Basic Properties of Gases

A.    Dalton's Law of Partial Pressures

1.    partial pressure - the "part" of the total air pressure caused by one component of a gas 

     Gas            Percent            Partial Pressure (P)
    ALL AIR        100.0%                760 mm Hg
    Nitrogen       78.6%                   597 mm Hg    (0.79 X 760)
    Oxygen          20.9%                l59 mm Hg    (0.21 X 760)
    CO₂              0.04%                  0.3 mm Hg    (0.0004 X 760) 

2.    altitude - air pressure @ 10,000 ft = 563 mm Hg
3.    scuba diving - air pressure @ 100 ft = 3000 mm Hg

B.    Henry's Law of Gas Diffusion into Liquid

1.    Henry's Law - a certain gas will diffuse INTO or OUT OF a liquid down its concentration gradient in proportion to its partial pressure

2.    solubility - the ease with which a certain gas will "dissolve" into a liquid (like blood plasma)

HIGHest solubility in plasma            Carbon Dioxide
                                                      Oxygen
                                        
LOWest solubility in plasma             Nitrogen

C.    Hyperbaric (Above normal pressure) Conditions

1.    Creates HIGH gradient for gas entry into the body

2.    therapeutic - oxygen forced into blood during: carbon monoxide poisoning, circulatory shock, asphyxiation, gangrene, tetanus, etc.

3.    harmful - SCUBA divers may suffer the "bends" when they rise too quickly and Nitrogen gas "comes out of solution" and forms bubbles in the blood

The small intestine

Digestion within the small intestine produces a mixture of disaccharides, peptides, fatty acids, and monoglycerides. The final digestion and absorption of these substances occurs in the villi, which line the inner surface of the small intestine.

This scanning electron micrograph (courtesy of Keith R. Porter) shows the villi carpeting the inner surface of the small intestine.

The crypts at the base of the villi contain stem cells that continuously divide by mitosis producing

• more stem cells
• cells that migrate up the surface of the villus while differentiating into
  1. columnar epithelial cells (the majority). They are responsible for digestion and absorption.
  2. goblet cells, which secrete mucus;
  3. endocrine cells, which secrete a variety of hormones;
• Paneth cells, which secrete antimicrobial peptides that sterilize the contents of the intestine.

All of these cells replace older cells that continuously die by apoptosis.

The villi increase the surface area of the small intestine to many times what it would be if it were simply a tube with smooth walls. In addition, the apical (exposed) surface of the epithelial cells of each villus is covered with microvilli (also known as a "brush border"). Thanks largely to these, the total surface area of the intestine is almost 200 square meters, about the size of the singles area of a tennis court and some 100 times the surface area of the exterior of the body.

Incorporated in the plasma membrane of the microvilli are a number of enzymes that complete digestion:

• aminopeptidases attack the amino terminal (N-terminal) of peptides producing amino acids.
• disaccharidasesThese enzymes convert disaccharides into their monosaccharide subunits.
  • maltase hydrolyzes maltose into glucose.
  • sucrase hydrolyzes sucrose (common table sugar) into glucose and fructose.
  • lactase hydrolyzes lactose (milk sugar) into glucose and galactose.

Fructose simply diffuses into the villi, but both glucose and galactose are absorbed by active transport.

• fatty acids and monoglycerides. These become resynthesized into fats as they enter the cells of the villus. The resulting small droplets of fat are then discharged by exocytosis into the lymph vessels, called lacteals, draining the villi.

Principal heart sounds

1. S1: closure of AV valves;typically auscultated as a single sound 

Clinical note: In certain circumstances, S1 may be accentuated. This occurs when the valve leaflets are “slammed” shut in early systole from a greater than normal distance because they have not had time to drift closer together. Three conditions that can result in an accentuated S1 are a shortened PR interval, mild mitral stenosis, and high cardiac-output states or tachycardia.

2. S2: closure of semilunar valves in early diastole , normally “split” during inspiration . S2: best appreciated in the 2nd or 3rd left intercostal space

Clinical note: Paradoxical or “reversed” splitting occurs when S2 splitting occurs with expiration and disappears on inspiration. Moreover, in paradoxical splitting, the pulmonic valve closes before the aortic valve, such that P2 precedes A2. The most common cause is left bundle branch block (LBBB). In LBBB, depolarization of the left ventricle is impaired, resulting in delayed left ventricular contraction and aortic valve closure.

3. S3: ventricular gallop, presence reflects volume-overloaded state 
 
 Clinical note: An S3 is usually caused by volume overload in congestive heart failure. It can also be associated with valvular disease, such as advanced mitral regurgitation, in which the “regurgitated” blood increases the rate of ventricular filling during early diastole.
 
4. S4: atrial gallop, S4: atrial contraction against a stiff ventricle, often heard after an acute myocardial infarction.

Clinical note: An S4 usually indicates decreased ventricular compliance (i.e., the ventricle does not relax as easily), which is commonly associated with ventricular hypertrophy or myocardial ischemia. An S4 is almost always present after an acute myocardial infarction. It is loudest at the apex with the patient in the left lateral decubitus position (lying on their left side).

Micturition (urination) is a process, by which the final urine is eliminated out of the body .
After being drained into the ureters, urine is stored in urinary bladder until being eliminated.

Bladder is a hollow muscular organ, which has three layers:

- epithelium : Composed of superficial layer of flat cells and deep layer of cuboidal cells.

- muscular layer : contain smooth muscle fibers, that are arranged in longitudinal, spiral and circular pattern . Detrusor  muscle is the main muscle of bladder. The thickening of detrusor muscle forms internal urinary sphinctor which is not an actual urinary sphincter. The actual one is the external urinary sphincter, which is composed of striated muscle and is a part of urogenital diaphragm.

- adventitia: composed of connective tissue fibers.

So: There are two phases of bladder function that depend on characterestics of its muscular wall and innervation :

1. Bladder filling : Urine is poured into bladder through the orifices of ureters. Bladder has five peristaltic contraction per minute . These contraction facilitate moving of urine from the ureter to the bladder as prevent reflux of urine into the ureter.. The capacity of bladder is about  400  ml. But when the bladder start filling its wall extends and thus the pressure is not increased with the increased urine volume.

2. Bladder emptying : When bladder is full stretch receptors in bladder wall are excited , and send signals via the sensory branches of pelvic nerves to the sacral plexus. The first urge to void is felt at a bladder volume of about 150 ml. In sacral portion of spinal cord the sensory signals are integrated and then a motor signal is sent to the urinarry blader muscles through the efferent branches of pelvic nerve itself.

In adult people the neurons in sacral portion could be influenced by nerve signals coming from brain ( Micturition center in pons ) that are also influenced by signals coming from cerebral cortex.

So: The sensory signals ,transmitted to the sacral region will also stimulate ascending pathway and the signals be also transmitted to the micturition center in the brain stem and then to the cerebrum to cause conscious desire for urination.

If micturition is not convenient the brain sends signals to inhibit the parasympathetic motor neuron to the bladder via the sacral neurons. 

It also send inhibitory signal via the somatomotor pudendal nerve to keep external urinary sphincter contracting.

When micturition is convenient a brain signal via the sacral neurons stimulate the parasympathetic pelvic nerve to cause contraction of detruser muscle via M-cholinergic receptors and causes relaxation of external urinary sphincter and the micturition occurs.

Sympathetic hypogastric nerve does not contribute that much to the micturition reflex. It plays role in prvrntion reflux of semen into urinary bladder during ejaculation by contracting bladder muscles.

Respiration involves several components:

Ventilation - the exchange of respiratory gases (O₂ and CO₂) between the atmosphere and the lungs. This involves gas pressures and muscle contractions.

External respiration - the exchange of gases between the lungs and the blood. This involves partial pressures of gases, diffusion, and the chemical reactions involved in transport of O₂and CO₂.

Internal respiration - the exchange of gases between the blood and the systemic tissues. This involves the same processes as external respiration.

Cellular respiration - the includes the metabolic pathways which utilize oxygen and produce carbon dioxide, which will not be included in this unit.

Ventilation is composed of two parts: inspiration and expiration. Each of these can be described as being either quiet, the process at rest, or forced, the process when active such as when exercising.

Quiet inspiration:

The diaphragm contracts, this causes an increase in volume of the thorax and the lungs, which causes a decrease in pressure of the thorax and lungs, which causes air to enter the lungs, moving down its pressure gradient. Air moves into the lungs to fill the partial vacuum created by the increase in volume.

Forced inspiration:

Other muscles aid in the increase in thoracic and lung volumes.

The scalenes - pull up on the first and second ribs.

The sternocleidomastoid muscles pull up on the clavicle and sternum.

The pectoralis minor pulls forward on the ribs.

The external intercostals are especially important because they spread the ribs apart, thus increasing thoracic volume. It's these muscles whose contraction produces the "costal breathing" during rapid respirations.

Quiet expiration:

The diaphragm relaxes. The elasticity of the muscle tissue and of the lung stroma causes recoil which returns the lungs to their volume before inspiration. The reduced volume causes the pressure in the lungs to increase thus causing air to leave the lungs due to the pressure gradient.

Forced Expiration:

The following muscles aid in reducing the volume of the thorax and lungs:

The internal intercostals - these compress the ribs together

The abdominus rectus and abdominal obliques: internal obliques, external obliques- these muscles push the diaphragm up by compressing the abdomen.

Respiratory output is determined by the minute volume, calculated by multiplying the respiratory rate time the tidal volume.

Minute Volume = Rate (breaths per minute) X Tidal Volume (ml/breath)

Rate of respiration at rest varies from about 12 to 15 . Tidal volume averages 500 ml Assuming a rate of 12 breaths per minute and a tidal volume of 500, the restful minute volume is 6000 ml. Rates can, with strenuous exercise, increase to 30 to 40 and volumes can increase to around half the vital capacity.

Not all of this air ventilates the alveoli, even under maximal conditions. The conducting zone volume is about 150 ml and of each breath this amount does not extend into the respiratory zone. The Alveolar Ventilation Rate, AVR, is the volume per minute ventilating the alveoli and is calculated by multiplying the rate times the (tidal volume-less the conducting zone volume).

AVR = Rate X (Tidal Volume - 150 ml)

For a calculation using the same restful rate and volume as above this yields 4200 ml.

Since each breath sacrifices 150 ml to the conducting zone, more alveolar ventilation occurs when the volume is increased rather than the rate.

During inspiration the pressure inside the lungs (the intrapulmonary pressure) decreases to -1 to -3 mmHg compared to the atmosphere. The variation is related to the forcefulness and depth of inspiration. During expiration the intrapulmonary pressure increases to +1 to +3 mmHg compared to the atmosphere. The pressure oscillates around zero or atmospheric pressure.

The intrapleural pressure is always negative compared to the atmosphere. This is necessary in order to exert a pulling action on the lungs. The pressure varies from about -4 mmHg at the end of expiration, to -8 mmHg and the end of inspiration.

The tendency of the lungs to expand, called compliance or distensibility, is due to the pulling action exerted by the pleural membranes. Expansion is also facilitated by the action of surfactant in preventing the collapse of the alveoli.

The opposite tendency is called elasticity or recoil, and is the process by which the lungs return to their original or resting volume. Recoil is due to the elastic stroma of the lungs and the series elastic elements of the respiratory muscles, particularly the diaphragm.

Membrane Potential

• Membrane potentials will occur across cell membranes if
  • 1) there is a concentration gradient of an ion
  • 2) there is an open channel in the membrane so the ion can move from one side to the other

The Sodium Pump Sets Up Gradients of Na and K Across Cell Membranes

• All cells have the Na pump in their membranes
  • Pumps 3 Nas out and 2 Ks in for each cycle
  • Requires energy from ATP
    • Uses about 30% of body's metabolic energy
  • This is a form of active transport- can pump ions "uphill", from a low to a high concentration
  • This produces concentration gradients of Na & K across the membrane
  • Typical concentration gradients:

•  
• The ion gradients represent stored electrical energy (batteries) that can be tapped to do useful work
• The Na pump is of ancient origin, probably originally designed to protect cell from osmotic swelling

Inhibited by the arrow poisons ouabain and digitalis