MT 5 - Digestion and energy metabolism Flashcards

Question

59. Water transport

Answer 1

* Enters with food and GI secretion * Small intestine water transport is mainly regulated by osmosis. * By abs. of digested luminal contents, contents in lumen become hyperosmotic, and water reabs. rapidly occurs.

Answer 2

•Abs. according to the need of the animal •Iron transported to the animal by food is generally in water-nonsoluble complexes, which abstract abs. o These complexes dissociate at low pH, with help of gastric HCl secretion. o The destruction of complexes reduces Fe3+ to Fe2+. o Transferrin, secr. by enterocytes in duodenum and jejunim, binds two iron ions and forms a Tf-Fe complex. o Receptors at the surface of brush border bind the complex, and take them up by endocytosis o In the cytoplasm, the receptor is released, and the complex moves to the basolateral side where iron is released. o Free transferrin mol. are secr. back to intestinal lumen. o Ferritrin will bind to excess Fe molecules

Answer 3

-Carbohydrate: •Microbial digestion happens in colon in simple stomach herbivores. •Microbial digestion of cellulose is important because: o Some carbs are not abs. in small intestines o Carbs not abs. represents osmotic P in colon, and would cause water loss if not digested down to VFA o They also neutralize acetic products, ensure long retention time, and dilute fermentation products. -Protein •Common features with ruminant forestomach. •Bacteria in colon receive urea from blood to balance N-metabolism •Rabbit: Microbial digestion occurs in cecum. •In order to not loose microbial vitamins and proteins, rabbit digest their food two times.

Answer 4

-Motions of the colon: •Slow waves of colon arise from circular muscle layer and extend from there to longitudinal fibers. •The stimuli from pacemaker areas spread both directions, which makes retrograde motions and mixing of intestinal content possible (antiperistalsis). Peristalsis + antiperistalsis = mixing •Dog and cat: aboral mass peristalsis -Lieberkühn glands in colon prod. mucin for mechanical protection as well as feces formation, and HCO3- for buffering of VFA. -Composition, dry mass and pH of feces vary greatly among the domestic species. -Its color is based on stercobilin -Contain organic indigestible subst. only to a small degree •Proteins in feces originate from detached epithelium of large intestines, and from microbial origin.

Answer 5

-Rectum: main activity is regulation of storage and evacuation of feces. -Most domestic mammals are unable to voluntarily regulate defecation, but e.g. in the dog a conditioned response can be developed. -Defecation is under hypothalamic and cortical control. 1. Empty rectum •A feces evacuation can be used if 15-20 mmHg P is exerted on the wall of rectum, and therefore feces are pushed from previous intestinal section, to the rectum. •Spontaneous evacuation prevented by closing of inner and outer sphincter. 2. Feces gets into the rectum •Afferent nerve fibers reach the S1-S4 segments of spinal cord 3. Feces evacuation reflex •From medullary center, efferent stimulus incr. the contraction of rectum and peristalsis, and relaxes the tone of sphincter. •Simultaneously with this the stimulus of somatic pudendal nerve causes the relaxation of external sphincter. •During feces evacuation reflex caused by dilation and stretching of the wall of rectum, longitudinal muscles also contract. The consequence of this is shortening of rectum, and processing of its content in the aboral direction.

Answer 6

-Food intake: •Center of food intake is the hypothalamus •High temp and protein in food decr food intake •Low temp and egg prod. incr. food intake •Beak is adapted for food-intake, no teeth, no soft palate, no parotid gland, unified oral-pharyngeal cavity. -Esophagus: •Peristalsis passes food to the crop or directly to stomach. •Crop: temporal storage of food, and softening of it. -Glandular stomach: •Primary function is secretion of gastric enzymes. *Mucous glands - mucin *Complex glands - HCl, pepsinogen, mucin prod. -Muscular stomach •The inner layer is a ceratinoid layer, consisting of secretion of gizzard glands, detached epithelial cells and fragments of food. •Motility is synchronized with the glandular stomach -Duodenum: peristaltic and segmented contraction. -Ileum: Fermentation occur -Liver: Bile neutralizes the chyme and emulsifies lipids, and in some species it contains amylase. -Pancreas: Pancreatic enzymes digest into the lumen, enterocyte enzymes digest in small intestines at brush border -Cecum: two kinds of contractions: 1.Mixing: less powerful, but more frequent 2.Propulsive: stronger, but less frequent •Small contractions mix the content, stronger ones pass it along by peristalsis and antiperistalsis. -Colon, cloaca: •Almost permanent anti-peristalsis passes urea from cloaca to colon/ceca, thus filling up the ceca. •To recollect important end-products of microbial digestion, birds ingest parts of their feces. They are coprophagia. Significant because of vitamin supply.

Answer 7

- Unit of (heat) energy: Calorie - 1 kcal = 1000 cal (heat) - 1 cal = 4.184 J - 1 calorie: amount of E required to raise the temp. of 1 gram of water by 1o Celsius. - Combustion of heat of a nutrient is equal to the amount of heat yielded by burning 1g of that nutrient. - Heat content of nutrients is measured by a bomb calorimeter. - The amount of heat measured by the bomb calorimeter is the maximum amount of heat that can be yielded by that nutrient in the body. - Combustion heat of carbohydrates and fats is equal to their physiological caloric value. - Proteins are not entirely combusted in the body. Some metabolites of proteins appear in the urine, which contain further combustible E

Answer 8

-Total Energy – Gross Energy (GE) (E excreted in faeces)->Digestible Energy (DE)(Fermentative E, E in urine)->Metabolizable Energy (ME)(Heat production, specific dynamic action)

Answer 9

- BMR – Basal Metabolic Rate: the energy production measured in an individual in complete resting state - RMR – Resting Metabolic Rate: measured in animals, and is very difficult to satisfy all criteria necessary for measurement * Components: specific dynamic action and continous utilisation of E - Diff. bw. BMR & RMR: the amount of E needed by the animal above the E used for vital processes during measurement of E in resting state.

Answer 10

•Somatic NS: Skeletal muscle •Sympathetic autonomic NS: Metabolic processes •Malnutrition: decr. MR to a fifth of their normal values. •Endocrine system: incr. in metabolic rate: oEpinephrine, Norepinephrine oGrowth hormone oThyroid hormone •Specific dynamic action: 1–3 hours after food intake, the BMR incr. •Temperature: oInternal temp. changes alter metabolism by changing the velocity of chem. reactions in the body (van’t Hoffs law). oEnvironmental temp. changes, under low critical/over high critical temp. incr. metabolism. •Persistent changes in environmental temp.–acclimatisation mechanisms of thyroid hormones. •Muscular activity: Incr. in metabolism •Production: Requires higher E, above RMR, depends on type of product

Answer 11

-Direct - Lavoisier & Laplace’s Direct Calorimetry *Chamber containing the animal is surrounded by ice. The amount of ice melted and water prod. was used to estimate heat generation. *Disadvantages: Expired air and evaporation off the body are not measured. Animal is in a chamber of high humidity. -Direct- Complex Direct Calorimetry: emission of water vapour from the body is also taken into account. •Water of known temp. enters the outer casing of the heat isolated chamber •Heat emitted from the animal heats up the water and so the temp. of the water leaving the casing is measured. From this value and the velocity of the flow, heat production can be calculated •Advantages: E turnover can also be measured during motion or work -Direct- Compensation Calorimeter: •2 chambers of identical thermal capacity are connected, and in a space of constant temp. •Animal in one chamber, electric bulb of known output in the other. •Animal heats up its chamber, the bulb will warm up its chamber to keep the temp. equal in both chambers. •E used by the bulb will be the same as the output of heat produced by the animal. -Direct - Gradient Calorimeter: •Double walled chamber: inner wall is a good heat conductor, outer wall keeps a constant temp.. •The heat diff. bw. the two walls is measured to calculate the amount of heat dissipated. •Quick, simple and reliable calorimetric measurement -Indirect Calorimetry: 1.Open system (Douglas bag): Environmental/atmospheric O2 inspired, expired air is measured. 2.Closed system (Krogh’s device): No atmospheric O2 inhaled. Oxygen is added to the system. Indicator directly shows amount of consumed O2. *Disadvantage: Restricted ability to measure the O2-dependant E prod. only. -Direct & Indirect Calorimetry : O2 consumption and CO2 prod. of the animal can also be determined. *Gives exact and reliable data.

Answer 12

-RQ=CO2(vol./time)/O2(vol./time) •Hyperventilation: RQ incr. •Metabolic acidosis: RQ incr. – respiratory compensation of acidosis increases the amount of expired CO2. •After exercise: RQ falls (0.5) – paying back of O2 debt •Fattening: RQ > 1 •Starving: RQ < 0.5 •RQ values can provide information about the qualitative composition of E sources

Answer 13

-Hunger: lateral nucleus o Lesion: aphagia (loss of ability to swallow) o Stimulation: hyperphagia (abnormally incr. apetite) -Satiety (being full): ventromedial nucleus o Lesion: hyperphagia o Stimulation: aphagia • Appetite: amygdale and prefrontal cortex • Nutritional regulatory signals: o Glucostatic:  Increased glu level->satiety  Decreased glu level->hunger o Aminostatic: Incr. free aa. in EC-fluid inhibits eating, and vice versa o VFA effect: Incr. free VFAs in the blood->food intake is decr. or terminates -Effects of GI tract: •Hormonal effects •Gastric and intestinal filling •Temperature – high temp decr food intake •Estrogen – low estrogen level incr sensation of hunger •Volemia – hydrated organs leads to incr food intake, while dehydrated do not •Density of the population •Hierarchy hormonal effects on hunger •Night-day cycle

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MT 5 - Digestion and energy metabolism Flashcards

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