ENERGYCHAPTER 23
DIGESTION
Eating (ingestion)
Physical breakdown
Chemical breakdown
Absorption
Transport
Elimination (egestion)
OVERVIEW OF THE DIGESTIVE
SYSTEM
The digestive tract can be split into two
parts:
the alimentary canal (alimentary tract,
gastrointestinal tract, GI tract)
accessory organs
Alimentary Canal
Oral Cavity
Teeth
Incisors
Cuspids (canines)
Premolars
Molars
Esophagus
Stomach
Small Intestine
Most digestion and
absorption take place
here.
Large Intestine
Water absorption
Some vitamins absorbed
Formation of feces
Accessory Organs
Aid in digestion
but food does
not pass
through them.
Salivary Glands
Saliva lubricates food
Enzymes digest carbohydrates
Liver
Over 500 functions
Filters toxins and wastes
Produces bile
Gallbladder
Stores and
concentrates bile
Gallstones
Pancreas
Digestive enzymes
Pancreatic juice
Bicarbonate
Appendix
Function not well
understood
Contains lymphatic
tissue
Possible reservoir for
beneficial bacteria
Nutrients in Food
VITAMINS
Organic
Body can’t make
Need to obtain from diet
Need in small amounts
Many are coenzymes, others regulate
metabolic processes
MINERALS
Inorganic substances
Body can’t make
Must be obtained from diet.
Found naturally in the soil and absorbed by plants
Examples: Calcium, phosphorous, iron
Important for nerve and muscle function, blood coagulation, blood pH maintenance, enzyme function, etc.
WATER
Universal solvent
Essential to most of the chemical reactions
in the body
Dissolves some foods for easier digestion
Balances fluids, blood pH, and body
temperature.
FATS
Used to form cell membranes, protective
membranes around nerve cells, and
certain hormones.
Cushion delicate structures and provide
energy.
Body stores excess energy as fats in
adipose tissue
CARBOHYDRATES
Include sugars, such as fructose and
sucrose, and more complex molecules
such as starch and glycogen.
Although the body can use several
carbohydrates as energy sources, all are
broken down to glucose before being
used in cellular respiration.
PROTEINS
Found in all living cells and in nonliving structures
such as hair and nails.
Most enzymes and some hormones are proteins
and are important for growth and repair.
Can be used for energy production.
Proteins are formed from chains of amino acids.
Your body can make some of these amino acids,
but others must come from your diet.
MECHANICAL DIGESTION
Physically breaking down the food
Mastication- the process of chewing
Stomach churning
Dissolving of food in the fluids of the
digestive system
CHEMICAL DIGESTION
The breakdown of food molecules into their
individual components by acids and enzymes
Proteins: amino acids.
Carbohydrates (polysaccharides or
disaccharides): monosaccharides (simple sugars
such as glucose).
Fats: fatty acids.
Once the food has been broken down into small
molecules, they can be absorbed into the blood.
Many organs use both mechanical and chemical digestion at the same time.
Teeth grind food while amylase in your saliva breaks down carbohydrates.
The stomach mashes and grinds the food while pepsin breaks down proteins into smaller fragments.
The small and large intestines continue to mix chyme as it passes through.
Bile begins to separate molecules of fat to make it easier to digest.
Most digestive enzymes come from the pancreas and small intestine.
Pancreatic juicereduces the acidity of the chyme so enzymes can function at the proper pH.
CELLULAR RESPIRATION
The main purpose of carbohydrates is to provide the energy necessary to make ATP during cellular respiration.
All carbohydrates can enter glycolysis.
If the body runs short on glucose, the cells can use fats and amino acids in cellular respiration.
Fats and some amino acids are converted to acetyl CoA, which then enters the citric acid cycle.
THE DIGESTIVE SYSTEM IN THE
HUMAN BODYMuscular system- sphincters, peristalsis (smooth
muscle- involuntary).
Circulatory system- transports nutrients throughout body.
Lymphatic system- lymphatic vessels called lactealsabsorb fats in small intestine and empty into subclavian veins.
Integumentary system- UV light causes epidermis to produce Vitamin D, which is necessary for calcium absorption in the intestine.
THE URINARY SYSTEM
THE FUNCTION OF THE URINARY
SYSTEM
To rid the body of wastes, the kidney performs
three major functions:
1. Filtration
2. Reabsorption
3. Secretion
FILTRATION
When the blood reaches a nephron, it passes into a collection of capillaries called the glomerulus, which is surrounded by a cup-shaped structure called the Bowman’s capsule.
Because the blood flowing into the glomerulus is under higher pressure than the fluid in the Bowman’s capsule, plasma moves from the glomerulus into the Bowman’s capsule.
This plasma carries smaller molecules such as urea, vitamins, salt, and glucose with it, while blood cells and proteins remain in the blood vessel.
The fluid that enters the Bowman’s capsule is called the filtrate.
REABSORPTION
When the filtrate flows from the Bowman’s capsule into the proximal convoluted tubule, it enters the reabsorption phase.
The tubule is designed to contain the wastes and ensure that the beneficial molecules and minerals are reabsorbed into the capillaries that surround it.
Glucose, sodium, potassium, and calcium ions are actively transported back into the capillaries.
Most of the water in the proximal tubule and loop of Henle diffuses back into the capillaries by osmosis.
Some reabsorption continues to occur in the distal convoluted tubule.
SECRETION
In the distal convoluted tubule, additional
substances move from the blood into the tubule in
the secretion phase.
Substances such as urea, various ions, drugs, and
other waste products are secreted.
Hydrogen ions may also be secreted into the
tubule to adjust the pH of the blood.
The remaining fluid that flows out of the collecting
ducts of the renal pyramids into the renal pelvis is
urine.
URINE
95% water
Urea
Uric acid
Creatinine
small quantities of pigments,
hormones, enzymes, vitamins,
and various inorganic
substances.
WATER BALANCE