Circulatory System(Part - 1) - Notes, Zoology, Class 11 PDF Download

Circulatory System

BODY FLUIDS AND CIRCULATION

INTRODUCTION :-
An expanded pipe line system is present in human body. It is called closed circulatory system. A continuous chemical exchange of materials between animal body and environment among different tissues of the body, is done through this system. In this way digested nutrients from digestive system, oxygen from respiratory organs, hormones from endocrine glands are distributed to all the cells of body. Also the transport of CO₂ from body cells to respiratory organs, NH₃, urea etc. excretory substances to excretory organs is the function of circulatory system. The whole circulatory system is formed by the mesoderm of embryo. Except the inner lining of blood vessels and heart which are of endodermal origin.
Types of circulatory system on basis of complexity and evolution.

In human beings(on the basis of circulating fluid ) two types of circulatory system are observed .

(1) Blood circulatory system : It consist of  :- Blood , Blood vessels, Heart .

(2) Lymphatic system : It consist of  lymph, lymph capillaries, lymph vessels, lymph nodes, lymphoid tissues/organs

• The study of blood vascular system or circulatory system is called–Angiology.

William Harvey is known as father of angiology. He called heart as the "Pumping station of body"

CIRCULATION OF BLOOD

Single Circuit :- Example : Fishes

Double Circuit :- Example - Man, Rabbit

Transitional type circuit :– Two circuits are not completely separate Example – FROG – Blood mixes in ventricles Evolutionary sequence is present in vertebrates.

 (1) Fishes have a tubular " Venous-Heart" In their heart, deoxygenated blood enters from one side and from the other side enters inside the gills for purification. This is called the" Single Heart Circuit." 

(2) In amphibians (like Frog) and Reptiles the auricles are divided into right and left. Right auricle gets impure and left auricle gets pure blood from the body. But only 1 ventricle is present or is incompletely divided so after coming here the pure and impure blood mix up.

• In some reptiles (Crocodile, Gavialis and Alligator) and in all birds and mammals the heart is divided into 2 auricles and 2 ventricles so while circulating inside the heart the pure and impure blood remain separated. The right portion of the heart collects impure blood from the body and sends it to the lungs for purification, while the left portion takes pure blood from the lungs and distributes it to the whole body.

The right portion of the heart is called as the "Pulmonary-Heart" and the left portion is termed as the "Systemic-heart". This is termed as "Double Circulation of Heart".because the blood has to pass through the heart twice before being delivered to systemic organs. l Types of heart on the basis of type of blood which it receives –

(i) Venous/Branchial (fishes)

(ii) Arterial (prawn)

(iii) Arterio venous (lung fishes, tetrapods)

Path of Blood in Double Circuit (Man) 

•  It was first discovered by " William-Harvey. "

STRUCTURE OF HEART

EXTERNAL STRUCTURE :-

Heart is situated at the ventral side of mediastinal space of thoracic cavity in between the lungs. Left lung has cardiac notch, heart is 5×3.5 inches in size, weight 300 gm. It is enclosed in coelomic epithelium. Its triangular superior-broad portion is tilted slightly towards right (dorsal) side. Its lower narrow portion is tilted towards left side. Covering of heart is called pericardium which consists of two layers :

(i) Outer : Parietal pericardium in which two sub layers are present :

(a) Outer : Fibrous connective tissue layer

(b) Inner : Simple squamous epithelium (Serous membrane)

(ii) Inner : Visceral pericardium or epicardium made up of simple squamous epithelium (Serous membrane).

The narrow space in between these two membranes is called pericardial cavity.

A serous fluid is present in this cavity it is called pericardial fluid. It is secreted by the pericardium. Pericardial cavity is a true coelom (as it lies between two layers of mesoderm).

Functions of pericardial fluid : 

(1) It prevents the heart from external jerks.

(2) It provides moisture to heart. It prevents the two membranes from collapsing.

(3) It prevents the heart from the bad effect of friction at the time of contraction.

•  The heart of man is four chambered 2 auricles and 2 ventricles. It is pinkish in colour and conical in shape.

The broad upper part of heart is called auricular part or base and lower conical part is called ventricular part (its tip is called apex).

In between the auricles and ventricles, a clear groove is present, which is known as coronary sulcus. This groove is more towards auricles, by the effect of this the auricular surface is smaller than ventricles.

(a) Auricles- Auricular part of heart is smaller and of dark colour. Its walls are thin. It is divided into right and left auricles by fissure called interauricular sulcus, which is shifted slighty towards left. Therefore out of these two, right auricular surface is bigger than left auricle.

Each auricle forms an bulbous structure called auricular appendages. It covers a small part of ventricle of its side.

(b) Ventricles- Ventricular part is broad, muscular and of light colour. Ventricles have thicker walls than auricles.

The grooves which divide the two ventricles are termed as Inter-ventricular groove or sulcus. It is oblique or tilted toward Right. It does not reach till the tip or apex of the heart, So the right ventricle is smaller than the left ventricle.

•  Left ventricle is more muscular and thick walled then right because it has to pump blood into those arteries which take blood throughout the body while right ventricle has to pump blood only to the lungs.

Systemic heart

-left part of the heart ( i.e. left auricle and left ventricle) contain the blood which is to be pumped into the systemic circulation, therefore it is called systemic heart. The main purpose of  such a circulation is to transport oxygen, as well as nutrients to the body tissues, and to remove carbondioxide and other harmful nitrogenous waste from them.

Pulmonary heart –

Right part of the heart ( i.e. right auricle and right ventricle) contain the blood which is to be pumped in pulmonary circulation for oxygenation, therefore it is called pulmonary heart. The pulmonary circulation is responsible for regular oxygenation of the impure deoxygenated blood which is received by the right auricle.