Each hormone in the body is unique.  Each one is different in it's chemical composition, structure, and action.  With respect to their chemical structure, hormones may be classified into three groups: amines, proteins, and steroids.

 Amines- these simple hormones are  structural variation of the amino acid tyrosine.  This group includes thyroxine from the thyroid gland and epinephrine and norepinephrine from the adrenal medulla.

Proteins- these hormones are chains of amino acids.  Insulin from the pancreas, growth hormone from the anterior pituitary gland, and calcitonin from the thyroid gland are all proteins.  Short chains of amino acids are called peptides.  Antidiuretic hormone and oxytocin, synthesized by the hypothalamus, are peptide hormones.

Steroids- cholesterol is the precursor for the steroid hormones, which include cortisol and aldosterone from the adrenal cortex, estrogen and progesterone from the ovaries, and testosterone from the testes.

Conductivity :

 Means ability of cardiac muscle to propagate electrical impulses through the entire heart ( from one part of the heart to another)  by the excitatory -conductive system of the heart.
 
Excitatory conductive system of the heart involves:

1. Sinoatrial node ( SA node) : Here the initial impulses start and then conducted to the atria through  the anterior inter-atrial pathway ( to the left atrium) , to the atrial muscle mass through the gap junction, and to the Atrioventricular node ( AV node ) through anterior, middle , and posterior inter-nodal pathways.
The average conductive velocity in the atria is 1m/s.

2- AV node : The electrical impulses can not be conducted directly from the atria to the ventricles , because of the  fibrous skeleton , which is an electrical isolator , located between the atria and ventricles. So the only conductive way is the AV node . But there is a delay in the conduction occurs in the AV node .
This delay is due to:
- the smaller size of the nodal fiber.
- The less negative resting membrane potential
- fewer gap junctions.

There are three sites for delay:
- In the transitional fibers , that connect inter-nodal pathways with the AV node ( 0.03 ) .
- AV node itself ( 0.09 s) .
- In the penetrating portion of Bundle of Hiss ( 0.04 s)  .
This delay actually allows atria to empty blood in ventricles during the cardiac cycle before the beginning of ventricular contraction  , as it prevents the ventricles from the pathological high atrial rhythm.
The average velocity of conduction in the AV node is 0.02-0.05 m/s

3- Bundle of Hiss : A continuous with the AV node that passes to the ventricles through the inter-ventricular septum. It is subdivided into : Right and left bundle. The left bundle is also subdivided into two branches: anterior and posterior branches .

4- Purkinje`s fibers: large fibers with velocity of conduction 1.5-4 m/s.
the high velocity of these fibers is due to the abundant gap junctions , and to their nature as very large fibers as well.
The conduction from AV node is a one-way conduction . This prevents the re-entry of cardiac impulses from the ventricles to the atria.
Lastly: The conduction through the ventricular fibers has a velocity of 0.3-0.5 m/s.

Factors , affecting conductivity ( dromotropism)  :

I. Positive dromotropic factors :

1. Sympathetic stimulation : it accelerates conduction and decrease AV delay .
2. Mild warming
3. mild hyperkalemia
4. mild ischemia
5. alkalosis

II. Negative dromotropic factors :

1. Parasympathetic stimulation
2. severe warming
3. cooling
4. Severe hyperkalemia
5. hypokalemia
6. Severe ischemia
7. acidosis
8. digitalis drugs.

Nucleic Acids:

• Two major types: DNA
• RNA (including mRNA, tRNA, & rRNA) 
  • Both types have code which specifies the sequence of amino acids in proteins
  • DNA = archival copy of genetic code, kept in nucleus, protected
  • RNA = working copy of code, used to translate a specific gene into a protein, goes into cytoplasm & to ribosomes, rapidly broken down
• Nucleic acids are made of 5 nucleotide bases, sugars and phosphate groups
• The bases make up the genetic code ; the phosphate and sugar make up the backbone
• RNA is a molecule with a single strand
• DNA is a double strand (a double helix) held together by hydrogen bonds between the bases
  • A = T; C= G because:
    • A must always hydrogen bond to T

C must always hydrogen bond to G

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

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 
 

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