Membrane Potential

• Membrane potentials will occur across cell membranes if
  • 1) there is a concentration gradient of an ion
  • 2) there is an open channel in the membrane so the ion can move from one side to the other

The Sodium Pump Sets Up Gradients of Na and K Across Cell Membranes

• All cells have the Na pump in their membranes
  • Pumps 3 Nas out and 2 Ks in for each cycle
  • Requires energy from ATP
    • Uses about 30% of body's metabolic energy
  • This is a form of active transport- can pump ions "uphill", from a low to a high concentration
  • This produces concentration gradients of Na & K across the membrane
  • Typical concentration gradients:

•  
• The ion gradients represent stored electrical energy (batteries) that can be tapped to do useful work
• The Na pump is of ancient origin, probably originally designed to protect cell from osmotic swelling

Inhibited by the arrow poisons ouabain and digitalis

Bronchitis = Irreversible Bronchioconstriction
 .    Causes - Infection, Air polution, cigarette smoke

a.    Primary Defect = Enlargement & Over Activity of Mucous Glands, Secretions very viscous
b.    Hypertrophy & hyperplasia, Narrows & Blocks bronchi, Lumen of airway, significantly narrow
c.    Impaired Clearance by mucocillary elevator
d.    Microorganism retension in lower airways,Prone to Infectious Bronchitis, Pneumonia
e.    Permanent Inflamatory Changes IN epithelium, Narrows walls, Symptoms, Excessive sputum, coughing
f.    CAN CAUSE EMPHYSEMA

The Adrenal Glands

The adrenal glands are two small structures situated one at top each kidney. Both in anatomy and in function, they consist of two distinct regions:

• an outer layer, the adrenal cortex, which surrounds
• the adrenal medulla.

The Adrenal Cortex

cells of the adrenal cortex secrete a variety of steroid hormones.

• glucocorticoids (e.g., cortisol)
• mineralocorticoids (e.g., aldosterone)
• androgens (e.g., testosterone)

• Production of all three classes is triggered by the secretion of ACTH from the anterior lobe of the pituitary.

Glucocorticoids

They Effect by raising the level of blood sugar (glucose). One way they do this is by stimulating gluconeogenesis in the liver: the conversion of fat and protein into intermediate metabolites that are ultimately converted into glucose.

The most abundant glucocorticoid is cortisol (also called hydrocortisone).

Cortisol and the other glucocorticoids also have a potent anti-inflammatory effect on the body. They depress the immune response, especially cell-mediated immune responses. 

Mineralocorticoids

The most important of them is the steroid aldosterone. Aldosterone acts on the kidney promoting the reabsorption of sodium ions (Na⁺) into the blood. Water follows the salt and this helps maintain normal blood pressure.

Aldosterone also

• acts on sweat glands to reduce the loss of sodium in perspiration;
• acts on taste cells to increase the sensitivity of the taste buds to sources of sodium.

The secretion of aldosterone is stimulated by:

• a drop in the level of sodium ions in the blood;
• a rise in the level of potassium ions in the blood;
• angiotensin II
• ACTH (as is that of cortisol)

Androgens

The adrenal cortex secretes precursors to androgens such as testosterone.

Excessive production of adrenal androgens can cause premature puberty in young boys.

In females, the adrenal cortex is a major source of androgens. Their hypersecretion may produce a masculine pattern of body hair and cessation of menstruation.

Addison's Disease: Hyposecretion of the adrenal cortices

Addison's disease has many causes, such as

• destruction of the adrenal glands by infection;
• their destruction by an autoimmune attack;
• an inherited mutation in the ACTH receptor on adrenal cells.

Cushing's Syndrome: Excessive levels of glucocorticoids

In Cushing's syndrome, the level of adrenal hormones, especially of the glucocorticoids, is too high.It can be caused by:

• excessive production of ACTH by the anterior lobe of the pituitary;
• excessive production of adrenal hormones themselves (e.g., because of a tumor), or (quite commonly)
• as a result of glucocorticoid therapy for some other disorder such as
  • rheumatoid arthritis or
  • preventing the rejection of an organ transplant.

The Adrenal Medulla

The adrenal medulla consists of masses of neurons that are part of the sympathetic branch of the autonomic nervous system. Instead of releasing their neurotransmitters at a synapse, these neurons release them into the blood. Thus, although part of the nervous system, the adrenal medulla functions as an endocrine gland.The adrenal medulla releases:

• adrenaline (also called epinephrine) and
• noradrenaline (also called norepinephrine)

Both are derived from the amino acid tyrosine.

Release of adrenaline and noradrenaline is triggered by nervous stimulation in response to physical or mental stress. The hormones bind to adrenergic receptors  transmembrane proteins in the plasma membrane of many cell types.

Some of the effects are:

• increase in the rate and strength of the heartbeat resulting in increased blood pressure;
• blood shunted from the skin and viscera to the skeletal muscles, coronary arteries, liver, and brain;
• rise in blood sugar;
• increased metabolic rate;
• bronchi dilate;
• pupils dilate;
• hair stands on end (gooseflesh in humans);
• clotting time of the blood is reduced;
• increased ACTH secretion from the anterior lobe of the pituitary.

All of these effects prepare the body to take immediate and vigorous action.

Hemostasis - the  stopping of the blood. Triggered by a ruptured vessel wall it occurs in several steps:

1) vascular spasm - most vessels will constrict strongly when their walls are damaged. This accounts for individuals not bleeding to death even when limbs are crushed. It also can help to enhance blood clotting in less severe injuries.

2) platelet plug - platelets become sticky when they contact collagen, a protein in the basement membrane of the endothelium exposed when the vessel wall is ruptured. As they stick together they can form a plug which will stem the flow of blood in minor vessels.

3) Formation of the Blood Clot:

A) release of platelet factors - as platelets stick together and to the vascular wall some are ruptured releasing chemicals such as thromboxane, PF3, ADP and other substances. These become prothrombin activators. Thromboxane also makes the platelets even stickier, and increases the vascular constriction. These reactions are self perpetuating and become a cascade which represents a positive feedback mechanism.

B) prothrombin activators : prothrombin (already in the blood) is split into smaller products including thrombin, an active protease.

C) thrombin splits soluble fibrinogen, already present in the plasma, into monomers which then polymerize to produce insoluble fibrin threads. The fibrin threads weave the platelets and other cells together to form the actual clot. This occurs within four to six minutes when the injury is severe and up to 15 minutes when it is not. After 15 minutes the clot begins to retract as the fibrin threads contract, pulling the broken edges of the injury together and smoothing the surface of the clot causing the chemical processes to cease. Eventually the clot will dissolve due to enzymes such as plasmin also present in the blood.

The extrinsic pathway: when tissues are damaged the damaged cells release substances called tissue thromboplastin which also acts as a prothrombin activator. This enhances and speeds coagulation when tissue damage is involved.

Anti-thrombin III - this factor helps to prevent clotting when no trigger is present by removing any thrombin present. Its function is magnified many times when heparin is present. Therefore heparin is used clinically as a short-term anticoagulant.

Vitamin K - stimulates the production of clotting factors including prothrombin and fibrinogen in the liver. This vitamin is normally produced by bacteria in the colon. Coumarin (or coumadin) competes with Vitamin K in the liver and is used clinically for long-term suppression of clotting.

Several factors important to clotting are known to be absent in forms of hemophilia. These factors are produced by specific genes which are mutated in the deficient forms. The factors are  VIII, IX, and XI.

Calcium is necessary for blood clotting and its removal from the blood by complexing with citrate will prevent the blood from clotting during storage

Control of processes in the stomach:

The stomach, like the rest of the GI tract, receives input from the autonomic nervous system. Positive stimuli come from the parasympathetic division through the vagus nerve. This stimulates normal secretion and motility of the stomach. Control occurs in several phases:

Cephalic phase stimulates secretion in anticipation of eating to prepare the stomach for reception of food. The secretions from cephalic stimulation are watery and contain little enzyme or acid.

Gastric phase of control begins with a direct response to the contact of food in the stomach and is due to stimulation of pressoreceptors in the stomach lining which result in ACh and histamine release triggered by the vagus nerve. The secretion and motility which result begin to churn and liquefy the chyme and build up pressure in the stomach. Chyme surges forward as a result of muscle contraction but is blocked from entering the duodenum by the pyloric sphincter. A phenomenon call retropulsion occurs in which the chyme surges backward only to be pushed forward once again into the pylorus. The presence of this acid chyme in the pylorus causes the release of a hormone called gastrin into the bloodstream. Gastrin has a positive feedback effect on the motility and acid secretion of the stomach. This causes more churning, more pressure, and eventually some chyme enters the duodenum.

Intestinal phase of stomach control occurs. At first this involves more gastrin secretion from duodenal cells which acts as a "go" signal to enhance the stomach action already occurring. But as more acid chyme enters the duodenum the decreasing pH inhibits gastrin secretion and causes the release of negative or "stop" signals from the duodenum.

These take the form of chemicals called enterogastrones which include GIP (gastric inhibitory peptide). GIP inhibits stomach secretion and motility and allows time for the digestive process to proceed in the duodenum before it receives more chyme. The enterogastric reflex also reduces motility and forcefully closes the pyloric sphincter. Eventually as the chyme is removed, the pH increases and gastrin and the "go" signal resumes and the process occurs all over again. This series of "go" and "stop" signals continues until stomach emptying is complete.

Respiration occurs in three steps :
1- Mechanical ventilation : inhaling and exhaling of air between lungs and atmosphere.
2- Gas exchange : between pulmonary alveoli and pulmonary capillaries.
3- Transport of gases from the lung to the peripheral tissues , and from the peripheral tissues back to blood .
These steps are well regulated by neural and chemical regulation.

Respiratory tract is subdivided into upper and lower respiratory tract. The upper respiratory tract involves , nose , oropharynx and nasopharynx , while the lower respiratory tract involves larynx , trachea , bronchi ,and lungs .

Nose fulfills three important functions which are :

1. warming of inhaled air .

b. filtration of air .

c. humidification of air .

Pharynx is a muscular tube , which forms a passageway for air and food .During swallowing the epiglottis closes the larynx and the bolus of food falls in the esophagus .

Larynx is a respiratory organ that connects pharynx with trachea . It is composed of many cartilages and muscles and

vocal cords . Its role in respiration is limited to being a conductive passageway for air .

Trachea is a tube composed of C shaped cartilage rings from anterior side, and of muscle (trachealis muscle ) from its posterior side.The rings prevent trachea from collapsing during the inspiration. 

From  the trachea the bronchi are branched into right and left bronchus ( primary bronchi) , which enter the lung .Then they repeatedly branch into secondary and tertiary bronchi and then into terminal and respiratory broncholes.There are about 23 branching levels from the right and left bronchi to the respiratory bronchioles  , the first upper  17 branching are considered as a part of the conductive zones , while the lower 6 are considered to be respiratory zone. 

The cartilaginous component decreases gradually from the trachea to the bronchioles  . Bronchioles are totally composed of smooth muscles ( no cartilage) . With each branching the diameter of bronchi get smaller , the smallest diameter of respiratory passageways is that of respiratory bronchiole. 

Lungs are evolved by pleura . Pleura is composed of two layers : visceral and parietal .
Between the two layers of pleura , there is a pleural cavity , filled with a fluid that decrease the friction between the visceral and parietal pleura.
 

Respiratory muscles : There are two group of respiratory muscles:

1. Inspiratory muscles : diaphragm and external intercostal muscle ( contract during quiet breathing ) , and accessory inspiratory muscles : scaleni , sternocleidomastoid , internal pectoral muscle , and others( contract during forceful inspiration).
 

2. Expiratory muscles : internal intercostal muscles , and abdominal muscles ( contract during forceful expiration)