What Is Cholesterol Homeostasis?

This entry is aimed at the content chapter of "Secondary Environment and Steady State of the Human Body" of Senior 2 biology, and adopts "problem solving teaching" for teaching design. Introduce first, then introduce the internal environment step by step, and gradually deepen on the basis of student problems to achieve teaching goals.

Homeostasis

Teaching environment: classroom with multimedia

Students have a certain biological knowledge base, but they do not understand the content of this chapter, so they need to do a preliminary work before class.

Knowledge and skills:

1. Explain the concept of the steady state of the internal environment.

2. Briefly describe the steady-state regulation mechanism.

3. Understand the physiological significance of homeostasis.

4. Through the teacher's multimedia explanation, students master the role of the urinary system, circulatory system, endocrine system and nervous system in maintaining the internal environment

Process and method:

1. Perform experiments to understand that organisms have mechanisms to maintain internal environment stability.

2. Try to explain the mechanism by which the organism maintains pH stability.

Emotional attitudes and values:

1. Focus on maintaining the relationship between the internal environment's steady state and health.

2. Develop self-care awareness and habits.

3. Use this knowledge to care for family, relatives and friends.

4. Establish a rigorous and careful scientific spirit and scientific attitude that dares to question and respect the facts.

Teaching focus

(1) The composition and physical and chemical properties of the internal environment.

(2) The internal environment is the medium through which cells exchange material with the external environment.

(3) Study of the role of the urinary system and the circulatory system in maintaining the stability of the internal environment

2. Teaching difficulties

(1) The physical and chemical properties of the internal environment.

(2) The internal environment is the medium through which cells exchange material with the external environment.

(3) Grasp the urinary process of the kidney, and the relationship between the capillaries in the circulatory system and several other systems

1. The concept of the internal environment: The internal environment refers to the extracellular fluid in the human body (in the body of higher multicellular animals), which is the liquid environment on which human cells depend.

Intracellular fluid (exists in cells, accounting for about 2/3)

Body fluid plasma

Extracellular fluid

(Exists outside cells, about 1/3) lymph

2. Differences in living environment between single-cell organisms and multi-cell organisms

(1) Single-celled organisms (such as Paramecium) living in water can directly exchange materials with the external environment.

(2) Most cells in the human body are not in direct contact with the external environment and cannot directly exchange materials with the external environment.

2. Homeostasis

The metabolic activities of the cell and the continuous change of the external environment will inevitably affect the physical and chemical properties of the internal environment, such as pH, osmotic pressure, temperature, and the content of various chemical substances, but the internal environment can maintain relative stability through the body's regulatory activities .

(1) Plasma pH steady state

During the metabolism of the human body, many acidic substances such as lactic acid and carbonic acid are produced; human foods (such as vegetables and fruits) often contain some alkaline substances (such as sodium carbonate). When these acidic and alkaline substances enter the blood, the pH of the blood changes.

There are many pairs of substances in the plasma that buffer the pH, and each pair consists of a weak acid and the corresponding strong base salt, such as H2CO3 / NaHCO3, NaH2PO4 / Na2HPO4, and so on. Due to the regulating effect of the buffer substance in the blood, the pH value of the blood will not change greatly, and is usually stable between 7.35 to 7.45.

Balance and regulation of water and inorganic salts

1. Water balance and regulation

Water balance

Source: Drinking water and food are the main pathways, as well as water produced by material metabolism.

Way to go: Kidney urination is the main route. In addition, skin is excreted through sweat, lungs breath, and bowel movements.

Water balance adjustment

2. Balance and regulation of inorganic salts

Sodium salt mainly maintains the osmotic pressure of extracellular fluid; potassium salt mainly maintains the osmotic pressure of intracellular fluid.

Blood sugar balance

blood sugar balance

Blood glucose balance adjustment

Regulate the center-hypothalamus; related hormones-insulin, glucagon, epinephrine

Regulation: nerve-humoral regulation

Regulating hormones: raise blood sugar-glucagon and epinephrine

Reduce blood sugar-insulin

Chapter Introduction: Allow students to read the chapter introduction and appreciate the importance of the internal environment.

[Paper writing] Section 1 The environment in which cells live

[Introduction to the section] Introduced as "question discussion", students think and answer, and can conduct group discussions.

[Tips for Health Answering Teacher] 1. Figure 1 shows blood cells in human blood, including red blood cells, white blood cells, etc .; Figure 2 shows the unicellular animal Paramecium.

2. Blood cells live in plasma. Paramecium lives directly in the external water environment. The living environment of the two is similar: both are liquid environments; the difference is that blood cells live in the blood plasma of the body and do not directly exchange materials with the external environment, while Paramecium lives directly in the external environment; Compared with the environment, the physical and chemical properties of plasma are more stable, such as the temperature is basically constant.

[Question] "Focus in this section" once again aroused students' thinking.

[Board] One, somatic cells are born in extracellular fluid

Body fluids-Whether male or female, there are a large number of water-based fluids in the body. These fluids are collectively called body fluids.

Intracellular fluid (exists in cells, accounting for about 2/3)

Body fluid plasma

Extracellular fluid

(Exists outside cells, about 1/3) lymph

[Thinking and discussing] Students answer after discussion and the teacher prompts.

1. Extracellular fluid refers to body fluids that exist outside the cell, including plasma, interstitial fluid, and lymph. Blood cells live directly in plasma, most cells in the body live directly in interstitial fluid, and a large number of lymphocytes live directly in lymph fluid. It can be seen that extracellular fluid is the environment in which cells in the body live directly.

2. The same point: they all belong to extracellular fluid, which together constitute the human internal environment, and the basic chemical composition is the same.

Different points: (1) there are different parts in the human body: plasma is located in blood vessels, tissue fluid is distributed between tissue cells, and lymph is distributed in lymphatic vessels; (2) the types of cells living in it are different: It is various tissue cells in the body, various blood cells exist in plasma, and lymphocytes exist in lymph; (3) the chemical components contained are different, such as plasma contains more protein, and tissue fluid and lymph Very little protein.

3. Tip: When plasma flows through the capillaries, water and everything that can penetrate the walls of the capillaries can seep into the arterial end of the capillaries, enter the interstitial cell space and become tissue fluid. Most of the tissue fluid is at the end of the capillary vein. It can be re-infiltrated into the plasma. A small amount of interstitial fluid can also infiltrate the capillary lymphatic vessels to form lymph, and the lymph flows into the plasma through the lymphatic circulation from the left and right subclavian veins. The relationship between them is shown in Figure 1-2. It can be seen that the extracellular fluid of the whole body is an organic whole.

Paper writing Relationship between plasma, interstitial fluid, and lymph

Internal environment-The liquid environment with extracellular fluid is called the internal environment.

Composition of extracellular fluid

[Data analysis] Students analyze and answer, the teacher prompts.

1. Tip: The chemical substances in the table can be divided into inorganic substances and organic substances. Inorganic substances include water and inorganic salt ions (such as Na +, K +, Ca2 +, Mg2 +, Fe2 +, Cl-, HPO42-, SO42-, HCO3-), etc. Organic substances include sugars (such as glucose), proteins (such as serum albumin, Serum globulin, fibrinogen, etc.), lipids (such as various fatty acids, fats, lecithin, cholesterol), amino acid nitrogen, urea nitrogen, other non-protein nitrogen and lactic acid.

2. It also contains gas molecules (mainly oxygen and carbon dioxide), various hormones that regulate life activities, and other organic substances (such as vitamins).

3. More Na + and Cl- content. Their role is mainly to maintain plasma osmotic pressure.

4. Maintain plasma acid-base balance.

5. Tips: For example, glucose in plasma is mainly derived from sugars in food. The starch in food is digested by the digestive system, decomposed into glucose, absorbed by the villi of the small intestine, enters the blood, and is transported throughout the body through the blood circulation. After entering the tissue cells, glucose is mainly used for oxidizing energy, eventually generating carbon dioxide and water, and being discharged into the internal environment. Carbon dioxide is transported to the lungs through the blood circulation and is excreted through the respiratory system, while excess water is mainly excreted in the kidneys through the formation of urine. (Other reasonable answers are also possible.)

[Board] Third, the osmotic pressure and pH of extracellular fluid

[Sidebar Thinking Questions]

Tip: The normal saline of mammals is a 0.9% NaCl solution. The osmotic pressure provided by such a solution is the same as that of extracellular fluids such as plasma, so it is an isotonic solution of plasma. If the mass fraction of the NaCl solution used during the infusion is lower than or higher than 0.9%, the tissue cells will absorb or lose water.

[Board] Fourth, the internal environment is the medium for the cell to exchange material with the external environment

[Thinking and discussing] Students answer after discussion and the teacher prompts.

1. Tip: Na + and Cl- come directly from food and can be directly absorbed without digestion. Glucose and amino acids are mainly derived from sugars and proteins in food. Carbohydrates and proteins are two types of macromolecular substances that must be digested by the digestive system and broken down into glucose and amino acids before they can be absorbed. The above substances are actively transported into the capillaries in the villi of the small intestine through the small intestine, transported through the blood circulation to the capillaries throughout the body, and then enter the interstitial fluid and lymph through the substance exchange process.

2. Hint: CO2 produced by cell metabolism combines with H2O, and the following reactions occur under the action of carbonic anhydrase:

CO2 + H2OH2CO3H ++ HCO3-.

HCO3- reaches extracellular fluid, ie, interstitial fluid, plasma, or lymph, by exchanging with extracellular anions. Mainly related to the respiratory system.

3 Tip: The human body has a body temperature regulation mechanism to keep the temperature of extracellular fluid constant. For details, please refer to Chapter 2 of the textbook on human body temperature adjustment. Organs and systems involved in body temperature regulation include skin, liver, skeletal muscle, nervous system, endocrine system, and respiratory system.

4 Tips: The metabolic waste produced by the cells in the body is mainly excreted through the skin secretion of sweat, the formation of the urinary system, the excretion of urine and the exhalation of the respiratory system. The excretion pathways of the urinary system and the respiratory system are the main ones. For example, urea in plasma is excreted mainly through urine formed by the kidneys. The CO2 in the plasma enters the capillaries around the alveoli through the pulmonary arteries. Because the partial pressure of CO2 in the blood is greater than the partial pressure of CO2 in the alveoli, CO2 diffuses from the blood to the alveoli and is expelled from the body by exhalation.

The effect of teaching can be seen through the questions that students do after class.

Basic questions

(1) What are the main factors affecting the physical and chemical properties of blood?

(2) What is the pH of normal human blood?

(3) What is the way to adjust the blood pH to a normal range?

Deepening questions

(1) Why do people think about illness when their body temperature rises?

(2) What happens when the calcium content in the blood is too low or too high?

(3) What are the consequences of excessive urea and inorganic salts in the body?

These questions are listed based on the content of the course. If students can understand the meaning of the question, understand the meaning of the question. Then the main teaching tasks of this lesson are basically completed.

(4) What is the role of our urinary system in maintaining the stability of the internal environment?

In maintaining the stability of the internal environment of the urinary system, the kidneys can first filter the blood to form urine, and uniformly excrete the metabolic waste produced by each cell in the internal environment, thereby adjusting the balance of water, inorganic salts and acid-base pH. Then we understand the function of the urinary system in maintaining the stability of the internal environment. Once the metabolic wastes accumulate in the tissue fluid outside the cell, it will cause a balance between the factors in our internal environment and ultimately affect us Everyday life

(5) What is the main cause of uremia, a urinary system disease that is more common in our daily lives?

In this lesson, we discussed two major issues related to the internal environment. That is: the concept of the internal environment and the components it contains, the physiological significance of homeostasis. In particular, the homeostasis of the internal environment, we clarified the concept of homeostasis by taking the buffer to adjust the pH of blood as an example, and illustrated the physiological significance of homeostasis by taking enzymatic reactions and blood calcium as examples. In fact, the regulation of homeostasis is very complicated, and we will continue to discuss it in "Neural Regulation" and "Body Fluid Regulation" in Chapter 4.