Circulatory System
Animal Transport Systems
KEY CONCEPTS Functions of Circulatory System:
▪ Function 1. Nutrient and waste transport
▪ Diffusion 2. Oxygen and carbon dioxide transport
▪ Simple systems 3. Thermoregulation (physiological)
▪ Open and closed systems 4. Hormone control
▪ One and two cycle systems 5. Body defences
▪ Components of the mammalian heart 6. Structural
▪ Electrical activity of the heart
▪ Foetal and reptilian hearts Circulatory systems~ transport systems that transport two things:
▪ Lymphatic system matter (molecules) & energy (heat & chemical energy)
▪ Control of blood flow
Circulatory systems link exchange surfaces with cells throughout the body
▪ Diffusion ▪ Simple Systems
⤷ molecular trade that an animal carries out with its → One adaptation for efficient exchange is a simple
environment—gaining O2 and nutrients while body plan that places many or all cells in direct
releasing CO2 and other waste products involves contact with the environment
all cells in the body → Each cell can thus exchange materials directly
⤷ Small molecules in and around cells, including O2 with the surrounding medium
and CO2 , undergo diffusion → Animals that lack a simple body plan display an
⤷ Diffusion~ random thermal motion when there is a alternative adaptation for efficient exchange: a
difference in gradient. circulatory system
⤷ Such movement is slow for longer distances. → Such systems move fluid between each cell’s
⤷ It takes time to diffuse due to the proportional immediate surroundings and the body tissues ~
square of the distance. exchange has to occur over very short distances.
→ Some animals have body shapes that put them in
contact with their environment, enabling them to
live without a distinct circulatory system.
→ No circulatory system – e.g. Single-celled
organisms: flatworms
→ In hydras, jellies, and other cnidarians, a central
gastrovascular cavity functions in the distribution
of substances throughout the body, as well as in
digestion. (unspecialized system)
→ Cnidarians use coelom (3 layers) or
pseudocoelom (2 layers)
→ An opening at one end connects the cavity to the
surrounding water.
→ In animals with a gastrovascular cavity, fluid
bathes both the inner and outer tissue layers,
facilitating exchange of gases and cellular waste
→ Only the cells lining the cavity have direct access
to nutrients released by digestion.
→ because the body wall is a mere two cells thick,
nutrients only need to diffuse a short distance to
reach the cells of the outer tissue layer.
→ A flat body optimizes exchange by increasing
TJW NOTES surface area and minimizing diffusion distances.
,▪ Open and Closed Circulatory Systems
⇾ A circulatory system has three basic components:
• circulatory fluid
• a set of interconnecting vessels
• a muscular pump, the heart
⇾ Heart ~ powers circulation by using metabolic energy to elevate the circulatory fluid’s hydrostatic
pressure, the pressure the fluid exerts on surrounding vessels.
⇾ The fluid then flows through the vessels and back to the heart.
⇾ By transporting fluid throughout the body, the circulatory system functionally connects the aqueous
environment of the body cells to the organs that exchange gases, absorb nutrients, and dispose of
wastes
⇾ Circulatory systems are either open or closed
⇾ The fact that both open and closed circulatory systems are widespread among animals suggests that
each system offers evolutionary advantages.
⇾ The lower hydrostatic pressures typically associated with open circulatory systems allow them to use less
energy than closed systems.
⇾ The benefits of closed circulatory systems include blood pressure high enough to enable the effective
delivery of O2 and nutrients in larger and more active animals.
⇾ Closed systems are also particularly well suited to regulating the distribution of blood to different organs
Open circulatory system Closed circulatory system
→ The circulatory fluid, called hemolymph, is also the → A circulatory fluid called blood is confined to
interstitial fluid that bathes body cells. vessels and is distinct from the interstitial fluid
→ Includes arthropods such as insects, mollusks, → One or more hearts pump blood into large vessels
sea-squirts (tunicates~ belong to phylum that branch into smaller ones that infiltrate the
Chordata) & hagfish tissues and organs.
→ Contraction of the heart pumps the hemolymph → Chemical exchange occurs between the blood and
through the circulatory vessels into interconnected the interstitial fluid, as well as between the
sinuses ~ spaces surrounding the organs. interstitial fluid and body cells
→ Within the sinuses, the hemolymph and body cells → Annelids (including earthworms), cephalopods
exchange gases and other chemicals. (including squids and octopuses), and all
→ Relaxation of the heart draws hemolymph back in vertebrates have closed circulatory systems.
through pores, which have valves that close when → Advantages of closed systems:
the heart contracts. ⤷ Can be under high pressure
→ Body movements periodically squeeze the sinuses, – fast movement of blood
helping circulate the hemolymph (such as – ultra filtration
peristaltic movements) ⤷ More controllable
– blood is directed to specific tissue
– no mixing of different fluids
TJW NOTES
, Organization of Vertebrate Circulatory Systems
• Cardiovascular system~ is often used to describe the heart and blood vessels in vertebrates. Blood
circulates to and from the heart through an amazingly extensive network of vessels
• The three main types of blood vessels:
⤷ Arteries~ carry blood from the heart to organs throughout the body.
Within organs, arteries branch into arterioles.
⤷ Capillaries~ microscopic vessels with very thin, porous walls.
Networks of capillaries, called capillary beds, infiltrate tissues, passing within a few cell diameters of
every cell in the body.
Across the thin walls of capillaries, dissolved gases and other chemicals are exchanged by diffusion
between the blood and the interstitial fluid around the tissue cells
⤷ Veins~ the vessels that carry blood back to the heart.
At their “downstream” end, capillaries converge into venules
Artery → Arteriole → Capillary bed → Venule → Vein
• Arteries and veins are distinguished by the direction in which they carry blood, not by the O2 content.
• Arteries - carry blood away from the heart toward capillaries
• Veins - return blood toward the heart from capillaries.
• The only exceptions are the portal veins, which carry blood between pairs of capillary beds.
• The hepatic portal vein, for example, carries blood from capillary beds in the digestive system to capillary
beds in the liver.
• The hearts of all vertebrates contain two or more muscular chambers.
• The chambers that receive blood entering the heart are called ~ atria (singular, atrium).
• The chambers responsible for pumping blood out of the heart are called ~ ventricles.
▪ One Cycle Systems (Single Circulation) ▪ Two Cycle Systems (Double Circulation)
→ In sharks, rays, and bony fishes, blood travels → Amphibians, reptiles, and mammals have two
through the body and returns to its starting circuits of blood flow ~ double circulation
point in a single circuit ~ single circulation → The pumps for the two circuits are combined
→ These animals have a heart that consists of two into a single organ, the heart.
chambers: an atrium and a ventricle. → Having both pumps within a single heart
→ Blood entering the heart collects in the atrium simplifies coordination of the pumping cycles.
before transfer to the ventricle. → In one circuit, the right side of the heart pumps
→ Contraction of the ventricle pumps blood to a oxygen poor blood to the capillary beds of the
capillary bed in the gills, where there is a net gas exchange tissues, where there is a net
diffusion of O2 into the blood and of CO2 out of movement of O2 into the blood and of CO2 out
the blood. of the blood.
→ As blood leaves the gills, the capillaries converge → Pulmonary circuit~ because gas exchange takes
into a vessel that carries oxygen-rich blood to place in the lungs.
capillary beds throughout the body. → For many amphibians, it is called the
→ Following gas exchange in the capillary beds, pulmocutaneous circuit ~ because gas exchange
blood enters veins and returns to the heart. takes place in capillaries in both the lungs and
→ In single circulation, blood that leaves the heart the skin.
passes through two capillary beds before → Blood flows to the heart twice for every time it
returning to the heart. flows to the lungs
→ When blood flows through a capillary bed, blood → Systemic circuit~ begins with the left side of the
pressure drops substantially heart pumping oxygen-enriched blood from the
→ The drop in blood pressure in the gills limits the gas exchange tissues to capillary beds in organs
rate of blood flow in the rest of the animal’s and tissues throughout the body.
body. → The now oxygen-poor blood returns to the heart,
→ As the animal swims, however, the contraction completing the circuit.
and relaxation of its muscles help accelerate the → Heart repressurizes the system so blood
relatively sluggish pace of circulation. TJW NOTES pressure is high when blood reaches the tissue
→ Blood pressure is ↑ in systemic circuit
