bio lab

EXERCISE 18: THE BLOOD CIRCULATORY SYSTEM (INTERNAL TRANSPORTATION)



Blood Circulatory System

  • transports digested food from the digestive tract to the different parts of the body. 



  • It transports oxygen from the lungs to different parts; carbon dioxide from different tissues or cells of the body to the lungs; hormones from the endocrine glands to target cells and organ




Parts of the blood circulatory system:

  1. Heart

pumping organ



  1. Blood Vessels

    1. Arteries

    2. Veins

    3. Capillaries 



  1. Blood

medium for transport and contained in the vessels.



A freshly killed toad should be used in this exercise. By means of sharp pair of scissors, make a single longitudinal incision through the skin along the mid-ventral line and expose the muscles of the ventral surface of the trunk. Next, make two parallel incisions through the muscles of both side of the linea alba from the pelvic girdle to the xiphisternum. Under the linea alba, adhering to it, is the ventral abdominal vein. Be careful not to cut this vein. Beyond the point where the ventral abdominal vein leaves the muscles, cut the muscles crosswise joining the parallel incisions previously made. Now cut forward through the median ventral line up to the lower jaw. Open the body cavity being very careful not to destroy the blood vessels running from the region of the heart laterally to the body wall passing at the base of the forelimb. Now you are ready to start your study of the blood circulatory system.



I. HEART.



  1. External Anatomy of the Heart.

1. Ventricle

  • conical posterior portion of the heart

  • pale in color

  • hard because of its thick wall.



2. Auricles. 

  • This is the anterior expanded thin-walled, dark, and softer parts of the heart. 

  • The auricles are divided into right and left side. 



3. Conus arteriosus. 

  • This is a swollen and pale structure 

  • located dorsal to the right auricle and obliquely across the ventral surface of the latter. 

  • usually embedded with fats which are yellowish in color.




  1. Internal Parts of the Heart

Open the heart frontally by cutting the ventral walls of the auricles and the ventricle. Locate and identify the following structures. You may use stereomicroscope to see the parts as described below.



1. Interauricular septum

membranous partition between the right and left auricular cavities or chambers.



2. Sino-auricular opening

  • single big opening on the dorsal surface of the right auricle. 

  • This is the opening of the sinus venosus to the right auricle.



3. Pulmo-auricular opening

  • a small opening on the dorsal surface of the left auricle. 

  • This is the entrance of the pulmonary vein into the left auricle.



The right auricle is bigger than the left auricle. It is the right that receives a bigger volume of deoxygenated blood from different parts of the body. The left auricle receives a smaller volume of oxygenated blood from the lungs.



4. Ventricular cavity or chamber 

  • single cavity in the ventricle and this extended into its thick wall by numerous pockets, the ventricular pockets.



5. Auriculo-ventricular (AV) opening 

  • a single opening of the right and left auricles into the ventricle.



6. Auriculo-ventricular (AV) valve

  • the structure that guards the AV opening.

  • prevents the backflow of the blood from the ventricle to the auricles when the former contracts.



7. Chordae tendinae

  • fiber-like structures that anchor the AV valve to the muscular wall of the ventricle.



8. Semilunar valve 

  • a small and half-moon-shaped valve at the entrance of the ventricle to the conus arteriosus. 

  • This valve can be seen only in good dissection under a stereomicroscope. 

  • This valve prevents the backflow of blood from the conus arteriosus to the ventricle after the blood leaves the latter.



9. Spiral valve or S-shaped blood

  • this is inside the conus arteriosus.

  • This directs the oxygenated and the deoxygenated blood from the ventricle into their proper arteries.



II. VENOUS SYSTEM.



Veins

  • thin-walled and collapsible. 

  • carry blood toward the heart. 



Three classes of veins:

  • Systemic Veins

    • pour blood directly to the heart

    • In toads, there are systemic veins, the two precaval veins, and one postcaval vein.



  • Portal Veins

    • pour blood to organs other than the heart. 

    • There are two portal veins;

      • One Hepatic Portal Vein

receives blood from the digestive organs and pours it to the liver.



  • Two Renal Portal Veins

receive blood from the hindlimbs and pour to the kidneys



  • Pulmonary Veins

    • receive blood from the lungs and pour it to the heart.



A. Systemic Veins.

To look for these open the parietal pericardium and expose the heart. Hold the apex of the heart, lift and bring it gently forward, you will see the sinus venosus on the dorsal side of the heart particularly on the right auricle. Note three big veins that enter into sinus venosus, the two precaval veins (anterior or superior vena cavae) on its antero-lateral angles, and one postcaval vein (posterior or inferior vena cava) on its posterior end.



1. Precaval veins.

Follow one of these veins a little away from the heart. This receives three main tributaries: the external jugular vein, innominate vein, and the subclavian vein.



a. External jugular vein

the anterior tributary of the precava. Receives two smaller tributaries:



(1) Maxillary (Mandibular) vein 

- the lateral branch coming from the angles of the jaws. 

- This drains blood from the jaws and also receives blood from the thyroid glands.



(2) Lingual vein 

- anterior and medial branch draining blood from the tongue, hyoid, and floor of the buccal cavity.



b. Innominate vein

the middle tributary of the precava which receives two small tributaries: 



(1) Internal jugular vein 

the anterior vein draining blood coming from the brain, spinal cord, and various parts of the head.



(2) Subscapular vein 

the posterior tributary draining blood from the region of the shoulder and forelimbs.



c. Subclavian vein 

the main posterior tributary of the precava. Receives two small tributaries: 



(1) Brachial vein 

the bigger vein coming and draining blood from the forelimbs.



(2) Musculo-cutaneous vein

a small posterior tributary which in turn receives two smaller tributaries:



(a) Muscular vein - drains blood from the muscles of the chest



(b) Cutaneous vein - comes from the skin and drains blood from it



2. Postcaval vein

This is the principal vessel draining the posterior regions of the body. To follow it from the sinus venosus, it pierces the liver, receiving a pair of hepatic veins from it. Lift up the liver and see the big postcava emerging from its posterior border. Follow this posteriorly, it receives a number of small tributaries from both the left and right kidneys. These are the renal veins. One of the renal veins receives ovarian veins (in the females) or spermatic veins (in the males) from the ovaries and testes, respectively. The postcava extends only up to the kidneys.




B. Portal Veins.



1. Hepatic Portal Veins

  • Drain blood from the different parts and organs of the digestive tract and glands. 

  • This can be seen as a dark vessel coursing along the pancreas and entering the liver. 



Look for the following veins that empty into the hepatic portal veins.



a. Gastric veins - coming from the stomach and two in number. One comes from the left side of the stomach, the left gastric vein, and the other comes from the right side of the stomach, the right gastric vein.



b. Pancreatic vein - a small vein receiving blood from the pancreas.



c. Intestinal veins - coming from the small and large intestines, spreading fan-like



d. Splenic vein - a short and small vein coming from the spleen and emptying into the intestinal vein.



2. Renal Portal Veins

These are two veins, each receiving blood from the hindlimbs and dorsal body wall, and pours blood into the system of capillaries in the kidney. 



Remoral vein 

coming from the anterior portion of the thigh. It is under the rectus femoris anticus. Follow this anteriorly. This branches into two at the base of the thigh; a medial branch, the pelvic vein, and a lateral and anterior one, the external iliac vein. 



The external iliac vein joins with the sciatic vein which drains blood from the entire hindlimb and medial to the former. This union forms the renal portal vein. Follow this anteriorly. This courses along the lateral edge of the kidney. At about the middle portion of the kidney, the renal portal vein receives one or two dorso-lumbar veins from the dorsal body wall.



The Pelvic vein from one side will unite with the pelvic vein from the other side to form the ventral abdominal vein. The ventral abdominal vein receives the vesical vein from the urinary bladder and continuous anteriorly along the linea alba. This empties into the hepatic portal vein. The blood from one femoral vein, therefore, can go to the heart by way of the liver through the ventral abdominal vein of by way of the kidneys through the renal portal veins.




C. Pulmonary Veins.

To look for these, hold the apex of the heart and pull it upward. Two small veins from the lungs can be seen clearly leading to the and pull it upward. They unite before entering the left auricle. These are the pulmonary veins which carry oxygenated blood from the lungs to the heart.



III. ARTERIAL SYSTEM.

Arteries are thick-walled vessels, thick enough to maintain the shape of the blood vessel without collapsing. They carry blood away from the heart, so begin by tracking the arteries from the heart.



The bulging blood vessel arising from about the right side of the heart and running obliquely across the ventral surface of the right auricle is the conus arteriosus. This is embedded with fats. This vessel continues forward into smaller vessel, the truncus arteriosus which splits shortly into two branches. Each of these should be followed farther. Identify the 3 main branches of the truncus arteriosus; the common carotid artery, pulmo-cutaneous artery, and systemic artery.



A. Common Carotid Artery.



This is the most anterior and the smallest of the three branches. Shortly beyond its origin, it divides into two:



1. External carotid artery

medial branch supplying blood to the floor of the mouth.



2. Internal carotid artery

the lateral and larger branch, going mainly to the brain. At the base of this vessel, near the point where the two carotids split, is a spherical, dark enlargement, the carotid gland.



B. Pulmo-cutaneous Artery.

This is the most posterior of the branches of the truncus arteriosus. This branches into two, the pulmonary artery and cutaneous artery.



1. Pulmonary artery

the medial or inner branch that goes to the lung.



2. Cutaneous artery 

the lateral branch which is much longer than the former and proceeds laterally to the skin.



C. Systemic Artery.

This is the middle and the biggest branch of the truncus arteriosus. It passes laterally and ventrally, and unites with the other systemic artery of the opposite side and continues posterior until this unites with the other on the other side. Identify the following branches:



1. Laryngeal artery

the first and small branch of the systemic artery and arises from Its base. This supplies blood to the larynx.



2. Occipito-vertebral artery

the small branch of the systemic artery at the level of the base of the forelimb. This goes dorsally and supplies blood to the orbit, nose, and the spinal cord.



3. Subclavian artery

another small branch of the systemic artery also at the level of the base of the forelimb. This goes laterally along the anterior border of the big white second spinal nerve into the forelimb and becomes the brachial artery.



4. Esophageal artery 

another small artery arising from the inner surface of the systemic artery and goes to the esophagus.



D. Dorsal Aorta.

This is an unpaired artery formed from the union of the left and right systemic arteries. This proceeds posteriorly between the two kidneys and dorsal to the postcaval vein. To look for this, lift one of the kidneys from the dorsal body wall and bring it to the opposite side. Identify the branches of the dorsal aorta.



1. Coeliaco-mesenteric artery

unpaired medial branch arising from anterior end of the dorsal aorta, a little posterior to the point of union of the tow systemic arteries. The coeliaco-mesenteric artery branches into:



a. Coeliac artery - the unpaired anterior branch. It further branches into:



(1) Gastric artery supplies blood to the stomach. It branches into the left gastric artery, going to the left side of the stomach, and right gastric artery, supplying blood to the right side of the stomach.



(a) Hepatic artery a branch from the right gastric artery that goes to the liver.



(b) Pancreatic arteries small branches from the right and left gastric arteries which go to the pancreas.



b. Anterior mesenteric artery 

the posterior branch of the coeliaco-mesenteric artery. It further branch into:





(1) Splenic artery - this goes to the spleen.



(2) Intestinal artery - spreading fanlike to the small intestine



(3) Anterior hemorrhoidal artery - supplying blood to the anterior portion of the large intestine.



2. Urogenital arteries 

paired arteries arising from a common stem which in turn branches from the ventral surface of the dorsal aorta. These arteries supply blood to the kidneys and gonads.



3. Lumbar arteries

paired arteries arising from the dorsal side of the dorsal aorta that supply blood to the dorsal body wall.



4. Posterior mesenteric artery 

a small unpaired branch of the dorsal aorta just in front of the point where the dorsal aorta branches into two common iliac arteries. The posterior mesenteric artery supplies blood to the posterior portion of the large intestine. In the female specimens, this artery gives off the uterine arteries to the uteri or ovisacs.



5. Common illac arteries 

the two branches arising from the splitting of the dorsal aorta posteriorly. Follow one of the common iliac arteries and identify the following branches:



a. Epigastro-vesicle artery 

the front branch which is covered partly by the nerves of the lumbo-sacral plexus. This branches into:



(1) Epigastric artery - this supplies blood to the ventral abdominal wall.



(2) Recto-vesicle artery - this supplies blood to the rectum and urinary bladder.



b. Femoral artery

the next and posterior branch of the common iliac artery. This supplies blood to the anterior portion of the thigh and goes with the femoral vein.



c. Sciatic artery 

this is the continuation of the common iliac artery after the femoral artery branches from the former. This supplies blood to the hindlimb.



E. Capillaries.

These are microscopic blood vessels connecting arteries to veins in all parts of the body. 



Some of the capillaries are so small that the RBCs pass through them in single file. 



The flow of the blood in an artery is slightly pulsating and proceeds into its branches. 



The flow of the blood in the vein is steady and is from the tributaries. 



Look for the dark-colored, irregular bodies scattered around. These are chromatophores or pigment cells responsible for the coloration of the skin.




Review Questions:



1. How can you explain the differences in size of the auricles?

The right auricle is larger than the left because it receives deoxygenated blood from the entire body through the sinus venosus. In contrast, the left auricle receives a smaller volume of oxygenated blood from the lungs via the pulmonary vein, requiring less capacity.



2. What is the function of the valves? Of the chordae tendinae?

Valves:

Prevent the backflow of blood during the contraction of the heart.

Ensure unidirectional blood flow between chambers (e.g., from auricles to ventricles and from ventricles to arteries).



Chordae Tendinae:

Anchor the atrioventricular (AV) valves to the walls of the ventricle.

Prevent the valves from inverting into the auricles during ventricular contraction, maintaining proper closure.



3. In a three-chambered heart, will there be any mixture of venous and arterial blood in the ventricle? Support your answer. 

Yes, there will be some mixture of venous and arterial blood in the ventricle.

In amphibians, the single ventricle is partially divided by ventricular pockets and the spiral valve, which direct oxygenated blood to systemic circulation and deoxygenated blood to pulmonary circulation. However, the absence of a complete septum allows for limited mixing of blood in the ventricle.



4. Explain how the spiral valve operates in conducting oxygenated and the deoxygenated blood form the ventricle to the proper arteries?

The spiral valve within the conus arteriosus is structured to direct blood flow effectively:

Oxygenated blood from the left auricle is directed to the systemic arteries, supplying the body.

Deoxygenated blood from the right auricle is directed to the pulmonary arteries, leading to the lungs.




5. Why are capillaries considered the functional parts of the circulatory system?

Capillaries are the sites of exchange between blood and tissues:

Deliver oxygen and nutrients to cells.

Remove carbon dioxide and metabolic wastes from cells.

Their thin, single-cell walls facilitate diffusion, making them the most important part of the circulatory system for maintaining cellular function.



6. Trace the course of the blood from the capillaries of the intestines to the capillaries of the hindlimbs.

Capillaries of the Intestines: Collect absorbed nutrients and waste.

Hepatic Portal Vein: Carries nutrient-rich blood to the liver.

Liver: Filters and processes nutrients; blood exits via the hepatic vein.

Posterior Vena Cava: Transports blood to the right auricle of the heart.

Right Auricle: Pumps deoxygenated blood to the ventricle.

Ventricle: Pumps blood to the lungs via the pulmonary arteries.

Lungs: Blood is oxygenated and returned to the heart via the pulmonary veins.

Left Auricle: Receives oxygenated blood from the lungs and sends it to the ventricle.

Ventricle: Pumps oxygenated blood to the systemic circulation, including the hindlimbs.

Systemic Arteries: Distribute oxygenated blood to the capillaries of the hindlimbs, where oxygen and nutrients are delivered to tissue



EXERCISE 19: NERVOUS SYSTEM

The nervous system controls the rapid activities of the body such as muscular contraction, rapidly changing the visceral events, and even the rates of secretion of some endocrine glands. The vertebrate nervous system is divided into:



I. Central Nervous System



A. The Brain

enclosed in the skull



B. The Spinal Cord

enclosed in the neural canal of the vertebral column.



II. Peripheral Nervous System



A. Cranial Nerves

originating from the brain



B. Spinal Nerves

originating from the spinal cord



III. Autonomic Nervous System



A. Sympathetic Motor System

controls adrenergic responses ("fight and flight" responses)



B. Parasympathetic Motor System  controls 

cholinergic responses ("relaxation" responses)




The Central Nervous System.



A. The Brain.

The brain is the anterior and much expanded part of the central nervous system. It is covered by a tough membrane, the dura mater.



1. Dorsal Aspect of the Brain.



a. Telencephalon (Cerebral Hemispheres) the anterior region, enlarged and triangular in shape. This split into two lobes by a sagittal groove and constricted anteriorly to form the olfactory bulbs to which the olfactory nerves arise. The cerebral hemisphere is the seat of memory and other higher faculties.



b. Diencephalon (Twixt Brain) 

the narrow depressed region behind the telencephalon. A thin vascular membrane called the anterior or first choroid plexus may be seen on its dorsal surface. It is often tom off in dissection. Locate the pineal body or epiphysis at the center of the dorsal surface which is a small elevation ascending dorsally to the brow spot, the rudimentary third eye. The diencephalon something to do with balance and vision.



C. Mesencephalon (Midbrain)

the third region which is easily recognized by a pair of rounded bodies, the optic lobes, apparently concerned with inhibition of spinal cord reflexes.



d. Metencephalon (Cerebellum) 

the very narrow transverse region directly behind the preceding. It controls equilibrium.



e. Myelencephalon (Medulla Oblongata)

a long and narrowing posteriorly and continuous with the spinal cord. At its dorsal surface is a triangular depression, the fourth ventricle, roofed by the posterior or second choroid plexus. Usually the plexus is removed. The choroid plexus carries the nourishment to the brain. The medulla oblongata directs most bodily activities.



2. Ventral Aspect of the Brain.



a. Optic chiasma

the point of crossing of the two optic nerves which comes from the eyes, and located ventral of the diencephalon.



b. Indundibulum 

a bilobed flat structure which forms the ventral extension of the diencephalon, beneath and posterior to the optic chiasma.



c. Hypophysis or Pituitary Body

a rounded body attached to the preceding and fits into a depression in the floor of the skull, the sella turcica. Sometimes, it is not present because it was left in sella turcica when the brain was removed from the skull. This structure is an endocrine gland.



B. The Spinal Cord.

This is posterior and the longest part of the central nervous system, cylindrical in form, and extends posteriorly from the medulla oblongata, and terminates into a tapering structure, the filum terminale.



1. Dorsal Aspect of the Spinal Cord.



a. Dorsal median fissure 

a groove that runs longitudinally along the mid-dorsal surface of the spinal cord.



b. Brachial enlargement

the enlarged or expanded part of the spinal cord at the the forelimbs.



c. Sacral (Lumbo-sacral) enlargement

the enlarged or expanded part of the spinal cord at the level of the hindlimbs. This is a little smaller than the preceding. and from which big spinal nerves to the hindlimbs arise.



d. Filum terminale

the tapering end of the spinal cord, which appears as a very slender fiber, and located in the urostyle (last vertebra). The numerous spinal nerves that arise from the posterior portion of the spinal cord together with the filum terminale constitute the cauda equina (horsetail).



2. Ventral Aspect of the Spinal Cord. 

The structures that are found in the ventral side are the same structures already identified in the dorsal aspect, except the ventral median fissure, the longitudinal groove or depressed line that runs along the mid-ventral surface of the spinal cord.



C. The Cavities of the Brain and Spinal Cord.

The central nervous system of the toad and frog, like other chordates, is hollow. The cavities of the brain are called ventricles while that of the spinal cord is central canal. The ventricles serve as passageway through which cerebrospinal fluid flows. The cerebrospinal fluid is a watery substance that serves as cushion for the entire central nervous system, protecting the soft tissues from jolts and blows.



1. First and Second (Lateral) ventricles

the two cavities found in the telencephalon, one in each cerebral hemisphere.



2. Third ventricle

located inside the diencephalon.



3. Foramen of Monro

the opening of the left and right ventricles to the third ventricle.



4. Optocoeles

the cavities inside the optic lobes.



5. Fourth ventricle 

the largest of the cavities and located on the dorsal surface of the medulla oblongata.



6. Aqueduct of Sylvius or Iter

a single narrow cavity located in the mesencephalon and connects the third ventricle to the fourth ventricle.



7. Central Canal

a narrow cavity found inside the whole length of the spinal cord. This continuous anteriorly to the fourth ventricle the holeral cathal can be seen in an intact spinal cord.



D. Histology of the Spinal Cord.



1. Meninges (sing. meninx)

membranous coverings of the spinal cord and the brain. There are two in the frog and toad, the dura mater and pia mater.



a. Dura mater

the outer and thick dense connective tissue, and located a little farther from the spinal cord



b. Pia mater

the inner and thin membranous structure that is the contact with the outer surface of the spinal cord. In some specimens, this is partly destroyed and lifted away from the spinal cord.



2. Subdural space

the space between the dura mater and pia mater. This space is filled with cerebrospinal fluid.



3. Ventral fissure 

a wide and shallow depression located at the mid-ventral surface of the cord.



4. Dorsal fissure 

a narrow and deeper depression located at the mid-dorsal surface of the cord.



Note the difference between the dorsal and ventral sides of the cord, i.e. the dorsal is narrower than the ventral side.



5. Ventral spinal artery

the blood vessel lying inside the ventral fissure.



6. Central canal 

the small space located at the center of the cross-section of the spinal cord. This is lined with simple columnar epithelium, and filled up with cerebrospinal fluid.



7. White matter 

the outer or peripheral substance of the spinal cord. This is composed of nerve cell bodies, and naked nerve fibers.



8. Gray matter 

the inner or central compact substance of the spinal cord. This is composed of nerve cell bodies, and naked nerve fibers.



9. Dorsal horns

a pair of projections from the dorso-lateral angles of the gray matter.



10. Ventral horns 

a pair of projections from the ventro-lateral angles of the gray matter. The dorsal homs are narrower and longer than the ventral homs.



11. Motor cells

are large darkly-stained stellate or multipolar nerve cells found in broad and short ventral homs of the gray matter.




The Peripheral Nervous System.



A. The Cranial Nerves.

There are ten pairs of cranial nerves in the toad and frog, twelve in higher vertebrates. Most of these on account of their minute size cannot be seen, except perhaps their points of origin from the brain. These are numbered in the order in which they originate from the brain.



  1. Olfactory Nerves (I) - Sense of smell

  2. Optic Nerves (II) - Vision

  3. Oculomotor Nerves (III) - Eye movement

  4. Trochlear Nerves (IV) - Eye movement

  5. Trigeminal Nerves (V) - Sensation from the face and motor functions such as biting and chewing

  6. Abducens Nerves (VI) - Eye movement

  7. Facial Nerves (VII) - Control of facial expressions and taste sensations

  8. Vestibulocochlear Nerves (VIII) - Hearing and balance

  9. Glossopharyngeal Nerves (IX) - Taste and other functions of the throat

  10. Vagus Nerves (X) - Control of the heart, lungs, and digestive tract



B. The Spinal Nerves and Sympathetic Nervous System.

There are ten pairs of spinal nerves in the frog, corresponding to the ten vertebrae. Each spinal nerve is formed by the union of the dorsal and ventral roots of the spinal cord inside the neural canal. It emerges from the ventral column through the intervertebral foramina as white cord. The first pair of the spinal nerves arises between the first and the second vertebrae. The second pair is big and arises between the second and third vertebrae; the third pair between the third and fourth vertebrae. The first 3 pairs are joined by branches to form the brachial plexus innervating the forelimb. The 4th, 5th, 6th pairs innervate the abdominal wall and they do not form a plexus. The last 3 or 4 pairs, i.e. the 7th, 8th, 9th, and 10th spinal nerves are joined by cross branches to form the lumbo-sacral plexus mainly supplying the hindlimb.



The sympathetic nervous system consists mainly of two sympathetic nerve trunks running on both side of the dorsal aorta. It also extends to the systemic arteries. Dissect this very carefully or examine demonstration specimens. Note the fine strands, the rami communicans, from the spinal nerves to the sympathetic nerve trunk. The enlargement at the junction of the sympathetic nerves and the communicating branches are the sympathetic ganglia.