Plasma:  is the straw-colored liquid in which the blood cells are suspended.

Plasma transports materials needed by cells and materials that must be removed from cells:

• various ions (Na⁺, Ca²⁺, HCO₃⁻, etc.
• glucose and traces of other sugars
• amino acids
• other organic acids
• cholesterol and other lipids
• hormones
• urea and other wastes

Most of these materials are in transit from a place where they are added to the blood

• exchange organs like the intestine
• depots of materials like the liver

to places where they will be removed from the blood.

• every cell
• exchange organs like the kidney, and skin.

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

Regulation of glomerular filtration :

1. Extrinsic regulation : 

- Neural regulation : sympathetic and parasympathetic nervous system which causes vasoconstriction or vasodilation respectively .
- Humoral regulation : Vasoactive substances may affect the GFR , vasoconstrictive substances like endothelin ,Angiotensin II , Norepinephrine , prostaglandine F2 may constrict the afferent arteriole and thus decrease GFR , while the vasodilative agents like dopamine , NO , ANP , Prostaglandines E2 may dilate the afferent arteriole and thus increase the filtration rate .

2. Intrinsic regulation : 

- Myogenic theory ( as in the intrinsic regulation of cardiac output) .
- Tubuloglomerular feedback: occurs by cells of the juxtaglomerular apparatus that is composed of specific cells of the distal tubules when it passes between afferent and efferent arterioles ( macula densa cells ) , these cells sense changes in flow inside the tubules and inform specific cells in the afferent arteriole (granular cells ) , the later secrete vasoactive substances that affect the diameter of the afferent arteriole.

There are three types of muscle tissue, all of which share some common properties:

• Excitability or responsiveness - muscle tissue can be stimulated by electrical, physical, or chemical means.
• contractility - the response of muscle tissue to stimulation is contraction, or shortening.
• elasticity or recoil - muscles have elastic elements (later we will call these their series elastic elements) which cause them to recoil to their original size.
• stretchability or extensibility - muscles can also stretch and extend to a longer-than-resting length.

The three types of muscle: skeletal, cardiac, and visceral (smooth) muscle.

Skeletal muscle

It is found attached to the bones for movement.

cells are long multi-nucleated cylinders.

 The cells may be many inches long but vary in diameter, averaging between 100 and 150 microns.

 All the cells innervated by branches from the same neuron will contract at the same time and are referred to as a motor unit.

 Skeletal muscle is voluntary because the neurons which innervate it come from the somatic or voluntary branch of the nervous system.

That means you have willful control over your skeletal muscles.

 Skeletal muscles have distinct stripes or striations which identify them and are related to the organization of protein myofilaments inside the cell.

Cardiac muscle

This muscle found in the heart.

 It is composed of much shorter cells than skeletal muscle which branch to connect to one another.

 These connections are by means of gap junctions called intercalated disks which allow an electrochemical impulse to pass to all the connected cells.

 This causes the cells to form a functional network called a syncytium in which the cells work as a unit. Many cardiac muscle cells are myogenic which means that the impulse arises from the muscle, not from the nervous system. This causes the heart muscle and the heart itself to beat with its own natural rhythm.

But the autonomic nervous system controls the rate of the heart and allows it to respond to stress and other demands. As such the heart is said to be involuntary.

Visceral muscle is found in the body's internal organs and blood vessels.

 It is usually called smooth muscle because it has no striations and is therefore smooth in appearance. It is found as layers in the mucous membranes of the respiratory and digestive systems.

It is found as distinct bands in the walls of blood vessels and as sphincter muscles.

Single unit smooth muscle is also connected into a syncytium similar to cardiac muscle and is also partly myogenic. As such it causes continual rhythmic contractions in the stomach and intestine. There and in blood vessels smooth muscle also forms multiunit muscle which is stimulated by the autonomic nervous system. So smooth muscle is involuntary as well

Events in Muscle Contraction - the sequence of events in crossbridge formation:

1) In response to Ca²⁺ release into the sarcoplasm, the troponin-tropomyosin complex removes its block from actin, and the myosin heads immediately bind to active sites.

2) The myosin heads then swivel, the Working Stroke, pulling the Z-lines closer together and shortening the sarcomeres. As this occurs the products of ATP hydrolysis, ADP and Pi, are released.

3) ATP is taken up by the myosin heads as the crossbridges detach. If ATP is unavailable at this point the crossbridges cannot detach and release. Such a condition occurs in rigor mortis, the tensing seen in muscles after death, and in extreme forms of contracture in which muscle metabolism can no longer provide ATP.

4) ATP is hydrolyzed and the energy transferred to the myosin heads as they cock and reset for the next stimulus.

Excitation-Contraction Coupling: the Neuromuscular Junction  

Each muscle cell is stimulated by a motor neuron axon. The point where the axon terminus contacts the sarcolemma is at a synapse called the neuromuscular junction. The terminus of the axon at the sarcolemma is called the motor end plate. The sarcolemma is polarized, in part due to the unequal distribution of ions due to the Sodium/Potassium Pump.

1) Impulse arrives at the motor end plate (axon terminus) causing  Ca²⁺ to enter the axon.

2) Ca²⁺ binds to ACh vesicles causing them to release the ACh (acetylcholine) into the synapse by exocytosis. 

3) ACH diffuses across the synapse to bind to receptors on the sarcolemma. Binding of ACH to the receptors opens chemically-gated ion channels causing Na⁺ to enter the cell producing depolarization.

4) When threshold depolarization occurs, a new impulse (action potential) is produced that will move along the sarcolemma. (This occurs because voltage-gated ion channels open as a result of the depolarization -

5) The sarcolemma repolarizes:

a) K⁺ leaves cell (potassium channels open as sodium channels close) returning positive ions to the outside of the sarcolemma. (More K⁺ actually leaves than necessary and the membrane is hyperpolarized briefly. This causes the relative refractory period) (b) Na⁺/K⁺ pump eventually restores resting ion distribution.  The  Na⁺/K⁺ pump is very slow compared to the movement of ions through the ion gates. But a muscle can be stimulated thousands of times before the ion distribution is substantially affected.

6) ACH broken down by ACH-E (a.k.a. ACHase, cholinesterase). This permits the receptors to respond to another stimulus. 

Excitation-Contraction Coupling:

1) The impulse (action potential) travels along the sarcolemma. At each point the voltaged-gated Na+ channels open to cause depolarization, and then the K+ channels open to produce repolarization.

2) The impulse enters the cell through the T-tublules, located at each Z-disk, and reach the sarcoplasmic reticulum (SR), stimulating it.

3) The SR releases Ca²⁺ into the sarcoplasm, triggering the muscle contraction as previously discussed. 

4) Ca²⁺ is pumped out of the sarcoplasm by the SR and another stimulus will be required to continue the muscle contraction.

A small fraction of cardiac muscle fibers have myogenicity and autorhythmicity.

Myogenicity is the property of spontaneous impulse generation. The slow sodium channels are leaky and cause the polarity to spontaneously rise to threshold for action potential generation. The fastest of these cells, those in the SA node, set the pace for the heartbeat.

Autorhythmicity - the natural rhythm of spontaneous depolarization. Those with the fastest autorhythmicity act as the 1. heart's pacemaker.

Contractility - like skeletal muscle, most cardiac muscle cells respond to stimuli by contracting. The autorhythmic cells have very little contractility however. Contractility in the other cells can be varied by the effect of neurotransmitters.

Inotropic effects - factors which affect the force or energy of muscular contractions. Digoxin, epinephrine, norepinephrine, and dopamine have positive inotropic effects. Betal blockers and calcium channel blockers have negative inotropic effects 

Sequence of events in cardiac conduction: The electrical events in the cardiac cycle.

1) SA node depolarizes and the impulse spreads across the atrial myocardium and through the internodal fibers to the AV node. The atrial myocardium depolarizes resulting in atrial contraction, a physical event.

2) AV node picks up the impulse and transfers it to the AV Bundle (Bundle of His). This produces the major portion of the delay seen in the cardiac cycle. It takes approximately .03 sec from SA node depolarization to the impulse reaching the AV node, and .13 seconds for the impulse to get through the AV node and reach the Bundle of His. Also during this period the atria repolarize.

3) From the AV node the impulse travels through the bundle branches and through the Purkinje fibers to the ventricular myocardium, causing ventricular depolarization and ventricular contraction, a physical event.

4) Ventricular repolarization occurs.