the circulatory system

failure is unacceptable

Blood - characteristics

contained in the heart and blood vessels; never stationary; bright or dark red; 5-6l; salty and slightly alkaline.

Blood - functions

Transport (digested food from alimentary canal to tissues; oxygen from lungs to tissues; carbon dioxide from tissues to lungs; excretory material from tissues to liver, kidneys or skin; distribution of hormones directly into blood; distribution of heat throughout the body) and Protection (through clotting to prevent loss of blood and entry of germs; through engulfing of bacteria by leukocytes; through antibodies and antitoxins).

Serum

plasma from which the clotting factor fibrinogen has been removed

Plasma

Liquid part of blood, made mostly of water, in which oxygen, nutrients, and minerals are dissolved

Erythrocytes (RBC)

minute biconcave disc-like structures that contain a respiratory pigment haemoglobin, that allows them to carry oxygen throughout the body.

Haemoglobin

a pigment containing iron, found in red blood cells, which combines with: oxygen to form oxyhaemoglobin, an unstable compound that readily gives up oxygen to needy tissues; carbon dioxide in a small quantity to form carbaminohaemoglobin; carbon monoxide readily to form a stable compound carboxyhaemoglobin which reduced the oxygen carrying capacity.

Erythrocytes (RBC) - production and death

In adults - produced in the marrow of long bones; In embryo - produced in liver and spleen; In children - produced in marrow of all bones until age 5
average life span - 120 days
destroyed in spleen, liver and bone marrow; iron part retained, rest excreted as bile pigment bilirubin.

Erythrocytes (RBC) - adaptations

Mature RBCs lack nuclei, mitochondria and endoplasmic reticula; Loss of nucleus makes them biconcave, increasing surface area to volume ratio for absorbing more oxygen; Loss of mitochondria makes it so the oxygen isn't used for cellular respiration and is delivered to tissues unconsumed, and so the glucose in plasma isn't used by RBCs and is transported fully; Loss of ER makes RBCs flexible enough to move through narrow capillaries.

Leukocytes (WBC)

Amoeboid cells having a nucleus and lacking haemoglobin, produced in red bone marrow, lymph nodes and sometimes in liver and spleen, whose average lifespan is 2 weeks and whose main function is to fight disease.

Diapedesis

Process by which WBCs can squeeze through the walls of capillaries and into the surrounding tissues using pseudopodia.

Leukocytes (WBC) - types

They are divided into two types, Granular and Non-Granular. Granular include neutrophils, basophils and eosinophils. Non-granular include lymphocytes and monocytes.

Neutrophils

Most abundant type of leukocyte; granular cytoplasm; produced in bone marrow; nucleus with 3-4 lobes; main function is to engulf bacteria by phagocytosis.

Eosinophils

Type of leukocyte; large cytoplasmic granules; produced in bone marrow; nucleus with 2 lobes; main function is to engulf bacteria, secrete antitoxins; associated with allergy

Basophils

Type of leukocyte; granules stain with basic dyes; produced in bone marrow; large and indistinctly lobed nucleus; main function is to release chemicals (histamine) for inflammation.

Lymphocytes

Type of leukocyte; agranular; smallest of WBCs; single large nucleus; produced in bone marrow, spleen and other lymph glands (like tonsils); main function is to produce antibodies.

Monocytes

Type of leukocyte; agranular; largest of WBCs; large, kidney-shaped nucleus; produced in bone marrow; transform into macrophages at the site of infection; main function is to ingest germs.

Leukocytes (WBC) - functions

Phagocytosis, Inflammation (reaction of tissues to injury, destruction of germs and damaged cells), Formation of antibodies (especially lymphocytes produce antibodies which kill or neutralise germs).

Phagocytosis

Process in which WBCs, specifically neutrophils, engulf particle-like solid substances, especially bacteria. Defensive mechanism against disease causing germs.

Pus

Fluid product of inflammation composed of dead white blood cells and the debris of dead tissue cells destroyed by bacteria.

Thrombocytes (platelets)

minute oval or round structures, non-nucleated, produced in the red bone marrow, with a life span of 3-5 days, destroyed in the spleen, whose main function is to release a chemical substance thrombokinase which initiates the process of clotting of blood.

Clotting of Blood - steps

- platelets disintegrate at the site of the wound to release a substance called thrombokinase (or thromboplastin or factor X).
- thrombokinase acts as an enzyme and with the help of calcium ions present in plasma, it converts inactive prothrombin to active thrombin. Vitamin K is essential for production of prothrombin.
- thrombin in the presence of calcium ions reacts with fibrinogen of blood plasma to form insoluble fibrin which is a solid thread-forming substance. The fibrin threads form a mesh at the wound.
- the mesh squeezes out the rest of the plasma which is in the form of a clear liquid called serum. a solid mass called clot or thrombus is left behind.

Haemophilia

a sex-linked inheritable disease characterized by loss or impairment of the normal clotting ability of blood, so that a minor wound may result in fatal bleeding.

Heart

A muscular organ located in the centre of the chest between the two lungs, about the size of a closed fist, covered with a double walled membrane called pericardium which is filled with friction-reducing pericardial fluid, divided into 4 chambers.

Auricles

The upper chambers of the heart, whose major function is to receive blood from the body and pump it into the very next ventricles. they have thinner walls.

Ventricles

The lower chambers of the heart, whose major function is to pump blood throughout the whole body, especially the left ventricle. they have thicker walls.

Anterior Vena Cava (or superior vena cava)

Blood vessel entering the right auricle, which brings deoxygenated blood from the upper regions of the body to the heart.

Posterior Vena Cava (or inferior vena cava)

Blood vessel entering the right auricle whose function is to bring blood from the lower region of the body to the heart

Pulmonary Vein

Blood vessels (two from each lung) which bring oxygenated blood back from the lungs to the heart.

Aorta

Blood vessel leaving the body that arises from the left ventricle and carries oxygenated blood to supply it to all parts of the body

Pulmonary Artery

Blood vessel leaving the heart which arises from right ventricle and brings deoxygenated blood to the lungs for oxygenation

Coronary Arteries

blood vessels that branch from the aorta and carry oxygen-rich blood to the heart muscles. coronary veins carry the blood back to right auricle.

Myocardial Infarction

"deadening" of an area of the heart caused due to blockage in any coronary artery or branch thereof. Also called heart attack.

Angina Pectoris

Chest pain due to insufficient supply of blood to the heart muscle.

right atrioventricular valve (tricuspid valve)

located at the aperture between right atrium and right ventricle, it has three thin triangular leaf-like flaps, the apices of which are held in place by chordae tendinae which arise from muscular projections of the ventricular wall known as papillary muscles. Prevents backflow of blood from right ventricle to right atrium.

left atrioventricular (bicuspid, mitral) valve

located between the left atrium and left ventricle, having two thin triangular leaf-like cusps. Prevents backflow of blood from left ventricle to left atrium.

pulmonary semilunar valve

located at the opening of the right ventricle into the pulmonary artery. Pocket shaped and three in number. Prevents backflow of blood from pulmonary artery to left ventricle.

aortic semilunar valve

located at the point of origin of aorta from the left ventricle. Pocket shaped and three in number. Prevents backflow of blood from aorta to left ventricle.

Cardiac Cycle: Systole

contraction phase - blood from atria enters the ventricles, blood from right ventricle enters pulmonary artery while blood from left ventricle enters aorta.

Cardiac Cycle: Diastole

relaxation phase, blood enters the ventricles.

sinoatrial node (SAN)

located in the walls of the right auricle neat opening of superior vena cava, initiates heartbeat.

atrioventricular node (AVN)

located in the interarticular septum near the tricuspid valve, conducts impulse produced in SAN to the bundle of HIS.

Bundle of HIS

bundle of muscle fibres, beginning from AVN and extending till interventricular septum. contains branches of fibres running along the wall of the ventricle called Purkinje fibres. conducts the impulse from AVN to Purkinje Fibres.

Artery

Blood vessel with thick muscular walls an narrow lumen, carrying blood away from heart, in which blood flows in spurts. smallest branch is arteriole which is highly muscular.

Vein

Blood vessel with thin muscular walls and wider lumen carrying blood towards the heart in which blood flows uniformly and which contains thin pocket-shaped valves to prevent backflow. smallest united branch is venule which have weaker muscular coats compared to arterioles.

Capillaries

Very narrow blood vessels whose wall consists of a single layer of squamous epithelium, no muscles, which allow outward diffusion of oxygen, inward diffusion of carbon dioxide, outward and inward diffusion of materials like glucose, amino acids, urea, hormones, etc and leukocytes to squeeze through. They can dilate and constrict

double circulation

A circulatory system where blood flows twice through the heart before it completes one full round; once in the short pulmonary circulation and once in the long systemic circulation.

hepatic portal system

veins starting from the stomach and intestines enter the liver as a combined hepatic portal vein. In the liver they break up into capillaries and a new vein called hepatic vein is reformed which joins posterior vena cava.

Utility of Hepatic Portal System

Food absorbed by the stomach and intestines is first brought to the liver which acts as a store to regulate the quantity of nutrients or toxins flowing into the general blood circulation.

portal vein

vein that starts and ends with capillaries.

pulse

alternate expansion and elastic recoil of the walls of arteries during ventricular systole.

blood pressure

Pressure exerted by the blood upon the walls of the blood vessels, especially arteries, usually measured by means of a sphygmomanometer.

tissue fluid

intercellular fluid that bathes the cells, from which cells absorb oxygen and other required substances and into which they give out carbon dioxide and waste materials.

lymph

tissue fluid that enters lymph vessels, containing a cellular part of only leukocytes (mostly lymphocytes).

Functions of Lymph

- it is nutritive - supplies nutrition and oxygen to those parts where blood cannot reach.
- it drains away excess tissue fluid and metabolites
- absorption - fats from the intestine are absorbed through lymphatics (lacteals in intestinal villi)
- defence - lymphocytes and monocytes defend the body and fight bacteria. they also localise the infection.

Spleen

Large lymphatic organ, situated in the abdomen behind the stomach and above the left kidney, which acts as a blood reservoir for emergency situations like haemorrhage, stress, etc. and produces lymphocytes, destroys worn-out RBCs and in embryo, produces RBCs.