1) Storage - the stomach allows a meal to be consumed and the materials released incrementally into the duodenum for digestion. It may take up to four hours for food from a complete meal to clear the stomach. 
2) Chemical digestion - pepsin begins the process of protein digestion cleaving large polypeptides into shorter chains . 
3) Mechanical digestion - the churning action of the muscularis causes liquefaction and mixing of the contents to produce acid chyme. 
4) Some absorption - water, electrolytes, monosaccharides, and fat soluble molecules including alcohol are all absorbed in the stomach to some degree.

Hyperventilation

1. Treatments :Rebreath air, hold breath (Increase CO₂)
   Give oxygen for Hypoxemia

Blood Pressure

Blood moves through the arteries, arterioles, and capillaries because of the force created by the contraction of the ventricles.

Blood pressure in the arteries.

The surge of blood that occurs at each contraction is transmitted through the elastic walls of the entire arterial system where it can be detected as the pulse. Even during the brief interval when the heart is relaxed — called diastole — there is still pressure in the arteries. When the heart contracts — called systole — the pressure increases.

Blood pressure is expressed as two numbers, e.g., 120/80.

Blood pressure in the capillaries

The pressure of arterial blood is largely dissipated when the blood enters the capillaries. Capillaries are tiny vessels with a diameter just about that of a red blood cell (7.5 µm). Although the diameter of a single capillary is quite small, the number of capillaries supplied by a single arteriole is so great that the total cross-sectional area available for the flow of blood is increased. Therefore, the pressure of the blood as it enters the capillaries decreases.

Blood pressure in the veins

When blood leaves the capillaries and enters the venules and veins, little pressure remains to force it along. Blood in the veins below the heart is helped back up to the heart by the muscle pump. This is simply the squeezing effect of contracting muscles on the veins running through them. One-way flow to the heart is achieved by valves within the veins

Exchanges Between Blood and Cells

With rare exceptions, our blood does not come into direct contact with the cells it nourishes. As blood enters the capillaries surrounding a tissue space, a large fraction of it is filtered into the tissue space. It is this interstitial or extracellular fluid (ECF) that brings to cells all of their requirements and takes away their products. The number and distribution of capillaries is such that probably no cell is ever farther away than 50 µm from a capillary.

When blood enters the arteriole end of a capillary, it is still under pressure produced by the contraction of the ventricle. As a result of this pressure, a substantial amount of water and some plasma proteins filter through the walls of the capillaries into the tissue space.

Thus fluid, called interstitial fluid, is simply blood plasma minus most of the proteins. (It has the same composition and is formed in the same way as the nephric filtrate in kidneys.)

Interstitial fluid bathes the cells in the tissue space and substances in it can enter the cells by diffusion or active transport. Substances, like carbon dioxide, can diffuse out of cells and into the interstitial fluid.

Near the venous end of a capillary, the blood pressure is greatly reduced .Here another force comes into play. Although the composition of interstitial fluid is similar to that of blood plasma, it contains a smaller concentration of proteins than plasma and thus a somewhat greater concentration of water. This difference sets up an osmotic pressure. Although the osmotic pressure is small, it is greater than the blood pressure at the venous end of the capillary. Consequently, the fluid reenters the capillary here.

Control of the Capillary Beds

An adult human has been estimated to have some 60,000 miles of capillaries with a total surface area of some 800–1000 m². The total volume of this system is roughly 5 liters, the same as the total volume of blood. However, if the heart and major vessels are to be kept filled, all the capillaries cannot be filled at once. So a continual redirection of blood from organ to organ takes place in response to the changing needs of the body. During vigorous exercise, for example, capillary beds in the skeletal muscles open at the expense of those in the viscera. The reverse occurs after a heavy meal.

The walls of arterioles are encased in smooth muscle. Constriction of arterioles decreases blood flow into the capillary beds they supply while dilation has the opposite effect. In time of danger or other stress, for example, the arterioles supplying the skeletal muscles will be dilated while the bore of those supplying the digestive organs will decrease. These actions are carried out by

• the autonomic nervous system.
• local controls in the capillary beds

Blood is a liquid tissue. Suspended in the watery plasma are seven types of cells and cell fragments.

• red blood cells (RBCs) or erythrocytes
• platelets or thrombocytes
• five kinds of white blood cells (WBCs) or leukocytes
  • Three kinds of granulocytes
    • neutrophils
    • eosinophils
    • basophils
  • Two kinds of leukocytes without granules in their cytoplasm
    • lymphocytes
    • monocytes

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