digestive system. function of the digestive system primary function: breaks down macromolecules into...
TRANSCRIPT
Function of the digestive system
Primary function: breaks down macromolecules into substances the body can use
Other functions: house helpful bacteria, excrete solid waste
Digestion Digestion – the breakdown of macromolecules into components more easily be absorbed/utilised by the body
Biologists consider the digestive system an external surface
Why do you think that is?
Digestion is mechanical AND chemical
Mechanical digestion◦ Physical breakdown of large food portions
Chemical digestion◦ Molecular degradation of foodstuffs by chemical substances (acid, enzymes, etc.)
Enzymes & digestion Enzymes – proteins that catalyse metabolic chemical reactions
An enzyme’s structure determines its function
Denaturation = the loss of protein structure◦ Caused by low/high pH and high temperature
Enzymes & digestion cont’d
Digestive enzymes rapidly break down macromolecules into smaller subunits (monomers) for absorption into the body
Enzymes are named for what they act on and end in “______ase”◦ eg. Lactase breaks down lactose
◦ Sucrase breaks down _________
◦ ______ breaks down lipids (fats)
Enzymes are present throughout theGI tract
The mouth Digestion begins in the mouth
◦ Mechanical digestion = teeth◦ Chemical digestion = enzymes begin breaking down sugars
Tongue & salivary glands◦ Produce saliva to dampen solid food◦ Saliva contains digestive enzymes◦ Tongue presses softened food against hard
palate forming a bolus (ball) for swallowing
Pharynx◦ Swallowing causes epiglottis to direct food
down the esophagus
Esophagus◦ Muscular tube that carries bolus to the stomach via peristalsis
Peristalsis◦ Radial contraction of muscles that propagates a wave down a
tube
The esophagus & peristalsis
The stomach Stomach
◦ Site of chemical digestion by HCl (pH 1.5 – 3.5)◦ Mucus-lined walls protected from damage◦ Acid may splash up into unprotected
esophagus, causing heartburn
Why are the walls wrinkled?
◦ Food may enter small intestine via pyloric sphincter only when liquefied (chyme)
Accessory organs The initial segment of the small intestine, the duodenum, is where accessory organs contribute to digestion
Accessory organs:◦ Liver – produces bile to breakdown
lipids (fats)◦ Gall bladder – stores excess bile◦ Pancreas – produces additional
digestive enzymes (insulin, lipase, etc.)
◦ The bile duct adds bile/digestive enzymes to the duodenum
The small intestine Small intestine (duodenum, jejunum & ileum)
◦ Responsible for absorbing majority of nutrients (into blood stream)◦ ~6m long and houses some bacteria that aid in digestion◦ Maximizes surface area to boost absorption
Nutrient absorption To maximize surface area, the small intestine is lined with two structures:1. Villi
◦ finger-like projections on inner surface of SI
2. Microvilli◦ hair-like projections on surface of villi
These form the absorptive surface where nutrients enter the bloodstream (‘blood-gut’ barrier)
Large intestine & fecal formation
Large intestine (AKA the colon)◦ Absorbs water from slurry entering from SI◦ Removal of water solidifies leftovers into feces for excretion◦ Houses primary gut microflora
◦ Bacteria digest unused macromolecules to yield useful nutrients (eg. E. coli produce vitamin K)◦ ~1x1014 bacterial cells (we know about ~5% of them)◦ Bacteria may produce organic gases while metabolising
leftover nutrients… (what does this cause?)
Rectum, anus & defecation
Rectum◦ Tail end of colon◦ Site of fecal collection (when full, time to poop!)
Anus◦ Sphincter that controls departure of fecal matter
(defecation)
Fun fact: 1/3 the dry mass of every poop is bacterial cells (this is why we ALWAYS wash our hands post-poop)