A4 - Digestive and excretory system Flashcards
What is the function of the digestive system
The function of the digestive system is to break down the food you eat into smaller, soluble molecules which can then be absorbed into the blood stream or lymphatic system. Waste parts of food are passed out of the body as faeces.
What organs make up the digestive system
Are there any organs in the digestive system that do not come into contact with the food?
Yes, there are some accessory organs that produce and secrete chemicals which are necessary for digestion, but the food does not come into contact with these organs.
What happens in the mouth during digestion
Digestion begins in the mouth. Ingested food is broken down mechanically by the teeth and mixed with saliva. Saliva contains salivary amylase, an enzyme that begins the chemical digestion of starch.
What is peristalsis and where does it occur in the digestive system?
Peristalsis is the alternate contraction and relaxation of the muscle layers to push the food down into the stomach. It occurs in the thick layer of muscle in the oesophagus.
What is the role of the stomach in digestion?
The role of the stomach is to churn the food and mix with stomach acid and enzymes.
What is the duodenum and what happens there during digestion
The duodenum is the first part of the small intestine where food passes in small quantities from the stomach. Pancreatic juice with hydrolytic enzymes and bile from the liver are added to the duodenum. These secretions enter the duodenum at the sphincter of Oddi.
What is the function of the jejunum and ileum in the small intestine
The jejunum and ileum are the last two parts of the small intestine where the products of digestion are absorbed across the walls and into the bloodstream or lymphatic system. The walls of the ileum contain finger-like projections called villi that protrude into the lumen of the tube, which provides a large surface area for absorption.
What is the purpose of the Pancreas
Soft pink gland supported by mesentery, within the loop of the duodenum
- Endocrine function: produces insulin and glucagon
- Exocrine function: produces and secretes pancreatic juice containing digestive enzymes directly into the duodenum via the pancreatic duct to aid digestion of all food types
- Pancreatic juice is produced by clusters of cells called acini cells
- Epithelial cells lining the pancreatic ducts secrete hydrogen carbonate ions that make the pancreatic juice alkaline
- Islets of Langerhans contain beta cells that secrete insulin in response to increased blood glucose levels and alpha cells that secrete glucagon in response to lowered blood glucose levels
What is the purpose of the Gall bladder
- Small muscular sac around 10cm in length
- Stores bile made in the liver
- Bile is released from the gall bladder into the duodenum via the bile duct when food moves from the stomach into the duodenum at the sphincter of Oddi
- Bile contains salts to emulsify fats, increasing their surface area for digestion
- Bile also contains hydrogen carbonate ions to neutralize stomach acid
What is the purpose of the Liver
Large gland in the abdomen, in front of the stomach
- Consists of hexagonal shaped liver lobules, inside which are hepacytes
- Oxygenated blood enters the liver from the hepatic artery and nutrient-rich blood comes from the ileum via the hepatic portal vein
- Deoxygenated blood leaves the liver in the hepatic vein
- Hepacytes make bile that enters canaliculi and passes to the gall bladder where it is stored until it is needed
- Bile contains salts that emulsify fats to increase their surface area for digestion, hydrogen carbonate to neutralize acid chyme, bilirubin and biliverdin which are the products of broken-down red blood cells and cholesterol
- Liver also stores glycogen, helps regulate blood glucose levels, makes plasma proteins, stores fat-soluble vitamins and metabolizes alcohol, drugs and other toxins
- Breaks down excess amino acids to make urea for removal at the kidneys
What is the purpose of the Large intestine
Appendix contains lymphoid tissue and bacteria that may help recolonize gut microbiota
- Colon makes up the majority of the large intestine and has four parts: ascending colon, transverse colon, descending colon, and sigmoid colon
- Colon mucosa consists of columnar epithelial cells, no villi or folds, and few to no digestive enzyme-secreting cells
- Colon wall has a membrane of goblet cells that secretes mucus to protect the wall from the acids and gases produced by bacteria that live in the colon
- Gut bacteria are essential for production of vitamins B and K
- In the colon, water and minerals are absorbed from the undigested food into the blood
- Undigested food residues that remain produce feces
- Feces containing undigested food residue, gut bacteria, sloughed off epithelial cells, and other excretory products such as bilirubin, pass into the rectum to be stored
- More water is then absorbed, and the feces pass into the anal canal to be expelled
What is the purpose of the Anus
- Stretching of the rectum wall initiates the defecation reflex and forces feces into the anal canal
- Impulses reach the brain, and we make voluntary decisions as to whether or not we open the external anal sphincter
what is digestion
The process by which large molecules in food are broken down into smaller molecules that can be absorbed by the body.
What is Absorption
The process by which the digested molecules are taken up by the cells lining the gut and transported into the bloodstream.
What is Assimilation
The process by which the absorbed molecules are transported to the body cells and used for various metabolic processes.
What are Amino Acids
Building blocks of proteins that are used to build hormones and enzymes or converted to ammonia and then urea by the liver for excretion in urine.
Glucose
A simple sugar that is used for cellular respiration or converted to glycogen and stored in the liver.
Fatty Acids
Molecules used to make cellular membranes, provide insulation, or stored as body fat.
Mechanical digestion
When you bite and chew food, large pieces are broken down into smaller ones. The action of the stomach-churning food is another example of mechanical digestion.
Chemical digestion
Enzymes that hydrolyse macromolecules are present in saliva, gastric juice, enteric juice and pancreatic juice. This hydrolysis of macromolecules to smaller molecules is chemical digestion.
Nutrient absorption
The main site of nutrient absorption is the ileum, which has a large surface area for absorption due to its long, folded structure and villi with microvilli. Glucose and amino acids are absorbed into the bloodstream by active transport, while glycerol and fatty acids move by diffusion and are formed into chylomicrons.
Active transport of glucose and amino acids
Sodium ions are actively transported out of epithelial cells lining the villi and into the ileum lumen, decreasing the concentration of sodium ions in the cells. Sodium ions diffuse back down their concentration gradient across the cells, carrying glucose or amino acids with them.
Formation of chylomicrons
Glycerol and fatty acids move by diffusion through the cell surface membrane of the epithelial cells of the villi. Inside the epithelial cells, they are combined to form triglycerides, which are then modified to form chylomicrons that diffuse out of the epithelial cells and into a lymphatic vessel.
