Mechanical breakdown of food continues, this includes the churning of food across the rugae (lines in the wall (muscles) of the stomach)
Gastricjuices are released (HCl, mucus, pepsinogen)
HCl chemically breaks down food and kills foreign substances (eg. bacteria), HCl converts pepsinogen into active form pepsin.
Pepsin breaks down proteins into shorter chains
The food becomes a semi-liquid called chyme
Mucus protects stomach from being digested by HCl
The Pyloric Sphincter
Controls the movement of food into the small intestine. Moves like a drawstring on a bag.
At this point the food is semi liquid and 5% digested
The undigested matter is known as chyme.
More on the stomach…
The innermost mucosa of the stomach is folded into deep pits called GASTRIC PITS.
These pits are lined with specialized cells that secrete various substances that aid in digestion. Collectively, all of these secretions are called Gastric JUICES.
The GASTRIC JUICES are composed of:
Hydrochloric Acid (HCl) - kills bacteria entering with food and converts inactive pepsinogen to active pepsin.
Water & Salts
Pepsin active form of the enzyme pepsinogen, that initiate the digestion of protein
Mucus - secreted by mucosa cells and a THICK layer of mucus protects the stomach’s inner layer (wall) from HCl and pepsin → as both can degrade the protein in the cell membranes of the stomach cells
More on the Pepsin..
PEPSIN breaks down PROTEINS and/or LARGE POLYPEPTIDES into SMALLER POLYPEPTIDES
Pepsinogen is the inactive form of PEPSIN (active form)
This activation only occurs in an acidic environment (low pH_ of HCl in the stomach.
Protein digestion begins in the stomach, but it is not complete
The small polypeptides, produced after the action of pepsin, will undergo further chemical digestion in the SMALLINTESTINES, to be broken down into their amino acids subunits…
SmallIntestine
About 2.5 cm wide, 7 m long
Coiled Loop
There is Gastric Juice here as well to help with chemical digestion of chyme
Three parts of the smallintestine:
Duodenum: first 25 cm where the majority of digestion occurs
Jejunum: 3m long
Ileum: 4 m long
Small Intestine - Duodenum
Chemical digestion of food
Has tubes (ducts) leading from liver and pancreas
Bile and digestive enzymes enter from the ducts and are mixed with the chyme
Disaccharidases (sucrase, maltase, lactase) are released to further break down carbs
Small Intestine - Jejunum&Ileum
Responsible for nutrient absorption
Molecules of fat, protein and carbohydrates get absorbed into the bloodstream and then are transported to liver
Pushes undigested material into large intestine
Absorption in Small Intestine
The interior of the small intestine is covered in finger-like tube extensions called villi (singular = villus)
villi greatly increase the surface area of the small intestine thus increased absorption
Each villus has hair like extensions called microvilli (singular = microvillus)
These will also increase the surface area of the interior small intestine and thus increase absorption
Characteristics of Villi
1 - Project into the SI, and are bathed in the digested nutrient molecules
2 - one cell layer thick (thin enough for absorption of nutrient molecules EASILY)
3 - contain blood vessels (capillaries) and a lymph vessel
(lacteal) inside of them to absorb the nutrient molecules
Label this
A) Large Intestine
B) Transverse Colon
C) Ascending Colon
D) Appendix / Cecum
E) Anus
F) Rectum
G) Descending Colon
Large Intestine - Colon
• water and dissolved minerals are absorbed from undigested food
• bacteria break food down further and produce vitamins (B12, K) and amino acids