Digestive System

o PANCREATIC Hormones that affect the secretion of pancreatic enzymes

secretin - chyme (acidic food product) enters the duodenum & stimulates secretion of pancreatic juice rich in sodium bicarbonate cholecystikinin (cck) - fats and proteins enter the duodenum & stimulates secretion of digestive enzymes, influences the secretion of bile from the gallbladder

Six essential activities that occur during digestion are:

1. Ingestion 2. Propulsion 3. Mechanical digestion 4. Chemical digestion 5. Absorption 6. Defecation pneumonic Icky pussy means cyphylis alive der

Each villus (SMALL INTESTINE)

Each villus has a network of CAPILLARIES and fine LYMHATIC VESSELS called LACTEALS close to its surface. The epithelial cells of the villi transport nutrients from the lumen of the intestine into capillaries and lacteals. Capillaries absorb AMINO ACIDS and CARBS, while LACTEALS absorb GLYCEROL and FATTY ACIDS. The name lacteal comes from the milk-like appearance of the fluid inside them, caused by the suspended fat droplets. EACH LACTEAL CONNECTS TO A LYMPH DUCT, WHICH CARRIES THE FAT DROPLETS TO VEINS NEAR THE HEART. Thus, much of the incoming lipid does not get screened by the liver before it is distributed to the rest of the body. Many of the absorbed nutrients are transported via the blood vessels to the hepatic portal vein to the liver. THE LIVER REGULATES THE AMOUNT OF CARBOHYDRATES SENT TO HEART. BLOOD REGULATION

Nerve Regulators

Extrinsic and Intrinisic nerves. Extrinsic nerves come to the digestive organs from the brain or the spinal cord The intrinsic, or inside, nerves make up a very dense network embedded in the walls of the esophagus, stomach, small intestine, and colon. The intrinsic nerves are triggered to act when the walls of the hollow organs are stretched by food. They release many different substances that speed up or delay the movement of food and the production of juices by the digestive organs. Vagotomy: involves cutting branches of the vagus nerve CNX, a nerve that transmits messages from the brain to the stomach. Interrupting the messages sent through the vagus nerve reduces acid secretion. However, the surgery may also interfere with stomach emptying.

There are good reasons why all the blood is sent through the liver.

First, the blood from the gut is often very high in certain nutrients, such as glucose, especially right after a meal. The high levels would be dangerous for other organs, such as the brain. The liver acts as a regulator, taking excess nutrients out of the blood after a meal. It stores these nutrients, and can add them to the blood at times when there is little coming in (i.e. between meals). Only after the liver has adjusted the nutrient levels is the blood returned to general circulation via the heart. A second reason that blood from the gut is diverted to the liver is that it needs screening for possible toxins. Poisonous substances are likely to enter the body through the mouth and get into the blood by diffusion. Alcohol is one such example. Provided it is not overloaded, the liver may be able to detoxify poisons before they reach more vulnerable or sensitive organs.

A. Mouth

INGESTION begins when food is placed in the mouth. Digestion begins in the mouth when the salivary glands secrete mucous and enzymes (AMYLASE) initiate digestion. CHEWING (mastication, mechanical breakdown) also takes place in the mouth.

• Pancreatic digestive hormones

Insulin and glucagon o Insulin - lowers blood glucose levels when blood glucose levels are too high o Glucagon - raises blood glucose levels when blood glucose levels are too low

E. Four basic layers (tunics) of the intestines

MUCOSA SUBMUCOSA MUSCULARIS EXTERNA SEROSA

THE LIVER PRODUCES

PRODUCES BILE/excretes BILE • The liver produces COAGULATION FACTORS I (fibrinogen), II (prothrombin), V, VII, IX, X and XI, as well as protein C, protein S and antithrombin. • The liver also produces INSULIN-LIKE GROWTH FACTOR (IGF-1) a HORMONE that plays an important ROLE in CHILDHOOD GROWTH and has ANABOLIC EFFECTS IN ADULTS major site of THROMBOPOITEN production o Thrombopoietin is a HORMONE that REGULATES the PRODUCTION of PLATELETS by the bone marrow • The liver synthesizes ANGIOTENSINOGEN, a HORMONE that is responsible for RAISING BLOOD PRESSURE activated by RENIN, an enzyme that is released when the kidney

Absorption and Transport of Nutrients

The mucosa of SMALL INTESTINE CONTAINS MANY FOLDS (PLICA CIRCULARIS) that ARE COVERD W TINY FINGERLIKE PROJECTION CALLED VILI. In turn, the VILLI ARE COVERED W MICROSCOPIC PROJECTIONS CALLED MICROVILLI. These structures create a VAST SURFACE AREA through which nutrients can be absorbed

Small Intestines

The small intestines are comprised of the: • Duodenum • Jejunum • Ileum The small intestines FUNCTIONS are to COMPLETE DIGESTION and ABSORB NUTRIENTS The digested NUTRIENTS are ABSORBED through the INTESTINAL WALLS and TRANSPORTED throughout the body via the CIRCULATORY SYSTEM. The MESSENTARY houses blood vessels, lymph vessels, and nerves. It is the MESSENTARY that ABSORBS digested NUTRIENTS from the SMALL INTESTINGES. The mesentery consist of several folds of the peritoneum that connect the intestines to the dorsal abdominal wall. The MESSENTARY SUSPENDS and STABILIZES the JEJUNUM and ILEUM, parts of the small intestine, to the BACK WALL of the ABDOMEN.

Stomach

The stomach has three mechanical tasks. • First, it stores the swallowed food and liquid. The fundus, the highest portion of the stomach, relaxes to accept large volumes of swallowed material. • The second job where food, liquids, and digestive juice are mixed together occurs in the body region of the stomach. • The third task, which occurs in the pyloric region of the stomach, is to empty its contents slowly into the small. • Also located inside the stomach are small folds called RUGAE • After food enters the stomach, the stomach must produce Hydrochloric Acid (HCl) by Parietal Cells and Pepsinogen by the Chief Cells/Zymogenic Cells. HCl will then convert pepsinogen to Pepsin (a protease that will breakdown protein).

Esophagus

a hollow organ of the DIGESTIVE TRACT that connects the MOUTH to the STOMACH, it is approximately 10 INCHES LONG and CONTAINS A LAYER OF MUSCLE that enables their walls to move. Swallowed food is pushed into the esophagus, a hollow organ of the digestive tract, which connects the throat above with the stomach below, it is approximately 10 inches long, and contains a layer of muscle that enables their walls to move. At the JUNCTION of the ESOPHAGUS AND STOMACH, there is a RING-LIKE MUSCHLE, called the LOWER ESPHOGYEAL sphincter (cardiac sphincter), closing the passage between the two organs. As food approaches the closed sphincter, the sphincter relaxes and allows the food to pass through to the stomach.

mesocolon

attaches the colon to the dorsal abdominal wall; the mesocolon is called ascending, descending or transverse, according to the portion of the colon to which it attaches.

9 areas in the colon(Large Intestine)

cecum with appendix, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon, rectum, anus. ILEOCEAL REGION LOCATED AT JUNCTURE OF SMALL AND LARGE INTESTINE

• Submucosa

connective tissue that supports the mucosa

The nervous and circulatory systems also play major roles

in the digestive system.

• Mucosa

involved in absorption and secretion

Accessory Organs B. Pancreas

is a gland organ in the digestive and endocrine system of vertebrates. both an endocrine gland and exocrine gland o Endocrine - producing several important hormones o Exocrine - producing several important pancreatic enzymes/juice. These enzymes help in the further breakdown of carbohydrates, protein, and fat in chyme

Accessory Organs A. Liver

is a vital organ; it has a wide range of functions, a few of which are: • Detoxification(Methylation) most medicinal products i.e drug metabolism • Plasma protein synthesis - albumin, globulins, fribrinogen, regulatory & clotting proteins MAINSTAY/DEGRADATION OF PROTEIN METABOLISM • production of biochemicals necessary for digestion(BILE)-EMULSIFIES FATS -LIPID METABOLISM: CHOLESTEROL SYNTHESIS, lipogenesis(production of triglycerides) -produces COAGULATION FACTORS -1ST TRIMESTER FETUS=LIVER is the MAIN SITE OF RBC PRODUCTON, 32nd week GESTATION, BONE MARROw assumes -PRODUCES -THROMBOPOIETIN- HORMONE REGULATES PRODUCTON OF PLATELETS by BONE MARROW

digestion

is the process by which food and drink are broken down into a small enough MOLECULAR WEIGHT, so the body can use them to build and nourish cells and to provide energy. Digestion involves MIXING food with DIGESTIVE JUICES which break large molecules of food into smaller molecules while moving through the digestive tract.

Peristalsis

looks like an OCEAN WAVE traveling through the muscle (LONGITUDNAL and CIRCULAR MUSCLES push food from the mouth to the anus). The muscle of the organ contracts to create a narrowing and then propels the narrowed portion slowly down the length of the organ. These waves of narrowing push the FOOD AND FLUID IN FRONT of them through each hollow organ.

Inside these hollow organs is a lining called

mucosa In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce enzymes to help digest food.

• Pancreatic digestive enzymes

o Fluid consists of water, sodium bicarbonate, & enzymes o Stops the action of pepsin and sets the environment in the duodenum for digestive enzymes o The enzymes are: Pancreatic amylase - digests carbohydrates Pancreatic lipase - digests lipid/fat Trypsin & Chymotrypsin and Carboxypeptidase - which are proteases that digests protein Ribonucleases & deoxyribonucleases - digests nucleic acids (DNA & RNA) enzymes are produced in an inactive form o Prevents digesting self

HOW DOES LIVER INCREASE/DECRESE BLOOD GLUCOSE LEVELS

o INCREASES BLOOD GLUCOSE LEVELS: Gluconeogenesis (the synthesis of glucose from certain amino acids, lactate or glycerol) Glycogenolysis (the breakdown of glycogen into glucose) o DECREASES BLOOD GLUCOSE LEVELS: Glycogenesis (the formation of glycogen from glucose)(muscle tissues can also do this)

• PANCREATIC Regulation of digestive enzymes

o The Vagus nerve (x) stimulates secretions of enzymes

• Liver Breakdown

o The breakdown of insulin and other hormones o The liver breaks down hemoglobin, producing pigments bilirubin and biliverdin, failure to do so, may result in jaundice o The liver breaks down or modifies toxic substances (e.g., methylation) most medicinal products in a process called drug metabolism. o The liver converts ammonia to urea.

• The liver stores a multitude of substances:

o including glucose (in the form of glycogen, 7 day supply) o vitamin A (1-2 years' supply) o vitamin D (1-4 months' supply) o vitamin B12 (1-3 years' supply) o iron and copper.

• Muscularis externa

responsible for gut movement such as peristalsis

• Serosa

secrete a serous lubricating fluid which reduces friction from muscle movement

The digestive system is made up of

the DIGESTIVE TRACT and other ORGANS that help the body BREAK DOWN AND ABSORB FOOD. It is a series of hollow organs joined in a long, convoluted tube from the MOUTH to the ANUS.

Two digestive accessory organs

the LIVER and the PANCREAS, produce DIGESTIVE JUICES that reach the intestine through small tubes called ducts. The GALLBLADDER store/secretes the LIVERS digestive enzymes(BILE) until they are needed in the intestine.

Organs that make up the digestive tract are the

the mouth, esophagus, stomach, small intestine, large intestine (also called the colon), rectum, and anus.

digestive glands that act first are in the mouth

the salivary glands. 1.0-1.5 liters of saliva • 70% by submandibular glands • 25% by parotids - produce the enzyme amylase, amylases have an optimum pH of 6.7-7.0 5% by sublingual glands

B. Saliva

• 99.4% water • 0.6% includes - Electrolytes (Na+, Cl-, and HCO3-), Buffers. Glycoproteins (mucins), Antibodies, Enzymes, Waste products

F. Large Intestines/Colon

• the large intestine is mainly responsible for storing waste (feces), reclaiming water, maintaining the water balance, absorbing some vitamins, such as vitamin K, and providing a location for flora-aided fermentation.