Digestive System Flashcards
Functions of the digestive system
- Ingestion—taking in food
- Digestion—breaking food into nutrient molecules
- Absorption—movement of nutrients into the bloodstream
- Defecation—excretes to rid the body of indigestible waste
2 main groups of organs in Digestive System
o Digestive tract (gastrointestinal, or GI, tract)
Continuous, coiled, hollow tube
These organs ingest, digest, absorb, defecate
Begins with the mouth ends with the anus
o Accessory digestive organs
Include teeth, tongue, and several large digestive organs
Assist digestion in various ways
Connected to the GI tract by ducts
• Secrete chemicals which aid in chemical breakdown and absorption of food
Organs of the digestive tract
o Mouth o Pharynx o Oesophagus o Stomach o Small / Large intestine o Anus
Accessory organs
- Salivary glands
- teeth
- Pancreas
- Liver
- Gallbladder
Name the components of the mouth
- Mouth (oral cavity)
o Mucous membrane–lined cavity - Lips (labia)
- Cheeks
- Hard palate
- Soft palate
- Uvula
- Vestibule
- Oral cavity proper
- Tongue
- Tonsils
Functions of the mouth
- Mastication (chewing) of food
- Tongue mixes masticated food with saliva
o Chemical breakdown of food - Tongue initiates swallowing
o Propulsion by pushing food to the pharynx - Taste buds on the tongue allow for taste
Describe the pharynx
- Serves as a passageway for foods, fluids, and air
- Food passes from the mouth posteriorly into the:
o Nasopharynx
Connects nasal cavity to the oropharynx
o Oropharynx
Posterior to oral cavity
Foods, liquids and air passes through
o Laryngopharynx
Below the oropharynx and continuous with the oesophagus - Food is propelled to the oesophagus by two skeletal muscle layers in the pharynx
o Longitudinal outer layer
o Circular inner layer - Alternating contractions of the muscle layers (peristalsis) propel the food through pharynx inferiorly
Anatomy of oesophagus
o About 10 inches long
o Runs from pharynx to stomach through the diaphragm
o Passes through opening in diaphragm
Physiology of oesophagus
o Conducts food by peristalsis (slow rhythmic squeezing) to the stomach
When food reaches the top of the oesophagus following swallowing a wave of peristalsis beings pushes food into the stomach
o Passageway for food only (respiratory system branches off after the pharynx)
What are the 4 layers of tissue in digestive tract organs
o Mucosa
o Submucosa
o Muscularis externa
o Serosa
Describe the mucosa
- Innermost, moist membrane consisting of:
o Surface epithelium that is mostly simple columnar epithelium
Except for oesophagus — stratified squamous epithelium
Covered in mucous secreted by cells or glands
o Small amount of connective tissue (lamina propria)
Contains blood vessels, lymphatic vessels and mucous secreting vessels (some parts of the body)
o Scanty smooth muscle layer (thin) - Lines the cavity (known as the lumen)
Describe the submucosa
- Just beneath the mucosa
- Soft, irregular dense connective tissue with blood vessels, nerve endings, mucosa-associated lymphoid tissue, and lymphatic vessels
o Glands and tissues secrete substances that aid in secretion and absorption
Explain the Muscularis Externa
- Surrounds submucosal layer
- Propels food through Digestive Tract by peristalsis
- Performs mechanical digestion
o Churns food - Has two layers:
o Inner circular layer
o Outer longitudinal layer
o Layer of nerve fibers between the layers regulate the activity of each layer
Describe the serosa
- Thin, serous membrane which helps to reduce friction
- Outermost layer of the wall
- Contains fluid-producing cells
- Divided into:
o Visceral peritoneum
Innermost layer that is continuous with the outermost layer
o Parietal peritoneum
Outermost layer that lines the abdominopelvic cavity by way of the mesentery
Name the Digestive tract nerve plexuses
2 intrinsic nerve plexuses that are part of the autonomic nervous system
o Submucosal nerve plexus
o Myenteric nerve plexus
Regulate mobility and secretory activity of the GI tract organs
Name the stomach regions
o Cardial (cardia)
Near the heart and surrounds the cardio oesophageal sphincter (allows food to enter from oesophagus)
o Fundus
Expanded portion lateral to the cardiac region
o Body
Midportion
Greater curvature is the convex lateral surface
Lesser curvature is the concave medial surface
o Pylorus
Funnel-shaped terminal end
Continuous with small intestine through the pyloric sphincter or pyloric valve
Anatomy of the stomach
- C-shaped organ located on the left side of the abdominal cavity
- Stomach can stretch and hold 4 L (1 gallon) of food when full
- Varies from 15 – 25 cm in length
- Diameter and volume depend on how much food it contains
o Rugae
Internal folds of the mucosa present when the stomach is empty
What is the stomach omentum
- Lesser Omentum
o Double layer of the peritoneum
o Extends from liver to the lesser curvature of stomach - Greater Omentum
o Another extension of the peritoneum
o Covers the abdominal organs and attaches to posterior boy wall
Structure of the stomach mucosa and cells
- Simple columnar epithelium composed almost entirely of mucous cells
- Mucous cells produce bicarbonate-rich alkaline mucus
o Clings to the stomach mucosa and protections from damage against acid - Chief cells
o Produce inactive protein-digesting enzymes (pepsinogens) - Parietal cells
o Produce hydrochloric acid that activates enzymes
Conversion of pepsinogen and pepsin
o Makes stomach contents acidic - Mucous neck cells
o Produce thin acidic mucus (different from the mucus produced by mucous cells of the mucosa) with an unknown function - Enteroendocrine cells
o Produce local hormones such as gastrin
Stomach functions
- Temporary storage tank for food
- Site of food breakdown
o Three layers of muscle allow to move food along tract and breakdown - Chemical breakdown of protein begins
o Most occurs within the pyloric region - Delivers chyme (thick) (processed food) to the small intestine via the pyloric sphincter
Describe the small intestine
- The body’s major digestive organ
- Longest portion of the digestive tract (2–4 m, or 7–13 feet, in a living person)
- Site of nutrient absorption into the blood and all water absorption
- Muscular tube extending from the pyloric sphincter to the ileocecal valve
- Suspended from the posterior abdominal wall by the mesentery
Small intestine subdivisions
- Duodenum (5%)
- Jejunum (40%)
- Ileum (60%)
Describe chemical digestion in the small intestine
- Begins in the small intestine can only process a small amount of food at a time pyloric sphincter controls movement of chyme into small intestine prevents small intestine from being overwhelmed
- Enzymes produced by intestinal cells and pancreas are carried to the duodenum by pancreatic ducts
o Chemical breakdown of food ends in the pancreatic ducts
Small Intestine Structural Modifications
- Increase surface area for food absorption
- Decrease in number toward the end of the small intestine
o Villi
Finger like projections formed by the mucosa
• House a capillary bed and lacteal
Contains tubular indentations (intestinal crypts)
Each contain a lymphatic capillary (lacteal) as well as blood capillaries
o Microvilli
Tiny projections of the plasma membrane (brush border enzymes)
o Circular folds (plicae circulares)
Deep folds of mucosa and submucosa
Peyer’s patches
- Collections of lymphatic tissue
- Located in submucosa
- Increase in number toward the end of the small intestine
- More are needed there because remaining food residue contains much bacteria
o Must be prevented from entering the blood stream
Large Intestine positioning and features
- Larger in diameter, but shorter in length at 1.5 m, than the small intestine
- Extends from the ileocecal valve to the anus
Presence of large colon ease bacteria
• Responsible for B vitamin synthesis and Vitamin K
Large intestine functions
propulsion and elimination of waste
- Absorption of water, electrolytes and some vitamins are additional but limited functions
Subdivisions of large intestine
o Cecum o Appendix o Colon o Rectum o Anal canal
Cecum
- Saclike first part of the large intestine (first to receive food)
- Connects to large intestine by the ileocecal valve
o Usually, closed opens in response to gastrin (released by the stomach)
o Partially controlled by the nervous system
o When open digestive remnants of food travel from the ileum to the cecum
Appendix
o Hangs from the cecum
o Accumulation of lymphoid tissue that sometimes becomes inflamed (appendicitis)
Contains lymphocytes that help protect the body from infection organisms
• Does not protect against appendicitis
Describe the colon
Ascending
o Travels up right side of abdomen and makes a turn at the right colic (hepatic) flexure
Transverse
o Travels across the abdominal cavity and turns at the left colic (splenic) flexure
Descending
o Travels down the left side
Sigmoid
o S-shaped region; enters the pelvis exits at the rectum
- Sigmoid colon, rectum, and anal canal are located in the pelvis
Describe the anal canal and anus
- Anal canal ends at the anus
- Anus
o Opening of the large intestine
o External anal sphincter
Formed by skeletal muscle and is voluntary
o Internal anal sphincter
Formed by smooth muscle and is involuntary
o These sphincters are normally closed due to constriction except during defecation - The large intestine delivers indigestible food residues to the body’s exterior
Describe the salivary glands
- Three pairs of salivary glands empty secretions into the mouth
- Located within tissue surrounding the oral cavity
o Parotid glands (largest)
Found anterior to the ears
Mumps affect these salivary glands
o Submandibular glands
Lie on the medial side of the mandible
o Sublingual glands
Both submandibular and sublingual glands empty saliva into the floor of the mouth through small ducts
Describe the Saliva
- Mixture of mucus and serous fluids
- Composed mostly of water
- Helps to moisten and bind food together into a mass called a bolus
- Contains:
o Salivary amylase
Begins starch digestion
Breaks down complex carbohydrates into shorter chains of sugar chains
o Lysozymes and antibodies
Inhibit bacteria
o Lingual lipase
Initiates the breakdown of fats - Dissolves chemicals so they can be tasted
Describe the pancreas
- Functions as an exocrine and endocrine gland
- Soft, pink triangular gland
- Found posterior to the parietal peritoneum
o Mostly retroperitoneal - Secretes products into the blood and lumen
- Extends across the abdomen from spleen to duodenum
- Produces a wide spectrum of digestive enzymes that break down all categories of food
- Secretes enzymes and pancreatic juice into the duodenum
o Pancreatic juices contain digestive enzymes (proteases break down proteins / amylases breaks down starches / lipases break down lipids) - Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from stomach
- Hormones produced by the pancreas
o Insulin
o Glucagon
o Involved in regulating blood glucose levels
Describe features of the liver
- Largest gland in the body
- Located on the right side of the body under the diaphragm
- Consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament
Liver’s role to produce bile
- Bile leaves the liver through the common hepatic duct and enters duodenum through the bile duct
o Duodenum uses bile to breakdown lipids - Bile is yellow-green, watery solution containing:
o Bile salts and bile pigments (mostly bilirubin from the breakdown of hemoglobin)
Are emulsifying agents greatly increases surface area of fats and assisting breakdown by lipase enzymes
o Makes about 1L/day at a constant rate only needed following food intake
- Bile emulsifies (breaks down) fats
Describe the gall bladder
- Green sac found in a shallow fossa in the inferior surface of the liver
o Releases bile after a meal that contains fat
Controlled by several bile sphincters (bile sphincters, pancreatic sphincter and hepatopancreatic sphincter)
o When no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder
o While in the gallbladder, bile is concentrated by the removal of water
o When chyme containing fat enters the duodenum gallbladder contracts the gallbladder spurts out stored bile
Common bile duct and hepatopancreatic duct sphincter relax to allow bile to flow to duodenum and emulsify the fat
What is propulsion
Movement of foods from one region of the digestive system to another
What is Ingestion
Placing of food into the mouth
Explain food breakdown: mechanical breakdown
• Mixing of food in the mouth by the tongue
• Churning of food in the stomach
• Segmentation in the small intestine
Mechanical digestion prepares food for further degradation by enzymes
Food breakdown: digestion
Digestion occurs when enzymes chemically break down large molecules into their building blocks
Each major food group uses different enzymes
• Carbohydrates are broken down to monosaccharides (simple sugars)
• Proteins are broken down to amino acids
• Fats are broken down to fatty acids and glycerol
Absorption
End products of digestion are absorbed in the blood or lymph
Food must enter mucosal cells and then move into blood or lymph capillaries
Defecation
Elimination of indigestible substances from the GI tract in the form of feces
Food breakdown
Presence of food or rising pH causes the release of the hormone gastrin
o Gastrin causes stomach glands to produce:
Protein-digesting enzymes (pepsin), active protein digesting enzyme (renin)
Mucus
Hydrochloric acid
o Hydrochloric acid makes the stomach contents very acidic
o Acidic pH
Activates pepsinogen to pepsin for protein digestion
Provides a hostile environment for microorganisms
• Works on digesting milk protein in infants; not produced in adults
o Alcohol and aspirin are virtually the only items absorbed in the stomach
Food propulsion
- Peristalsis:
o Waves of peristalsis occur from the fundus to the pylorus, forcing food past the pyloric sphincter - Grinding:
o The pylorus meters out chyme into the small intestine (3 ml at a time) - Retropulsion:
o Peristaltic waves close the pyloric sphincter, forcing contents back into the stomach; the stomach empties in 4–6 hours
• Segmentation
o Movement of materials back and forth to foster mixing in the small intestine
Activities of the Small Intestine
- Chyme breakdown and absorption
o Intestinal enzymes from the brush border function to:
Break double sugars into simple sugars
Complete some protein digestion
o Intestinal enzymes and pancreatic enzymes help to complete digestion of all food groups
o Pancreatic enzymes play the major role in the digestion of fats, proteins, and carbohydrates
o Alkaline content neutralizes acidic chyme and provides the proper environment for the pancreatic enzymes to operate
Release of pancreatic juice from the pancreas into the duodenum is stimulated by
Vagus nerves
Local hormones that travel via the blood to influence the release of pancreatic juice (and bile)
• Secretin
• Cholecystokinin (CCK)
o Hormones (secretin and CCK) also target the liver and gallbladder to release bile
Bile
• Acts as a fat emulsifier
• Needed for fat absorption and absorption of fat-soluble vitamins (K, D, E, and A)
o Water is absorbed along the length of the small intestine
o End products of digestion
Activities of the large intestine - nutrient breakdown and absorption
o No digestive enzymes are produced
o Resident bacteria digest remaining nutrients
Produce some vitamin K and some B vitamins
Release gases
o Water, vitamins, ions, and remaining water are absorbed
o Remaining materials are eliminated via feces
Activities of the large intestine - Propulsion of food residue and defacation
o Sluggish peristalsis begins when food residue arrives
o Haustral contractions are the movements occurring most frequently in the large intestine
o Mass movements are slow, powerful movements that occur three to four times per day
o Presence of feces in the rectum causes a defecation reflex
Internal anal sphincter is relaxed
Defecation occurs with relaxation of the voluntary (external) anal sphincter
Disorders of the digestive system
- Gastroesophageal reflux o Movement of chyme from stomach into lower oesophagus - Ulcers o Break in the protective lining of the stomach, duodenum or lower oesophagus - Gastroenteritis o Inflammation of the stomach or intestine - Inflammatory bowel disease o Ulcerative colitis o Chrohn’s disease - Constipation and diarrhoea - Hepatitis - Pancreatitis - Gallstones
Explain the lips
Protect the anterior opening o Assist with injection by grabbing food and pulling into mouth o Under voluntary control o Stops food or liquid from leaking out o Made of orbicularis oris
Explain the Cheeks, hard palate, soft palate, uvula, oral cavity proper and vestibule
Cheeks
o Form the lateral walls of oral cavity
- Hard palate
o Forms the anterior roof of oral cavity
o Made of maxilla and palatine bones - Soft palate
o Forms the posterior roof oral cavity
o Formed from a fold of mucous membrane - Uvula
o Fleshy projection of the soft palate
o Helps prevent food from entering nasal cavity when swallowing - Vestibule
o Space between lips externally and teeth and gums internally - Oral cavity proper
o Area contained by the teeth
Explain the tonsils
Part of the bodies defence system o Palatine Located at posterior end of oral cavity o Lingual Located at the base of the tongue
Explain the tongue
Attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth
o Lingual Frenulum anchors tongue to floor of mouth and limits posterior movements
