Section 1: Cell Physiology

physiology

pathophysiology

What is the complex organization from cells to organ systems?

cells → tissues → organs → organ systems

___ and integration exists at all levels of organization.

Regulation

autocrine signaling

cell targets self

gap junction signaling

cell targets connected neighboring cell through gap junctions

paracrine signaling

cell targets a nearby cell

endocrine signaling

cell utilizes hormones through the bloodstream to target further cells

homeostasis

physiological tendency to maintain a stable environment according to external changes

negative feedback control

promotes stability by sensing a moment of change and limiting an action

ex: BP regulation

positive feedback control

promotes change in one direction by sensing a moment of change and enhancing

ex: childbirth contractions

feed-forward control

anticipates change and acts before a moment of change

cell membrane

separates cell compartments; sets the intracellular and extracellular environments; allows for a concentration gradient for cell activity

What 3 components make up a cell membrane?

phospholipid bilayer, proteins, cholesterol

phospholipid bilayer

inner hydrophobic tails and outer hydrophilic heads; semipermeable to small hydrophobic/lipid-soluble solutes (ex: EtOH, cortisone)

Proteins add ___ to a membrane.

specificity

integral proteins

pass through membrane

ex: channels, pores, carriers, enzymes

peripheral proteins

partially embedded in membrane

ex: enzymes, intracellular signal mediators

cholesterol

bidirectionally moderate membrane fluidity and permeability depending on temperature

High temperatures on cholesterol ___ fluidity.

decrease

Low temperatures on cholesterol ___ fluidity.

increase

eukaryotic cell mass composition

70-85% water

10-20% proteins

2-9% lipids

1-6% carbohydrates

cell fluid composition

TBW = 2/3 ICF + 1/3 ECF = 2/3 ICF + (1/4 plasma + ¾ ISF)

1/3 ECF = ¼ plasma + ¾ ISF

ICF

intracellular fluid

high [K+] and [PO₄^3-]; human body is ~60% water

ECF

extracellular fluid

ISF + blood plasma w/n vasculature; high [Na+], [Cl-], and [HCO₃^-]

ISF

interstitial fluid

w/n ECF but outside of vasculature, separated from blood plasma by capillary walls

The ___/___-___or sodium pump creates the concentration difference between ICF and ECF.

Na+/K+-ATPase

diffusion

permeable to a solute; solute travels down the [ ] gradient from high to low [ ]

osmosis

selectively permeable to water; water travels from low to high [solute]

Distribution of body fluids across cell membranes is determined by ___ forces based on ___.

osmotic forces; electrolytes

Distribution of body fluids across capillaries are determined by ___ and ___ ___ pressures

hydrostatic; colloid osmotic

hydrostatic pressure (HP)

pushing pressure exerted by fluid on a surface → fluid pushed out

ex: BP against capillary walls → blood flow

osmotic pressure

pulling pressure exerted by solutes on fluid → osmosis in

isosmotic

same osmolarity/[solute] as body fluids

hyperosmotic

higher osmolarity/[solute] than body fluids

hypoosmotic

lower osmolarity/[solute] than body fluids

oncotic pressure/colloid osmotic pressure (Π)

osmotic pressure exerted by proteins (albumin) in a bld vessel’s plasma that pulls water into the vessel

HP_C

capillary hydrostatic pressure

favors outward movement of fluids in capillaries; depends on vessel BP

Π_C

capillary oncotic pressure

opposes water filtration out of capillaries; depends on [protein] in blood

P_i

interstitial hydrostatic pressure

opposes filtration out of capillaries; ISF pressure against the capillary

Π_i

interstitial oncotic pressure

favors water movement out of the capillaries via proteins pulling it

FILT = ___ (__ - ___ + ___ + ___)

K_f (HP_C - P_i + Π_C + Π_i)

What are some methods of transport across a membrane?

ion channels, pores, passive transport (diffusion, osmosis), and active transport

ion channels

allow ion diffusion b/n compartments; ungated; highly selective based on size, shape, and charge distribution

aquaporins

specifically allow water to pass b/n compartments through the membrane via osmotic pressure gradient

ex: renal cortical collecting ducts during reabsorption

What are the 3 kinds of membrane transporters regarding direction?

uniporters, symporters, antiporters

uniporters

membrane transport protein specific for a single molecule

symporters

membrane transport protein specific for a cation/atom down the [ ] gradient and another molecule in the same direction

ex: Na and water

antiporters

membrane transport protein specific for an ion down the [ion] gradient and another molecule in the opposite direction

ex: Na⁺/K⁺-ATPase or sodium pump

passive (diffusion) transport

uses difference in [ ] to transport down the [ ] gradient; no mediator/channel/carrier needed; no energy needed

simple diffusion

diffusion of lipid-soluble/non-polar molecules through the membrane; no energy needed

What 2 factors affect the net rate of diffusion?

1. difference in [ ]

2. pressure

Net diffusion is directly proportional to/dependent on ___ ___ (C₀-C_i).

concentration difference

High pressure ___ energy available to create movement from ___ to ___ pressure.

increases; high; low

facilitated diffusion

diffusion of water-soluble molecules; depends on # of gated channels or carrier proteins; subject to a V_max

___ diffusion is subject to a maximal rate of ___ (V_max).

Facilitated; uptake

The rate of facilitated diffusion is ___ than that of passive diffusion at ___ [solute].

greater; low

The rate of facilitated diffusion uptake reaches V_max at ___ [solute].

higher

Since ___ ___ is not dependent on carriers, it is not limited like facilitated diffusion’s V_max.

simple diffusion

primary active transport

pumps molecules against the [ ] gradient; requires energy (ex: ATP)

ex: Na⁺/K⁺-ATPase

Na⁺/K⁺-ATPase / sodium pump

most common example of primary active transport; requires ~2/3 cell energy to conform ion binding sites; regulates osmotic balance by maintaining a negative intracellular [ ]

321NOKIA

secondary active transport

co-transport or counter-transport; indirect use of energy stored in the membrane from another molecule during primary active transport

co-transport

co-porters; substances transported in the same direction as the driving ion

ex: SGLT (sodium glucose transport)

counter-transport

anti-porters; substances transported in opposite direction as the driving ion

ex: Na⁺/H⁺ exchange in renal and intestinal cells for pH balance

ligand-gated channels

channels that opens to a specific ligand

ex: acetylcholine, epinephrine in neuromuscular junctions

One ligand can have ___ receptors, but receptors can only bind ___ ligand.

multiple; one

voltage-gated channels

channels that open with a change in membrane voltage; ion-specific

gap junctions

formed b/n 2 adjacent cells; open to allow ion and small molecule passage

vesicular membrane transport

package substance into lipid membrane vesicles for transport via exocytosis, endocytosis, or transcytosis; requires ATP

exocytosis

vesicular expulsion of intracellular products

endocytosis

vesicular engulfing of extracellular products via phagocytosis or pinocytosis

phagocytosis

“eating” of large particles for endocytosis

pinocytosis

“eating” of fluids and small particles for endocytosis

transcytosis

vesicular transport of substances across the membrane

ex: capillary endothelial and intestinal epithelium

signal transduction

cellular processes of substances binding and activating/deactivating cells for communication or activity

agonist

hormones, neurotransmitters, steroids that bind a receptor and activate

antagonist

hormones, neurotransmitters, steroids that bind a receptor and deactivate

2nd-messenger systems

signal transduction from extracellular signals and receptors → intracellular mediators, signals, and receptors; more than 1 signal messenger for activity to happen

ex: G-proteins, cAMP, cGMP, Ca²⁺, calmodulin

protein kinases

phosphorylate other proteins/cells

ex: Ca²⁺-calmodulin-dependent kinases, G-proteins

Ca²⁺-calmodulin-dependent kinases

protein kinase in smooth muscle contractxn, hormone secretion, and neurotransmitter release

heterotrimeric guanosine triphosphate (g-proteins complex)

membrane-bound binding proteins that cause phosphorylation of GDP → GTP'; process can be inactivated by GTPase

In g-protein-coupled signal transduction, more steps can ___ the resulting signal intracellulary.

amplify

nuclear receptors

signal receptors w/n the nucleus; accessible intracellularly by lipid-soluble signals, steroids, and thyroid hormones

steroids and thyroid hormones

directly bind to to nuclear receptor to alter DNA and mRNA transcription over some time; increase protein synthesis