AdenosineTriphosphate (ATP)

• Animal cells cannot directly use most forms of energy
  • Most cellular processes require energy stored in the bonds of a molecule, adenosine triphosphate (ATP)
  • ATP is referred to as the energy currency of the cell

It is a nucleotide, formed from:

• the base adenine (the structure with 2 rings),
• the 5 carbon sugar deoxyribose (one ring)
• 3 phosphates

Energy is stored in the bonds between the phosphates and is released when the bonds are broken

Bleeding Disorders

A deficiency of a clotting factor can lead to uncontrolled bleeding.

The deficiency may arise because

• not enough of the factor is produced or
• a mutant version of the factor fails to perform properly.

Examples:

• von Willebrand disease (the most common)
• hemophilia A for factor 8 deficiency
• hemophilia B for factor 9 deficiency.
• hemophilia C for factor 11 deficiency

In some cases of von Willebrand disease, either a deficient level or a mutant version of the factor eliminates its protective effect on factor 8. The resulting low level of factor 8 mimics hemophilia A.

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

White Blood Cells (leukocytes)

White blood cells

• are much less numerous than red (the ratio between the two is around 1:700),
• have nuclei,
• participate in protecting the body from infection,
• consist of lymphocytes and monocytes with relatively clear cytoplasm, and three types of granulocytes, whose cytoplasm is filled with granules.

Lymphocytes: There are several kinds of lymphocytes, each with different functions to perform , 25% of wbc The most common types of lymphocytes are

• B lymphocytes ("B cells"). These are responsible for making antibodies.
• T lymphocytes ("T cells"). There are several subsets of these:
  • inflammatory T cells that recruit macrophages and neutrophils to the site of infection or other tissue damage
  • cytotoxic T lymphocytes (CTLs) that kill virus-infected and, perhaps, tumor cells
  • helper T cells that enhance the production of antibodies by B cells

Although bone marrow is the ultimate source of lymphocytes, the lymphocytes that will become T cells migrate from the bone marrow to the thymus where they mature. Both B cells and T cells also take up residence in lymph nodes, the spleen and other tissues where they

• encounter antigens;
• continue to divide by mitosis;
• mature into fully functional cells.

Monocytes : also originate in marrow, spend up to 20 days in the circulation, then travel to the tissues where they become macrophages. Macrophages are the most important phagocyte outside the circulation. Monocytes are about 9% of normal wbc count

Macrophages are large, phagocytic cells that engulf

• foreign material (antigens) that enter the body
• dead and dying cells of the body.

Neutrophils

The most abundant of the WBCs. about 65% of normal white count  These cells spend 8 to 10 days in the circulation making their way to sites of infection etc  Neutrophils squeeze through the capillary walls and into infected tissue where they kill the invaders (e.g., bacteria) and then engulf the remnants by phagocytosis. They have two types of granules: the most numerous are specific granules which contain bactericidal agents such as lysozyme; the azurophilic granules are lysosomes containing peroxidase and other enzymes

Eosinophils : The number of eosinophils in the blood is normally quite low (0–450/µl). However, their numbers increase sharply in certain diseases, especially infections by parasitic worms. Eosinophils are cytotoxic, releasing the contents of their granules on the invader.

Basophils : rare except during infections where these cells mediate inflammation by secreting histamine and heparan sulfate (related to the anticoagulant heparin). Histamine makes blood vessels permeable and heparin inhibits blood clotting. Basophils are functionally related to mast cells.  . The mediators released by basophils also play an important part in some allergic responses such as hay fever and an anaphylactic response to insect stings.

Thrombocytes (platelets):

Thrombocytes are cellular derivatives from megakaryocytes which contain factors responsible for the intrinsic clotting mechanism. They represent fragmented cells  which contain residual organelles including rough endoplasmic reticulum and Golgi apparati. They are only 2-microns in diameter, are seen in peripheral blood either singly or, often, in clusters, and have a lifespan of 10 days.

The Cardiac Cycle: the sequence of events in one heartbeat.

systole - the contraction phase; unless otherwise specified refers to left ventricle, but each chamber has its own systole.

diastole - the relaxation phase; unless otherwise specified refers to left ventricle, but each chamber has its own diastole.

1) quiescent period - period when all chambers are at rest and filling. 70% of ventricular filling occurs during this period. The AV valves are open, the semilunar valves are closed.

2) atrial systole - pushes the last 30% of blood into the ventricle.

3) atrial diastole - atria begin filling.

4) ventricular systole - First the AV valves close causing the first heart sound, then after the isovolumetric contraction phase the semilunar valves open permitting ventricular ejection of blood into the arteries.

5) ventricular diastole - As the ventricles relax the semilunar valves close first producing the second heart sound, then after the isovolumetric relaxation phase the AV valves open allowing ventricular filling.

Properties of cardiac muscle

Cardiac muscle is a striated muscle like the skeletal muscle , but it is different from the skeletal muscle in being involuntary and syncytial .

Syncytium means that cardiac muscle cells are able to excite and contract together due to the presence of gap junctions between adjacent cardiac cells.

Cardiac muscle has four properties , due to which the heart is able to fulfill its function as a pumping organ. Studying and understanding these properties is essential for students to understand the cardiac physiology as a whole.

1. Rhythmicity ( Chronotropism )
2. Excitability ( Bathmotropism ) 
3. Conductivity
4. Contractility