VISHAL KUMAR 2020/2021
MEDICAL PHYSIOLOGY FINAL EXAM
TOPIC 1
1.1. Body fluid compartments and their determination. The extracellular and
intravascular fluid
Body fluid compartments:
Values used here are based on a 70 kg male.
- Total body water (TBW): 60% of body weight = 42L
TBW distributed between ICF and ECF, separated by a cell membrane
- ICF: 40% of body weight (2/3 of TBW) = 28L
- ECF: 20% of body weight (1/3 of TBW) = 14L
Interstitial fluid (surrounds cell externally) = ¾ of ECF = 10,5L
Plasma (liquid component of blood) = ¼ of ECF = 3,5 L
Capillary wall separates the interstitial fluid and plasma
Determination of body fluid compartments
The various fluid compartments are measured by the dilution method (Volume = mass /cc).
Marker substances will be distributed only to places that it can reach. Large molecules (like
mannitol) cannot cross the cell membrane, so it will be distributed only to the ECF, but not
to the ICF. ICF cannot be measured directly, but if we can measure the total volume and ECF,
we can calculate the volume of ICF
- Total fluid compartment: deuterium (also known as heavy water)
- ECF: inulin
- Blood plasma: blood protein concentration / protein-bound dye (Evans-blue)
,VISHAL KUMAR 2020/2021
The extracellular and intravascular fluid
- ECF includes transcellular fluid, which is contained within epithelial-lined spaces
Transcellular fluid: 1L of TBW
- ECF composes 1/3 of the total body water (14L)
Capillary endothelium separates intravascular fluid from interstitial and
transcellular fluid
Intravascular fluid Interstitial fluid Transcellular fluid
- Mixture of blood - CSF
cells, proteins and - Ocular fluid
ions Surrounds cell externally - Synovial joint fluid
- Plasma = EC - Fluids in pleural cavity
component - Fluids in peritoneal cavity
Ionic composition of extracellular and intracellular fluids
ECF ICF
Na+ 135 – 147 mM 10 – 15 mM
K+ 3,5 – 5,0 mM 120 – 150 mM
Ca2+ 2,1 – 2,8 mM (total blood plasma) 100 nM (free)
1,1 – 1,4 mM (free)
Cl- 95 – 105 mM 20 – 30 mM
HCO3- 22 – 28 mM 12 – 16 mM
Osmolarity 290 mOsm 290 mOsm
pH 7,4 7,2
,VISHAL KUMAR 2020/2021
1.2. Structure, permeability and transport functions of the cell membrane.
Transepithelial transports
Structure and permeability of the cell membrane
Cell membranes are composed primarily of phospholipids, in addition to proteins,
cholesterol and glycolipids. The lipid component means that the cell is permeable to lipid-
soluble substances, such as CO2, O2, fatty acids, NO and steroid hormones. Impermeable to
water-soluble substances like ions, glucose and amino acids. The protein component
functions as transporters, enzymes, hormone receptors, antigens and ion and water
channels.
Plasma membrane lipids
- Forms a selectively permeable membrane
- Phospholipids are amphipathic: hydrophobic fatty acid tails pointing inwards and
hydrophilic glycerol head (most abundant: choline-containing = sphingomyelin)
- Cholesterol functions to reduce fluidity of the membrane – breaking up the
continuity of the phospholipids, maintaining the fluidity at the optimum level (not
too fluid when it is hot, and not too solid when it is cold)
- Glycolipids (sugar groups attached to the polypeptide chain): maintenance of cell
stability and also for cellular recognition (ex. Antigens for ABO blood group)
- some phospholipids play a role in signal transduction. I.e. with Gq G-protein coupled
receptor activation, the PIP2 in the membrane is cleaved by phospholipase C,
releasing IP 3, which leads to increased IC Ca 2+
- Functions:
1. Transport of molecules
2. Source of 2nd messenger (ex. Phosphatidylinositol 4,5-bisphosphate = PIP2)
3. Provide surface
Plasma membrane proteins
- Proteins are classified into integral and peripheral proteins
- Integral proteins are embedded in the membrane by their hydrophobic and
hydrophilic parts
- Integral proteins include transmembrane proteins that cross the membrane multiple
times, allowing contact with both ECF and ICF
- Peripheral proteins bind to these integral proteins
- Functions:
Selective transport of molecules (ex: channels, gates)
Cell recognition via surface antigens (ex: T-cell receptor)
Plasma membrane receptor (ex: GPCR)
Tissue organization via adhesion molecules (ex: cell adhesion molecules)
Enzymatic activity (ex: ATPase)
Determination of cell shape by linking the cytoskeleton to the membrane (ex:
integrin)
, VISHAL KUMAR 2020/2021
Transport processes through the plasma membrane
1- Simple diffusion
- Does not require a transport protein
- Passive transport, driving force: chemical gradient (concentration difference)
- Linearly related with concentration gradient -> no saturation
- Simple diffusion results from thermal regulation of molecules (Brownian motion =
random, uncontrolled movement of particles in a fluid as they constantly collide with
other molecules)
- Particles diffuse from areas of high
concentration to areas of low concentration
Diffusion explained by Fick’s 1st law:
- Diffusion coefficient (D) tells how easy it is for
something to diffuse (bigger molecules have
smaller D’s)
- Driving force: concentration difference between
the two sides of the membrane (Δc)
- Distance/thickness along which the diffusion
occurs (Δx)
Rate depends on the hydrophobicity and the size of the solute
Transport:
- O2, CO2, CO, NO, urea, hydrophobic hormones (steroid hormones) are transported
via diffusion
- Only few water-soluble molecules can diffuse (Water itself, glucose, ions)
- Peptides, proteins, disaccharides (glucose) do not diffuse across the membrane
2-Protein-mediated membrane transport
Transport proteins can either be:
- Channels: which are gates that can alter
between blocking or allowing passive
transport
passive, gated, fast transport
can be saturated, but only with rare and extremely high ion concentration
protein must undergo a conformational change (gated)
- Carriers: are enzymes that allow specific substances to cross
Passive, cyclic, slow transport
Can be saturated
Protein must undergo a conformational change (cyclic)
Carried charge can be electroneutral or electrogenic (ions)
MEDICAL PHYSIOLOGY FINAL EXAM
TOPIC 1
1.1. Body fluid compartments and their determination. The extracellular and
intravascular fluid
Body fluid compartments:
Values used here are based on a 70 kg male.
- Total body water (TBW): 60% of body weight = 42L
TBW distributed between ICF and ECF, separated by a cell membrane
- ICF: 40% of body weight (2/3 of TBW) = 28L
- ECF: 20% of body weight (1/3 of TBW) = 14L
Interstitial fluid (surrounds cell externally) = ¾ of ECF = 10,5L
Plasma (liquid component of blood) = ¼ of ECF = 3,5 L
Capillary wall separates the interstitial fluid and plasma
Determination of body fluid compartments
The various fluid compartments are measured by the dilution method (Volume = mass /cc).
Marker substances will be distributed only to places that it can reach. Large molecules (like
mannitol) cannot cross the cell membrane, so it will be distributed only to the ECF, but not
to the ICF. ICF cannot be measured directly, but if we can measure the total volume and ECF,
we can calculate the volume of ICF
- Total fluid compartment: deuterium (also known as heavy water)
- ECF: inulin
- Blood plasma: blood protein concentration / protein-bound dye (Evans-blue)
,VISHAL KUMAR 2020/2021
The extracellular and intravascular fluid
- ECF includes transcellular fluid, which is contained within epithelial-lined spaces
Transcellular fluid: 1L of TBW
- ECF composes 1/3 of the total body water (14L)
Capillary endothelium separates intravascular fluid from interstitial and
transcellular fluid
Intravascular fluid Interstitial fluid Transcellular fluid
- Mixture of blood - CSF
cells, proteins and - Ocular fluid
ions Surrounds cell externally - Synovial joint fluid
- Plasma = EC - Fluids in pleural cavity
component - Fluids in peritoneal cavity
Ionic composition of extracellular and intracellular fluids
ECF ICF
Na+ 135 – 147 mM 10 – 15 mM
K+ 3,5 – 5,0 mM 120 – 150 mM
Ca2+ 2,1 – 2,8 mM (total blood plasma) 100 nM (free)
1,1 – 1,4 mM (free)
Cl- 95 – 105 mM 20 – 30 mM
HCO3- 22 – 28 mM 12 – 16 mM
Osmolarity 290 mOsm 290 mOsm
pH 7,4 7,2
,VISHAL KUMAR 2020/2021
1.2. Structure, permeability and transport functions of the cell membrane.
Transepithelial transports
Structure and permeability of the cell membrane
Cell membranes are composed primarily of phospholipids, in addition to proteins,
cholesterol and glycolipids. The lipid component means that the cell is permeable to lipid-
soluble substances, such as CO2, O2, fatty acids, NO and steroid hormones. Impermeable to
water-soluble substances like ions, glucose and amino acids. The protein component
functions as transporters, enzymes, hormone receptors, antigens and ion and water
channels.
Plasma membrane lipids
- Forms a selectively permeable membrane
- Phospholipids are amphipathic: hydrophobic fatty acid tails pointing inwards and
hydrophilic glycerol head (most abundant: choline-containing = sphingomyelin)
- Cholesterol functions to reduce fluidity of the membrane – breaking up the
continuity of the phospholipids, maintaining the fluidity at the optimum level (not
too fluid when it is hot, and not too solid when it is cold)
- Glycolipids (sugar groups attached to the polypeptide chain): maintenance of cell
stability and also for cellular recognition (ex. Antigens for ABO blood group)
- some phospholipids play a role in signal transduction. I.e. with Gq G-protein coupled
receptor activation, the PIP2 in the membrane is cleaved by phospholipase C,
releasing IP 3, which leads to increased IC Ca 2+
- Functions:
1. Transport of molecules
2. Source of 2nd messenger (ex. Phosphatidylinositol 4,5-bisphosphate = PIP2)
3. Provide surface
Plasma membrane proteins
- Proteins are classified into integral and peripheral proteins
- Integral proteins are embedded in the membrane by their hydrophobic and
hydrophilic parts
- Integral proteins include transmembrane proteins that cross the membrane multiple
times, allowing contact with both ECF and ICF
- Peripheral proteins bind to these integral proteins
- Functions:
Selective transport of molecules (ex: channels, gates)
Cell recognition via surface antigens (ex: T-cell receptor)
Plasma membrane receptor (ex: GPCR)
Tissue organization via adhesion molecules (ex: cell adhesion molecules)
Enzymatic activity (ex: ATPase)
Determination of cell shape by linking the cytoskeleton to the membrane (ex:
integrin)
, VISHAL KUMAR 2020/2021
Transport processes through the plasma membrane
1- Simple diffusion
- Does not require a transport protein
- Passive transport, driving force: chemical gradient (concentration difference)
- Linearly related with concentration gradient -> no saturation
- Simple diffusion results from thermal regulation of molecules (Brownian motion =
random, uncontrolled movement of particles in a fluid as they constantly collide with
other molecules)
- Particles diffuse from areas of high
concentration to areas of low concentration
Diffusion explained by Fick’s 1st law:
- Diffusion coefficient (D) tells how easy it is for
something to diffuse (bigger molecules have
smaller D’s)
- Driving force: concentration difference between
the two sides of the membrane (Δc)
- Distance/thickness along which the diffusion
occurs (Δx)
Rate depends on the hydrophobicity and the size of the solute
Transport:
- O2, CO2, CO, NO, urea, hydrophobic hormones (steroid hormones) are transported
via diffusion
- Only few water-soluble molecules can diffuse (Water itself, glucose, ions)
- Peptides, proteins, disaccharides (glucose) do not diffuse across the membrane
2-Protein-mediated membrane transport
Transport proteins can either be:
- Channels: which are gates that can alter
between blocking or allowing passive
transport
passive, gated, fast transport
can be saturated, but only with rare and extremely high ion concentration
protein must undergo a conformational change (gated)
- Carriers: are enzymes that allow specific substances to cross
Passive, cyclic, slow transport
Can be saturated
Protein must undergo a conformational change (cyclic)
Carried charge can be electroneutral or electrogenic (ions)
