Serum Proteins

Proteins make up 6–8% of the blood. They are about equally divided between serum albumin and a great variety of serum globulins.

After blood is withdrawn from a vein and allowed to clot, the clot slowly shrinks. As it does so, a clear fluid called serum is squeezed out. Thus:

Serum is blood plasma without fibrinogen and other clotting factors.

The serum proteins can be separated by electrophoresis.

• The most prominent of these and the one that moves closest to the positive electrode is serum albumin.
• Serum albumin
  • is made in the liver
  • binds many small molecules for transport through the blood
  • helps maintain the osmotic pressure of the blood
• The other proteins are the various serum globulins.
  • alpha globulins (e.g., the proteins that transport thyroxine and retinol [vitamin A])
  • beta globulins (e.g., the iron-transporting protein transferrin)
  • gamma globulins.
    • Gamma globulins are the least negatively-charged serum proteins. (They are so weakly charged, in fact, that some are swept in the flow of buffer back toward the negative electrode.)
    • Most antibodies are gamma globulins.
    • Therefore gamma globulins become more abundant following infections or immunizations. 

Oxygen Uptake in the Lungs is Increased About 70X by Hemoglobin in the Red Cells

• In the lungs oxygen must enter the blood
• A small amount of oxygen dissolves directly in the serum, but 98.5% of the oxygen is carried by hemoglobin
• All of the hemoglobin is found within the red blood cells (RBCs or erythrocytes)
• The hemoglobin content of the blood is about 15 gm/deciliter (deciliter = 100 mL)
• Red cell count is about 5 million per microliter

Each Hemoglobin Can Bind Four O₂ Molecules (100% Saturation)

• Hemoglobin is a protein molecule with 4 protein sub-units (2 alphas and 2 betas)
  • Each of the 4 sub-units contains a heme group which gives the protein a red color
  • Each heme has an iron atom in the center which can bind an oxygen molecule (O2)
  • The 4 hemes in a hemoglobin can carry a maximum of 4 oxygen molecules
• When hemoglobin is saturated with oxygen it has a bright red color; as it loses oxygen it becomes bluish (cyanosis)

The Normal Blood Hematocrit is Just Below 50%

• Blood consists of cells suspended in serum
• More than 99% of the cells in the blood are red blood cells designed to carry oxygen
  • 25% of all the cells in the body are RBCs
• The volume percentage of cells in the blood is called the hematocrit
• Normal hematocrits are about 40% for women and 45% for men

At Sea Level the Partial Pressure of O₂ is High Enough to Give Nearly 100% Saturation of Hemoglobin

• As the partial pressure of oxygen in the alveoli increases the hemoglobin in the red cells passing through the lungs rises until the hemoglobin is 100% saturated with oxygen
  • At 100% saturation each hemoglobin carries 4 O₂ molecules
  • This is equal to 1.33 mL O₂ per gram of hemoglobin
• A person with 15 gm Hb/deciliter can carry:
  • Max O₂ carriage = 1.33 mL O₂/gm X 15 gm/deciliter = 20 mL O₂/deciliter
• A plot of % saturation vs pO2 gives an S-shaped "hemoglobin dissociation curve"
• At 100% saturation each hemoglobin binds 4 oxygen molecules

At High Altitudes Hemoglobin Saturation May be Well Below 100%

• At the alveolar pO₂ of 105 mm Hg at sea level the hemoglobin will be about 97% saturated, but the saturation will fall at high altitudes
• At 12,000 feet altitude alveolar pO₂ will be about 60 mm Hg and the hemoglobin will be 90% saturated
• At 29,000 feet (Mt. Everest) alveolar pO₂ is about 24 mm Hg and the hemoglobin will be only 42% saturated
• At very high altitudes most climbers must breath pure oxygen from tanks
• During acclimatization to high altitude the hematocrit can rise to about 60%- this increases the amount of oxygen that can be carried
• Hematocrits above 60% are not useful because the blood viscosity will increase to the point where it impairs circulation

Graded Contractions and Muscle Metabolism

The muscle twitch is a single response to a single stimulus. Muscle twitches vary in length according to the type of muscle cells involved. .

Fast twitch muscles such as those which move the eyeball have twitches which reach maximum contraction in 3 to 5 ms (milliseconds).  [superior eye] and [lateral eye] These muscles were mentioned earlier as also having small numbers of cells in their motor units for precise control.

The cells in slow twitch muscles like the postural muscles (e.g. back muscles, soleus) have twitches which reach maximum tension in 40 ms or so.

 The muscles which exhibit most of our body movements have intermediate twitch lengths of 10 to 20 ms.

The latent period, the period of a few ms encompassing the chemical and physical events preceding actual contraction.

This is not the same as the absolute refractory period, the even briefer period when the sarcolemma is depolarized and cannot be stimulated. The relative refractory period occurs after this when the sarcolemma is briefly hyperpolarized and requires a greater than normal stimulus

Following the latent period is the contraction phase in which the shortening of the sarcomeres and cells occurs. Then comes the relaxation phase, a longer period because it is passive, the result of recoil due to the series elastic elements of the muscle.

We do not use the muscle twitch as part of our normal muscle responses. Instead we use graded contractions, contractions of whole muscles which can vary in terms of their strength and degree of contraction. In fact, even relaxed muscles are constantly being stimulated to produce muscle tone, the minimal graded contraction possible.

Muscles exhibit graded contractions in two ways:

1) Quantal Summation or Recruitment - this refers to increasing the number of cells contracting. This is done experimentally by increasing the voltage used to stimulate a muscle, thus reaching the thresholds of more and more cells. In the human body quantal summation is accomplished by the nervous system, stimulating increasing numbers of cells or motor units to increase the force of contraction.

2) Wave Summation ( frequency summation) and Tetanization- this results from stimulating a muscle cell before it has relaxed from a previous stimulus. This is possible because the contraction and relaxation phases are much longer than the refractory period. This causes the contractions to build on one another producing a wave pattern or, if the stimuli are high frequency, a sustained contraction called tetany or tetanus. (The term tetanus is also used for an illness caused by a bacterial toxin which causes contracture of the skeletal muscles.) This form of tetanus is perfectly normal and in fact is the way you maintain a sustained contraction.

Treppe is not a way muscles exhibit graded contractions. It is a warmup phenomenon in which when muscle cells are initially stimulated when cold, they will exhibit gradually increasing responses until they have warmed up. The phenomenon is due to the increasing efficiency of the ion gates as they are repeatedly stimulated. Treppe can be differentiated from quantal summation because the strength of stimulus remains the same in treppe, but increases in quantal summation

Length-Tension Relationship: Another way in which the tension of a muscle can vary is due to the length-tension relationship. This relationship expresses the characteristic that within about 10% the resting length of the muscle, the tension the muscle exerts is maximum. At lengths above or below this optimum length the tension decreases.

The Types of muscle cells. There are three types, red, white, and intermediate.

Intermediate Fibers: sometimes called "fast twitch red", these fibers have faster action but rely more on aerobic metabolism and have more endurance. Most muscles are mixtures of the different types. Muscle fiber types and their relative abundance cannot be varied by training, although there is some evidence that prior to maturation of the muscular system the emphasis on certain activities can influence their development

The Nervous System Has Peripheral and Central Units

• The central nervous system (CNS) is the brain and spinal column
• The peripheral nervous system (PNS) consists of nerves outside of the CNS
• There are 31 pairs of spinal nerves (mixed motor & sensory)
• There are 12 pairs of cranial nerves (some are pure sensory, but most are mixed)

The pattern of innervation plotted on the skin is called a dermatome

The Nervous System Has Peripheral and Central Units

• The central nervous system (CNS) is the brain and spinal column
• The peripheral nervous system (PNS) consists of nerves outside of the CNS
• There are 31 pairs of spinal nerves (mixed motor & sensory)
• There are 12 pairs of cranial nerves (some are pure sensory, but most are mixed)

The pattern of innervation plotted on the skin is called a dermatome

Cell, or Plasma, membrane

• Structure - 2 primary building blocks include

protein (about 60% of the membrane) and lipid, or

fat (about 40% of the membrane).

The primary lipid is called phospholipids, and molecules of phospholipid form a 'phospholipid bilayer' (two layers of phospholipid molecules). This bilayer forms because the two 'ends' of phospholipid molecules have very different characteristics: one end is polar (or hydrophilic) and one (the hydrocarbon tails below) is non-polar (or hydrophobic):

• Functions include:
  • supporting and retaining the cytoplasm
  • being a selective barrier .
  • transport
  • communication (via receptors)