Homework 6

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Ohio University, Main Campus *

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3450

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Biology

Date

Dec 6, 2023

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docx

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Uploaded by ProfessorArmadilloMaster858

Human Physiology (BIOS 3450) – Homework #6 _____ ______________ NAME DUE DATE : Fri, Apr 7 by 8:35am – Print out and drop off in-class or at Life Sciences Bldg 241 The total grade you receive for this homework will be either 0% or 100%. YOU WILL RECEIVE 100% ONLY IF YOU SHOW YOUR WORK AND ANSWERS TO ALL QUESTIONS. Example: You show your work and answers to all but one question  score = 0%. Example: For one of the questions you only give your answer in a couple words but don’t give the work that lead you to that answer  score = 0%. 1) List the partial pressure of CO 2 at each stage from the atmosphere, to the lungs, to the blood leaving the pulmonary capillaries, to the blood entering the systemic capillaries, to the blood leaving the systemic capillaries, and finally back up to the blood entering the pulmonary capillaries. Describe at each stage why the partial pressure increases, decreases, or remains the same. CO2, just like any other gas, flows according to the pressure gradient from high to low. The partial pressure of CO2 in the atmosphere is low due to the percentage of CO2 in the air, it is about 0.3 mm Hg. The partial pressure in the lungs is high, around 45 mm Hg, this means that the pressure difference will drive CO2 out of the lungs to the atmosphere. The partial pressure in the capillaries is 40 mm Hg, versus 45 mm Hg in the blood returning to the capillaries. The partial pressure of CO2 is lower in the blood because cellular respiration continuously produces CO2. In tissues, PCO2 is around 45 mm Hg and the PCO2 in blood is 40 mm Hg, this means that the pressure difference will diffuse out of the tissue and enter the blood. 2) Where in the circulatory system, and under what conditions, would % hemoglobin saturation be 50%? …97.5%? In both cases, explain your answers in terms of the O 2 -Hb dissociation curve and the P O2 at that place in the circulatory system. At the systemic capillaries, the percent of hemoglobin saturation increases until 75% and then the % hemoglobin saturation reaches 50% at a PO2 of 25 mm Hg. The released O2 diffuses into the tissue. At the pulmonary capillaries, the % hemoglobin saturation reaches 97.5% at PO2 of about 100 mm Hg. The O2 diffuses into the hemoglobin, then the PO2 in the blood rises. 3) Explain the net glomerular filtration pressure in terms of the three underlying pressures that lead to it. Does the net filtration pressure force fluid into or out of the glomerular capillaries? There are three underlying pressures that lead to net glomerular filtration pressure. The first one is glomerular capillary pressure. This is blood pressure within the capillaries that tends to be higher than in systemic capillaries. This is because efferent arterioles are much smaller than afferent arterioles and there is a high vascular resistance in efferent arterioles. The next underlying pressure is plasma-colloid osmotic pressure. This is when plasma proteins are stuck inside the glomerular capillaries, and they displace H2O. The last pressure is Bowman’s capsule hydrostatic pressure. This is pressure exerted by the fluid in Bowman’s capsule, which tends to push fluid out of the capsule. Overall, the net filtration pressure takes 10 mm Hg out of the glomerular capillaries and puts them into Bowman’s capsule. 4) Say an individual’s plasma concentration of glucose is 2 mg/mL, whereas the normal concentration is 1 mg/mL. a) Will this person excrete glucose in their urine? Explain how you arrived at your answer using the normal glomerular filtration rate (125 mL/min) and the tubular maximum of glucose (375 mg/min). If the individual has a plasma glucose concentration of 2 mg/mL, the total amount of glucose filtrated by the kidneys would be (125*2) = 250 mg/min, but the maximum amount of glucose the kidneys can reabsorb is 375 mg/min, therefore there is no excretion of glucose in the urine. b) What is the renal threshold of glucose? Again, explain how you arrived at your answer using the normal glomerular filtration rate and the tubular maximum of glucose. The renal threshold is the amount of glucose that should be present in blood so that it appears in the urine. The maximum rate of reabsorption in the kidneys is 375 mg/min, and the glomerular filtration rate is 125 mL/min. Therefore, if you take 375/125 = 3 mg/mL. This means that the renal threshold is 3mg/mL.

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