Chp 23 PP Flashcards
Digestive Processes
1) Ingestion
2) Movement of food
3) Digestion
- Mechanical digestion
- Chemical digestion
4) Absorption
5) Defecation
Digestive organs divided into 2 main groups
1) GI (alimentary) tract
2) Accessory structures
- cheeks, teeth, tongue, salivary glands
- liver, gallbladder, pancreas
3 pairs salivary glands
- Parotid glands
- Submandibular glands
- Sublingual glands
digests carbohydrates
salivary amylase
Functions of Saliva
- Water dissolves food for taste and digestion
- Mucous moistens and lubricates food
- Mucous lubricates oral surfaces for smooth actions in swallowing and speech
- Cl- ions activate amylase
- HCO3- and PO4- ions buffer bacterial acids
- IgA, lysozymes, cyanide, defensins: protect against microorganisms
what stimulates salivation
Food (mechanically, chemically)
behavioral – memories from cortex
starts digestion
continues after ingestion is complete
irritating foods or nausea
Functions of Saliva
Water dissolves food for taste and digestion
Mucous moistens and lubricates food
Mucous lubricates oral surfaces for smooth actions in swallowing and speech
Cl- ions activate amylase
HCO3- and PO4- ions buffer bacterial acids
IgA, lysozymes, cyanide, defensins: protect against microorganisms
Secretion of Saliva - 1-1.5 L l day is under what control
Primarily under nervous control
if your parasympathetic nervous system is turned on what happens to the salivary secretions
normal salivary secretions
saliva swallowed
most reabsorbed
if your sympathetic nervous system is turned on what happens to salivary glands
reduced flow (dry mouth)
mastication
Chewing
Food mixed with saliva
Shaped into a
bolus
salivary amylase breaks down and converts polysaccharides (starches
to disaccharides (maltose) and monosaccharides (glucose) [no enzymatic action with cellulose which is also a polymer of glucose]
how is bolus moved to the stomach
through three phases…
buccal
pharyngeal
Esophageal
facilitated by saliva
what parts of the body are used to move bolus from the mouth to stomach
mouth
pharynx
esophagus
buccal phase is
Voluntary
Moves bolus to oropharynx
Pharyngeal phase
-Involuntary
Receptors in oropharynx stimulate medulla and pons to:
1) Block mouth with tongue
2) Block nasopharynx with soft palate
3) Raise larynx to seal epiglottis, blocking airways
4) Relax upper esophageal sphincter
-Bolus is moved through pharynx into esophagus
Esophageal stage
- Upper esophageal sphincter closes
- Gastroesopaheal sphincter opens
- Esophagus controls involuntary peristaltic movement
- Epiglottis reopens
- Bolus moves from esophagus to stomach
Peristalsis
Involuntary, rhythmic contraction of muscularis
Controlled by medullary centers
A movement activity: inner circular layer of smooth muscle contracts behind bolus to push it forward; outer longitudinal muscle contracts to pull esophagus wall up
Physiology of Esophagus
Upper esophageal sphincter
Peristalsis
Lower esophageal (“cardiac”) sphincter
Sharp transition from nonkeratinized stratified squamous epithelium to simple columnar epithilium
Esophageal epithelium resistant to abrasion but not to acid and proteolytic enzyme attack – acid reflux disease
Physiology of digestion - Mechanical digestion
- peristaltic movement (mixing waves) back and forth between body and pylorus
- 3 muscle layers: longitudinal, circular, and oblique
- chyme
Physiology of digestion - Chemical digestion
parietal cells secrete intrinsic factor for B12 absorption
parietal cells secrete HCl by active transport
chief cells secrete pepsinogen (inactive precursor)
parietal cells secrete HCl by active transport
- kills microbes, denatures proteins
- causes some acid hydrolysis of food molecules
- stimulates secretion of hormones for bile & pancreatic juice flow
chief cells secrete pepsinogen (inactive precurso)
- activated to pepsin by HCl acid and by other pepsins
- only an effective protease at acid pH
- cleaves proteins into smaller peptides
Stomach: Mucosa contains
Gastric gland chief cells
Simple columnar epithelium with goblet cells and gastric pits
Simple columnar epithelium with goblet cells and gastric pits
Goblet & gastric pit mucous cells secrete mucin
Gastric gland G cells (enteroendocrine)
Gastric gland chief cells secrete
Secrete pepsinogen (inactive precursor)
Secrete rennin in neonates
Secrete gastric lipase in neonates
chief cells Secrete pepsinogen (inactive precursor)
activated to pepsin by HCl acid and by other activated pepsin enzymes
only an effective protease at acid pH
cleaves proteins into smaller peptides
chief cells Secrete rennin in neonates
curdles milk to increase time for gastric processing
chief cells Secrete gastric lipase in neonates
splits short chain triglycerides common in milk
limited role in digestion since it works best at pH 5-6
Simple columnar epithelium with goblet cells and gastric pits
Secretes
2-3 L l day
Gastric gland parietal cells
Secrete
intrinsic factor for B12 absorption
HCl by active transport
- kills microbes, denatures proteins
- causes some acid hydrolysis of food molecules
- stimulates secretion of hormones for bile & pancreatic juice flow
Goblet & gastric pit mucous cells secrete
mucin
1-3 mm mucus layer in the stomach prevents self-digestion
Gastric gland G cells (enteroendocrine)
Secrete
gastrin, histamine, serotonin, somatostatin
Absorption
of mucosa
Impermeable to diffusion of most molecules into the bloodstream
Absorbs a few lipid soluble compounds:
certain drugs (e,g., aspirin)
alcohol
Physiology of the liver - processes vital to life
- Storage – oil-soluble vitamins, iron, other nutrients and minerals
- Phagocytosis
- Removal of dietary toxins, hormones, drugs
- –detoxify or store or secrete compounds into bile
- –metabolize thyroid, steroid hormones
- Synthesis of bile salts
- Excretion of bile - bilirubin
- Activation of Vitamin D (?)
Pathologies of the liver –
hepatitis (viral, toxic), cirrhosis, cancer
Gall Bladder shape
Pear-shaped sac, 7-10 cm long
Gall Bladder physiology
- stores and concentrates bile between meals
- CCK stimulates bile release for fatty meals
- when the small intestine is empty, the hepatopancreatic sphincter closes, forcing bile into the gallbladder for storage
cirrhosis
harden liver
Summary: Digestive Hormones
enteroendocrines Gastrin Gastric Inhibitory Peptide Secretin Cholecystokinin
Small Intestine: Segmentation
primary action of small intestine when food is present
a form of mechanical digestion
a mixing activity
alternate contraction, relaxation of antagonistic smooth (circular and longitudinal) muscle segments in the intestine
controlled by the autonomic nervous system
Small Intestine: Peristalsis
as absorption continues, distension decreases and true peristalsis starts
a movement which propels chyme onward
these weak movements which occur only after most nutrients have been absorbed
only fat soluble vitamins
ADEK
vitamins that can be toxic to the liver
ADEK
Stomach Regulated by combination of
neuronal and hormonal factors
3 phases of stomach
Cephalic
Gastric
Intestinal
Cephalic phase
stimuli
effect
Stimuli sight smell taste thoughts/memories
Effect
Parasympathetic impulses increase gastric secretion
Gastric phase neural mechanism
negative feedback
in the gastric phase distension activates
stretch receptors causing myenteric and vagovagal reflexes to release Ach
Ach stimulates gastric juice secretion
In the gastric phase chemoreceptors respond to
partially digested proteins, caffeine and rising pH
Stimulate gastrin secretion from G cells
Gastric phase (cont.) Gastrin
Inhibited at pH < 2 Gastrin transported in the blood to the gastric glands Greatly stimulates HCl secretion Stimulates histamine secretion Slightly stimulates pepsinogen secretion Contracts lower esophageal sphincter Increases gastric motility Relaxes pyloric sphincter
Control of HCl secreting parietal cells happens in what phase
Gastric phase
gastric phase is stimulated by three signal chemicals
gastrin
acetylcholine
histamine
All three needed for strong H+ secretion
gastrin
acetylcholine
histamine
blockage of the histamine H2 receptor decreases
HCl secretion
Intestinal phase has
excitatory and inhibitory components:
Intestinal phase…. Excitatory
Very short phase
Initiated by chyme entry into duodenum
Stretch receptors stimulate release of intestinal (enteric) gastrin
Chemoreceptors detect fatty acids, & glucose in the duodenum
Stimulate enteric gastrin release
Intestinal phase…
Inhibitory
Enterogastric reflex:
Enterogastrone secretion
Enterogastric reflex
stretch receptors, chemoreceptors trigger 3 reflexes that
1) Inhibit vagoval reflex
2) Inhibit myenteric reflex
3) Activate sympathetic nervous system to close pyloric sphincter
- Inhibit gastric secretion
Enterogastrone secretion
Enteroendocrine cells in the small intestine release:
- Cholecystokinin (CCK)
- Gastric inhibitory peptide (GIP)
- Secretin
- Vasoactive intestinal peptide (VIP)
Hormones inhibit gastric secretion
Food normally passes through stomach in
4 hours
regulate gastric emptying
Hormonal/neuronal reflexes
Large meals and large amounts of liquid increase stomach
stomach distension increasing rate of emptying
Stomach emptying inhibited by the
enterogastric reflex, enterogastrones, and fat in the duodenum
Pancreatic juice
Mostly water some salts, bicarbonate, enzymes
alkaline, pH 7.1-8.2
buffers acidic gastric juice, stops pepsin activity, creates proper alkaline pH for enzymes acting in the intestine
pancreatic juice enzymes include
pancreatic amylase
trypsinogen,
chymotrypsinogen,
procarboxypeptidase (inactive zymogens)
pancreatic lipase
ribonuclease and deoxyribonuclease
Regulation of Pancreatic Secretion is done by
Neural control from parasympathetic division of ANS via vagus nerve
Autoregulation by sensing the presence of fatty acids and amino acids in the acidic chyme
Hormonal control by the secretion of enteroendocrines from duodenum
Secretin – stimulates secretion of water, HCO3-
CCK – stimulates secretion of enzymes
Liver: Blood Supply- two sources
Hepatic artery - oxygenated blood from aorta
Hepatic portal vein -deoxygenated blood:
- absorbed nutrients and toxins from the stomach and intestines
- hormones from the pancreas
- breakdown products of RBCs from the spleen
Blood mixes in the sinusoids
(liver cells) modify and exchange molecules with the blood
Hepatocytes
livers central veins return blood to
the systemic circulation via the hepatic vein and inferior vena cava
Liver bile secretion Bile from the hepatocytes enters
bile capillaries (canaliculi)
Canaliculi empty into small bile ducts
Hepatic ducts join the cystic duct from the gallbladder to form the common bile duct
Gallbladder stores bile
Common bile duct meets pancreatic duct at the hepatopancreatic ampulla (of Vater)
Bile
800-1000 ml/day
Yellow, brownish, or olive-green liquid
pH 7.6-8.6, mostly water, bile salts, bile acids, cholesterol, lecithin (phospholipid), bile pigments, ions
Part digestive secretion, part excretory product
- bile salts help in emulsification of ingested fats
- bilirubin and other bile pigments are wastes from lipid catabolism
Regulation of bile production/secretion
nervous control from
parasympathetic division of ANS via vagus nerve
Regulation of bile production/secretion
autoregulation by sensing the
resence of fatty acids and amino acids in the acidic chyme
Regulation of bile production/secretion
hormonal control by
the secretion of the enteroendocrines, CCK and secretin, from the duodenum
Liver Lipid metabolism
stores, metabolizes some triglycerides
synthesizes new cholesterol
degrades excess cholesterol for bile salt production
Liver Carbohydrate metabolism
regulates blood glucose levels
glycogenesis (insulin)
glycogenolysis (glucagon)
gluconeogenesis (glucagon)
Liver protein metabolism
deaminates AA’s by removing amino groups (-NH2) from AA’s
deaminated AA’s used for ATP production or changed to carbohydrates or fats as needed
detoxifies ammonia (NH3) by synthesizing urea (1 CO2 + 2 NH3 = urea)
can convert AA’s from one to another (transamination)
synthesizes and secretes most plasma proteins
Liver metabolize three things
carbohydrate
lipid
protein
Physiology of the liver - processes vital to life
stores
oil-soluble vitamins, iron, other nutrients and minerals
Liver removes
dietary toxins, hormones, drugs
detoxify or store or secrete compounds into bile
metabolize thyroid, steroid hormones
Liver synthesis
bile salts
Liver uses what to break down things
phagocytes
Liver excretes
bile - bilirubin
Pathologies of the liver
hepatitis (viral, toxic), cirrhosis, cancer
Pear-shaped sac, 7-10 cm long
gall bladder
gall bladder stores concentrates
bile between meals
what stimulates bile release for fatty meals
CCk
when the small intestine is empty, the hepatopancreatic sphincter
closes, forcing bile into the gallbladder for storage
pathology for the gall bladder is
gall stones
what are your digestive hormones aka enteroendocrines
Gastrin
Gastric Inhibitory Peptide
Secretin
Cholecystokinin
a form of mechanical digestion in the small intestine
Segmentation
primary action of small intestine when food is present
segmentation
a mixing activity in the small intestine
segmentation
alternate contraction, relaxation of antagonistic smooth (circular and longitudinal) muscle segments in the small intestine
segmentation
what system is segmentation controlled by
autonomic nervous system
as absorption continues, distension does what and what starts
distension decreases and true peristalsis starts
a movement that propels chyme onward
peristalsis
these weak movements which occur in the small intestine only after most nutrients have been absorbed
peristalsis
Primary active transport electrolyte in the small intestine
Na+
facilitated diffusion electrolyte in the small intestine
K+
Active Transport electrolyte in the small intestine
Fe
which electrolyte in the small intestine is Active transport, vitamin D is a cofactor?
Ca2+
Fat-soluble vitamins in the small intestine
ADEK
water soluble vitamins in the small intestine
BC
What nutrients does the small intestine absorb
Lipids are emulsified by bile salts, forming micelles
Small intestine absorbs how many L /day
8.3
Total volume of water absorption added to the small intestine/day
9.3
~2.3 L from ingestion
~7.0 L from secretions
The rest of the water that isn’t absorbed in the small intestine is reabsorbed as
The rest of the water (~1.0L/day) passes to large intestine where most is reabsorbed (~0.9 L/day)
Completion of absorption, especially final absorption of H2O
Large Intestine
Normal flora manufacture certain vitamins (B complex, K)
Formation and expulsion of feces
Large Intestine
What 4 areas is the large intestine divided into
cecum
colon
rectum
anal canal
Chyme passage regulated by?
ileocecal sphincter
when the cecum is full, the sphincter is?
contracted
Colon movements start when
chyme passes sphincter
what does the large intestine digest and through what mechanism
digestion of chyme by bacteria
following a meal what occurs in the large intestine
gastroileal reflex: ileal motility increases, sphincter relaxes, chyme moves to the cecum
when the cecum is full, the sphincter contracts
