Essay Questions
Explain how blood flows through the mammalian heart. Be sure to discuss the role of contraction and relaxation of the different heart chambers.
1. Blood that has been oxygenated in the lungs travels into the heart in the pulmonary veins and enters the left atrium. The atrium builds pressure until it contracts. 2. Blood flows through the opened, left AV valve to enter the left ventricle and the atrium relaxes to close the AV valve. 3. The left ventricle builds pressure, contracts, and pumps the oxygenated blood through the Aortic Valve into the systemic aorta, from which it flows to the entire systemic circuit (body tissues - lungs). As blood moves to the body, the ventricle relaxes 4. The blood, now partly deoxygenated flows into the venae cavae, then into the right atrium 5. The atrium contract and blood flows through the right AV valve to enter the right ventricle 6. The atrium relax, and the right AV valve closer. The right ventricle contracts and pumps the deoxygenated blood through the opened PV into the pulmonary trunk from which it flows to the lungs in the pulmonary circuit. The cycles begins again as oxygenated blood travels through the pulmonary veins back to the left atrium.
Where does nutrient absorption take place in the GI tract? Describe the mechanisms of nutrient absorption for proteins, carbohydrates, and lipids.
Absorption of all the products of digestion of all 5 foodstuffs takes place in the midgut of the GI tract. Monosaccharides, amino acids, and water-soluble vitamins are all hydrophilic (cannot diffuse across membrane), therefore they require a transporter protein in the cell membrane. Glucose absorption: glucose must first enter the cell from the gut lumen across the apical, brush-border cell membrane (this is done using a co-transporter (sodium-glucose transporter; active transport)), and then it must exit the cell into the blood across the basolateral cell membrane (passive transport, aka facilitated diffusion). Amino Acids: as many as seven distinct transporter proteins for amino acids are found in the apical, brush-border membranes. Each is specialized to transport a distinct set of amino acids into the epithelial cells. Many carry out secondary active transport using energy drawn from electrochemical gradients of Sodium or other ions. Fatty Acids: because these products are hydrophobic, they can pass through the membrane by simple diffusion. In the midgut, as fatty acids are produced by digestion they are dramatically solubilized by combing with bile salts to produce micelles. These micelles are not absorbed themselves, however, the fatty acids and other molecules dissociate from the micelles next to the apical membranes of gut epithelial cells and then move through the membrane by diffusion.
Compare and contrast avian, fish, and mammalian respiration. Be sure to discuss the relationship of flow between the oxygen-containing medium and blood, and how this relates to the efficiency of gas exchange.
Birds: have anterior and posterior air sacs. The air sacs aren't involved in gas exchange, but they pump air into the parabronchi at which gas exchange occurs. For fish, gas exchange occurs at the gill filaments located in the gills. The gill filament contain large amounts of capillaries. Counter-current exchange allows passive diffusion along the entire capillary bed. Blood is pumped via a single chamber heart in a single, unidirectional loop. For mammals, air in the bronchioles is led to alveolar ducts. The alveolar ducts end in thin-walled sacs called the alveoli. Each alveolus is surrounded by a network of capillaries, through which oxygen and carbon dioxide are exchanged. Exchange of gasses occurs via simple diffusion.
Explain the costs of living in a marine environment for a bony fish, a shorebird, and a mammal. What mechanisms do these animals use to maintain homeostasis?
Bony fish are hyposmotic regulators. That is, their blood osmotic pressure are far lower than the osmotic pressure of the seawater. Therefore, water tends to leave the body by osmosis. Their internal ion concentrations are also lower than that of seawater so they risk gaining excess ions from their environment. However, gill epithelium of bony fishes is positively charged on the inside, repelling sodium. Water loss is by urination is replaced using the active uptake of sodium and chloride in later parts of the intestine facilitate the osmotic uptake of water. Excess divalent ions are expelled in urine and excess monovalent ions are excreted by the gills. Shorebirds are also hyposmotic regulators. Birds risk losing water by pulmonary evaporation and gaining excess salt from the food they eat and sometimes drinking seawater. To cope with excess salt intake, birds have salt glands located in the head. They produce concentrated salt solutions that are discharged into the nasal passages. Salt glands are also able to extract pure H2O from seawater Mammals are capable of producing concentrated urine, which is a key to hyposmotic regulation.
Describe the process of airflow during both inhalation and exhalation through the bird respiratory system. What is the main surface of gas exchange in birds?
Inhalation: Air flows through the mesobronchus of each lung to enter the posterior sacs and posterior secondary bronchi. Both anterior and posterior air sacs expand. Suction, therefore is developed in both sets of air sacs and both receive gas. First, the posterior air sac is filled with fresh air from the environment. Second, the anterior air sac is filled with stale air that passed over the respiratory exchange surfaces in the parabronchi. The direction of ventilation is from posterior to anterior. Exhalation: Bother air sacs are compressed and discharge gas. Air exiting the posterior air sacs predominantly enters the posterior secondary bronchi to pass anteriorly through the parabronchi. Gas exiting the parabronchi anteriorly, combined with gas exiting the anterior air sacs, is directed into the mesobronchus via the anterior secondary bronchi and exhaled. The exhaled gas is gas that passed across the respiratory exchange surfaces.
Explain the steps involved in the cross-bridge cycle as it relates to muscle contraction.
Step 1:The binding of the myosin to the actin: the myosin head changes its confirmation (its shape) and binds to a binding site on the actin. Troponin and tropomyosin have bound to calcium and revealed the binding site. The myosin head is currently hanging onto an inorganic phosphate that it tore away from ADP. Step 2:Power stroke: The myosin head tears away from the inorganic phosphate and it changes shape (pushed forward). Myosin pulls actin toward the middle of the sarcomere. Step 3: Rigor: Myosin loses the ADP; changes shape and binds to the actin. Myosin is in a low-energy form. Step 4:Unbinding of myosin from actin: the myosin head is still bent, new ATP binds to the myosin head and myosin releases the actin. Step 5:Cocking of the myosin head: the new ATP rips the myosin head from the actin and returns to its original position where it can attach to another phosphate group and makes the ATP into ADP.
What is the importance of body temperature to animals? Explain the concept of the thermoneutral zone for endotherms, and how endotherms cope with temperatures below their thermoneutral zone.
Temperature is important for animals because temperature affects the rate of tissue processes, protein conformation, etc. The thermoneutral zone for endotherms is when the animal's metabolic rate remains constant at all the different ambient temperatures in the TNZ. Endotherms modify its insulation to maintain a constant metabolic rate in the TNZ (as temp decrease, insulation increases). Endotherms cope with temperatures below their thermoneutral zone by modifying the rate of metabolic heat production. The animal must raise its metabolic heat production to stay warm.
Explain how a signal is transmitted across a chemical synapse between neurons. Start with arrival of the action potential in the presynaptic cell and end with initiation of an action potential in the postsynaptic cell
The arrival of an action potential at the presynaptic terminal triggers the release of a chemical neurotransmitter across the synapse. The neurotransmitter binds to a receptor, and the binding of the neurotransmitter leads to the production of an electrical signal in the postsynaptic cell (in the cell body). The signal self-propagates along the axon, the conducting component of the neuron. At the end of the axon, there are division into presynaptic terminals where neural output occurs. The presynaptic terminals form synapses with other neurons or other types of cells.
Compare and contrast the digestion of carbohydrates, lipids, and proteins in the general GI tract. Where does digestion occur for each nutrient group, and what physiological processes are involved in their digestion?
The digestion of Carbohydrates: complex carbohydrates are broken down into dissacharides and monosaccharides by enzymes like dissacharidases, sucrases, lactase, etc. These enzymes are present in the apical membranes of the midgut epithelium. The digestion of Proteins: involves a larger array of enzymes than those used for digesting carbohydrates. This is because proteins are often required for the complete breakdown of chemical bonds that must be hydrolyzed for digestion. These enzymes are known as endopeptidases and exopeptidases. Usually begins in the stomach and continues in the midgut. The digestion of proteins produces free amino acids and oligopeptides. The free amino acids are what gets absorbed into the blood. The digestion of Lipids: Lipid digestion involves fewer types of chemical bonds that must by hydrolyzed, and thus fewer enzymes are required. However, lipids are insoluble in water. Therefore, enzymes and non-enzymatic emulsification processes. The midgut is the principle site of lipid digestion because of the presence of pancreatic lipases and bile salts. The digestion of fats and oils produced fatty acids, glycerol, and 2-monoacyloglycerols
What are the five main nutritional groups, and why are these nutrients required by animals? Describe one challenge associated with each group.
The five main nutritional groups are carbohydrates, proteins, fats, vitamins, and minerals. Proteins function in movement, some help catalyze reactions in the body needed for different physiological processes, they make up half the organic matter in a mammal, etc. A challenge associated with proteins is that they are not stored and there are only 10 essential amino acids that animals can synthesize. Also, nitrogen from the atmosphere can not be used to build proteins. Lipids are useful for storing energy, signaling, and as structural components of cell membranes. A challenge associated with lipids is, that many animals, including mammals, lack the enzyme needed to create the double bonds at the omega 3 and 6 position. Therefore, omega 3 and 6 are essential fatty acids. The rest must be ingested. There is also a process known as emulsification, that is required for lipid digestion. Carbohydrates are important for structural support and shape of cells and tissues, they function as storage compounds, and act as transport compounds. One challenge associated with carbohydrates is that many animals are unable to digest cellulose, chitin, or some other structural polysaccharides. Vitamins are important for all sorts of different things. Vitamin A, for example helps maintain teeth, bones, skin, and soft tissue health. Vitamin B helps with brain function. A challenge associated with vitamins is that none of them can be synthesized and must be ingested in small quantities. Minerals are similar to vitamins and help promote growth, strength, and overall health at all organismal levels. Minerals must be obtained from an animal's diet and a mineral deficiency can cause serious health problems.
Explain how urine is produced in the nephrons of the mammalian kidney. What processes contribute to urine production?
The nephron of a kidney is a blind-ended tube and at the blind end, the Bowman's capsule is closely associated with the glomerulus. Glomerular filtration produces cell-free and protein-free filtrate from blood plasma. Then tubular reabsorption selectively moves substances from the filtrate back into the blood. After reabsorbing water and solutes, tubular secretion moves unwanted substances from the blood into the filtrate which produces urine. The processes are filtration, reabsorption, and secretion.
Compare and contrast the three classes of hormones
The three classes of hormones are steroid, peptide hormones, and amine hormones. A steroid is a hormone derived from cholesterol. All have the same structure and can pass through the phospholipid layer directly into the cell where they bind to intercellular receptors and results in the alteration of gene transcription. Results can be quick and longer lasting. Peptide hormones are chains of amino acids that can vary in length; anywhere from 3 to 200 amino acids. These hormones are soluble in aqueous solutions and act by binding to receptors. The peptide never enters the cell, but it influences signal transduction of the receptor and initiates cellular response to the hormone. Finally, amine hormones are modified amino acids. Most are soluble in aqueous solutions and act via membrane-bound receptors
