Human Physiology
Human Physiology

Human Physiology

Lead Author(s): John Redden, Joe Crivello

Student Price: Contact us to learn more

Focused on pure human physiology, this textbook uses interactivity to extend the subject beyond the page.

What is a Top Hat Textbook?

Top Hat has reimagined the textbook – one that is designed to improve student readership through interactivity, is updated by a community of collaborating professors with the newest information, and accessed online from anywhere, at anytime.


  • Top Hat Textbooks are built full of embedded videos, interactive timelines, charts, graphs, and video lessons from the authors themselves
  • High-quality and affordable, at a significant fraction in cost vs traditional publisher textbooks
 

Key features in this textbook

Top Hat’s Human Physiology contains interactive diagrams, custom illustrations, pop-up definitions, and interactive 3D models to keep students actively engaged when learning the material.
Includes Focus on Disease, Thought Questions, and In the Clinic call-out sections that present key concepts in a relatable way for students to grasp!
Complete test bank of 400 questions for instructors to use.

Comparison of Human Physiology Textbooks

Consider adding Top Hat’s Human Physiology textbook to your upcoming course. We’ve put together a textbook comparison to make it easy for you in your upcoming evaluation.

Top Hat

John Redden & Joe Crivello, Human Physiology, Only One Edition needed

Pearson

Dee Unglaub Silverhorn, Human Physiology: An Integrated Approach (8th ed.)

Cengage

Lauralee Sherwood, Human Physiology: From Cells to Systems (9th ed.)

McGraw-Hill

Stuart Fox, Human Physiology (14th ed.)

Pricing

Average price of textbook across most common format

Up to 40-60% more affordable

Lifetime access on any device

$197.71

Hardcover print text only

$172.68

Hardcover print text only

$174.72

Hardcover print text only

Always up-to-date content, constantly revised by community of professors

Content meets standard for Introduction to Anatomy & Physiology course, and is updated with the latest content

In-Book Interactivity

Includes embedded multi-media files and integrated software to enhance visual presentation of concepts directly in textbook

Only available with supplementary resources at additional cost

Only available with supplementary resources at additional cost

Only available with supplementary resources at additional cost

Customizable

Ability to revise, adjust and adapt content to meet needs of course and instructor

All-in-one Platform

Access to additional questions, test banks, and slides available within one platform

Pricing

Average price of textbook across most common format

Top Hat

John Redden & Joe Crivello, Human Physiology, Only One Edition needed

Up to 40-60% more affordable

Lifetime access on any device

Pearson

Dee Unglaub Silverhorn, Human Physiology: An Integrated Approach (8th ed.)

$197.71

Hardcover print text only

Cengage

Lauralee Sherwood, Human Physiology: From Cells to Systems (9th ed.)

$172.68

Hardcover print text only

McGraw-Hill

Stuart Fox, Human Physiology (14th ed.)

$174.72

Hardcover print text only

Always up-to-date content, constantly revised by community of professors

Constantly revised and updated by a community of professors with the latest content

Top Hat

John Redden & Joe Crivello, Human Physiology, Only One Edition needed

Pearson

Dee Unglaub Silverhorn, Human Physiology: An Integrated Approach (8th ed.)

Cengage

Lauralee Sherwood, Human Physiology: From Cells to Systems (9th ed.)

McGraw-Hill

Stuart Fox, Human Physiology (14th ed.)

In-book Interactivity

Includes embedded multi-media files and integrated software to enhance visual presentation of concepts directly in textbook

Top Hat

John Redden & Joe Crivello, Human Physiology, Only One Edition needed

Pearson

Dee Unglaub Silverhorn, Human Physiology: An Integrated Approach (8th ed.)

Cengage

Lauralee Sherwood, Human Physiology: From Cells to Systems (9th ed.)

McGraw-Hill

Stuart Fox, Human Physiology (14th ed.)

Customizable

Ability to revise, adjust and adapt content to meet needs of course and instructor

Top Hat

John Redden & Joe Crivello, Human Physiology, Only One Edition needed

Pearson

Dee Unglaub Silverhorn, Human Physiology: An Integrated Approach (8th ed.)

Cengage

Lauralee Sherwood, Human Physiology: From Cells to Systems (9th ed.)

McGraw-Hill

Stuart Fox, Human Physiology (14th ed.)

All-in-one Platform

Access to additional questions, test banks, and slides available within one platform

Top Hat

John Redden & Joe Crivello, Human Physiology, Only One Edition needed

Pearson

Dee Unglaub Silverhorn, Human Physiology: An Integrated Approach (8th ed.)

Cengage

Lauralee Sherwood, Human Physiology: From Cells to Systems (9th ed.)

McGraw-Hill

Stuart Fox, Human Physiology (14th ed.)

About this textbook

Lead Authors

John Redden, Ph.DUniversity of Connecticut

John Redden has taught A&P for many years, from small to ultra-large classes. He currently serves as a National Academies Education Mentor in the Sciences Assistant Director of Faculty Development programs at the University of Connecticut’s Center for Excellence in Teaching and Learning.

Joseph F. Crivello, Ph.DUniversity of Connecticut

Joseph F. Crivello has taught A&P for the past 34 years. He is currently a Teaching Fellow of the HHMI/Hemsley Summer Teaching Institute and is the Premedical Advisor to the University.

Contributing Authors

Melissa MarcucciUniversity of St. Joseph

Melissa FoxWingate University

Angela HessBloomsburg University of Pennsylvania

Andrew LokutaUniversity of Wisconsin

Kristen KimballUniversity of Connecticut

Michele MooreButler University

Matthew OrangeCentral Connecticut State University

Chad WayneUniversity of Houston

Gerald BrasingtonUniversity of Southern Carolina

Kira WersteinIowa State University

Bruce PichlerUniversity of North Georgia

Ron GerritsMilwaukee School of Engineering

Chris TrimbyWisconsin Institute for Science Education & Community Engagement

Adam SullivanBrown University

Explore this textbook

Read the fully unlocked textbook below, and if you’re interested in learning more, get in touch to see how you can use this textbook in your course today.

Chapter 1: Introduction to Physiology

​Figure 1.1. Scientists have been searching for centuries for clues to unlock the mysteries of the body. On the left, a physician performs a visual urinalysis. On the right, a portable glucometer determines the concentration of glucose in the blood with a simple finger prick. [1, 2]​


1.1 Objectives

​ After completing this chapter, you should be able to:


1.2​ Introduction

​A healthy body is the product of sound decision making, physical activity, and genetics. But what does it mean to be “healthy”? At this point in your life, you have most likely been bombarded with health information from television, magazines, Google searches, and friends. It’s overwhelming, but increasingly important, to be able to evaluate the validity of the massive amount of medical information you receive on a daily basis. Especially if, eventually, you would like to be the person giving sound advice to others. Understanding your body begins with anatomy (physical structure) and physiology (how things work). Together, these two subjects can provide a foundation for making informed decisions about health, wellness, and the diagnosis and treatment of disease.

Consider that 10% of the United States population is living with a disease known as diabetes, which was characterized more than 2000 years ago as an untreatable and fatal disease of the kidney (since physicians observed that diabetics urinated excessively). Scroll through the timeline below to follow the history of the diagnosis and treatment of this once deadly disease.

​As a result of centuries of work that has only been superficially summarized here, a disease that was once a guaranteed death sentence is now manageable and soon to be cured – all because of our understanding of human physiology.

So, why are you getting a history lesson in your science textbook? Because it’s not uncommon for students learning about physiology to lose perspective and get lost in the details of the many systems they study. The body is a marvel of complexity. You will inevitably wonder why you are learning this information – but you might find some comfort in knowing that the physicians and scientists who preceded you on this journey of discovery very likely asked themselves the same questions at some point in their career (and occasionally forgot to do their homework, too). Just as others have connected the dots between the renal, circulatory, digestive, and endocrine systems to solve the mystery of diabetes, you might one day apply the things you’re learning about here to do something great. At a minimum, you will learn quite a bit about health and disease. And truthfully, why wouldn't you want to learn more about one of the greatest and most important gifts you have been given, your body?

Question 1.01

Take a minute or two to think through the following questions, and reply to enter your thoughts . Where do you see yourself in 5 years? How is college helping you get there? How does this course relate to those goals?


1.3​ Structure Dictates Function

Anatomy and physiology are essential to our ability to decipher the inner workings of the human body.

Anatomy and physiology are complementary subjects because structure dictates function. In this textbook we focus on physiology. At the cellular level, you will see how a change in the structure of proteins will affect their functions. More than 30 million people live with sickle cell disorder, which gives them more than a 300-fold increase in their risk of stroke in comparison to a healthy individual. Sickle cell disease is the result of a single amino acid substitution! How can an individual know that cells in your gut and kidney are specialized for absorption simply by looking at them under a microscope? How can we predict the action of a muscle just by looking at its attachment to bones? These are all questions that will be answered within this book, and once you’re comfortable with the relationship between structure and function, it will become much easier to predict how changes in structure can produce the changes in physiology that characterize countless diseases.

Question 1.02

Physiology is the study of ______________.

In order to fully appreciate this link between structure and function, it is also important to consider how other complementary disciplines such as evolutionary biology, comparative physiology, and histology have shaped our understanding of our bodies. Evolutionary biology allows us to see the structure/function relationship for a given structure as a continuous work in progress that has been honed over the millennia by climate, environmental, and genetic influences. Comparative physiology provides insight into how we are similar, and distinct, from other species. However, these differences have developed over thousands of years, and few changes have happened in the time that humans have been able to study physiology, even though the field is over 4000 years old! That said, new discoveries are made every single day due to advances in technology. 

​ Other advancements in imaging of tissues and systems has been fundamental to how modern medicine understands disease. The use of medical imaging enables scientists to gain more a detailed understanding of how diseases manifest in cells and tissues. The use of medical imaging provides clinicians with a database of abnormal and normal anatomy and physiology images that serve as a repository for interpreting how disease manifests in the various tissues of the body. Today, scientists and clinicians combine histological examination of tissues and more advanced, gross imaging techniques such as magnetic resonance imaging (MRI or functional MRI (fMRI)) and computed tomography (CAT) scanning to look at organ systems and gain significant information about the health of an individual (Figure 1.2).

Figure 1.2. The use of microscopes, CT scanning, and MRI all provide increasingly complex pictures of anatomical structure leading to a deeper understanding of normal and abnormal human physiology. a) Sophie Lutterlough, an entomologist at the Smithsonian Museum of Natural History (1983), uses the microscope to examine the fine ultrastructure of insects and classify thousands of species. b) and c) CAT scan and MRI images, respectively, provide increasing amounts of skeletal and soft tissue structural detail giving us insight in the normal physiology of these structures. [3, 4, 5]​


Question 1.03

Question 1.03

How do microscopes, CT scans, and fMRI contribute to our understanding of physiology?

Click here to see the answer to Question 1.03.​

Physiology is an understanding of how events at micro (molecular and cellular) levels affect macroscopic systems (organs and individuals). An excellent example of how is this work can be gained by an examination of the four major biomolecules that act as unique building blocks that come together to form functional cells, tissues, and organs.

​Table 1.1 lists the four classes of biomolecules along with their major functions. The cell can assemble biomolecules into organelles, cells, tissues, organs, and eventually, the whole organism. For example, Figure 1.3 highlights the structural assembly of a phospholipid with its charged hydrophilic sections and hydrophobic sections, which enable it to assemble into a cellular barrier that permits certain molecules to pass through it.

ANP01_BiomoleculesTable.jpg
Table 1.1 There are four major classes of biomolecules – our body uses these molecules as building blocks to form our cells, tissues, and organs.


​​Figure 1.3. The phospholipid structure enables semi-permeable cell membrane assembly.​


​The 3-dimensional (3D) shape of a protein is dependent on the amino acids that make up the protein (Figure 1.4; and see the chapter on Cell Structure and Function). This 3D shape gives a protein its function by allowing it to fit into crevices or holes that have complementary shapes. This is similar to watching a toddler put her triangle toy block through a triangular hole, but struggle trying  to put it through a circular hole. If proteins are folded incorrectly or unfolded completely, they stop functioning.

​An example of this is mad-cow disease (bovine spongiform encephalopathy). If a person eats a hamburger that contains infectious particles from a sick cow, these particles enter the brain and cause proteins to unfold, producing a severe sickness.

Figure 1.4. The sequence of


amino acids, known as the primary structure of a protein, dictates its folding


pattern (secondary and tertiary structure) leading to a functional


conformation. The structural assembly of hemoglobin’s four subunits (quaternary


structure) forms a stable structural assembly capable of binding and


transporting O2.​


Biomolecules also work together. For example, proteins and lipids assemble together to make organelles such as the mitochondria. The mitochondria also demonstrate a structure/function relationship, as their membrane creates a dual compartment organelle forming specialized folds known as cristae. Proteins embedded within the inner mitochondrial membrane of the cristae form the electron transport chain, which is used to produce ATP. Without the coordination of membrane structure and embedded proteins as seen in Figure 1.5, the mitochondria could not produce significant energy in the form of ATP for the cell.

Figure 1.5. Mitochondrial


membranes are arranged into cristae, which contain the embedded proteins that


are critical for the formation of ATP.​

​A final example linking structure and function is the anatomy of lung tissue. Each alveolus is assembled from thin-walled cells that establish an extended surface for gas exchange. The diagram in Figure 1.6 indicates how the wall of the alveolus is made up of simple squamous epithelial cells (see the chapter on The Respiratory System). This thin, flat surface increases the surface area for the exchange of O2 and CO2 that takes place in the lungs.

Figure 1.6. The thin wall of the alveolus forms an optimal surface for gas exchange. ​[6]

The examples discussed here highlight only a few ways in which anatomy complements function. All of the above will be covered in greater detail later in the text. As you progress through the various chapters of the textbook, pay attention to this pattern, which is apparent at all levels of organization.

1.3.1​ Levels of Organization

Here is a video introduction to the levels of organization within the human body:

​A key to understanding how the body functions is to fully understand how it is organized from the molecular level, to the cellular level, to the level of tissues, then organs, organ systems, and then the entire body. Examining the assembly of the smallest units (atoms) into coordinated parts (biomolecules), into more complex components (cells, tissues, and organs) (see interactive diagram below) is often a helpful strategy for learning about a new body system. This is because each organism can be reduced to its functional organ systems, which are assembled from individual organs. At the foundation of the organ is a complex arrangement of tissues, which are composed of many cells. These cells are given their unique functions by the biomolecules and atoms found within them. Together, these molecules work to maintain homeostasis in the human body.


Question 1.04

Question 1.04

What specializations might allow one tissue to produce a hormone, and another to facilitate nutrient exchange? Is it possible for the same organ to serve both these functions?

Click here to see the answer to Question 1.04.

The assembly of smaller components to form a complex organism results in an independent human being.​ Interact with the diagram below to see how organisms exist within life's grand biosphere. 

     


Question 1.05

The heart is a biological pump that creates pressure to send nutrient- and O2-rich blood through circulatory vessels to supply body organs. What is the heart an example of?

A

A tissue

B

An organ

C

A system

D

An organ system


1.3.2​ Characteristics of Life

You are alive, your computer isn’t (not yet, anyways!). Have you ever considered what it is about living organisms that makes them different from non-living things? Here are some general characteristics of human physiology:

  • Energy production and consumption. Living things must eat. This brings nutrients into the body that can be used to produce energy. The energetic currency of the human body, our primary energy source, is ATP (adenosine triphosphate). Humans are heterotrophs; we don't make our own energy and must eat to survive. ATP can be generated from the breakdown of carbohydrates, fats, or proteins. It is used to drive numerous cellular processes that require energy input. As you are reading this, ATP is being consumed in the retina of your eye in order to give you the ability to detect light and distinguish colors. As you scroll with your mouse, the skeletal muscles in your arms and fingers are consuming ATP in order to produce movement. In nearly every chapter of this text, you will encounter examples of how the cells that form a particular tissue “spend” their ATP allowance.​
  • Growth/repair. Consider the many differences between an infant and yourself, or between you and your parents and grandparents as proof that the human body changes over time. Cells, tissues, and organs form, grow, and age over time. During our long lives, injury is inevitable and the ability of a tissue to repair itself is essential.
  • Adaptation. ​Humans respond and adapt to changes in our environment. These changes can be reversible or permanent. For example, hikers ascending Mount Everest may experience difficulty breathing due to the reduced O2 levels at this very high altitude. Over time, however, stem cells in the bone marrow produce more red blood cells (erythrocytes), which help maintain O2 flow to the tissues. Upon returning to their native elevation, the level of red blood cells in the hikers will return to normal. A more permanent change occurs in response to exposure to the carcinogens found in cigarette smoke, which damage lung tissues and alter their structure. In this case, breathing will remain challenging even if the smoker is able to eventually quit as happens in emphysema.
  • Reproduction. Wouldn’t it be great if the money in your checking account could reproduce? Unfortunately, only living creatures have the ability to reproduce. Although individual organisms do not need to reproduce to survive, reproduction is required for the survival of the species.
Question 1.06

Which of the following are characteristics of life?

A

Energy consumption

B

Reproduction

C

Responding to external stimuli

D

Growth


Question 1.07

Bitter taste perception is an important protective mechanism in humans and animals. Bitter tastes are usually linked to poisonous, spoiled, or generally non-desirable food choices and thus, avoiding such choices can protect from illness. This is an example of _______.

A

Organization

B

Repair

C

Adaptation

D

Growth


In summary, humans and other living organisms are capable of sustaining life because of their innate structural organization, their ability to use energy to do work, interact with their environment, and their capability to grow, repair, and reproduce.

1.3.3​ Cells as the Living Unit of Life

Figure 1.7. Cells contain essential internal components (organelles) to sustain life as independent units.​

​The smallest functional unit of life, possessing all of the qualities essential to sustain life, is the cell. Cells are the  building blocks of tissues and contain all the necessary machinery to sustain homeostasis through metabolism and maintenance/repair (the next chapter is dedicated to Cell Structure and Function). All individual cells comprise at least three shared components: a membrane surrounding genetic material that floats in cytosolic fluid (Figure 1.7). In human cells, these three components are joined by several additional membrane-bound organelles whose individual functions establish a higher level of cellular complexity (further discussed in the next chapter). Human cells rely on the complex steps of gene expression to become specialized. The multiple steps of gene expression are carried out in the nucleus, cytosol, endoplasmic reticulum, and Golgi apparatus, and it results in production of the specific proteins required for a particular cell type to function. This specialization, better known as cell differentiation, is essential for the formation of many different types of cells. How this specialization occurs is of interest to biomedical researchers today. How does a muscle cell know to become a muscle cell, and a nerve cell to become a nerve cell? Deconstructing how the cues and signals that a cell receives are translated into the instructions for differentiation allows us to understand more complicated processes like development, tissue repair, and immunity.

In the human body, there are approximately 200 different cell types that can be divided into 4 major categories of tissue according to their shared functions:

  • Epithelial tissue
  • Muscle tissue
  • Nerve tissue
  • Connective tissue

Within each category, the cells are further grouped by variations in function. For example, epithelial cells come in various shapes and arrange in single or multiple layers. These arrangements enable epithelial cells in various organs to carry out diverse roles in protection, secretion, and absorption.

1.3.4 Tissues

Figure 1.8. Cells in the human body can be assembled into four tissue types: connective, epithelial, muscle, and nervous.​

​Tissues assemble from combinations of these four common cell types working together to serve a shared function. Tissues are the intermediate level of structural and functional organization between the cell and organ. The coordination and assembly of common cells through cell junctions, cell adhesion molecules, and cell attachment to the extracellular matrix strengthens the integrity of the tissues. Proteins such as collagen and elastin localized within the extracellular matrix and junctional complexes act as tethering ropes to align and bind cells.

Question 1.08

Groups of cells that are similar in structure and perform a common or related function form ______________.

A

An organ

B

A tissue

C

An organism

D

An organ system


1.3.4.A 
Epithelium

​Epithelial tissues can be found lining the walls of open tubes and they provide a secretory (outward) and/or absorptive (inward) surface. They are also found covering exposed surfaces as a source of protection. The structure of an epithelial cell serves to create two important surfaces that are organized by the arrangement of junctional proteins to create segregated regions of the plasma membrane. The two surfaces are known as the apical and the basolateral surfaces. The apical surface faces the lumen of the organ it is lining and the basolateral surface is tethered to the extracellular matrix. This polarization of the two cellular surfaces is translated to the tissue level and creates an environment for movement of nutrients between the apical and basolateral surfaces. The basolateral surface is part of the underlying connective tissue layer, which contains a connection to the vasculature. The movement of ions, nutrients, and gases between these two spaces is critical for the homeostasis of body systems. Consider the example of absorption of nutrients from the partially digested stomach contents in the small intestinal lining. The apical surface of the intestinal lining contains carriers that enable nutrients and ions to be transported from the digestive system into the bloodstream.

Question 1.09

An inability to absorb (take up/internalize through the tissue surface) digested nutrients and secrete digestive enzymes might indicate a disorder in which tissue type?

A

Epithelial

B

Muscle

C

Nervous

D

Connective


1.3.4.B ​
Muscle

​Without the attachment of muscles to bone or the layering of smooth muscle in the digestive tract, essential processes like breathing and swallowing would not be possible. The assembly of contractile proteins within muscle cells makes them ideally suited for the generation of mechanical force. There are three types of muscle in the human body:

  • Skeletal muscle
  • Smooth muscle
  • Cardiac muscle

Skeletal muscle, which is voluntary , allows us to choose when and how to move. Smooth muscle, which is involuntary, is not directly controlled by conscious thoughts. The constriction and dilation of arteries is controlled by layers of smooth muscle in the artery walls. The wall of the heart is the only organ in the body composed of cardiac muscle. While in structural appearance, cardiac muscle looks similar to skeletal muscle, it is more specialized and under involuntary control.

1.3.4.C ​Nervous Tissue

Nervous tissue comprises glia and neurons. Glial cells provide protection, support, and nourishment to the cells within the nervous system. Nerves provide the tracks for long distance communication within the body, and are made up of neurons, which transmit electrical signals from the nervous system to organs. In doing so, nerves provide control over many voluntary and involuntary processes in the body including muscle contraction and enzyme secretion.

1.3.4.D ​Connective Tissue

Connective tissues are a collection of cells and proteins that provide support and integrity to other tissues and structures in the body. Connective tissues in the body differ in the arrangement of their cells, fibers, and fluid matrix (ground substance). The matrix contributes to its tensile strength and defines the function for a given connective tissue. Some connective tissues are less ordered, such as hyaline cartilage, which is well suited for flexible structures like the earlobe. Other connective tissues have rope-like structures with densely packed fibers and cells, making this anatomical arrangement ideal for connecting bone to bone, such as with a ligament.

Question 1.10

The degree of order of the cells, matrix, and fibers within a given type of connective tissue will contribute to its ______________.


Question 1.11

An inability to exert control over one’s foot coupled with the loss of sensation in the toes suggest an injury to what type of tissue?

A

Connective

B

Nervous

C

Epithelium

D

Muscle


1.3.5​ Organs and Systems

The idea of “growing” a brain, heart, or kidney in a laboratory has been explored by many movies, and highlights a question that has given scientists many sleepless nights! If we know the cells and tissues that comprise an organ, then why can’t we create organs? The answer is complicated. It turns out that our bodies are more than just the sum of their parts. If you think of the human body as a jigsaw puzzle, then the easiest answer is that we have most of the pieces, but are still working out the details on how they fit together. Until we can make more connections between the individual pieces, the bigger picture is still a bit fuzzy (especially because, unlike a jigsaw puzzle, we are three dimensional!). Although this text won’t discuss how organs develop in detail, we will spend some time looking at the structure of the finished products. Each organ in the human body is assembled from tissues that are bundled together and folded into a three-dimensional shape (most are tube-like). Examining the tissues that form an organ will often reveal clues about its function within the body.

Similarly, organs work together in interdependent systems that serve a larger function for the body. Although we will discuss each in greater detail later in the book, the major systems are summarized in the table below:

Table 1.2. The major physiological systems within the human body.


Question 1.12

Someone experiencing frequent fluctuations in his or her weight, along with an abnormal Na+ or K+ balance, is likely to have a disorder in what body system?

There are eleven major organ systems in the human body, and they function independently to carry out interdependent processes. This means that that while each system carries out a particular function, eventually all systems intersect with each other in some way. As an example, let’s see if we can connect two systems that might appear to be very disjointed – the circulatory system and the musculoskeletal systems. The circulatory system contains the heart and blood vessels. The heart pumps to create pressure that pushes blood into arteries, capillaries, and eventually to our tissues. However, as blood travels further from the heart it is stripped of nutrients and O2. In order to be replenished, it must be returned to the heart, but the pressure in the return vessels, the veins, is very low, making it difficult to move blood through. Although there are adaptations in veins that help to overcome this problem, this process is greatly helped by skeletal muscle. Because veins are situated between skeletal muscles, they get a pressure boost when skeletal muscles contract during normal movement and “squeeze” them.

Question 1.13

Question 1.13

Consider the functions of the kidney in the urinary system and the blood vessels in the circulatory system. What tissue type is common to both systems, and what is its function in each?

Click here to see the answer to Question 1.13.

​The interdependency of body systems also has a significant impact on the diagnosis and treatment of disease. For example, observing someone with asthma might lead you to the conclusion that asthma is a breathing disorder that affects the lungs in the respiratory system. However, this complicated disorder also involves the nervous, immune, and muscular systems as well. In actuality, for individuals that suffer from asthma, physical and environmental factors such as exercise, pollen, chemical fumes, dust, and individualized allergens can trigger constriction of the smooth muscle surrounding small airways and increase mucus production. This causes the airways to narrow and leads to difficulties with breathing, coughing, wheezing, and shortness of breath that characterize the disease. In order to manage these symptoms during an attack, asthma sufferers often carry an inhaler filled with a medication known as albuterol, which binds to receptors used by the nervous system to relax smooth muscle and dilate the airways. In order to prevent the attacks from happening in the long term, they might take medication to desensitize or suppress their immune response to these benign environmental factors.

Often, exploring disease and clinical situations for disorders like asthma enables you to dive deeper into the fascinating world of anatomy and physiology by reinforcing the connections between organ systems, which is why you can expect to hear about some in every chapter of this book!

Question 1.14

Based on the table above, which body systems might be important for regulating blood pressure?

A

Integumentary

B

Endocrine

C

Reproductive

D

Nervous

E

Immune/Lymphatic

F

Cardiovascular

G

Respiratory

H

Urinary

I

Musculoskeletal

J

Digestive


1.3.6​ Relationship Between Physiology and Anatomy

To understand physiological processes, one needs an understanding of how they are affected by the anatomical structure of the human body. We do not discuss anatomical structures in this book; instead, we focus on physiological processes. But students need to understand that anatomy directly affects physiology. An example of this is given by by body cavities. Body cavities allow for the precise control of the environment around organ systems, aiding in their ability to carry out their physiological function. As an example, the heart and lungs are found within the thoracic cavity. Contraction of the diaphragm, a muscle that borders the bottom of the thoracic cavity, changes the volume of the thoracic cavity and aids in respiration and the return of venous blood to the heart!

​Welcome to your first interactive diagram! By hovering your cursor over the diagram below, you should see multiple blue hotspots appear. You can interact with each spot by hovering over it. Sometimes you will uncover additional text to read, sometimes an additional image, and in some cases, you will see a video to watch. In this example, the hot spots will help you to identify and remember the cavities and sub-cavities of the human body.​


1.4 Homeostatic Set Points

​The images below show how several components of a feedback system coordinate in order to maintain body temperature homeostasis.

Figure 1.9. The components of a feedback control system.​
​Figure 1.10. Temperature regulation is dependent on regulation by feedback control.​

Now that we understand the importance of structure and function and the hierarchy of complexity within the human body, it is easier to appreciate how disruption of normal body processes in one system can affect those in another. This is especially true when one experiences illness, i.e. a disruption in homeostasis. The compensatory mechanisms from interdependent systems are crucial to restore balance within the body.

TQ 1.01

Can you think of a physiologic process that is not under the control of a homeostatic reflex system?

Hover here to see the answer to Thought Question 1.01.


​Survival is dependent on the ability of the human body to maintain an internal balance. As previously discussed, the processes that maintain steady conditions within the human body are collectively referred to as homeostasis. A homeostatic set point ensures the overall balance among all organ systems of the human body and is maintained automatically in a healthy, well-functioning individual. For example, the classic example of a homeostatic set point is the body’s ability to maintain a constant internal temperature, as shown in Figure 1.10. The integumentary, circulatory, and immune systems coordinate together to ensure a constant internal temperature of approximately 98.6°F. The sweat glands in the skin enable cooling, changes in circulation of blood to the skin can prevent heat loss, and the immune mediators can work to increase metabolism and heat production through fever in order to prevent illness and infection.

Question 1.15

Which part of the brain monitors homeostasis and plays a role in regulating internal set points?

A

Thalamus

B

Cortex

C

Pancreas

D

Hypothalamus


1.4.1​ Homeostasis: Feedback Control Loops

Most biological systems are a part of a closed loop, where the stimulus and response have a relationship to one another. For example, in the endocrine system, the a change in body conditions may initiate the release of hormones and trigger a physiological process that will in turn modify this process. Such processes are called feedback control loops, as shown in Figure 1.11a, and can work to inhibit or to stimulate another physiological process. Stimuli, such as elevated blood sugar after a meal, trigger the release of specific hormones that establish a feedback mechanism. This type of feedback is referred to as negative feedback because the outcome of the activation loop is a return of an important physiological process to its homeostatic set-point. If blood glucose is elevated after a meal (hyperglycemia) (Figure 1.11b, stimulus), insulin is secreted by pancreatic beta cells (sensor) in response to hyperglycemia. Once insulin (controller) is released, it can bind to receptors on insulin-responsive tissues (effectors) such as liver, fat, and skeletal muscles, and the tissues will respond by increasing glucose transport into the cells. This process will then lower blood glucose back to baseline. To simplify, the release of the hormone initiates a physiological response that returns internal conditions to an established set point.

​Figure 1.11. Feedback loops regulate internal set points in body systems. A. Negative (–) and positive (+) mechanisms work to regulate physiological processes. B. Blood glucose is regulated through a negative feedback mechanism involving insulin.​


A woman in her 60s is rushed to the emergency department (ED) after having lost consciousness at a Singing Christmas Tree event. The emergency medical technician (EMT) reports that in addition to losing consciousness, the woman was tachycardic (~100 bpm), warm to the touch and diaphoretic (sweaty). During the physical exam, the patient reported that she had not been feeling well lately, but was not taking medications, had no recent surgeries, and has not been diagnosed with anything. As time passed she slowly became a little more coherent and her heartrate began to normalize, but she suddenly vomited on the floor. Rapid blood tests reveal hypoglycemia (reduced blood glucose). 

Question 1.16

What is wrong with this patient?

A

She forgot to eat

B

She walked to the concert and was badly out of shape

C

She had a tumor causing over-secretion of insulin

D

She was taking over-the-counter supplements

Hover here to find out how this condition would be treated. 


​A positive feedback loop is initiated by a stimulus, which elicits a physiological response that results in an increase in the original stimulus. Positive feedback mechanisms initiate responses that amplify the body’s response to a particular stimulus. For example, the process of lactation is regulated by positive feedback. When the baby suckles on the mother’s nipple, a stimulus is communicated to the hypothalamus in the brain, which responds by initiating prolactin release from the pituitary gland. This leads to more milk production, allowing continued suckling and more prolactin release and greater milk production. 

Another example of a positive feedback mechanism is blood clotting. The initial tear in the vascular endothelium releases chemicals that activate platelets to adhere to the site of the tear. As platelets begin to aggregate, they release additional chemicals, which aid in the attraction of more platelets. Clotting proceeds until the tear in the endothelium is fully sealed by the activity of platelets and other essential clotting components.

Question 1.17

The body maintains a relatively constant internal environment by using ______________ feedback mechanisms, which attempt to return the stimulus back to baseline.

​An attempt to modulate internal conditions might include multiple body system involvement. For example, multiple body systems and steps are involved in the feedback loop to regulate hypoxia due to altitude. Acutely, hypoxia is detected by chemoreceptors, which carry messages to the hypothalamus and initiate the release of norepinephrine. Norepinephrine will increase heart rate and breathing rate to ensure adequate oxygenation of blood and delivery to tissues. With prolonged hypoxia, reduced O2 levels are sensed at the level of the kidney. The kidney can release erythropoietin (EPO), a hormone. EPO can activate stem cells in the bone marrow to differentiate into new red blood cells to attempt to deliver increased amounts of O2. All of these key organ systems (respiratory, cardiovascular, urinary, and skeletal) work together to ensure adequate O2 levels reach the tissue, and thus, reverse the hypoxia. In some situations, the stimulus and response are unrelated. This is known as an open system or feed forward mechanism. For example, you may produce saliva in response to the smell of food, or your heart may beat faster before starting a race. In both of these situations, your body’s response doesn’t impact the stimulus. Instead, feed forward mechanisms are usually pre-emptive, and help the body to prepare itself for something you are anticipating to happen (in this case, digesting the breakfast you are about to eat, and increasing blood flow to your muscles and lungs you will need for the race).

Question 1.18

According to Figure 1.11, positive feedback mechanisms would ______________ stimulus levels.


TQ 1.02

Based on what you have learned about feedback processes in the human body, during labor, why does it usually take a long time for the contractions to proceed to the point when the child is born (delivery)?

​Hover here to see the answer to Thought Question 1.02.


1.4.2 Homeostasis: Fluid Compartment Regulation

The regulation of fluid compartment volume is critical for whole body homeostasis. Loss of blood volume results in disruption of ion balance in tissues as well as water movement between compartments. Fluid imbalance can lead to dehydration of cells, imbalance in ion concentrations and if prolonged, cell death.

At the cellular level, ion concentrations in the fluid inside cells (intracellular fluid; ICF) and in the fluid outside/around cells (extracellular fluid; ECF) must be tightly regulated in order to control shifts in water between these compartments (Figure 1.12). This regulation is critical because shifts in tissue fluid and water volume can further impact plasma volume. This is because movement of water through the semi-permeable plasma membranes of cells is driven by osmosis and is heavily influenced by ion concentrations within these compartments. Loss of plasma volume drives the movement of water from tissues into the blood, and shifts in ion concentration and/or water at the tissue level influence ICF and ECF volumes and can potentially dysregulate physiological processes.

Question 1.19

Shifts in ion concentrations within the ICF and ECF can cause water to move by the process of ______________.

Figure 1.12. Water is found inside cells (ICF), around cells (IF), and within plasma.​

​Under normal conditions, several body systems influence this distribution of fluid volumes globally through actions that regulate output of urine by the kidney and intake of water. Proportionally, the distribution of fluid volume across these three compartments is greatest in the ICF, with it constituting 60% of total fluid volume. The remaining 40% of body fluid is within the ECF (extracellular fluid), with the great majority (~80%) of that fluid found in the interstitial fluid and 20% in the plasma (Figure 1.13) (interstitial fluid and plasma are components of the ECF). This distribution across compartments is tightly regulated to ensure that fluid intake and output are matched. This delicate balance is maintained primarily by feedback regulation in the kidney involving several hormones as well as hydrostatic and colloid osmotic pressures in the capillary beds.

​Figure 1.13. The proportional distribution of total body fluids.​

​While osmotic pressure is a driving force for water movement into and out of cells, other forces are at play to drive the movement of larger volumes of fluid between compartments at the level of the capillary. The role of such forces is understood by examining the process of capillary filtration. Hydrostatic pressure, the pressure against the capillary wall caused by the pumping of the heart, and colloid osmotic pressure, the pressure caused by the attractive force of albumin, proteins, and other ions within the plasma, influence filtration of fluid at the level of the capillary. Hydrostatic pressure is higher than colloid osmotic pressure at the arterial end, driving plasma and nutrients out of the capillary. As the blood travels to the venous end of the capillary, hydrostatic pressure is significantly lower than the colloid osmotic pressure, resulting in a driving force inward for fluid. This process enables approximately 90% of the filtered fluid from the arterial end to be returned at the venous end of the capillary. The remaining volume is recycled through the lymphatic system before returning to the blood volume at the level of the heart.

Question 1.20

Solutes in the plasma contribute to what driving force in capillary filtration?

A

Hydrostatic pressure

B

Osmosis

C

Colloid osmotic pressure

D

Leakage


This video reviews this process and demonstrates the importance of the various pressures in regulating fluid homeostasis within body compartments.

​Fluid balance is critical in health and human disease. Trauma, surgery, or diseases that cause loss of water and/or electrolytes can disturb fluid volumes in these compartments leading to systemic complications with blood pressure and perfusion of tissues. Additional exploration of fluid balance and regulation can be found in the chapter on the Renal System and Long-Term Blood Pressure Regulation.

TQ 1.03

How do changes in hydrostatic pressure, such as those seen in hypertensive patients with chronic high blood pressure, impact capillary filtration? What related physical symptoms might occur as a result of prolonged high blood pressure?

Hover here to see the answer to Thought Question 1.03.


Question 1.21

Question 1.21

Describe how loss of plasma can impact interstitial fluid volume.

​​Click here to see the answer to Question 1.21.


Question 1.22

Question 1.22

Diabetics can develop dehydration due to hypoglycemia (low blood sugar) and glycosuria (high glucose in the urine) leading to excessive urination. Based on what you learned about fluid movement in compartments, why do you think this happens?

​​​Click here to see the answer to Question 1.22.

Question 1.23

What topic did you understand the least from this chapter? Explain. (Remember that we are looking for what you understood the least and not necessarily something that you didn’t understand.)


1.5 In-Chapter Feedback​

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1.6 Answers to Discussion Questions

​​Answer to Question 1.03

The ability to effectively 'see' smaller and smaller structures within the body has allowed us to understand physiological function as a consequence of anatomical structures.

Click here to return to Question 1.03

​​​Answer to Question 1.04

Expression of different proteins (from genes) allows cells to specialize for one task versus another. Since an organ is made from many diverse cell types, it's possible for it to have more than one function.

Click here to return to Question 1.04

​Answer to Question 1.13

Connective tissue. The kidney filters the blood and produces urine, which is the waste from many metabolic processes. The filtered blood returns to circulation and the urine waste is expelled from the body.

Click here to return to Question 1.13

Answer to Question 1.21

Loss of plasma will result in the movement of tissue fluid into the plasma from interstitial fluid in order to maintain blood pressure.

​Click here to return to Question 1.21

Answer to Question 1.22

Glucose is a solute. When there is too much glucose in the urine in the kidneys, this creates an osmotic pressure that pulls water out of the blood and into the urine. So, the person urinates more water, loses water in the body, and becomes dehydrated.

​​Click here to return to Question 1.22


1.7 Image Citations

[1] Image courtesy of Wellcome Images under CC BY 4.0.

[2] Image courtesy of ​Darryl Leja, NHGRI under CC BY 2.0.

[3] Image courtesy of Harold E. Dougherty in the Public Domain.

[4] Image courtesy of Arielinson under CC BY-SA 4.0.

[5] Image courtesy of Erik1980 under CC BY-SA 3.0.

[6] Image courtesy of OpenStax Anatomy and Physiology under CC BY 4.0.

The branch of science concerned with the bodily structure of humans, animals, and other living organisms, especially as revealed by dissection and the separation of parts.
The study of function and processes essential for maintenance of life.
Visualization technique dependent on the movement of hydrogen ions as small magnets.
A series of X-ray images taken from different angles and using computer processing to create cross-sectional images, or slices, of the bones, blood vessels, and soft tissues inside your body.
A molecule that is present in living organisms, including large macromolecules such as proteins, carbohydrates, lipids, and nucleic acids as well as small molecules such as primary metabolites, secondary metabolites, and natural products.
Having an affinity for water.
Tending to repel or fail to mix with water.
Rod-shaped organelles that can be considered the power generators of the cell, converting oxygen and nutrients into adenosine triphosphate (ATP).
Folds of the mitochondrial inner membrane that provide an increase in the surface area for processes that help to produce ATP in the final steps of cellular respiration.
Tiny air sac of the lungs that allows for rapid gaseous exchange.
The ability of biological systems to maintain a relatively constant internal environment in the face of changing external environmental factors.
A lipid bilayer that forms the outer boundary of a cell or organelle.
Pertaining to DNA and expression of genes within DNA.
Relating to the fluid component of the cytoplasm excluding the organelles and other suspended intracellular structures.
Substance produced by cells and secreted into the environment in which the cells are embedded, contains collagen, other structural proteins and fluid, and can influence the behavior of the cells.
Definition
Cavity of a physiological structure, like a blood vessel.
Definition
A mixture of water, salts, and proteins surrounding cells.
Inflammatory disease of the airways of the lungs characterized by variable and recurring symptoms of wheezing, coughing, chest tightness, and shortness of breath.
The anatomical compartments within the human body where organs are located.
Hair and nail growth is not homeostatically regulated. There is no advantage in using energy to regulate these processes. The disadvantage is that they can grow very long and interfere with normal activities.
Established threshold required for a particular physiological process to maintain a constant internal balance.
Cells and chemicals responsible for fostering the immune response.
A physiological control system that takes the system output into consideration and enables the system to adjust its performance to meet a desired output response.
A physiological reaction whereby the product of the reaction regulates the reaction and causes a reversal of the original stimulus in order to reestablish the set point.
Surgical removal of the tumor.
A feedback process in which the effects of a small disturbance in a physiological system results in an increase in the magnitude of the perturbation and a resulting increase in the physiological outcome.
A deficiency in the amount of oxygen getting to the tissues.
Childbirth is based on the increasing levels of oxytocin that cause the uterine contractions. Under positive feedback, oxytocin levels increase, which results in increasing strong contractions by the upper uterus that will ultimately result in the birth of the child.
The fluid part of blood in which the cells are suspended
Pressure exerted on the wall of a vessel due to the volume of the fluid.
Pressure exerted by proteins, notably albumin, on a vessel's plasma (blood/liquid) that usually tends to pull water into the blood.
Fluid movement into and out of a capillary as a result of hydrostatic and osmotic pressures.
Hydrostatic pressure is responsible for moving nutrients from the blood into the interstitial fluid. This pressure must decrease in order for fluid to be absorbed back into the blood. Changes in blood pressure will result in a shift in fluid balance between the blood and tissues. It may lead to disorders like edema, where excessive fluid accumulates in the tissues.