2.6 Organ Systems and Homeostasis Study Guide

2.6 Organ Systems and Homeostasis

(Bio.2.6)

Explore this Phenomenon

Though not often deadly to a human, many spiders are able to inject poison when they bite something.

Many spiders are able to inject venom when they bite their victims, resulting in a red, swollen, and/or itchy spot on the skin.

1. Your body must maintain homeostasis to stay alive. How do you think your body responds to the spider’s venom to maintain homeostasis?
2. What are three questions you could investigate to learn more about how your body maintains homeostasis in the presence of changing conditions, like a spider bite?

Bio.2.6 Interacting Systems

Ask questions to develop an argument for how the structure and function of interacting organs and organ systems, that make up multicellular organisms, contribute to homeostasis within the organism. Emphasize the interactions of organs and organ systems with the immune, endocrine, and nervous systems. (LS1.A)

Multicellular organisms are made of systems that interact with each other to help maintain homeostasis. As you read this chapter, pay attention to how the structure of different organs and organ systems affects their functions and ability to help maintain homeostasis.

Organs and Organ Systems

In section 2.4 you learned about homeostasis, and in section 2.5 you learned about the different levels of organization of life. In this section, you will be learning how organs and organ systems work together to help your body maintain homeostasis.

Remember that organisms are made of many different parts called organs. Organs are made of one or more types of tissues. Human organs include the brain, stomach, kidney, and liver. Plant organs include roots, stems, and leaves.

Organs work together to perform a specific function forming an organ system. Organ systems also work together to perform tasks. Examples of organ systems in a human include the skeletal, nervous, and reproductive systems. Organ systems in a plant include the root and reproductive systems.

The previous figure shows how multiple organs work together to transport blood around the body. The heart and blood vessels are two of the organs that work together and form the circulatory system.

The Nervous System

The nervous system, together with the endocrine system, controls all the other organ systems. The nervous system sends one type of signal around the body, and the endocrine system sends another type of signal around the body.

The nervous system works by sending and receiving electrical signals. The main organs of the nervous system are the brain and the spinal cord. The signals are carried by nerves in the body, similar to the wires that carry electricity all over the house. The signals travel from all over the body to the spinal cord and up to the brain, as well as moving in the other direction. The messages released by the nervous system traveled through nerves. Similar to the electricity that travels through wires, nerves quickly carry electrical messages around the body.

The Endocrine System

The endocrine system is a system of organs that releases chemical messenger molecules, called hormones, into the blood. The endocrine system is important in controlling metabolism, growth and development, reproduction, and salt, water, and nutrient balance in blood and other tissues.

Organs of the Endocrine System

The endocrine system is made up of many glands that are located in different areas of the body. Hormones are chemical messenger molecules that are made by cells in one part of the body and cause changes in cells in another part of the body. Hormones regulate the many and varied functions that keep you alive.

Hormones are made and secreted by cells in endocrine glands. Endocrine glands are organs that secrete hormones directly into the blood or the fluid surrounding a cell rather than through a duct. The primary function of an endocrine gland is to make and secrete hormones. The endocrine glands collectively make up the endocrine system. The major glands of the endocrine system are shown below. Many other organs, such as the stomach, heart, and kidneys, secrete hormones and are considered to be part of the endocrine system.

 The glands of the endocrine system are the same in males and females, except for the testes, which are found only in males, and the ovaries, which are found only in females.

 Unlike the nervous system, whose actions help the body react immediately to change, the endocrine system controls change that happen to the body over long periods of time, which can be minutes, hours, or even years. The endocrine system is more like starting up an oil or gas powered water-heating system. You flick on the switch to heat up water for a bath, but it takes a certain length of time for the result - hot water - to occur.

The Immune System

The immune system is a defense system. It comprises many biological structures, including individual white blood cells and entire organs. The function of the immune system is to protect the host from bacteria and viruses, and other causes of disease, such as tumor cells. To function properly, the immune system must be able to detect a wide variety of bacteria and viruses, and be able to distinguish pathogens from the body’s own cells, so that it doesn’t destroy cells of the body. The immune system must also be able to distinguish cancerous or damaged cells from healthy cells.

Does this organism look like a space alien? A scary creature from a nightmare? In fact, it’s a 1-cm long worm that lives in the human body and causes serious harm. It enters the body through a hair follicle of the skin when it’s in a much smaller stage of its life cycle. Like this worm, many other organisms can make us sick if they manage to enter our body. Fortunately for us, our immune system is able to keep out most such invaders.

The body’s first line of defense consists of different types of barriers that keep most pathogens out of the body. Pathogens are disease-causing agents, such as bacteria and viruses. These and other types of pathogens are described in the next table. Regardless of the type of pathogen, however, the first line of defense is always the same.

Types of pathogens that commonly cause human diseases include bacteria, viruses, fungi, and protozoa. Which type of pathogen causes the common cold? Which type causes athlete’s foot?

Mechanical Barriers

Mechanical barriers physically block pathogens from entering the body. The skin is the most important mechanical barrier. In fact, it is the single most important defense the body has. The outer layer of the skin is tough and very difficult for pathogens to penetrate.

Mucous membranes provide a mechanical barrier at body openings. They also line the respiratory, GI, urinary, and reproductive tracts. Mucous membranes secrete mucus, a slimy substance that traps pathogens. The membranes also have hair-like cilia. The cilia sweep mucus and pathogens toward body openings where they can be removed from the body. When you sneeze or cough, pathogens are removed from the nose and throat. Tears wash pathogens from the eyes, and urine flushes pathogens out of the urinary tract.

Chemical Barriers

Chemical barriers destroy pathogens on the outer body surface, at body openings, and on inner body linings. Sweat, mucus, tears, and saliva all contain enzymes that kill pathogens. Urine is too acidic for many pathogens, and semen contains zinc, which most pathogens cannot tolerate. In addition, stomach acid kills pathogens that enter the GI tract in food or water.

Biological Barriers

Biological barriers are living organisms that help protect the body. Millions of harmless bacteria live on the human skin. Many more live in the GI tract. The harmless bacteria use up food and space so harmful bacteria cannot grow.

Organ Systems Work Together to Maintain Homeostasis

In section 2.4 you learned how the cell membrane helps a cell maintain homeostasis. Organs and organ systems work together to help your body maintain homeostasis.

One example of an organ working to maintain homeostasis is the way your pancreas works to keep the sugar in your blood relatively stable. When blood sugar is high, the pancreas releases the hormone insulin. The insulin signals cells to take in more sugar, lowering the amount of sugar in the blood. When blood sugar is low, the pancreas releases a different hormone, called glucagon. The glucagon signals cells and the liver to release sugar into the bloodstream.

The nervous, endocrine, and immune systems work together to help your body maintain homeostasis. For example, your nervous system can sense when you are in a dangerous situation. Your nervous system detects danger through sight, smell, or sound, and will send a signal to your endocrine system. Your endocrine system will respond to the signal by releasing adrenaline. The adrenaline travels to different cells in your body. The release of adrenaline causes your heart to beat faster, the release of glucose into your bloodstream, and the relaxing of muscle tissue in your lungs to allow for increased breathing. These changes are referred to as the fight or flight response, because they prepare your body to either fight or run away from danger.

You can learn more about the fight or flight response and how your nervous and endocrine systems work together by watching this video:

https://learn.genetics.utah.edu/content/cells/cellcom/ .

Putting It Together

Though often not deadly to a human, many spiders are able to inject poison when they bite something.

Many spiders are able to inject venom when they bite their victims, resulting in a red, swollen, and/or itchy spot on the skin.

1. How has your understanding of how your body can maintain homeostasis changed?
2. Use what you have learned about how organs and organ systems can work together to maintain homeostasis to explain how your body can recover from changing conditions, such as a spider bite.