Topic 6: Human Physiology

Transcription

1 Topic 6: Human Physiology 6.1 Digestion and Absorption D.1 Human Nutrition D.2 Digestion Essential Understandings: The structure of the digestive system allows it to move, digest, and absorb food. A balanced diet is essential to human health D

2 Human Nutrition Essential nutrients chemicals found in foods we eat and are used by the body Absorbed to give energy, prevent diseases, strengthen bones, etc. Those molecules that our body cannot synthesize are called ESSENTIAL NUTRIENTS Essential amino acids, essential fatty acids, minerals, most vitamins

3 Minerals Inorganic Long-lived within the body Usually need a very small amount/intake of minerals Examples: calcium for bone, iron for haemoglobin Electrolytes: those minerals that are easily dissolved in a fluid medium (eg. Blood or cytoplasm) calcium (Ca 2+ ), iron(fe 2+ ), sodium (Na + ), chloride (Cl - ), magnesium (Mg 2+ )

4 Vitamins Organic (carbon based) Need in small quantities Vitamin C essential in humans; without it, scurvy will result (think pirate s teeth!)

5 From i-biology.net

6 Digestion Prepares food for use by all body cells The physical and/or chemical breakdown of food Large food molecules need to be digested PRIOR to the nutrients being absorbed Digestion is an enzyme-facilitated chemical process Did you know: the average person eats more than 500kg of food per year!

7 Digestion Large food molecules are usually polymers (such as polysaccharides, proteins and lipids) polymers are too large to be absorbed from the digestive tract into the circulatory system Simply put, they are too large to move across the membranes of the small intestine epithelial cells Polysaccharides > monosaccharides, polypeptides > amino acids lipids > glycerol and fatty acids Monomers (monosaccharides, amino acids, glycerol, and fatty acids) are now small enough to be absorbed by small intestine epithelial cells, these can be moved by either diffusion, facilitated diffusion, or active transport through membrane proteins

8 Hydrolysis. again. Water-Splitting Reaction used to break down large organic molecules Enzymes are needed in these reactions

9 Role of enzymes in digestion at body temperature (37 C in mammals), reaction rates are too slow to be efficient at hydrolysis reactions of large food molecules hydrolytic reactions in the digestion of large food molecules are exothermic, but occur very slowly due to considerable activation energy enzymes lower activation energy (Ea), catalyzing hydrolysis reactions of large food molecules into their monomers By lowering the Ea of the reactions, high temperatures are not required High temperatures would cause proteins to denature and cells to be damaged Reactions can happen more quickly at our normal body temperature

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11 Anatomy of the human digestive system: A long, muscular tube with many sections and areas Begins with the mouth and ends with the anus

12 The Digestive Tract Major Organs Mouth Pharynx Esophagus Stomach Small Intestine Large Intestine Anus

13 The Digestive Tract - Accessory Organs/Parts Organs that are not in the digestive tract but help in the process of digestion: Teeth Tongue Salivary Glands Liver Gall Bladder Pancreas

14 Physical Digestion Physically breaking food stuff into smaller pieces WITHOUT chemically changing it into different molecules Increases the exposed SA for chemical digestion to occur Mechanical Changes the physical form of food Chew, tear, grind, mash, mix

15 Mouth (Oral Cavity) Teeth Physical / mechanical digestion Incisors - cut Canines - hold, tear Premolars - crush, grind Molars - chew, grind

16 Mouth (Oral Cavity) Saliva Mostly water and mucus Acts as a lubricant Moistens food Contains enzymes (salivary amylase) that begins digestion of starch (to glucose) Salivary Glands produce and secrete saliva into the oral cavity Tongue Mixes and rolls food into tiny mashed up bits (BOLUS) Pushes food toward pharynx

17 Esophagus straight muscular tube 10 inches (25 cm) long connects mouth to the stomach Food takes about 4 to 8 seconds as it passes through to stomach Peristalsis propels food (bolus) and liquid slowly down the esophagus into the stomach Smooth muscles - controlled by the ANS (autonomic nervous system) Action of peristalsis is controlled by two layers of muscles: longitudinal and circular

18 Stomach a large, expandable, muscular and glandular organ Churns and grinds bolus into smaller pieces (mechanical digestion) by muscular contractions Food mixes with gastric juices secreted by stomach wall - Acid kills bacteria - Pepsin begins chemical digestion of proteins Image From Pearson HL Biology 2 nd Edition

19 Composition of Gastric Juice Image From Pearson HL Biology 2 nd Edition

20 Stomach - Sphincters Cardiac (Gastroesophageal) Sphincter Limits backflow of gastric juices up the esophagus Failure = heartburn (acid reflux) Pyloric Sphincter Limits flow of gastric juices into the small intestine

21 Hydrochloric Acid (HCl) From Parietal cells (within gastric pits) Function Breaks up connective tissues to increase SA for pepsin enzyme activity Kills bacteria Activates pepsin by reacting with pepsinogen Pepsinogen Function Pepsin Precursor Pepsinogen + HCl pepsin (protein) (enzyme)

22 Pepsin Function - Enzyme that digests proteins into peptides Optimal activity is at low ph (pepsin) Protein + water a.a. strands (polypeptide fragments)

23 Chyme Semi-fluid mass of partially digested material Exits the stomach (expelled into duodenum) ph of 2 (very acidic)

24 Small Intestine: Duodenum, Jejunum, Ileum 1. Duodenum (Approx. 10in; connected to stomach) ph: Site of DIGESTION Produces and receives numerous digestive enzymes (amylase, trypsin) and hormones, pancreatic juices and BILE (produced by liver, stored in gall bladder) Pancreatic juice adds sodium bicarbonate to neutralize acidic chyme (for optimal enzyme activity) 2. Jejunum (Approx. 8ft) & 3. Ileum (Approx. 12ft) Food moves through intestine through peristalsis Site of ABSORPTION (primarily the ileum) Folds allow for an increased SA Has VILLI (finger-like projections) -> increase SA for absorption and have a rich blood supply

25 Small intestine - Villi

26 Small Intestine - Enzymes

27 Large Intestine - larger in diameter than small intestine - 5ft (1.5m) in length - ph: Includes Cecum, colon, rectum, anus

28 Large Intestine Function: Water reabsorption Store indigestible materials (ie. Cellulose) Site of 100 trillion bacteria!!! - Including E. coli; Compacts undigested wastes for defecation - Faeces: 40% water - Faeces are stored in rectum

29 Anus Faeces containing undigested food, dead cells and other wastes are expelled from anus NOTE: This is NOT called excretion!

30 Digestion vs Absorption vs Assimilation Digestion = breaks down food into smaller molecules Absorption = movement of these molecules from lumen of digestive tract across the membranes of cells lining the digestive tract and enter into the lymphatic system or circulatory system (blood) Assimilation = following digestion and absorption nutrients are taken into somatic cells (tissues) and converted to the biomass of the organism (taken in and used)