digestive

Question 1

Digestive system process

Answer 1

ingestion
digestion (mechanical and chemical)
absorption
secretion (into lumen, paracrine signaling, into blood (hormones))
motility (mixing and propulsion)
excretion
defense mechanisms
regulation - hormones and ANS

Question 2

Digestive system= 2 groups of organs

Answer 2

1. Alimentary canal (GI tract)
   - mouth to anus
   - digests food and absorbs fragments
   - mouth, pharynx, esophagus, stomach, small intestine, and large intestine
2. Accessory digestive organs
   - teeth, tongue, gallbladder
   - digestive glands : salivary glands, liver, gallbladder, pancreas

Question 3

Digestion (2 kinds) and objective

Answer 3

Mechanical: chewing, mixing, segmentation

Chemical - enzymes

• carbs, prots, lipids, nucleic acids
• dif enzymes are active in dif organs

Objective: breakdown of foodstuffs into smaller pieces that the cell can use

Question 4

Absorption

Answer 4

movement of substances from lumen, across intestinal epithelium, into blood or lymph

can be active or passive

Question 5

Secretion

Answer 5

release of substances from glandular epithelium of digestive tract and accessory organs into the lumen

release of hormones into the blood that affect target cells that regulate digestive functions

release of paracrines for local control

Question 6

Motility

Answer 6

movement as a result of contraction of smooth muscle in walls of digestive organs

• segmental = mixing
• propulsion = peristalsis = forms bolus

mechanical digestion

Question 7

Defense mechanisms

Answer 7

• Important bc it’s open to outside world –> mucus membrane
• mucus is secreted by epithelium
• enzymes (lysozymes)
• acidity of stomach
• Lymphoid tissue (MALT) = collections of lymphocytes along digestive tract

Question 8

Excretion

Answer 8

removal of wastes, unabsorbed and undigested products via defecation in form of feces

Question 9

GI Regulation: mechanoreceptors and chemoreceptors

Answer 9

-Respond to stretch, changes in osmolarity and pH, and presence of substrate and end product of digestion

• initial reflexes that either
  1. activate/inhibit digestive glands or
  2. stimulate smooth muscle to mix and move lumen contents

Question 10

GI regulation: intrinsic and extrinsic controls

Answer 10

Short refleces = enteric nerve plexuses (gut brain) respond to stimuli in GI tract

Long relexes = respond to stimuli inside or outside GI tract –> involve CNS centers and autonomic nerves

Hormones from cells in stomach and small intestine stimulate target cells in same or dif organs to secrete or contract

Question 11

Peritoneum and peritoneal cavity

Answer 11

Peritoneum = serous membrane of abdominal cavity

• visceral peritoneum on external surface of most digestive organs
• parietal peritoneum lines body wall

Peritoneal cavity

• bt two peritoneums
• fluid lubricates mobile organs

Mesentery = double layer of peritoneum

• routes for blood vessels, lymphatics, and nerves
• holds organs in place and stores fat

retroperitoneal organs are posterior to peritoneum

Intraperitoneal organs ARE surrounded by peritoneum

Question 12

Blood supply: splanchnic circulation

Answer 12

Branches of aorta serving digestive organs

• hepatic/splenic/left gastric arteries
• inferior/superior mesenteric arteries

Hepatic portal circulation

• drains nutrient-rich blood from digestive organs
• delivers it to the liver for processing

Question 13

Histology of alimentary canal

Answer 13

4 layers/tunics

Mucosa
submucosa
muscularis externa
serosa

Question 14

Mucosa (func and layers)

Answer 14

lines the lumen

Functions: dif layers perform 1 or all 3

• secretes mucus, digestive enzymes, and hormones
• abdorbs end products of digestion
• protects against infectious disease

3 sublayers: epithelium, lamina propria, and muscularis mucosae

Question 15

Mucosa epithelium

Answer 15

simple columnar epithelium and mucus secreting cells (most of the tract)
-mucus protects digestive organs from enzymes and eases food passage

may secrete enzymes and hormones (e.g. stomach and small intestine)

Question 16

Mucosa: lamina propria and muscularis mucosae

Answer 16

Loose areolar CT

• capillaries for nourishment and absorption
• lymphoid follicles (part of MALT) –> defend against microorganisms

Muscularis mucosae = smooth muscle –> local movements of mucosa

Question 17

submucosa

Answer 17

areolar CT

• blood and lymphatic vessels
• lymphoid follicles
• submucosal nerve plexus

Question 18

Muscularis externa

Answer 18

• responsible for segmentation and peristalsis
• inner circular and outer longitudinal layers
• circular layer thickens in some areas –> sphincters
• myenteric nerve plexus b/t two muscle layers

Question 19

Serosa: (tissue and func)

Answer 19

Visceral peritoneum

• areolar CT covered with mesothelium in most organs
• replaced by fibrous adventitia in esophagus
• retroperitoneal organs have both an adventitia and serosa

Func

• secrete fluid - decrease friction
• part of peritoneum –> binds organs to surrounding structures and body wall (visceral layer, peritoneal cavity, and parietal layer)
• extensions provide support to abdominal organs, blood vessels, nerves

Question 20

Folds of serosa

Answer 20

Lesser omentum = bt stomach and liver
Falciform ligament = attach liver to abdominal wall
greater omentum = extends below stomach
mesentery proper = small intestine and pancreas to posterior wall
mesocolon = large intestine to posterior wall (also transverse and sigmoid mesocolon)

Question 21

Enteric NS
definition
what it supplies
plexuses
how it's linked to NS

Answer 21

• Intrinsic nerve supply of alimentary canal –> enteric neurons (more than spinal cord)
• major nerve supply to GI tract wall: control motility and secretions
• submucosal nerve plexus regulates glands and smooth muscle in mucosa
• myenteric nerve plexus controls GI tract motility

Linked to CNS via afferent visceral fibers
Long ANS fibers synapse with enteric plexus
-sympathetic impulses inhibit digestive activities
-parasympathetic impulses stimulate digestive activities

Question 22

Mouth

Answer 22

oral (buccal) cavity

• bounded by lips, cheek, palate (hard and soft), and tongue
• oral orifice is anerior opening
• lined with stratified squamous epithelium
• begins posterior to teeth

Question 23

Lips and cheeks

Answer 23

• contain orbicularis oris and buccinator muscles
• oral vestibule = recess internal to lips (labia) and cheeks, external to teeth and gums
• oral cavity proper lies within teeth and gums
• labial frenulum = medun attachment of each lip to gum

Question 24

Palate

Answer 24

Hard palate = palatine bones and palatine processes of maxillae
-slightly corrugated to help create friction against tongue

Soft palate = fold fomed mosly of skeletal muscle

• closes of nasopharynx during swallowing
• uvula projects downward from its free edge

Question 25

tongue

Answer 25

skeletal muscle Func: -repositioning and mixing food during chewing -form bolus initiate swallowing, speech, and taste intrinsic muscles change shape of tongue extrinsic muscles alter tongues position Lingual frenulum = attachment to floor of mouth Lingual lipase - secreted by serous cells beneath foliate and vallate papillae - fat-digesting enzyme functional in stomach --> must be activated by acid in stomach

Question 26

Salivary glands

Answer 26

Major salivary glands: - produce saliva and lie outside oral cavity - parotid, submandibular, and sublingual Minor salivary glands -scattered thoughout oral cavity --> augment slightly

Question 27

Functions of saliva

Answer 27

cleanse mouth dissolve food chems for taste moistens food --> compacts into bolus begins breakdown of starch with enzymes

Question 28

Submandibular gland and Sublingual gland

Answer 28

Submandibular - medial to body of mandible - duct opens at base of lingual frenulum - secretes mixture of enzyme and mucous saliva Sublingual gland - anterior to submandibular gland uner tongue - opens via 10-12 ducts into floor of mouth - secretes a more mucous rich saliva

Question 29

Parotid gland

Answer 29

- anterior to ear --> external to masseter muscle - parotid duct opens into oral vestibule next to second upper molar - mumps is inflammation of parotid glands - secretes a more watery, enzyme rich saliva

Question 30

Composition of saliva

Answer 30

97-99.5% water; slightly acidic - electrolytes = Na, K, Cl, PO4, HCO - salivary amylase and lingual lipase - mucin - metabolic wastes: urea and uric acid - lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms

Question 31

control of saliva

Answer 31

1500 ml/day -intrinsic glands continuously keep mouth moist major salivary glands activated by parasympathetic nervous system when: - ingested food stimulates chemoreceptors and mechanoreceptors in mouth - salivatory nuclei in brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)

Question 32

Digestive processes that happen in the mouth

Answer 32

``` ingestion mechanical breakdown (chewing) propulsion (deglutition = swallowing) digestion (salivary amylase and lingual lipase) NO ABSORPTION (except for a few drugs) ```

Question 33

Pharynx

Answer 33

food passes from moth to oropharynx to laryngopharynx - allows passage of foods, fluids, and air - stratified squamous epithelium lining; mucus producing glands - skeletal muscle layers: inner longitudinal and outer pharyngeal constrictors ``` Oropharynx = digestive and respiratory func Laryngopharynx = digestive and respiratory func Nasopharynx = just respiratory; no digestion ```

Question 34

Esophagus

Answer 34

Secretes mucus, transports food --> no enzymes and no absorption Mucosa = protection against wear and tear: stratified squamous epithelium Submucosa secretes mucous Muscularis divided in thirds - Superior 1/3 = skeletal muscle - Middle 1/3 = skeletal and smooth muscle - Inferior 1/3 = smooth muscle - 2 sphyncters = upper esophageal (regulates movement into esophagus) and lower esophageal (regulates movement into stomach) Adventitia - no serosa - attaches to surroundings

Question 35

Deglutition

Answer 35

involves tongue, soft palate, pharynx, and esophagus - requires coordination of 22 muscle groups - Buccal phase = voluntary contraction of tongue - Pharyngeal-esophageal phase = involuntary (primary vagus erve) --> control center in medulla and lower pons

Question 36

Actual steps of deglutition

Answer 36

1. buccal phase: UES is contracted and tongue presses against hard palate, forcing food bolus into oropharynx 2. pharyngeal-esophageal phase starts as uvula and larynx rise to prevent food from entering respiratory passageways--> tongue blocks moth and UES relaxes to let food into esophagus 3. constrictor muscles of pharynx contract, forcing food through esophagus --> UES contracts after food has entered 4. peristalsis moves food through esophagus to stomach 5. LES, surrounding cardinal oriface opens and food enters stomach