digestion - exam 2 Flashcards
how can simple animals have direct exchange w/ the environment
thin, flat shape
very few cell layers
live in moist environments
specialized exchange surfaces for complex animals
composed of living cells
thin
large surface area – folds & branches
moist – intersitital fluid
external or internal
connected to circulatory system
herbivore teeth
ridges & grooves good for grinding up the cellulose in plants
carnivore teeth
sharp to rip flesh
digestive tract
mouth –> esophagus –> stomach –> small intestine –> large intestine –> rectum –> anus
mechanical digestion in mouth
physical breaking down of food
use teeth to chew – bolus
chemical digestion in mouth
using enzymes to break down food
salivary amylase
breaks down starch
mucus
coats bolus & helps it slip down the esophagus
antibacterial agents
makes sure we don’t get sick from bacteria on food
mechanical digestion in stomach
peristalsis / churning
chemical digestion in stomach
gastric juice digests proteins
Hydrochloride acid
pH 2
kills bacteria
denatures proteins
activates protease
pepsin
protease
enzyme that breaks down proteins
can activate pepsinogen
why don’t pepsin & HCl damage cells that make them
they make inactive forms & release them into the lumen - where they are activated
chief cell
makes pepsinogen
pepsinogen
inactive form of pepsin
parietal cell
HCl
activates pepsinogen
why aren’t cells lining stomach damaged by pepsin & HCl
gastric juices not released until food arrives in stomach
mucus cells secrete protective mucus
rapid mitosis – the cells do get destroyed by HCl but they are replaced very quickly
chemical digestion in the small intestine
takes place in the duodenum
aided by accessory organs
pH = ~7.5
pancreatic amylase
breaks down carbs during chemical digestion in small intestine
pancreatic proteases
break down proteins during chemical digestion in small intestine
trypsin & chymotrypsin
trypsin & chymotrypsin
secreted as inactive precursors -
trypsinogen & chymotrypsinogen
activated in the small intestine - in the wall of the duodenum
pancreatic nucleases
break down nucleic acids during chemical digestion in small intestine
pancreatic lipase
break down fats during chemical digestion in small intestine
fats in hydrophobic globules
mechanical digestion in small intestine
bile emulsifies fats
breaks them into smaller fat globules that give lipase a larger surface area to break them down
bile
made in the liver
stored in the gall bladder
where does absorption occur
across the small intestine
folds provide more surface area
large circular folds
increase the surface area for more efficient absorption
villi
smaller folds on the large circular folds
lined w/ epithelial tissue
vessels & lacteal
microvilli
villi on the epithelial cells of the villi
where do the breakdown products of carbs, proteins, & nucleic acids go
directly into the bloodstream
where do the breakdown products of fats go
epithelial cell where triglycerides get put back together to form a chylomicron
chylomicron
contains triglycerides
type of lipo protein complex
moves into the lacteal
then the liver
then the bloodstream
role of large intenstine
reabsorption of water
water/undigested material (feces) becomes more solid
feces eliminated from the body
plant eater digestive system
longer small intestines
large cecum
benefit of longer small intestine for plant eaters
more time for chemical digestion
more time for absorption to occur
cecum
anaerobic (no oxygen) chamber
cellulose digestion microbes live there
rumen
anaerobic chamber w/ cellulose digestion microbes
rumen in cows
digests grass into rumen
rumen regurgitates it back into the mouth
more mechanical digestion
digests it for real
homeostasis
maintenance of internal balance despite external factors
positive feedback
the products of a reaction leads to an increase in that reaction
moves system away from homeostasis
child birth
negative feedback
a control mechanism that “dampens” a stimulus
hormone
chemical messenger released into bloodstream that acts on distant target cells
hormone = signal in the signal transduction pathway
what happens if glucose is too high
beta cells in pancreas release insulin into the blood
it binds to receptor in a body cell – signal transduction
blood glucose level declines & returns to homeostasis
what happens if glucose is too low
alpha cells of pancreas release glucagon into blood
it binds to liver cell
liver stores glycogen so it releases some back into the blood stream
blood glucose level rises & returns to homeostasis
leptin
appetite-suppressing hormone secreted by adipose (fat) cells
leptin w/ weight gain
gain weight
more leptin secreted =
decreased food intake (less appetite)
increased metabolic rate
returns to “homeostatic” size
leptin w/ weight loss
lose weight
less leptin secreted =
increased food intake (more appetite)
decreased metabolic rate
returns to “homeostatic” state
