Anatomy and Digestion Flashcards
(103 cards)
1
Q
What is the alimentary canal?
A
This is a tube beginning with the mouth and ending at the anus in which digestion and absorption of nutrients occurs.
It has a tubular structure.
Lumen (digesta) is exterior to the body (i.e. the inside of the canal)
2
Q
What is the gastrointestinal tract (GIT)?
A
This is the region of the alimentary canal that runs from the stomach to the colon.
3
Q
What are the layers of the alimentary canal from innermost to outermost?
A
mucosa, submucosa, muscularis, serosa
4
Q
Describe the mucosa
A
This is the innermost layer of the alimentary canal.
It is the interface with the lumen.
Absorption and secretion occurs here.
5
Q
Describe the submucosa.
A
Structural and immune cells are found here
6
Q
Describe the muscularis.
A
This is a muscle for motility. It helps move the digesta.
7
Q
Describe the serosa.
A
This is the outermost layer of the alimentary canal and is the interface with the body.
8
Q
What are the pregastric functions?
A
prehension, mastication, ensalivation, swallowing
9
Q
What is prehension?
A
Grasping food and bringing it to the mouth.
Its mechanisms vary with behavior and diet.
In some animals, the importance of incisor integrity is key.
10
Q
What is mastication?
A
Mastication is the physical reduction of feed.
It is especially important in nonruminant herbivores.
11
Q
Describe salivation and the glands associated with it.
A
Three main glands secrete fluids with different compositions. The relative size of these glands differs between species.
The three glands are: parotid, sublingual, and the submaxillary (aka submandibular)
12
Q
Describe the parotid gland.
A
This gland secretes a serous (watery) mixture containing water, enzymes, and ions.
13
Q
Describe the sublingual gland.
A
This gland secretes mucous, and mucus (mucin) is its main constituent.
14
Q
Describe the submaxillary gland.
A
This gland secretes a mixed liquid comprised of mucus, ions, enzymes, and water.
15
Q
What are the functions of saliva?
A
Salvia…
- moistens feed (via ions and water)
- lubricates food (aids in swallowing)
- aids in starch digestion (amylase)
- buffers rumen pH
- helps recycle nitrogen (urea) in ruminants
- other specialized functions
ex. Draculin, an enzyme secreted in vampire bats’ saliva, prevents blood from coagulating
16
Q
Describe swallowing (deglutition).
A
Swallowing is a reflex initiated by the presence of food in the pharynx. The action stops respiration.
Propulsion of food to the stomach then occurs via esophageal peristalsis.
The reflex of swallowing is the most similar among species.
17
Q
What are the major functions of gastric digestion in a nonruminant?
A
- mixed and mechanical breakdown of feed (further breakdown after mastication)
- hydrolytic digestion by acid enzymes (especially of protein)
- reservoir for controlled release of digesta to the small intestine
18
Q
Describe the stomach.
A
The size and shape varies among species.
It is lined by nonglandular or secretory (aka glandular) epithelium that secretes acid and enzymes.
Its functions are storage, mixing, and partial digestion of food.
It has a limited absorptive capacity, and can absorb some things like drugs or alcohol.
19
Q
Describe the four regions of the stomach.
A
Esophageal: nonglandular portion that connects directly to the esophagus
Cardiac: secretory or glandular portion that has mucus producing cells for lubrication and protection on the stomach lining from acid. It is the top portion of the stomach.
Fundus (aka Fundic): a secretory portion covered with gastric pits. These pits contain chief (peptic) cells with secrete proteolytic enzymes like pepsinogen, as well as parietal cells, which secrete HCl. HCl activates pepsinogen to pepsin and drops the stomach pH.
Pyloric: contains mucus secreting cells and endocrine G cells, which secrete the hormone gastrin. The gastrin stimulates HCl production by the parietal cells in the fundus.
20
Q
What are the three phases of gastric secretion?
A
cephalic, gastric, intestinal
21
Q
Describe the cephalic phase.
A
There is a vagal reflex, this phase is involuntary and is controlled by the brain.
There is increased gastric motility, enzyme secretion (pepsinogen), and HCl secretion.
22
Q
Describe the gastric phase.
A
This phase begins when food enters the stomach.
It is a local reflex that depends on the presence of food in the stomach.
It is reinforced by gastrin, a peptide hormone secreted by the stomach.
The gastric phase sees the increase of HCl and pepsinogen secretion.
23
Q
Describe the intestinal phase.
A
This phase begins with the presence of food in the small intestine.
It is stimulated by duodenal distension, which tells the brain to decreases stomach secretions to prepare for absorption.
It is also stimulated by H+, osmolarity, and nutrients.
There is a decrease in HCl secretion and gastric motility.
The enzymes secretin and CCK are released.
24
Q
Describe gastric motility and the emptying of the stomach.
A
Motility aids in mixing, mechanical, and hydrolytic reduction of feed to chyme.
Emptying is stimulated by distension of the antral wall (the region near the pylorus) and the presence of liquid chyme.
25
What does the pancreas secrete and what is its function?
The pancreas secretes enzymes and bicarbonate.
The bicarbonate's function is to neutralize HCl entering the small intestine from the stomach. It is a pH buffer that allows pancreatic enzymes to function without being denatured by the low stomach pH.
The enzymes function to digest carbs, fats, proteins, and nucleic acids.
The functions of the pancreas are exocrine functions.
26
What does the liver secrete and what are its functions.
It secretes bile salts, bicarbonate, and organic waste products.
The bile salts function to solubilize water-insoluble fats.
Bicarbonate neutralizes HCl entering from the stomach.
Organic waste in eliminated in feces.
27
Describe bile salts.
Bile salts are made in the liver from cholesterol, but they are stored in the gallbladder.
They help solubilize fats.
28
Discuss the small intestine.
The small intestine varies in length among species.
The majority of digestion in the GIT occurs here, and lots of absorption happens here as well.
It adds secretions to the digesta.
The portions of the small intestine are the duodenum, jejunum, and ileum.
29
Describe the cells found in the small intestine.
The types of cells in the lumen of the small intestine include:
- absorptive
- mucus secreting
- endocrine
- stem cells
Like the stomach, there are glandular and non-glandular cells.
There is a very fast turn over rate of cells that occurs every 3-6 days.
30
What does the duodenum do?
This is the site of addition of many digestive juices.
- secretions from enterocytes (ex. lactase, sucrase)
- pancreatic juices (enzymes and bicarbonate) from common bile duct
- bile secretions (biles salts) from common bile duct
31
Define enterocyte
cells of the intestinal lining
32
What does the jejunum do?
The jejunum is where most of the absorption occurs.
The compounds must be simple enough to be absorbed.
Further digestion occurs here if needed.
The jejunum is filled with folds, villi, and microvilli which increase the absorptive surface area of the small intestine.
33
What occurs in the ileum?
Less absorption happens here, but there is an absorptive capacity present if needed.
The ileum contains gut associated lymphoid tissue (GALT).
34
Describe GALT
Gut Associated Lymphoid Tissue
This is the intestinal immune system present in the ileum.
It is responsible for the formation of Peyer's patches.
Peyer's patches: immunological tissue which samples contents of the GI tract and protects the host. It is an aggregation of lymphoid tissue.
35
Describe the large intestine.
Consists of the cecum, colon, and rectum.
The size and shape of the large intestine varies among species.
Herbivores have more total capacity than omnivores or carnivores. This is especially true in regards to non-ruminant herbivores.
The ratio of the cecum to colon is variable.
In humans, the cecum is a blind pouch called the appendix.
36
What are the functions of the large intestine?
The large intestine has a high capacity for water absorption.
Little enzyme of hormone secretion occurs here.
In non-ruminant herbivores that are hindgut fermenters, there is considerable bacterial fermentation in the cecum and colon. This leads to the absorption of volatile fatty acids (VFA's), but not protein and vitamins produced by bacteria.
37
Define nutritional ecology.
The adaptation of animals to their environments by development of dietary habits and physiological mechanisms that allow them to exploit available food sources in their habitats.
ex. Darwin's Galapogos finches
38
Differentiate between herbivores, omnivores, and carnivores.
These are examples of dietary habit.
Herbivores: consume only plant matter (ex. cows)
Omnivores: consume plant and animal material (ex. pigs)
Carnivores: consume only animal material (ex. lions)
39
Discuss the sub-categories by dietary habit.
a. obligate vs. facultative (ex. cats are obligate carnivores)
b. digestive anatomy or physiology (ex. ruminants vs. nonruminants)
c. specified food source (ex. frugivore, folivore, insectivore)
d. way in which they eat (ex. selector vs. non-selector, browser vs. grazer)
40
Give some examples of pregastric adaptations to food sources.
Prehensile adaptations
- forelimbs, snouts, tongues, lips
Masticatory adaptations
- large canines and incisors, specialized molars, relative toothlessness of endentates (anteater, sloth, armadillos)
Deglutition
- varies little with diet, but quantity and composition of saliva varies considerably
41
How does gastric capacity and structure vary among species?
a. capacity is greatest in pregastric fermenters (stomach=reservoir)
b. small stomach in carnivores related to nutritive density of diet
c. distribution and composition of epithelial lining varies between species and dietary adaptations
42
What type of stomach tissue varies the most among species?
Nonglandular tissue
fermenters tend to have more nonglandular tissue
43
How does the small intestine adapt to feed sources?
Intestinal length and functions adapt to the feed sources.
In the small intestine, there is less variation among species than in the stomach and hindgut. However, the small intestine is generally shorter in carnivores than in herbivores.
44
How does the large intestine adapt to feed sources?
The importance of hindgut fermentation dictates variation in structure and size. If the animal relies on hindgut fermentation for the majorit of its energy, the large size of their large intestine reflects that.
Some hindgut fermentation occurs in most species and is extensive in others.
45
What is the significance of fermentative digestion?
Nearly all animals have some fermentative capacity.
The importance is directly related to fiber intake.
The location of fermentation varies, but the function doesn't. It largely deals with maintaining a microbial community and acquiring energy.
46
What animal's digestive processes in most similar to that of a human?
Swine
47
What is the crop of a bird?
It is a pouch in the esophagus that lubricates and stores food.
48
What is the proventriculus of the bird?
This is the true gastric stomach of the bird; acid secretion occurs here.
49
What is the ventriculus of the bird?
This is the gizzard. It masticates and breaks down digesta with its muscled lining.
50
What is the cloaca?
This is the shared pathway between the reproductive, urinary, and digestive tracts.
51
Are dogs omnivores or carnivores? Describe their digestion.
Dogs are omnivores like pigs. They have a short small intestine that has limited fermentation occur.
52
Describe cat diets and digestion.
Cats are obligate carnivores with short small intestines where limited fermentation occurs. Compared to wild cats, house cats have plant material added to their diets to make their feces harder and easier to clean.
53
What are some examples of non-ruminant fermenters?
horses, rabbits, elephants
54
What does it mean to be a pregastric fermenter?
Fermentation occurs before gastric digestion in the digestive tract.
55
What is the key feature of all ruminants?
They have four stomach compartments.
56
What are some examples of ruminants?
Domestic: sheep, cows, goats
non-domestic: giraffes, bison, deer, water buffalo, duikers (world's smallest ruminant)
57
Why are sheep important in research settings?
They are smaller than cows and have multiple offspring.
They have large amounts of pre-gastric fermentation, as well as a non-glandular rumen and reticulum.
58
Describe stomach and GIT compartments as percents of body weight.
Ruminants have the largest stomach and GIT as a percent of their body weight.
For instance, humans and sheep are similar weights, but sheep have 20x more stomach volume and 5x more GIT volume than humans.
Forage feeders give up size and speed for the ability to use low quality and abundantly available feed.
59
What do rumen microbes provide the host species?
1. MPS (microbial protein synthesis)
2. Breakdown of beta 1,4 linkages in cellulose
3. Biohydrogenation (saturating unsaturated fats)
60
What are the four chambers of the ruminant stomach?
1. Reticulum
2. Rumen
3. Omasum
4. Abomasum
61
Describe the fermentative capacity of ruminants.
Ruminants have 83% fermentative capacity. 80-85% of total daily energy needs of ruminants is acquired by fermentation.
62
What are the Rs?
Rumination: regurgitation of partly digested feed from the reticulo-rumen.
Regurgitation
Remastication
Reglutination (reswallowing)
The process of rumination allows for more leisurely physical breakdown of feeds after initial ingestion.
63
Describe the reticulum.
Honeycomb structure
Main function is mixing and regurgitation
Digesta can pass between the rumen and reticulum, often referred to as the reticulo-rumen
No enzymes are secreted here, as microbes make them
64
Describe the rumen
This is the main stomach compartment, and can contain as much volume as 30-40 gallons in Holstein cows.
This is the main site of VFA production and absorption.
The surface of the rumen is covered by papillae to aid with absorption.
65
What are VFAs?
VFAs are volatile fatty acids, a byproduct of carbohydrate breakdown by rumen microbes.
The three VFAs are:
acetate (2C)
propionate (3C)
butyrate (4C)
Acetate and butyrate production see CO2 and CH4 produced as waste from leftover carbons
66
Which feeds affect VFA production?
Propionate is formed via starch fermentation.
Acetate is formed by cellulose fermentation.
67
How does the reticulo-rumen mix feed?
There are rhythmic contractions. Sharp contractions of the reticulum and a wave of a contractions pass caudally over the rumen, and individual sacs contract and relax in sequence.
68
What is eructation?
Belching of the waste gases aided by contractions of the reticulum and rumen.
69
Describe the omasum.
This compartment is important for water absorption.
It also absorbs residual VFAs and bicarbonate.
It represents around 1/3 of the surface area of the forestomach.
The omasum is described as the manyplies due to the folds in it that increase its surface area.
70
What is the reticulo-omasal orifice?
"The gate keeper of the lower tract"
A "strainer" that does not allow course fiber to enter the lower tract. The small opening of this oraifice ensures that the animal ruminates and absorbs as much material as possible before allowing it to pass through.
71
Describe the abomasum.
This is the true stomach of the ruminant.
It is glandular, and secretes HCl, pepsin, etc.
It also secretes lysozymes to degrade bacterial cell walls that make it that far in the digestive process.
There is a constant flow of digesta here compared to non-ruminants.
72
Describe displaced abomasum.
Normally, the rumen is on the left side of the body in cattle, and the abomasum is on the right.
LDA - rumen is near empty and extra gas causes it to rise, causing the abomasum to move underneath it.
- most common
- often after parturition
- not as life threatening
RDA: gas in the abomasum causes it to rise out of position
- blockage of digesta flow
- may progress into a complete torsion affecting blood flow to the liver (AV or RVA) - lower survival rate
To prevent displacement or to prevent it from happening again, the abomasum can be tacked to the right side of the cow.
73
Describe the microbes of the rumen.
Bacteria
- 200 that can be cultures, possible 5000 or more species, and 25 types at high concentrations
Archaea
Protozoa
Fungi
All four organisms produce VFAs
74
In the symbiotic relationship between the ruminant and the microbes, what does the host provide?
- warm, wet, anaerobic environment
- frequent additions of substrate (feed)
- constant mixing
- continuous removal of microbial wastes by absorption of VFAs and eructation of fermentation gases
- provision of saliva, which contains buffers that keeps the pH near neutral and ions to stabilize the osmotic environment
75
In the symbiotic relationship between the ruminant and the microbes, what doe the microbes provide?
- digestion of cellulose and hemicellulose, allowing for the use of low quality, but highly abundant food sources (all cellulases are of microbial origin)
- synthesis of high quality protein with the appropriate amino acid profile that have the ability to meet 50-80% of the animal's protein requirements
- synthesis of vitamins B, C, and K
76
What is the normal body temperature of a ruminant animal?
101 degrees F
77
What is the average rumen pH, and what are some complications that can occur is it is not in this range?
Average pH is 6.0 to 6.5
At lower pH, there is a decreased microbial growth rate, and the size of the papillae decreases.
The pH can vary naturally, as it decreases after a meal due to microbial fermentation, and increases during rumination.
A range of 1.1 pH units is normal.
78
What are some of the adaptations of the host to its microbial population?
Microbes get almost all of the free sugars and most of the starch eaten by the host. As a result, ruminants absorb very little glucose and are always hypoglycemic. Circulating blood glucose is always low in the ruminant because they get most of their energy from VFAs.
The majority of the glucose made in the ruminant is made in the liver from propionate.
79
Describe rumen bacteria.
Rumen bacteria account for 60-90% of total microbial mass.
They are almost exclusively anaerobic.
They can have a rapid turnover time, and can be attached to particles or floating in solution.
Populations present depend on their competitiveness.
80
What are the classifications of rumen bacteria?
1. Cellulolytic
- digest cellulose and hemicellulose
- produce acetate
2. Amylolytic
- digest starch and simple sugars
- produces more propionate
3. Proteolytic
- digest amino acids as energy
- produce isoacids (smelly, lesser VFAs) and NH3
81
Describe rumen archaea
The archaea are described as methanogens
They use H2 and NH3
There is an energy loss of 6-12% associated by the production of methane.
82
What are some similarities and differences between bacteria and archaea?
They are similar in size, shape, appearance, and reproduction.
Archaea cell walls do not contain peptidoglycan.
Archaea are generally more similar to eukarya than bacteria.
Each utilize different metabolic pathways.
83
Describe rumen protozoa
They are relatively large in size, and are very mobile.
They are single celled eukaryotes
They have a slow turnover
Protozoa consume large particles like starch granules, bacteria, smaller protozoa, cellulose, and proteins
84
Of all the rumen microbes, which is most responsible for the majority of fermentation.
The bulk of fermentative activity, digestion, and VFA production is done by bacteria.
85
Describe rumen fungi.
They are present in low amounts (5-10% of microbial mass)
They digest tougher fibers, and may be important in making fibers more accessible to other microbes.
86
What are some benefits of rumination?
Most ruminants chew cud 10-11 hours a day, which has many benefits.
1. particle size reduction of a course diet means only small particles pass from the rumen
2. rumination increases the surface area for microbial digestion
3. it breaks down waxes and other coatings on plant or seed surfaces that cannot be digested
87
Describe what two things affect ingested feeds.
1. Digestion in the rumen implies that there is a disappearance of nutrients via metabolism by rumen microbes
- Digestion rate is impacted by nutrient type (starch is digested faster than fiber), feed particle size and processing, and the capacity of the microbes present
2. Passage from the rumen
- passage rate increases with increasing intake
- feed, feed processing, animal size, level of production, environment, etc. all change rate of passage
- dependent of size and density (large and dry particles do not pass quickly compared to small and moist particles; forages pass slower than concentrates)
88
What is physically effective fiber?
This refers to the ability of feed to stimulate rumination by ruminants. It is mostly determined by forage particle size.
Physically effective fiber stays in the fiber mat initially.
89
How is saliva tied to rumination?
Rumination results in copious saliva production (55 gallons/day in dairy cows)
It does not contain amylase
Saliva prevents bloat by blocking the formation of bubbles
Parotid salvia (most important) is rich in Na+, K+, HCO3-, and HPO4-, which act as important buffers against rumen acids
Saliva contains urea for nitrogen recycling from the blood
90
Describe nitrogen recycling.
N recycling is a conservation mechanism to better utilize dietary N.
23-92% of plasma urea is recycled to the digestive tract, and it is recycled as urea by saliva or by diffusion through the rumen wall.
Overall, this supplies additional N to the microbes.
Urea is broken down to ammonia
91
What are RUP and RDP?
RUP = rumen undegradable protein
- has important AA profile meant for digestion in the intestines rather than for repackaging by microbes
RDP = rumen degradable protein
- protein broken down in the rumen
- provides N and AA for the microbes
- need both NPN and true protein
- essential for maximal microbial growth
- okay if poor AA profile, since bacteria will make it into higher quality AA
92
Describe amino acids leaving the rumen
1. microbial protein
- microbes washed out of the rumen
- 50-80% of dietary N is for the microbes
- AA composition unaffected by dietary source
- limited by energy as well as N
2) RUP
93
What are some examples of protein sources for ruminants?
- NPN - Urea (280% CP)
- ensiling - very high rumen digestibility
- protected amino acids by encapsulation
94
What process decreases protein digestibility in the rumen?
heat and formaldehyde treatment decreases digestibility
95
What must be taken into account when balancing the diet for ruminants in regard to protein?
Must balance diet for both RDP for bacteria and RUP for the small intestine (for animal)
Overall, the needs of the microbes and the host must be considered.
Ruminal AA output is hard to predict because of variable loss and synthesis.
96
In regards to protein, what is a major difference between pregastric and hindgut fermenters?
Hindgut fermenters do not get access to microbial proteins.
97
What is biohydrogenation and why is it important?
Rumen microbes saturate fats.
This is important because unsaturated fats can be toxic to microbes, and they can inhibit fiber digestion.
In hindgut fermenters, microbial proteins alter fats, but the animal cannot absorb them.
98
What factors provide the optimum environment for rumen microbes?
1. Good rumen environment
- stable and high pH
- reduction of anti-microbial factors (high oil, bad silage)
- adequate fiber and long forage for rumen function
2. Energy for bacteria
- maximize amount of starch and fiber digested
- synchronize digestibility of carbs and N
3. Feed additives (yeast, growth factors, branch chain AA)
99
What are pseudo-ruminants? Examples?
These animals are pregastric fermenters, but are not ruminants because they do not have a rumen. Instead, they have a 3-chambered stomach.
Examples are llamas and alpacas. Their stomach chambers are labeled as C1, C2, and C3 (gastric stomach).
They also have small hindguts.
100
What are some other pregastric fermenters?
Hippos: 2 fermentation compartments and small hindgut
Kangaroo: nonglandular upper portion of stomach, small hindgut
Colobus monkey: moderate nonglandular upper portion of stomach, small hindgut
Hoatzin: bird with a fermentation stomach
101
What categories of postgastric fermentation are there?
Colonic fermenters and cecal fermenters
102
What are some examples of colonic fermenters?
Horses: moderate SI
Elephants: simple SI
103
What are some examples of cecal fermenters?
Rabbits: perform coprophagy
Rats
Capybara: large cecum and simple SI
