Ch23 - Digestive System Flashcards
Name the five essential activities in digestive processes
- ingestion - eating
- propulsion and mixing - peristalsis and segmentation
- digestion - Chemical and physical breakdown of polymers
- absorption - the movement of monomers across a cell membrane and into blood
- elimination - defecation
What are the three control mechanisms of digestion
- Receptors - Mechanoreceptors(stretch) and Chemoreceptors (osmolarity and pH
- Extrinsic control (outside the system) - Neural (long reflexes involving the CNS) and Hormonal (Endocrine glands secrete hormones that affect activity)
- Intrinsic Control (inside the system) - Neural (short reflexes of ‘gut brain’ respond to stimuli in GI tract) and Hormonal (enteroendocrine cells stimulate target cells in the same or different digestive organs)
Describe the peritoneum of the abdominal cavity
Parietal layer lines body wall
Visceral layer covers the abdominal organs
The cavity between the parietal and visceral layer is filled with serous fluid that acts as a lubricant
Describe the mesenteries and their function
Extensions of the peritoneal membrane’s
- anchor organs to the body wall
- Carry blood and lymph vessels and nerves fibers
- Store fat
(EXAM) compare/contrast the location of digestive system organs. Intraperitoneal and retroperitoneal
Intraperittoneal - organs are inside the peritoneal cavity (most of the organs within the DS)
Retroperitoneal - organs like posterior to the peritoneum and are embedded in the body wall. The posterior surface is covered by adventitia
Name the two blood supply systems Of the digestive system
Splanchnic circulation - hepatic, splenic, left gastric, mesenteric arteries
Hepatic Portal System - carries blood from DT to the liver for processing of nutrients
Name the four basic layers (tunics) of the digestive tract walls and their main function
- mucosa (inner most) - carries out digestion and absorption
- submucosa (2nd innermost) - supplies mucosa with blood, lymph vessels, nerves.
- Muscularis extrena (2nd outermost) - smooth muscle w/ inner/outer layers, responsible for peristalsis and segmentation (EXAM). Also contains the myenteric nerve plexus ‘gut brain’
- Serosa (outermost) - Visceral peritoneum. Joined to mesenteries and anchor the organs. produces serous fluid. ADVENTITIA covers retroperitoneal organs
Describe the enteric nervous system of the DT
intrinsic nervous system within the digestive tract with 2 nerve plexus
1. submucosal nerve plexus in submucosa regulates glands and smooth muscle in the mucsoa
2. Myenteric nerve plexus in the muscularis externs that controls GI tract motility/contraction
Linked to the CNS via sympathetic (inhibit digestion) and parasympathetic fibers (stimulate digestion)
what does the mucosa in the mouth do
Protection against abrasion and releases defensins when damaged
What does the hard palate in the mouth do
Tongue forces food against this hard structure to assist in forming a bolus
What does the soft palate in the mouth do
Uvula blocks nasopharynx doing swallowing
What is the function of the tongue and the four types of papillae
It moves and mixes food with saliva to form a bolus. Initiate swallowing speech and tasting
4 types of papillae on Tongue are
1. filiform papillae - smallest and not involved in tasting. rough surface
2. fungiform papillae - reddish, scattered. have taste buds
3. circumvallate papillae - V-shaped row in back of tongue. have taste buds
4. foliate papillae - on the lateral aspect of the posterior tongue. have taste buds
Describe the intrinsic and extrinsic salivary glands
intrinsic - (buccal glands) small and scattered in mucosa
extrinsic - large paired glands that empty saliva through ducts (parotids, submandibular, and sublingual)
Describe the composition of saliva
pH 6.75-7.00
mostly water w/ions (Na, K, Cl, PO4)
Salivary amylase (ENZYME)
small amounts of metabolic waste (urea, uric acid)
Describe the function of saliva
cleans mouth, dissolves chemicals, helps moisten and form BOLUS. Contains SALIVARY AMYLASE and releases protection against bacteria (antibody IgA)
3 Types of teeth
Incisors (I) - chisel shaped for cutting
Canines (C) - fanglike teeth that tear or pierce
Premolars (PM), Molars (M) - broad crowns for grinding/crushing
NOTE: 20 deciduous teeth, 32 permanent teeth
What are the dental formulas for teeth
2I, 1C, 2PM, 3M
General structure of teeth (outer to inner)
enamel - dentin - pulp cavity - pulp - root canal
Describe the role of the pharynx in digestion
To skeletal muscle layers contract to move food to the esophagus by peristalsis
Describe the role of the esophagus in digestion
A 10 inch tube connecting the laryngopharynx to stomach
it has 2 sphincters: Upper esophageal (closed except during swallowing) and Gastroesophageal (prevents back flow from stomach)
Describe the structure of the esophagus wall
upper 1/3 is skeletal muscle involved in conscious control (swallowing)
lower 1/3 is smooth muscle involved in unconscious control (peristalsis)
middle 1/3 is a mixture of both
NOTE: Has Advantitia instead of serosa and anchors to surrounding tissues
describe the 2 phases of deglutition (swallowing)
Buccal phase - voluntary control (act of swallowing)
Pharyngeal-esophageal phase - involuntary control - peristalsis of bolus into stomach
histology of stomach walls and 4 types of cells within
The stomach has a third muscularis externa layer - circular, longitudinal and OBLIQUE
Gastric pits and gastric glands release and produce gastric juice
FOUR types of cells:
-Parietal cells - produce intrinsic factor and HCl - activation of pepsinogen
-Cheif cells - produce the inactive enzyme pepsinogen. HCl and pepsinogen form pepsin, which begins protein breakdown
-Enteroendocrine cells - release enteric hormones into blood which regulates gastric activity
-Mucous Neck cells - produce a thin acidic mucus
How does the stomach protect against self digestion
mucosa produces a thick layer of alkaline mucus and the stem cells at entrance to gastric pits undergo rapid mitosis (3-6days)
Pepsinogen is released in its inactive form which prevent self digestion of cells.
homeostatic imbalances in the stomach
Gastritis - inflammation caused by breaches to the mucosal barrier
Gastric ulcers - erosion of the stomach wall by bacteria
Pernicious anemia - caused by lack of intrinsic factor. B12 doesn’t get absorbed (B12 required for Iron absorption)
describe the 3 regulation phases of gastric secretion
- Cephalic phase - thought, smell and taste of food triggers the long reflex and increases secretion of cells
- Gastric phase - food entering stomach triggers neural long&short reflexes and hormonal controls via DISTENSION (stretching of stomach walls) and CHEMICAL STIMULI (presence of protein, pH, caffeine)
- Intestinal phase (INHIBITORY) - enteroastric reflex allows time for chyme to be processed in the small intestine before more is released from the stomach
Gastric motility mechanisms - how the stomach stretches to accommodate food
- receptive relaxation - response to thought/taste of food
- adaptive relaxation - muscles relax in response to stretching as food enters
- plasticity - smooth muscle can be stretched w/o increasing tension (or else vomit would occur)
- Unique Peristalsis - increased intensity towards pylorus and PACEMAKER cells in longitudinal layer set rhythm of contraction (3/min). Intensity depends on the amount of food present
Gastric emptying
usually occurs in 3-4 hours
chyme enter the duodenum and receptors respond to stretch and chemical signals. Enterogastric reflex inhibits gastric secretion and gastric emptying.
Larger volume speeds emptying but fatty or high protein chyme remains in the duodenum for 6 hours which slows emptying. DIET is related to rate of digestion
gross anatomy of the small intestine
majort organ of digestion and absorption
2-4m long from pyloric sphincter to ileocecal valve
three major parts: Duodenum (retroperitoneal), Jejunum, Ileum.
Folds held in place by mesenteries
Duodenum
receives secretions from the liver, gall bladder and pancreas from the HEPATOPANCREATIC AMPULLA at the MAJOR DUODENAL PAPILLA.
Secretions are controlled by the hepatopancreatic sphincter (Sphinter of Oddi)
modifications to the small intestine to accommodate a larger surface area (200 sq. m)
Plicae circulares - circular folds that force the chyme to slowly spiral through allowing time for digestion and absorption
Villi - motile fingerlike extensions that have lacteals and capillaries for absorption
Microvilli - on the villi that form a brush border of enzymes allowing for quicker digestion/breakdown
Mucosa of small intestine
lots of goblet cells, and scattered enteroendocrine cells.
contain INTESTINAL glands (crypts) between the villi that produce intestinal juice (mostly water).
Lamina propria - huge capillary network to absorb nutrients
Brush border enzymes attached to surface aid in digestion of carbs and proteins
the cells involved in producing intestinal juice in the Intestinal glands of the small intestine
- secretory cells - 1-2L/day of alkaline juice
- stem cells - in base of crypts, replace epithelium every 3-6 days
- Paneth cells - secrete antimicrobial agents (defensins and lysozyme)
NOTE: stimulus for release depends on acidity of chyme
Submucosa of small intestine
Has PEYER’S PATCHES (lymphoid tissue)
duodenum has BRUNNER’S GLANDS - produce alkaline mucus
muscularis extern of the small intestine
has two layers of smooth muscle.
Segmentation and peristalsis
NOTE: most of the small intestine is retroperitoneal so it has adventitia instead of serosa
describe the enterogastric reflex (EXAM!!)
a. chyme from stomach contains partially digested carbs and proteins, fats, and has a low pH
b. entrance of chyme triggers a reflex which inhibits release of more chyme from stomach, but it stimulates activity of Small Intestine
c. controls the rate of delivery of chyme so that the small intestine can process it properly
d. low pH must be raised so enzymes can function properly
e. chyme must mix: with bile to EMULSIFY fats, and enzymes to facilitate digestion
