Attached Glands: Definition, Types, Functions, Structure and Purpose of These Organs

The attached glands are organs that secrete digestive fluids that contain substances called enzymes (enzymes have the function of the breakdown and synthesis of food).

The adjoining glands of digestion are as follows:

Salivary glands

Saliva is produced and secreted by the salivary glands. The basic secretory units of the salivary glands are groups of cells called acini. These cells secrete a fluid containing water, electrolytes, mucus, and enzymes, which flow from the acinus into the collecting ducts.

Inside the ducts, the composition of the secretion is altered. Much of the sodium is actively reabsorbed, potassium is secreted, and large amounts of bicarbonate ions are secreted.

Bicarbonate secretion is of tremendous importance to ruminants because, together with phosphate, it provides a critical buffer that neutralizes the massive amounts of acid produced in forest stomachs.

Small collecting ducts within the salivary glands lead to larger ducts, which eventually form a single large duct that empties into the oral cavity.

Most animals have three main pairs of salivary glands that differ in the type of secretion they produce:

  • The parotid glands produce a serous, watery discharge.
  • The submaxillary (mandibular) glands produce a mixed serous and mucous discharge.
  • The sublingual glands secrete a saliva that is predominantly mucous in character.

The basis for different saliva-secreting glands of different composition can be seen by histological examination of the salivary glands. There are two basic types of acinar epithelial cells :

  • Serous cells, which secrete a watery fluid, essentially devoid of mucus.
  • Mucous cells, which produce a very rich mucus secretion.

The acini in the parotid glands are almost exclusively of the serous type, whereas those in the sublingual glands are predominantly mucous cells.

In the submaxillary glands, acini composed of both serous and mucous epithelial cells are common. Saliva secretion is under the control of the autonomic nervous system, which controls both the volume and the type of saliva secreted.

Parasympathetic stimulation of the brain produces greatly improved secretion, as well as increased blood flow to the salivary glands.

Powerful stimuli to increase salivation include the presence of food or irritants in the mouth, and thoughts or the smell of food.

Knowing that salivation is controlled by the brain will also help explain why many psychic stimuli also induce excessive salivation, for example why some dogs salivate throughout the house when howling.

Functions of saliva

Saliva fulfills many roles, some of which are important to all species and others to only some:

Lubrication and Clogging –  Mucus in saliva is extremely effective in binding chewed food together into a slippery bolus that (normally) glides easily through the esophagus without inflicting damage to the mucosa.

Saliva also covers the oral cavity and esophagus, and food basically never directly touches the epithelial cells of those tissues.

Solubilizes dry food:  to be tasted, the molecules in food must be solubilized.

Oral hygiene:  the oral cavity is emptied almost constantly with saliva, which drives away food debris and keeps the mouth relatively clean.

Saliva flow decreases considerably during sleep, allowing bacteria populations to accumulate in the mouth; the result is a dragon’s breath in the morning. Saliva also contains lysozyme, an enzyme that smooths many bacteria and prevents the overgrowth of oral microbial populations.

Initiates Starch Digestion:  In most species, serous acinar cells secrete an alpha-amylase that can begin to digest dietary starch into maltose. Amylase is not present, or is present only in very small amounts, in the saliva of carnivores or cattle.

Provides buffers and alkaline fluids:  this is of great importance in ruminants, which have non-secretory breasts.

Evaporative cooling –  clearly important in dogs that have very underdeveloped sweat glands – watch a dog panting after a long run and this function will be clear.

Diseases of the salivary glands and ducts are not uncommon in animals and man, and excessive salivation is a symptom of almost any injury to the oral cavity.

The saliva dripping seen in rabid animals is not actually the result of excessive salivation, but rather due to pharyngeal paralysis, which prevents saliva from being swallowed.

Liver

Your liver is the largest solid organ in your body. On average, it weighs about 3 pounds in adulthood. This organ is vital for the metabolic functions and the immune system of the body. Without a functioning liver, a person cannot survive.

The position of the liver is mainly in the upper right portion of the stomach, just below the diaphragm. A portion of the liver also enters the upper left abdomen.

Structure of the liver

The liver is a crescent-shaped organ that is fairly straight at the bottom. It is slightly inclined in the body cavity, with the left portion on the stomach and the right on the first part of the small intestine.

The liver has two main parts, or lobes. Each lobe is divided into eight segments. Each segment has an estimated 1,000 lobes, or small lobes. Each of these lobes has a small tube (duct) that flows into the common hepatic duct.

Compared to the rest of the body, the liver has a significant amount of blood flowing through it: an estimated 13 percent of the body’s blood is in the liver at any one time.

Purpose of the liver

The main functions of the liver are in the metabolic processes of the body. These include:

  • Break down or convert substances.
  • Extract energy.
  • Make toxins less harmful to the body and remove them from the bloodstream.

The liver does this by receiving nutrient-dense blood from the digestive organs through a vein known as the portal vein.

The many cells of the liver, known as hepatocytes, accept and filter this blood act as small sorting centers, determining:

  • What nutrients should be processed.
  • What should be stored.
  • What should be removed through the stool.
  • What should return to the blood.

The liver stores vitamins and minerals such as copper and iron, and releases them if the body needs them. The liver also helps break down fats in a person’s diet. Stores fat or releases it as energy.

It also manufactures an estimated 800 to 1,000 milliliters of bile a day. This bile is transported through a bile duct to the small intestine. The small intestine uses bile to further break down fats. Any extra bile is stored in the gallbladder.

The liver breaks down proteins as well. The by-product of this process is called ammonia, which can be toxic to the body in large amounts. The liver converts toxic ammonia into a substance called urea. The liver releases it into the blood where the kidneys excrete it in the urine.

The liver also breaks down alcohol in the blood and many medications you take.

As if these functions weren’t enough, the liver also plays an important role in the following:

  • Creating immune system factors that can fight infection.
  • Creating proteins responsible for blood clotting.
  • Break down old and damaged red blood cells.
  • Store extra blood sugar as glycogen.

By considering these factors, it is easy to see how important the liver is to a person’s health.

Liver regeneration

The liver is truly an amazing organ, as it has the ability to regenerate itself. This means that after injury or surgery to remove tissue, liver tissue can grow back to some extent.

The liver begins to grow causing existing cells to enlarge. Then the new liver cells begin to multiply.

Within a week after removing two-thirds of the liver, the liver can return to the same weight it was before surgery. The liver is known to fully regenerate after performing up to 12 partial liver removal surgeries.

Pancreas

The pancreas is a glandular organ that produces a number of essential hormones for the body. It forms an integral part of the digestive system.

The pancreas is located below and behind the stomach, in the curve of the duodenum, which is a part of the small intestine. The pancreas secretes fluids that help break down food in the small intestine, along with bile and other fluids that help metabolism of fats and proteins.

Pancreas function

The pancreas is also critical for the production of insulin and glucagon, which regulate blood glucose levels. If the pancreas stops producing insulin, this leads to diabetes and a number of associated health problems.

Other problems that affect the pancreas include pancreatic cancer. This is a particularly difficult cancer to detect as the tumor is usually not palpable (cannot be felt) due to the position of the pancreas.

People with pancreatic cancer usually only begin to show symptoms when the tumor becomes large enough to interfere with neighboring organs.