Digestive System Fig 23.1

Organs of the digestive system GI Tract Organs- mouth, pharynx, esophagus, stomach, small intestine, large intestine GI tract also called the alimentary canal, digestive tract or gut Accessory Digestive Organs- teeth, tongue, salivary glands, gall bladder, liver, pancreas

Gastrointestinal 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 Microvilli on each cell, outcropping, makes surface area much larger. Villi of SI are large outcroppings, on top of the villi are the microvilli. Stomach villi as well.

Figure 23.22

Know there’s smooth muscle, and that there are some layers Know there’s smooth muscle, and that there are some layers. Gastric pits formed by epithelium dips. 23.15 b and c

Digestive System Gastrointestinal Tract Activities/Processes 1. Ingestion-intake of food 2. 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 These are overlapping, some occur in many places, some only in one place.

23.2

Overview of the functions of the Gastrointestinal Tract Table 23.2

Microscopic Anatomy of the stomach. read pp 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 Part of the mucosa. Most of digestion is completed, and absorption is occuring. Capillary beds in the villi/microvilli.

Accessory Digestive Organs: Liver, Gall Bladder, Pancreas 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 Large gland, not actually a glad necessarily, but glandular. Bigger you are, and more activity, will produce more hormones. Bile is synthesized in liver, stored in gall bladder, released in duodenum. Amphipathic molecule.

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.

Flow through liver, hepatic vein Flow through liver, hepatic vein. High processing kind of organ, called the triad. Bile duct venule comes up too. 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 If liver is damaged, can replace a lot of it.

Fig. 23.25

Accessory Digestive Organs: Liver, Gall Bladder, Pancreas 2. 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. Pancreas- digestive function-produces pancreatic juice containing digestive enzymes (proenzymes) for release into duodenum via the main and accessory ducts

Don’t’ need to know names of the enzymes, just know proenzymes are released into duodenum from pancreas.

Flowchart of chemical digestion and absorption of foodstuffs optional Fig. 23.32

Fig. 23.32

hepatic portal circulation Extra Credit assignment!