REAL DIGESTIVE SYSTEM Flashcards
ALL ABOUT THE SMALL INTESTINE
LAYERS - SMSM
The mucosa is folded into finger-like projections called villi 🡪 absorption of a very large amount of food molecules is permitted as surface area is increased
- The small intestine absorbs usable food substances (i.e. nutrients – monosaccharides, amino acids, fatty acids, vitamins, etc.)
The large intestine absorbs water and dissolved minerals (i.e. ions) from the indigestible food residues
The small intestine is composed of four main tissue layers, which are (from outside to centre):
Serosa – a protective outer covering composed of a layer of cells reinforced by fibrous connective tissue
Muscle layer – outer layer of longitudinal muscle (peristalsis) and inner layer of circular muscle (segmentation)
Submucosa – composed of connective tissue separating the muscle layer from the innermost mucosa
Mucosa – a highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen
DUODENUM
JEJUNUM
ILEUM
- Duodenum produces enzymes like peptidase 🡪 break peptides into amino acids.
- Coiled part of the small intestine
Absorption of small molecules (nutrients)occurs - absorption occurs by diffusion aNd active transport
The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut.
- Outline the role of peristalsis in the digestive process.
- The food bolus is propelled along the gut by a wave of a muscular contraction and relaxation known as peristalsis. Circular muscles in the gut wall in front of the bolus relax, whilst those just behind it contract. This is how the bolus travels down the esophagus, into the stomach, and on through the entire gut.
Villi absorb monomers formed by digestion as well as mineral ions and vitamins.
- Define absorption.
- List materials absorbed by the villi cells of the small intestine.
- the absorption/INTAKE of nutrients into the blood stream
- LIPIDS: GYLCEROL AND FATTY ACIDS/CARBOHYDRATES/ PROTEINS/VITAMINS, ETC.
- GLUCOSE/VITAMINS/MINERAL IONS/FATTY ACIDS
Villi increase the surface area of epithelium over which absorption is carried out.
- Explain the four adaptations that increase the surface area for absorption on the small intestine.
- Label the following on a diagram of a villi: capillary, epithelial cell, lacteal, and goblet cell.
- Many villi protrude into the lumen, greatly increasing the surface area for absorption.
- Microvilli on the surface of each cell increase surface area even further and often called the “brush border”.
- Single-cell layer of epithelial cells
Short path for diffusion. - Circular Folds (Plicae Circulares or Valves of Kerckring); increase the surface area available for absorption by causing the chyme to spiral as it passes through the small intestine, allowing for more efficient absorption
- State the function of the following villi structures: capillary, epithelial cell, lacteal, and goblet cell.
- Lacteals (lymph vessels) = Allow for rapid absorption and transport of lipids.
- Capillaries close to epithelium = Short path for diffusion, rich supply of blood.
- Goblet cell: secrete mucus in order to protect the mucous membranes where they are found
- Goblet cell: secrete mucus in order to protect the mucous membranes where they are found
The structure of cells of the epithelium of the villi is adapted to the absorption of food.
- Outline the role of the following structures of villi epithelial cells: tight junctions, microvilli, mitochondria, pinocytic vesicles, proteins imbedded on the apical surface and proteins imbedded on the basal surface.
Tight junctions- ensures all absorbed substances must pass through the epithelial cells
MicrovilLi - increase SA further
mitochondria - provide ATP for active transport of amino acids
pinocytic vesicles- for uptake of fluids and dissolved solutes THROUGH THE INVAGINATION AND PINCHING OFF OF THE MEMBRANE
proteins imbedded on the apical surface and proteins imbedded on the basal surface - active transport, facilitated diffusion
Identification of villus epithelium cells that absorb digested foods from electron micrographs.
- List four features that can be used to identify villus epithelium cell as viewed in electron micrographs.
Different methods of membrane transport are required to absorb different nutrients.
- List four methods of membrane transport required to absorb nutrients.
- SIMPLE DIFFUSION, FACILITATED DIFFUSION, ACTIVE TRANSPORT, ENDOCYTOSIS (PINOCYTOSIS)
- Describe the absorption of triglycerides.
The free fatty acids and monoglycerides are reconstructed back into triglycerides, which are gathered into a chylomicron that leaves the cell via exocytosis
- Lipases break down the lipids into fatty acids and glycerol.
- These molecules can pass through the plasma membrane of the cell, entering the epithelial cells of the intestinal lining.
- The bile salts surround long-chain fatty acids and monoglycerides, forming tiny spheres called micelles.
- The micelles move into the brush border of the small intestine where the long-chain fatty acids and monoglycerides diffuse out of the micelles into the absorptive cells.
- The long-chain fatty acids and monoglycerides recombine in the absorptive cells to form chylomicrons which contain triglycerides, cholesterol, and other lipids
- Describe the absorption of glucose by villus epithelial cells./Describe transport of glucose into and through villi capillaries.
- Glucose is hydrophilic and polar so cannot pass through the lipid area of the membrane.
- Glucose is transported into the epithelial cell coupled to the movement of sodium ions into the 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
GO TO SLIDESHOW FOR MORE INFO.
Processes occurring in the small intestine that results in the digestion of starch and transport of the products of digestion to the liver.
- Describe the structure of starch.
IGNOREEEE
- Starch is a polysaccharide composed of glucose monomers and accounts for ~ 60% of the carbohydrates consumed by humans
Starch can exist in one of two forms – amylose with branched chains of 𝝰-glucose linked by 1,4 bonds (linear) or amylopectin with chains of 𝝰-glucose linked by 1,4 bonds with some 1,6 bonds (branched chains)
- Outline the source, function and specificity of amylase.
- The digestion of starch is initiated by salivary amylase in the mouth and continued by pancreatic amylase in the intestines
- Any 1,4 bond in starch molecules can be broken down by this enzyme as long as there is a chain of at least 4 glucose monomers.
- Because of the specificity of its active site, amylase cannot break 1,6 bonds in amylopectin.
- Outline the digestion of maltose, maltotriose and dextrins into glucose.
-Amylase digests amylose into maltose/MALTRIOSE subunits (disaccharide) and digests amylopectin into branched chains called dextrins.
Both maltose and dextrin are digested by enzymes (maltase) which are fixed to the epithelial lining of the small intestine
The hydrolysis of maltose/ dextrin results in the formation of glucose monomers.
