Download Circulatory System

Circulatory System
Objectives

Label a drawing of the horse’s circulatory system

Discuss the process of circulation in the horse

List the three components of blood

Describe the function of blood components

Describe the four chambers of the heart

List in order the steps in blood flow

Fully describe the function of the types of blood vessels
Heart

Located on the left side of the thoracic cavity, more or less between
the lungs.
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Surrounded by the pericardium – tough membranous sac

Four chambers
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Right atrium

Right ventricle

Left atrium

Left ventricle
Heart

Beating of the heart is controlled internally, but force and rate is regulated
by the central nervous system. When called upon, it beats faster and with
more force to move additional blood as needed.

Average horse heart weighs 7 – 8 pounds
Blood flow

Oxygenated blood:

Blood leaves the heart for circulation through the body from the left
ventricle.

Blood travels a path through progressively smaller arteries (blood vessels)
until it reaches the capillary beds.

Exchanges oxygen and nutrients for carbon dioxide and water and
other metabolic by-products
Blood flow

From the capillary beds, blood flow is conducted by progressively
larger veins to the vena cave (largest vein) to the right atrium of the
heart.

Blood then moves to the right ventricle through the mitral valve to
the right ventricle.

From the right ventricle blood flows to the lungs where it exchanges
CO2 for oxygen.

It then travels back to the left atrium, through the left mitral valve to
the left ventricle where the process continues.
Blood:

Blood is fluid tissue

Red alkaline fluid composed of:

Red blood cells

White blood cells

Plasma

Blood clots almost immediately when exposed to air.

About 7% of the horse’s weight is blood tissue
Blood Cells

Red cells

Contain hemoglobin that carries oxygen to the body

Originate in the bone marrow, liver and spleen

Also are the carriers of CO2 back to the lungs for exchange
White Cells

White cells are the soldiers of the immune system

Are manufactured with specific antibody properties as needed.

At any given time, antibodies are needed for proper immunity.
Plasma

Plasma is primarily the liquid (water) portion of the blood

Contains clotting properties that will stop bleeding
Blood vessels

Arteries:

Carry oxygenated blood

Thick walled, need to have strength to withstand pressure

At each heart beat arteries expand, then relax between beats.

Why we can feel the pulse.
Veins

Veins have thinner walls

One way valves opening to the heart

Carry unoxygenated blood back to the heart

Often located in muscle mass, so as the muscles contract, blood is
forced back to the heart

Venous blood is directed to the vena cava vessels, Cranial vena
cava and Caudal vena cava
Cappilaries

Microscopic mat of vessels that carry Oxygen and food to each cell

Walls are thin enough for Oxygen, food and CO2 to pass through
Lymph
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Well defined nodes and vessels

Nodes act as filters

Assists in carrying food to and from the digestive tract
Physiology of circulation

Heart beat is controlled by intricate set of nerves

Consists of contraction and relaxation of heart muscles

Split second rest between beats

Average equine heart rate: 38 -40 beats per minute