exchange

• Give 5 ways that villi increase efficiency of absorption.

  1. Increase surface area.

  2. Thin walls.

  3. Have muscles, can mix and move content of ileum along so maintains gradient.

  4. Well supplied with blood vessels, can move blood along so also maintains gradient.

  5. Covered in microvilli which further increase surface area
• Give two methods of absorbing amino acids and monosaccharides into blood.

  Facilitated diffusion and cotransport.
• Why can't charged ions diffuse across a membrane?

  Hydrophobic nature of the fatty acid tail of the phospholipids in membrane repels charge
• Name the two types of facilitated diffusion.

  Protein channels and carrier proteins.
• Describe how protein channels work.

  Protein channels are water filled across membrane allowing specific water-soluble ions to pass through. Ions bind with protein causing it to change it's shape in such a way that it closes one side and the ion is released out of membrane
• Describe how carrier proteins work.

  Carrier proteins are used when specific molecules bind with the protein to change its shape in such a way that the molecule is release to the inside of the membrane. It can then leave via diffusion
• Why can only some ions pass through these channels?

  Because each proteins' substrate has a specific shapes, which means ions need to have the complimentary parts which fit the shape of the protein it's binding with
• Describe how cotransport works.

  Sodium ions inside epithelial cells are constantly actively transported out by a pump which creates a gradient. When sodium ions naturally diffuse back into cell, they carry an amino acid or glucose molecule with them. Can then be passed into blood through other methods.
• Does cotransport require energy?

  Even though glucose/amino acids are moving against their concentration gradient, they do not require energy because it is powered by sodium ion concentration gradient.
• What happens after emulsification of triglycerides?

  The monoglycerides and fatty acids remain in association with the bile salts that initially helped them to emulsify the lipid droplets.
• What is the name for the collection of monoglycerides and fatty acids?

  A micelle
• What is the size of a micelle?

  Tiny, 4-7nm in diameter
• How are the molecules in a micelle released individually into the epithelial cell of the ileum?

  Due to movement within the lumen of the ileum the micelle contacts the epithelial cell and the monoglycerides and fatty acids can diffuse across the membrane.
• What happens to the lipid molecules when inside the epithelial cell?

  Molecules are transported to the endoplasmic reticulum where they are recombined into triglycerides. They then move into the Golgi apparatus and associate with cholesterol and lipoproteins
• What is the name given to the structure formed from triglycerides, cholesterol and lipoproteins?

  Chylomicrons
• What are chylomicrons adapted to do?

  Transport lipids
• How do chylomicrons move out of epithelial cells?


  By exocytosis
• What is a lacteal?


  The lymphatic vessels of the small intestine that chylomicrons absorb into
• Structure - Stomach

  A muscular sac with an inner layer that produces enzymes.
• Role - Stomach


  Its role is to store and digest food, especially proteins. It has glands that produce enzymes, which digest protein.
• Structure - Ileum

  A long muscular tube, consisting of villi and microvilli.
• Role - Ileum

  Food is further digested by enzymes produced by its walls and glands. Inner walls are folded into villi, which gives them a large surface area. This alongside microvilli adapts the ileum for its purpose of absorbing the products of digestion into the bloodstream.
• Role - Large Intestine

  The LI absorbs water.
• Role - Rectum

  The faeces are stored here before periodically being removed via the anus in a process called egestion.
• Role - Salivary Glands

  These secretions contain the enzyme amylase, which hydrolyses starch into maltose.
• Role - Pancreas


  Large gland situated below the stomach. Produces pancreatic juice, which contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch.
• Chemical Digestion

  Hydrolyses large, insoluble molecules to small and soluble ones.
• Carbohydrate Digestion

  1. Salivary amylase hydrolyses starch to maltose. It contains mineral salts that help to maintain the pH at around neutral (=optimum)

  2. Stomach has acidic pH, which denatures the amylase and prevents further hydrolysis of starch.

  3. Small intestine mixes with pancreatic juice, which contains proteases and pancreatic amylase, which hydrolyses remaining starch to maltose. Alkaline salts to maintain pH.

  4. Ileum's wall produces maltase, which hydrolyses maltose to alpha-glucose.
• Sucrase


  Hydrolyses the single glycosidic bond in the sucrose molecule, to produce the two monosaccharides glucose and fructose.
• Lactase


  Hydrolyses the single glycosidic bond in the lactose molecule, to produce glucose and galactose.
• Lipid Digestion


  Lipase, produced by the pancreas, hydrolyses the ester bond found in triglycerides to form fatty acids and monoglycerides. Lipids are firstly split up into tiny droplets (micelles) by bile salts, produced by the liver. This process is called emulsification and increases the surface area of the lipids so lipase action is sped up.
• Protein Digestion


  Peptidases hydrolyse large, complex molecules called proteins.
• Endopeptidases


  hydrolyse the peptide bonds between the amino acids in the central region of a protein molecule forming a series of peptide molecules.
• Exopeptidases

  hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. In this way, they progressively release dipeptides and single amino acids.
• Dipeptidases


  hydrolyse the bond between the two amino acids of a dipeptide. Dipeptidases are membrane-bound, being part of the cell-surface membrane of the epithelial cells lining the ileum.
• What is the oesophagus?


  A muscular tube that connects the mouth to the stomach.
• What is the function of the large intestine?

  Absorbs water
• what is tissue fluid?

  the environment around the cells of multicellular organisms
• what affects the amount of material that is exchanged in an organism?

  size and metabolic rate- higher metabolic rate= more materials exchanged
• what is passive exchange?

  exchange that requires no metabolic energy e.g. through diffusion and osmosis