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.

 Acute Obstructive Disorders
 1.    Heimlich maneuver
 2.    Bypass, tracheostomy w/catheter to suck up secretion

Chemical Controls of Respiration

A.    Chemoreceptors (CO2, O2, H+)

1.    central chemoreceptors - located in the medulla
2.    peripheral chemoreceptors - large vessels of neck

B.    Carbon Dioxide Effects

1.    a powerful chemical regulator of breathing by increasing H+ (lowering pH)
    
a. hypercapnia            Carbon Dioxide increases -> 
                        Carbonic Acid increases ->
                        pH of CSF decreases (higher H+)- >
                        
DEPTH & RATE increase (hyperventilation)

b. hypocapnia - abnormally low Carbon Dioxide levels which can be produced by excessive hyperventilation; breathing into paper bag increases blood Carbon Dioxide levels

C.     Oxygen Effects

1.    aortic and carotid bodies - oxygen chemoreceptors

2.    slight Ox decrease - modulate Carb Diox receptors
3.    large Ox decrease - stimulate increase ventilation
4.    hypoxic drive - chronic elevation of Carb Diox (due to disease) causes Oxygen levels to have greater effect on regulation of breathing

D.    pH Effects (H+ ion)

1.    acidosis - acid buildup (H+) in blood, leads to increased RATE and DEPTH (lactic acid)

E.    Overview of Chemical Effects

 Chemical                             Breathing Effect

increased Carbon Dioxide (more H+)     increase
decreased Carbon Dioxide (less H+)     decrease

slight decrease in Oxygen             effect CO2 system
large decrease in Oxygen             increase ventilation

decreased pH (more H+)                 increase
increased pH (less H+)                 decrease

Typical Concentration Gradients and Membrane Potentials in Excitable Cells

The Na Pump is Particularly Important in the Kidney and Brain

• All cells have Na pumps in their membranes, but some cells have more than others
• Over-all Na pump activity may account for a third of your resting energy expenditure!
• In the kidney the Na pump activity is very high because it is used to regulate body salt and water concentrations
  • Kidneys use enormous amounts of energy: 0.5% of body weight, but use 7% of the oxygen supply
• Pump activity is also high in the brain because Na and K gradients are essential for nerves
  • The brain is another high energy organ; it is 2% of body weight, but uses 18% of the oxygen supply

In the Resting State Potassium Controls the Membrane Potential of Most Cells

• Resting cells have more open K channels than other types
• More K+ passes through membrane than other ions- therefore K+ controls the potential
• Blood K+ must be closely controlled because small changes will produce large changes in the membrane potentials of cells
  • Raising K will make the membrane potential less negative (depolarization)
• High blood K+ can cause the heart to stop beating (it goes into permanent contraction)

During an Action Potential Na Channels Open, and Na Controls the Membrane Potential

• Whichever ion has the most open channels controls the membrane potential
• Excitable cells have Na channels that open when stimulated
• When large numbers of these channels open Na controls the membrane potential

Neurons :

Types of neurons based on structure:

a multipolar neuron because it has many poles or processes, the dendrites and the axon. Multipolar neurons are found as motor neurons and interneurons. There are also bipolar neurons with two processes, a dendrite and an axon, and unipolar neurons, which have only one process, classified as an axon.. Unipolar neurons are found as most of the body's sensory neurons. Their dendrites are the exposed branches connected to receptors, the axon carries the action potential in to the central nervous system.

Types of neurons based on function:

• motor neurons - these carry a message to a muscle, gland, or other effector. They are said to be efferent, i.e. they carry the message away from the central nervous system.
• sensory neurons - these carry a message in to the CNS. They are afferent, i.e. going toward the brain or spinal cord.
• interneuron (ie. association neuron, connecting neuron) - these neurons connect one neuron with another. For example in many reflexes interneurons connect the sensory neurons with the motor neurons.

Exchange of gases takes place in Lungs

• A person with an average ventilation rate of 7.5 L/min will breathe in and out 10,800 liters of gas each day
• From this gas the person will take in about 420 liters of oxygen (19 moles/day) and will give out about 340 liters of carbon dioxide (15 moles/day)
• The ratio of CO₂ expired/O₂ inspired is called the respiratory quotient (RQ)
  • RQ = CO₂ out/O₂ in = 340/420 = 0.81
  • In cellular respiration of glucose CO₂ out = O₂ in; RQ = 1
  • The overall RQ is less than 1 because our diet is a mixture of carbohydrates and fat; the RQ for metabolizing fat is only 0.7
• All of the exchange of gas takes place in the lungs
• The lungs also give off large amounts of heat and water vapor