The digestive system

We need food in order to live; it is the fuel for our body’s energy and growth. There are three main kinds of food: protein (found in meat, cheese, and nuts, for example), carbohydrates (found in bread and potatoes), and fat (found in oils and butter). Proteins are used for repairing the body and for growing; carbohydrates and fats are needed for providing energy.

Digestion is a process that begins when we put food in our mouths and ends when the food has been absorbed into the bloodstream. It takes up to eighteen hours for digestion to occur. This is not surprising because our food has to travel through more than 26 feet of coiled-up tubing called the small intestine. On its journey food gets broken down by acid and enzymes. An enzyme is a chemical that changes food into a substance we can easily absorb.

When we chew, our teeth break up food into small pieces for swallowing. Food then travels down a muscular tube called the esophagus, to the stomach. The stomach is a thick muscular sac positioned on the left side of the body just beneath the ribs. The upper region of the stomach, closest to the heart, is called the cardiac region. Below that is the crescent part of the sac called the fundus. The pyloric region is tubular and connects the stomach to the small intestines. The wall of the stomach is made up of three thick layers of muscle. One layer is composed of longitudinal, one of circular, and the other of oblique (diagonal) fibers. The powerful contractions of these muscles break up the food, mix it with gastric juice, and move it down the tract. Gastric juice is a mixture of hydrochloric acid and enzymes that further digest the food. Gastric juice and mucus are secreted by the small gastric glands in the lining of the stomach. The mucus helps protect the stomach from its own digestive enzymes and acid. The partially digested food, called chyme, is pushed through the pyloric sphincter into the small intestine. The pyloric sphincter is similar in structure and function to the lower esophageal sphincter.

In the small intestine food is broken up into useful substances and waste substances by enzymes, which are produced by a gland called the pancreas. Inside the small intestine finger-like bumps, known as villi, contain blood vessels that absorb the useful substances into the bloodstream. Waste substances remain and pass into the large intestine, where water is absorbed until the waste becomes solid. This waste is later expelled from the rectum.

II. COMPREHENSION CHECK.

1. Mark the following statements as true or false:

a) Food is the fuel for our body.

b) Fats and proteins are used for providing energy.

c) Digestion doesn’t last long.

d) Food is broken down by acid.

e) The stomach is a thin muscular sac positioned on the right side of the body.

f) The pyloric region is circular and connects the stomach to the large intestines.

g) Gastric juice is a mixture of hydrochloric acid and proteins.

h) The mucus protects the stomach from its digestive enzymes.

i) In the small intestine food is broken up into waste substances by enzymes produced by the gastric glands.

j) Waste substances pass into the large intestine and are later expelled from the rectum.

2. Check your understanding of the text by answering the questions:

a). What are the main kinds of food?

b). Why are carbohydrates used?

c). What is digestion?

d). What is an enzyme?

e). What happens when we chew?

f). Where does food get after swallowing?

g). How is the upper region of the stomach called?

h). Where is the fundus?

i). What is the wall of the stomach made up of?

j). What happens to food as a result of the contractions of the stomach muscles?

k). Where are gastric juice and mucus secreted?

l). What is the pyloric sphincter like?

m). What absorbs useful substances?

3. Find in each paragraph the sentence which conveys the main idea.

III. LANGUAGE FOCUS.

1. Complete the chart filling in the missing derivatives (where possible):

2. Looking through the lists of words below match the words which are: a) contrary or b) similar in meaning:

3. Find the words in the text that mean:

coiled-up tubing

chemical changing food into easily absorbed substances

muscular tube

muscular sac located on the left side of the body

crescent part of the sac

mixture of hydrochloric acid and enzymes

partially digested food

4. Translate into English using the vocabulary of the Unit:

а). Чтобы жить, человеку нужна пища.

б). Белки, углеводы и жиры – три основные вида пищи.

в). Пищеварение начинается, когда пища попадает в рот.

г). Ферменты преобразуют пищу в легко поглощаемые вещества.

д). Желудок представляет собой толстый мышечный мешочек, расположенный с левой стороны, ниже ребер.

е). Сокращения желудочных мышц расщепляют пищу и смешивают ее с желудочным соком.

ж). Кровеносные сосуды поглощают полезные вещества.

з). Отходы выводятся из тела человека через прямую кишку.

IV. FOLLOW-UP ACTIVITIES.

1. Name all parts of the digestive system and explain their functions.

2. Write an essay about the digestive system.

ADDITIONAL TEXT

I. Read the text carefully. Be ready to fulfil the tasks that follow.

NUTRITION

To understand nutrition, you have to understand that it is a combination of the many integrated processes involved in an organism’s absorption and use of materials. Most of the actual absorption takes place on a molecular level. Organisms must procure the food, which is then broken down to chemical constituents that are absorbed by the cells. These atoms and molecules provide the raw materials that constitute, maintain, and run the organisms. The energy produced by the raw materials is usually measured in units known as calories; one calorie is the amount of energy needed to raise one gram or cubic centimeter (cc) of water one degree centigrade. The calories usually referred to in biology and nutrition are kilogram-calories (Kcal); each 1000 gram-calories. When calories are discussed below, they are kilogram-calories; that is, the amount of heat required to raise the temperature of 1000 grams (one kilogram) of water from 14.5^oC to 15.5^oC.

Breaking down the nutrient materials we call food involves a series of processes that in the aggregate are known as digestion. Digestion is the physical and/or chemical breakdown of food into sizes small enough to be passed across cell membranes. Our food is the result of other organisms’ procurement of nutrients from the environment. Eating other organisms, or their parts, saves us considerable time and energy.

Green plants and a number of additional life forms can survive without consuming other organisms. Animals, however, could not exist without the green plants that synthesize the majority of molecules that are passed on to other organisms. (In addition, it should be remembered that green plants generate oxygen and consume carbon dioxide, while most animals consume oxygen and generate carbon dioxide.)

Of the four basic macromolecules found in living things, proteins, carbohydrates, and fats are so abundant, readily accessible, and nutritionally useful that they have become the primary molecular units representing the food in our diets. Nucleic acids, the fourth group of macromolecules, are not abundant enough to be an important dietary item.

II. POST-READING TASKS.

1. Define the following concepts: nutrition, a calorie, digestion.

2. Name the basic macromolecules found in living organisms and explain their role.

3. Imagine that you are making a speech on the topic “Nutrition”.

UNIT 9

I. PRE-READING AND READING TASKS.

1. Study the meaning and pronunciation of these words:

2. Try to guess the meanings of the following words and word combinations:

3. Read and translate the text.

BREATHING

The respiratory system in man and other air-breathing vertebrates includes the lungs and the tubes by which air reaches them. Normally air enters the human respiratory system by way of the external nares or nostrils, but it may also enter by way of the mouth. The nostrils, which contain small hairs to filter incoming air, lead into the nasal cavities, which are separated from the mouth below by the palate. The nasal cavities contain the sense organs of smell, and are lined with mucus-secreting epithelium which moistens the incoming air. Air passes from the nasal cavities via the internal nares into the pharynx, then through the glottis and into the larynx. The larynx is often called the “Adam’s apple”, and is more prominent in men than women. Stretched across the larynx are the vocal cords.

The opening to the larynx, called the glottis, is always open except when swallowing, when a flap-like structure (the epiglottis) covers it. Leading from the larynx to the chest region is a long cylindrical tube called the trachea, or windpipe. In a dissection, the trachea can be distinguished from the esophagus by its cartilaginous C-shaped rings which serve to hold the tracheal tube open. In the middle of the chest, the trachea bifurcates into bronchi which lead to the lungs. In the lungs, each bronchus branches, forming smaller and smaller tubes called bronchioles. The smaller bronchioles terminate in clusters of cup-shaped cavities, the air sacs. In the walls of the smaller bronchioles and the air sacs are the alveoli, which are moist structures supplied with a rich network of capillaries. Molecules of oxygen and carbon dioxide diffuse readily through the thin, moist walls of the alveoli. The total alveolar surface area across which gases may diffuse has been estimated to be greater than 100 square meters.

Each lung, as well as the cavity of the chest in which the lung rests, is covered by a thin sheet of smooth epithelium, the pleura. The pleura is kept moist, enabling the lungs to move without much friction during breathing. The pleura actually consists of two layers of membranes which are continuous with each other at the point at which the bronchus enters the lung, called the hilus (roof). Thus, the pleura is more correctly a sac than a single sheet covering the lungs.

The chest cavity is closed and has no communication with the outside. It is bounded by the chest wall, which contains the ribs on its top, sides, and back, and the sternum anteriorly. The bottom of the chest wall is covered by a strong, dome-shaped sheet of skeletal muscle, the diaphragm. The diaphragm separates the chest region (thorax) from the abdominal region, and plays a crucial role in breathing by contracting and relaxing, changing the intrathoracic pressure.

Just prior to inspiration, at the conclusion of the previous expiration, the respiratory muscles are relaxed and no air is flowing into or out of the lungs. Inspiration is initiated by the contraction of the dome-shaped diaphragm and the intercostal muscles. When the diaphragm contracts, it moves downward into the abdomen. Simultaneously, the intercostal muscles which insert on the ribs contract, leading to an upward and outward movement of the ribs. As a result of these two physical changes, the volume of the chest cavity increases and hence the pressure within the chest decreases. Then, the atmospheric pressure, which is now greater than the intrathoracic pressure, forces air to enter the lungs, and causes them to inflate or expand. During exhalation, the intercostal muscles relax and the ribs move downward and inward. At the same time, the diaphragm relaxes and resumes its original dome shape. Consequently, the thoracic volume returns to its pre-inhalation state, and the pressure within the chest increases. This increase in pressure, together with the elastic recoil of the lungs, forces air out of the lungs causing them to deflate.

II. COMPREHENSION CHECK.

1. Provide evidence to support or disprove the following statements:

a) The nasal cavities are not separated from the mouth.

b) The vocal cords are stretched across the larynx.

c) The opening to the larynx, called the glottis, is always closed.

d) In the walls of the smaller bronchioles and the air sacs are the alveoli.

e) Molecules of oxygen and carbon dioxide can hardly diffuse through the thick walls of the alveoli.

f) The chest cavity is bounded by the chest wall, which contains the ribs on its top, sides, back and front.

g) The diaphragm separates the chest region from the abdominal region and doesn’t play any role in breathing.

h) A little air flows into or out of the lungs prior to inspiration.

i) When the diaphragm contracts, it moves towards the abdomen.

2. Prepare extensive answers to the questions below:

a) What does the respiratory system in man include?

b) By what way does air enter the human respiratory system?

c) How does air pass from the nasal cavities into the larynx?

d) What is the glottis?

e) What is the trachea?

f) What is the structure of bronchi and lungs?

g) What enables the lungs to move without much friction during breathing?

h) What does the pleura consist of?

i) Does the chest cavity have communication with the outside?

j) What makes the volume of the chest cavity increase?

k) What forces air to enter the lungs and makes it get out of the lungs?

III. LANGUAGE FOCUS.

1. Fill in the table with the derivatives of the following words (where possible):

2. Make sure you can supply the plural for each of the following nouns:

3. Looking through the lists of words below match the words which are: a) contrary or b) similar in meaning:

4. Say this in English:

а). Ноздри, содержащие маленькие волоски для очищения поступающего воздуха, ведут в носовые полости.

б). Трахея отличается от пищевода хрящевыми с-образными кольцами.

в). Каждый бронх разветвляется, образуя бронхиолы – трубочки все уменьшающегося размера.

г). Подсчитали, что общая площадь поверхности альвеол, через которую могут диффундировать газы, составляет более 100 м².

д). Плевра скорее представляет собой мешок, чем пелену, покрывающую легкие.

е). Диафрагма представляет собой крепкий куполообразный слой скелетных мышц.

ж). Во время выдыхания межреберные мышцы расслабляются и ребра двигаются вниз и внутрь.

IV. FOLLOW-UP ACTIVITIES.

1. Describe the process of breathing in man.

2. Write an essay about the respiratory system in man and other air-breathing vertebrates.

ADDITIONAL TEXT

I. Read the text carefully to fulfil the tasks that follow.

RESPIRATORY SYSTEM

Respiration has two distinct meanings. It refers to the oxidative degradation of nutrients such as glucose through metabolic reactions within the cell, resulting in the production of carbon dioxide, water, and energy. Respiration also refers to the exchange of gases between the cells of an organism and the external environment. Many different methods for exchange are utilized by different organisms. In man, respiration can be categorized by three phases: ventilation (breathing), external respiration, and internal respiration.

Breathing may be defined as the mechanical process of taking air into the lungs (inspiration) and expelling it (expiration). It does not include the exchange of gases between the bloodstream and the alveoli. Breathing must occur in order for respiration to occur; that is, air must be brought to the alveolar cells before exchange can be effective. One distinction that can be made between respiration and breathing is that the former ultimately results in energy production in the cells. Breathing, on the other hand, is solely an energy consuming process because of the muscular activity required to move the diaphragm.

The phenomenon in which the cells of an organism exchange oxygen and carbon dioxide directly with the surrounding environment is termed direct respiration. This form of respiration is a fairly simple process and occurs in small, aquatic animals such as paramecia or hydras. In these animals, dissolved oxygen from the surrounding water diffuses into the cells, while carbon dioxide within the cell diffuses out; no special respiratory system is needed.

With the evolution of animals into larger and more complex forms, it became impossible for each cell to exchange gases directly with the external environment. Consequently, it became necessary for these organisms to have a specialized organ system that would function in gas exchange with the environment. This structure must be thin-walled, and its membrane must be differentially permeable. In addition, the membrane must be kept moist so that oxygen and carbon dioxide could dissolve in it, and it must have a good blood supply. The process of respiration employing this organ system is called indirect respiration. For indirect respiration, the lower vertebrates developed gills and the higher vertebrates developed lungs.

During indirect respiration, gas exchange between the body cells and the environment may be categorized into two phases: an external and an internal phase. External respiration is the exchange of gases by diffusion that occurs between the lungs and the bloodstream. Oxygen passes from the lungs to the blood and carbon dioxide passes from the blood to the lungs. Internal respiration takes place throughout the body. In the latter, there is an exchange of gases between the blood and other tissues of the body, with oxygen passing from the blood to the tissue cells and carbon dioxide passing from the cells to the blood. This phase, along with the external phase, relies on the movement of gases from a region of higher concentration to one of lower concentration.

II. POST-READING TASKS.

1. Define the following concepts: respiration, breathing, direct (indirect) respiration, external (internal) respiration.

2 Explain the difference between:

a) breathing and respiration,

b) direct and indirect respiration,

c) external and internal respiration.

3. Write an essay describing respiration and its phases.

UNIT 10

I. PRE-READING AND READING TASKS.

1. Go through the list of words below:

2. Make sure you can supply an adequate translation for each of the following words and word combinations:

Read and translate the text.

REPRODUCTION

It takes two cells for human sexual reproduction to occur: a woman’s egg-cell and a man’s sperm-cell. These cells have to meet and join together in order for a baby to be made. This process is called fertilization, and it normally only occurs when a couple has had sexual intercourse.

Sperm look a bit like tadpoles. About 500 million sperm are made each day in the male testes. As with the female’s eggs, each sperm contains genes that will help determine an offspring’s looks and personality. The sperm’s tail is used to help it swim. Sperm have a long journey, up the vagina to the uterus and then on to the fallopian tube, in their search for an egg.

Women usually release one egg each month from one of their two ovaries. The egg is sent from the ovary down the fallopian tube, which is where fertilization occurs. One sperm penetrates the egg, by breaking through its outer wall. Other sperm are then prevented from entering. The sperm and egg join together to form a cell that divides, again and again, to form a clump that attaches to the uterine wall. This clump of cells soon forms an embryo, which grows into a fetus.

The head soon grows, the arms and legs appear, and the fetus begins to look like a human being. A tube, called the umbilical cord, carries the fetus’s blood to and from the placenta. In the placenta the fetus’s blood mixes with the mother’s blood. When the baby is ready to be born, chemicals signal the mother'’ uterus to push the baby out. The umbilical cord is cut, leaving the new-born baby with a small scar – the belly button.

To grow and survive the fetus needs nutrition and oxygen from its mother’s blood. Inside the placenta there are vessels linking the mother’s and fetus’s blood. Waste chemicals from the fetus’s blood are taken away by the mother’s blood, and the mother’s blood feeds the fetus. After two months the main parts of the baby’s body are formed. At this stage it looks rather strange as its head seems too big for its body. At five months the toenails, fingernails, and all the main organs have formed. Even the eyelashes have appeared. By seven and a half months it looks almost a new-born baby. It is about 15 inches long, while at birth a baby is usually 19.5 inches. If the baby were born at this earlier stage, it would still be able to survive if given special care and attention. When a baby is born early it is called premature.

II. COMPREHENSION CHECK.

1. Ask one or two questions to each paragraph to reveal the main idea.

2. Put the statements below in the correct order according to the contents of the text.

a) When one sperm penetrates the egg other sperm are prevented from entering.

b) An embrio grows into a fetus which needs nutrition and oxygen from its mother’s blood.

c) Sperm move up the vagina to the uterus and then to the fallopian tube in their search for an egg.

d) A tube which carries the fetus’s blood to and from the placenta is called an umbilical cord.

e) When the baby is ready to be born chemicals signal the mother’s uterus to push the baby out.

f) After two months the main parts of the baby’s body are formed.

g) A woman’s egg-cell and a man’s sperm-cell have to meet and join together for fertilization.

III. LANGUAGE FOCUS.

1. Match the words that are contrary in meaning:

2. Make sure you can supply the plural for these nouns:

3. Complete the sentences below:

a) Each female’s egg and each sperm contain genes that……

b) The egg is sent from the ovary down the fallopian tube where ….

c) When a baby is born, the umbilical cord is cut, leaving …..

d) Inside the placenta there are vessels …..

e) When a baby is born early ….

IV. FOLLOW-UP ACTIVITIES.

1. Sum up what you have learned about:

a) male’s sexual organs,

b) female’s sexual organs,

c) the process of fertilization,

d) the development of the fetus.

2. Write an essay about reproduction in man.

ADDITIONAL TEXT

I. Read and translate the text carefully. Be ready to fulfil the tasks that follow.

REPRODUCTION

Asexual reproduction is quite simple compared to sexual reproduction in that it requires only one organism; no partner is necessary. Therefore, in most asexual species, every mature individual can reproduce, enabling the population to increase far more rapidly than the otherwise comparable sexual species that require two individuals to reproduce.

Many organisms take full advantage of asexual reproduction. For instance, each time an amoeba divides, it produces two genetically identical replicas of itself. And many species of single-celled as well as multicellular organisms produce asexually reproductive cells known as spores that float in the air or water and eventually produce genetic replicas of the parent.

Another asexual mode of reproduction involves budding. In budding, part of the parent sprouts smaller offspring that separate and become distinct individuals. Many plants reproduce vegetatively, sprouting new plants from leaves, roots, or some other part of the parent. In parthenogenesis, an egg can develop into an adult without being fertilized by a sperm cell.

Another form of asexual reproduction is fragmentation, in which part of an organism separates from the whole, and a new individual regenerates from that part. Such fragmentation sometimes occurs when an organism is in danger; pieces of the injured organism then regenerate into whole organisms. Starfish, for example, have this reproductive capacity. Worms and planaria can also fragment and then regenerate the missing portion of their body.

Cloning is another type of asexual reproduction that involves the production of copies that are genetically identical, although they may not look identical. This happens with many plant species – such as when one plant grows from a seed and then many other plants sprout up from the roots.

Sexual reproduction is costly to a species in that it requires both a male and a female to produce as many offspring as one asexual organism can produce, but there are also benefits to such an expensive reproductive mode.

For sexual reproduction to occur, specialized cells from both the male and female come together and unite. Yet merely combining any two cells is not adequate. Rather, certain cells first undergo a peculiar type of cell division called meiosis, creating gametes called germ cells.

In animals, undifferentiated male germ cells are located in the testes. These cells undergo two meiotic divisions, called meiosis I and meiosis II, creating four sperm cells. Undifferentiated at first, these sperm cells, known as spermatids, undergo differentiation before becoming mature spermatozoa. This process, spermatogenesis, is the result of the division and maturation of a single diploid primary spermatocyte, producing four spermatozoa. In female animals, all the undifferentiated germ cells are located in the ovaries, where oogenesis occurs. Oogenesis comprises the series of steps that produce an egg from a primary oocyte, which is also called an ovum.

In terms of weight, a human egg, though extremely tiny (much smaller than the head of a pin), is approximately 58,000 times heavier than a single sperm cell. In terms of length, a completely differentiated sperm cell is about 1/3 the diameter of a human egg.

Only one sperm cell can fertilize each egg. When the sperm cell penetrates the egg, it contributes its haploid (sometimes called monoploid or 1N) genetic complement of chromosomal DNA to the haploid (1N) egg, creating a diploid (2N) zygote.

II. POST-READING TASKS.

1. Define:

a) asexual reproduction and discuss the different types that exist,

b) sexual reproduction,

c) spermatogenesis and oogenesis.

2. Compare and contrast asexual and sexual reproduction.

3. Write an essay describing asexual and sexual reproduction.

Date: 2016-11-17; view: 659; Нарушение авторских прав