Enzymes and Digestion
Digestion
Mouth → Stomach → Small Intestine → Large Intestine
(+Liver, Pancreas, and Gall Bladder)
Mouth
1. Salivary Glands
a. Produces salivary amylase and saliva for early digestion of amylose and
amylopectin, polymers of glucose that are found in starch.
2. Teeth
a. Chewing and mixing food with saliva is a part of a process called mechanical
digestion.
Food is now called bolus, and bolus reaches the esophagus, where peristalsis
(rhythmic movement of esophageal muscles in this case) occurs to push bolus down to the
esophagus to the cardiac sphincter. Cardiac sphincter opens up and lets the food into the
stomach.
*Vomiting is reverse peristalsis.
Stomach
1. Gastric Glands
a. Produces gastric juice, which is composed of HCl and pepsinogen (inactive
form of enzyme pepsin, inactive enzymes are classified as zymogens).
Pepsinogen, in the presence of HCl, breaks down into pepsin. Pepsin is
responsible for breaking down proteins into smaller polypeptides.
*Ulcer is caused by bacteria called Helicobacter Pylori. It produces urease to neutralize
the stomach acid (HCl) and invades into the stomach cells. Stress and excess stomach
acid may also contribute to ulcer.
*Bolus is now called the acid chyme.
Acid chyme is now let into the small intestine through the pyloric sphincter.
Small Intestine
- Small in diameter
- Very long
Divided into 3 zones: Duodenum (first 25 cm), jejunum (absorption), ileum (absorption).
1. Duodenum
a. Chemical digestion (absorption)
b. Interstitial glands release:
i. Maltase
ii. Peptidase
iii. Lactase, galactase, dextrinase
2. Jejunum
a. Absorption
3. Ileum
a. Absorption
, Liver
Produces bile – Emulsifier – breaks down fat and *alcohol dehydrogenase
Stores glucose in chain form – glycogen.
4 lobes; each composed of smaller lobules.
Under diaphragm, over abdominal cavity.
Contains hepatocytes, (cytes = cells). Hepatitis (inflammation of liver)
Functions of the Liver
1. Regulation of nutrients in blood.
a. E.g. glucose → glycogen
2. Store nutrients
a. E.g. glucose as glycogen
b. Iron (from red blood cells)
c. Vitamin A/retinol – need for vision
d. Vitamin D/calciferol – need for bone
3. Synthesis of
a. Cholesterol, also part of bile (structure of cell membrane) + phospholipids (same)
b. Blood plasma proteins (related to blood clotting)
i. Albumin – Blood clotting
ii. Fibrinogen – Blood clotting
iii. Prothrombin – Blood clotting
iv. Globulins – Immune system
4. Detoxification
a. Drugs + alcohol
b. Food preservatives
c. Metabolic products that need to be broken down
5. RBC (red blood cell) and Hb (hemoglobin) Breakdown
a. RBC lives around 120 days
Pancreas
Secretes (into duodenum):
- Pancreatic amylase
- Protease
- Lipase
*Hormonal activity:
High blood sugar causes insulin release from the pancreas.
Insulin → Uptake of glucose in blood increase → Puts glucose in tissue cells for use and in
liver for long term storage (glycogen).
Glucagon → Release of glucose from glycogen from liver for use when low blood sugar level.
Insulin and glucagon are released by beta islet cells and alpha islet cells, respectively.
Large Intestine
- Large in diameter
Divided into 3 zones: Cecum, colon (3 parts), rectum (last 20 cm).
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