JWSS Biology Chapter 5B Nutrition in Humans

Name:______________________ ( ) Sec 3 G3 Biology Chapter 5 Notes Class: Sec 3_____ Date: ____________ ABSORPTION (d) describe the structure of a villus and its role, including the role of capillaries and lacteals in absorption state the function of the hepatic portal vein as the transport of blood rich in absorbed nutrients from the small intestine to the liver What is Absorption? Absorption is the process whereby digested food substances are absorbed into the body cells. How is the small intestine adapted for absorption? • The surface area to volume ratio is increased for absorption. Structure of a villus Concentration Gradient The continual transport of absorbed nutrients away by the many capillaries in the villus help to maintain a concentration gradient for the absorption of digested food substances.

Sec 3G3 Science BIO Chapter 5 Notes 2 Glucose and Amino Acids Absorbed by diffusion into the blood capillaries of the villi Absorbed by active transport Fatty Acids and Glycerol Absorbed by diffusion into the epithelium, then combines to form minute fat globules which enter the lacteals. Adaptation of the Small Intestine Function One-cell thick epithelium • Shorter diffusion distance , Faster rate of absorption of digested food substances. Villi and Microvilli • To increase surface area to volume ratio to increase the rate of absorption of the digested food substances into the body. • Presence of many capillaries ensure that a concentration gradient is maintained for faster rate of absorption. Long • To provide sufficient time for absorption to occur TRANSPORT AND ASSIMILATION OF ABSORBED NUTRIENTS What is assimilation? (own understanding: how does our body use the absorbed nutrients?) Assimilation is the process whereby some of the absorbed food substances are converted into new protoplasm or used to provide energy. Hepatic Portal Vein • After absorption in the small intestine, the blood capillaries carry the nutrients away from the small intestine. • The blood capillaries unite to form a larger hepatic portal vein that leads to the liver. • Fats are carried by lymphatic capillaries that join to form larger lymphatic vessels which discharge fats into the bloodstream.

Sec 3G3 Science BIO Chapter 5 Notes 3 Utilisation of Nutrients Glucose 1. Converted into glycogen in the liver for storage 2. Some glucose transported out of the liver and distributed around the body 3. Source of energy. Sugar is oxidised during respiration in cells Amino Acids 1. Converted into new protoplasm that is used for growth and repair of worn-out parts 2. Used to form enzymes and hormones 3. Excess amino acids are deaminated Fats 1. Normal conditions: fats are not broken down when there is sufficient supply of glucose 2. Used to build protoplasm 3. Fasting: Fats broken down to provide energy 4. Excess fats stored in adipose tissues. Adipose tissues protect organs by acting as shock absorbers. Need to know how to label the blood vessels, organ (liver)

Sec 3G3 Science BIO Chapter 5 Notes 4 FUNCTIONS OF THE LIVER Regulation of Blood Glucose Concentration 1. Helps to keep the amount of blood glucose constant 2. After a heavy meal: 3. During fasting:

Sec 3G3 Science BIO Chapter 5 Notes 5 Islets of Langerhans of pancreas stimulated to release insulin into the blood Islets of Langerhans of pancreas stimulated to release glucagon into the blood

Sec 3G3 Science BIO Chapter 5 Notes 6 Production of Bile 1. Plays an important role in fat digestion. 2. Secretes bile which is stored in the gall bladder Iron Storage 1. Red blood cells become worn out after 3 -4 months and need to be replaced 2. These worn -out RBCs are destroyed in the spleen and their haemoglobin is brought to the liver 3. Liver breaks down the haemoglobin and stores the iron released in the process 4. Bile pigments also formed from breakdown of haemoglobin Protein Synthesis 1. Produces prothrombin and fibrinogen which are essential for clotting of blood Deamination of amino acids 1. Excess amino acids transported to the liver 2. Amino groups removed and converted into urea 3. This is called deamination (must write!) 4. Remains of the amino acid are converted into glucose and then into glycogen

Sec 3G3 Science BIO Chapter 5 Notes 7 Detoxification • Harmful substances may be absorbed into the blood and is made harmless by the liver. The process of converting harmful substance into harmless ones is known as detoxification. • e.g. Alcohol is broken down to acetaldehyde in the liver by an enzyme called alcohol dehydrogenase The Effects of Excessive Consumption of Alcohol On the Digestive System 1. Stimulates acid secretion in the stomach leading to increased risk of gastric ulcers 2. Prolonged alcohol abuse may lead to cirrhosis of the liver: liver cells destroyed and replaced with fibrous tissue. May lead to haemorrhage or bleeding in the liver 3. May lead to liver failure and death Liver cirrhosis Slows down brain function (thus increasing reaction time) Reduced self- control Increased risk of gastric ulcers Symptoms of drunkenness Frequent intake leads to addiction

Sec 3G3 Science BIO Chapter 5 Notes 8 On the Nervous System 1. Depressant: Slows down brain functions 2. Reduced self-control: becomes carefree, removes inhibitions, self-control reduced. Effect on Reaction Times 1. Slurred speech, blurred vision and poor muscle coordination 2. Deterioration in judgement 3. Reaction time increases (SLOWER reaction) Social Implications 1. Frequently drinking alcohol can make someone addicted and thus, becomes dependable on alcohol 2. Neglect work and families and exhibit violent behaviour towards family members