Digestion and Excretion

1
Digestion and Excretion
2
The Need for Digestion

• Digestion the process of breaking down food
  particles into molecules small enough to be
  absorbed by cells
• Polymers are too large to pass through the cell
  membrane in humans
• The mitochondria will use the digested nutrients
  to make energy
• There are four macromolecules carbohydrates,
  proteins, lipids, and nucleic acids

3
Carbohydrates

• Sugars
• Polymers large molecules
• Carbohydrate polymers are polysaccharides
• Monomers small subunits
• Carbohydrate monomers are simple sugars or
  monosaccharides
• Ex glucose, sucrose, lactose, maltose
• The functions of carbohydrates are
• 1. to store energy
• 2. to provide building materials for the body

4
Lipids

• Fats and oils
• Polymers are sometimes called triglycerides
• Monomers are 1 glycerol and 3 fatty acids
• The energy stored in lipids is for long-term use
  and is not used up quickly
• It takes a lot of exercise to burn fat
• Vegetable oils contain unsaturated fats meats
  and dairy contain saturated fats
• Unsaturated fats are less likely to cause heart
  disease than saturated fats

5
Nucleic Acids

• Carry hereditary information
• Polymers are DNA and RNA
• Monomers are nucleotides

6
Proteins

• Proteins are large polymers made of amino acid
  monomers
• There are 20 different amino acids
• The order of the amino acids determines the
  proteins properties

7
Enzymes

• Enzymes proteins that speed up reactions in
  organisms
• Also called organic catalysts
• Work on substances called substrates
• Substrates are turned into products
• Condensation synthesis enzymes help make a big
  molecule from smaller ones
• Hydrolysis enzymes help break a larger
  molecules down into smaller pieces

8

• Enzymes have an area called the active site that
  matches the shape of the substrate
• Enzymes are specific for their substrates
• The active site and substrate are said to fit
  together just as a key fits in a lock (lock and
  key model)
• Enzymes are not changed or used up in reactions
• Enzymes speed up reactions by lowering the
  activation energy
• Activation energy the energy needed to get a
  reaction started

9
1
2
Enzyme-substrate complex
Products
4
3
Enzyme breaks the bond holding the substrate
together
10

• Enzymes lose their specific shape (they denature)
  if they are exposed to unfavorable conditions
• Most enzymes work best at 37C and a neutral pH
• Pepsin, an enzyme in the stomach, works best at
  an acidic pH

11
Types of Digestion

• Extracellular digestion food is broken down by
  enzymes outside the body
• Fungi have special structures called rhizoids
  that secrete enzymes onto food
• The food is then absorbed by the fungus

Rhizoids
12

• Intracellular digestion food is broken down by
  enzymes inside the cells
• The amoeba engulfs its food using extensions of
  its cytoplasm called psuedopods
• Process is called phagocytosis
• The paramecium uses hair-like extensions called
  cilia to push food into its oral groove

13
Human Digestion

• Human digestion is intracellular
• Unlike the amoeba and paramecium, humans have
  digestive organs

14
(No Transcript)
15
Pathway of Digestion

• 1. Mouth site of mechanical and chemical
  digestion
• Teeth grind up food (mechanical)
• Salivary glands secrete saliva into the mouth
• Saliva contains the enzyme salivary amylase that
  breaks down carbohydrates (chemical)
• Epiglottis closes off the trachea when you
  swallow
• 2. Peristalsis rhythmic waves of muscle
  contractions that push food down the esophagus

16

• 3. Stomach both mechanical and chemical
  digestion occurs
• The walls grind and churn food
• Gastric juice contains pepsin and hydrochloric
  acid
• Pepsin enzyme that breaks down proteins
• 4. Small intestine where most chemical digestion
  occurs
• Has many finger-like projections called villi
  that absorb nutrients into the blood
• Other organs secrete substances into the small
  intestine

17

• Pancreas secretes enzymes for breaking down
  lipids, proteins, and carbohydrates
• Liver makes bile, which breaks fat globules into
  smaller pieces
• Called emulsification
• Allows enzymes to digest the fats
• Gall bladder stores bile until it is needed
• 5. Large intestine absorbs water from undigested
  material
• No digestion occurs
• Undigestible matter becomes feces, which pass
  through the rectum and anus

18
Diseases

• Peptic ulcers form when the protective mucus
  lining of the stomach is destroyed by bacteria
• Helicobacter pylori
• The hydrochloric acid breaks down the stomach
  wall
• Pancreatitis happens when the duct that connects
  the pancreas to the small intestine is blocked
• Enzymes build up in the pancreas and start to
  digest it

19

• Colon cancer occurs in the large intestine
• May be genetic
• May be caused by low-fiber diets where the feces
  remain in the intestine for too long
• Fiber roughage

20
Excretory System

• Excretion the removal of metabolic wastes from
  the body
• Includes the liver, skin, and kidneys
• The liver breaks down old red blood cells,
  recycles useful materials, and breaks down extra
  amino acids
• The skin gets rid of water and salts through
  sweat
• Kidneys filter the blood

21
(No Transcript)
22
(No Transcript)
23
Kidneys

• Filter wastes out of the blood
• Urea is a waste made by cells during metabolism
• The filtering is done by microscopic structures
  called nephrons in the kidneys
• Blood is brought to the kidneys by the renal
  artery and enters the glomerulus of the nephron
• Wastes leave the blood and enter Bowmans capsule
• Urine is made as the wastes travel through the
  tubule

24

• Urine leaves the kidneys through the ureters
• Urine is stored in the urinary bladder
• The urethra carries urine out of the body

25
Diseases

• Nephritis inflammation of the kidney caused by a
  bacterial infection
• If not treated with antibiotics, it can lead to
  kidney failure
• Kidney stones are caused by a build up of calcium
• May pass on their own (painful!) or require
  surgery