Digestive System Flashcards
Catabolic reactions vs anabolic reactions
C: break down molecules to supply energy
A: synthesis of macromolecules
Digestion is ____ and is accomplished by _____
Breakdown of polymers into their building blocks accomplished by enzymatic hydrolysis
Primary and secondary function of the digestive system
P: digestion and absorption of foods
S: protection from disease
Digestion is accomplished in these locations: (3)
GI tract, gut or alimentary canal
GI tract is
Muscular tube from the mouth to the anus
GI lumen
inside of the gut, compartment where usable components of food are extracted and wastes are left to be excreted as feces
Innermost lining of the lumen is composed of ____ which are attached to the ____
Epithelial cells
Basement membrane
Surface of epithelial cells on basement membrane facing the lumen care called:
Sides and bottom of epithelial cells forming the opposite surface of the lumen are called:
Apical surface
Basolateral surface
In the small intestine, the apical surface epithelial cells have outward folds on their plasma membranes called ___ meant to
Microvilli
INC surface area
Apical surface is separated from the remained of the cell surface by: ___ which
Tight junctions
Create a barrier separating body fluids from exterior environment
Two layers of smooth muscle lining the gut:
Circular: encircles it
Longitudinal: length of the gut
GI motility definition
Rhythmic contraction of the GI smooth muscle
GI motility is determined by 5 factors:
- Automaticity (spontaneous depolarization)
- Functional syncytium (one cell has AP the impulse spreads to other cells)
- Enteric nervous system (GI own NS)
- Hormonal input
- PNS allows sphincters to relax (food passes through gut) and SNS does opposite
GI motility serves two purposes:
Moves food through the gut and mixes food
Mixing of food in GI is accomplished by:
Disordered contractions resulting in churning
Movement of food through GI is accomplished by:
Orderly contraction (peristalsis)
How does peristalsis (orderly contraction of GI) operate?
Contraction of circular muscle at point A prevents food at point B from moving backward
Contraction of longitudinal muscle at point B contract to shorten the gut so it is pulled up over the food and the food moves toward point C
Circular muscles contract at point B to prevent food moving backwaters and longitudinal muscles contract, and so on
Bolus
Ball of food moving through the GI tract
Enteric NS relation to the PNS and SNS
SNS and PNS can control the ENS but the ENS can also operate independently of them (without their control)
PNS/SNS still have overriding ability
ENS relates
local blood flow, gut movement and exchange of fluid from gut-lumen
ENS is made up of two networks of neurons
Myenteric plexus: gut motility
Submucosal plexus: enzyme secretion, gut blood flow and ion/water balance to lumen
Submucal plexus is sparse:
in areas where enzyme secretion, gut blood flow and ion/water balance to lumen is not needed (i.e. anus and esophagus)
Two types of secretion: endocrine glands and exocrine glands
Endocrine: Ductless glands whose secretions are picked up by capillaries and enter the bloodstream
Exocrine: secrete products into DUCTS that drain into GI lumen
Exocrine glands are composed of
Specialized epithelial cells organized into sacs called acini (acinus) that secrete products to pass into ducts
Gastric glands
In stomach; release secretions directly into the gut
Secrete acid and pepsinogen
Goblet cells
Found along entire GI tract
Specialized mucus secreting cells
Mucus: slimy liquid that lubricates and protects the gut
Mucus membrane
Any surface covered with mucus
Water as a secretion in the GI system
Any meal must be dissolved in water and most of the water is then reabsorbed into the small intestine and colon is responsible for reclaiming whatever water is left
Endocrine secretion from the pancreas
Don’t empty into glands, are picked up into the blood stream (endocrine glands)
Mouth three roles in digestion of food
Fragmentation, lubrication and enzymatic digestion
Mastication
chewing to accomplish fragmentation
Incisors and cuspids and molars
I: Front teeth for cutting
C: Canine teeth for tearing
M: grinding
Saliva
Accomplishes lubrication and some digestion
Salivary amylase (ptyalin)
Hydrolyzes starch, breaking it into fragments (smallest yield is disaccharide)
Lingual lipase
Fat digestion enzyme in saliva
No digestion of ___ occurs in the mouth
Proteins
Lysozyme
Attacks material cell walls in the mouth
–Innate immunity happens in the mouth
A bolus of food passes through the ___, over the ____ and into the ___ where it is conveyed into the stomach by ____
A bolus of food passes through the pharynx, over the epiglottis and into the esophagus where it is conveyed into the stomach by peristalsis
Upper esophageal sphincter and lower esophageal sphincter
U: near top of esophagus
L: near heart at end of esophagus at entrance to stomach to regulate reflux from stomach into esophagus
Stomach three purposes
partial digestion, regulated release of food into small intense and destruction of microorganisms
Stomach pH is ___ and the effects of this are (3)
2
- destruction of microorganisms
- acid-catalyzed hydrolysis of proteins
- conversion of pepsinogen (inactive) to pepsin (active)
Pepsin is secreted by ___ in the stomach wall
Its function:
Chief cells
Catalyzes proteolysis (protein breakdown)
Inactive form of pepsin secreted by the GI tract
Zymogen
Chyme
Food mixed with gastric secretions
Pyloric sphincter
Prevents passage of food from stomach into duodenum (first part of the small intestine)
Opening of the pyloric sphincter occurs to:
And is inhibited when:
Empty the stomach
Small intestine already has a large load of chyme
Opening of the pyloric sphincter is mediated by the hormone
Chloecystokinin (secreted by epithelial cells in the wall of the duodenum / small intestine)
G cells secrete Gastrin which is
hormone that stimulates acid and pepsin secretion and gastric motility
Histamine is stimulated by ___ and causes:
Stomach stretching and gastrin release
Stimulates acid release
Small intestine takes food from the ____ and is made up of three parts:
Stomach
Ileum, jejunum and duodenum
Digestion is completed in the
Absorption begins in the
Duodenum and jejunum
Duodenum
Key feature allowing small intestine to accomplish absorption is its ____ which is made possible from (3)
Surface area
Length, villi, microvilli
Villi and microvilli of small intestine
V: Macroscopic multicellular projections in the wall of the small intestine
M: Microscopic foldings of the cell membrane of individual epithelial cells
Brush border
Brush like appearance of microvilli give the lumen surface of the small intestine this name
Three important features of the villus on the intestine
- Capillaries allowing carb nutrients and AA to be transported from the gut to the liver
- Lacteals (small lymphatic vessels) absorb dietary fats and transport them to the thoracic duct, emptying into the bloodstream
- Peyer’s patches: Lymphocytes that monitor GI contents and confer immunity to gut pathogens and toxins
Pancreatic duct on the duodenum
delivers exocrine secretions of pancreas (digestive enzymes and bicarbonate)
Common bile duct on the duodenum
Delivers bile containing acids
Bile is stored in the ___ until it is needed and has two main functions:
Gallbladder
Vehicle for disposal/excretion of waste by the liver
Essential for digestion of fats
Sphincter of Oddi
Both the pacreatic duct and common bile duct empty into the duodenum via the sphincter of oddi
Duodenal enterokinase
Activates pancreatic zymogen trypsinogen to trypsin
Brush border enzymes
DO work on the surface of the epithelial cell rather than being secreted
Hydrolyze the smallest carbs and proteins into monosaccharides and AA
Three main duodenal hormones:
Chloecystokinin (CCK)
Secretin
Enterogastrone
Chloecystokinin (CCK): response to fats in the duodenum
Secretin: response to acid in the duodenum
Enterogastrone: decreases stomach emptying
Chloecystokinin (CCK) duodenal hormone causes
Pancreas to secrete digestive enzymes, stimulate gall bladder contraction/bile release and decreases gastric motility
Secretin hormone in the duodenal causes
Pancreas releases large amounts of high-pH/basic aqueous buffer, usually HCO3- in water
Neutralizes HCL released by the stomach (Duodenum pH must be slightly basic or neutral)
Ileocecal valve
Separates the ileum from the cecum (first part of the large intestine) and controls entrance of chyme into the colon
Jejunum and ileum function
To absorb substances not absorbed in the duodenum
Colon/Large intestine role
Absorb water and minerals
Form and store feces until defecation
Cecum
First part of the colon
Appendix
Appendage of the cecum composed of lymphatic tissue
Rectum
last part of the colon where feces exits the rectum
Anal sphincter
Controls defecation
Internal vs external anal sphincter
I: smooth muscle under autonomic control
E: skeletal muscle under voluntary control
Colonic bacteria are important for two reasons:
- Presence of normal bacteria help keep dangerous bacteria from proliferating due to competition for space and nutrients
- Supply vitamin K which is essential for blood clotting
GI accessory organs include
Pancreas, liver, gallbladder and salivary glands
Pancreatic hormones
Pancreatic amylase function
Hydrolyzes polysaccharides into disaccharides
Pancreatic hormones
Pancreatic lipase function
Hydrolyzes triglycerides at surface of micelle
Pancreatic hormones
Pancreatic nuclease function
Hydrolyze dietary DNA and RNA
Pancreatic hormones
Pancreatic proteases function
hydrolyzing polypeptides to di- or tri- peptides
secreted in zymogen inactive form, must be activated by removal of a portion of the polypeptide chain
PNS and SNS function over pancreatic secretion
PNS: increases it “rest and digest”
SNS: reduces it
Endocrine pancreas consist of islets of langerhans which is made up of three cells, each:
secrete a particular hormone into the bloodstream
Three types of cells in the islets of langerhans
alpha cells, beta cells and delta cells
Islets of Langerhans:
alpha cell function
secrete glucagon in response to low blood sugar to mobilize stored fuels by stimulating the liver to hydrolyze glucose into the bloodstream and stimulating adipocytes to release fats into the bloodstream
Islets of Langerhans:
beta cell function
Secrete insulin in response to elevated blood sugar to remove glucose from the blood for storage as glycogen and fat
Islets of Langerhans:
delta cell function
Secretes somatostatin
Inhibits digestive processes
Lowering blood glucose
What does this and why
Insulin does this
Essential because excess glucose in the bloodstream will destroy many cellular systems
Raising blood glucose
What does this and why
Glucagon, epinephrine, cortisol
Makes sense that there is more means of raising blood glucose than lowering it because low blood glucose is fatal immediately whereas high levels is harmless in short term
Function of the liver
Create and release bile
Function of bile
Turns large fat particles into small fat particles called micelles which have more surface area and are easily digested
Helps fatty particles to diffuse across the intestinal mucus membrane
Gallstone
Large crystal formed from bile made with ingredients in incorrect proportions
Gallbladder secretion is controlled by
PNS & CCK stimulate the gallbladder wall’s contraction
Hepatocytes function (2)
Extract nutrients from blood passing through the liver
Makes changes based on what is and is not present in the blood
Both the liver and skeletal muscle are capable of storing and breaking down glycogen into glucose BUT
Only the liver can secrete it into the bloodstream because it has the enzyme needed to dephosphorylate it
Lipids exist in the intensive and enter the lymphatic system in molecules called chylomicrons which are degraded by lipases into chylomicron remnants
These remnants are taken up by ____ and combined with proteins to make ___ that ____
These remnants are taken up by hepatocytes and combined with proteins to make lipoproteins that re-enter the bloodstream
Many ___ and ____ are made in the liver and secreted into the bloodstream
Lipoproteins and plasma proteins
Ghrelin hormone
Stimulates hunger when the stomach is empty
Peptide YY
Colon is full the jejunum produces this to reduce appetite
Leptin hormone
Appetite suppressant released from fat that maintains stable lipid content in fat
INC triglyceride levels and suppresses appetite until levels are normal
Ghrelin, peptide YY and leptin are all primarily regulated by
Hypothalamus
Chylomicrons (large particles of proteins and fats) enter tiny lymphatic capillaries known as ___ which merge into larger lymphatic vessels which eventually empty into the _____
Lacteals
Thoracic duct which empties into the blood stream
Causing milky blood “lipemia”
Fat soluble vitamins
A, D, E, K
Require bile acids for absorption
Excess stored in adipose tissue (fat)
Water soluble vitamins
B(all), C, Biotin and Folate
Excess secreted by kidneys in urine
