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)

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.

• The Autonomic Nervous System (ANS) Controls the Body's Internal Environment in a Coordinated Manner

• The ANS helps control the heart rate, blood pressure, digestion, respiration, blood pH and other bodily functions through a series of complex reflex actions
• These controls are done automatically, below the conscious level
• To exert this control the activities of many different organs must be coordinated so they work to accomplish the same goal
• In the ANS there are 2 nerves between the central nervous system (CNS) and the organ. The nerve cell bodies for the second nerve are organized into ganglia:
  • CNS -> Preganglionic nerve -> Ganglion -> Postganglionic nerve -> Organ
• At each junction neurotransmitters are released and carry the signal to the next nerve or organ.

• The ANS has 2 Divisions, Sympathetic and Parasympathetic

   

• Comparison of the 2 systems:

• 	Anatomical Location	Preganglionic Fibers	Postganglionic Fibers	Transmitter (Ganglia)	Transmitter (Organs)
  Sympathetic	Thoracic/ Lumbar	Short	Long	ACh	NE
  Parasympathetic	Cranial/ Sacral	Long	Short	ACh	ACh

   

  The Sympathetic is the "Fight or Flight" Branch of the ANS

• Emergency situations, where the body needs a sudden burst of energy, are handled by the sympathetic system
• The sympathetic system increases cardiac output and pulmonary ventilation, routes blood to the muscles, raises blood glucose and slows down digestion, kidney filtration and other functions not needed during emergencies
• Whole sympathetic system tends to "go off" together
• In a controlled environment the sympathetic system is not required for life, but it is essential for any stressful situation

• The Parasympathetic is the Rest and Digest Branch of the ANS

• The parasympathetic system promotes normal maintenance of the body- acquiring building blocks and energy from food and getting rid of the wastes
• It promotes secretions and mobility of different parts of the digestive tract.
• Also involved in urination, defecation.
• Does not "go off" together; activities initiated when appropriate
• The vagus nerve (cranial number 10) is the chief parasympathetic nerve
• Other cranial parasympathetic nerves are: III (oculomotor), VII (facial) and IX (glossopharyngeal)

• The Hypothalamus Has Central Control of the ANS

• The hypothalamus is involved in the coordination of ANS responses,
• One section of the hypothalamus seems to control many of the "fight or flight" responses; another section favors "rest and digest" activities

• The Adrenal Medulla is an Extension of the Sympathetic Nervous System

• The adrenal medulla behaves like a combined autonomic ganglion and postsynaptic sympathetic nerve (see diagram above)
• Releases both norepinephrine and epinephrine in emergency situations
  • Releases a mixture of epinephrine (E = 80%) and norepinephrine (NE = 20%)
  • Epinephrine = adrenaline
• This action is under control of the hypothalamus

• Sympathetic & Parasympathetic Systems

• Usually (but not always) both sympathetic and parasympathetic nerves go to an organ and have opposite effects
• You can predict about 90% of the sympathetic and parasympathetic responses using the 2 phrases: "Fight or Flight" and "Rest and Digest".
• Special cases:
  • Occasionally the 2 systems work together: in sexual intercourse the parasympathetic promotes erection and the sympathetic produces ejaculation
  • Eye: the sympathetic response is dilation and relaxation of the ciliary muscle for far vision (parasympathetic does the opposite)
  • Urination: the parasympathetic system relaxes the sphincter muscle and promotes contraction of muscles of the bladder wall -> urination (sympathetic blocks urination)
  • Defecation: the parasympathetic system causes relaxation of the anal sphincter and stimulates colon and rectum to contract -> defecation (sympathetic blocks defecation)

• Organ	Parasympathetic Response "Rest and Digest"	Sympathetic Response "Fight or Flight"
  Heart (baroreceptor reflex)	Decreased heart rate Cardiac output decreases	Increased rate and strength of contraction Cardiac output increases
  Lung Bronchioles	Constriction	Dilation
  Liver Glycogen	No effect	Glycogen breakdown Blood glucose increases
  Fat Tissue	No effect	Breakdown of fat Blood fatty acids increase
  Basal Metabolism	No effect	Increases ~ 2X
  Stomach	Increased secretion of HCl & digestive enzymes Increased motility	Decreased secretion Decreased motility
  Intestine	Increased secretion of HCl & digestive enzymes Increased motility	Decreased secretion Decreased motility
  Urinary bladder	Relaxes sphincter Detrusor muscle contracts Urination promoted	Constricts sphincter Relaxes detrusor Urination inhibited
  Rectum	Relaxes sphincter Contracts wall muscles Defecation promoted	Constricts sphincter Relaxes wall muscles Defecation inhibited
  Eye	Iris constricts Adjusts for near vision	Iris dilates Adjusts for far vision
  Male Sex Organs	Promotes erection	Promotes ejaculation

   

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.

Water: comprises 60 - 90% of most living organisms (and cells) important because it serves as an excellent solvent & enters into many metabolic reactions

• Intracellular (inside cells) = ~ 34 liters
• Interstitial (outside cells) = ~ 13 liters
• Blood plasma = ~3 liters

40% of blood is red blood cells (RBCs)

plasma is similar to interstitial fluid, but contains plasma proteins

serum = plasma with clotting proteins removed

intracellular fluid is very different from interstitial fluid (high K concentration instead of high Na concentration, for example)

• Capillary walls (1 cell thick) separate blood from interstitial fluid
• Cell membranes separate intracellular and interstitial fluids

• Loss of about 30% of body water is fatal

Ions = atoms or molecules with unequal numbers of electrons and protons:

• found in both intra- & extracellular fluid
• examples of important ions include sodium, potassium, calcium, and chloride

Ions (Charged Atoms or Molecules) Can Conduct Electricity

• Giving up electron leaves a + charge (cation)
• Taking on electron produces a - charge (anion)
• Ions conduct electricity
• Without ions there can be no nerves or excitability
  • Na⁺ and K⁺ cations  
  • Ca²⁺ and Mg²⁺ cations  control metabolism and trigger muscle contraction and secretion of hormones and transmitters

Na+ & K+ are the Major Cations in Biological Fluids

• High K+ in cells, high Na+ outside
• Ion gradients maintained by Na pump (1/3 of basal metabolism)
• Think of Na+ gradient as a Na+ battery- stored electrical energy
• K+ gradient forms a K+ battery
• Energy stored in Na+ and K+ batteries can be tapped when ions flow

• Na+ and K+ produce action potential of excitable cells

Alveolar Ventilation: is the volume of air of new air , entering the alveoli and adjacent gas exchange areas each minute . It equals to multiplying of respiratory rate by ( tidal volume - dead space).
Va = R rate X (TV- DsV)
     = 12 X ( 500-150)
     = 4200 ml of air.