digestive system 6.1

Question 1

Outline the role of peristalsis in the digestive process.

Answer 1

Peristalsis is the involuntary, wave-like contraction of muscle layers of the small intestine

• helps prevents backward movement of food and maintains the forward movement of the material
• also mixes food with intestinal enzymes.

Question 2

List the name and substrate of the three major classes of enzymes secreted by the pancreas.

Answer 2

LIPASE:
hydrolyzes fats (triglycerides) to 3 fatty acids and glycerol.

Trypsin:
hydrolyzes protein into polypeptides

Pancreatic AMYLASES:
hydrolyzes starch into maltose.

Question 3

List the name, substrate and product of 5 enzymes produced by gland cells in the small intestine wall.

Answer 3

Maltase: hyrdolyzes maltose into 2 glucose molecules

Lactase: hydrolyzes lactose into glucose and galactose

Sucrase digests sucrose into glucose and fructose,

Peptidase: hydrolyzes peptides into amino acids

Nucleosidases: hydrolyzes nucleotides into base, sugar and phosphate.

Question 4

Describe why enzymes produced by gland cells in the small intestine wall often remain immobilized in the cell membrane.

Answer 4

The enzymes which are produced by gland cells in the small intestine are immobilized so that they remain in the cell membrane and can be reused again and again.

Question 5

List three adaptations that increase the surface area for absorption on the small intestine.

Answer 5

inner layer of the small intestine is covered by numerous folds

The surface of these folds contains villi which are finger-like projections that further increase the surface area for better absorption

Microvilli on the villi epithelial cells even further increase surface area to improve absorption

Question 6

Draw the villi as viewed in cross section.

Answer 6

see notion

Question 7

State the function of the following villi structures: capillary, epithelial cell, lacteal, and goblet cell.

Answer 7

villus capillary: maintains concentration radient for absorption by rapidly transporting absorbed products (sugars and amino acids) away from small intestine.

EPITHELIAL CELL:
thin layer of cells that create a tissue covering the villi. allows fast diffusion of nutrients from the small intestine lumen into the blood.
they contain:
Microvilli that further increase surface area to improve absorption.
Protein pumps in the cell membrane to carry out active transport of nutrients into the cell.
Channel proteins in the cell membrane carry out facilitated diffusion of nutrients into the cell.
Embedded enzymes within the membrane to complete digestion.
Large number of mitochondria provide ATP to fuel the active transport of nutrients into the cell.
Tight junctions between the cells to create an impermeable barrier between the fluid of the intestinal lumen and the intercellular fluid.
Pinocytotic vesicles formed by endocytosis of the fluid with the products of digestion.

LACTEAL:
a vessel of the lymphatic system with the villus that absorbs fats and transports them away from small intestine

GOBLET CELL:
are found scattered among the epithelial lining of the small intestine. These cells secrete mucus that protect the epithelial cells and serves as a lubricant for the digested food material as it passes through the digestive system.

Question 8

Define absorption.

Answer 8

Absorption is the taking in of digested substances through the epithelial cell membrane from the lumen of the gut. Absorption occurs in the small intestine.

Question 9

List materials absorbed by the villi cells of the small intestine.

Answer 9

Monosaccharide carbohydrates such as glucose, fructose, and galactose.
Any amino acids
Components of fat molecules such as fatty acids, monoglycerides and glycerol.
Nitrogenous bases from digested nucleic acid nucleotides.
Mineral ions such as calcium, potassium and sodium.
Vitamins such as ascorbic acid (vitamin C).

Question 10

List four methods of membrane transport required to absorb nutrients.

Answer 10

Simple diffusion of nutrients down a concentration gradient (eg: fatty acids).
Facilitated diffusion of nutrients through channel proteins (eg: fructose).
Active transport of nutrients against a concentration gradient through protein pumps (eg: ions, glucose and amino acids).
Endocytosis by means of vesicles of large molecules (eg: cholesterol in lipoprotein particles).

Question 11

Describe the absorption of triglycerides.

Answer 11

Fat molecules (triglycerides) are digested by pancreatic lipase within the lumen of small intestine
products of the digestion are fatty acids, monoglycerides and glycerol, which are absorbed into the epithelial cells on villi.
fatty acid diffuse across the epithelial cell membrane
Within the epithelial cell, they are again converted into triglycerides
triglycerides are coated with proteins to form chylomicrons (a lipoprotein) inside the golgi apparatus which then enter into lacteals by exocytosis.

Question 12

Describe the absorption of glucose.

Answer 12

Glucose cannot pass through the plasma membrane by simple diffusion because it is polar and therefore hydrophilic

Glucose is transported into the epithelial cell through a sodium-glucose cotransport protein
The cotransport protein couples transport of sodium down its concentration gradient (established by the active transport of sodium out of the cell by the sodium-potassium pump) into the cell with the transport of glucose against its concentration gradient into the cell

Active transport requires ATP (from many mitochondria within the cells).

Question 13

Describe the structure of starch.

Answer 13

Starch is a polymer of alpha-glucose monomers
is both amylose (by 1,4 bonds) and amylopectin (by 1,4 bonds and occasional by 1,6 bonds)

Question 14

Describe transport of glucose into and through villi capillaries.

Answer 14

the glucose moves out of the epithelial cell and moves into the villi capillary via
Glucose channels that allow the glucose to move by facilitated diffusion into blood capillaries in the villus.

Glucose in the blood is then carried via the hepatic portal vein to the liver where excess glucose can be absorbed by liver cells and converted to glycogen for storage.

Question 15

Explain the use of dialysis tubing as a model for the small intestine.

Answer 15

Dialysis tubing is an artificial semipermeable membrane tubing that facilitates the flow of tiny molecules in solution based on differential size
Pores in the tubing allow water and small molecules or ions to pass through freely, but not large molecules
These properties mimic the wall of small intestine
Dialysis tubing can be used to model absorption by passive diffusion and osmosis

Question 16

State the role of the digestive system.

Answer 16

The digestive system is a collection of organs that collectively digest food, absorb nutrients and excrete waste.

Question 17

Draw a diagram of the human digestive system.

Answer 17

see notion

Question 18

Outline the function of the digestive system structures (alimentary canal)

Answer 18

mouth: contains structures such as the teeth, tongue, and the salivary glands - that work together to aid in the mechanical digestion and swallowing of food.

esophagus: functions as the conduit for food and liquids that have been swallowed in the mouth to reach the stomach

stomach: mechanically digests food
also secretes a mixture of acid, mucus, and digestive enzymes that helps to chemically digest proteins

small intestine: Partially digested food from the stomach is mixed with bile from the liver and pancreatic juice from the pancreas to complete digestion
Then, absorbs the nutrients and minerals from the food

large intestine: the large intestine absorbs water and vitamins (e.g. K and B12) while converting undigested food into feces.

Question 19

Outline the function of the digestive system structures (accessory organs)

Answer 19

salivary glands: Salivary glands release saliva into the mouth through many tiny ducts. helps to moisten and chemically digest starch in the mouth before swallowing

pancreas: functioning as an exocrine gland, secretes pancreatic juice into the lumen of the small intestine.
Pancreatic juice has a basic pH in nature due to the high concentration of bicarbonate ions
Bicarbonate is useful in neutralizing the acidic gastric acid
Pancreatic juice also contains enzymes to digest down the proteins (protease), lipids (lipase), carbohydrates (amylase), and nucleic acids (nuclease) in food

liver: the production of bile -> passes through the bile ducts to be stored in the gallbladder

gall blader: stores bile produced in the liver until it is needed for digesting fat in the small intestine.
Bile travels through the bile ducts and is released into the small intestine where it emulsifies large masses of fat
The emulsification of fats by bile turns the large clumps of fat into smaller pieces that have more surface area and are therefore easier for lipase to digest

Question 20

Outline the function of the four layers of tissue found in the wall of the small intestine.

Answer 20

MUCOSA LAYER:
inner layer of epithelial tissue and is specialized for the absorption of nutrients

SUBMUCOSA LAYER:
provides blood vessels, lymphatic vessels, and nerves

Muscle layer: outer layer of longitudinal muscle (peristalsis) and inner layer of circular muscle (segmentation)

SEROSA LAYERS:
functions as connective tissue
helps suspend the gut in abdominal cavity by attaching itself to surrounding structures

Question 21

Label the four layers of tissue found in the wall of the small intestine as viewed with a microscope or in a micrograph.

Answer 21

see notion

Question 22

Outline the digestion of maltose, maltotriose and dextrins into glucose.

Answer 22

Amylose 1,4 bonds can be broken apart by amylase to form the disaccharide maltose and the trisaccharide maltotriose
Amylase cannot break the 1,6 bond seen in amylopectin
These larger fragments containing this 1,6 bond of amylopectin are called dextrins
These dextrins are further broken down by Alpha dextrinase into maltose
and maltotriose, which are then hydrolyzed into glucose by maltase.

Question 23

Outline the source, function and specificity of amylase

Answer 23

fucntion: digests starch is called amylose
Source: Saliva contains amylase and some starch digestion begins in the mouth. most starch digestion occurs in the small intestine, catalysed by pancreatic amylase

Specificity: breaks the 1,4 bonds in starch molecules as long as there is a chain of at least four glucose monomers. The product of the digestion is the disaccharide maltose