The Interdependency of the Digestive System, Respiratory System, and Cardiovascular Systems
In the supply, of nutrients and the removal of waste products in the human system, four organ system are involved; the digestive system, the circulatory system, respiratory system and excretory system. The digestive system comprises of the mouth, stomach, small intestine and the liver.
The digestion of the carbohydrate begins in the mouth. The predominant carbohydrate is the starch. In the mouth, enzyme salivary amylase hydrolyses the starch to disaccharides and trisaccharide. The remaining starch from the mouth is taken to the duodenum, the upper chamber of the small intestine where it is hydrolyzed by enzyme pancreatic amylase. The enzymes located in the intestinal epithelium breaks the disaccharides and the trisaccharide into monosaccharide (simple sugar). Enzyme maltase breaks maltose into glucose, enzyme sucrose breaks sucrose into glucose and fructose and enzyme lactase breaks lactose into glucose and galactose. The monosaccharide is absorbed into the intestinal epithelium through diffusion, and active transport, and they are secreted into the interstitial fluid and enter the capillaries (Starr and McMillan 2010).
The larger protein complexes are first broken down into smaller particles by the teeth (McMillan 2010). The hydrochloric acid in the stomach keeps the pH at the required standard for enzyme pepsin and enzyme renin. It also breaks down the plant cell walls and connective tissues of animal food substances. Enzyme pepsin breaks down larger polypeptides to smaller ones, and in the small intestine, the surface of epithelium contains enzyme trypsin that further breaks down polypeptides into amino acids. The individual amino acids are absorbed into the intestinal epithelium through active transport by the use of carriers (McMillan 2010).
Fats are majorly consumed in the form of triglycerides. The digestion begins in the mouth, and the process continues in the small intestine by the action of enzyme lipase. The bile salt is secreted by the liver and it helps in breaking up large lipid droplets into small lipid droplets through the process of emulsification. In the small intestine, the lipids are converted into fatty acids and monoglycerides. The particles are absorbed into the lymphatic vessels, and they travel thoracic duct and enter the circulation.
After the digested food enters the capillaries, they eventually drain into the hepatic portal vein, which empties into the sinusoidal capillaries in the liver. The circulation is referred to as the hepatic portal system. The blood in the hepatic portal vein is oxygenated and contains nutrients absorbed from the gut, which it carries to the liver for storage, metabolism conversion or excretion (McMillan 2010). The nutrients are transported to the rest of the body by the blood. The nutrients enter the capillaries after which they enter the body cells through the process of diffusion and active transport. In cases where the particles are big, the process of phagocytosis also referred to as cell eating, is used.
The respiratory system
The first phase of respiration involves breathing. The exchange of respiratory gases occurs between the blood and tissues in the lungs. The oxygen inhaled diffuses in the blood capillaries after which, it incorporates with hemoglobin. Hemoglobin helps in transporting the oxygen to the body cells. The oxygenated blood leaves the lung and enters the heart through pulmonary vein. The blood is then pumped to the rest of the body. The oxygen detaches itself from hemoglobin, and it diffuses into the body cells (McMillan 2010).
The urinary system
It consists of the kidney, ureter, bladder, sphincter and urethra. Renal artery carries blood that contains urea water and other wastes to the kidney for purification. The blood flows through the nephron and the urine forms through the processes: filtration, reabsorption and secretion. The blood pressure forces water and solutes through spaces between the cells for reabsorption. The urine formed, flows from the kidney to the bladder via the ureters.
The flow chart of the absorption of carbohydrates, proteins and lipids
Starr, C. and McMillan, B. (2010). Human Biology. Belmont, CA: Lachina publishing