Through the past semester I’ve come to realise that though the subjects are taught seperately that they are intrinsically linked. We’ve just finished the function of the digestive system in physiology and are now looking at the digestive system in anatomy and in histology. In addition to which we are also looking at animal nutrition. Today we started with looking at the salivary glands of the mouth which not only product enzymes to help start the digestion of food but help the movement of food along the digestive tract. These are located in the base and roof of the mouth along with the cheek and on the surface of the tongue.
The glandular stomach then also secretes mucus and digestive enzymes along with “gastric juice” to help the digestion of food. Then entering the top of the small intestine with the duodenum you have the entrances of the pancreatic and hepatic (liver) ducts which add more digestive power to the mix.
We finished today looking at the rectum and anus including the histology of the anal sacs (which contain the anal glands) in the dog which as vets we have the pleasure of expressing. For something that can contain so much foul smelling liquid these glands are extremely small under the microscope!
Start of my second week of my second semester, last week vanished in a blur and this week I have tried to plan my time better to get a lot more of the research for my Emergency First Aid for Animals book completed.
Now I think I have previously said before how the stomach with ruminants is divided into four different compartments; the rumen and reticulum, omasum and the abomasum. Each of these has a specific role to play in digestion and specific structure to match. This is known as the complex stomach and the esophagus enters this between the reticulum and rumen. The rumen is the largest stomach compartment and is connected to the reticulum with a large opening allowing food to be passed back and forth between the two. Remembering that ruminants eat plant matter the rumen is where fermentation takes place with a large amount of bacteria and protozoa act on the contents breaking it down. The surface of this is covered in small papillae (low conical projections) and looks like this.
The reticulum has a honeycomb like structure and sits next to the rumen and starts the mechanical breakdown of food into fine particles. This compartment is usually involved in “hardware disease” where cows swallow screws, nails wire or other hardware and it embeds into the lining. Occasionally this will completely penetrate the reticulum lining causing disease and as the reticulum sits next to the diaphragm will head into the thorax towards the heart.
The last structure unique to compound stomach is the omasum which is where the final stage of mechanical digestion takes place before the plant matter enters to Abomasum which is basically the same as a simple stomach. The lining of the omasum consists of really large muscular folds which help the mechanical breakdown of food into tiny particles suitable for digestion in the stomach and intestine. Below you can see the size of these folds in relation to the Rumen and Reticulum (its so big I’ve had to put multiple different pictures together to make it!)…
After this the food then enters the abomasum which is the same as the simple glandular stomach and enzymes and gastric juices start to digest the food here before it then enters the small intestine.
This afternoon in Physiology we finished up looking at the endocrine system which is responsible for controlling the body systems using chemical messengers (aka hormones). There are several different hormones and I do have plans to do a diary entry in depth on each hormone in the near future so will leave this here until then.
Well now that I know the bones, muscles and ligaments it is time to learn about everything else that actually makes the body work. The start of this is with Splanchnology which is the study of viscera or soft internal organs of the body. Today started at 7am with the anatomy lecture which was looking at the structures of the mouth, tongue and teeth which was pretty interesting (and a relatively easy topic to learn before we start the stomach next week).
Now the mouth is where digestion starts, with the teeth being responsible for the mastication or mechanical breakdown of food and a wide range of glands secreting digestive enzymes and saliva to help the process. Now within the mouth there are two cavities, the space inside the teeth, and the space between the teeth to the lips and cheeks. Within the space inside the teeth (Cavum oris proprium) there is the tongue which has a range of different types of glands at various positions and in varying numbers depending on the species. In fact the actual shape of the tongue even varies within species with the tongue of a horse containing cartilage, the tongue of the dog having a groove in the middle, and the tongue of the cow being split into two parts divided by.a groove across the middle.
There is also the mouth to pay attention to with the hard palate forming the roof of it lined with ridges across it and off course the teeth Now some of you may already know that ruminants (cows) actually do not have upper front teeth. Instead the have a hard pad made from tough tissue called the pulvinus dentalis. Wanna see it? Thought you would so here goes maybe my one and only dissection picture ever!
As you can see it looks almost like the same material as horns at the front where the incisors normally are, you also have papilla along the sides which help with movement of food. At the front if you can look closely you can see that there is something that looks like an upside down “v” – this is the papilla incisiva which are the openings for the ductus incisivi which secrete digestive juices.
There are several classes of teeth when it comes to animals, with some animals having combinations of more than one type.
Brachyodont – Where the tooth has stopped growing after reaching a certain point and its surface wears down with use. This type of tooth is divided into the crown, body and root and is the type of teeth that humans have.
Hypsodont – Where the tooth never stops growing (as long as the animal is alive) which means that it does not have a crown, instead it is just divided into the root and body. The most common examples are the teeth in rodents, rabbits, and more exotically the tusks of the boar or elephant!
Semihypsodont – Where the tooth continues to grow until it starts to wear out, the most common example are the incisors of the horse. This has the benefit of the tooth growing so that the surfaces of the teeth perfectly meet allowing the cutting of fine grass.
The patterns of the occlusial surface (the part that meets with the opposite upper or lower tooth allowing chewing) actually also vary among different species, with some being multitubercular where it has bumps or bunodont where it is flat. These are also divided into selenodont where it has moon like patterns, or lophodont where it has folds and ridges.