GNP111: ANATOMY AND PHYSIOLOGY
Organization of Human Body
1.0 Learning Outcomes:
After studying this session, students are expected to be able to:
•
Define and discuss the levels of organization of the human body,
•
Describe how the body is organized from simple to more complex levels, and
•
Explain the characteristics of life exhibited by human beings.
2.0 Main Content
2.1
Structures of the Human Body
I. Atoms, molecules and compounds: - At its simplest level, the body is composed of atoms.
The most common elements in living organism are carbon, hydrogen, oxygen, nitrogen
phosphorus and sulphur.
II. Cells
The cell is the basic living unit of all organisms. The simplest organisms consist of single
cells. It is estimated that humans are composed of 10 to 100 trillion cells. An average-sized
cell is one-fifth the size of the smallest dot you can make on a sheet of paper with a sharp
pencil. Light microscopes allow us to visualize general features of cells have long been
recognized as the simplest units of living matter that can maintain life and reproduce
themselves. Cells are the basic structural and functional units of the human body and there
are many different types of cells (e.g., sperm, muscle, nerve, blood, and so on: Fig 1).
Fig. 1: Some types of cells
III. Tissues
Tissues are somewhat more complex units than cells. A tissue is an organization of a great
many similar cells that perform a specific function with varying amounts and kinds of
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nonliving, intercellular substance between them. The basic types of tissues in the human body
include epithelial, muscular, nervous, and connective tissues.
➢ Epithelial tissue: - Found in the outer layer of skin, lining of organs, blood and lymph vessels
and body cavities.
➢ Connective tissue: - Connects and supports most part of the body. They constitute most part
of skin, bone and tendons.
➢ Muscle tissue: - Produces movement through its ability to contract. This constitutes skeletal,
smooth and cardiac muscles.
➢ Nerve tissue: - Found in the brain, spinal cord and nerves. It responds to various types of
stimuli and transmits nerve impulses.
Fig. 2: Tissues
IV. Organs
An organ is an organization of several different kinds of tissues arranged together to perform
a particular special function (such as the heart, lungs, kidneys, liver, stomach, etc). For
example, the stomach is an organization of muscular, connective, epithelial, and nervous
tissues. The muscular and connective tissues form its wall, epithelial and connective tissues
form its lining, and nervous tissue extends throughout both its wall and its lining.
V. Systems
A system is an association of organs that have a common function. There are 11 major
systems in the human body, including digestive, nervous, endocrine, circulatory, respiratory,
urinary, reproductive, muscular, lymphatic, skeletal, and integumentary. Systems are the most
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complex of the component units of the human body. (MIS CRUNDLER.... i.e. M =
muscular, I = integumentary, S = Skeletal, C = circulatory, R = respiratory, U = urinary, N =
nervous, D = digestive, L = lymphatic, E = endocrine, R = reproductive).
2.2
Body Functions
Body functions are the physiological or psychological functions of body systems. The body's
functions are ultimately its cells' functions. However, survival is the major body's concern.
Survival depends on the body's ability to carry out “Homeostasis”. Homeostasis is the
maintenance of a fairly constant internal environment of an organism. The name homeostasis
was suggested by an American physiologist, Walter B. Cannon (1871-1945). It comes from
two Greek words - "homeo," meaning the same, and "stasis," meaning standing. Literary it
means "Standing or staying the same".
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.
2.3 Characteristics of Life
All living organisms have certain characteristics that distinguish them from non-living forms:
(MR NIGER D). The basic processes of life include organization, metabolism,
responsiveness (irritability), 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. Most diseases
often arise as a result of disruption of the balance in these processes.
➢ Organization (levels):
Atoms › Molecules › Macromolecules › Compounds › Organelles › Cells › Tissues ›
Organs › Systems
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➢ Metabolism
Metabolism is the complete set of all chemical reactions that occur in living cells (in
the body). The two stages of metabolism are Anabolism (which involves building up
of complex substances from simpler ones) and Catabolism (breaking down of
complex substances into simpler building blocks and release of energy). Metabolic
processes need substances like water, food, oxygen, heat, pressure, which all must be
regulated. An example of a catabolic process is cellular respiration. While a good
example of anabolic process is the growth and mineralization of bones.
Fig. 3: Levels of Organization
➢ 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.
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➢ 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 fibres to shorten and
thus to produce movement is called contractility.
➢ Reproduction
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.
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Self-Assessment Questions
1. Define the term Organ and give examples
2. Define system
3. List the characteristics of life and explain any four (4).
4. What do you understand by the term Homeostasis?
References/Further Readings
❖ Kathryn, A. Booth, Terri. D. Wyman (2008). Anatomy, physiology, and
pathophysiology for allied health.
❖ Kent M. Van De Graff, R.Ward Rhees, Sidney Palmer (2010) Schaum’s outline of
human anatomy and physiology 3 rd ed.
❖ Philip Tate (2012) Seeley’s principles of anatomy & physiology 2nd ed.
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CONTINUATION OF HOMEOSTASIS
Homeostasis
Homeostasis is the maintenance of a relatively constant internal environment in an ever
changing external environment. The mechanisms which work towards its achievement are
called homeostatic mechanisms. Essentially all the organs and tissues of the body perform
functions that help to maintain these constant conditions. For instance:
i.
the lungs provide oxygen to the extracellular fluid to continually replenish the
oxygen that is being used by the cells,
ii.
the kidneys maintain constant ion concentrations, and
iii.
the gastrointestinal system provides nutrients.
Each body system contributes to the homeostasis of other systems and of the entire being. No
system of our body works in isolation, and our well-being depends upon the well-being of all
the interacting body systems. A disruption within one system generally has consequences for
several additional body systems. Let us consider some brief explanations of how various
body systems contribute to the maintenance of homeostasis.
The Body Systems and Their Contributions to Homeostasis
•
Nervous System (NS)
This system is made up of the brain, spinal cord, nerves and receptors. The nervous system,
along with the endocrine system, serves as the primary control centre of our body. It operates
at a subconscious level and controls many functions of the internal organs, including the level
of pumping activity by the heart, movements of the gastrointestinal tract, and secretion by
many of the body’s glands. 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 them at optimum
levels.
NS also controls contraction of muscles. The nervous system also regulates various systems
such as the respiratory (controls rate and depth of breathing), cardiovascular system (controls
heart rate and blood pressure), endocrine organs (causes secretion of antidiuretic hormone
ADH and oxytocin), the digestive system (regulates the digestive tract movement and
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secretion), and the urinary system (helps adjust renal blood flow and also controls voiding the
bladder). The nervous system is also involved in sexual behaviours and functions.
•
Endocrine system
The endocrine system consists of which secrete hormones into the bloodstream. Each
hormone has an effect on one or more target organs/tissues. In this way, the system regulates
the metabolism and development of most body cells and body systems. For example, bone
growth is regulated by several hormones, and the endocrine system helps with the
mobilisation of calcium and phosphate into and out of the bones. 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 central nervous system (CNS) development and
behaviours. In the cardiovascular system hormones are needed in the regulation of RBC's
production, and blood pressure. Hormones also have anti-inflammatory effects as well as
stimulate the lymphatic system. In summary, the endocrine system has a regulatory effect on
basically every other body systems.
•
Skeletal system
It consists of all bones in the body, cartilages and ligaments. The skeletal system serves as an
important mineral reserve. For example, if blood levels of calcium or magnesium are low and
the minerals are not available in the diet, they will be taken from the bones. On the other hand
the skeletal system provides calcium needed for all muscle contractions. Lymphocytes and
other cells relating to the immune response are produced and stored in the bone marrow. The
skeletal system aids in protection of the nervous system, endocrine organs, chest and pelvic
regions in which vital organs are housed.
•
Integumentary system
This system is composed of the skin that is the epidermis, dermis and adipose tissue, nails,
hair, receptors, oil glands and sweat glands. The integumentary system is involved in
protecting the body from invading microbes, regulating body temperature through sweating
and vasodilation, or shivering and piloerection, and regulating ions balance in the blood. It
also helps synthesise vitamin D which interacts with calcium and phosphorus absorption, a
factor that is very important for bone growth and maintenance. Hair on the skin guards
entrance into the nasal cavity or other orifices preventing invaders from getting further into
the body. The skin also helps maintain balance by excretion of water and other solutes. The
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keratinised epidermis limits fluid loss through the skin, thus providing mechanical protection
against environmental hazards.
•
Lymphatic system
The lymphatic system is composed mainly of the lymphatic vessels, lymph nodes, thymus,
spleen and the bone marrow. It has three principal roles. First is the maintenance of blood and
other body fluid volumes. Excess fluid that leaves the capillaries when under pressure would
build up and cause edema, but for the role of the lymphatic system. Secondly, the lymphatic
system absorbs fatty acids and triglycerides from fat digestion so that these components of
digestion do not enter directly into the blood stream. Thirdly, the lymphatic system is
involved in defending the body against invading microbes, and also in the immune response.
This system assists in body maintenance such as bone and muscle repair after injuries. It also
assists in maintaining the acid pH of urine required to fight infections in the urinary system.
The tonsils (either of the two masses of lymphatic tissue, one on each side of the oral
pharynx) are the body helpers that defend against infections and toxins absorbed from the
digestive tract. The tonsils also protect against infections entering into the lungs.
•
Respiratory system
The components of the respiratory system are the nasal cavity, pharynx, larynx, glottis,
epiglottis, bronchi, bronchioles, alveoli and the lungs. The respiratory system works in
conjunction with the cardiovascular system to provide oxygen to cells within every body
system for cellular metabolism. The respiratory system also removes carbondioxide. Since
CO2 is mainly transported in the plasma as bicarbonate ions, which act as a chemical buffer,
the respiratory system also helps maintain proper blood pH levels, a fact that is very
important for homeostasis. The respiratory system also helps the lymphatic system by
trapping pathogens and protecting deeper tissues from invading microorganisms.
•
Urinary system
Its main components are the kidneys, ureter, bladder and urethra. Toxic nitrogenous wastes
cumulate as urea, uric acid and creatinine. The urinary system rids the body of these wastes.
It is also involved in the maintenance of blood volume, blood pressure and electrolyte
concentrations within the blood. The kidneys produce a hormone (erythropoietin) that
stimulates red blood cell production. They also play an important role in maintaining the
water content of the body and the level of salts in the extracellular fluid.
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•
Cardiovascular system
It consists of the heart, blood vessels and the blood. The cardiovascular system ensures the
normal functioning of other body systems by transporting hormones, oxygen and nutrients to
them and taking away waste products from them thereby providing all living body cells with
a fresh supply of oxygen and nutrients and also removing carbon dioxide and other toxic
wastes from their surroundings. Homeostasis is disturbed if the cardiovascular or lymphatic
systems are not functioning properly. The cardiovascular system also contains sensors to
monitor blood pressure. They are called baroreceptors. They detect the amount of stretch of
the blood vessels and relay information via the nerves to the CNS which brings about the
appropriate responses that regulate the blood pressure.
•
Muscular system
This system is made of skeletal muscles such as biceps, quadriceps, and gastrocnemius
muscles and smooth or involuntary muscles such as cardiac muscle, intestinal muscles and
muscles of the blood vessels. The muscular system is largely responsible for movement,
posture, balance, gait, secretion by glands and maintenance of body temperature through heat
production. It also contributes to blood glucose balance by storing glucose in form of
glycogen. Muscles also aid in moving blood through veins, protect deep blood vessels and
help the lymphatic system move lymph.
•
Digestive system
Its components include oral cavity, esophagus, stomach, intestines, liver and pancreas. The
nutrients needed by the body are derived from the diet. Food is taken in by the mouth and
broken down into its component parts by enzymes in the gastrointestinal tract (or gut). The
digestive products are then absorbed into the blood across the wall of the intestine and pass to
the liver via the portal vein. The digestive system absorbs organic substances, vitamins, ions,
and water that are needed all over the body. The liver makes nutrients available to the tissues
both for their growth and repair and for the production of energy.
•
Reproductive system
The main components of this system are the ovaries, testes, prostate, uterine tubes, uterus,
vagina and penis. The reproductive system is responsible for the production of sperm cells
and oval for the production of new offspring. The sex hormones do have various effects on
other body systems, and an imbalance can lead to various disorders.
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Body Fluids
Composition of Body Fluids
The Body fluids contain water and solids.
•
Water is an important component of the human body. It constitutes approximately
60% of body weight. In terms of volume, total body water in adult man is about 42
litres. Because water can get through cell barriers, the human body must carefully
balance the electrolyte concentration of extracellular fluids. If the fluid becomes too
dilute, water flows into cells, potentially causing them to swell and burst. On the
other hand, if the salt concentration outside the cell is too high, water will flow out
of the cell, leading to possible collapse.
•
The Solids are organic and inorganic substances.
✓ Organic substances are glucose, amino acids and other proteins, fatty acids
and other lipids, hormones and enzymes.
✓ Inorganic substances present in body fluids are sodium, potassium, calcium,
magnesium, chloride, bicarbonate, phosphate and sulphate.
Body Fluid Compartments
These are the general considerations and inter-relationships of body fluid spaces. Body fluids
can be divided into two (2) main compartments: “Intracellular fluid” (ICF) and
“Extracellular fluid” (ECF), as shown in the figure below:
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Fig. 4: Organization of body fluids and electrolytes into compartments
1. Intracellular fluid (ICF)
ICF consists of all fluid within the cells of the body and is the largest fluid compartment,
accounting for 40% of the body weight. It volume is about 28 litres in adults. Much of the
ICF compartment is found within muscle cells. The primary electrolytes of the ICF
compartment are potassium and phosphate. The ICF compartment contains only small
quantities of sodium and chloride ions and almost no calcium ions. The cells contain 4 times
as much protein as the plasma.
Intracellular fluid provides body cells their turgor as well as a medium within which
biochemical reactions can take place.
2. Extracellular fluid (ECF)
All the fluids outside the cells are collectively called the extracellular fluid. Together these
fluids account for about 20% of the body weight, or about 14 litres. The ECF supports the
cells and allows transport of nutrients and waste products. The extracellular fluid is divided
into the interstitial fluid and the blood plasma. There is another small compartment of fluid
that is referred to as transcellular fluid.
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a) Interstitial fluid (IF)
It is the fluid that surrounds the cells in the various tissues of the body. It is about threequarter (3/4) of the ECF volume. It includes the water contained within the bone and dense
connective tissue. The remaining one quarter (1/4) of the ECF is fluid inside the blood vessels,
that is, the plasma.
b) Plasma
c) Transcellular fluid (TCF)
This is the fluid located in special compartments of the body. It is usually considered to be a
specialised type of extracellular fluid. Their total volume is only about 0.3 litre and they serve
important functions. This compartment includes fluid in the synovial, peritoneal, pericardial,
and intraocular spaces, as well as the cerebrospinal fluid.
The Cell Organization, Structure and Function
Introduction
The basic living unit of the body is the cell. The human body is made up of several cells that
perform basic functions that sustain life. Different types of cells aggregate to form organs that
ultimately perform different functions. While different organs perform different functions, the
body must function in harmony. Each type of cell is specially adapted to perform one or a
few particular functions. For instance, the red blood cells, numbering 25 trillion in each
human being, transport oxygen from the lungs to the tissues.
➢ Cytology: - It is a branch of science concerned with a study of cells.
Cell Theory explains about:
•
All living organisms are composed of cell and cell products.
•
Cell is the basic unit of structure & function of all living organisms.
•
All cells come from the division of pre existing cell.
•
An organism as a whole can be understood through the collective activities &
interactions of its cells.
General Characteristics of Cell
•
Needs nutrition and oxygen
•
Produces its own energy necessary for its growth, repair and other activities
•
Eliminates carbon dioxide and other metabolic wastes
•
Maintains the medium, i.e. the environment for its survival
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•
Shows immediate response to the entry of invaders like bacteria or toxic substances
into the body
•
Reproduces by division. There are some exceptions like neuron, which do not
reproduce.
Organisation of the Cell
The cell has two major parts namely the nucleus and the cytoplasm. The nucleus is separated
from the cytoplasm by a nuclear membrane, and the cytoplasm is separated from the
surrounding fluids by a cell membrane, also called the plasma membrane. The cytoplasm
contains the cell organelles (permanent structures with characteristic morphology that are
highly specialized in specific cellular activity). The different substances that make up the cell
are collectively called protoplasm. Protoplasm is composed mainly of five basic substances
(Inclusions): water, electrolytes, proteins, lipids, and carbohydrates.
•
Proteins
After water, the most abundant substances in most cells are proteins, which normally
constitute 10% to 20% of the cell mass. These can be divided into two types:
structural proteins and functional proteins.
•
Lipids
The biologically important lipids are the fatty acids, triglycerides, phospholipids and
sterols. Fatty acids can be saturated or unsaturated while phospholipids are found in
cell membranes where they act as a structural component. Fatty acids also serve as an
important source of energy in the body.
•
Carbohydrates
Carbohydrates are organic molecules made up of equal amounts carbon and water.
They perform both structural and functional roles. They also help in cell signalling.
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Fig 5.1: A generalised Structure of Animal Eukaryotic Cell
Cell Structure and Function
The structural and functional characteristics of different types of cells are determined by the
nature of the proteins present. The generalized cell functions include movement of substances
across the cell membrane, cell division to make new cells, and protein synthesis. Now, let’s
look at the cell structures/organelles and their functions.
1. Cell Membrane (Plasma Membrane)
Plasma membrane is a thin outer membrane, which maintains the integrity of the cell. It
keeps the cell and its contents separate and distinct from the surrounding. It is a double
layered measuring about 4.5nm and made of phospholipids, cholesterol, glycolipid, &
carbohydrate (oligosaccharides). Therefore, the layer is referred to as Phospholipid bilayer.
Functions of Plasma membrane:•
Separate the cytoplasm inside a cell from extra cellular fluid.
•
Separate cells from one another.
•
Provide an abundant surface on which chemical reaction can occur.
•
Regulate the passage of materials into and out of cells.
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•
It is also selectively permeable, because it let allow some things in and keeps others
out.
Fig 5.2: Structure of the cell membrane (showing double layer)
Fig 5.3: Structure of the cell membrane
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2. Nucleus
The nucleus is usually a spherical organelle, though its shape may vary in some cells.
It is surrounded by a membrane called nuclear membrane. The nuclear membrane has
double layer and the two layers are fused at some points to produce nuclear pores
which are thought to allow molecules pass between the nucleus and cytoplasm. the
nuclear pores are composed of multiple proteins, collectively referred to as
nucleoporins.
There is a smaller spherical structure within the nucleus, the nucleolus. The nucleolus
is a discrete densely stained structure found in the nucleus. It is not surrounded by a
membrane, and is sometimes called a sub-organelle. It is visible when cell is not
dividing and contains RNA for protein manufacture. The fluid contained within the
nucleus is called nucleoplasm to differentiate it from the fluid in the rest of the cell
which is referred to as cytoplasm. The cell nucleus contains the majority of the cell's
genetic material in the form of multiple linear DNA molecules organized into
structures called chromosomes.
Fig 5.4: Structure of the nucleus
3. Cytoplasm
Cytoplasm is a matrix (gel-like fluid) inside the cell. It is the medium for chemical
reaction. It provides a platform upon which other organelles can operate within the
cell. All of the functions for cell expansion, growth and replication are carried out in
the cytoplasm of a cell. Within the cytoplasm, materials move by diffusion, a physical
process that can work only for short distances.
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4. Endoplasmic reticulum (ER) and Ribosomes
The endoplasmic reticulum (ER) is a series of membranous channels that travel across
the cytoplasm of most eukaryotic cells. It forms a continuous network extending from
the cell membrane to the nuclear membrane. In many parts of the cell, the
endoplasmic reticulum is associated with small dense granules lying along the outer
border of its membrane. These structures are known as ribosomes. They impart a
rough appearance to the endoplasmic reticulum, so that the ER is called the Rough
endoplasmic reticulum (RER) in these regions, which are usually associated with
active protein synthesis. On the other hand, the Smooth endoplasmic reticulum (SER)
does not contain ribosomes and is associated with cellular regions which are involved
in the synthesis and transport of lipids or the detoxification of a variety of poisons.
NB: The ribosomes are found in two (2) forms: Stationary type (embedded in rough
endoplasmic reticulum) and Mobile type: found freely and injects proteins directly
into cytoplasm.
Fig.5.5: Structure endoplasmic reticulum
5. Golgi apparatus
The Golgi apparatus is also referred to as the Golgi complex or Golgi body. This
organelle exists as stacks of flattened sacs, or vesicles that are continuous with the
channels of the SER. Their major function is the storage, modification, and packing of
materials produced for secretory export.
Explanation: Secretory granules are formed in the Golgi apparatus. These granules
are packages of highly concentrated protein. Once protein has been formed by the
ribosomes, it accumulates in the Golgi apparatus where it is concentrated and may be
modified and then packaged into vesicles of the secretory granules. These vesicles
fuse with the cell membrane and then open up to release the protein from the cell. Cell
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carbohydrate may be added to the protein within the Golgi body to form
glycoproteins. Mucus is also formed in this area.
Fig.5.6: Golgi apparatus and Secretory vesicles
6. Mitochondria (singular: Mitochondrion)
The mitochondrion is called the “powerhouse” of the cell. Mitochondria are rounded
or cigar-shaped organelles that are particularly prominent in cells with high metabolic
activity. Their name was derived from their threadlike appearance (Greek word:
mitos, meaning‘‘thread’’) under the light microscope. Without the mitochondria, cells
would be unable to extract enough energy from the nutrients, and essentially all
cellular functions would cease. In the mitochondria, the very important compound
adenosine triphosphate (ATP) is formed. This ATP provides energy that is used for
various cellular processes, such as the contraction of a muscle cell.
The mitochondrion is bounded by two membranes; a smooth outer membrane and a
folded inner membrane. The folds (Cristae) project into the interior of the organelle
and have a variety of enzymes embedded in them. These enzymes are involved in the
systematic degradation of organic molecules to yield energy for the cell.
Fig.5.7: Mitochondrion
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7. Lysosomes
Lysosomes are similar in shape to mitochondria but are smaller and consist of a single
boundary membrane. They are vesicular organelles that form by breaking off from the
Golgi apparatus and then dispersing throughout the cytoplasm. They contain powerful
enzymes that would digest the cellular contents if they were not contained within the
impermeable lysosomal membrane. Rupture of this membrane releases these
enzymes. The lysosome plays a role in intracellular digestion and may also be
important in the destruction of certain structures during the process of development.
8. Peroxisomes
Peroxisomes are similar to lysosomes except that the enzymes contained in these
organelles are oxidative in function. Peroxisomes are involved in the oxidative
deamination of amino acids, a reaction vital to the conversion of proteins to other
kinds of compounds.
9. Flagella and cilia
Flagella and cilia are hair-like projections held at one end and capable of movements
at the other end. They are encased in a membrane continuous with the cell membrane.
They play an important role in cell motility because of their coordinated beating
motion. Example, human sperm cell has an active beating flagellum at its posterior
end. Flagella and cilia may be treated as a single kind of organelle: if the structures
are few in number and relatively long, they are called flagella; if short and numerous,
they are considered cilia.
Both flagella and cilia derive their motility from structures called microtubules. As
their name implies, these are elongated, hollow, cylindrical structures; they are
assembled from two protein subunits called α-and β-tubulin, which combine to form a
unit building block for the microtubule.
10. Centrosome
The centrosome contains two centrioles. They lie close to the nucleus. Centrioles
probably play a role in the formation of the spindle fibres, essential for cell division,
(mitosis and meiosis). At the beginning of cell division, the two centrioles divide,
thus forming four centrioles, one pair goes to one end of the cell and the other pair to
the opposite end. The centrioles function to pull the chromosome pairs apart. In this
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way, one set of chromosomes goes to one side of the cell and the other set to the
other. When the cell divides, each new cell has a complete set of chromosomes.
Fig 5.8: Centrioles
11. Vacuoles
These are discrete, clear regions within the cell that contain water and dissolved
materials. The vacuole may act as a reservoir for fluids and salts that might otherwise
interfere with metabolic processes (storage, digestion, and waste removal) occurring in
the cytoplasm. The membrane surrounding the vacuole is called a tonoplast. Many
protozoans have a contractile vacuole, which periodically contracts and forces fluid and
salts out of the cell.
Fig 5.9: Vacuoles
12. Plastids
In almost all plant cells, a variety of tiny membrane-enclosed sacs are found that
contain pigments or provide storage space for starch. These organelles are called
plastids. Chloroplasts are included in this group.
“The chloroplasts are plastid containing chlorophyll and other pigments”; in plants
that carry out photosynthesis.
13. Cytoskeleton
•
Determination of shape of the cell
•
Stability of cell shape
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•
Cellular movements
14. Microfilament (Smallest fibres)
•
1. Structural support
•
2. Maintenance of the characteristic shape of the cell
•
3. Permit contraction
15. Microtubules (largest fibres)
•
Movement of organelles within the cell
•
Movement of chromosomes during cell division
•
Cell extensions
Movement across-cell membrane
Movements across membrane take place in two ways. These are passive and active transport.
Passive movement uses energy whereas active movement consumes energy in the form of
ATP.
a) Passive movement (Downhill Movement):
This takes place when substances can cross the semi permeable plasma membrane and
organelles membranes and move down the concentration gradient (downhill) without
using energy.
It includes:
i.
Simple diffusion: is the movement of particles (solutes) from a region of higher
solute concentration to a region of lower solute concentration. Example, air in alveoli
of the lungs.
ii.
Facilitated diffusion: larger molecules, which are not soluble in lipid need protein
channel to pass through the plasma membrane. No direct energy needed. Example:
Amino acid passes through the cell membrane.
iii.
Osmosis: a special process referring to the passage of water through a selectively
permeable membrane from a region of high water concentration to a region of low
water concentration.
Human cells or other body fluids contain many dissolved substances (called solutes)
such as salts, sugars, acids, and bases. The concentration of solutes in a fluid creates
the osmotic pressure of the solution, which in turn determines the movement of
water through membranes.
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As an example here, we will use sodium chloride (NaCl). Human cells have NaCl
concentration of 0.9%. With human cells as a reference point, the relative NaCl
concentrations of other solutions may be described with the following terms:
•
•
•
Isotonic—a solution with the same salt concentration as in cells. The blood
plasma is isotonic to red blood cells.
Hypotonic—a solution with a lower salt concentration than in cells. Distilled
water (0% salt) is hypotonic to human cells.
Hypertonic—a solution with a higher salt concentration than in cells.
Seawater (3% salt) is hypertonic to human cells.
Figure 5.10: Demonstration of osmotic pressure caused by osmosis at a semi
permeable membrane
Figure 5.11: Effects of isotonic, hypertonic, and hypotonic solutions on cell
volume.
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iv.
Filtration: small molecules pass through selectively permeable membrane in
response to force of pressure. Filtration utilizes pressure to push substances through a
membrane. Example: - filtration in the kidney in the process of urine formation.
b) Active movements across membranes:
Active Transport/Uphill Movement is the transport of substances up their concentration
gradient (uphill), i.e. from a lower to a higher concentration. It requires energy, which is
obtained mainly by breakdown of high energy compounds like adenosine triphosphate (ATP).
❖ Explanation: initially, passive movement of substances could continue till equilibrium
is reached. But if equilibrium is reached and still more molecules are needed, they
must be pumped through the membrane against concentration gradient. Active
transport moves substances against a concentration gradient from a region of lower
concentration to a region of higher concentration. It requires a carrier molecule and
uses energy (ATP). One example of such processes is Sodium – potassium pump and
calcium pump.
❖ Substances, which are transported actively, are in ionic form and non-ionic form.
Substances in ionic form are sodium, potassium, calcium, hydrogen, chloride and
iodide. Substances in non-ionic form are glucose, amino acids and urea.
c) Bulk Transport: This refers to transfer of particles that are too large to cross cell
membrane. It includes:
i.
Endocytosis: taking in of substances into the cell through plasma membrane.
Vesicles are formed to transfer particles and droplets from outside to inside the
cell. It includes:
✓ Pinocytoss (cell drinking)
✓ Phagocytosis (cell eating)
✓ Receptor–mediated Endocytosis- i.e. endocytosis with the help of
receptor.
ii.
Exocytosis (opposite to endocytosis): to remove undigested/unwanted particles
out of the cell. Here, secretory vesicles are moved from the inside to the
outside of the cell.
NB: The main difference between the above processes is that active transport requires
energy while the others do not.
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Differences between Osmosis and Diffusion
Osmosis
Diffusion
It refers to the process by which water, or
It is the tendency of molecules to move from
other solvents, moves through a semian area of high concentration to an area of
permeable membrane, from an area of low
low concentration.
concentration to an area of high
concentration
osmosis only occurs
permeable membrane
across
a
semi-
Diffusion occurs with or without a
membrane between two areas of different
concentrations of molecules
In osmosis, water freely moves across a
membrane from an area of low solute
concentration, or hypotonic solution, to one
of high solute concentration, or hypertonic
solution
Gases and substances dissolved in a liquid
diffuse from an area of high concentration
to one of low concentration
It is not affected by a rise in temperature
It increases with a rise in temperature
because heat increases the random
movement of molecules
For example salt placed outside a cell will
draw out the cell's water through osmosis,
dehydrating it.
For instance, during respiration, oxygen
naturally diffuses into the cell while carbon
dioxide diffuses out.
Summary on Meaning of Cell Division
Cell division is the process by which new cells are formed for growth, repair, and
replacement in the body. This process includes division of the nuclear material and division
of the cytoplasm. All cells in the body (somatic cells), except those that give rise to the eggs
and sperm (gametes), reproduce by Mitosis. Egg and sperm cells are produced by a special
type of nuclear division called Meiosis in which the number of chromosomes is halved.
Division of the cytoplasm is called Cytokinesis.
1. Mitosis—one cell with the diploid number of chromosomes divides once to form two
cells, each with the diploid (2n) number of chromosomes (46 for humans).
✓ DNA replication forms two sets of chromosomes during interphase (preparatory
stage).
✓ Stages of mitosis include prophase, metaphase, anaphase, and telophase.
✓ Cytokinesis is the division of the cytoplasm following telophase.
✓ Mitosis is essential for growth and for repair and replacement of damaged cells.
✓ Most adult nerve and muscle cells seem unable to divide; their loss may involve
permanent loss of function.
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2. Meiosis: one cell with the diploid number of chromosomes divides twice to form four
cells, each with the haploid (n) number of chromosomes (23 for humans).
✓ Oogenesis in the ovaries forms egg cells.
✓ Spermatogenesis in the testes forms sperm cells.
✓ Fertilization of an egg by a sperm restores the diploid number in the fertilized
egg.
Mutation
Mutation refers to the alteration or a change in nature, form, or quality.
✓ Genetic mutation refers to change in DNA sequence within a gene or
chromosome of an organism, which results in the creation of a new character. It is
characterized by a genetic change that brings about abnormal cell functions or
responses and often leads to a series of mutations.
Assignment:
Read and Write extensively on the occurrence of Mutation in humans (not more than 4
pages).
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BODY TISSUES
Introduction:
In some ways, the human body is like a complex machine, such as a car. Not all parts of a car
can be made from a single type of material. Metal, capable of withstanding the heat of the
engine, cannot be used for windows or tires. Similarly, the many parts of the human body are
made of collections of specialized cells and the materials surrounding them. Muscle cells that
contract to produce body movements have a structure and function different from that of
epithelial cells that protect, secrete, or absorb.
In both plants and animals, groups of similar cells are organized into loose sheets or bundles
called a tissue. The word “tissue” comes from a French verb meaning “to weave”. Tissues
carry out a specific activity. Knowledge of tissue structure and function is important in
understanding how individual cells are organized to form tissues and how tissues are
organized to form organs, organ systems, and the complete organism. There is a relationship
between the structure of each tissue type and its function and between the tissues in an organ
and the organ’s function. The structure and function of tissues are so closely related that you
should be able to predict the function of a tissue when given its structure, and vice versa.
Definitions:
1. Tissues can be defined as group of cells that have a similar structure and act together
to perform a specific function.
2. Histology (also called microscopic anatomy or microanatomy) is defined the branch
of biology that deals with the study of microscopic anatomy of cells, tissues and
organs.
There are four (4) different types of tissues in Animals:
•
Epithelial tissues
•
Connective tissues
•
Nervous tissues
•
Muscular tissues
Epithelial Tissues
Epithelial tissue covers the whole surface of the body. It is made up of cells closely packed
and arranged in one or more layers. This tissue is specialised to form the covering or lining of
all internal and external body surfaces. Epithelial tissue that occurs on surfaces on the interior
of the body is known as endothelium. Epithelial cells are packed tightly together, with almost
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no intercellular spaces and only a small amount of intercellular substance. Epithelial tissue,
regardless of the type, is usually separated from the underlying tissue by a thin sheet of
connective tissue; basement membrane. The basement membrane provides structural support
for the epithelium and also binds it to neighbouring structures.
Types of Epithelial Tissue
Epithelial tissue can be divided into two (2) groups depending on the number of layers of
which it is composes. Epithelial tissue which is only one cell thick (single layered) is known
as simple epithelium. If it is two or more cells thick (such as the skin), it is known as
stratified epithelium. There’s also pseudo-stratified, which is single layered but seem to have
many layer.
a) Simple epithelium:
Simple epithelium can be subdivided according to the shape and function of its cells:
i.
Squamous (pavement) epithelium.
Squamous cells have the appearance of thin, flat plates. The shape of
the nucleus (horizontal flattened) usually corresponds to the cell form
and help to identify the type of epithelium. They form the lining of
cavities such as the mouth, blood vessels, heart and lungs and make up
the outer layers of the skin.
Fig 6.1: Simple squamous epithelium
ii.
Simple Cuboidal Epithelium.
As their name implies, cuboidal cells are roughly square or cuboidal in shape.
Each cell has a spherical nucleus in the centre. Cuboidal epithelium is found in
glands and in the lining of the kidney tubules as well as in the ducts of the
glands. They also constitute the germinal epithelium which produces the egg
cells in the female ovary and the sperm cells in the male testes.
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Fig 6.2: Simple cuboidal epithelium
iii.
Simple Columnar Epithelium
Columnar epithelial cells occur in one or more layers. The cells are elongated
and column-shaped. The nuclei are elongated and are usually located near the
base of the cells. Columnar epithelium forms the lining of the stomach and
intestines. Some columnar cells are specialised for sensory reception such as in
the nose, ears and the taste buds of the tongue. Goblet cells (unicellular glands)
are found between the columnar epithelial cells of the duodenum. They secrete
mucus or slime (a lubricating substance which keeps the surface smooth).
Fig 6.3: Simple columnar epithelium
iv.
Ciliated Columnar Epithelium
These are simple columnar epithelial cells, but in addition, they possess fine
hair-like outgrowths (cilia) on their free surfaces. Movement of the cilia in a
certain direction causes the mucus, which is secreted by the goblet cells, to
flow in that direction. Ciliated epithelium is usually found in the air passages
like the nose. It is also found in the uterus and Fallopian tubes of females. The
movement of the cilia propel the ovum to the uterus.
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Fig 6.4: ciliated columnar epithelium
v.
Glandular Epithelium
These are columnar epithelium with goblet cells. Some parts of the gland
epithelium consist of such a large number of goblet cells that there are only a
few normal epithelial cells left. Columnar and cuboidal epithelial cells often
become specialised as gland cells which are capable of synthesising and
secreting certain substances such as enzymes, hormones, milk, mucus, sweat,
wax and saliva.
Fig 6.5: Glandular epithelium
b) Stratified (Compound)Epithelium:
Where body linings have to withstand wear and tear, the epithelia are composed of
several layers of cells and are then called compound or stratified epithelium. The top
cells are flat and scaly and it may or may not be keratinised (i.e. containing a tough,
resistant protein called keratin). The mammalian skin is an example of dry,
keratinised, stratified epithelium. The lining of the mouth cavity is an example of an
unkeratinised, stratified epithelium.
Fig 6.6: Stratified epithelium
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i.
Stratified Squamous epithelium:
In this type of epithelium, the outer cells are flat. Stratified squamous
epithelium is subdivided in to two based on presence of keratin. These are NonKeratinized and Keratinized stratified squamous epithelium. Non-keratnized
stratified squamous epithelium is found in wet surface that are subjected to
considerable wear and tear. Example: - Mouth, tongue and vagina.
In keratinized, stratified squamous epithelium the surface cell of this type
forms a tough layer of material containing keratin. Example: Skin.
ii.
Stratified cuboidal epithelium:
This is a rare type of epithelium. It is found in sweat glands duct, conjunctiva
of eye, and cavernous urethra of the male urogenital system, pharynx &
epiglottis. Its main function is secretion.
iii.
Stratified columnar epithelium,
This tissue is uncommon to the body. Stratified columnar epithelium is found
in milk duct of mammary gland & anus layers. It functions in protection and
secretion.
c) Transitional epithelium:
Here, the cells of the outer layer of the epithelium tend to be large and rounded rather
than flat. This feature allows the tissue to be stretched without breakage. It is found in
Urinary bladder, part of Ureters & Urethra.
d) Pseudo stratified epithelium:
This type of epithelial tissue lines the larger excretory ducts of many glands,
epididymis, parts of male urethra and auditory tubes. Its main function is protection &
secretion.
Functions of Epithelial Tissue
I.
Protection
Epithelial cells from the skin protect underlying tissue from mechanical injury, harmful
chemicals, invading bacteria and from excessive loss of water.
II.
Sensation
Specialised epithelial tissues containing sensory nerve endings and receptors are found in
the skin, eyes, ears, nose and on the tongue.
III.
Secretion
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In glands, epithelial tissue is specialised to secrete specific chemical substances such as
enzymes, hormones and lubricating fluids.
IV.
Selective Absorption
Certain epithelial cells lining the small intestine absorb nutrients from the digestion of
food.
V.
Excretion
Epithelial tissues in the kidney excrete waste products from the body and reabsorb needed
materials from the urine. Sweat is also excreted from the body by epithelial cells in the
sweat glands.
VI.
Diffusion
Simple epithelium promotes the diffusion of gases, liquids and nutrients. Because they
form such a thin lining, they are ideal for the diffusion of gases (e.g. walls of capillaries
and lungs).
VII.
Cleaning
Ciliated epithelium assists in removing dust particles and foreign bodies which have
entered the air passages.
VIII.
Reduces Friction
The smooth epithelial cells that line the entire circulatory system reduce friction between
the blood and the walls of the blood vessels.
Connective tissues
This is the most widespread and abundant type of tissue in the human body. Its function is
primarily to support, anchor and connect various parts of the body. Although connective
tissue exists in a number of forms, all types have three basic structural elements: cells, fibres
and intercellular substance (ground substance).
The proportions of the cells, fibres, and intercellular substance vary, depending on a
particular nature and function of the connective tissue. For example, a strong connective
tissue needs a greater proportion of the collagen fibres and fewer cells (like the one which is
found in tendons and ligaments). On the other hand, a connective tissue composed of mostly
cells would not be very strong. An example would be an adipose (fat) connective tissue.
The most common cell types are fibroblasts, which produce fibres and other intercellular
materials. The two most common types of fibres are: collagen (collagenous) and elastic.
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Collagen fibres are for strength while the elastic ones are for elasticity of the tissue. Both the
cells and the fibres are embedded in the intercellular substance.
Classification of Connective Tissue
1. Connective Tissue Proper: This includes all organs and body cavities connecting
one part with another and, equally important (separating one group of cells from
another). This is a very large and diverse group of tissues, it includes
•
Adipose tissue (fat),
•
Areolar (loose) tissue, and
•
Dense regular tissue, among others.
2. Specialized Connective Tissues: This group includes cartilage, bone, and blood.
Cartilage and bone form the skeletal framework of the body while blood is the
vascular (transport) tissue of animals.
Connective tissue proper
a) Areolar (Loose) Connective Tissue:
Areolar connective tissue is the most widespread connective tissue of the body. It attaches the
skin to the underlying tissue. It also fills the spaces between various organs and thus holds
them in place as well as cushions and protects them. It also surrounds and supports the blood
vessels. In areolar, collagen fibres are predominant. The cellular elements (such as fibro
blasts) are difficult to be distinguished in the areolar connective tissue. But, one type of cells
(the mast cells) is usually visible.
Fig 6.7: Schematic representation of the areolar connective tissue
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Fig 6.8: Microscopic view of areolar connective tissue.
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