6.1 Digestion and Absorption Flashcards
mouth
Voluntary control of eating and swallowing
Mechanical digestion by chewing
Chemical digestion by saliva
Saliva moistens food to make a bolus
Salivary glands
Produces saliva
Saliva digests starches (contains amylase)
Esophagus
Movement of food by peristalsis (waves of muscle contractions) from the mouth to the stomach
Stomach
Muscle contractions churn contents (mechanical digestion)
Stomach acid kills foreign bacteria and other pathogens in food
Initial stages of protein digestion by the enzyme pepsin
Small intestine - duodenum (start of SI)
Bile from liver and gallbladder neutralize stomach acid and emulsifies fats.
Pancreatic amylase and lipase digests carbohydrates and fats
Trypsin digests polypeptides
Small intestine - ileum (lower half of SI)
Absorbs nutrients into the blood via the villi and microvilli
Pancreas
Secretion of lipase, amylase and protease into the SI
Neutralizes acidic chyme using sodium bicarbonate
Liver
Secretion of bile used to break up lipid droplets
Gallbladder
Storage of bile from liver and regulated release of bile into SI
Large intestine
Reabsorption of water into the blood
Formation of feces
Rectum
Storage of feces
Anus
Release of feces
Peristalsis
a series of muscle contractions that moves food through the alimentary canal
Peristalsis steps
- Contraction of longitudinal muscle expand the lumen in front of the food giving it space to move into.
- Contraction of circular muscles behind the food propels it forwards.
In the small intestine peristalsis also…
mixes food with enzymes and forces the products of digestion into contact with the wall of the intestine
The pancreas synthesises the three main types of digestive enzyme:
amylase to digest starch
lipases to digest lipids
proteases to digest proteins and polypeptides
Release of enzymes mediated by…
hormones created and secreted by the stomach
Digestive enzymes are created in…
pancreatic gland cells on ribosomes on the rough ER and processed by Golgi and secreted by exocytosis
Ducts within the pancreas merge into…
larger ducts and pancreatic duct which release pancreatic juice into the small intestine
large food molecules need to be…
digested before the nutrients can be absorbed
type of reaction to digest?
catabolic
products of digestion are
soluble, small enough for absorption to blood and tissues
pancreas enzymes
Amylase
starch —> Maltose
Lipase
triglycerides —> Fatty acids, glycerol
Phospholipase
phospholipids —-> fatty acids, glycerol, phosphate
Protease
proteins, polypeptide —-> Shorter peptides
Small intestine enzymes
Nuclease
DNA, RNA —> Nucleotides
Maltase
Maltose —> Glucose
Lactase
Lactose —> Glucose, galactose
Sucrase
Sucrose —> Glucose, fructose
Exopeptidase
Peptides —> dipeptides
Dipeptidase
Dipeptides —> Amino acids
Mucosa
inner lining, includes villi
Submucosa
connective tissue (between the mucosa and muscle)
Muscular layer
inner circular and outer longitudinal muscle perform peristalsis
Serosa
protective outer layer
Epithelial cells
single outer layer of cells on each villus
Many villi protrude into the lumen, greatly increasing the…
surface area for absorption.
Absorption:
the uptake of molecules into the blood from the lumen of the ileum.
Microvilli
on the surface of each cell to 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.
Single-cell layer of epithelial cells
Short path for diffusion
villi absorbs both…
vitamins and minerals
Fatty acids Monoglycerides
transport: Simple diffusion
Once inside epithelium cells, fatty acids combine with monoglycerides to which cannot diffuse back into lumen on SI
Fatty acids
transport: Facilitated diffusion via transmembrane proteins
Once inside epithelium cells, fatty acids combine with monoglycerides to which cannot diffuse back into lumen on SI
Glucose
transport: Facilitated diffusion via glucose channels
Polar molecules, large so simple diffusion cannot occur
Sodium
transport: Active transport
Na+ pumped into epithelial cells
Sodium and glucose
transport: Sodium-glucose cotransporter
Facilitated diffusion
Transfer Na+ and glucose together
The digested glucose is absorbed and then transported to various body tissues (process)
Glucose is co-transported* with sodium ions into the epithelial cells (of the villus).
Glucose moves by facilitated diffusion into the lumen of the villus.
Glucose then diffuses a short distance into the adjacent capillaries where it dissolves into the blood plasma.
Blood in the capillaries moves to to venules then to the hepatic portal vein which transports the glucose to the liver.
The liver absorbs excess glucose which it converts to glycogen for storage.
