Gen 1103 – Lectures
Lecture 1 - Fluid homeostasis theory
- Water is the most important molecule in the body, the water content in your body
decreases when you get older. This decrease differs between male and female, the
water content depends on % of body fat. This is why female have less water content
than males when they grow older.
- You have a distribution of water (Total water = 60% of body weight in male, total
water = 65% in baby’s and 50% in females), you have intracellular (ICV) and
extracellular fluid (ECV). Intercellular compartment is the fluid in the cells, and
extracellular fluid is the fluid outside of the cells. Extracellular fluid is divided in the
plasma (in the vessels), and the interstitial fluid (this is between plasma and ICF). The
ICV is 2/3 of the total water in your body and ECV is 1/3 of the total water.
- The total intake of your body is ingestion (what you eat and drink), and metabolism.
Your intake and output must be the same, because otherwise you will have water
build up in the body. Your output is done by one of the following systems, skin, lungs
(Breathing), feces, urine.
- The equivalence is used when you are talking about the concentration of
electrolytes. This is mol * valency.
- The osmolarity is the total amount of mol per liter: osmol/l. You also have the total
amount of mol per kg that is the osmolality.
- Diffusion is the random thermal motion of molecules. If you want to calculate the
number of molecules that are transported by diffusion depends on the difference in
concentration, on the distance, and the area.
- Ficks law: Diffusional flux J = D * A* Concentration difference / d.
- The osmotic pressure is the pressure needed to get the same amount of fluid inside
of the cell and outside of the cell.
- Tonicity determines the osmotic flow of water across the cell membrane. Hypotonic
cell swells, isotonic cell stays the same, hypertonic cell shrinks. In a
hypertonic solution the cell will shrink, because the osmolarity on the outside of the
cell is higher than on the inside of the cell. For hypotonic solutions, the cell will swell.
The osmolarity inside is higher than the osmolarity on the outside of the cell. This
will cause swelling.
- The capillary endothelium has a higher permeability than the cell membrane. The
cell membrane is not easily accessible for the electrolytes and proteins and
phosphates. But steroids can pass by because they are lipophilic.
- As soon as the osmolarity changes, there is water transport between inside and
outside of the cell.
- All body fluids have similar osmolarity and equal numbers of positive and negative
charges. The balance between intracellular and extracellular, is very important in
maintaining organ function. For example, arrythmia in the heart is caused because of
irregularities in osmolarity
- The permeability for potassium is higher than the permeability of sodium. You can
see that sodium is pumped out of the cell and potassium is pumped into the cell.
- There are different mechanisms for transport across the cell membrane: diffusion,
active transport or osmosis. Water will use osmosis for transportation via
aquaporins. This is always passive transport.
, - Exchange between plasma and interstitial fluid will take place by diffusion or
osmosis. Proteins will not easily pass the endothelial cell layer. Other processes that
are used for transportation, is transcytosis. This uses vesicles to transport something
across the endothelial cell layer.
- Filtration happens across capillaries. Filtration is determined by hydrostatic pressure
and colloid osmotic pressure (this is the pressure caused by the selective permeable
membrane this way the proteins cause a pressure difference).
Filtration = Kf [(Pc-Pi)-(PIc-PIi)]
- The hydrostatic pressure is at the arteriolar side higher, than at the venular end the
hydrostatic pressure drops. That way reabsorption takes place.
- Lymph vessels return excess interstitial fluid to plasma compartment. Functions of
the lymphatic system, circulation (returning excess fluid and proteins to plasma),
digestion (transport of fat from intestines to plasma), immunity (assist in capturing
and destroying pathogens).
- The smallest lymphatic capillaries do not have a basement membrane which make
them much more permeable. Terminal lymphatic capillaries consist of endothelial
cells that overlap allowing interstitial fluid to flow in. Also, they have valves, which
causes the fluid in the lymph vessel to not return back in the terminal lymph
capillaries.
- The amount of lymph flow depends on the tissue hydrostatic pressure. The
mechanism is compression of lymph capillaries, this is caused by muscle contraction.
- You can distinguish edema by intracellular edema: changes in osmolarity, and
extracellular edema: - disruption of blood flow or lymphatic flow.
Lecture 2 – Fluid homeostasis practice (Body water compartments Practical excerisces)
- You can get access by nutrients and drugs via different ways. Intake of the drug or
food in the GI – tract. The nutrition will go into the interstitial fluid and will either go
into the cell or stay in the interstitium. You can either inject (subcutaneously or
intramuscular) or deliver the drugs via infusion of the drug in the blood. Orally is the
last option.
- Fluid will go in the body by extracellular compartment and will go out of the body via
extracellular fluid. Fluid will never directly go into the cells of the body. Water will go
out of the body, by urine, feces, sweat, and lungs.
- Osmosis is the driving force what happens to water between intracellular fluid and
interstitial fluid. Starling forces are the driving force what happens to water between
interstitial fluid and extracellular fluid.
- The composition of the ECF, is the same in the plasma and IF except for proteins in
the plasma, the capillary wall allows these ions to pass between IF and plasma. The
ICF differs a lot compared to the ECF. Sodium is in extracellular and Potassium is in
the intracellular.
- In a Steady homeostasis, Osmolality is the same in both compartments at any time.
- The body wont complete dry out because we have osm intracellular and osm
extracellular. But the osmoles composing the osmolality are mainly sodium, chloride
and bicarbonate. While intracellular it is mainly potassium, phosphate and organic
anions. At any time, osmolality should be the same in both body compartments.
- mOsm / L = mOsm / kg in the body. Osmolality = mOsm / kg
, - Sum of Body osmoles (dissolved in water), 280mOsm/kg * kg = 5040. For
intracellular and extracellular fluid, the same calculation takes place only with lower
kilogram.
- When you add 360mOsm NaCl to your system, total amount is 5040 + 360 = 5400
total in the body. kg = 300mOsm/kg. At any time in the body there will an
equilibrium between inside and outside of the cell.
- When you add 360 mOsm to the ECF, you will all get the mOsm in the ECF. You will
have 2040mOsm in the ECF. When you have added this, you can calculate the new
volume by 2040mOsm / 300mOsm/L = 6,8 L. So, you will see expansion of cells in the
ECF and dehydration of the ICF.
- When you add water to the ECF, you will drop the osmolality. The new number of
osmoles will be former osmoles 5040/ 19 (18+1) = 265mOsm/kg. This will cause
intracellular edema.
- When you give an 1L isotonic fluid to a patient, you will not see a change in mOsm
because the osmolality is the same in the fluid. This way the osmolality of the ECF
will stay the same but you will have 1 L fluid more in the ECF. This will cause
extracellular expansion. This is what we often want to see after medical help.
- You are drinking more water than solutes so a low osmolarity, this can cause edema
because the osmolality must stay the same between ICF and ECF. But we can dilute
our urine, so our urine osmolality can differ a lot. The Minimal urine dilution is
50mOsm/kg.
- You cannot drink too much water, because you will have cerebral edema eventually
when there is too much water.
- When you drink an isotonic sports drink, you will not change your urine composition,
but you will increase urine volume. But you will not dilute it. When you do not drink
the whole day, you will have dehydration of the ICF and the brain will get in trouble.
The solution for this, you should start drinking. The other part of the solution is
highly concentrated, the urine loses less water than solutes. When you have not
been drinking for a while, the urine gets very concentrated. This is the product of the
anti-diuretic hormone system.
- High ECF osmolality due to low water concentration will release ADH by the
pituitary. This ADH will bind to the V2 receptor in de collecting duct, this will activate
the moving of aquaporins in the apical side of the collecting tubule cells. This will
increase water reabsorption.
- Low ECF will immediately stop ADH release, this will cause the aquaporins to go
away. This will cause high volume of urine and low volume of ions in the urine.
Lecture 3 – Biological clock
- We have a variety of rhythms, because the earth circles around the sun. All these
physical processes generate different circumstances on the earth, life has evolved
and adapted to these processes.
- Circadian rhythms are rhythms that are about 24hs long. Most of our activities are
imprinted by this 24h changes of light and temperature. We have this because the
compensatory mechanisms have evolved in anticipation of environmental changes
that are coming up to maintain homeostasis.
- We have an internal clock that prepares us for things that are coming. Efficient use of
resources; you will produce offspring when circumstances are optimal. Temporal
