15- Human Physiology

Digestion Overview

Mechanical Digestion: The physical breakdown of food into smaller pieces through chewing and churning movements in the digestive tract.
Chemical Digestion: The biochemical process through which enzymes break down food molecules into simpler forms that can be absorbed by the body.

Breaking Down Larger Food Molecules: The digestive system's primary role is to convert large food substances into smaller, usable molecules. This is crucial for effective nutrient utilization.
Absorbing Smaller Molecules: Nutrients must be absorbed into the bloodstream to be distributed to cells and used for energy, growth, and cellular repair.

Lipids ➔ Glycerol + Fatty acids
Starch ➔ Monosaccharides (simple sugars that the body can use as energy)
Nucleic acids ➔ Nucleotides (building blocks of DNA and RNA)
Proteins ➔ Amino acids (the body utilizes these for various functions, including muscle repair and enzyme production)
Vitamins and minerals are absorbed directly without undergoing digestion, playing vital roles in metabolic processes.

Approximately 30 feet long, composed primarily of smooth muscle which aids in the process of peristalsis, rhythmic contractions that move food through the digestive tract.

Mouth: The starting point of digestion; saliva, which contains enzymes such as amylase, begins the breakdown of starches.
Pharynx: The muscular tube that connects the mouth to both the esophagus and the trachea, directing food towards the digestive system and air towards the respiratory system.
Esophagus: Transports food to the stomach via peristalsis; this section does not involve digestion but is crucial for moving food.
Stomach: The environment is highly acidic where gastric juices activate enzymes, specifically pepsinogen, to pepsin, initiating the digestion of proteins into smaller peptides.
Small Intestine: A vital location for nutrient absorption; composed of three parts: duodenum, jejunum, and ileum. It is approximately 6 meters long and operates at a pH of around 8, enabling the neutralization of stomach acids and the digestion of various nutrients.
Large Intestine: Responsible for water reabsorption, production of certain vitamins (such as vitamin K), and egestion of indigestible food materials.

Salivary Glands: Secretes saliva rich in enzymes to initiate carbohydrate digestion.
Liver: Produces bile (with a pH of 11) which emulsifies fats, detoxifies substances in the blood, recycles red blood cells, and synthesizes cholesterol.
Gallbladder: Stores bile produced by the liver; while not essential for survival, it aids in fat digestion by releasing bile into the small intestine when needed.
Pancreas: Produces important digestive enzymes (amylase, protease, and lipases) and secretes bicarbonate to neutralize the stomach acid entering the small intestine.

Defined as the removal of metabolic wastes (carbon dioxide, nitrogenous wastes) from the body.

Skin: Excretes excess water and salts through sweat glands, helping regulate body temperature and fluid balance.
Lungs: Excrete water vapor and carbon dioxide during respiration, aiding in gas exchange and maintaining acid-base balance in the blood.
Liver: A site for deamination of amino acids, converting excess proteins into urea, which is then excreted via the kidneys.
Urinary System: Composed of kidneys, ureters, bladder, and urethra, plays a crucial role in filtering blood and eliminating waste products.

Filters approximately 1500 liters of blood daily and produces roughly 1.5 liters of urine, a process vital for maintaining body fluid balance and electrolyte levels.

Components of Nephron:
- Glomerulus: Network of capillaries where blood filtration occurs.
- Proximal Convoluted Tubule: Reabsorbs nutrients, electrolytes, and water back into the bloodstream from the filtrate.
- Loop of Henle: Plays a critical role in water reabsorption; regulates concentration of urine.
- Distal Convoluted Tubule: Involved in the final modifications of filtrate, including selective reabsorption and secretion.
- Collecting Duct: Site where antidiuretic hormone (ADH) influences water reabsorption, helping the body manage hydration levels.

Controls all voluntary and involuntary actions in the body, including reflexes, muscle movements, and maintenance of homeostasis through complex signaling between various parts of the body.

Neurons are comprised of a cell body, dendrites (which receive signals), and axons (which transmit signals to other neurons or muscles).

Composed of glands that produce hormones to regulate various body functions such as metabolism, growth, and stress responses, thereby maintaining overall homeostasis.

Positive Feedback: Mechanism that enhances or amplifies changes; for example, the release of oxytocin during childbirth increases contractions and milk release.
Negative Feedback: Mechanism that counteracts changes to maintain stability; an example is the regulation of hormone levels, where high hormone levels may signal to decrease production.