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Lesson Note

Subject: Biology
Topic: Regulations of Internal Environment
Subtopic: Homeostasis (The Kidney)

Lesson Objectives: At the end of the lesson, learners should be able to:

Lesson Summary/Discussion


Structure of the Kidney

The kidneys are one of the organs of the body which perform various functions such as osmoregulation, excretion, maintenance of acid-base balance etc.
The kidneys are reddish-brown in colour and bean-shape. They are found in vertebrate animals. They are located on the left and right in the retroperitoneal space, and in adult humans are about 12 centimetres (4+1⁄2 inches) in adults. They receive blood from the paired renal arteries; blood exits into the paired renal veins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder. They are located just below the rib cage.

Diagram of the kidney

Functions of the kidneys
The kidneys perform a number of functions among which are:
1. Osmoregulation
Meaning: Osmoregulation is defined as the process whereby an animal regulates the balance between water and salts in its body fluids. The
body does not have room for excess or shortage of water or salt, hence the need to always maintain their levels in the body fluid.

The kidneys carry out osmoregulation in man. When the osmotic concentration of blood is higher than that of the cell content by means of
sugar, mineral salts, amino acids and other plasma solutes, the kidneys extract these substances from the blood or body cells and absorb more water. When these substances are
present in small amount in the blood, it creates higher osmotic pressure in the body cells, thus decreasing the osmotic concentration of blood and the kidneys extract more water than usual. By the action of Anti-Diuretic Hormone (ADH), more concentrated urine is produced thus keeping the osmotic concentration of blood and
cells fairly constant, Osmoregulation in man, especially loss of water, it also carried out through.
Sweating by skin and expiration or exhalation by the lungs.

2. Excretion: The kidneys are also involved in the removal of metabolic waste products from the body in form of urine. The process involved in the formation of urine occurs in three phases which are (i) ultra-filtration, (ii) selective reabsorption and (iii) hormonal secretion. Blood is brought to the kidneys by renal artery. As it circulates through the capillaries or
glomerulus of each Bowman’s capsule, water, urea, nitrogenous compounds, mineral salts sugar, glucose and plasma solutes are filtered into the capsule. This process of filtering materials from the glomerulus into the Bowman’s
capsule is called ultra filtration.

The fluid in the capsule or glomerular filtrate now flows down the tubule. At the proximal convoluted tubule and Henle’s loop, some water, sugar, amino acid and salts which are useful to the body are reabsorbed into the blood capillaries against concentration gradient by active transport. This process of reabsorbing useful materials back into the blood is called selective reabsorption.

The fluid in the tubule becomes more
Concentrated as it flows through the distal tubule.
Where more water is reabsorbed by the action of Anti-diuretic hormone (ADH) and urine if finally formed.
The urine gradually trickles into the renal pelvis and is propelled by peristalsis through the ureter into the urinary bladder. When the bladder is full,it contracts, discharging the urine out of the body through the urethra.

3. Maintenance of acid-base balance:
The kidneys also maintain the acid-base balance in the body. When the body fluids becomes acidic that is, the concentration of the acids becomes more than the concentration of the, more acid is excreted by the kidneys with the urine. Excessive loss of bases is prevented at the same time by the kidneys. If the concentration of a base becomes higher, more salts will be excreted with the urines stass
Conditions Affecting the Functioning of the Kidneys.
There are different conditions of factors that affect the functioning of the kidneys. These include environmental temperature, drugs,
habitats and diseases.

a. Environmental Temperature:
Temperalure affects the functioning of the kidneys. On cold days, there is every tendency to urinate more than we do on hot days. On hot days, much water is lost by sweating. But on cold days, very little or no water is lost by
Sweating, hence more of the excess water in the body is lost through the kidneys. Under this condition, the kidneys are under stress as they have to remove excess water, salts and other waste products from the body.
b. Drugs: Most drugs taken by human
beings do affect the functioning of the kidneys.
Among the essential drugs which affect the kidneys are diuretics. These are usually taken to get rid of excess water out of the body.

c. Habitats: Habitats, especially aquatic habitats, do affcct the functioning ofthe kidneys. In fresh water habitats, the animals live in an environment which is hypotonic to their body fluid, i.e. body fluid is more concentrated than its water environment. Asa result, fresh water
animals experience a constant inflow of water into their body. The fresh water animals are able to solve this problem of excessive intake ofwater
by excreting salts and other nitrogenous wastes through the urine, thereby maintaining a normal salt and water balance in the body.

In marine habitats, the animals live in an environment which is hypertonic to their body fluid, i.e. the body fluid is less concentrated than its water environment. As a result, the marine
animals experience constant outflow or loss of it body water to the surrounding saline or salty water. These marine animals are able to solve this excessive loss of water by either the reabsorption of urea back into the blood thereby leading to an increase in body salts and making
the body fluid to have high concentration, or they drink plenty of salt water so that the concentration of blood fluid is raised.
4. Diseases: Diseases such as nephritis, kidney stones, diuresis, dropsy, etc. can affect the normal functioning of the kidneys.

Diseases of the kidneys
I. Diuresis: Diuresis is a condition in which the cells of the kidney tubules are not reabsorbing water from the glomerular filtrate and as a result, a large amount of water is passed out in urine. Diuresis can also occur from a
patient suffering from diabetes insipidus-a condition in which the production of ADH (Anti-diuretic hormone) becomes reduced. Less water is reabsorbed and the patient produces a lot of urine-about 5- 20 1litres a day.
Effects of Diuresis: It leads to excretion of large anmount of uine.
Diuresis leads to loss of weight. no
It also leads to emaciation.

There is high thirst for a lot of wate.
Remedy wolt.
Surgical operation should be performed on the patient. Drugs such as diuretics should be administered to get rid of excess water in the body.

II. Dropsy or Oedema: Dropsy is a
condition in which the cells of Bowman’s capsules are unable to absorb water from the blood in the tubules. As a result, a lot of water is retained in the blood or tissue. This leads to the swelling of some parts of the body such as the face and ankles.

Effects of Oedema:

  • It leads to swelling in faces and ankles.
  • It causes sluggishness.
  • It leads to abdominal pain.
  • There is constant weakness or fatigue.


  • The patient should seek medical treatment from specialist doctor.
  • Kidney transplant can be performed if the condition is critical.

2. Nephritis: Nephritis is a condition in which the blood vessels in Bowman’s capsule (glomerular) becomes inflamed and porousas a result of which they cannot carry out the function ofultra-filtration completely. This will result in the passage of most of the useful materials in the blood fluid with urine. Nephritis can also be caused by bacterial infection.
Effects of Nephritis:

  • Inflammation of the kidney
  • Presence ofamino acids in urine
  • Weakness of the body
  • Fever and Pains


  • Use of dialysis -an artificial kidney can be adopted to take over the work of nomal kidney.
  • Kidney transplant- The diseased kidneycan be replaced with a healthy one.
  • Use of antibiotics Antibiotics can be used especially if the disease is caused by bacteria.

3. Kidney Stones: Kidney stones are
caused by some discased growths within the tubules. These diseased growths may narrow urine passage, thus reducing free flow of urine,
In most cases, the diseased growths may block the urine passages making the removal of urine extremely difficult.
Effects of Kidney Stones:

  • It obstructs the passage of urine.
  • Pain is experienced on passing out urine.
  • Severe abdominal pain is experienced.
  • It leads to high blood pressure, fever, chills, blood in urine.


  • Surgery called nephrectomy can be perfomed. This involves the opening up of the kidney to remove the stones.
  • Patient should avoid excess intake of calcum.
  • A lot of water should be taken.
  • There should be reduction in protein intake.

Done studying? See previous lessons in Biology

Lesson Evaluation / Test

  1. Describes the structure of the kidney using diagram.
  • List and explain three major functions of the kidney.
  • Mention any three diseases of the kidney, their effects and remedies.
  • Mention and explain three factors that affects the functioning of the kidney.

Questions answered correctly? Bravo!

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