gastrointestinal system

food processing and storage~ functions of gastrointestinal system

• mechanical digestion: breaks down food into smaller particles

• chemical digestion: converts food into substances that can be absorbed

• moves food through GI tract (peristalsis)

• stores nutrients until needs (in the liver)

absorption~ functions of gastrointestinal system

provides absorption of nutrients and water, mainly from smaller intestine

reabsorption and elimination~ functions of gastrointestinal system

• reabsorbs water for reuse by the body, large intestine~ 10-15%

• forms feces from remaining waste products; produces defecation

manufacture~ functions of gastrointestinal system

• manufactures enzymes, hydrochloric acid, intrinsic factor, mucus to assist in digestion

• manufactures vitamin K and some B complex vitamins in large intestine

metabolism

the process by which the body changes food and drink into energy

catabolism

the breakdown of large molecules into smaller ones, producing heat + energy (over production of energy results in body storage as fat or glycogen)

ATP

the energy carrying molecule- stores and releases energy; used to power processes

anabolism

the building up of smaller substances into new organized substances to be used by the body

peristalsis

wave like contractions of the GI tract by which contents are propelled through the GI tract

bilirubin

orange/yellow fluid that is a waste product formed from the process of breaking down of red blood cells. secreted from liver to gallbladder as bile

enzyme

a protein that activates or speeds up a chemical reaction (ends in “ase” ex: lipase)

sphincter

circular muscle that guards an opening

peritoneum

serous membrane that lines walls of body cavities

peritoneal cavity

the space within the peritoneum not occupied by the abdominal organs

abdominal cavity

larger space that houses various organs including the peritoneal cavity

alimentary canal

mouth to anus. the digestive tract; tube like structure responsible for digestion and absorption of food

ingestion~ stages of digestion

taking in of food

digestion (breakdown)~ stages of digestion

mechanical and chemical conversion of food into useable molecules

absorption~ stages of digestion

transfer of nutrients into capillary and lymphatic circulation for use by the body

egestion

elimination of waste products by defecation

3 divisions

upper GI tract

• mouth; pharynx; esophagus; stomach

lower GI tract

• small intestines; appendix; large intestines (colon); rectum/anus

accessory organs

• salivary glands; liver; gallbladder; pancreas

omentum

the omentum is the large fold that hangs like an apron over the intestines (greater omentum) and connects the stomach to the liver (lesser omentum), providing immune functions and holds organs in place

messentery

layered peritoneum located in abdomen

• attaches intestines to posterior wall of abdomen and holds them in place

• provides structure and support for portal circulation system (arteries and veins)

tissue layers of the gastrointestinal tract

4 layers

• mucosa (innermost, meets lumen)

• submucosa

• muscularis (peristalsis)

  • 2 layers: circular, longitudinal

  • except in stomach (3 layers)

• serosa (outermost)

same 4 layers throughout GI tract but mucosal and submucosal layers vary in structure by section

upper gastrointestinal system

• oral cavity (mouth, tongue & accessory organ of upper GI- salivary glands)

• pharynx- inlet to esophagus & larynx

• stomach

mouth and pharynx

forms a bolus of food to send down esophagus to stomach

mouth

receives food; ingestion

• tongue: senses temperature, mixes food with saliva

• teeth: cut/tear & grind food

salivary glands (3 pairs)

• salivary amylase (enzyme) begins digestion of carbohydrates (starch)

• lysozymes (antimicrobial enzyme) in saliva attack harmful bacteria, prevent overgrowth of pathogenic species

pharynx

passageway for food & air between mouth and esophagus. splits into larynx (to trachea) and esophagus (to stomach). epiglottis closes to protect larynx/lungs. food is swallowed down esophagus to stomach

esophagus

• peristalsis with 2 layers involuntary muscle

• mucosal layer cells secrete mucus

lower esophageal sphincter (LES aka cardiac sphincter)

opens to allow food to pass into stomach

stomach

churning + HCL (hydrochloric acid) + enzymes = turns contents into chyme

• pyloric sphincter (closes until food is digested into chyme that is ready to pass into small intestine)

structure of the stomach

• muscular collapsible pouch

  • food bolus mixes with hydrochloric acid (HCL) & enzymes

  • muscle layers churn food

  • result = food turned into chyme (semi-liquid)

• 3 sections: fundus, body, pylorus

• when empty collapses into folds called rugae

• 3 muscle layers: longitudinal, circular, oblique

stomach tissue layers

4 layers of tissue in stomach

• mucosa- inner lining, with specialized cells called gastric pits

• submucosa- blood & lymphatic vessels and nerves

• muscularis (3 layers): longitudinal, circular, oblique

• serosa- outermost

mucous cell~ stomach cells & secretions

mucus: protects stomach lining, especially from HCL

parietal cell~ stomach cells & secretions

hydrochloric acid (HCL): kills pathogens and converts pepsinogen to pepsin (pH is 1)

intrinsic factor: necessary for absorption of B12
*lack= pernicious anemia

chief cell~ stomach cells & secretions

pepsinogen: addition of HCL changes it to pepsin (enzyme) which begins digestion of proteins

gastric lipase: begins digestion of fats

the churning action

• 3 muscle layers of the stomach; secretions break down (digest) food. fluid is allowed to pass via the pyloric canal

• once the stomach has digested (broken down) the food into chyme it is ready to be passed into the small intestine

chyme

semi fluid partially digested food and secretions formed into the stomach (pH is approximately 2)

pyloric sphincter

open and allow chyme to pass into the small intestine

• pyloric sphincter marks the end of the upper GI tract

lower gastrointestinal system

small intestines; large intestine/colon; rectum; anus

small intestine

largest portion of digestive tract

• most digestion and absorption processes occur here

• 80-90% of water reabsorbed (7-8 L)

• 3 sections: (total length about 20ft)

  • duodenum (10-12ft); jejunum (8ft); ileum (11ft)

• plicae circularis, villi & microvilli increase surface area

small intestine tissues

• mucosa layer: secretes mucus and enzymes

specialized into:

• plicae circularis: circular folds in intestinal walls; villi: fingerlike projections; microvilli: brush like border on absorptive epithelial cells lining the villi

• epithelial cells: absorption

• goblet cells: secrete mucus

the plicae circularis, villi and microvilli collectively increase the surface area available to absorb nutrients into blood vessels and lacteals

duodenum

most digestion (breakdown) occurs here

• first site for absorption of many minerals and vitamins (ex: iron)

• duodenum receives:

  • chyme from stomach; bile from gallbladder assists in fat digestion/emulsification; pancreatic juice: enzymes and bicarb

• cells lining the duodenum secrete hormones and enzymes (referred to as brush border enzymes)

duodenum~ accessory organs (liver, gallbladder, pancreas) join the party

by the time food passes through duodenum, most digestion (breakdown) is complete, and nutrients are in an absorbable form

1) pyloric sphinceter

of the stomach relaxes and chyme leaves stomach, enters duodenum

• chyme is acidic (pH of 2); must be neutralized

2) pancreas → pancreatic juice

• bicarbonate: raises pH to approximately 6.5; to neutralize acidic chyme

pancreatic enzymes:

• lipase breaks down fats

• amylase breaks down carbohydrates into simple sugars

• proteases (multiple) break down proteins to amino acids

3) liver makes bile

stored in gallbladder

• bile from gallbladder is released; emulsifies fats into smaller particles so that enzymes (lipases) can break them down

4) intestinal juice from duodenal wall cells

• various hormones

• enzymes (brush border)

  • for digestion of proteins and carbs

jejunum & ileum

most nutrient and fluid absorption occurs here

• jejunum: vitamins, minerals, lipids; ilium: b12 and others

• fats are absorbed into lacteals, aka lymph capillaries, directly to circulation. fat/lipid molecules are too big to pass into blood capillaries so are absorbed into lymphatic system then into general circulation

• carbs and proteins are absorbed through the absorptive epithelial cells into the villi into the blood capillaries. they are the transported via the hepatic portal vein to the liver for further processing.

3 primary functions of large intestine

1. absorbing electrolytes and about 1.5-2 liters of water

2. producing and absorbing vitamins- intestinal bacteria produce vitamin K necessary for blood clotting and some B vitamins

3. forming and propelling feces toward defecation

intestinal bacteria also inhibit growth of pathogens and protect our gut (bacterial flora important for immune function)

large intestine

from ileum, receives water, remaining food waste and dead cells from GI tract

• cecum: fluid & electrolyte absorption

• appendix: finger like appendage; plays role in maintaining normal flora

• colon (4 sections)

  • ascending and transverse: absorption of water, electrolytes & vitamins synthesized by normal flora (K & some B)

  • descending and sigmoid: hold, concentrate and transport waste

• rectum: chamber with 2 sphincters (1 involuntary and 1 voluntary)

• anus: where defecation occurs

compacts and concentrates stool (water is absorbed) as it passes through the colon to eventually become formed stool

tissue layers of large intestine

• villi not present

• goblet cells produce mucus

• no enzymes secreted

• still same 4 layers of tissue: mucosa; submucosa; muscularis, circular/longitudinal; serosa

rectum | elimination

• after water reabsorption, undigested material (stool), bacteria and plant fiber pass into the rectum

• the presence of stool will stimulate nerve endings

• peristaltic waves and relaxation of the anal sphincters leads to defecation (stool exits through anus)

rectum: chamber with 2 sphincters (1 involuntary and 1 voluntary) at opening to anus

anus: where defecation occurs

accessory organs of digestion

liver; gallbladder; pancreas

the liver

largest glandular organ, necessary for life; only the brain has more functions than liver; 500 functions

4 functions

1. nutrient processing/metabolism

2. detoxification/filter blood

3. produce/manufacture

4. storage

portal circulation

• nutrients and water are absorbed into intestinal capillaries of the hepatic portal system and transported to the liver for processing

• hepatic portal vein lacks valves, so blood can “backflow”

hepatic portal system

1. small intestine absorbs products of digestion

2. nutrient molecules travel in hepatic portal vein to liver

3. liver monitors blood content

4. blood enters general circulation by way of the hepatic veins, which empty into the interior vena cava

1) nutrient processing and metabolism~ liver functions

• proteins: used for making plasma proteins; remainder sent to general circulation

• lipids: makes triglycerides and processes lipids from general circulation

• carbohydrate processing and metabolism

  • glucose: produce ATP (energy) or stored as glycogen; remaining stored as adipose/fat

  • monitors amount of glucose in blood and works in conjunction with pancreas to keep this balanced by release/storage of glycogen as needed

2) bilirubin pathways; detoxifies/filters blood~ liver functions

• old RBCs broken down in spleen- byproduct is bilirubin

• bilirubin: the bilirubin is sent to the liver for processing

• liver processes bilirubin which is then excreted in urine or in bile

• with liver diseases like cirrhosis, the liver is unable to process the bilirubin, resulting in jaundice

2) protein pathways; detoxifies/filters blood~ liver functions

• waste product of protein consumption is ammonia

• healthy liver converts ammonia to urea to be excreted in urine

• liver disease: if liver unable to process ammonia, result is toxicity and confusion (aka hepatic encephalopathy)

kupffer cells

type of white blood cell (immune cells) within the liver that prevents foodborne pathogens absorbed in the GI tract from reaching system blood circulation

medications~ liver functions

“first pass effect”

example: about 80-85% of medication lost in intestines and filtration in the liver, leaving about 15% going into blood circulation. overuse may lead to liver damage

alcohol (ETOH)~ liver functions

alcohol is processed in the liver. overuse may lead to fatty liver disease, liver inflammation, and cirrhosis

3) produces (manufactures)~ liver functions

• bile (sent to gallbladder for storage)

• heparin (anticoagulant)

• plasma proteins

  • fibrinogen and prothrombin (clotting factors)

  • albumin (maintenance of BP- osmotic pressure)

  • globulin (to make immunoglobulins)

4) stores (and releases as needed)~ liver functions

• fats & proteins in limited amounts

• glucose stored in the form of glycogen

• fat soluble vitamins (A,D,E,K)

• B complex vitamins, iron, minerals (iron)

gallbladder

• stores bile

• concentrates the bile

• releases it into the duodenum via the common bile duct when fats are detected in the small intestine

• bile emulsifies fats in chyme, breaking it down into smaller particles so the enzyme lipase can begin breaking it down into absorbable particles, to lacteals then general circulation

pancreas

long, glandular organ located posterior to stomach with exocrine (and endocrine) functions

exocrine function to release “Pancreatic Juice”

pancreatic juice contains:

• digestive enzymes vital for digestion and necessary for life

  • amylase- breakdown starch/carbohydrates

  • protease- multiple/breakdown proteins

  • lipase- breakdown lipids

• bicarbonate to neutralize acidity of chyme and ensure proper enzyme reactions

results in pH approx. 6.5pH and breakdown of proteins, carbohydrates, and fats by pH sensitive enzymes

gastroenterology

the medical specialty focused on the digestive system

gastroenterologist

a doctor specializing in digestive system disorders

ulcer

an open sore, often in the stomach or small intestine

diarrhea

frequent, loose stools (malabsorption)

constipation

difficulty in passing stools

colonoscopy

a procedure to examine the large intestine with a flexible tube

biopsy

the removal of a tissue sample for exmaination

gastroparesis

slowed stomach emptying

gastrostomy

a surgically created opening inthe stomach for feeding

GI assessment & data gathering

physical assessment

• observation/inspect: distention, ascites, hemorrhoids, stool appearance

• bowel sounds/auscultate: normal frequency approx. 5-35 min; low to moderate pitch, gurgling, clicking, rumbling

data gathering/history

• recent weight gain or loss?

• ability to purchase, prepare, and store food

• ability to chew and swallow- any coughing or gagging with chewing?

• any symptom of digestive disorders?

• pattern of bowel elimination and stool appearance?

GI assessment~ sounds

absent

• no sound: no bowel sound after auscultating for 5 minutes

hypoactive

• 1 sound: 1 bowel sound every 3-5 min

normal

• normal sounds: 5-30 bowel sounds per min

hyperactive

• >30 sounds per minute

diagnostic testing

laboratory testing

• blood; breath; stool

radiographic evaluations

• xray; CT; MRI

endoscopic procedures

• upper endoscopy; colonoscopy

diagnostic laboratory testing

laboratory blood and urine tests

• CBC & CMP: complete blood count & comprehensive metabolic panel

• UA (urinalysis): includes urine bilirubin

• lipid panel: may require fasting up to 12 hours before test

• CEA: test for colorectal cancer

• liver function test (LFT): AST, ALT, ALP, Albumin, total protein, amino acid catalysts, lipids & prothrombin

• hepatitis profile: detects antibodies to the various forms of hepatitis

• pancreatic enzymes: amylase, lipase, protease (increased in pancreatitis)

breath tests

detects digestion & absorption issues

• urea breath tests (UBT): detects Helicobacter pylori

• hydrogen breath test: tests for intolerance of lactose, fructose, sucrose, and sorbitol

stool tests

• examination for pathogens: C. diff, parasites, blood & fat

• fecal occult test (guaiac test): checks for hidden blood in stool