Page 115 - 84 human physiolofy part-1

The Muscular System

Major side effects can include liver tumors and cancer, jaundice, high blood pressure, kidney
tumors, severe acne, and trembling. In males, side effects may include shrinking of the testicles and
breast development. In females, side effects may include growth of facial hair, menstrual changes, and
deepened voice. In teenagers, growth may be halted prematurely and permanently.

The therapeutic use of steroids can be realized by patients and their doctors by using them in a
manner that is beneficial to the person.

Smooth Muscle Contraction

• Contractions are initiated by an influx of calcium which binds to calmodulin.
• The calcium-calmodulin complex binds to and activates myosin light-chain kinase.
• Myosin light-chain kinase phosphorylates myosin light-chains, causing them to interact
with actin filaments. This causes contraction.

The calcium ions leave the troponin molecule in order to maintain the calcium ion concentration in
the sacoplasm. As the calcium ions are being actively pumped by the calcium pumps present in the
membrane of the sarcoplasmic reticulum creating a deficiency in the fluid around the myofibrils.This
causes the removal of calcium ions from the troponin.Thus the tropomyosin-troponin complex again
covers the binding sites on the actin fiaments and contraction ceases.

Cardiac Muscle

Cardiac muscle cells within the myocardium are arranged
in layers that completely encase the chambers of the heart. The
contraction of these cells pressurizes the blood inside the
chambers of the heart so that the blood can travel out of the
heart to the rest of the body. Cardiac muscle contains elements
of both striated skeletal muscle and smooth muscle. The
striated structure of cardiac muscle is due to the arrangement
of thick myosin and thin actin filaments which are similar to
the arrangement of skeletal muscle. Compared to skeletal muscle, cardiac muscle is much shorter and
has several branching processes. Intercalated disks join the ends of cardiac muscle cells to each other.
Gap junctions are situated adjacent to intercalated disks which is similar to those found in many
smooth muscle cells. One percent of cardiac cells do not contract because the non-contracting cells
have specialized features that aid in heart excitation. The non-contracting cells form a network known
as the conducting system and contact other cardiac muscle cells at gap junctions. The conduction
system begins the heartbeat and assists in spreading the contraction impulse rapidly through out the
heart. Certain cardiac muscle cells also secrete atrial natriuretic peptide (ANP)[1] which inhibits
sodium reabsorbtion in the kidneys.

ATP in the Human Body

Muscles cells, like all cells, use ATP as an energy source. The total quantity of ATP in the human
body at any one time is about 0.1 Mole. The energy used by human cells requires the hydrolysis of 200

Wikibooks | 115