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).
What is facilitated diffusion? What is transported using this method?
It is where a channel protein (door for food basically) helps hydrophilic food molecules pass through the hydrophobic portion of the plasma membrane. Certain monosaccharides, vitamins, and some minerals are transported by facilitated diffusion, but its mainly thought of as transport for monosaccharides.
What is osmosis?
Osmosis transports water molecules. The molecules will diffuse across the membrane in response to movement of ions and hydrophilic monomers (solutes). This means that water moves from a low solute concentration to a high solute concentration when the solute cannot easily cross the membrane and there is an unequal balance. Water diffuses to even the concentrations. Osmosis occurs in both the small and large intestine.
What is simple diffusion? What is transported using this method?
Simple diffusion is where hydrophobic materials can freely pass through the hydrophobic portion of the plasma membrane. Once absorbed, lipids will often pass first into lacteals rather than being transported by blood. This method is for triglycerides. fatty acids.
What is bulk transport/endocytosis?
When vesicles form around fluid containing dissolved materials - the membrane bends and forms a vesicle around materials then closes and takes them into the cell. This is also called pinocytosis or cell drinking. The process allows materials to be ingested in large amounts and hence takes less time than shuttling via membrane proteins.
What happens in the liver after absorption?
The absorbed materials are transported to the liver for processing via the hepatic portal vein. The liver then monitors and processes nutrients in the blood before it passes into general circulation (it detoxifies materials).
In detail, describe the structure and processes of the large intestine.
The large intestine is large in diameter but not length, its lining consists of simple columnar epithelium but it is not folded into villi like the small intestine, instead it contains tubular glands called crypts which contain goblet cells. Goblet cells produce mucus which lubricates the colon wall, aids the formation of faeces and provides a location for gut bacteria. The large intestine’s overall function is to reabsorb water and electrolytes and pass the remaining material to the rectum for defecation. It also incubates good bacteria which produce vitamin K and ferment some undigested carbohydrate to produce short chain fatty acids.
What is bilirubin?
Waste product of recycling red blood cells.
What is folic acid?
B vitamin that everyone needs, especially important for pregnancy.
What are the fat soluble vitamins? What are the water soluble ones?
Fat soluble: A, D, E, K
Water soluble: C, B1, B2, Niacin, etc.
What is synthesis?
combination of 2 or more substances to create something
Describe the liver. What are five of its functions?
The liver is the largest homeostatic organ, it has over 500 functions. It receives a high and constant blood supply from the body and its overall job is to detoxify the blood. It’s five functions are carbohydrate metabolism, fat metabolism, protein metabolism, production of bile, and detoxification and storage.
What is carbohydrate metabolism in the liver?
The liver stores excess glucose as glycogen (controlled and powered by insulin and glucagon) but it also makes more glucose, if there isn’t enough in the body, from glycerol and amino acids (gluconeogenesis).
What is fat metabolism in the liver?
The liver converts excess carbohydrates and proteins in the body into fatty acids and triglyceride (adipose storage). Fat metabolism is also the synthesis of lipoproteins, cholesterol, and phospholipids.
What is protein metabolism in the liver?
The liver makes plasma proteins (protein circulating in the blood) and clotting factors. It also deanimates amino acids, meaning it removes the nitrogen from amino acids and the nitrogen is excreted in the urine as urea. Transanimation also occurs which is the synthesis of new amino acids.
Describe the production of bile in the liver.
Bile is made from water, mucus, bilirubin, bile salts, and cholesterol. Bilirubin is produced when the liver breaks down worn out red blood cells. Overall, the liver produces bile.
Describe detoxification and storage in the liver.
The liver (detoxifies) metabolises drugs, alcohol, and toxins because most of these things enter the body through the digestive system. The liver also inactivates hormones and stores a variety of vitamins as well as folic acid, iron, copper, etc.
What are micronutrients and why do we need them.
Micronutrients are things like vitamins (organic compounds required for normal metabolism), minerals (chemical elements needed to form certain molecules or assist certain processes), and non-protein factors that are necessary for normal functioning and often co-factors for enzyme reactions. Micronutrients have to be obtained from our diet and bad things can happen if we don’t get them/enough of them. Too much however can also be detrimental in some cases. Examples of minerals include calcium, phosphorus, iron, and zinc.
