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SABITHA S S 18121971008


The students are already aware that excretion is a physiological process and in humans kidneys are the major excretory organs. This book aims to give a comprehensive overview on the structure and functions of kidney. It describes the physiological functions of the kidney which includes structure of kidney, its associated parts, formation of urine, how kidneys help in maintaining homeostasis and the disorders associated with kidney. This book is written in a way that is simple and easy for the IX standard students to understand. I hope that the textbook “Kidney” will be a beneficial aid for students. The students could know more in detail about how our body keeps the internal environment devoid of waste through excretory organ, kidney and thus protects it. With love and regards, Sabitha S S

CONTENT 1. Kidneys and associated parts


2. Internal structure of Kidney


3. Formation of Urine


4. Kidney Diseases


5. Healthy Kidney



Kidneys and Associated Parts

Several byproducts are formed in cells as a result of metabolic activities. If the amount of these byproducts exceeds a certain limit, it becomes harmful to our body. Nitrogenous compounds formed by the metabolism of amino acids and nucleic acids, carbon dioxide and water which are the byproducts of respiration etc., are the main excretory products in human beings. Excretion is the process of elimination of these wastes from the body. This is one of the methods to maintain homeostasis. The human excretory system includes skin, liver, lungs and kidneys as the excretory organs. Only a very small quantity of impurities is expelled through sweat. Urea, salt and water are expelled from the body mainly through urine. How is urine formed from blood? Which organ helps in this process? Kidneys Kidneys are the major excretory organs in human beings. Kidneys are the organs which filter urea, vitamins, salts and other substances harmful to the human body from blood and expel them through urine.


Human beings have a pair of kidneys. They are bean-shaped and are located in the abdominal cavity on either sides of the vertebral column (See figure 1.1). Compared to the right kidney, the left kidney is located slightly higher. Each kidney is covered by a strong but soft membrane.

Figure 1.1 Position of kidneys in human body

Kidneys and Associated Parts Kidneys perform the function of excretion with the help of its associated parts. The associated parts of kidney include renal vein, renal artery, a pair of ureters, urinary bladder and urethra. Kidneys along with these associated parts constitute the main human excretory system. See figure 1.2.


Figure 1.2 Kidneys and associated parts

Blood with high pressure reaches the kidney through renal artery which is a branch of aorta. The filtered blood reaches the venacava through renal vein. Analyze the comparison between the renal vein and renal artery given in table 1.1.

Figure 1.3 Renal vein and renal artery


Renal Artery

Renal Vein

It carries oxygenated blood.

It carries deoxygenated blood.

It contains more urea.

It contains less urea.

It is a blood vessel that is attached

It is attached from the inferior vena

to the aorta.


The pressure by which blood flows The pressure by which the blood is is higher.

lower in the renal vein. Table 1.1

The kidneys functions in the formation of urine. Urine formed in the kidneys reaches the urinary bladder through the ureters. The urinary bladder is a muscular sac-like structure, which stores urine. It is emptied by the process of micturition, i.e. the act of urination. Urethra is a tube arising from the urinary bladder and helps to expel urine out of the body. Complete illustration 1.1 given below.

Illustration 1.1 Kidneys and associated parts


Grossly, the kidneys weigh about 150 g in the male and about 135 g in the female. They are typically 10-12 cm in length, 5-7 cm in width, and 2-3 cm in thickness.

LET US ASSESS 1. Illustrate kidney and its parts. 2. Prepare a short note on the position and size of the kidney.

EXTENDED ACTIVITIES  Prepare a chart showing kidneys and its associated parts.



Internal Structure of Kidney

We all know that kidneys help to remove waste materials from our body. But how do they do this. To know about this we should understand the internal structure of kidney. Each kidney is comprised of about 12 lakh ultrafilters. These are called nephrons. Nephrons are the basic structural and functional units of kidneys. These ultrafilters helps in filtering out the waste materials from the blood.

Figure 2.1 Nephron


Analyse illustration 2.2 given below. Identify the internal structures of the kidney.

Illustration 2.1 Internal structure of kidney

The kidney is mainly divided into three parts and the position of the nephrons can also be seen in these parts Cortex: Ultrafilters of nephrons are present. Medulla: Long tubules of nephrons are present. Pelvis: Nephrons absent. Urine from the filters flows into this part.


You have understood how nephrons are arranged in the kidneys. Analyse illustration 2.2 given below and prepare a table including the parts and peculiarities of nephron.

Illustration 2.2


Each nephron has two parts – the glomerulus and the renal tubule. Glomerulus is a tuft of capillaries formed by the afferent vessel – a fine branch of renal artery. Blood from the glomerulus is carried away by an efferent vessel. The renal tubule begins with a double walled cup-like structure called Bowman’s capsule, which encloses the glomerulus. Peritubular capillaries are the blood capillaries seen around the renal tubules as the continuation of the efferent vessel. The long tubule which connects the Bowmann's capsule and the collecting duct is the renal tubule. Collecting duct is the part where renal tubules enter. Absorption of water takes place. Urine is collected and is carried to the pelvis.

Kidneys have the highest flow of blood as compared to heart and brain. On reaching 40 years of age, 1% of the nephrons start degenerating every year.


LET US ASSESS 1. State true or false. a. Blood from the glomerulus is carried away by an afferent vessel. b. Each kidney is comprised of about 12 lakh ultrafilters. 2. Name the following. a. The blood capillaries seen around the renal tubules as the continuation of the efferent vessel. b. The dark coloured inner part of kidney.

EXTENDED ACTIVITIES  Make a model of nephron using scrap materials.



Formation of Urine

Waste is excreted from the human body, mainly in the form of urine. Our kidneys play a major role in the process of excretion. Constituents of normal human urine include 95 per cent water and 5 per cent solid wastes. It is produced in the nephron, which is the structural and functional unit of the kidney. Urine formation in our body is mainly carried out in three phases namely Glomerular filtration Reabsorption Secretion Analyse illustration 3.1 and understand the process of formation of urine. When blood flows through the glomerulus, ultrafiltration takes place through its small pores. The glomerular filtrate formed as a result of this is collected in the capsular space. When glomerular filtrate flows through renal tubeless to the collecting duct, essential components are reabsorbed to the peritubular capillaries. The absorption of excess water from the glomerular filtrate takes place in the collecting duct. What is left behind is urine.


Illustration 3.1 Formation of urine


Urine flows from the kidney to the urinary bladder through the ureter and is stored there temporarily. It is expelled through urethra as and when the bladder is filled. Washing out disease causing germs from the urinary tract also takes place during the process of micturition (passing out of urine). How does avoiding timely urination affect our body? Analyse the description given below and list out the healthy habits to be followed.

Avoiding urination for a long time prevents the expulsion of bacteria that may be present in the urinary tract and urinary bladder. This causes infection in the inner membrane of the urinary bladder. Females are more susceptible to urinary tract infection, when compared to males.

You have understood that urine, the main excretory product contains water, urea and salts. Shall we conduct an experiment to understand the presence of urea in urine? Conduct the experiment with the help of your teacher and write down the procedure in your Science diary. (Hint: When sodium hypobromite reacts with urea, urea breaks down to form carbon dioxide and nitrogen.)


PLAN OF EXPERIMENT Aim:……………………………………………………………………………....... Materials required:…………………………………………………………………. Procedure: Take 2ml of urine in a test tube. Add 4-5 drops of sodium hypobromite solution into it using a dropper. Observe whether effervescence occurs. Observation:………………………………………………………………………... Inference:…………………………………………………………………………...

The entire blood in the body passes through kidneys at least 350 times in 24 hrs. About 1800 litres of blood is filtered to form 170 litres of glomerular filtrate.

Approximately 127 ml of glomerular filtrate is formed in every minute. Out of this almost 126 ml is reabsorbed to blood. As a result, 1.5 litres of urine is formed from 170 litres of the glomerular filtrate.


LET US ASSESS 1. Statements related to the formation of urine are given below. Arrange them in the figure appropriately. a. Ultrafiltration takes place. b. Collects urine. c. Glucose, amino acid, sodium, potassium etc. are reabsorbed here. d. Urea, sodium, potassium ions etc are secreted here.

2. Glucose, amino acids etc. found in the glomerular filtrate are absent in urine. Why?


EXTENDED ACTIVITIES  Visit a medical lab, collect information regarding urine test and prepare a chart showing the normal level of components in










Kidney Diseases

Kidneys play a major role in maintaining the concentration of body fluids. They regulate the pH and the amount of water and salts present in the blood. Analyse how the kidneys maintain homeostasis, based on illustration 4.1 and the inferences you have drawn so far about kidneys and prepare notes in your Science diary.

Illustration 4.1 Kidneys and maintenance of homeostasis Kidney Diseases Bad health habits, life style and infection by microorganisms adversely affect the health of kidneys. Kidney disease means your kidneys are


damaged and can‘t filter blood the way they should. You are at greater risk for kidney disease if you have diabetes or high blood pressure. If you experience kidney failure, treatments include kidney transplant or dialysis. Some of the kidney disorders include Nephritis, Kidney stone and Uremia. Nephritis A condition in which the tissues in the kidney become inflamed and have problems filtering waste from the blood is called nephritis. Nephritis may be caused by infection, inflammatory conditions (such as lupus), certain genetic conditions, and other diseases or conditions. It may also be caused by taking certain medicines or being exposed to certain chemicals.


Signs and symptoms include blood and protein in the urine; high blood pressure; swelling of the face, hands, feet, and legs; fatigue; and anemia. If not treated or controlled, nephritis may lead to kidney damage and kidney failure. It is also called glomerulonephritis. Kidney stone Kidney stone are hard deposits made of minerals and salts that form inside the kidneys. Diet, excess body weight, some medical conditions, and certain supplements and medications are among the many causes of kidney stones. Kidney stones can affect any part of your urinary tract — from your kidneys to your bladder. Often, stones form when the urine becomes concentrated, allowing minerals to crystallize and stick together.


A kidney stone usually will not cause symptoms until it moves around within the kidney or passes into one of the ureters. Some symptoms include: Severe, sharp pain in the side and back, below the ribs; Pain that radiates to the lower abdomen and groin; Pain that comes in waves and fluctuates in intensity; Pain or burning sensation while urinating Uremia. Uremia occurs when your kidneys become damaged. The toxins, or bodily waste, that the kidneys normally send out through urine end up in the bloodstream instead. These toxins are known as creatinine and urea. Uremia is a serious condition and, if untreated, can be life-threatening. Uremia is a major symptom of renal failure. Uremia is also a sign of the last stages of chronic kidney disease.


At the beginning of chronic kidney disease, you may not notice any symptoms. However, by the time uremia has started, your kidneys are much damaged. Uremia may cause you to have some of the following symptoms: extreme tiredness or fatigue; cramping in your legs; little or no appetite; headache; nausea; vomiting; trouble concentrating. The kidney diseases are summarized in table 4.1. Disease


Symptoms Turbid and dark

Inflammation of kidneys Nephritis

due to infection or intoxication.

coloured urine, back pain, fever, oedema on

Deposition of crystals of Kidney stone

calcium salts in kidney or urinary tract.

Different types of kidney Uremia

diseases, nephritis, diabetes, high blood pressure.

face and ankle Pain in the lower abdomen, blockage of urine, dizziness, vomiting Anaemia, loss of body weight, dizziness suffocation, diarrhea, production of urine stops gradually.

Table 4.1 Kidney diseases


Kidney stones can be the size of a pea or — although rare — can grow to the size of a golf ball. The largest kidney stone ever recorded, according to Guinness World Records, was just over 5 inches at its widest point.

LET US ASSESS 1. Identify the kidney disease from the reasons given below. a. Different types of kidney diseases, nephritis, diabetes, high blood pressure. b. Inflammation of kidneys due to infection or intoxication. c. Deposition of crystals of calcium salts in kidney or urinary tract. 2. Explain how kidneys help in maintaining homeostasis.


EXTENDED ACTIVITIES  Arrange an awareness programme in your school by collecting information from a doctor, on the topic 'Our life style and health of kidney.'



Healthy Kidney

When kidney diseases become severe, excretory substances do not get filtered and remain in the blood. How can the lives of those suffering from kidney failure be retained? The lives of the kidney failed patients can be retained through two major methods. This includes Haemodialysis Kidney Transplantation

Haemodialysis Haemodialysis is the process of purifying blood by passing it through artificial kidney, when the kidneys become nonfunctional. A kidney can filter 100-150 quarts of blood every day. If the kidneys are not functioning properly, waste starts accumulating in the blood. This results in coma or even death. To cure this, the patient is subjected to dialysis. Dialysis maintains the body balance in the following ways:  It controls blood pressure.  It removes excess water and metabolic wastes from the body.  Prevents chemicals such as potassium, bicarbonate and sodium from reaching hazardous levels.


Dialysis is done when a person is suffering from a critical kidney disorder – grave kidney damage or previously severe renal failure. It is required when the kidney loses 90% of its efficiency and has a glomerular filtration rate of less than 15. This treatment may continue for months or years since most kidney failures are irreversible. However, dialysis is not a permanent solution; instead, it should be seen as a temporary alternative to substitute the kidney‘s function until the kidney can repair itself. Analyse illustration 5.1 and write the steps of haemodialysis in your Science diary.

Illustration 5.1 Haemodialysis


Kidney Transplantation Have you heard about kidney transplantation? When does kidney transplantation become necessary? A single healthy kidney is enough to purify blood. But, when both the kidneys of an individual get damaged completely, a fully functioning kidney should be received from a donor to save life.

Figure 5.1 Kidney transplantation Kidney of a healthy person who died in an accident or of a completely healthy person can be transplanted after considering the matching of blood groups and tissues.


 Living donors o Evaluate donors on physical, medical and psychological grounds. o Assure the patient that there will be no long term harm to donor. o Live donor procedure are mostly laproscopic, hence less painfull, less scarring and faster recovery.  Deseased donors o Brain dead (bd) donors o Donation after cardiac death  Brain dead or ―beating heart‖ donors are considered dead but the pumping heart continues to perfuse the other organs.  Donation after cardiac death is elective donation of organ by patient himself or the relatives to withdraw life support as they have slim chances of survival.

During transplantation, damaged kidneys are not removed. Instead a new kidney is connected below the nonfunctional kidney, with the recipient's renal artery and renal vein. The ureter of the transplanted kidney is attached to the urinary bladder of the recipient.


Benefits: Significantly reduced risk of mortality Life expectancy can triple Reduced risk of heart attack, stroke, heart failure Reduced infection-related hospitalization Improved quality of life More likely to stay employed. Kidney transplantation is a life extending procedure. A patient may live up to 15 years longer with a kidney transplant than if kept on a dialysis. Patients will have more energy, a less restricted diet, and fewer complications with a kidney transplant. Analyse the illustration 5.2 regarding organ donations. Organs including kidney can be donated. Collect more information and news excerpts about kidney donation and design a poster including the attitude to be shown towards kidney patients. Display it on the bulletin board.

Illustration 5.2 Organ donation


The first artificial kidney was designed by the Dutch doctor, Dr. Willem Johan Kolff.

Dr. Joseph E.Murray conducted the first kidney transplantation surgery.


LET US ASSESS 1. Can the lives of those suffering from kidney failure be retained? If yes, how? 2. Name the personality who a. Conducted the first kidney transplantation surgery. b. Designed the first artificial kidney.

EXTENDED ACTIVITIES  Perform a short play on the topics ‗Kidney donation‘ and ‗Health of kidneys‘.




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