Lecture 5- The hind gut or large intestine and maintenance energy

Question 1

What is the general description of the large intestine?

Answer 1

large intestine= colon, cecum, appendix and rectum -cecum= pouch below the junction of the small and large intestines (at the ileocecal vave) -appendix lymphoid tissue= houses good bacteria? -colon= most of the large intestine -not coiled (unlike the small intestine) -3 sections- ascending, transverse and descneding -terminal portion is S shaped then straignthens to form recturm -one line missing

Question 2

What are the 2 types of post gastric fermentations?

Answer 2

1. Caecal fermenters • Mainly rodents, rabbits and other small herbivores • Often associated with coprophagy and caecotrophy (eat their shit again= caecotroph -coprophagy= eating shit of other species) 2. Colonic fermenters • Includes true herbivores (e.g., horse), omnivores (e.g., pig and human), and carnivores (e.g., cat and dog) • Horse has some expanded caecal fermentation in addition to greatly expanded colonic fermentation • Degree of colonic sacculation is related to importance of fibre digestion and fermentative capacity

Question 3

What are some examples of caecal digesters?

Answer 3

-capybara: grazer -rabbit: selective herbivore -rat, mouse: omnivores

Question 4

What are some examples of colonic digesters?

Answer 4

-sacculated: -Elephant, horse, zebra: grazers -New World monkeys: folivores -Pig, human: omnivores -unsacculated: -panda: herbivore -dog, cat: carnivore

Question 5

What are the functions of the large intestine (3)?

Answer 5

• Re-absorption of water and compact indigestible matter into faeces • Site of absorption of vitamins produced by bacteria (e.g. fermentation) • Storage of faecal matter prior to defecation -main function is the storage of fecal matter but also absorption of water, condense the waste material

Question 6

What does the large intestine look like?

Answer 6

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Question 7

What is the histology of the large intestine?

Answer 7

• Absence of villi – unlike the small intestine (no enzymatic function only to protect the wall of the large intestine) • Presence of goblet cells for mucus secretion • Deep intestinal glands present in the wall

Question 8

What is the physiology of the large intestine?

Answer 8

• Re-absorption in the large intestine includes:

• Water • Vitamins – K, biotin, and B5
• Organic wastes – urobilinogens and sterobilinogens
• Bile salts
• Toxins

• Mass movements of material through colon and rectum

• Defaecation reflex triggered by distention of rectal walls

-organic waste= from blood etc. -mass movements of material through colon and rectum=eating a meal triggers defecation quite often (viz PIC- stretch reflexes!)

Question 9

What is maintenance energy?

Answer 9

the energy you need to keep yourself alive

• just to keep going
• need to memorise this diagram
• what you cannot digest, and also need e to get rid of fecal matter
• then energy that you can digest and then the energy that
• maintenance costs energy

Question 10

What is a respiration calorimeter?

Answer 10

• Measures heat produced by an animal • Lavoisier and Laplace developed the first animal calorimeter in 1780 • Guinea pig in a chamber surrounded by ice -the can not if one animal is more efficient in digestion -the 1st is for guineapig

Question 11

What does direct and indirect calorimetry do?

Answer 11

• Direct calorimetry actually measures the amount of heat given off • Indirect calorimetry measures oxygen consumption and carbon dioxide production and estimates heat given off mathematically

Question 12

What is a Douglas bag?

Answer 12

-bag you put on a human and measure the respiration -can limit activity of the subject and the duration of measurement (extremely uncomfortable to wear)

Question 13

What is the PowerLab?

Answer 13

-modified Douglas bag, used for sheep -The modified PowerLabTM exercise physiology system allows the measurement of acute, real time gas exchange in sheep.

Question 14

What is maintenance?

Answer 14

• The amount of energy (or protein) needed to maintain an animal in zero energy (or protein) balance
• Strictly speaking, maintenance requirement is only measurable in a mature, non-pregnant, non-lactating animal
• But in practice the concept is widely applied to productive animals

Question 15

What is efficiency?

Answer 15

• Maintenance feed requirements have a major effect on efficiency of feed utilisation • For instance >40% energy intake is used to support maintenance

Question 16

What are the components of maintenance?

Answer 16

-basal metabolism, muscular work and temperature metabolism

Question 17

What is basal metabolism?

Answer 17

• Metabolic rate in post absorptive state, with minimal activity, thermal and behavioural stress
• Affected by:
• Body size
• Species
• Age
• Previous level of nutrition
• Climate

Question 18

What is the relationship between body size and heat?

Answer 18

• The bigger an animal, the more heat it produces
• Relationship is curvilinear
• Plotted on logarithmic scale = relationship becomes linear

Question 19

What is this: log H = 1.84 + 0.75 log W?

Answer 19

• H = 69 W0.75 • H is heat production (kcal/d) • W is body weight (kg) • W0.75 is termed metabolic body weight -• Considerable species variation around the mean; 69 W0.75 • Sheep 75 -calculation to get the basal metabolic rate

Question 20

What is dimensional analysis?

Answer 20

-the relationship between BMR and body mass -The relationship between surface area (A) and length (L) is: A α L2 -The relationship between mass (m), density (ρ) and volume (V) is: m = ρV -The relationship between length (L) and volume (V) is: V α L3 -The relationship between mass (m) and length (L) is: m α L3 -Length is therefore proportional to the cube root of the mass L α m0.33 -If the area is proportional to the square of the length then A α m0.67 -An animal gives up its heat to the environment in proportion to the surface area (m x constant k) – therefore ΔE/Δt = k. m0.67 -Heat generation is proportional to the metabolic rate – therefore BMR = k. m0.67 -•Actually the relationship is not quite as first noted by the theory, Kleiber observed that the relationship between mass and metabolic rate was: -BMR = k. m0.75 -The relationship holds true over 27 magnitudes of mass – from the simplest enzyme system to the metabolic performance of a whale!!

Question 21

What is the relationship of basal heat production and age?

Answer 21

• Basal heat production, corrected for metabolic body weight, declines quickly from birth to weaning, then more slowly to maturity -metabolic rate goes down as you age -cannot eat as much

Question 22

What is the relationship of basal heat production and climate?

Answer 22

• Prolonged cold causes increased basal heat production • Prolonged heat caused decreased basal heat production

Question 23

How does muscular work affect the maintenance?

Answer 23

• Effects of exercise on maintenance requirements depend on
• Work intensity
• Work duration
• NRC tables usually add a correction factor of 10% of fasting heat production to account for effects of activity
• Would be higher in grazing animals

Question 24

How does temperature regulation affect maintenance?

Answer 24

• When environmental temperature falls below the animal’s lower critical temperature, heat production must increase if normal body temperature is to be maintained

• thermoneutral zone
• between lower and upper critical zones
• above or below= will need more energy to maintain energy

Question 25

What is lower critical temperature affected by?

Answer 25

• Lower critical temperature is affected by • Level of feed intake • Body size • Tissue insulation (condition) • Coat insulation -smaller people= colder quicker -tissue insulation= fat = if little= get colder faster

Question 26

What affects the rate at which heat production increases with environmental temperature decreasing?

Answer 26

• Rate at which heat production increases with decreasing environmental temperature below critical is independent of feed intake

Question 27

What is the effect of energy intake on energy balance?

Answer 27

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