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inferior vena cava conveys deoxygenated blood (blood low in oxygen) from the lowerextremities of the body to the heart

superior vena cava coveys deoxygenated blood from the upper extremities of the body tothe heart

aorta conveys oxygenated blood (blood high in oxygen) away from the heartHeart

The heart is a hollow organ about the size of a fist and is composed of special muscle

tissue (cardiac muscle). It lies under the breast bone in the centre of the cardiothoracic cavity. In

the average lifetime the heart beats 250 million times and pumps 340 million litres of blood. Theheart is a sophisticated pump that is controlled by an electrical current that is initiated in the

brain.

The heart is divided into a left and right side by a muscular wall called the septum and

has four chambers.

Heart chambers and valves

The chambers of the heart include the: right atrium which receives deoxygenated blood (low in oxygen) from all over the body right ventricle receives blood from the right atrium and sends it to the lungs via the

pulmonary artery to become oxygenated and get rid of carbon dioxide left atrium receives oxygenated blood from the lungs and sends it to the left ventricle left ventricle receives blood from the left atrium and sends it out to the body via the aorta.

The heart wall consists of three layers - the endocardium is the inner lining, themyocardium is the muscle layer and the pericardium is the outer covering.

The chambers of the heart are separated by valves:

tricuspid valve is located between the right atrium and right ventricle bicuspid (mitral) valve is located between the left atrium and left ventricle pulmonary valve is between the right ventricle and the pulmonary artery aortic valve is between the left ventricle and the aorta

The major vessels that carry blood to and from the heart are:

inferior vena cava conveys deoxygenated blood (blood low in oxygen) from the lowerextremities of the body to the heart

superior vena cava coveys deoxygenated blood from the upper extremities of the bodyto the heart

aorta conveys oxygenated blood (blood high in oxygen) away from the heartBlood vessels

The cardiovascular system consists of arteries and veins and capillaries. Arteries carry

oxygenated blood to the cells of the body, veins carry deoxygenated blood away from the cells.

Arteries

Arteries are tubes that carry oxygenated blood (high in oxygen) away from the heart.

Arteries have thick, muscular, elastic walls. They branch off forming arterioles with thinnerwalls that then become capillaries. Arteries carry blood rich in oxygen and nutrients.

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Blood that comes from a wound to an artery is bright red and spurts. The aorta is the

largest artery and as it leaves the heart it branches into smaller arteries, eventually they become

capillaries.

Veins

Veins are tubes that carry deoxygenated blood (low in oxygen) from the cells back to theheart where it is pumped to the lungs so that the blood can pick up more oxygen. The veins haveone-way valves that help move the blood toward the heart.

Veins have thinner muscular walls. They carry blood back to the heart that is low in

oxygen and high in carbon dioxide, a waste product.

Capillaries

Capillaries are very small vessels that surround the cells of the body and facilitate the

movement of oxygen and nutrients into the cells and carbon dioxide and waste products awayfrom the cells.

Blood Blood is made up of a liquid (plasma) and cells. Blood is connective tissue, a red body

fluid made up of liquid (plasma) and cells. The body contains 5 to 6 litres of blood. Fifty-five

percent of the blood is plasma.

Plasma

Plasma is a straw coloured watery fluid in which the blood cells are suspended.

It contains antibodies (gamma globulin) and antitoxins, plasma proteins, mineral salts,nutrients, waste products such as urea and creatinine, gases such as oxygen and carbon dioxide,

hormones and enzymes.

The blood cells float in the plasma. They are produced in the bone marrow and lymphatic

tissues of the body.The bone marrow, liver and spleen destroy worn-out blood cells.

Blood cellsThere are 3 types of blood cells.

1. Erythrocytes or red blood cells (RBC) - carry most of the oxygen and small amounts ofcarbon dioxide. Haemoglobin carries the oxygen molecule and gives blood its colour.There are approximately 5 million RBC per cubic millimetre of blood and the average

life span is 100 - 120 days.

2. Leucocytes or white blood cells (WBC) - help fight infection as they can attackmicroorganisms. There are 7,000 - 8,000 WBC per cubic millimetre.

3. Thrombocytes (platelets) - are parts of cells which plug small leaks in the walls of bloodvessels and initiate blood clotting. There are 200,000 to 400,000 per cubic millimetre.

THE

The kidneys are a pair of bean-shaped organs found along the posterior wall of theabdominal cavity. The left kidney is located slightly higher than the right kidney because the

right side of the liveris much larger than the left side. The kidneys, unlike the other organs of the

abdominal cavity, are located posterior to the peritoneum and touch the muscles of the back. Thekidneys are surrounded by a layer of adipose that holds them in place and protects them from

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physical damage. The kidneys filter metabolic wastes, excess ions, and chemicals from the blood

to form urine.

UretersThe ureters are a pair of tubes that carry urine from the kidneys to the urinary bladder.

The ureters are about 10 to 12 inches long and run on the left and right sides of the body parallelto the vertebral column. Gravity and peristalsis of smooth muscle tissue in the walls of theureters move urine toward the urinary bladder. The ends of the ureters extend slightly into the

urinary bladder and are sealed at the point of entry to the bladder by the ureterovesical valves.

These valves prevent urine from flowing back towards the kidneys.

Urinary Bladder

The urinary bladderis a sac-like hollow organ used for the storage of urine. The urinary

bladder is located along the bodys midline at the inferior end of thepelvis. Urine entering theurinary bladder from the ureters slowly fills the hollow space of the bladder and stretches its

elastic walls. The walls of the bladder allow it to stretch to hold anywhere from 600 to 800

milliliters of urine.

Urethra

The urethra is the tube through which urine passes from the bladder to the exterior of the

body. The female urethra is around 2 inches long and ends inferior to the clitoris and superior tothe vaginal opening. In males, the urethra is around 8 to 10 inches long and ends at the tip of the

penis. The urethra is also an organ of the male reproductive system as it carries sperm out of the

body through the penis.The flow of urine through the urethra is controlled by the internal and external urethral

sphincter muscles. The internal urethral sphincter is made of smooth muscle and opens

involuntarily when the bladder reaches a certain set level of distention. The opening of the

internal sphincter results in the sensation of needing to urinate. The external urethral sphincter ismade of skeletal muscle and may be opened to allow urine to pass through the urethra or may be

held closed to delay urination.

Maintenance of HomeostasisThe kidneys maintain the homeostasis of several important internal conditions by

controlling the excretion of substances out of the body. Ions. The kidney can control the excretion of potassium, sodium, calcium, magnesium,

phosphate, and chloride ions into urine. In cases where these ions reach a higher than

normal concentration, the kidneys can increase their excretion out of the body to return

them to a normal level. Conversely, the kidneys can conserve these ions when they arepresent in lower than normal levels by allowing the ions to be reabsorbed into the blood

during filtration.

pH. The kidneys monitor and regulate the levels of hydrogen ions (H+) and bicarbonateions in the blood to control blood pH. H+ ions are produced as a natural byproduct of themetabolism of dietary proteins and accumulate in the blood over time. The kidneys

excrete excess H+ ions into urine for elimination from the body. The kidneys also

conserve bicarbonate ions, which act as important pH buffers in the blood.

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Osmolarity. The cells of the body need to grow in an isotonic environment in order tomaintain their fluid and electrolyte balance. The kidneys maintain the bodys osmotic

balance by controlling the amount of water that is filtered out of the blood and excretedinto urine. When a person consumes a large amount of water, the kidneys reduce their

reabsorption of water to allow the excess water to be excreted in urine. This results in the

production of dilute, watery urine. In the case of the body being dehydrated, the kidneysreabsorb as much water as possible back into the blood to produce highly concentratedurine full of excreted ions and wastes. The changes in excretion of water are controlled

by antidiuretic hormone (ADH). ADH is produced in the hypothalamus and released by

the posteriorpituitary gland to help the body retain water. Blood Pressure. The kidneys monitor the bodys blood pressure to help maintain

homeostasis. When blood pressure is elevated, the kidneys can help to reduce blood

pressure by reducing the volume of blood in the body. The kidneys are able to reduce

blood volume by reducing the reabsorption of water into the blood and producing watery,dilute urine. When blood pressure becomes too low, the kidneys can produce the enzyme

renin to constrict blood vessels and produce concentrated urine, which allows more water

to remain in the blood.

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