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name the three main end products of digestion and indicate ...

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name the three main end products of digestion and indicate a main use of each in the body.

name the glands present in a monograstic stomach and indicate a function of each.

compare and contrast fibre digestion of cattle/goats with that of horses/rabbits.
(Discuss both similarities and differences.)

Explain the roles of each of the following.gizzard
crop
proventriculus

what are the main functions of the liver with respect to digestion and utilization of nutrients.

a dog consumes a dogfood containg 20% protein. Describe how digestion occurs for this nutrient, indicating all the steps including both chemical and mechanical digestion from the time the food enters the mouth until the time nutrients are absorbed.

the formation of urine in the kidney depends upon three processes, flitration, reabsorption, and secretion. in detail, describe each of these three processes.

name two hormonal control mechanisms of kidney function and give one factor causing the release of each into the bloodstream, and indicate the resulting action.

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Submitted: 8 years ago.
Category: Homework
Expert:  DrTutor replied 8 years ago.
Are you only asking Ryan to answer. These are simple question in biology. I can do, too!
Customer: replied 8 years ago.
Reply to DrTutor's Post: no you can go ahead and answer any of my questions.
Expert:  DrTutor replied 8 years ago.
Sorry for all the confusion. I will get the answers posted soon, and make sure they are correct.
Expert:  DrTutor replied 8 years ago.

I just want to inform you I have completed the answers, 10 pages with pictures and illustrations. I have them in the MS word format. I don't think it is likely that it can be sent via "cut and paste". However I will try first. If any problem I can send you the doc via email. Cheers.


Q1. name the three main end products of digestion and indicate a main use of each in the body.


ANSWER amino acids ,these are the building blocks of the body. They not only construct major part of the body but also help in energy utilization, in case , body has non availability of carbohydrate substrate.


Glucose and fructose , these are the end products of carbohydrate digestion. By the metabolic activity of body cells derive energy in the form of heat or ATP from glucose. Glucose is the prime source of energy in the body.


Fatty acids and glycerol, these also include the energy storages in the body and also help body in drastic conditions.

Q2. name the glands present in a monograstic stomach and indicate a function of each.


ANSWER
Four major types of secretory epithelial cells cover the surface of the stomach and extend down into gastric pits and glands:



  • Mucous cells: secrete an alkaline mucus that protects the epithelium against shear stress and acid

  • Parietal cells: secrete hydrochloric acid!

  • Chief cells: secrete pepsin, a proteolytic enzyme

  • G cells: secrete the hormone gastrin

There are differences in the distribution of these cell types among regions of the stomach - for example, parietal cells are abundant in the glands of the body, but virtually absent in pyloric glands.


Q3. compare and contrast fibre digestion of cattle/goats with that of horses/rabbits.
(Discuss both similarities and differences.)







The stomach of ruminants has four compartments: the rumen, reticulum, omasum and abomasum, as shown in the following diagram:



The ruminant stomachs, as seen from the right side


Collectively, these organs occupy almost 3/4ths of the abdominal cavity, filling virtually all of the left side and extending significantly into the right. The reticulum lies against the diaphragm and is joined to the rumen by a fold of tissue. The rumen, far and away the largest of the forestomaches, is itself sacculated by muscular pillars into what are called the dorsal, ventral, caudodorsal and caudoventral sacs. In many respects, the reticulum can be considered a "cranioventral sac" of the rumen; for example, ingesta flows freely between these two organs. The reticulum is connected to the spherical omasum by a short tunnel.


The abomasum is the ruminant's true or glandular stomach. Histologically, it is very similar to the stomach of monogastrics.


The interior of the rumen, reticulum and omasum is covered exclusively with stratified squamous epithelium similar to what is observed in the esophagus. Each of these organs has a very distinctive mucosa structure, although within each organ, some regional variation in morphology is observed. The images below are from a sheep.








The interior surface of the rumen forms numerous papillae that vary in shape and size from short and pointed to long and foliate.






Reticular epithelium is thrown into folds that form polygonal cells that give it a reticular, honey-combed appearance. Numerous small papillae stud the interior floors of these cells.






The inside of the omasum is thrown into broad longitudinal folds or leaves reminiscent of the pages in a book (a lay term for the omasum is the 'book'). The omasal folds, which in life are packed with finely ground ingesta, have been estimated to represent roughly one-third of the total surface area of the forestomachs.










The anatomic features described above are exemplified by cattle, sheep and goats. Certain other animals are also generally called ruminants, but have slightly different forestomach anatomy. Camelids (camels, llamas, alpacas, vicunas) have a reticulum with areas of gland-like cells, and an omasum that is tubular and almost indistinct. These animals are occasionally referred to as pseudoruminants or as having "three stomachs" rather than four.


A final note on anatomy. Stratified, squamous epithelium such as found in the rumen is not usually considered an absorptive type of epithelium. Ruminal papillae are however very richly vascularized and the abundant volatile fatty acids produced by fermentation are readily absorbed across the epithelium. Venous blood from the forestomachs, as well as the abomasum, carries these absorbed nutrients into the portal vein.




























The anatomic features described above are exemplified by cattle, sheep and goats. Certain other animals are also generally called ruminants, but have slightly diffe



1.


Q4. Explain the roles of each of the following.gizzard crop proventriculus


ANSWER there are numerous variants in stomach anatomy of vertebrates and also their epithelial lining. These modifications are according to the habit and habitat of the animal.


CROP. In birds there develop part way down the esophagus a distensible sac, the crop
which serves as a place for the temporary storage of grain or other food; in doves the crop lining exudes, in both sexes, a milky material with which, regurgitated, the young are fed.


GIZZARD It is the modification of stomach in vertebrates and epithelial linings.in birds and crocodailians there is present a distal muscular compartment the gizzard. In grain eating birds small stones are swallowed to lodge in the gizzard and aid this rough walled chamber in its function as a grinding mill substituting for the lost teeth.


PROVENTRICULUS. This is the proximal stomach region of bird and crocodiles. It is notable for the arrangement of fundus glands in a series of pockets, giving the appearance of compound glands. The fundal region of stomach is characterized by the presence of tubular glands which produce enzymes prominently pepsin, which help in protein digestion. And also hydrochloric acid which gives the gastric juice an acid condition favorable for the action of pepsin.


Q5. a dog consumes a dogfood containg 20% protein. Describe how digestion occurs for this nutrient, indicating all the steps including both chemical and mechanical digestion from the time the food enters the mouth until the time nutrients are absorbed.


ANSWER


Food gets broken down into a simple form that can be absorbed and used by the body in a process called “digestion.” In mammals, this process takes place in the digestive or alimentary tract--often simply called the “gut.” This is a hollow tube the food passes through and is acted upon by secretions from organs that discharge into the tube. These secretions contain digestive enzymes that speed up the process of hydrolysis, by which food is broken down.

The three major classes of nutrients that need to be digested are carbohydrates, protein and fat. Other nutrients (minerals, vitamins and water) are absorbed in more or less the same form as they are found in food. But they may need to be released from proteins, fats or carbohydrates before they can be absorbed.



Digestion begins in the mouth

Digestion begins in the mouth, where food is mechanically broken down and mixed with saliva before it’s swallowed. Although dogs aren’t strictly carnivores, their teeth are particularly suited to meat eating, and can cut, chew and crush food. Still, many dogs have a tendency to bolt down their food, often chewing only the toughest of foods before swallowing.

The sight and smell of food stimulates the flow of saliva, causing the dribbling and “lip smacking” often seen at mealtimes! Once the food arrives in the mouth, its taste and physical presence help increase saliva production. Saliva contains mucus, a very effective lubricant that coats the food to help with swallowing.


What the stomach does

When food is swallowed, it passes down the esophagus, whose muscles contract with a “wave” motion called peristalsis, and arrives at the stomach within a few seconds. The stomach has several functions. It’s a storage organ; it’s a mixing bag, where more digestive enzymes are added to the food; and it’s a regulator valve that controls the rate of flow into the small intestine. Protein digestion begins in the stomach.

The stomach secretions contain protein-digesting enzymes (proteases), hydrochloric acid, and mucus. The major enzyme, pepsin, is secreted in an inactive form, pepsinogen, to stop it from digesting the cells that produce it. Pepsinogen is activated in the stomach in the presence of hydrochloric acid, which also creates the correct acid environment for the enzymes to function at their optimum rate. Mucus lubricates the food, and protects the lining of the stomach wall (which is largely protein) from being digested by its own enzymes. The secretion of acid, mucus and enzymes depends on the composition and quantity of food eaten, and is regulated by hormones and nerves.

The wall of the stomach is muscular, particularly in the pyloric region. The stomach contents are mixed thoroughly, and push towards the pyloric sphincter--a muscular ring that acts as a regulator valve. By this time, the mixture is a thick milky liquid called chyme, and several factors control its passage into the small intestine. Strong waves in the stomach cause the pyloric sphincter to relax, and allow food to pass into the duodenum (the first part of the small intestine). Chyme passes through more easily when it’s very fluid.

On the other hand, the rate of emptying is reduced by the presence of chyme, acids, fats or irritants in the duodenum, which inhibit movements in the stomach. This ensures that the stomach contents are well mixed and sufficiently well digested before they leave the stomach. It also ensures that the small intestine doesn’t receive more chyme than it can cope with efficiently.


The work of the small intestine

The duodenum is the main site for digestion in the small intestine. Here, more enzymes are added to the chyme, some of which come from the intestinal wall and others from the pancreas. The pancreas is one of the major glands of the body, and has two functions: releasing digestive enzymes into the gut, and releasing hormones into the blood. Pancreatic juice also contains sodium bicarbonate, which neutralizes the acid chyme arriving in the duodenum, and provides an alkaline environment for optimum functioning of pancreatic and intestinal enzymes. These enzymes include proteases to continue protein digestion, amylase for carbohydrate digestion, and lipase for fat digestion. Enzymes in the intestinal juice generally start off the later stages of digestion.

The regulation of pancreatic juice release is largely controlled by two hormones--secretin and pancreozymin. These are secreted from cells in the wall of the small intestine. Another important function of the pancreas is to secrete the hormone insulin into the bloodstream to control blood sugar levels.

The liver is the other major organ associated with the small intestine. Bile is produced continuously in the liver, stored in the gall bladder, and passed into the gut through the bile duct when it’s needed. Bile contains bile salts that act like detergents by turning fat into tiny globules that can then be processed by the lipase enzymes in pancreatic juice. It’s the pigments in bile that give feces their characteristic color.

The digestion of food is completed in the small intestine, and once the food has been broken down to its simplest form, it can be absorbed across the wall of the intestine and into the blood. The end products of digestion are carried to the liver, where they are metabolized. Fat is absorbed into the lymph vessels, and is later transferred to the bloodstream.

The small intestines are very long, and absorption takes place along its entire length. Folds and finger-like projections, villi, in the lining of intestinal wall dramatically increase the surface area for absorption. In some dogs, the absorptive area of the small intestine may be as large as the floor of a small room!


The role of the large intestine

By the time the food that’s been eaten reaches the large intestine, most of the nutrients have been digested and absorbed. In this part of the gut, water is absorbed, and some fermentation of dietary fiber by bacteria takes place. This process is responsible for the production of gas, often associated with flatulence!

Feces are around 60-70% water, and the rest is made up of undigested food, dead bacteria and some inorganic material. The feces are stored in the rectum and evacuated through the anal sphincter. Although defecation is voluntary, problems may occur in old age or during bouts of diarrhea or other illness.


Measuring the digestibility of food

For any given food, we can discover the amount of each nutrient present, using chemical analysis. But this doesn’t give a true picture of the actual nutritional value of the food, since only nutrients absorbed from the digestive system are of use to the animal. A proportion of each nutrient eaten will inevitably be lost in the feces.

Digestibility is a better measure, because it shows the availability of the nutrient content of the food. We can calculate digestibility from the difference between the nutrient intake in food and that voided in feces.

Since feces consist not only of undigested, unabsorbed material but also cell debris and material excreted into the digestive tract, the difference between intake and output measured in this way is called “apparent digestibility.” To measure true digestibility, it’s necessary to use control diets free of the nutrient being studied, to establish the output when the intake is zero. For most practical purposes, apparent digestibility is used, as it measures the net amount of digestion.

Within the same species, digestibility is more a characteristic of the food than the individual animal. But the digestibility of a particular food will be different if it’s fed to two different species of animal—dog and cat, for example--because of differences in their digestive systems.

One way of illustrating these differences is to compare the length of the gut with body length. Herbivores such as the horse have a high ratio, since vegetative foods generally require more prolonged digestion than animal-derived materials. In omnivores such as dogs and people, the ratio is lower. And carnivores such as cats have the lowest ratio of all.

So, diets with a high vegetable content tend to have lower digestibility in dogs because of their indigestible fiber content, whereas the digestibility of meat-based diets is usually very high.
Digestibility values provide an index that can be used to estimate how much of the food must be fed to a normal, healthy individual in order to supply the correct amount of nutrients and energy. Where the digestibility value is low, a larger quantity of the food must be eaten to meet the requirements of the animal. Similarly, a diet of low digestibility will result in the production of a greater volume of feces.






Q6. the formation of urine in the kidney depends upon three processes, flitration, reabsorption, and secretion. in detail, describe each of these three processes.


ANSWER in renal mechanism of urine formation follows following steps


1. is ultra filtration which occurs in the malpigian tubules of the kidney cells the hydrostatic pressure of the blood at the afferent glomerular arteriole is about 70mmHg in contrast to 25mmHg inother capillaries of the body. This pressure is suffient to overcome resisting forces and brings ultrafiltration. The total pressure exerted by the forces opposing filtrationis 50mmHg. Thses forces are colloidal osmotic pressure of the plasma proteins, hydrostatic pressure of the fluid in the bowman’s capsulesand resist to the blood flow in the tubule. Thus, peculiar renal circulation gives net filtration forces of 25mmHg as aresult 20% of plasma flowing through the glomeruli gets filtered. Average no. of glomeruli for two kidneys is 2,000,000 in man and amount of filtration averages about 120ml/min or 170 liters/day.


As a result of ultra filtration excepts blood corpuscles higher molecular weight plasma proteins and rest of all other substances filtered off at the melpigian tubules of the body.


So at the end of first stage glomerular filtrate contains low molecular weight proteins, 95% water glucose salt and urea.


Selective absorption


Reabsorption is carried out in the tubular part of the nephron which is richly supplied with blood vessels branching out from the efferent glomerular arteriole. The glomerular filtrate is very much dilute as compared to the urine that is eliminated out. During second stage, concentration of the filtrate is brought about by the processof selective reabsorption it involves the no. of substances like glucose, amino acids, salts water etc. which are filtered off unavoidably at the glomerulus during filtration. At the same time nonessential substances like excess of water electrolytes and waste products like urea uric acid are allowed to pass.the term renal threshold denotes the plasma concentration above which a given substances appears in the urine e.g., in man it is 125 to 160mg/100ml plasma. Water absorption is like passive diffusion while other materials are through electrolyte gradients. Some substances undergo continous exchange b/w lumen of the tubule and peritubular fluid. Some substances including sugars, amino acids, lipids as well as many mono and divalent ions are absorbed or secreted by the cells either by facilitated diffusion or active transport. For example, the clearance of potassium is normally about 1/5 its filtration rate. Glucose is generally totally reabsorbed.


The nature of excreta depends largly on the osmotic state of body fluids and in turn water economy.


Tubular secretion a few substances are added to urine step by step. Urine formation entirlyby the tubular secretion is physiologically significant as it involoves practically no water loss.


Q7. What are the main functions of the liver with respect to digestion and utilization of nutrients?


ANSWER.


Liver also take an important role in the digestive process. Liver produces bile. Bile is an alkaline secretion produced by hepatic secretions. It plays an important role in fat digestion. It creats alkaline medium essential for the pancreatic activity. It also acts as antiseptic agent killing harmful bacteria in the chime. Bile salts in the bile juice activates pancreatic lipase and also facilitates emulsification of fats. Thus increasing the surface area of oil and water interface at which lipase can act thereby favouring the absorption of fat droplets. The hydro tropic action of bile also converts otherwise insolubly fatty acids into soluble components.


Q8. name two hormonal control mechanisms of kidney function and give one factor causing the release of each into the bloodstream, and indicate the resulting action.


There are two hormones which take part in the hormonal activity of kidney function. These are secreted from the adrenal glands present at the superior lobe of the kidney. One is epinephrine and other is norepinephrine. Both these hormones increase the heart rate, however ,epinephrine is more potent in this respect. Both increase systolic blood pressure but epinephrine has no effect on diasystolic pressure. Epinephrine increases blood flow through skeletal muscles, liver and brain, whereas norepinephrine either has no effect or decrease it. Both of these hormones produce constriction of the skin capillaries( cutaneous vasoconstriction) renal blood flow is decreased by these hormones. Epinephrine causes generalized vasodialtion, whereas norepinephrine causes vasoconstriction. Epinephrine enhances oxygen consumption and glucose output from the liver.


A number of stress conditions like physical exerting certain emotional states, exposure to cold, fall of arterial blood pressure, asphyxia and hypoglycemia are from adrenal medulla.


Adrenal cortex regulates the electrolyte balance in the body through kidney function.









































































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