1. The Muscular System

Muscles play a crucial role in body movements, posture, and various involuntary functions. The human body has over 600 muscles, contributing about 40% of body weight.

Types of Muscles

1. Skeletal Muscles (Voluntary Muscles)
   • Attached to bones and responsible for movement.
   • Examples: Muscles in arms and legs.
   • They hold the skeleton together and provide body shape.
2. Cardiac Muscles (Heart Muscles)
   • Found only in the heart.
   • Involuntary in function.
   • They enable continuous heart contractions at about 70 beats per minute.
3. Smooth Muscles (Involuntary Muscles)
   • Present in internal organs like the stomach, intestine, and blood vessels.
   • Responsible for involuntary movements like digestion and circulation.

Functions of Muscles

• Muscles work in pairs: one contracts while the other relaxes.
• Examples:
  • Biceps and triceps: Biceps contract when the arm is bent, while triceps relax.
  • Facial muscles: Help in expressing emotions like happiness and sadness.
• Exercise strengthens muscles, improves blood circulation, and enhances oxygen supply.

Importance of a Healthy Muscular System

• A diet rich in proteins and carbohydrates is essential for muscle growth and repair.
• Poor posture and lack of exercise can lead to muscle pain and vertebral column disorders.

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2. The Digestive System

Digestion is the process of breaking down food into a soluble form for absorption into the blood. The digestive system includes the alimentary canal (about 9 meters long) and digestive glands.

Major Organs and Functions

1. Mouth
   • Digestion begins here.
   • Teeth types: Incisors, canines, premolars, molars (each with specific functions).
   • Saliva (contains ptyalin) helps break down starch into maltose.
2. Oesophagus
   • A muscular tube that pushes food from the pharynx to the stomach.
3. Stomach
   • Secretes gastric juice, which contains:
     • Hydrochloric acid (HCl): Makes food acidic.
     • Pepsin: Helps break down proteins.
     • Mucus: Protects the stomach lining.
4. Small Intestine
   • 6 meters long.
   • Digestion and nutrient absorption occur here.
   • Digestive juices from liver, pancreas, and intestinal glands help in digestion.
5. Large Intestine
   • 1.5 meters long.
   • Absorbs water and removes undigested waste.
6. Liver
   • The largest gland in the body.
   • Secretes bile, which helps digest fats.
   • Stores glucose and removes toxins.
7. Pancreas
   • Secretes pancreatic juice containing:
     • Trypsin (digests proteins).
     • Lipase (digests fats).
     • Amylase (breaks down carbohydrates).

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3. Effects of Tobacco, Alcohol, and Smoking on the Digestive System

• Chewing tobacco and smoking can lead to:
  • Inflammation of the mouth, pharynx, and intestine.
  • Damage to teeth and gums.
  • Increased risk of cancer.

4. Important Glands and Their Functions

Organ	Gland	Secretion	Function
Mouth	Salivary glands	Ptyalin	Converts starch into maltose
Stomach	Gastric wall	HCl, Pepsin, Mucus	HCl makes food acidic, Pepsin breaks down proteins, Mucus protects the stomach
Liver	Liver	Bile	Helps digest fats
Pancreas	Pancreas	Pancreatic juice	Converts proteins, fats, and carbohydrates into simpler forms

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Exercises:

Q1. Fill in the blanks with the right wordfrom the brackets.

(a) The process of digestion starts fromthe ………….. . (stomach / mouth)

(b) Eyelids have ………………. muscles (voluntary / involuntary) .

(c) ……………. is not a function of themuscular system. (Production of blood cells / Performing movements)

(d) Muscles of the heart are ……………. (ordinary muscles / cardiac muscles)

(e) Pushing forward the food that has beenchewed is the function of the ………… . (stomach / oesophagus).

ANSWERS: Fill in the Blanks

1. The process of digestion starts from the mouth.
2. Eyelids have involuntary muscles.
3. Production of blood cells is not a function of the muscular system.
4. Muscles of the heart are cardiac muscles.
5. Pushing forward the food is the function of the oesophagus.

Q2. Match the Following

Group A	Group B
Cardiac muscles	We never feel tired
Muscles	Always function in pairs
Pepsin	Enzyme of gastric juice
Cramps	Uncontrolled, painful muscle contractions
Skeletal muscles	Chewing movements of jaws

Q3. Who is Telling a Lie?

Organ	False Statement
Tongue	My taste buds can only detect sweet taste.
Large Intestine	I am 7.5 meters long. (False, it’s 1.5 meters long)
Appendix	Digestion is impossible without me.
Lungs	I play an important role in digestion.

Q4. Give Reasons

1. Food becomes acidic in the stomach to help digest proteins with pepsin.
2. Cardiac muscles are involuntary as they work automatically without conscious control.
3. Intoxicating substances harm the digestive system and can cause diseases.
4. Strong muscles help maintain posture and movement.

Q5. Answer the Following

1. Types of Muscles:
   • Skeletal muscles (Voluntary)
   • Cardiac muscles (Involuntary)
   • Smooth muscles (Involuntary)
2. Acidity is caused by excess secretion of HCl in the stomach, leading to burning sensation and discomfort.
3. Types of Teeth and Functions:
   • Incisors: Cutting food.
   • Canines: Tearing food.
   • Premolars & Molars: Grinding food.

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