Human Digestive System Overview

Study Notes

The digestive process begins in the mouth with salivary amylase breaking down food.
Salivary glands release enzymes that convert large polysaccharides into smaller ones.
Chewing increases the surface area of food for enzyme action.

The tongue shapes food into a bolus and directs it to the pharynx.
Food enters the esophagus after swallowing, with the epiglottis preventing airway blockage.
Muscle contractions in the esophagus push food into the stomach.

The stomach can hold over half a gallon of food and fluid, stretching as necessary.
Gastric juice, secreted by epithelial cells, facilitates food liquefaction and chemical breakdown.
Hydrochloric acid (HCl) in gastric juice kills bacteria and assists in food digestion.
Amylase is inactivated by HCl, maintaining only partial digestion of polysaccharides during this stage.
Pepsinogen is the inactive precursor of pepsin, activated by HCl to prevent self-digestion of cells.
Mucus secreted by epithelial cells protects them from damage by acid and enzymes.
The stomach begins churning and secreting gastric juices in response to signals from the brain.

Once food is present, gastric juice secretion increases, and the stomach thoroughly mixes food with digestive enzymes.
The pyloric sphincter controls the release of chyme into the small intestine, taking 2 to 6 hours to empty.

The small intestine, particularly the duodenum, continues digestion and nutrient absorption.
The pancreas and the small intestine produce enzymes that aid in digesting carbohydrates, proteins, and fats.
Bicarbonate neutralizes stomach acid entering the small intestine.

The jejunum absorbs sugars, amino acids, and fatty acids, aided by villi and microvilli.
The ileum absorbs bile salts and Vitamin B12 and secretes digestive enzymes.
The large intestine absorbs water and electrolytes, converting waste into stool.

Kidneys filter waste products from blood, while dialysis treats kidney failure by removing waste and balancing fluids.
The liver detoxifies harmful substances, such as converting ammonia into less toxic urea.

Nephrons in the kidneys filter blood, reabsorbing water and nutrients while concentrating waste into urine.
Urea exits the kidneys through ureters to the bladder, which signals when it is full.

The bladder stretches as it fills, sending signals to the brain, indicating the need to urinate.
Control over urination is maintained via a muscular valve at the bladder's exit, leading to the urethra.

Comprises neurons transmitting signals, processing sensory information, and controlling actions.
Divided into the central nervous system (CNS) and peripheral nervous system (PNS).
The autonomic nervous system regulates unconscious processes, while the somatic nervous system governs voluntary actions.