Digestive Tract And Accessory Organs Flashcards
The mouth is
A stratified squamous epithelial mucosa-lined cavity for ingestion
The lips & cheeks are
skeletal muscle covered by skin that help to keep food between teeth when we chew
The palate forms
The roof of the mouth
Palate that aids in manipulation of food
Hard palate
Palate that rises during swallowing to close the nasopharynx
Soft palate
The tongue
- is made of skeletal muscle
- Repositions and mixes food with saliva, initiates swallowing, & aids in speech production
Taste buds are housed in
The papillae on the tongue surface
Cells types that make up the minor and major salivary glands
◦ Serous cells – produce a watery secretion (enzymes, ions, mucin)
◦ Mucous cells – produce mucus
Along with water saliva contains
◦ Electrolytes
◦ Salivary amylase & lingual lipase, mucins, lysozyme
◦ Antibodies
◦ Small amount of metabolic waste
Mastication
begins the mechanical breakdown of food & mixes food with saliva
The 20 teeth that are lost to make way for the permanent dentition are
Primary dentition (deciduous or baby teeth)
The 32 teeth, including wisdom teeth (third molars)
Permanent dentition
Incisors are used for
Cutting
Canines (cuspids) are used to
tear or pierce
Premolars (bicuspids) & molars (tricuspids) are used for
grinding
3 regions of the tooth are
◦ Enamel-covered crown
◦ Neck surrounded by gingiva (gums)
◦ Root embedded in the jawbone
Cement is
The calcified connective tissue that anchors the root to the periodontal ligaments
◦ Holds tooth in the bony socket of the jaw
Dentin is
A bone-like material that underlies the enamel & surrounds the pulp cavity (which contains blood & nerve supply)
The Oropharynx & laryngopharynx provide a
common passageway for food, fluids, & air
Food is propelled into the esophagus by
Muscular contraction within the walls
The Esophagus provides a passageway for food & fluids from
the laryngopharynx to the stomach, where it joins at the cardiac orifice
The Esophagus provides a passageway for food & fluids from
The laryngopharynx to the stomach, where it joins at the cardiac orifice
Keeps the cardiac orifice closed when food is not being swallowed
Gastroesophageal (cardiac) sphincter
2 major phases of deglutition (swallowing):
- Buccal phase – voluntary
◦ Occurs in mouth – bolus of food is
forced into oropharynx by tongue - Pharyngeal-esophageal phase – involuntary
◦ Food is squeezed through pharynx &
into esophagus
◦ Controlled by swallowing centre of
medulla & pons
Bolus being churned is
Mechanical breakdown via extra oblique layer of smooth muscle in stomach
Hydrolysis of the churned food begins
Protein digestion (via pepsin) which turns food into chyme
Folds in the stomach that wall allow stomach to expand
◦ Empty stomach – volume of ~50 ml
◦ Full capacity – 4 L Major regions include:
◦ Cardia, fundus, body, & pylorus
Rugae
Stomach’s surface epithelium of mucosa is composed of
simple columnar epithelium
◦ Surface mucous cells – produce a protective coat of alkaline mucus
Columns of secretory cells that produce gastric juice are found in
Gastric pits which extend to gastric glands
Mucous neck cells secrete
Mucus
Parietal cells secrete
- HCL to activate pepsin which denatures proteins
- intrinsic factor of glycoprotein which is required for absorption of vitamin B12 in small intestine
Chief cells secrete
◦ Pepsinogen – the inactive form of pepsin (hydrolyzes proteins in positive feedback mechanism)
◦ Gastric lipase – hydrolyzes a small portion of lipids (~15%)
G cells secrete
enteroendocrine cells that secrete gastrin
◦ Stimulates gastric secretions &
promotes movement of food along the GI tract (facilitates digestion)
H and Cl ions are secreted
Separately so they can later be assembled into HCL
Protons (H+) are secreted into stomach lumen by
proton pumps (H+-K+ ATPase powered by ATP)
Chloride ions (Cl-) move into parietal cells
via Cl-/HCO3- antiporters & diffuse into stomach lumen through Cl- channels
◦ Resulting increase in bicarbonate (HCO3-) in blood leaving the stomach – alkaline tide
In the stomach HCL secretion is stimulated by
◦ Acetylcholine (ACh) – released from parasympathetic neurons
◦ Gastrin – produced by G cells
Histamine, a paracrine released from mast cells in lamina propria enhances the effects of
ACh & gastrin
First cephalic (reflex) phase is triggered by
Aroma, taste, sight, or thought
◦preparatory phase
◦↑ saliva secretion & gastric gland acuity
The second Gastric phase is triggered by
Stretch & chemical stimuli
◦ Neural & hormonal mechanisms ↑gastric secretion & motility
The third Intestinal phase is
The distention of duodenum to inhibit gastric motility & emptying
◦ Neural & hormonal factors slow exit of chyme &
enhance digestion of food in small intestine
The liver is
The largest gland in the body (~3 lbs) – our only internal organ that can regenerate
The liver is composed of
Four lobes of lobules, made of plates hepatocytes (liver cells)
hepatocytes (liver cells)
◦ Secrete bile
◦ Process blood-borne nutrients, store fat-soluble vitamins
◦ Play important roles in detoxification
Hepatocytes surround a central vein that drain
hepatic sinusoids (highly permeable capillaries)
The portal triad is composed of
- the Branch of hepatic artery
- the Branch of hepatic portal vein
- the Bile duct
Supplies hepatocytes with oxygen-rich blood
- O2 to the liver
The Branch of the hepatic artery
Carries venous blood rich in nutrients from the intestines
• O2 deficient blood goes through liver
• Filters out glucose/nutrient to store
Branch of the hepatic portal vein
Attached to bile canaliculi
The bile duct
Function of the gallbladder
Stores & concentrates bile that is not needed immediately for digestion
- stored until lipid rich food is consumed
Bile is both a
◦Digestive secretion which functions in emulsification & absorption
of lipids by bile salts
◦Excretory product – bilirubin (pigment; derived
from heme)
These form when bile salts are insufficient or excessive cholesterol crystalizes
Gallstones
- small clusters of exocrine cells that produce pancreatic juice
- compose 99% of the pancreas
Pancreatic acini
- endocrine tissue
- compose 1% of the pancreas
Pancreatic islets
Pancreatic juice contains:
◦ Mainly water & some salts
◦ Bicarbonate (HCO3-) – helps neutralize acidic chyme
◦ Several enzymes (inactive forms)
Pancreatic proteases digest
proteins into peptides
Enteropeptidase is the brush-border enzyme that
activates
trypsinogen into trypsin (which activates the other proteases)
digests starch
Pancreatic amylase
Primary triglyceride-digesting enzyme
Pancreatic lipase
Digests nucleic acids to nucleotides
◦ Ribonuclease (RNA) & deoxyribonuclease (DNA)
Pancreatic nucleases
Hormones from _______ stimulate secretion of pancreatic juice & bile in response to chyme
small intestine enteroendocrine cells
Cholecystokinin (CCK) – secreted in response to
fats & proteins in chyme
Secretin secreted in response to
acidic chyme
NS that stimulates secretion when stomach is active
Parasympathetic
Stimulate bile secretion
Reabsorbed bile salts returning to liver
Small intestine is
The major site for digestion & absorption
Blood from the intestine drains into the
hepatic portal system, where it is routed to the liver
Duodenum is
The mixing bowl
Jejunum is
Where most nutrient digestion & absorption takes place
Ileum is
Where some absorption (e.g., B12, bile salts) takes place
Allow more time & mixing for nutrient absorption in small intestine
Deep circular folds that force chyme to slowly spiral
Increase SA of the small intestine
Mucosa with finger-like villi & microvilli (absorptive cell plasma membrane folds)
Mucosa of the small intestine is composed mostly of
absorptive cells (absorb & digest nutrients)
Tubular glands in the small intestine that contain several types of secretory cells
Intestinal crypts
Goblet cells of the small intestine
produce mucus
Enteroendocrine cells of the small intestine
produce hormones (e.g., CCK & secretin)
Paneth cells of the small intestine
produce antimicrobial compounds that can destroy invasive bacteria (secretes lysozyme and is capable of phagocytosis)
Stem cells of the small intestine
replace the other cell types (villus epithelium is renewed every 2-4 days)
Intestinal juice is secreted in response to
acidic chyme, containing mostly water & mucus
Intestinal juice with pancreatic juice provides a
Liquid medium to help nutrient absorption
Brush-border enzymes that are present in plasma membrane of the microvilli of absorptive cells
◦Carbohydrate digesting – e.g., sucrase, lactase,
maltase (disaccharides → monosaccharides)
◦Peptidases – peptides → di- & tripeptides, a.a.
◦Nucleotide digesting – nucleosidases &
phosphatases
Following a meal chyme is mixed and propelled through the intestine via
Segmentation & some peristalsis working together
Between meals the remnants are moved toward large intestine in waves via
migrating motor complex (type of peristalsis)
The ileocecal valve is
A one-way valve from the small intestine to the large intestine that relaxes to allow chyme to enter the cecum
The large intestine
Absorbs water & eliminates indigestible food residues as feces
The first part of the large intestine is
The Cecum
The appendix is
A mass of lymphoid tissue & bacterial storehouse capable of recolonizing the gut when necessary
The segments of the colon in order are
ascending, transverse, descending & sigmoid colon
The rectum has 3
valves that stop feces from being passed during flatulence
The last segment of large intestine that opens to the body’s exterior at the anus
Anal canal
A unique feature of the large instestine is the teniae coli which is
three bands of longitudinal smooth muscle in the muscularis layer
A unique feature of the large instestine is the Haustra which are
Pocket-like sacs caused by partial contraction (tone) of teniae coli
Epiploic appendices – fat-filled pouches of visceral peritoneum (unknown function)
A unique feature of the large intestine is Epiploic appendices which are
fat-filled pouches of visceral peritoneum (unknown function)
Movements that aid mechanical digestion & propulsion in the large intestine are
Haustral contractions – slow segmenting movements triggered by stretch (aid water absorption)
Peristalsis – slow, 3-4 contractions/min
Mass peristalsis – slow, powerful waves that drive contents into rectum (activated by food in stomach)
The thick mucosa of the large intestine contains
- intestinal crypts (glands)
- absorptive cells – water, ions, some vitamins
- a large number goblet cells – mucus producing
Functions of the complex community of bacteria & other microorganisms that live in the digestive tract
◦ Ferment some of the indigestible carbohydrates
◦ Synthesize B complex vitamins & vitamin K
◦ Influence behaviour of the immune system
◦ Also help to protect against ingested pathogens &
may affect some diseases
Feces are forced into the rectum by
Mass peristalsis which stretches the rectal wall & initiates the defecation reflex
In defecation contraction of the sigmoid colon & rectum while relaxing the internal anal sphincter is stimulated by
The Parasympathetic NS
In defecation conscious control allows relaxation of the
External anal sphincter
Intra-adominal pressure to assist in defecation is increased via
Valsalva’s manoeuvre
