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Human Anatomy Lesson (2018)

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Harvey Mudd College
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The heart has four chambers and many valves. Additionally, it has blood vessels which brings blood to the heart and those which take blood away from the heart. Some of the blood vessels include vena cava, pulmonary artery, pulmonary vein, and aorta.

To perform this function, the heart has many adaptations. First, it is divided into four chambers; left atrium, left ventricle, right atrium, and right ventricle (Rosdahl and Kowalski 2008, p.225). This allows for efficient double circulation and also prevents the oxygenated and deoxygenated blood from mixing. Second, the ventricles are thicker than the auricles. Thicker ventricles enable generation of higher pressure needed to pump blood to all the body parts. Thirdly, the heart has unidirectional valves which prevent backflow of blood (Rosdahl and Kowalski 2008, p.225).

Digestive system (2018).

The digestive system of a human being is comprised of the mouth, the esophagus, the stomach, the small intestine, and the large intestine. Additionally, the pancreas, the liver, the duodenum, and the bile duct are vital parts of the digestive system. The digestive system has many adaptations to its function. For instance, the small intestine is highly coiled to slow down the movement of food (Akhilesh 2008, p.5). This allows more time for digestion and absorption of the final products of digestion. There is also the presence of the pancreas, which produces release a digestive fluid directly into the small intestine through its duct. The pancreas produces lipase, trypsin, and amylase. Lipase digests fats; trypsin digests protein while amylase digests starch (Brunner 2010, p. 981). Third, the bile produces bile salts which are useful in emulsification of fats.

Endocrine System

WebMd (2018)

The endocrine system consists of the pineal gland, pituitary gland, and the hypothalamus found in the brain. Additionally, it is made of the adrenal gland and the pancreas.

Excretory System (2018).

The major excretory organ in human beings is the kidney. The kidney is comprised of the renal cortex, renal medulla, and renal pelvis. The functional unit of the kidney is known as the kidney nephron. Some of the structural adaptations of the kidney nephron to its functions include highly coiled proximal convoluted tubule to enable maximum reabsorption of substances, the presence of afferent and efferent arteriole which help to generate high pressure for ultrafiltration, and the presence of a dense network of blood capillaries.

Nervous System (2018) The nervous system is comprised of the brain, the spinal cord, and the nerves associated with two. Some of the structural adaptations of the nerves to their functions include the presence of the sheath which acts as an insulator, the presence of nodes of Ranvier which help to speed the propagation of nerve impulse, and the presence of dendrites used for communication between two nerves.

The Importance of Homeostasis within the Human Body

The term homeostasis can be defined as the capability of an organism to maintain a constant internal environment despite the changes in both the internal and the external environment. The importance of a constant internal environment was first noted by Claude Bernard, the French physiologist in 1859. The ability of multicellular organisms to maintain a stable internal environment enables them to live freely in a continuously changing external environment. Homeostasis is derived from the Greek terms homeo and stasis which means same and staying respectively. The process of homeostasis is under the control of endocrine systems and the nervous systems, whose functions are coordinated.

Homeostasis plays a vital role in the lives of living organisms. First, it enables the enzymes to work under their optimal conditions. Specifically, for enzymes to work efficiently, both the body temperature and the ph should be maintained at a constant. Secondly, homeostasis helps to maintain various substances at equilibrium in the body. For instance, the homeostatic control of water is achieved with the help of antidiuretic hormone or vasopressin which influence the permeability of the kidney tubules. Thirdly, it allows organisms to be largely independent of their abiotic or non-living factors, such as temperature. Because mammals can maintain constant internal temperature despite fluctuations in the temperature of the external environment, they can occupy a wide range of areas (from tropics to arctic). Fourthly, homeostasis is vital for osmoregulation; the process of keeping salt and water at a balance. Lastly, homeostasis is vital for the maintenance of a constant supply of nutrients and hormones such as glucose and thyroid hormones respectively

How the Endocrine System is involved in Homeostasis

The endocrine system is comprised of glands which release hormones into the bloodstream. Some of the glands involved in osmoregulation include pituitary gland, adrenal gland, and thyroid gland. Hormones are chemical messenger molecules that are secreted in part of the body and transported to another part of the body (known as the target cells) where it causes changes (Kang 2013, p. 50). The primary role of hormones in homeostasis is to respond to alterations that complicate how the body works by stimulating the appropriate responses to bring about the normal functioning of the body.

In the process of homeostasis, hormones work are regulated through a mechanism called a feedback loop. The secretion of hormones from the endocrine glands occurs when these glands are stimulated. There are three ways in which the endocrine glands can be stimulated. First, the concentration of a particular substance in the bloodstream can stimulate the glands to release hormones. For instance, a high concentration of glucose in the bloodstream stimulates the pancreas to release insulin hormone into the bloodstream while a low concentration of glucose in the bloodstream stimulates the pancreas to release glucagon hormone into the bloodstream. Second, the release can occur through direct stimulation from the nervous system. For example, when an individual senses fear, the nervous system stimulates the secretion of adrenaline hormone from the adrenal glands. Lastly, the nervous system can indirectly trigger the release of hormones through the release of hormones. For example, the hypothalamus releases hormones which trigger the secretion of other hormones.

After the endocrine glands are stimulated, they release its hormones into the bloodstream. The hormone is then transported to the target tissues through the circulatory system. Interaction of the hormones with the target tissues causes the target tissues to bring about the desired effect, which acts as a new stimulus to the endocrine organ. In positive feedback mechanism, the endocrine organ releases more of its hormone while in a negative feedback mechanism, there is decreased the production of the hormone (Alters 2000, p.362).

Examples of Homeostasis within the Human Body


Osmoregulation refers to the regulation of the osmotic pressure (salt and water balance) of its body fluids. It is useful for keeping the body fluids from becoming too dilute or too concentrated. The homeostatic control of osmotic pressure is achieved through the coordination of the hypothalamus (the nervous system), the circulatory system, the pituitary gland (the endocrine system), and the kidney (the excretory system).

The hypothalamus detects the osmotic pressure of blood and also controls how much ADH is secreted by the pituitary gland. When the osmotic pressure of the bodily fluids rises beyond the optimum, the hypothalamus sends impulses to the pituitary gland, which then releases antidiuretic hormone into the bloodstream. The antidiuretic hormone is transported to the target organ (the kidney). Upon reaching the kidney, antidiuretic hormone increases the permeability of the tubules to water. Consequently, there is increased reabsorption of water into the bloodstream leading to lowering of osmotic pressure to normal. Conversely, when the osmotic pressure of the bodily fluids decreases below the normal, there is less stimulation of pituitary gland. Consequently, little antidiuretic hormone is released. Therefore, there is reduced permeability of the kidney tubules to water. Because of this, there is decreased reabsorption of water into the bloodstream leading to increased osmotic pressure to normal.


Thermoregulation is the control of body temperature at a constant. In mammals, thermoregulation is under the control of the hypothalamus. The hypothalamus has thermo-receptors which detect changes in the internal temperature. The hypothalamus sends signals to various organs of the body. For instance, when the hypothalamus detects a higher-than-normal temperature, it sends impulses to the skin. Various changes occur in the skin to bring about a decrease in temperature. One of these changes is vasodilation, the dilatation of blood vessels. Vasodilation enables more heat to be carried by the blood near the skin surface, where it can be lost to the air. Additionally, there is increased production of sweat from the sweat glands. Sweat travels up the sweat duct and is lost to the surface of the skin, through the sweat pore. When water in the sweat evaporates, cooling takes place. Furthermore, hairs on the skin lie flat, leading to heat loss. These mechanisms help to increase heat loss and in the restoration of the body temperature to normal.

On the other hand, when the hypothalamus detects a lower-than-normal temperature, it also sends impulses to the skin. Changes which occur in the skin include vasoconstriction, which reduces heat loss through the skin. Moreover, there is decreased the production of sweat from the sweat glands, hence decreased heat loss. Furthermore, hairs on the skin stand, leading to trapping of air. These mechanisms help to lower heat loss and in restoration of temperature back to normal

Regulation of Glucose

The regulation of blood glucose is under the control of two hormones (insulin and glucagon), which are secreted by the islets of Langerhans of the pancreas. Insulin is secreted by the beta cells of the islet of Langerhans. Its secretion is stimulated by higher-than-normal blood glucose levels. When insulin is secreted into the bloodstream, it lowers the glucose level to normal by converting excess glucose to glycogen and fats and by increasing the oxidation of glucose (respiration). On the other hand, when the blood glucose is lower than normal, glucagon is released into the bloodstream. Glucagon raises the blood glucose to be normal by converting fats and glycogen to glucose and by decreasing the rate of respiration.



Akhilesh, T., 2008. Longman Science Biology 10. Pearson Education India, p.5.

Alters, S., 2000. Biology: understanding life. Jones & Bartlett Learning, p.362.

Brunner, L.S., 2010. Brunner & Suddarth's textbook of medical-surgical nursing (Vol. 1). Lippincott Williams & Wilkins, p.981. (2018). The Excretory System of Human Body - Definition and Information. [Online] Available at: [Accessed 14 Jan. 2018].

Human Anatomy Lesson (2018). Blood Vessels In Heart Cardiovascular System The Heart The Cardiovascular System [online] Available at: [Accessed 14 Jan. 2018].

Kang, J., 2013. Nutrition and metabolism in sports, exercise and health. Routledge...

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