Digestive System Fig 23.1

Digestive System

Organs of the digestive systemOrgans of the digestive system– GI Tract OrgansGI Tract Organs- mouth, pharynx, esophagus,

stomach, small intestine, large intestine

GI tract also called the alimentary canal, digestive tract or gut

– Accessory Digestive OrgansAccessory Digestive Organs- teeth, tongue, salivary glands, gall bladder, liver, pancreas

Gastrointestinal MucosaGastrointestinal Mucosa- moist covering and lining membrane lining the inside of the GI tract

absorbs nutrients- aided by large surface area due to villi and microvilli esp. in sm. intestine

secretes mucin —> mucous for lubrication, protection

protects- mucosal immune functions (MALT)

gastric mucosa has specialized secretory cells

Figure 23.22

23.15 b and c

Digestive SystemGastrointestinal Tract Activities/ProcessesGastrointestinal Tract Activities/Processes

1. Ingestion-intake of food2. Propulsion-movement of food through the GI tract

Peristalsis-alternative contraction and relaxation of adjacent sections of the alimentary tract resulting in food propulsion

3. Mechanical digestion-chewing,mixing, stomach churning, segmentation

Segmentation-alternative contraction and relaxation of non- adjacent sections of the alimentary tract, resulting in mixing of food

4. Chemical digestion-catabolic steps which break down complex molecules to monomers or fragments which can be absorbed by the GI tract

5. Absorption uptake of nutrients from the lumen of the GI tract into blood or lymph via passive and active transport

6. Defecation- elimination of indigestible substances from the body

23.2

Overview of the functions of the Gastrointestinal Tract

Table 23.2

Microscopic Anatomy of the stomach *read pp 869 to 871

up to “Digestive Processes….”

Secretory cells of the gastric pits: Know what Chief cells, Parietal cells and Enteroendocrine cells of the stomach mucosa are and their function(s)

23.15c

The small intestine duodenum, jejunum, ileum

• Digestion is completed and most absorption occurs here– Villi-fingerlike projections containing

underlying:• Capillary bed- Absorbs most nutrients and water

soluble drugs and some lipophilic drugs

• Lymphatic capillary (lacteal)- Absorbs fats and highly lipophilic drugs

1. Liver-1. Liver-largest gland in the body located below the diaphragm-has numerous functions

function in GI tract processes-production of bile, a yellow-green alkaline fluid containing bile salts that is released into the small intestine (duodenum) via the bile duct; main function of bile →is to emulsify fats

Accessory Digestive Organs: Liver, Gall Liver, Gall Bladder, PancreasBladder, Pancreas

Liver Functions

• carbohydrate metabolism/storage• detoxification• serum protein production• hormone inactivation• protein metabolism/urea production• lipid metabolism• iron recycling• cholesterol synthesis

Structure of the liver-

A. gross anatomy

4 lobes- left, right,caudate and quadrate functional units- liver lobules

B. microscopic anatomy of liver lobules- hepatocytes- mature liver cells that perform most of the liver functions

arranged in ‘plates’;

high regeneration capacity

B. microscopic anatomy of liver lobules optional Fig 23.25

hepatocytes-

Perform main

Functions of the

Liver.

Fig. 23.25

B. microscopic anatomy of liver lobules

hepatocytes- mature liver cells that perform most of the liver functions

arranged in ‘plates’;

high regeneration capacity

Fig. 23.25

Accessory Digestive Organs: Liver, Gall Liver, Gall Bladder, PancreasBladder, Pancreas

2. Gall Bladder2. Gall Bladder-thin-walled muscular sac located below the ventral portion of the liver that stores and concentrates bile

bile transferred from liver to gall bladder via common hepatic duct

3. Pancreas3. Pancreas- digestive function-produces pancreatic juice containing digestive enzymes (proenzymes) for release into duodenum via the main and accessory ducts

Flowchart of chemical digestion and absorption of foodstuffs

optional Fig. 23.32

Fig. 23.32

hepatic portal circulation hepatic portal circulation