CIRCULATORY SYSTEMS

As in plants, materials are transported in water throughout the animal body. Principles of physical pressure and bulk flow again important to operation of system.

GENERAL TYPES OF CIRCULATORY SYSTEMS

Gastrovascular cavities - Cnidaria, Platyhelminthes

• fluid from environment exchanges materials with body fluids in single-opening digestive cavity

Open circulatory systems - arthropods, many molluscs, nematodes

• blood in vessels part of time
• empties into sinuses in body part of time

Closed circulatory systems - annelids, vertebrates, some molluscs

• blood always contained in vessels

Question: Which type of circulatory system would operate with the highest pressure? How would this affect the rate of delivery of blood? The maximum supportable metabolic activity?

VERTEBRATE CIRCULATORY SYSTEMS

Components of system

heart - pumps blood throughout body

• cardiac muscle - generates own electrical impulse to contract; rate modified by nervous system
• atria - thinner walled receiving chambers
• ventricles - thicker walled delivery chambers
• divided into right and left sides to varying degrees in vertebrates

arteries - carry blood away from heart

• thick wall; high in elastin - expand and recoil

Question: Why is the thick wall and elastic nature of arteries important? What would happen if they lost their elasticity?

arterioles

• high in smooth muscle - constrict and dilate as needed

Question: What is the purpose of the smooth muscle in arterioles? Give an example of how it would function in a specific circumstance.

capillaries

• walls one cell layer thick
• tiny pores between cells

Question: Based on their structure, what is the function of capillaries? Why?

veins & venules - carry blood back to heart

• thinner walls
• one-way valves to prevent back flow when squeezed by surrounding muscle

Question: How do the structural features of veins reflect the conditions they operate under? Explain.

blood - transport of many important materials, heat, water

• 4 - 5 liters in adult human

plasma - mostly water with many dissolved materials

Question: List as many different things that would be transported in the plasma as you can think of, then look up more.

erythrocytes = red blood cells

• oxygen carried on Hb
• anucleate in mammals, nucleated in other verts
• flattened, concave discs, about same diameter as capillary; pass though single file
• short-lived - constantly replaced (millions per second!!) from cells in bone marrow

Question: What is the significance of the relative sizes of RBCs and capillaries?

Question: Why would RBCs have such a short life span?

leukocytes = white blood cells of many types

• function in immune response
• combat infectious organisms
• remove dead, foreign, abnormal tissue/cells
• also originate in bone marrow

platelets - fragments of cells, originate in bone marrow, involved in clotting

LEARN PATHWAY THROUGH HEART FROM LAB AND FIGURES  IN TEXTBOOK

• Note variations in general pathways among fish, amphibians & reptiles, and mammals & birds. (Fig 42.4 in textbook)
  
• Learn chambers, valves, and pathway through of heart and body of mammals. (Fig 42.5 and 42.6)
  

EXCHANGE AT CAPILLARIES

No carrier mediated transport systems, either active or passive in capillary walls

gases - follow own pressure gradient, as previously described

small solutes - follow own concentration gradient

Question: Give examples of small solutes, and indicate what direction their concentration gradient would be.

smaller proteins - may pass through small pores between cells in walls of capillary

large solutes (most proteins) - can not pass through capillary walls

water - two forces affect net movement of water

1. Protein concentration high in plasma, low in tissue fluid; other solute similar in both

Question: In what direction would water tend to move based on this? Why?

2. High hydrostatic pressure of blood in capillaries

Question: In what direction would water tend to move based on this?

Question: Since overall the hydrostatic pressure slightly exceeds the osmotic pressure, what will be the net movement of water?

Question: The cumulative effect of the leaking of water and small proteins from the blood capillaries is the loss of 3- 4 liters of fluid per day in a person. How does this compare to the typical blood volume of a human?

LYMPHATIC SYSTEM

• system of vessels and nodes that returns lost fluid and small proteins to cardiovascular system

Pathway of lymph fluid

• lymph capillaries in tissues -> larger & larger lymph vessels -> large veins near heart
• filtered by lymph nodes along the way

lymph vessels

• move fluid along toward heart by contraction of nearby skeletal muscles
• also contraction of smooth muscle in wall when stretched

lymph nodes

• meshwork of short fibers that trap old cells, parts of cells
• many leukocytes that destroy trapped material
• critical in immune function

Question: What effects would result from a lymph vessel that was blocked?

Question: Why do the lower legs and ankles swell and feel stiff after sitting for a long time, as on a plane?

Question: Why does a physician often feel a person's neck area if s/he suspects an infection?

Spleen - lymphoid tissue, but not involved in conveying lymph fluid

• filters blood in similar manner nodes filter lymph fluid

Question: What cells in particular would the spleen handle in very large numbers?

BLOOD PRESSURE - see lab material

ECG (electrocardiogram) - see lab material