M2.2.5 - Digestion Flashcards
Absorption
The movement of small nutrients into the body across a membrane
e.g. from the small intestine into blood capillaries
Occurs through
- Diffusion
- Facilitated diffusion
- Active transport
Assimilitation
The use of absorbed nutrients to form parts of an organism e.g. amino acids from food is used to build new proteins
Digestion osmosis
Passive transport
- e.g. if the chyme (semi-digested food) is dilute, water is absorbed from it into the villi capillaries of the intestinal mucosa. Conversely, water can also flow from plasma into the chyme, until it is isosmotic.
Facilitated diffusion example
e.g. Glucose uses a glucose transporter protein, amino acids also use transport systems
Active transport
Substances transported actively in the digestive system
Ion uptake, e.g. sodium, calcium, magnesium and iron, and transport of disaccharides
Sodium-potassium pump
Disaccharides (complex sugar), dipeptides and tripeptides (complex amino acids) are also actively transported.
Endocytosis example
Humans: Immunoglobulins is absorbed via receptor mediated endocytosis.
Vascular plants: endocytosis transports SUCROSE from the phloem into the cells of the sink
Different systems of absorption
What substances go into the bloodstream/lymphatic system. What substances remain unchanged through absorption
- Bloodstream: Amino acids, carbohydrates and minerals
- Lymphatic system: fatty acids, glycerol
Only a small amount of fluid is absorbed
Immunoglobulins, breast milk and oral vaccines remain unchanged through absorption
Stomach absorption
The stomach is a poor absorptive area. Only highly lipid soluble substances (alcohol, aspirin) can be readily absorbed
* No villi: low surface area
* Tight junctions: does not allow much movement of material between cells
Small intestine absorption
Features + functions
Where most food particles are absorption.
- Villi and microvilli: high surface area, very efficient
- Smooth muscle in the wall causes peristalsis- involuntary contraction and relaxation, moving food through the tract
- Duodenum (first section) pancreatic juices released into the area. Bicarbonate ions neutralise acidic chyme from the stomach. Most of absorption occurs here.
- Jejunum (middle section): plicae (fold/ridge) within villi, increase surface area. Some water absorption.
- Ileum (last section): villi becomes smaller → less absorption of digested products.
- Peyer’s patches: small clusters of lymphatic tissue that inhibit spread of microflora from the large intestine
Elimination
Passing undigested material out of the alimentary canal
Large intestine structure
- Consists of the caecum, appendix, colon and rectum. In humans, the caecum and appendix are bypassed, with food entering the ascending colon.
- No villi, as only absorption of water occurs.
- Movement of material controlled by a sphincter muscle and valve, preventing backflow. Movement by peristalsis.
- The material entering the colon are undigested substances, compacting into faeces. Colon terminates in the rectum.
Large intestine microflora
- Some microflora can produce absorbable vitamins, but if spread to other parts of the body can become pathogenic
E.g. vitamin K, a lipid-soluble vitamin which helps blood clot
Large intestine absorption
- Water, mineral ions and some vitamins are absorbed across the cell membrane into the bloodstream
- Faeces moves by mass movement caused by peristalsis
Mechanical digestion
- The process of applying force to break down food
- Begins in the mouth with chewing - teeth shapes changed as the diet evolved. (Incisors vs molars)
- Churning motion of the stomach further breaks down food
- Mechanical digestion increases surface area of food so that chemical digestion enzymes can act on it faster
Chemical digestion
- Large complex molecules are broken down chemically by digestive enzymes
- Begins in the mouth with salivary amylase breaking carbohydrate starch into simpler sugars
- Stomach: gastric juices - HCl breaks down food; acid kills bacteria; digestive enzymes split up proteins. Mixed with the bolus, it becomes chyme
- There are different enzymes in the small intestine
- The molecules are broken down into substances that can be used for cell reactions and synthesising other substances.
Chemical digestion enzymes
Amylase, protease, lipase
- Carbohydrates with amylase → glucose
- Proteins with protease → amino acids
- Lipids with lipase → glycerol + fatty acids
Carbohydrate breakdown
- Amylase breaks down carbohydrates → glucose
Disaccharides breakdown
- Disaccharides broken down into monosaccharides in the duodenum by maltase, sucrase, and lactase enzymes
- Resulting monosaccharides are absorbed into the bloodstream and transported to cells to be used in energy-harnessing metabolic pathways
Protein breakddown
- In the stomach, the protease pepsin break protein down into single amino acids
- Amino acids get absorbed into the bloodstream through the small intestine
Lipid digestion
- Occurs in small intestine
- Bile salts emulsify (break down) lipids, allowing lipase to divide lipids into fatty acids + monoglycerides
- Monoglycerides and fatty acids leave the small intestine and recombine into chylomicrons, which enter the bloodstream
Vitamins absorption
- Fat-soluble: absorbed in the same way as lipids
- Water-soluble: directly absorbed into the bloodstream through the intestines
Liver function
- Digested food that has been absorbed into the bloodstream travels to the liver
- Liver keeps sugars, glycogen, and protein levels in balance in the body. Also detoxifies blood
- Is the centre of food metabolism
