Digestive System Flashcards
Define digestion
The process that breaks down complex food substances into simple, soluble molecules that are small enough to be absorbed into the body cells
Define physical digestion
Mechanical breakdown of food into smaller particles to provide large surface area to volume ratio for faster rate of chemical digestion by digestive enzymes
Define chemical digestion
Breakdown of large food molecules into small soluble molecules catalysed by digestive enzymes through hydrolytic reactions.
Describe digestion in mouth
Act of taking food into mouth is called ingestion. Chewing breaks down food into pieces to increase surface area to volume ratio for faster rate of chemical digestion by digestive enzymes. Saliva produced by salivary glands in mouth moistens and soften food. Contains salivary amylase which digests starch into maltose. Thoroughly chewed food rolled into bolus in preparation for swallowing. After swallowing, bolus enters oesophagus. Digestion of starch continues in oesophagus
What is optimum pH of salivary amylase
6.5-7.5
Define peristalsis
A rhythmic wave like muscular contraction of the wall (towards the stomach for oesophagus)
In small intestine, which is longitudinal muscle and which is circular muscle
Inner muscle is circular muscle and outer muscle is longitudinal muscle
Describe physical digestion in stomach
Stomach is elastic, muscular bag, with thick muscular walls
Food is churned and mixed with gastric juice by peristaltic contractions of stomach wall for hours. Partly digested food becomes liquefied, forming chyme which passes into duodenum in small amounts
Describe chemical digestion in stomach
In presence of food, gastric glands contained in stomach secrete gastric juice, consisting mainly of hydrochloric acid and two enzymes, pepsin and rennin
Hydrochloric acid - acidic medium suitable for action of enzymes in stomach, kills bacteria, converts pepsinogen(inactive) to pepsin(active)
Pepsin(optimum pH - 2) - digests proteins to polypeptides by hydrolysis
Describe liver, pancreas, gallbladder
Pancreas is gland lying below stomach which produces several digestive enzymes
Liver is largest gland that produces bile, alkaline liquid containing bile salts and bile pigments
Gall bladder stores bile
Describe bile
Function is to emulsify fats, to physically break them down into tiny fat droplets to increase surface area to volume ratio for faster digestion by lipase
Does not contain digestive enzymes
Creates alkaline environment for enzymes action and reduces acidity of chyme
Describe enzymes produced by pancreas and their action (in pancreatic juice)
Pancreatic amylase - starch to maltose
Trypsin - Protein to polypeptides
Pancreatic lipase - Emulsified fat to fatty acids + glycerol
Describe enzymes produced by intestinal gland and their action (in intestinal juice)
Peptidase - Polypeptides to amino acids
Maltase - Maltose to glucose
Sucrase - Sucrose to glucose + fructose
Lactase - Lactose to glucose + galactose
Intestinal lipase - emulsified fat to fatty acids + glycerol
What does the small intestine consist of
Duodenum, jejunum, highly coiled ileum
Why is small intestine long
To provide sufficient time for absorption of food substances to take place
Describe villi adaptation and function of small intestine
Inner walls of small intestine have many transverse folds bearing many finger-like projections called villi. Each villus possesses numerous microvilli
This increases surface area to volume ratio for faster absorption of digested food substances by diffusion
Why epithelium of villus of small intestine one cell thick
To reduce the distance for digested products to diffuse into capillaries and lacteal
Describe blood capillary adaptation of small intestine
Small intestine consists of dense network of blood capillaries and lacteal within the villi.
This continuous transport of digested food substances maintains a steep concentration gradient for absorption of digested products by diffusion
Describe absorption of digested products in small intestine
Glucose and amino acids are absorbed by facilitated diffusion into blood capillaries of villi. They are absorbed by active transport when there is lower concentration in intestinal lumen than in blood capillaries. Fatty acids and glycerol diffuse into epithelial cells and recombined to form minute fat globules before diffusing into the lacteal. Most water and minerals absorbed in large intestine
Describe transportation of digested products away from small intestine
Blood capillaries of small intestine join to form venules which join to form hepatic portal vein. Hepatic portal vein carries mainly glucose and amino acids to the liver to be processed. Fat globules are transported away from small intestine by lacteal
Define assimilation
The utilisation of absorbed nutrients and how body deals with excess nutrients
Describe assimilation of glucose
Glucose is substrate for respiration to release energy for cellular activities. Excess glucose is converted into glycogen by liver cells and stored. This stimulated by insulin produced by pancreas. Glycogen converted into glucose by liver cells when blood glucose level is low, stimulated by glucagon produced by pancreas
Describe assimilation of amino acids
Required to make new cell materials that are used for growth and repair of worn-out parts of body. Required to make enzymes and hormones. Excess amino acids are deaminated in the liver. Amino group is removed and converted into urea to be excreted in the urine
Describe assimilation of lipids
Required to maintain cell membranes
Required in production of steroids hormones.
Fats are required to protect vital organs such as heart and kidneys.
When there is inadequate supply of glucose, fats will be broken down in liver to provide energy
Excess fats stored in adipose tissues under skin. Fats droplets collect in cytoplasm and fat droplets increase in size and number to form one large globule of fat in middle of cell, pushing cytoplasm into thin layer and nucleus to one side.
