Exam 3 - Lecture 19

Front 1

What is partial pressure? How do gases diffuse?

Back 1

Ventilation and gas exchange are accomplished by the respiratory system. The circulatory system is responsible for moving gases and other materials around the body

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Gas exchange between the environment and cells is based on diffusion

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O2 is high in the environment and low in tissues

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CO2 is high in the tissues and low in the environment

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O2 thus tends to move from the environment into the tissues and CO2 tends to move

from tissues into the environment

Gases In Air

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76% N2, 21% O2, 3% other gases (CO2, Ar, etc.)

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Fewer molecules are present at higher elevations

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In air and water, gas molecules move from regions of higher partial pressure to

regions of lower partial pressure

Partial pressure is the pressure of a particular gas in a mixture of gases

Front 2

1.

What are the four steps of gas exchange? Briefly describe each.

Back 2

1.

Gas Exchange: Four Steps

Ventilation – Air or water moves through a specialized gas-exchange organ, such as

lungs or gills

2.

Gas exchange – Diffusion of O2 and CO2 between air or water and blood at the

respiratory surface

3.

Circulation – Dissolved gases are transported throughout the body (along with

nutrients, etc.)

Cellular respiration – Cells uses O2 and produce CO2. In tissues where respiration

leads to low O2 and high CO2 levels, gas exchange occurs between blood and cells

Front 3

Gases diffuse in the largest amounts when what conditions are met? (Fick’s Law)

Back 3

Gases diffuse in the largest amounts when three conditions are met:

• Surface area for gas exchange is large

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Respiratory surface is extremely thin

Partial pressure gradient of the gas across the surface is large

Front 4

1.

How do human lungs pump air?

Back 4

1.

(a) During inhalation the diaphragm and rib muscles contract, increasing the volume of the lung (lowering pressure). During exhalation the diaphragm and rib muscles relax, decreasing the volume of the lung cavity (increasing pressure)
(b) A model of negative pressure ventilation

Front 5

1.

Homeostatic control: What happens when you exercise?

Back 5

• Exercising – Active muscle tissue takes up more O2 from the blood

1.

Homeostatic Control: Ventilation

o The partial pressure of O2 drops and partial pressure of CO2
o CO2 reacts with H2O to form carbonic acid
o Signals from neurons and pH detectors in the medullary respiratory center

cause breathing rate to increase

Front 6

What are the major components of blood? Briefly describe their functions.

Back 6

Blood

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Blood is a fluid CT with many functions, including transport of gases (O2, CO2),

nutrients, wastes, etc.

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Four major blood components:

o Red blood cells (RBCs) – involved in gas transport
o White blood cells (WBCs) – part of the immune system
o Platelets – cell fragments that participate in clotting, along with coagulation

factors
o Plasma – the ECM, composed of water, proteins and other miscellaneous

elements

Front 7

What is cooperative binding? Describe how this works with O2 and hemoglobin.

Back 7

Hemoglobin Transports O2 to Tissues

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Hemoglobin consists of four polypeptide chains. Each group is bound to a non-

protein group called a heme

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Each heme contains Fe2+, which can bind to an O2 molecule

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Cooperative binding makes hemoglobin very sensitive to changes in PO2

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The Oxygen-Hemoglobin equilibrium curve is sigmoidal. This shape occurs because the binding of each successive O2 molecule to a hemoglobin subunit causes a conformational change in the protein that makes the remaining subunits much more likely to bind oxygen (cooperative binding)

Cooperative binding of O2 by hemoglobin results in greater O2 delivery than non- cooperative binding. The hemoglobin is almost 100% saturated with O2 until it arrives at tissues

Front 8

What is the Bohr shift?

Back 8

The Bohr shift makes hemoglobin more likely to release O2 to tissues with low pH. As pH drops, O2 becomes less likely to stay bound to hemoglobin at all values of tissue PO2. Exercising tissues have a lower pH than resting tissues, and thus receive more O2 from hemoglobin

Front 9

Most CO2 is transported to the lungs in the form of .

Back 9

Carbonic anhydrase is key to CO2 transport in blood. This enzyme catalyzes the formation of carbonic acid. CO2 diffusing into RBCs is quickly converted into bicarbonate ions and protons

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This reaction maintains a partial pressure gradient favoring entry of CO2 into RBCs

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H+ produced by the reaction bind to deoxygenated hemoglobin

Most CO2 in blood is transported to the lungs in the form of HCO3-

Front 10

1.

Blood vessels: Know the structures and functions of arteries, capillaries, and veins

Back 10

1.

Blood Vessels

Arteries are tough, thick-walled vessels that take blood away from the heart. Small

arteries are called arterioles

2.

Capillaries are vessels whose walls are one cell thick, allowing for exchange of

molecules between blood and other tissues. Network of capillaries are capillary

beds.

Veins are thin-walled vessels that return blood to the heart. Small veins are called

venules.

Front 11

What is the sequence of blood flow through the human heart? What initiates its contraction?

Back 11

Electrical Activation of the Heart
• Pacemaker cells initiate contraction in the vertebrate heart. They are located in

the sinoatrial (SA) node, a region of the right atrium

Front 12

How does BP change throughout the circulatory system? Gas partial pressures?

Back 12

Blood Pressure Drops Dramatically in the Circulatory System

Capillary blood pressure drops because the amount of mechanical resistance to flow is a function of the total cross-sectional area of the vessels.

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In capillaries, blood flow is slower relative to arteries and veins because the same amount of fluid is passing though a much larger area

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Gas partial pressures vary throughout the circulatory system