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Physiology - NEETMDS- courses
NEET MDS Lessons
Physiology

 Pain, Temperature, and Crude Touch and Pressure

General somatic nociceptors, thermoreceptors, and mechanoreceptors sensitive to crude touch and pressure from the face conduct signals to the brainstem over GSA fibers of cranial nerves V, VII, IX, and X.

The afferent fibers involved are processes of monopolar neurons with cell bodies in the semilunar, geniculate, petrosal, and nodose ganglia, respectively.

The central processes of these neurons enter the spinal tract of V, where they descend through the brainstem for a short distance before terminating in the spinal nucleus of V.

Second-order neurons then cross over the opposite side of the brainstem at various levels to enter the ventral trigeminothalamic tract, where they ascend to the VPM of the thalamus.

Finally, third-order neurons project to the "face" area of the cerebral cortex in areas 3, 1, and 2 .

Discriminating Touch and Pressure

Signals are conducted from general somatic mechanoreceptors over GSA fibers of the trigeminal nerve into the principal sensory nucleus of V, located in the middle pons.

Second-order neurons then conduct the signals to the opposite side of the brainstem, where they ascend in the medial lemniscus to the VPM of the thalamus.

 Thalamic neurons then project to the "face" region of areas 3, I, and 2 of the cerebral cortex.

 Kinesthesia and Subconscious Proprioception

Proprioceptive input from the face is primarily conducted over GSA fibers of the trigeminal nerve.

The peripheral endings of these neurons are the general somatic mechanoreceptors sensitive to both conscious (kinesthetic) and subconscious proprioceptive input.

Their central processes extend from the mesencephalic nucleus to the principal sensory nucleus of V in the pons

The subconscious component is conducted to the cerebellum, while the conscious component travels to the cerebral cortex.

Certain second-order neurons from the principal sensory nucleus relay proprioceptive information concerning subconscious evaluation and integration into the ipsilateral cerebellum.

Other second-order neurons project to the opposite side of the pons and ascend to the VPM of the thalamus as the dorsal trigeminothalamic tract.

Thalamic projections terminate in the face area of the cerebral cortex.

Oxygen Transport in Blood: Hemoglobin

A.    Association & Dissociation of Oxygen + Hemoglobin

1.    oxyhemoglobin (HbO2) - oxygen molecule bound
2.    deoxyhemoglobin (HHb) - oxygen unbound
    
H-Hb     +    O2  <= === => HbO2 + H+

3.    binding gets more efficient as each O2 binds
4.    release gets easier as each O2 is released

5.    Several factors regulate AFFINITY of O2

a.    Partial Pressure of O2
b.    temperature
c.    blood pH (acidity)
d.    concentration of “diphosphoglycerate” (DPG)

B.    Effects of Partial Pressure of O2

1.  oxygen-hemoglobin dissociation curve

a.    104 mm (lungs) - 100% saturation (20 ml/100 ml)
b.    40 mm (tissues) - 75% saturation (15 ml/100 ml)
c.    right shift - Decreased Affinity, more O2 unloaded
d.     left shift- Increased Affinity, less O2 unloaded


C.    Effects of Temperature
    
1.    HIGHER Temperature    --> Decreased Affinity (right)
2.    LOWER Temperature        --> Increased Affinity (left)

D.    Effects of pH (Acidity) 

1.    HIGHER pH    --> Increased Affinity (left)
2.    LOWER pH    --> Decreased Affinity (right) "Bohr Effect"
a.    more Carbon Dioxide, lower pH (more H+), more O2 release

E.    Effects of Diphosphoglycerate (DPG)

1.    DPG - produced by anaerobic processes in RBCs
2.    HIGHER DPG    > Decreased Affinity (right)
3.    thyroxine, testosterone, epinephrine, NE - increase RBC metabolism and DPG production, cause RIGHT shift

F.    Oxygen Transport Problems

1.    hypoxia - below normal delivery of Oxygen

a.    anemic hypoxia - low RBC or hemoglobin
b.    stagnant hypoxia - impaired/blocked blood flow
c.    hypoxemic hypoxia - poor lung gas exchange

2.    carbon monoxide poisoning - CO has greater Affinity than Oxygen or Carbon Dioxide 
 

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

HEART DISORDERS

  1. Pump failure => Alters pressure (flow) =>alters oxygen carrying capacity.
    1. Renin release (Juxtaglomerular cells) Kidney
    2. Converts Angiotensinogen => Angiotensin I
    3. In lungs Angiotensin I Converted => Angiotensin II
    4. Angiotensin II = powerful vasoconstrictor (raises pressure, increases afterload)
      1. stimulates thirst
      2. stimulates adrenal cortex to release Aldosterone
        (Sodium retention, potassium loss)
      3. stimulates kidney directly to reabsorb Sodium
      4. releases ADH from Posterior Pituitary
  2. Myocardial Infarction

     

    1. Myocardial Cells die from lack of Oxygen
    2. Adjacent vessels (collateral) dilate to compensate
    3. Intracellular Enzymes leak from dying cells (Necrosis)
      1. Creatine Kinase CK (Creatine Phosphokinase) 3 forms
        1. One isoenzyme = exclusively Heart (MB)
        2. CK-MB blood levels found 2-5 hrs, peak in 24 hrs
        3. Lactic Dehydrogenase found 6-10 hours after. points less clearly to infarction
      2. Serum glutamic oxaloacetic transaminase (SGOT)
        1. Found 6 hrs after infarction, peaks 24-48 hrs at 2 to 15 times normal,
        2. SGOT returns to normal after 3-4 days
    4. Myocardium weakens = Decreased CO & SV (severe - death)
    5. Infarct heal by fibrous repair
    6. Hypertrophy of undamaged myocardial cells
      1. Increased contractility to restore normal CO
      2. Improved by exercise program
    7. Prognosis
      1. 10% uncomplicated recovery
      2. 20% Suddenly fatal
      3. Rest MI not fatal immediately, 15% will die from related causes
  3. Congenital heart disease (Affect oxygenation of blood)
    1. Septal defects
    2. Ductus arteriosus
    3. Valvular heart disease
      1. Stenosis = cusps, fibrotic & thickened, Sometimes fused, can not open
      2. Regurgitation = cusps, retracted, Do not close, blood moves backwards

Proteinuria—Protein content in urine, often due to leaky or damaged glomeruli.

Oliguria—An abnormally small amount of urine, often due to shock or kidney damage.

Polyuria—An abnormally large amount of urine, often caused by diabetes.

Dysuria—Painful or uncomfortable urination, often from urinary tract infections.

Hematuria—Red blood cells in urine, from infection or injury.

Glycosuria—Glucose in urine, due to excess plasma glucose in diabetes, beyond the amount able to be reabsorbed in the proximal convoluted tubule.

Carbohydrates:

  • about 3% of the dry mass of a typical cell
  • composed of carbon, hydrogen, & oxygen atoms (e.g., glucose is C6H12O6)
  • an important source of energy for cells
  • types include:
    • monosaccharide (e.g., glucose) - most contain 5 or 6 carbon atoms
    • disaccharides
      • 2 monosaccharides linked together
      • Examples include sucrose (a common plant disaccharide is composed of the monosaccharides glucose and fructose) & lactose (or milk sugar; a disaccharide composed of glucose and the monosaccharide galactose)
    • polysaccharides
      • several monosaccharides linked together

Examples include starch (a common plant polysaccharide made up of many glucose molecules) and glycogen (commonly stored in the liver)

Functional Divisions of the Nervous System:

1) The Voluntary Nervous System - (ie. somatic division) control of willful control of effectors (skeletal muscles) and conscious perception. Mediates voluntary reflexes.

2) The Autonomic Nervous System - control of autonomic effectors - smooth muscles, cardiac muscle, glands. Responsible for "visceral" reflexes

MDS SUBJECTS

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