The human digestive system performs various vital functions, including ingestion, which involves physically putting food into your mouth. Mechanical breakdown begins in the mouth, primarily through the actions of your teeth and tongue. When you swallow food, your stomach continues mechanical digestion by ripping, tearing, and crushing it.
However, on a microscopic level, it's chemical breakdown that plays a crucial role in digestion. This involves enzymes, acids, and other molecules that break down macromolecules into smaller ones, allowing them to be absorbed into the bloodstream and nourish your body.
Throughout your digestive tract, from the mouth to the large intestine, glands secrete substances such as saliva to assist in the breakdown and movement of food. Absorption occurs as your body takes in nourishing molecules into the bloodstream, while excretion involves eliminating waste from the alimentary canal, which is another term for your digestive tract or GI tract.
This tube-like structure, connected from the mouth to the anus, is composed of various parts, each with its unique function. Some parts may be more expanded, twisty, or long, but they are all connected in sequence. Accessory organs like the liver and pancreas play vital roles in digestion and will be covered later.
The journey begins with the mouth, where salivary glands release saliva to initiate chemical digestion, especially of carbohydrates through enzymes like salivary amylase. Your tongue helps with chewing and swallowing, and your teeth, while not technically bones, play a significant role in mechanical digestion.
The hard palate and soft palate contribute to the swallowing process. The soft palate, with its uvula, aids in preventing food from entering the nasal cavity during swallowing.
Now, let's delve into the anatomy of teeth. Dentin, a major component of teeth, lies beneath the enamel, which is the hardest substance in the human body. Beneath the dentin is the pulp, containing nerves and blood vessels. Teeth can have different numbers of roots and serve various functions, from cutting and tearing (incisors and canines) to grinding (molars).
Wisdom teeth, or third molars, often need to be removed when they become impacted and cause problems. The process of swallowing involves the coordinated effort of the tongue, pharyngeal muscles, soft palate, and epiglottis to move food from the mouth to the oesophagus. Peristalsis, wave-like muscular contractions, then propel the food down the oesophagus into the stomach.
In the stomach, digestion continues through mechanical churning and the release of gastric juice. Gastric pits contain gastric glands that produce hydrochloric acid and pepsinogen, which, when combined, form pepsin, aiding in protein digestion. Gastrin and ghrelin are hormones that regulate stomach function and hunger.
The stomach has four regions: the cardia, fundus, body, and pylorus, each with specific roles in digestion and storage. The pyloric sphincter controls the passage of chyme, a mixture of gastric juice and partially digested food, into the small intestine.
Moving on to the small intestine, it plays a central role in both digestion and absorption of nutrients. Its surface area is maximized by villi, finger-like projections, and microvilli, tiny structures on epithelial cells that increase absorption efficiency. Blood vessels and lacteals transport nutrients from the small intestine to the bloodstream and lymphatic system.
Finally, at the end of the small intestine (ileum), you'll find the appendix, a small, finger-like projection that can be associated with immune system function.
The term "vermiform" refers to a worm-like appearance, and the appendix does indeed resemble a small, worm-like pouch situated near the opening into the large intestine, known as the colon. It is considered a vestigial structure, a remnant from our ancestors, reduced in size and significance over time. Some theories suggest that this structure was more substantial in our ancestors who consumed raw meat, aiding in the digestion of meat and bacteria. However, as cooking became a common practice, the need for a large appendix diminished. Over millions of years, its size gradually decreased, and in the distant future, it might even disappear entirely.
When the appendix becomes infected, a condition known as appendicitis poses serious health risks. Excessive bacteria accumulation can lead to inflammation and potentially life-threatening ruptures. An appendectomy, the surgical removal of the appendix, is a common procedure since the appendix is not considered vital.
The large intestine begins near the appendix, looping around the small intestine. Its primary function is the reabsorption of water, making faeces solid. Diarrhea occurs when this process is disrupted, typically due to infections. Additionally, the large intestine absorbs some nutrients, although fewer than the stomach and small intestine. The large intestine consists of four regions: the ascending colon, transverse colon, descending colon, and sigmoid colon, ultimately leading to the rectum and anus.
The rectum, the final 15 centimetres of the digestive tract, is responsible for storing faeces before excretion. This ability to store waste evolved to allow for controlled waste elimination and territorial marking. The anus serves as the exit point for faeces, equipped with two anal sphincters. The internal anal sphincter operates involuntarily, responding to faecal accumulation, while the external anal sphincter can be consciously controlled. Haemorrhoids may develop due to the irritation of blood vessels around the rectum, often caused by hard faeces, leading to bleeding. Maintaining a high-fibre diet, proper hydration, and avoiding excessive straining during bowel movements can reduce the risk of haemorrhoids.
The liver, gallbladder, and pancreas are crucial accessory organs in digestion. The liver is the largest internal organ and performs various functions, including carbohydrate, lipid, and amino acid metabolism, glycogen storage, waste product removal, drug and hormone breakdown, phagocytosis and antigen presentation for immune support. The gallbladder stores bile produced by the liver, aiding in fat digestion. The pancreas produces digestive enzymes like amylase, lipase, nucleases, and proteases, helping break down carbohydrates, fats, DNA, RNA, and proteins.
Several digestive conditions and disorders can affect the gastrointestinal tract:
• Gastritis: An irritation or infection of the stomach lining, often treatable with antibiotics.
• Ulcers: Sores that can develop anywhere along the digestive tract; typically, H. pylori bacteria causes stomach ulcers.
• Gallstones: The buildup of bile salts in the gallbladder, leads to the formation of stones.
• Cholera: A severe infection causing massive diarrhoea and fluid loss; treatable with antibiotics and rehydration therapy.
• Hepatitis: Inflammation of the liver due to viral infections (A, B, C, D, or E).
• Jaundice: A yellowing of the skin and eyes due to excess bilirubin in the bloodstream.
• Cirrhosis: A liver disease caused by prolonged damage from toxins or alcohol abuse.
• Constipation: Difficulty passing stool due to hard and dry faeces, often alleviated with a high-fibre diet, increased water intake, and dietary changes.
• Diarrhoea: Frequent and loose bowel movements caused by infections or other factors.
• Lactose intolerance: Inability to digest lactose due to a lack of the enzyme lactase; manageable with dietary changes or lactase supplements.
• Gingivitis: Gum infection often caused by poor oral hygiene practices; preventable with regular brushing and flossing.
• Maintaining good digestive health involves a balanced diet, hydration, and proper oral hygiene, which collectively contribute to overall well-being.