Circulatory System- Science Notes for CTET 2020: FREE PDF

EVS/ Science Study Notes Free PDF

In many teaching exams including CTET 2020, UPTET 2020 STET 2020 etc. Science may be an interesting subject having and 30 questions of Science content and 30 questions of Science Pedagogy in CTETand other State TET Exams. Science comprising of various branches of studies like chemistry, physical science, and life science.

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Circulatory system is concerned with the circulation of body fluids to distribute various substances to various body parts. The circulatory system is also known as the cardiovascular system.
• It is an organ system that allows blood to circulate and transport nutrients (such as electrolytes and amino acids), oxygen, carbon dioxide, hormones, and blood cells.
• These are circulated to and from cells in the body to nourish it. The components of the human circulatory system include the heart, blood, red and white blood cells, platelets, and the lymphatic system.

Functions of Circulatory System:
1. Transport of various substances such as nutrients, waste products, respiratory gases, metabolic intermediates (Such as lactic acid from muscle to liver), and vitamins hormones etc.
2. Regulation of body pH by means of buffer, body temperature homeostasis, water balance etc.
3. Prevention of disease by means of antibodies and antitoxins.
4. Support or turgidity to certain organs like penis and nipples.

Differences between Open and Closed Circulatory System:

Open Circulatory System Closed Circulatory System
1.      In open circulatory system blood flows through large open spaces and channels called lacunae and sinuses among the tissues. 1. In closed circulatory system blood flows through a closed system of chambers called heart and blood vessels.
2.      Tissues are in direct contact with the blood. 2.      Blood does not come in direct contact with tissue.
3.      Blood flow is very slow and blood has very low pressure. 3.      Blood flow is quite rapid and blood has a high pressure.
4.      Exchange of gases and nutrients takes place directly between blood and tissues. 4.      Nutrients and gases pass through the capillary wall to the tissue fluid from where they are passed on to the tissues.
5.      Less efficient as volume of blood flowing through a tissue cannot be controlled as blood flows out in open space. 5.      More efficient as volume of blood can be regulated by the contraction and relaxation of the smooth muscles of the blood vessels.
6.      Open circulatory system is found in higher invertebrates like most arthropods such as prawn, insects, etc., and in some molluscs. 6.      Closed circulatory system is found in echinoderms, some molluscs, annelids and all vertebrates.


7.      Respiratory pigment, if present, is dissolved in plasma; RBCs are not present.

7.      Respiratory pigment is present and may be dissolved in plasma but is usually held in RBCs.

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Heart of vertebrates:

Class of Vertebrates Characteristics Example

1.      Pisces

(= Branchial heart)

Thick, muscular, made of cardiac muscles, has two chambers (i) auricle and (ii) ventricle. The heart is called venous heart since it pumps deoxygenated blood to gills for oxygenation. This blood goes directly from gills to visceral organs (single circuit circulation). A sinus venosus and conus arteriosus is present. Lung fishes have 2 auricles and 1 ventricle. Labeo, Scoliodon,


2.      Amphibians Heart consists of

(a) Two auricles

(b) Undivided ventricle

(c) Sinus venosus

(d) Truncus arteriosus

(conus + proximal part of aorta) Right auricle receives blood from all the visceral organs (deoxygenated) via precaval and post caval. Pulmonary artery carries deoxygenated blood to lungs for oxygenation. This blood returns to left auricle via pulmonary vein (Double circuit circulation)

Frog,  Toad
3.      Reptiles Heart consists of :

(a) Left and right auricle

(b) Incompletely divided ventricle

(Ventricle in crocodiles gavials and alligator is completely divided)

(c) Sinus venosus

(d) Conus arteriosus divided into right systemic, left systemic and pulmonary arch.

Lizards, Snakes, Turtles
4.      Aves Heart consists of

(a) Left and right auricle

(b) Left and right ventricle

(c) Complete separation of arterial and venous circulation

(d) Only right systemic arch is present

Pigeon, Sparrow
5.      Mammals Same as bird except that mammals have left systemic arch. Rabbit, Man


Human Heart:

Circulation of Blood through Heart:
1. The heart pumps blood to all parts of the body.
2. The deoxygenated blood is drained into right auricle through superior and inferior vena cava and coronary sinus whereas the pulmonary veins carry oxygenated blood from lungs to the left auricle. This is called as Auricular circulation.
3. About 70% of the auricular blood passes into the ventricles during diastole. This phase is called diastasis.
4. The rest of 30% of blood passes into the ventricles due to auricular systole (contraction).
5. In this way, blood reaches the ventricles and is called ventricular filling.
6. During ventricular systole (which starts first in left ventricle than in right ventricle), the pressure increases in the ventricles, thus, forcing the oxygenated blood from left ventricle into systemic aorta and deoxygenated blood from right ventricle into pulmonary aorta.
7. The systemic arch distributes the oxygenated blood to all the body parts except lungs while pulmonary aorta carries the deoxygenated blood to lungs for oxygenation.

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Electrocardiogram (ECG):
1. A graphic record of electrical events occurring during a cardiac cycle is called Electrocardiogram.
i. Depolarization waves: They represent the generation of the potential difference. These waves appear only when both electrodes of galvanometer are in different fields. When both the electrodes are in same field, there are no deflection and wave drops down to base line.
ii. Re-polarization waves: They appear when depolarization is over and the muscle fibre is returning to its original polarity. When both electrodes are in same polarity (means 100% re-polarization and 100% depolarization), there is no deflection.
a. P wave: Indicates impulse of contraction generated by S.A. node and its spread in atria causing atrial depolarization. The interval PQ represents atrial contraction and takes 0.1 seconds.
b. QRS complex: Indicates spread of impulse of contraction from A.V node to the wall of ventricles through bundle of His and purkinje fibres causing ventricular depolarization. This complex also represents repolarization of S.A. node.
The RS of QRS wave and ST interval show ventricular contraction (0.3 seconds). QRS is related to ventricular systole.
c. T wave: Indicates repolarization during ventricular relaxation.

Lymphatic System:
The lymphatic system is an extension of the circulatory system. It consists of a fluid known as lymph, lymph capillaries and lymph ducts.
A. Lymph: It can be defined as blood minus RBC’s. In addition to the blood vascular system all vertebrate possess a lymphatic system. It is colorless or yellowish fluid present in the lymph vessels. It is a mobile connective tissue like blood and is formed by the filtration of blood.
B. Lymph Capillaries: Small, thin, lined by endothelium resting on a basement membrane and fine whose one end is blind and other end unites to form lymphatic ducts.

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C. Lymphatic Ducts or Vessels: Numerous, present in various parts of body. These vessels are like veins as they have all the three layers – tunica externa, tunica media and tunica interna, and are provided with watch pocket or semilunar valves but valves are more in number than veins.

Differences Between Lymph and Blood:

S. No. Characters Blood Lymph
1. RBC Present Absent
2. Blood Platelets Present Absent
3. WBC Present, generally 7000/cu mm Present, generally 500 – 75000/cu mm
4. Plasma Present Present
5. Albumin : Globulin Albumin > Globulin Albumin > Globulin
6. Fibrinogen More Less
7. Coagulation Property More Less
8. Direction of flow Two way, heart to tissues and tissues to heart One way, tissues to heart
9. Rate of flow Fast Slow
10. Glucose, urea CO2 Less More

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