Vital Capacity: The vital capacity (VC) is the maximum volume which can be ventilated in a single breath. VC= IRV+TV+ERV. VC varies with gender, age, and body build. Measuring VC gives a device for diagnosis of respiratory disorder, and a benchmark for judging the effectiveness of treatment. (4600 ml)

Vital Capacity is reduced in restrictive disorders, but not in disorders which are purely obstructive.

The FEV₁ is the % of the vital capacity which is expelled in the first second. It should be at least 75%. The FEV₁ is reduced in obstructive disorders.

Both VC and the FEV₁ are reduced in disorders which are both restrictive and obstructive

Oxygen is present at nearly 21% of ambient air. Multiplying .21 times 760 mmHg (standard pressure at sea level) yields a pO₂ of about 160. Carbon dioxide is .04% of air and its partial pressure, pCO₂, is .3.

With alveolar air having a pO₂ of 104 and a pCO₂ of 40. So oxygen diffuses into the alveoli from inspired air and carbon dioxide diffuses from the alveoli into air which will be expired. This causes the levels of oxygen and carbon dioxide to be intermediate in expired air when compared to inspired air and alveolar air. Some oxygen has been lost to the alveolus, lowering its level to 120, carbon dioxide has been gained from the alveolus raising its level to 27.

Likewise a concentration gradient causes oxygen to diffuse into the blood from the alveoli and carbon dioxide to leave the blood. This produces the levels seen in oxygenated blood in the body. When this blood reaches the systemic tissues the reverse process occurs restoring levels seen in deoxygenated blood.

The Body Regulates pH in Several Ways

• Buffers are weak acid mixtures (such as bicarbonate/CO₂) which minimize pH change
  • Buffer is always a mixture of 2 compounds
    • One compound takes up H ions if there are too many (H acceptor)
    • The second compound releases H ions if there are not enough (H donor)
  • The strength of a buffer is given by the buffer capacity
    • Buffer capacity is proportional to the buffer concentration and to a parameter known as the pK
  • Mouth bacteria produce acids which attack teeth, producing caries (cavities). People with low buffer capacities in their saliva have more caries than those with high buffer capacities.
• CO₂ gas (a potential acid) is eliminated by the lungs
• Other acids and bases are eliminated by the kidneys

SPECIAL SOMATIC AFFERENT (SSA) PATHWAYS

Hearing

The organ of Corti with its sound-sensitive hair cells and basilar membrane are important parts of the sound transducing system for hearing. Mechanical vibrations of the basilar membrane generate membrane potentials in the hair cells which produce impulse patterns in the cochlear portion of the vestibulocochlear nerve (VIII)

Special somatic nerve fibers of cranial nerve VIII relay impulses from the sound receptors (hair cells) in the cochlear nuclei of the brainstem

These are bipolar neurons with cell bodies located in the spiral ganglia of the cochlea.

Vestibular System

The vestibulocochlear nerve serves two quite different functions.

The cochlear portion, conducts sound information to the brain,

The vestibular portion conducts proprioceptive information.

It is the central neural pathways

Special somatic afferent fibers from the hair cells of the macula utriculi and macula sacculi conduct information into the vestibular nuclei on the ipsilateral side of the pons and medulla.

These are bipolar neurons with cell bodies located in the vestibular ganglion.

 Some of the fibers project directly into the ipsilateral cerebellum to terminate in the uvula, flocculus, and nodulus, but most enter the vestibular nuclei and synapse there.

Vision

The visual system receptors are the rods and cones of the retina.

Special somatic afferent fibers of the optic nerve (II) conduct visual signals into the brain

Fibers from the lateral (temporal) retina of either eye terminate in the lateral geniculate body on the same side of the brain as that eye.

SSA II fibers from the medial (nasal) retina of each eye cross over in the optic chiasm to terminate in the contralateral lateral geniculate body.

Area 17 is the primary visual area, which receives initial visual signals.

Neurons from this area project into the adjacent occipital cortex (areas 18 and 19) which is known as the secondary visual area. It is here that the visual signal is fully evaluated.

The visual reflex pathway involving the pupillary light reflex - in which the pupils constrict when a light is shined into the eyes and dilate when the light is removed.

Some SSA II fibers leave the optic tract before reaching the lateral geniculates, terminating in the superior colliculi instead.

From here, short neurons project to the Edinger­Westphal nucleus (an accessory nucleus of III) in the midbrain, which serves as the origin of the preganglionic parasympathetic fibers of the oculomotor nerve (GVE III).

The GVE III fibers in turn project to the ciliary ganglia, from which arise the postganglionic fibers to the sphincter muscles of the iris, which constrict the pupils.

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

Surface Tension

1.    Maintains stability of alveolus, preventing collapse

2.    Surfactant (Type II pneumocytes) = dipalmityl lecithin

3.    Type II pneumocyte appears at 24 weeks of gestation;
    1.    Surfactant production, 28-32 weeks;
    2.    Surfactant in amniotic fluid, 35 weeks.
    3.    Laplace equation for thin walled spheres P = 2T
        a.    P = alveolar internal pressure r
        b.    T = tension in the walls r = radius of alveolus
        
4.    During normal tidal respiration

    1.    Some alveoli do collapse (Tidal pressure can't open)
    2.    Higher than normal pressure needed (Coughing)
    3.    Deep breaths & sighs promote re-expansion
    4.    After surgery/Other conditions, Coughing, deep breathing, sustained maximal respiration

Abnormalities of Salt, Water or pH

• Examples:
  • Hyperkalemia: caused by kidney disease & medical malpractice
    • High K+ in blood- can stop the heart in contraction (systole)
  • Dehydration: walking in desert- can lose 1-2 liters/hour through sweat
    • Blood becomes too viscous to circulate well -> loss of temperature regulation -> hyperthermia, death
  • Acidosis: many causes including diabetes mellitus and respiratory problems; can cause coma, death