Solved Question Paper Human Anatomy and Physiology September 2024 PDF

Agrasen Institute of Paramedical, Deoli (Tonk) First Sessional Theory Exam – September’2024 HUMAN ANATOMY AND PHYSIOLOGY SOLVED QUESTION PAPER Q. 1.Write functions of skeletal system. Classify bones and write in detail about the...

Agrasen Institute of Paramedical, Deoli (Tonk) First Sessional Theory Exam – September’2024 HUMAN ANATOMY AND PHYSIOLOGY SOLVED QUESTION PAPER Q. 1.Write functions of skeletal system. Classify bones and write in detail about the gross and microscopic anatomy of bones with suitable diagram. Ans. The primary functions of the skeletal system include movement, support, protection production of blood cells, storage of minerals and endocrine regulation. Support The primary function of the skeletal system is to provide a solid framework to support and safeguard the human body and its organs. This helps in maintaining the overall shape of the human body. Protection: The skeletal system also helps to protect our internal organs and other delicate body organs, including the brain, heart, lungs and spinal cord by acting as a buffer. Our cranium (skull) protects our brain and eyes, the ribs protect our heart and lungs and our vertebrae (spine, backbones) protect our spinal cord. Movement: Bones provide the basic structure for muscles to attach themselves onto so that our bodies are able to move. Tendons are tough inelastic bands that attach our muscle to that particular bone. Storage: The bone matrix of the skeletal system is mainly involved in storing or preserving different types of essential minerals which are required to facilitate growth and repair of the body cells and tissues. The cell-matrix acts as our calcium bank by storing and releasing calcium ions into the blood cell when required. Regulation of Endocrine glands: The bone cells present within the skeletal system plays an important role in releasing the synthesized hormones from the respective endocrine glands for the further requirement by the body for different metabolisms. Apart from these functions, the skeletal system also contributes to the regulation of blood sugar. CLASSIFICATION OF BONES: GROSS ANATOMY OF BONE: A long bone has two main regions: the diaphysis and the epiphysis. The diaphysis is the hollow, tubular shaft that runs between the proximal and distal ends of the bone.  Inside the diaphysis is the medullary cavity, which is filled with yellow bone marrow in an adult. The outer walls of the diaphysis (cortex, cortical bone) are composed of dense and hard compact bone, a form of osseous tissue. The wider section at each end of the bone is called the epiphysis, which is filled internally with spongy bone, another type of osseous tissue. Red bone marrow fills the spaces between the spongy bone in some long bones. Each epiphysis meets the diaphysis at the metaphysis. When the bone stops growing in early adulthood (approximately 18–21 years), the epiphyseal plate becomes an epiphyseal line. Lining the inside of the bone adjacent to the medullary cavity is a layer of bone cells called the endosteum. These bone cells (described later) cause the bone to grow, repair, and remodel throughout life. On the outside of bones there is another layer of cells that grow, repair and remodel bone as well. These cells are part of the outer double layered structure called the periosteum. Flat bones, like those of the cranium, consist of a layer of diploë (spongy bone), covered on either side by a layer of compact bone. The two layers of compact bone and the interior spongy bone work together to protect the internal organs. If the outer layer of a cranial bone fractures, the brain is still protected by the intact inner layer. MICROSCOPIC ANATOMY OF BONES: Each group of concentric circles makes up the microscopic structural unit of compact bone called an osteon (this is also called a Haversian system). Each ring of the osteon is made up of collagen and calcified matrix and is called a lamella (plural = lamellae). The collagen fibers of adjacent lamellae run at perpendicular angles to each other, allowing osteons to resist twisting forces in multiple directions. Running down the center of each osteon is the central canal, or Haversian canal, which contains blood vessels, nerves, and lymphatic vessels. The endosteum also lines each central canal, allowing osteons to be removed, remodeled and rebuilt over time. Canaliculi connect with the canaliculi of other lacunae and eventually with the central canal. This system allows nutrients to be transported to the osteocytes and wastes to be removed from them. Q. 2. Write in detail on - a) Events of Cardiac Cycle Ans. “Cardiac cycle refers to the sequence of events that take place when the heart beats.” The cardiac cycle attributes to a comprehensive heartbeat from its production to the commencement of the next beat. It comprises diastole, the systole, and the intervening pause. The occurrence of a cardiac cycle is illustrated by a heart rate, which is naturally indicated as beats per minute. A healthy human heart beats 72 times per minute which states that there are 72 cardiac cycles per minute. The cardiac cycle involves a complete contraction and relaxation of both the atria and ventricles and the cycle last approximately 0.8 seconds Cardiac Cycle: Phases Atrial Diastole: In this stage, chambers of the heart are calmed. That is when the aortic valve and pulmonary artery closes and atrioventricular valves open, thus causing chambers of the heart to relax. Atrial Systole: At this phase, blood cells flow from atrium to ventricle and at this period, atrium contracts. Isovolumic Contraction: At this stage, ventricles begin to contract. The atrioventricular valves, aortic valve and pulmonary artery valve close, but there won’t be any transformation in volume. Ventricular Ejection: Here ventricles contract and emptying. Pulmonary artery and aortic valve close. Isovolumic Relaxation: In this phase, no blood enters the ventricles and consequently, pressure decreases, ventricles stop contracting and begin to relax. Now due to the pressure in the aorta – pulmonary artery and aortic valve close. Ventricular Filling Stage: In this stage, blood flows from atria into the ventricles. It is altogether known as one stage (first and second stage). After that, they are three phases that involve the flow of blood to the pulmonary artery from ventricles. b) Classification of Joints Classification of Joints: A. Functional Classification:- 1. Synarthrosis 2. Amphiarthrosis 3. Diaarthrosis  B. Structural Classification:- 1. Fibrous Joint 2. Cartilaginous Joint 3. Synovial Jont Functional Classification:- Synarthrosis An immobile or nearly immobile joint is called a synarthrosis. The immobile nature of these joints provide for a strong union between the articulating bones. This is important at locations where the bones provide protection for internal organs. Examples include sutures, the fibrous joints between the bones of the skull that surround and protect the brain. The manubriosternal joint, the cartilaginous joint that unites the manubrium and body of the sternum for protection of the heart Amphiarthrosis An amphiarthrosis is a joint that has limited mobility An example of this type of joint is the cartilaginous joint that unites the bodies of adjacent vertebrae. Another example of an amphiarthrosis is the pubic symphysis of the pelvis. Diarthrosis A freely mobile joint is classified as a diarthrosis These types of joints include all synovial joints of the body, which provide the majority of body movements. Most diarthrotic joints are found in the appendicular skeleton and thus give the limbs a wide range of motion. These joints are divided into three categories, based on the number of axis of motion provided by each. Diarthroses are classified as uniaxial (for movement in one plane), biaxial (for movement in two planes), or multiaxial joints (for movement in all three anatomical planes). A uniaxial joint only allows for a motion in a single plane (around a single axis). The elbow joint, which only allows for bending or straightening, is an example of a uniaxial joint. A biaxial joint allows for motions within two planes. An example of a biaxial joint is a metacarpophalangeal joint (knuckle joint) of the hand. A joint that allows for the several directions of movement is called a multiaxial joint (polyaxial or triaxial joint). This type of diarthrotic joint allows for movement along three axes. The shoulder and hip joints are multiaxial joints. They allow the upper or lower limb to move in an anterior-posterior direction and a medial-lateral direction. In addition, the limb can also be rotated around its long axis. This Structural Classification:- 1. Fibrous Joint 2. Cartilaginous Joint 3. Synovial Jont Fibrous Joint A fibrous joint is where the adjacent bones are united by fibrous connective tissue. Example: Sutures - only found between the flat, plate-like bones of the skull. Gomphoses: They are found where the teeth articulate with their sockets in the maxilla (upper teeth) or the mandible (lower teeth). Syndesmoses: They are comprised of bones held together by an interosseous membrane. The middle radioulnar joint and middle tibiofibular joint are examples of a syndesmosis joint. Cartilagenous Joint In a cartilaginous joint, the bones are united by fibrocartilage or hyaline cartilage. There are two main types: 1. Synchondroses (primary cartilaginous) and 2. Symphyses (secondary cartilaginous). Synchondroses: In a synchondrosis, the bones are connected by hyaline cartilage. These joints are immovable (synarthrosis). An example of a synchondrosis is the joint between the diaphysis and epiphysis of a growing long bone. Symphyses: Symphysial joints are where the bones are united by a layer of fibrocartilage. They are slightly movable (amphiarthrosis). Examples include the pubic symphysis, and the joints between vertebral bodies. Synovial Joint A synovial joint is defined by the presence of a fluid-filled joint cavity contained within a fibrous capsule. They are freely movable (diarthrosis) and are the most common type of joint found in the body. Synovial joints can be sub-classified into several different types, depending on the shape of their articular surfaces and the movements permitted: Hinge – permits movement in one plane – usually flexion and extension. E.g. elbow joint, ankle joint, knee joint. Saddle – named due to its resemblance to a saddle on a horse’s back. It is characterised by opposing articular surfaces with a reciprocal concave-convex shape. E.g. carpometacarpal joints. Plane – the articular surfaces are relatively flat, allowing the bones to glide over one another. E.g. acromioclavicular joint, subtalar joint. Pivot – allows for rotation only. It is formed by a central bony pivot, which is surrounded by a bony-ligamentous ring E.g. proximal and distal radioulnar joints, atlantoaxial joint. Condyloid – contains a convex surface which articulates with a concave elliptical cavity. They are also known as ellipsoid joints. E.g. wrist joint, metacarpophalangeal joint, metatarsophalangeal joint. Ball and Socket – where the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. It permits free movement in numerous axes. E.g. hip joint, shoulder joint. Q. 3.Define Cell. Draw a neat and labeled diagram of Cell. Write in detail about various cell organelles with their functions. Ans. The cell is the smallest unit of living tissues. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cytoplasm, the semi-fluid substance of a cell contains all of the organelles such as – 1. Microsomes 2. Endoplasmic reticulum 3. Golgi apparatus 4. Mitochondria 5. Lysosomes 6. Peroxisomes 7. Cytoskeleton 8. Cystosol 1. Microsomes: They are extremely small bodies present in the cytoplasm. It contains ribosomes & granular matrix. Ribosomes serves as the site of protein synthesis, in the process information carried in the genetic code is converted into protein molecules. Eukaryotic cell Prokaryotic cell Free Particle Free Particle 10 million 15000 50% protein & 50% rRNA 40 % protein & 60% rRNA The small and large subunits of Prokaryotes contain a small 30S eukaryotes are designated 40S and subunit and a large 50S subunit. 60S, respectively. 2. Endoplasmic Reticulum: Endoplasmic reticulum is a continuous membrane system that forms a series of flattened sacs within the cytoplasm of eukaryotic cells. Serves multiple functions, being important particularly in the synthesis, folding, modification, and transport of proteins. Differences in certain physical and functional characteristics distinguish the two types of ER, known as rough ER and smooth ER. Rough ER Named for its rough appearance, which is due to the ribosomes attached to its outer (cytoplasmic) surface. The ribosomes on rough ER specialize in the synthesis of proteins. Smooth ER By contrast, is not associated with ribosomes, and its functions differ. The smooth ER is involved in the synthesis of lipids, including cholesterol and phospholipids, which are used in the production of new cellular membrane. 3. Golgi apparatus: Golgi apparatus, also called Golgi complex or Golgi body, membrane-bound organelle of eukaryotic cells that is made up of a series of flattened, stacked pouches called cisternae. It is responsible for transporting, modifying, and packaging proteins and lipids into vesicles for delivery to targeted destinations. It is located in the cytoplasm next to the endoplasmic reticulum and near the cell nucleus. 4. Mitochondria: Mitochondrion, membrane-bound organelle found in the cytoplasm of almost all eukaryotic cells The primary function of which is to generate large quantities of energy in the form of adenosine triphosphate (ATP). Mitochondria are typically round to oval in shape and range in size from 0.5 to 10 μm. In addition to producing energy, mitochondria store calcium for cell signaling activities, generate heat, and mediate cell growth and death. The number of mitochondria per cell varies widely—for example, in humans, erythrocytes (red blood cells) do not contain any mitochondria, whereas liver cells and muscle cells may contain hundreds or even thousands. The outer mitochondrial membrane is freely permeable to small molecules and contains special channels capable of transporting large molecules. In contrast, the inner membrane is far less permeable, allowing only very small molecules to cross into the gel-like matrix that makes up the organelle’s central mass. 5. Lysosomes: They are small spherical or oval bodies surrounded by a membrane that maintains an acidic environment within the interior via a proton pump. They are responsible for the digestion of macromolecules, old cell parts, and microorganisms. Lysosomes contain a wide variety of hydrolytic enzymes (acid hydrolases) that break down macromolecules such as nucleic acids into nucleotides , proteins into amino acids, and polysaccharides into glucose (monosaccharides). 6. Peroxisomes: Membrane-bound organelle occurring in the cytoplasm of eukaryotic cells. Peroxisomes play a key role in the oxidation of specific biomolecules. They also contribute to the biosynthesis of membrane lipids known as plasmalogens. 7. Cytoskeleton: The cytoskeleton is the network of fibres forming the eukaryotic cells, prokaryotic cells and archaeans. These fibres in the eukaryotic cells contain a complex mesh of protein filaments and motor proteins that help in cell movement. It provides shape and support to the cell, organizes the organelles and facilitates transport of molecules, cell division and cell signalling. A cytoskeleton structure comprises the following types of fibres: 1. Microtubules 2. Microfilaments 3. Intermediate Filaments Microtubules appear like small, hollow, round tubes with a diameter of about 24 nanometers. They are made up of a protein, tubulin. Thirteen tubulins link to form a single tube. Microtubules are very dynamic structures, which reveal that they can change quickly. They keep growing or shrinking steadily. These help in transporting cellular materials and dividing chromosomes during cell division. Microfilaments are thread-like protein fibres, 3-6 nm in diameter. They are particularly found in muscle cells. They consist of the protein actin, responsible for muscle contraction. These are also responsible for cellular movements including cytokinesis, contraction, and gliding. The intermediate filaments are about 10 nm in diameter and provide tensile strength to the cell. They facilitate the formation of keratins and neurofilaments. 8. Cystosole: Between all these organelles is the space in the cytoplasm called the cytosol. The cytosol contains an organized framework of fibrous molecules that constitute the cytoskeleton, which gives a cell its shape, enables organelles to move within the cell, and provides a mechanism by which the cell itself can move. Q. 4. Write short notes on – a) Development and growth of bones Formation of bone is called as ossification or osteogenesis. By the end of the eighth week after conception, the skeletal pattern is formed in cartilage and connective tissue membranes and ossification begins. There are two types of ossification: intramembranous and endochondral. 1. Intra-membranous 2. Endochondral or Inra-cartilagenous Intramembranous ossification involves the replacement of sheet-like connective tissue membranes with bony tissue. Bones formed in this manner are called intramembranous bones. They include certain flat bones of the skull and some of the irregular bones. The future bones are first formed as connective tissue membranes. Osteoblasts migrate to the membranes and deposit bony matrix around themselves. When the osteoblasts are surrounded by matrix they are called osteocytes. Endochondral ossification involves the replacement of hyaline cartilage with bony tissue. In this process, the future bones are first formed as hyaline cartilage models. During the third month after conception, the perichondrium that surrounds the hyaline cartilage becomes infiltrated with blood vessels and osteoblasts and changes into a periosteum. The osteoblasts form a collar of compact bone around the diaphysis. At the same time, the cartilage in the center of the diaphysis begins to disintegrate. Osteoblasts penetrate the disintegrating cartilage and replace it with spongy bone. This forms a primary ossification center. Ossification continues from this center toward the ends of the bones. After spongy bone is formed in the diaphysis, osteoclasts break down the newly formed bone to open up the medullary cavity. The cartilage in the epiphyses continues to grow so the developing bone increases in length. Later, usually after birth, secondary ossification centers form in the epiphyses. Ossification in the epiphyses is similar to that in the diaphysis except that the spongy bone is retained instead of being broken down to forms a medullary cavity. When secondary ossification is complete, the hyaline cartilage is totally replaced by bone except in two areas. A region of hyaline cartilage remains over the surface of the epiphysis as the articular cartilage and another area of cartilage remains between the epiphysis and diaphysis. This is the epiphyseal plate or growth region. b) Physiology of muscle contraction The arrangement and interactions between thin and thick filaments allows for the sarcomeres to generate force. When signaled by a motor neuron, a skeletal muscle fiber is activated. Cross bridges form between the thick and thin filaments and the thin filaments are pulled which slide past the thick filaments within the fiber’s sarcomeres. While the sarcomere shortens, the individual proteins and filaments do not change length but simply slide next to each other. This process is known as the sliding filament model of muscle contraction. The filament sliding process of contraction can only occur when myosin-binding sites on the actin filaments are exposed by a series of steps that begins with Ca++ entry into the sarcoplasm. Tropomyosin winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin. The troponin-tropomyosin complex uses calcium ion binding to TnC to regulate when the myosin heads form cross-bridges to the actin filaments. Cross-bridge formation and filament sliding will occur when calcium is present, and the signaling process leading to calcium release and muscle contraction is known as Excitation-Contraction Coupling c) Erythropoesis with suitable diagrammatic chart The production of all blood cells begins with the haemocytoblast, a multipotent haematopoietic stem cell. Haemocytoblasts have the greatest powers of self-renewal of any adult cell. They are found in the bone marrow and can be mobilised into the circulating blood when needed. Some haemocytoblasts differentiate into common myeloid progenitor cells, which go on to produce erythrocytes, as well as mast cells, megakaryocytes and myeloblasts. The process by which common myeloid progenitor cells become fully mature red blood cells involves several stages. First, they become normoblasts (eryhthroblasts), which are normally present in the bone marrow only. Then, they lose their nucleus as they mature into reticulocytes, which can be thought of as immature red blood cells. Some of these are released into the peripheral circulation. Finally, reticulocytes lose their remaining organelles as they mature into erythrocytes-which are fully mature red blood cells. the average lifespan of a red blood cell is approximately 120 days. During this maturation process, there is nuclear extrusion – i.e. mature erythrocytes have no nucleus. Nucleated red blood cells present in a sample of bone marrow can indicates the release of incompletely developed cells. This can occur in pathology such as thalassaemia, severe anaemia or haematological malignancy. d) Structures of blood vessels Blood vessels are flexible tubes that carry blood, associated oxygen, nutrients, water, and hormones throughout the body. Arteries and veins are comprised of three distinct layers while the much smaller capillaries are composed of a single layer. Tunica Intima The inner layer (tunica intima) is the thinnest layer, formed from a single continuous layer of endothelial cells and supported by a subendothelial layer of connective tissue and supportive cells. In smaller arterioles or venules, this subendothelial layer consists of a single layer of cells, but can be much thicker in larger vessels such as the aorta. Tunica Media Surrounding the tunica intima is the tunica media, comprised of smooth muscle cells and elastic and connective tissues arranged circularly around the vessel. This layer is much thicker in arteries than in veins. Fiber composition also differs; veins contain fewer elastic fibers and function to control caliber of the arteries, a key step in maintaining blood pressure. Tunica Externa The outermost layer is the tunica externa or tunica adventitia, composed entirely of connective fibers and surrounded by an external elastic lamina which functions to anchor vessels with surrounding tissues. The tunica externa is often thicker in veins to prevent collapse of the blood vessel and provide protection from damage since veins may be superficially located. Q. 5. Write in detail on - a) Conduction system of the heart with suitable diagram The cardiac conduction system is a network of specialized cardiac muscle cells that initiate and transmit the electrical impulses responsible for the coordinated contractions of each cardiac cycle. These special cells are able to generate an action potential on their own (self-excitation) and pass it on to other nearby cells (conduction), including cardiomyocytes. The parts of the heart conduction system can be divided into those that generate action potentials (nodal tissue) and those that conduct them (conducting fibers). The sinuatrial (SA) node is the primary impulse initiator and regulator in a healthy heart. This aspect makes the SA node the physiological pacemaker of the heart. Other parts sequentially receive and conduct the impulse originating from the SA node and then pass it to myocardial cells. Upon stimulation by the action potential, myocardial cells contract synchronously, resulting in a heartbeat. The sinuatrial node (SA node) is a flat, elliptical collection of specialized nodal tissue which is located in the superior postero-lateral wall of the right atrium near the opening of the superior vena cava. The internodal conduction pathways are a part of the intra-atrial conduction network. Not only do these pathways travel within the right atrium, but they also form direct points of communication between the sinuatrial and atrioventricular nodes. The internodal conduction pathway is divided into anterior, middle and posterior branches:- The anterior internodal pathway originates from the anterior margin of the SA node. It continues anteriorly, coursing around the superior vena cava where it gives off Bachmann’s bundle. The anterior internodal band continues anteroinferiorly toward the atrioventricular (AV) node where it enters the node by way of its superior margin. The middle internodal pathway arises from the posterosuperior margin of the SA node. It continues behind the superior vena cava toward the border of the interatrial septum. The pathway turns caudally in the interatrial septum to enter the AV node through its superior margin. Finally, the posterior internodal pathway emerges from the posterior margin of the sinus node. It takes a posterior course around the superior vena cava and the pathway then enters the interatrial septum where it enters the AV node through its posterior surface. The atrioventricular node (AV node) and is often called the secondary pacemaker of the heart. It functions as a conduction of electrical activity from the SA node to the ventricles of the heart. It is the only pathway by which the action potential can cross from the atria to the ventricles. The AV node is smaller than the SA node and is located in the posteroinferior part of the interatrial septum. The atrioventricular (AV) bundle (of His) is the initial segment of the AV node that penetrates through the fibrous trigone into the membranous part of the interventricular septum. A unique and important feature of the AV bundle is that it only allows the ‘forward’ movement of action potentials. Therefore, the retrograde transmission of electrical impulses from the ventricles to the atria is not allowed in a normal functioning heart. As the node moves from the membranous to the muscular interventricular septum, it bifurcates into right and left bundles. The right bundle branch, emerges from the AV bundle in the membranous interventricular septum. Before moving superficially to the subendocardiac layer space. It travels to the right side of the interventricular septum where it gives of branches to the ventricular walls before going on toward the ventricular apex. The left bundle branches from the atrioventricular bundle at the start of the muscular interventricular septum. The branches will go on to activate the anterior and posterior papillary muscles, interventricular septum and the walls of the left ventricle. The right and left bundles are populated with subendocardiac branches (Purkinje fibers). These cells can be much larger than those of the surrounding heart muscles and they function quite differently than the preceding cells in the AV node. Purkinje fibers are found throughout the entire length of both bundles in the subendocardiac layer. They extend toward the cardiac apex, then curve upward and backward through the walls of the ventricles. b) Structure and types of epithelial tissues Epithelial tissue or epithelium forms the outer covering of the skin and also lines the body cavity. Epithelial tissue is formed from a tightly fitted continuous layer of cells. One surface of the epithelial tissue is exposed to either the external environment or the body fluid. The other surface is attached to tissue by a membrane, which consists of fibers and polysaccharides secreted by epithelial cells. There is little intercellular material present between cells. There are specialised junctions present between the cells of the epithelium that link individual cells. Types of epithelial tissues: Q. 6. Define cardiovascular system. Write in detail about the structure of human heart with neat and labeled diagram. Human cardiovascular system, organ system that conveys blood through vessels to and from all parts of the body, carrying nutrients and oxygen to tissues and removing carbon dioxide and other wastes. The heart is to serve as a muscular pump propelling blood into and through vessels to and from all parts of the body. The arteries, which receive this blood at high pressure and velocity and conduct it throughout the body, have thick walls that are composed of elastic fibrous tissue and muscle cells. The arterial tree — the branching system of arteries — terminates in short, narrow, muscular vessels called arterioles, from which blood enters simple endothelial tubes (i.e., tubes formed of endothelial, or lining, cells) known as capillaries. These thin, microscopic capillaries are permeable to vital cellular nutrients and waste products that they receive and distribute. From the capillaries, the blood, now depleted of oxygen and burdened with waste products, moving more slowly and under low pressure, enters small vessels called venules that converge to form veins, ultimately guiding the blood on its way back to the heart. The heart consists of four chambers – two atria and two ventricles: Blood returning to the heart enters the atria, and is then pumped into the ventricles. From the left ventricle, blood passes into the aorta and enters the systemic circulation. From the right ventricle, blood enters the pulmonary circulation via the pulmonary arteries. The right atrium receives deoxygenated blood from the superior and inferior vena cavae, and from the coronary veins. It pumps this blood through the right atrioventricular orifice (guarded by the tricuspid valve) into the right ventricle. The left atrium receives oxygenated blood from the four pulmonary veins, and pumps it through the left atrioventricular orifice (guarded by the mitral valve) into the left ventricle. The right ventricle receives deoxygenated blood from the right atrium, and pumps it through the pulmonary orifice (guarded by the pulmonary valve), into the pulmonary artery. The left ventricle receives oxygenated blood from the left atrium, and pumps it through the aortic orifice (guarded by the aortic valve) into the aorta. The Heart Wall: The epicardium is the outermost layer of the heart, formed by the visceral layer of the pericardium. It is composed of connective tissue and fat. The connective tissue secretes a small amount of lubricating fluid into the pericardial cavity. In addition to the connective tissue and fat, the epicardium is lined by on its outer surface by simple squamous epithelial cells. The myocardium is composed of cardiac muscle and is an involuntary striated muscle. The myocardium is responsible for contractions of the heart. The endocardium is the innermost layer of the heart chambers and extends over the valves, papillary muscles, and corda tendineae. The valves of the heart are made up of folding of the endocardium. Valves of the Heart: To prevent backflow of blood, the heart is equipped with valves that permit the blood to flow in only one direction. There are two types of valves located in the heart: 1. The atrioventricular valves (tricuspid and mitral) and 2. The semilunar valves (pulmonary and aortic). The atrioventricular valves are thin, leaflike structures located between the atria and the ventricles. The right atrioventricular opening is guarded by the tricuspid valve, so called because it consists of three irregularly shaped cusps, or flaps. The leaflets consist essentially of folds of endocardium (the membrane lining the heart) reinforced with a flat sheet of dense connective tissue. The left atrioventricular opening is guarded by the mitral, or bicuspid, valve, so named because it consists of two flaps. The mitral valve is attached in the same manner as the tricuspid, but it is stronger and thicker because the left ventricle is by nature a more powerful pump working under high pressure. The semilunar valves are pocketlike structures attached at the point at which the pulmonary artery and the aorta leave the ventricles.  The pulmonary valve guards the orifice between the right ventricle and the pulmonary artery.  The aortic valve protects the orifice between the left ventricle and the aorta. Q. 7. Write short notes on – a) Various types of lymph nodes with their pathological significance Cervical Lymph Nodes: Cervical lymph nodes are present in the head and neck region. They are further broken down by their location: Anterior cervical lymph nodes are those nearest the front of the neck. These typically swell with cold or strep throat. Posterior cervical lymph nodes are located behind the band of muscles on the side of the neck. These often swell with infectious mononucleosis. Occipital lymph nodes are located at the back of the neck at the base of the skull. These often swell with infections like HIV. Supraclavicular Lymph Nodes: Supraclavicular lymph nodes are located just above the collarbone (clavicle). Most of the time, the enlargement of supraclavicular lymph nodes is a sign of a serious disease such as lung cancer or lymphoma (a type of blood cancer). Axillary Lymph Nodes: Axillary lymph nodes are the lymph nodes located in the armpit (axilla). There are usually between 10 and 40 lymph nodes in the axilla. The axillary lymph nodes are important in the diagnosis of breast cancer. When cancer cells are shed from a breast tumor, they first travel to the axillary nodes. Mediastinal Lymph Nodes: Mediastinal lymph nodes reside in the center of the chest cavity between the lungs. Checking mediastinal lymph nodes is essential to the staging of lung cancer and some lymphomas. Inguinal Lymph Nodes: Inguinal lymph nodes are located in the groin. Because they are responsible for filtering lymphatic fluids from the feet to the groin, they can become swollen for many reasons. These include injuries, sexually transmitted diseases, skin infections, yeast infections, and cancer. Retroperitoneal Lymph Nodes: Retroperitoneal lymph nodes are situated at the back of the abdomen behind the tissues that cover the abdominal wall. These are the nodes to which testicular cancer first spreads. They can only be seen in imaging studies. Mesenteric Lymph Nodes: Mesenteric lymph nodes lie deep within the abdomen in the membranes that surround the intestine. These nodes often become swollen due to gastroenteritis (stomach flu) but are also sometimes affected by inflammatory bowel disease (IBD) and lymphoma. Pelvic Lymph Nodes: Pelvic lymph nodes are situated in the lower abdomen in the area that contains the hip bones, bladder, rectum, and reproductive organs. Pelvic lymph nodes are only seen in imaging studies. Swollen pelvic lymph nodes may be a sign of bladder, prostate, cervical, ovarian, or anal cancer. b) Mechanism of blood clotting Blood clotting is the process by which blood from its liquid state changes to a gel-like consistency. Normal hemostasis is the responsibility of a complex system of three individual components: blood cells (platelets), cells that line the blood vessels (endothelial cells), and blood proteins (blood-clotting proteins). The hemostatic mechanism involves three physiologically important reactions: (1) The formation of a blood clot, (2) The formation of a platelet plug, and (3) Changes associated with the wall of the blood vessel after injury of its cells. Blood Coagulation Pathway The process of blood coagulation leads to haemostasis, i.e. prevention of bleeding or haemorrhage. Blood clotting involves activation and aggregation of platelets at the exposed endothelial cells, followed by deposition and stabilisation of cross-linked fibrin mesh. Primary haemostasis involves platelet aggregation and formation of a plug at the site of injury, and secondary haemostasis involves strengthening and stabilisation of platelet plug by the formation of a network of fibrin threads. The secondary haemostasis involves two coagulation pathways, the intrinsic pathway and the extrinsic pathway. Both pathways merge at a point and lead to the activation of fibrin, and the formation of the fibrin network. Platelet Activation The blood circulating in the blood vessel does not clot under normal circumstances. The blood coagulation process is stimulated when there is any damage to the endothelium of blood vessels. It leads to platelet activation and aggregation. When collagen is exposed to the platelets due to injury, the platelets bind to collagen by surface receptors. This adhesion is stimulated by the von Willebrand factor released from endothelial cells and platelets. This forms additional cross-linking and activation of platelet integrins, which facilitate tight binding and aggregation of platelets at the site of injury. This leads to primary haemostasis. Blood Coagulation Cascade The process of coagulation is a cascade of enzyme catalysed reactions wherein the activation of one factor leads to the activation of another factor and so on. The three main steps of the blood coagulation cascade are as follows: 1. Formation of prothrombin activator  2. Conversion of prothrombin to thrombin 3. Conversion of fibrinogen into fibrin 1. Formation of prothrombin activator The formation of a prothrombin activator is the first step in the blood coagulation cascade of secondary haemostasis. It is done by two pathways, viz. extrinsic pathway and intrinsic pathway. Intrinsic Coagulation Pathway It is the longer pathway of secondary haemostasis. The intrinsic pathway begins with the exposure of blood to the collagen from the underlying damaged endothelium. This activates the plasma factor XII to XIIa. XIIa is a serine protease, it activates the factor XI to XIa. The XIa then activates the factor IX to IXa in the presence of Ca2+ ions. The factor IXa in the presence of factor VIIIa, Ca2+ and phospholipids activate the factor X to Xa. Common Pathway The factor Xa, factor V, phospholipids and calcium ions form the prothrombin activator. This is the start of the common pathway of both extrinsic and intrinsic pathways leading to coagulation. 2. Conversion of prothrombin to thrombin Prothrombin or factor II is a plasma protein and is the inactive form of the enzyme thrombin. Vitamin K is required for the synthesis of prothrombin in the liver. The prothrombin activator formed above converts prothrombin to thrombin. Thrombin is a proteolytic enzyme. It also stimulates its own formation, i.e. the conversion of prothrombin to thrombin. It promotes the formation of a prothrombin activator by activating factors VIII, V and XIII. 3. Conversion of fibrinogen into fibrin Fibrinogen or factor I is converted to fibrin by thrombin. Thrombin forms fibrin monomers that polymerise to form long fibrin threads. These are stabilised by the factor XIII or fibrin stabilising factor. The fibrin stabilising factor is activated by thrombin to form factor XIIIa. The activated fibrin stabilising factor (XIIIa) forms cross-linking between fibrin threads in the presence of Ca2+ and stabilises the fibrin meshwork. The fibrin mesh traps the formed elements to form a solid mass called a clot. c) Types of connective tissues Support and connect different tissues and organs of the body. They originate from the mesoderm (the middle germinal layer of the embryo). Connective tissue is made up of a few cells present in the intercellular framework of protein fibers secreted by the cells, known as collagen or elastin. The cells also secrete a thin gel of polysaccharides, which together with fibers make matrix or ground substance. Types of Connective Tissues: 1. Loose Connective Tissue 2. Dense Connective Tissue 3. Specialised Connective Tissue Loose connective tissues are present all over the body, where support and elasticity both are needed. Blood vessels, nerves and muscles, all have a loose connective tissue wrapping Areolar Tissue: It is present under the skin and supports epithelium. It contains randomly distributed fibers, fibroblasts, mast cells and macrophages. It supports the organs present in the abdominal cavity, fills the space between muscle fibers and wraps around blood and lymph vessels. Adipose Tissue: They are present under the skin and store fat. It acts as a shock absorber and helps in maintaining body temperature in colder environments. Reticular Connective Tissue: It is made up of reticular fibers. It supports the internal framework of organs such as liver, lymph nodes and spleen. In the dense connective tissue, fibroblast cells and fibers are compactly packed. Their main function is to support and transmit mechanical forces. On the basis of the arrangement of collagen fibers, they are divided into two types: Dense regular tissue: In the dense regular connective tissue, the orientation of fibers are regular. The collagen fibers are present between the parallel running bundles of fibers. Examples of dense regular tissue are tendons and ligaments. Dense irregular tissue: There are many fibers including collagen, which are oriented irregularly or randomly. The irregular arrangement gives uniform strength in all directions. This type of tissue is present in the dermis of the skin. Specialized connective are supportive connective tissue, that help in maintaining correct posture and support internal organs, e.g. cartilage and bone. Cartilage: Cartilage is mostly present in the embryonic stages and works as a supporting skeleton. Most of the cartilage is replaced by bones in adults, however, it supports some structures in adults too. In humans, cartilage is present between the bones of the vertebral column, in the external ear, nose and hands. Bones: Bone is the hardest connective tissue and helps in maintaining the shape and posture of the body, it protects internal organs. They are rich in collagen fibers and calcium, which give strength. Blood: Blood is made up of various cells present in the plasma. The blood contains red blood cells (RBCs), white blood cells (WBCs) and platelets. RBCs have haemoglobin and transport oxygen. WBCs form a defense system and protect from foreign antigens. Platelets are important for blood clotting. Plasma contains proteins, water, hormones, salts, etc. to transport to different parts of the body. Lymph: Lymph drains into the blood and transports absorbed fat to the blood, which cannot enter the bloodstream directly. Lymph has white blood cells in the liquid matrix. They help in getting rid of toxins and waste materials. They contain WBCs, which help in fighting infection. d) Composition and functions of blood. Composition of Blood: The characteristic colour is imparted by hemoglobin, a unique iron-containing protein. Hemoglobin brightens in colour when saturated with oxygen (oxyhemoglobin) and darkens when oxygen is removed (deoxyhemoglobin). The red blood cells (erythrocytes) constitute about 45 percent of the volume of the blood, and the remaining cells (white blood cells, or leukocytes, and platelets, or thrombocytes) less than 1 percent. The fluid portion, plasma, is a clear, slightly sticky, yellowish liquid. After a fatty meal, plasma transiently appears turbid. Within the body the blood is permanently fluid, and turbulent flow assures that cells and plasma are fairly homogeneously mixed. The total amount of blood in humans varies with age, sex, weight, body type, and other factors, but a rough average figure for adults is about 60 millilitres per kilogram of body weight. An average young male has a plasma volume of about 35 millilitres and a red cell volume of about 30 millilitres per kilogram of body weight. Functions of Blood: Blood is responsible for the following body functions: Fluid Connective Tissue Blood is a fluid connective tissue composed of 55% plasma and 45% formed elements including WBCs, RBCs, and platelets. Since these living cells are suspended in plasma, blood is known as a fluid connective tissue and not just fluid. Provides oxygen to the cells Blood absorbs oxygen from the lungs and transports it to different cells of the body. The waste carbon dioxide moves from the blood to the lungs and is exhaled. Transports Hormones and Nutrients The digested nutrients such as glucose, vitamins, minerals, and proteins are absorbed into the blood through the capillaries in the villi lining the small intestine. The hormones secreted by the endocrine glands are also transported by the blood to different organs and tissues. Homeostasis Blood helps to maintain the internal body temperature by absorbing or releasing heat. Blood Clotting at Site of Injury The platelets help in the clotting of blood at the site of injury. Platelets along with the fibrin form clot at the wound site Transport of waste to the Kidney and Liver Blood enters the kidney where it is filtered to remove nitrogenous waste out of the blood plasma. The toxins from the blood are also removed by the liver. Protection of the body against pathogens The White Blood Cells fight against infections. They multiply rapidly during infections.