Digestion Flashcards
Digestion
The breakdown of large, complex organic molecules into smaller components that can be used by the body.
Molecules need to be small enough so they can diffuse across the plasma membrane.
Ingestion
The consumption of, or taking in of nutrients.
Digestion
The chemical breakdown of large organic molecules into smaller components by enzymes.
Absorption
The transport or delivery of digested nutrients to body tissue.
Egestion
The elimination of waste materials from the body.
Digestive Tract (alimentary canal)
The digestive tract in a normal adult human is between 6.5 and 9 metres long.
It is one continuous tube.
The Mouth
Physical/Mechanical breakdown of food with chweing/tearing of food:
- increases surface area
- Easier chemical breakdown/digestion
What does the mouth contain and what does it do
Contains amylase (enzymes)
- which break down starches into simple sugars
- Saliva lubricates the food, forming bolus - a ball of food that is swallowed
Swallowing
A coordinated activity of the tongue, soft palate, pharynx and oesophagus.
Epiglottis: Flexible cartilage guarding the entrance to the larynx. The epiglottis prevents food from entering the trachea.
The Oesophagus
Straight muscular tube that is about 25cm long which connects the mouth with the stomach. (4-8 secs)
The bolus of food moves down the oesophagus propelled by wave-like muscular contractions; peristalsis.
- Moving the food all the way through
the gastrointestinal tract.
Stomach
Temporary storage for food (4hrs)
Site of protein digestion
Movement of food into and out of the stomach is controlled by circular muscles called…
Sphincters.
Lower oesophageal sphincter (aka cardiac sphincter)– allows food in, stops food from going back up into the oesophagus.
Pyloric Sphincter – slowly releases partially digested food (chyme) into small intestine.
Glastric Fluids and what they consist of
Millions of cells lining the stomach secrete various fluids
- Mucus (coats/protects lining of stomach)
- Hydrochloric acid (kills harmful digested substances and converts pepsinogen to pepsin)
Pepsin
Is a protein digesting enzyme – breaks large protein molecules chains into smaller ones.
Acidity of the Stomach
The pH of the stomach normally ranges between 2.0 and 3.0 on the pH scale.
The high acidity allows pepsin to work and makes the HCl effective at killing pathogens.
Due to the acidity, the lining of the stomach is constantly being replaced. (replaced approx. every 6 days.)
Stomach Ulcers
Lesions in the lining of the stomach. They occur when the protective mucus lining breaks down and the cell membranes are exposed to HCl and pepsin.
Small Intestine
The majority of chemical
digestion occurs in the first
of three sections of the small
intestine.
Duodenum
About 30cm long. Contains opening from bile duct and pancreatic duct through which bile and pancreatic enzymes enter the small intestine.
Jejunum
About 3 metres long.
Additional chemical digestion
due to secretion of juices from
the lining.
Ileum
About 4 metres long.
Final and longest section of the
small intestine. Responsible for
re-absorption of nutrients.
Chyme
Food enters into the small intestine as chyme. The chyme is acidic due to HCI so it needs to be nuetralised (enters into the pancreas)
Pancreas
Accessory Organ
Releases digestive chemicals
Secretes digestive enzymes
Secretin (hormone)
Stimulates the pancreas to secrete a solution that contains bicarbonate ions into the small intestine where it neutralises the chyme – pH changed from 2.0 to 9.0 – this change inactivates the pepsin.
Digestive Enzyme (Protein) - Trypsinogen
Released into small intestine where it is converted to trypsin – converted by the enzyme enterokinase.
Digestive Enzyme (Protein) - Trypsin
Breaks down large protein chains into smaller ones.
Digestive Enzyme (Protein) - Erepepsins
Then released from pancreas – break smaller protein chains into individual amino acids.
Pancreas and Carbohydrates
Amylase released from pancreas and breaks down large carbohydrate chains into disaccharides.
When the carbohydrates are broken down into dissacharides, what happens next?
Releases disaccharide enzymes which break the disaccharides into individual sugar molecules (e.g. lactase – breaks disaccharide lactose into galactose and glucose monosaccharides)
Pancreas and Lipids
The pancreas releases lipases which break fat down into fatty acids and glycerol.
What does the lipases include
Pancreatic lipase and phospholipase.
What process do lipids undergo before being broken down and where does it occur
Lipids need to be emulsified and they enter the liver.
Liver and Gall Bladder
Large acessory organ
Constantly produces a liquid known as bile
Bile is stored in the gall bladder until it is needed in the small intestine. PPT 13.0 Slide 28
What does the presence of lipids in the small intestine trigger?
Triggers the release of a hormone called cholecystokinin (CCK) which triggers the release of bile from gall bladder.
What does bile contain
Bile contains bile salts that emulsifies fats which means it breaks them into small droplets so they can be digested.
Small Intestine
Chyme remains in the small intestine for 4-8 hours.
Mucosa (inner wall) of the small intestine
Mucosa (inner wall) secretes several enzymes that act on chyme.
Pancreatic enzymes also act on chyme.
Digested nutrients absorbed through intestinal walls.
What happens to the materials in the small intestine
Cross the mucosa into the blood stream and other parts of the body for storage or further chemical change.
Small intestine has folded inner walls covered with finger-like projections called
Villi
Each villus has thinner projections that increase surface area to absorb nutrients called
Microvilli
What does each villus contain
A capillary network along with a lacteal.
- Lacteal – a vessel of the lymphatic system.
End products of carbohydrtes (monosaccharides) and protein (amino acids) digestion enter the….
Capillary Network
They travel to the liver via the hepatic portal vein.
What do amino acids rely on?
Amino acids rely on Na+-dependent co-transport system which moves them from the small intestine into the epithelial cells of the villus. Facilitated diffusion.
End products of fat digestion (glycerol and fatty acid chains) are absorbed into the….
Lacteal
- Drains into the blood stream via the thoracic duct (vein
near the neck).
Fatty acids and glycerol delivered to the epithelium cells via
Bile salt micelles. PPT 13.0 Slide 36
Triglycerides (fats from meats) are…
Resynthesised and packaged with cholesterol and phospholipids to make them water soluble.
Chylomicron
Small fat globules which are transported by exocytosis to the lacteals.
All food/chyme is moved along the small intestine via……….
Peristalsis.
The large Intestine
Colon
Stores waste products long enough (8-10 hours) so that water can be reabsorbed from the wastes.
Some inorganic salts, minerals and vitamins are also absorbed
What is the large intestine home to…
Several types of bacteria.
These bacteria use the waste products to synthesise vitamins B and K – example of a symbiotic relationship.
Cellulose
Found in cell walls of plant cells and cannot be digested in humans
Cellulose provides
Bulk (fibre, roughage) which promotes the movement of waste products out of the colon.
Less fibre means waste products stay in your body for longer.
Where is waste pushed?
Into the expanded portion (rectum) and reamin until secreted via anus.
The appendix serves as a ‘storm shelter’ for…
good bacteria, allowing them to recolonise the gut following an infection.`
Appendicitis
Obstruction within the appendix followed by Bacterial infection
Ruptured (untreated inflamanations) appendix, releases toxic bacteria into abdominal cavity and blood stream– can lead to life-threatening infection.
Differences between mammalian guts – Omnivores, herbivores (foregut and hind gut digestion), and carnivores
Because meat is easily digested compared to plant material, the digestive system of a carnivore is typically shorter than an herbivore of comparable size. In carnivores, the caecum is sometimes reduced and may be partially replaced by the appendix. … True carnivores lack enzymes in their saliva to help them digest food. Herbivores, on the other hand, can have very complex digestive systems that can include multiple stomach chambers and regurgitating food for rechewing, because plant materials are much harder to digest.
