Chapter Objectives

After studying this chapter, students should be able to . . . 1. describe in a general way, the topics studied in physiology and the importance of physiology in modern medicine. 2. describe the characteristics of the scientific method. 3. define homeostasis and describe how this concept is used in physiology and medicine. 4. explain the nature of negative feedback loops and how these mechanisms act to maintain homeostasis. 5. explain how antagonistic effectors help to maintain homeostasis. 6. explain the nature of positive feedback loops and how these function in the body. 7. distinguish between intrinsic and extrinsic regulation, and explain, in a general way, the roles of the nervous and endocrine systems in body regulation. 8. explain how negative feedback inhibition helps to regulate the secretion of hormones, using insulin as an example. 9. list the four primary tissues and their subtypes and describe the distinguishing features of each primary tissue. 10. relate the structure of each primary tissue to its functions. 11. describe how the primary tissues are grouped into organs, using the skin as an example. 12. describe the nature and significance of the extracellular and intracellular compartment of the body and explain the significance of this compartmentalization.
To those of you who are writing notes: feel free to use material from the on-line physiology book made by prior classes of Provo College students. Here is the link to the homeostasis chapter. You can copy/paste any of this material, as it is free of copyrights.

Introduction to Physiology

Here is a fun video introducing physiology

Scientific Method

Difference between a hypothesis and a theory

• Theories are statements of the general world that incorporate a number of hypotheses. A hypothesis is a step in the scientific method that is capable of being refuted by experiments, observations, or the natural world.

History of Physiology

• Father of Physiology: Erasistratus, he attempted to apply physical laws to function. 304-250 b.c?
• Aristotle, and Galen were also noted in their work.
• Father of modern physiology is Claude Bernard. He noted the constancy of the body regardless of the outside environment. Walter Cannon coined the term homeostasis.(1813-1878)

Homeostasis and Feedback Control

The human body consists of trillions of cells all working together for the maintenance of the entire organism. While cells may perform very different functions, all the cells are quite similar in their metabolic requirements. Maintaining a constant internal environment with all that the cells need to survive (oxygen, glucose, mineral ions, waste removal, and so forth) is necessary for the well-being of individual cells and the well-being of the entire body. The varied processes by which the body regulates its internal environment are collectively referred to as homeostasis. The word comes from the Greek homoios (same, like, resembling) and stasis (to stand, posture).

Positive and Negative Feedback

When a change of variable occurs, there are two main types of feedback to which the system reacts:

• Negative feedback: This is how the body regulates most systems. Negative feedback is a reaction in which the system responds in such a way as to reverse the direction of change. Since this tends to keep things constant, it allows the maintenance of homeostasis. For instance, when the concentration of carbon dioxide in the human body increases, the lungs are signaled to increase their activity and expel more carbon dioxide. Thermo regulation is another example of negative feedback. When body temperature rises, receptors in the skin and the hypothalamus sense a change, triggering a command from the brain. This command, in turn, effects the correct response, such as sweating and vasodilation to decrease the body temperature.
  • Set point: The normal levels of the body, example there is a set point for the body temperature , blood glucose concentration.
  • Integrating center: When the sensors detect a deviation from a particular set point they relay this to the integrating center.
  • Effectors: Defend the set point against deviation. Muscles or glands act to restore the set point.
  • Example: The thermostat of an air conditioner or heater has a set temperature like a set point. When the thermostat detects temperature deviation a sensor will tell the integration center to activate the effectors to start the air conditioner or heater to return the temperature to the set point.

• Positive feedback: A response to amplify the change in the variable. This has a destabilizing effect, so does not result in homeostasis. Positive feedback is less common in naturally occurring systems than negative feedback, but it has its applications, particularly when a response should be amplified. For example, in nerves, a threshold electric potential triggers the generation of a much larger action potential. Blood clotting and events in childbirth are other types of positive feedback. In childbirth, pressure on the cervix causes release of oxytocin from the hypothalamus. The oxytocin stimulates uterine contraction, which causes even more pressure on the cervix (and thence more oxytocin released). This continues, with more and more oxytocin being released and the uterus contracting more and more frequently. The cycle is broken when the baby is born and there is no more pressure on the cervix. All positive feedback cycles need something to stop the cycle--otherwise it would cycle out of control.
• Here is a video that gives an example of positive and negative feedback. For the positive feedback example, estrogen stimulates (has a positive effect upon) the release of hormones (GnRH and LH) which in turn increase the levels of estrogen. In the negative feedback, progesterone inhibits the release of GnRH and LH, and estrogen levels fall.

Neural and Endocrine Regulation

Nervous System

The nervous system, along with the endocrine system, serves as the primary control center of the body working below the level of consciousness. For example, the hypothalamus of the brain is where the body's "thermostat" is found. The hypothalamus also stimulates the pituitary gland to release various hormones that control metabolism and development of the body. The sympathetic and parasympathetic divisions of the nervous system alternatively stimulate or inhibit various bodily responses (such as heart rate, breathing rate, etc) to help maintain proper levels. It also controls contractions like the arrector pili muscles (involved in thermo regulation) and skeletal muscles, which in addition to moving the body, also cause bone thickening and maintenance, which affects bone composition. The nervous system also regulates various systems such as respiratory (controls pace and depth of breathing), cardiovascular system (controls heart rate and blood pressure), endocrine organs (causes secretion of ADH and oxytocin), the digestive system (regulates the digestive tract movement and secretion), and the urinary system (it helps adjust renal blood pressure and also controls voiding the bladder). The nervous system is also involved in our sexual behaviors and functions.

Endocrine System

The endocrine system consists of glands which secrete hormones into the bloodstream. Each hormone has an effect on one or more target tissues. In this way the endocrine system regulates the metabolism and development of most body cells and body systems. To be more specific, the Endocrine system has sex hormones that can activate sebaceous glands, development of mammary glands, alter dermal blood flow and release lipids from adipocytes and MSH can stimulate melanocytes on our skin. Our bone growth is regulated by several hormones, and the endocrine system helps with the mobilization of calcitonin and calcium. In the muscular system hormones adjust muscle metabolism, energy production, and growth. In the nervous system hormones affect neural metabolism, regulate fluid/electrolyte balance and help with reproductive hormones that influence CNS development and behaviors. In the Cardiovascular system we need hormones that regulate the production of RBC's, elevate and lower blood pressure. Hormones also have anti-inflammatory affects as well as stimulates the lymphatic system. In summary, the endocrine system has a regulatory effect on basically every other body system.

Feedback Control of Hormone Secretion

Hormone secretion happens in response to a specific chemical stimuli. In order for the body to keep homeostasis it has a closed-looped system called negative feedback inhibition. An example of this is the hormone insulin which secretes when there is a rise in blood glucose. Insulin causes the lowering of blood glucose which then inhibits further secretion of insulin which brings our body back to a state of homeostasis.

The Primary Tissues

The basic unit of structure and function are cells. Cells that are grouped together to perform a similar function are called tissues. There are four major tissues in the body, the primary tissues:

• Muscle Tissue- Specialized for contraction. There are three types:

• Skeletal Muscle- Most often attached to bones at both ends by means of tendons. This contractions causes the skeletal frame to move. The tongue, superior esophagus, anal sphincter, and diaphragm are exceptions because they do not make the skeletal frame move but are composed of skeletal muscle. It is striated tissue and arranged in bundles. It is in parallel arrangement to allow movement to be individual.
  

• Cardiac Muscle-Cardiac muscle is striated and found only around the heart. Myocardial cells are short, branched and are interconnected to form a continuous fabric. Cardiac muscle cells have tight contacts between them that stain darkly--these are called intercalated discs. The intercalated discs allow depolarization (which starts at the sinoatrial node, the heart's pacemaker) to spread between cells so that they all contract as a unit. These electrical connections between adjacent muscle cells are found only in cardiac muscle.

• Smooth Muscle-No striations seen when observed under the microscope. Found in digestive tract, blood vessels, bronchiole's, and the ducts of the urinary and reproductive systems. The uterus and bladder are examples of organs with thick layers of smooth muscle. Within tubes (such as the GI tract or blood vessels) the smooth muscle is found in a circular layer and a longitudinal layer. These two layers work together to move food smoothly through the digestive tract (this movement is called peristalsis)

• Nervous Tissue- The function of Nervous Tissue is to communicate between parts of the body. It is composed of neurons and neuroglia. All nervous tissue of an organism makes up its nervous system (Brain, Spine, Spinal Cord and nerves throughout the organism). Nervous tissue is made of nerve cells. These cells react to stimuli and bring about a response.

• Connective Tissue- Involved in structure and support.Blood, cartilage, and bone are considered connective tissues. Loose connective tissue holds organs and epithelial in place. Dense connective tissue forms ligaments and tendons.

• Epithelial Tissue- Composed of a layer of cells. It lines both outside (skin) and inside cavities of the body. Epithelial cells are classified by their shape, stratification, and specializations.

• Squamous cells- Flat cells with an irregular flattened shape.
• cells- Have a shape similar to a cube, meaning its width is the same size as its height.
• Columnar cells- Are taller than they are wide.
• Transitional cells- Found lining organs that can stretch, such as the bladder. Since the cells can slide over each other, the appearance of this epithelium depends on whether the organ is distended or contracted: if distended, it appears as if there are only a few layers; when contracted, it appears as if there are several layers.

Organs and Systems

Organ: An Organ is a structure that has more than one of the tissues, usually all four. Tissues within the organ all serve a purpose for the function of the particular organ. We often think of the heart, lungs, or liver as examples of organs, but the skin is also an organ (the largest one), and every bone is an organ. Often an organ will have one main tissue (such as cardiac muscle in the heart).
System: Different organs of the body that work together to perform related functions. The entire body can be looked at as composed of nine major systems: Integumentary, Nervous, Skeletal, Muscular, Circulatory, Immune, Respiratory, Urinary, Digestive, and Reproductive. Each system has its own organs which carry out the functions of that system.

Muscular System

The muscular system is one of the most versatile systems in the body. The muscular system contains the heart, which constantly pumps blood through the body. The muscular system is also responsible for involuntary (e.g. goosebumps, digestion, breathing) and voluntary (e.g. walking, picking up objects) actions. Muscles also help protect organs in the body's cavities

Cardiovascular System

The cardiovascular system, to needing to maintain itself within certain levels, plays a role in maintenance of other body systems by transporting hormones (heart secretes ANP and BNP) and nutrients (oxygen, EPO to bones,etc.), taking away waste products, and providing all living body cells with a fresh supply of oxygen and removing carbon dioxide. Homeostasis is disturbed if the cardiovascular or lymphatic systems are not functioning correctly. Our skin, bones, muscles, nervous system, endocrine, lymphatic system, lungs, digestive tract, urinary system and reproductive use the cardiovascular system as its "road" or "highway" as far as distribution of things that go on in our body. There are many risk factors for an unhealthy cardiovascular system. Some diseases associated are typically labeled "uncontrollable" or "controllable." The main uncontrollable risk factors are age, gender, and a family history of heart disease, especially at an early age.

Digestive System

Without a regular supply of energy and nutrients from the digestive system all body systems would all surely suffer. The digestive system absorbs organic substances such as, vitamins, ions, and water that are needed all over the body. In the skin the digestive tract provides lipids for storage in the subcutaneous layer. Food goes through three types of processes in the body: digestion, absorption, and elimination. Mechanics of digestion can be chemical digestion, movements, ingestion absorption, and elimination. In order to maintain a healthy and efficient digestive system we have to remember the components involved.

Body-Fluid Compartments

All tissues,organs, and systems can be divided into Two major compartments.

• Intracellular compartment(inside the cell)
• Extracellular compartment(outside the cell)

These two compartment are primarily water, however, they are separated by the cell membrane surrounding each cell. The extracellular compartment is divide into two sections one being blood plasma and the other interstitial fluid(tissue fluid). Blood plasma and tissue fluid communicate freely through blood capillaries in most parts of the body.

Review Questions

1. What does a single celled protozoan need?
a. energy
b. building blocks
c. ATP
d. minerals
e. all of the above

2. The cell expends a lot of its energy to maintain a charge across its membrane, it does this by actively:
a. pumping potassium out
b. pumping sodium in
c. pumping potassium in and sodium out
d. a and b only
e. none of the above

3. The body is _______% fluid.
a. 52
b.89
c.56
d.10

4. Fluid inside the cell is called?
a.blood
b.cytoplasm
c.urea
d.intracellular fluid

5._______ are organized into different functional structures and are highly dependent upon each other.
a. atoms
b. DNA strands
c. cells
d. dendrites


6. How many cells are in the human body?
a. 600 thousand
b. One million
c. Six billion
d. 100 trillion


7. What is interstitial fluid similar to?
a. plasma
b. blood
c. water
d. saliva

8. Adult stem cells can be found in all of the following locations, except:
a. bulge of hair follicle
b. brain
c. lungs
d. intestine
e. bone marrow

9. Which of the following cells has no nucleus?
a. red blood cell
b. osteoblast
c. osteocyte
d. white blood cell

10. Which of the following is false about extracellular fluids?
a. it contains glucose
b. it contains amino acids and fatty acids
c. it has larger amounts of potassium than interstitial fluid
d. it contains CO2

11. Homeostasis is like cruise control, it must have:
a. a mean for adjustment
b. a set point
c. detectors to realize it needs adjustment
d. all of the above
e. none of the above

12. I went into the bookstore and noticed that I was going to have to fork out
nearly $200 dollars for my new physiology text book. Desperate for money I
was forced to donate some plasma A LOT of plasma in order to get my new book. This plasma is a subdivision of which major compartment.
a. intracellular compartment
b. epidermal compartment
c. median-basilic compartment
d. extracellular compartment

13. I was walking in the jungle on a wild safari and as I was admiring a spider
monkey swinging from branch to branch I found my self falling into a huge
pit of quicksand. As I was sinking I was thinking about my death and
realized, like many deaths I would die because:
a. my cells need oxygen to survive
b. my cells cant get the proper nutrition from sand
c. insufficient levels of ATP
d. your cells wont die until your heart stops

14. Sweating and shivering are an example of what?
a. positive feedback
b. negative feedback
c. hormonal imbalance
d. aging

15.Glands are derived from:
a. nervous tissue
b. connective tissue
c. muscular tissue
d. epithelial tissue


16. For the Halo 3 debut the news showed footage of people rushing into the store to get their copy. They focused in on a guy that was pacing back and forth dripping in sweat anxious to get his copy. Sweat is secreted by exocrine glands. This means his sweat:
a. is produced by epithelial cells
b. is a hormone
c. is secreted into a duct
d. is produced outside the body

17. The most imediate need for a cell is?
a. glucose
b. gas exchange
c. protein
d. fatty acids