functions of the digestive system ingestion- bringing in food/nutrients mechanical processing-...
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Functions of the digestive system
Ingestion- bringing in food/nutrients Mechanical processing- mechanically
breaking food down, chewing, etc. Digestion- chemically breaking food down Secretion- release of nutrients Absorption- movement of nutrients to the
blood stream Excretion- removal of waste
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Organization of Digestive Tract
The digestive tract is lined w/ mucous membranes to protect the epithelium of the digestive tract, and to help food move through
Stratified in areas of high stress, like the mouth and simple in the small intestine where absorption takes place
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Movement of Digestive Materials Peristalsis- waves of muscular
contractions that move a bolus, along the digestive tract
Segmentation- cycles of contraction that churn and fragment bolus
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Control of Digestive Functions
Neural Mechanisms- sensory neurons in the digestive tract stimulate motor neurons to control the smooth muscle of the digestive tract
Hormonal control- a lot of digestion is controled by hormones, there are atleast 18 involved in digestion
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Oral Cavity The tongue- mechanical processing of
food Salivary glands- 3 pairs, produce 1-1.5
liters of saliva a dayLubrication and moisteningSalivary amylase- digests complex
carbohydrates Teeth- mechanical digestion
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Digestive Tract
Pharynx- Passageway from the mouth to the esophagus
Esophagus- hollow muscular tube, which moves food through using peristalsis
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Stomach Four Regions
Cardia- superior portion that connects w/ the esophagus, contains lots of mucous glands to protect stomach lining
Fundus- upper curve of the stomach Body- largest region, gastric glands release
acid and enzymes, mixes food Pylorus- last section, connects to the
duodenum
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Gastric Glands
Parietal cells- secrete HCl to keep stomach pH at 1.5-2.0. Acidic environment kills most microorganisms, breaks down proteins, breaks down plant cell walls, activates pepsin (protein digesting enzyme)
Chief cells- Secrete pepsin
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Pyloric glands
Mostly produce mucous Produces hormone gastrin, which
stimulates secretion of the parietal and chief cells, as well as contractions of the stomach walls to mix and stir contents
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Regulation of gastric activity Cephalic phase- prepares stomach for arrival of
food, stimulates mucous, acid, and enzyme activity
Gastric phase- begins w/ the arrival of food, 3-4 hours while ingested foods are processed
Intestinal phase- controls rate of chyme leaving stomach and entering the duodenum
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Small Intestine
Absorption of nutrients Duodenum- “mixing bowl”, mixes chyme
and digestive secretions from pancreas and liver
Jejunum- most chemical digestion and absorption
Ileum- connects to the large intestine
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Pancreas organ posterior to the stomach, secretes
enzymes and buffers into the duodenum Secretes insulin and glucagon to control blood
sugar levels Secretes pancreatic juice- consists of an
alkaline solution to neutralize acidity of the chyme and enzymes to complete digestion
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Liver
Divided into two lobes, left and right Hepatocytes- adjust circulating levels
of nutrients Secretes bile, which helps break
down fats
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Physiology of the liver Metabolic regulation- regulates
composition of blood before it is sent to the rest of the body Carbohydrate metabolism- if blood
glucose drops, hepatocytes break down glycogen into glucose. If blood glucose increases, hepatocytes remove glucose and store it as glycogen or store it as fat
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Liver physiology cont. Lipid metabolism- regulate circulating
levels of fats Amino acid metabolism Removal of waste Vitamin storage- fat soluble vitamins
are stored (A, D, E, and K) Mineral storage and Drug inactivation
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Liver Regulation
Remove debris and pathogens from the blood
Plasma proteins- regulate osmotic pressure of the blood
Removal of toxins Synthesis and secretion of bile- emulsifies
fats so they can be digested
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Gallbladder
Stores bile, which can become more concentrated the longer it remains in the gall bladder
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Large Intestine
Cecum- first section of large intestine, connects to the ileum
Colon Ascending Transverse Descending Sigmoid colon
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Physiology of the large intestine
Reabsorption of water Absorption of vitamins- K (used by the
liver to make clotting factors, Biotin (glucose metabolism), Vitamin B5 (used for making steriod hormones) These are made by bacteria living in the
colon
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