Circulatory System in Mammals

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CLASS: SS2

SUBJECT: BIOLOGY                                PERIOD(S): 3

TOPIC: CIRCULATORY SYSTEM IN MAMMALS

SUBTOPIC 1: Structure of the circulatory system

Subtopic 2: Types of circulation

Subtopic 3: Mechanism of circulation

Previous Knowledge: Students are familiar with  the topic

Objectives: at the end of the period(s) students should be able to

PERIOD 1: Describe the structure of the components of the circulatory system

1. Describe the types of circulation

PERIOD 2: Compare and contrast the various mechanisms of transportation.

REFERENCES: Essential Biology for Senior Secondary Schools  1-3 MC Michaels pg 285 – 292

Modern Biology for Senior Secondary Schools 1-3 pg 301 – 311

CONTENT

Circulatory system refers to the continous movement or flow of blood round the body involving the heart and the blood vessels. A circulatory system has the following features.

1. A circulatory fluid, which is usually blood
2. A pumping device or heart to drive the fluid around the body and
3. A system of branched tubes or vessels connected to the heart through which the fluid can circulate.

There are 3 major categories of circulatory system in animals namely:

1. Open and closed circulatory system
2. Single and double circulatory system
3. Pulmonary and systemic circulatory system.

Open circulatory system – can be found in some animals like mollusks and insects. The heart pumps blood out into a blood vessel which branches and opens into spaces in the body cavity called haemocoels. The organs and tissues are bathed in blood and exchange of materials occurs between the body cells and the blood. Blood in the spaces eventually flow into the vessels leading to the heart. Valves in the heart and vessels flow in one direction .

Closed circulatory system –

This system can be found in all vertebrates and some invertebrates like annelids. The blood is contained within vessels and is always confined within the cavities of the vessels and heart and never coems in contact with the body cells. Arteries carry blood from the heart and branch and enter various organs and tissues where they divided into smaller vessels (arterioles) which branch again and again to form fine vessels (capillaries). Capillaries are found in between all body cfells and they exchange materials with body cells by diffusion. Capillaries unit to form venuoles which joine together to form vein which carry blood back to the heart. Oxygenated blood is confined to the left part ofhte heart and leaves the heart at high pressure while deoxygenated blood is confined to the right part of the blood and returns to the ehart at low pressure.

Single circulatory system: The Blood passes through the heart only once everytime it makes one complete movement round the body. This system is common in fish which has only two chambered heart (One auricle and one ventricle each) The single circulation is not efficient. The arteries form capillary network at the gills and also at the organs and tissues. Each time this happens, the blood pressure decreases and blood that collects in the veins is at low pressure and move sluggishly. To help blood flow in the veins leading to the heart, valves are present in veins and some veins are replaced by blood spaces.

Double circulatory system

The blood passes  through the heart twice every time it makes one complete movement round the body and each time the blood passes through the heart, it goes through a separate pathway. Double circulation gives rise to two pathways namely:

1. Pulmonary Circulation – Blood circulates from the heart to the lungs and back to the heart
2. Systemic circulation : Blood circulates from the heart to all other parts of the body and back to the heart.

In one complete circulation, blood from any part of the body enters the heart for the first tiem and sent to the lungs for oxygenation. From the lungs, it is brought back to the heart and second time befor it is pumped to all the parts of the body. Frogs exhibit partial double circulation since the oxygenated and deoxygenated blood are not completely separated as in mammals

BLOOD VESSELS

Blood vessels are tubes which transport blood to or from the ehart and there are 3 major types of blood vessels namely:

1. Arteries – have thick, muscular, elastic walls which are capable of withstanding high pressure of the blood (Blood is at high pressure of the blood (Blood is at high pressure, flows fast and in spurts) Arteries transports oxygen blood from the heart except that in the pulmonary arteries. Arteries are capable of constricting or circulating and thereby regulate the amount of blood. Valves are absent except for the semi-lunar valves near the heart.
2. Veins have fairly thick slightly elastic wall with large lumen. Veins carry deoxygenated blood back to the heart except the pulmonary vein. The blood is at low pressure, flows slowly and smoothly valves are present to prevent backflow of blood. The flow of blood is assisted by the movement of the skeletal muscles.
3. Capillaries are tiny blood vessels (One cell thick) which links arteries to the veins. They are found in the junction between arteries and veins around tissues and organs in the body. Capillaries have thin walls which allows easy diffusion of dissolved food substances, waste products and oxygen. Blood pressure is hgihter at arterioles and then at the venules end of the capiilariy network. Therefore blood flows smoothly. The blood is oxygenated at arteriole end and deoxygenated at venule and except that in the lung capillaries.

DIFFERENCES BETWEEN ARTERY AND VEIN

THE HEART

The heart is a conical hollow, muscular organ which works continuously pumping blood round the body throughout an organisms lifetime. It is about the size of a clenched fist and weighs about 300grams. The heart is located in the chest (thoracic cavity) just behind the breast bone (sternum ) and between the lungs and it is made up of special muscles (cardiac muscles) and enveloped  in a two layered tough protective membranous bag, the pericardium. Pericardial fluid fills the space between the 2 layers.

The pericardial fluid reduce friction caused by the heart’s pumping action. Each pumping action of the heart is called the heartbeat which is caused by the alternate contraction and relaxation of the four heart chambers. Heartbeat occurs in 2 stages namely:

1. Diastole: This is the first stage during which the 2 auricles contact creating a high blood pressure. This pressure causes the bicuspid and tricuspid valves to fold downwards into the ventricles, allowing deoxygenated blood to enter the right ventricle from the right auricle and oxygenated blood to enter the left ventricles from the left auricle. Once the ventricles are full, the cuspid valves close up the apertures between the upper and lower chambers of the heart.
2. Systole – this is the second stage which involves the contraction of the two ventricles which results in the blood being forced into the two trunks of the main arteries and out of the heart. Deoxygenated blood from the right ventricle passes into the pulmonary artery while oxygenated blood from the left ventricle passes into the aorta.

When at rest, the average human heart contracts and relaxes about 70-72 tones per minute (up to 100 or more during activity, 200 heartbeats per minute in small animals, 12 in big animals like elephant0 and pumps about 14,000 litres of blood a day.

STRUCTURE OF THE HEART

The hearts has 4 chambers: 2 upper this walled atriacle or auricles and 2 lower thick walled ventricles. The right side of the heart is separted form the left by a wall called septurn. Two large veins, the superior (anterior) and inferior(posterior) venae cavae supply deoxygenated blood from parts of the body (except the lungs) into the right auricles. The pulmonary veins supply oxygenated blood into the the left auricle. The right auricle opens into the right ventricle and this is controlled by the tricuspid valve which has  3 flaps which are attached by chordate  tendinae (cord like tendons) to the right ventricle walls which allow unidirectional blood flow from the right auricle to the right ventricle. Bicuspid or mitral valve controls the opening of the left auricle into the left ventricle (has 2 flaps) The right ventricle opens into the pulmonary artery, which branches into 2, one  to the right lung and this other to the left lung and they carry deoxygenated blood to the lungs. The left ventricle opens into the large aorta (largest artery) which branches to distribute oxygenated blood to the parts of the body except of the longs. Semilunar valves in tehse arteries prevents blood backflow into the ventricles. Blood enters the aotar at a very high pressure (about 105mmHg) and blood entering the pulmonary artery is at a much lower pressure (about 16mmHg) It is because the contraction of the left ventricle must send blood round the much longer systemic circulation therefore the wall of the left ventricle is at least three times thicker than that of the right ventricle.

Examples of major arteries in the body and the organs they supply

INSTRUCTIONAL MATERIALS: Pictures and videos

TEACHING METHODS PROCEDURES

Step 1: Teacher revises the previous topic and introduce the new topic

Step II: Teacher defines circulatory system and mentions the categories of the circulatory system

Step III: Teacher explains the function of each blood vessel in detail and mention the differences between an artery and a vein

Step IV: Teacher describes the structure and function and the mammalian heart.

Step V: Teacher allows students to ask questions  and write note under content on the board.

CLASSROOM (ACTIVITIES)

PERIOD 1: Students discuss circulatory system in man.

PERIOD 2: Students discuss the types of circulatory system and blood vessels

PERIOD 3: Students discuss the structure and function of the heart.

EVALUATION ;

Period 1: Mention the components of the mammalianblood

Period 2:    List 4 differences between artery and vein

Period 3: How many times does a man’s heart beat in a minute

SUMMARY/CONCLUSION: Teacher summarizes the topic, marks the students notes and makes corrections where necessary.

ASSIGNMENT(S)

Period 1: Describe three ways by which the blood protects the body against diseases causing organisms

Period 2: Make a large labeled diagram of the outline of the blood circulatory system in mammals.

Period 3: Draw and label the mammalian heart.