/embed/BGeSDI03aaw?enablejsapi=1

32

OsmosisOsmosis& Tonicity& Tonicity

33

Definition of OsmosisDefinition of Osmosis

https://content.openclass.com/eps/pearson-reader/api/item/ab914c98-1923-486b-bdb4-b9187be18b9e/1/file/silverthornHP7-071415-MJ-BO/OPS/img/9812205021.png

Three key elements for definition of osmosis:1. movement of water2. across a differentially permeable membrane3. toward a higher total particle concentration

Molecules may pass through a membrane according to:- size- charge- polarity- hydrophobicity

Water moves across the water-permeable membrane tohigher total particle concentration.

The term osmolality is preferred over osmolaritybecause the mass of water is fixed relative to thenumber of particles.

Water passes through the membranetoward higher total particle concentration

34

OsmosisOsmosis

https://kmbiology.weebly.com/uploads/6/0/1/1/6011704/190346.jpg?580

The ability of water to pass through a cell membrane is dependent upon:1. the concentration gradient2. density of water channels (aquaporins)    - which is partially regulated by the translation & insertion      (or withdrawal) of these proteins in the cell membrane

Isosmotic solutions have the same number of particles per unit volume (or mass).- A solution with higher total particle concentration is hyperosmotic to a solution with   lower total particle concentration.- A solution with lower total particle concentration is hyposmotic to a solution with    higher total particle concentration.

Water moves from hyposmotic to hyperosmotic.

35

OsmosisOsmosis

https://content.openclass.com/eps/pearson-reader/api/item/ab914c98-1923-486b-bdb4-b9187be18b9e/1/file/silverthornHP7-071415-MJ-BO/OPS/img/9812205021.png

In general, the osmolarity of a simplesolution is the product of molarity & thenumber of particles per molecule.- glucose: 1 particle- NaCl: 2 particles- MgCl2: 3 particles- urea: 1 particle

300 mM glucose = 300 mM urea = 150 mM NaCl

In reality, ionic bonds do not completelydissociate; thus Osm/mol is usually lessthat the number of ions in the molecule

36

Osmotic PressureOsmotic Pressure

https://chem.libretexts.org/@api/deki/files/42811/c0d01b7aef63f35303c43d781b0b3d15.jpg?revision=1

A pressure gradient (difference) is created by an imbalance in total particle number across themembrane.  Technically, osmotic pressure is the force necessary to oppose the osmotic movement ofwater into another compartment with higher total particle concentration.

37

OsmoregulationOsmoregulation

http://www.pathwaymedicine.org/images/renal/Body-Fluid-Shifts-Figure-1.png

The physiological regulation of osmolality involves multiplephysiological systems, including the endocrine system, kidneys, GIsystem, integument, etc.

Physiological osmolarity is ~280-296 mOsM- often rounded to 300 mOsM for purposes of calculation- unit: milliosmoles per liter (osmolarity) or kilogram (osmolality)

Disease may cause movement of body wateracross compartments- amount of water changing compartments isdependent upon the concentration of the fluid andthe ability of physiological systems to compensate

38

TonicityTonicity

http

Whereas osmosis is the physico-chemical process responsible for the movement of water acrosscell membranes, tonicity describes the physical consequences of the migrating water:- cells swell or shrink due to movement of water across the cell membrane- and body compartment volume changes (e.g. edema)

1. If a membrane-bounded compartment (cell) swells when placed in another solution, the solution is     hypotonic with respect to the compartment (cell).2. By contrast, a hypertonic solution will cause the membrane-bounded     compartment (cell) to lose water (and volume).3. If there is no change in cell volume the cell is isotonic to the solution. 

Tonicity is determined by the extent to which particles are able (or unable) to traverse the cellmembrane:- membrane-permeable particles will pass through the membrane until equilibrium is achieved  (with no change in volume)

39

Consequences of TonicityConsequences of Tonicity

https://upload.wikimedia.org/wikipedia/commons/thumb/7/76/Osmotic_pressure_on_blood_cells_diagram.svg/1280px-Osmotic_pressure_on_blood_cells_diagram.svg.png

Thus, tonicity depends upon the relative concentrations of nonpenetrating solutes in the cell and inthe solution.- as water migrates across the membrane toward the greater concentration of nonpenetrating solutes

Again, only solutes that are unable to cross the cell membrane cause significant movement of water(and thereby alter tonicity).

40

Consequences of TonicityConsequences of Tonicity

h41

Consequences of TonicityConsequences of Tonicity

h42

Application of TonicityApplication of Tonicity

h

Intravenous Fluids (IV’s) are used to:- supply essential fluid when oral hydration is impractical - maintain normal electrolyte (ion) levels in ECF and cells - to provide metabolic fuel – usually glucose, nutrients, drugs, etc.

Isotonic IV (total particle concentration comparable to ICF)- should induce no movement of fluid across membranes - usually for rehydration; fluid remains in ECF (vascular compartment) - NSS (Normal Saline Solution/ 0.9% NaCl) or- D5W (5% dextrose in water) - contains no electrolytes but as glucose is    metabolized, remaining water has hypotonic effect

Hypotonic IV (total particle concentration lower than ICF)- tends to cause fluid to flow into cells (increasing their volume) - may be used in severe dehydration - but may also cause vascular collapse or cellular damage - e.g. 0.45% NaCl (half strength normal saline) or 2.5% dextrose in H2O

43

Application of TonicityApplication of TonicityHypertonic IV (total particle concentration greater than ICF):- generally > 350 mEq/L - acts to reduce volume of cells - D5NSS (5% Dextrose in normal saline solution) or - D10W ( 10% Dextrose in water) - rarely for patients with hyponatremias (Na deficits) with edema - not recommended for many clinical conditions (e.g. diabetic ketoacidosis)

https://slideplayer.com/slide/13942950/85/images/9/Common+IV+Solutions+and+Tonicity.jpg44

Introductory Principles: HomeostasisIntroductory Principles: Homeostasis

http://www.wou.edu/chemistry/files/2019/01/Temperature-regulation-in-homeostasis-with-feedback.png

Physiological homeostasis oftendepends upon inhibitory(negative) feedback- critical physiological processes are  regulated within a narrow range- there are compensatory  mechanisms to resist  deviations from the  normal range  - as hormone levels rise,    mechanisms act to    lower hormone release    and limit physiological    response

45