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Three things an animal’s diet must supply:
- Chemical energy
- Organic building blocks
- Essential Nutrients
4 types of essential nutrients?
- amino acids
- fatty acids
organic molecules required in the diet in small amounts
What caused scurvy?
Vitamin C deficiency, sailors didn’t eat fresh fruit
simple inorganic nutrients required in small amounts
when a diet does not provide enough chemical energy
long-term absence of one or more essential nutrients from the diet
Undernourished individuals will:
- use up stored fats and carbs
- break down their own proteins
- lose muscle mass
- suffer protein deficiency of the brain
the process of breaking food down into molecules small enough to be absorbed
Intracellular vs. Extracellular Digestion
- intracellular: food particles are engulfed by phagocytosis, takes place inside the cell
- Extracellular: takes place in chambers outside the body
What does Mechanical Digestion do?
- increases the surface area of food
What does Chemical Digestion do?
splits food into small molecules that can pass through membranes
Advantage of having a digestive tube with two openings?
- because food moves from one end to the other, each region can be specialized to break down food farther and farther
- much more efficient
What are the four stages of digestion?
the act of eating
What are the four types of feeders
What types of feeders are humans?
What are substrate feeders?
live in or on their food source
What are fluid feeders?
suck nutrient-rick fluid from a living host
What does mammalian digestive system consist of? (2 things)
- Alimentary canal (tube through which food moves down)
- Accessory glands (bring components to aid digestion)
What happens during mechanical digestion? (3)
- teeth help break food into smaller pieces
- salivary glands deliver saliva to lubricate food
- salivary amylase initiates breakdown of glucose polymers
What is the role of salivary amylase?
- quickly samples whether food has sugar or not (great evolutionary advantage)
- initiates breakdown of glucose polymers
What is peristalsis? How does it work?
- mechanism by which food is pushed along alimentary canal
- muscles behind the food contract and relax ahead of the food, pushing it forward
What is gastric juice?
acidic juice in the stomach that converts a meal to acid chyme
Why is gastric juice good at its job?
It has a very low pH of 2, meaning it is very acidic, which helps it kill bacteria and denature proteins
How is gastric juice produced?
- Chief cells secrete inactivated pepsinogen (need a low pH to activate it)
- Parietal cells secrete HCl, which lowers the pH and activates pepsinogen into pepsin
- Positive feedback loop starts (more and more is activated)
- Lots of acid in the stomach
Function of mucous cell
protects the lining of the stomach from the acid environment
Function of sphincter
- helps keep the acid in the stomach
- when not properly closed, the acid from stomach can travel up a little which causes heartburn
How is heartburn caused?
sphincter not closed properly, acid from stomach travels up and starts to chew up esophagus
Why do herbivores have a longer digestive track than carnivores?
Because plants are made of cellulose, which is harder to digest
What is absorption?
when nutrient molecules enter body cells
What is the first stage in receiving food from intestines?
- once nutrients are absorbed through epithelial cells, they make it into your body
- capillary beds absorb nutrients and pump them into liver
What does the pancreas do? (2)
- produces proteases trypsin and chymotrypsin that are activated in the lumen of the duodenum
- neutralizes acid from stomach because its solution is basic
What are the two main functions of the pancreas?
- aid in digestion (secrete things into digestive track)
- secrete hormones (into endocrine system, released into blood, not digestive system)
What does the liver do?
- produces bile, which aids in the digestion/absorption of fats
- stored in the gallbladder
How are nutrients absorbed?
hepatic portal vein carries nutrient rich blood from the capillaries of the villi to the liver, then to the heart
What does the liver do?
- regulates nutrient distribution
- interconverts many organic molecules
- detoxifies many organic molecules
How are fats absorbed?
- instead of using blood to carry fats, fat particles clump together into chylomicrons
- which are dumped into lacteal (part of lymphatic system)
- lymph vessel dumps it into arteries instead of liver
What is the appendix?
extension of the human cecum, minor role in immunity
Role of Cecum
aids in fermentation of plant material and connects small and large intestines
Absorption in the large intestine
- colon of large intestine is connected to small intestine
- colon recovers water that has entered alimentary canal
- houses bacteria that live in unabsorbed organic material
What do herbivores specifically have longer than carnivores?
they have a longer cecum to break down cellulose
Overview of digestion
- mouth- salivary glands lubricate and break down food
- Peristalsis pushes food down esophagus
- Stomach acid helps break down food into acid chyme
- Secretions from pancreas/liver aid in further digestion
- Go through small and large intestines
- Food/nutrients are taken through hepatic portal vein into the liver
- Fats go directly to veins through the lymphatic system
- Lastly, water is absorbed by colon
What 4 hormones control appetite?
What hormones tell you to eat?
What hormones tell you to stop/suppress appetite?
Why is mouse without leptin obese?
because it keeps eating, its regulatory feedback is broken so it does not know when to stop
How do hormones control appetite?
- When stomach is empty, it produce ghrelin, which tells you that you’re hungry
- After eating, stomach stretched and ghrelin production goes down
- After eating signals are also sent to suppress appetite
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