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

Functions

Manufacture - blood proteins - albumen, clotting proteins , urea - nitrogenous waste from amino acid metabolism , bile - excretory for the bile pigments, emulsification of fats by bile salts

Storage - glycogen , iron - as hemosiderin and ferritin , fat soluble vitamins A, D, E, K

Detoxification -alcohol , drugs and medicines , environmental toxins

Protein metabolism -

• transamination - removing the amine from one amino acid and using it to produce a different amino acid. The body can produce all but the essential amino acids; these must be included in the diet.
• deamination - removal of the amine group in order to catabolize the remaining keto acid. The amine group enters the blood as urea which is excreted through the kidneys.

Glycemic Regulation - the management of blood glucose.

• glycogenesis - the conversion of glucose into glycogen.
• glycogenolysis - the breakdown of glycogen into glucose.

gluconeogenesis - the manufacture of glucose from non carbohydrate sources, mostly protein

Functions of the nervous system:

1) Integration of body processes

2) Control of voluntary effectors (skeletal muscles), and mediation of voluntary reflexes.

3) Control of involuntary effectors (  smooth muscle, cardiac muscle, glands) and mediation of autonomic reflexes (heart rate, blood pressure, glandular secretion, etc.)

4) Response to stimuli

5) Responsible for conscious thought and perception, emotions, personality, the mind.

Bile contains:

• bile acids. These amphiphilic steroids emulsify ingested fat. The hydrophobic portion of the steroid dissolves in the fat while the negatively-charged side chain interacts with water molecules. The mutual repulsion of these negatively-charged droplets keeps them from coalescing. Thus large globules of fat (liquid at body temperature) are emulsified into tiny droplets (about 1 µm in diameter) that can be more easily digested and absorbed.

• bile pigments. These are the products of the breakdown of hemoglobin removed by the liver from old red blood cells. The brownish color of the bile pigments imparts the characteristic brown color of the feces.

Structure of a nerve:

A peripheral nerve is arranged much like a muscle in terms of its connective tissue. It has an outer covering which forms a sheath around the nerve, called the epineurium. Often a nerve will run together with an artery and vein and their connective coverings will merge. Nerve fibers, which are axons, organize into bundles known as fascicles with each fascicle surrounded by the perineurium. Between individual nerve fibers is an inner layer of endoneurium.

 The myelin sheath in peripheral nerves consists of Schwann cells wrapped in many layers around the axon fibers. Not all fibers in a nerve will be myelinated, but most of the voluntary fibers are. The Schwann cells are portrayed as arranged along the axon like sausages on a string. Gaps between the Schwann cells are called nodes of Ranvier. These nodes permit an impulse to travel faster because it doesn't need to depolarize each area of a membrane, just the nodes. This type of conduction is called saltatory conduction and means that impulses will travel faster in myelinated fibers than in unmyelinated ones.

The myelin sheath does several things:

1) It provides insulation to help prevent short circuiting between fibers.

2) The myelin sheath provides for faster conduction.

3) The myelin sheath provides for the possibility of repair of peripheral nerve fibers. Schwann cells help to maintain the micro-environments of the axons and their tunnel (the neurilemma tunnel) permits re-connection with an effector or receptor  CNS fibers, not having the same type of myelination accumulate scar tissue after damage, which prevents regeneration.

Bile - produced in the liver and stored in the gallbladder, released in response to CCK . Bile salts (salts of cholic acid) act to emulsify fats, i.e. to split them so that they can mix with water and be acted on by lipase.

Pancreatic juice: Lipase - splits fats into glycerol and fatty acids. Trypsin, and chymotrypsin - protease enzymes which break polypeptides into dipeptides. Carboxypeptidase - splits dipeptide into amino acids. Bicarbonate - neutralizes acid. Amylase - splits polysaccharides into shorter chains and disaccharides.

Intestinal enzymes (brush border enzymes): Aminopeptidase and carboxypeptidase - split dipeptides into amino acids. Sucrase, lactase, maltase - break disaccharides into monosaccharides. Enterokinase - activates trypsinogen to produce trypsin. Trypsin then activates the precursors of chymotrypsin and carboxypeptidase. Other carbohydrases: dextrinase and glucoamylase. These are of minor importance.