The Digestive System

By Kyra Michalak

Why is it Important?

• Digestion-is the process where food and fluids are broken down into their smallest parts so the cells can use these nutrients to build and be nourished creating energy for the body

• The digestive system is made up of hollow organs

• Organs- mouth, esophogus, stomach, small intestine, large intestine, or the colon, and also the rectum and anus

The Mouth: Structure

• Food starts in the Oral Cavity or the mouth, where there are accessory organs such as tongue, teeth, and the salivary glands which contain salivary amylase

• Salivary Glands- they are organs that produce saliva which moistens food to make it softer as it passes through the mouth, pharynx, and esophagus

After the Mouth

• Pharynx- is the throat that is like a funnel and it passes chewed food from the mouth and into the esophagus

• Esophagus- muscular tube connects the stomach and pharynx or the upper gastrointestinal tract.

• At the end of this there is the esophageal or cardiac sphincter which traps food in the stomach

Stomach: Function

• Stores food/liquid• The muscles of the upper stomach relax, next

mixing occurs, and then empty the contents into the small intestine but the kind of food effects the emptying(fats stay the longest, proteins also stay, but carbs leave relatively quickly).

Stomach: Structure

• A muscular sac and is in the abdominal cavity on the left side and is separated into the fundic region, the body region, and the antrum region.

• the walls contain a layer of muscle • mucous covers the mucosa keeping the acidic

digestive Juice from destroying the stomach• mucous cells- produce a mucous that forms a gel

coat that attaches to the surface of the epithelium

Regions in Stomach• Lamina propria consists of glands which empty

into the gastric pits • Cardiac region- is near the opening of the

esophagus and has cardiac glands which have mucus-secreting cells

• Fundic region• large part of the stomach.• glands=gastric or fundic which extend to the

muscularis mucosae and then it is from here where three to seven glands open at the gastric pit

Fundic Region Cells

• Mucous neck cells- secrete a soluble mucous• Parietal cells- Secrete HCL and are very eosinphilic and

also secrete an intrinsic factor- which is a glycoprotein, needed for maturation of red blood cells.

• Chief Cells-secrete lipase which breaks down fats to fatty acids

• Enteroendocrine cells- produce gastrin, which signals the production of HCL and is sent into blood vessels

• Undifferentiated cells- replace mucous cells, parietal, chief and enterendocrine cells

Pyloric Region• Is the region in the stomach close to the pyloric

sphincter which has pyloric glands• These glands secrete mucous• Muscularis mucosae- Layer of smooth muscle that

extends from the inner inner layer into the lamina propria

• Sub mucosa- is made of dense, irregular connective tissue containing many blood vessels

• Muscular Externa- consists of three layers. This mixes chyme and sends it into the small intestine

• Serosa- covers the stomach and is a thin connective tissue

Small Intestine: Structure

• largest component of the digestive tract• Is made up of three segments (the duodenum,

jejunum, and ileum) and is part of the lower gastrointestinal tract and takes up a large portion of space in the abdominal cavity

• It uses enzymes from the pancreas and bile from the liver to break down food

Small Intestine: StructureVilli

• The mucosa- is covered by thin projections called villi- The surface is covered with a columnar epithelium; base of the villi are intestinal glands called crypts, which are tubular structures.

• The absorptive cell is the cell from epithelium which each have around 3000 microvilli-these are protrusions from the cell membrane

• Villi and microvilli- increase the absorptive surface by 600 times

Small Intestine: StructureCells

• Absorptive Cells- used for the transport of substances

• Goblet Cells- Secrete mucous which is a large glycoprotein and these cells appear pale

• Paneth cells- located in the bases of the crypts. There are granules which contain an antibacterial enzyme, glycoproteins and it also serves to regulate naturally occuring bacteria in the intestine

Small Intestine: Structure Cells

• Enteroendocrine cells-Produce cholecystokinin or CCK

• Micro fold cells- They endocytose antigens in order to carry them to other cells where responses to these antigens can begin.

• Undifferentiated cells- stem cells at the base of crypts and are what create the other cells

Small Intestine: Structure

• The submucosa mostly characterizes the duodenum and the jejunum, and the illeum is characterized by the mucosa

• Duodenum- has Brunner’s glands which produce an alkaline fluid that has neutral glycoproteins and it is this secretion that protects the small intestine from the acidic chyme of the stomach

Small Intestine: Structure/Functions

• Muscularis Externa- is made of two layers where the inner layer is made for mixing and the outer layer is for peristalsis

• Ileum- abosorbs bile salts and b12 • Jejunum- where absorption of nutrients is

sent into the bloodstream

Accessory Organs: FunctionsLiver

• Liver- is an accessory organ whose main function is to process nutrients. It receives the raw materials from the intestine and then makes many chemicals the body needs to function while it also detoxifies chemicals

• bile is secreted from here into the small intestine helps to digest fat

• Gallbladder- Bile is stored and recycled here where it is then absorbed into the duodenum in order to aid in the digestion of fats

Accessory Organs: FunctionPancreas

• Secretes digestive enzymes into the duodenum which work to break down carbs, proteins, and fats. It also secretes insulin into the bloodstream which is a hormone that metabolizes sugar

• The pancreatic juice breaks food into amino acids, nucleotides, fatty acids and monosacharides

Large Intestine: Function/Strucure

• Functions to eliminate feces, absorb water, and it also contains symbiotic bacteria that break down wastes

• Is made up of Teniae coli- bands of smooth muscle, haustra- sacs that are like pockets, epiploic appendages- fat filled pouches

Large Intestine: StructureColon

• Connects small intestine to the rectum• waste (stool) is the left over material from the

digestive process, and it moves through the colon by peristalsis

• A mass movement or contractile waves will empty into the rectum where there are also smooth muscle contractions

Large Intestine: StructureRectum/Anus

• Rectum- the chamber that connects the colon to anus, lets a person know the stool needs to be extracted, and holds the stool.

• sphincters relax and the rectum contracts, pushing the stool through

• Anus- the final part of the digestive tract- has 3 pelvic floor muscles and 2 anal sphincters

• there is the internal rectum which is very tight all the time except when stool is present. The external sphincter will relax, releasing the contents.

Physiology: Ingestion3 Main Movements- Swallowing,

peristalsis, segmentation• The mouth is where food is ingested where

large molecules are broken down• Swallowing- uses smooth and skeletal muscles

in mouth, tongue, and pharynx to push food into esophagus which is mechanical digestion

• The esophageal sphincter closes the entry way between the stomach and esophogus

Physiology: Ingestion/Movements

• Peristalsis- movement formed by smooth muscles that move food down the tract involuntarily and all the way into the intestines.

• Peristalsis is when the muscles around the organs contract pushing the food slowly along

• Segmentation- occurs only in the small intestine where fragments of the small intestine contract which increases absorption of nutrients, because food comes in contact with the walls of the intestine.

Physiology: Mechanical and Chemical Digestion

• Is the physical breakdown of food into smaller pieces and begins with the chewing and also the muscular mixing of the food in the stomach and intestines

• Chemical digestion- beings also in the mouth with salivary amylase that makes complex carbs into simple carbs while the pancreas uses a lot of chemical digestion

Physiology: Secretion

• Digestive system secretes around 7 liters of fluid a day

• Fluids: Saliva, mucos, hydrochloric acids, enzymes and bile

Physiology: Absorption• Carbs- starch/fiber- starch is digested by an enzyme in

pancreatic juice/saliva which breaks it into maltose, then an enzyme in small intestine breaks it into glucose

• Sugars- broken down into glucose and fructose by an enzyme in the small intestine and then absorbed into the blood.

• Fibers- are indigestible and passes through the intestines, but some are soluble where it dissolves in water.

• Protein- an enzyme in stomach and in small intestine from the pancreatic juice breaks them into amino acids and is absorbed into the blood

Physiology: Absorption• Fats- bile produced in liver dissolve fat and

pancreatic juice and intestinal enzymes break the molecules into fatty acids or cholesterol

• Vitamins- classified by the fluid in which they may be dissolved: water-soluble vitamins (B and C vitamins) and not easily stored, leave through urine, and Fat-soluble vitamins (A, D, E, and K) which are stored in liver and fat tissue.

• Water and Salt- also come from juices secreted by digestive glands.

• Excretion-gets rid of wastes through defaction

Hormone Regulators

• Produced and released by mucosa cells, travel through body then back to digestive system

• Gastrin- causes cell growth in stomach, small intestine, and colon. Makes stomach produce acid to digest food

• Secretin- makes pancreas release digestive juice and stimulates stomach to produce pepsin

• CCK- causes cell growth in pancreas, enzymes to be made in pancreatic juice, and gallbladder to empty

Nerve Regulators

• Extrinsic(outside nerves) are form the brain and spinal cord, release acetylcholine and adrenaline

• Intrinsic- network of nerves in the walls of esophagus, stomach, small intestion and colon

Celiac Disease: What is It?

• An immune disease where people can’t eat or consume products that have gluten.

• Gluten is a protein and if people have this disease, it will ruin their small intestine

• Why? The immune system will attack it, destroying the small intestine damaging the villi which prevents you from absorbing the necessary nutrients

Celiac Disease: Symptoms/ Diagnosis• Stomach pain, diarrhea, weight loss,slowed

growth• Blood tests are accurate for these symptoms

can be similar to other dieases• Then a biopsy will be taken from your small

intestine• Treatment- Gluten-free diet, such as no

wheat, rye, and barely

Celiac Disease: Research

• National Institute of Diabetes and Digestive and Kidney Diseases(NIDDK) are studying different options for diagnosis

• Studying treatments through drugs• Enzymes that may change the gluten,

preventing the immune reaction• Also promoting educational materials

Sources• http://www.highlands.edu/academics/divisions/scipe/biology/faculty/harnden/

2122/notes/digest.htm• http://digestive.niddk.nih.ov/ddiseases/pubs/yrrd/• http:/science.nationalgeographic.com/science/health-and-human-body/human-

body/digestive-system-articles/• http://www.cchs.net/health/health-info/docs/1600/1699.asp?index=7041• http://www.courseweb.uottawa.ca/medicine-histology/english/gastrointestinal/

gastro- smal...• http://www.courseweb.uottawa.ca/medicine-histology/english/Gastrointestinal/

gastro_stomach.htm• http://www.elu.sgul.ac.uk/rehash/guest/scorm/254/package/content/index.htm