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Chapter 3 Notes
Enzyme – a protein that speeds up a specific chemical reaction, such as breaking the
bonds of a nutrient, without undergoing change itself. A protein catalyst.
Tissues – systems of cells working together to perform specialized tasks. (Ex: muscles,
nerves, blood and bone)
Organs – discrete structural units made of tissues that perform specific jobs. (Ex: the
heart, liver, and brain)
Body system – a group of related organs that work together to perform a function. (Ex:
circulatory system, nervous system, respiratory system)
The Body Fluids and the Cardiovascular System
Blood – the fluid of the cardiovascular system; composed of water, red and white blood
cells, other formed particles, nutrients, oxygen, and other constituents.
Lymph – the fluid that moves from the bloodstream into tissue spaces and then travels in
its own vessels, which eventually drain back into the bloodstream
Arteries – blood vessels that carry blood containing fresh oxygen supplies from the heart
to the tissues
Veins – blood vessels that carry blood, with the carbon dioxide it has collected, from the
tissues back to the heart
Capillaries – minute, web like blood vessels that connect arteries to veins and permit
transfer of materials between blood and tissues.
Plasma – the cell-free fluid part of blood and lymph
Extracellular fluid – fluid residing outside the cells that transports material to and from
the cells
Intracellular fluid – fluid residing inside the cells that provides the medium for cellular
reactions
Lungs – the body’s organs of gas exchange. Blood circulating through the lungs releases
its carbon dioxide and picks up fresh oxygen to carry to the tissues
Intestine – the body’s long, tubular organ of digestion and the site of nutrient absorption.
Liver – a large, lobed organ that lies just under the ribs. It filters the blood, removes and
processes nutrients, manufactures materials for export to other parts of the body, and
destroys toxins, or stores them to keep them out of circulation
Kidneys – Pair of organs that filter wastes from the blood, makes urine, and releases it to
the bladder for excretion from the body.
Body fluids supply the tissues continuously with energy, oxygen, and nutrients, including
water. They constantly circulate to pick up fresh supplies and deliver wastes to points of
disposal. Every cell continuously draws oxygen and nutrients and releases carbon
dioxide and other wastes into them.
- The body’s circulating fluids are the blood and the lymph.
- blood travels within the arteries, veins, and capillaries, as well as within the heart’s
chambers.
- lymph travels in separate vessels of its own. Ciculating around the cells are other fluids
such as the plasma of the blood, which surrounds the white and red blood cells, and the
fluid surrounding muscle cells. The fluid surrounding cells (extracellular fluid) is derived
from the blood in the capillaries; it squeezes out through the capillary walls and flows
around the outsides of cells, permitting exchange of materials. Some extracellular fluid
returns to the body by reentering the capillaries. The fluid remaining outside the
capillaries forms lymph, which travels around the body by way of lymph vessels. The
lymph eventually returns to the bloodstream near the heart where large lymph and blood
vessels join.
-the fluid inside cells (intracellular fluid) provides a medium in which all cell reactions
take place. Its pressure also helps the cells hold their shape. Intracellular fluid is drawn
from the extracellular fluid.
-blood circulates to the lungs where it picks up oxygen and releases carbon dioxide
wastes from the cells. Then the blood returns to the heart, heartbeat pushes fresh
oxygenated blood from the lungs out to all body tissues.
- as blood passes through the digestive system the blood delivers oxygen to the cells there
and picks up most nutrients other than fats and their relatives from the intestine for
distribution elsewhere. All blood leaving the digestive system is routed directly to the
liver which chemically alters the absorbed material to make them better suited for use by
other tissues. Blood passes through the kidneys and is cleaned of wastes.
- lymphatic vessels pick up most fats from the intestine and then transport them to the
blood.
- to make sure you have efficient circulation of fluid to all your cells, you need an ample
fluid intake. This means drinking sufficient water to replace what is lost each day.
Key point – Blood and lymph deliver nutrients to all the body’s cells and carry waste
materials away from them. Blood also delivers oxygen to cells. The cardiovascular
system ensures that these fluids circulate properly among all organs.
The Hormonal and Nervous System
Hormones – chemicals that are secreted by glands into the blood in response to
conditions in the body that require regulation. These chemicals serve as messengers,
acting on other organs to maintain constant conditions.
Pancreas – an organ with two main functions. One is an endocrine function (endo
meaning into the blood) – the making of hormones such as insulin, which it releases
directly into the blood. The other is an exocrine function (exo meaning out into a body
cavity or onto the skin surface) – the making of digestive enzymes, which it releases
through a duct into the small intestine to assist in digestion.
Insulin – a hormone from the pancreas that helps glucose enter cells from the blood
Glucagon – a hormone from the pancreas that stimulates the liver to release glucose into
the bloodstream.
-blood also carries hormones from one system of cells to another. Hormones
communicate changing conditions that demand responses from the body organs.
-hormones are secreted and released directly into the blood by glands. Each gland
monitors a condition and produces one or more hormones to regulate it.
-when the pancreas detects a high concentration of glucose, it releases insulin. Insulin
stimulates muscle and other cells to remove glucose from the blood and to store it. The
liver also stores glucose. When the blood glucose level falls, the pancreas secretes
glucagons, which the liver responds by releasing into the blood some of the glucose it
stored earlier.
-nutrition affects the hormonal system. Fasting, feeding, and exercise alter hormonal
balances. (ex: people who become very thin have an altered hormonal balance that may
make them unable to maintain their bones)
-Hormones affect nutrition. They regulate hunger and affect appetite. They carry
messages to regulate the digestive system, telling the digestive organs what types of food
have been eaten and how much of each digestive juice to secrete in response. A hormone
produced by the fat tissue informs the brain about the degree of body fatness and helps to
regulate appetite. Hormones also regulate the menstrual cycle or women, and they affect
the appetite changes many women experience during the cycle and in pregnancy.
Cortex – the outermost layer of something. The brain’s cortex is the part of the brain
where conscious thought takes place.
Hypothalamus – a part of the brain that senses a variety of conditions in the blood, such
as temperature, glucose content, salt content, and others. It signals other parts of the
brain or body to adjust those conditions when necessary.
Fight-or-flight reaction – the body’s instinctive hormone- and nerve – mediated reaction
to danger. Also known as the stress response.
Neurotransmitters – chemicals that are released at the end of a nerve cell when a nerve
impulse arrives there. They diffuse across the gap to the next cell and alter the membrane
of that second cell to either inhibit or excite it.
Epinephrine – the major hormone that elicits the stress response
Norepinephrine – a compound related to epinephrine that helps to elicit the stress
response
Metabolism – the sum of all physical and chemical changes taking place in living cells;
includes all reaction by which the body obtains and spends the energy from food.
How does the nervous system interact with nutrition?
-the nervous system is the body’s major communication system. With the brain and the
spinal cord it receives and integrates information from sensory receptors all over the body
(sight, hearing, touch, smell, taste, and others) which communicate to the brain the state
of both the inner and outer worlds.
-role in hunger regulation is coordinated by the brain. The sensations of hunger and
appetite are perceived by the cortex. Deep inside the brain the hypothalamus monitors
many body conditions, including the availability of nutrients and water. To signal hunger
(the physiological need for food) the digestive tract sends messages to the hypothalamus
by way of hormones and nerves. The signals also stimulate the stomach to intensify its
contracting and secretions, causing hunger pangs and gurgling sounds.
-hormonal and nervous systems work together to enable a person to respond to physical
danger. Fight-or-flight reaction (or stress response). When danger is detected, nerves
release neurotransmitters and glands supply epinephrine and norepinephrine. Every
organ of the body responds and metabolism speeds up. The pupils of the eyes widen, so
you can see better; the muscles tenses up so you can jump, run, or struggle with
maximum strength; breathing quickens and deepens to provide more oxygen; the heart
races to rush oxygen to the muscles, and blood pressure rises so that the fuel the muscles
need for energy can be delivered; the liver pours glucose from it’s stores, and the fat cells
release rat; the digestive system shuts down to permit all the body’s systems to serve the
muscles and nerves. In ancient times, stress usually involved physical danger, and the
response was violent physical exertion. Now, stress is seldom physical but the body
reacts the same. Daily exercise as part of a healthy lifestyle releases pent-up stress and
helps to protect the heart.
Key Point – The nervous system joins the hormonal system to regulate body processes
through communication among all the organs. Together, the hormonal and nervous
systems respond to the need for food, govern the act of eating, regulate digestion, and call
for the stress response.
The Immune System
Microbes – bacteria, viruses, or other organisms invisible to the naked eye, some of
which cause diseases. Also called microorganisms.
Antigen – a microbe or substance that is foreign to the body
Immune system – a system of tissues and organs that defend the body against antigens,
foreign materials that have penetrated the skin or body linings
Lymphocytes – white blood cells that participate in the immune response; B-cells and Tcells
Phagocytes – white blood cells that can ingest and destroy antigens. The process by
which phagocytes engulf materials is called phagocytosis.
T-cells – lymphocytes that attack antigens. T stands for the thymus gland of the neck,
where the T-cells are stored and matured.
B-cells – lymphocytes that produce antibodies. B stands for bursa, an organ in the
chicken where B-cells were first identified.
Antibodies – proteins, made by cells of the immune system, that are expressly designed
to combine with and inactivate specific antigens.
Many of the body’s tissues cooperate to maintain defenses against infection.
-the skin presents a physical barrier, and the body’s cavities (lungs, digestive tract) are
lined with membranes that resist penetration by invading microbes and other unwanted
substances. These linings are highly sensitive to vitamin and other nutrient deficiencies.
If an antigen penetrates the body’s barriers the immune system rushes in to defend the
body against harm. Of the 100 trillion cells that make up the human body, one in every
hundred is a white blood cell. The actions of two types of white blood cells, the
phagocytes and the lymphocytes are of interest.
*Phagocytes – these scavenger cells travel throughout the body and are the first to defend
body tissues against invaders. When a phagocyte recognizes a foreign particle, such as a
bacterium, it forms a pocket in its own outer membrane, engulfing the invader. Then the
phagocytes may attack with oxidative chemicals or may otherwise digest or destroy them.
They also leave a chemical trail that helps other immune cells to join the defense against
infection.
*T-Cells – Killer T-cells recognize chemical messages from phagocytes and “read” and
“remember” the identity of an invader from the messages. They then seek out and
destroy all foreign particles having the same identity. T-cells defend against fungi,
viruses, parasites, some bacteria, and some cancer cells. Helper T-cells do not attack
invaders but help other immune cells to do so.
--People suffering against the disease AIDS are rendered defenseless against other
diseases because HIV selectively attacks and destroys their helper T-cells.
*B-cells – B-cells respond rapidly to infection by dividing and releasing antibodies into
the bloodstream. Antibodies travel to the site of the infection and stick to the surface of
foreign particles, killing or inactivating infection. They also retain a chemical memory of
each invader and if the encounter recurs, the response is swift.
--Immunizations work this way – a disabled or harmless form of a disease-forming
organism is injected into the body so that the B-cells can learn to recognize it. Later, if
the real live infectious organism invades, the B-cells quickly release antibodies to destroy
it.
Key Point – The immune system enables the body to resist diseases.
The Digestive system
Digestive system – the body system composed of organs that break down complex food
particles into smaller absorbable products
Digest – to break molecules into smaller molecules, a main function of the digestive tract
with respect to food
Absorb – to take in, as nutrients are taken into the intestinal cells after digestion, the main
function of the digestive tract with respect to nutrients
The Digestive Tract
After eating, the brain and hormones direct the many organs of the digestive system to
digest and absorb chewed and swallowed food. The tract is a flexible, muscular tube
extending from the mouth through the throat, esophagus, stomach, small intestine, large
intestine, and rectum to the anus (26 feet). Only when a nutrient or other substance
passes through the wall of the digestive tract does it actually enter the body’s tissues.
Digestive system’s job is to digest food to its components and then to absorb the nutrients
and some nonnutrients, leaving behind the substances, such as fiber, that are appropriate
to excrete. To do this, the system works on two levels, mechanical and chemical.
Key point – the digestive tract is a flexible muscular tube that digests food and absorbs its
nutrients and some nonnutrients. Ancillary digestive organs aid digestion.
Peristalsis – the wavelike musclcular squeezing of the esophagus, stomach, and small
intestine that pushes their contents along
Stomach – a muscular, elastic, pouchlike organ of the digestive tract that grinds, and
churns swallowed food and mixes it with acid and enzymes, forming chime
Sphincter – a circular muscle surrounding, and able to close, a body opening
Chyme – the fluid resulting from the actions of the stomach upon a meal
Pyloric valve – the circular muscle of the lower stomach that regulates the flow of
partially digested food into the small intestine, also called pyloric sphincter
Small intestine – the 20ft length of small-diameter intestine, below the stomach and
above the large intestine, that is the major site of digestion of food and absorbtion of
nutrients
Large intestine – the portion of the intestine that completes the absorption process
Colon – the large intestine
Feces – waste material remaining after digestion and absorption are complete, eventually
discharged from the body
Mechanical Aspects of Digestion
-begins in the mouth. Large, solid food pieces are torn into shreds that can be swallowed.
Chewing adds water in the form of saliva to soften rough or sharp foods to prevent
tearing the esophagus. Saliva also moistens and coats each bite of food making it
slippery so that it can easily pass down the esophagus.
-stomach and intestines liquefy foods through mashing and squeezing actions
(peristalsis). Stomach also holds swallowed food for a while and mashes it into fine
paste, stomach and intestines add water so the paste becomes more fluid as it moves
along
-sphincter muscle at the base of the esophagus squeezes the opening at the entrance to the
stomach to narrow it and prevent the stomach’s contents from going back up the
esophagus as the stomach contracts.
-stomach stores food in a lump in its upper portion and squeezes the food little by little to
the lower portion. There the food is ground and mixed thoroughly, ensuring that
digestive chemicals mix with the entire thick liquid mass, which is now chyme.
-pyloric valve controls the exit of chyme from the stomach, letting small amounts into the
small intestine at a time over a few hours.
-when contents arrive in the large intestine digestion and absorbtion are nearly complete.
Large intestine/colon reabsorbs the water donated earlier by digestive organs and to
absorb minerals, leaving fiber and undigested materials (feces) for excretion. Fiber
provides bulk for the colon’s muscles to work.
-rectum stores fecal material to be excreted at intervals. From mouth to rectum, transit
can take from a single day to as long as three days.
Key point – the digestive tract moves food through its various processing chambers by
mechanical means. The mechanical actions include chewing, mixing by the stomach,
adding fluid, and moving the tract’s contents by peristalsis. After digestion and
absorption, wastes are excreted.
Gastric juice – the digestive secretion of the stomach
pH – a measure of acidity on a point scale. Solution with a pH of 1 is a strong acid,
solution with a pH of 7 is neutral, solution with a pH of 14 is a strong base.
Mucus – a slippery coating of the digestive tract lining (and other body linings) that
protects the cells from exposure to digestive juices (and other destructive agents).
Bile – a cholesterol-containing digestive fluid made by the liver, stored in the gallbladder,
and released into the small intestine when needed. It emulsifies fats and oils to ready
them for enzymatic digestion
Emulsifier – a compound with both water-soluble and fat-soluble portions that can attract
fats and oils into water, combining them
Pancreatic juice – fluid secreted by the pancreas that contains both enzymes to digest
carbohydrate, fat, and protein and sodium bicarbonate, a neutralizing agent
Bicarbonate – a common alkaline chemical, a secretion of the pancreas
Chemical Aspect of Digestion
- chemical digestion begins in the mouth, where food is mixed up with an enzyme in
saliva that acts on carbohydrates. Disgestion continues in the stomach where stomach
enzymes and acid break down protein. Digestion then continues in the small intestine;
there the liver and gallbladder contribute bile that emulsifies fat, and the pancreas and
small intestine donate enzymes that continue digestion so that absorption can occur.
Bacteria in the colon break down certain fibers.
If “I am what I eat”, then how does a sandwhich become “Me”?
(wait for slides online or get notes from someone else from class)