Explain production of urine class 10th ICSE Selina...

Urine is produced in the kidneys by tiny filtering units called nephrons. In Class 10 ICSE, urine formation is usually explained in three main steps:

1. Ultrafiltration

This happens in the Malpighian capsule, which includes the glomerulus and Bowman’s capsule.

Blood enters the glomerulus through the afferent arteriole. Since the afferent arteriole is wider than the efferent arteriole, blood is under high pressure. This pressure forces water and small dissolved substances out of the blood into Bowman’s capsule.

The filtered fluid contains:

• Water
• Glucose
• Amino acids
• Salts
• Urea

Large molecules like blood cells and plasma proteins do not pass through because they are too large.

This filtered fluid is called glomerular filtrate.

2. Selective Reabsorption

This happens mainly in the proximal convoluted tubule and other parts of the nephron.

Useful substances from the filtrate are reabsorbed back into the blood. These include:

• All glucose
• Amino acids
• Much of the water
• Required salts

This is called selective reabsorption because only useful substances are taken back into the blood.

3. Tubular Secretion

This occurs mainly in the distal convoluted tubule.

Extra waste substances are secreted from the blood into the tubule. These include:

• Excess salts
• Hydrogen ions
• Potassium ions
• Drugs and toxins

This helps maintain the proper chemical balance of the blood.

Formation of Urine

After filtration, reabsorption, and secretion, the remaining fluid becomes urine. It contains mainly:

• Water
• Urea
• Excess salts
• Other waste substances

Urine passes from the collecting duct into the renal pelvis, then through the ureter to the urinary bladder, where it is stored. Finally, it is passed out through the urethra.

Simple flow chart

Blood → Glomerulus → Bowman’s capsule → Tubule → Collecting duct → Renal pelvis → Ureter → Urinary bladder → Urethra

One-line summary

Urine is produced in the nephron by ultrafiltration of blood, selective reabsorption of useful substances, and tubular secretion of extra wastes.

Micturition means the passing out of urine from the urinary bladder through the urethra. It is also called urination.

Urine is formed in the kidneys and passes through the ureters into the urinary bladder, where it is stored for some time.

When the bladder becomes full, its walls stretch. This sends nerve impulses to the spinal cord and then to the brain. The brain gives a feeling or urge to urinate.

During micturition:

1. The muscles of the urinary bladder contract.
2. The sphincter muscles relax.
3. Urine passes out through the urethra.

In small children, micturition is mostly a reflex action. In older children and adults, it is partly under voluntary control, because we can control the external sphincter for some time.

Definition for ICSE Class 10:

Micturition is the process of expelling urine from the urinary bladder through the urethra.

Circulation — Class 10 ICSE Biology

Circulation is the movement of blood through the body. It helps in transporting useful substances to body cells and removing waste materials from them.

The circulatory system includes:

Heart → Blood vessels → Blood

Functions of Circulation

Circulation helps to transport:

• Oxygen from lungs to body cells
• Carbon dioxide from body cells to lungs
• Digested food from small intestine to body cells
• Hormones from endocrine glands to target organs
• Wastes like urea to kidneys for removal
• Heat to maintain body temperature

Human Heart

The human heart is a muscular organ located in the chest cavity. It has four chambers:

1. Right atrium
2. Right ventricle
3. Left atrium
4. Left ventricle

The right side of the heart carries deoxygenated blood, while the left side carries oxygenated blood.

Blood Vessels

There are three main types of blood vessels:

1. Arteries

Arteries carry blood away from the heart.

Most arteries carry oxygenated blood, except the pulmonary artery, which carries deoxygenated blood from the heart to the lungs.

2. Veins

Veins carry blood towards the heart.

Most veins carry deoxygenated blood, except the pulmonary vein, which carries oxygenated blood from the lungs to the heart.

3. Capillaries

Capillaries are very thin blood vessels. They connect arteries and veins and allow exchange of materials between blood and body cells.

Double Circulation

Human beings have double circulation, which means blood passes through the heart twice during one complete round of circulation.

It has two parts:

1. Pulmonary Circulation

This is circulation between the heart and lungs.

Right ventricle → Pulmonary artery → Lungs → Pulmonary vein → Left atrium

In the lungs, blood gives out carbon dioxide and takes in oxygen.

2. Systemic Circulation

This is circulation between the heart and the rest of the body.

Left ventricle → Aorta → Body parts → Vena cava → Right atrium

Oxygenated blood is supplied to body cells, and deoxygenated blood returns to the heart.

Flow of Blood Through the Heart

Body → Vena cava → Right atrium → Right ventricle → Pulmonary artery → Lungs → Pulmonary vein → Left atrium → Left ventricle → Aorta → Body

Importance of Double Circulation

Double circulation is important because:

• Oxygenated and deoxygenated blood remain separate.
• Body cells receive oxygen-rich blood.
• It helps maintain high blood pressure for efficient circulation.
• It supports the high energy needs of humans.

Definition for ICSE

Circulation is the continuous movement of blood through the heart and blood vessels to transport materials throughout the body.

Human Heart — Class 10 ICSE Biology

The human heart is a muscular organ that pumps blood throughout the body. It is the main organ of the circulatory system.

Location

The heart is located in the thoracic cavity, between the two lungs. It is slightly tilted towards the left side.

It is protected by a double-layered membrane called the pericardium. The fluid between the layers reduces friction during heartbeat.

Structure of Human Heart

The human heart has four chambers:

1. Right auricle / right atrium
2. Right ventricle
3. Left auricle / left atrium
4. Left ventricle

The upper chambers are called auricles or atria.
The lower chambers are called ventricles.

Right Side and Left Side

The right side of the heart receives and pumps deoxygenated blood.

The left side of the heart receives and pumps oxygenated blood.

The two sides are separated by a muscular wall called the septum. This prevents mixing of oxygenated and deoxygenated blood.

Valves of the Heart

Valves prevent the backflow of blood.

Main valves:

Tricuspid valve: Between right atrium and right ventricle.

Bicuspid / mitral valve: Between left atrium and left ventricle.

Semilunar valves: Present at the openings of the pulmonary artery and aorta.

Major Blood Vessels

Vena cava brings deoxygenated blood from the body to the right atrium.

Pulmonary artery carries deoxygenated blood from the right ventricle to the lungs.

Pulmonary veins bring oxygenated blood from the lungs to the left atrium.

Aorta carries oxygenated blood from the left ventricle to the whole body.

Flow of Blood Through the Heart

Body → Vena cava → Right atrium → Right ventricle → Pulmonary artery → Lungs → Pulmonary veins → Left atrium → Left ventricle → Aorta → Body

Working of the Heart

The heart works by rhythmic contraction and relaxation.

When the heart muscles contract, blood is pumped out. This is called systole.

When the heart muscles relax, chambers fill with blood. This is called diastole.

One complete contraction and relaxation of the heart is called a heartbeat.

Importance of the Heart

The heart:

• Pumps oxygenated blood to all body cells
• Sends deoxygenated blood to lungs for purification
• Maintains continuous circulation
• Helps transport food, oxygen, hormones and wastes

Definition for ICSE

The human heart is a four-chambered muscular organ that pumps blood throughout the body and maintains circulation.