Bio 102 - Digestion (1)

Enterogastric Reflex

1. Duodenum fills with chyme. 2. Sensory stretch receptors are stimulated. When full, the stimulated receptors send signals to right place in brain. The brain sends signals to stomach to stop churning. The stomach then pinches off, letting the duodenum of small intestine to empty off. Afterwards, brain sends signals to stomach to begin churning again.

Medical Considerations of the Liver (Cirrhosis)

1.) Cirrhosis - hepatic cells degenerate and connective tissue hardens and becomes non functioning. The loss of flexibility forces liver to work extra hard. The liver can be transplanted, can regenerate, and stem cell therapies are being developed.

Organs of Digestive System (Accessory Organs)

Accessory organs are not apart of the alimentary canal but aid in the process by providing enzymes, mechanics, and support - salivary glands, teeth, pancreas, liver, and gall bladder.

Gastroesophageal Reflux Disease (Acid Reflux)

Acid chyme backs up into the esophagus. The flap that keeps door closed on bottom of esophagus opens up, letting acid go thru.

Bile

Bile doesn't do any digesting (breaking down). It is a yellowish-greenish liquid secreted by hepatic cells. It is made of water, bile salts, bile pigments, cholesterol, and electrolytes. Bile salts emulsify fat globules and allow lipase to work after emulsification...greater surface area for lipase to eat at! Emulsify is turning the big globule into smaller ones by breaking it APART not breaking down, the lipase do that (from polymers to monomers). Bile is stored in gallbladder. Bile is introduced into the small intestine in the presence of fatty food.

Peristalsis (How Food Moves)

Food moves down the alimentary canal in a process called peristalsis. Peristalsis is wave like movements (squeezing) which propels and push the food through the tube (lumen) of the digestive tract. Process creates digestive sounds.

Gastric Juice

Gastric juice is the main liquid in stomach (digestive juice). Made of: 1. Pepsinogen which is the precursor to pepsin for protein digestion. 2. Water and Intrinsic factor, a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 (cobalamin) later on in the ileum of the small intestine. 3.) Hydrochloric acid (one of the most acidic chemicals) which activates the pepsinogen to become pepsin (which breaks down protein), and kills bacteria. 4.) Lipase, which breaks down fat is not effective here. It is mostly effective in babies under 1. These components make up gastric juice. The mucus from mucosa protects the lining of stomach from being burned by the acid, or from the pepsin eating protein that is further down

Medical Considerations of the Liver (Hepatitis)

Hepatitis - creates inflammation of the liver. Many types are defined by where they come from. Hep A. is infectious, comes from fecal material and is temporary. Hep. B is blood borne (STD), and lasts around 6 months. Hep. C is chronic, most common, from blood contamination (needles, etc.) Hep. D is blood borne, from IVDA drug abuse. Newest form and can be short term or chronic.

Medical Considerations of the Liver (Jaundice)

Jaundice - bile pigments are retained and escape into the blood. Body can't convert pigments quick enough. Common in newborns.

Hepatocytes

Liver cells, working cells of the liver. They are arranged in groups (pie-shaped) called hepatic lobules. They monitor what comes in from the small intestine like nutrients, toxins and drugs. They monitor glucose level to take up or release glucose. They do not metabolize carbs, fats, or proteins. It is not a digestive organ. Makes urea from highly toxic ammonia.

Processes of the Mouth

Mastication is the chewing of food. The mouth then mixes masticated food with saliva. This is the beginning of digestion both physically and chemically. The teeth is breaking food down into smaller pieces and enzymes in saliva are chemically breaking down carbohydrates. The oral cavity also initiates swallowing by the tongue (this is voluntary, but after food is pushed back, everything else is taken care of by alimentary canal and is involuntary). Lastly, the tongue allows for the sense of taste.

Functions of the Digestive System

Mechanical processing (chewing, churning in stomach) and motility of food (moving food thru system). Another function is secretion of digestive enzymes into digestive tract. Certain organs will secrete enzymes into tract to help break molecules down. The digestive system also digests (break down) carbohydrates, lipids, and proteins (biomolecules) with the help of enzymes. In addition, it will absorb nutrients (monomers) across the tube wall into blood stream Lastly, it will eliminate undigested materials ( things we don't need).

Mixing and Emptying Of the Stomach

Peristalsis in stomach churns chyme and pushes it toward the pyloric sphincter. The churning opens it up. Pyloric sphincter relaxes and opens. Small amounts of chyme (gastric acid + food) are pushed through. Lower esophageal sphincter prevents reflux. Takes around 3-6 hours.

Function of Stomach

Stomach stores food and mixes food with gastric juice. Stomach begins the digestion (breaking down ) of proeins. Stomach helps control food into small intestine by portioning off a little at a time into small intestine. It has limited absorption of water, specific salts, specific lipid-soluble drugs like aspirin, and alcohol.

The Tongue (swallowing)

Swallowing is a voluntary action as our skeletal muscles push food into pharynx. After that, digestion becomes involuntary - sensory receptors in pharynx are stimulated to keep food from moving up into the nasal cavity. The epiglottis closes off the larynx and trachea so the food goes down the esophagus, not the trachea

The Alimentary Canal

The alimentary canal is a muscular tube about 8 meters long. There are similarities through this canal such as similarities in structure, motility through out, and innervation. Food is part of the external environment.

Esophagus

The esophagus is not an airway. Long passage for food. It connects pharynx to stomach through diaphragm. It is behind trachea. The esophagus is part of alimentary canal so it is lined with smooth muscle, peristalsis can occur. Epiglottis is a flap of connective tissue at top of esophagus and closes off trachea.

Other Functions of Livers

The liver has around 33 function. The liver processes nutrient-rich blood from the small intestine via the hepatic portal vein. The liver stores excess glucose as glycogen. When needed, liver converts back to glucose. If not used for a period of time, liver will convert it to fat. The liver breaks down red blood cells. It also stores iron and some vitamins. It is a blood reservoir (200-400 ml).

Liver

The liver is the largest gland in the body. It forms and secretes bile into gall bladder. Bile is made of bile salts. It secretes cholesterol into bile and can regenerate some liver cells if needed (like if a piece of liver fragmented or something?). In real life it is brown. The gallbladder stores bile, and emulsifies fat in chyme. It secretes bile when needed into duodenum. Greenish in real life.

Layers of the Alimentary Canal (Mucosa)

The mucosa is the innermost layer that food touches. It is a moist membrane. It protects against acids (gastric acid), and secretes mucus and digestive enzymes. Most of the time, the mucosa has microvilli, projections that aid in absorption. Blood vessels supply microvilli with oxygen and nutrients.

Layers of the Alimentary Canal (Muscular Layer)

The muscular layer is smooth muscle circling the tube and going lengthwise. This muscle moves the tube and its contents through a process called peristalsis.

The Mouth (Oral Cavity)

The oral cavity consists of teeth, palate (roof of mouth), tonsils, salivary glands, and the tongue. This is the beginning of the digestive system.

Organs of Digestive System (Alimentary Canal)

The organs that are in the digestive tract (alimentary canal) are directly involved in the process - oral cavity, pharynx, esophagus, stomach, small intestine, and colon (anus).

Pancreas

The pancreas has exocrine cells (releases substances to outside of body), and endocrine cells (releases substances to inside like blood stream). the exocrine cells release four types of digestive enzymes and bicarbonate into duodenum. These are enzymes for all four categories of food (biomolecules). The ezymes are secreted into the small intestine. Pancreatic juice are the four types of digestive enzymes and bicarbonate. Bicarbonate neutralizes the acid in chyme. Endocrine cells release hormones to blood. Our body makes two quarts of pancreatic juice a day.

Pharynx

The pharynx is in throat and what we see in the mirror. It is the passage way for air and food. Bolus, a blob of food, is propelled into esophagus by peristalsis. Tonsils located here to attack bacteria.

Salivary Glands (an accessory organ)

The salivary glands are an accessory organ. There are three pairs of accessory glands, one by the ear, under tongue, and in/by throat. Salivary glands produce saliva. Saliva moistens food, and binds the food particles (result of mastication), with mucin, a slimy like protein. Saliva also begins the digestion of carbohydrates and cleanses mouth and teeth. The main contents of saliva are the salivary amylase (ends in -ase, enzyme), mucins (proteins), and water.

Layers of the Alimentary Canal (Serosa)

The serosa is the outermost layer. It protects everything inside and lubricates the alimentary canal. This lubrication allows i to avoid tears and abrasion.

Small Intestine

The small intestine is the major digestive organ. It is the site of nutrient absorption into the blood. There are three parts of the small intestine: duodenum (beginning), jejunum, and llium. The accessory organs involved with small intestine are pancreas, liver, and gall bladder.

Stomach

The stomach is located on the left side towards the middle. It is the holding tank for food. Food enters at lower esophageal sphincter. When stomach contracts, the flap is closed. When stomach relaxes, flap opens. Rugae are the folds (wrinkles) inside the stomach that are apparent when stomach is empty. When food enters the stomach, rugae allows stomach to expand. There are three layers of muscle for churning because it does it so much! Food empties through the pyloric sphincter into small intestine. Protein is only biomolecule we break down in stomach.

Layers of the Alimentary Canal (Submucosa)

The submucosa nourishes surrounding tissue and transports absorbed material. It is below mucosa.

Teeth Diagram

The teeth is an accessory organ. It's function is mastication. Humans have 2 sets of teeth andare supposed to have 32 adult teeth in total. The shape of teeth determine their function. Molars grind, and canines tear. Enamel is outer layer and is hardened calcium. It's harder than bone! Dentin is living, bone-like and inside enamel. pulp is blood vessels and nerves while root anchors the teeth.

Gall Stones

When stones try to pass into small intestine, there is pain. We can still function without our gall bladders, it's just not very efficient for our body. Our liver will just slowly drip bile into small intestine. When our bile contains too much cholestrol, excess may form into crystals; bilirubin, excess leads to formation of stones; and/or gallbladder doesn't empty correctly (hence concentration of bile), it leads to formation of gall stones.