Digestion (Core)Stephen Taylor

i-Biology.net

Gall

Liver: Secretion of surfactants in bile to break up lipid droplets

Gall Bladder- storage and regulated release of bile

Pancrease- secretion 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 lactose-free milk?

http://www.northland.cc.mn.us/biology/biology1111/animations/enzyme.html

Human Digestive EnzymesRemember: 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 carbohydratesExample: salivary amylase

Substrate: starch Product: maltoseSource: mouth (salivary glands)

Optimum pH: 7-7.8

Proteases break down polypeptidesExample: pepsin

Substrate: polypeptides Product: amino acidsSource: stomachOptimum pH: 2

Lipases break down fats and lipidsExample: pancreatic lipase

Substrate: triglycerides Product: fatty acids & glycerolSource: 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.mcgraw-hill.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

http://www.youtube.com/watch?v=Uzl6M1YlU3w

http://www.youtube.com/watch?v=bNMsNHqxszc

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.

Single-cell layer of epithelial cellsShort path for diffusion.

Capillaries close to epitheliumShort path for diffusion, rich supply of blood.

Lacteals (lymph vessels)Allow for rapid absorption and transport of lipids.

Rich blood supplyMaintains concentration gradients between lumen and blood.

Many villi protrude into the lumen, greatly increasing the surface area for absorption.

Images from: http://en.wikipedia.org/wiki/Intestinal_villi

Microvilli on the surface of each cell increase surface

area even further.

Microvasculature of Intestines

http://www.youtube.com/watch?v=P1sDOJM65Bc

http://www.youtube.com/watch?v=jsVgi8hoFFc

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.

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