Anatomy and Physiology – Body Functions and Life Processes

Anatomy and Physiology – Body Functions and Life Processes

BODY FUNCTIONS & LIFE PROCESS

Body Functions

• Body functions are the physiological or psychological functions of body
• systems. The body's functions are ultimately its cells' functions. Survival is
• the body's most important business. Survival depends on the body's
• maintaining or restoring homeostasis, a state of relative constancy, of its
• internal environment.
• More than a century ago, French physiologist, Claude Bernard (1813-1878),
• made a remarkable observation. He noted that body cells survived in a
• healthy condition only when the temperature, pressure, and chemical
• composition of their environment remained relatively constant. Later, an
• American physiologist, Walter B. Cannon (1871-1945), suggested the name
• homeostasis for the relatively constant states maintained by the body.
• Homeostasis is a key word in modern physiology. It comes from two Greek
• words – "homeo," meaning the same, and "stasis," meaning standing.
• "Standing or staying the same" then is the literal meaning of homeostasis.
• However, as Cannon emphasized, homeostasis does not mean something set
• and immobile that stays exactly the same all the time. In his words,
• homeostasis "means a condition that may vary, but which is relatively
• constant."
• Homeostasis depends on the body's ceaselessly carrying on many activities.
• Its major activities or functions are responding to changes in the body's
• environment, exchanging materials between the environment and cells,
• metabolizing foods, and integrating all of the body's diverse activities.
• The body's ability to perform many of its functions changes gradually over
• the years. In general, the body performs its functions least well at both ends
• of life – in infancy and in old age. During childhood, body functions
• gradually become more and more efficient and effective. During late
• maturity and old age the opposite is true. They gradually become less and
• less efficient and effective. During young adulthood, they normally operate

with maximum efficiency and effectiveness.

Life Process

• All living organisms have certain characteristics that distinguish them from
• non-living forms. The basic processes of life include organization,
• metabolism, responsiveness, movements, and reproduction. In humans, who
• represent the most complex form of life, there are additional requirements
• such as growth, differentiation, respiration, digestion, and excretion. All of

these processes are interrelated. No part of the body, from the smallest cell to a complete body system, works in isolation. All function together, in finetuned balance, for the well being of the individual and to maintain life.

• Disease such as cancer and death represent a disruption of the balance in
• these processes.
• The following are a brief description of the life process:
• Organization
• At all levels of the organizational scheme, there is a division of labor. Each
• component has its own job to perform in cooperation with others. Even a
• single cell, if it loses its integrity or organization, will die.
• Metabolism
• Metabolism is a broad term that includes all the chemical reactions that
• occur in the body. One phase of metabolism is catabolism in which complex
• substances are broken down into simpler building blocks and energy is
• released.
• Responsiveness
• Responsiveness or irritability is concerned with detecting changes in the
• internal or external environments and reacting to that change. It is the act of
• sensing a stimulus and responding to it.
• Movement
• There are many types of movement within the body. On the cellular level,
• molecules move from one place to another. Blood moves from one part of
• the body to another. The diaphragm moves with every breath. The ability of
• muscle fibers to shorten and thus to produce movement is called
• contractility.
• Reproduction
• For most people, reproduction refers to the formation of a new person, the
• birth of a baby. In this way, life is transmitted from one generation to the
• next through reproduction of the organism. In a broader sense, reproduction
• also refers to the formation of new cells for the replacement and repair of old
• cells as well as for growth. This is cellular reproduction. Both are essential
• to the survival of the human race.
• Growth
• Growth refers to an increase in size either through an increase in the number
• of cells or through an increase in the size of each individual cell. In order for
• growth to occur, anabolic processes must occur at a faster rate than catabolic
• processes.
• Differentiation
• Differentiation is a developmental process by which unspecialized cells
• change into specialized cells with distinctive structural and functional
• characteristics. Through differentiation, cells develop into tissues and
• organs.
• Respiration
• Respiration refers to all the processes involved in the exchange of oxygen
• and carbon dioxide between the cells and the external environment. It
• includes ventilation, the diffusion of oxygen and carbon dioxide, and the
• transport of the gases in the blood. Cellular respiration deals with the cell's
• utilization of oxygen and release of carbon dioxide in its metabolism.
• Digestion
• Digestion is the process of breaking down complex ingested foods into
• simple molecules that can be absorbed into the blood and utilized by the
• body.
• Excretion
• Excretion is the process that removes the waste products of digestion and
• metabolism from the body. It gets rid of by-products that the body is unable
• to use, many of which are toxic and incompatible with life.
• The ten life processes described above are not enough to ensure the survival
• of the individual. In addition to these processes, life depends on certain
• physical factors from the environment. These include water, oxygen,

nutrients, heat, and pressure.

ANATOMICAL TERMINOLOGY

• Before we get into the following learning units, which will provide more
• detailed discussion of topics on different human body systems, it is
• necessary to learn some useful terms for describing body structure. Knowing
• these terms will make it much easier for us to understand the content of the

following learning units. Three groups of terms are introduced here:

 Directional Terms

• Planes of the Body
• Body Cavities

Directional Terms

• Directional terms describe the positions of structures relative to other
• structures or locations in the body.
• Superior or cranial – toward the head end of the body; upper (example, the
• hand is part of the superior extremity).
• Inferior or caudal – away from the head; lower (example, the foot is part of
• the inferior extremity).
• Anterior or ventral – front (example, the kneecap is located on the anterior
• side of the leg).
• Posterior or dorsal – back (example, the shoulder blades are located on the
• posterior side of the body).
• Medial – toward the midline of the body (example, the middle toe is located
• at the medial side of the foot).
• Lateral – away from the midline of the body (example, the little toe is
• located at the lateral side of the foot).
• Proximal – toward or nearest the trunk or the point of origin of a part
• (example, the proximal end of the femur joins with the pelvic bone).
• Distal – away from or farthest from the trunk or the point or origin of a part
• (example, the hand is located at the distal end of the forearm)
• Planes of the Body
• Coronal Plane (Frontal Plane) – A vertical plane running from side to side;
• divides the body or any of its parts into anterior and posterior portions.
• Sagittal Plane (Lateral Plane) – A vertical plane running from front to
• back; divides the body or any of its parts into right and left sides.
• Axial Plane (Transverse Plane) – A horizontal plane; divides the body or
• any of its parts into upper and lower parts.
• Median plane – Sagittal plane through the midline of the body; divides the

body or any of its parts into right and left halves.

Body Cavaties

• The cavities, or spaces, of the body contain the internal organs, or viscera.
• The two main cavities are called the ventral and dorsal cavities. The ventral
• is the larger cavity and is subdivided into two parts (thoracic and
• abdominopelvic cavities) by the diaphragm, a dome-shaped respiratory
• muscle.
• Thoracic cavity
• The upper ventral, thoracic, or chest cavity contains the heart, lungs, trachea,
• esophagus, large blood vessels, and nerves. The thoracic cavity is bound
• laterally by the ribs (covered by costal pleura) and the diaphragm caudally
• (covered by diaphragmatic pleura).
• Abdominal and pelvic cavity
• The lower part of the ventral (abdominopelvic) cavity can be further divided
• into two portions: abdominal portion and pelvic portion. The abdominal
• cavity contains most of the gastrointestinal tract as well as the kidneys and
• adrenal glands. The abdominal cavity is bound cranially by the diaphragm,
• laterally by the body wall, and caudally by the pelvic cavity. The pelvic
• cavity contains most of the urogenital system as well as the rectum. The
• pelvic cavity is bounded cranially by the abdominal cavity, dorsally by the
• sacrum, and laterally by the pelvis.
• Dorsal cavity
• The smaller of the two main cavities is called the dorsal cavity. As its name
• implies, it contains organs lying more posterior in the body. The dorsal
• cavity, again, can be divided into two portions. The upper portion, or the
• cranial cavity, houses the brain, and the lower portion, or vertebral canal
• houses the spinal cord.
• Here is what we have learned from Introduction to the Human Body:
• The human body is a single structure but it is made up of billions of
• smaller structures of four major kinds: cells, tissues, organs, and
• systems.
• An organ is an organization of several different kinds of tissues so
• arranged that together they can perform a special function.
• A system is an organization of varying numbers and kinds of organs
• so arranged that together they can perform complex functions for the
• body.
• Ten major systems include the skeletal, muscular, nervous, endocrine,
• cardiovascular, lymphatic, respiratory, digestive, urinary, and the
• reproductive system.
• Body functions are the physiological or psychological functions of
• body systems. Survival of the body depends on the body's maintaining
• or restoring homeostasis, a state of relative constancy, of its internal
• environment.
• Human life process includes organization, metabolism,
• responsiveness, movements, reproduction, growth, differentiation,
• respiration, digestion, and excretion. All these processes work
• together, in fine-tuned balance, for the well-being of the individual
• and to maintain life.
• Life depends on certain physical factors from the environment, which
• include water, oxygen, nutrients, heat, and pressure.
• Useful terms for describing body parts and activities include:
• o Directional terms
• o Terms describing planes of the body
• o Terms describing body cavities
• Cell
• The cell (from Latin cella, meaning "small room") is the basic structural,
• functional, and biological unit of all known living organisms.Cells is the
• smallest unit of life that can replicate independently, and are often called the
• "building blocks of life".
• Cells, the smallest structures capable of maintaining life and reproducing,
• compose all living things, from single-celled plants to multibillion-celled
• animals. The human body, which is made up of numerous cells, begins as a
• single, newly fertilized cell.
• Almost all human cells are microscopic in size. To give you an idea how
• small a cell is, one average-sized adult body, according to one estimate,
• consists of 100 trillion cells
• Two-thirds of a cell is water, which means that two-thirds of your whole
• body is water. The rest is a mixture of molecules, mainly
• proteins, lipids and carbohydrates. Your cells turn the raw materials in the
• food you eat into the molecules your body needs, using thousands of
• different chemical reactions.
• The nucleus is surrounded by a membrane called the nuclear envelope,
• which protects the DNA and separates the nucleus from the rest of the cell.
• Plasma membrane (illustration) the plasma membrane is the outer lining of
• the cell.
• The cell (from Latin cella, meaning "small room") is the basic structural,
• functional, and biological unit of all known living organisms. Cells are the
• smallest unit of life that can replicate independently, and are often called the
• "building blocks of life". The study of cells is called cell biology.
• Cells consist of cytoplasm enclosed within a membrane, which contains
• many bimolecular such as proteins and nucleic acids. Organisms can be
• classified as unicellular (consisting of a single cell; including bacteria)
• or multi cellular (including plants and animals). While the number of cells in
• plants and animals varies from species to species, humans contain more than
• 10 trillion cells. Most plant and animal cells are visible only under the
• microscope, with dimensions between 1 and 100 micrometres.
• The cell was discovered by Robert Hooke in 1665, who named the
• biological unit for its resemblance to cells inhabited by Christian monks in a
• monastery. Cell theory, first developed in 1839
• Schleiden and Theodor Schwann, states that all organisms are composed of
• one or more cells, that cells are the fundamental unit of structure and
• function in all living organisms, that all cells come from preexisting cells,
• and that all cells contain the hereditary information necessary for regulating
• cell functions and for transmitting information to the next generation of
• cells. Cells emerged on Earth at least 3.5 billion years ago.
• Cells are considered the basic units of life in part because they come in
• discrete and easily recognizable packages. That's because all cells are
• surrounded by a structure called the cell membrane — which, much like the
• walls of a house, serves as a clear boundary between the cell's internal and
• external environments. The cell membrane is sometimes also referred to as
• the plasma membrane.
• Cell membranes are based on a framework of fat-based molecules called
• phospholipids, which physically prevent water-loving, or hydrophilic,
• substances from entering or escaping the cell. These membranes are also
• studded with proteins that serve various functions. Some of these proteins
• act as gatekeepers, determining what substances can and cannot cross the
• membrane. Others function as markers, identifying the cell as part of the
• same organism or as foreign. Still others work like fasteners, binding cells
• together so they can function as a unit. Yet other membrane proteins serve as
• communicators, sending and receiving signals from neighboring cells and
• the environment — whether friendly or alarming
• Cells are the smallest common denominator of life. Some cells are
• organisms unto themselves; others are part of multicellular organisms. All
• cells are made from the same major classes of organic molecules: nucleic
• acids, proteins, carbohydrates, and lipids. In addition, cells can be placed in
• two major categories as a result of ancient evolutionary events: prokaryotes,
• with their cytoplasmic genomes, and eukaryotes, with their nuclear-encased
• genomes and other membrane-bound organelles. Though they are small,
• cells have evolved into a vast variety of shapes and sizes. Together they
• form tissues that themselves form organs, and eventually entire organisms
• Cells are of two types, eukaryotic, which contain a nucleus, and prokaryotic,
• which do not. Prokaryotes are single-celled organisms, while eukaryotes can
• be either single-celled or multicellular.
• Prokaryotic cells
• Prokaryotic cells were the first form of life on Earth, characterized by having

vital biological processes including cell signaling and being self-sustaining.

They are simpler and smaller than eukaryotic cells, and lack membranebound organelles such as the nucleus. Prokaryotes include two of the domains of life, bacteria and archaea. The DNA of a prokaryotic cell consists of a single chromosome that is in direct contact with the cytoplasm.

• The nuclear region in the cytoplasm is called the nucleoid.
• Most prokaryotes are the smallest of all organisms ranging from 0.5 to
• 2.0 µm in diameter.
• A prokaryotic cell has three architectural regions:
• Enclosing the cell is the cell envelope – generally consisting of a plasma
• membrane covered by a cell wall which, for some bacteria, may be
• further covered by a third layer called a capsule. Though most
• prokaryotes have both a cell membrane and a cell wall, there are
• exceptions such as Mycoplasma (bacteria) and Thermoplasma (archaea)
• which only possess the cell membrane layer. The envelope gives rigidity
• to the cell and separates the interior of the cell from its environment,
• serving as a protective filter. The cell wall consists of peptidoglycan in
• bacteria, and acts as an additional barrier against exterior forces. It also
• prevents the cell from expanding and bursting (cytolysis) from osmotic
• pressure due to a hypotonic environment. Some eukaryotic cells (plant
• cells and fungal cells) also have a cell wall.
• Inside the cell is the cytoplasmic region that contains the genome (DNA),
• ribosome and various sorts of inclusions. The genetic material is freely
• found in the cytoplasm. Prokaryotes can carry extra chromosomal
• DNA elements called plasmids, which are usually circular. Linear
• bacterial plasmids have been identified in several species
• of spirochetebacteria, including members of the
• genus Borrelia notably Borrelia burgdorferi, which causes Lyme
• disease.[13] Though not forming a nucleus, the DNA is condensed in
• a nucleoid. Plasmids encode additional genes, such as antibiotic
• resistance genes.
• On the outside, flagella and pili project from the cell's surface. These are
• structures (not present in all prokaryotes) made of proteins that facilitate
• movement and communication between cells.
• Eukaryotic cells
• Plants, animals, fungi, slime moulds, protozoa, and algae are all eukaryotic.
• These cells are about fifteen times wider than a typical prokaryote and can
• be as much as a thousand times greater in volume. The main distinguishing

feature of eukaryotes as compared to prokaryotes is compartmentalization: the presence of membranebound organelles (compartments) in which specific metabolic activities take place. Most important among these is a cell nucleus, an organelle that houses the cell's DNA. This nucleus gives the eukaryote its name, which means "true kernel (nucleus)". Other differences include:

• The plasma membrane resembles that of prokaryotes in function, with
• minor differences in the setup. Cell walls may or may not be present.
• The eukaryotic DNA is organized in one or more linear molecules,
• called chromosomes, which are associated with histoneproteins. All
• chromosomal DNA is stored in the cell nucleus, separated from the
• cytoplasm by a membrane. Some eukaryotic organelles such
• as mitochondria also contain some DNA.
• Many eukaryotic cells are ciliated with primary cilia. Primary cilia play
• important roles in chemosensation,mechanosensation, and thermo
• sensation. Cilia may thus be "viewed as a sensory cellular antennae that
• coordinates a large number of cellular signaling pathways, sometimes
• coupling the signaling to ciliary motility or alternatively to cell division
• and differentiation."
• Motile cells of eukaryotes can move using motile cilia or flagella. Motile
• cells are absent in conifers and flowering plants. Eukaryotic flagella are
• less complex than those of prokaryotes.
• All cells, whether prokaryotic or eukaryotic, have a membrane that envelops
• the cell, regulates what moves in and out (selectively permeable), and
• maintains the electric potential of the cell. Inside the membrane,
• the cytoplasm takes up most of the cell's volume. All cells (except red blood
• cells which lack a cell nucleus and most organelles to accommodate
• maximum space for hemoglobin) possess DNA, the hereditary material
• of genes, and RNA, containing the information necessary to build
• various proteins such as enzymes, the cell's primary machinery. There are
• also other kinds of bimolecular in cells. This article lists these primary
• components of the cell, then briefly describes their function.
• Membrane
• The cell membrane, or plasma membrane, is a biological membrane that
• surrounds the cytoplasm of a cell. In animals, the plasma membrane is the
• outer boundary of the cell, while in plants and prokaryotes it is usually
• covered by a cell wall. This membrane serves to separate and protect a cell
• from its surrounding environment and is made mostly from a double layer of
• phospholipids, which are amphiphilic (partly hydrophobic and
• partly hydrophilic). Hence, the layer is called a phospholipids bilayer, or
• sometimes a fluid mosaic membrane. Embedded within this membrane is a
• variety of protein molecules that act as channels and pumps that move
• different molecules into and out of the cell. The membrane is said to be
• 'semi-permeable', in that it can either let a substance (molecule or ion) pass
• through freely, pass through to a limited extent or not pass through at all.
• Cell surface membranes also contain receptor proteins that allow cells to
• detect external signaling molecules such as hormones.
• Genetic material
• Two different kinds of genetic material exist: deoxyribonucleic acid (DNA)
• and ribonucleic acid (RNA). Cells use DNA for their long-term information
• storage. The biological information contained in an organism is encoded in
• its DNA sequence. RNA is used for information transport (e.g., mRNA)
• and enzymatic functions (e.g., ribosomal RNA). Transfer RNA (tRNA)
• molecules are used to add amino acids during protein translation.
• Prokaryotic genetic material is organized in a simple circular DNA molecule
• (the bacterial chromosome) in the nucleoid region of the cytoplasm.
• Eukaryotic genetic material is divided into different, linear molecules
• called chromosomes inside a discrete nucleus, usually with additional
• genetic material in some organelles
• like mitochondria andchloroplasts (see endosymbiotic theory).
• A human cell has genetic material contained in the cell nucleus (the nuclear
• genome) and in the mitochondria (the mitochondrial genome). In humans the
• nuclear genome is divided into 46 linear DNA molecules
• called chromosomes, including 22 homologous chromosome pairs and a pair
• of sex chromosomes. The mitochondrial genome is a circular DNA molecule
• distinct from the nuclear DNA. Although the mitochondrial DNA is very
• small compared to nuclear chromosomes, it codes for 13 proteins involved
• in mitochondrial energy production and specific RNAs.
• Foreign genetic material (most commonly DNA) can also be artificially
• introduced into the cell by a process called transfection. This can be
• transient, if the DNA is not inserted into the cell's genome, or stable, if it is.
• Certain viruses also insert their genetic material into the genome.
• Cells, the smallest structures capable of maintaining life and reproducing,
• compose all living things, from single-celled plants to multibillion-celled
• animals. The human body, which is made up of numerous cells, begins as a
• single, newly fertilized cell.
• Almost all human cells are microscopic in size. To give you an idea how
• small a cell is, one average-sized adult body, according to one estimate,

consists of 100 trillion cells!