Digestion (Core)
Stephen Taylor
i-Biology.net
Liver: Secretion of
surfactants in bile to
break up lipid
droplets
Gall Bladderstorage and
regulated
release
Gall
of bile
Pancreasesecretion of
lipase, amylase
and protease
Peristalsis
• 2 functions in the GI tract.
1. Propulsive movement of food forward at an
appropriate rate for digestion and
absorption.
2. Mixing movements – caused by peristalsis
and local intermittent contractions.
Peristalsis
• The propulsive movement in the GI is
achieved by peristalsis.
Peristalsis
• Constriction of circular muscles behind the
food constricts muscles behind the food
preventing it from being pushed back towards
the mouth
Muscle Contraction for Peristalsis
The smooth muscle of the gut is formed from short cells, not elongated fibers.
Often continuous interspersed with short periods of vigorous contraction.
Peristalsis
• Occurs in one direction
• Vomiting uses abdominal muscles
Enzymes review:
• What type of biological molecule is an enzyme?
• How do enzymes work?
• How are enzymes produced through protein synthesis?
• What are the effects of temperature, pH and substrate
concentration on the rate of enzyme activity?
• How are immobilized enzymes used in the production of lactosefree milk?
http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.html
Human Digestive Enzymes
Remember: enzymes are specific to their substrates and
each enzyme has its own optimum pH.
Three main types of enzymes in human digestion:
Amylases break down carbohydrates
Example: salivary amylase
Substrate: starch Product: maltose
Source: mouth (salivary glands)
Optimum pH: 7-7.8
Proteases break down polypeptides
Example: pepsin
Substrate: polypeptides Product: amino acids
Source: stomach
Optimum pH: 2
Lipases break down fats and lipids
Example: pancreatic lipase
Substrate: triglycerides Product: fatty acids & glycerol
Source: pancreas, delivered into small intestine
Optimum pH: 7.2 – 7.5
Digestive system diagram from: http://www.teachervision.fen.com/digestive-system/printable/57730.html
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html
Pancreatic
• 2 types gland tissue
– Islets of Langerhans secrete hormones insulin and
glucagon into blood
– Reminder synthesizes and secretes digestive
enzymes into gut in response to eating
– Glands secrete enzymes into ducts then into
intestions
Pancreatic Juice
Contains enzymes digesting 3 macromolecules
– Amylase: starch
– Lipases: trigycerides, phospholipids
– Proteases: proteins, peptides
Intestine enzymes
• Starch digested to maltose by amylase
• Triglycerides digested to fatty acids and
glycerol or fatty acids and monoglycerides by
lipase
• Phospholipds digested into fatty acids,
glycerol, and phosphate by phospholipase
• Proteins and polypeptides digested to shorter
peptides by protease
Intestine enzymes
• Small intestine produces
• Nucleases digest DNA and RNA into
nucleotides
• Maltase digests maltose into glucose
• Lactase digests lactose into glucose and
galactose
• Sucrase digests sucrose into glucose and
fructose
• Exopeptidases digest peptids into dipeptides
• Dipeptidesases digest dipeptides
Intestinal Wall
Adaptations to Absorption
Getting digested food molecules into the
blood from the lumen of the ileum.
Many villi protrude into the lumen, greatly
increasing the surface area for absorption.
Single-cell layer of epithelial cells
Short path for diffusion.
Microvilli on the surface of
each cell increase surface
area even further.
Lacteals (lymph vessels)
Allow for rapid absorption and transport of lipids.
Capillaries close to epithelium
Short path for diffusion, rich supply of blood.
Rich blood supply
Maintains concentration gradients between
lumen and blood.
Images from: http://en.wikipedia.org/wiki/Intestinal_villi
Microvasculature of Intestines
Methods of absorption
• Triglycerides digested into fatty acids and
monoglycerides, absorbed into villus by
diffusion
• Fatty acids also absorbed by facilitated
diffusion using protein pumps called fatty acid
transporters
• Inside the epithelium cells, fatty acids
combine w/ monoglycerides producing
triglycerides
Methods of absorption
• Triglycerides coalesce w/ cholesterol to form
lipoprotein (droplets coated in phospholipids
and protein)
• Lipoproteins released by exocytosis through
plasma membrane where they enter the
lacteal or enter blood stream
Methods of absorption
• Glucose cannot pass through plasma
membrane by simple diffusion
• Sodium-potassium pump
• Sodium-glucose co-transporter proteins in
microvilli transfer sodium and glucose
together from lumen to cytoplasm of
epithelium. Passive facilitated fusion
• Glucose channels allow facilitated diffusion
from villus into blood capillaries.
@IBiologyStephen
Please consider a donation to charity via Biology4Good.
Click here for more information about Biology4Good charity donations.
This is a Creative Commons presentation. It may be linked and embedded but not sold or re-hosted.