Digestive & Respiratory Systems: Anatomy, Functions & Diseases

Posted on Oct 7, 2024 in Biology

Digestive System

Gastrointestinal Tract

The gastrointestinal tract is a long tube that extends from the mouth to the anus. It’s responsible for the digestion and absorption of food.

Parts of the Digestive System:

Oral Cavity (Mouth)
  • Salivation: Saliva contains amylase (breaks down complex carbohydrates), lysozyme (kills bacteria), and mucin (lubricates food).
  • Chewing: Mechanically breaks down food into smaller pieces.
  • Swallowing: Chewed food mixed with saliva (bolus) is pushed by the tongue to the pharynx and then into the esophagus via the epiglottis.
  • Peristaltic Movements: Muscle contractions that move food through the digestive tract.
Pharynx and Esophagus
  • The esophagus connects the pharynx to the stomach.
  • The cardia is the entrance to the stomach and prevents reflux.
  • The stomach lining (mucosa) protects it from the acidic environment.
Stomach
  • The stomach contains gastric juice with pepsin (digests proteins) and hydrochloric acid (kills bacteria and activates pepsin).
  • After about 3 hours, the bolus becomes chyme.
  • The pylorus (a valve) controls the release of chyme into the small intestine.
Small Intestine
  • Approximately 7 meters long and divided into three sections: duodenum, jejunum, and ileum.
  • Bile: Produced by the liver and stored in the gallbladder; bile salts help break down fats.
  • Pancreatic Juice: Contains sodium bicarbonate (neutralizes stomach acid) and enzymes like trypsin (digests proteins).
  • Intestinal Juice: Secreted by the mucosa; contains enzymes to complete chemical digestion.
  • Chyle: Mixture of chyme and digestive secretions.
  • Absorption: The small intestine has villi and microvilli to increase surface area for absorption. Lacteals (lymphatic capillaries) absorb fats.
Large Intestine
  • Approximately 1.5 meters long and divided into three sections: cecum, colon, and rectum.
  • Cecum: End of the small intestine; connects to the appendix.
  • Colon: Absorbs water and mineral salts; contains symbiotic bacteria (microbiota).
  • Rectum: Stores feces before elimination through the anus.
  • Ileocecal Valve: Prevents backflow from the large intestine to the small intestine.
  • Peristaltic Movements: Move feces through the large intestine and trigger defecation.

Accessory Glands

  • Salivary Glands: Three pairs of glands that produce saliva.
  • Liver: Large organ in the upper abdomen; produces bile, stores glucose, and detoxifies the blood.
  • Pancreas: Produces pancreatic juice and hormones like insulin and glucagon (regulate blood sugar levels).

Processes of the Digestive System

  • Ingestion: Intake of food.
  • Digestion:
    • Mechanical Digestion: Chewing and mixing of food.
    • Chemical Digestion: Breakdown of complex molecules into simpler ones by enzymes.
  • Absorption: Uptake of nutrients into the bloodstream.
  • Egestion: Elimination of undigested waste (feces).
  • Secretion: Release of substances (e.g., enzymes, hormones) for specific functions.

Respiratory System

The respiratory system is responsible for taking in oxygen and releasing carbon dioxide.

Parts of the Respiratory System

Nasal Cavity

  • Air enters through the nostrils.
  • Respiratory Epithelium: Warms and humidifies the air.
  • Olfactory Epithelium: Provides the sense of smell; connected to sinuses.

Pharynx

  • Tonsils: Part of the immune system.

Larynx

  • Contains the epiglottis (prevents food from entering the trachea) and vocal cords.

Trachea

  • About 12 cm long tube supported by cartilaginous rings.
  • Produces mucus to trap particles, and cilia move mucus and trapped particles out of the respiratory tract.

Bronchi

  • Two tubes that branch from the trachea into the lungs.
  • Bronchi further divide into smaller tubes called bronchioles.

Alveoli

  • Tiny air sacs at the end of bronchioles.
  • Surrounded by capillaries (blood vessels) for gas exchange.

Lungs

  • Two large, spongy organs containing the bronchi, bronchioles, and alveoli.
  • Protected by a membrane called the pleura.
  • The right lung has three lobes, and the left lung has two lobes.

Diaphragm

  • A sheet of muscle responsible for breathing.

Processes of the Respiratory System

Inhalation

  • Diaphragm contracts and moves downward.
  • Intercostal muscles (between ribs) contract and lift the rib cage.
  • Lungs expand, and air enters.

Gas Exchange

  • Oxygen from the alveoli diffuses into the blood in the capillaries.
  • Carbon dioxide from the blood diffuses into the alveoli.

Exhalation

  • Diaphragm relaxes and moves upward.
  • Intercostal muscles relax, and the rib cage moves downward.
  • Lungs contract, and air is expelled.

Diseases of the Digestive System

  • Caries (Tooth Decay): Destruction of tooth enamel by bacteria.
  • Gastroesophageal Reflux Disease (GERD): Incompetent cardia allows stomach acid to flow back into the esophagus, causing heartburn.
  • Gingivitis: Inflammation of the gums.
  • Gastric Ulcers: Damage to the stomach lining, often caused by bacteria or NSAID use.
  • Appendicitis: Inflammation of the appendix.
  • Colon Cancer: Uncontrolled growth of cells in the colon.
  • Diverticulosis: Formation of small pouches (diverticula) in the colon wall.
  • Gastroenteritis: Inflammation of the stomach and intestines, often caused by infection.
  • Diarrhea: Loose, watery stools due to insufficient water absorption in the large intestine.
  • Cholera: Severe diarrhea caused by bacterial infection.
  • Constipation: Infrequent or difficult bowel movements.
  • Hepatitis: Inflammation of the liver, often caused by viral infection or alcohol abuse.
  • Cirrhosis: Scarring of the liver, often caused by chronic alcohol abuse or hepatitis.
  • Gallstones: Hardened deposits in the gallbladder.

Diseases of the Respiratory System

  • Nasal Catarrh (Common Cold): Viral infection of the upper respiratory tract.
  • Sinusitis: Inflammation of the sinuses.
  • Pharyngitis: Inflammation of the pharynx (sore throat).
  • Tonsillitis: Inflammation of the tonsils.
  • Laryngitis: Inflammation of the larynx, often causing hoarseness or loss of voice.
  • Bronchitis: Inflammation of the bronchi, often caused by infection or irritants.
  • Pneumonia: Infection of the lungs.
  • Influenza (Flu): Viral infection of the respiratory system.
  • COVID-19: Viral respiratory illness caused by the SARS-CoV-2 virus.
  • Asthma: Chronic respiratory disease characterized by inflammation and narrowing of the airways.
  • Pleurisy: Inflammation of the pleura.
  • Chronic Obstructive Pulmonary Disease (COPD): Progressive lung disease that makes it difficult to breathe, often caused by smoking. Includes emphysema (damaged alveoli) and chronic bronchitis (inflammation of the bronchi).
  • Lung Cancer: Uncontrolled growth of cells in the lungs, often caused by smoking.