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

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

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

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

Oral Cavity The tongue- mechanical processing of food Salivary glands- 3 pairs, produce liters of saliva a day Lubrication and moistening Salivary amylase- digests complex carbohydrates Teeth- mechanical digestion

Digestive Tract Pharynx- Passageway from the mouth to the esophagus Esophagus- hollow muscular tube, which moves food through using peristalsis

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

Gastric Glands Parietal cells- secrete HCl to keep stomach pH at Acidic environment kills most microorganisms, breaks down proteins, breaks down plant cell walls, activates pepsin (protein digesting enzyme) Chief cells- Secrete pepsin

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

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

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

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

Liver Divided into two lobes, left and right Hepatocytes- adjust circulating levels of nutrients Secretes bile, which helps break down fats

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

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

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

Gallbladder Stores bile, which can become more concentrated the longer it remains in the gall bladder

Large Intestine Cecum- first section of large intestine, connects to the ileum Colon Ascending Transverse Descending Sigmoid colon

Physiology of the large intestine Reabsorption of water Absorption of vitamins- K (used by the liver to make clotting factors, Biotin (glucose metabolism), Vitamin B 5 (used for making steriod hormones) These are made by bacteria living in the colon