Digestive System 14.1- 14.9!!Gastrointestinal Tract:

• Mouth: It is the entrance of the GI tract

o Process of chewing occurs here which breaks down food into smaller and smaller chunks in order it to be small enough to swallow

o An effective food processor

o There is a large amount of bacteria, that live between the teeth

▪ The bacteria then can dissolve the enamel, which creates cavities (dental caries)

▪ Can cause inflammation of the gums- gingivitis

▪ Decay that causes inflammation of the periodontal membrane- periodontitis

o Teeth break down the food (grinds and tear food apart into smaller

• Tongue: Positions food over the teeth in order for it to be broken down to smaller pieces

o Skeletal muscle enclosed in a mucous membrane

o Voluntary control over the movement

o Contributes to taste and speech

• Saliva: Moistens food in order to be broken down further

o 3 Glands: Parotid, sublingual and submandibular

▪ Located below the haw and tongue

▪ All 3 glands connect to the oral cavity

o Moistens food, which makes it easier to chew and swallow

o Mucin is part of saliva that holds food particles together

o Salivary amylase beings digestion of carbohydrates

o Bicarbonate maintains the pH of the mouth (6.5-7.5)

o Lysozymes prevents bacterial growth

• Pharynx: Delivers the food to the esophagus

o Stops breathing temporarily during swallowing reflex

o Tongue and jaws push the bolus into the pharynx

o Before swallowing, muscles keep esophagus closed

o Receptors initiate the swallowing reflex; it cannot be stopped

▪ It closes the passageway of air

o Soft palate rises to close passage to nasal cavity

o Epiglottis bends to close off trachea, and open the esophagus

o Tongue pushes the food back even further, and it slides down to esophagus

• Esophagus: muscular tube (skeletal and smooth muscle) that transports the food from the mouth to the stomach

o Lining of esophagus produces lubricating mucus that helps food slide down

o Thick foods can stick to the mucosa but gets dislodge and slides down; this is because of contractions that occur

o Peristaltic contractions enable the esophagus to transport food fore and against gravity

o Contains the lower esophageal sphincter that opens when food arrives and closes once it goes through to the stomach

▪ Prevents reflux of stomach contents back into the esophagus

▪ Sphincter can malfunction and back flow can occur causing acid reflux/ heart burn

• more common during weight gain, pregnancy and age

• Can be caused by a hiatal hernia

• Stomach: the place where food is held

o Food storage: stores food, it can shrink and expand

o Digestion: digests proteins, produces enzymes, kills bacteria, mixes acids with food, breaks food down and pushes contents into the small intestines

o Regulation of delivery: regulates the delivery rate of how frequent food can enter the small intestines

o Gastric pits secretes HCl, pepsinogen (which is then converted into pepsin enzyme)

o HCl, pepsinogen, and fluid secreted are known as gastric juices

o pH=2

o Pepsin dissolves connective tissues in food, and proteins into amino acids

o Food in stomach is called chyme

o Pyloric sphincter is between stomach and small intestines; regulates food entry into small intestines

o Cells in the stomach constantly secrete mucus to protect the lining of the stomach

▪ If damaged then it becomes a peptic ulcer

o Mucosal cells also secrete intrinsic factor that allows B12 to be absorbed in the small intestines

o Some cells secrete gastrin

o Muscles contractions make the stomach small when empty or expand when full

o Stretching signals peristalsis to increase

▪ It allows chyme to move into the small intestines, by squeezing

o 2-6 hours for stomach to empty completely after a meal

o Peristalsis declines as the stomach empties

o Chyme that has high acid or fat will stimulate to release a hormone that decreases peristalsis so nutrients can be absorbed during the small intestines

o Stomach doesn’t absorb anything, however minimal alcohol and drugs will penetrate with minimal absorption

• Small Intestines: digest and absorbs the nutrients from the chyme

o Digestion: digests proteins because of the strong acids and pepsin, carbohydrates and lipids also get digests.

▪ CHO, Proteins, and Lipids in the small intestines involves neutralizing the acidic gastric juices and adding digestive enzymes from the intestines and pancreas

o Absorption: macromolecules are broken down to single units (amino acids, monosaccharides, fatty acids, and glycerol)

▪ Must be small enough to be transported across mucosal cells into the blood

▪ 90% of absorption occurs here

o 3 Sections: duodenum, jejunum, and ileum

▪ Duodenum- most digestion occurs here

▪ Jejunum and ileum- most absorption occurs here

o Contains villi (large folds covered with microscopic projections) and each villi has microvilli

▪ Enlarges the surface area (500x) when it comes to absorption of nutrients

▪ Each villi has blood capillaries that transport nutrients that are small enough for the blood cappillaries, and lacteals transport larger molecules via lymph

• Large Intestines: absorbs the remaining nutrients and water, and stores solid waste

o Has 4 sections: ascending colon, transverse colon, descending colon, and sigmoid colon

o A pouch that receives the chyme from the small intestines is called a cecum

▪ A small finger projection attached to it is called the appendix

• No digestive function, but can be infected or inflamed

o Feces is stored in the sigmoid colon

▪ Contains 5% bacteria weight

• Bacteria releases by products that are useful such as vitamin K

o Defecation is controlled by neural reflexes

▪ Internal anal sphincter- keeps anus closed by contractions

• When feces enters rectum, internal anal sphincter relaxes and rectum contracts

▪ External anal sphincter- voluntary contraction, skeletal muscle, potty training is controlling this sphincter

• Rectum: Where waste materials is stored temporarily, until the body needs to release the waste, stimulates the desire to secrete waste

• Anus: Where feces and waste materials leave the body

• Organs form a hollow tube in which the space within this tube is the area in which the food travels is called the lumen- Gastrointestinal tract (GI tract)

Accessory Organs:

• Assist the digestive system (Know the roles and functions of each)

o Pancreas: Endocrine/exocrine gland that secretes/produces several hormones into the blood/digestive tract

▪ Sodium bicarbonate:

• Works best in neutral pH

• Neutralizes stomach acid in small intestine so it can digestive molecules more

▪ Digestive enzymes: most enzymes involved in the digestion come from pancreas

• Protease: Digests proteins

o Trypin, chymotrypsin, and carboxypeptidase

• Pancreatic amylase: Digests carbohydrates and it is helped by salivary amylase

• Lipase: Digests lipids

o Small intestine doesn’t produce lipase so its important!

o Salivary Glands: produce saliva in order to pass food through to the stomach

▪ 3 glands: Parotid, submandibular, and sublingual

▪ Connect via oral cavity via ducts

▪ Release mucin, salivary amylase, bicarbonate, and lysozymes

o Liver: Facilitate digestion and lipids by producing bile

▪ Contains electrolytes, cholesterol, bile salts, lecithin and pigments

▪ Bile emulsify lipids in the small intestines so they can become smaller particles and be digested by lipase

▪ Hepatic portal system carries nutrient rich blood directly from the digestive organs to the liver via the hepatic portal vein

▪ Important organ for processing and storing nutrients from the body

▪ Other functions of liver:

• Stores fat-soluble vitamins (ADEK) and iron

• Stores and converts glucose and glycogen

• Manufactures plasma proteins

• Synthesizes and stores lipid

• Inactivating toxic chemicals

• Converts ammonia to urea

• Destroys old RBCs

o Gallbladder: Stores bile, and concentrates bile by removing water, transported into the small intestines by common bile duct

Tissue Layers:

• Walls of the GI tract have 4 layers:

o Mucosa: innermost tissue layer, all nutrients must cross the mucosa to enter the blood

o Submucosa: connective tissue containing: blood vessels, lymph vessels, and nerves

▪ Food that are absorbed across the mucosa enter the blood and lymph vessels here

o Muscularis: responsible for motility and movement

▪ Two or three layers of smooth muscle

▪ Muscle is in circular way, not lengthwise like others

▪ Stomach has diagonal sublayer

o Serosa: outermost layer, connective tissue that protects the other 3 layers and attaches the digestive system to the walls of the body cavities

Functions of Digestive System

• Mechanical processing and movement: Chewing breaks food into smaller pieces and mixes contents of the lumen and propel it forward

• Secretion: Fluids are secreted into the GI tract at various places

o Several hormones regulate digestion that are secreted into the bloodstream

• Digestion: Contents of the lumen are broken down both mechanically and chemically into smaller particles

• Absorption: Nutrient molecules pass across the mucosal layers of the GI tract and into the blood and lymph

• Elimination: Undigested material is eliminated from the body via the anus

Movement of the GI Tract:

• Peristalsis propels food forward towards the stomach

o Bolus stretches esophagus causing muscle in the front to relax and the muscle behind to contract

o Peristaltic wave of contraction ripples through the organs of the GI tract, mixing contents of the esophagus and intestines forwards

o Occurs in all parts but mostly in the esophagus

• Segmentation mixes food

o Short sections of smooth muscle contracts and relaxes randomly

o Results in mixing back and forth the contents of lumen

o Food particles are pressed against the mucosa allowing the body to absorb the nutrients

o Occurs mostly in the small intestines

Pathway Through The System:

• Teeth – mechanical break down of food

o 4 types of teeth: sharp edge incisors (cut food), pointed canines (tear food), premolars and molars (flat surface that grind and crush food)

o Children have 20 teeth, adults have 32

o Tooth has crown is the visible part of tooth, and the root is the part that is inserted in the root

• Tongue – positions food over teeth and mashes it against the root of the mouth

o Contributes to taste and speech

• Saliva – moistens food with the help of mucin (holds food together), salivary amylase (digests carbs), bicarbonate (maintains pH of mouth), and lysozymes (inhibits bacteria growth)

o 3 glands: parotid, submandibular, and sublingual

• Pharynx – transports food from mouth to the esophagus

o Voluntary- tongue and jaws push the bolus into the pharynx

o Involuntary- swallowing reflex that closes the trachea so food doesn’t enter the lungs

• Epiglottis – closes the trachea while food passes from the pharynx to the esophagus

• Esophagus – transports the bolus towards the stomach, using movements such as peristalsis, produces mucus that helps food slide down, as a sphincter at the bottom to allow food to enter the stomach

• Stomach:

o Functions- Food storage (stores food until digestion and absorption), Digestion (digests food into smaller particles by using enzymes), Regulation of delivery (regulates rate of which food is delivered to the small intestines)

o Structure- Figure 14.7 (mucosa, submucosa, muscularis, serosa, oblique layer, circular layer, longitudinal layer)

o Chemicals- pepsin (enzyme that digests protein), HCl (breaks down everything), pepsinogen (hormone that activates pepsin), intrinsic factor (protein that binds

vitamin B12 so it can be absorbed in SI), mucus (absorbs minimal vitamins and alcohol and protects lining of the stomach)

o Peptic ulcer formation- mucus lining becomes damaged that leaves tissue to be vulnerable, forms in esophagus or small intestines

• Small intestine:

o Functions - Digestion (digests macromolecules, neutralizes acidic gastric juices and adds digestive enzymes) & Absorption (macromolecules are absorbed through villi)

o Regions - duodenum (most digestion), jejunum and ileum (most absorption)

o Structure and Role of villi and microvilli (Figure 14.9)- enlarge surface area when it come to absorption of nutrients, contains lacteals and blood capillaries

• Pancreas:

o Digestive enzymes (proteases [digests proteins], pancreatic amylase [digests carbohydrates], lipase [digests lipids-important] and sodium bicarbonate [neutralizes acidity])

o Delivers these enzymes into the duodenum

• Liver:

o Digestion and absorption of lipids by producing bile (electrolytes, cholesterol, bile salts,lecithin and pigments)

o Role of bile- emulsifies lipids in order to become smaller droplets so it can be absorbed

o Hepatic portal system- carries nutrient rich blood from digestive organs to the liver

o Other functions of the liver- storing fat soluble vitamins, store and converts glucose and glycogen, manufacture plasma proteins, synthesizing and storing lipids, inactivating toxic chemicals, converting ammonia to urea, and destroying old RBCs

o Why injury to this organ can be dangerous- overexposure to toxic chemicals can impair the liver by killing liver cells

• Gallbladder:

o Concentrates bile and secretes it into small intestine via bile duct

o Can be removed, and if it is removed, the liver dispenses bile into the small intestines right away

• Large intestine:

o Functions- absorbs remaining nutrients along with water, and store waste for elimination

o Regions- Appendix, colon (ascending, transverse, descending and sigmoid), rectum & anus

o Bacterial component- some bacteria releases by products that we use such as vitamin K

o Eliminating waste is a neural reflex that is both involuntary and voluntary that uses sphincters

• Sphincters:

o Lower esophageal- located at the bottom of the esophagus, prevents contents of stomach to rising, allows how much bolus enters the stomach at a time, prevents acid reflux

o Pyloric- located at the bottom of the stomach connecting the small intestines, allows how much chyme is allowed to enter the small intestines at a time

o Internal anal- Inside the anus, keeps the anus closed by contractions, and relaxes when feces pass through

o External anal- Outside the anus, voluntary contraction, skeletal muscle, actually going to release waste

• Nutrient absorbtion- Proteins and carbs by active transport

o Proteins- enzymes break down proteins into amino acids, then they are actively transported into the mucosal cells

▪ Move via facilitated diffusion towards the capillaries

o Carbohydrates- digestion occurs all over the digestive tract, eventually breaking them down to monosaccharides

▪ Use different active transport proteins to go to the capillaries (same as proteins)

o Lipids – broken down and then reassembled

▪ 1. Bile salts + fat globules turns to

▪ 2. Emulsion droplets which lipase comes and digests them into smaller particles which then turns to

▪ 3. Bile salts+ fatty acids and monosaccharides which then turns to

▪ 4. Micelles (a mixture of bile salts and lecithin with FA and monosaccharides)

▪ 5. Enter the epithelial cell layer, in which micelles combine with other micelles to form a triglycerides, but also protein surrounds each triglycerides that form a chylomicrons

▪ 6. Then they travel towards the lacteal (opening of lymph vessel) in order to be transported to the correct area in the body

o Water – osmosis

▪ High concentration of water compared to other areas of the body

▪ Diffusion of water is strong

▪ Too much food placed in the large intestines leads to diarrhea

▪ Feces in the large intestines for a long period of time leads to constipation

o Vitamins & minerals – various pathways

▪ Fat-soluble vitamins dissolve in the miscalls and absorbed by diffusion in the membrane of the mucosal cell (like lipids)

▪ Water soluble vitamins are absorbed via active transport or diffusion (channels or pores)

▪ Minerals- not lipid soluble so they use active transport or diffusion by specific transport proteins, pores or channels

▪ Body fluids (acids, enzymes…etc)- are digested and reabsorbed by the digestive system it self

Endocrine and Nervous System Regulate Digestive System:

• Regulation involves motility and secretions of the organs

• To maintain a constant internal environment

• Promote rapid, efficient digestion and absorption

• Volume and content of food:

o When stomach stretches, neural reflexes increase peristalsis and secretion of gastric juice

o Promotes the release of gastrin that trigger the release of more gastric juice

o Stretching of duodenum increases segmentation to mix chyme

o Duodenum secretes secretin and cholecystokinin (CCK)

▪ Acid in chyme triggers secretin stimulates pancreas to release water and bicarbonate to neutralize

▪ Fat and protein triggers CCK which signals the pancreas to secrete more digestive enzymes

• CCK and stretching of duodenum stimulate gallbladder to release bile

o Secretin, CCK and stretching of duodenum inhibits stomach motility and secretions

o If chyme is released to the small intestine too fast, then small intestines will slow stomach activity

o Gastrin and neural reflex involving stretching of the stomach increase motility of the large intestine after eating

• Nutrients used or stored until needed:

o Regulation of organic metabolism involves interact between all organs

o 1. Constant communication of what we need and what we store. Macromolecules can be converted to storage and recycled when needed

o 2. Bodies store excess for the future, which increase body weight

o 3. The body uses the stored excess when we need to use it, which decrease weight

Eating Disorders:

• Anorexia Nervosa: dieting excessively and stops eatting

o Mental illness with highest mortality rate

o Refuse to maintain a healthy body weight, weigh less than 85% of ideal weight

o Fear of gaining weight

o Distorted view of their body weight and shape

o Missing 3 period cycles/ hormone problems

o Malnutrition, hair loss, fatigue, and moodiness, low bone mass

• Bulimia Nervosa: binge and purge

o Eating a lot of food and then not eating any

o Vomiting, taking laxatives, diuretics, enemas, fasting, excessive exercising

o Binge behaviour occurs twice a week for three months

o Worrying about body shape and weight, however they are normal weight

o Ulcers, heartburn, rectal bleeding, mouth issues

• Binge Eating Disorder: no control over how much they eat, even eat when not hungry

• Most of these disorders are mental illnesses

Digestive Disorders:

• Lactose intolerance: cannot digestive the lactose due to lack of lactase enzyme

o Diarrhea (retention of fluids in intestines), gas, bloating, cramps (bacterial fermentation)

• Peptic ulcers: erosions of mucosal lining of the stomach or duodenum

o Infection of bacteria that can live in acidic environment

▪ Helicobacter pylori

o Chronic inflammation increases gastric acid secretion and damages mucosal lining

o Constant usage of NSAID’s causes peptic ulcers

o Heal on their own after treatment

• Celiac disease: destruction of villi that line the small intestines

o Malabsorption of nutrients

o Genetic disorder

o Fatigue, depression, malnutrition

o Blood work determines this disease

• Diverticulosis: small sacs produced when the mucosal lining of the large intestines protrudes to other layers

o No discomfort, but can develop to diverticulitis which is inflammation

▪ Antibiotics help this

o Develop this by not eating enough fibre, which produces smaller feces which narrow the colon

• Colon polyps: noncancerous growths from the mucous membrane

o Removing them is recommended

o Colonoscopy is used to determine polyps

• Hepatitis: inflammation of liver that is caused by toxic substances or viruses

o Type A: transmitted by food and water

o Type B: blood and body fluids

▪ Leads to liver failure if untreated

▪ Jaundice, nausea, abdominal pain, and arthritis

o Type C: infected blood

▪ Chronic hepatitis, cirrhosis, liver cancer

• Gallstones: excessive cholesterol, calcium and bile salts create stones

o Can obstruct bile flow, cause intense pain

o Can be removed by removing surgery or dissolving the stones via vibrations and laser treatments

• Malnutrition: unbalanced or insufficient diet

o Over nutrition or undernutrition

o 13 million are undernourished

o Lack of nutrients can cause effects

▪ Vitamin A= eye damage and night blindness

o Stunts growth and increases infections

• Obesity: overweight individuals

o 13% in 1990 to 36% in 2010 for USA

o Body weight has genetic and environmental factors

▪ Fat genes

▪ Inbalance of caloric intake and expenditure

o Physical activity and balanced diet can decrease obesity