Digetsive System Physiology Flashcards
Alimentary canal
GI tract Mouth Pharynx Esophagus Stomach Small intestine (duodenum, jejunum, ileum) Large intestine
Accessory glands
Teeth Tongue Salivary glands Gallbladder Liver Pancreas
Digestive activities
6 essential activities Ingestion Propulsion Mechanical digestion Chemical digestion (involves secretion) Absorption Defecation
Digestive tract
Same general structure from esophagus to anus
4 major tissue layers
Mucosa = innermost layer, secretions, absorption
Submucosa = blood/ nerve supply
Muscularis externa = motility
Serosa = outer CT layer
GI tract sensory receptors
Mechanoreceptors = respond to stretch (as food moves through)
Chemoreceptors = respond to osmolarity, pH changes, and digestive substrates and end products (food)
Both initiate reflexes that activate or inhibit digestive glands and stimulate smooth muscle to mix and move lumen contents
Extrinsic/intrinsic controls
Extrinsic = from outside digestive tract
Intrinsic = within digestive tract
Both affect motility and secretion of enzymes and hormones
GI tract regulatory mechanisms
Intrinsic and extrinsic controls
Short reflexes = enteric nerve plexuses (gut brain) respond to stimuli in GI tract
Hormones = from stomach and small intestine, stimulate target cells in same or different organs
Long reflexes = respond to stimuli inside or outside GI tract (eg - smell or thoughts of food), autonomic control/central nervous system
Four digestive processes
Motility
Secretion
Absorption
Digestion
Motility
Muscular contractions that mix and move forward the contents of the digestive tract
2 types
Peristalsis = propulsive
Segmentation = mixing movements, promotes digestion of food, facilitates absorption
Secretion
Hormones = CCK, gastrin, secretin, affect motility and secretions
Digestive enzymes = mouth, stomach, small intestine
Mucous = mouth, stomach, small intestine
Absorption
Villi and microvilli = increases surface area for absorption
Digestion
Mechanical digestion by chewing
Chemical break-down by enzymes of carbohydrates, proteins, and fats
Digestion of carbohydrates
Starch = usually 2/3 of carbohydrates
Disaccharides = sucrose, lactose
Monosaccharides = glucose
Complex carbohydrates = fibre
Enzymes = Amylase from salivary glands that act in the mouth and pancreas that act in the small intestine
Small intestine enzymes = from the small intestine, act in the small intestine, lactase, maltase
Complex carbohydrates digestion
Humans lack enzymes to digest complex carbohydrates (eg - oligosaccharides, galactosidase)
Fibre moves to large intestine for E.Coli digestion (fermentation, gas production)
Protein digestion
50-60g per day needed
Essential amino acids
Enzymes = pepsin (stomach), trypsin/chymotrypsin, carboxypepsidase, aminopeptidase (from pancreas, acts in small intestine)
Dipeptidase (from small intestine)
Many enzymes needed to break the bonds between different amino acids
Fat digestion
Non-polar Need emulsifier (bile = made in liver, stored in gallbladder, increases surface area for lipase) Enzymes = lipase (from pancreas, acts in small intestine)
Fat absorption
Lipase acts on emulsified droplets
Get monoglyceride and fatty acids
Can enter absorptive cells or form mice,small
Within cell - forms chylomicron (absorbed into lymph)
Nucleic acids and vitamins
Nucleic acids = digested by nuclease (from pancreas, acts in small intestine)
Vitamins = absorbed whole by carriers
Mouth
Chewing = increases surface area, decreases choking
Secretion of
Mucous = lubrication
Salivary amylase = starch digestion
Swallowing reflex
Triggered by food in pharynx
Contractions coordinated by medulla
Esophagus
Long muscular tube
Separated from stomach by gastroesophageal sphincter or valve
Heartburn or acid reflux = faulty valve
Hiatal hernia
Part of stomach moves into chest
Symptoms = heart burn (increased with age) or asymptomatic
Treat = avoid large food intake and spicy food, surgery may be required
Stomach
Sections = fundus, body, antrum Sphincters = gastroesophageal, pyloric Rugae = deep folds, allow for expansion
4 functions of the stomach
Storage
Mixing
Secretion
Absorption
Storage in stomach
Mostly in body of stomach
Can expand 20x
50ml-1L
Secretion in stomach
Acid = activates pepsin, parietal cells, breaks down connective tissue and muscle, kills pathogens Pepsin = protein digestion, chief cells Mucous = protects wall from acid (stomach wall also protected by tight junctions and high cell replacement) Pepsinogen = inactive form, converted to pepsin by HCl, stomach pH can drop to 2-3
Intrinsic factor of stomach
Helps in absorption of B12 in small intestine
Mixing and emptying in stomach
Formation of chyme (glop/slop)
Some moves into small intestine, rest is stored
Absorption in stomach
Aspirin and alcohol
Gastric emptying and mixing as a result of Antral peristaltic contractions
Peristaltic contraction from fundus sweeps towards pyloric sphincter
Contraction becomes more vigorous as it reaches thick-muscled antrum
Antral peristaltic contraction propels chyme forward
Small portion of chyme is pushed through partially opened sphincter into duodenum (strong contraction = more chyme emptied)
When peristaltic contraction reaches pyloric sphincter the sphincter is closed
Chyme that was being propelled forward hits sphincter and is tossed back into the antrum (mixing is accomplished)
Stomach - hormones
Gastrin = increased HCl secretion, increased pepsinogen, increased motility
Stimulated by = proteins, distension, smell
Gastritis
Inflammation of stomach
Irritating agents = aspirin, alcohol, coffee, tabcco
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
Helicobacter pylori
Stomach and duodenum
Symptoms = pain, bleeding (hematemesis or melena)
Treatment = reduction of contributory factors, antacids, surgery in severe cases
Small intestine
21 feet long
1cm diameter
Duodenum
Jejunum
Ileum
Site of digestion, secretion, and absorption
Alternate between segmentation and peristalsis
Small intestine digestion
Secretions from pancreas and gallbladder dump into duodenum
Gallbladder (bile)
Pancreas (amylase, trypsin/chymotrypsin, pepsidases, lipase, nucleases, bicarbonate (neutralizer))
Pancreatic enzymes, substrates, and action
Act on duodenum
Trypsin/chymotrypsin/elastase = proteins, break peptide bonds in proteins to form peptide fragments
Carboxypeptidase = proteins, splits off terminal amino acid from carboxyl end of protein
Lipase = fats, splits off two fatty acids from triglycerides forming free fatty acids and monoglycerides
Amylase = polysaccharides, splits polysaccharides into glucose and maltose
Ribonuclease/deoxyribonuclease = nucleic acids, splits nucleic acids into free mononucleotides
Cholecystokinin (CCK)
A small bolus of food enters the small intestine and triggers the release of the hormone CCK
CCK acts on pancreas and gallbladder to increase release of enzymes and bile
CCK is released if duodenum is distended or if fat content in the small intestine increases
Gastric inhibition
Distinction of duodenum inhibits gastric emptying
Allows time for digestion and absorption in the small intestine
Secretion (hormone)
Released if small intestine is acidic
Effects = causes pancreas to release bicarbonate (neutralizes acid), increased bile formation in liver, inhibits gastric motility
Motilin
Promotes motility in small intestine
Small intestine absorption
Amino acids/sugars = into villi capillaries
Fatty acids = into lacteals of lymph vessels then into blood
Via carriers
Carbohydrates = quickly absorbed, first 1/2 of jejunum, 2-3 hours to empty stomach
Fats/proteins = slower to digest, 8-10 hours to empty stomach
Fat-soluble vitamins = with micelles
Water-soluble vitamins = by carriers, water reabsorbed by osmosis (follows solute, 95%)
Electrolyte and water absorption
Along length of small intestine
Iron and calcium are absorbed in duodenum
Na+ is coupled with absorption of glucose and amino acids
Ca++ absorption is regulated by vitamin D and parathyroid hormone (PTH)
Malabsorption syndrome
Disease of small intestine
Small intestine can’t absorb nutrients (fats and minerals)
Diarrhea, foul feces
Causes = disease of intestinal wall, blocked exocrine ducts
Diet therapy = bleeding (decrease in vitamin K), malnutrition
Regional enteritis
Disease of small intestine
Crohn’s disease
Inflammatory bowel disease (IBD)
Exacerbation/remission
Symptoms = anorexia, flatulence, pain, diarrhea/constipation
Supportive treatment = low-residue diet, medication, surgery
Inguinal hernia
Outpouching of small intestine and peritoneum
More common in males
Strangulated hernia = parts of small intestine are caught and twisted, cuts off blood supply to organ
Treatment = surgical repair
Large intestine
Ileocecal valve Cecum and appendix Ascending colony Transverse colon Descending colon Rectum Haustral contractions (slow movement) Na+/water reabsorption E. Coli digestion of fibre (incomplete)
Defecation reflex
Distension of rectum
Parasympathetic response (relaxes sphincters, contracts rectal walls)
Can override with higher brain centres
Daily secretions
Food drink = 2L/day Saliva = 1.5L/day Stomach = 2L/day Bile = 0.5L/day Pancreas = 1.5L/day Small intestine = 1.5L/day Total = 9L/day
Daily absorption
Small intestine = 8.5L/day
Large intestine = 400ml/day
Remaining feces = 100ml/day
Appendicitis
Disease of the colon
Inflammation of the appendix
Symptoms = abdominal pain (shifts to right lower quadrant), nausea and vomiting, fever, leukocytosis
Intestinal obstruction
Disease of the colon Blockage in intestine or bowel Tumours Hernias Adhesions Volvulus (twisting) Intussusception (folding) Paralytic obstruction Symptoms = abdominal pain, distension, nausea and vomiting Treatment = nasogastric sectioning, surgery
Ulcerative colitis
Disease of the colon
Chronic inflammation of the colon
Symptoms = lower abdominal pain, blood in stools, anemia, diarrhea
Treatment = dietary limitations, stress reduction, mild sedatives, anti-inflammatories, surgery
Irritable bowel syndrome
Disease of the colon
Aka spastic colon
Inflammation of the bowel with chronic lesions
Symptoms = abdominal pain, altered motility, diarrhea or constipation
Causes = spicy foods and seasonings, caffeine, alcohol, stress
Treatment = avoidance of causative factors
Dysentery
Disease of the colon
Acute inflammation of the colon
Massive diarrhea with blood pus and mucous
Severe abdominal pain
Treatment dependant on cause (antibiotics if bacterial)
Diverticulosis and diverticulitis
Diseases of the colon
Diverticulosis = condition of diverticula or little out pouches
Diverticulitis = outpouches fill with fecal material, become irritated and inflamed
Symptoms = lower abdominal pain, cramping
Treatment = antibiotics, dietary modification
Colon polyps
Disease of the colon
Inward projections of mucosal lining
Suspicious polyps excited
Pre cancerous? Colo-rectal cancer
Hemorrhoids
Disease of the rectum
Varicose veins in rectum (internal or external)
Causes = pressure in anal area, constipation, prolonged standing, pregnancy and childbirth
Prevention = good bowel habits (fibre and fluids), exercise, avoid laxatives
Treatment = medications, warm sitz baths, manual reduction, cryosurgery, hemorrhoidectomy
Pancreas
Exocrine and endocrine functions
Duct cells = secrete bicarbonate
Acinar cells = secrete enzymes
Endocrine cells = secrete insulin and glucagon
Pancreas diseases
Pancreatitis = inflammation of pancreas
Symptoms = pain radiating to back, nausea and vomiting, foul feces, necrosis, bleeding
Alcohol, women over 40
Liver
Largest organ
Receives blood via hepatic artery and hepatic portal vein (from gut, rich in nutrients)
Hepatocytes = liver cells, arranged in sinusoids
Liver functions
Not related to digestion
Metabolic processing of the major nutrients
Detoxifying or degrading body wastes and hormones, drugs, and other foreign compounds
Synthesizes plasma proteins
Stores glycogen, fats, iron, copper, and vitamins
Makes clotting factors
Activates vitamin D
Removes bacteria and worn-out red blood cells
Excretes cholesterol and bilirubin
Formation of bile
~900ml/day Cholesterol based Stored in gallbladder between meals Bilirubin (porphyrin rings from Hb) gives bile yellow colour Cholesterol Lecithin Bile salts (important in fat digestion, derived from cholesterol) Water
Bile salts
Recycled within gut
Gallbladder
Stores and concentrates bile
Contracts with CCK
Hepatitis
Liver disease
Symptoms = jaundice and liver enlargement, myalgia and abdominal pain, clay or light coloured stools, dark coloured urine, malaise, anorexia, fever, ascites
Treatment = rest, good nutrition, anti-virals, transplant
Prevention = good hygiene, vaccination, special care when handling needles and body fluids
Viral hepatitis most common, 5 types = A,B,C,D,E
Hepatitis A
Aka infectious hepatitis Benign Incubates for 2-6 weeks Oral-fecal spread Contaminated food
Hepatitis B
Aka serum hepatitis
Can lead to chronic hepatitis or cirrhosis
Spread by blood, urine, feces, saliva, and semen
Incubates 2-6 months
Hepatitis C
Spread by blood or sexual contact
Persists for months or years
Can lead to cirrhosis (~20%)
May require transplant
Hepatitis D
Delta virus
Needs hepatitis B to replicate
Spreads like B
Leads to chronic disease
Hepatitis E
Uncommon in North America
Oral-fecal spread
Often water contamination
Cirrhosis
Liver disease Chronic Irreversible Degenerative Alcohol Toxins Disease Loss of normal liver cells No organization Scar tissue Symptoms = nausea, weight loss, weakness, inflammation then degeneration (hobnailed (nodular)), ascites (high abdominal venous pressure, organs swell, bleeding) Treatment = transplant
Liver cancer
Primary and benign tumours are rare (metastasis)
Discovered late or end stage
Gallstones
Gallbladder disease
Consists of cholesterol, bilirubin, and calcium
Can block ducts
If small = gravel
5 f’s for risk = female, fair complexion, fat, fertile, forty and over
Cholelithiasis
Gallbladder disease
Gall stones in gallbladder or bile ducts
Symptoms = nausea and vomiting, right upper quadrant pain with fat intake
Cholecystitis
Inflammation of gallbladder (eg-blockage)
Symptoms = right upper quadrant pain, nausea and vomiting after eating
Treatment = surgical excision
