Session 2: Digestive System Flashcards
What is the alimentary canal?
A long continuous tube from mouth to anus. The alimentary canal makes up the digestive system with other accessory organs (liver, gall bladder, pancreas).
What is the role of the digestive system?
Breakdown of complex mixture of food we eat into smaller molecules that can be absorbed by the blood and into the body. We actually only need the broken down molecules of food, e.g. nutrients.
What is the difference between mechanical and chemical digestion?
Mechanical digestion is the physical breakdown of food (e.g. chewing) where chemical digestion is the breakdown of food using chemical reactions, which are generally but not always enzyme based.
What is the function of the mouth? What are the substances involved in this process?
The mouth uses mechanical digestion to moisten food into bolus (ball of chewed food) and it begins starch digestion. This process increases the surface area for enzymes later on, and takes place using teeth, which are shaped to fit their function, and the tongue. Substances involved in the process include saliva, which lubricates food and has some antimicrobial properties, and salivary amylase, which turns starch to maltose.
What is the function of the oesophagus? What are the substances involved in this process?
The oesophagus is muscle which transports food from the mouth to the stomach via peristalsis (muscular contractions). The substance involved is mucus, which is used for lubrication and protection from the digestive contents (oesophagus is protected from acid, food, etc. that may be present).
What is the function of the gall bladder?
The gall bladder stores bile and controls its release.
What is bile?
Bile helps with digestion –> it breaks fats into fatty acids/large droplets into smaller droplets to increase surface area (emulsifies fats).
What is the overall function of the liver? What are the substances involved in this process?
The liver processes and stores nutrients, controls bile synthesis and secretion (produces bile) and is involved in detoxification. Bile is a substance involved which emulsifies fats and removes waste products.
What is the overall function of the stomach? What are the substances involved in this process?
The stomach is a heavily folded muscular bag which main function is protein digestion, but it also stores and churns food with gastric juices (water, HCl, enzymes), and kills microbes/pathogens. The stomach is known for its acidity, which is why HCl is one of the substances involved, along with pepsinogen and mucus. HCl has antimicrobial properties, and it activates pepsinogen and begins protein digestion.
What is the function of the pancreas? What are the substances involved in this process?
The pancreas produces and secretes enzymes (lipase and protease), hormones (insulin and glucagon), and bicarbonate. Substances involved include lipase which breaks down triglycerides into fatty acids and monoglycerides, trypsinogen which is the inactivated form of trypsin (breaks down proteins to amino acids), amylase which breaks down starch into maltose, and bicarbonate which neutralises stomach acid.
What is the overall function of the small intestine? What are the substances involved in this process?
The small intestine performs the remaining chemical digestion, neutralises stomach acid, and absorbs nutrients. Substances involved are maltase (maltose to glucose), sucrase (sucrose to fructose and glucose), lactase (lactose to glucose and galactose), and mucus for lubrication and protection from digestive contents. The enzymes present are more in the walls of the intestine, not released into it.
What is the overall function of the large intestine? What are the substances involved in this process?
The large intestine absorbs water and ions and stores bacteria for vitamin K synthesis and fermentation of undigested carbohydrates to short chain fatty acids. Mucus is the substance involved which is used for lubrication, protection from digestive contents, and it houses gut bacteria.
What is peristalsis? What are two muscles involved and what do they do?
Peristalsis is the movement of food through the digestive system using waves of muscular contractions. It is an unconscious and involuntary movement controlled by the nervous system. The circular muscle behind food prevents it from being pushed in the wrong direction. The longitudinal muscle moves food along the gut.
How is food shaped in the oesophagus compared to the small intestine?
Food is a bolus in the oesophagus and a semi-fluid called chyme in the small intestine.
What is the oesophageal sphincter and what does it do? Then, what is acid reflux?
A small constricting gap that prevents food and stomach acid from going back up oesophagus. Acid reflux is when the sphincter is wide open, and when acid passes through it can damage the oesophagus creating the heartburn sensation and oesophageal ulcers.
What are the five stages of the digestive system?
Ingestion (intake of food by swallowing or absorption), digestion (treatment of a substance to promote decomposition), absorption (nutrients and simple molecules from food absorbed into the body through intestinal cavities), assimilation (formation of new compounds from absorbed molecules), and elimination (excretion of unwanted materials).
In detail, describe the structure and function of the stomach including detailed description of the substances involved in chemical digestion.
The stomach is made of 3 thick layers of muscle that contract and relax to churn and physically break up food (mechanical digestion). In terms of chemical digestion, parietal cells produce hydrochloric acid which in turn activates pepsinogen, goblet cells produce mucus, and other cells secrete the hormone gastrin which increases acid secretion and gastric acid.
What are gastric ulcers and how do they develop?
Gastric ulcers are sharp pains and heartburn 1/2 to 1 hour after food, as well as weight loss, and stomach bleeding. It can develop when food spends longer than usual in the stomach, there is reflux of bile and enzymes from small intestine into stomach, or the muscosa (stomach lining) is damaged. Gastric ulcers are also caused by helicobacter pylori bacteria, it is the only bacteria that isn’t killed by stomach acid, but it can be cured with simple 2 week antibiotic treatment.
In detail, describe the structure and process of the small intestine.
The small intestine is 7 metres long, named for its diameter and not its length, it has 3 main sections: the duodenum (upper), jejunum (middle), and ileum (lower). It receives chyme from the stomach through the pyloric sphincter. The inner epithelial lining of the intestine is highly folded into many finger-like projections called villi, which in turn have microvilli. This greatly increases surface area for absorption as the small intestine’s main function is absorption of nutrients into the blood and body.
There are 7 key features of the small intestine that help with absorption. List them and their purpose.
Microvilli to increase surface area. Rich blood supply for capillaries to rapidly transport products. Single layer epithelium that minimises diffusion distance between lumen and blood. Lacteals which absorb lipids into the lymphatic system. Membrane proteins that facilitate transport of digested materials into epithelial cells. Membrane bound digestive enzymes that further chemical digestion (maltase, sucrase, lactase). And tight junctions between adjacent cells which create impermeable barrier that maintains concentration gradients and one-way movement.
Describe the structure of the pancreas and what it produces.
The pancreas has pancreatic gland cells that surround the ends of tubes (ducts) and eventually drain pancreatic juice into the lumen of the small intestine. The pancreas produces digestive enzymes: lipase, amylase, trypsin.
What is absorption? what is absorbed?
Digested molecules and nutrients need to be absorbed from the lumen of the small intestine, through the epithelial cells of the villi and into the blood or lymph (lacteals). The products that are absorbed are monosaccharides, amino acids, fatty acids, minerals (calcium, potassium, sodium, etc.), and vitamins. The physical and chemical properties of the nutrients dictate how they are absorbed (method).
What are the five methods of absorption?
Secondary Active Transport, Facilitated Diffusion, Osmosis, Simple Diffusion, and Bulk Transport/Endocytosis.
What is Secondary Active Transport (Co-transport)? What is transported using the method?
It is a type of absorption where the energy required to move one substance across a membrane is provided by another substance. In this case, glucose and amino acids are co-transported across the epithelial membrane by the active translocation of sodium ions (in other words sodium powers the movement of glucose).
