jimtrue.com : school : BSC2011 : CH 42: Animal Systems - Circulatory (pp. 871-886)

Posted by Jim True on August 14, 2005 3:01 PM. Last Updated October 22, 2006 9:23 PM

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CH 42: Animal Systems - Circulatory (pp. 871-886)

Functions

Transport -

of respiratory gases (except in C.Insecta).
of nutrients.
of liquid, gaseous and small solid wastes
of hormones, secreted substances that regulate metabolic processes.

Temperature Regulation - Increase or decrease body heat by vessel constriction or dilation.

System Types

the phylum Porifera exhibits no circulatory system. all fluid motio is from water propelled through chambers by chaoocytes.

Gastrovascular Cavity (GVC) - The more primitive phyla possess a simple sac-like digestive fluid filled cavity.

The movement of fluid in this GVC and water movemtn around the outside of the body continuously bathe cells with fluid.
Phyla Cnidaria and Platyhelminthes.

Open - Pump (heart) and blood vessels are usually present, but circulatory and body fluids freely mix in one or more large chambers (sinuses) in the body.

P.Nematoda - body fluids slosh in pseudocoelom.
P. Arthropoda, Mollusca (most) - Heart connects to open ended blood vessels which empty into open spaces (sinuses) around tissues in which body and circulatory fluids mix.

Arthropods have a large hemocoel, blood filled sinus that is remnant of blastocoel.
Since the blood and body fluids mix, the fluid is referred to as hemolymph.
In most animals with circulatory systems, gas transport for respiration is accomplished by blood cells possessing respiratory pigments (hemocyanin and hemoglobin are two major types).
Insect blood has NO respiratory pigments and NO gas transport function!

P. Echinodermata - Most transport is via coelomic circulation. Blood carrying circulatory vessels are rudimentary and basically for carrying nutrients.

Closed - Circulatory fluids propelled by heart through a continuously connected series of tubes of varying diameters.

Circulatory fluids remain separate from body fluids.
Found in C.Cephalopoda of P.lMollusca, Annelida and Chordata.

The Heart

Heart The circulatory pump.
In primitive chordates and most invertebrates (either open or closed systems), it is just a single chamber with muscular walls pushing fluids.
In vertebrates, the heart exhibits an increasing number of chambers to separate systemic (body) and respiratory circulation.
Simplest is 2 chambers, advanced is 4.
Fshes (Agnatha, Chondric, Ostei) - Possess 2 main chambers, one atrium (receives blood) and one ventricle (pumps blood).

Fishes have single circulation system, ie no separation of systemic and respiratory flow.
Deoxygenated blood flows through heart to gills, oxygenated blood from gills to body.
Circulation is assisted by swimming.

C. Amphibia and most C.Reptilia - 3 chambered heart (two atria, one ventricle) . Double circulation pattern.

Deoxygenated blood enters right atrium from body then is mostly pumped to lungs.
Oxygenated blood enters left atrium from lungs and is mostly pumped to body.
Little mixing of oxygenated and deoxygenated blood in ventricle.
This is because the ventricle basically alternates pumping oxygen-rich and oxygen-poor blood.
Most reptiles have an incomplete septum that partly divides the ventricle.
the septum is complete in crocodilians.

Order Crocodilia of C. Reptilia, C. Aves and C. Mammalia - 4 chambered heart divided into pulmonary (lung) and systemic (body) circuits.

Right atrium and right ventricle - deoxygenated blood.

Left atrium and left ventricle - oxygenated blood.

Right ventricle and left atrium - chambers of pulmonary circuit (heart to lungs and back).

Right atrium and left ventricle - chambers of systemic circuit (heart to rest of body and back).

Heartbeat originates in a special muscle.

Sinoatrial node in the right atrium regulates heartbeat ("pacemaker").

Nerve impulses from the SA node cause alternate relaxation (diastole) and contraction (systole). The blood pressure from the force of heart contractions alternates between these two actions.

BP - systolic pressure/diastolic pressure.

Heart beat and BP highly variable, depending on age, size, health, activity, body temperature and other factors.

A second node, the atrioventricular node, receives the signal from teh SA node and delays the transmission slightly to allow the atria to fully empty.

Smaller animals typically have higher heartbeat rates, e.g. mouse 400bpm, human 70 bpm, elephant 25 bpm, blue whale <10 bpm.

In normal human life span, heart beats about 2,500,000,000 times pumping 300,000 tons of blood!

Vertebrate Circulation

Blood Vessels -

Arteries and Arterioles - ALL carry blood AWAY from the heart.

Arterioles are branches of arteries throughout organs.

Walls are composed of three layers:

Inner endothelium (tunica intima)

middle layer of smooth muscle (tunica media)

outer layer of connective tissue (tunica externa)

Arterial and arteriole walls are thick to withstand high pressure of blood pumped by heart.

Tunica media is especially thick.

Vessels can constrict/dilate to maintain BP.

Both are circular or nearly so in cross section.

Pulmonary artery (right ventricle) and aorta (left ventricle) connect directly to heart.

Pulmonary arteries (left and right branches) are the ONLY arteries to carry deoxygenated blood.

Veins and Venules - These vessels ALL carry blood TOWARDS the heart.

Have 3 layers but tunica media is thin.

Have an irregular outline when seen in cross section.

Possess internal one way valves to prevent back flow of blood under low pressure, especially from extremities in systemic circuit.

Vena cava (right atrium) and pulmonary veins (left atrium) connect directly to heart.

Pulmonary veins (four, two right and two left) are the ONLY veins to carry oxygenated blood.

Capillaries - Microscopic in diameter (7-10 micrometers).

Only one layer, the endothelium. Allows for easy diffusion across surface.

Capillary "beds" connect at tissues, exchange substances by diffusions.

Arterial capillaries supply nutrients and O2.

Venous capillaries remove wastes and Co2

Lymphatic System - Extensive system of thin walled vessels that are separate from the circulatory vessels but intertwine with them at the capillary beds.

Connects to circulatory system at the vena cava.

Two main functions:

Accessory drainage system - Fluids forced out of the capillaries by blood pressure are recovered and returned to the circulatory system.

Immune Defense - Lymph nodes are swellings along the lymphatic vessels.

Store and replicate immune system components, e.g. white blood cells.

Nodes also act as bacterial filters.

Blood - Combination of a fluid (plasma) with numerous cells in suspension.

Plasma - mainly H2O plus dissolved salts and ions (electrolytes), proteins, gases (CO2, O2, N2), plus dissolved metabolic wastes.

Cellular components of blood include:

Erythrocytes ("red" + "cell") - Commonly known as "red blood cells" or RBC's.

Nucleated in some vertebrates but not in mammals.

Extremely small (~7 microns). Carry O2 and CO2 by means of a respiratory pigment, hemoglobin (Fe based - turned red when exposed to O2). Hemocyanin is in most invertebrates (Cu based - turns blue-green).

Present in enormous numbers (humans 5.4 million/ml in males, 4.8 million/ml in females).

Short lived and produced by other cells.

Produced in the red bone marrow in humans, and the kidneys and spleen of other mammals.

RBC's are destroyed in the liver, bone marrow and the spleen.

Leukocytes ("white" + "cell") - Known as "white blood cells" or WBC's because the cell membrane is largely transparent.

Involved in immune defense.

WBC's are nucleated, several different types present.

Cells destroy foreign invaders by phagocytosis or secretion of chemicals.

Far fewer (healthy human ~5-10 thousand/ml).

Platelets - Tiny cells which are critical in clotting of blood.

In animal is wounded, platelets adhere to wound and release substance to attract other platelets.

Also release a protein called fibrin that forms a mesh to "dam up" wound.

More numerous than WBC's, ~250-400 thousand/ml.

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