9-2: Why and How We Eat Flashcards
feeding mechanisms in animals
- suspension feeder
- substrate feeders
- fluid feeders
- bulk feeders
suspension feeders
sift small food particles from the water (humpback whale, clams, oysters, etc.)
substrate feeders
live in or on their food source (caterpillars, moth larvae, fly larvae, termites, etc.)
fluid feeders
suck nutrient-rich fluid from a living host (mosquitoes, aphids, bees, hummingbirds, etc.).
bulk feeders
eat large pieces of food, and have many adaptations
to kill their prey (majority of animals).
digestive systems
• No specialized digestive systems (sponges)
• Gastrovascular cavity with just one opening (cnidarians)
• Alimentary canal with two openings (animals with more complex body plans)
• Digestion in animal bodies within these systems can occur in the
following ways:
-Intracellular digestion
-Extracellular digestion
- Combination of intra and extracellular digestion
Intracellular digestion
-occurs within individual cells inside vacuoles
-brings the whole food
particles inside the cell by
phagocytosis.
-Animals that perform
intracellular digestion are
sponges (sedentary feeders
with no specialized digestive
system
Extra/intracellular digestion in gastrovascular cavity
-Gastrovascular cavity is a chamber within the
body, which has only one opening.
-It is found in cnidarians (jellyfish, hydra, sea anemones)
-Even though digestion begins extracellularly
in gastrovascular cavity by enzymes secreted
from the gland cells, it is the nutritive cells
that engulf these food particles, so most of
the hydrolysis of macromolecules occurs
intracellularly.
• The undigested remains are eventually
expelled through the same opening by which
the food entered.
Extracellular digestion in alimentary canals
-more complex body plan have a digestive tube with two openings, which allows animals to feed more frequently.
- mechanical grinding of food into smaller pieces, and
• chemical breakdown, until food is small enough for absorption, which mostly
occurs in intestine.
• Digestion in alimentary canals is extracellular (enzymes break the food into small
molecules outside of cells, and then they pass the cell membranes)
Stages of food processing in alimentary canals
• Ingestion: the act of eating • Digestion: the process of breaking food down into soluble molecules - small enough to absorb • Absorption: uptake of nutrients by body cells • Elimination: the passage of undigested material out of the digestive compartment
Liver Functions
- Regulates distribution of
nutrients to the rest of the body - Detoxifies substances before they spread widely
Lipids
- lipids go into the lymphatic system first. The main
reason is that, even after being digested into smaller components by the lipase in the small intestine, they are still too big to enter the capillaries. So they enter the lymphatic system before they are carried to the capillaries
-note that this lymphatic system is within the small intestine
itself (lymphatic vessels called lacteals are found at the core of each villus)
mouth
Mechanical and chemical processing
pharynx + esophogus
Food transport
stomach
Mechanical and chemical processing
small intestine
Chemical processing and absorption
large intestine
Absorption of water and compressing undigested material
and bacteria into feces
rectum
holding feces
anus
eliminating feces
salivary glands
secretes enzymes, lubricates
liver
secretes bile salts, detoxifies digested food
gallbladder
stores bile
pancreas
secretes enzymes
pancreas enzymes
- function in small intestine
1) Breaking peptide bonds - carboxypeptidase
- chymotrypsin
- trypsin
- pepsin
2) Breaking carbs - pancreatic amylase
3) Breaking nucleic acids - nucleases
4) Breaks lipids - pancreatic lipase
salivary glands enzymes
salivary amylase
stomach enzymes
HCl
liver enzymes
bile salts which emulsify fats in small intestine
beginning of digestion
• Saliva from salivary glands lubricates;
• Teeth chew;
• Tongue shapes them into a bolus and
provides help with swallowing;
• Carbohydrates break down by salivary amylase;
• Some fats start to break down by lingual lipase
Bolus in pharynx and esophogus
• The throat, or pharynx, is the junction that opens to both the esophagus and the trachea. • The esophagus connects to the stomach. • The trachea (windpipe) leads to the lungs. • The esophagus conducts Timbits from the pharynx down to the stomach by peristalsis. • Swallowing causes the epiglottis to block entry to the trachea, and the bolus is, therefore, guided to the digestive system and not to the respiratory system
in stomach
• Coordinated contraction and relaxation of stomach muscle churn the stomachʼs contents. • Sphincters prevent Timbits from re-entering the esophagus and regulate their entry into the small intestine. • Both, mechanical and chemical digestion happens here • Secretes gastric juice: - Contains HCl and enzymes -Turns food to chyme • Chemical: -Proteins (by pepsin) - Some lipids (by gastric lipase) • pH is ~ 2 (kills bacteria and denatures proteins)
gastric gland cells
• Goblet (mucus) cells
• Chief cells (produce inactive pepsinogen)
• Parietal cells (produce H+ and Cl- separately)
• Gastric juice is made up of hydrochloric acid (HCl) and pepsin.
• Pepsin is a protease, or protein-digesting enzyme, that cleaves
proteins into smaller peptides.
parts of small intestine
- Duodenum digests more than it absorbs
- Jejunum absorbs most of the nutrients
- Ileum absorbs certain left overs
Duodenum
-is the first and the shortest segment of the small intestine. It receives partially digested food (known as chyme) from the stomach and plays a vital role in the chemical digestion of chyme in preparation for absorption in the small intestine. Most digestion occurs here, and not much absorption.
Jejunum
is the middle segment of the small intestine found between the duodenum and the ileum. Most of the nutrients present in food are ABSORBED by the jejunum before being passed on to the ileum for further absorption.
Ileum
is the third and final part of the small intestine. Its function is to mainly absorb vitamin B12 and bile salts and
whatever products of digestion were not absorbed by the jejunum. The pH
in the ileum is more neutral.
Functions of liver
• Detoxifies the blood; • Stores some vitamins, iron, and glycogen as sugar reserve; • Coverts glycogen to usable sugar when needed; • Breaks down hemoglobin, insulin and other hormones; • Coverts ammonia to urea; • Destroys old erythrocytes.
small intestine summary
• The small intestine is the longest compartment of the alimentary canal.
• Most enzymatic hydrolysis of
macromolecules from ex-Timbits
occurs here.
• The first portion of the small intestine is the duodenum, where chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself.
• The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen.
• The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorption.
large colon
• Colon begins with the cecum • aids in the fermentation of plant material;
-connects where the small and large intestines
meet.
• The human “cecum” is an appendix
-plays a minor role in immunity • •The colon
-completes the reabsorption of water that
began in the small intestine;
-houses bacteria necessary for our digestion.
