PULMONARY ARTERY

          pulmonary artery

The pulmonary artery conveys the venous blood from the right ventricle of the heart to the lungs. It is ashort, wide vessel, about 5 cm. in length and 3 cm. in diameter, arising from the conus arteriosus of the rightventricle. It extends obliquely upward and backward, passing at first in front and then to the left of the ascending aorta, as far as the under surface of the aortic arch, where it divides, about the level of the fibrocartilage between the fifth and sixth thoracic vertebræ, into right and left branches of nearly equal size

. Relations.—The whole of this vessel is contained within the pericardium. It is enclosed with the ascendingaorta in a single tube of the visceral layer of the serous pericardium, which is continued upward upon them from the base of the heart. The fibrous layer of the pericardium is gradually lost upon the external coats ofthe two branches of the artery. In front, the pulmonary artery is separated from the anterior end of the second left intercostal space by the pleura and left lung, in addition to the pericardium; it rests at first upon the ascending aorta, and higher up lies in front of the left atrium on a plane posterior to the ascending aorta. On either side of its origin is the auricula of the corresponding atrium and a coronary artery, the left coronary artery passing, in the first part of its course, behind the vessel. The superficial part of the cardiac plexus lies above its bifurcation, between it and the arch of the aorta.


The right branch of the pulmonary artery (ramus dexter a. pulmonalis), longer and larger than the left, runs horizontally to the right, behind the ascending aorta and superior vena cava and in front of the right bronchus, to the root of the right lung, where it divides into two branches. The lower and larger of these goes to the middle and lower lobes of the lung; the upper and smaller is distributed to the upper lobe.


The left branch of the pulmonary artery (ramus sinister a. pulmonalis), shorter and somewhat smaller than the right, passes horizontally in front of the descending aorta and left bronchus to the root of the left lung, where it divides into two branches, one for each lobe of the lung.
Above, it is connected to the concavity of the aortic arch by the ligamentum arteriosum, on the left of whichis the left recurrent nerve, and on the right the superficial part of the cardiac plexus.
 Below, it is joined to theupper left pulmonary vein by the ligament of the left vena cava.

The terminal branches of the pulmonary arteries will be described with the anatomy of the lungs.

BONES

Bones and Joints form the skeletal system of body.There are about 206 bones in human body. Main functions of skeletal system are -

1. Giving support and protection to soft tissues and vital organs.

2. Giving attachment to muscles and assisting in body movements.

3. Formation of blood cells in the red bone marrow.

4. Storage of mineral salts like calcium and phosphorous.

Composition of Bone
Bone is structurally a complex organ and has the following composition.
water - 25%

Ossein,Osseomucoid and Osseo Albumin (organic solids) - 35%

inorganic salts of calcium - 45%

Calcium salts impart hardness to bones.

Structure of bone tissue: Refer to Cell and Tissues.

Functions of bone marrow :

Bone marrow performs functions of -
1) Formation of blood cells(Haemopoeisis)

2) Destruction of old RBC with the help of reticulo endothelial
cells(haemolysis)
3) Protection of body against infections by microbes with the help of reticuloendothelial cells against foreign particles(Defence mechanism)

4) Against foreign particles(Defence mechanism

Ossification
Ossification is the process of bone formation. Development of bones takes place from spindle shaped cells called osteoblasts.
There are two types of ossification.

They are-

1) Intra membranous ossification.
2) Intra cartilaginous ossification.

1. Intra membranous ossification : Type of ossification in which, dense connective tissue is replaced by deposits of calcium, forming bone is called as intramembranous ossification.

Ex: Bones of skull are formed by this process.

2. Intra cartilaginous ossification : Type of ossification in which,
cartilages are replaced by bone is called as intracartilaginous ossification. Most of the bones of the body are formed by this process

Types of Bones
Bones are mainly three types. They are - 1) Long bones. 2)Short bones 3) Flat bones 4) Irregular bones 5) Seasmoid bones.

1. Long bones: Long bones are found in limbs. A long bone has two ends. Ends of a long bone are called as epiphyses. These two ends are connected by shaft, which is called as diaphysis. Periosteum is the outer membrane covering the bone. Periosteum is followed by layer of compact bone. Central medullary canal is inside this.
               Through nutrient foramen, arteries enter. Medullary canal contains yellow bone marrow. Extremities consist of mass of spongy bone, which contains red bone marrow. Yellow bone marrow contains fat and blood cells but is not rich in blood supply or red blood cells. Long bones develop from three centres called
centres of ossification. Centre of ossification present in shaft is called diaphysis and centres of ossification present at the ends of the bones are called epiphyses. Line of cartilage between epiphysis and diaphysis is called epiphyseal cartilage or epiphyseal plate.Epiphyseal plate separates epiphysis and diaphysis approximately upto 25 years of age.After this age,fusion of diaphysis and epiphysis takes place.After fusion,growth in length of bone becomes impossible.Acromegaly is growth of bone occurings after fusion of diaphysis and epiphysis by the overactivity of growth hormone.It will be confined mostly to the bones of face and limbs.This growth will be abnormal. Gigantism is growth occuring in immature bones before fusion of diaphysis with epiphysis due to excessive secreion of growth hormone.

2. Short bones : Short bones do not have shaft. They contain spongy substance covered by shell of compact bone.ex: small bones of wrist and ankle.

3. Flat bones : They contain two layers of compact bone with spongy substance between the two layers. They are found in pelvis and scapula.

4. Irregular bones : Bones which do not fall into any category are irregular bones. ex: vertebrae and bones of face.

5. Seasmoid bones : They are small bones and develop in tendons of muscles. ex: Patella of knee joint

THE SCIATIC NERVE

The sciatic nerve

The sciatic nerve (L4, 5, S1–3) is the largest nerve in the body  . It is broad and flat at its origin, although peripherally it becomes rounded. The nerve emerges from the greater sciatic foramen distal to piriformis and under cover of gluteus maximus, crosses the posterior surface of the ischium, crosses obturator internus, with its gemelli, quadratus femoris and descends on adductor magnus (Figs 183, 184). Here it lies deep to the hamstrings and is crossed only by the long head of biceps. The sciatic nerve terminates by dividing into the tibial and common peroneal nerves . The level of this division is variable—usually it is at the mid-thigh, but the two nerves may be separate even at their origins from the sacral plexus
Branches
The trunk of the sciatic nerve supplies the hamstring muscles (biceps, semimembranosus, semitendinosus) and also the adductor magnus, the latter being innervated also by the obturator nerve.
All the muscle branches apart from the one to the short head of biceps arise on the medial side of the nerve; its lateral border is therefore the side of relative safety in its operative exposure.
Clinical features
1◊◊The sciatic nerve may be wounded in penetrating injuries or in posterior dislocation of the hip associated with fracture of the posterior lip of the
acetabulum, to which the nerve is closely related (Fig. 168).
Damage to the sciatic nerve is followed by paralysis of the hamstrings
and all the muscles of the leg and foot (supplied by its distributing branches); there is loss of all movements in the lower limb below the knee joint with foot
drop deformity. Sensory loss is complete below the knee, except for an area along the medial side of the leg, over the medial malleolus and down to the hallux, which is innervated by the saphenous branch of the femoral nerve.
2◊◊The sciatic nerve is accompanied by a companion artery (derived from the inferior gluteal artery) which bleeds quite sharply when the nerve is divided during an above-knee amputation. The artery must be neatly isolated and tied without any nerve fibres being incorporated in the ligature, since this would be followed by severe pain in the stump.
 The tibial nerve
The tibial nerve (L4, 5, S1–3) is the larger of the two terminal branches of thesciatic nerve; it traverses the popliteal fossa superficial to the popliteal vein and artery, which it crosses from the lateral to the medial side.

Branches
a) in popliteal fossa
•◊◊muscular—to gastrocnemius, soleus and popliteus;
•◊◊cutaneous— the sural nerve, which descends over the back of the calf, behind the lateral malleolus to the 5th toe; it receives a communicating branch from the common peroneal nerve and supplies the lateral side of the leg, foot and 5th toe;

•◊◊articular—to the knee joint. It then descends deep to soleus, in company with the posterior tibial vessels, passes on their lateral side behind the medial malleolus to end by dividing into the medial and lateral plantar nerves.

b) in the leg
The tibial nerve supplies flexor hallucis longus, flexor digitorum longus and tibialis posterior. Its terminal plantar branches supply the intrinsic muscles and skin of the sole of the foot, the medial plantar nerve having an equivalent distribution to that of the median nerve in the hand, the lateral plantar nerve being comparable to the ulnar nerve.

The common peroneal (fibular) nerve
The common peroneal nerve (L4, 5, S1, 2) is the smaller of the terminal branches of the sciatic nerve. It enters the upper part of the popliteal fossa, passes along the medial border of the biceps tendon, then curves around the neck of the fibula where it lies in the substance of peroneus longus and divides into its terminal branches, the deep peroneal and superficial peroneal nerves
Branches While still in the popliteal fossa, the common peroneal nerve gives off the lateral cutaneous nerve of the calf, a peroneal (sural) communicating branch and twigs to the knee joint, but has no muscular branches.

The deep peroneal (fibular) nerve
The deep peroneal nerve pierces extensor digitorum longus, then descends, in company with the anterior tibial vessels, over the interosseous membrane and then over the ankle joint. Medially lies tibialis anterior, while laterally lies first extensor digitorum longus, then extensor hallucis longus. Its branches are:
•◊◊muscular — to the muscles of the anterior compartment of the leg — extensor digitorum longus, extensor hallucis longus, tibialis anterior, peroneus tertius—and extensor digitorum brevis;

•◊◊cutaneous — to a small area of skin in the web between the 1st and 2nd toes.
The superficial peroneal (fibular) nerve
The superficial peroneal nerve runs in the lateral compartment of the leg.

Its branches are:
•◊◊muscular— to the lateral compartment muscles (peroneus longus and brevis);
•◊◊cutaneous—to the skin of the distal two-thirds of the lateral aspect of the leg and to the dorsum of the foot (apart from the small area between the 1st and 2nd toes supplied by the deep peroneal nerve).

Clinical features
The common peroneal nerve is in a particularly vulnerable position as it winds around the neck of the fibula. It may be damaged at this site by the pressure of a tight bandage or plaster cast or may be torn in severe adduction injuries to the knee. Damage to this nerve is followed by foot drop (due to paralysis of the ankle and foot extensors) and inversion of the foot due to paralysis of the peroneal muscles with unopposed action of the foot flexors
and invertors). There is also anaesthesia over the anterior and lateral aspects of the leg and foot, although the medial side escapes, since this is innervated by the saphenous branch of the femoral nerve.

THE HEART

The Heart
The heart is a hollow, muscular organ about the size of a fist. It is responsible for pumping blood through the blood vessels by repeated, rhythmic contractions. The heart is composed of cardiac muscle, an involuntary muscle tissue that is found only within this organ. The term "cardiac" (as in cardiology) means "related to the heart” and comes from the Greek word kardia, for "heart." It has a four chambered, double pump and is located in the thoracic cavity between the lungs.
The cardiac muscle is self-exciting, meaning it has its own conduction system. This is in contrast with skeletal muscle, which requires either conscious or reflex nervous stimuli. The heart's rhythmic contractions occur spontaneously, although the frequency or heart rate can be changed by nervous or hormonal influence such as exercise or the perception of danger.
Myocardium
The myocardium is the muscular tissue of the heart. The myocardium is composed of specialized cardiac muscle cells with an ability not possessed by muscle tissue elsewhere in the body. Cardiac muscle, like other muscles, can contract, but it can also conduct electricity, like nerves. The blood to the myocardium is supplied by the coronary arteries. If these arteries are occluded by atherosclerosis and/or thrombosis, this can lead to angina pectoris or myocardial infarction due to ischemia (lack of oxygen). Failure of the heart to contract properly (for various reasons) is termed heart failure, generally leading to fluid retention, edema, pulmonary edema, renal insufficiency, hepatomegaly, a shortened life expectancy and decreased quality of life
Pericardium
The pericardium is the thick, membranous sac that surrounds the heart. It protects and lubricates the heart. There are two layers to the pericardium: the fibrous pericardium and the serous pericardium. The serous pericardium is divided into two layers; in between these two layers there is a space called the pericardial cavity.
Epicardium
The layer next to the heart is the visceral layer, also known as the Epicardium. This is the inner most layer and consists of connective tissue.
Heart Chambers
The heart has four chambers, two atrium and two ventricles. The atriums are smaller with thin walls, while the ventricles are larger and much stronger.
Atrium
There are two atria on either side of the heart. On the right side is the atrium that holds blood that needs oxygen. The left atrium holds that blood that has been oxygenated and is ready to be sent to the body. The right atrium receives de-oxygenated blood from the superior vena cava and inferior vena cava. The left atrium receives oxygenated blood from the left and right pulmonary veins.
Ventricles
The ventricle is a heart chamber which collects blood from an atrium and pumps it out of the heart. There are two ventricles: the right ventricle pumps blood into the pulmonary circulation for the lungs, and the left ventricle pumps blood into the systemic circulation for the rest of the body. Ventricles have thicker walls than the atria, and thus can create the higher blood pressure. Comparing the left and right ventricle, the left ventricle have thicker walls because it needs to pump blood to the whole body. This leads to the common misconception that the heart lies on the left side of the body.
Septum
The interventricular septum (ventricular septum, or during development septum inferious) is the stout wall separating the lower chambers (the ventricles) of the heart from one another. The ventricular septum is directed backward and to the right, and is curved toward the right ventricle. The greater portion of it is thick and muscular and constitutes the muscular ventricular septum. Its upper and posterior part, which separates the aortic vestibule from the lower part of the right atrium and upper part of the right ventricle, is thin and fibrous, and is termed the membranous ventricular septum.
Valves
The two atrioventricular (AV) valves are a one-way valve that ensures blood flows from the atria to the ventricles, and not the other way. The two semilunar (SL) valves are present in the arteries leaving the heart; they prevent blood from flowing back into the ventricles. The sound heard in a heart beat is the heart valves shutting. The right AV valve is also called the tricuspid valve because it has three flaps. It is located between the right atrium and the right ventricle. The tricuspid valve allows blood to flow from the right atrium into the right ventricle when the heart is relaxed during diastole. When the heart begins to contract, the heart enters a phase called systole, and the atrium pushes blood into the ventricle. Then, the ventricle begins to contract and blood pressure inside the heart rises. When the ventricular pressure exceeds the pressure in the atrium, the tricuspid valve snaps shut. The left AV valve is also called the bicuspid valve because it has two flaps. It is also known as the mitral valve due to the resemblance to a bishop's mitre (a type of hat). This valve prevents blood in the left ventricle from flowing into the left atrium. As it is on the left side of the heart, it must cope with a lot of strain and pressure; this is why it is made of only two cusps, as there is less to go wrong. There are two remaining valves called the Semilunar Valves. They have flaps that resemble half moons. The pulmonary semilunar valve sits between the right ventricle and the pulmonary trunk. The aortic semilunar valve sits between the ventricle and the aorta.
Subvalvular Apparatus
The chordae tendinae are attached to papillary muscles that cause tension to better hold the valve. Together, the papillary muscles and the chordae tendinae are known as the subvalvular apparatus. The function of the subvalvular apparatus is to keep the valves from prolapsing into the atria when they close. The subvalvular apparatus have no effect on the opening and closing of the valves. This is caused entirely by the pressure gradient across the valve.
Complications With The Heart
The most common congenital abnormality of the heart is the bicuspid aortic valve. In this condition, instead of three cusps, the aortic valve has two cusps. This condition is often undiagnosed until the person develops calcific aortic stenosis. Aortic stenosis occurs in this condition usually in patients in their 40s or 50s, an average of 10 years earlier than in people with normal aortic valves. Another common complication of rheumatic fever is thickening and stenosis (partial blocking) of the mitral valve. For patients who have had rheumatic fever dentist are advised to prophylactally administer antibiotics prior to dental work to prevent bacterial endocarditis that occurs when bacteria from the teeth enter the circulation and attach to damaged heart valves.
Passage of Blood Through the Heart
While it is convenient to describe the flow of the blood through the right side of the heart and then through the left side, it is important to realize that both atria contract at the same time and that both ventricles contract at the same time. The heart works as two pumps, one on the right and one on the left that works simultaneously. The right pump pumps the blood to the lungs or the pulmonary circulation at the same time that the left pump pumps blood to the rest of the body or the systemic circulation. Venous blood from systemic circulation (deoxygenated) enters the right atrium through the superior and inferior vena cava. The right atrium contracts and forces the blood through the tricuspid valve (right atrioventricular valve) and into the right ventricles. The right ventricles contract and force the blood through the pulmonary semilunar valve into the pulmonary trunk and out the pulmonary artery.
This takes the blood to the lungs where the blood releases carbon dioxide and receives a new supply of oxygen. The new blood is carried in the pulmonary veins that take it to the left atrium. The left atrium then contracts and forces blood through the left atrioventricular, bicuspid, or mitral, valve into the left ventricle. The left ventricle contracts forcing blood through the aortic semilunar valve into the ascending aorta. It then branches to arteries carrying oxygen rich blood to all parts of the body.
Blood Flow After The Heart
Aorta-Arteries-Arterioles-Capillaries-Venules-Veins-Vena Cava
Blood Flow Through Capillaries
From the arterioles, the blood then enters one or more capillaries. The walls of capillaries are so thin and fragile that blood cells can only pass in single file. Inside the capillaries, exchange of oxygen and carbon dioxide takes place. Red blood cells inside the capillary releases their oxygen which passes through the wall and into the surrounding tissue. The tissue then releases waste, such as carbon dioxide, which then passes through the wall and into the red blood cells.

CRANIAL NERVES

CRANIAL NERVES
The peripheral nervous system includes 12 cranial nerves 31 pairs of spinal nerves. It can be subdivided into the somatic and autonomic systems. It is a way of communication from the central nervous system to the rest of the body by nerve impulses that regulate the functions of the human body
The twelve cranial nerves are
I Olfactory Nerve for smell
II Optic Nerve for vision
III Oculomotor for looking around
IV Trochlear for moving eye
V Trigeminal for feeling touch on face
VI Abducens to move eye muscles
VII Facial to smile, wink, and help us taste
VIII Vestibulocochlear to help with balance, equilibrium, and hearing
IX Glossopharengeal for swallowing and gagging
X Vagus for swallowing, talking, and parasympathetic actions of digestion
XI Spinal accessory for shrugging shoulders
            XII Hypoglossal for tongue more divided into different regions as muscles
The 10 out of the 12 cranial nerves originate from the brainstem, and mainly control the functions of the anatomic structures of the head with some exceptions. CN X receives visceral sensory information from the thorax and abdomen, and CN XI is responsible for innervating the sternocleidomastoid and trapezius muscles, neither of which is exclusively in the head.
Spinal nerves take their origins from the spinal cord. They control the functions of the rest of the body. In humans, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. The naming convention for spinal nerves is to name it after the vertebra immediately above it. Thus the fourth thoracic nerve originates just below the fourth thoracic vertebra. This convention breaks down in the cervical spine. The first spinal nerve originates above the first cervical vertebra and is called C1. This continues down to the last cervical spinal nerve, C8. There are only 7 cervical vertebrae and 8 cervical spinal nerves.