Digestive System physiology Flashcards
What constitutes the gastrointestinal tract?
-Mouth
-Pharynx
-Esophagus
-Stomach
-Small intestine (duodenum, jejunum, ileum)
-Large intestine
What are the accessory glands of the GI tract?
-Teeth/tongue
-Salivary glands
-Gallbladder
-Liver
-Pancreas
What are the six essential activities of the digestive system?
-Ingestion
-Propulsion
-Mechanical digestion
-Chemical digestion
-Absorption
-Defecation
What are the four major tissue layers of the digestive tract? What is their defining characteristic?
Mucosa:
-innermost layer
-secretes mucous
-absorption
-finger-like projections
Submucosa:
-lymphatics, blood, and nerve supply
Muscularis externa:
-Circular and longitudinal muscle to increase motility
Serosa:
-Outer connective tissue later to aid in stretchiness and recoil
The same general structure from esophagus to anus
What are the sensory receptors in the GI tract and what do they respond to?
Mechanoreceptors:
-responds to stretch as food moves through
-reflex contraction
Chemoreceptors:
-responds to osmolarity and pH changes
-digestive substrates and end products
Both activate or inhibit digestive glands, and stimulate smooth muscle to mix and move lumen contents
Intrinsic (short reflexes) controls of the GI tract
-Enteric nerve plexuses (gut brain) respond to stimuli in GI tract
-Hormones from the stomach and small intestine stimulate target cells in same or different organs
Extrinsic controls of the GI tract
-Respond to stimuli inside or outside the GI tract (thought or smell of food)
-Autonomic control
-Input to the local nerve plexus into the gut
-Can receive input from the chemoreceptors, osmoreceptors, or mechanoreceptors
Which activity does the colon mostly do?
-Mostly absorption
-Small amount of secretion
Which activity does the small intestine mostly do?
-Secretion AND absorption
What is motility?
-Muscular contractions that mix and move forward the contents of the digestive tract
Two types of motility?
Peristalsis:
-Propulsive
-Alternates between no movement and movement so that you can absorb nutrients
Segmentation:
-Mixing movements
-Promotes digestion of foods
-Facilitates absorption and mixing time
Where are digestive enzymes secreted?
-Mouth
-Stomach
-Small intestine
Where is mucous secreted?
-Mouth
-Stomach
-Small intestine
What do hormones affect?
Motility and secretions
What do villi and microvilli do? What do they contain inside?
-Increase surface area for absorption
-Capillary beds and lacteals (lymphatic)
What is mechanical digestion?
-Chewing
-Chemical break-down by enzymes
What are the different kinds of carbohydrates?
-Starch: usually 2/3 of carbohydrates
-Dissaccarides: sucrose and lactose
-Monosaccarides: glucose (doesn’t need to be broken down)
-Complex carbohydrates: fibre
Where does amylase come from / where does it act on?
From salivary glands - acts in mouth
From pancreas - acts in small intestine
What does amylase do?
-breaks down starch into dissaccarides while chewing
-inactivated when swallowed by pH, so we get more from pancreas
Where do lactase and maltase come from / act on?
From mucosa and submucosa cells in SI wall - acts in SI
What do lactase and maltase do?
-break down dissaccarides into monosaccarides to be absorbed directly into blood
Why does gas production occur with fibre?
-humans lack the enzyme to completely digest complex carbs
-fibre moves to LI for E.Coli digestion
-fermentation and gas production occur
How many grams of protein do you need per day?
50-60 g
Where does pepsin come from / act on?
Comes from chief cells in stomach - acts in stomach
What does pepsin do?
-breaks down protein into polypeptides
Where do trypsin/chymotrypsin, carboxypepsidase, and aminopeptidase come from / act on?
come from pancrease - acts in SI
(carbo and amino also come from the SI wall)
What does trypsin/chymotrypsin do?
breaks down proteins into polypeptides
What do carboxypepsidase and aminopeptidase do?
-breaks down polypeptides into depeptides
Where does dipeptidase come from / act on?
SI - SI
-brush border enzymes (SI cells)
What does dipeptidase do?
breaks down dipeptides into amino acids to be absorbed directly into blood
What role does bile play in fat digestion?
-emulsifier: binds water molecule to fat molecule to make small fat molecules
-increases surface area for lipase to be more effective
-does not chemically change the fat
Which enzymes play a role in fat digestion? Where are they made and where do they act?
-lipase
from pancreas, acts in SI
What does lipase do?
-turns smaller fat globules into either glycerol (monoglyceride) or fatty acids
-glycerol becomes sugar to be absorbed into blood
-fatty acids are either turned into micelles while waiting for absorption or can enter absorptive cells
-within cells, they form chylomicrons to be absorbed into the lymph lacteals
what do nucleases do? where do they come from / act on? what else helps them?
-digest nucleic acids
from pancreas - act in SI
-brush border enzymes (SI)
how are vitamins absorbed?
carriers
what function does chewing have?
-increases surface area
-reduces choking
-secretion of mucous (lubrication) and salivary amylase for starch digestion
what triggers the swallowing reflex?
-food in the pharynx
-contractions coordinated by medulla
which sphincter or valve separates the esophagus from the stomach?
gastroesophageal
what causes heartburn and acid reflux?
a faulty valve in the esophagus
hiatal hernia
-part of stomach moves into the chest
-symptoms: heart burn
-treat: avoid large food intake/spicy food, or surgery
sections of the stomach
-fundus (superior portion)
-body (middle portion)
-antrum (distal portion
which sphincter separates the stomach from the duodenum?
pyloric sphincter - limits amount of food into small intestine
what are rugae?
-deep folds in stomach that allow for expansion
4 functions of the stomach
-storage
-mixing
-secretion
-absorption
how much can the stomach expand? for what function?
20x (50mL to 1L)
occurs in the body of stomach for storage
which stomach cells cause secretions? how does this process work
chief cells: releases pepsinogen for protein digestion
parietal cells: releases HCl (hydrochloric acid), activates pepsinogen into pepsin
why is there mucous in the stomach wall and why are acid and pepsinogen secreted separately? why is there high cell replacement and tight junctions?
-to protect the wall from the acid in the gastric pits
-maintains wall integrity
what does the stomach pH drop to?
2 - 3
what does pepsin break down and kill?
-connective tissue and muscle
-kills pathogens
what does mixing and emptying create in the stomach?
chyme - moves into SI or is stored
which two chemicals have quick absorption but break down the mucous layer in the stomach wall?
aspirin and alcohol
what does gastrin do?
-it is a hormone that activates the stomach
-increases HCl secretion
-increases pepsinogen
-increases motility
what stimulates gastrin release?
-parasympathetic stimulation
-proteins
-distension in stomach
-smell
as stretch in the intestine increases, gastrin is _________.
decreased
Cephalic phase of stomach digestion
-Stimulation of taste and smell receptors inputs to hypothalamus and medulla
gastric phase of stomach digestion
stretch receptors are activated in stomach to increase gastrin
intestinal phase of stomach digestion
-presence of low pH, partially digested foods in duodenum when stomach begins to empty
what are some inhibitory events of stomach digestion?
-loss of appetite, depression
-excessive acidity
-emotional upset
-distension of duodenum
what other hormones increase HCl secretion?
ACh
Histamine
Gastrin
Somatostatin
Gastritis
-inflammation of stomach
-caused by irritating agents: aspirin, alcohol, coffee, tobacco or helicobacter gastritis (bacterial cause)
-symptoms: epigastric pain, bloating, nausea, blood in vomit
peptic (gastric) ulcer
-hole caused by inflammation and necrosis
-caused in part by pepsin or helicobacter pylori (bacteria)
-in stomach or duodenum
-symptoms: pain, bleeding (hematemesis or melena)
-treatment: reduction of inflammatory factors, antacids, surgery in severe cases
how long is the SI?
21 feet long, 1 cm diameter
which secretions from the pancreas and gall bladder dump into the duodenum?
-bile (gallbladder)
-amylase
-trypsin
-pepsidases
-lipase
-nucleases
-bicarbonate
what does bicarbonate do?
neutralizes stomach pH
are enzymes released from the pancreas active or inactive?
inactive - were they active, they would digest the very cells that make them.
-enterokinase activates them
what does cholecystokinin (CCK) do?
-triggered by small bolus of food entering the SI
-CCK acts on the pancreas and gall bladder to increase release of enzymes and bile
-chemoreceptors tell the pancreas which enzymes we need
triggering factors for CCK release
-stretch receptors in duodenum
-fat content increases in SI
what does secretin do?
-released if SI is acidic
-causes pancreas to release bicarbonate to neutralize acid
-increases the bile formation in liver and inhibits gastric motility
where is CCK made?
duodenal mucosa (brush layer enzymes)
where is gastrin made?
stomach mucosa (G cells)
where is motilin made?
duodenal mucosa
what does motilin do?
-stimulates migrating motility complex in proximal duodenum
where is secretin made?
duodenal mucosa
how long does it take carbs and fats and proteins to digest?
carbs: 2-3 hours in first 1/2 of jejunum
fats and proteins: 8-10 hours
how are fat-soluble vitamins absorbed?
micells
how are water-soluble vitamins absorbed?
carriers
how does water reabsorption occur?
follows solutes using osmosis
how is sodium absorbed?
-in duodenum
-coupled with glucose and amino acids
how is calcium absorbed?
-regulated by vitamin D, parathyroid hormone, and calcitonin
-in duodenum
malabsorption syndrome
-SI can’t absorb nutrients
-fats and minerals
-diarrhea and foul feces
-causes: disease of intestinal wall, blocked exocrine ducts
-treat: malnutrition, diet therapy
Regional enteritis
-Inflammation of small intestine (Crohn’s disease, Inflammatory bowel disease)
Symptoms: anorexia, flatulence, pain, diarrhea, constipation
Treat: low-residue diet, medications, surgery
Inguinal hernia
-outpouching of small intestine and peritoneuon into grown area
-more common in males
-can get strangulated, where intestine is caught and twisted
-cuts off blood supply to organ
treat: surgery
what are the valves in the large intestine?
Ileocecal valve (between ileum and cecum)
what are the sphincters in the large intestine?
-external and internal anal phincter
Which contractions occur in the LI?
Haustral contractions: slow movements
What is reabsorbed in the large intestine?
Sodium and water
What triggers the defecation reflex?
-Distention of the rectum
-Parasympathetic response: relaxes sphincters and contracts rectal walls
-Can over-ride with higher brain centres
Total daily secretions
9 L/ day
How much liquid is excreted in feces a day?
100 mL / day
Daily absorption of small intestine and large intestine
Small intestine: 8.5 L / day
Large intestine: 400 mL / day
Appendicitis
-Inflammation of appendix
-Disease of colon
Symptoms: abdominal pain (in right lower quadrant), nausea, vomiting, fever, leukocytosis
Intestinal obstruction
-Blockage in large intestine or bowel
-Tumours, hernias, adhesions (fibroids)
-Volvulus (twisting) intussusception (wall folds back on itself)
-Paralytic obstruction
Symptoms: abdominal pain, distention, nausea and vomiting
Treat: nasogastric suctioning, surgery
Ulcerative colitis
-Chronic inflammation of colon
Symptoms: lower abdominal pain, blood in stool, anemia, diarrhea
Treat: dietary limitations, stress reduction, sedatives, anti-inflammatories, surgery
Irritable bowel syndrome
-Spastic colon
-Inflammation of bowel with chronic lesions
Symptoms: abdominal pain, altered motility, diarrhea or constipation
Causes: spicy foods, caffeine, alcohol, stress
Treatment: avoidance of causative factors
Dysentery
-Acute inflammation of colon
-Massive diarrhea with blood, pus, mucous, severe abdominal pain
Treat: antibiotics if bacterial
Diverticulosis vs Diverticulitis
Diverticulosis: condition of diverticula or little outpouches of large intestine
Diverticulitis: outpouches fill with fecal material and become irritated and inflammed
Symptoms: lower abdominal pain, cramping
Treat: antibiotics, dietary modification
Colon polyps
-Inward projections of mucosal lining
-Suspicious polyps excised if risk of cancer
Hemorrhoid
-Varicose veins in rectum either internal or external
Causes: pressure in anal area, constipation, prolonged standing, pregnancy, childbirth
Treatment: medications, warm baths, manual reduction, hemeroidectomy
What functions does the pancreas have?
Exocrine and endocrine
What do the duct cells of the pancreas secrete?
Bicarbonate
What do the acinar cells of the pancreas secrete?
Enzymes
What do the endocrine cells of the pancrease secrete?
Insulin and glucagon
Pancreatitis
-Inflammation of pancrease
Symptoms: pain radiating to back, nausea, vomiting, foul feces
Causes: alcohol, female over 40
Where does the liver receive blood from?
Hepatic artery and hepatic portal vein (from gut)
Blood is rich in nutrients
What are hepatocytes? How are they arranged?
Liver cells. Sinusoids
Liver functions not related to digestion
-Metabolic processing of major nutrients
-Detoxifying or degrading body wastes, hormones, drugs, other foreign things
-Synthesizes plasma proteins
-Stores glycogen, fats, iron, copper, vitamins
-Makes clotting factors
-Activates vitamin D
-Removes bacteria and worn-out red blood cells
-Excretes cholesterol and bilirubin
How much bile is formed per day?
900 mL per day
Where is bile formed between meals?
Gall bladder
What are the components of bile?
-Bilirubin (gives bile yellow colour)
-Cholesterol
-Lecithin (protein)
-Bile salts (forms mycelles, derived from cholesterol)
-Water
Where are bile salts recycled?
Recycled within gut and brought back to liver through hepatic portal vein
What does the gall bladder do?
-Stores and concentrates bile
-Contracts with CCK release
Hepatitis
-Inflammation of the liver
Causes: chemical actions of drugs, toxic substances, chronic alcoholism, viruses
Symptoms: liver enlargement, jaundice, abdominal pain, dark-coloured urine, malaise, anorexia, fever, ascites
Treatment: rest, good nutrition, anti-virals, transplants
Which type of hepatitis is most common?
Viral
Hepatitis A
-Infectious
-Benign
-Incubates for 2-6 weeks
-Oral-fecal spread
-Contaminated food
Hepatitis B
-Serum hepatitis
-Can lead to chronic hepatitis or cirrhosis
-Spread by blood, urine, feces, saliva, semen
-Incubates 2-6 months
Hepatitis C
-Spread by blood or sexual contact
-Persists for months or years
-Can lead to cirrhosis
Hepatitis D
-Delta virus
-Needs hepatitis B to replicate
-Leads to chronic disease
Hepatitis E
-Uncommon in north america
-Oral-fecal spread
-Water contamination
Cirrhosis
-Chronic, irreversible, degenerative damage
-Caused by alcohol, toxins
-Loss of normal liver cells
-Scar tissue
Symptoms: nausea, weight loss, high abdominal venous pressure, organs swell
Liver cancer
-Primary and benign tumours are rare
-Usually metastatic
-Discovered late or end stage
Gallstones
-Consists of cholesterol, bilirubin, and calcium
-Can block ducts
Risks: female, caucasian, fat, fertile, forty or older
Cholelithiasis
-Gallastones in gallbladder or bile ducts
Symptoms: nausea/vomiting, RUQ pain with fat intake
Cholecystitis
Inflammation of gallbladder
Symptoms: RUQ pain, nausea and vomiting
Treatment: surgical excision
