Contractility : Means ability of cardiac muscle to convert electrical energy of action potential into mechanical energy ( work).
The excitation- contraction coupling of cardiac muscle is similar to that of skeletal muscle , except the lack of motor nerve stimulation. 

Cardiac muscle is a self-excited muscle , but the principles of contraction are the same . There are many rules that control the contractility of the cardiac muscles, which are:

1. All or none rule: due to the syncytial nature of the cardiac muscle.There are atrial syncytium and ventricular syncytium . This rule makes the heart an efficient pump.

2. Staircase phenomenon : means gradual increase in muscle contraction following rapidly repeated stimulation..

3. Starling`s law of the heart: The greater the initial length of cardiac muscle fiber , the greater the force of contraction. The initial length is determined by the degree of diastolic filling .The pericardium prevents overstretching of heart , and allows optimal increase in diastolic volume.

Thankful to this law , the heart is able to pump any amount of blood that it receives. But overstretching of cardiac muscle fibers may cause heart failure.

Factors affecting  contractility ( inotropism)

I. Positive inotropic factors:

1. sympathetic stimulation: by increasing the permeability of sarcolemma to calcium.
2. moderate increase in temperature . This due to increase metabolism to increase ATP , decrease viscosity of myocardial structures, and increasing calcium influx.
3. Catecholamines , thyroid hormone, and glucagon hormones.
4. mild alkalosis
5. digitalis
6. Xanthines ( caffeine and theophylline )

II. Negative inotropic factors:

1. Parasympathetic stimulation : ( limited to atrial contraction)
2. Acidosis
3. Severe alkalosis
4. excessive warming and cooling .
5. Drugs ;like : Quinidine , Procainamide , and barbiturates .
6. Diphtheria and typhoid toxins.

The hepatic portal system

The capillary beds of most tissues drain into veins that lead directly back to the heart. But blood draining the intestines is an exception. The veins draining the intestine lead to a second set of capillary beds in the liver. Here the liver removes many of the materials that were absorbed by the intestine:

• Glucose is removed and converted into glycogen.
• Other monosaccharides are removed and converted into glucose.
• Excess amino acids are removed and deaminated.
  • The amino group is converted into urea.
  • The residue can then enter the pathways of cellular respiration and be oxidized for energy.
• Many nonnutritive molecules, such as ingested drugs, are removed by the liver and, often, detoxified.

The liver serves as a gatekeeper between the intestines and the general circulation. It screens blood reaching it in the hepatic portal system so that its composition when it leaves will be close to normal for the body.

Furthermore, this homeostatic mechanism works both ways. When, for example, the concentration of glucose in the blood drops between meals, the liver releases more to the blood by

• converting its glycogen stores to glucose (glycogenolysis)
• converting certain amino acids into glucose (gluconeogenesis).

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)

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

Typical Concentration Gradients and Membrane Potentials in Excitable Cells

The Na Pump is Particularly Important in the Kidney and Brain

• All cells have Na pumps in their membranes, but some cells have more than others
• Over-all Na pump activity may account for a third of your resting energy expenditure!
• In the kidney the Na pump activity is very high because it is used to regulate body salt and water concentrations
  • Kidneys use enormous amounts of energy: 0.5% of body weight, but use 7% of the oxygen supply
• Pump activity is also high in the brain because Na and K gradients are essential for nerves
  • The brain is another high energy organ; it is 2% of body weight, but uses 18% of the oxygen supply

In the Resting State Potassium Controls the Membrane Potential of Most Cells

• Resting cells have more open K channels than other types
• More K+ passes through membrane than other ions- therefore K+ controls the potential
• Blood K+ must be closely controlled because small changes will produce large changes in the membrane potentials of cells
  • Raising K will make the membrane potential less negative (depolarization)
• High blood K+ can cause the heart to stop beating (it goes into permanent contraction)

During an Action Potential Na Channels Open, and Na Controls the Membrane Potential

• Whichever ion has the most open channels controls the membrane potential
• Excitable cells have Na channels that open when stimulated
• When large numbers of these channels open Na controls the membrane potential

The pituitary gland is pea-sized structure located at the base of the brain. In humans, it consists of two lobes:

• the Anterior Lobe and
• the Posterior Lobe

The Anterior Lobe

The anterior lobe contains six types of secretory cells All of them secrete their hormone in response to hormones reaching them from the hypothalamus of the brain.

Thyroid Stimulating Hormone (TSH)

TSH (also known as thyrotropin) is a glycoprotein The secretion of TSH is

• stimulated by the arrival of thyrotropin releasing hormone (TRH) from the hypothalamus.
• inhibited by the arrival of somatostatin from the hypothalamus.

 TSH stimulates the thyroid gland to secrete its hormone thyroxine (T₄).

Some develop antibodies against their own TSH receptors making more T₄ causing hyperthyroidism. The condition is called thyrotoxicosis or Graves' disease.

Hormone deficiencies

A deficiency of TSH causes hypothyroidism: inadequate levels of T₄ (and thus of T₃ )..

Follicle-Stimulating Hormone (FSH)

FSH is a heterodimeric glycoprotein Synthesis and release of FSH is triggered by the arrival from the hypothalamus of gonadotropin-releasing hormone (GnRH).

FSH in females :In sexually-mature females, FSH (assisted by LH) acts on the follicle to stimulate it to release estrogens.

FSH in males :In mature males, FSH acts on spermatogonia stimulating (with the aid of testosterone) the production of sperm.

Luteinizing Hormone (LH)

LH is synthesized within the same pituitary cells as FSH and under the same stimulus (GnRH). It is also a heterodimeric glycoprotein

LH in females

In sexually-mature females, LH

• stimulates the follicle to secrete estrogen in the first half of the menstrual cycle
• a surge of LH triggers the completion of meiosis I of the egg and its release (ovulation) in the middle of the cycle
• stimulates the now-empty follicle to develop into the corpus luteum, which secretes progesterone during the latter half of the menstrual cycle.

LH in males

LH acts on the interstitial cells (also known as Leydig cells) of the testes stimulating them to synthesize and secrete the male sex hormone, testosterone.

LH in males is also known as interstitial cell stimulating hormone (ICSH).

Prolactin (PRL)

Prolactin is a protein of 198 amino acids. During pregnancy it helps in the preparation of the breasts for future milk production. After birth, prolactin promotes the synthesis of milk.

Prolactin secretion is

• stimulated by TRH
• repressed by estrogens and dopamine.

Growth Hormone (GH)

• Human growth hormone (also called somatotropin) is a protein
• The GH-secreting cells are stimulated to synthesize and release GH by the intermittent arrival of growth hormone releasing hormone (GHRH) from the hypothalamus. GH promotes body growth

In Child

• hyposecretion of GH produces dwarfism
• hypersecretion leads to gigantism

In adults, a hypersecretion of GH leads to acromegaly.

ACTH — the adrenocorticotropic hormone

ACTH acts on the cells of the adrenal cortex, stimulating them to produce

• glucocorticoids, like cortisol
• mineralocorticoids, like aldosterone
• androgens (male sex hormones, like testosterone

Hypersecretion of ACTH cause of Cushing's disease.