Exam 3

What is surface area-to-volume ratio (SA:V)?

Surface area divided by volume; it describes area available relative to body size

What are the two factors affecting SA:V?

Shape and size

What is diffusion and does it require energy?

Net movement of molecules from high to low concentration, it does not require energy

How does shape affect SA:V?

It affects diffusion efficiency

How does SA:V affect diffusion?

Higher SA:V = faster exchange

How does SA:V affect heat exchange?

Heat exchange directly depends on SA:V ratio. Higher SA:V = faster heat loss or gain

Which loses heat faster, small or large organisms?

Small organisms because they have higher SA:V

Which conserves heat better, small or large organisms?

Large organisms because they have lower SA:V

Which of these organs has the greatest SA:V ratio and why?

• Small intestine

• Skin

• Liver

Small intestine b/c it has a lot of folds and contact with its environment

Why does the liver have a low surface area to volume ratio?

B/c it is a big, chunky mass of tissue which means it has a large volume and makes the ratio lower

What things/shapes contribute the most to surface area?

More complicated shapes with a lot of thin, branching parts are going to contribute a lot to surface area

Organisms seek to __ SA:V ratio

optimize

Why are cells usually small?

Small cells have high SA:V, making exchange across membranes more efficient

Why do tropical plant leaves have high SA:V?

To maximize gas exchange

Why do cacti have a low-SA:V trunk?

It helps minimize water loss

What is homeostasis?

Maintaining a stable internal state despite changing condition

What does homeostasis regulate?

Temperature, water balance, pH, hormones, metabolites, O2 and CO2

What is negative feedback?

A response that counteracts a change and returns conditions toward a set point

What is positive feedback?

A response that reinforces a change, making the response stronger

What is an example of negative feedback?

Body temperature regulation: sweating cools the body when it is too warm and shivering warms the body when it is too cold

What is an example of positive feedback?

Blood clotting: activated platelets recruit more platelets to the site of injury

How does negative feedback stop a response?

Enough of the response signal causes further production to stop

What is the easiest way to identify negative feedback?

Opposite response = brings the body back to normal

What is the easiest way to identify positive feedback?

Same direction = makes the original change bigger

Are breathing rate and CO2 regulation negative or positive feedback?

Negative feedback

Is childbirth a positive or negative feedback loop?

Positive feedback

Which does not dispel heat well and has a greater risk of overheating, small or large bodies?

Large bodies

What is endothermy?

Using metabolic heat to help maintain a constant internal temperature

What is ectothermy?

Cannot effectively regulate body temp and rely mainly on external heat sources to regulate body temperature

What is heterothermy?

Using endothermic and ectothermic strategies at different times or in different regions

Why is 'cold-blooded' misleading?

Ectotherms can become very warm by absorbing heat from their environment

How does environmental temperature affect an endotherm's body temperature?

Body temperature stays relatively constant

How does environmental temperature affect an ectotherm's body temperature?

Body temperature rises or falls with the environment

What happens to endotherm metabolism in colder temperatures?

Metabolic rate increases to produce more heat

What happens to ectotherm metabolism in colder temperatures?

Metabolic rate decreases

What is the thermoneutral zone?

Temp range where an endotherm maintains body temperature without extra metabolic heat production

What is basal metabolic rate?

Minimum energy needed to maintain basic life functions at rest

What is countercurrent heat exchange?

Opposite-flowing blood transfers heat, warming returning blood while conserving core heat

Why does heat transfer to veins during countercurrent exchange?

A temperature difference always exists, so heat moves from warmer blood to cooler blood

What is Fick's equation?

Q = DA (P1 - P2)/L

What is Fick's law of diffusion?

It explains what affects the rate of gas exchange

What does Q represent in Fick's equation?

The rate of gas diffusion or exchange between points 1 and 2

What does D represent?

Diffusion coefficient: depends on the gas, medium, and temperature of the system

What does A represent?

Cross-sectional surface area available for gas exchange

What does P1 - P2 represent?

The difference in partial pressure driving diffusion

How does increasing cross-sectional surface area affect gas exchange and diffusion?

It increases the rate of both

How does increasing the partial pressure difference affect diffusion?

Increases the rate of diffusion

How does increasing diffusion distance affect gas exchange?

Decreases the rate of diffusion

In Fick's Law, can the diffusion coefficient (D) change? When?

Yes, it changes with the molecule, medium, or temperature

What are the 4 steps of gas exchange in the order shown in this photo?

1. Ventilation

2. Gas exchange

3. Circulation

4. Cellular respiration

What is ventilation?

Moves air or water over gas exchange surfaces

What is perfusion?

Circulation of blood into, over, and away from the gas exchange surfaces

What are the two ways biological systems optimize the diffusion rate through active movement of gases and blood?

1. Maintain a steep partial pressure gradient through ventilation and perfusion

2. Reduce diffusion path length

Why is the water median is harder to breathe in?

There is less oxygen, higher density, and viscosity, making it harder to move

How are fish gills structured, and where does gas exchange occur?

Gill arches have vessels and support filaments, which contain lamellae where gas exchange occurs

What are lamellae in fish gills?

Thin structures with large surface area where gas exchange occurs

Why are fish gills so efficient at gas exchange?

Lamellae provide a large surface area and short diffusion distance

Why is countercurrent exchange efficient?

It maintains an oxygen pressure gradient along the entire gill, allowing more oxygen to enter the blood

What is concurrent exchange?

Water and blood flow in the same direction; they quickly approach equilibrium, reducing oxygen transfer

What is countercurrent exchange?

Water and blood flow in opposite directions across the gills

Exchange is more complete with concurrent or countercurrent flow, and why?

Countercurrent flow b/c a gradient of O2 saturation exists over the full length of exchange surfaces

Why is concurrent flow less efficient for respiration?

At equilibrium, there is no more gas exchange so there is no net movement and it is not able to extract oxygen for the entire length of the lamella

What is the big difference between concurrent and countercurrent flow and why is countercurrent highly efficient for respiration?

There is always net movement in countercurrent flow, but in concurrent flow, there is no net movement

In countercurrent exchange, which has higher O2 levels: water or blood?

Water

Where does gas exchange occur in mammalian lungs?

In the alveoli

Why are alveoli effective for gas exchange?

They provide a large surface area and a thin diffusion barrier

Order of gas exchange in the human body:

1. Trachea

2. Bronchi

3. Bronchioles

4. Alveoli

What is the respiratory tract lined with and what does it do?

It is lined with mucus and surfactant, which trap microbes/debris and reduce the work of breathing

How does gas exchange work in the alveoli?

It allows the blood to quickly take up oxygen through red blood cell hemoglobin and pass out of the lungs, back into the heart, and into circulation

How does gas exchange in mammalian alveoli follow Fick's Law?

Maximize D and A, minimize L, and maintain a large P1 − P2 through perfusion

What happens to gas exchange in emphysema?

Alveoli break down, reducing surface area and increasing volume which decreases gas exchange

What is the ventilation-perfusion (V/Q) ratio?

The relationship between air reaching alveoli (ventilation) and blood reaching them (perfusion)

What is the average healthy V/Q ratio?

When V and Q are similar

What is the shunt perfusion V/Q ratio, and what factors mess up ventilation?

Low V/Q, close to zero, and airway obstruction or pneumonia

What is dead space ventilation, and what factors mess up perfusion?

High V/Q, and pulmonary embolism or cardiogenic shock

What is the difference between shunt perfusion and dead space ventilation?

Shunt perfusion is perfusion w/o ventilation, and dead space ventilation is ventilation w/o perfusion

What happens to O2 and CO2 at the lungs?

O2 enters the blood, and CO2 leaves the blood

What happens to O2 and CO2 at body tissues?

O2 leaves the blood, and CO2 enters the blood

What protein carries most oxygen in the blood?

Hemoglobin in red blood cells

How many O2 molecules can one hemoglobin bind?

Up to four

How is most CO2 transported in the blood?

As bicarbonate ions (HCO3-)

Birds and mammals have a ___ -chambered heart and their pulmonary and systemic circuits are totally ___

Four, separate

At body tissues, how is CO2 transported in the blood?

CO2 enters RBCs: ~70% becomes HCO3-, ~20% binds hemoglobin, and ~5% dissolves in plasma, and HCO3- is pumped back into blood plasma, and Cl- ions are pumped out

At the lungs, how does the process happens in reverse?

HCO3- converts back into CO2, which leaves the blood and is exhaled

What does the oxygen dissociation curve show?

The relationship between oxygen partial pressure (pO2) and hemoglobin oxygen saturation

Why is the oxygen dissociation curve S-shaped (sigmoidal)?

Cooperative binding b/c binding one O2 makes it easier for hemoglobin to bind the next O2 molecules

What happens as O2 binds to hemoglobin in the oxygen dissociation curve, and which events are the most favorable?

Hemoglobin changes shape with each O2 binding, the 2nd and 3rd binding are very favorable

What does high hemoglobin affinity for O2 mean?

Hemoglobin binds oxygen more easily and holds onto it more tightly

What happens to hemoglobin affinity at lower pH and higher CO2? What type of effect is it?

Affinity decreases, helping hemoglobin unload O2 to active tissues; this is the Bohr effect

What is the Bohr effect?

Higher CO2 and lower pH reduce hemoglobin's oxygen affinity, promoting oxygen unloading

Which has the highest O2 affinity (in order): adult hemoglobin, fetal hemoglobin, or myoglobin?

Myoglobin has the highest, followed by fetal hemoglobin, then adult hemoglobin

Loading and unloading in the oxygen dissociation curve is very efficient at

Lower pO2

What is tonicity?

A solution's effect on water movement into or out of a cell

What happens to an animal cell in a hypertonic solution?

Water leaves; the cell shrivels

What happens to an animal cell in a hypotonic solution?

Water enters; the cell swells and may burst

What happens to an animal cell in an isotonic solution?

No net water movement; cell stays normal

What happens to a plant cell in a hypotonic solution?

Water enters; the cell becomes swollen and stiffens but retains its shape b/c a cell wall is present

What happens to a plant cell in a hypertonic solution?

Water leaves; the membrane pulls away from the cell wall

What happens to a plant cell in an isotonic solution?

The cell becomes limp b/c there is no net movement of water