The arteries through which the blood flows away the heart belong to yang ; while the veins through which the blood flows backward to the heart and the lymph vessels through which the lymph flows backward to the heart belong to yin .

The heart is the motive power of blood circulation . All the factors which strengthen excitability and contractility of the heart , strengthen tonicity of the blood vessels , increase blood volume , and raise blood pressure are yang , all the factors which perform the opposite functions are yin .

In microcirculation , all the factors which can cause relaxation of the arterioles , acceleration of bloodflow in the capillaries , filling of the capillaries , and increasing of the number of the opening capillaries are yang , while all the factors which can cause contraction of the arterioles , deficiency of perfusion of the capillaries , deceleration of bloodflow in the capillaries , and decreasing of the number of the opening capillaries are yin .

For hemorrheological characters , the decreasing of hematocrit is yang , while the increasing of it is yin . The decreasing of whole blood viscosity is yang , while the increasing of it is yin . The increasing of fibrinogen is yang , while the decreasing of it is yin . The shortening of erythrocyte electrophoresis time is yang , while the lengthening of it is yin . The rising of sedimentation rate is yang , while the falling of it is yin .

For genesis of tissue fluid , all the factors which increase the genesis of tissue fluid are yin , while all the factors which decrease the genesis of tissue fluid are yang .

For genesis and regurgitation of lymph , all the factors which can promote the genesis and regurgitation of lymph are yang ; while all the factors which can inhibit the genesis and regurgitation of lymph are yin .

F.Yin and Yang for respiration

For respiratory movement,the inspiratory movement is yang , while the expiratory movement is yin . There are the respiratory centers which regulate respiratory movement in the cerebral cortex , pons , medulla oblongata and spinal cord . The centers promoting inspiration are yang , while the centers promoting expiration are yin .

The increasing of [H⁺] and CO₂ in the blood can strengthen respiration , belonging to yang ; while the increasing of O₂ in the blood can weaken respiration , belonging to yin .

G.Yin and Yang for digestion

The digestive system performs the functions of movement ,secretion and absorption . Generally speaking , the factors promoting movement of the digestive canal and secretion of the digestive glands belong to yin ; while the factors promoting absorption of the nutrients and water by the digestive canal belong to yang .

H.Yin and Yang for Energy Metabolism and Thermoregulation

Generally speaking , the factors promoting decomposition of substances and release of energy in the body belong to yang , while the factors inhibiting decomposition of substances in the body , or promoting synthesis of substances and store of energy in it belong to yin .

The main centers of thermoregulation are located in the hypothalamus . The fronter area of the hypothalamus which lies posterior to the optic chiasma mainly promote heat dissipation,belonging to yin ; the rearer area of the hypothalamus mainly promote heat production , belonging to yang . Activity of the muscle , excitement of the sympathetic nerve , secretion of thyroxine , adrenaline , and adrenal cortical hormone can increase heat production , belonging to yang .

The sweat glands are controlled by the sympathetic nerves . The sympathetic postganglionic fibers which control the sweat glands are generally cholinergic fibers , belonging to a part of yin within yang . However , some sweat glands in the face , hands and feet are controlled by the sympathetic adrenergic fibers which belong to a part yang within yang . Therefore , when emotional excitement occurs and the adrenergic fibers of the sympathetic nervous system excites , diaphoresis of such parts as the hands,feet and forehead will occur.

There are diaphoretic centers in the hypothalamus . Stimulation on the anterior portion of cat's hypothalamus which belongs to yin can cause diaphoresis on its claw and metatarsus , while stimulation on the posterior portion of its hypothalamus which belongs to yang can cause decreasing of secretion of the sweat glands .

I.Yin and Yang for Uropoiesis

Generally speaking , increasing of renal bloodflow and rising of glomerular filtration pressure belong to yang ; decreasing of glomerular filtration area caused by fibrosis and atrophy of the glomeruli belongs to yin ; decreasing of glomerular filtration area caused by hyperplasia of the capillary endothelial cells belongs to yang . Increasing of glomerular capillary permeability , which belongs to yang , can cause filtering out of the erythrocytes , leukocytes and plasma protein , forming albuminuria or hematuria . Increasing of reabsorption of water , mineral salts and organic materials by the uriniferous tubules and collecting tubules belongs to yang ; while decreasing of that belongs to yin .Increasing of secretion of K⁺ , H⁺ and NH₃ by the uriniferous tubules and collecting tubules belongs to yin ; which decreasing of that belongs to yang.

J.Yin and Yang for Nervous System

Increasing of excitability of the nervous system belongs to yang ; while increasing of inhibition of it belongs to yin .

Central excitatory transmitters belong to yang ; while central inhibitory transmitters belong to yin .

The content of noradrenaline and that of 5-hydroxytryptamine relate to characters and psychoses. The person in whose body noradrenaline increases has an irascible temperament , and he or she is provocative ; while the person in whose body 5-hydroxytryptamine increases has a calm temperament . The maniacal psychosis relates to increasing of noradrenaline , belonging to yang ; while the depressive psychosis relates to increasing of 5-hydroxytryptamine , belonging to yin .

For the central nervous system and peripheral nervous system which control body movement , the central regions and fiber components which control the extensors and abductors belong to yang ; the central regions and fiber components which control the flexors and adductors belong to yin .

For the vegetative nervous system , the sympathetic nervous system belongs to yang ; while the parasympathetic nervous system belongs to yin . For the sympathetic postganglionic fibers , the sympathetic adrenergic fibers are a part of yang within yang ; while the sympathetic cholinergic fibers are a part of yin within yang .

K.Yin and Yang for Endocrine

The hormones secreted by the endocrine glands can be divided into two kinds : one is nitrogenous hormones , the other is steroid hormones . The nitrogenous hormones act on the receptors on the surface of cell membrane , and they regulate the cells by taking cAMP and cGMP as second messenger . Generally speaking , all the hormones which increase cAMP and decrease cGMP belong to yang ; while all the hormones which decrease cAMP and increase cGMP belong to yin . However , for some hormones , their natures of yin and yang must be determined by analysing other factors . The steroid hormones directly enter the nucleus and regulate the transcription of DNA , thus performing physiological functions . The natures of yin and yang for the steroid hormones can be determined by their day and night rhythms and physiological functions .

Therefore , we can call the hormones belonging to yang nature as yang-natured hormones , and the hormones belonging to yin nature as yin-natured hormones ( Table 2-1) .

Table 2-1 Classification of Yin and Yang for the Main Hormones

L.Yin and Yang for Immunity

Immunization in organism can be divided into specific immunity and nonspecific immunity .

For nonspecific immunization , increasing of cAMP and decreasing of cGMP can promote the phagocytosis of the neutrophilic granulocytes , macrophages and monocytes , belonging to yang ; decreasing of cAMP and increasing of cGMP can inhibit the phagocytosis of the neutrophilic granulocytes , macrophages and monocytes , belonging to yin .

For specific immunization , in the process of immunoreaction , all metabolisms relating to lymphocyte transformation have close relation with cGMP and cAMP . The process of lymphocyte transformation needs coordination of growth and decline of yin and yang . When the lymphocytes are stimulated , yin dominates , performing the function of starting immunoreaction . Then , dominance of yang strengthens , It causing the exposure of the genes on DNA and promoting the entrance of polynucleotide into the cells . After that , dominance of yang weakens , while dominance of yin strengthens . In this time , synthesis of DNA , RNA and protein and division of cells occur.

Immunoreaction is regulated by the vegetative nervous system and endocrine system . The regulation of hypothalamus to immunoreaction is realized by the functions of the vegetative nerves and endocrine glands . There exist of hydrocortisone , insulin , growth hormone , estrogen , androgen , thyroxine,β-adrenaline and acetylcholine in cell membrane and cytoplasm . Under general situation , hydrocortisone , sex hormones , catecholamine and sympathetic adrenergic fibers can cause immunosuppression ; growth hormone , thyroxine , insulin and parasympathetic cholinergic fibers can cause immunological facilitation . Here , the anterior lobe of the hypothalamus is a parasympathetic center , belonging to yang . The function of immunosuppression of hydrocortisone , sex hormones , catecholamine and sympathetic adrenergic fibers belongs to yang , the function of immunological facilitation of growth hormone , insulin and parasympathetic cholinergic fibers belongs to yin , but the function of thyroxine belongs to yang .

For the cells in connective tissue which relate to immunization , the macrophages belong to yang ; while the plasma cells and mast cells belong to yin .

To sum up , the nonspecific immunization belongs to yang ; the specific immunization takes yin as main nature , but takes yang as assistant nature . Therefore , yang deficiency can result in falling of the nonspecific immunization ; both yin deficiency and yang deficiency can result in falling of the specific immunization . When yin deficiency occurs , the functions of both T lymphocytes and B lymphocytes weaken , that is to say , both the cellular immunity and humoral immunity weaken . When yang deficiency occurs , mainly the humoral immunity of B lymphocytes weaken . Yin deficiency is the manifestation of weakening of the function of the parasympathetic nervous system and decreasing of secretion of the yin-natured hormones ; while yang deficiency is the manifestation of weakening of the function of the sympathetic nervous system and decreasing of secretion of the yang-natured hormones . Therefore , for the person with yang-natured constitution , his or her nonspecific immunity is stronger . When he or she is infected by bacteria , acute inflammatory response will occur . For the person with yin-natured constitution , his or her specific immunity is stronger . When he or she is infected by virus , immunoreaction will occur , and he or she is easy to suffer from allergic diseases . It may be seen that only when the organism is in the state of coordination of yin and yang , his or her immunity can be in the best state .

(2).Yin and Yang at the Levels of Cell and Molecule

A.Yin and Yang for Cells : For a whole cell , the nucleus is located in the center of the cell , and contains DNA , belonging to yin . The cytoplasm and cell membrane are located in the periphery . The cytoplasm contains RNA from which proteins can be translated and synthesized ; the various organelles perform different functions and maintain the life activities of a cell ; the cell membrane performs the functions of substance exchange , regulation and protection . Therefore , the cytoplasm and cell membrane belong to yang . Hormones and neurotransmitters regulate the functions of a cell through the receptors on the cell membrane by taking cAMP and cGMP as second messengers , or they realize this regulation by entering directly the nucleus and acting on DNA . Generally speaking , the increasing of synthesis and renew rate of DNA , RNA and functional proteins shows activeness of the functions of cells , belonging to yang ; on the contrary , the decreasing of synthesis and renew rate of DNA , RNA and functional proteins shows inactiveness of the functions of cells , belonging to yin . On the other hand , the quickening of synthesis and duplication of DNA , RNA and structural proteins , and the accelerating of division of cells belong to yin . Therefore , when yin and yang states of cells are studied by taking DNA , RNA and proteins as index , whether the cells are in functional active state , or in divisional active state must be differentiated . The former belonging to yang , while the latter belonging to yin . When yang is excessive , the functions of the cells will be active , the synthesis and renew rate of DNA , RNA and functional proteins will rise ; when yin is excessive , division of the cells will be active , and the synthesis and duplication of DNA , RNA and structural proteins will accelerate . When yang is insufficient , the cells will be hypofunctional , and the synthesis and renew rate of DNA , RNA and functional proteins will fall .

When yin is insufficient , the function of cell division will decline , and the synthesis and duplication of DNA , RNA and structural proteins will decelerate .

B.Yin and Yang for Inorganic Elements : For the essential macroelements in human body, sodium,potassium,calcium and magnesium assume alkalinity inside body,belonging to yin ;phosphorus, sulfur and chlorine assume acidity inside body , belonging to yang . For sodium, potassium , calcium and magnesium , they can be subdivided into yin and yang . The stronger the alkalinity of a kind of ion is , the stronger its yin nature is ; while the stronger the acidity of a kind of ion is , the stronger its yang nature is . Therefore , the yang nature of phosphorus , sulfur and chlorine increases progressively in turn , while the yin nature of these elements decreases progressively in turn . For trace elements , iron , cobalt , molybdenum , fluorine and bromine belong to yang ; copper , manganese and chromium belong to yin ; zinc and selenium belong to neutrality . Inorganic iodine generally belongs to yin , but when it is insufficient , excess of yang will occur . Iodine which makes up thyroxine belongs to yang .

(3).Yin and Yang in the Sense of Biothermodynamics

Human body is a biothermodynamic system . In this system , increasing of entropy is yang , while decreasing of entropy is yin .

[2].Rhythms of Yin and Yang

One cycle of the earth's revolution around the sun is a year ; one cycle of the moon's revolution around the earth is a month ; one cycle of the earth's rotation is a day . In the long evolutional process , to adapt to the changes of nature , human body gradually forms changes of year rhythms , month rhythms and day rhythms .

(1).Year Rhythms

A.Year Rhythms of Yin and Yang of Nature : When the earth revolves around the sun for one cycle , it undergoes spring , summer , autumn and winter four seasons , or twenty-four solar terms . In a year , atmospheric temperature shows a tendency to go up in spring and summer which belong to yang , and it shows a tendency to go down in autumn and winter which belong to yin . At the Beginning of Autumn , " Yin energy slightly increases , but yang energy slightly decreases ," atmospheric temperature starts decreasing from peak value ; at the Beginning of Spring ," Yang energy slightly increases , but yin energy slightly decreases ", atmospheric temperature starts increasing from minimum value . This tallies with the actual result from determination . For yearly change of relative humidity , in general , it is minimum in summer and maximum in winter . For yearly change of atmospheric pressure , in general , it is the lowest in summer and the highest in winter .

B.Year Rhythms of Yin and Yang of Human Body : Noradrenaline in the brain shows change of year rhythm . Its highest concentration appears in January to July , while its lowest concentration appears in August to October . The cyclic change of 5-hydroxytryptamine in the brain is contrary to that of noradrenaline . Here , noradrenaline belongs to yang , and its concentration increases in spring and summer but decreases in autumn and winter ; while 5-hydroxytryptamine belongs to yin , and its concentration decreases in spring and summer but increases in autumn and winter . 24-hour output of catecholamine in urine is the lowest in summer and the highest in winter . Catecholamine belongs to yang . It decreases in summer when yang energy of nature is the strongest and increases in winter when yin energy of nature is the strongest so as to coordinate balance in the body . In July to September , the secretion of testosterone in the male is the highest . Testosterone belongs to yang , and it reaches peak value in summer and autumn when yang energy is strong to match with rhythm of nature .

Pulse condition shows change of year rhythm. In winter , pulse rate is quicker than that in summer . Pulse tends to be sunken in winter and spring and to be floating in summer and autumn . The amplitude parameters of sphygmograms are maximum in summer and minimum in winter . Quickness , float and high amplitude of pulse belong to yang , but the contrary belong to yin . To coordinate yin and yang in the body , pulse quickens in winter when yin energy is strong , while it slows in summer when yang energy is strong . Pulse tends to be sunken in winter and spring and to be floating in summer and autumn ; the amplitude parameters of the sphygmograms are maximum in summer and minimum in winter ; these match with yin and yang rhythms of nature .