Introduction to Physiology

Characteristics of human cells (3)

• O2 reacts w/ nutrients to release energy

• deliver products of rxns into surrounding fluids

• when cells die they are regenerated

Homeostasis

property of cells, tissues, and organisms that allows the maintenance and regulation of the stability and constancy needed to function properly

milieu exterieur

physically surrounds whole organism

milieu interieur

liquid that bathes structures in body, isolates structures from environment

For steady-state balance, there must be a _______ so that deviations from this baseline can be monitored

"set point"

For steady-state balance, sensors that monitor deviations from the set point must generate __________ that can lead to changes in either input or output, or both, to maintain the desired set point

"effector signals"

For steady-state balance, ________ must respond in an appropriate way to the effector signals generated by the set point monitor

"effector organs"

Sensitivity of a steady-state balance system depends on:

• nature of sensor

• time needed for effector signal generation

• how fast effector organs respond to signals

Water balance determines __________ of body fluids

osmolality

Total body water correlates inversely with

body fat

ICF is ______ of total body water vs ECF is _________ of total body water

2/3, 1/3

Interstitial fluid

fluid that bathes cells, ultrafiltrate of plasma

______ is in constant motion throughout the body (by diffusion)

ECF

ECF contains

large amounts Na+ and Cl-

ICF contains

K+ and Mg2+, little Ca2+

Parameters of constants with narrow range

ph, Na+ conc, blood volume, arterial pressure, body temp, plasma glucose + O2, ions

Parameters of constants with large range

blood glucose level

Extracellular fluid is transported through the body in two stages

-movement of blood through the body in blood vessels -movement of fluid between capillaries and intercellular spaces between the tissue cells

Walls of capillaries permeable to most molecules in plasma blood except

plasma proteins

Blood pumped by heart also passes through walls of

GI tract

Endocrine hormones

released by glands or specialized cells into the circulating blood and influence the function of target cells at another location in the body

Neuroendocrine hormones

secreted by neurons into the circulating blood and influence the function of target cells at another location in the body

Paracrines

secreted by cells into the extracellular fluid and affect neighboring target cells of a different type

Autocrines

secreted by cells into the extracellular fluid and affect the function of the same cells that produced them

Nervous system regulates ________ activities while hormonal system regulates __________ activities

muscular + secretory, metabolic

Negative-feedback mechanism is responsible for

homeostasis, prevents deviations

4 elements of negative feedback mechanism

• system sense parameters

• system compares input signal with set-point

• system multiplies error signal to make output signal

• output signal activates effector mechanism that opposes source of input signal

Positive feedback loop leads to

instability

Advantageous instances of positive feedback loops

blood clot, childbirth, ovulation

O2 maintenance in ECF depends on

oxygen-buffering function of hemoglobin

System that regulates arterial blood pressure

baroreceptor system

Chemical rxns of cells take place

among dissolved chemicals or at surface of suspended particles/membranes

Ions

provide inorganic chemicals for rxns + for control mechanisms

Structural proteins

microtubules that make cytoskeleton

Functional proteins

enzymes

Plasma membrane - functions

• selective transport

• cell recognition

• cell communication

• tissue organization

• membrane-dependent enzymatic activity

• cell shape

Plasma membrane is made of

proteins and lipids

Phospholipids are

amphipatic

Proteins in cell membrane may be _____ or __________

integral, peripheral

Integral membrane proteins are in cell membrane by _________ interactions

hydrophobic

Transmembrane protein

span the lipid bilayer one or more times → in contact with both ECF and ICF

carrier proteins

bind with molecules or ions that are to be transported, and through conformational changes in the protein molecules, move the substances through the interstices of the protein to the other side of the membrane

channel proteins

free movement of water, as well as selected ions or molecules

Peripheral membrane proteins attached to cell membrane through

electrostatic interactions

Aquaporins/water channels

for water movement in/out cell

Regulation of the amount of H 2O that can enter or leave the cell via AQPs occurs primarily by

altering the number of AQPs in the membrane

Selectivity

nature of the ions that pass through the channel

Channel conductance

number of ions that pass through the channel and the range of conductance is considerable

Ion channels fluctuate between an open state or a closed state, a process called

gating

Factors that control gating

• membrane voltage

• extracell agonist/antagonists

• intracell messenger

• stretch of plasma membrane

Active transport

use the energy in ATP to drive the movement of molecules/ions across the membrane

With the hydrolysis of each ATP molecule, it transports ________ Na + ions out of the cell and _____ K + ions into the cell

3, 2

Primary active transport of H+ ions important at 2 places

• gastric glands of stomach

• distal tubules and cortical collecting ducts of kidneys

Uniporter/facilitated transporter

transports 1 molecule across membrane

symporters vs antiporters

moves 2+ molecules across membrane in same direction vs diff direction

Simple vs facilitated diffusion

facilitated requires carrier protein interaction

Osmosis

passive movement of water, from low to high solute conc

Osmotic pressure

amount of pressure to stop osmosis (of NaCl solution), determined by the number of solute molecules dissolved in the solution

Oncotic pressure

osmotic pressure generated by large molecules in solution

Tonicity

effect of the solution on the volume of a cell

Isotonic, hypotonic vs hypertonic

hypotonic - cell swells, osmolarity of ECF decreases hypertonic - cell shrinks, osmolarity of ECF increases

Specific gravity

total conc of all molecules in solution

Insensible water loss

respiratory tract and through skin

changes in excretion of water are mainly controlled by

ADH

Components extracellular fluid

• interstitial fluid

• plasma

• transcellular fluid

Plasma - function

exchanges substances through capillary membranes

Donnan effect

uneven distribution across 2 sides of membrane, more cations in plasma than interstitial fluid

osmolality vs osmolarity

osmolality - conc expressed as osmoles per kg osmolarity - expressed as osmoles per L

Calculated osmolarity

2 (Na+) + 2 (K+) + Glucose + Urea

Hypoanetremia vs hyperanetremia

dependent on plasma Na conc, hypoanetremia cell swells, hyperanetremia cell shrinks

Hyperanetremia causes

dehydration, diabetes

Plasma - contents

• electrolytes

• organic compounds

• metabolites

Colour differentiation of plasma

• pink is hemolysis

• brown/green is elevated bilirubin

• cloudy is cryoglobulinemias

variations in plasma protein concentrations can be caused by

• rate of protein synthesis

• rate of removal

• volume of distribution

Plasma protein conc aids in assessing

state of hydration

Albumin levels

low in hepatic cirrhosis high in low plasma colloid osmotic pressure

Starling forces

hydrostatic pressure of arterioles (37mmHg) and venules (17mmHg)

edema

if conc of plasma proteins diminished, accumulates in extravascular tissue

hypoalbuminaemic state

decreased plasma oncotic pressure, less movement of interstitial fluid back into blood in venules = edema

Edema is caused by

• increase in capillary hydrostatic pressure

• decrease in plasma oncotic pressure

• increase in capillary permeability

Cytokines

control activity and growth of cells, coordinate immune responses

plasma contains __________ which is absent in serum

fibrinogen

Osmosis