, • nutrients are used as raw materials for synthesizing essential compounds
(anabolism) or converted into energy to continue functioning (catabolism).
• The digestive system, working with the cardiovascular and lymphatic systems,
provides the needed nutrients in the form of organic molecules (such as
carbohydrates, fats, or proteins).
• the digestive tract is also an endocrine organ that produces a variety of
hormones.
24-1 The digestive system, consisting of the digestive tract and accessory organs,
functions primarily to break down and absorb nutrients from food and to eliminate
wastes
• The digestive system (alimentary system) = a muscular tube, the digestive
tract aka gastrointestinal (GI) tractor alimentary canal, and accessory organs.
major • oral cavity (mouth) → pharynx (throat), esophagus, stomach, small intestine,
and large intestine → anus.
-
extrem
• Accessory digestive organs; teeth, tongue, and glandular organs (salivary
glands, liver, pancreas, gallbladder)
• These structures have overlapping functions that all contribute to the main
function of the digestive system (break down food, absorb nutrients, and
eliminate waste)
,Functions and Processes of the Digestive System
• the digestive system performs six integrated processes.
1. Ingestion takes place when food enters the oral cavity. is an active process
2. Mechanical digestion and propulsion involve the crushing and shearing of food
and then propelling the food along the digestive tract.
• Mechanical digestion may not be required before ingestion. Liquids and
yogurt
• preliminary mechanical digestion: Tearing and mashing with the teeth, followed
by squashing and compressing by the tongue,
• Swirling, mixing, and churning motions of the stomach and intestines provide
mechanical digestion after ingestion.
• Mechanical digestion increases the surface area of ingested materials, making
them more susceptible to the actions of enzymes.
3. Chemical digestion refers to the chemical breakdown of food into small organic
and inorganic molecules for absorption
• Simple molecules in food, such as glucose, can be absorbed intact.
4. Secretion is the release of water, acids, enzymes, buffers, and salts by the
epithelium of the digestive tract, glandular organs, and the gallbladder.
glandular organs and gallbladder secrete into ducts that enter into digestive tract.
5. Absorption is the movement of organic molecules, electrolytes (inorganic ions),
vitamins, minerals, and water across the digestive epithelium.
• These materials are absorbed into the interstitial fluid of the digestive tract for
distribution to body cells.
6. Defecation is the elimination of wastes from the body. The digestive tract and
glandular and secretory organs discharge wastes in secretions that enter the
lumen of the tract. These wastes are dehydrated and compacted into matter called
feces and ejected from the digestive tract through the anus
, the digestive system also plays a protective role. The lining of the digestive tract
safeguards surrounding tissues against (1) the corrosive effects of digestive acids
and enzymes; (2) mechanical stresses, such as abrasion; and (3) bacteria from
food and live in the digestive tract.
digestive epithelium and its secretions provide a nonspecific defense against
these bacteria. When bacteria reach the underlying layer of areolar tissue, the
lamina propria, macrophages and other cells of the immune system attack them
Relationship between the Digestive Organs and the Peritoneum: The Mesenteries
D peritoneal cavity
• Is contained in the abdominopelvic cavity
• is lined by peritoneum ( a serous membrane consisting of a superficial
mesothelium covering a layer of areolar tissue)
• Liver disease, kidney disease, and heart failure can increase the rate at which
fluids move into the peritoneal cavity.
• the volume within the peritoneal cavity is very small
•
2 parts : serosa, or visceral peritoneum and parietal peritoneum
• The serosa= visceral peritoneum, covers organs that project into the peritoneal
cavity.
• continuously produces peritoneal fluid, which lubricates the surfaces
• the serosa covers their anterior surfaces and portions of their lateral surfaces
• The parietal peritoneum lines the inner surfaces of the body wall.
• a thin layer of peritoneal fluid separates the parietal and visceral surfaces and
can slide without friction and resulting irritation. The membrane secretes and
reabsorbs
• ascites - abdominal swelling caused by buildup of fluid
• This fluid can distort internal organs and cause symptoms like heartburn,
indigestion, and lower back pain.
• Portions of the digestive tract are suspended within the peritoneal cavity by
sheets of serous membrane that connect the parietal peritoneum with the
visceral peritoneum.
