Physiology: Body Fluids, Pulse and Homeostasis

• Physiology is the study of how the body functions to sustain life.
• Pathophysiology examines how physiological processes are altered by disease or injury.

Body Fluids

• Interstitial fluid is the liquid surrounding body cells, providing their liquid environment and is the main component of the extracellular fluid (ECF).
• Intracellular fluid refers to the cytosol or cytoplasm within cells.
• Extracellular fluid consists of blood plasma (20%) and interstitial fluid (80%).
• Plasma constitutes the colorless fluid portion of blood, lymph, or milk, suspending corpuscles or fat globules.

Pulse

• Pulse is the rhythmic throbbing of arteries as blood flows through them, caused by the heartbeat.
• Pulse can determine heart rate, rhythm, and strength

Homeostasis

• Homeostasis is the body's drive to maintain a stable equilibrium among interdependent elements.
• Homeostasis is crucial for providing a stable environment for specialized cells within organs and systems.
• Homeostatic set points are specific conditions, like oxygen levels, glucose concentration, pH, and temperature, maintained by the body.
• Idealized conditions swing around a set point by negative feedback loops

Homeostasis Maintenance

• Maintained through Negative Feedback Loops.
• A stimulus elicits a response that counteracts or reverses the original stimulus.

Negative Feedback Loops

• Negative feedback loops maintain set points by negating deviations
• Involves sensors detecting deviations, an integrating center determining a response, and effectors producing the response
• This cycle operates continuously (24/7)

Negative Feedback Loop - Steps

• A sensor detects a deviation from a set point
• An integrating center determines the response (often the brain or endocrine system)
• Effectors are activated to produce a response correcting the deviation from homeostasis

Positive Feedback Loops

• A stimulus elicits a response that amplifies the original stimulus

Components of Feedback Loops

• Sensors detect deviations from set points
• Integrating centers determine the appropriate response
• Effectors produce the response to counteract the deviation

Set Point

• Set points are the average levels for bodily measurements, like a temperature set point of 98.6 degrees

Laminar vs. Turbulent Flow

• Laminar flow is a silent, nonturbulent flow in parallel layers where fluid moves unobstructed.
• Turbulent flow is erratic, causing sounds at systole and diastole due to obstructed blood flow

Blood Pressure

• Blood pressure is the force of blood against arterial walls, that depends on heart action, arterial elasticity, and blood volume/viscosity

Korotkoff Sounds

• Sounds heard by medical personnel when measuring blood pressure non-invasively

Heart Cycle

• Systole (systolic) refers to the contraction of the heart.
• Diastole (diastolic) refers to the relaxation of the heart.

Cell membrane

• Cell membrane is a hydrophobic barrier to hydrophilic molecules, selectively allowing hydrophobic molecules to pass.
• The cytosol/cytoplasm carries out biochemistry within the cell.

Cell Membrane Composition

• The cell membrane is a hydrophobic barrier to hydrophilic molecules.
• It selectively allows certain hydrophobic molecules to pass through

Simple/Passive Diffusion

• Molecules move from areas of high to low concentration, without energy input

Hydrophilic Molecules

• Water-loving molecules can form:
  • Covalent bonds: sharing of electrons (polar covalent, unequal sharing)
  • Ionic bonds: transfer of electrons due to significant electronegativity differences

Ions

• Ions dissociate or separate when placed in water

Hydrophobic Molecules

• Water-hating molecules, like triglycerides

Phospholipids

• Phospholipids resemble triglycerides, featuring a glycerol backbone, two fatty acids, and a polar head group with a phosphate, making them amphipathic

Critical Mycelar Concentration (CMC)

• CMC the amount of phospholipids needed to form mycel and form a bilayer in water to create artificial cells (mycel)

Polar vs. Nonpolar

• Polar molecules have unequal electron sharing are hydrophilic.
• Nonpolar molecules have equal electron sharing are hydrophobic.

Phospholipid Bilayer

• Phospholipid bilayers are not bound together; they protect lipid tails.

Transmembrane Proteins

• Transmembrane proteins are integrated into the cell membrane, creating passageways for hydrophilic molecules and controlling molecule entry/exit.

Cholesterol

• Cholesterol is primarily hydrophobic but contains an OH group, giving it amphipathic qualities.
• It can be located near hydrophilic head groups, blocking theoretical passageways.

Carbohydrates

• Carbohydrates are exclusively on the cell's exterior and facilitate recognition and communication

Fluid Mosaic Model

• Lipids move around the surface which creates "art work" due to protein movement
• Proteins and carbs can tether lipids together which decreases mobility of the cell

Mechanisms of Transport

• Three mechanisms transport molecules in and out of cells: simple/passive diffusion, facilitated diffusion, and active transport
• Diffusion drives movement in simple/passive diffusion and facilitated diffusion.

Net Diffusion

• Net diffusion is the measurable movement of particles down a concentration gradient
• Diffusion occurs constantly due to thermal energy from one high concentrated area to a lower concentrated area

Thermal Energy

• Every molecule in solid, liquid, and gas forms has thermal energy
• Thermal energy consists of kinetic and potential energy of constituent particles.

Simple Diffusion Molecules

• N2, O2, CO2 diffuse easily, being hydrophobic gases.
• Small, uncharged polar molecules (ethanol, urea, water) are slightly permeable
• Water permeability varies based on membrane cholesterol levels

Non-Permeable Molecules

• Large, uncharged polar molecules (glucose, fructose) are impermeable.
• Ions (K+, Mg2+, Ca2+, Cl-, HCO3-, HPO42-) are also impermeable due to charge.
• Charged polar molecules (amino acids, ATP, glucose 6-phosphate, proteins, nucleic acids) cannot pass through

Diffusion Rate Factors

• Diffusion rate is affected by size (smaller area increases collision), molecular weight (larger decreases rate), membrane thickness (thicker decreases rate).
• Diffusion rate is affected by shape (long/skinny increases rate), and hydrophobic character

Osmosis

• Osmosis is the diffusion of water across a membrane.
• Water moves to areas of higher solute concentration and lower water concentration until concentrations are equal.
• Water only considers total molecule concentration

Solutes

• Non-electrolytes cannot conduct electricity
• Electrolytes can conduct electricity

Concentration

• Concentration is the amount of molecules within a defined volume compared to the same volume of other solutions

Osmolarity

• Osmolarity is the total number/concentration of solutes in a solution.
• 2 osmoles equals 2 moles of solutes

Fick's Law

• Fick's Law is CPSA/mw*X

Hydrostatic/Osmotic Pressure

• Pressure exerted by water

Crenation

• Shrinking of cells in hypertonic solutions

Hemolysis

• Swelling and bursting of blood cells in hypotonic solutions

Dynamic Equilibrium

• Molecules and water move equally across a membrane, maintaining constant concentrations, but molecules are still moving

Tonicity

• Tonicity refers to a solution
• Tonicity is the effect a solution has on cell volume
• Tonicity defines whether water movement occurs

Isotonic State

• There is no net water movement

Hypotonic State

• Water moves into the cells, causing them to swell and potentially lyse from hyposmotic (too few osmoles)

Hypertonic State

• Water moves out of the cells, causing them to shrink. This is due to too many solutes outside the cell, making it hyperosmotic

Isosmotic State

• Indicates equal solute concentration inside and outside the cell, but doesn't confirm if molecules can cross the cell membrane.

Isotonic and Isosmotic Relationship

• Isotonic solutions are always isosmotic, but isosmotic solutions are not necessarily isotonic.

Pressure

• Pressure is the physical force exerted on an object by something in contact

Moles

• A mole is 6.0 x 10^23 molecules

Molarity

• Molarity (M) is 1 mole of compound dissolved in water up to 1 liter

Facilitated Diffusion

• Molecules move across the cell membrane via transport proteins down the concentration gradient
• Also referred to as carrier-mediated diffusion

Channels

• Channels are membrane proteins that open and allow molecules to diffuse into the cell
• Most channels are gated

Membrane Permeability

• Channels and carriers/transporters alter membrane permeability for specific molecules

Channel Transport Rate

• An open channel can potentially transport between 10^7 to 10^8 molecules per second

Potassium Channels

• Potassium channels are constitutively open

Channel Opening Mechanisms

• Ligand gating occurs when a ligand binds to a membrane protein, changing its shape
• Voltage gating responds to changes in charge around the membrane

Carriers/Transporters

• Change shape upon molecule binding, moving molecules down the concentration gradient
• Binding grooves typically face the area of highest concentration

Gated Channels

• All channels except potassium channels are gated

Carrier/Transporter Rate Limit

• The slow rate of molecule movement across the membrane causes the plateau.
• The ligand must bind, change shape, and release

Uniporters

• Transport a single molecule down its concentration gradient

Symporters

• Move molecules in the same direction
• One molecule moves down its concentration gradient, the other doesn't have to

Antiporters

• Move molecules in opposite directions
• One molecule moves down its concentration gradient; the other doesn't have to.

Transporter Rate

• Transporters can move 10^2-10^4 molecules per second

Secondary Active Transport

• Utilizes a carrier/transporter protein to move two molecules, where one goes down and the other goes against its gradient.
• Uses the energy of diffusion
• Basically, energy comes from outside of the molecule itself.

ATPase Pumps

• ATP driven, so they are the slowest
• ATP is needed to move molecules against their concentration gradient
• Pumps cannot bind low concentration molecules until a phosphate from ATP is bound.
• Hydrolyzing ATP releases a phosphate to bind to the pump, changing its shape
• Important ATPase pump: Sodium Potassium ATPase pump

Sodium Potassium ATPase Pump

• The pump originally binds neither sodium nor potassium.
• The pump becomes phosphorylated by ATP, enabling it to bind sodium (low concentration inside the cell)
• Sodium binding triggers the release of the phosphate group
• Potassium then binds, changing the shape and releasing the potassium inside before restarting the cycle
• This pump does not agree that it's like an antiporter as neither move down concentration gradient, though it requires ATP and has antiporter-like activity
• It binds 3 sodium (releasing them outside) and 2 potassium (releasing them inside)
• Phosphorylated has high affinity for Na when open to the ICF
• Dephosphorylated has high affinity for K when open to the ECF; low affinity for Na

Passive vs. Facilitated Diffusion

• Passive/simple diffusion utilizes the molecule's thermal energy
• Facilitated diffusion requires a uniporter, symporter, or antiporter

Active Transport

• ATP driven (e.g., Sodium Potassium ATPase pumps)
• Secondary transport facilitated via symporters and antiporters

Endocytosis

• Process when something inside the cell
• Large molecules remain inside the vesicle when inside of the cell

Receptor Mediated Endocytosis

• The cell specifically binds something on the outside of the cell and forms a pocket around it

Phagocytosis

• Larger molecules are engulfed by entire bacteria and are taken into the interior of the cell

Exocytosis

• Molecules are produced and stored in a vesicle and fuse to the membrane when the cell want to release it for too large to pass through the membrane

Digestion Molecules

• Carbohydrates broken into monosaccharides
• Proteins are broken into amino acids
• Lipids (triglycerides) into fatty acids and monoglycerides

Digestion System

• Mouth (buccal cavity) -> pharynx -> pharynx splits into trachea and esophagus -> empties into the stomach -> small intestine (duodenum, jejunum, ileum) -> colon (ascending, transverse, descending) -> out of anal canal -> anus

Accessory Organs of Digestion

• Mouth - teeth, tongue, salivary glands
• Liver, pancreas, gall bladder

Amylase

• Amylase is used for preliminary chemical digestion and it increases the water content already
• Sheer off all carbohydrates, but doesn't generally digest sugars down to monosaccharides

Deglutition

• Swallowing. Voluntary (1st 1/3 of esophagus under skeletal muscle control), begins movement to stomach. Involuntary (last 2/3's under smooth muscle and autonomic nervous system control).

Stomach

• Stomach does not sterilize food by HCl which denatures bacteria, fungi and mold
• Physically separated through mixing, separation, unfolding of biomolecules (carbs, proteins, lipids)
• Proteins are divided into protein peptides
• Regulates homeostasis by slowly releasing small chyme amounts to slowly absorb the meal

Digestion Location

• Digestion does NOT occur in the mouth or stomach but there is some chemical processing

Small Intestine

• Digestion begins here, aided by accessory organs

Pancreas

• Releases bicarbonate (base) to neutralize the acidic solution from the stomach.
• Produces digestive enzymes like trypsin, aminopeptidase (to break down proteins), amylase, maltase (to break down carbs), and lipase (to break down lipids)
• Molecules can be chemically digested into monomers here

Lipids in Small Intestine

• Lipids accumulate, requiring separation for enzyme access.
• The liver releases bile, that emulsifies the fat for lipid enzyme access

Bile Storage

• Bile is stored in the gall bladder and liver

Enzymes

• Catalyst proteins.
• Highly specific to molecules they interact with (substrate specificity)
• Act as a vice, hold substrates in correct positions
• Enzyme cannot force molecules together or apart that aren't already going to

Catalyst

• A substance that promotes a chemical reaction without undergoing permanent change.
• A catalyst increases the rate of a reaction

Enzyme Energy Use

• Cells do use a lot of energy when making enzymes