Weds 5/20/15. Membranes - finish last lecture outline. Digestive System Nutrition Types of digestion & digestive systems Vertebrate digestive system

Transcription

1 Membranes - finish last lecture outline Weds 5/20/15 Digestive System Nutrition Types of digestion & digestive systems Vertebrate digestive system structures and functions // accessory organs mechanism of digestion & absorption of macromolecules role of hormones

2 Animal Nutrition & Digestion Nutrient any substance consumed by an animal that is needed for Absorption 5 categories of organic nutrients Carbohydrates / Proteins / Lipids / Nucleic acids Vitamins Inorganic nutrients minerals, e.g., Ca 2 +(calcium), K+(potassium), Fe 3+ (iron) water

3 Essential Nutrients: n Certain compounds cannot be synthesized from any ingested or stored precursor molecule n 4 groups (1) Essential amino acids Carnivores and omnivores readily obtain all 8 in meat Most plants do not contain every essential amino acid in sufficient quantity

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5 Essential Nutrients: (2) Essential fatty acids Certain Unsaturated fatty acids found Strict carnivores obtain them from Example: Linoleic Acid Unsaturated fat that is needed for membrane phospholipids

6 Essential Nutrients: (3) Minerals (Table 41.2) Examples: Calcium (Ca) bone formation, blood clotting, nerve & muscle function Phosphorus (P) bone formation, acid/base balance, nucleotides Potassium (K) acid-base balance, water balance, nerve function Chlorine (Cl) acid-base balance, gastric juice production, nerve function and osmotic balance Sodium (Na) acid-base balance, water balance and nerve function Iron (Fe) hemoglobin and electron carrier, enzyme cofactor

7 Essential Nutrients: (4) Vitamins (Table 41.1) Important organic nutrients Fat-soluble vitamins e.g. Water-soluble vitamins e.g. Not all animals Examples: Water soluble: B 2 component of coenzymes FAD (cellular respiration) B 3 component of coenzymes NAD+ and NADP+ (cellular respiration & photosynthesis C used in collagen synthesis & antioxidant Fat soluble A component of visual pigments; epithelial tissues D aids in absorption of calcium & phosphorus (can be synthesized with exposure to sunlight) K important in blood clotting

8 Examples of role of vitamins: Vitamin D Vitamin C

9 Deficiencies in Essential Nutrients can cause: - deformities, disease and death Vitamin A deficiency causes:

10 Essential Nutrients: n Animals may consume monomers, polymers, or both n Polymers must be broken down into monomers

11 Thought Question: Hummingbirds are well adapted to obtain sugary nectar from flowers, but they also forage on insects and spiders, particularly during the breeding season. Why, given the evolution of specializations to feed on nectar, do hummingbirds also feed on insects and spiders? What is the benefit? Key Concept: -

12 Principles of digestion and absorption Digestion requires enzymes capable of hydrolyzing bonds Products of digestion must be absorbed across plasma membranes Minerals, vitamins and monomers do not require digestion Digestion: intracellular digestion constrained on

13 Digestion: extracellular digestion increase in support Types of Digestive Systems: (1) Gastrovascular cavity Simple extracellular digestion Food particles eventually fig 41.7

14 Types of Digestive Systems: (2) Alimentary canal Single elongated tube with entry and exit ends fig 41.8 Lined by epithelial cells Synthesize and secrete Secrete hormones Transport of Several specialized regions Storage area

15 (3) Vertebrate digestive systems Alimentary canal or gastrointestinal (GI) tract Anterior end functions primarily in Middle portion functions in storage and Upper part of small intestine and associated organs (liver, gallbladder, pancreas) primarily responsible for Posterior part functions in fig 41.9

16 Food Processing: Four stages 1. Inges3on: 2. Diges3on: Food is broken down into molecules that are small enough for the body to absorb a. Mechanical Diges4on: b. Chemical Diges4on: Proteins Polysaccharides, Disaccharides Fats Nucleic Acids Enzyma3c Hydrolysis Amino acids Monosaccharides Glycerol, acids Nucleo4des Bacteria that inhabit an animal s gut also aid in the diges4on of some macromolecules 3. Absorp3on: 4. Elimina3on:

17 Digestion of macromolecules: Mouth / Oral Cavity: all animals ingest their food for digestion jaw w/ teeth mechanical grinding of food saliva Saliva also contains: 1. Mucus: Mixture of water, salts, cells, and mucins (slippery glycoproteins that protect the lining of mouth from abrasions and lubricate food for easier swallowing) 2. Buffers: 3. Antibacterial agents: Lysozymes that destroy

18 Pharynx & esophagus pathway only swallowing begins in esophagus as voluntary action tongue pushes food to back of mouth for swallowing go down through epiglottis fig 41.10

19 Stomach: mechanical and chemical digestion flow from esophagus via peristalsis waves of contractions saclike organ evolved for storing food partially digests proteins glands secrete hydrochloric acid pepsinogen converted to pepsin (protease) to begin food reduced to chyme control into and out of stomach via

20 Cells of the stomach HCl and Pepsin very low acidity in stomach due to HCl (ph-2) fig Parietal cells: actively pumps chloride ions combine in the lumen of the stomach Chief cells: release pepsinogin pepsin à Mucous cells:

21 Are the epithelial cells that line the stomach vulnerable to acid ph and pepsin diges3on? Yes, but these cells also secrete mucus that protects against self- diges4on Epithelial cells replicate frequently which enables the lining of the stomach to be replaced every three days What is a gastric ulcer? What is the cause of stomach ulcers? How are stomach ulcers treated? 21

22 Small intestine longest compartment (6m!) 1 st part duodenum Hydrolytic enzymes found on luminal surface or secreted by pancreas into lumen (discussed later) fig 41-13

23 Small intestine remaining regions (jejunum and ileum): vitamins, mineral and water also absorbed Pathway absorbed products take: fig 41-13

24 Passive or active absorption Nutrients must be absorbed by the epithelial cells via: Small intestine is specialized for increased surface area Mucosa is Villi Epithelial cells of villi covered Increases surface area 600-fold Increases likelihood of encountering digestive enzyme and being absorbed

25 Small intestine: final chemical digestion & absorption Absorption of nutrients: maximized surface area = fig capillary network absorbs fatty acids and monoglycerides go via Lacteal (lymphatic vessel) allows for larger fat particles to enter, eventually dumped into blood

26 Accessory organs: pancreas secrets digestive enzymes // liver de-toxification of blood, storing glycogen (ready source of energy) and fatsoluble vitamins: gall bladder

27 Large Intestine: much shorter than small intestine but wider diameter primary function to store and concentrate fecal matter and absorb some salt and water houses good bacteria digest produce vitamins B 1, B 2, B 6, B 12 & K folic acid breaks down cecum - more developed in herbivores appendix - tube off of large intestine fig 41.15

28 Digestive Systems Adapted to Diet: segments of digestive system are specialized in function enhancement of regions critical for digestion of particular food types reduction or loss of areas with little functional value e.g., insectivores have short digestive systems - e.g., ruminants have specialized stomachs (& cecum) to help

29 Mutualisms w/ microbes: fig mutualistic relationships between cows & hoatzin house bacteria in stomach or crop respectively bacteria have

30 Digestion of macromolecules & lipids: fig 41.12

31 Mechanisms of digestion and absorption Carbohydrates In typical omnivore, most are starch and cellulose with some monosaccharides and disaccharides Mouth fig S.I. additional starch digestion by Small intestine monosaccharides transported across Fructose absorbed by facilitated diffusion. Glucose & Galactose via secondary active transport

32 Mechanisms of digestion and absorption Proteins stomach releases pepsinogen à pancreas secretes fig enzymes activated in small intestine small intestine enzymes complete digestion to transported into interstitial fluid and into blood stream amino acids move into epithelial cells by 2nd active transport out of cell into circulatory system by facilitated diffusion

33 Mechanisms of digestion and absorption fig Fat digestion entirely in small intestine pancreatic lipase phospholipids & bile salts emulsify fat into bile salts form micelles - keeping gradually release small lipids into intestine epithelium

34 Fat Diges3on Requires Bile Salts: These salts act as detergents and increase surface area for diges4on. Bile salts have a hydrophobic and a hydrophilic side Large lipid droplet Mix with bile salts Micelle These will a@ach to fat globules, emulsifying them, and causing them to form micelles Triglyceride Pancrea4c Lipase Glycerol Fa@y acids Monoglycerides Bile also aids in the destruc4on of red blood cells that are no longer func4onal and helps break 34 down toxins

35 Mechanisms of digestion and absorption Fat Triglycerides reform inside intestinal cells packaged in SER (coated in proteins, phospholipids & cholesterol form chylomicrons released by exocytosis from will enter into general blood circulation fig 41.14

36 Good review figure enzymatic activity and absorption: sugars and amino acids à fats à broken down à surrounded by micelle absorbed into S.I. and reformed into lipoprotein à lacteal (lymphatic)

37 Vitamins, minerals and water Do not require digestion Absorbed in complete form Fat-soluble vitamins follow pathway for fat absorption Water-soluble vitamins typically not stored and will be flushed out of system Small amounts of water absorbed in stomach but most in small intestine

38 Role of Hormones: Gastrin stretch of stomach stimulates the release travels via bloodstream stimulates Cholecystokinin (CCK) & Secretin stimulated by presence of chyme from pancreas fig stimulates release of bile from gallbladder secretin stimulates pancreas to CCK stimulate release of digestive enzymes What happens in the presence of high levels of fat?? (pg 909)

39 Draw a flow chart of the sequence of events that occurs when chyme enters the small intestine: - think about hormones, acidity, digestion Chyme enters small intestine

40 Role of Hormones: Energy Storage: excess energy in body à decrease in energy in body à oxidizing 1g of fat liberates more energy than 1g of carbohydrate fig 41.21

41 Role of Hormones: regulation of blood glucose levels normal range mg/mL importance of glucose key source of carbon for carbon skeletons of organic molecule two hormones: fig 41.21

42 Role of Hormones: regulation of blood glucose levels insulin à stimulates glucagon à stimulates fig 41.21

43 Role of Hormones: regulation of blood glucose levels Diabetes: Type 1 insulin-dependent early onset production of insulin Type 2 non-insulin-dependent excess body weight & lack of exercise leading causes fig 41.21

44 Impact on public health Heartburn 1 in 4 in the US suffer Many contributing factors Ulcers Most common in stomach, esophagus and small intestine 6-7% of US adults 2005 Nobel Prize for revolutionary discovery that Helicobacter pylori caused ulcers Diarrhea Over 1 billion cases in the US each year /many causes Cholera caused by At least 2,000 people die each year Chief concern is loss of