Bothrops alternatus

The Bothrops alternatus, known as yarará in Argentina, is a life-threatening venomous snake of the warm and humid regions of South America. It belongs to the genus Bothrops and the family Viperidae. It is found found in Brazil, Paraguay, Argentina, and Uruguay. It can also be encountered in Venezuela.

The glands of Bothrops alternatus secretes cytotoxic venom, which destroys the tissue around the bitten area. This causes severely necrotized tissues (gangrene). Thus, there have been many cases in which amputation of the hand or foot was required in order to avoid septicemia (blood-poisoning).

Physical Description

The Bothrops alternatus snake is brown with white-grey, inverted V-shaped markings that border dark brown patterns and has a triangular head. Its eye has vertical, slit pupils. As a member of the family Viperidae, it has long tubular fangs. The adult female can have a maximum length of 1.60 m, with 1.30 m being the average length.

Below, a Bothrops alternatus snake curled up on the ground in Brazil

The head of a Bothrops a.

The same species slithering on the sand on a river shore.

 

Cape Cobra

The Cape cobra (Naja nivea) is a dangerous venomous snake one can encounter in South Africa and Namibia. Since it belongs to the family Elapidae, its glands secrete neurotoxic venom. It is found mostly in dry environments, from sea level to high lands at 2,500 m (7,600 ft). It inhabits the Kalahari semi-desert areas in Botswana, the savanna and the fynbos of the Cape provinces, and the dry rocky hills in the desert of Namibia, as well as in dry riverbeds.

Physical Description

The Cape cobra is a slender snake, with broad head. It has smooth and dull scales, which are arranged in 19 to 21 rows at mid body, with the ventral side having an average of 200 rows. Although the adult can measure between 1.20 and 1.50 m in length, the maximum recorded size is 2.30 m. Several distinct color forms have been observed, from uniform yellow, to orange, and dirty yellow, speckled with dark brown. Juveniles have a broad black band on the throat, which disappear over time. When it feels threatened, it spreads out its hood.

Below, the Cape cobra lying on a rock. A yellow specimen, with dark speckles.

 The Naja nivea is usually terrestrial, living on ground level, but sometimes it climbs trees and bushes as it is known to look for bird nests in the Kalahari. It feeds on a wide variety of small animals, such as rodents (rats and mice), lizards, frogs, and other snakes. However, it is sometimes hounded and killed by Meerkats and mongoose. The female of the species lay between 8 and 20 eggs in December and January in a hole or termite hill in warm areas.

Warning

The Cape cobra is a major snakebite hazard in South Africa, both to human beings (farmers/tourists) and to stock. It accounts for most snakebites fatalities in South Africa. This is due to the fast onset of paralysis caused by the neurotoxic venom. There is paralysis of the head and neck muscles first, then total paralysis spreads to the ribcage intercostal muscles, diaphragm and lungs. Since this snakebite is an urgent medical case. Patients need treatment with ventilator/tube to help him/her breathe by artificial expansion of chest, and anti-venom treatment and Doxapram.

Below, a adult, in brownish yellow scales.

Map of southern portion of Africa, showing the distribution areas of the Cape cobra.

Peringuey’s Adder

The Peringuey’s adder (Bitis peringueyi) is a venomous snake, which is endemic to the Namib desert, along the coast of Namibia, Africa. Although it is small in size, its bite could be dangerous. Since it fits in the Viperidae family, its venom contains cytotoxins. It often slithers into loose sand, leaving the eyes exposed as it lies in wait for its prey.

It measures between 20 to 30 cm in length, one of the smallest adder in Africa. It is ‘rusty’ brown, with small dark and white spots along its body. It has a triangular flattened head, with its eyes unusually located high on it. The subcaudals are smooth, except for small keels situated towards the tip. It is known for its ability to sidewind as it advances in smooth lateral curves. It feeds on desert lizards.

Below, photo of the Peringuey’s adder

Epithelial Tissue

The epithelial tissue, or epithelium, is membranous tissue that covers the surface of the body and lines internal organ cavities, glands, and blood vessels. Externally, it forms the skin. When it lines internal cavities and the lumen of arteries, it is called endothelium. The underside of the epithelium is attached to connective tissue by a thin layer of basement membrane. Although epithelial tissue lacks blood vessels, nutrients diffuse to the epithelium from underlying connective tissues, which do have blood vessels.

The epithelial tissue is classified by the number of layers of cells and by their shapes. Thus, when it consists of a single layer of cells, it is called 'simple'. When it consists of two or more layers, it is called 'stratified'. When it is made up of flattened epithelial cell, it is 'squamous'. When it is constituted by cube-like cells, it is 'cuboidal'; and when it is formed by elongated cells, it is 'columnar'.

Simple squamous epithelium lines the lung alveoli, the heart cavities, and the lymphatic and blood vessels; this type allows materials to seep through by diffusion. Stratified squamous epithelial tissue lines the esophagus, mouth, and vagina.

Simple cuboidal epithelium lines ducts, kidney tubules, the ovaries, and secretory portion of small glands. Stratified cuboidal epithelial tissue, on the other hand, covers the inner walls of mammary glands, sweat glands, pancreas, and salivary glands.

Simple columnar epithelium lines the passages of respiratory system, such as the bronchi, as well as the trachea. Whereas stratified columnar epithelial tissue covers inner walls of male urethra and the ducts of some glands.

Epimysium and Perimysium

Epimysium and perimysium are two thin sheath of connective tissues that wrap around skeletal muscles. The difference is that the former wraps externally around each muscle, whereas the perimysium extends inwardly from the epimysium to surround each one of the fascicles that make up a muscle. A fascicle is a bundle of fibers. Each one of these bundles of skeletal muscle fibers is called fascicle. Each muscle fiber of a fascicle is in turn surrounded by another layer of connective tissue; it is called endomysium, which is thinner than the other layers mentioned above.

Thus, these three thin layers of collagen connective tissue (epimysium, perimysium, and endomysium) enclose and separate all parts of a skeletal muscle. This disposition allows the fascicles and fibers to move somewhat independently without getting damaged by sudden muscular contraction. They facilitate transfer of contractile force to muscle attachments. This arrangement of sheets of connective tissue enveloping muscles and fascicles also allows nerves and blood vessels, such as arteries and veins, to run through them.

To summarize, each individual skeletal muscle is externally surrounded by epimysium, which lies directly under the fascia that ends up in the tendon. Each fascicle in turn is wrapped up by perimysium, whereas each muscle fiber is enveloped by endomysium.

Internal Iliac Artery

The internal iliac artery is an important blood vessel that supplies the organs and tissues of the pelvic region. It originates as one of the two branches into which the common iliac artery divides; the other is the external iliac. It gives off many arterial branches of tortuous course that supply the bladder, genitals, uterus, rectum, muscles of the perineal region, as well as the gluteus maximus and piriformis muscle.

As soon as it arises from the common iliac, the internal iliac artery descends obliquely and medially into the cavity of the true pelvis along the line of the sacro-iliac joint. Then, at the upper border of the greater sciatic foramen, it forks into an anterior and a posterior trunk. All the the arteries arising from the anterior trunk are viseral branches, while those originating from the posterior trunk are parietal offshoots, with the exception of the inferior gluteal and obturator artery, which are the only parietal branches arising from the anterior trunk.

Branches of Internal Iliac Artery

1) Umbilical Artery. It is one of its largest branches in the embryonic period. It arises from the anterior trunk of the internal iliac and runs forwards to the wall of pelvis. Then it gives off the superior vesical arteries, which supply the urinary bladder and the ureter.

2) Uterine Artery/of the vas deferens. It originates from the anterior trunk and extends under the peritoneum forwards and medially. In the female, it irrigates the uterus; in males, the vas deferens duct and the seminal vesicles.

3) Middle Rectal Artery. It arises also from the anterior trunk of internal iliac as a small blood vessel that sometimes is absent in some individuals. However, it sometimes originates from the inferior vesical artery.

4) Internal Pudendal Artery. It is an offshoot of the anterior trunk of internal iliac. It has a rather long an tortuous course, giving off several smaller branches that supply the external genitalia and the perineum.

5) Iliolumbar Artery. It arises from the posterior trunk. Running forwards and upwards, it sends terminal branches to the pelvic muscles and bone.

6) Lateral Sacral Arteries. They spring off the posterior trunk; then they run medially to supply the sacrum, the skin of the sacral region, deep muscles of the lower back, and the piriformis, coccygeus, and levator ani muscles.

7) Superior Gluteal Artery. It also arises from the posterior trunk as a large branch. It leaves the cavity of the pelvis through the greater sacrosciatic foramen, giving off branches to the piriformis, and the gluteus maximus and the gluteus medius.

8) Inferior Gluteal Artery. It is the only parietal branch that arises from the anterior trunk of internal iliac. It supplies the gluteus maximus and quadratus femoris muscle.

9) Obturator Artery. It branches from the anterior trunk. Running on the side wall of the true pelvis, it gives off smaller arteries to supply the external obturator muscle.

Below, schematic picture of blood vessels of pelvis region, exhibiting the internal iliac artery.

 

External Pudendal Arteries

The external pudendal arteries are a pair of blood vessels of the inguinal region, supplying the skin of the pubic and genital area. Although in some individuals there are three arteries, in most cases there are only two blood vessels. They are 1) the superficial external pudendal and 2) the deep external pudendal artery. They both originate from the first portion of femoral artery.

1) The superficial external pudendal artery. It arises from the medial surface of femoral artery, right below the inguinal ligament. Then it pierces the superficial fascia of thigh (cribriform fascia) and runs medially across the spermatic cord, ascending to the suprapubic region (lower part of abdomen, where it branches to supply the skin above the genital region.

2) The deep external pudendal artery. It also originates from the medial side of femoral artery, just below the site of origin of the superficial external pudendal. Then it runs over the pectineus muscle, pierces the fascia of thigh and approaches the scrotum where it forks into either the scrotal branches (in males) or labial branches (in females), supplying the skin of this region. Some of these terminal branches anastomoses with branches of the internal pudendal artery.

Below, image of thigh and inguinal region, showing the two external pudendal arteries arising from the femoral artery.

Internal Pudendal Artery

The internal pudendal artery is a blood vessel of the lower pelvic region which supplies the human genitalia. It arises from the anterior trunk of the internal iliac artery. Then it extends downwards and laterally, leaving the true pelvis through the greater sacrosciatic foramen. Next it arches over the ischial spine and runs medially and forwards.

Following a tortuous course, the internal pudendal artery enters the true pelvis again but through the lesser sciatic foramen, below the pelvic diaphragm. It enters the ischiorectal fossa, running laterally on its wall, reaching the posterior border of the urogenital diaphragm. There, on the inferior pubic ramus, it pierces the urogenital diaphragm from the depth to the surface dividing into six terminal branches:

1) the artery of the bulb of the penis, or the artery of the vestibule in females;

2) the urethral artery, which supplies the membranous urethra;

3) the deep artery of penis, or clitoris (in females);

4) the inferior rectal artery, which supplies the skin and the fatty tissue in the anus and fatty tissue.

5) transverse perineal artery, which supplies the scrotum;

6) scrotal/labial branches.

Below, image and diagram of arteries in the pelvic region. You can see the right common, internal iliac, with its anterior and posterior trunk, and the internal pudendal artery. (Side view)

Internal Carotid Artery

The internal carotid artery is one of the two blood vessels that supply the brain with oxygenated blood; the other is the basilar artery. It arises from the common carotid artery at the level of the upper border of the thyroid as one of the two branches into which this artery divides, the other is the external carotid.

From its point of origin, the internal carotid artery runs upwards, medially and parallel to the jugular vein. Along its course to the base of the skull, the artery travels on the wall of pharynx medial to the parotid gland, from which it is separated by the stylohyoid and stylopharyngeous muscles. As it keeps ascending, it enters the carotid canal, following its bends, emerging through the foramen lacerum into the cavity of the skull.

The internal carotid artery usually gives off no branches in its cervical course. However, it sends the caroticotimpanic branch in the carotid canal of the petrous part of the temporal bone; this small artery supplies the mucous membrane of the tympanic cavity. Farther upwards, in the cavity of skull, the internal carotid gives off the ophthalmic artery, which supplies the eye and neighboring tissues.

Before it becomes the middle cerebral artery, the internal carotid gives off the anterior cerebral, the posterior communicating, which are part of the arterial circle of Willis, and the anterior choroid artery, which supplies the third ventricle, optic chiasm, internal capsule, globus pallidus, and hippocampus. Right at the base of brain, the internal carotid becomes the middle cerebral artery.

Below, schematic image of brain arteries, showing the internal carotid artery and its branches. The middle cerebral is the continuation of the internal carotid. (Side view).

Below, inferior surface of human brain. You can see the two main arteries that supply the brain; the basilar and the internal carotid.

 

Ophthalmic Artery

The ophthalmic artery is the main blood vessel which supplies the eye and nearby structures. It arises from the internal carotid artery at the level the middle cranial fossa at the base of the skull. Then it runs forwards through the optic foramen into the orbit, laterally to the optic nerve and medially to the superior rectus muscle. Just before it enters the orbit, it gives off its first branch, which is the central retinal artery, which supplies the retina.

In the orbit, the ophthalmic artery crosses over the optic nerve, traveling obliquely towards the medial wall of the orbit. As it runs in a lateral-medial direction, it gives off the lacrimal, the anterior meningeal, supraorbital, and the ciliary arteries, which provides the sclera, the choroid, and ciliary muscle and body with oxygenated blood. At the medial angle of the eye, the ophthalmic artery divides into two terminal branches; the supratrochlear artery, which supplies the frontalis muscle and the pericranium, and the dorsalis nasal artery, which irrigates the skin of the side of nose root.

Below, image of orbit, with the eye, showing the internal carotid and the ophthalmic artery, with some of its branches.

Middle Cerebral Artery

The middle cerebral artery is one of the main blood vessels of the human brain. It supplies a large area of the cerebral cortex and the basal ganglia. Being a paired artery, there is one for each cerebral hemisphere. It is in this artery or in one of its branches that most of the cerebral strokes occur, either through occlusion or through rupture and bleeding.

The middle cerebral artery is the continuation of the internal carotid artery, which changes its name after it has given off the anterior cerebral, the posterior communicating, and the anterior choroidal artery. From its point of origin, the middle cerebral artery travels laterally and then enters deep into the lateral sulcus (sylvian fissure), running slightly backwards. In this first portion, it gives off the lenticulostriate (or anterolateral central) arteries, which are four branches that supply the basal ganglia.

Then the middle cerebral artery runs upward in the lateral sulcus and emerges on the superior and lateral surface of the cerebral hemisphere. Along the way, it sends important branches that supply a large area of the brain with oxygenated blood; these branches are the cortical, orbital, frontal, parietal, temporal, and striate artery, supplying large areas of the frontal, parietal, and temporal lobe of the cerebral hemisphere, as well as the insula.

Below, schematic image of inferior surface of human brain, showing the internal carotid and the middle cerebral artery as its continuation. You can also see both the vertebral and the basilar artery.

 

Brachiocephalic Trunk

The brachiocephalic trunk is a short and thick artery which supplies the head, right shoulder, and right arm. It originates from the first portion of arch of aorta. Then it runs upwards, obliquely to the right, to divide at the level of the right sternoclavicular joint into two important branches; the right common carotid artery, which supplies the head, and the right subclavian artery, which supplies the right shoulder and arm with oxygenated blood.

The brachiocephalic trunk is also known as the innominate artery, which is 4 cm in length. In some individual, it also gives off the thyroidea ima artery, which supplies the inferior part of thyroid gland and trachea. Also the following developmental variants are rarely encountered: 1) the brachiocephalic trunk is absent, with the right common carotid and the right subclavian artery arising straight from the arch of aorta; 2) the innominate artery originates from the left side instead of the right; 3) a least frequent occurrence when there are two brachiocephalic trunks instead of one.

Below, you can see a schematic image of heart and arch of aorta, showing the innominate artery (brachiocephalic trunk).

 

Aorta

The aorta is the largest blood vessel of the body. It is the main artery that supplies every organ and tissue through a complex network of arterial branches. All arteries constituting the greater systemic circulation emerge from the aorta, which arises from the aortic orifice in the left ventricle of heart. It is divided into the ascending aorta, the arch of the aorta, and the descending aorta. The descending aorta is subdivided in turn into the thoracic aorta and the abdominal aorta.

The ascending aorta originates from the aortic orifice as a continuation of the aortic vestibule of the left ventricle. Then it ascends obliquely to the right and front to be continuous with the arch of the aorta. At its origin, the ascending aorta is dilated; this is called the bulb of the aorta. The wall of this bulb forms three bulges called the sinuses of the aorta, which correspond to the position of the three semilunar cusps of the aortic valves.

The arch of the aorta forms an upward convexity, running from front to back to be continuous with the descending aorta. A small constriction can be seen at the junction of the arch with the descending aorta; it is called the aortic isthmus. The arch of aorta gives rise to three large arteries; the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery.

The descending aorta is the continuation of the arch of the aorta. It runs from the level of the third and fourth thoracic vertebra to that of the fourth lumbar vertebra, where it forks into the right and left common iliac artery. Just before it divides into the common iliacs, it gives off the median sacral artery, which arises from its posterior side. The portion of the aorta that stretches from the third thoracic vertebra to the diaphragm is called the thoracic aorta, while the part that runs from the diaphragm until the fourth lumbar vertebra is called abdominal aorta.

Below, schematic image of the aorta, where you can see its portions and its branches.

Pulmonary Veins

The pulmonary veins drain oxygenated blood from the lungs into the left atrium. They emerge from the hila of the lungs, usually two veins from each lung, two left and two right ones. However, sometimes their number could vary from 3 to 5 in some individuals. A superior pulmonary and an inferior pulmonary vein can be distinguished in each pair. On arising from the hilum of lung, all the veins run transversely to the left atrium and enter its posterolateral portion.

The right pulmonary veins are longer than the left and lie inferiorly to the right pulmonary artery, behind the superior vena cava, right atrium, and ascending aorta. The left pulmonary veins, on the other hand, pass in front of the aorta. The pulmonary veins from the left lung are lobar veins; it means that each drain a single lobe with their corresponding name.

The hilum of lobe, like the hila of lungs, is an anatomical depression whose shape and depth vary with each individual. The hilum of lung may have the appearance of a hemispheric pit. The hila of the lobes are often round or oval. The hila of individual lobes are components of the hilum of lung.

Below, posterior aspect of human heart, showing the pulmonary veins that carry oxygenated blood from the lungs to left atrium, and the ordinary veins that drain the myocardium.

Pulmonary Trunk

The pulmonary trunk is a large artery which carries venous blood from the heart right ventricle into the lungs. It is the only artery in the body which conveys deoxygenated blood. It measures between 5 to 6 cm in length and around 2.5 cm in width. It divides into two smaller artery; the right and the left pulmonary artery.

The pulmonary trunk originates from the pulmonary orifice of right ventricle as a continuation of the infundibulum. Its first portion ascends from right to left in front, and to the left of the ascending aorta. Then it curves around the ascending aorta. When it is under the arch of aorta, it divides into the left pulmonary artery and the right pulmonary artery. Each of these arteries travels into the hilum of the corresponding lung.

The pulmonary trunk right artery is a little longer and wider than the left and passes transversely from left to right behind the ascending aorta and superior vena cava, and in front of the right bronchus; then in the root of the right lung, it forks into three branches, each entering the hilum of the corresponding lobe of the right lung. The left artery, on the other hand, also runs transversely, but from right to left in front of ascending aorta and left bronchus; in the root of the left lung, it divides into two branches, which enter the hilum of the corresponding lobe of the left lung.

A fibromuscular band, called ligamentum arteriosum, stretches from the angle of division of the pulmonary trunk to the anterior surface of the concavity of the arch of the aorta. This band is a fibrous remnant of the ductus arteriosus, which, during the intrauterine period, drains most of the blood from the pulmonary trunk into the aorta. After birth, it gets atrophied and closed up to become the ligamentum arteriosum.

Below, image of human heart showing the pulmonary trunk.

Pulmonary trunk in anatomical context of rib cage.

Interventricular Septum

The interventricular septum is the muscular partition which divides and isolates the right ventricle from the left ventricle. It is an inner projection of the myocardium that separates both lower cavities of the heart. It is formed by three muscular layers of both ventricles. It is almost as thick as the wall of the left ventricle and it slightly bulges into the right ventricle.

The upper portion of the interventricular septum is thin and it is called the membranous part. The septal cusp of the tricuspid valve is attached to it. The bundle of Hiss travels through it, dividing in two as the septum becomes thicker. On the left and right side, this dividing wall is covered by the endocardium.

Below, schematic image of the human heart, exhibiting the interventricular septum.