Encyclopedia of Family Medicine

Chapter 2 Human Body and Nutrition (2)
There are cold feeling points and hot feeling points on the skin, and there are more cold points than hot spots. It is estimated that there are 25 cold feeling points and about 3 hot feeling points on the skin of the whole body.Generally speaking, when the external temperature is below 45 degrees Celsius, there will be a warm feeling, and when it exceeds 45 degrees Celsius, there will be a hot feeling, which is because the pain nerves are excited.

The role of sweating

Sweat glands are small glands located in the skin.It consists of a small tube with a diameter of 0.3-0 mm and a length of about 4-5 mm.The small tubes are curled into a ball inside the skin, like a small ball of wool. This is the gland of the sweat gland, which is in charge of secreting sweat.The inner end of the hepatic duct is a blind end, and the outer end opens on the surface of the skin. The opening looks like a small funnel, called a sweat pore.Sweat is excreted from here.

Human sweat glands are very developed, with about 200 to 500 million sweat glands in the whole body.There are abundant capillaries around each sweat gland, and the moisture and other components in the sweat are permeated from the blood.When the weather is hot or when strenuous exercise is performed, the sweat glands spread all over the body, and the secretion of a large number of sweat glands is stepped up. For a long time, 5-10 kilograms of sweat can be produced a day, enough to hold half a bucket of water.

The first function of sweating is to dissipate heat and regulate body temperature.When the external temperature is close to or exceeds the skin temperature, the heat dissipation methods of radiation, conduction and convection are not very effective. At this time, the main form of body heat dissipation is sweating and evaporation.It is determined that each 1 gram of sweat can take away 0 kcal of heat when it evaporates from the skin.

Dogs and chickens don't have sweat glands, so these animals dissipate heat by panting and flapping their wings.

出汗的第二个功能是排泄。汗液里99．2~99．7%是水分，另外0．2~0．8％是氯化钠（盐）、尿素、乳酸、钾、钙等物质。出汗对调节身体的水盐代谢具有一定作用。

There are about 100 milligrams of sodium chloride in every 300 grams of sweat.When sweating too much in a high temperature environment, pay attention to replenishing water and salt, otherwise it is easy to suffer from heat stroke.The heat stroke caused by salt deficiency is mainly manifested as muscle cramps, so it is also called heat cramps.

hair metabolism

Hair, like all tissues in our body, is constantly metabolized.The life of hair is divided into two periods: the growth period and the rest period, collectively known as the hair cycle.

Anagen is the period of hair growth, growing an average of 320 microns per day.After entering the telogen phase, the hair no longer grows.

The growth period of human hair is 2-7 years, and the resting period is 5-6 months.The hair that enters the resting period will fall off automatically as long as it encounters slight mechanical stimulation, such as washing or combing, which is called physiological hair loss.After the old hair falls off, new hair will grow from the hair bulb of the hair root to replace the old with the new.

我们黄种人平均有头发108 000根。在某一个特定时间里，我们头上的头发85~90％是处于生长期的，另10~15％则是处在休止期的。休止期的头发约有1万根左右。休止期按6个月计算，每天就会有约60根头发脱落，多时可达100根。

Life experience tells us that more hair sheds every autumn, which is not the same as the shedding and molting of some animals.Animal hair enters the telogen phase almost at the same time, so hair removal is more concentrated.And human hair is "individual", each hair has its own separate growth period and rest period, generally there is no phenomenon that most hairs enter the rest period at the same time.If the hair on a certain scalp enters the telogen phase and falls off at the same time, this is "alopecia areata", don't worry, this kind of alopecia areata will heal on its own.The reason for more hair loss in autumn is that in summer, the sun is exposed to ultraviolet rays, excessive sweating, and sweat accumulation, etc., so that the hair in the resting period will go through a transition period of 1 to 2 months, and then fall off more in autumn.

There are 400 to 900 sebaceous glands per square centimeter on the scalp, which secrete sebum at any time, moisturizing and maintaining the hair.

Growth period of deciduous teeth and permanent teeth
Baby teeth begin to erupt 6-7 months after birth, and by the end of 2 years, all 20 deciduous teeth will appear.

乳牙萌出的时间早晚有些差别，早者4个月已见，晚者9~10个月方才出来，都在正常范围之内。满周岁时大约长出6~8个乳牙。乳牙总数大约等于婴儿月龄减6。

Permanent teeth begin to erupt at age 6. The first permanent teeth erupt at the age of 6 are the first molars, also known as 6th age teeth. There are 6 4th-year-old teeth, because they are the first permanent teeth to erupt, like 4 pillars erected at the key positions of the gums, which have an impact on the growth of all teeth, so special attention should be paid to the protection of 6th-year-old teeth.

恒牙共有32颗，包括8颗门齿（又叫切齿）、4颗尖齿（又叫犬齿）、8颗小臼齿、8颗大臼齿及4颗智齿（又叫尽头牙）。

The stomach is the warehouse of the human body

The stomach is a warehouse for storing food, and traditional Chinese medicine calls the stomach "the sea of ​​water and valleys".

The stomach is between the esophagus and the 12th intestine, and is the widest part of the digestive tract. Its shape and position change with the amount of content and body position.

The stomach is divided into 4 parts, the part near the esophagus is the cardia, the enlarged part of the upper part of the stomach is the bottom of the stomach, the part from the bottom of the stomach is the body of the stomach, and the part near the 12-denum is called the pylorus.

The inner wall of the stomach is covered with a layer of gastric mucosa with a thickness of about 0.3 to 1.5 mm. There are three kinds of glands growing on the gastric mucosa: namely, cardiac glands, fundic glands and pyloric glands.The combined quantity of the three glands is astonishing, and the amount of gastric juice secreted every day is about 1500-2500 milliliters.

The cardia and pyloric glands mainly secrete mucus, which protects the gastric mucosa.Neither the strong stimulation of gastric acid nor the strong digestion of pepsin can damage the gastric mucosa, mainly because mucus is always secreted before gastric acid and pepsin, and is evenly distributed on the stomach wall.This ingenious self-protection function of the gastric mucosa is one of the breathtaking masterpieces of nature.

The function of the stomach:

(1) Store food.Liquid food stays in the stomach for a short time, oily food stays in the stomach for a long time, and mixed food stays in the stomach for about 4 to 6 hours.

(2) Pepsin can digest protein in food.

(3) Manufacture intrinsic factor and absorb vitamin B12.

(4) Stomach acid can kill bacteria that enter the stomach with food.

When there is food in the stomach, the direction of gastric peristalsis is from the cardia to the pylorus. When the contents of the stomach are emptied and the blood sugar is consumed to a low level, the stomach will reverse the direction of peristalsis from the pylorus to the cardia. This is called hunger peristalsis. Make people feel hungry.

The liver is the "chemical factory" of the human body

The liver is the largest internal organ in the human body, and the liver of an adult weighs about 1500 grams.The liver is located in the upper right part of the abdominal cavity, below the transverse diaphragm, and inside the right costal arch. It is fixed by 8 ligaments, a layer of capsule and rich connective tissue.

The liver is divided into left and right lobes, the left lobe is small and thin, and the right lobe is large and thick.There is a door in the lower center of the liver, called the hepatic hilum, from which blood vessels, nerves and lymphatic vessels enter the liver, and the common bile duct, which is responsible for transporting the bile secreted by the liver, also exits the liver from here, sending bile to the gallbladder and twelve In the intestines.

The basic unit of liver structure is the hepatic lobule, which is about 1.5 mm in diameter.Under the microscope, it can be clearly seen that there are numerous irregular polygonal hepatocytes in the hepatic lobule.There are 1-2 central veins in the center of the hepatic lobule, and liver cells are arranged radially around the central vein.Between the hepatic lobules are arteries, venous vessels, and small bile ducts.The bile secreted by the hepatic lobules enters the small bile ducts, which finally merge into a large common bile duct.

The liver can secrete about 800-1000 ml of bile every day.The bile salts in bile emulsify fats into tiny droplets for the enzymes in the digestive juices to digest.

All kinds of nutrients absorbed from the intestine must be processed by the liver before entering the blood circulation of the whole body. Therefore, the liver is not only a digestive gland, but also an important metabolic organ.The liver processes the nutrients absorbed from the intestinal tract into something that the human body can use, and then sends it to the whole body through the blood circulation.If the nutrients absorbed by the intestines are not needed by the body temporarily, the liver can also store these substances.It seems that the liver is not only like a chemical factory, but also like a warehouse.

Most of the various toxic and harmful substances entering the human body are also detoxified in the liver and then excreted from the body.

The human body absorbs nutrients mainly through the small intestine

The stomach undergoes preliminary processing of the food, so that the food becomes porridge-like chyme. With the peristalsis of the stomach, it passes through the exit pylorus of the stomach in batches and enters the small intestine.

The small intestine is divided into three sections from top to bottom: the duodenum, jejunum, and ileum.The total length of the small intestine is about 6-9 meters.

The small intestine following the stomach is called the duodenum.Its name suggests that it is about as long as 12 human fingers lined up, about 25 centimeters.Both the common bile duct from the liver and the pancreatic duct from the pancreas are at the opening of the duodenum, so the duodenum plays an important role in digestion.

The small intestine below the duodenum is the most important part of the intestine, called the jejunum. More than 90% of the nutrients we eat are absorbed in this small intestine.

The mucosa of the inner wall of the jejunum is folded into a corrugated groove ring by ring.Some folds are as high as 7 mm.There are also 500 million small intestinal villi densely packed on the jejunal mucosa.Due to the folds and so many small intestinal villi, the total area of ​​the small intestinal mucosa reaches 550 square meters, which is equivalent to the size of a basketball court.This creates favorable conditions for the full digestion and absorption of food.

The last section of the small intestine is called the ileum, and the digestion and absorption capacity of the ileum is relatively poor.The end of the ileum communicates with the cecum, the head of the large intestine, and sends food residues to the large intestine.There is an ileocecal office between the ileum and the cecum, which prevents the contents of the large intestine from flowing back into the small intestine.

The composition and function of the large intestine
The large intestine consists of three parts: cecum, colon and rectum. The large intestine of an adult is about 1.5 meters long.

The beginning of the large intestine is a blind end, called the cecum, and the human cecum is only about 6 to 8 cm long.The cecum of herbivores is very developed. For example, the cecum of a horse is 60 to 70 centimeters, the volume of the cecum of a rabbit is 30 times that of the stomach, and the length of the cecum of an Australian kangaroo is 2 times that of the body.

At the lower end of our human cecum, there is a small growth like an earthworm, about 5 to 7 cm long, which is the appendix.The lumen of the appendix is ​​narrow and easily blocked and inflamed.So far, people have not figured out what the function of the appendix in the end.

From the cecum up is the colon.The colon wraps around the small intestine and circles the entire abdominal cavity in a large circle, like a "gate". The ascending colon starts from the lower right abdomen; the transverse colon turns to the left under the liver in the upper right abdomen; The abdomen turns downward again, and this section is called the descending colon; after reaching the left lower abdomen, the colon turns a bend and connects to the rectum. This section is shaped like the word "B", so it is called the sigmoid colon.

The transverse section of the colon, namely the lower part of the transverse colon, is hung with a curtain-like membrane called the greater omentum.In addition to protecting the internal organs such as the gastrointestinal tract, the omentum is also one of the fat stores in the body.When people are fat, they will have a big belly, mainly because there is too much fat in the omentum.

There are food residues and water in the colon, which is a weak alkaline environment, which is very suitable for bacterial growth. The colon has almost become the base camp of bacteria.The colon seems to have no important role other than storing food scraps, absorbing water and small amounts of inorganic salts.However, the importance of the colon appears to have increased due to the presence of large numbers of bacteria.Because bacteria can synthesize vitamins such as vitamin K in the process of metabolism, which can be supplied to the human body.

The rectum is about 15 to 20 cm long and is the last section of the digestive tract. Feces are excreted from the rectum through the anus.

The main functions of the urinary system

The human body has a complete system for excreting waste water. This is the sewer in our body, that is, the urinary system, including the kidneys, and the ureters, bladder and urethra that cooperate with the kidneys to complete the urination task.

Kidneys, commonly known as kidneys, are shaped like broad beans. The two together weigh about 250 grams and are located on both sides of the back waist.

The main function of the kidneys is to excrete all metabolic wastes that can dissolve in water in the body.

The way the kidneys excrete waste is extremely ingenious.When the renal artery enters the kidney, it is immediately brought into a plexus of microvascular plexus, each microvascular plexus forms a glomerulus, and the glomerulus is tightly wrapped by two layers of membranes.These two membranes are connected by a small tube called the renal tubule.Glomeruli, membranes and renal tubules form a basic functional unit of the kidney, called nephron, also known as nephron.Each kidney has 100 to 150 million nephrons.The nephron is a small filter.The diameter of a glomerulus is about 0.02 cm, and the total filtering area of ​​all the glomeruli of the two kidneys together is 1 square meters.

平均每分钟约有1．5升血液流经肾脏，一天中流往肾脏的血液量大约是2000升。人体内的全部血液被肾脏过滤一遍所需时间不过4分钟。这就是说，我们全身上的血液每昼夜要流过肾脏360次。每昼夜肾脏约从过滤的2000升血液中产生出1~2公升尿液。

When the kidney is sick and loses its ability to filter urine, an artificial kidney, also called renal dialysis, can be used to remove waste from the blood.In recent years, kidney transplantation, that is, replacing a diseased kidney with a healthy kidney, has been widely used.

There is a ureter under each kidney, which drains the urine into the bladder, and finally excretes the urine through the urethra.

The important role of the respiratory system

One of the basic conditions for maintaining human life activities is to constantly inhale oxygen.And excrete the carbon dioxide produced by the metabolism in the body at any time.The organ that performs this important function is the respiratory system.

The respiratory system includes the respiratory tract and the lungs.The respiratory tract is the tube that transports gases, including the nose, mouth, throat, trachea, and bronchi.The respiratory tract is further divided into upper respiratory tract and lower respiratory tract. The upper respiratory tract includes the nose, mouth, and throat, and the lower respiratory tract includes the trachea and bronchi.

There are abundant blood vessels on the mucous membrane of the respiratory tract, the mucous membrane is covered with a layer of mucus, and there are also slender cilia, so the respiratory tract has the following functions: ① humidify and warm the inhaled air; ② filter the air to prevent dust from entering Lungs; ③ It also has a disinfection effect on the air.

The trachea is about 12 cm long and 2 cm thick, and the lower end is divided into left and right main bronchi.The right main bronchus is a direct extension of the trachea, and the angle is relatively straight, so there are more chances of tracheal foreign bodies getting stuck in the right main bronchus than the left.

The lungs are divided into left and right lungs, which are located on the left and right sides of the chest cavity.The right lung is divided into upper, middle and lower lobes, while the left lung has only upper and lower lobes.

The bronchi are divided into bronchioles, which are further divided into bronchioles, until the terminal bronchioles exchange gas with the lungs - the alveoli.

Alveoli are the smallest breathing units in the lungs.Consists of a very thin membrane surrounded by a network of capillaries.The gases in the blood and the air in the alveoli, mainly oxygen and carbon dioxide, can be fully exchanged here.

Types of muscles in the human body
Muscle is one of the basic tissues of the human body, composed of muscle cells.Muscle cells are fibrous.They are thin and long, so they are also called muscle fibers.Muscle has the characteristic of contraction, and it is the power source of physiological activities such as body and limb movement, digestion, respiration, circulation, and excretion in the body.

There are three types of muscles in the human body:

——Smooth muscle: distributed in the stomach, blood vessels, trachea and other parts.The contraction and relaxation of smooth muscle are dominated by autonomic nerves and hormones, and cannot follow the subjective will of human beings, so it is also called involuntary muscle.

- Myocardium: The muscles that make up the wall of the heart.The heart muscle has an automatic rhythm and conduction system, so the heart muscle beats rhythmically.

- Skeletal muscle: Named because it is attached to the bone.There are stripes on the muscle fibers, so it is also called striated muscle.Because it can move voluntarily, it is also called voluntary muscle.

Our whole body has 639 skeletal muscles.The largest muscle is the quadriceps on the front of the thigh, which can weigh up to 2 kg in an adult.The smallest skeletal muscles weigh only a few grams.

Among the ranks of more than 600 voluntary muscles, there are some special muscles, which are facial muscles, also called facial muscles.They are different from the general skeletal muscle where both ends are attached to the bone road.Some are attached to the bone at one end and the other end is attached to the skin; some both ends are only attached to the subcutaneous tissue.People's various expressions such as joy, anger, sorrow, and joy are produced by the facial muscles pulling the facial skin.

Muscle, like other tissues in our body, is "use it or lose it".Muscles that are often exercised will become thick and strong, while muscles that are not exercised and exercised will atrophy and become weak.Lack of muscle exercise is one of the outstanding problems that endanger the health of modern people.

"Life lies in movement", today, we feel that this sentence is a wise saying.

Bones are the backbone of the body
Bones are the scaffolding of our body.

The bones in our body are divided into three types according to their location: skull, trunk and limb bones.

全身的骨头共有212块，分布如下：头颅25块；脊柱34块；胸廓25块；肩胛带4块；手臂6块；手掌54块；骨盆6块，腿部6块；脚掌52块。

These 212 bones are of different sizes and shapes, and each has its own unique function. These bones also have their own names.The ingenious combination of these more than 200 bones forms a complete human skeleton.

骨骼的功能主要有：（1）构成人体的支架和外形；（2）在肌肉牵引下产生有效的动作；（3）保护内脏器官；（4）造血，制造红血球、骨盆、脊椎骨、肩胛骨和颅骨等扁状骨头的骨髓腔里都有制造红血球的红骨髓。四肢长骨的骨髓腔里几乎都是脂肪，叫黄骨髓。基本上不具备造血功能；（5）储存钙质。

(End of this chapter)