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