Chapter 37 Health Alt Flashcards
Each end of the esophagus is opened and closed by a sphincter. What are they?
The upper esophageal sphincter prevents air from entering the esophagus during respiration. The lower esophageal sphincter (cardiac sphincter) prevents regurgitation from the stomach and caustic injury to the esophagus.
What digestive processes does the GI tract do?
It carries out these digestive processes:
1. Ingestion of food
2. Propulsion of food and wastes from the mouth to the anus
3. Secretion of mucus, water, and enzymes
4. Mechanical digestion of food particles
5. Chemical digestion of food particles
6. Absorption of digested food
7. Elimination of waste products by defecation
8. Immune and microbial protection against infection
What that mouth do?
The mouth is the site for mastication (chewing) and mixing of food with saliva. There are 32 permanent teeth in the adult mouth, and they are important for speech and mastication.
how many layers does the GI have? & what is controlled by?
Layers
-Mucosa
-Submucosa
-Muscularis
-Serosa or adventitia
Controlled by local and autonomic nervous system stimuli
-Enteric (intramural) plexus
-A network of intrinsic nerves that controls mobility, secretion, sensation, and blood flow is located solely within the GI tract and controlled by local and autonomic nervous system stimuli through theenteric (intramural) plexuslocated in different layers of the gastrointestinal walls
Salivary Glands & what they do
3 glands whihc secrete about 1 L of saliva per day
-Submandibular
-Sublingual
-Parotid
Saliva
-Water with mucus, sodium, bicarbonate, chloride, potassium, and salivary alpha-amylase (carbohydrate digestion)
-Controlled by sympathetic and parasympathetic fibers
Peristalsis
-Coordinated sequential contraction and relaxation of outer longitudinal and inner circular layers of muscles
-Primary and secondary (Peristalsis that immediately follows the oropharyngeal phase of swallowing is calledprimary peristalsis. If a bolus of food becomes stuck in the esophageal lumen,secondary peristalsis—a wave of contraction and relaxation independent of voluntary swallowing—occurs.)
-helps move food down to stomach
Steps that come with Swallowing:
Swallowing is coordinated by the swallowing center in the medulla.
During theoropharyngeal (voluntary) phase, which takes place in less than 1 second, the following steps occur:
1.Food is segmented into a bolus by the tongue and forced posteriorly toward the pharynx.
2.The superior constrictor muscle of the pharynx contracts so the food cannot move into the nasopharynx.
3.Respiration is inhibited, and the epiglottis slides down to prevent the food from entering the larynx and trachea.
Theesophageal (involuntary) phasetakes 5 to 10 seconds and proceeds as follows:
1.The bolus of food enters the esophagus.
2.Waves of relaxation travel the esophagus, preparing for the movement of the bolus.
3.Peristalsis, the sequential waves of muscular contractions that travel down the esophagus, transports the food to the lower esophageal sphincter, which is relaxed at that point. The bolus moves at 2 to 6 cm/sec.
4.The bolus enters the stomach, and the sphincter muscles return to their resting tone.
The Functions of the Stomach:
-Stores food
-Secretes digestive juices
-Mixes food with the juices
-Propels partially digested food (chyme)
Areas in the Stomach
Functional areas
->Fundus
->Body
->Antrum
Boundaries
->Cardiac orifice
->Pyloric sphincter
->Pylorus
-explanation to the boundaries: The lower esophageal sphincter, where food passes through thecardiac orificeat the gastroesophageal junction into the stomach. Thepyloric sphincter, which relaxes as food is propelled through thepylorus (gastroduodenal junction)into the duodenum.
Gastric Motility
-Swallowing
->Causes relaxation (to receive a bolus of food from the esophagus)
->Facilitated by gastrin and cholecystokinin
-Motilin
->Increases peristalsis
-Secretin
->Decreases peristalsis (inhibitory)
-Gastric mixing and emptying
->Retropulsion
->Rate dependent on volume, osmotic pressure, and chemical composition
Stimulations of the Gastric Secretions
Stimulation of gastric secretion
-Eating
-Gastrin
-Paracrine pathways
-Acetylcholine
-Chemicals
->Ethanol, coffee, protein
gastric secretion phases:
-Cephalic phase: stimulated by the thought, smell, and taste of food
-Gastric phase: stimulated by distention of the stomach
-Intestinal phase: stimulated by histamine and digested protein
Gastric Secretions
Stomach secretes:
- gastric juices- including acid
-pepsinogen
-mucus
-enzymes
-hormones
-intrinsic factor (necessary for the intestinal absorption of vitamin B12)
-gastroferrin (facilitates the absorption of iron in the small intestine)
Acid, Pepsin, & Mucus
Acid
->Secreted by parietal cells
->Dissolves food fibers, acts as a bactericide against swallowed microorganisms, and converts pepsinogen to pepsin.
->Acid secretion is stimulated by the vagus nerve, which releases acetylcholine and stimulates the secretion of gastrin; gastrin then stimulates the release of histamine from enterochromaffin cells in the gastric mucosa. Histamine stimulates acid secretion by activating histamine receptors (H2receptors) onacid-secreting parietal cells.
Pepsin
->Secreted by chief cells
->Proteolytic enzyme
->Breaks down protein and forms polypeptides in the stomach
Mucus
->Stimulated by prostaglandins
->Mucosal barrier
->Gastric mucosal blood flow
->Prostaglandins protect the mucosal barrier by stimulating the secretion of mucus and bicarbonate and by inhibiting the secretion of acid.
Small Intestine
Has 3 segments:
-> Duodenum (supplied by gastroduodenal artery)
-> Jejunum (supplied by superior mesenteric artery)
-> Ileum (supplied by superior mesenteric artery)
How they work together:
-The duodenum begins at the pylorus and ends where it joins the jejunum at a suspensory ligament called theTreitz ligament.The end of the jejunum and the beginning of the ileum are not distinguished by an anatomic marker. These structures are not grossly different, but the jejunum has a slightly larger lumen than the ileum. Theileocecal valve, orsphincter, controls the flow of digested material from the ileum into the large intestine and prevents reflux into the small intestine.
Small Intestine is innervated by what ?
Innervated by enteric nerves
->Myenteric (Auerbach) plexus
->Submucosal (Meissner) plexus
-Secretion, motility, pain sensation, and intestinal reflexes (e.g., relaxation of the lower esophageal sphincter) are mediated parasympathetically by the vagus nerve.
-Sympathetic activity inhibits motility and produces vasoconstriction. Intrinsic reflexive activity is mediated by the myenteric (Auerbach) plexus and the submucosal (Meissner) plexus of the enteric nervous system.
Small Intestine: Absorption
Absorption through villi
->Enterocytes
->Microvilli (tiny projections that together form the mucosal surface)
->Brush border
->Lamina propria
->Lacteal
->Crypts of Lieberkühn
-Each villus secretes some of the enzymes necessary for digestion and absorbs nutrients
Intestinal Digestion & Absorption
-Digestion is initiated in the stomach bc of
->Actions of gastric hydrochloric acid and pepsin
-Continues in proximal portion of small intestine by
->Action of pancreatic enzymes, intestinal enzymes, and bile salts
->Carbohydrate breakdown into monosaccharides & disaccharides
->Proteins degraded into amino acids & peptides
->Fats emulsified
-Nutrients absorbed by active transport, diffusion, or facilitated diffusion
Intestinal Motility
-The movements of the small intestine facilitate both digestion and absorption
->Haustral segmentation (Segmentation. Localized rhythmic contractions of circular smooth muscles divide and mix the chyme, enabling it to have contact with digestive enzymes and the absorbent mucosal surface, and then propel it toward the large intestine.)
->Peristalsis (Peristalsis. Waves of contraction along short segments of longitudinal smooth muscle allow time for digestion and absorption. The intestinal villi move with contractions of the muscularis mucosae, a thin layer of muscle separating the mucosa and submucosa, with absorption promoted by the swaying of the villi in the luminal contents.)
-Neural reflexes facilitate motility, digestion, and absorption
->Ileogastric reflex: inhibits gastric motility when the ileum becomes distended. This prevents the continued movement of chyme into an already distended intestine.
->Intestinointestinal reflex: inhibits intestinal motility when one part of the intestine is overdistended. Both of these reflexes require extrinsicinnervation.
->Gastroileal reflex: which is activated by an increase in gastric motility and secretion, stimulates an increase in ileal motility and relaxation of the ileocecal valve. This empties the ileum and prepares it to receive more chyme. The gastroileal reflex is probably regulated by the hormones gastrin and cholecystokinin.
Large Intestine
-Consists of:
->the cecum, appendix, colon (ascending, transverse, descending, sigmoid), rectum, and anal canal.
-Two sphincters control the flow of intestinal contents through the cecum and colon:
->the ileocecal valve, which admits chyme from the ileum to the cecum
->therectosigmoid canal, which controls the movement of wastes from the sigmoid colon into the rectum.
Large Intestine nerve innervation
-Extrinsic parasympathetic innervation occurs through vagus nerve
-Vagal stimulation increases rhythmic contraction of the proximal colon
-Blood supply is derived primarily from branches of the superior and inferior mesenteric arteries
Large Intestine Movement
-Colonic movement primarily segmental
->Fecal mass massaged
->Water absorbed
->Peristaltic movements promote the emptying of the colon
->Gastrocolic reflex
->Causes the fecal mass to pass rapidly into the sigmoid colon and rectum
->Defecation reflex
->Stimulated by the movement of feces into the sigmoid colon and rectum
Immunity & the GI system
-Gut-associated lymphoid tissue (GALT)
->Major role in immune defenses by killing many microorganisms
->Mucosal secretions produce antibodies (IgA)
->Paneth cells produce defensins and other antibiotic peptides and lysozymes important to mucosal immunity
->Peyer patches (collections of lymphocytes, plasma cells, and macrophages) produce immunoglobulin A as a component of the gut-associated lymph tissue in the small intestine
Intestinal Microbiome
-Numbers of bacteria increase from proximal to distal GI tract
->Highest in colon
-Multiple factors affect normal composition of bacterial flora
->Genetics, diet, environmental, drugs
-Alert immune system to protect against infection
-Sterile at birth but it is colonized within a few hour.
-Bacteria in stomach are relatively sparse
->Acid kills ingested pathogens and inhibits bacterial growth
-Low concentration of aerobes in duodenum and jejunum
->Suppressed by bile acid, intestinal motility, and antibodies
