Circulatory System
Last Updated on Tuesday, 12 July 2011 04:39 Written by Sandesh Monday, 24 May 2010 05:54
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CIRCULATORY SYSTEM OF FROG
The transport of nutrients, gases, hormones, wastes etc. through fluid connective tissue is called circulation. The organs involved in circulation comprise circulatory system. The circulatory system can be divided into the following parts:
A. Vascular System:
a. The blood
b. The heart
c. The blood vessels
B. The Lmphatic System:
a. The Lymph
b. The Lymph sinuses and Lymph vessels
c. The Lymph hearts
A. THE VASCULAR SYSTEM
a) The Blood
The vascular system comprise of blood. The blood is the transport medium. It is the liquid connective tissue. Blood has red fluid matrix or intercellular substance called plasma. It is almost colourless and is composed of many kinds of substances. It is the viscous fluid, forming about 2/3 of blood by volume. The major constituent of plasma is water which forms about 90% volume of plasma. In addition to water, the plasma contains many inorganic substances such as salts of sodium, (sodium chloride and sodium carbonate). Presence of these salts makes the plasma alkaline in nature. The organic substances of plasma are proteins, digested food substances, excretory substances, hormones, gases, antigens and antibodies. About 7% volume of plasma is due to plasma Proteins, namely albumins and globulins. Plasma also contains different kinds of cells floating in it. These cells are called blood corpuscles. In the plasma of frog there are three types of corpuscles, namely:
• erythrocytes or Red Blood Corpuscles (RBC)
• leucocytes or White blood Corpuscles (WBC)
• platelets or thrombocytes
• Erythrocytes (red blood corpuscles): The red blood corpuscles or erythrocytes are typically flattened cell which appears biconvex view along its edges. It is filled with cytoplasm of faint straw colour and contains a definite rounded nucleus in the center. When aggregated, erythrocytes provide red colour to blood. Thus they are popularly known as red blood corpuscles. The red colouration is due to the presence of haemoglobin. Chemically it is a protein, the globin combined with metallic pigment haematin which contains iron in its composition. Haemoglobin enables the blood to carry a great load of oxygen in form of oxyhaemoglobin. The oxyhaemoglobin is bright red and therefore, it gives arterial blood its characteristic colour. Lifespan of RBC is about 120 days.
• Leucocytes (white blood corpuscles):
These are small, nucleated semi-transparent cells, numbering about 5300/ccubic millimeter. They are capable of changing their shape and moving independently through the intercellular spaces among the tissues by amoeboid movement. They are found almost every where in the body. They act as scavengers and soldiers. When bacteria invade any part of the body, the leucocytes gather there and attack and feed on the bacteria and break down tissue cells by engulfing particles. This process is called phagocytosis; hence leucocytes are often called phagocytes.
There are two typesof WBC- granulocytes and agranulocytes according to the presence or absence of granules int he cytoplasm.
Granulocytes are again classified into three types, according to the type of dye in which they can be stained: Acidophils or Eosinophils 3%- granular cytoplasm can be stained in acidic dyes such as eosin.
Basophils 1% – stained in basic dyes such as methylene blue.
Neutrophils- stain with either dyes (Polymorphs 70%, Lymphocytes 25% and Monocytes 1%)
The main function of leucocytes is to neutralize toxin produced by bacteria. The Monocytes are the largest white blood corpuscles and are phagocytic in nature. All types of leucocytes are manufactured in liver and spleen of embryo but in adult they are formed in the bone marrow.
• Thrombocytes or platelets:
These are smallest corpuscles in blood. They are especially concerned with the clotting of blood. The tendency to clot depends upon the number of thrombocytes present. They are made in bone marrow.
Function of blood includes:
• transport of O2 from lungs, mouth cavity and skin
• removal of CO2
• transport of food materials
• transport of waste matter
• clotting of the blood
• regulation of body temperature
B) THE HEART
External Structure
Heart of frog is a conical muscular organ, lying in mid-ventral line at the level of fore limbs. It is reddish in colour and is enclosed in a double layered bag known as pericardium. The outer layer of this bag is called perietal layer whereas inner layer is called visceral layer. Enclosed between these two layers is pericardial fluid which lubricates heart for free movement and saves it from friction.
Chambers:
The heart of frog is three chambered. There are two anterior purple coloured auricles and a single posterior pinkish ventricle. The two auricles are demarcated by inter-auricular groove or septum. They are also clearly marked off from ventricle by auriculo-ventricular groove or coronary sulcus.
Besides these three chambers, there are two additional chambers in frog’s heart. These are, Sinus Venosus and Truncus Arteriosus.
Sinus venosus is dark coloured, thin-walled triangular chamber attached dorsally to heart. It if formed by the union of three caval veins, two anterior pre-cavals and one posterior post cavals.
Truncus arteriosus is thick-walled, tubular chamber attached ventrally to heart at the anterior region of ventricle. It runs above anteriorly and bifurcates into two branches. Each of these branch further breaks into three chambers namely; carotid, systemic and pulmonary arches.
Internal Structure
Internally heart appears as a hollow muscular chamber. Various chambers are separated by valves to keep the blood in one direction.
1. Auricles:
The two auricles, right and left are thin-walled chambers, completely separated from each other by inter-auricular septum. Right auricle is slightly larger than the left auricle.
Sinus venosus opens into the dorsal wall of right auricle through a large aperture, the sinu-auricular aperture. It lies medially close to the inter-auricular septum and is guarded by a pair of flap-like sinu-auricular valve.
Common pulmonary vein opens into the left auricle near septum by a small opening which is without valves. It brings oxygenated blood from lungs.
Both the auricle opens into ventricle through auriculo-ventricular aperture guarded by a pair of flap-like auriculo-ventricular valves.
2. Ventricle:
A single posterior ventricle has thick, muscular and spongy wall. The inner surface of ventricle has irregular strands or trabeculae known as columnea cornea with depressions called fissures. These greatly reduce the chamber of ventricle. Flaps of auriculo-ventricular valves are attached to the ventricle by thread-like chorda tendinea.
3. Truncus arteriosus:
Opening of ventricle into Truncus arteriosus is guarded by three valves which prevent back-flow of blood. Trnucus arteriosus has been divided into two parts; proximal thin-walled, Pylangium or Conus arteriosus and distal thick-walled Synanagium or Ventral aorta. The cavity of Conus is divided incompletely by a longitudinal spiral valve into left dorsal cavum pulmocutaneum and right ventral cavum aorticum. The spiral valve is attached dorsally and free ventrally.
Cavum aorticum communicates with pulmocutaneous arteries through Ventral aorta anteriorly and cavum pulmocutaneum posteriorly.
Synangium communicates behind with cavum aorticum and in front with the systemics and carotids which run to trunk and head. Cavum pulmocutaneum bears an aperture leading towards pulmocutaneous arteries guarded by pulmocutaneum valve.
Working of heart
Heart is a muscular organ which constantly beats during life to pump blood under the circulatory system. Contraction of heart is known as systole and, while its relaxation is called diastole. Different chambers of heart contract in a regular sequence and the valves present prevent the backflow of blood.
When sinus venosus contracts, its deoxygenated venous blood is poured into the right auricle through sinu-auricular aperture. Meanwhile the oxygenated blood from lungs is poured into the left auricle through common pulmonary vein. Now the two auricles contract at the same time, forcing their blood into ventricle through auricular-ventricular aperture.
Old theory:
According the old view, ventricle contains three type of blood; oxygenated, deoxygenated and mixed.
Left part of the ventricle contains oxygenated blood received from left auricle
right part contains deoxygenated blood received from right auricle and
the middle part contains mixed blood
The bloods of different types do not mix due to their viscous nature and also because of the presence of columnae cornea. When ventricle contracts follow actions occurs:
iii. first the deoxygenated blood from right side goes into cavum pulnocutaneum and then into the common opening of pulmonary arches which carry blood into the lungs and skin for purification.
iv. mixed blood is first pushed into cavum aorticum from where it flows to the systemic arches. From there it is supplied to limbs and trunk.
v. oxygenated blood is forced into the truncus arteriosus from where it passes towards carotid arches to be supplied into head region.
New theory:
This theory was given by Vandervale (1933) and Foxon (1951). They observed that the pure and impure blood coming from left and right auricles respectively got completely mixed in the ventricle. This mixed blood is distributed through common carotid, systemic and pulmocutaneous arches to all the parts of the body. Following actions were also observed in working of heart:
• The richly vascular lining of bucco-pharyngeal cavity of frog and skin causes oxygenation of greater amount of blood than the lungs. Lungs are only occasionally used for respiration.
• Blood reaching the right auricle through sinus venosus is not completely deoxygenated. It is mixed blood containing some oxygenated blood from bucco-pharyngeal cavity as well as skin.
Questions:
1. Describe the internal structure and working mechanism in the heart of frog. (5+3=8) HSEB 2060/62
2. Draw well labeled diagrams of external and internal structures of heart. 3 marks
C) THE BLOOD VESSELS
Three types of blood vessels occur. These are Arteries, Capillaries and Veins.
i) Arteries: Those blood vessels which carry oxygenated blood away from hear are called arteries. As they contain blood under high pressure caused by the powerful contraction of the ventricle, their walls are thicker and more elastic. The arteries are devoid of valves and thus blood flows in them in greater speed. Their wall consist of three layers:
• Tunica intima- It is the inner most elastic layer made up of endothelial cells.
• Tunica media- It is the muscular middle layer. This layer is greatly developed due to which the arteries are non-collapsible.
• Tunica externa- It is the outermost fibrous coat.
The arteries gradually decrease in size and pass over into arterioles, arterial capillaries and finally into the true capillaries.
ii) Capillaries: They are most abundant in those tissues or organs where extensive metabolism occurs, such as muscles and glands. The structure of capillaries is determined by its function which is to bring blood into the closest possible relation with the surrounding tissues. For this reason their walls are extremely thin and lack both tunica media and tunica externa. They form the most important part of the complex system of blood vessels in vertebrae body.
iii) Veins: From capillaries the blood passes into venules and then into the veins and then finally returned into the heart. The veins thus always begin with the capillaries. They are always thin-walled and collapsible. Of the three layers of their wall, the outer most tunica externa or fibrous coat is highly developed. The flow of blood in vein is much slower than in arteries in spite of the same size of arteries and veins. The diameter of veins is larger. By the time blood reaches veins, the pressure is very much reduced. the onward flow of blood is helped by:
presence of semi-lunar valves,
contraction of the muscles of the body,
sucking action of heart.
The difference between arteries and veins:
Arteries Veins
1. They contain blood flowing away from heart. 1. Contain blood flowing towards the heart.
2. They contain blood under great pressure 2. Contain blood under very little pressure.
3. They have thick, muscular and highly elastic wall. 3. Their walls are thin and less elastic.
4. They are not collapsible. 4. They are collapsible.
5. Their lumen is smaller. 5. Their lumen is greater.
6. The contained blood flows fast and with jerks caused by the beating of heart. 6. Blood flows with less speed.
7. They are devoid of valves. 7. Presence of valves.
8. Carry oxygenated bright red blood. 8. Carry deoxygenated purple blood
Work: Distinguish between veins and arteries. 3 marks question
THE ARTERIAL SYSTEM
The arterial system starts with truncus arterious which divides into the two large left and right branches. These branches further sub-divides into three major vessels or aortic arches:
1. Common carotid – head
2. Pulmocutaneous arches – lungs and skin
3. Systemic – body and internal organs
1. Common carotid Arch: It is a short vessel and divides into external and internal carotids.
a) External carotid- It is also called lingual-carries blood to tongue and adjacent parts
b) Internal carotid- It forms a little swelling at its base, the carotid labyrinth which is probably a sense organ and control blood pressure.
2. Pulmocutaneous Arch: It divides into the two main arteries, pulmonary to lungs and cutaneous to skin of dorsal and ventral sides.
3. Systemic Arch: It is the longest of the three arches with the greatest distribution of blood. The systemic arches curves dorsally around the oesophagus and joins each other behind the heart to form dorsal aorta. The systemic of either side gives rise to three arteries:
a) Oesophageal- a small artery to supplying blood to oesophagus
b) Occipto vertebral- to the posterior part of head and vertebral column and spinal chord
c) Sub-clavian- large artery supplying blood into the forelimbs.
4. Dorsal aorta: It is formed by the union of systemic arches of both sides. It runs posteriorly, lying mid-dorsally just below the vertebral column. It gives off following arteries:
a. Coeliaco-mesentry- It is a single large artery arising from the junction of two systemic arches. It has two main branches, the coeliac to stomach, pancreas and liver and anterior mesenteric to spleen and intestine.
b. Gonadial- A pair of short arteries to gonads, spermatic in male and ovarian in female
c. Renal- While passing between the kidneys, dorsal aorta sends off 5-6 pairs of small renal arteries in a series into the both kidneys.
d. Posterior mesenteric: It arises from the posterior end of dorsal aorta and runs to the large intestine or rectum.
e. Common iliacs: the dorsal aorta finally bifurcates posteriorly into common iliacs, each supplying :- an epigastric to ventral body wall and urinary bladder
femoral to hip and upper thigh
sciatic to lower leg
THE VENOUS SYSTEM
Venous system includes those blood vessels in which blood of body is returned to the heart. In frog it can be studied in four parts:
1. Pulmonary veins
2. Caval veins
3. Portal veins (renal portal and hepatic portal veins)
1. Pulmonary veins:
Oxygenated blood from two lungs is collected by right and left pulmonary veins. These veins unite to form common pulmonary vein which opens directly into the left auricle on the dorsal side.
2. Caval viens:
Deoxygentaed blood form rest of the body is travels towards heart in three large vessels, two anterior vene cavae and a single posterior vana cavae, all three opening into the sinus venosus.
a) Anterior vene cavae or precavals: The right and left precavals or anterior venae cavae collects blood form the anterior collects blood form the anterior parts of the body. Each precaval is formed by the union of 3 major veins. These include:
i. External jugular: It is formed by sinus lingual form tongue and mandibular from the outer margin of the lower jaw.
ii. Innominate: It is formed by internal jugular from cranial cavity and orbit and sub-scapular from shoulder and back of arm.
iii. Subclavian: It is formed by the branchial from forelimb and the musculo-cutaneous from side of the body and head.
b) Posterior vena cavae or postcaval: The single postcaval is a large, dark-coloured vein lying ventral to dorsal aorta. Its posterior end is formed between the two kidneys form which it drains blood by 5-6 pairs of renal veins. It also receives a genital vein, (spermatic in males and ovarian in females) from gonads directly. The postcavals then run forwards, dorsally to the liver and receive a short, stout hepatic veins, before opening into the sinus venosus.
3. The portal system: The frog has two well-developed portal systems, renal portal system and hepatic portal system.
a. Renal Portal system:
The veins which carry blood to kidney constitute the renal portal system. Blood of each hind leg is collected by two veins, an outer femoral and an inner sciatic. On entering the abdominal cavity, the femoral divides into the dorsal renal portal and a ventral pelvic vein.
The renal portal unites with the sciatic and while running along the border of kidney of its side, it receives blood from lumbar region by a dorso- lumbar vein.
The pelvic veins of both sides unite to form an anterior abdominal vein. It receives blood from urinary bladder and ventral abdominal wall and runs forward to enter liver into which it breaks up into capillaries.
b. Hepatic portal system:
A large hepatic portal vein is formed by the union of several branches from stomach, intestine, spleen and pancreas. It carries blood laden with digested food,, away from alimentary canal to liver. In liver the hepatic vein breaks up into the capillaries.
