chp 23 exam 4 Flashcards
Mouth is where food is
Associated organs:
Mouth is where food is chewed and mixed with enzyme-containing saliva that begins process of digestion, and swallowing process is initiated
Mouth
Tongue
Salivary glands
Teeth
Mouth (Introduction)
AKA oral (buccal) cavity
- Bounded by lips anteriorly, cheeks laterally, palate superiorly, and tongue inferiorly
- Oral orifice
- -anterior opening
- Walls of mouth lined with stratified squamous epithelium
- -Tough cells that resist abrasion
- -Cells of gums, hard palate, and part of tongue are keratinized for extra protection
- Lips (labia):
- Cheeks
- Oral vestibule
- Oral cavity proper
- Labial frenulum
Lips and cheeks -Lips (labia): orbicularis oris muscle -Cheeks buccinator muscles -Oral vestibule recess internal to lips and cheeks, external to teeth and gums -Oral cavity proper lies within teeth and gums -Labial frenulum median attachment of each lip to gum
Palate
Palate
- Palate forms the roof of the mouth and has two distinct parts
- Hard palate: formed by palatine bones and palatine processes of maxillae with a midline ridge called raphe
- —-Mucosa is slightly corrugated to help create friction against tongue
- Soft palate: fold formed mostly of skeletal muscle
- –Closes off nasopharynx during swallowing
- –Uvula: fingerlike projection that faces downward from free edge of soft palate
Tongue (Introduction)
Intrinsic muscles
Extrinsic muscles
- Tongue occupies floor of mouth
- Composed of interlacing bundles of skeletal muscle
- Functions include:
- -Gripping, repositioning, and mixing of food during chewing
- -Formation of bolus, mixture of food and saliva
- -Initiation of swallowing, speech, and taste
- Intrinsic muscles change shape of tongue
- Extrinsic muscles alter tongue’s position
- Lingual frenulum: attachment to floor of mouth
Tongue (Papillae)
- Filiform papillae:
- Fungiform papillae:
- Vallate (circumvallate) papillae
- Foliate papillae:
Superior surface bears papillae, peglike projections of underlying mucosa
- Filiform papillae: gives tongue roughness to provide friction; only one that does not contain taste buds; gives tongue a whitish appearance
- Fungiform papillae: mushroom shaped, scattered widely over tongue; vascular core causes reddish appearance of tongue
- Vallate (circumvallate) papillae: 8–12 form V-shaped row in back of tongue
- Foliate papillae: located on lateral aspects of posterior tongue
(Terminal Sulcus)
Terminal sulcus: groove located posterior to vallate papillae
- Marks division between:
- -Body: portion of tongue that resides in oral cavity
- -Root: posterior third residing in oropharynx
-Does not contain papillae, but still bumpy because of lingual tonsil, which lies deep to its mucosa
Ankyloglossia
- congenital condition in which children are born with an extremely short lingual frenulum
- Often referred to as “tongue-tied” or “fused tongue”
- Restricted tongue movement distorts speech
- Treatment: surgical snipping of frenulum
Salivary Glands (Introduction) -Functions of saliva Major (extrinsic) salivary glands Minor salivary glands
-Functions of saliva Cleanses mouth Dissolves food chemicals for taste Moistens food; compacts into bolus Begins breakdown of starch with enzyme amylase
Major (extrinsic) salivary glands
- outside of the oral cavity
- produce most of the saliva
Minor salivary glands
- are scattered throughout oral cavity
- make a little saliva
Major salivary glands include:
Parotid:
- anterior to ear and external to masseter muscle
- parotid duct opens into oral vestibule next to second upper molar
Submandibular
- medial to body of mandible
- duct opens at base of lingual frenulum
Sublingual
- anterior to submandibular gland under tongue
- 10–12 ducts into floor of mouth
Two types of secretory cells
- Parotid and submandibular
- Sublingual gland consist
Serous cells:
- -Secretion is mostly water
- -Plus: enzymes, ions, bit of mucin
Mucous cells
-produce mucus
- Parotid and submandibular glands contain mostly serous cells
- Sublingual gland consists mostly of mucous cells
Xerostomia
- dry mouth
- -too little saliva being made
- Remember that normal salivary gland function is vital for oral health
- -Lack of moisture may lead to difficulty with chewing and swallowing
- -Can lead to oral infections
Possible Causes
-medications, diabetes, HIV/AIDS, and Sjögren’s syndrome (autoimmune disease affecting moisture-producing glands throughout body)
Composition of saliva
-Mostly water (97–99.5%)
-Slightly acidic (pH 6.75 to 7.00)
-Electrolytes
Na+, K+, Cl−, PO42−, HCO3−
-Digestive enzymes: salivary amylase and lingual lipase
-Proteins: mucin, lysozyme, and IgA
-Metabolic wastes: urea and uric acid
-Immune functions
—Lysozyme, IgA, defensins, protect against microorganisms
—nitric oxide from nitrates in food also help protect you from microorganisms
Control of salivation
- Major salivary glands activated by
- -Strong sympathetic stimulation
- 1500 ml/day can be produced
- Minor glands continuously keep mouth moist
- Major salivary glands activated by parasympathetic nervous system when:
- -Ingested food stimulates chemoreceptors and mechanoreceptors in mouth
- -Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)
- –That’s why when you’re nervous your mouth gets dry
- Smell/sight of food or upset GI can act as stimuli
Teeth
Mastication
baby teeth adult teeth
wisdom teeth
Teeth
-Found in gomphoses of the mandible and maxilla
Mastication
process of chewing that tears and grinds food into smaller fragments
Primary (baby teeth)
-20 deciduous teeth, or milk or baby teeth
erupt between 6 and 24months of age
Permanent teeth 32 deep-lying (under baby teeth) -enlarge and develop -roots of baby teeth are resorbed from below --loosen and fall out -Occurs around 6–12years of age -All are in by the end of adolescence
- Wisdom teeth (3rd molars)
- –Third molars may or may not emerge around 17–25 years of age
Clinical – Homeostatic Imbalance (Decay)
- Decaying primary teeth can be painful and may lead to serious infection
- Can cause damage to the permanent teeth
- Primary teeth deserve as much attention as permanent teeth!
- Primary teeth serve as important “place holders” for developing permanent teeth
- Primary teeth can be kept healthy by brushing and limiting exposure to sugary liquids, especially from prolonged bottle feeding.
Teeth are classified according to shape:
Teeth are classified according to shape: -Incisors chisel shaped for cutting -Canines fanglike teeth that tear or pierce -Premolars (bicuspids) broad crowns with rounded cusps used to grind or crush -Molars broad crowns, rounded cusps best grinders During chewing, upper and lower molars lock together, creating tremendous crushing force
Dental formula
Dental formula: shorthand indicator of number and position of teeth
- Shows ratio of upper to lower teeth for only half of mouth; other side is mirror image
- Primary
- permanent
Tooth structure
Tooth structure
Each tooth has two major regions:
-Crown: exposed part above gingiva (gum)
-Covered by enamel, the hardest substance in body
—Heavily mineralized with calcium salts and hydroxyapatite crystals
—Enamel-producing cells degenerate when tooth erupts, so no healing if tooth decays or cracks; needs artificial repair by filling
- Root: portion embedded in jawbone
- -Connected to crown by neck
cement
Periodontal ligament
Gingival sulcus:
Dentin:
Cement: calcified connective tissue
Covers root; attaches it to periodontal ligament
Periodontal ligament
- Forms fibrous joint called gomphosis
- Anchors tooth in bony socket (alveolus)
Gingival sulcus: groove where gingiva borders tooth
Dentin: bonelike material under enamel
Maintained by odontoblasts of pulp cavity
Pulp cavity
pulp
root canal
apical foramen
Pulp cavity: surrounded by dentin
Pulp: connective tissue, blood vessels, and nerves
Root canal: as pulp cavity extends to root
Apical foramen at proximal end of root
Entry for blood vessels, nerves, etc.
impacted tooth
Impacted tooth
-a tooth that remains trapped in the jawbone
-Painful
-Wisdom teeth are most commonly involved.
Treatment: surgical removal
dental carries
dental plaque
-Dental caries (cavities): demineralization of enamel and dentin from bacterial action
- Dental plaque
- -film of sugar, bacteria, and debris
- -adheres to teeth
- Acid from bacteria dissolves calcium salts
- Proteolytic enzymes digest organic matter
- Prevention
- –daily flossing and brushing
gingivitis
Gingivitis
Plaque calcifies to form calculus (tartar)
disrupts seal between gingivae and teeth
Anaerobic bacteria infect gums
Infection is reversible if calculus removed
periodontitis
Periodontitis (periodontal disease)
-Neglected gingivitis can escalate to disease
-Immune cells attack bacterial intruders and own tissues
destroys periodontal ligaments
activates osteoclasts
Cells that dissolve bone so tooth falls out
-May increase heart disease and stroke two ways:
Promotes atherosclerotic plaque formation
Bacteria entering blood can cause clot formation in coronary and cerebral arteries
-Risk factors: smoking, diabetes mellitus, oral piercings and poor oral hygiene
The Pharynx
Food passes from mouth into oropharynx and then into laryngopharynx
Allows passage of food, fluids, and air
Stratified squamous epithelium lining with mucus-producing glands
External muscle layers consists of two skeletal muscle layers
Inner layer of muscles runs longitudinally
Outer pharyngeal constrictors encircle wall of pharynx
The Esophagus
Muscular tube that runs from laryngopharynx to stomach
Is collapsed when not involved in food propulsion
Goes through the diaphragm at esophageal hiatus
Joins stomach at cardial orifice
Gastroesophageal (cardiac) sphincter surrounds cardial orifice
Keeps orifice closed when food is not being swallowed
Mucus cells on both sides of sphincter help protect esophagus from acid reflux
The Esophagus (Structure)
Four tunics
Mucosa
Stratified squamous epithelium
Changes to simple columnar at stomach
Submucosa
Has esophageal glands that secrete mucus to aid in bolus movement
Muscularis externa
skeletal muscle at the beginning (superior)
mixed in skeletal and smooth muscle in the middle
smooth muscle at the end (inferior)
Serosa is replaced by adventitia
heartburn
hiatal hernia
Heartburn
Caused by stomach acid regurgitating into esophagus
First symptom of gastroesophageal reflux disease (GERD)
Causes
excess food/drink, extreme obesity, pregnancy, running
Hiatal hernia
part of stomach protrudes above diaphragm
Can lead to esophagitis, esophageal ulcers, or even esophageal cancer
Deglutition
and two phases:
Reminder
The pharynx and esophagus job is to pass food from mouth to stomach
Deglutition (swallowing)
Requires coordination of 22 muscle groups and two phases:
Buccal phase
voluntary contraction of tongue
Pharyngeal-esophageal phase
involuntary phase that primarily involves vagus nerve
Controlled by swallowing center in medulla and lower pons
stomach
Stomach
temporary storage tank that starts chemical breakdown of proteins
Converts bolus of food to paste-like chyme
Extremely expandable
Empty stomach ~50 ml can expand to 4 L when full
When empty, stomach mucosa forms many folds called rugae
major regions of stomach
Major regions of the stomach
Cardial part (cardia): surrounds cardial orifice
Fundus: dome-shaped region beneath diaphragm
Body: midportion
Pyloric part: wider and more superior portion of pyloric region, antrum, narrows into pyloric canal that terminates in pylorus
Pylorus is continuous with duodenum through pyloric valve (sphincter controlling stomach emptying)
curvatures and mesenteries
Greater curvature: convex lateral surface of stomach
Lesser curvature: concave medial surface of stomach
Mesenteries extend from curvatures and hold the stomach to other digestive organs
Lesser omentum
Runs from lesser curvature to liver
Greater omentum: drapes inferiorly from greater curvature over intestine, spleen, and transverse colon
Blends with mesocolon, mesentery that anchors large intestine to abdominal wall
Contains fat deposits and lymph nodes
Histology of the Stomach
has an extra
Four Tunics
Modified muscularis and mucosa
Muscularis Externa Modifications
Has regular circular and longitudinal smooth muscle layers AND extra third layer, the oblique (diagonal) layer
allows stomach to churn, mix, and move chyme
Also allows pummeling motion
increases physical breakdown and forces chyme into small intestine
Mucosa Modifications
Simple columnar epithelium entirely composed of mucous cells
Secrete two-layer coat of alkaline mucus
Surface layer traps a bicarbonate-rich fluid layer beneath it
Gastric pits
lead into gastric glands
gastric glands make gastric juice
Glandular Cells of the Stomach (Mucous Neck Cells)
types of gland cells
mucous neck cells
Types of gland cells
Glands in fundus and body produce most gastric juice
Mucous neck cells, Parietal cells, Chief cells, Enteroendocrine cells
Mucous neck cells
Secrete thin, acidic mucus of unknown function
parietal cells
Parietal cells
Secretions include:
Hydrochloric acid (HCl)
pH 1.5–3.5; denatures protein, activates pepsin, breaks down plant cell walls, and kills many bacteria
Intrinsic factor
Glycoprotein required for absorption of vitamin B12 in small intestine
secrets HCL and intrinsic factor
chief cells
Chief cells Secretions include: Pepsinogen: inactive enzyme that is activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism) Lipases Digests ~15% of lipids
secrets Pepsinogen lipase
enteroendocrine cells
Enteroendocrine cells
Secrete chemical messengers into lamina propria
Act as paracrines
Serotonin and histamine
Hormones
Somatostatin (also acts as paracrine) and gastrin
secretes hormones and paracrine
mucosal barrier
Mucosal barrier protects stomach thick layer of bicarbonate-rich mucus tight junctions between epithelial cells prevent juice seeping underneath tissue damaged epithelial cells are quickly replaced surface cells replaced every 3–6 days
gastritis
ulcers
Gastritis
Inflammation caused by anything that breaches stomach’s mucosal barrier
Peptic or gastric ulcers
Can cause erosions in stomach wall
If erosions perforate wall, can lead to peritonitis and hemorrhage
Most ulcers caused by bacterium Helicobacter pylori
Can also be caused by non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin
reminder of what the stomach does
Denatures proteins by
Pepsin carries out enzymatic digestion
Reminder of what the stomach does: Carries out breakdown of food Serves as holding area for food Delivers chyme to small intestine Denatures proteins by HCl Pepsin carries out enzymatic digestion of proteins Milk protein (casein) is broken down by rennin in infants Results in curdy substance
Protein Digestion in the Stomach
-Milk protein (casein
broken down by
-Denatures proteins by HCl
-Pepsin
Enzyme that digests of proteins
-Milk protein (casein
broken down by rennin in infants
Makes “curds”
Alcohol, Aspirin and Intrinsic Factor
Alcohol and aspirin
absorbed into blood through the mucosa
both are lipid soluble
Intrinsic factor
Synthesis and secretion is the only stomach function essential to life
Required vitamin B12 absorption
Reminder:
B12 needed for red blood cells to mature
Lack of intrinsic factor causes pernicious anemia
Treated with B12 injections
Regulation of Gastric Secretion (Introduction)
neural and hormonal
Gastrin
stimulates
Gastric mucosa secretes >3 L of gastric juice/day
Regulated by:
Neural mechanisms
Parasympathetic (Vagus nerve) stimulation increases secretion
Sympathetic stimulation decreases secretion
Hormonal mechanisms
Gastrin
stimulates HCl secretion by the stomach
Stimulates gastrin antagonist hormones by the small intestine
gastric secretions are broken down into three phases
Gastric secretions are broken down into three phases
Cephalic (reflex) phase
Gastric phase
Intestinal phase
cephalic phase
Cephalic (reflex) phase
Conditioned reflex triggered by aroma, taste, sight, thought
Varies based on life experience!
gastric phase
Gastric phase
Lasts 3–4 hours
Releases two-thirds of the gastric juice
Stimulation of gastric phase
Distension (stretching) activates stretch receptors
initiates both long and short reflexes
Chemical stimuli
i.e partially digested proteins, caffeine, and low acidity
activate enteroendocrine G cells to secrete gastrin
Release of gastrin initiates HCl release from parietal cells and activates enzyme secretion
Buffering action of ingested proteins causes pH to rise, which activates more gastrin secretion
inhibition of gastric phase
Inhibition of gastric phase
Low pH
Inhibits gastrin secretion
Happens between meals
Also occurs during digestion as negative feedback mechanism
The more protein, the more HCl acid is secreted, causing decline in pH, which inhibits gastrin secretion
intestinal phase
Intestinal phase
Brief stimulation followed by inhibition
Stimulation of intestinal phase
Partially digested food enters small intestine,
Causes a brief release of intestinal (enteric) gastrin
Causes gastric glands of stomach to continue secretion
Stimulatory effect is really short!
Overridden by inhibitory stimuli as intestine fills
inhibition of intestinal phase
two mechanisms
Inhibition of intestinal phase
Four main factors in duodenum cause inhibition of gastric secretions:
Distension of duodenum due to entry of chyme
Presence of acidic chyme
Presence of fatty chyme
Presence of hypertonic chyme
Protect intestine from being overwhelmed by too much chyme or acidity
Two mechanisms
enterogastric reflex and enterogastrones
Regulation of Gastric Secretion (Enterogastric Reflex and Enterogastrones)
Enterogastric Reflex
Enterogastrones
Duodenal enteroendocrine cells release two important
Enterogastric reflex
Neural control
Duodenum inhibits acid secretion in stomach by:
Enteric nervous system short reflexes
Sympathetic nervous system and vagus nerve long reflexes
Enterogastrones Hormonal control Duodenal enteroendocrine cells release two important hormones that inhibit gastric secretion Secretin Cholecystokinin (CCK)
Mechanism of HCl Formation
Parietal cells pump H+ (from carbonic acid breakdown) into stomach lumen via H+/K+ ATPase (proton pumps)
As H+ is pumped into stomach lumen, HCO3− is exported back to blood via Cl− and HCO3− antiporter
Resulting increase of HCO3− in blood leaving stomach is referred to as alkaline tide
Cl− is pumped out to lumen to join with H+, forming HCl
(Stomach Filling)
Two factors cause pressure to remain constant until 1.5 L of food is ingested
Response of the stomach to filling
Stretches to accommodate incoming food
Two factors cause pressure to remain constant until 1.5 L of food is ingested
Receptive relaxation
reflex-mediated relaxation of smooth muscle
coordinated by swallowing center of brain stem
Gastric accommodation
intrinsic ability of smooth muscle to exhibit stress-relaxation response
enables hollow organs to stretch without increasing tension or contractions
(Contraction of the Stomach)
Basic electrical rhythm (BER) is set by
Contractions are strongest near
30 ml of chyme produced is either:
Gastric contractile activity
Peristaltic waves move toward pylorus
About 3 waves per minute
Basic electrical rhythm (BER) is set by enteric pacemaker cells
Pacemaker cells are linked by gap junctions so that entire muscularis contracts (Sounds familiar?)
Distension and gastrin increase force of contraction
Contractions are strongest near pylorus region
30 ml of chyme produced is either:
~3 ml spurts into duodenum
Rest of 27 ml forced backward into stomach
Only liquids and small particles are allowed to pass through pyloric valve
(Gastric Emptying) Regulated by the Controls how much Prevents Stomach empties in High fatty chyme entering duodenum can increase time to
Regulation of gastric emptying
Regulated by the Duodenum
Controls how much chyme enters
Prevents overfilling
Duodenal receptors respond to stretch and chemical signals
Enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling
Stomach empties in ~4 hours
High fatty chyme entering duodenum can increase time to 6hours or more
Carbohydrate-rich chyme moves quickly through duodenum!
This means that high carb meals do not keep us feeling full as long!
emesis
Vomiting (emesis) is caused by:
Extreme stretching
Intestinal irritants
I.e. bacterial toxins, excessive alcohol, spicy food, certain drugs
Chemicals and sensory impulses stimulate emetic center of medulla
Excessive vomiting can lead to dehydration and electrolyte and acid-base imbalances (alkalosis)
Liver, Gallbladder and Pancreas (Introduction)
Liver, gallbladder, and pancreas are accessory organs associated with small intestine
Liver: Makes bile
Bile emulsifies fats
Gallbladder: Stores bileLiver, Gallbladder and Pancreas (Introduction)
Pancreas:
Produces several digestive enzymes
Produces bicarbonate to neutralize stomach acid
liver anatomy
Gross anatomy of the liver
Largest gland in body
weighs ~3 lbs
Consists of four primary lobes: right, left, caudate, and quadrate
Falciform ligament
Separates larger right and smaller left lobes
Suspends liver from diaphragm and anterior abdominal wall
Round ligament (ligamentum teres)
Remnant of fetal umbilical vein along free edge of falciform ligament
Gross anatomy of the liver (cont.) Lesser omentum anchors liver to stomach Hepatic artery and vein enter liver at porta hepatis Bile ducts Common hepatic duct leaves liver Cystic duct connects to gallbladder Bile duct union of common hepatic and cystic ducts
The Liver (Histology)
Microscopic anatomy of the liver
Liver lobules
Hexagonal structural and functional units
Composed of hepatocytes (liver cells)
Form hepatic plates
Filter and process nutrient-rich blood
Central vein located in longitudinal axis
Portal triad
In each corner of lobule contains:
Branch of hepatic artery, which supplies oxygen
Branch of hepatic portal vein, which brings nutrient-rich blood from intestine
Bile duct, which receives bile from bile canaliculi
The Liver (Histology Cont.)
Liver sinusoids
Stellate macrophages
Liver sinusoids
leaky capillaries located between hepatic plates
Blood from the hepatic portal vein and hepatic artery proper enters the sinusoids
Empties into central vein
Stellate macrophages (hepatic macrophages) in liver sinusoids remove debris and old RBCs
The Liver (Histology: Hepatocytes)
Hepatocytes have increased rough and smooth ER, Golgi apparatus, peroxisomes, and mitochondria Hepatocyte functions Produce ~900 ml bile per day Process bloodborne nutrients Example: store glucose as glycogen and make plasma proteins Store fat-soluble vitamins Perform detoxification Example: converting ammonia to urea
(Bile)
Bilirubin:
Composition
Yellow-green, alkaline solution:
Bile salts: cholesterol derivatives that function in fat emulsification and absorption
Bilirubin: pigment formed from heme
Bacteria break down bile in intestine
Makes feces brown
Cholesterol, triglycerides, phospholipids, and electrolytes
Enterohepatic circulation
Recycling mechanism that conserves bile salts
Bile salts
Reabsorbed into blood by ileum (the last part of small intestine)
Returned to liver via hepatic portal blood
Resecreted in newly formed bile
About 95% of secreted bile salts are recycled, so only 5% is newly synthesized each time!
hepatitis
cirrhosis
Hepatitis
Usually viral infection, drug toxicity, wild mushroom poisoning
Cirrhosis
Progressive, chronic inflammation from chronic hepatitis or alcoholism
Liver → fatty, fibrous → portal hypertension
Liver transplants successful, but livers are scarce
Liver can regenerate to its full size in 6–12 months after 80% removal
So HIGHLY regenerative
The Gallbladder
Gallbladder is a thin-walled muscular sac on ventral surface of liver
Functions to store and concentrate bile by absorbing water and ions
Contains many honeycomb folds that allow it to expand as it fills
Muscular contractions release bile via cystic duct, which flows into bile duct
gallstones
Gallstones (biliary calculi):
Caused by too much cholesterol or too few bile salts
Can obstruct flow of bile from gallbladder
Painful when gallbladder contracts against sharp crystals
Obstructive jaundice
bile salts and pigments to build up in blood, resulting in jaundiced (yellow) skin
Jaundice can also be caused by liver failure
Gallstone treatment
crystal-dissolving drugs, ultrasound vibrations (lithotripsy), laser vaporization, or surgery
The Pancreas (Introduction)
Location mostly retroperitoneal deep to greater curvature of stomach head is encircled by duodenum tail ends at the spleen Exocrine function produce pancreatic juice Acini clusters of secretory cells t produce zymogen granules with proenzymes Ducts secretes to duodenum via main pancreatic duct smaller duct cells produce water and bicarbonate Endocrine function secretion of insulin and glucagon by pancreatic islet cells
pancreatic juice
Pancreatic juice 1200–1500 ml/day Watery, alkaline solution (pH 8) neutralize acidic chyme Electrolytes, mostly HCO3− Digestive enzymes Proteases (for proteins) secreted in inactive form to prevent self-digestion Amylase (for carbohydrates) Lipases (for lipids) Nucleases (for nucleic acids)
Bile and Pancreatic Secretion into the Small Intestine
Hepatopancreatic sphincter
Bile duct and pancreatic duct unite in wall of duodenum
Fuse together in bulblike structure called hepatopancreatic ampulla
Ampulla opens into duodenum via volcano-shaped major duodenal papilla
Hepatopancreatic sphincter controls entry of bile and pancreatic juice into duodenum
Accessory pancreatic duct: smaller duct that empties directly into duodenum
Bile and Pancreatic Secretion into the Small Intestine (Regulation)
Regulation of bile and pancreatic secretions
neural and hormonal controls
Hormonal controls include:
Cholecystokinin (CCK)
Secretin
Bile secretion is increased when:
Enterohepatic circulation returns large amounts of bile salts
Secretin, from intestinal cells exposed to HCl and fatty chyme, stimulates gallbladder to release bile
Hepatopancreatic sphincter is closed, unless digestion is active
Bile is stored in gallbladder and released to small intestine only with contraction
small intestine anatomy
Small intestine
major organ of digestion and absorption (where most of it happens)
2–4 m long (7–13 ft)
Small diameter of 2.5–4 cm (1.0–1.6 inches)
Begins at the pyloric sphincter
Where the stomach empties in
Ends at the ileocecal valve,
point at which it joins large intestine
Small diameter of 2.5–4 cm (1.0–1.6 inches)
subdivision of small intestine
Subdivisions Duodenum mostly retroperitoneal ~25.0 cm (10.0 in) long curves around head of pancreas has most features Jejunum ~2.5 m (8 ft) long attached posteriorly by mesentery Ileum ~3.6 m (12 ft) long attached posteriorly by mesentery joins large intestine at ileocecal valve
blood supply and nerve supply of digestive supply
Blood supply: Superior mesenteric artery brings blood supply Veins (carrying nutrient-rich blood) drain into superior mesenteric veins, then into hepatic portal vein, and finally into liver Nerve supply Parasympathetic innervation vagus nerve Sympathetic innervation thoracic splanchnic nerves
microscopic anatomy of small intestine
Modifications of small intestine for absorption
Modified to have huge surface area for absorption
Increased 600× to ~200 m2 (size of a tennis court)
Modifications include:
Circular folds
Villi
Microvilli
Microscopic Anatomy (Modifications of the Small Intestine)
Circular folds Permanent folds ~1 cm deep that force chyme to slowly spiral through lumen allows more time for nutrient absorption Villi Fingerlike projections of mucosa ~1 mm high contain lacteals capillariy bed and lymphatic capillaries for absorption Microvilli Brush border Cytoplasmic extensions of mucosal cell Brush border enzymes membrane-bound enzymes carbohydrate and protein digestion
intestinal crypts
Intestinal crypts
Five main types of cells found in villi and crypts
enterocytes, goblet cells, enteroendocrine cells, paneth cells, stem cells
Enterocytes
Most of the epithelial cells
Simple columnar absorptive cells bound by tight junctions and contain many microvilli
Function
Villi: absorb nutrients and electrolytes
Crypts: produce intestinal juice, watery mixture of mucus that acts as carrier fluid for chyme
goblet cells
enteroendocrine cells
paneth cells
stem cells
Goblet cells mucus-secreting cells found in epithelia of villi and crypts Enteroendocrine cells Produce enterogastrones examples: CCK and secretin Found scattered in villi but some in crypts Paneth cells Deep in crypts Secrete antimicrobial agents defensins and lysozyme Stem cells Continuously divide Produce other cell types Villus epithelium renewed every 2–4 days
Microscopic Anatomy (MALT)
Mucosa-associated lymphoid tissue (MALT)
protects intestine against microorganisms
Individual lymphoid follicles
Peyer’s patches (aggregated lymphoid nodules)
In the lamina propria
More in distal part of small intestine
Why? where bacterial numbers increase
Lamina propria also contains large numbers of plasma cells that secrete IgA
Submucosa consists of areolar tissue
Duodenal glands
In the duodenum
Secrete alkaline mucus to neutralize acidic chyme
Intestinal Juice
Secreted in response to
Major stimulus for production is
Mostly
1–2 L secreted daily
Secreted in response to distension or irritation of mucosa
Major stimulus for production is hypertonic or acidic chyme
Slightly alkaline and isotonic with blood plasma
Mostly water but also contains mucus
Mucus is secreted by duodenal glands and goblet cells of mucosa
Digestive Processes in the Small Intestine
(Introduction and Enzymes)
Takes ____ in small intestine to absorb all nutrients and most water
Enzymes for digestion come from:
Starting with chyme From stomach Carbohydrates and proteins partially digested Fats undigested Takes 3–6 hours in small intestine to absorb all nutrients and most water Enzymes for digestion come from: Liver and pancreas bile, bicarbonate, digestive enzymes not brush border enzymes Brush border enzymes bound to plasma membrane Responsible for final digestion of chyme
regulating chyme entry
Regulating chyme entry
Chyme entering duodenum is usually hypertonic
has to be slow to prevent osmotic loss of water from blood
Low pH of chyme has to be adjusted upward
Chyme has to be mixed with bile and pancreatic juice to continue digestion
Enterogastric reflex and enterogastrones control movement of food into duodenum to prevent it from being overwhelmed
(Motility of the Small Intestine After a Meal)
After a meal
Segmentation is most common motion of small intestine
Initiated by intrinsic pacemaker cells
Mixes/moves contents toward ileocecal valve
Intensity is altered by long and short reflexes and hormones
Parasympathetic increases motility; sympathetic decreases it
(Motility of the Small Intestine Between Meals)
initiated by rise in hormone
Between meals
Peristalsis increases
initiated by rise in hormone motilin in late intestinal phase (every 90–120 minutes)
Meal remnants, bacteria, and debris are moved toward large intestine
Complete trip from duodenum to ileum takes ~2 hours
(Control of the Ileocecal Valve)
Ileocecal sphincter relaxes and admits chyme into large intestine when:
increases motility of ileum
Ileocecal valve control
Ileocecal sphincter relaxes and admits chyme into large intestine when:
Gastroileal reflex enhances force of segmentation in ileum
Gastrin increases motility of ileum
Ileocecal valve flaps close when chyme exerts backward pressure
Prevents regurgitation into ileum
Large intestine
has three unique features
Large intestine
Three unique features
Teniae coli: three bands of longitudinal smooth muscle in muscularis
Haustra: pocketlike sacs caused by tone of teniae coli
Epiploic appendages: fat-filled pouches of visceral peritoneum
subdivisions of large intestine
Subdivisions of large intestine
Cecum: first part of large intestine
Appendix: masses of lymphoid tissue
Part of MALT of immune system
Bacterial storehouse capable of recolonizing gut when necessary
Twisted shape of appendix makes it susceptible to blockages
Colon: has several regions, most which are retroperitoneal (except for transverse and sigmoid regions)
Ascending colon: travels up right side of abdominal cavity to level of right kidney
Ends in right-angle turn called right colic (hepatic) flexure
Transverse colon: travels across abdominal cavity
Ends in another right-angle turn, left colic (splenic) flexureDescending colon: travels down left side of abdominal cavity
Sigmoid colon: S-shaped portion that travels through pelvis
Subdivisions of large intestine (cont.) Rectum: three rectal valves stop feces from being passed with gas (flatus) Anal canal last segment of large intestine that opens to body exterior at anus Has two sphincters Internal anal sphincter smooth muscle External anal sphincter skeletal muscle
(Peritoneum and the Large Intestine)
Retroperitoneal Cecum, appendix, and rectum Colon (except transverse and sigmoid) Intraperitoneal regions anchored to posterior abdominal wall by mesentery sheets called mesocolons
appendicitis
Appendicitis
Acute inflammation of appendix
Usually results from a blockage by feces that traps infectious bacteria
Most common in adolescence when entrance to appendix is at widest
Venous drainage can be impaired
Ruptured appendix can cause peritonitis
Symptoms
Pain in umbilical region, moving to lower right abdominal quadrant
Loss of appetite, nausea, and vomiting
Treatment
Surgical removal (appendectomy), or in some cases, with antibiotics.
Large Intestine-Mucosa
Mucosa
Thicker than other areas
Simple columnar epithelium
Except in anal canal
Stratified squamous epithelium to withstand abrasion
No circular folds, villi, or digestive secretions
Lots of deep crypts goblet cells
Remember goblet cells? What do they make?
Microscopic Anatomy (Anus)
Mucosa of anal canal
Anal columns
long ridges or folds
Anal recesses
between anal columns
secrete mucus to aid in emptying
Pectinate line
horizontal line that parallels anal sinuses
Visceral sensory nerves innervate area superior to this line
Region insensitive to pain
Somatic nerves innervate inferior to this line
Region sensitive to pain
Superficial hemorrhoidal veins in the anal canal form hemorrhoids if inflamed
Bacterial Flora (What is living in the Large intestines?)
Bacterial flora: consist of 1000+ different types of bacteria
Wowza! Outnumber our own cells 10 to 1
Enter from small intestine or anus to colonize colon
Metabolic functions
Fermentation
Ferment indigestible carbohydrates and mucin
Release irritating acids and gases (~500 ml/day)
Vitamin synthesis
Synthesize B complex and some vitamin K needed by liver to produce clotting factors
Keeping pathogenic bacteria in check
Beneficial bacteria outnumber and suppress pathogenic bacteria
Immune system destroys any bacteria that try to breach mucosal barrier
How?
Epithelial cells recruit dendritic cells to mucosa to sample microbial antigens and present to T cells of MALT, triggering production of IgA that restricts microbes
Bacterial Flora (Bacteria Keep Us Healthy!)
Gut bacteria and health
Kinds and proportions of gut bacteria may influence:
Gut bacteria and health
Kinds and proportions of gut bacteria may influence:
Body weight
Susceptibility to various diseases
including diabetes, atherosclerosis, fatty liver disease
Our moods
Manipulating gut bacteria may become a routine health-care strategy in future!
Antibiotic-associated diarrhea
Antibiotic-associated diarrhea
accounts for 14,000 deaths per year
Clostridium difficile
Most common cause of antibiotic-associated diarrhea
Anaerobic bacterium often found in the large intestine
Usually controlled by “good” bacteria
If other bacteria are killed by antibiotics C. difficile takes over
Can cause pseudomembranous colitis (inflammation of colon)
May lead to bowel perforation and sepsis
Are resistant to many antibiotics and difficult to treat
New treatment
fecal transplants to replace healthy bacteria to suppress C. difficile
Digestive Processes in the Large Intestine
12–24 hours
No food breakdown occurs except by bacteria
Absorption of
Vitamins (made by bacterial flora), water, and electrolytes (especially Na+ and Cl−)
Major function of large intestine is propulsion of feces to anus and defecation
NOTE: Large intestine is not essential for life
motility of large intestine
Motility of the large intestine Haustral contractions most contractions of colon haustra sequentially contract in response to distension Slow segmenting movements Mostly in ascending and transverse colon Gastrocolic reflex initiated by food in stomach Results in mass movements slow, strong peristaltic waves activated three to four times per day Descending colon and sigmoid colon are pretty much for storage
Diverticula
Diverticulosis
Diverticulitis
Diverticula Herniations of mucosa Cause: Low-fiber diet Diverticulosis Presence of diverticula Common in sigmoid colon Affects half of people > 70 years Diverticulitis Inflamed diverticula May rupture and leak into peritoneal cavity May be life threatening
IBS
Irritable bowel syndrome
Recurring abdominal pain, stool changes, bloating, flatulence, nausea, depression
Stress is a common precipitating factor
Stress management is important in treatment
defecation
Valsalva’s maneuver
Defecation
Mass movements force feces toward rectum
Defecation reflex
A spinal reflex triggered by distension
Parasympathetic signals
Stimulate contraction of sigmoid colon and rectum
Relax internal anal sphincter
Conscious control allows relaxation of external anal sphincter
Muscles of rectum contract to expel feces
Valsalva’s maneuver
Closing of glottis, contraction of diaphragm and abdominal wall muscles cause increased intra-abdominal pressure
Levator ani muscle contracts, causing anal canal to be lifted superiorly and allowing feces to leave body
Diarrhea
Diarrhea
Watery stools
Large intestine does not have enough time to absorb remaining water
Causes
irritation of colon by bacteria or jostling of digestive viscera (occurs in marathon runners)
Prolonged diarrhea may lead to:
dehydration and electrolyte imbalance (acidosis and loss of potassium)
Constipation
Constipation Food remains in colon for too long Too much water is absorbed Stool becomes hard and difficult to pass Causes Insufficient fiber or fluid in the diet Improper bowel habits Lack of exercise Laxative abuse
Mechanisms of Digestion and Absorption
Digestion breaks down ingested foods into their chemical building blocks
Only these molecules are small enough to be absorbed across wall of small intestine
Digestion
Catabolic
Breaks macromolecules down into monomers small enough for absorption
Intrinsic and accessory gland enzymes are involved in digestion
Enzymes carry out hydrolysis
Water is added to break chemical bonds
Mechanisms of Absorption
Absorption
process of moving substances from lumen of gut into body
Lumen? What is it?
Molecules pass through epithelial cells rather than between
Due to tight junctions
Enter cell through apical membrane (lumen side)
Exit through basolateral membrane (blood side)
Remember epithelial tissue structure?
Lipid molecules can be absorbed passively through membrane
Why?
Polar molecules are absorbed by active transport
Why?
Most nutrients are absorbed before chyme reaches ileum
-So most are absorbed in the duodenum and jejunum
Digestion of Carbohydrates (Introduction)
Only monosaccharides can be absorbed
Polysaccharides (starch) and disaccharides are broken down
Begins in mouth with salivary amylase
Then broken down into lactose, maltose, and sucrose
Final breakdown into monosaccarides (glucose, fructose, galactose)
Starch digestion in the small intestine
Pancreatic amylase
Breaks down starch to oligosaccharides and disaccharides
Brush border enzymes
dextrinase, lactase, glucoamylase, maltase, and sucrase
Break oligosaccharides and disaccharides into
lactose, maltose, and sucrose; and then into monosaccharides (glucose, fructose, galactose)
Digestion of Carbohydrates (Absorption)
Monosaccharides enter the cell
Co-transported across apical membrane
Mostly by secondary active transport with Na+
Monosaccharides exit the cell
exit across the basolateral membrane by facilitated diffusion
Clinical – Homeostatic Imbalance (Lactose Intolerance)
Lactase deficiency
cannot consume lactose
Lactose remains undigested
creates an osmotic gradient in intestine that prevents water from being absorbed
So-diarrhea
Can even pull water from interstitial space into intestinal lumen
Bacterial metabolism of lactose causes
produces large amounts of gas
results in bloating, flatulence, and cramping pain
Treatment
add lactase enzyme “drops” to milk or take a lactase tablet before consuming milk products
Digestion of Proteins (Introduction)
Source of protein
Dietary
digestive enzymes and proteins from breakdown of mucosal cells
Proteins break:
Large polypeptides then
Small polypeptides and small peptides
Finally into amino acid monomers, with some dipeptides and tripeptides
Digestion begins in stomach
Remember: pepsinogen is converted to pepsin at pH 1.5–2.5
Becomes inactive in high pH of duodenum
Digestion of Proteins (Steps)
Steps of protein digestion in intestine
Pancreatic proteases
trypsin and chymotrypsin
cleave protein into smaller peptides
carboxypeptidase
takes off one amino acid at a time from the end
Brush border enzymes
aminopeptidases, carboxypeptidases, and dipeptidases
break oligopeptides and dipeptides into amino acids
Amino acids
cotransported across apical membrane of epithelial cell via secondary active transport carriers (Na+ or H+)
Amino acids exit across basolateral membrane via facilitated diffusion
Emulsification, Digestion, and Absorption of Fats (Step 1: Emulsification)
Emulsification
Remember: triglycerides and their breakdown products are insoluble in water
Bile salts break large fat globules into smaller ones
Emulsification, Digestion, and Absorption of Fats (Step 2: Digestion by Lipase)
Digestion
pancreatic lipases break down fat into monoglyceride plus two free fatty acids
Emulsification, Digestion, and Absorption of Fats (Step 3: Micelle Formation )
Micelle formation
products from digestion become coated with bile salts and lecithin
Emulsification, Digestion, and Absorption of Fats (Step 4: Diffusion)
Diffusion
lipid products leave micelles and cross epithelial membrane via diffusion
Emulsification, Digestion, and Absorption of Fats (Step 5: Chylomicron Formation and transport
Chylomicron formation
lipid products are converted back into triglycerides and packaged with lecithin and lipoproteins (together called chylomicron)
Chylomicron transport
Chylomicrons are put out of the cell using exocytosis
On basolateral side then go into the lymphatic lacteal
Eventually emptied into venous blood at thoracic duct
Once in blood, chylomicrons are
Once in blood, chylomicrons are broken into free fatty acids and glycerol by lipoprotein lipase so they can be used by cells
Short-chain fatty acids can diffuse directly into blood
Digestion of Nucleic Acids
Ingested food has DNA and RNA because our food is made of cells!
Pancreatic nucleases
hydrolyze nucleic acid to nucleotide monomers
Phosphate, sugar and a nitrogen containing base
Brush border enzymes,
nucleosidases and phosphatases
break nucleotides down
nitrogenous bases, pentose sugars, and phosphate ions
Breakdown products are actively transported by special carriers in epithelium of villi
Absorption of Vitamins
Fat-soluble vitamins
Water-soluble vitamins
Vitamin B12 (
Vitamin absorption In small intestine Fat-soluble vitamins (A, D, E, and K) carried by micelles diffuse into absorptive cells Water-soluble vitamins (C and B) absorbed by diffusion or by passive or active transporters Vitamin B12 (large, charged molecule) binds with intrinsic factor absorbed by endocytosis In large intestine vitamin K and B vitamins from bacterial metabolism are absorbed
Absorption of Electrolytes
Absorption of electrolytes
What is an electrolyte?
Most ions are actively transported
Along length of small intestine
Iron and calcium are absorbed in duodenum
Na+ absorption is coupled with active absorption of glucose and amino acids
Cl− is actively transported
K+ diffuses in response to osmotic gradients
lost if water absorption is poor
Iron and calcium absorption is related to need
Ionic iron is stored in mucosal cells with ferritin
When needed, transported in blood by transferrin
Ca2+ absorption I
regulated by vitamin D and parathyroid hormone (PTH)
Absorption of Water
Absorption of water
9 L water enter small intestine daily
Most from GI tract secretions
95% is absorbed in the small intestine by osmosis
Most of rest is absorbed in large intestine
Net osmosis occurs if concentration gradient is established by active transport of solutes
Water uptake is coupled with solute uptake
Malabsoprtion
Malabsorption
Caused by anything that interferes with delivery of bile or pancreatic juice
Or damaged intestinal mucosa
For Example: from bacterial infection or some antibiotics
Gluten-sensitive enteropathy (celiac disease)
common malabsorption disease
Immune reaction to gluten
Gluten causes immune cell damage to intestinal villi and brush border
Treatment: eliminate gluten from diet
