Topic 5.1 Digestion
5.1.1 Explain why digestion of large food molecules is essential.
Digestion is necessary because it breaks large food molecules into smaller molecules that can be absorbed into the villi of the small intestine and eventually travel through the blood. Simple molecules can then dissolve in blood and go into circulation to reach every part of the body.
5.1.2 Explain the need for enzymes in digestion.
During digestion, four different groups of molecules are commonly encountered. Each is broken down into its molecular components by specific enzymes. Enzymes called amylases break down starch. Proteins are broken down into short chains of amino acids or individual amino acids by enzymes called proteases. Fats are broken down into glycerol and fatty acids by enzymes called lipases. Nucleic acids are broken down into nucleotides by enzymes called nucleases.
5.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase.
One amylase
Source= salivary glands in the mouth and in the pancreas
Substrate= starch
Product= maltose and oligosaccharides
Optimum pH= 7
One protease (pepsin)
Source= glands in stomach wall
Substrate= proteins
Product= peptides
Optimum pH= 2
One lipase
Source= pancreas
Sustrate= fats
Product= fatty acids and monoglycerides
Optimum pH= basic (higher than 7).
5.1.4 Draw a diagram of the digestive system.
5.1.5 Outline the functions of the stomach, small intestine, and large intestine.
Stomach functions
Storage
Because of its accordion like folds (called rugae), the wall of the stomach can expand to store two to four liters of material. Temporary storage is important because you eat considerably faster than you can digest food and absorb nutrients.
Mixing
The stomach mixes the food with water and gastric juice to produce a creamy medium called chyme.
Physical breakdown
Three layers of smooth muscles in the muscularis externa churn the contents of the stomach, physically breaking food down into smaller particles. In addition, HCL denatures proteins and loosens the cementing substances between cells. The HCL also kills most bacteria that may accompany the food.
Chemical breakdown
The enzyme pepsin chemically breaks down proteins. Only after pepsinogen is secreted into the stomach cavity can protein digestion begin.
Controlled release
A valve at the end of the stomach, the pyloric sphincter, regulates movement of chyme into the small intestine.
Small intestine functions
Mechanical digestion
Segmentation mixes the chyme with enzymes from the small intestine and pancreas. Bile from the liver separates into smaller fat globules. Peristalsis moves the chyme through the small intestine.
Chemical digestion
Enzymes from the small intestine and pancreas break down all four groups of molecules found in food into their component molecules.
Absorption
The small intestine is the primary location in the GI tract for absorption of nutrients.
Carbohydrates, proteins, nucleic acids, water-soluble vitamins, Vitamin B12, lipids, fat-soluble vitamins, water, and electrolytes.
Large intestine functions
Mechanical digestion
Rhythmic contractions of the large intestine produce a form of segmentation called haustral contractions in which food residues are mixed and forced to move from one haustrum to the next. Peristaltic concentrations produce mass movements of larger amounts of material.
Chemical digestion
Digestion occurs as a result of bacteria that colonize the large intestine. They break down indigestible material by fermentation, releasing various gases. Vitamin K and B vitamins are also produced by bacterial activity.
Absorption
Vitamins B and K, some electrolytes (Na+ and Cl-) and most of the remaining water is absorbed by the large intestine.
Defecation
Mass movement of feces into the rectum stimulates defecation reflex that opens the internal anal sphincter. Unless the external and sphincter is voluntarily closed, feces are evacuated through the anus.
5.1.6 Distinguish between absorption and assimilation.
Absorption is the passage of digested substances through the wall of the intestine into the blood capillaries in bodies. Assimilation is a process by which food becomes incorporated with the body without being broken down.
5.1.7 Explain how the structure of the villus is related to its role in absorption of the end products of digestion.
Villi (singular villus) are fingerlike projections, in the small intestine, that cover the surface of the mucosa giving it a velvety appearance. They increase the surface area over which absorption and digestion occur. The spaces between adjacent villi lead to deep cavities at the bases of the villi called intestinal crypts. Glands that empty into the cavities are called intestinal glands, and the secretions are collectively called intestinal juice.
Topic 5.2 - The Transport System
5.2.1 Draw a diagram of the heart showing all four chambers, associate blood vessels and valves.
5.2.2 Describe the action of the heart in terms of collecting blood, pumping blood and opening and closing valves.
The blood is collected by the atria, and is then pumped out by the ventricles into the arteries. Atrio-ventricular and semilunar valves control the direction of flow.
5.2.3 Outline the control of the heartbeat in terms of the pacemaker, nerves and adrenalin.
The wall of the right atrium is made of a specialized tissue forming a structure called the sinoatrial node (SAN) also known as the pacemaker. It spontaneously produces electrical impulses that spread to the two atria causing them to contract. The brain controls the heart rate and the pacemaker receives two nerves from the brain stem. One of these nerves, the sympathetic nerve, releases, nor adrenaline, and causes the heart rate to increases. The parasympathetic nerve releases acetylcholine and lowers the heart rate. The hormone adrenaline is released by the adrenal gland and prepares the body to situations of stress by increasing the heart rate and also blood sugar levels.
5.2.4 Explain the relationship between the structure and function of arteries, capillaries and veins.
Arteries carry blood that is pumped out by the thick walls of the ventricles. They have thick walls because this is when the blood has the highest pressure. These walls are made of connective tissue, elastic and muscle fibers and a layer of endothelial cells. The elastic tissue allows the arteries to expand and recoil. This helps push the blood in the circulation. Veins have thinner walls. They carry blood from the body back to the heart. They have thinner layers of connective, elastic, and smooth muscle fibers. Capillaries only have one layer of endothelium as their walls. This allows substances to pass in and out of capillaries for exchange of materials. They have a very narrow diameter, but there are many capillaries allowing a large exchange of materials.
5.2.5 State that blood is composing of plasma, erythrocytes, leucocytes (phagocytes and lymphocytes), and platelets.
Blood is composed of plasma, erythrocytes, leucocytes (phagocytes and lymphocytes), and platelets.
5.2.6 State that the following are transported by the blood: nutrients, oxygen, carbon dioxide, hormones, antibodies and urea.
Nutrients, oxygen, carbon dioxide, hormones, antibodies and urea are transported by blood.
Topic 5.3 - Pathogens and Disease
5.3.1 Define pathogen.
A pathogen is an organism or virus that causes a disease.
5.3.2 State one example of a disease caused by members of each of the following groups: viruses, bacteria, fungi, protozoa, flatworms and roundworms.
Viruses: Influenza
Bacteria: Cholera
Fungi: Athlete's foot
Protozoa: Malaria
Roundworms: Ascaris eggs contained in contaminated food are swallowed, circulate through the blood stream, reach the lungs, grow into larvae in the nasal cavities, swallowed into the stomach where they grow into adult worms and start the cycle again
Flatworms: Pork tapeworm.
5.3.3 List six methods by which pathogens are transmitted and gain entry to the body.
- From the air
- Direct contact
- Through food
- Cuts in the skin
- Blood transfusion
- Animals and insects.
5.3.4 Describe the cause, transmission and effects of one human bacterial disease.
Diptheria is a bacterial disease the is breathed in and infects the nose, throat, and larynx. The bacteria releases toxins that destry tissues in the heart nerves and glands.
Objectives 5.3
5.3.5 Explain why antibiotics are effective against bacteria but not viruses.
Antibiotics block protein synthesis in bacteria but not eukaryotic cells. Bacteria and animal cells synthesize proteins in a similar manner, though the proteins involved are not the same. Those antibiotics that are useful as antibacterial agents use these differences to bind or inhibit the function of the bacterial proteins. In this way, they prevent the synthesis of new proteins and new bacterial cells without damaging the patient. Viruses consist of genetic material and are not complete cells. Antibiotics do not, therefore, block virus reproduction.
5.3.6 Explain the cause, transmission, and social implications of AIDS.
CAUSE: The HIV virus causes AIDS, but the origin of the virus is unconfirmed.
TRANSMISSION: AIDS is commonly transmitted via blood (from mother to child, transfusions, or contaminated needles) or via sexual intercourse.
SOCIAL IMPLICATIONS: Social implications of AIDS includes the ostracizing of homosexuals (or homophobia), the ostracizing of people with the HIV virus, unease over blood transfusions, or changes in sexual behavior, including reductions in promiscuity and the increase use of condoms.
Objectives 5.4
5.4.1 Explain how skin and mucous membranes act as barriers against pathogens.
If the pathogens never enter the body, they are never dangerous, and the skin plays a key role in keeping the pathogen from entering the body. When unbroken, it is almost impossible for any microorganisms to penetrate. Weak points are those not protected by the skin, but these areas usually have defenses of their own:
Lungs: mucus and cilia transport mucus to the throat
Stomach: very acidic environment
Eyes: tears contain enzymes, which destroy bacterial cell walls
Vagina: mucous and acidic environment
Mucus is often used as a barrier against pathogens through trapping microorganisms and preventing further entry.
5.4.2 Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues.
Leucocytes (white blood cells) are the bodys defense against pathogens after they have entered the body. They can be found in the blood and in the bodys tissues (lungs). Several different kinds of leucocytes exist, some of which are phagocytic (will eat any cell which is recognized as foreign through a code on the outside of the cell surface membrane).
5.4.3 State the difference between antigens and antibodies.
Antigen-any molecular configuration that certain lymphocytes recognize as nonself and that triggers an immune response
Antibody (or immunogloblin)-a globular protein that recognizes an antigen; antigen-binding receptor; only B cells make antibodies, then position them at their surface or secrete them
5.4.4 Explain antibody production.
Antibodies are produced by the B-lymphocytes or B-cells, a type of leucocyte. Like all bloods cells, they are produced in the bone marrow and differentiate here before moving to the lymph nodes. When an antigen has entered the body, a phagocytic leucocyte will ingest the invader and travel to a B-cell in the lymph nodes. Here the phagocytic leucocyte will present the antigen to the B-cell. The presence of another leucocyte (a T helper cell) will then cause the B-cell to clone itself many times. A few of these cloned cells will remain as memory cells but the majority differentiate into plasma cells. Plasma cells secrete large amounts of antibodies (but only one kind), which are released into the lymph, which drains into the blood.
Memory cells are kept so that the antibody production will be faster at the next invasion of the same antigen.
T-cells also originate from the bone marrow, but travel to the thymus in an immature state and mature there. Two types develop: T helper cells and cytotoxic T cells. The T helper cells play a role in the production of antibodies by B-cells and interact with the phagocytes and the B-cells to come to the production of the correct antibodies. Cytotoxic T cells directly kill pathogens through cell-mediated response.
5.4.5 Outline the effects of HIV on the immune system.
When infected, the HIV virus will specifically infect and destroy the T helper cells (lymphocytes). This interferes with their specific defense, their ability to produce antibodies, and often leads to a number of opportunistic diseases like rare forms of pneumonia and skin cancer.
Also, HIV replicates in an immune system cell; therefore, by creating more of itself, it is killing the cells that would normally destroy it.
Objectives 5.5
5.5.1 List the features of alveoli that adapt them to gas exchange.
- Large surface area through a dense network of capillaries
- Thin, creating a short diffusion distance
- Moist (gases need to dissolve before passing through membranes)
- Good blood supply to maintain the concentration gradient
5.5.2 State the difference between ventilation, gas exchange, and cell respiration.
Ventilation: Breathing is the ventilation of the lungs. In involves muscular movement and therefore requires energy. Oxygen will diffuse from the air in the lungs into the blood only if the concentration of oxygen in the air in the lungs is higher than that in the blood. As the oxygen diffuses into the blood, the concentration of oxygen in the air of the lungs decreases. By refreshing the air in the lungs, the concentration gradient is maintained.
Gas Exchange: the movement of oxygen from the air in the lungs into the blood and the excretion of carbon dioxide
First, oxygen dissolves in the film of water around the cells that make the walls of the alveoli. The dissolved oxygen then diffuses through the alveoli cells and through the walls of the capillaries into the erythrocytes in the blood. The circulation of the blood will take the oxygen away from the area of gas exchange, maintaining the concentration gradient. Carbon dioxide, produced in the tissues, moves in the opposite direction. The blood carries carbon dioxide to the lungs where it diffuses from the blood, across the walls of the capillaries and the walls of the alveoli into the air in the lungs. The circulatory system will continue to bring blood carrying carbon dioxide to the lungs, and ventilation of the lungs will refresh the air so that the concentration gradient is maintained.
Cell Respiration: process of releasing energy from food (large organic molecules), often using oxygen as the ultimate electron acceptor
Catabolic, energy-yielding pathway; electrons fall from organic molecules to oxygen
Three stages: glycolysis, Krebs cycle, and electron transport and ATP synthesis
Glycolysis: glucose to Pyruvate, occurs in cytoplasm; yields 2 ATP
Krebs: Pyruvate to carbon dioxide and water, occurs in the mitochondrial matrix; involves liberation of electrons and hydrogen, which coenzymes deliver to an electron transport system; yields 2 ATP
Electron transport and ATP synthesis: occurs in the inner mitochondrial membrane, 34 ATP yield
All dependent on each other: ventilation requires energy provided by cell respiration, gas exchange depends on a concentration gradient of respiratory gases maintained by ventilation, and cell respiration is more efficient when using oxygen as its electron acceptor; oxygen needed and carbon dioxide produced are exchanged with the environment via gas exchange.
5.5.3 Explain the necessity for a ventilation system.
It is needed to obtain oxygen for the organism and to get rid of carbon dioxide that is produced as a by-product. It also helps maintain concentration gradients in the alveoli. A true ventilation system is needed for larger animals when diffusion of oxygen through cells is not enough to supply all the oxygen needed in the organism.
5.5.4 Draw a diagram of the ventilation system including trachea, bronchi, bronchioles, and lungs.
5.5.5 Explain the mechanism of ventilation in human lungs including the action of the internal and external intercostal muscles, and diaphragm and the abdominal muscles.
The air in the lungs constantly needs to be refreshed. The intercostal muscles contract and move the ribcage up and outward. The diaphragm contracts, flattening it downward. Both actions increase the volume of the chest cavity, resulting in a decreased pressure, and as a result, the air will flow into the lungs.
When the intercostal muscles and diaphragm relax, they will return to their original position. The volume decreases, and an increase in pressure will make the air leave the lungs. In forced expiration the abdominal muscles contract, increasing the pressure in the abdominal cavity. This pushes the diaphragm up further.
Objectives 5.6
5.6.1 State that homeostasis involves maintaining the internal environment at a constant level or between narrow limits, including blood pH, oxygen, and carbon dioxide concentrations, blood glucose, body temperature, and water balance.
Homeostasis-state in which physical and chemical aspects of internal environment are being maintained within ranges suitable for cell activities
Examples of homeostasis: maintenance of oxygen and carbon dioxide concentrations, blood glucose levels, body temperature, and water balance
5.6.2 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms.
Negative feedback- the control of a process by the result or effect of the process in such a way that an increase or decrease in the results or effects is always reversed
Requires sensors to measure the current situation, which need to pass the information to where the desired value or norm is known and compare the current situation to the norm. If the two are not the same, a mechanism is activated to bring the current value closer to the norm, usually turning off the mechanism. The action taken aims at changing a situation so that the action is no longer required.
5.6.3 State that the nervous and the endocrine systems are both involved in homeostasis.
Both the nervous system and endocrine systems are involved in homeostasis.
5.6.4 State that the nervous system consists of the central nervous system (CNS) and peripheral nerves and is composed of special cells called neurons that can carry electrical impulses rapidly.
The nervous system can be divided into the Central Nervous System (CNS) and the peripheral nerves. The CNS is the brain and spinal cord, and everything else is peripheral. The peripheral nerve cells are called neurons. Their function is to transport messages in the form of electrical impulses to specific sites. This is done very quickly by local depolarization of the cell membrane of the neuron.
5.6.5 Describe the control of body temperature including the transfer of heat in blood, the roles of sweat glands and skin arterioles, and shivering.
Mammals and birds have thermoreceptors in their skin and in the heat center in their brain, monitoring temperature changes in the environment and in blood temperature.
If the organism is too hot, it can cool down by:
- Vasodilation: the blood vessels in the skin become wider which increases the flow of blood to the skin; as a result the skin becomes warmer which increases heat loss to the environment. Convection and radiation are increased.
- Sweating: evaporation of fluid from the skin; change of phase from liquid to gas; requires energy which is taken from the body; panting has the same effect
- Deceased metabolism: any reaction produces heat as a by product
- Behavior adaptations (ex, birds bathe, rodents retreat into burrows, dogs dig holes)
If the organism is too cold, it can warm up by:
- Vasoconstriction: the blood vessels in the skin contract, decreasing the flow of blood to the skin; the skin becomes colder, reducing the heat loss to the environment; convection and radiation are decreased
- Shivering: any reaction will produce heat as a by product; muscular contractions produce a lot of heat
- Increase metabolism: increase production of heat
- Fluffing of hair or feathers: increase the thickness of the insulating layer of air
- Thick layer of brown fat or blubber
- Special hair structure
