Animal Physiology (lecture 19)

Question 1

What is the primary purpose of circulation (the circulatory system)?

Answer 1

Circulation permits the exchange of nutrients, gases and waste between an organism and its environment.

Question 2

Describe gas exchange in single celled organisms.

Answer 2

Single celled organisms can exchange directly with the environment, through diffusion.

Question 3

Describe gas exchange in Porifera and organisms with a gastrovascular cavity.

Answer 3

Porifera and organisms with a gastrovascular cavity have a body wall that is 2 cells thick, meaning both the inner (in contact with cavity) and outer layers (in contact with environment) of cells are in contact with the water environment, permitting direct exchange by diffusion.

Question 4

How do complex multicellular organisms perform gas exchange? (3)

Answer 4

Organisms with many cell layers need a circulatory system. These systems transport CO2 and O2 between respiratory organs and the rest of the body. They also transport nutrients from the digestive system to the rest of the body.

Question 5

All circulatory systems are composed of what 3 components? What two types of circulatory systems are there?

Answer 5

All circulatory systems are composed of 3 main components; a circulatory fluid (i), blood vessels (ii) and a muscular pump (heart) (iii). Circulatory systems can either be open or closed.

Question 6

Describe the open circulatory system. (4)

Answer 6

The fluid (i) in an open circulatory system is called hemolymph, consisting of a mix of blood and interstitial fluid. This is because the blood is only confined to short blood vessels (ii) that are either entering or exiting the heart. This fluid bathes the internal organs directly, and is pumped by one or more hearts (iii). Arthropods and Mollusks (except cephalopods) have an open circulatory system.

Question 7

Describe the closed circulatory system. (5)

Answer 7

In a closed circulatory system, blood (i) is confined to blood vessels (ii). Heart(s) (iii) pump blood into larger vessels, which branch into smaller vessels (capillaries) within organs. Gas exchange occurs between the blood in vessels and the interstitial fluid surrounding the cells (not the cells themselves). Annelids, Cephalopods and Chordata all have closed circulatory systems.

Question 8

Describe the circulatory system within the Phylum Chordata.

Answer 8

Phylum Chordata have a closed circulatory system with a 2-4 chambered heart. The following is true for all closed circulatory systems: blood flows from the heart to the arteries to the capillaries, where gas exchange occurs. Blood then flows from capillaries to the veins and then back to the heart.

Question 9

Describe the fish circulatory system.

Answer 9

Fish (2 chambered heart)
A fish’s heart consists of 1 atrium and 1 ventricle. Their type of circulatory system is called single circulation, since with every pump, blood flows through 2 capillary beds (gills and body organs) before returning to the heart. Blood pressure drops in capillary beds, giving oxygen more time to diffuse into the tissue (this is true for all organisms). In fish, body movement (swimming) helps with blood flow. This movement is required for fish to push blood completely through their single circulation circulatory system. Blood enters the heart through atria and leaves from ventricles.

Question 10

Describe the amphibian circulatory system.

Answer 10

Amphibians have 2 Atria and 1 Ventricule. Their type of circulatory system is called double circulation, wherein blood is pumped twice; once to the respiratory organs and once around the body. This is more efficient than single circulation; it ensures strong flow from lungs to organs (higher blood pressure).

Oxygenated and deoxygenated blood can mix in the single ventricle of the heart before being pumped around the body (loss in efficiency).

In most Chordata, the capillary bed that oxygenates the blood is referred to as the pulmonary circuit (lungs). In Amphibians, it is referred to as the pulmocutaneous circuit, because these capillaries are found both in the lungs and in the skin of the organism.

Question 11

The reptile circulatory system resembles that of amphibians. In what way are they different?

Answer 11

Most reptiles have 2 Atria and 1 Ventricle. Their circulatory systems resemble those of amphibians except that reptiles have an incomplete septum in the single ventricle of their hearts, which reduces the mixing of oxygenated and deoxygenated blood, thus making their circulatory systems more efficient.

Question 12

Describe the circulatory systems of mammals, birds and crocodiles.

Answer 12

These organisms have 2 Atria and 2 Ventricles. In this case, the left and right ventricles are completely separate (complete septum), meaning there is no mixing of oxygenated and deoxygenated blood. 4 chambered hearts are the most efficient and increase oxygen delivery to cells.

Question 13

Explain the importance of gas exchange.

Answer 13

Our cells require the gas exchange to perform cellular respiration;
O2 + glucose (C6H12O6) → CO2 + H2O
All eukaryotic organisms (and aerobic prokaryotes) must take in O2 and get rid of CO2.

Question 14

Gas exchange occurs between a _____ _____ and a _____ _____.

Answer 14

Gas exchange occurs between a respiratory medium and a respiratory surface.

Question 15

What is the respiratory medium? (2)

Answer 15

The respiratory medium is either air (21% O2) or water (wherein the concentration of O2 varies).

Question 16

What is the respiratory surface?

Answer 16

The respiratory surface is the part of the animal where exchange between the organism and the environment occurs (by diffusion), such as the gills or lungs. These surfaces must remain moist for O2 to diffuse easily.

Question 17

In _____ organisms, gas exchange occurs over the entire surface (_____ _____).

Answer 17

In unicellular organisms, gas exchange occurs over the entire surface (plasma membrane).

Question 18

In _____, _____ and _____, all cells are in contact with the respiratory _____, either via the water surrounding the organism or the water within its _____ _____(or just _____ for porifera).

Answer 18

In Porifera, Cnidaria and Flatworms, all cells are in contact with the respiratory medium, either via the water surrounding the organism or the water within its gastrovascular cavity (or just cavity for porifera).

Question 19

In _____ and _____, gas exchange can occur through the _____, and so this respiratory _____ must remain _____.

Answer 19

In Annelids and Amphibians, gas exchange can occur through the skin, and so this respiratory surface must remain damp.

Question 20

For respiration, terrestrial animals use _____ that are in contact with the _____, otherwise they use the _____ system (in insects).

Answer 20

For respiration, terrestrial animals use lungs that are in contact with the air, otherwise they use the tracheal system (in insects).

Question 21

Describe respiration / gas exchange in aquatic animals.

Answer 21

In aquatic animals, gas exchange occurs when water moves across (through) the gills (large surface area). To maximize efficiency of the gas exchange, gills utilize countercurrent exchange, meaning that blow flow in the gill capillaries is in the opposite direction to the flow of water over the gills. This means that the concentration of O2 in water is always higher than the concentration of O2 in blood, ensuring that the oxygen will always diffuse into the blood. In general, countercurrent exchange maximizes exchange, even as the concentration of O2 in the water decreases as it passes over the gills.

Question 22

What happens to blood pressure in the gill capillary bed? What is the result? In the gills of aquatic animals, what condition must be met so that respiration can continue to occur?

Answer 22

Blood pressure drops in the gill capillary bed to further maximize O2 uptake. However, water has to constantly flow over the gills for gas exchange to occur (gulping/ swimming with mouth open).

Question 23

Describe respiration / gas exchange in land animals (excluding insects).

Answer 23

Internal respiration surfaces open to the atmosphere through a system of narrow tubes. Land animals have the advantage of there being a higher concentration of O2 in the air than in water. O2 & CO2 also diffuse faster through air than water, meaning respiratory surfaces do not need to be as thoroughly ventilated (ventilation meaning the passage of the respiratory medium). However, diffusion drops if the respiratory surface dries up, a problem only land animals have to deal with.

Question 24

How do insects, such as grasshoppers, perform respiration?

Answer 24

Insects, such as grasshoppers, have a tracheal system for respiration (this is the most common among land animals, considering how many insects there are).

Question 25

Describe the tracheal system.

Answer 25

In insects, tiny tubes (tracheoles) branch throughout the body and carry air directly to cells for gas exchange to occur. Air enters the tracheal system through external openings called spiracles, located along the sides of the insect’s body.

The greatest advantage of the tracheal system is that O2 is delivered directly to every cell in the body.

Question 26

Describe lungs and compare them to the tracheal system.

Answer 26

Lungs are highly vascularized and are restricted to one location in the body. Thin layers of cells (closely associated with capillaries) serve as the respiratory surface that exchanges gases with air. The gap between the restricted lungs and the rest of the body is bridged by the circulatory system.

Question 27

Describe negative pressure breathing.

Answer 27

Humans, reptiles and birds use negative pressure breathing. During inhalation, air is pulled into the lungs when the lungs expand via the ribcage (rib muscles) and diaphragm (diaphragm contracts / moves down). During exhalation, air moves out as lungs return to resting volume (diaphragm relaxes / moves up).

When lungs expand, the air pressure in the lungs decreases so that it is lower than the outside atmosphere, drawing air inwards.

Question 28

Describe positive pressure breathing (air gulping).

Answer 28

Air is pushed (against the pressure gradient) into the lungs by closing the nostrils and contracting the buccal cavity (increasing pressure in the buccal cavity forces air into the lungs where pressure is lower). Frogs also use their skin (since positive pressure breathing isn’t very efficient) as a respiratory surface, which must remain moist to remain effective.

During inspiration, the nostrils open and the buccal cavity expands. The nostrils then close, the glottis opens and the buccal cavity contracts, thus causing the lungs to expand.

During expiration, the buccal cavity expands and the lungs contract. Then, the nostrils open, the glottis closes and the buccal cavity contracts.

Question 29

Describe the bird respiratory system.

Answer 29

Birds have a very efficient respiratory system (because of how much energy is needed to fly). Their lungs are connected to 8-9 air sacs (posterior and anterior). Air sacs expand during inhalation and retract during exhalation (the lungs do not expand), but only the lungs are involved in gas exchange.

Question 30

Step by step, explain the bird respiration process.

Answer 30

The air from the outside enters the posterior air sacs during the 1st inhalation. The air leaves the posterior air sacs and enters the lungs during the 1st exhalation. The air then leaves the lungs and enters the anterior air sacs during 2nd inhalation and then leaves the organism (from the anterior air sacs) during 2nd exhalation.

Question 31

Why is the bird respiratory system the most efficient respiratory system?

Answer 31

Air only moves in one direction through the respiratory system and is completely changed with every breath (while mammals have a bidirectional air flow, resulting in mixed air in the lungs which have a lower concentration of O2).

Question 32

Describe the respiratory surface of the lungs.

Answer 32

The respiratory surface of the lung is highly vascularized (there are many blood vessels). From the lungs, oxygenated blood travels back to the heart and is then pumped around the body to supply all tissues with O2.