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Human Anatomy and Physiology

Digestion Process

The process of digestion occurs in the digestive system. This process is the source of energy for all living creatures. Digestion involves the breakdown of large junks of food into small molecules that can be absorbed into the system.

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The process occurs in three key steps. These are Ingestion, Digestion, and Absorption.


This process occurs when food is put in the mouth. It is chewed and mixed with amylase enzymes found in saliva. Starch is digested in the mouth. Food clumps known as boluses are formed and swallowed through peristalsis via the esophagus and get into the stomach. Peristalses are contractions that help the food boluses to move into the stomach via the esophagus. Reflex action dictates that the epiglottis will close the trachea. This action prevents food from entering the windpipe.


This occurs in the stomach which produces gastric enzymes. Food is churned and mixed with these enzymes. The mixture produced is called chyme (Turley, 2007). Protein digestion is done here. They are broken into amino acids ready for absorption.

The liver is the one that is responsible for bile production. The bile is stored in the gall bladder. It is transported to the duodenum through a duct. The liver cleans the blood from the small intestines through a process called detoxification. Detoxification of substances like Ammonia occurs in the liver.

The chyme leaves the stomach into the duodenum. Pancreatic enzymes (amylase, trypsin, and chymotrypsin, lipase) and bile released from the liver act on chyme. Bile emulsifies the fats. Amylase breaks down starch into maltose. Trypsin and chymotrypsin break the large proteins into smaller compounds: amino acids. Lipase acts on fats to produce fatty acids.

In the Duodenum

The chyme leaves the stomach into the duodenum. Pancreatic enzymes (amylase, trypsin, and chymotrypsin, lipase) and bile released from the liver act on chyme. Bile emulsifies the fats. Amylase breaks down starch into maltose. Trypsin and chymotrypsin break the large proteins into smaller compounds: amino acids. Lipase acts on fats to produce fatty acids.

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The digestion process occurs with the help of hormones like gastrin, cholecystokinin (CCK), and gastric inhibitory peptide and secretin. Gastrin triggers the release of gastric juice in the stomach (Turley, 2007).

Secretin is responsible for triggering the liver to release bile. CCK triggers the release of bile by the gall bladder. It also triggers the production of pancreatic juice by the pancreas.

The Gastric Inhibitory Peptide is responsible for the blocking of the production of gastric juice by the gastric glands. This leads to the stoppage of the process of churning that is done by the muscles of the stomach.


Absorption occurs in the small intestines. It is about 3 meters in length. It has absorption surfaces lined villi and microvilli (Marieb, 2008). These are finger-like projections that increase the surface area of absorption. Beneath the villi, there is a lymph vessel to absorb lymph. The other is a blood vessel to absorb the amino acids and glucose. These processes occur through active transport. Fatty acids are absorbed into the blood system through diffusion.

The undigested food-like fiber moves into the colon after which it is excreted through the anus. Water is reabsorbed into the body through the colon. Sodium ions and Vitamin K are also absorbed here.

Respiration Process

Oxygen is the most essential gas in the human body. It helps to break down food molecules to produce energy through oxidation. This process occurs in three key steps. These are External, Internal, and Cellular.

External Respiration

This is the physical respiration process. Air moves into the lungs through the inspiration process. After the gas exchange, carbon dioxide is expelled through the process of expiration.

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Air is transported moves into the body through the nose. It is transported via the trachea into the bronchi and bronchioles. The air is cleaned through ciliary action by the mucus and cilia found in the bronchioles (Marieb, 2008). At the same time, it is warmed. At the alveoli, oxygen is absorbed into the underlying blood capillaries while carbon dioxide diffuses to the outside of the blood capillaries.

Internal Respiration

Gases are transported to all parts of the body by the red blood cells. The component responsible for gas transport in red blood cells is known as hemoglobin. At the respiratory surfaces of tissues and cells, oxygen is released by the red blood cells.

Cellular Respiration

This takes place within the cell. Cellular respiration occurs in the cell’s mitochondria. Food substrates are broken down to release energy with the help of enzymes and oxygen. There are two kinds of respiration. This depends on the oxygen levels or concentration.

The first kind, aerobic respiration occurs utilizes oxygen. Glucose is broken down through glycolysis to produce water and energy in the form of Adenosine tr-phosphate or ATP. The gas that is produced in this reaction is carbon dioxide. On the contrary, anaerobic respiration takes place in a complete lack of oxygen. The end products of this kind of respiration are alcohol and acids. This process produces less energy.

In the glycolysis process, glucose is oxidized to form pyruvic acid. This pyruvic acid is the fuel that drives the Kreb cycle. The by-products of the Kreb cycle are the ones that will be utilized in the Electron Transport System. This process utilizes oxygen (Marieb & Hoehn, 2008).

Blood Circulation

The main organ in blood circulation is the heart. This organ is very powerful and muscular and is responsible for pumping blood so that it can reach all organs. It is located on the left-hand side of the ribs just behind the left lung. It pumps every second to ensure that the body is supplied with fresh oxygenated blood. It also ensures that waste products of respiration like carbon dioxide are removed from the blood. The circulatory process occurs through the help of blood vessels.

Circulatory Organs

The other organs that support it are blood vessels and cells. The blood vessels are the veins, the arteries, and the blood capillaries. The cells involved are the red and the white blood cells. Blood is red. It is made up of water, plasma, and cells. It has got a sticky texture. Blood that has a high concentration of oxygen is scarlet red in color. Blood that has high levels of carbon dioxide is dark red. Blood contains red and white blood cells. The red blood cells are the ones that are responsible for transporting oxygen and carbon dioxide throughout the body. This is because they contain a hemoglobin component that binds oxygen and carbon dioxide making them be able to transport it. The white blood cells play a role in safeguarding the body against attacks by diseases (Marieb, & Hoehn, 2009).

Blood Vessels

Arteries transport blood from the heart to other organs. They have a smaller lumen when compared to veins. They transport blood under high pressure. They are located deep in the body. On the contrary, veins transport blood to the heart. They transport blood under low pressure. The small veins are known as venules.

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Blood Circulation from the Heart

The heart can be divided into four halves. It has got the right and left atrium. The other one is the right and the left ventricle. Blood from the body is collected from the smallest organs by capillaries. The capillaries release the blood into the veins. The superior and inferior venacava transport blood to the heart. They release it into the right atrium. It moves via the tricuspid valve into the right ventricle. From here it moves into the pulmonary artery. It is then transported to the lungs for the removal of carbon dioxide and the addition of oxygen. After the blood takes up oxygen it is then transported by the pulmonary vein from the lungs to the heart. The blood from the pulmonary vein is emptied into the left atrium. It moves into the left ventricle through the bicuspid valve. From the left ventricle, blood moves into the aorta. This is the biggest artery in the human body. It is then transported to all parts of the body.

Blood Circulation

After leaving the aorta, the arteries divide to form smaller arteries. These are known as arterioles. Blood from the arterioles diffuses into the body via capillaries which are microscopic. At the capillary level, oxygen and glucose are released into the boy cells. They diffuse from the surface into the cells. At the same time, carbon dioxide and the by-products of respiration are released into the bloodstream. The veins carry the by-products of respiration and carbon products back to the heart where the cycle will begin once again.

The lymphatic system

The other circulation system is the lymphatic system. It ensures that lymph which is a plasma-like substance is circulated to all lymph nodes and parts of the body (Sanders & Scanlon, 2006).


Marieb. E.N. (2008). Anatomy & Physiology Coloring Workbook: A Complete Study Guide. 9 th Ed. San Francisco: CA, Pearson Benjamin Cummings.

Marieb, & Hoehn, K.(2009). Human Anatomy and Physiology with Interactive Physiology 10-System Suite. 8th ed. Benjamin Cummings.

Sanders, T. & Scanlon, V. C. (2006). Essentials of Anatomy and Physiology.

Turley, M. S. (2007). Medical Language: Immerse Yourself. New York: NY, Pearson; Prentice Hall.

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