week one

What is a cell membrane?

A cell membrane is a flexible, fragile transparent barrier that contains a cell's contents and separates them from the surrounding environment. It both defines the limits of the cell and plays a dynamic role in many cellular activities.

What is a fatty acid?

A fatty acid is one of the two building blocks of triglycerides, a type of lipid. Fatty acid chains vary. The length of a triglyceride's fatty acid chains and their type of C-C bonds determine how solid the molecule is at a given temperature. There are saturated and unsaturated fats (which are further broken into monounsaturated and polyunsaturated). There are also trans fats, which are oils that have been solidified with the addition of hydrogen atoms at the sites of double carbon bonds to reduce them into single carbon bonds. These increase the risk of heart disease; omega-3 fatty acids, in contrast, reduce it.

What is a monoglyceride?

A monoglyceride is made up of one fatty acid. It is one of the products of the digestion/emulsification of fats (along with glycerol and fatty acids). Fatty acids and monoglycerides enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct.

What is a monomer? What is a polymer?

A monomer is a small molecule, a single unit. A polymer is made up of monomers.

What is a triglyceride?

A triglyceride is one of the most abundant lipids in the body. Triglycerides are composed of two building blocks, fatty acids and glycerol. Their synthesis involves the attachment of three fatty acids to a single glycerol molecule (which releases three water molecules). The result is an E shaped molecule that resembles the tines of a fork. The glycerol backbone is the same in all triglycerides, but fatty acid chains vary. Triglycerides represent the body's most abundant and concentrated source of usable energy. When they are oxidized, they yield large amounts of energy. They are stored chiefly in fat deposits beneath the skin and around body organs, where they help insulate the body and protect deep body tissues from heat loss and injury.

What is ATP?

ATP is 1 sugar, 3 phosphates, and 1 nitrogen base. ADP is adenosine diphosphate. to release energy for work, the 3rd phosphate is broken off. that third phosphate later comes back on through an enzyme reaction in metabolism.

How are bile salts amphipathic?

Amphipathic = containing both hydrophilic and hydrophobic elements. One side is one, and one side is the other.

In what direction does a variable change as a result of a positive feedback response to stress?

An imbalance is sensed in the variable, which leads to a response to bring it back to balance, but rather than being cut off or reduced, the change just keeps growing more effective. As the change grows more and more strong, it also stimulates the effector's response more and more. This can happen with hyperthermia, when the body depresses hypothalamic activity, and body temperature increases metabolic rate which in turn increases body temperature again. Positive feedbacks are much more rare. They move the variable in the same direction as the stress. They are used in childbirth (through heavy stimulation of hormones to get the process done more quickly) and in blood clotting (speeding up process to stop blood loss). The end game here is to remove the stimulus causing the response.

What are ionic bonds?

An ionic bond forms when electrons are completely transferred from one atom to another, creating a compound. When this type of bond occurs and atoms gain or lose electrons, ions (charged particles) result. Negatively charged ions (anions) result when an atom gains an electron and acquires a net negative charge from having more electrons than protons (ex. Cl-). Positively charged ions (cations) result when an atoms loses an electron and acquires a net positive charge from having less electrons than protons (ex. Na+). Because of this, both anions and cations result with ionic bonds. Most compounds formed in ionic bonding are salts.

What does basal metabolic rate measure?

Basal metabolic rate = amount of heat produced by the body per unit of time when it is under basal conditions (rest). In other words, the energy supply a person's body needs in order to perform essential life activities, like breathing, kidney function, heartbeat, etc. Average is 60-72 kilocalories/hour. In contrast, total daily energy expenditure refers to that and the extra energy you exert daily, beyond just surviving.

Can enzymes be used more than once?

Because enzymes are not changed during the reaction, they are reusable, and cells only need small amounts of each enzyme.

Compare bond strength (dissociation energy) of single, double & triple covalent bonds. Which has the most potential energy?

Bonds between atoms determine the behavior of molecules. In physiology, covalent bonds are stronger than ionic (or hydrogen). Everything is in water, our solvent. These bonds store the most energy for cellular work. Ionic bonds are weaker than covalent because they can be broken by water. Polar and non polar molecules do not readily bond; polar are hydrophilic and non polar are hydrophobic. The larger the bond, the more bond dissociation energy. Therefore, single have less than double, which have less potential energy than triple bonds.

What is food made of?

Carbohydrates, lipids, and proteins (and also minerals and vitamins). The molecules for these look different, so the way they are broken down will be different. For example, in simple sugar carbohydrates (monosaccharides), they are made up of numerous hydroxyl groups, contain covalent bonds that store energy, and are polar molecules. Lipids are made up of carbon and hydrogen chains, have covalent bonds that store energy, and are non polar molecules.

Out of catabolism and anabolism: Which has a net release of energy? Which builds larger molecules? Which breaks molecules down into smaller parts?

Catabolism has a net release of energy. Anabolism builds larger molecules. Catabolism breaks molecules down into smaller parts.

How is a tissue different from a cell?

Cells are specialized for particular functions. Groups of cells similar in structure and function make up tissues. It is the structural level below tissue. When a group of cells/tissue is indispensable, its loss can severely damage the body.

Why is cellulose (fiber) beneficial if we can't digest it?

Cellulose helps move foodstuffs along the gastrointestinal tract by providing us with fiber (bulk), aiding in defecation. It is the most abundant organic polymer on the earth.

Why do chemical bonds matter in metabolism?

Chemical reactions involve the making and breaking of bonds between ions. Although the total number of atoms remains the same, the atoms appear in different combinations. Synthesis reactions underlie all anabolic activities (such as growth and tissue repair) and decomposition reactions underlie all catabolic activities (such as food digestion and breakdown of glycogen when blood sugar declines). Exchange reactions focus on breaking and building bonds (like when ATP reacts with glucose to become ADP). Chemical bonds are essentially necessary for life. Additionally, the liver serves as an example through glycogenesis (storing glucose) and glycogenolysis (breaking down and releasing glucose). The food we eat are chemical bonds between molecules. These come into the body and create potential energy in ATP.

Where is cholesterol used in the body?

Cholesterol is essential for human life. It is found in cell membranes and is the raw material used to make vitamin D, steroid hormones (vital for homeostasis and including sex hormones), and bile salts. If we lack estrogen, it can lead to amenorrhea through loss of estrogen.

What is cholesterol? Where does it come from?

Cholesterol is the single most important steroid molecule (type of lipid; flat molecules formed of four interlocking carbon rings; made largely of of hydrogen and carbon atoms; fat soluble). We ingest cholesterol in animal products like meat, eggs, and cheese. Some of its is also made by the liver, which secretes cholesterol's breakdown products in bile.

What are common waste products that must be removed from the body?

Common waste products that must be removed are carbon dioxide, water and urea. We get rid of water primarily through urine. We get rid of carbon dioxide by exhaling. We get rid of kinetic energy/heat all the time.

Which organic molecules have polar covalent bonds so that they are readily water soluble? Which are hydrophobic & why?

Concerning carbohydrates, monosaccharides are water soluble/hydrophilic, but disaccharides and polysaccharides are too large to dissolve in water without being broken down to monosaccharide units. Concerning lipids, they are insoluble in water/hydrophobic but readily dissolve in other lipids and in organic solvents like alcohol and acetone. However, phospholipids are a bit trickier; they have two fatty acid chains rather than three, because a phosphorus-containing portion takes the third place. Because this portion has a negative charge, phospholipids have special chemical properties and polarity. This charged region is hydrophilic, and the fatty acids, which are nonpolar, are hydrophobic. The presence of phospholipids in cell membranes then allows cells to be selective about what may enter or leave.

What is the role of connective tissue?

Connective tissue fills internal spaces, provides structural support, and stores energy. It is found everywhere in the body. It is mainly concerned with protecting, supporting, and binding together other body tissues. Examples are bone, cartilage, dense fibrous tissue, loose connective tissue (areolar, adipose, reticular). Connective hallmarks include variations in blood supply, and an extracellular matrix.

What are catabolic (decomposition) chemical reactions?

Decomposition reactions underlie all catabolic (destructive) activities in body cells, and are important in digestion of food into building blocks and breakdown of glycogen into glucose when blood sugar declines. They occur when a molecule is broken down into smaller molecules, atoms, or ions (AB > A + B). Bonds are always broken, and the products are smaller and simpler than the original molecules. As bonds are broken, chemical energy is released. During catabolism, bond energy of foods is released and captured to make adenosine triphosphate (ATP), the energy rich molecule used to energize all cellular activities, including catabolic reactions. Essentially: catabolic reactions lead to cellular building blocks.

How do Type I and II diabetes relate to high glucose levels?

Diabetes relates to a buildup of glucose circulating, not going where it should normally go. This causes fatigue, increased rates of cellular damage, and relates to other diseases (like Alzheimer's). Type I can only be treated with insulin, but Type II can be treated with diet and exercise.

Does emulsification occur through mechanical or chemical digestion?

Emulsification is mechanical digestion, breaking things down at a molecular level, but not using bonds yet. After, chemical digestion occurs through enzymes, which break covalent bonds between individual levels to their smallest subunit, monomers. It is not until this enzyme stage that monomers are absorbed into the body; anything left in the lumen of the small intestine afterwards is deposited as waste.

Use the energy balance equation to predict how to lose weight.

Energy intake = total energy output (heat + work + energy storage). To lose weight, a person must not take in more energy than they are exerting through those factors. Rather, they must have more total energy output than energy intake. When intake and outtake are balanced, our weight is stable; when they are imbalanced, we either gain or lose weight. Increasing BMR won't necessarily help with weight loss.

How do enzymes make metabolism more efficient?

Enzymes are essential to virtually every biochemical reaction in the body, and increase the rates of chemical reactions by at least a millionfold. However, they also determine just which reactions are possible at a given time. Without them, biochemical reactions would happen too slowly to sustain life. Enzymes are also very specific in their activities, each controlling only one/a small group of chemical reactions and acting only on specific molecules. Many are produced as inactive and must become active, and many stop being active after performing their catalytic function.

What is an enzyme?

Enzymes are functional proteins that act as biological catalysts. Catalysts, in turn, are substances that increase the rate of a chemical reaction without becoming part of the product or being changed themselves. Enzymes have active sites on their surfaces that interact chemically with other molecules of complementary shape and charge (substrates). When these bond, it results in an enzyme-substrate complex, and the substrate undergoes structural changes that result in a new product. Some enzymes build larger molecules and others break things into smaller pieces/modify the substrate. Once the reaction occurs, the enzyme releases the product. Enzymes are part of chemical digestion, breaking bonds. Any time a molecule changes bonds, it has potential to change shape due to the influence of enzymes. This makes it easier to break apart molecules.

Does an enzyme require ATP?

Enzymes do not require ATP; it is the very act of bonding that changes the molecule's shape and changes its own shape. The enzyme helps the body place less energy into breaking bonds, so that metabolism is more efficient. Afterwards, enzymes return to their original shapes.

How does food move through the body?

Food moves through the body due to peristalsis, which is serious contracting and relaxing of the smooth muscle of the small intestine. This is constant, but food has a certain amount of time to get absorbed before being expelled. Technically, this is occurring outside of the body - it is in the lumen of the small intestine, which is space connected to the exterior of the body.

Compare the lines for surface area, volume and the ratio of SA/V as a "cuboidal" cell increases in length.

For side of cuboidal cell, 1cm > ratio is 6, 2cm > ratio is 3, 3cm > ratio is 2. SA and V both independently increase the bigger the sides get, but the ratio decreases exponentially. This means that there is more stuff inside with less surface exposed. SA = 6 x s x s. V = s x s x s. The greater the size, the less big stuff is able to fit in its surface area, because SA/V ratio is smaller.

Explain how GLUT4 carriers transport glucose in muscle.

Glucose cannot enter cells on its own as it is too large. Rather, it uses a transporter to get in. Insulin binds to the cell membrane and causes the exocytosis of glucose transporters (like GLUT4) to the membrane, which then allow glucose to enter the cell. Without receptors for insulin, transporters for glucose are unavailable.

Which complex carbohydrate is most rapidly catabolized?

Glycogen is catabolized more rapidly than starch or other complex carbs. This is because it has many branches that give it more SA. We intake food, it goes into the body, glycogen goes into the liver and muscles, then is dispersed as glucose to the body's cells.

Predict the variation in bile & pancreatic enzyme release into the intestines with a meal high or low in fat, and between meals (fasting state).

High in fat > High bile and high pancreatic enzyme. Low in fat > Low bile and moderate pancreatic enzyme (high if high other digestible types of foods). Between meals > Low bile and low pancreatic enzyme.

What is homeostasis?

Homeostasis describes the body's ability to maintain relatively stable internal conditions even though the outside world is continuously changing. The body demonstrates homeostasis when its needs are being adequately met and it is functioning smoothly. Communication within the body is essential for homeostasis and is accomplished chiefly by the nervous and endocrine systems, which use electrical signals delivered by nerves or blood borne hormones as information carriers. (Negative) feedback loops are used to maintain homeostasis. For example, if a house gets cold, the receptor (thermostat) detects it, the control center (also thermostat) decides to release heat, and the effector (heater) produces a response, restoring balance.

Why is homeostasis called a dynamic equilibrium?

Homeostasis does not refer to an unchanging body, but rather a dynamic state of equilibrium in which internal conditions change and vary, but always within relatively narrow limits.

Hypoglycemia under a negative feedback loop?

Homeostasis is disturbed by decreasing blood glucose levels. The alpha pancreatic cells detect this and send out glucagon. Glucagon causes the liver, skeletal muscles, and adipose tissue to break down and release glucose. Balanced is restored, and levels are regular again.

Hyperglycemia under a negative feedback loop?

Homeostasis is disturbed by increasing blood glucose levels. Beta pancreatic cells detect this (after delay for digestion) and send out insulin. Insulin causes the intake of glucose by body cells, storage, etc. Balanced is restored, and levels are regular again. Leftover insulin is then deposited in waste. In this case, receptor and control center = pancreatic cells, effector = all body cells.

What do the terms hyperglycemia and hypoglycemia mean?

Hormones like insulin and glucagon are vitally important in this process of controlling the blood sugar level and hanging glucose in all body fats. The pancreatic islets, little masses of endocrine tissue in the exocrine tissue of the pancreas, manufacture these hormones and excrete them appropriately during fed and fasting states. A high level of glucose in the blood stimulates the release of insulin from the beta cells of the islets. Insulin acts on almost all body cells, increasing their ability to import glucose across their plasma membranes. Once inside the cells, glucose is oxidized for energy or converted to glycogen or fat for storage, and insulin also speeds up these effects. Because it sweeps glucose out of the blood, it is said to have a hypoglycemic effect. As the blood glucose level falls, the stimulus for insulin release ends (negative feedback). Insulin is necessary for the use of glucose by body cells; without it, cells could not use glucose at all. Glucagon acts as an antagonist of insulin, meaning its release by the alpha cells of the islets is stimulated by a low blood level of glucose. Its action is hyperglycemic; its primary target is the liver, which it stimulates to break down stored up glycogen to glucose, then release the glucose into the blood.

What is a hydrogen bond?

Hydrogen bonds are weak bonds formed when a hydrogen atom bound to an "electron hungry" oxygen or nitrogen atom is attracted by another such atom, and the hydrogen atom forms a bridge between them. Electrons are not involved in these types of bonds. They are common between water molecules, which is reflected in the "balled up" surface tension of water. These are also important intramolecular bonds, meaning they help to bond different parts of the same molecule together into special 3D shapes. These bonds are helpful in maintaining the structure of protein molecules and DNA. In hydrogen bonds, negative ends are attracted to positive ends of other molecules. This creates surface tension in water (ex. tear film). Hydrogen bonds just involve hydrogen.

What makes up simple sugars?

Hydrogen, carbon, and oxygen make up simple sugars -- carbon and water, essentially. Their structures are made up of carbon rings and numerous hydroxyl groups, which are polar/charged molecules, and therefore hydrophilic. These are polar covalent bonds, and more bonds = more energy. If a hydroxyl was bonded to a water molecule, that would be a hydrogen bond.

How does water interact with hydrophilic substances?

Hydrophilic substances easily interact with water because the charged ends of molecules are attracted to one another. Ion compounds are generally hydrophilic.

What makes a molecule hydrophobic?

Hydrophobic substances are not interested in water. In this case, water molecules end up interacting with themselves, forming a "cage" around molecules/bonds. Covalent molecules are often hydrophobic.

How does blood pressure work under a negative feedback loop?

If blood pressure starts decreasing, the response from the effector causes it to increase again. This relates to the dynamic equilibrium of homeostasis; when something varies within a normal range and maintains its stability that way.

How do bile salts aid lipid digestion? What is emulsification?

In bile, bile salts emulsify fats by physically breaking large fat globules into smaller ones, thus providing more SA for fat-digesting enzymes to work on. Un-emulsified fats are emulsified in the small intestine, and then they are broken down further by pancreatic lipase. Emulsification is when two liquids that normally don't mix are combined, breaking one down better. Fats are hydrophobic, meaning water builds a cage around them creating a large globule with a low SA/V ratio. Bile salts act as a buffer, breaking down fat globules to make them more dissolvable in water so they have more SA/V, and can be digested/absorbed more easily through attachment of enzymes.

What are covalent bonds?

In covalent bonds, atoms share electrons so that each atom is able to fill its valence shell at least part of the time. In non polar molecules, electrons are shared equally across the molecule so that each valence shell has enough electrons to satisfy its needs; charge is the same. These are generally considered true chemical bonds (in contrast to ionic compounds), creating molecules.

What is a polar covalent bond?

In polar covalent bonds, electrons are not shared equally across the whole molecule. This is because a molecule's shape plays a major role in determining how it can interact with other atoms/molecules, and may result in unequal electron sharing. Electrons spend more time near the larger nucleus, creating a slightly negative charge at that end and a slightly positive charge at the other ends. For example, a water molecule is formed when two hydrogen atoms bond covalently to a single oxygen atom. Because the molecule is V-shaped and oxygen has a stronger electron-attracting ability, the electrons spend more time in vicinity of the oxygen. A molecule with two charged poles is formed, as the hydrogen atoms have a slight positive charge and the oxygen has a slight negative charge. The fact that water is a polar molecule is significant because body tissues are 60-80% water.

What is insulin resistance? How is this harmful to cells?

Insulin resistance is a situation in which a person's insulin receptors are unable to respond to insulin even though the body is producing it. It occurs in Type II diabetes. This is harmful because insulin is the only hormone that decreases the blood glucose level, and it is needed for glucose to be used by body cells. Without it, essentially no glucose can get into cells to be used for energy.

Do ionic or covalent bonds dissociate readily in water?

Ionic bonds more readily dissociate in water. This is because salts easily separate into their already formed ions, and then they are spread apart through the influence of polar water molecules. These molecules orient themselves with their slightly negative ends toward cations, and positive ends toward anions, pulling the ionic bonds apart. When placed in a water solvent, negative ends of water molecules (oxygen) are attracted to positive ends of ionic compounds (ex. sodium in NaCl), and positive ends (hydrogen) are attracted to negative ends (ex. chloride). This is a hydrophilic reaction.

Describe the advantages of a higher SA/V for a cell. Why is SA/V important in physiology? Give an example.

It is important to think about cellular adaptations that increase this ratio (like with the circular folds in the small intestine). This idea of SA/V is applicable across the body in various ways. Everything is physiology involves exchange across a membrane (ex. heat/gas/water/solute exchange across membranes). Surface area = how much of the object is exposed, V = how much space is inside the shape. Smaller cells are better for digestion with more SA. If the small intestine wants more nutrients to come across the membrane more efficiently, it is better to have smaller cells, as more surface (membrane) area relative to volume of food. SA also contributes to how quickly enzymes break down food.

What are the differences between kinetic vs. potential energy? Give examples.

Kinetic energy drives collisions between particles by keeping them constantly moving. Particles must collide forcefully and overlap their outermost shells will that of other particles in order for them to react chemically. Several factors influence kinetic energy/speed of particles and force of collision: higher temperature, higher kinetic energy; higher particle concentration, higher number of collisions; smaller particle size, the faster they move; if catalysts are present, molecules need less energy to interact. Potential chemical energy goes into the body through carbs, proteins, and fats; as potential cellular energy in the form of ATP, it is used for cellular work.

What are lipids?

Lipids have hydrogen, carbon, and oxygen, but the ratio/arrangement is different than in carbs. They have long chains of hydrogen and carbon.

Why does BMR decrease with age & why is it lower for females, on average?

Many factors influence this, like surface area, gender, amount of thyroxine, and age. Children and adolescents require large amounts of energy for growth, and therefore will have higher BMRs than older people, whose muscles begin to atrophy. There are body composition differences in gender; women have less skeletal muscles and more adipose tissue. Young people are growing a lot, meaning there cells are working more, whereas older people are losing muscle mass, bone mass, activity level, hormone levels, etc. Fewer basal metabolic activities means lower BMR. Higher BMR = greater SA/V (thin and small), male, increased thyroxine production, young, strong emotions. Lower BMR = lower SA/V (large and heavy), female, decreased thyroxine production, old.

Explain the difference between mechanical & chemical breakdown of food by the digestive system. Explain the roles of smooth muscle tissue in the movement of food through the digestive system as well as mechanical breakdown of food.

Mechanical breakdown physically fragments food into smaller particles, increasing surface area and preparing food for further degradation by enzymes. For example, chewing (mouth), churning (stomach), and segmentation (small intestine). This is operating at the cellular level. Chemical breakdown involves digestion, the sequence of steps in which large food molecules are chemically broken down to their building blocks by enzymes (small intestine, large intestine). This is operating at the molecular level.

When is medical intervention needed for homeostatic imbalance?

Medical intervention is necessary when homeostatic imbalance leads to disease, which is often a disturbance of homeostasis. As we age, our body organs become less efficient and our internal conditions become less stable, which places us at increasing risk for illness. For example, blood sugar imbalances can lead to diabetes. Another huge reason for medical intervention is homeostatic imbalance in the form of hypothermia, which results from prolonged exposure to cold and the body's inability to maintain an adequately high body temperature even with vasoconstriction and shivers. This can lead to frostbite, decreased vital signs, coma, and death. The opposite problem occurs with hyperthermia, when prolonged elevated body temperature cannot be reduced enough with evaporation and radiation. Here, the activity of the hypothalamus is depressed until it results in a positive feedback loop where body temperature increases metabolic rate, which increases heat production. This can lead to permanent brain damage, fatal heat stroke, and collapse due to heat exhaustion.

What is metabolism?

Metabolism = all chemical reactions that occur within the body and all of its cells that are necessary to sustain life. This includes breaking down complex substances into simple building blocks (catabolism, like in digestion), making larger structures from small ones (anabolism), and using nutrients and oxygen to produce molecules of ATP. It depends on the digestive and respiratory systems to make nutrients and oxygen available to blood, and on the cardiovascular system to distribute the needed substances throughout the body. Metabolism is regulated by hormones secreted by the glands of the endocrine system. Metabolism happens at the cellular and molecular level.

Name one monosaccharide & one disaccharide (simple sugars).

Monosaccharides are the structural building blocks of carbohydrates because they are joined to form the molecules of the two other groups. They have one sugar. One example (and the most important) is glucose, the universal cellular fuel. Disaccharides are formed when two simple sugars are joined by dehydration synthesis (one monosaccharide gives up OH, another H, and water molecule is released as the two are bonded). One example is sucrose, or cane sugar (glucose-fructose). A polysaccharide is a complex carb made up of many monomers, such as starches.

Compare the number of covalent double carbon (C=C) bonds in monounsaturated and polysaturated fats. How do these double bonds alter the density & stiffness of the triglyceride?

Monounsaturated fats are fatty acids that contain one double bond between carbon atoms (ex. olive oil is rich in these types of fats). They have only one kink in the chain. Polyunsaturated fats are fatty acids that contain more than one double bond between carbon atoms (ex. soybean and safflower oils are rich in these types of fats). They have many kinks.

What foods that you eat are mainly composed of lipids? Protein? Fat?

Most dietary lipids are neutral fats (triglycerides). Saturated fats are found in animal products (meat and dairy) and in a few plant products. Unsaturated fats are found in seeds, nuts, and vegetable oils. Cholesterol, another type of lipid, can be found in egg yolk, meats, and milk products. Animal products contain the most protein. Complete proteins include eggs, milk, fish, and most meat proteins. Incomplete proteins include legumes, nuts, and cereals (low in one or more essential amino acids, which our bodies can't make).

What are the benefits of a negative feedback response? When does a negative feedback response occur (in normal range, outside normal range, outside of the tolerance limits)?

Most homeostatic control mechanisms are negative feedback loops. In these systems, the net effect of the response to the stimulus/change is to either shut off the original stimulus or reduce its intensity. The human body uses this type of system to regulate body temperature, heart rate, blood pressure, breathing rate, the release of hormones, and blood levels of glucose, oxygen, carbon dioxide, and minerals. Every time something heads toward an imbalance, the body utilizes a negative feedback loop to keep it in check. It is beneficial because it helps the body respond to the change and reach a balance, but then reduces the body's response so that it does not lead to an imbalance in the opposite direction. With positive feedback loops, the problem is that the body keeps responding after it reaches a homeostatic balance. It would not be helpful, for instance, if the body utilized shivers and vasoconstriction to rise the body's temperature back to normal, but then kept going until the body's temperature was too high.

What elements are present in all organic molecules?

Most organic compounds are very large covalent molecules, but their interactions with other molecules typically involve only small, reactive parts of their structure called functional groups. Organic molecules are essential for life. Many organic compounds are polymers (chainlike molecules made of many similar or repeating units/monomers, which are joined together via dehydration synthesis and broken apart by hydrolysis). All organic molecules -- carbs, lipids, proteins, and nucleic acids -- are formed and broken this way. All organic molecules (bar a few exceptions) contain carbon.

Describe the main organs of the digestive system. What is the function of each?

Mouth -- breaks up food particles, assists in producing spoken language. Pharynx -- swallows. Salivary glands -- saliva moistens and lubricates food. Amylase digests polysaccharides. Esophagus -- transports food. Liver -- produces bile, in which bile salts and phospholipids help the digestive process. Bile salts emulsify fats by breaking large fat globules down into smaller ones, providing more surface area for fat-digesting enzymes to work on. Breaks down and builds up many biological molecules, stores vitamins and iron, destroys old blood cells, and destroys poisons. Stomach -- stores and churns food; Pepsin digest protein; HCI activates enzymes, breaks up food, and kills germs; mucus protects the stomach wall; limited absorption. Small intestine -- the body's major digestive organ. It prepares usable nutrients for their journey to the cells of the body by breaking down chyme with brush border enzymes that work with pancreatic enzymes and bile. Completes digestion, mucus protects gut wall, absorbs nutrients and most water, Peptidase digests proteins, Sucrases digest sugars, and Amylase digests polysaccharides. Pancreas -- contributes pancreatic juice rich with enzymes that work with brush border enzymes to complete starch digestion, half of protein digestion (through Trypsin and chymotrypsin), fat digestion (through Lipase), and nucleic acid digestion. Also, pancreatic juice contains a rich supply of bicarbonate ions that is very basic and helps to neutralize acidic chyme from the stomach. Hormones regulate blood glucose levels. Large intestine -- re-absorbs some water ions, forms and stores feces. Rectum -- stores and expels feces. Anus -- opening for elimination of feces.

What is the role of muscle tissue?

Muscular tissue contracts to produce active movement (skeletal, smooth, cardiac).

What is the difference between sodium atom (Na) vs. sodium ion (Na+) or chlorine (Cl) vs. chloride ion (Cl-)

Na and Cl are the atoms existing on their own with neutral charges. Na+ and Cl- are the versions of these atoms that exist in an ionic bond together, when Na gives one of its electrons to Cl's valence shell. This balances both atoms and produces a positive charge in sodium (through loss of electron) and a negative charge in chloride (through addition of electron.

What is the role of nervous tissue?

Nervous tissue conducts electrical impulses and carries information.

How does food get into our bodies?

Normally food is: consumed, mechanically digested, chemically digested, brought into our cells, and metabolized. The energy and building blocks created are used to make new parts of our body. Food gets divided into small, molecular pieces for digestion. The digestive tract runs throughout the entire body. Food must be ingested, digested, and the nutrients absorbed. Normally food is consumed, mechanically digested, and chemically digested. Enzymes break food down to make it easier to digest. The surface area of the digestive tract makes nutrients more easily absorbed. Nutrients are used to help the body, then what is not needed is released as waste.

How is a tissue different from an organ?

Organs are the structural level above tissue, and are made up of organized tissues. Most organs contain several tissue types, and the arrangement of tissues determines each organ's structure and abilities.

Compare the roles of bile (salts) from the liver, and pancreatic enzymes in digestion.

Pancreatic juice is rich in enzymes that help with starch, fat, nucleic acid, and half of protein digestion. It neutralizes acidity after food travels through the stomach. Juice from the pancreas contains amylase and proteases, but also sodium bicarbonate. In contrast, bile does not have enzymes and works to emulsify fats, separating large fat globules into smaller tiny ones. This is turn provides a much larger surface area for the pancreatic lipases to work on. Bile is made by the liver but food does not travel through there; rather, it is released from the gallbladder and goes into the small intestine. This is why someone who has had their gallbladder removed is encouraged to eat a low fat diet. Both of these substances are necessary for fat digestion and absorption. The large intestine does not have digestive enzymes, so relying solely on this results in fat stool and possible blood clotting issues.

What is the structure of a phospholipid molecule? Which region of this molecule is hydrophilic? Which is hydrophobic?

Phospholipids have one glycerol atom, two fatty acids, and one phosphorus containing group that takes the place where normally a third fatty acid would be in a triglyceride. Because this phosphorus containing portion has a negative charge, it leads to a special situation in which the charged regions are hydrophilic while the fatty acids are hydrophobic. The presence of phospholipids in cell membranes therefore allows cells to be selective about what may enter or leave.

How do complex carbs differ from simple sugars?

Polysaccharides have branched shapes. This increases their SA for enzymes to do work, such as with starch and glycogen. They are catabolized by enzymes working at the ends of the branches in, and working at the corners of branches.

Give some examples of dietary lipids that are liquid vs. solid at room temperatures. What does molecular shape have to do with liquidity?

Saturated fats (butter, meat) > solid. Straight chains, only single covalent bonds between carbon atoms; pack closely together. Unsaturated fats (oils) > liquid. Kinked chains, double covalent bonds between carbon atoms; cannot pack closely together.

Describe the 3-dimensional structural differences between saturated, monounsaturated & polyunsaturated fatty acids.

Saturated fats are fatty acid chains with only single covalent bonds between carbon atoms. The chains are straight, and the molecules in the chain pack closely together at room temperature, forming a solid (ex. butter). These (and long fatty acid chains) are more common in animal fats. Unsaturated fats (monounsaturated and polyunsaturated) are fatty acids with one or more double bonds between carbon atoms. These bonds cause the chains to kink, so they cannot pack closely enough together to solidify. Therefore, these act as oils (liquid at room temperature), along with short fatty acid chains. These are also more healthy than saturated fats. Essentially: saturated fats are fully straight, have the max number of hydrogens, and no double bonds. Unsaturated fats have kinks, less hydrogen, and carbon double bonds.

Compare the 3-dimensional structures of glycogen, cellulose & starch.

Starch has several branches, glycogen has many more branches, and cellulose is stacked together in rows (making it harder for the enzymes to break it apart).

Describe these parts of a homeostasis loop: stress, receptor, integrator/controller, effector, response.

Stress is the response the body has to stressors/environmental changes, which take it out of its balanced homeostatic state. The receptor is a type of sensor that monitors and responds to changes in the environment. To respond to these stimuli, it sends input information to the control center along the afferent pathway. The control center determines the level at which a variable is to be maintained. It then analyzes the information it receives and determines the appropriate response/course of action. The effector provides the means for the control system's response to the change/stimulus. Information flows to the effector along the efferent pathway. The results of the response then feed back to influence the stimulus, either by reducing/cutting off the amount of change or increasing it so the reaction continues at an even faster rate. Essentially, stimulus produces change in variable, leading to imbalance in homeostasis > the receptor detects the change > information is sent to the controller > the controller decides what to do > information about what response to make is sent to effector > effector engages in response to reduce the change in the variable or increase it.

What are anabolic (synthesis) chemical reactions?

Synthesis reactions underlie all anabolic (building) activities in body cells, and are important for growth and repair of damaged tissues. The formation of a protein molecule through joining amino acids into long chains is also a synthesis reaction. They occur when two or more atoms or molecules combine to form a larger, more complex molecule (A + B > AB). They always involve bond formation. Because energy must be absorbed to make bonds, synthesis reactions are energy storing reactions. Essentially: anabolic reactions build new blocks into macromolecules.

Why is increased SA of the lipid substrate important?

The active sites of enzymes bind at specific places on a lipid, on exposed surfaces; the more surface is exposed, through emulsification, the more breakdown that can occur efficiently, increasing the rate of digestion.

What is the role of epithelial tissue?

The epithelial tissue is the lining, covering, and glandular tissue of the body. It covers all free body surfaces and creates boundaries, inside and out, and contains versatile cells. Nearly all substances that the body gives off or receives must pass through epithelium. Functions include protection, absorption, filtration, and secretion. For example, epithelium specialized to absorb substances lines some digestive system organs like the stomach and small intestine, which absorb food nutrients into the body. Also produces glandular secretions Epithelial hallmarks include that the cells fit closely together, membranes always have one free surface or edge, the anchored (basal) surface rests on a basement membrane, the cells have no blood supply of their own, and regenerate themselves easily.

What are the four basic tissue types?

The four basic tissue types are epithelial (covering), connective (support), nervous (control), and muscle (movement).

Why does gallbladder removal lead to greasy stool?

The gallbladder stores bile salts made by the liver. Normally, the gallbladder releases bile into the small intestine to aid with fat digestion. Fats are not water soluble because they are non polar. Without being dissolved in water (which normally just forms a cage around them instead), their big globular state leaves less exposed surface relative to volume for enzymes to bind and break the lipids down into smaller pieces for fast digestion and absorption. However, bile salts help emulsify fats due to their amphipathic state; they act as a buffer with their hydrophobic ends being attracted to fats and their hydrophilic ends being attracted to water. This helps the fats dissolve in water, creating smaller pieces and more SA for enzymes to bind to. Thus, enzymes are able to break fats down into even tinier pieces, so digestion is efficient, as is absorption into the epithelial cells lining the intestinal tract. Without the gallbladder, bile salts are not stored in advance. The liver still releases bile, but it cannot wait for fat digestion, so there is generally not enough to break down fats with the same efficiency, leading to greasy stool as fats are left behind in waste. Further, the majority of water absorption occurs in the large intestine. Due to osmosis, water is attracted down its concentration gradient, and will rush toward a heavy concentration of solutes (like non broken down fats leftover in the large intestine).

Explain the events in the normal regulation of plasma glucose (blood sugar).

The liver is vitally important in helping to maintain the blood glucose level within the normal range (~100 mg glucose/100 ml of blood). After a carb-rich meal, thousands of glucose molecules are removed from the blood and combined to form the large glycogen polysaccharide molecules, which are then stored in the liver. This occurs in glycogenesis. Later, as body cells continue to remove glucose from the blood to meet their needs, the blood glucose level begins to drop. At this point, the liver cells break down the stored glycogen through glycogenolysis, and release glucose bit by bit to the blood to maintain blood glucose homeostasis.

What does the liver store? Where are they stored?

The liver makes bile, which the gallbladder stores; it is then released into the SI to help break lipids down. However, the liver also stores glycogen (a complex carb), contributing to long term energy stores. The more recently someone has eaten, the more glycogen will be stored in reserves. Glucose is a common currency for body cells, but lipids and proteins can be catabolized for energy. So the liver stores glucose in the form of glycogen. Through glycogenesis, glucose is transformed into glycogen; through glycogenolysis, glycogen is broken down into glucose again.

Why are bile salts and pancreatic enzymes introduced into the first part of the small intestine?

The reason this happens in the first part of the small intestine is because when chyme enters, it stimulates the mucosa cells to produce several hormones, including secretin and cholecystokinin (CKK), which influence the release of both pancreatic juice and bile. Both enzymes stimulate pancreatic release, but secretin causes the liver to increase bile output while CKK encourages the gallbladder to release stored bile. The structural modifications that create more surface area to make chyme travel slowly through the small intestine also start disappearing more toward the end.

How does the esophagus compare to the intestines in form and function? What is similar? What is different?

The small intestine absorbs nutrients while the esophagus transports food to the stomach. Regarding morphology, both have lumen (empty opening surrounded by other tissue/cells), but the esophagus has a smooth edge while the small intestine has villi that poke out and increase surface area, along with picae (folds) and microvilli. These work together to create a much larger surface area. The higher the SA/V ratio of the digestive tract, the faster the rate of digestive absorption.

How are phospholipids arranged in a membrane?

The structure of a cell membrane consists of two phospholipid fat layers arranged "tail to tail," with cholesterol and floating proteins scattered among them. Some phospholipids also have sugar groups attached, forming glycolipids. The proteins, which are free to move around the lipid layer, form a constantly changing mosaic. The oil-like phospholipid bilayer forms the basic fabric of the membrane. The hydrophilic heads lie on the inner and outer surfaces of the membrane (where water, the main component of both intracellular and extracellular fluids can reach them), while the non polar and hydrophobic tails avoid water and line up in the center of the membrane. This self-orienting property of the phospholipids allows biological membranes to reseal themselves quickly when they are torn. Also, the hydrophobic makeup of the membrane interior makes it relatively impermeable to most water-soluble molecules.

Compare the metabolic contributions of various parts of the body.

The weight of tissue is 40% skeletal muscle, 33% skin, bone, and gut, 21% adipose tissue, and 6% organs. However, the metabolic rates of these are 58% organs, 22% skeletal muscle, 16% miscellaneous, and less than 5% adipose tissue.

What are the hierarchical levels of organization in the human body?

There are six levels of structural organization in the human body. 1) In the chemical level, atoms (tiny building blocks of matter) combine to form molecules (such as water, sugar, and proteins). 2) In the cellular level, molecules associate with each other in order to form cells. (smallest units of living things). Cells have some similar structures and functions, but individual cells have differing roles, shapes, and sizes. 3) In the tissue level, tissues are constituted by groups of similar cells that have a common function. There are four types of tissue. This level occurs in complex organisms but not simple organisms. 4) In the organ level, complex functions become possible. Organs are composed of 2 or more tissue types that perform a specific function in the body. 5) In the organ system level, a group of organs works together to achieve a specific purpose. 6) In the organism level, 11 different organ systems make up the living human being. This is the highest level of structural organization, and is the sum total of all structural levels working together to keep us alive.

What is the function of the gallbladder?

This is the small sac near the inferior surface of the liver. When food digestion isn't occurring, bile backs into the cystic duct and enters the gallbladder to be stored. Here, bile is concentrated by the removal of water. When fatty food enters the small intestine, a hormonal stimulus prompts the gallbladder to contract so that stored bile is released.

What are tolerance limits?

Tolerance limits are the max and min levels that variables can reach before they fail to function and can no longer recover. This is when medical intervention would be necessary.

Describe the changes in plasma glucose, insulin production, and cellular responses to insulin in Type I Diabetes.

Type I is the more severe type of diabetes, in which insulin is not produced. To regulate the blood glucose level here, insulin must be infused continuously by an insulin pump worn externally, or by a regimen of carefully planned insulin injections administered throughout the day. Without insulin production, glucose accumulates in the blood (because glucose transporters cannot come to cell surface). Cells cannot take it in like they would in a normal feedback loop.

Describe the changes in plasma glucose, insulin production, and cellular responses to insulin in Type II Diabetes.

Type II is the more mild type of diabetes. People with this produce insulin, but their insulin receptors are unable to respond to it (insulin resistance). These diabetics are treated with special diets or oral hypoglycemic medications that prod the islets into action and increase the sensitivity of the target tissues to insulin, and of beta cells to the stimulating effects of glucose. Without being able to respond to insulin, glucose accumulates in the blood because cells, and without transporters rising to surface, cells cannot take in glucose.

How do villi, microvilli, and circular folds contribute to increasing SA relative to V in the intestines?

Villi are fingerlike projections of the mucosa that give it a velvety appearance and feeling. Within each individual one, there is a rich capillary bed and a lacteal, and nutrients are absorbed via mucosal cells into both (tissue level). Microvilli are tiny projections of the plasma membrane of the mucosa cells that give the cell surface a fuzzy appearance (brush border). The plasma membranes bear brush border enzymes, which complete the digestion of proteins and carbohydrates (cellular level). Circular folds are deep folds of mucosa and submucosa layers which form a corkscrew slide to increase surface area and force chyme to travel slowly through the small intestine so nutrients can be absorbed more efficiently (organ level).

How is the surface area to volume ratio of the intestines increased? Explain how the higher SA/V ratio will speed up digestion & absorption of food.

Villi, microvilli, and circular folds increase the surface area of the small intestine. The greater the surface area in comparison to the volume of food, the more efficiently food will move through the digestive tract/the more quickly nutrients will be absorbed. Mechanical breakdown of food helps here, too, as the food becomes smaller relative to SA.

Are all parts of the body under homeostatic control?

Virtually every organ system plays a role in maintaining the constancy of the internal environment -- adequate blood levels of vital nutrients must be continuously present, and heart activity and blood pressure must be monitored and adjusted so that the blood is propelled with enough force to reach all body tissues. Body temperature must be controlled, and wastes must be eliminated.

How is water's role as a solvent important?

Water is a solvent, meaning it is a liquid in which smaller substances (solutes) can be dissolved or suspended, and it is an excellent one due to its polarity. Tiny solutes result in solutions, whereas larger solute particles result in suspensions, and intermediate in colloids. Molecules cannot react chemically unless they are in solution, so virtually all chemical reactions in the body depend on water's solvent properties. Small reactive chemicals (salts, acids, bases) dissolve easily in water and become evenly distributed. Because nutrients, respiratory gases (oxygen and CO2), and wastes can dissolve in water, water can act as a transport and exchange medium in the body, exchanging materials through blood and cells. In contrast, non polar molecules (no charge) do not dissolve easily in water.

In what direction does a variable change as a result of a negative feedback response to a stress?

When there is a change to the variable that makes it imbalanced, the negative feedback system effector does something to raise it to a balanced state. However, once it reaches this balanced state, the effector cuts off the response so that the variable stays in balance. This is how body temperature regulation works. Negative feedback moves the variable away from/in the opposite direction of the stress. So the stress rises the variable and the feedback lowers it back to balance again.

What is unique about the ratio of Carbon, Hydrogen & Oxygen in a carbohydrate?

With slight variations, the hydrogen and oxygen atoms in carbohydrates appear in the same ratio as water (two hydrogen to one oxygen). They are classified according to size and solubility in water as monosaccharides, disaccharides, and polysaccharides.

What happens to the body if glucose is too high or too low?

Without insulin, the blood level of glucose rises to a dramatically high level (ex. 600 mg/100 ml). When this happens, glucose begins to spill into the urine because the kidney tubule cells cannot reabsorb it fast enough. Water then follows in being flushed out of the body, leading to dehydration and diabetes mellitus. Because cells lack access to glucose, fats and proteins are broken down and used to meet the body's energy requirements. Body weight then declines. Loss of body proteins leads to a decreased ability to fight infections. When large amounts of fats are used for energy, the blood becomes acidic (acidosis) as ketones (intermediate products of fat breakdown) appear in the blood (ketosis). Coma and death will eventually result.