Molecular Biology Of The Cell: Cardiovascular System

Cardiovascular system consists of different parts like heart, arteries, capillaries, veins, coronary vessels and portal veins. Heart performs function of supplying oxygenated blood to the tissues of the body and deoxygenated blood to the lungs. 

Superior and inferior vena cava brings deoxygenated blood from lung to the right atrium. This deoxygenated blood is emptied into the right ventricle by passing through the tricuspid valve into the right ventricle. From right ventricle this blood is pumped into the pulmonary artery through pulmonary valve for re-oxygenation and removal of carbon dioxide. Blood is purified in the lungs and this newly purified and oxygenated blood enters left atrium through pulmonary vein. This blood then passed through the mitral valve into the left ventricle. From left ventricle blood is pumped to the different parts of the body through aortic semilunar valve and aorta which is main artery of the body. Aorta gives many branches called as arteries and these arteries supplies oxygenated blood to the all other body parts. Wall of aorta is elastic and this aid in maintaining blood pressure through entire human body. Aorta gives rise to arteries of larger size at its origin and its size goes on decreasing at the end. These arteries further become narrower into the arterioles which are small diameter blood vessel and these arterioles has muscular wall. These arterioles further branched into the capillaries and these capillaries are the smallest blood vessels in the human body with one cell layer thickness. Diameter of these capillaries is around 5 – 10 µm. These capillaries are the connecting link between arterioles and venules. These capillaries facilitate the exchange of oxygen, carbon dioxide, water, nutrients and waste matter between blood and body tissues. Individual capillaries do not carry out this function; however network of capillaries those are supplying to the different tissues and organs perform this function of transport. Venules are the small blood vessel which supplies deoxygenated blood from the capillaries to the veins. Venules have the diameter in the range form 7-50 µm. Walls of venules comprised of three layers such as inner endothelium, middle layer of muscle and elastic tissue and outer fibrous connective tissue.  Many venules combine to form veins. These veins carry deoxygenated blood from the body tissues to the heart and pulmonary and umbilical veins are exception for this, as these veins carry oxygenated blood to the heart. Veins are also called as capacitance vessels because around 60 % blood volume is contained in the veins. Adult human body has about four to five liters of blood. Blood is a liquid connective tissue and performs the function of transport of nutrients, waste matter and gases and helps in maintaining homeostasis of the body. Blood is comprised of red blood cells, white blood cell, platelets and liquid plasma. Red blood cells are biconcave in shape and it performs the function of transport of oxygen in the blood. White blood cells functions as body’s immune system.

Part 2.

Respiratory system componentStructureFunction
TracheaIs a cartilaginous tube, In Adult human inner diameter of trachea is about has 25 millimetres and a length is approximately 10 to 16 centimetres, trachea contains about 15-20 C-shaped tracheal hyaline cartilages.Trachea performs the function of transporting the air which person breaths in through nose to the lungs. Trachea also performs function of preventing entry of microbes and harmful substances into the lungs. 
BronchusTrachea divides into right bronchus and left bronchus. In adult human, right bronchus is 2.5 cm long and left bronchus is 5 cm longAlveolar ducts and alveoli of bronchus contain squamous epithelium and it permits exchange of gases like oxygen and carbon dioxide between lungs and blood in the blood vessels which spreads across the alveolar ducts and alveoli. 
BronchioleBronchi divide further into bronchioles. Bronchioles are approximately less than 1 mm in diameter and its wall consist of ciliated cuboidal epithelium and a layer of smooth muscle.Bronchioles carry oxygen from nose to the alveoli or air sacs in the lungs and stabilize ventilation. Constricting and expanding property of smooth muscular walls of the bronchioles help to control airflow and stop irritants from entering in the lungs.  
LungsHuman has right lung and left lung. Total weight of lung is approximately 1.3 kg. Lungs are located in the chest region in between rib cages. Right lung is divided in to three parts like upper, m idle and lower lobe. Horizontal fissure separates upper lobe form the middle lobe. Oblique fissure separates middle and upper lobe. Oblique fissure divides left lung into upper and lower lobe.    Lung performs function of breathing in which air enters and leaves the lung. In respiration, oxygen is inhaled into the body through nose and expelled carbon dioxide from the blood. Air is inhaled into the lungs in inspiration and it is expelled put in expiration. This exchange of gas occurs at alveoli of lung. Lung performs function of protection from infection due to presence of clilia on the epithelium and contains mucous. Lung clears all the air-borne infection through a process called mucociliary secretion.   
DiaphragmDiaphragm is a dome shaped sheet of skeletal muscle and fibrous tissue.Diaphragm performs important role in breathing. When diaphragm contract, thoracic cavity volume increase and air is drained into the lungs.

Part 3.

Digestive  system componentStructureFunction
MouthMouth contains salivary glands, teeth and the tongue. Vestibule and the oral cavity proper are the two regions of the mouth. Mouth is lined by mucous membrane.Moth performs function of chewing and breaking of food and mixing with saliva to make food more absorbable.
EsophagusEsophagus is a muscular tube between pharynx and stomach. In adults its average length id 25 cm. Esophagus is divided into cervical, thoracic and abdominal parts.Esophagus transports food from mouth to stomach through muscular peristalsis.
StomachStomach is J shaped organ and connects duodenum and esophagus. Stomach is divided into four sections like gastric cardia, fundus, body and pylorus.Gastric acid comprising of hydrochloric and sodium chloride, plays significant role in the digestive process. Pylorus aids in emptying food content in the small intestine.
Small intestineSmall intestine connects stomach to the large intestine. In human adults, average length of small intestine is around 7.0 m and diameter is around 2.5-3 cm. Small intestine is divided in to three parts like duodenum (approximately 20-25 cm long), jejunum (approximately 2.5 m long) and ileum (approximately 3.0 m long).Small intestine performs function of proteins, carbohydrate and lipids under the influence of photolytic enzymes, amylases and lipases respectively. Villi and microvilli present on the inner wall of the intestine facilitate absorption of nutrients. Gut flora in the intestine supports immune system of the body.  
Large intestineIn human average length of large intestine is approximately 1.5 metre. It comprises of cecum (8.7 cm inner corcumference), colon, rectum (5.7 cm), and anal canal. Colon comprises of ascending (6.6 cm), transverse (5.8 cm) and descending colon (6.3 cm).Large intestine is specifically performing function of processing waste material.
AlveoliAlveoli is a hollow cavity at the end of respiratory tree.Exchange of gases between lungs and blood.
Nasal cavityNasal cavity is a hollow space and the entry point of respiratory tract. It is lined with mucus membrane and hairs.Air enters into body and get filtered  through nasal cavity.
LarynxHollw muscular organ between laryngopharynx to the trachea.Aid air passage to lungs.
EpiglottisIt is made of elastic cartilage present at entrance of larynx.It prevents aspiration.


Air is inhaled and exhaled in and out of the body through nose. At the time of inspiration oxygen enters into the body and during expiration carbon dioxide is thrown out form the body.   This whole process is called as breathing or ventilation. When air is inhaled, diaphragm gets contracted and there is increase in the volume of thoracic cavity and decrease in the pressure in the thorax region which results in the enlargement of the lungs and this leads to the entry of the inhaled air along with oxygen into the lungs through trachea, bronchi, and bronchioles. In trachea due to the presence of cilia and mucociliary action air and oxygen without contamination enters the lung. At the terminal end of the bronchiole alveolar ducts and sacs are present. These alveolar ducts and sacs are innervated with the blood capillaries. Surface of alveoli are main location for the gaseous exchange. Oxygen inhaled from the environment which is present in the alveolar duct and sacs passed through the alveolar capillaries into the blood stream through process of diffusion. This oxygenated blood enters the left atrium of the heart and pumped into left ventricle. From left ventricle blood is transported to different parts of the body through aorts, arteries. These arteries are innervated to different parts of the body and supply oxygen through the blood. Also carbon dioxide which is collected as waste product forms the different parts of the body comes into contact with the surface of alveolar ducts and sacs through alveolar capillaries. Superior and inferior vena cava collect deoxygenated blood from the lung to the right atrium and again pass on to the right ventricle. From right ventricle blood pumped into the pulmonary artery and carried to the lungs for re-oxygenation. This deoxygenated blood while transporting through lungs comes into contact with alveolar air and there is a very thin wall of approximately 0.5 µm thickness present between blood and air. Hence, pressure of gas (PO2 and PCo2) in the blood automatically gets equilibrated with the alveoli. Increase in the PCo2 leads to the slight decrease in the POand this result in the deep and faster breathing and inhalation of more oxygen until POreturns to normal level. On the other side if PCo2 falls and PO2 increases and this leads to the slower breathing and exhalation of carbon dioxide gets reduced. Gas exchange in the lungs mainly occurs through the process of diffusion that means gases like oxygen and carbon dioxide moves from the high concentration to the low concentration. If POis less in alveoli, oxygen diffuse into alveoli and if PCo2 is more in blood capillaries, carbon dioxide diffuse into alveoli and exhaled through expiration. This carbon dioxide gets transported into the alveolar venules through diffusion. This carbon dioxide once entered into the alveoli, gets expelled out through the route of bronchiole, bronchi, trachea and nose. During this exhalation of carbon dioxide diaphragm gets relaxed and chest and abdomen returns to their elasticity directed position. This resting position of the thorax leads to the exhalation of the carbon dioxide.  


Digestive enzymes are the enzymes which break down macromolecular polymers like fats, carbohydrate and proteins in to their smaller forms and convert them into easily absorbable form. Based on their target macromolecules enzymes can be classified as lipases which break down proteins into their peptides and amino acids, amylases break down polymeric carbohydrates into monomeric carbohydrates, lipases break down fats and lipids into fatty acids and glycerol. Different parts of the digestive tract secrets different enzymes and these enzymes plays different role in the digestion of the food.

Salivary glands in the mouth secrets different enzymes like lingual lipase, salivary amylase and lysozyme. Enzymes of the salivary gland perform both the functions of digestion of food substances and prevention of infection due to food.    

Stomach secrets gastric enzymes. Pepsin secreted by the stomach breaks down proteins into peptide and amino acids. This protein digestion for the first time starts in the stomach and digestion of carbohydrates and fays starts in the mouth. Gastric chief cells secrets gastric lipase which is an acidic lipase facilitates fat hydrolysis. Pancreatic juice of the pancreases secrets different enzymes like trypsinogen, chymotrypsinogen carboxypeptidase and elastases are the proteolytic enzymes. Pancreatic lipases and amylase digest lipids and carbohydrate respectively. Pancreas also secrets sterol esterase and phospholipase.

Some of the enzymes available in the small intestine are primarily secreted by the pancreas and transported to the small intestine through pancreatic duct. These enzymes enter the small intestine under the influence of cholecystokinin hormone. Across the lining of the small intestine there are many enzymes secreted and these enzymes digest chime form stomach into smaller particles which are more absorbable. Peptones and polypeptides get converted in to amino acids by erepsin. Maltose gets converted into glucose by maltase. Lactose gets converted into glucose and galactose by lactase. Sucrose gets converted into glucose and fructose by sucrose.  

Cardiovascular System: Cardiovascular system through its numerous blood vessels and blood transport important nutrients, oxygen, hormones and enzymes to cells in the entire body. Cardiovascular system also performs function of removing nitrogenous waste from the body and expelling carbon dioxide from the blood. Cells need oxygen and n the blood capillaries, oxygen diffuses out of the blood and transports in the cells of the human body. Cells required to remove carbon dioxide, gets absorbed into blood circulation transported to the lungs for purification.  Cells requisite nutrients like carbohydrates, proteins, fats, minerals and vitamins. Blood supplies these nutrients to the cells.

Respiratory system: Oxygen intake and removal of carbon dioxide is very essential for cells for normal functioning. Respiratory system inhale oxygen from the atmosphere through breathing. This inhaled oxygen enters lungs and oxygen enters into the blood capillaries (arteries). This inhaled oxygen through blood capillaries (arteries) transported to the cells present in the different parts of the body. Carbon dioxide exchange occurs between cells of the body and blood capillaries (venules). Carbon dioxide transported from the blood capillaries to the heart and subsequently to the lungs. From lungs carbon dioxide expeleeted through breathing.    

Gastrointestinal system:

Every cell requires nutrients for their growth and maintenance. Digestive system brakes down the consumed food in the form of macromolecules into the smaller and easily absorbable particles. Carbohydrates, fats, and proteins get digested into sugars, fatty acids, and amino acids, respectively. These sugars, fatty acids, and amino acids can be easily absorbed.   This digestive process occurs both through mechanical and enzymatic means. This digested food material easily gets absorbed through the intestine as intestine is the main site for the absorption. Intestine contains villi and microvilli and this villus contains blood vessels and food gets absorbed. Absorbed food nutrient is transported to the cells through blood vessels.


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