Encyclopedia of Family Medicine

Chapter 3 Human Body and Nutrition (3)
The height of a person is determined by the bones, and mainly depends on the length of the bones of the lower limbs.There are three peaks in the growth of bones from birth to adulthood: the first is within half a year after birth, with an average monthly growth of 2 cm in length; the second is from 5 to 1 years old, during which the height is about 3 cm; The third is the puberty period, that is, from 20 to 12 years old to 13 to 22 years old. During this period, the average annual height growth is 23 to 6 centimeters, and the maximum can reach 8 to 10 centimeters.Girls generally reach the age of 11, and boys generally reach the age of 19. The bone growth is over, and the growth of height will naturally stop.

From the perspective of chemical composition, bones are composed of two types of substances: one is organic matter, mainly protein and glial fibers; the other is inorganic salts, mainly calcium phosphate and calcium carbonate.

The heart is the life pump of the human body
From the time the fetus begins to form a heart at 2 weeks, to birth, growing up, aging, and until the last breath of life, our heart has to work continuously for a lifetime.The beating of the heart promotes blood circulation, transports oxygen and nutrients to various tissues of the body, transports away waste, and ensures the smooth progress of life activities.

The heart of an adult is about the size of your own fist and weighs about 250 grams.The heart is surrounded by a membrane called the pericardium, which has a protective effect on the heart.The heart is divided into four chambers: the left atrium, left ventricle, right atrium, and right ventricle.

The left atrium receives oxygen-rich and nutrient-rich blood from the lungs.The left atrium contracts to send blood into the left ventricle, and the left ventricle contracts to send blood into the aorta and on to the body.Blood flows from the left ventricle through the whole body and then returns to the right atrium of the heart. This cycle is called the systemic circulation, also known as the general circulation.

The right atrium pumps blood into the right ventricle, and the right ventricle contracts to send blood into the pulmonary artery. When the blood flows through the lungs, it discharges carbon dioxide, carries oxygen, and then returns to the left atrium of the heart through the pulmonary veins.This section of circulation is called the pulmonary circulation, also known as the small circulation.

Under the impetus of the heart, the blood runs continuously along the large circulation and the small circulation, and the life is endless and the circulation is endless.

There are valves between the atria and ventricles, as well as between the heart and the arteries, to ensure that the blood flows in one direction and cannot flow back.Heart sounds are the sounds produced by valves opening and closing.

Calculated at 75 beats per minute, each cardiac cycle is 0.8 seconds.In 0 seconds, 8 seconds for ventricular contraction and 0.3 seconds for relaxation; 0.5 seconds for atrial contraction and 0 seconds for relaxation.That is, both the atrium and the ventricle have much longer diastolic or rest periods than systolic periods.This is why the heart can keep beating without getting tired.

Blood vessels are the transport conduits of the human body

The circulatory system composed of various types of blood vessels and the heart is a sealed network of pipes throughout the body in our body, in which blood circulates to complete the task of transporting oxygen, nutrients and metabolic waste.Blood vessels are important transportation channels in the human body.

The blood vessels that carry blood from the heart to the body are called arteries.Arterial blood vessels can pulsate with the beating of the heart, and arteries in the superficial parts of the body can be touched by hand.Every part of the body, every tissue and organ, has an arterial branch to supply blood.For example, the head has the common carotid artery, the liver has the hepatic artery, the heart has the coronary arteries, and so on.

The walls of arterial vessels are rich in elastic fibers.Therefore, the arteries have better elasticity and can withstand the pressure generated by the contraction of the heart.This pressure on the arteries is called blood pressure.

The blood vessels responsible for carrying blood throughout the body back to the heart are called veins.Veins are generally accompanied by arteries and have the same name, such as the vein accompanying the femoral artery is called the femoral vein.

Veins, as the name suggests, are immobile blood vessels.The blood in the venous blood vessels has no power. The reason why the venous blood can flow in the direction of the heart is mainly by the negative pressure generated by the diastole of the heart, by the contraction and extrusion of the muscles around the blood vessels, and by the veins born in the venous blood vessels. Because of the venous valve, the blood in the vein can only flow to the heart and not back.

The smallest blood vessels that connect arterioles and venules are called capillaries.Capillaries are formed by branching off the ends of arterioles.Capillaries join to form venous plexuses.The oxygen and various nutrients loaded in the blood can only be unloaded when they reach the capillaries.Carbon dioxide and other wastes produced in the body can only enter the blood and be transported away through the capillaries.

Cycle of blood circulation
Pushed by the pressure generated by the contraction of the heart, blood flows continuously along the blood vessels, and its main function is transportation.For example, various nutrients digested and absorbed from the intestine.In addition, the oxygen inhaled from the lungs is transported to the whole body by the blood to supply the needs of various tissues and organs; the carbon dioxide and various wastes produced by the tissues of the whole body in the life activities also rely on the blood to transport them to the lungs and kidneys for excretion go out.

我们身体里究竟有多少血液呢？在心血管系统中流动着的全部血量约占体重的8％，或说占体重的约1／13。一个体重60公斤的人，他的循环血量约有4.8公斤，相当于每公斤体重有血液80毫升。

In a calm state, not all the blood in the body is involved in the circulation, but part of it is stored in the capillaries of the liver, spleen, and skin.We call these organs "blood banks".

Blood is red because red blood cells contain a red protein called hemoglobin.

In 1 cubic millimeter of blood, there are about 500 million red blood cells, slightly more in men and slightly less in women.The average lifespan of red blood cells is about 120 days, and the metabolism of red blood cells is very fast. In 120 days, all the red blood cells in our blood will be renewed.

White blood cells are the guards of our body.Its main function is to engulf bacteria that invade the body.The number of inflamed white blood cells in the body will increase. Generally speaking, the number of white blood cells remains between 5000 and 10000 per cubic millimeter.

Platelets are small, colorless blood cells.Its main function is to coagulate blood together with other coagulation substances in plasma.There are 20 to 40 platelets per cubic millimeter, and the average lifespan of platelets is only a few days.

Functions of the Lymphatic System

The lymphatic system includes lymphatic vessels, lymph nodes, spleen and the lymph fluid that runs in it.

Lymphatic vessels are a set of pipeline systems from thin to thick, and from small to large. The smallest lymphatic vessels are called lymphatic capillaries.The beginning of the lymphatic capillary is the blind end, which receives the fluid between tissue cells and infiltrates into the tube to form lymph.The capillary lymphatic vessels converge to form small, medium and large lymphatic vessels, and finally the two largest lymphatic vessels, the thoracic duct and the right lymphatic duct, are connected to the large vein at the root of the neck, and the lymph fluid flows into the blood circulation.

Lymphatic vessels are tubes composed of a thin layer of endothelial cells, and the lymphatic fluid in the tubes is not pushed forward by the beating of the heart, and there is no pressure, so it is difficult for the lymphatic vessels to feel its existence at ordinary times.It is easy to find it only when it is inflamed. For example, sometimes the hands or feet are inflamed, and red lines appear on the arms or legs. This is the inflamed lymphatic vessels. The lymphatic vessels are highly permeable, so inflammation and malignant tumors can easily pass through the lymphatic vessels Transfer the tube to another location.

There are many lymph nodes along the way of the lymphatic vessels.Lymph nodes are mainly glandular structures formed by the collection of lymphocytes, broad bean-shaped, and are mostly distributed in the neck, mesentery, armpits, groin, and hilum.Lymph nodes have the function of phagocytizing foreign matter such as bacteria and metastatic tumor cells, so lymph nodes have the function of eliminating harmful substances that invade the body.

The spleen is the most important place for storing blood and the largest lymphoid organ, with functions such as filtering blood, destroying aging red blood cells, regulating blood volume and producing lymphocytes.About 12 cm long, located in the upper left part of the abdominal cavity.

The tonsils located in the throat are lymphoid tissues similar in structure to the spleen and lymph nodes, and also have the function of destroying bacteria.If frequent inflammation becomes a lesion, it can be removed surgically.

Functions of the endocrine system
Endocrine glands are proposed as opposed to exocrine glands. Exocrine glands, such as salivary glands, sweat glands, lacrimal glands, etc., excrete secretions through ducts, while endocrine glands do not have ducts, and their secretion hormones directly enter the blood circulation to run To the whole body to play a role.

The various hormones produced by the endocrine glands have a significant impact on the physiological functions of the human body. In addition to regulating the development, digestion, metabolism, libido, hair growth and tone of the human body, they also affect the secondary sexual characteristics (that is, some of the main physiological characteristics of men and women). characteristics), and govern human behavior and other related factors.

The endocrine glands mainly include the pituitary gland, hypothalamus, thyroid, parathyroid, adrenal glands, pancreatic islets, and gonads.

The pituitary gland is an oval organ about 1 cm wide and 5 cm high and weighs less than 1 gram.Although the pituitary gland is small, it is the most important endocrine gland.It is involved in the function of almost all endocrine glands.The pituitary gland secretes gonadotropins, thyroid-stimulating hormones, and adrenocorticotropic hormones to promote the function of each gland.It also secretes growth hormone (high tube length), vasopressin and prolactin, which have the functions of promoting growth, raising blood pressure, and promoting milk secretion.

The hypothalamus is close to the pituitary gland, and the hypothalamus directly controls some functions of the pituitary gland by secreting neurohormones.

The thyroid gland is located below the Adam's apple in the front of the neck. Thyroxine, which is produced from protein and iodine, regulates the body's metabolism.

The adrenal glands are located at the upper ends of the kidneys on both sides. The adrenal cortex hormones secreted can regulate the metabolism of sugar and protein, and the sex corticosteroids can promote the development of secondary sexual characteristics of men and women.

Sex hormones secreted by male and female gonads regulate the functioning of the entire reproductive system.

Insulin secreted by pancreatic islets in the pancreas regulates blood sugar metabolism.

Components of the female reproductive system
Female reproductive organs include the ovaries, fallopian tubes, uterus, vagina, clitoris, Bartholin's glands, labia majora, and labia minora.

The ovary is the most important female reproductive organ, it can produce female reproductive cells - eggs, and can also secrete female hormones.The ovaries are located on both sides of the uterus. The ovaries of adult women are about 4 cm long and 2 cm wide, and are oval in shape.In the parenchyma of the ovary there are many groups of cells of various sizes called follicles.There is a large cell in the center of each follicle, which is the largest cell in the human body-the egg cell.Adult healthy women excrete mature egg cells from the ovaries about once every 28 days.The estrogen and progesterone secreted by the ovary can promote the growth of breast and endometrium, etc.

The fallopian tubes are the tubes that transport the egg cells, one on the left and one on the left.One end is a trumpet-shaped opening, and the other end leads to the uterine cavity.Sperm and eggs are generally fertilized in the fallopian tube, the tube wall smooth muscle and mucous membrane cilia are active, pushing the fertilized egg to move towards the uterus, and finally reach the uterus to form an embryo.

The shape of the uterus is like an upside-down pear, with the large upper part called the fundus and the narrow lower part called the cervix, which is connected to the vagina.A series of periodic changes occur in the endometrium of adult women, including the stages of endometrial hyperplasia, secretion, shedding and repair.Menstruation is the period when the intimal shedding is accompanied by bleeding.If you are pregnant, the endometrium and muscles will gradually thicken to meet the needs of the fetus.

The mons pubis, labia minora, clitoris, vagina and accessory glands form the female external genitalia, or vulva.The front ends of the labia minora meet to form the clitoris, and there is a small undeveloped spongy tissue inside, which has a structure similar to that of a male penis and can also be erected.The vestibule of the vagina is formed between the labia minora on both sides, and there are Bartholin glands, which secrete fluid and help lubricate.There is an annular or half-moon-shaped flap of mucous membrane around the vaginal opening, the hymen.

Components of the male reproductive system
When a child is born, the heart, lung, digestive, urinary and other systems begin to work, only the reproductive system basically has nothing to do before the age of 10.After the puberty period, the reproductive organs mature. Around the age of 15, girls have regular ovulation and menstruation, and boys have sperm production and nocturnal emission, marking the gradual maturity of sex and the function of the reproductive system. Start running.

In terms of reproductive function, men are much simpler than women.Male reproductive organs include the penis, urethra, bulbourethral glands, prostate, scrotum, vas deferens, epididymis and testes.

The most important male reproductive organs are the testicles, and the others are accessory reproductive organs.The testis is the male gonad, which has two major functions: one is to produce sex cells, that is, germ cells—sperm, and the other is to produce sex hormones.Sperm are shaped like tadpoles, with an oval head followed by a neck and a long tail.Adult sperm is about 0.06 mm long, and under favorable conditions, it can survive for as long as 100 hours.

The testes can produce hundreds of millions of sperm every day, and normal semen contains about 1 million sperm per milliliter.Sperm can only be active in semen. Semen is seminal plasma, which is composed of fluids secreted by the prostate, seminal vesicles, and bulbourethral glands.Semen is alkaline, which can neutralize the acidity in the female vagina, which is conducive to the movement of sperm.

Sperm are divided into two types according to the sex-determining chromosomes they contain: one with chromosome X and one with chromosome Y.If a sperm with an X chromosome enters the egg at the time of fertilization, the fetus is a female; if a sperm with a Y chromosome enters the egg, the fetus is a male.It can be seen that the sex of the offspring is determined by the sperm.In hundreds of millions of sperm, X and Y are half and half, and the determination of the sex of the fetus is purely accidental.

blood type is inherited

A person's blood type is determined by the blood types of their parents, that is, inherited.

If both sides of a couple are type O, but their child is type A, B or AB, it can be asserted that the child was not born to the couple.But if the child is also type O, it is not certain that the child is their biological child, because other blood types may also give birth to children with type O blood.

human body's nutritional needs

Relying on various biological resources on the earth, human beings develop national diets with unique styles according to local and time conditions, and can constitute nutrition in many different ways and various foods, all in order to obtain the same result: That is, to get all the nutrients people need through the diet, and there are both sufficient quantities and appropriate proportions.To sum up, the most basic requirements of the human body for nutrition are:
(1) Supply heat and energy so that it can maintain body temperature and meet the needs of physiological activities and labor;
(2) Constitute body tissues and supply materials needed for growth, development and tissue self-renewal;

(3) Protect the function of organs, regulate the metabolic response, so that the work of each part of the body can be carried out normally.

The nutritional function of food is achieved through the nutrients it contains, and these effective ingredients are called nutrients.They include: protein, fat, carbohydrates (also called sugars), vitamins, minerals (trace elements), and water and dietary fiber.

It is known that there are about 50 kinds of substances necessary for the human body.In reality, there is no food that can provide nutrients according to the quantity required by the human body and the desired suitable ratio.Therefore, in order to meet the nutritional needs, it is necessary to ingest a variety of foods and find out the most beneficial and delicious food ratio.Experience has shown that it is more beneficial for healthy people to consume nutrients in the amounts recommended by science.

nutrition science

Sun Simiao, a doctor in the Tang Dynasty, first realized that he would get beriberi (or vitamin B deficiency) if he did not eat omnivorous food and only ate white rice.People have realized through long-term practice that no natural food can contain all kinds of nutrients that the human body needs.Even the well-recognized nutritional products like milk and eggs are inevitably "fly in the ointment".For example, the milk that babies depend on is deficient in iron.If a half-year-old baby is supplemented with iron-containing complementary foods at an inappropriate time, nutritional anemia will occur; another example is eggs, which are nutrient-rich, but lack the vitamin C needed by the human body.Therefore, it is impossible to maintain human health by relying on one kind of food, no matter how large the quantity is.That is to say, eating a full stomach does not mean that there is enough nutrition, unless the food you eat also contains various nutrients that the human body needs.The reverse is also true, although the quality is fine but the quantity is insufficient, it is also impossible to maintain health and promote growth.Therefore, in order to ensure reasonable nutrition, the variety of food should be as diverse as possible, so that the quantity of calories and various nutrients is sufficient and the proportion is appropriate, and excessive and insufficient will cause adverse consequences.Excessive nutrition, such as excessive calorie intake, can cause obesity, which in turn induces hypertension, diabetes, coronary heart disease, etc. The consequences are more serious than obesity itself.Nutritional deficiency can cause nutritional edema, as well as a series of diseases such as anemia, night blindness, beriberi, pellagra, scurvy, and rickets.In conclusion, the consequences of malnutrition (excessive and deficient) are severe.Therefore, the diet must be restrained, pay attention to nutritional science.

nutritionally reasonable standards

(End of this chapter)