Digestive System Flashcards
Alimentary canal
-mouth
-pharynx
-esophagus
-stomach
-small intestine
-large intestine
Differentiate between organs of alimentary canal and accessory organs or structure.
-The alimentary canal, or GI tract, is the continuous muscular digestive tube that winds through the body digesting and absorbing foodstuff; its organs include: the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
-Accessory digestive organs or structures aid digestion physically and produce secretions that break down foodstuff in the GI tract; the organs involved are the teeth, tongue, gallbladder, salivary glands, liver and pancreas.
6 functions of digestive system
- Ingestion:
■ occurs when materials enter digestive tract - Propulsion:
■ Peristalsis (movement of food through tract) - Mechanical breakdown:
■ Teeth
■ Tongue
■ Stomach churning
■ Segmentation - Digestion:
■ is the chemical breakdown of food
■ into small organic fragments
■ for absorption by digestive epithelium - Absorption:
■ movement of nutrients
■ across digestive epithelium
■ into interstitial fluid of digestive tract - Defecation :
■ Eliminate indigestible substances in feces
Lining of digestive tract
■ Protects surrounding tissues against:
■ corrosive effects of digestive acids and enzymes
■ mechanical stresses, such as abrasion
■ bacteria
Name one organ of the alimentary canal found in the thorax. Name 3 organs located in abdominal cavity.
Esophagus;
Stomach, small intestine, large intestine
Which digestive system activity actually moves nutrients from outside to inside the body?
Absorption
Bacteria
■ Is ingested with food or resides in digestive tract
■ Attacked by macrophages, and immune system cells
■ In lamina propria (underlying layer of areolar tissue)
Peritoneal cavity
■ Is located within the abdominopelvic cavity
■ Lined with peritoneum (simple squamous epithelium) membrane consisting of:
■ superficial mesothelium covering a layer of areolar tissue
Parietal and visceral layers
-of peritoneum
-continuous w/ one another via several extension (mesenteries, falciform ligament, lesser and greater omenta)
-separated by a potential space containing serous fluid, which decreases friction during organ activity
All organs of GI tract have the same basic pattern of tissue layers in their walls
All have mucosa, submucosa, muscular externa, and serosa (or adventitia). Intrinsic nerve plexuses (enteric nervous system) are found w/in the wall
Digestive viscera are served by the…
Splanchnic circulation, consisting of aterial branches of the celiac trunk and aorta and hepatic portal circulation
How does the location of the visceral peritoneum differ from that of the parietal peritoneum?
Visceral- outermost layer of digestive organ
Parietal- serous membrane covering the wall of abdominal cavity
Peritoneal fluid
■ Is produced by serous membrane lining
■ Provides essential lubricant
■ Separates parietal and visceral surfaces
■ Allows sliding without friction or irritation
Peritoneal cavity disorders
■ Peritonitis
■ Inflammation of the peritoneal membrane
■ Caused by:
■ piercing abdominal wound
■ perforating ulcer
■ ruptured appendix
■ Membranes stick together, localizing infection
■ Can be fatal w/bacterial invasion
■ Ascites
■ The accumulation of Peritoneal Fluid that causes abdominal effusion
■ Can distort abdominal organs and result in:
■ heartburn,
■ indigestion
■ lower back pain.
Peritoneal cavity disorders
■ Peritonitis
■ Inflammation of the peritoneal membrane
■ Caused by:
■ piercing abdominal wound
■ perforating ulcer
■ ruptured appendix
■ Membranes stick together, localizing infection
■ Can be fatal w/bacterial invasion
■ Ascites
■ The accumulation of Peritoneal Fluid that causes abdominal effusion
■ Can distort abdominal organs and result in:
■ heartburn,
■ indigestion
■ lower back pain.
Of the following, which is/are retroperitoneal?
Stomach, pancreas, liver
Pancreas
What is the name of the venous portion of splanchnic circulation?
Hepatic portal circulation
Mesenteries
■ Are double sheets of peritoneal membrane
■ Suspend portions of digestive tract within peritoneal cavity by sheets of serous membrane:
-that connect parietal peritoneum
-with visceral peritoneum
■ Areolar tissue between mesothelial surfaces:
-provides an route to and from the digestive tract
-for passage of blood vessels, nerves, and lymphatic vessels
■ May attain status as a separate organ
-One contiguous structure
-Functions not well understood
■ Stabilize positions of attached organs
■ Prevent intestines from becoming entangled
Describe the location and function of peritoneum.
The peritoneum is a serous membrane that covers the abdominal walls and most abdominal organs. It has two layers, the inner (visceral) layer and the outer (parietal) layer. It provides protection and stability to the abdominal organs, allowing minimal movement.
Retroperitoneal
Give examples
Retroperitoneal: regarding anything that is posterior to the mesentery, lying against dorsal abdominal wall.
-Organs: most of the duodenum, the pancreas, ascending and descending colon, and the rectum.
Splanchnic circulation and indicate the important of hepatic portal system.
blood flow through the abdominal organs including the stomach, liver, pancreas, spleen, and intestines, while the hepatic portal system is a specific part of this circulation that delivers nutrient-rich blood from the digestive tract directly to the liver via the hepatic portal vein, allowing the liver to process absorbed nutrients and toxins before they enter the systemic circulation
the hepatic portal system is crucial for the liver’s vital functions in regulating blood chemistry and metabolism
Tissue composition and general function of 4 layers of alimentary canal
- Mucosa - innermost layer - SECRETION of mucous, digestive enzymes, and hormones. ABSORPTION of end products of digestion into the blood. PROTECTION against infection.
- Submucosa - extensive VASCULAR network supplies surrounding tissue, ELASTIC fibers enables stomach to regain normal shape after large meal.
- Muscularis Externa - SEGMENTATION and PERISTALSIS. Forms sphincters that act as valves.
- Serosa - Outermost layer - PROTECTIVE layer of areolar connective tissue covered with mesothelium.
Mesenteries development
■ During embryonic development:
-digestive tract and accessory organs are suspended in peritoneal cavity by:
-dorsal mesentery
-ventral mesentery
When sensors in the GI tract are stimulated they trigger reflexes. What types of digestive activity may be put into motion via those relfexes?
Reflexes associated with/ the GI tract promote muscle contraction and secretion of digestive juices or hormones
The term “gut brain” does not really mean there is a brain in the digestive system. What does it refer to?
Enteric nervous system, the web of neurons closely associated w/ the digestive organs
Jerry has been given a drug that inhibits parasympathetic stimulation of his digestive tract. Should he “eat hearty” or temporarily refrain from eating? Why?
Temporarily refrain from eating b/c parasympathetic NS stimulated digestive activities
Lesser omentum
-stabilizes position of stomach
-provides access route for blood vessels and other structures entering or leaving liver
Dorsal mesentery
■ Is on ventral surface of stomach
■ Enlarges to form an enormous pouch, called the greater omentum
Greater omentum
■ Extends inferiorly between:
-the body wall and
-the anterior surface of small intestine
■ Hangs like an apron:
-from lateral and inferior borders of stomach and attaches to the large intestine
■ Adipose tissue in greater omentum:
-pads and protects surfaces of abdomen
-provides insulation to reduce heat loss
-stores lipid energy reserves
-Contains many lymph nodes- site of peritoneal immune response
Describe stimuli and controls of digestive activity
Digestive activities within the GI tract are triggered by mechanical and chemical stimuli [e.g., stretching of organ by food, osmolarity, pH, etc.] and are detected by mechanoreceptors and chemoreceptors.
• Controls of digestive activity are both intrinsic [“in-house”] and extrinsic.
a. Neural mechanisms [Enteric Nervous System (ENS)]: the ENS has roughly as many neurons as the spinal cord, and as many neurotransmitters as the brain, but whose functions remain largely unknown…
❊ Short [myenteric] reflexes control smooth muscle contraction and glandular secretion as relatively localized activities involving small segments of the digestive tract; this mechanism is usually considered parasympathetic, but the plexus also contains sensory neurons, motor neurons and interneurons for local reflexes whose internal workings operate entirely outside the control of the CNS.
❊ Long reflexes involve interneurons and motor neurons in the CNS and provide a higher level of control over digestive and glandular activities.
b. Hormonal mechanisms involve as many as 18 hormones, affecting almost every aspect of digestive function.
c. Local mechanisms involve prostaglandins, histamines and other chemicals released into the interstitial fluid and affecting adjacent cells…
Oral mucosa tissue type
Stratified squamous epithelial
Tongue
-mucosa-covered skeletal muscle
-intrinsic muscles: allow change of shape
-extrinsic muscles: allow change in position
Saliva
-produced by minor salivary glands and 3 pairs of major salivary glands: parotid, submandibular, and sublingual
-largely water, contains ions, proteins, metabolic wastes, lysozyme, defensins, IgA, salivary amylase, and mucin
-moistens and cleanses the mouth
-moistens food, aiding their compaction
-dissolves food chemical to allow for taste
-begins digestion of starch (salivary amylase)
-saliva output ⬆️ by PNS initiated by activation of chemical and pressure receptors in the mouth and by fight or smell of food
Teeth
-bulk of tooth is dentin, which surround the central pulp cavity
-periodontal ligament secures the tooth to bony alveolus
Mesentery proper
■ Is a thick mesenterial sheet
■ Permits some independent movement
■ Suspends all but first 25 cm of small intestine
■ Does not surround the initial portion of small intestine (duodenum) and pancreas (they are retroperitoneal)
■ Fuses with posterior abdominal wall, locking structures in position
Which structure forms the roof of the mouth?
Palate forms roof of mouth. Hard palate supported by bone is anterior to soft palate (no bony support)
Name 3 antimicrobial substances found in saliva.
-lysozyme
-defensins
-IgA antibodies
Which tooth substance is harder than bone? Which tooth regions includes nervous tissue and blood vessels?
Enamel is harder than bone
Pulp consists of nervous tissue and blood vessels
Describe the composition and functions of saliva, and explain how salivation is regulated
Salivary glands produce saliva, which cleanses the mouth, dissolves food chemicals for taste, moistens food, and contains chemicals that begin the breakdown of starches.
Saliva Composition: 1.0-1.5 liters/day, 97- 99.5% water, but also IgA, lysozyme, defensins, mucins and salivary amylase; production of a bolus.
Regulation: Parasympathetic [watery saliva] and sympathetic [more viscous saliva] stimulation.
Mesocolon
■ A mesentery associated with a portion of the large intestine:
-transverse mesocolon supports transverse colon
-sigmoid mesocolon supports sigmoid colon
-Ascending and descending colon are retro peritoneal
Blood supply: Splanchnic circulation
■ Branches of aorta serving digestive organs
-Hepatic, splenic, and left gastric arteries
-Inferior and superior mesenteric arteries
■ Hepatic portal circulation
-Drains nutrient-rich blood from digestive organs
-Delivers it to the liver for processing
Digestive epithelium
■ Mucosal epithelium is simple or stratified:
-depending on location, function, and stresses
■ Oral cavity, pharynx, and esophagus:
■ mechanical stresses
■ Stomach, small intestine, and most of large intestine:
-absorption
-simple columnar epithelium with goblet cells
Enteroendocrine cells
■ Are scattered among columnar cells of digestive epithelium
-Secrete hormones that:
-coordinate activities of the digestive tract and accessory gland
Lining of digestive tract
■ Folding increases surface area for absorption:
– longitudinal folds, disappear as digestive tract distends
– permanent transverse folds (plicae)
Deglutition (swallowing)
Buccal phase
-upper esophageal sphincter is contracted (closed)
-tongue presses against hard palate, forcing food bolus into oropharynx
Deglutition: pharyngeal-esophageal phase begins
-tongue blocks mouth
-soft palate and its uvula rise, closing off nasopharynx
-larynx rises so that epiglottis blocks trachea
-upper esophageal sphincter relaxes; food enter esophagus
Deglutition: pharyngeal esophageal phase continues (steps 3-5)
3)
-constrictor muscles of pharynx contract, forcing food into esophagus inferiorly
-upper esophageal sphincter contracts after food enter
4)
-peristalsis moves food through esophagus to stomach
5)
-gastro esophageal sphincter orifice opens. After food enter the stomach sphincter closes, preventing regurgitation
Esophagus extends…
Extends from laryngopharynx and joins the stomach at cardial orifice, which is surrounded by gastroesophageal sphincter
Esophageal mucosa
-stratified squamous epithelium
-its muscular is is skeletal muscle superiority and changes to smooth muscle inferiorly
-it has adventitia rather than serosa
Lamina propria
■ Consists of a layer of areolar tissue that contains:
-blood vessels
-sensory nerve endings
- lymphatic vessels
-smooth muscle cells
-scattered lymphoid tissue
Muscularis mucosae
■ Narrow band of smooth muscle and elastic fibers deep to the lamina propria
Peristalsis
Progressive, wavelike constrictions that move foodstuff through alimentary tube organs
Pharynx and esophagus are primarily food conduits that conduct food to stomach by peristalsis
Swallowing
Initiated by the mouth (buccaneers phase) after the tongue has compacted food and saliva into a bolus. Pharyngeal-esophageal phase is controlled reflexively by the swallowing center in the medulla and pons. When peristaltic wave approaches gastroesophageal sphincter, the sphincter relaxes to allow food to enter stomach
To which 2 organ systems does the pharynx belong to?
Digestive and respiratory systems
Submucosa
■ Is a layer of dense irregular connective tissue with many elastic fibers
■ Has large blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus- intrinsic neurons
Muscularis externa
■ Is dominated by smooth muscle cells
■ cells arranged in 2 concentric layers:
-inner layer encircles lumen (circular muscle)
-outer layer contains muscle cells parallel to tract (longitudinal layer)
How is the Muscularis external of the esophagus unique in the body?
Undergoes transformation along its length from skeletal muscle superiority to smooth muscle near stomach
Muscularis externa functions
■ Involved in mechanical processing
-Segmentation – Mixing
-Peristalsis - movement of materials along digestive tract
■ Circular layer thickens to form sphincters
Enteric Nervous System (ENS)
■ The brain of the gut or the little brain
■ Made of of the myenteric and submucosal plexuses with:
■ motor neurons
-sensory neurons
-Chemoreceptors
- stretch receptors
-interneurons
-ANS inputs
■ Can work independent of CNS
What is the functional significance of epithelial change seen at esophagus-stomach junction?
Esophagus is merely a chute for food passage and is subjected to a good deal of abrasion, which a stratified squamous epithelium can w/stand. Stomach mucosa is secretory mucosa served well by simple columnar epithelium
How are the respiratory passages blocked during swallowing?
Larynx rises and epiglottis covers its lumen so that foodstuffs are diverted into esophagus posteriorly
Submucosal plexus
■ Also called plexus of Meissner
■ Innervates the mucosa and submucosa
■ Involved primarily in sensation and motor input to
-mucosal and
-submucosal
-glands
■ (squeezes out the GI juices)
Myentric plexus
■ Muscularis externa movements coordinated by myenteric plexus of the ENS:
-Located between the circular and longitudinal layers
ANS and ENS parasympathetic vs sympathetic
Parasympathetic
■ parasympathetic division of ANS is dominant
■ Mostly by the Vagus nerve (X)
■ PNS generally stimulates GI activity
-Except in sphincters
Sympathetic
■ Sympathetic input from thoracic and upper lumbar cord
■ Innervate the myenteric and submucosal plexuses
■ Generally Inhibitory
-Except in sphincters and extreme SNS events
Name the 3 phases of gastric secretion
-cephalic
-gastric
-intestinal
J-shaped stomach
-lies in upper left quadrant of the adbdomen
-major regions: cardiac, fundus, body, pyloric part
-when empty: its internal surface exhibits rugae
Stomach mucosa
-simple columnar epithelium dotted with gastric pits that lead into gastric glands
-secretory cells in gastric glands include:
-Pepsinogen-producing chief cells
-parietal cells, which secrete hydrochloric acid and intrinsic factor
-mucous neck cells, which produce mucus
-Enteroendocrine cell, which secrete hormones and paracrines
Mucosal barrier
-protects stomach from self-digestion and HCl
Protein digestion
-intimated in the stomach by activated pepsin and require acidic conditions (provided by HCL)
-few substances are absorbed in stomach
Protein digestion
-intimated in the stomach by activated pepsin and require acidic conditions (provided by HCL)
-few substances are absorbed in stomach
Mechanical breakdown in the stomach is triggered by…
Stomach dissension and coupled to food propulsion and stomach emptying
Food movement into the duodenum is controlled by
The pylorus and feedback signals from small intestines
Food movement into the duodenum is controlled by
The pylorus and feedback signals from small intestines
What cells set the rate of peristalsis?
Pacemaker cells in smooth muscle sheet
Serosa
■ Serous membrane covering muscularis externa:
-except in oral cavity, pharynx, esophagus, and rectum
Adventitia
■ Covers muscularis externa of oral cavity, pharynx, esophagus, and large intestine
■ Is a dense sheath of collagen fibers
■ Firmly attaches the digestive tract to adjacent structures
Cholceystokinin (CCK)
Site of production: duodenal mucosa
Stimulus of production: fatty chime
Target organ: stomach, liver/pancreas, gallbladder, hepatopancreatuc sphincter
Activity:
-in its stomachs secretory activity
-potentials secretin’s actions on these organs
-increases output if enzyme-rich pancreatic juice
-stimulates organ to contract and expel stored bile
-relaxes sphincter to allow entry of bile and pancreatic juice into duodenum
Glucose-dependent insulinotropic peptide (GIP) (or gastric inhibitory peptide)
Site of production: dudodenal mucosa
Stimulus production: fatty chime
Target organ: stomach, pancreas (beta cells)
Activity:
-inhibits HCL production (minor effect)
-stimulates insulin release
Gastrin
Site of production: stomach mucosa (Gcells)
Stimulus of production: food (particularly digested proteins) in stomach (chemical stimulation); ACTH released by nerve fibers
Target organs: stomach (parietal cells), small intestine, ileocecal valve, large intestine
Activity:
-increases HCL secretion
-stimulated gastric emptying (minor effect)
-stimulates contraction of intestinal muscle
-relaxes ileocecal valve
-stimulate mass movements
Histamine
Site of production: stomach mucosa
Stimulus of production: food in stomach
Target organ: stomach
Activity: activates parietal cells to release HCl
Intestinal gastrin
Site of production: duodenal mucosa
Stimulus of production: fasting; periodic release ever 1 1/2-2hrs by neural stimulus
Target organ: proximal duodenum
Activity: stimulates migrating motor complex
Secretin
Site of production: stomach mucosa
Stimulus of production: acidic chyme
Target organ: stomach, pancreas, liver
Activity:
-inhibits gastric gland secretion and gastric motility
-increases output of pancreatic juice rich in bicarbonate ions; potentiates CCK’s action
-increases bile output
Serotonin
Site of production: stomach mucosa
Stimulus of production: food in stomach
Target organ: stomach
Activity: causes constriction of stomach muscle
Smooth muscle
■ Along digestive tract:
-has rhythmic cycles of activity
-controlled by pacesetter cells
■ Cells undergo spontaneous depolarization:
-triggering contraction through entire muscular sheet
Somatostatin
Site of production: stomach mucosa; duodenal mucosa
Stimulus for production: food in stomach; stimulation by sympathetic nerve fibers
Target organs: stomach, pancreas, small intestine, gallbladder and liver
Activity:
-inhibits gastric secretion of all products
-inhibits secretion
-inhibits GI blood flow; thus inhibits intestinal absorption
-inhibits contraction of bile release
Vasoactive intestinal peptide (VIP)
Site of production: enteric neurons
Stimulus of production: chyme containing partially digested foods
Target organ: small intestine, pancreas, stomach
Activity:
-stimulates buffer secretion
-increases blood flow through intestinal capillaries
-relaxes intestinal smooth muscle
-increases secretion
-inhibits acid secretion
Pacesetter cells
■ Located in muscularis mucosae and muscularis externa:
-surrounding lumen of digestive tract
Bolus
■ Is a small, oval mass of digestive contents
Peristatic motion
• Circular muscles contract bolus:
■ while circular muscles ahead of bolus relax
• Longitudinal muscles ahead of bolus contract:
■ shortening adjacent segments
• Wave of contraction in circular muscles:
■ forces bolus down
Peristatic waves in stomach: propulsion
Waves move from fundus toward pylorus
Peristatic waves: grinding
Most vigorous waves and mixing action occur close to pylorus
Pyloric end of stomach acts as pump that delivers small amounts of chyme into duodenum
Peristaltic waves: retropulsion
Waves close pyloric valve forcing most of contents of pylorus back ward into stomach
How does the presence of food in small intestines inhibit gastric secretion and motility?
By triggering enterigastruc reflex and secretion of enterogastrones (hormones)
Segmentation
■ Cycles of contraction:
-Churn and fragment bolus
-mix contents with intestinal secretions
■ Does not follow a set pattern:
-does not push materials in any 1 direction
(Like mixing the bread crumbs into the hamburger meat)
Filiform (lingual) papillae
■ Fine projections on superior surface (dorsum) of tongue
■ Roughen the tongue
■ Covered in thick epithelium
■ Assists in moving materials
Filiform (lingual) papillae
■ Fine projections on superior surface (dorsum) of tongue
■ Roughen the tongue
■ Covered in thick epithelium
■ Assists in moving materials
Vallate (circumvallate) papillae
■ In the oropharynx
■ A V-shaped line
■ Rough boundary between body and back of tongue
Alkaline tide
when gastric glands are actively secreting, enough bicarbonate ions diffuse into the bloodstream from the interstitial fluid to increase the pH of the blood significantly.
Histology of esophagus
■ superior 1/3 – all skeletal muscle
■ middle 1/3 - skeletal muscle giving way to smooth muscle
■ inferior 1/3 – all smooth muscle
Liver
Loved organ overlying stomach
Produces bile, which secretes into common hepatic duct
Bile
Made continuously of hepatocytes
Bile salts and secretin stimulate bile production
Contains electrolytes, a variety of fatty substances, bile salts and bile pigments in aqueous form
Bile salts are emulsifying agents, they disperse fats and form water-soluble micelles, which solubilize the products of fat digestion
Gallbladder
Muscular sac that lies beneath the right liver lobe, stores and concentrates bile
Pancrea
Retroperioneal between the spleen and small intestine
Exocrine product: pancreatic juice is carried to duodenum via pancreatic duct
Hepatopancreatic ampulla
Bile duct and pancreatic duct join to form this.
Empty their secretions into duodenum through this
Pancreatic juice
HCO3- rich fluid containing enzymes that digest all categories of foods
Intestinal hormones and vagus nerves control secretions of pancreatic juice
Eructation
Burping
Flatus
Gas in colon
What is the importance of enterohepatic circulation?
Recycling mechanism for retaining bil salts needed for fat absorption
What is the functional difference between pancreatic ancini and islets?
Acini- produce exocribe products of pancreas (digestive enzymes and bicarbonate-rich juice)
Islets- produce pancreatic hormones (insulin, glucagon)
What is the makeup of fouid in the pancreatic duct? In the cystic duct? In the bile duct?
Pancreatic- bicarbonate rich, enzyme reich pancreatic juice
Cystic and bile- bile
What stimulates CCK release and what are its effects on digestive process?
Secreted in response to entry into duodenum if chyme rich in protein and fat. Causes pancreatic acini to secrete digestive enzymes, stimulates the gallbladder to contract and relaxes hepatopancreatic
4 functions of the stomach
- Storage of ingested food
- Mechanical breakdown of ingested food
- Disruption of chemical bonds in food material:
■ by enzymes - Production of intrinsic factor:
■ glycoprotein required for absorption of vitamin B12 in small intestine
Enterohepatic circulation
1) bile salts are secreted into duodenum (1st part of small intestine)
2) as bile salts travel through the small instestine they allow lipid digestion and absorption to occur
3)95% of bile salts are reabsorbed (last part of small intestine)
4) reabsorbed bile salts travel via hepatic portal vein back to liver, where they are recycled. Only 5% of bile salts are newly synthesized each time
Anatomy of stomach
■ The stomach is shaped like an expanded J:
-short lesser curvature forms medial surface
-long greater curvature forms lateral surface
■ Anterior and posterior surfaces are smoothly rounded
■ Shape and size vary:
-from individual to individual
-from 1 meal to the next
■ Can hold up to 4L
■ Stomach typically extends between levels of vertebrae T7 and L3
Gallbladder
Stores bile to help digest fat
Body (corpus)
The portion of
the stomach
into which food passes from the esophagus
Pylorus
portion of the stomach
■ Is divided into:
-The pyloric Antrum - portion that begins to narrow
-The Pyloric canal - narrowest region that gives way to
-the pyloric or gastro-duodenals sphincter which controls emptying
Fundus
Fundus - superior-most, bulbous and globe shaped
Portion of the stomach
Cardia
region between the stomach and esophagus
■ secretes protective mucus
Salivary amylase
Helps digest carbs
Lingual lipase
Helps digest lipids
Serous cells
Watery secretions of oral cavity (electrolytes and enzymes)
Hydrate oral cavity
Mucous cells
Viscous secretions of oral cavity (glycoproteins, mucins)
Lubricate food and dissolve food substances so taste buds can detect
Extrinsic salivary glands
-Outside oral cavity
-Have ducts to transport saliva into the oral cavity
-Secrete on stimulus:
o mechanoreceptors (chewing reflexes)
o chemoreceptors (stimulated by acidic substances)
-Produce 90% of total saliva
Glands:
o 2 parotid glands
o 2 submandibular glands
o 2 sublingual gland
Histology: serous and mucous
Intrinsic salivary glands
-Inside oral cavity
-No ducts
-Constantly secreting saliva
-Produce 10% of total saliva
o Buccal glands
o Labial glands
o Palatine glands, …
Histology: mainly mucous
Parotid gland
Duct:
o Parotid duct, Stensen duct
o Pierces muscles
o Empties into the oral cavity at the level of 2nd maxillary/upper molar
Histology:
o Mainly serous cells
Submandibular gland
Duct:
o Submandibular duct, Warthon’s duct
o Empties into the oral cavity near the lingual frenulum
Histology:
o Mixed serous and mucous cells
Sublinguial gland
Duct:
o Ducts of Rivinus,
o 10-20 ducts empty into the floor of the oral cavity
Histology:
o Mainly mucous cells
Stimuli for salivation
-chemoreceptors: react to acidic
-mechanoreceptors: react to chewing
-other stimuli: seeing, smelling, thinking of food
-➡️➕ superior and inferior salivary nucleus
-➡️activates motor fibers to send ➕for salivation
Mucosal barrier
The mucosal barrier prevents the corrosion of the stomach
-The defects in this barrier contribute to the erosions that may happen as in peptic ulcer diseases
(i) Mucous cells
-The mucous cells in the stomach secrete molecules that form the mucosal barrier. The cells include:
o Foveolar cells
o Mucous neck cells
(ii) Secretory molecules
The barrier is made up of:
o Water (95%)
o Electrolytes
-Sodium
-Potassium
o Phospholipids
o Mucin proteins
-Forms the thick mucosal barrier
o Bicarbonate
Cephalic phase accounts for _ of gastric secretion
1/3
Gastric phase account for _ of gastric secretion
2/3
Gastrin is secreted into blood by
G Cells in response to partially digested proteins
Effect of gastrin binding to parietal cell
Active H+/K+ pump: H+ leaves cell➡️⬇️pH
Effect of gastrin or ACh or secretin or histamine binding to chief cell
Release of pepsinogen via exocytosis
Pepsinogen➡️pepsin under what conditions
1.8-3.5 pH in the blood plasma
Alkaline tide
The sudden influx of bicarbonate ions during creation of hydrochloric acid by the parietal cells
refers to a condition, normally encountered after eating a meal, parietal cells also secrete bicarbonate ions across their basolateral membranes and into the interstitial fluid causing an increase in pH.
Antral D cells are ➕by
⬆️H+ in the blood
-releases somatostatin when ➖pepsin and HCl secretion
PNS acting on Antral D cells
-ACh (PNS) ➖D cells from releasing somatostatin
-⬆️pepsin and HCl secretion
PNS acting on G cells
Via ACh- ⬆️pepsin and HCl secretion
Gastrin and ACh act on the Antral D cells to
➖ the release of somatostatin
ACh acting on chief cell
➕pepsinogen release
ACh and gastrin acts on parietal cells
➕H+/K+ pump
Histamine acts on parietal cells
➕HCl secretion
Prostaglandin acts on partietal cells
➖HCl secretion
ACh/ gastrin acting on enterochromaffin like cells (ECL)
➕histamine release
Somatostatin acting on ECL
➖ release of histamine
Contents of chyme
-glucose
-H+
-partially digested proteins (peptones)
-fatty acid
Parietal cells
Secrete HCl and intrinsic factor (important in absorbing vit B12)
pH level for irreversible inactivation of pepsinogen
7.2
Secretin function in the stomach
➖gastrin secretion
o Secretin travels through the blood vessels reaching the antral G-cells of the stomach → bind to the receptors on the G-cells → inhibit the G-cells → the
release of gastrin will be inhibited → hydrochloric acid secretion will be inhibited
Secretin function in the liver
➕ liver to make bile
Travels to the liver
-➡️binds➡️➕hepatocytes to convert cholesterol ➡️ bile acids (main component of bile that helps emulsify fats)
-➡️⬆️bile synthesis➡️⬆️[bile acids]
-➡️bile drains into common hepatic duct
-➡️passes through common hepatic duct which joins cystic duct of gallbladder forming common bile duct
-➡️common bile duct fuses w/ main pancreatic duct forming hepatopancreatic ampulla
-➡️hepatopancreatic sphincter (wraps around ampulla) relaxes to release bile into duodenum
-bile reacts w/ fatty acids to emulsify it
Bile contents
-bile acids and salts
-phospholipids
-cholesterol
-pigments
-H2O
-electrolyte chemicals
Common bile duct
Common hepatic duct (liver) + cystic duct (gallbladder)
Hepatopancreatic ampulla
Common bile duct + main pancreatic duct
Hepatopancreatic sphincter
-wraps around ampulla
-relaxes to release bile into duodenum
Secretin function in the pancreas
Responds to acidic chyme
➕Ductal epithelial cells to make HCO3-
-binds to receptor on acinar ductal epithelial cells
-➡️➕release of HCO3-
-➡️react w/ H+ to neutralize it
CCK
Released by I cells
-➕by ⬆️ concentrations of:
1) fatty acids (fatty chyme)
2) peptones
3) oligosaccharides (hyperosmolar chyme)
Functions of CCK in the stomach
➖release of HCl
Importance: duodenum is filled w/ partially digested substances➡️ so slowing acid secretion slows down the emptying of stomach
-⬆️[H+] in chyme can also damage duodenal lining
-CCK reaches parietal cells
-➡️➖H+/K+ pump
-➡️➖ release of HCl
Lesser omentum
-stabilizes portion of stomach
-provides access route for blood vessels and other structures entering or leaving the liver
Function of CCK in the liver
Accentuates action of secretin
-binds➡️⬆️bile synthesis➡️⬆️[bile acids]➡️bile acids react w/ fatty acids and emulsify it ➡️helps in digestion and fat absorption
Falciform ligament
-help stabilize liver:
-attach it to diaphragm and abdominal wall
Gallbladder function
Helps in concentrating bile by getting rid of a lot of H2O and electrolytes
CCK function in the gallbladder
Causes gallbladder contractions and relaxes hepatopancreatic sphincter
-binds➡️gallbladder contracts➡️squeeze out concentrated bile➡️CCK binds to receptors on hepatopancreatic sphincter and relaxes it➡️bile released into duodenal mucosa
Acinar cells of the pancreas are concentrated w/
Granules rich in digestive enzymes
1)pancreatic proteases- helps in digestion and absorption of proteins
2)pancreatic amylase- helps in digestion and absorption of oligosaccharides and polysaccharides
3) pancreatic lipase- helps in digestion and absorption of fatty acids
4) pancreatic nuclease
CCK function in pancreas
Binds to receptors on acinar cells and ➕ fusion of vescicles w/ cell membrane
-release substances (enzymes) via exocytosis
-enzymes are precursors, which means they are inactive and need to undergo certain chemical reactions in duodenum to be activated
-importance: active form can react w/ epithelial cells of pancreas, digesting it➡️ pancreatitis
Greater omentum
Formed when dorsal mesentery enlarges
-extends inferiority between:
-body wall
-anterior surface of small intestine
-hangs like an apron
-form connection between ventral surface of stomach and large intestine
Peptide YY and neurotensin chemical
Released by different types of endocrine cells
-endocrine cells ➕ by stretch
-⬆️chyme in intestine➡️ did tension of wall➡️➕different endocrine cells➡️ release peptide YY and neurotensin➡️ move through blood➡️bind to parietal cells➡️➖ H+/K+ pump➡️⬇️HCl production
Importance: prevents ⬆️⬆️⬆️ release of acidic chyme into duodenum
Gastric inhibitory peptide (GIP)
Released by K cells which respond to ⬆️[oligosaccharides/polysaccharides] and ⬆️[fats]
GIP functions in the stomach
➖gastric secretion and ➖chyme from entering duodenum
-binds to parietal cells➡️➖ release of HCl
GIP function in pancreas
➕insulin release
-islets of langerhans contains receptors that are sensitive to glucose
-➕ release of insulin
-insulin (⬇️ blood glucose levels)
-released during fed state
-importance ⬆️glucose and AA uptake➡️⬆️glycogenesis (glucose➡️glycogen), lipogenesis, and protein synthesis
Islets of langerhans
Groups of pancreatic cells secreting insulin and glucagon
Greater omentum tissue type
Adipose
-pads and protects surfaces of abdomen
-provides insulation to reduce heat loss
-stores lipid energy source
-contains many lymph nodes- site of peritoneal immune response
Parietal cells largest ➕
ACh➡️➕HCl secretion
ACh function in pancreas
Binds to beta cells➡️➕release of insulin
Relaxes hepatopancreatic sphincter by binding to receptor
ACh function in gallbladder
Binds to gallbladder➡️help gallbladder contractions
Effects of chemoreceptors detecting ⬆️[H+]
⬇️HCl secretion
APs act on pyloric sphincter- contracts➡️prevents chyme from being release
Mesentery proper
-thick mesenterial sheet
-helps in storing fats, and allowing blood vessels, lymphatics, and nerves to supply intestines
-fuses w/ posterior abdominal wall
Layers of mucosal barrier
1) mucosal gel layer
-location: top
-H2O (95%)
-Na+
-K+
-phospholipids
-mucin proteins
-⬆️viscosity and forms thick mucosal barrier
-prevents H+ from damaging epithelial layer
2)HCO3-
-location: bottom; right above mucosal cells
-if ⬆️pepsin secretion and tries to move through gel layer, HCO3- will ➖ pepsin and turns it into pepsinogen
-if H+ penetrate through gel layer➡️combine w/ HCO3-➡️H2CO3➡️CO2 (burping gas) and H2O
Layer of intestinal wall Contains neurons that control glandular secretion
Submucosal plexus
Tissue type of oral cavity, pharynx, and esophagus
Stratified squamous- mechanical stresses
Tissue type of stomach, small intestine and most of large intestine
Simple columnar w/ goblet cells- absorption
Myenteric plexus of ENS
Coordinated movements of muscularis externa
location: between inner circular and outer longitudinal layers
Enteroendocrine cells
Location: scattered among columnar cells- where absorption takes place
Secretes hormones that coordinate activities of GIT and accessory gland
Absorption
In digestion, absorption is the process of moving nutrients, water, and electrolytes from the small intestine into the bloodstream and then to the body’s cells
Lamina propria
Layer of areolar tissue that contains:
1) blood vessels
2) sensory nerve endings
3) lymphatic vessels
4) smooth muscle cells
5) scattered lymphoid tissue
PNS ➕ all GI activity except of
Contraction of sphincters (SNS)
During peristalsis, the circular muscles contract_ to the bolus
Proximal
Goblet cells
-mucosa layer
-simple columnar
-secrete mucous
Muscularis mucosal
Moves mucosa- movement alters mucosal folds and move the villi to aid digestion and absorption
Myenteric plexus
Network of intrinsic neurons
-location: between smooth muscle layers
-interconnected w/ submucosal plexus
ENS
Submucosal plexus + Myenteric plexus
Serosa
Serous membrane covering external surface of GIT
-location: inside peritoneal cavity
-reduces friction
Muscles and tissue of esophagus
Muscle:
Upper 1/3: striated
Middle 1/3: striated and smooth
Lower 1/3: smooth
Stratified squamous
Rugae
Folds in stomach that flatten w/ distention
Muscles of stomach
Thin in fundus and body➡️ weak contractions
⬆️muscle thickness in pyloric region➡️strong contraction (important for mixing ingested food w/ gastric juice and emptying chyme into small intestine)
Small intestine
Most digestion and absorption (90% of nutrient absorption)
-juices in S. Intestine neutralize acidic chyme, restore osmolality, and continue digestion of macromolecules
-breakdown products of macromolecules are absorbed across epithelium into blood or lymph nodes
Most absorption takes place in
Jejunum
-# of fold (pilcae(permanent)) ⬆️ in jejunum➡️⬆️absorptive SA
-covered by villi (also ⬆️absorptive SA-longest in jejunum)
Large intestine
Absorbs H2O and electrolytes from chyme
Teniae coli
Smooth longitudinal muscles of colon
Haustra
Small pouches caused by sacculation; gives colon segmented appearance
Tissue type of distal anal canal
Stratified squamous
USE
Thick circular muscle @ superior end of esophagus
-skeletal muscle
-when constricted prevents air from entering esophagus
LES
@ gastroesophageal junction
-no thickened circular muscle
-prevents reflux of gastric contents into esophagus
Pyloric sphincter
Controls rate of gastric emptying
Ileocecal sphincter
Separates terminal ileum from cecum
-distension of terminal ileum opens sphincter to permit flow of chyme into L intestine
-distension of colon: closes sphincter preventing reflux into ileum
Anal sphincters
1)internal- circular smooth muscle- involuntarily
2)external- skeletal muscle-voluntary
Both relaxes➡️ deification
Liver
Produce bile
-produced continuously by hepatocytes and is stored and concentrated in gallbladder
Bile function
Digestion and absorption of fats
Pancreas
Produces digestive juice (contains enzymes to digest all major foodstuffs, and HCO3- to neutralize chyme from stomach)
Esophageal hiatus
Where esophagus pierces diaphragm
Hiatal hernia
When part of stomach protrudes through esophageal hiatus
Functions of the tongue
1) manipulation of food
2) mechanical breakdown
3) sensory analysis of food
4) enzyme secretion
Cephalic phase
➕salivation of gastric juice and gastric contractions- mediated by CN 10
1)sight
2)smell
3)taste
4)thought
Gastric phase
Food in stomach
-production of gastric secretion➡️⬆️gastric motility
Intestinal phase
Food in intestine
-secretion of HCO3-, digestive enzymes and bile begin segmenting contraction in S. Intestine
Characteristics of GI hormones
1) peptides
2) individual enteroendocrine cells in mucosa secrete GI hormones
3) enter circulatory system, not GIT- transported to liver and ❤️ before retuning the GIT to act
Gastrin
-➕HCl secretion in stomach and growth of gastric colonic mucosae
-secreted by G cells
CCK
-secreted by I cells in duodenum and jejunum
-➕gallbladder contraction➡️ bile moves into S intestine
-➕pancreas to release digestive enzymes into S intestine
-➕growth of pancreas and mucosa of gallbladder
-➖gastric emptying
Secretin
-secreted by S cells in duodenum
-➕liver and pancreas to secrete HCO3- into S intestine➡️⬇️acidity
-➕growth of pancreas
-➖gastric acid secretion
GIP
-secreted by cells of duodenum and jejunum
-in presence of glucose, ➕secretion of insulin by pancreas
Motilin
-secreted by cells of duodenum and jejunum (every 90min during fasting)
-➕ of migrating motility complex(contents of S intestine swept toward terminal ileum)
-released when chyme enters small intestines
During buccal phase of swallowing, what structure is elevated to block contents of cavity from entering nasopharynx?
Soft palate
2 types of secretory cells in gastric glands
1)parietal cells
2)chief cells
Mesentery
Connects intestines to posterior abdominal wall
Enterokinase
Brush border enzyme that intiates digestion process in intestines by converting trypsinogen➡️trypsin(breaks down protein)
Sucrase
Sucrose➡️ glucose and fructose
Maltase
Maltose➡️2 glucose
Lactase
Lactose➡️glucose and galactose
Pancreas location
Behind stomach and infront of spine
Crypt of lieberkühn
Intestinal gland found in between epithelial lining of small and large intestine
Functions of pancreas
1) endocrine cells
-of pancreatic islets (of langerhans)
-secrete insulin and glucagon into bloodstream
2) exocrine cells
-acinar cells
-epithelial cells of duct system
-produce enzymes that help digest food
Hepatocytes functions
Metabolic regulation
1) blood reservoir/composition of circulating blood
2)nutrient metabolism
3) waste product removal
4)nutrient storage
5) drug inactivation
6) produce bile
Hematological regulation:
7) produce enzymes and plasma proteins
8) detoxification of blood
9) removal of antibodies and circulating hormones
Blood leaves liver via
Hepatic veins (open into inferior vena cava)
Liver lobules
Basic functional units of liver
-each lobe is divided by connective tissue (interlobular septum)
Glands of L intestine
-dominated by goblet cells(lubricate fecal matter)
-does not produce enzymes
Enterohepatic circulation
Circulation of bile salts:
1)enter duodenum
2)travel through small intestine
3) reabsorbed in terminal ileum
4) return to liver in hepatic portal blood
Absorption in large intestine
Reabsorption of H2O and H2CO3 and electrolytes
Reabsorption of bile salts:
-in cecum
-transported in blood to liver
Absorption of vitamins (vitamin D and K) produced by bacteria
Absorption of organic wastes
Deification reflex
1)➕stretch receptors
2) short reflex: ➕of Myenteric plexus in sigmoid colon and rectum
2a)➕PNS motor neurons in sacral spinal cord
2b)➕somatic motor neurons
3) short reflex: ⬆️local peristalsis
4)relaxation of internal analsphincter➡️feces move into anal canal
5) contraction of external anal sphincter
6) voluntary relaxation of external sphincter ➡️deification
W/o CCK
■ Hepatopancreatic sphincter remains closed
■ Bile exiting liver in common hepatic duct cannot flow through common bile duct into duodenum
■ Bile enters cystic duct:
■ is stored in gallbladder
Amylase is denatured by
Acid in stomach
Where is pepsin active?
Stomach
Denatures when entering duodenum
