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Animal Nutrition and Digestion
Animal Nutrition and Digestion

Animal Nutrition and Digestion Questions

Bring on the tough stuff

1. Describe a situation where renin is released but ADH is not.

2. Where do the stages of food ingestion, digestion, absorption, and elimination take place along that alimentary canal?

3. Describe osmoregulation in a saltwater fish.

4. In digestion, where and why does active transport become important?

5. How does the proximal tubule regulate pH?

6. Describe a situation where blood may become hypoosmotic? When does blood become hyperosmotic?

7. Patients with diabetes insipidus have genetic mutations that block ADH's ability to increase aquaporin channels in the collecting tubule. How might this affect urine concentration?

8. Compare and contrast the three types of nitrogenous waste.

9. Describe the physiological responses to increased blood osmolarity.

10. Describe the ways in which kidneys maintain homeostasis.

11. Describe the role of ammonia in the proximal tubule.

12. The drug furosemide blocks the transport of Na+ and Cl- ions specifically in the ascending Loop of Henle. How might this drug affect urine volume and concentration?

Possible Answers

1. Describe a situation where renin is released but ADH is not.

Renin is released with low blood volume or pressure while ADH is released when high blood osmolarity is sensed. If a lot of blood is lost through that nasty paper cut, blood volume will be affected and blood osmolarity will remain constant.

2. Where do the stages of food ingestion, digestion, absorption, and elimination take place along that alimentary canal?

Food ingestion starts in the oral cavity. Food then flows through the pharynx and esophagus that leads to the stomach. At the stomach, both mechanical and chemical food digestion begins. From the stomach, digested food passes into the small intestine where more digestion and absorption occur. From the small intestine, waste moves into the large intestine where it is packed and stored before it leaves us as Number 2.

3. Describe osmoregulation in a saltwater fish.

Saltwater fish tend to be hypoosmotic to their surroundings. Their internal salt concentrations are lower than that of the salt water surrounding them. That means that sea water can be dehydrating, as water flows out of the fish through osmosis. To regulate their body fluids, marine fish will excrete small amounts of highly concentrated urine from their kidneys and excrete salt from their gills.

4. In digestion, where and why does active transport become important?

Active transport is a crucial component to the absorption of nutrients at the microvilli in the small intestine. While passive transport does not require energy to generally move nutrients down their concentration gradient, active transport requires energy and takes less time. Expenditure of energy allows nutrients to move against their concentration gradient, and allows concentrations to build up. Specifically, active transport of sugars is a critical part of absorption in the small intestine.

5. How does the proximal tubule regulate pH?

At the reabsorbtion stage in the proximal tubule, body fluid pH is regulated with both active and passive transport. First, the cells lining the tubule secrete H+ and ammonia (NH3). The ammonia buffers the filtrate, trapping the H+ ions, and forms the ammonium ion (NH4+). The more acidic the filtrate, the more ammonia that is produced and secreted into the filtrate. Secondly, the proximal tubules also reabsorb HCO3- (a natural buffer) back into the interstitial fluid. When this HCO3- leaves the filtrate, it buffers the pH in the surrounding body fluids.

6. Describe a situation where blood may become hypoosmotic? When does blood become hyperosmotic?

Hypoosmotic blood can be the result of any situation in which too much water is consumed or reabsorbed by the blood. If excess water is consumed without balanced salt intake, a person can become disoriented, and may start seeing green giraffes. Hyperosmotic blood can occur when a person is sweating due to excess heat or exercise. When they sweat, people lose water and the salt concentration in the blood rises.

7. Patients with diabetes insipidus have genetic mutations that block ADH's ability to increase aquaporin channels in the collecting tubule. How might this affect urine concentration?

ADH release is stimulated under conditions of high blood osmolarity, and acts to lower osmolarity by increasing water reabsorption into the blood. If aquaporin channels are unable to increase water absorption in cases of high blood osmolarity, too much water will be excreted in the urine. Severe dehydration can occur, and it is also likely that a high volume of very dilute urine will be excreted.

8. Compare and contrast the three types of nitrogenous waste.

Nitrogenous waste is excreted as ammonia, urea, or uric acid. Ammonia is quite toxic, and is only tolerable in very low concentrations. Because it is water soluble, many aquatic species are able to effectively dilute the ammonia concentrations, and it is often lost through the gills and into the surrounding water through diffusion.
Urea is produced in the liver and is the result of a highly energetic reaction between ammonia and carbon dioxide. Although its production requires a lot of energy, urea has very low toxicity (it is safe at high concentrations), and therefore does not require much water for its storage. Animals who may have limited access to water will excrete urea because little water is lost during its excretion.

Uric acid is the final form of nitrogenous waste. It's not water soluble (so no water is lost during its excretion) and relatively safe when stored in high concentrations. But uric acid requires a great deal of energy to be produced from ammonia, making it energetically expensive.

9. Describe the physiological responses to increased blood osmolarity.

When high blood osmolarity is sensed by the pituitary gland, antidiuretic hormone (ADH) is released. ADH will add aquaporin channels to the collecting duct to increase water permeability. As water flows out of the filtrate and back into the blood, urine becomes more concentrated and volume decreases.

10. Describe the ways in which kidneys maintain homeostasis.

A kidney removes nitrogenous waste, ions, and other waste from the blood. It maintains water balance and is critical in regulating blood osmolarity. Through the proximal and distal tubules, the kidney also monitors and regulates blood pH. Because hormonal control of blood volume and pressure is mediated through the kidney, this organ also maintains blood volume and pressure.

11. Describe the role of ammonia in the proximal tubule.

Ammonia is secreted into the proximal tubule lumen to maintain the filtrate pH when hyrodgen ions get added and make the filtrate too acidic.

12. The drug furosemide blocks the transport of Na+ and Cl- ions specifically in the ascending Loop of Henle. How might this drug affect urine volume and concentration?

When furosemide blocks NaCl reabsorption by the thick ascending Loop, it will increase NaCl concentrations in the urine. Because the NaCl is no longer reabsorbed, the associated increase the osmolarity of the interstitial fluid will also not occur. Because water reabsorption at the descending Loop is dependent upon this osmolarity gradient, lower interstitial fluid osmolarity will decrease the water reabsorption. Decreased water reabsorption yields increased urine volume. Therefore, the furosemide diuretic increases NaCl concentration in the urine, but also increases its volume.

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