Animal Hormones

Animal hormones are specific chemical substances secreted by endocrine glands. These endocrine gland secretions are released into blood. They are conveyed in blood to regulate the function of tissue and organs elsewhere in the body. 

These organs where the hormones act are called “target organs”. Hormones are produced in small quantities. 

Human body has many endoendocrine glands and they have some common properties. 
1. They are ductless glands
2. They are highly vascularized structures
3. Their secretions are transported through blood 

Hormones can be transported as free molecules or as plasma protein bounded molecules. 

At the target organ, after carrying out its functions hormones are degraded by enzymes, excreted from body with urine or metabolize within liver and break down into simple molecules.

We can categorize animal hormones based on their chemical nature as peptide hormones, proteins, glycoproteins, amino acid derivatives, steroid hormones, inorganic gases, water insoluble hormones. 

2012-05-28 20:15:11

Smoke + Fog = Smog

The term smog was first used in 1905 by Dr H A Des Voeux to describe the conditions of fog that had smoke in it. Smog is a combination of various gases with water vapour and dust. 

A large part of the gases that form smog is produced when fuels are burnt. Smog forms when heat and sunlight react with these gases and fine particles in the air. Smog can affect rural areas as well as big cities. Its occurrences are often linked to heavy traffic, high temperatures, and calm winds. During the winter, wind speeds are low and cause the smoke and fog to stagnate; hence pollution levels can increase near ground level. This keeps the pollution close to the ground, right where people are breathing. 

It reduces visibility and harms the environment. Heavy smog greatly decreases ultraviolet radiation. In fact, in the early part of the 20th century, heavy smog in some parts of Europe resulted in a decrease in the production of natural vitamin D leading to a rise in the cases of rickets (bowing of bones in young children). 

Smog is misty and similar to fog, but very different in composition. In fact the word smog has formed as a combination of the words fog and smoke. The most harmful components of smog are ground-level ozone, sulphur dioxide and fine airborne particles. Ground-level ozone forms when pollutants released from vehicles and oil-based solvents react with heat and sunlight. Sulphur dioxide is released due to burn of coal. 

Smog is harmful to humans, animals, and plants. The effects of smog on human health were evident, particularly when smog persisted for several days. 

Many people suffered respiratory problems and increased deaths were recorded, notably those relating to bronchial causes. A mist of dense harmful smog would often cover the city of London. The first smog-related deaths were recorded in London in 1873, when it killed 500 people. London had one of its worst experiences with smog in December 1952. The Great London Smog lasted for five days and resulted in about 5000 deaths. In response to the Great London Smog, the government passed its first Clean Air Act in 1956.

Today, smoke and sulphur dioxide pollution in cities is much lower than in the past, as a result of legislation to control pollution emissions and cleaner emission technology.

2012-05-28 20:14:36


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