Biology Chapter 23

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CIRCULATORY SYSTEM: Circulatory systems facilitate(enable) exchange with all body tissues

To sustain life an animal needs to acquire nutrients, exchanges gases, and dispose of wastes.

These functions are enabled by the circulatory system

Circulatory system is needed for animals with complex and large bodies because they cannot exchange from diffusion alone

- Diffusion is unfit to transport materials over distances greater than a few cell widths therefore an internal transport system is necessary to bring resources close enough to cells for diffusion

Gastrovascular cavity

- Includes Cnidrians(hydras) and Flatworms

- Serves both in digestion and transport of substances throughout the body

- Nutrients and other materials have only a short distance to diffuse

- The cells can exchange materials directly with the gastrovascular fluid or with the water surrounding the animal

Animals with multiple layers of cells(true circulatory system)

- Muscular pump called heart

- Set of tubes called vessels

- Circulatory fluid(blood)

- Two types:

Open circulatory system (invertebrates, molluscs, arthropods)- Fluid is pumped through open-ended vessels and flows out among the tissues, therefore there is no distinction between the circulatory fluid and the interstitial fluid

Closed circulatory system (octopuses, humans, earthworms, vertebrates, squids)- The circulatory fluid(blood) is confined to vessels that keep the blood separated from the interstitial fluid

Three kinds of vessels:

Artery- Carries blood away from the heart into body organs and tissues

Vein- Returns blood to the heart

Capillary- Connects arteries and veins together

Key features:

Atrium- Receives blood from the veins(Oxygen rich blood)

Ventricle- Pumps blood to the gills(fishes) through large arteries(Oxygen poor blood)

Arterioles- Arteries branch into these, and they are small vessels that give rise to capllaries

Capillary Beds- Enter each organ and tissue in the body(thin wall of capillaries allows for chemical exchange between blood and interstitial fluid and converge into venules)

Venules- Converge into larger veins that return blood to the heart

- Cardiovascular system- Vertebrate circulatory system

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CIRCULATORY SYSTEM: Vertebrate cardiovascular systems reflect evolution

Single Circulation- Blood passes through the heart of a fish only once in each circuit through the body

- The blood starts in the ventricle, travels to the gill capillaries where blood pressure drops and transport oxygen rich blood through arteries into the body's organs and tissue; where it is then delivered to the atrium of the heart

Double Circulation(terrestrial animals with lungs)- Blood is pumped a second time after blood pressure has dropped in the lungs

- Pulmonary Circuit- Carries blood between the heart and gas exchange tissues in the lungs

- Systemic Circuit- Carries blood between the heart and the body's organs and tissues

- Frogs and other amphibians have three chamber hearts: Gas exchange occurs both in the lungs and across the thin and moist skin replacing the pulmonary circuit for a pulmocutaneous circuit

- Blood from the two atrium mixes into a single ventricle but a ridge still separates oxygen poor blood going into the pulmocutaneous circuit and oxygen rich blood going into the systemic circuit

- Turtles, snakes, and lizards= ventricle partially divided causing less mixture of diff bloods

- Crocodilians= ventricle completely divided

- In all birds and mammals the heart has four chambers: two atrium and two ventricles

- The right side handles oxygen poor blood; left side handles oxygen rich blood

- Supports the high metabolic rates of birds and mammals which are endothermic and use more energy

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CIRCULATORY SYSTEM: The human cardiovascular system and heart

PULMONARY CIRCUIT REGULATES BLOOD GOING IN AND OUT OF THE LUNGS AND STARTS FROM THE RIGHT VENTRICLE

- Pulmonary Arteries- Transports oxygen poor blood from the heart into the lungs

- Pulmonary Veins- Transports oxygen rich blood from the lungs into the heart

SYSTEMIC CIRCUIT REGULATES BLOOD GOING IN AND OUT OF THE BODY ORGANS AND TISSUES AND STARTS FROM THE LEFT VENTRICLE

​​​​​​​-Oxygen rich blood exists the heart through the aorta

-Superior Vena Cava- returns oxygen poor blood into the heart from the upper body after journeying the body tissues

-Inferior Vena Cava- returns oxygen poor blood from the lower body

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CIRCULATORY SYSTEM: The heart contracts and relaxes rhythmically

- Size of clenched fist

- Enclosed in a sac just under the sternum(breastbone)

- Formed mostly of cardiac muscle tissue

- Heart pumps oxygen poor blood to the lungs

- Heart pumps oxygen rich blood to the body

- Ventricles(pump blood to the lungs and body) have much thicker walls than the atrium because they are under much more pressure

- The left ventricle thicker than the right because it has to pump blood all the way around the body, but the right ventricle only has to pump it to the lungs BUT BOTH PUMP THE SAMLE VOLUME OF BLOOD

What keeps blood flowing in one direction?

- Flap like connective tissue valves are positioned in the exit of each chamber

- Atrioventricular valves(AV)= Between the atrium and the ventricle

- Semilunar valve= At the exit of each ventricle

- The valves are opened when pushed from one side and close when pushed from the other to prevent back flow

- Opening and closing of valves is what you hear("lub" = AV valves and "dup" is semilunar valves)

Cardiac Cycle- The contraction and relaxation of the heart in a rhythmic sequence

- When the heart contracts it pumps blood and when it relaxes blood fills its chambers

-Diastole- the heart is relaxed and blood flows into all four of the chambers

- Blood enters the right atrium from the vena cava and the left atrium from the pulmonary veins

- Ventricles are nearly filled with blood

- The AV valves are open and the seminular vavles are closed

-Systole- The contraction stage

- The atrium fills the ventricle with blood

- The ventricles contract(squeeze/reduce size)

- The AV valves close as the seminular vavles open to pump blood in large arteries

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