Download CHAPTER 38 Most of the food you eat is converted to fuel for your

CHAPTER 38
Most of the food you eat is converted to fuel for your body- specifically ATP. The body requires 6 primary nutrients:
1. Water: This is the most important one, because most of the body's processes take place in water. You should drink
about 1 liter per day.
2. Carbohydrates: You need simple carbs (sugars found in fruit, sugar cane, honey) and complex carbs (starches found in
grains, potatoes, and vegetables that are converted to sugars.
3. Fats: Your body needs essential fatty acids to produce cell membranes and certain hormones, and absorb fat soluble
vitamins. If you consume too much, it is stored as fat deposits in the body.
4. Proteins: Supply the raw materials for growth and repair of structures like skin/muscles. Contain essential amino acids.
5. Vitamins: Vitamins help regulate body processes by working with enzymes. There are 2 types:
-Fat Soluble: A, D, E, K- can be stored in fatty tissues.
-Water Soluble: C, B- dissolve in water and can not be stored. Must be eating every day. Supplements in large quantities
can be harmful. Too much A, D, E, & K can be toxic.
6. Minerals: Calcium (bones/teeth), iron (makes hemoglobin), magnesium, potassium, sodium. Are needed in very small
amounts.
If you eat a well balanced diet, you will receive all of the nutrients you need.
The digestive system consists of the mouth, pharynx, esophagus, stomach, small intestines, and large intestines. The
function of the digestive system is to convert foods into simpler molecules that can be absorbed and used by the cells in
the body.
When you take a bite of food, the teeth grind it while the salivary glands moisten it to make it easier to chew. Also, they
release an enzyme called amylase that breaks down starches (carbohydrates) to release sugars. The blob of food you
swallow is called a bolus, and it is pushed into the pharynx. As the food moves down, a flap of tissue called the epiglottis
sealed off the windpipe so food will stay in the esophagus. Contractions of smooth muscle (called peristalsis) in the
esophagus move food down to the stomach.
In the stomach, two types of digestion occur:
1. Chemical: Stomach acids and enzymes work to break down proteins.
2. Mechanical: Stomach muscles contract and churn to mix everything up, turning the bolus to chyme. After an hour or
two, the pyloric valve opens and allows the chyme to move into the small intestines.
The first part of the small intestines is the duodenum, and is where almost all of the digestive enzymes enter the small
intestines. These enzymes are secreted by the pancreas and liver. The pancreas releases enzymes to break down carbs,
proteins, and fats. It also secretes sodium bicarbonate that neutralizes the stomach acid. The liver produces bile, which is
loaded with fats and salts and acts as a detergent, breaking down the fats you eat so enzymes can more effectively reach
the molecules. Bile is stored in the gallbladder.
The duodenum is the shortest part of the small intestines, the next 2 parts- the jejunum and ileum- average about 6
meters long. By the time chyme reaches this part, most of the chemical digestion is complete and absorption can begin.
The SI is covered with tiny projections called villi, which are then covered with even tinier microvilli. This provides a huge
surface area for nutrient absorption.
Carbs and proteins are absorbed into capillaries surrounding the villi. Fats are absorbed by the lymphatic system. By the
time the chyme leaves the small intestines, it is basically nutrient free, and consists of water, cellulose (fiber), and other
undigestible substances. As the chyme moves through the large intestines, almost all of the water is absorbed, and the
remaining materials are feces that move into the rectum and are eliminated from the body.
Kidneys are the primary organ of the excretory system. They remove waste products from the blood, maintain blood pH,
and regulate the water content of the blood, and therefore blood volume. They are located on either side of the spinal
column in the lower back. A tube called the ureter carries urine to the bladder.
The functional unit of the kidney is called the nephron. Each one has it's own blood supply- an arteriole, a venule, and a
network of capillaries. Blood enters a nephron through the arteriole, impurities are filtered out and emptied into the
collecting duct. The purified blood exits the nephron through the venule.
There are two distinct processes of blood purification:
1. Filtration: Mainly takes place in the glomerulus- a network of capillaries in the upper nephron. Much of the fluid flows
into the Bowman's capsule. The filtered materials are water, urea, glucose, salts, amino acids, and some vitamins.
2. Reabsorption: Kidneys filter all of your blood every 45 minutes. Most of the water, amino acids, fats, and glucose in the
Bowman's capsule makes its way back into the blood through reabsorption. The remainder, called urine, drains into the
collecting ducts. It is concentrated in the loop of Henle, where water is conserved and the volume of urine is minimized.
Urine is stored in the bladder until it is released through a tube called the urethra.
Kidneys are controlled by the composition of the blood. When you drink a lot of water, it is quickly absorbed into the blood
thru the digestive system. The kidneys then quit reabsorbing so much water, and eliminate more of it as urine, keeping
your blood vessels from forcing water into your cells and causing your body to swell.
People can survive with one kidney, but if both are damaged there are only 2 ways to live. A kidney transplant or a
process called dialysis. This a a machine that purifies the blood. It generally has to be done several hours a day as often
as 3 times a week.
CHAPTER 39
The Endocrine System is made up of glands that release their products (hormones) into the bloodstream. These
hormones deliver messages throughout the body by attaching to a binding site on a target cell. A hormone can only affect
a cell that has a special binding site for it.
Hormones are in 2 groups:
1. Steroid Hormones: Are lipids (fats) and can cross cell membranes of target cells easily. Once inside, it binds to a
receptor protein. This complex enters the nucleus, binds to a DNA control sequence, initiates the transcription of mRNA
that moves into the cytoplasm and directs protein synthesis. Steroid hormones can turn on/off whole sets of genes,
producing dramatic changes in cell and organism activity.
2. Nonsteroid Hormones: Cannot pass through the cell membrane. Bind to receptors on the cell membrane. The activates
a messenger to carry the message of the hormone inside the cell. These messengers activate or inhibit a wide range of
cell activities by activating enzymes.
Glands of the Endocrine System
-Pituitary Gland: Regulates growth and reproduction. Controlled by hypothalamus. At the base of the skull. Secretes 9
hormones that regulate functions such as water reabsorption in kidneys, contractions of uterus during childbirth,
production of eggs/sperm, growth, milk production, and melanin production.
-Thyroid Gland: Located at base of neck. Major role in regulating body's metabolism. Produces the hormone thyroxine,
which increases the rate of protein, carb, and fat metabolism as well as cellular respiration. Too much thyroxine makes
you lose weight. Too little makes you gain. The thyroid gland also works with the parathyroid gland to regulate calcium in
the blood.
-Adrenal Glands: One on top of each kidney. Releases hormones that help the body deal with stress. Epinephrine and
norepinephrine are the hormones responsible for "fight or flight", which increases heart rate, blood pressure, and blood
flow to the muscles.
-Pancreas: Secretes insulin and glucagon to keep the level of glucose in the blood stable. Insulin stimulates cells to
remove sugar from the blood and store it as fat. Glucagon stimulates the liver to release glucose into the blood and
release stored fats.
When you eat, glucose levels rise in your blood. Pancreas releases insulin to remove it. A few hours after eating, glucose
levels start to drop in the blood, so the pancreas releases glucagon to increase glucose levels. When the pancreas fails to
produce insulin, glucose levels get too high and can damage cells. This leads to diabetes, and people have to have insulin
injections.
-Reproductive: Gonads are the reproductive glands. Ovaries in females produce eggs, testes in males produce sperm.
They also release hormones. Females release estrogen (development of eggs and female physical traits and
progesterone (prepares uterus for embryo). Males release testosterone (development of sperm and male physical traits).
For the first six weeks of development embryos are identical in appearance. During the 7th week, the reproductive glands
develop, and the hormones released cause the embryo to develop physically as a male or female. But it's not until
puberty, ages of 9-15, when the reproductive organs are fully functional and can produce sperm or eggs.
The main function of the male reproductive system is to produce and deliver sperm. An external sac called the scrotum
holds the testes. These keeps them 1-3 degrees cooler than the rest of the body, which is necessary for sperm
production. Within testis are clusters of hundreds of seminiferous tubules where sperm is produced.
Sperm produced in the seminiferous tubules are moved into the epididymis, where sperm matures and is stored. From
there, it moves into the vas deferens tube, which merges with the urethra- the tube that exits the body through the penis.
Glands produce a nutrient rich fluid called seminal fluid that nourishes the sperm. This fluid and sperm is called semen.
There are about 2.5 million sperm per drop of semen. Only one is needed to fertilize an egg.
The main function of the female reproductive system is to produce ova (egg). It also prepares the female's body to nourish
a developing embryo. Usually only one egg is produced per month. A female is born with thousands of immature eggs, but
only about 400 are ever released- one every 28 days or so after puberty is reached. Each ovary contains 400,000 follicles
that are clusters of cells that surround an egg and help it mature.
When a follicle has matured, its egg is released in a process called ovulation. The egg is swept from the surface of the
ovary into the opening of a Fallopian tube. During this journey, it can be fertilized by a sperm. After a few days, it goes into
the uterus. If fertilization has occurred, the egg remains in the uterus to develop. The outer end of the uterus is the cervix,
and beyond that is the vagina- a canal that leads outside the body.
The menstrual cycle starts at puberty and continues until a female is in her mid-40's. During this cycle, an egg develops
and is released from an ovary. If the egg is not fertilized, it is discharged along with the lining of the uterus. The menstrual
cycle is a 28 day cycle with four phases:
1. Follicular Phase: Begins when level of estrogen in blood is low. This causes a release of other hormones that cause a
follicle to develop to maturity. Generally, just one, sometimes 2 or 3. As the follicle develops, more estrogen is released,
causing the lining of the uterus to thicken. This phase takes about 10 days.
2. Ovulation: Last 3-4 days. Hypothalamus signals the pituitary gland to release hormones that cause the follicle to rupture
and release the mature egg into a Fallopian tube.
3. Luteal Phase: About 14 days. The follicle turns yellow and is now known as the corpus luteum. It continues to release
estrogen, but now progesterone too, which stimulates growth of blood vessels in the lining of the uterus.
4. Menstruation: If fertilization does not occur, the egg passes through the uterus. The lining of the uterus breaks off from
the wall and is discharged through the vagina. This lasts 3-7 days. A new cycle begins with the first day of menstruation.
If an egg is fertilized (it's now a zygote), it implants in the lining of the uterus and development begins. The zygote
undergoes cell division, and after 4 days is a solid ball of about 64 cells called a morula. There are 3 stages of early
development.
1. Implantation: The morula grows into a hollow ball called a blastocyst, which attaches to the wall of the uterus. The cells
in the blastocyst begin to specialize to develop the various tissues in the body. This is called differentiation.
2. Gastrulation: The blastocyst sorts itself into the primary germ layers- ectoderm, mesoderm, and endoderm= during
gastrulation. The ectoderm develops the skin and nervous system, the endoderm forms the lining of the digestive system
and digestive organs, and the mesoderm forms many of the body's internal tissues and organs.
3. Neurulation: This is the development of the nervous system. The mesodermal tissue forms a notochord, which
gradually develops into the spinal cord and rest of the nervous system.
After 8 weeks of development, the embryo is called a fetus. By the end of 3 months, most of the major organs and tissues
are fully formed. 4-6 months the tissues become more complex- heart becomes large enough to be heard, bone replaces
cartilage, hair grows. 6-9 months, organ systems mature, nervous system and lungs complete development.