Biology - Digestive System

Purpose of Digestion

To break down large molecules of food into smaller molecules, in order to obtain essential nutrients

• Large molecules are chemically inert, must be broken down and reassembled into usable products

• Large molecules typically insoluble, smaller subunits are and can be absorbed into cells

Mouth

• Begins mechanical digestion (chewing)!

• Begins chemical digestion (salivary glands secrete saliva that moistens food into soft bolus)!

Esophagus

• enters here after bolus swallowed

• is lined with epithelial tissue that pushes food down by peristalsis!

• glands in lining produce mucus so tube is moist and moves through easily!

• Epiglottis at top of trachea (next to epiglottis), closes to ensure bolus doesn’t enter

Stomach

• chemical digestion!

• gastric juice secreted: kills harmful substances and denatures proteins

• Mucus: protects stomach from acid

• Pepsin: breaks down protein

• food digested here for hours, then turned to chyme (creamy paste)

Small Intestine

• chemical digestion and absorption

• digestive enzymes secreted

• nutrients diffuse through intestinal wall into bloodstream for transportation

• has villi

• has 3 parts

Large Intestine

• reabsorbs fluid + electrolytes, sends 90% of water back to blood

• assimilation + starts elimination

• contains cecum (blind pouch at upper end),

  colon (longest part), rectum and anus

Rectum

• stores feces

Anus

• opening where waste is egested

• elimination

Pancreas

• secretes 2 hormones: insulin and glucagon to control blood sugar levels

• when acidic food enters small intestine, secretes bicarbonate to neutralize it

• secretes pancreatic juice (contains enzymes) into upper small intestine via pancreatic duct

Bile: what? where produced and stored?

• a substance that breaks down fats into smaller globules

• produced and synthesized in the liver

• stored in the gallbladder

Purpose of digestive Enzymes

Secreted into system to break down food further into smaller molecules (chemical digestion)

How do strcuture of villi aid function

They increase surface area in the small intestine, which aids in absorption

Diagram

(11)

Digestion VS Absorption VS Assimilation

Digestion - breaks larger molecules down into smaller molecules (physically and chemically)

Absorption - uptakes molecules into bloodstream (where they’re transported to tissues and their cells)

Assimilation -Molecules are taken in to be used. Converted into the fluid and solid parts of a cell/tissue