Science Natural Phenomena and Medicine

Chordate Characteristics

Published on 2012-02-13 08:28:00

The chordates are animals which belong to the phylum Chordata. It includes the vertebrates (animals with spinal column) and animals that have notochord, such as tunicates and lancelets. This phylum gets its name from one of its three distinctive features or characteristics. The first one is the notochord; all chordates at some time during their lifetimes possess a flexible supporting rod along the back, called the notocord, which stiffens the animal's body. In most chordates, the notochord is lo

Effects of Peptide hormones

Published on 2012-02-12 10:55:00

Peptide hormones and catecholamine effects are very important as they influence ion channels, enzyme activity, and the cytoplasmic JAK kinases activity. The receptors for peptide hormones and the catecholamine hormones are located on the outer surface of the target cell's plasma membrane. This location is important, since these hormones are too large and hydrophilic to diffuse through the plasma membrane. When activated by hormone binding, the receptors trigger one or more of the signal transduc

Hormone Metabolism and Excretion

Published on 2012-02-11 09:41:00

Once a hormone has acted on the target tissue, the concentration of the hormone in the blood must be restored to normal. This is necessary to prevent excessive, possibly harmful actions of prolonged exposure of target cells to hormones. A hormone’s concentration in the plasma depends upon (1) its rate of secretion by the endocrine gland, and (2) its rate of removal from the blood. Removal, or "clearance," of the hormone occurs either by excretion or by metabolic transformation. The liver and t

Hormone Receptors

Published on 2012-02-10 19:25:00

Because they are transported in the blood, hormones can reach virtually all tissues. Yet the response to a hormone is highly specific, involving only the target cells for that hormone. The ability to respond depends upon the presence on (or in) the target cells of specific receptors for those hormones. The receptors for peptide hormones and catecholamines are proteins located in the plasma membranes of the target cells. In contrast, the receptors for steroid hormones and the thyroid hormones are

Peptide Hormones

Published on 2012-02-09 12:37:00

Most hormones are either peptides or proteins. They range in size from small peptides having only three amino acids to small proteins (some of which are glycoproteins). For convenience, it is sometimes referred to all these hormones as peptide hormones. They are water-soluble hormones which consist of a few amino acids that introduce a series of chemical reactions to change the cell's metabolism. Examples of peptide hormones include hormones of the pituitary gland and parathyroid glands.In many

Lymph Flow Mechanism

Published on 2012-02-08 08:53:00

The lymphatic vessels beyond the lymphatic capillaries propel the lymph within them by their own contractions. The smooth muscle in the wall of the lymphatics exerts a pump-like action by inherent rhythmical contractions. Since the lymphatic vessels have valves similar to those in veins, these contractions produce a one-way flow toward the points at which the lymphatics enter the circulatory system. The lymphatic vessel smooth muscle is responsive to stretch, so when there is no accumulation of

Electroencephalogram (EEG)

Published on 2012-02-07 09:48:00

Electroencephalogram (EEG) is the records of the brain electrical activity. Neural activity is manifested by the electrical signals known as graded potentials and action potentials. The electrical activity in the brain’s neurons, particularly those in the cortex near the surface of the brain, can be recorded from the outside of the head. Electrodes, which are wires attached to the head by a salty paste that conducts electricity, pick up electrical signals generated in the brain and transmit th

Amine Hormones

Published on 2012-02-06 11:33:00

The amine hormones are all derivatives of the single amino acid tyrosine. They include the thyroid hormones, the catecholamines epinephrine and norepinephrine (produced by the adrenal medulla), and dopamine (produced by the hypothalamus). The amine hormones are stored in granules of cell cytoplasms.

Hormone Transport in the Blood

Published on 2012-02-05 08:56:00

Most peptide and all catecholamine hormones are water-soluble. Therefore, with the exception of a few peptides, these hormones are transported simply dissolved in plasma. In contrast, the poorly soluble steroid hormones and thyroid hormones are transported in the blood largely bound to plasma proteins. Even though the steroid and thyroid hormones exist in plasma mainly bound to large proteins, small concentrations of these hormones do exist dissolved in the plasma. The dissolved, or free, hormon

Diffusion Across the Capillary Wall

Published on 2012-02-04 09:54:00

There are three basic mechanisms by which substances move across the capillary walls in most organs and tissues to enter or leave the interstitial fluid: diffusion, vesicle transport, and bulk flow. Mediated transport constitutes a fourth mechanism in the capillaries of the brain. Diffusion and vesicle transport are described in this section, and bulk flow in the next. In all capillaries, excluding those in the brain, diffusion constitutes the only important means by which net movement of nutrie