Respiration and Circulation in Animals

• Materials are exchanged in complex multicellular animals through all diffusion occurring through the skin.

Respiration and Circulation

• Oxygen-poor blood circulates from systemic tissues to branchial hearts and then to the gills.
• Oxygen-rich blood circulates from the gills to the systemic heart and then to systemic tissues.

Learning Objectives

• Define the role of diffusion and bulk flow in gas exchange between the atmosphere and animal tissues.
• Describe the mechanism of tidal breathing in the mammalian lung.
• Explain how hemoglobin functions in O2 transport.
• Outline the structure and function of the circulatory system, with emphasis on the mammalian system.
• Explain how capillaries exchange dissolved materials with surrounding tissues.
• Describe the stages of the cardiac cycle.

Efficiency of Gas Diffusion

• The rate of diffusion between two points is proportional to the difference in partial pressure.
• The rate of diffusion is inversely proportional to the distance molecules travel.

Diffusion Times Over Distances

• Diffusion over 10 nm takes 23.8 ns.
• Diffusion over 50 nm takes 595 ns.
• Diffusion over 100 nm takes 2.38 μs.
• Diffusion over 1 μm takes 238 μs.
• Diffusion over 10 μm takes 23.8 ms.
• Diffusion over 100 μm takes 2.38 s.
• Diffusion over 1 mm takes 3.97 min.
• Diffusion over 1 cm takes 6.61 hours.
• Diffusion over 10 cm takes 27.56 days.

Atmospheric Pressure

• Atmospheric pressure is 760 mmHg.
• Partial pressure of N2 (pN2) equals 760 mmHg * 78% = 593 mmHg.
• Partial pressure of O2 (pO2) equals 760 mmHg * 21% = 160 mmHg.
• Partial pressure of CO2 (pCO2) equals 760 mmHg * 0.03% = 0.2 mmHg.

Gas Exchange in Larger Animals

• Gas exchange involves the bulk flow of air or water through respiratory organs.
• Gases diffuse over the respiratory surface.
• Gas exchange is typically linked to bulk flow via a circulatory system.
• Oxygen diffuses from the circulatory system into cells, and CO2 diffuses out.

Bulk Flow Rate

• The rate of bulk flow is determined by pressure and resistance.
• Pressure is generated by a pump.
• Resistance is how difficult it is to move fluid through a network of vessels.
• Smaller diameter vessels have higher resistance, and longer networks have higher resistance; higher diameter vessels have lower resistance.

Gas Transport in Mammals

• Gas transport involves diffusion and bulk flow mechanisms in the lungs, heart, and circulatory system.

Oxygen Partial Pressure

• Oxygen partial pressure is much higher inside the body (in cells).
• pO2 in the atmosphere is approximately 160 mmHg at sea level.
• pO2 in the lungs is approximately 100 mmHg.
• pO2 in cells is ≤40 mmHg.
• pCO2 in the atmosphere is approximately 0.2 mmHg.
• pCO2 in cells is >45 mmHg.

Adaptations for Respiratory Surfaces

• Having a large respiratory surface maximizes diffusion.
• A very short distance between the respiratory surface and circulatory system maximizes diffusion.
• Hemoglobin binds O2, removing it from the blood plasma at the exchange surface.

Aquatic Animals

• Aquatic animals use external gills.
• Fish use internal gills.

Fish Breathing

• Water enters through the mouth when the mouth is open and the gill cover is closed.
• Water is expelled from the gill cavity through the gill openings.

Fish Gas Exchange

• Fish have internal gills protected by an operculum behind the mouth cavity.
• As water goes through the gills, it loses saturation.
• There is more saturation of water than blood
• Countercurrent flow in fish gills maximizes the amount of oxygen picked up.

Air vs Water for Breathing

• Air breathing has three advantages: faster gas diffusion, higher O2 content/lower CO2 content, and less work to ventilate.

Mammalian Respiratory System

• Air passes through the larynx and trachea to the lungs.
• Blood flows to the lungs (poor in O2).
• Alveoli facilitate gas exchange.
• Red blood cells in pulmonary capillaries pick up O2 and release CO2.
• Blood flows from the lungs (rich in O2).

Blood Oxygen Levels

• If the pO2 in a person's blood plasma is below that in their red blood cells, more oxygen would diffuse into the red blood cells.

Tidal Ventilation

• Negative pressure draws air into the lungs during inhalation.
• Positive pressure expels air from the lungs during exhalation.

Control of Breathing in Mammals

• High CO2 and low pH (high H+) are detected by chemosensors in the medulla.
• Carotid bodies detect low O2.
• Breathing can also be controlled voluntarily.

Bar-Headed Geese

• Bar-headed geese undertake yearly migrations over the Himalayas without oxygen masks.

Bird Respiratory System

• The bird respiratory system is highly efficient with a one-way flow of air through the lungs.

Airflow in Bird Respiratory System

• Airflow in the bird respiratory system flows to the posterior air sacs, then the lung, then the anterior air sacs.

Bird Lungs

• Bird lungs contain parabronchi.

Respiratory Exchange in Invertebrates

• Respiratory exchange in invertebrates occurs via the skin (including skin gills), gills, lungs, or a tracheal system.

Oxygen Carriers

• O2 carriers like hemoglobin bind O2 and effectively lower pO2 in the tissue.

Oxygen Saturation

• The oxygen saturation curve is sigmoidal due to cooperative binding of oxygen by hemoglobin.
• Myoglobin binds oxygen more readily than hemoglobin, facilitating oxygen delivery to muscle tissues.
• Fetal hemoglobin's curve is left-shifted, allowing the fetus to take up O2 from the mother's circulation.

Circulatory System Components

• A pump, often a discrete heart is needed.
• Vessels included are arteries, veins and capillaries.
• Arteries carry blood away from the heart.
• Veins carry blood towards the heart.
• Capillaries connect arteries and veins in closed systems.
• Open circulation involves blood flowing through a vessel with muscular thickenings, emptying into an open body cavity.
• Closed circulation involves blood flowing through connected blood vessels, pumped by muscular hearts.

Capillaries

• Blood pressure decreases across the system.
• Resistance in capillary beds results in the greatest pressure drop.
• The total cross-sectional area of capillaries results in slow blood flow.
• Slow blood flow contributes to efficient capillary exchange.

Blood Pressure in Capillaries

• Pressure = pressure out.
• 32 mmHg of Osmotic Blood pressure.
• 10 mmHg of Net pressure.
• Pressure = pressure in
• Blood pressure of 15 mmHg.
• Osmotic pressure of 9 mmHg
• Net pressure of 24 mmHg.

Fish Hearts

• Fish hearts have gills.
• Deoxygenated blood enters the atrium from a main vein and is pumped into the ventricle, then pumped from the ventricle into a main artery.

Amphibian Hearts

• Mixed oxygenated and deoxygenated blood is pumped out of the common ventricle into separate arteries leading to the lungs and tissues.

Mammalian Blood Flow

• Blood flow through the mammalian heart involves deoxygenated blood entering the right atrium, passing to the right ventricle, and being pumped into the pulmonary arteries.
• Oxygenated blood returns from the lungs through the pulmonary veins to the left atrium, enters the left ventricle, and is pumped into systemic circulation.
• During diastole, the atria contract, filling the ventricles with blood.
• During systole, the ventricles contract, pumping blood out of the heart.

Pressure in Pulmonary Circuit

• Lower pressure in the pulmonary circuit prevents fluid leaking from capillaries into alveoli.
• Aorta mean pressure equals 95 mmHg.
• Pulmonary arteries mean pressure equals 14 mmHg.

Control of Heart Beat

• Pacemaker generates action potentials that spread through the atria, activating the AV node.
• Action potentials are transmitted to the base of the ventricles, and the depolarization spreads through the entire ventricle.
• Sympathetic stimulation speeds up heart rate, while parasympathetic stimulation slows it down.

Cardiac Wave of Depolarization

• Propagation through the heart is essential for proper muscle contraction.

Cardiac Cycle Stages

• During diastole, the ventricles relax, and atrio-ventricular valves open, allowing blood to flow into the atria and ventricles. The aortic and pulmonary valves shut.
• At the end of diastole, the atria contract, pushing blood into the ventricles.
• During systole, the ventricles contract, pushing blood out into the aorta and pulmonary arteries. The atrio-ventricular valves shut, and the aortic and pulmonary valves open.

Control of Cardiac Function

• Cardiac function is controlled by the autonomic nervous system.
• Sympathetic stimulation increases the rate of SA firing, while parasympathetic stimulation decreases it.
• Hormones and the Starling effect also play a role.
• The Starling effect is when the force of contraction adjusts for return volume amount.