Digestive System Pt 3 (Bio 11 Unit 3)

Bile Salts

• Bile salts are components of bile that break down large fat globules.
• Bile speeds up fat digestion.
• Bile is produced by the liver and stored and concentrated in the gall bladder when the stomach is empty.
• When there are fats in the small intestine, the hormone CCK is released.
• CCK is carried in the blood to the gall bladder and triggers the gall bladder to release bile salts.
• Bile salts emulsify, or break down, large fat globules into smaller droplets.
• This is physical digestion, not chemical digestion, since chemical bonds are not broken.
• The physical digestion prepares the fat for chemical digestion by increasing the exposed surface area on which fat-digesting enzymes, such as pancreatic lipase, can work.

Liver and Gall Bladder Problems

• Cholesterol, an insoluble component of bile, acts as a binding agent for the salt crystals found in bile.
• The crystals precipitate and form larger crystals called gallstones.
• Gallstones can block the bile duct, impairing fat digestion and causing considerable pain.
• Bile also contains pigments from hemoglobin breakdown.
• The characteristic brown color of feces results from hemoglobin breakdown.
• Obstruction of the bile duct or accelerated destruction of red blood cells can cause jaundice, turning skin and other tissues yellow.
• The liver stores glycogen and vitamins A, B12, and D.
• The liver detoxifies many substances in the body by making harmful chemicals soluble so they can be eliminated in the urine.
• Alcohol is broken down by the liver into usable materials and wastes.
• Alcohol can destroy liver tissue if consumed in large quantities.
• Damaged liver cells are replaced by connective tissue and fat, leading to cirrhosis of the liver, which can also result from nutritional deprivation or infection.

Liver Functions Summary

1. The liver produces bile, which contains bile salts that emulsify fats, forming small droplets and providing greater surface area upon which fat-digesting enzymes work.
2. Gallstones are formed from salt crystals and cholesterol in the gall bladder.
3. Jaundice is a yellowing of the skin caused by the accumulation of bile salts in the blood.
4. The liver stores glycogen and vitamins and detoxifies many harmful substances.
5. If liver tissue is destroyed, the liver cells are replaced by connective tissue and fat; this is called cirrhosis of the liver.

Absorption of Materials

• Chemical digestion is complete by the time food reaches the large intestine.
• The colon, the largest part of the large intestine, stores wastes long enough to reabsorb water.
• Some inorganic salts, minerals, and vitamins are also absorbed with the water.
• The stomach absorbs some water, specific vitamins, some medicines, and alcohol.
• The large intestine houses bacteria, such as E. coli, which are essential to life and use waste materials to synthesize vitamins B and K.
• Cellulose, a long-chain carbohydrate characteristic of plant cell walls, reaches the large intestine undigested and provides bulk, which stimulates bowel movements.
• Insufficient cellulose intake can lead to fewer bowel movements and potentially increase the risk of colon cancer.
• Fibre may reduce cholesterol levels and provide a balanced diet.
• Most absorption takes place within the small intestine.
• Villi, long fingerlike tubes, greatly increase the surface area of the small intestine.
• Microvilli, fine, threadlike extensions of the membrane, further increase the surface for absorption.
• Each villus is supplied with a capillary network and lymph vessels called lacteals that transport materials.
• Carbohydrates and amino acids are absorbed into the capillary networks; fats are absorbed into the lacteals.

Large Intestine and Absorption

1. Chemical digestion is complete by the time food reaches the large intestine.
2. The colon stores wastes long enough to reabsorb water.
3. The large intestine houses bacteria that use waste materials to synthesize vitamins.
4. Most absorption takes place in the small intestine.
5. Surfaces of the small intestine have villi; cells that line each villus have microvilli. Together, villi and microvilli increase the surface area available for absorption.

Homeostasis and Control Systems

• The body works best at an internal temperature of 37°C, with a 0.1\% blood sugar level, and at a blood pH level of 7.35.
• Homeostasis is the body’s ability to maintain a constant internal environment.
• Active balance requires constant monitoring or feedback about body conditions.
• Receptors sense information about blood sugar, body temperature, oxygen levels, and other body conditions.
• When homeostasis is disrupted, a monitor sends a signal to the coordinating centre (the brain) where the normal limits are set.
• The brain relays the information to the appropriate regulator, which helps restore balance.
• Examples of adjustments include an increase in heart rate during exercise or the release of glucose from the liver to restore blood sugar levels.