Lesson Note
Subject: Biology
Topic: The Heart As Circulatory System.
Lesson Objectives: By the end of the lesson, the learners should be able to:
1. Describe the structure of the heart;
2. Draw a well labeled diagram of the heart;
3. Differentiate between arteries and veins;
4. Explain systole and diastole;
5. Draw the cross section of the artery.
THE HEART
The heart is a muscular and powerful organ responsible for pumping blood in the system of mammals. It is located within the chest cavity and protected in the ribs and sternum. The pumping action of the heart is known as heart beat (heart beat). Heart beat per second varies from animal to animal and is often increased at moments of excitement e.g. Humans heart is about 72 beats per minutes.
The special muscles making up the heart is known as cardiac muscles and the heart is enclosed in a two layered tough protective membranes called the pericardium. Pericardial fluid fills the space between the heart and pericardium. It reduces the friction arising from pumping movement of the heart against its surrounding tissues.
STRUCTURE OF THE HEART
The human heart is divided into four chambers, the right and left auricles, the right and left ventricles. The walls of the ventricles are often thicker than those of the auricles. The left ventricles especially have a thick wall because it pumps blood out to all other parts of the body and this requires more pressure.
The heart is divided into two halves by a central barrier called septum. Bicuspid valves separate the left auricle and the left ventricle. This ensures that blood flows only in one direction i.e. from the auricles to the ventricles. Similarly the tricuspid valve exists between the right auricle and the right ventricle. It serves the same function as the former. These bicuspid valves are held in place by special fibers, non-elastic cords known as chordae tendineae.
HEART BEAT
The heart beat consist of alternate contractions and relaxation of the right and left auricles as well as the right and left ventricle. Human heart beat is about 72 beat per minutes this can be divided into two phases, namely
Diastole: This is the first stage of the heart beat; the two auricles contract forcing blood into the ventricles and oxygenated blood into the left ventricle. As the ventricles gets filled up, the cuspid valves are pushed up and closed.
Systole: This is the second phase of the heart beat. The ventricles contract sending blood out to the two tracks of the main arteries and out of the heart. Deoxygenated blood from the right ventricles passes into the pulmonary artery while oxygenated blood is sent into the aorta. The sequence repeats itself.
BLOOD VESSELS AND ORGANS SUPPLIED.
Blood Vessel (Artery) Organ Supplied
Carotid artery ……………………. Head
Pulmonary artery ………………….. Lungs
Hepatic artery ………………………… Liver
Gastric artery …………………………..Stomach
Mesenteric artery …………………….Intestine
Renal artery ……………………………. kidney
Gonadal artery …………………..….…Gonads
Intercostals artery ………………….. Wall of thorax
Corresponding veins accompany the arteries stated above
Take a quick test for this lesson.
1. Describe the structure of the heart.
2. Draw a well labeled diagram of the heart
3. Differentiate between arteries and veins
4. Explain systole and diastole.
5. Draw the cross section of the artery
6. What is pulmonary circulation?
Questions answered correctly? Bravo!!
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