The bulk of the pancreas is an exocrine gland secreting pancreatic fluid into the duodenum after a meal. However, scattered through the pancreas are several hundred thousand clusters of cells called islets of Langerhans. The islets are endocrine tissue containing four types of cells. In order of abundance, they are the:

• beta cells, which secrete insulin and amylin;
• alpha cells, which secrete glucagon;
• delta cells, which secrete somatostatin, and
• gamma cells, which secrete a polypeptide of unknown function.

Beta Cells

Beta cells secrete insulin in response to a rising level of blood sugar

Insulin affects many organs. It

• stimulates skeletal muscle fibers to
  • take up glucose and convert it into glycogen;
  • take up amino acids from the blood and convert them into protein.
• acts on liver cells
  • stimulating them to take up glucose from the blood and convert it into glycogen while
  • inhibiting production of the enzymes involved in breaking glycogen back down (glycogenolysis) and
  • inhibiting gluconeogenesis; that is, the conversion of fats and proteins into glucose.
• acts on fat (adipose) cells to stimulate the uptake of glucose and the synthesis of fat.
• acts on cells in the hypothalamus to reduce appetite.

Diabetes Mellitus

Diabetes mellitus is an endocrine disorder characterized by many signs and symptoms. Primary among these are:

• a failure of the kidney to retain glucose .
• a resulting increase in the volume of urine because of the osmotic effect of this glucose (it reduces the return of water to the blood).

There are three categories of diabetes mellitus:

• Insulin-Dependent Diabetes Mellitus (IDDM) (Type 1) and
• Non Insulin-Dependent Diabetes Mellitus (NIDDM)(Type 2)
• Inherited Forms of Diabetes Mellitus

Insulin-Dependent Diabetes Mellitus (IDDM)

IDDM ( Type 1 diabetes)

• is characterized by little or no circulating insulin;
• most commonly appears in childhood.
• It results from destruction of the beta cells of the islets.
• The destruction results from a cell-mediated autoimmune attack against the beta cells.
• What triggers this attack is still a mystery, although a prior viral infection may be the culprit.

Non Insulin-Dependent Diabetes Mellitus (NIDDM)

Many people develop diabetes mellitus without an accompanying drop in insulin levels In many cases, the problem appears to be a failure to express a sufficient number of glucose transporters in the plasma membrane (and T-system) of their skeletal muscles. Normally when insulin binds to its receptor on the cell surface, it initiates a chain of events that leads to the insertion in the plasma membrane of increased numbers of a transmembrane glucose transporter. This transporter forms a channel that permits the facilitated diffusion of glucose into the cell. Skeletal muscle is the major "sink" for removing excess glucose from the blood (and converting it into glycogen). In NIDDM, the patient's ability to remove glucose from the blood and convert it into glycogen is reduced. This is called insulin resistance. NIDDM (also called Type 2 diabetes mellitus) usually occurs in adults and, particularly often, in overweight people.

Alpha Cells

The alpha cells of the islets secrete glucagon, a polypeptide of 29 amino acids. Glucagon acts principally on the liver where it stimulates the conversion of glycogen into glucose (glycogenolysis) which is deposited in the blood.

Glucagon secretion is

• stimulated by low levels of glucose in the blood;
• inhibited by high levels, and
• inhibited by amylin.

The physiological significance of this is that glucagon functions to maintain a steady level of blood sugar level between meals.

Delta Cells

The delta cells secrete somatostatin. Somatostatin has a variety of functions. Taken together, they work to reduce the rate at which food is absorbed from the contents of the intestine. Somatostatin is also secreted by the hypothalamus and by the intestine.

Gamma Cells

The gamma cells of the islets secrete pancreatic polypeptide. No function has yet been found for this peptide of 36 amino acids.

Neural Substrates of Breathing

A.    Medulla Respiratory Centers

Inspiratory Center (Dorsal Resp Group - rhythmic breathing) → phrenic nerve→ intercostal nerves→ diaphragm + external intercostals

Expiratory Center (Ventral Resp Group - forced expiration) → phrenic nerve → intercostal nerves → internal intercostals + abdominals (expiration)

1.    eupnea - normal resting breath rate (12/minute)
2.    drug overdose - causes suppression of Inspiratory Center

B.    Pons Respiratory Centers

1.    pneumotaxic center - slightly inhibits medulla, causes shorter, shallower, quicker breaths
2.    apneustic center - stimulates the medulla, causes longer, deeper, slower breaths

C.    Control of Breathing Rate & Depth

1.    breathing rate - stimulation/inhibition of medulla
2.    breathing depth - activation of inspiration muscles
3.    Hering-Breuer Reflex - stretch of visceral pleura that lungs have expanded (vagal nerve)

D.    Hypothalamic Control - emotion + pain to the medulla

E.    Cortex Controls (Voluntary Breathing) - can override medulla as during singing and talking

Lung volumes and capacities: 
I. Lung`s volumes
1. Tidal volume (TV) : is the volume of air m which is inspired and expired during one quiet breathing . It equals to 500 ml.
 

2. Inspiratory reserve volume (IRV) : The volume of air that could be inspired over and beyond the tidal volume. It equals to 3000 ml of air.
 

3. Expiratory reserve volume (ERV) : A volume of air that could be forcefully expired after the end of quiet tidal volume. It is about 1100 ml of air.
 

4. Residual volume (RV) : the extra volume of air that may remain in the lung after the forceful expiration . It is about 1200 ml of air.
 

5. Minute volume : the volume of air that is inspired or expired within one minute. It is equal to multiplying of respiratory rate by tidal volume = 12X500= 6000 ml.
It is in female  lesser than that in male.
II. Lung`s capacities :
1. Inspiratory capacity: TV + IRV
2. Vital capacity : TV+IRV+ERV
3. Total lung capacity : TV+IRV+ERV+RV

1) Storage - the stomach allows a meal to be consumed and the materials released incrementally into the duodenum for digestion. It may take up to four hours for food from a complete meal to clear the stomach. 
2) Chemical digestion - pepsin begins the process of protein digestion cleaving large polypeptides into shorter chains . 
3) Mechanical digestion - the churning action of the muscularis causes liquefaction and mixing of the contents to produce acid chyme. 
4) Some absorption - water, electrolytes, monosaccharides, and fat soluble molecules including alcohol are all absorbed in the stomach to some degree.

Proteins:

• about 50 - 60% of the dry mass of a typical cell
• subunit is the amino acid & amino acids are linked by peptide bonds
• 2 functional categories = structural (proteins part of the structure of a cell like those in the cell membrane) & enzymes

Enzymes are catalysts. Enzymes bind temporarily to one or more of the reactants of the reaction they catalyze. In doing so, they lower the amount of activation energy needed and thus speed up the reaction

Cardiac Output:

Minute Volume = Heart Rate X Stroke Volume

Heart rate, HR at rest = 65 to 85 bpm  

Each heartbeat at rest takes about .8 sec. of which .4 sec. is quiescent period.

Stroke volume, SV at rest = 60 to 70 ml.

Heart can increase both rate and volume with exercise. Rate increase is limited due to necessity of minimum ventricular diastolic period for filling. Upper limit is usually put at about 220 bpm. Maximum heart rate calculations are usually below 200. Target heart rates for anaerobic threshold are about 85 to 95% of maximum.

Terms:

End Diastolic Volume, EDV - the maximum volume of the ventricles achieved at the end of ventricular diastole. This is the amount of blood the heart has available to pump. If this volume increases the cardiac output increases in a healthy heart.

End Systolic Volume, ESV - the minimum volume remaining in the ventricle after its systole. If this volume increases it means less blood has been pumped and the cardiac output is less.

EDV - ESV = SV

SV / EDV = Ejection Fraction The ejection fraction is normally around 50% at rest and will increase during strenuous exercise in a healthy heart. Well trained athletes may have ejection fractions approaching 70% in the most strenuous exercise.

Isovolumetric Contraction Phase - a brief period at the beginning of ventricular systole when all valves are closed and ventricular volume remains constant. Pressure has risen enough in the ventricle to close the AV valves but not enough to open the semilunar valves and cause ejection of blood. 

Isovolumetric Relaxation Phase - a brief period at the beginning of ventricular diastole when all valves are closed and ventricular volume is constant. Pressure in the ventricle has lowered producing closure of the semilunar valves but not opening the AV valves to begin pulling blood into the ventricle.

Dicrotic Notch - the small increase in pressure of the aorta or other artery seen when recording a pulse wave. This occurs as blood is briefly pulled back toward the ventricle at the beginning of diastole thus closing the semilunar valves.

Preload - This is the pressure at the end of ventricular diastole, at the beginning of ventricular systole. It is proportional to the End Diastolic Volume (EDV), i.e. as the EDV increases so does the preload of the heart. Factors which increase the preload are: increased total blood volume, increased venous tone and venous return, increased atrial contraction, and the skeletal muscular pump.

Afterload - This is the impedence against which the left ventricle must eject blood, and it is roughly proportional to the End Systolic Volume (ESV). When the peripheral resistance increases so does the ESV and the afterload of the heart. 

The importance of these parameters are as a measure of efficiency of the heart, which increases as the difference between preload and afterload increases