Anatomy & Physiology

Anatomy & Physiology Study Guide released into the interstitial fluid for transport to the general circulation by way of the lymphatic system. • Protein digestion involves a low pH (which destroys tertiary and quaternary structure), the gastric enzyme pepsin, and various pancreatic proteases. Peptidases free the amino acids that are absorbed and exported to interstitial fluid. • Humans ingest approximately 2000 mL of water each day, and their digestive secretions create about another 7000 mL. Nearly all of this water gets reabsorbed by osmosis. • Various processes, including diffusion, cotransport, and carrier-mediated and active transport, are responsible for the movements of cations (sodium, calcium, potassium, and so on) and anions (chloride, iodide, bicarbonate, and so on) into epithelial cells. • The water-soluble vitamins (except B12) diffuse readily across the digestive epithelium. Fat- soluble vitamins are enclosed within fat droplets and absorbed with the products of lipid digestion. Many age-related changes affect digestion and absorption: • Age-related changes include a thinner and more fragile epithelium due to a reduction in epithelial stem cell divisions, weaker peristaltic contractions as smooth muscle tone decreases, the effects of cumulative damage, increased cancer rates, and increased dehydration. The digestive system is extensively integrated with other body systems: • The digestive system has extensive anatomical and physiological connections to the nervous, endocrine, cardiovascular, and lymphatic systems.

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