40.1: Overview of the Circulatory System
In all animals, except a few simple types, the circulatory system is used to transport nutrients and gases through the body. Simple diffusion allows some water, nutrient, waste, and gas exchange into primitive animals that are only a few cell layers thick; however, bulk flow is the only method by which the entire body of larger more complex organisms is accessed.
Why are open circulatory systems advantageous to some animals?
- They use less metabolic energy.
- They help the animal move faster.
- They do not need a heart.
- They help large insects develop.
Some animals use diffusion instead of a circulatory system. Examples include:
- birds and jellyfish
- flatworms and arthropods
- mollusks and jellyfish
- None of the above
Blood flow that is directed through the lungs and back to the heart is called ________.
- unidirectional circulation
- gill circulation
- pulmonary circulation
- pulmocutaneous circulation
Describe a closed circulatory system.
A closed circulatory system is a closed-loop system, in which blood is not free in a cavity. Blood is separate from the bodily interstitial fluid and contained within blood vessels. In this type of system, blood circulates unidirectionally from the heart around the systemic circulatory route, and then returns to the heart.
Describe systemic circulation.
Systemic circulation flows through the systems of the body. The blood flows away from the heart to the brain, liver, kidneys, stomach, and other organs, the limbs, and the muscles of the body; it then returns to the heart.
40.2: Components of the Blood
Blood is the liquid that moves through the vessels and includes plasma (the liquid portion, which contains water, proteins, salts, lipids, and glucose) and the cells (red and white cells) and cell fragments called platelets. Blood plasma is actually the dominant component of blood and contains the water, proteins, electrolytes, lipids, and glucose. The cells are responsible for carrying the gases (red cells) and immune the response (white). The platelets are responsible for blood clotting.
White blood cells:
- can be classified as granulocytes or agranulocytes
- defend the body against bacteria and viruses
- are also called leucocytes
- All of the above
Platelet plug formation occurs at which point?
- when large megakaryocytes break up into thousands of smaller fragments
- when platelets are dispersed through the blood stream
- when platelets are attracted to a site of blood vessel damage
- none of the above
In humans, the plasma comprises what percentage of the blood?
- 45 percent
- 55 percent
- 25 percent
- 90 percent
The red blood cells of birds differ from mammalian red blood cells because:
- they are white and have nuclei
- they do not have nuclei
- they have nuclei
- they fight disease
Describe the cause of different blood type groups.
Red blood cells are coated with proteins called antigens made of glycolipids and glycoproteins. When type A and type B blood are mixed, the blood agglutinates because of antibodies in the plasma that bind with the opposing antigen. Type O blood has no antigens. The Rh blood group has either the Rh antigen (Rh+) or no Rh antigen (Rh–).
List some of the functions of blood in the body.
Blood is important for regulation of the body’s pH, temperature, and osmotic pressure, the circulation of nutrients and removal of wastes, the distribution of hormones from endocrine glands, the elimination of excess heat; it also contains components for the clotting of blood to prevent blood loss. Blood also transports clotting factors and disease-fighting agents.
How does the lymphatic system work with blood flow?
Lymph capillaries take fluid from the blood to the lymph nodes. The lymph nodes filter the lymph by percolation through connective tissue filled with white blood cells. The white blood cells remove infectious agents, such as bacteria and viruses, to clean the lymph before it returns to the bloodstream.
40.3: Mammalian Heart and Blood Vessels
The heart is a complex muscle that pumps blood through the three divisions of the circulatory system: the coronary (vessels that serve the heart), pulmonary (heart and lungs), and systemic (systems of the body). Coronary circulation intrinsic to the heart takes blood directly from the main artery (aorta) coming from the heart.
The heart’s internal pacemaker beats by:
- an internal implant that sends an electrical impulse through the heart
- the excitation of cardiac muscle cells at the sinoatrial node followed by the atrioventricular node
- the excitation of cardiac muscle cells at the atrioventricular node followed by the sinoatrial node
- the action of the sinus
During the systolic phase of the cardiac cycle, the heart is ________.
- contracting and relaxing
- filling with blood
Cardiomyocytes are similar to skeletal muscle because:
- they beat involuntarily
- they are used for weight lifting
- they pulse rhythmically
- they are striated
How do arteries differ from veins?
- Arteries have thicker smooth muscle layers to accommodate the changes in pressure from the heart.
- Arteries carry blood.
- Arteries have thinner smooth muscle layers and valves and move blood by the action of skeletal muscle.
- Arteries are thin walled and are used for gas exchange.
Describe the cardiac cycle.
The heart receives an electrical signal from the sinoatrial node triggering the cardiac muscle cells in the atria to contract. The signal pauses at the atrioventricular node before spreading to the walls of the ventricles so the blood is pumped through the body. This is the systolic phase. The heart then relaxes in the diastole and fills again with blood.
What happens in capillaries?
The capillaries basically exchange materials with their surroundings. Their walls are very thin and are made of one or two layers of cells, where gases, nutrients, and waste are diffused. They are distributed as beds, complex networks that link arteries as well as veins.
40.4: Blood Flow and Blood Pressure Regulation
Blood pressure is the pressure exerted by blood on the walls of a blood vessel that helps to push blood through the body. Systolic blood pressure measures the amount of pressure that blood exerts on vessels while the heart is beating. The optimal systolic blood pressure is 120 mmHg. Diastolic blood pressure measures the pressure in the vessels between heartbeats. The optimal diastolic blood pressure is 80 mmHg.
High blood pressure would be a result of ________.
- a high cardiac output and high peripheral resistance
- a high cardiac output and low peripheral resistance
- a low cardiac output and high peripheral resistance
- a low cardiac output and low peripheral resistance
How does blood pressure change during heavy exercise?
The heart rate increases, which increases the hydrostatic pressure against the artery walls. At the same time, the arterioles dilate in response to the increased exercise, which reduces peripheral resistance.