BIO Ch3 - Digestive system

Alimentary canal/gastrointestinal tract

The whole passage from the mouth to the anus

Mechanical digestion

Involves physically breaking food down into smaller parts

Chemical digestion

Involves chemical reactions using enzymes that change foods into simpler substances to be absorbed into the bloodstream for use in the body

Pathway of the human digestive system

Mouth, pharynx, epiglottis, oesophagus, stomach, small intestine, large intestine, rectum, anus

Process/action that moves food through the digestive system

Peristalsis

Mouth function

Mechanical digestion by the teeth

Salivary gland function

Secretes saliva that contains amylase for the chemical digestion of carbohydrates

Lingual gland

Secretes lipase for breaking down fats

Oesophagus function

Muscular tube that moves food to the stomach by peristalsis

Stomach function

• Mechanical digestion by churning

• Chemical digestion using acids and enzymes

Parietal cells

Secrete hydrochloric acid to create acidic conditions in the stomach

Chief cells

Secrete pepsinogen which is converted to the enzyme pepsin which breaks down proteins in the stomach

Goblet cells

Secrete muscus that lines the walls of the digestive tract

Liver function

Produces and secretes bile into the small intestine

Hepatic portal vein

Blood vessel that carries blood from the digestive system to the liver

Gall bladder

Stores bile

Bile

Fluid produced in the liver that emulsifies fats

Pancreas function

Secretes pancreatic fluid containing enzymes into the small intestine

Small intestine

• Digestion of carbohydrates, fats and proteins

• Absorption of nutrients into the blood

Duodenum

• First segment of the small intestine that digests carbohydrates, fats and proteins using bile and enzymes from pancreatic fluid

• Absorbs fatty acids and water-soluble vitamins

Jejunum

Second segment of the small intestine that absorbs glucose and amino acids

ileum

Third segment of the small intestine that absorbs bile salts and vitamin B12

Villi and microvilli function

Increase the surface area inside the small intestine to increase absorption of nutrients

Blood vessels in villi function

Transport carbohydrates and protein to the liver for processing

Lacteals (lymphatic vessels) in the villi function

Absorb fat and transports it around the body

Four sections of the large intestine

Caecum, colon, rectum, anus

Caecum

First part of the large intestine that absorbs water. It varies in size depending on the diet of the animal.

Colon

Second part of the large intestine that absorbs water and ions

Rectum

Third part of the large intestine that stores solid faeces

Anus

Fourth part of the large intestine that allows faeces to be excreted out of the body

Sphincters

Thickened rings of muscle that control the opening and closing of a tube

Oesophageal sphincter

Prevents the regurgitation of the stomach contents into the oesophagus

Pyloric sphincter

Controls the movement of chyme from the stomach to the small intestine

Bolus

A mass of chewed food mixed with saliva that exists from the mouth until the stomach

Chyme

A slurry of partially digested food produced in the stomach which passes to the small intestine

Gut microbiota

The population of organisms that live in the gut. They maintain immune and metabolic homeostasis and are responsible for digesting cellulose in herbivores

Autotroph

An organism that produces its own organic food from inorganic sources

Heterotroph

An organism that consumes organic material for nutrition

Monogastric

An animal with a single-chambered stomach

Ruminants

Animals that absorb nutrients by fermenting food in a specialised stomach before digestion

Foregut fermenter characteristics

Four-chambered stomach with rumen, reticulum, omasum and abomasum, small and large intestines are long (e.g. cow or sheep)

Rumen

First part of a ruminant’s stomach where fermentation occurs using gut microbiotaa

Reticulum

Second part of a ruminant’s stomach where dense food and heavy foreign objects are collected

Omasum

Third part of a ruminant’s stomach which absorbs water and acts as a filter

Abomasum

Fourth part of a ruminant’s stomach where acids and enzymes are secreted for digestion

Hindgut fermenter characteristics

Small stomach, large caecum (e.g. koala or horse)

Carnivore characteristics

Short intestine and colon, small caecum

Crop

Pocket stemming from a bird’s oesophagus that can temporarily store food

Gizzard

Second part of a bird’s stomach that may contain small stones for grinding food