Chapter 6: Nutrition in humans Flashcards
What is nutrition and its 4 stages?
Nutrition is a process by organisms obtain food and energy for growth of new cells and repair of worn-out tissues and maintenance of the body.
- Ingestion
- Digestion
- Absorption and assimilation
- Egestion
What organs make up the alimentary canal?
- Mouth
- Oesophagus
- Stomach
- Small intestine
- Large intestine
- Rectum
- Anus
What is peristalsis? Describe the process
Peristalsis is the rhythmic, wave-like muscular contractions in the walls of the alimentary canal. It helps with the movement of food along the alimentary canal. It also enables food to be mixed with digestive juices
It has 2 sets of muscles, circular muscles and longitudinal muscles.
As food enters, the walls contract. The circular muscles contract and longitudinal muscles relax, narrowing the lumen to push the food forward. When food enters somewhere, the wall dilates. The longitudinal muscles contract and the circular muscles relax. This widens lumen to allow food to enter.
What is digestion?
Describe the 2 forms of digestion
Digestion is the breakdown of large, complex and insoluble nutrient molecules, into smaller, simpler and soluble nutrient molecules
Physical digestion involves the mechanical break-up of large food into smaller particles to increase surface area to volume ratio for faster rate of chemical digestion catalysed by enzymes. (Chewing, peristalsis, churning of the stomach)
Chemical digestion involves the break-down of complex insoluble nutrient molecules into simpler, soluble nutrient molecules that can be absorbed. (Involved hydrolytic reactions catalysed by digestive enzymes)
Describe digestion in the mouth and oesophagus
- The chewing action of the teeth breaks up pieces of food into smaller pieces
- The tongue then rolls the food into small, slippery, round masses
- The salivary glands in the mouth secrete, saliva, which is mixed with the food by the tongue
- Saliva contains mucin which softens the food
- Salivary amylase catalyses the digestion of starch to maltose.
- Peristalsis in the walls of the oesophagus push the bolus into the stomach
Describe digestion in the stomach
Describe the role of gastric juice
- The entry of the bolus stimulates the release of gastric juice by the gastric glands through gastric pits on inner walls of the stomach.
- Peristalsis mixes the food with the gastric juice
- Churning of the stomach also breakdown large substances into smaller substances
Gastric juice is a dilute solution of hydrochloric acid, mucus and the enzyme, pepsin.
Pepsin catalyses the digestion of proteins into polypeptides.
Hydrochloric acid helps to denature salivary amylase to stop the action of salivary amylase. It also converts pepsinogen into pepsin, and provides an acidic medium for the action of pepsin by providing an optimum pH. Lastly, HCL kills harmful microorganisms in the food.
Describe digestion in the small intestine (Duodenum)
- Chyme enters the duodenum and stimulates the release of pancreatic juice by the pancreas, bile by the gall bladder, and intestinal juice by the small intestines
- These alkaline fluids neutralise the acidic chyme
- The alkaline medium is needed for the action of intestinal and pancreatic enzymes
- The gallbladder releases its stored blue, The bile passes through the bile duct into the duodenum.
- The pancreas secretes pancreatic juice, which contains the enzymes pancreatic amylase, pancreatic lipase and trypsin
- The intestinal juice secreted by the intestinal glands contains enzymes maltase, sucrase, lactase, peptidases and intestinal lipase.
How are carbohydrates digested (4 instances)
- Starch to maltose (salivary amylase)
- Starch to maltose(pancreatic amylase) and then glucose(Maltase)
- Lactose to glucose + galactose (lactase)
- Sucrose to glucose + fructose (sucrase)
How are proteins digested (2 instances)
Proteins to polypeptides (pepsin)
Proteins to polypeptides (trypsin) and then from polypeptides to amino acids (peptidase)
How are fats digested?
- Bile, which is made in the liver and stored temporarily at the gallbladder, is secreted.
- Bile breaks down large fats into small fat droplets that are suspended in water through emulsification.
- This increases surface are to volume ratio of fat molecules for a faster rate of digestion catalysed by lipase
How does having a large surface area help with absorption in the small intestines
A larger surface area increases surface area to volume ratio. This is done by the numerous folds in its inner wall. Inner walls contain villi, which possess microvilli on the epithelium. These finger-like projections also increase surface area to volume ratio for a faster rate of absorption.
How does a thin separating membrane of the small intestine increase its rate of absorption?
The one-cell thick walls of the villi make it easy for nutrients to pass through the bloodstream by reducing diffusion distance, to increase the rate of diffusion of nutrients into the villus. The length of the small intestine increases the time for absorption.
How does a steep concentration gradient in the small intestines help to increase the rate of absorption?
Many capillaries are present to carry away absorbed nutrients quickly, maintaining a constant concentration gradient. Blood capillaries network help to transport amino acids and glucose to the body. Lacteal helps to transport fats to the body.
Explain 3 structural features of the small intestines and their functions
- It is very long and highly coiled. This provides ample time for complete digestion and effective absorption of digested nutrient molecules.
- the inner walls of the intestines have numerous folds with many tiny-finger like projections called villi and microvilli. This helps to increase the surface area to volume ratio of the small intestines, allowing for a faster rate of absorption of digested nutrient molecules
- Each villi has a lacteal or lymphatic capillary surrounded by numerous blood capillaries. This facilitate the transport of fats, Amino acids and glucose to the liver, via the hepatic portal vein. The lymphatic capillary of the villi transports fats while the blood capillaries of the small intestines transport sugars and amino acids. The continual flow of absorbed nutrients in these capillaries maintain a steep concentration gradient to help with he absorption of nutrients by ensuring rapid diffusion.
How are nutrients absorbed in the small and large intestines by diffusion?
- Glucose and amino acids diffuse into blood capillaries
- Glycerol and fatty acids diffuse into the epithelium, and combine to form minute fat globules which enter the lymphatic capillary
