Excretion is the crucial physiological process by which the body eliminates metabolic waste products, such as urea and carbon dioxide, to maintain a stable internal environment. Several organs work together in this function. The lungs are responsible for expelling carbon dioxide generated during respiration, while the skin excretes sweat, a mixture of water, salts, and urea. However, the kidneys are the primary excretory organs, filtering waste substances from the blood to produce urine. The urinary system includes the kidneys, which are connected to the urinary bladder (where urine is stored) by tubes called ureters, and urine is expelled from the body through the urethra. Within the kidneys are nephrons, the basic functional units that carry out urine formation. Nephrons perform three key steps: filtration, where blood is filtered into Bowman’s capsule; reabsorption, where necessary molecules are selectively returned to the bloodstream; and secretion, where additional waste substances are actively moved into the kidney tubules. These processes result in the formation of urine, a concentrated solution mainly composed of urea, excess salts, and water. Adequate water intake is essential for the efficient removal of metabolic wastes by the kidneys, and maintaining healthy kidneys requires sufficient hydration along with a balanced diet.
(Review Questions)
MULTIPLE CHOICE QUESTIONS :
1. Put a tick mark (✓) against the most appropriate alternative in the
following statements :
(i) The kidneys are made up of tiny tubular units called :
(a) glomerulus
(b) nephrons
(c) capillaries
(d) neurons
(ii) In human beings, urea is produced in :
(a) liver
(b) kidney
(c) spleen
(d) urinary bladder
(iii) Besides water, the urine mainly contains :
(a) urea
(b) nitric acid
(c) glucose
(d) bile pigments
(iv) Filtration of excretory wastes from the blood occurs in:
(a) collecting tubule
(b) ureter
(c) urinary bladder
(d) nephrons
Short Answer Questions
1. Fill in the blanks :
- Nitrogenous wastes in the urine are in the form of urea and uric acid.
- The unit of human kidney is called nephron.
- Evaporation of sweat from skin surface has cooling effect.
2. Define the following:
(i) Excretion:
(ii) Excretory organs :
(iii) Dialysis :
(iv) Nephron:
Ans.
(i) Excretion: The process by which organisms eliminate metabolic wastes and toxins from their bodies to maintain internal equilibrium.
(ii) Excretory organs: Specialized biological structures responsible for filtering and expelling metabolic waste products from an organism.
(iii) Dialysis: A medical procedure that artificially filters waste products and excess fluid from the blood of individuals with kidney failure.
(iv) Nephron: The fundamental functional unit of the kidney, responsible for filtering blood and producing urine through filtration, reabsorption, and secretion.
3. Write True (T) or False (F) for the following statements in the spaces provided. Rewrite the false statements in correct form.
- Removal of solid undigested food is excretion
False
Correct: Removal of solid undigested food is egestion.
- The medulla of kidney passes urine into urinary bladder.
False
Correct: Medulla of kidney passes urine into funnel-like pelvis.
- Excess sugar in blood is a symption of diabetes.
True
- Urine is devoid of blood cells.
True
4. Name the blood vessel that brings blood to the kidneys.
Ans. Renal Artery
5. Where in the urinary system do the following processes take place ?
Ans.
- Urine formation: kidneys.
- Transport of urine away from kidney: urethra.
- Temporary storage of urine : urinary bladder.
Long Answer Questions
Question 1.
Define excretion. Write the four organs of human urinary system in their correct sequence.
Ans:
(i) Excretion:
Excretion is the fundamental biological process by which living organisms remove metabolic waste products and toxic substances from their systems to preserve a balanced internal state (homeostasis).
(ii) The four components of the human urinary system, arranged in the sequence of urine flow, are:
- Kidneys: These paired organs are the primary sites of urine production, where waste materials are filtered from the bloodstream.
- Ureters: These are the tubular structures that conduct urine from each kidney to the urinary bladder.
- Urinary Bladder: This is a distensible muscular sac that functions as a temporary storage vessel for urine.
Question 2.
Why is excretion necessary in living beings ?
Ans:
Excretion is a vital process for living organisms because it eliminates harmful metabolic waste products that can poison the body. It also plays a crucial role in maintaining homeostasis, the stable internal environment necessary for proper cell function, by regulating the levels of water, salts, and pH. Without excretion, these substances would accumulate to toxic levels, disrupting essential physiological processes and ultimately leading to death. Therefore, excretion is fundamental for removing waste, maintaining internal balance, and ensuring the survival of living beings.
Question 3.
What is meant by osmoregulation ?
Ans:
Osmoregulation is the process by which living organisms actively manage the osmotic pressure of their internal fluids, ensuring a stable balance of water and solute concentrations. This regulation is vital for maintaining homeostasis, the consistent internal environment necessary for proper cellular function. Osmoregulation prevents cells from shrinking or swelling due to changes in the surrounding fluid’s concentration. Organisms use various mechanisms, often involving specialized structures and energy expenditure, to control the movement of water and salts, allowing them to thrive in diverse environments with varying water and solute availability.
Question 4.
Describe the structure of kidney with the help of a labelled diagram.
Answer:
Section through the kidney to show different regions The kidneys is composed of:
- an outer darker area called Cortex
- an inner lighter area called Medulla.
The microscopic structure of kidney is formed of millions of tubules called renal tubules or nephrons.
Question 5.
What are the two ways by which a person can get relief in case of kidney failure ?
Ans:
When kidneys fail, two primary treatments offer relief. Dialysis involves artificially filtering the blood to remove waste products and excess fluid, either through a machine (hemodialysis) or using the abdominal lining as a filter (peritoneal dialysis). The other option is a kidney transplant, where a diseased kidney is replaced with a healthy one from a donor. While a transplant can offer a more normal life, it requires lifelong immunosuppressant medication. Both dialysis and transplantation are critical interventions for individuals with end-stage renal disease.
Question 6.
Draw a diagram of human excretory system and label the following parts : Kidney, ureter, urinary bladder and urethra.
Ans:
Question 7.
How are kidney stones formed ?
Ans:
Kidney stones develop when the concentration of certain minerals and salts in urine becomes excessively high, leading to a state of supersaturation. In this concentrated environment, these substances, such as calcium, oxalate, phosphate, or uric acid, begin to form tiny crystals. If there isn’t sufficient fluid to dilute these substances, these crystals can attract more of the same material and bind together, gradually increasing in size to form a kidney stone. Factors that contribute to this process include inadequate fluid intake (dehydration), diets high in specific substances, a family history of kidney stones, certain medical conditions, and even some medications. The type of stone formed depends on the specific minerals involved in the crystallization process.
Question 8.
What are the symptoms of an urinary tract infection ?
Ans:
Urinary tract infections (UTIs) commonly present with bothersome urinary symptoms, including a burning sensation or pain during urination, an increased frequency and urgency of urination, and the passage of only small volumes of urine. The appearance and smell of urine may also change, becoming cloudy or exhibiting a strong, unpleasant odor; hematuria (blood in the urine) can also occur. Additionally, individuals may experience pain or pressure in the lower abdominal region. When a UTI ascends to involve the kidneys (pyelonephritis or upper UTI), more systemic and severe symptoms can arise, such as pain in the back or side (flank pain), elevated body temperature (fever), feelings of nausea, episodes of vomiting, and shaking chills. Prompt recognition of these symptoms is crucial for seeking appropriate medical evaluation and treatment.
