Digestion Flashcards
Why do animals eat?
To obtain energy
To maintain cellular metabolism
To allow growth and reproduction
What type of trophs are all animals?
Heterotrophs
What do animals extract from food?
Proteins Carbs Fat Ions Trace elements Water Vitamins Essential amino acids
What type of teeth do carnivores have?
Enlarged canines for gripping killing and tearing prey
What type of teeth do herbivores have?
Incisors and canines to tear plants
Large molars and premolars to grind plant matter
What type of teeth do omnivores have?
Multipurpose teeth
What are gastroliths?
Stomach stones used to grind food
Describe the structure of the human digestive system
Mouth Stomach Small intestine Large intestine Rectum
What is the mouth for?
Responsible for breaking up large amounts of food and mixing it with saliva
What is the stomach for?
Responsible for mechanical mixing of food with stomach acid
What is the small intestine for?
Responsible for further mixing and absorption of nutrients and is aided by bile and pancreatic juice
What is the large intestine for?
Responsible for absorbing water and forming stool
What is the rectum for?
Responsible for storing stool before expulsion
What are the salivary glands for?
Secrete liquid and enzymes (salivary amylase) into the oral cavity for chemical digestion
How does the stomach digest?
In anticipation as well as the arrival of food, it releases HCl and pepsin
Coordinated contractions of muscle layers lead to mixing of food creating chyme
Where does chyme go after the stomach?
Released into small intestine duodenum via the pyloric sphincter
How does HCl chemically digest food?
Denatures proteins by breaking electrostatic interactions in the tertiary structure
Also sterilises food
Where does the HCl and pepsinogen come from?
Gastric pits are deep folds of the stomach mucosal epithelium
How does HCl activate pepsinogen?
Pepsinogen is an inactive precursor enzyme that is activated by HCl into pepsin
Describe the mucus-bicarbonate barrier
Bicarbonate neutralises the acid
Mucus is a physical barrier
What happens when chyme enters the duodenum?
Digestive enzymes are released from the pancreas and gallbladder and bicarbonate is released to neutralise the acid
What is gastrin?
A hormone produced by G cells and is innervated by the postganglionic fibres of the vagus nerve during parasympathetic stimulation
What is secretin?
A hormone that is produced by S cells and inhibits the production of gastrin and neutralises the duodenum pH
What is cholecystokinin?
A hormone that stimulates the release of bile and pancreatic juice
What are the 3 parts of the small intestine?
Duodenum
Jejunum
Ileum
How does absorption happen in the small intestine?
Na+/K+ ATPase generates a chemical gradient for Na+ and this requires energy
The gradient is used to cotransport other substrates into the luminal membrane
The interstitial membrane contains transporters (uniporters) which releases the substrates
How are fats digested?
Fats are emulsified into micelles through bile in the intestinal lumen
Pancreatic lipase hydrolyses the micelles into fatty acids and monoglycerides
They enter the cell by diffusion
Are resynthesised into triglycerides in the endoplasmic reticulum
Triglycerides are packaged with cholesterol and phospholipids in protein-coated chylomicrons
Chylomicrons are enclosed in vesicles and leave the cell by exocytosis and enter the lymphatic system
Where does the absorbed material go?
Transported by the portal vein to the liver for detoxification
What happens in the large intestine?
No digestive enzymes but bacterial digestion occurs
Salt and water are absorbed
What is aldosterone?
A steroid hormone that stimulates the absorption of Na+ and water
What is the appendix for?
A reservoir for beneficial microorganisms
Describe fermentation in the cecum in herbivores?
A microbial fermentation chamber called the cecum extends from the large intestine for bacterial digestion
What is coprophagy and why is it practiced?
Nutrient absorption in the cecum is inefficient so some eat waste to redigest and get more nutrients
