Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Digestive System Overview

The main feeding modes of heterotrophs is herbivore (feed on vegetation, e
...
deer,
cow), carnivore (feed on meat, e
...
coyote) and omnivore (feeds on both vegetation
and meat, humans are in this category)
...

IN INVERTEBRATES
Some have specialized digestive systems (e
...
earthworm)
...

VERTEBRATE DIGESTIVE SYSTEMS INCLUDE HIGHLY SPECIALIZED
STRUCTURES MOLDED BY DIET
Vertebrates include humans in which digestive system is a tubular gastrointestinal tract
and accessory digestive organs
There is mechanical digestion (breakdown of food by teeth – vertebrates, gizzard –
earthworms) and chemical digestion-hydroylsis of macromolecules to monomers, usually
involving enzymes(for fat bile is also needed)
...
Once broken down the monomers are absorbed across specialized
epithelia in the gut and enter the blood stream after passing through through the liver
...
Waste products of the digestive process pass
out through the anus
The digestive system includes the alimentary canal with food passing in the following
sequence (mouth or oral cavity with salivary glands) pharynx(oral and nasal cavities
meet at back of throat)esophagus stomach(enzymes for digestion) pyloric
sphincter of stomach  duodenum of small intestine (products of pancreas and liver
enter here) jejenum of small intestine  ileum of small inestine cecum of large
intestine ascending colon of large intestinetransverse colon of large intestine 
descending colon of large intestine  rectum  anus
...
The liver produces bile which emulsifies fats
...
All this is
secreted into the duodenum to help digestion (pg
...

Digestive Processes
The digestive system carries out the processes of ingestion, propulsion, mechanical
digestion, chemical digestion, absorption, and defecation
...
A mesentery is a double layer of
peritoneum that tether`s the movable digestive organs to the body wall
...

Many vertebrates have teeth, birds don’t so use a gizzard to aid food breakdown
...
It
is a chamber for ingestion and initial processing of food
...
The swallowing reflex is
triggered by pressure in the pharynx which causes the epiglottis to flap over the
glottis (opening to the windpipe or trachea – to prevent choking)
During swallowing, food passes from the mouth through the oropharynx (back of throat)
muscles squeeze food into and down the esophagus during swallowing
...
The internal surface exhibits folds to increase surface area
for digestive enzymes
...
B12)
...
Stomach pH is
very low, is very acidic
...
Its segments are
the duodenum, jejunum, and ileum
...
The acidic chyme is neutralized by bicarbonates
from the pancreas
...
The
bile duct from liver and gallbladder and main pancreatic duct join to empty into the
duodenum
...
Between the villi are the intestinal crypts (intestinal glands), which
secrete intestinal juice and goblet cells which produce mucus
...
Pancreas also is an endocrine gland
(remember glands that secrete enzymes for digestion are called exocrine), which
secretes hormones from clusters of cells called Islets of Langerhans (review
endocrine system for hormones and what they do with blood sugar regulation)
...
Blood flows
through the liver from the gut, cells (macrophages) remove debris from the blood
...
The gallbladder, a green muscular sac, stores and concentrates bile
...
When fatty chyme enters the small intestine, the gallbladder
squeezes bile into the bile duct and duodenum
...
Bile salts act to emulsify fat, they work like a detergent to break larger fat
droplets into smaller droplets and thus provide a larger surface area for lipase to act
on
...
Products of fat digestion are
absorbed differently, after entering epithelial cells they combine with proteins to form
chylomicrons which enter lacteals of the lymphatic system
...

The Large Intestine: Elimination of Waste Material
The large intestine, which concentrates feces by absorbing water, subdivisions are the
cecum and vermiform appendix, colon (ascending, transverse, descending, and
sigmoid), rectum, and anal canal
...
The
iIeocecal valve is connecting point between ileum of small intestine and cecum of
large intestine)
...

Variations in Vertebrate Digestive Systems
Animals like cows are ruminants which rechew regurgitated food
...

Cellulose is generally difficult to digest so they have this system
...
The digestive system of
different mammals reflect their different diets (carnivores have short digestive tract
compared with herbivores)
...

Liver modifies chemicals to maintain homeostasis
Liver helps detoxify substances that are ingested, including alcohol
...
It also forms many of the blood proteins and
regulates hormones
...
48
...
Food intake is under neuroendocrine
control (pg
...


4



---