· This system consists of blood vascular and lymphatic systems.
· It is the closed type and represents single circulation due to the mixing of both pure and impure blood.
A. Blood Vascular System
· It includes the heart and blood vessels.
a. Blood
· Fluid connective tissue
· Mesodermal in origin
· Consists of blood plasma and blood corpuscles.
i. Blood plasma
· Colorless or faint yellowish fluid.
· Forms 2/3rd of blood volume.
· Consists of:
2. WBCs or LEUKOCYTES
· Small nucleated semitransparent cells.
· 5300/mm3
· 5 different types:
A. Granulocytes (72% of total WBCs)
· Neutrophils
· Eosinophils
· Basophils
A. Blood Vascular System
· It includes the heart and blood vessels.
a. Blood
· Fluid connective tissue
· Mesodermal in origin
· Consists of blood plasma and blood corpuscles.
i. Blood plasma
· Colorless or faint yellowish fluid.
· Forms 2/3rd of blood volume.
· Consists of:
1. Water
2. Inorganic substances (Na+, K+, Cl–, HCO3–)
3. Acids, glucose, hormones, absorbed food materials, excretory products, antibodies etc.
2. Inorganic substances (Na+, K+, Cl–, HCO3–)
3. Acids, glucose, hormones, absorbed food materials, excretory products, antibodies etc.
· Blood corpuscles are of three types: RBCs, WBCs and Platelets.
1. RBC or ERYTHROCYTES
· Flattened, more or less elliptical. Biconvex when viewed along its edge.
· 22μ ✕ 16μ in dimension,
1. RBC or ERYTHROCYTES
· Flattened, more or less elliptical. Biconvex when viewed along its edge.
· 22μ ✕ 16μ in dimension,
· The average age of RBCin frog is 100 days. (RBC life span in humans is 120 Days or 4 months.)
· 3000-4000/mm3
· Nucleated
· Produced in kidneys, liver and spleen.
· 3000-4000/mm3
· Nucleated
· Produced in kidneys, liver and spleen.
· The bones of frogs do not contain red marrow.
· Contain Haemoglobin as a respiratory pigment.
· Contain Haemoglobin as a respiratory pigment.
2. WBCs or LEUKOCYTES
· Small nucleated semitransparent cells.
· 5300/mm3
· 5 different types:
A. Granulocytes (72% of total WBCs)
· Neutrophils
· Eosinophils
· Basophils
B. Agranulocytes (28% of Total WBCs)
· Lymphocytes
· Monocytes
· On dorsal surface: triangular and thin-walled Sinus venosus → formed by the union of two pre-cavals and one post caval → opens into the right atrium.
· Pulmonary veins open into the left atrium.
ii. INTERNAL STRUCTURE OF HEART
· Heart consists of 3 chambers: two atria and one ventricle with an atrioventricular aperture between them.
· Lymphocytes
· Monocytes
· Life span of WBC in the frog is 3-7 days.
· Some are phagocytic and others produce heparin, histamine etc.
· Formed in yellow bone marrow and spleen.
3. PLATELETS or THROMBOCYTES
· Smallest corpuscles in the blood.
· Discoid in shape. Spindle-shaped when viewed along the side.
· Nucleated
· Concerned with clotting of blood.
· Some are phagocytic and others produce heparin, histamine etc.
· Formed in yellow bone marrow and spleen.
3. PLATELETS or THROMBOCYTES
· Smallest corpuscles in the blood.
· Discoid in shape. Spindle-shaped when viewed along the side.
· Nucleated
· Concerned with clotting of blood.
Functions of blood
1. Transport oxygen and nutrients to the tissue
2. Transport harmful substances (ammonia, urea, uric acid etc.) from tissue to excretory organs.
3. Temperature regulation.
4. Transport hormones and other chemical messengers to target tissues.
5. Prevent ingress of microorganisms.
6. Healing of the wound
7. Buffering
· It is surrounded by a double layer of pericardium called outer parietal and inner visceral pericardium).
1. Transport oxygen and nutrients to the tissue
2. Transport harmful substances (ammonia, urea, uric acid etc.) from tissue to excretory organs.
3. Temperature regulation.
4. Transport hormones and other chemical messengers to target tissues.
5. Prevent ingress of microorganisms.
6. Healing of the wound
7. Buffering
HEART
· Muscular conical structure enclosed in the pericardial cavity, lying below the liver in the mid-ventral line, between the lungs.· It is surrounded by a double layer of pericardium called outer parietal and inner visceral pericardium).
· In between them, pericardial fluid is present.
i. EXTERNAL STRUCTURE OF HEART
· Atria and ventricle demarcated by a coronary sulcus.
· Right and left atria not demarcated externally.
· On the ventral surface, from the base of the ventricle arises Truncus arteriosus ⟶ passes forwards obliquely across the right atrium and divides near the anterior boundary of the heart into two diverging branches or trunks.
i. EXTERNAL STRUCTURE OF HEART
· Atria and ventricle demarcated by a coronary sulcus.
· Right and left atria not demarcated externally.
· On the ventral surface, from the base of the ventricle arises Truncus arteriosus ⟶ passes forwards obliquely across the right atrium and divides near the anterior boundary of the heart into two diverging branches or trunks.
 |
| The external structure of the heart of the frog |
· On dorsal surface: triangular and thin-walled Sinus venosus → formed by the union of two pre-cavals and one post caval → opens into the right atrium.
· Pulmonary veins open into the left atrium.
ii. INTERNAL STRUCTURE OF HEART
· Heart consists of 3 chambers: two atria and one ventricle with an atrioventricular aperture between them.
 |
| A well-labelled diagram of the internal structure of the heart of frog |
a) Right atrium or Auricle:
· 2 atria are respected internally by vertical inter auricular septum.
· Larger than left auricle.
· Receives blood from sinus venosus through the sinu-auricular aperture.
· Sinu-auricular aperture lies near the interauricular septum → guarded by two sinu-auricular valves.
b) Left atrium or Auricle:
· Smaller than right auricle.
· Opening of the pulmonary vein has valves because it carries pure blood in high pressure and opens obliquely on the left auricle.
c) Auriculoventricular (AV) aperture and valve
· Both auricles open into a single ventricle by the auriculoventricular (AV) aperture.
· The AV aperture is guarded by auriculoventricular valves → consisting of four flaps: 1 dorsal, 1 ventral, 2 lateral.
· Edges of valves attached to the wall of the ventricle by thin but tendinous threads called chordae tendineae.
d) Ventricle
· Thick-walled largest and muscular chamber.
· Consists of several longitudinal clefts (fissures) separated from each other by muscular projections: columnae carneae.
· Chordae tendineae hold the aurico-ventricular valves in a fixed position during powerful ventricular contraction.
· Columnne carneae and fissures increase the surface area of the ventricle.
· Ventricles open into truncus arteriosus. The opening is guarded by 3 semilunar valves.
· Larger than left auricle.
· Receives blood from sinus venosus through the sinu-auricular aperture.
· Sinu-auricular aperture lies near the interauricular septum → guarded by two sinu-auricular valves.
b) Left atrium or Auricle:
· Smaller than right auricle.
· Opening of the pulmonary vein has valves because it carries pure blood in high pressure and opens obliquely on the left auricle.
c) Auriculoventricular (AV) aperture and valve
· Both auricles open into a single ventricle by the auriculoventricular (AV) aperture.
· The AV aperture is guarded by auriculoventricular valves → consisting of four flaps: 1 dorsal, 1 ventral, 2 lateral.
· Edges of valves attached to the wall of the ventricle by thin but tendinous threads called chordae tendineae.
d) Ventricle
· Thick-walled largest and muscular chamber.
· Consists of several longitudinal clefts (fissures) separated from each other by muscular projections: columnae carneae.
· Chordae tendineae hold the aurico-ventricular valves in a fixed position during powerful ventricular contraction.
· Columnne carneae and fissures increase the surface area of the ventricle.
· Ventricles open into truncus arteriosus. The opening is guarded by 3 semilunar valves.
e) Truncus arteriosus
· Consists of:
– Thick-walled proximal pylangium/conus arteriosus
– Thin-walled distal synangium/ventral aorta.
· Pylangium or conus arteriosus semilunar valves at both ends cavity is incompletely divided by a longitudinal spiral valve into two halves.
– Right ventral half: Cavum aorticum
– Left dorsal half: Cavum pulmocutaneum
· Synangium or Ventral aorta or Bulbous aorta: divided by a horizontal partition called principal septum into the dorsal and ventral chamber.
Cavum pulmocutaneum → dorsal chamber → pulmocutaneous arteries → Cavum aorticum → ventral chamber → carotid
· Truncus arteriosus is divided into 2 aortic trunks each aortic trunk is further divided into 3 arches.
1. Carotid arch
2. Systematic arch
3 . Pulmocutaneous arch
· Heart of frog pumps mixed blood into all of three arteries namely carotid, pulmocutaneous and systemic, of each side.
· Histologically, the wall of the heart consists of 3 layers:
· Outer smooth visceral pericardium
· Middle muscular myocardium
· Inner endothelium
· In addition, there is a single patch of muscle fibres, the sinu-auricular node on the wall of sinus venosus, which acts as a pacemaker of the heart.
· Internal carotid artery: It is a larger and outer branch of the carotid arch.
2. Systemic arch:
b. Occipito-vertebral artery: It arises outwardly from the upper part of each systemic arch and supplies blood to the posterior region of the brain through the occipital artery and to the spinal cord and vertebrae through the vertebral artery.
c. Sub-clavian artery: It supplies blood to the shoulder region and continues in the forelimbs as the brachial artery.
Dorsal Aorta
· It is formed by the union of the two systemic arches and runs posteriorly between kidneys just beneath the vertebral column.
· Histologically, the wall of the heart consists of 3 layers:
· Outer smooth visceral pericardium
· Middle muscular myocardium
· Inner endothelium
· In addition, there is a single patch of muscle fibres, the sinu-auricular node on the wall of sinus venosus, which acts as a pacemaker of the heart.
WORKING MECHANISM OF HEART
· Myogenic in nature
· Heart of frog beats 64 times per minute
· One cardiac cycle completes in 0.92 sec
· Natural pacemaker (Sinu-atrial node or S.A. node) is present in sinus venosus near the sinu-auricular aperture.
· Consists of 2 phases – systole and diastole
· Sinus venosus receives impure blood from different parts of the body with the help of 2 precaval veins and one post caval vein. Then, it contracts to push blood into the right atrium through the sinu-auricular aperture.
· Left auricle receives pure blood from lungs through the pulmonary vein.
· Contraction of both auricles push the blood into the ventricle through Auriculo- ventricular aperture
· From ventricle blood is distributed throughout the body based on these 2 views.
A. Old view (Given by Brucke, 1858 AD)
I. Impure blood in right side ventricle – cavum pulmo-cutaneous – synangium –pulmocutaneous arch– lungs and skin for purification.
II. Mixed blood in the middle of ventricle – cavum aorticum – synangium – systemic arch - different body parts
III. Pureblood in the left side of ventricle – cavum aorticum – synangium - carotid arch – head
· According to this view, the spiral valve controls and directs the flow of different types of blood into different body parts.
B. Modern view (Given by Vandaar vael and Foxon, 1953 AD)
· A mixed type of blood is present only in ventricle – synangium – pylangium – 3 arches- mixed blood is distributed throughout the body.
· According to this view, the spiral valve has no functions.
· Heart of frog beats 64 times per minute
· One cardiac cycle completes in 0.92 sec
· Natural pacemaker (Sinu-atrial node or S.A. node) is present in sinus venosus near the sinu-auricular aperture.
· Consists of 2 phases – systole and diastole
· Sinus venosus receives impure blood from different parts of the body with the help of 2 precaval veins and one post caval vein. Then, it contracts to push blood into the right atrium through the sinu-auricular aperture.
· Left auricle receives pure blood from lungs through the pulmonary vein.
· Contraction of both auricles push the blood into the ventricle through Auriculo- ventricular aperture
· From ventricle blood is distributed throughout the body based on these 2 views.
A. Old view (Given by Brucke, 1858 AD)
I. Impure blood in right side ventricle – cavum pulmo-cutaneous – synangium –pulmocutaneous arch– lungs and skin for purification.
II. Mixed blood in the middle of ventricle – cavum aorticum – synangium – systemic arch - different body parts
III. Pureblood in the left side of ventricle – cavum aorticum – synangium - carotid arch – head
· According to this view, the spiral valve controls and directs the flow of different types of blood into different body parts.
B. Modern view (Given by Vandaar vael and Foxon, 1953 AD)
· A mixed type of blood is present only in ventricle – synangium – pylangium – 3 arches- mixed blood is distributed throughout the body.
· According to this view, the spiral valve has no functions.
VALVES PRESENT IN HEART AND VESSELS
| S.N | Valves | Location |
|---|---|---|
| 1. | Eustachian valve | Opening of inferior vena cava into sinus venosus |
| 2. | A pair of flap-like valves | Opening of sinus venosus to right auricle in sinu-auricular aperture |
| 3. | two pairs of flap-like valves | Auriculo ventricular aperture |
| 4. | Three semilunar valves | Opening of the ventricle to truncus arteriosus |
| 5. | Three spiral valves | In truncus arteriosus, it has a spiral cavity due to the presence of these three spiral valves. |
ARTERIAL SYSTEM OF FROG
· Those blood vessels which carry the pure or oxygenated blood from the heart to the different parts of the body except the pulmocutaneous artery through the different branches constitute the arterial system.· It starts from the truncus arteriosus arising from the ventricle.
· It divides into two-large left and small right aortic trunks.
· Each aortic trunk has three major arches: anterior common carotid arch, middle systemic arch and posterior pulmocutaneous arch.
1. Common Carotid Arch:
1. Common Carotid Arch:
· It arises from the anterior region of the aortic trunk around the side of the oesophagus and divides into two branches.
· Lingual or external carotid artery: It is a smaller inner branch that supplies blood to the tongue and lower jaw.
· Internal carotid artery: It is a larger and outer branch of the carotid arch.
· At its base, it bears a small swelling called “carotid labyrinth”.
· It is sensory in function as it checks the blood pressure and concentration of CO2 in blood.
· The internal carotid is divided into three branches- palatine artery to the roof of the buccal cavity, ophthalmic artery to the eye and cerebral artery to the brain.
2. Systemic arch:
· It is the middle and the largest branch arising from each aortic trunk.
· The two branches of the systemic arch curve around the oesophagus and unite below the heart at the middle line at the level of the 6th vertebra and form a dorsal aorta.
· Each systemic arch gives off three branches before forming the dorsal aorta.
a. Oesophageal artery: It is a small artery that arises inwardly from each systemic arch and supplies blood to the oesophagus.
a. Oesophageal artery: It is a small artery that arises inwardly from each systemic arch and supplies blood to the oesophagus.
b. Occipito-vertebral artery: It arises outwardly from the upper part of each systemic arch and supplies blood to the posterior region of the brain through the occipital artery and to the spinal cord and vertebrae through the vertebral artery.
c. Sub-clavian artery: It supplies blood to the shoulder region and continues in the forelimbs as the brachial artery.
 |
| Arterial system of frog |
Dorsal Aorta
· It is formed by the union of the two systemic arches and runs posteriorly between kidneys just beneath the vertebral column.
· It gives off many branches that supply blood to the posterior region of the body.
A. Coeliaco-mesenteric artery: It is a large and stout artery arising from the junction of two systemic arches and dorsal aorta and is divided into two arteries.
i. Coeliac-artery: It is also divided into two branches- gastric artery that supplies blood to the stomach and hepatic artery to the liver.
ii. Mesenteric artery: It divides into anterior and posterior mesenteric arteries.
a. Anterior mesenteric artery: It supplies blood to the duodenum by duodenal artery, pancreas by pancreatic artery, ileum by intestinal artery and spleen by the splenic artery.
b. Posterior mesenteric artery: It supplies blood to the large intestine or rectum.
Thus, the mesenteric artery supplies blood to the alimentary canal.
A. Coeliaco-mesenteric artery: It is a large and stout artery arising from the junction of two systemic arches and dorsal aorta and is divided into two arteries.
i. Coeliac-artery: It is also divided into two branches- gastric artery that supplies blood to the stomach and hepatic artery to the liver.
ii. Mesenteric artery: It divides into anterior and posterior mesenteric arteries.
a. Anterior mesenteric artery: It supplies blood to the duodenum by duodenal artery, pancreas by pancreatic artery, ileum by intestinal artery and spleen by the splenic artery.
b. Posterior mesenteric artery: It supplies blood to the large intestine or rectum.
Thus, the mesenteric artery supplies blood to the alimentary canal.
The dorsal aorta runs along the mid-line and gives rise to the following arteries.
a. Gonadial arteries: These are a pair of arteries, called spermatic arteries that supply blood to the testes in males and ovarian that supply blood to the ovaries in the female frog.
b. Renal arteries: While passing between the two kidneys, the dorsal aorta gives off 5-6 pairs of renal arteries that supply blood to both the kidneys.
a. Gonadial arteries: These are a pair of arteries, called spermatic arteries that supply blood to the testes in males and ovarian that supply blood to the ovaries in the female frog.
b. Renal arteries: While passing between the two kidneys, the dorsal aorta gives off 5-6 pairs of renal arteries that supply blood to both the kidneys.
· Posterior to the kidney, the dorsal aorta divides into the right and left common iliac. Each common iliac gives the following branches.
i. Hypo-epigastric artery: It supplies blood to the thigh muscle and urinary bladder.
ii. External femoral artery: It supplies blood to the thigh muscle.
iii. Internal sciatic artery: It supplies blood to the shank or lower leg.
3. Pulmocutaneous arch: It divides into two main arteries, pulmonary to the lung and cutaneous to the skin of dorsal and lateral sides and various other structures for the purification of blood.
i. Hypo-epigastric artery: It supplies blood to the thigh muscle and urinary bladder.
ii. External femoral artery: It supplies blood to the thigh muscle.
iii. Internal sciatic artery: It supplies blood to the shank or lower leg.
3. Pulmocutaneous arch: It divides into two main arteries, pulmonary to the lung and cutaneous to the skin of dorsal and lateral sides and various other structures for the purification of blood.
VENOUS SYSTEM IN FROG
· Those blood vessels that return the blood from the different parts of the body to the heart constitute the venous system.· Small capillaries unite to form venules, many of them fuse to form veins, which in turn unite to form vena cava.
· The venous system of frogs can be studied under the following headings:
a. Pulmonary veins
a. Pulmonary veins
b. Caval veins
c. Renal portal veins
d. Hepatic portal vein
a. Pulmonary veins
· Right and left pulmonary veins carry pure blood from the lungs to the heart.
a. Pulmonary veins
· Right and left pulmonary veins carry pure blood from the lungs to the heart.
· They join to form the common pulmonary vein.
· It opens in the left auricle on the dorsal side.
b. Caval veins
· Impure blood from the rest of the body is carried into the heart in three large vessels.
b. Caval veins
· Impure blood from the rest of the body is carried into the heart in three large vessels.
· Two anterior pre-cavals and one posterior post caval, all open into sinus venosus.
i. Pre-caval veins:
i. Pre-caval veins:
· The left and right pre-cavals collect venous blood from the anterior region of the body.
· Each pre-caval vein is formed by the fusion of three veins.
b. Innominate vein: It is formed by the internal jugular vein that collects blood from the brain and the sub-scapular vein that collects the blood from the shoulder.
c. Subclavian vein: It is formed by the brachial vein that collects blood from the forelimb and the musculocutaneous vein that collects the blood from the side of the body and head.
ii. Post-caval vein:
a. External jugular vein: It is formed by the lingual vein that collects blood from the tongue and the mandibular vein that collects the blood from the lower jaw.
b. Innominate vein: It is formed by the internal jugular vein that collects blood from the brain and the sub-scapular vein that collects the blood from the shoulder.
c. Subclavian vein: It is formed by the brachial vein that collects blood from the forelimb and the musculocutaneous vein that collects the blood from the side of the body and head.
 |
| The venous system of the frog |
ii. Post-caval vein:
· It collects the blood from the posterior part of the body.
· It lies ventral to dorsal aorta. Its posterior end is formed between two kidneys from where it drains blood by 5-6 pairs of renal veins.
· It also collects the blood from gonads through one pair of genital veins (spermatic in male, ovarian in female), from the liver through one pair of hepatic veins.
· The post-caval vein then opens to the sinus venosus.
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