Glands of the Human Body

Glands of the Human Body

Endocrine or Ductless Glands of the Human Body

Glands in the body release fluids or hormones that play an important role in maintaining the health of the body. Glands are classified as ducted and ductless glands. Ducted glands, also called exocrine glands, secrete some chemicals through ducts. Ductless glands are called endocrine glands. Glands receive signals from the brain to release useful fluids. Endocrine glands release hormones directly into the bloodstream. Hormones are the chemical messengers which facilitate the communication between the brain and the organs. As the nervous system uses nerves to send the required information, the glands in the human body use blood vessels as information channels. Here's an overview of the endocrine system.

Pituitary Gland

The pituitary gland, located at the base of the skull, is known as the 'master gland'. It controls the functions of other ductless glands. This tiny, pea-shaped gland is one of the most important parts of our body. It is divided into anterior and posterior pituitary.

This gland influences metabolism, reproduction and growth by releasing hormones like prolactin, thyroid stimulating hormone, adrenocorticotropic hormone, growth hormone, oxytocin, luteinizing hormone, follicle-stimulating hormone, etc.

Adrenal Glands

The adrenal glands look like triangular hats placed on the top of the kidneys. The length of an adrenal gland is about one or two inches and it weighs only a fraction of an ounce. Though small in size, these glands secrete almost three dozen hormones! The main functions of adrenal glands include carrying out the metabolic processes and helping the body deal with stress.

These glands regulate the 'fight or flight mechanism' of the body. Adrenal medulla releases adrenaline and noradrenaline while the adrenal cortex releases cortisol, corticosterone, cortisone, and aldosterone (which determines salt-water balance in the body).

Thyroid Gland

Thyroid gland, located in the neck, looks like a butterfly. It weighs less than an ounce. Situated below our voice box, thyroid's main function is to regulate body metabolism. Functions of the body are severely affected when thyroid does not work well. Overactive or under active thyroid gland leads to several health 

Hormones secreted by the thyroid play an important role in generation of heat and energy, protein synthesis, vitamins, protein, fat, and carbohydrate metabolism, release and functions of other hormones, increased sensitivity of the body to other hormones like adrenaline, etc. Thyroid hormones (T3 and T34) are produced with the help of iodine and tyrosine. Therefore experts recommend incorporation of iodized salt in regular diet.

Parathyroid Glands

Human beings have four parathyroid glands. They are as small as a grain of rice and are located on the posterior surface of the thyroid gland. These glands control the level of calcium in our blood and bones. They regulate the growth of muscles and bones by determining the distribution of calcium and phosphate in the body.

These glands also govern the function of the nervous and muscular system. Parathyroid hormone (PTH) activates vitamin D and enhances the absorption of calcium in the gastrointestinal tract. Low PTH levels lead to fatigue and anxiety.

Hypothalamus

Hypothalamus (part of the brain) is known as the 'control and relay center of the endocrine system'. The autonomic nervous system is governed by the hypothalamus. It plays an important role in certain metabolic processes. Located near the pituitary gland at the basal part of the skull (above the brain stem), it controls pituitary secretions.

All the automatically adjusted factors such as hunger, thirst, sleep, emotional behavior such as anger and sexual activity, body temperature, blood pressure, function of the cardiovascular system (heart rate), and abdominal visceral regulation are controlled by the hypothalamus. As we grow older, hypothalamus requires support to maintain optimum level of performance. Dysfunction of the hypothalamus results in depression or abnormal responses to stress.

It also leads to disturbances in the brain. Hormones released by the hypothalamus stimulate the release of other hormones like thyrotropin, prolactin, gonadotropin, corticotropin, growth hormone, etc. and inhibit the production of prolactin (by releasing dopamine), growth hormone (by releasing somatostatin), etc. The hormone oxytocin plays an important role in uterine contractions and lactation. The antidiuretic hormone vasopressin is also secreted by the hypothalamus.

Prostate

Prostate is a chestnut-sized gland, which plays an important role in the male reproductive system. It encircles the urethra below the bladder. It secretes an alkaline fluid which contains semen with spermatozoa and seminal vesicle fluid that is expelled during ejaculation. Thus it determines the fertility quotient of a man.

Prostate helps regulate blood pressure too. When an enlarged prostate creates pressure on the urethra and bladder, the man suffers from problems like difficulty in urination.

Gonads

Gonads are the reproductive glands - ovaries in women and testicles in men. They produce germ cells known as gametes. They release sex hormones. The almond-shaped ovaries are present on either side of the uterus. They produce ova or eggs. Important hormones, like estrogen and progesterone are secreted by them.

The testicles are hidden in the scrotum and are responsible for the production of sperms in males. They release the hormone testosterone. They have a built-in thermostat to keep the sperms at the correct temperature. Thus, these glands play an important role in fertilization and reproduction. They determine the male/female characters (like development of body/facial hair) of a person.

Thymus

The thymus, situated in the middle of the chest, beneath the upper part of the breastbone near the heart, is a pyramid-shaped small gland. It builds resistance for combating diseases and helps in one's physical development.

The size of the thymus grows during the neonatal and pre-adolescent periods. It is most active in the early years after birth. It plays an important role in the functioning of the immune system. As the body reaches puberty, it starts shrinking. In adults, it is difficult to identify thymus.

Pancreas

The pancreas, located behind the stomach, is yellowish in color. It is about 7.5 inches long and 1.5 inches wide. It is connected to the small intestine. Certain cells in the pancreas secrete digestive enzymes, which play an important role in the digestion of proteins, carbohydrates, and fats. Important hormones - insulin and glucagon are secreted into the blood stream by the pancreas.

Thus pancreas works as an endocrine as well as exocrine gland. As we all know, insulin helps lower the blood sugar level. But if glucose level is found to be too low, glucagon helps increase it. Malfunctioning of insulin-generating cells results in diabetes. Pancreas helps neutralize the chyme. (Chyme is the partly digested food. It is in the form of thick semi-fluid when it passes through the stomach.)

Pineal Gland

The pineal gland is located within the brain. It is safely positioned in the groove at the center of the brain, between the two hemispheres. It releases melatonin which supervises the biological clock of the body. It controls our walking and sleeping patterns.

Sexual development is also controlled by the pineal gland. Melatonin helps avoid and get over jet-lags. In the ancient times, the pineal gland was considered as the third eye, with supposed magical powers.

Exocrine or Ducted Glands of The Human Body

Lachrymal Glands

Tears are produced by the lachrymal glands. They are found in the eye cavities. Their function of producing tears is controlled by the nervous system. They help lubricate the eyes.

Sweat Glands

Sweat is the salty fluid secreted by the sweat glands. Sweat accumulates in the small glands located under the skin and it evaporates when the body experiences excessive heat. Thus, these glands help maintain the body temperature.

Salivary Glands

Salivary glands are located in and around the mouth and the throat. Saliva from salivary glands initiates the process of digestion. It helps moisten the mouth and prevents tooth decay. Malfunctioning of these glands causes dehydration.

Mammary Glands

Mammary glands exist in both sexes. But, the hormones released by the ovaries stimulate the growth of the mammary glands in females, at the onset of puberty. After the birth of a child, the milk from the mammary glands nourishes the baby. Various hormones determine the production and flow of breast milk.

Sebaceous Glands

Sebaceous glands lie under the skin. They secrete sebum. This fatty substance forms a water-repellent layer on the skin. It protects the skin and makes it supple. Sometimes, due to the presence of dust particles in the atmosphere, the pores on the skin get blocked. Obstruction in the path of the sebum
leads to the formation of blackheads. Blackheads are the root cause of acne.

Diseases Caused due to Functional Failure of Glands

Osteoporosis, diabetes, renal failure, multinodular goiter, hyper/hypothyroidism, polycystic ovaries and cancer are some of the diseases caused due to the failure of the glands in the human body.

Dwarfism, gigantism, outburst of acne, infertility, miscarriage, skin disorders, early/late puberty and excessive weight are some of the effects of hormonal imbalance in the body. The malfunctioning of one or more glands in the body can lead to mental disturbances, mood swings, depression and high/low blood pressure.

Balanced diet, various therapies like massage, shiatsu, aroma therapy, acupuncture, and regular exercise promote proper functioning of glands. Doctors may prescribe medications to improve the functions of the glands. In extreme cases, surgery is performed to remove a damaged gland. After the removal of the entire gland, hormone replacement therapy is usually recommended.

Chakra', the Sanskrit word, means 'wheel' or 'turning'. Body 'chakras' refer to the important centers on our body. They are considered as the focal points of the human body which receive and transmit energies. There are seven major 'chakras' according to the 'Indian Upanishadas'. It is interesting to find that the locations of the endocrine glands in the human body correspond with the locations of these 'chakras'.

The activation of these 'chakras' helps gain control over the functioning of glands and achieve peace of mind. Yoga and meditation help gain control over these glands. You can lead a peaceful life by learning stress management techniques. Stress leads to dysfunction of glands resulting in harmful diseases and disorders.

The functions of the endocrine and the exocrine systems are of extreme importance to the body. Proper functioning of the glands helps maintain weight, blood pressure, blood sugar levels, electrolyte balance, body temperature, heart rate, bone density, etc. With simple measures like healthy diet and regular exercise, you can maintain the health of the glands.

Blood

Human body is like a fine-tuned machine with some amazing working mechanisms. Each body system works in conjunction with others, precisely and efficiently. All of them are equally important for the healthy functioning of the body.

Blood is one of the vital components of the circulatory system, which also comprises the heart and the blood vessels. It is a common fact that the heart pumps blood that flows through the blood vessels and reaches all parts of the body. Do you have any idea about the total amount of blood in the human body?

Volume of Blood in the Human Body

Did you know that about seven to eight percent of the human body weight is made up of blood? A healthy adult with a body weight of 60 kilograms has approximately 4.2 to 4.8 liters of blood. So body weight is one of the factors that determine the quantity of blood in the human body. Other factors include age, gender, and health condition.

Usually, females are found to have slightly lesser amount of blood, as compared to males. Adults have more blood in their body, than in kids.

When compared to those living in low altitude areas, people living in higher altitudes have more blood in their body. They are found to have about 1.8 liters more blood, than those living at sea level.

Regions in higher altitudes have less atmospheric oxygen. So people living in such places have more blood to nourish the body cells with enough oxygen.

Blood Volume Test

How is Blood Volume Measured?

A blood volume test is conducted to determine the total amount of blood in the body as well as the volume of red blood cells and plasma. There are different methods of calculating the blood volume. Most of these tests are based on the principle of dilution and use tracer substances like dyes or radioactive chromium. The tracer is injected into the blood and the degree of dilution is noted to calculate the blood volume.

Why to Evaluate Blood Volume?

There are various medical conditions, which cause blood volume abnormalities. Blood loss may happen due to other reasons, like surgery. Such conditions warrant a blood volume test, so that the amount of blood, plasma and red blood cells in the body can be determined. This test is helpful in evaluating the condition of people having hypertension, congestive heart failure, syncope, septic shock, kidney failure, etc. The test is also used to detect conditions like polycythemia (high red cell level), anemia (low red cell level), hypovolemia (low blood volume) and hypervolemia (high blood volume). Though it is very rare, the test may sometimes trigger severe allergic reactions.

How Much Blood is Needed to Survive?

In short, the volume of blood in a human body is around five liters and this may drop due to certain medical conditions, surgery, injuries, etc. It is said that a blood loss of up to 15% of the total volume can be tolerated by a healthy adult, without any serious signs and symptoms. However, blood loss exceeding this limit can cause serious symptoms and complications, if immediate medical attention is not sought. An average human being can lose a maximum of 30 to 40% of the total blood volume and stay alive, provided he is given immediate treatment.

Functions of Blood

Blood carries out many important functions in the body, like transporting nutrients and oxygen to the body cells. It also takes away the waste materials from the cells. Blood is responsible for carrying hormones and chemicals to various parts of the body. It also plays a vital role in keeping the body temperature steady by transporting excess body heat to the skin, from where it is dissipated. Blood is an important component of the immune system, as it contains white blood cells that attack the foreign materials and pathogens that enter the body. The platelets in blood can coagulate and stop bleeding from wounds and other injuries. Blood coagulation is considered as the body's self-repair mechanism, which prevents further blood loss, that can be fatal. Kidneys play a key role in maintaining the blood volume.

Human blood consists of a yellowish fluid called plasma, in which the blood cells are suspended. 45% of the volume of blood is composed of red blood cells, 54.3% is plasma and the remaining 0.7% constitutes white blood cells. Almost 90% of plasma is water, which contains dissolved glucose, proteins, hormones, mineral ions, platelets and blood cells. The blood cells include red blood cells (RBCs or erythrocytes) and white blood cells (WBCs or leucocytes). Other than these two, there are platelets, which are also known as thrombocytes. The most abundant among them are the RBCs (around five million per cubic millimeter of human blood). The same amount of blood contains about 5,000 to 10,000 WBCs and 200,000 to 400,000 platelets. RBCs contain hemoglobin, which imparts the red color to blood, when oxygenated. A deficiency of hemoglobin can lead to anemia.

Function of Red Blood Cells

This article mulls on the crucial function of red blood cells. Red blood cells formed in the bone marrow have a short lifespan of only 100 - 120 days, within which they perform the crucial role of transporting oxygen to various parts of the body.

Blood forms 7% of a person's body weight and its volume may vary from one individual to another depending on the size. It is the life-maintaining fluid that circulates through the entire body, via blood vessels called arteries and veins. Blood plays a vital role in our existence as it carries oxygen, nourishment, vitamins, hormones, antibodies, heat and electrolytes to different parts of the body, which are essential for the body's proper functioning. They also carry and get rid of carbon dioxide and waste matter from the blood. The human blood is made up of 78% water and 22% solids. Blood contains plasma in which blood cells such as red blood cells (RBC), white blood cells (WBC) and blood platelets are suspended. All these components play very important roles in the body, however, in this article we will only focus on the function of red blood cells.

What are the Functions of Red Blood Cells

Red blood cells or RBCs are also referred to as erythrocytes and are the most abundantly found blood cells as compared to WBCs and platelets, accounting for about 45% of total blood volume. They are around 6 - 8 micrometers in size and the human body contains about 4 - 6 millions/mm3 of them. RBCs are biconcave lens-like cells that lack a cell nucleus and are made up of a protein called hemoglobin. In fact, 33% of RBC is nothing but hemoglobin. Embedded within this hemoglobin molecule is iron, whose function is to transport oxygen and carbon dioxide in the blood. This hemoglobin is also responsible for the biconcave shape and red color of the RBCs.

RBCs are formed in the bone marrow, under the influence of hormone erythropoietin (formed in the kidneys), by a process called erythropoiesis, in just 7 days. On maturing in the bone marrow, these cells are circulated in the body for almost 3 months before they are destroyed in the spleen, or recycled by the macrophages in the body. So the general lifespan of a red blood cell is only 3 months. Well, so what does the red blood cell do in its short lifespan and why is it so important for our existence? To understand this, we will have to look at some red blood cell functions.

Carries Oxygen

The main function of the red blood cell is to transport oxygen from the lungs, to the other tissues and cells of the body. And how does the RBC manage to do this? Well, the hemoglobin present in the RBC is a protein, which binds itself to the oxygen molecules inhaled. When a person inhales, oxygen from the atmosphere enters the body through the nostril and reaches the lungs. At the lungs, hemoglobin molecules bind themselves to the oxygen molecules and move to the heart. From the heart, the same oxygen-containing blood is pumped to the rest of the body parts (muscles, tissues and other organs). The hemoglobin molecules then release the oxygen molecules to the cells of the body. Basically, hemoglobin takes oxygen from high oxygen level areas and releases them in low oxygen level areas of the body. Thus, RBCs actually perform the function of transporting life-sustaining oxygen to the different parts of the body.

Carries Carbon Dioxide

The other function of the red blood cell is to partly carry carbon dioxide, which is a waste product of metabolic activities in the body. Carbon dioxide is actually formed in the cells as a result of the chemical reactions taking place. This waste product is then excreted through the blood plasma and RBCs. While the RBCs play a major role in eliminating carbon dioxide from the cells, blood plasma also accounts for a small amount of carbon dioxide removal. The hemoglobin in the RBCs bind the carbon dioxide molecules to form carbaminohaemoglobin. However, unlike oxygen molecules, carbon dioxide molecules do not bind to the iron part of hemoglobin. Instead, they combine with the amino acid groups on the hemoglobin polypeptide chains. Thus, RBCs transport carbon dioxide from the various cells of the body and take them to the lungs, from where it is discarded by exhalation.

This round trip of transporting oxygen to the tissues and then bringing waste materials to the lungs for elimination, takes the RBCs only 30 to 45 seconds. The ability of the RBC to transport oxygen depends on several factors like pH of the blood, temperature, etc. Moreover, the presence of carbon monoxide, hydrogen sulfide, etc. in the blood also affects hemoglobin's oxygen carrying capacity.

The exact process of oxygen transfer from the hemoglobin to the tissues of the body is a complex one. However, this was a simple way of explaining the function of red blood cells. Don't be fooled by the easy explanation and think that the RBC does nothing of great significance. If at all these RBCs stop functioning, then the body will surely have life-threatening issues. Blood disorders like sickle-cell anemia, hemolytic anemia, hemochromatosis, hereditary spherocytosis and various other red cell enzyme deficiencies can occur and pose a threat to one's life.

Circulatory System Organs and Their Functions

The human heart takes less than a minute to pump blood to every cell in the body.

The human circulatory system comprises the heart, blood and blood vessels which help in transferring essential nutrients and blood throughout the body. For every part of the body to function, every comprising cell requires myriad nutrients like sugars, vitamins, minerals and gases like oxygen. The circulatory system ensures that these vital molecules are collected from the appropriate sites, and delivered to every single cell of the body.

The knowledge of the structure and functions of these organs has helped physicians and medical experts find cures for many critical health problems.

The heart is the central organ of the circulatory system, and pumps blood into the blood vessels which carry it to all the body parts. The average heart rate in a normal person is 72 beats per minute, so one can imagine the speed at which blood flows through the body.

The amount of blood present in the human body is about 7% of the body weight. Also, the body processes about 2,000 gallons of blood. Through the course of one day this flowing blood covers an average distance of about 60,000 miles!

Organs of the Circulatory System

Primarily speaking, there are three basic components of the circulatory system: 

·         Blood―which carries the required molecules.

·         The Heart―which serves as a pump.

·         Blood Vessels―which transport blood throughout the body.

here are two circulatory divisions that function simultaneously:

·         The pulmonary circulation; transports the blood from the heart to the lungs for oxygenation, and brings it back to the heart. The rest of the body is not involved in this process.

·         The systemic circulation; carries the blood received through the pulmonary circuit, from the heart to the rest of the body; and transports deoxygenated blood back to the heart which then proceeds through the pulmonary circuit for oxygenation.

Both these circulatory units, thus function at the same time, and carry out the complex and rapid circulation of blood within the body.

Heart

The human heart is one of the most fascinating and crucial organs in the human body. It pumps oxygen-filled blood to every living cell in the body.

As the heart beats throughout the lifetime of an individual, and is important for survival, it is made of specialized muscles called cardiac muscles. The human heart is divided into four chambers. The upper chambers are known as atria, while the lower ones are called ventricles.

The interventricular septum divides the right and left ventricles, while the right and left atria are divided by the interatrial septum. It also has four unidirectional valves which control the flow of blood in and out of the chambers. The tricuspid valve ensures blood flow from the right atrium to the right ventricle; whereas the mitral valve controls blood flow from the left atrium to the left ventricle.

The pulmonary valve regulates blood flow from the right ventricle into the pulmonary artery which leads to the lungs. The aortic valve regulates blood flow from the left ventricle to the aorta. The aorta, arising from the heart branches into arteries, whereas the veins of the body converge to form the superior vena cava which carries deoxygenated blood into the heart.

Function of Human Heart

The main function of the heart is pumping blood throughout the body, and is constantly receiving, purifying, and transporting blood. The right atrium receives deoxygenated blood from the vena cava, which is then pumped into the right ventricle through the tricuspid valve.

The contraction of the ventricles results in pumping of the blood to the lungs through the pulmonary valve and pulmonary arteries. Oxygenated blood from the lungs is carried by the pulmonary veins, and it enters the left atrium. This blood is further pumped into the left ventricle via the bicuspid valve, and then through the aortic valve into the aorta. The aorta, and its branches supply the oxygen-rich blood to various parts of the body

Blood is a liquid tissue which is carried by the blood vessels for transporting oxygen and nutrients to the cells. It is composed of blood cells which are suspended in a liquid called blood plasma.

Components of Blood

The non-cellular component of blood comprises plasma which accounts for 55% of blood volume, and is made up of 92% of water. Various proteins, glucose, minerals, hormones, as well as gases like oxygen and carbon dioxide are present in the plasma. The cellular component is made up of red blood cells (erythrocytes), white blood cells (leukocytes) and platelets. The red blood cells contain a metalloprotein called hemoglobin, which plays a crucial role in the transport of oxygen and carbon dioxide.

Blood transfers the oxygen, obtained through inhalation in the lungs, to all the tissues of the body. Blood absorbs oxygen from the lungs while flowing in the capillaries near the small air sacs called alveoli. This oxygen is then permeated into the red blood cells, where it combines with hemoglobin. This oxygenated blood is transported to the heart, and then to various tissues.

Deoxygenation of Blood

In the heart, oxygen molecules bound to hemoglobin are released, and they diffuse through the capillaries to reach the tissue. Carbon dioxide molecules from the tissue diffuse into the blood stream through the capillaries, and bind to the hemoglobin molecules. This process is called deoxygenation of blood. This deoxygenated blood is then carried to the heart and routed to the lungs for oxygenation. In the lungs, the carbon dioxide molecules are replaced by oxygen molecules. The carbon dioxide molecules are transferred to the alveoli, and expelled during the exhalation process.

Blood carries nutrients to various parts of the body. It transports hormones from the endocrine glands to their target tissues. It also helps in the removal of metabolic waste products like lactic acid from muscles, and urea from the liver. Blood even helps regulate and maintain the body temperature.

Leukocytes or white blood cells promote immunity, and protect the body against various diseases and infections. The coagulating agent in blood helps in the blood-clotting process, thus preventing excessive bleeding in the event of an injury. Also antibodies, cytokines and other molecules present in blood play a vital role in providing immunity against foreign bodies and pathogens.

Though blood vessels are not organs, their presence is essential for every organ system of the body. Through an endless network comprising hundreds of thousands of blood vessels, blood is made accessible to every part of the body.

Structure of Blood Vessels

Blood vessels are an intricate network of hollow tubes which carry blood from the heart to different parts of the body, and back. The outermost layer is made up of connective tissue; the middle layer is made of smooth muscle cells; and the innermost layer comprises endothelial cells.

Arteries and veins have similar anatomies of three layers:

·         Middle: smooth muscle cells, and

·         Outermost: connective,

·         Innermost: endothelial cells;

except that the middle layer is thinner in veins. Some veins however, have valves that maintain a unidirectional blood flow. Capillaries are the smallest blood vessels. They have a special structure, with walls made of single layer of endothelial cells.

Function of Blood Vessels

Blood vessels ensure the transport of oxygen, nutrients, and metabolites to every cell of the body, and also enable the transport of carbon dioxide, toxins and other wastes to the respective excretory organs.

Arteries

They transfer oxygenated blood from the heart to various organs. This action is carried through its branches called arterioles. Arteries are said to be the supply train of the body as they bring the raw materials (blood and nutrients) essential for the functioning of different organs. However, the pulmonary artery is an exception, and it carries deoxygenated blood from the heart to the lungs.

Veins

They carry deoxygenated blood from various organs of the body to the heart. This action is carried out by its branches called venules. However, the pulmonary vein transports oxygenated blood from the lungs to the heart.

Capillaries

Capillaries are the smallest blood vessels in the body, and they play a major role in micro circulation. They are thin blood vessels where the exchange of nutrients takes place between the blood and the tissues. Capillaries network to form a capillary bed that supplies tissues with gases like oxygen as well as water, ions, nutrients and metabolites.

Supplementary Organs - Lungs

Lungs play an important role in pulmonary circulation, and the oxygen needed by the body comes through the air inhaled through lungs. Conversely, they are also responsible for exhaling the gaseous wastes like carbon dioxide generated in the body.

Structure of Lungs

Lungs are sponge-like, air-filled organs which are located in the thoracic cavity. The lungs are covered with a thin layer of tissue called the pleura. A thin layer of fluid is also present that lubricates the lungs as they contract and expand during respiration.

Function of Lungs

Lungs play a vital role in the processing of deoxygenated to oxygenated blood, and circulating it back to the heart. Deoxygenated blood from the heart through its right ventricle (pulmonary artery) is transported to the capillaries. Here, CO2 diffuses out of the red blood cells, into the alveoli, and oxygen present in the alveoli diffuses into the capillaries. This oxygen-rich blood is then transported through the capillaries to the pulmonary vein, and further to the left atrium of the heart.

Role of Other Organs

·         In the systemic circulation, the blood also passes through the kidneys to filter waste products from the blood. This is known as renal circulation.

·         Blood flow from the small intestine and spleen to the liver, through the hepatic portal vein, is known as portal circulation. Here, sugar and other products of digestion are filtered from blood.

·         This blood is then transported back to the heart through the inferior vena cava.

The circulatory system organs are essential for the proper functioning of the body, as this organ system allows the circulation of blood, enabling the transport of oxygen, carbon dioxide, nutrients, and hormones to all parts of the body.