# Biomedical Engineering Theory And Practice/Physiolgocial System
## Cardiovascular Structure and Function

As all the cell in the human body could not exchange with nutrients, oxygen, carbon dioxide, and the waste products of metabolism, energy and momentum, the high way network in the physiological system transport the mass between the cell in order to hold all the body. This high way network, called cardiovascular system, includes a pumping station, the heart; a working fluid, blood; a complex branching configuration of distributing and collecting pipes and channels, blood vessels; and a complicated means for intrinsic (inherent) and extrinsic (autonomic and endocrine) control.

### The blood

The blood supplies oxygen and nutrients including constitutional elements to tissues and remove waste products. Blood also transport hormones and other substances to tissues and organs.
Blood consists of plasma(55% of blood volume) and blood cell or hematocytes (approximately, %8±1 of body weight). Hematocytes are suspended in continus plasma fluid and could divided into red blood cells (erythrocytes, totalling nearly 95% of the formed elements), white blood cells(leukocytes, averaging <0.15% of all hematocytes), and platelets (thrombocytes, on the order of 5% of all blood cells). Hematocytes are derived in the active (“red”) bone marrow from undifferentiated stem cells (called hemocytoblasts) and matured through hematocytopoiesis.

## Endocrine System

'See also Wikipedia,endocrine system and Human Physiology/The endocrine system
The endocrine system means the collection of glands of an organism that secrete hormones(in other words, produce messengers like small molecules) directly into the circulatory system to be carried toward a distant target organ. In order to grow, maintain a constant temperature, produce offspring, or perform the basic actions and functions, essentially, hormones like small chemicals(in other words, messengers) should enter the blood stream. So, the endocrine system could provides an electrochemical connection from the hypothalamus of the brain to all the organs for controlling the body metabolism, growth and development, and reproduction.
The endocrinology is a relatively long history. But In the late 1960s as sensitive and relatively specific analytical methods introduced, the measurement of low concentrations of circulating hormones is easier and cheaper. Since then, it is easier to understand endocrine physiology and mechanisms of regulation and control. Competitive protein binding and radioimmunoassays brought progress of the study about the physiology of individual endocrine glands and of the neural control of the pituitary gland and the overall feedback control of the endocrine system. Cellular and molecular biology and recombinant DNA technology helped the endocrine system research, too.
At the same time, the interactive researches between mathematical modeling and experimental studies make it possible to understand endocrine dynamics.

### Hormones and signal, interaction between the tissue and the cell

Hormones can be classified into four groups (1) steroid hormones, (2) peptide and protein hormones, (3) amino acids derivatives, principally the aromatic amino acid tyrosine, and (4) the eicosanoids (fatty acid derivatives).
1. Steroids are lipids, more specifically, derivatives of cholesterol produced by chemical modification.
2. Peptide and protein hormones are synthesized in the cellular endoplasmic reticulum and then transferred to the Golgi apparatus where they are packaged into secretory vesicles for export.
3. Amino acid derivatives: There are two groups of hormones derived from the amino acid tyrosine;thyroid hormones and catecholamines. Thyroid hormones are basically a “double” tyrosine ring incorporating three or four iodine atoms. Catecholamines include epinephrine and norepinephrine that have the capability of functioning as both hormones and neurotransmitters.
4. Eicosanoids are large groups of polyunsaturated fatty acids derivatives like the prostaglandins, prostacyclins, leukotrienes, and thromboxanes.

### Hormone actions at cell level
## Nervous System

The nervous system can be defined as the network of nerve cells and fibers that that sends messages for controlling movement and feeling between the brain and the other parts of the body. This nervous system is composed of the brain and spinal cord, nerves, ganglia, and parts of the receptor organs and that receives and interprets stimulus and transmits impulses to the effector organs.

## Vision System

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