Digestive system- glands - class-XII

The optimum pH for the enzymatic activity of salivary amylase ranges from 6 to 7. Above and below this range, the reaction rate reduces as enzymes get denaturated. The enzyme salivary amylase is most active at pH 6.8. 

An amylase is an enzyme that catalyses the hydrolysis of starch into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion. Bile juice is secreted by liver. Pepsin and trypsin are produced in small intestine. 

• The liver receives blood supply from two sources. 
• The first is the hepatic artery which delivers oxygenated blood from the general circulation. 
• The second is the hepatic portal vein delivering deoxygenated blood from the small intestine containing nutrients. Hence, Deoxygenated blood is processed by hepatocytes.

• An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.
• The liver receives blood from two major blood vessels. The hepatic arterioles bring oxygen-rich blood from the heart.
• The hepatic portal vein brings blood rich in digested nutrients from the intestine. This means excess nutrients can be removed and stored before blood circulates around the body. Hence Arterioles provides oxygen to the liver.

There are three major parts of salivary glands that secrete saliva with the digestive enzyme such as parotid, submandibular and sublingual glands. Normally secretion of saliva is constant, regardless of the presence of food in the mouth. The amount of saliva secreted in 24 hours usually amounts from 1 liter to 1.5 litres. 

Saliva is produced by three pairs of major salivary glands: the parotid, submandibular, and sublingual glands.

• The sublingual gland is one of the three salivary glands present. They are located beneath the mucous membrane of the floor of the mouth. The other salivary glands are the parotid and the submandibular glands. 
• Brunner's glands are present in the duodenum of the small intestine and helps in the release of mucous and proteolytic enzymes. Lacrimal glands are exocrine glands that supply tears to the corner of the eye. 
• Adrenal glands are endocrine glands present above the kidneys that are involved in the production of a large number of different hormones. So, the correct answer is 'sublingual gland'.

Digestion of starch begins in the mouth, where salivary amylase (ptyalin) starts breaking down complex carbohydrates into maltose.

Salivary amylase is an enzyme specifically responsible for the hydrolysis of starch, which is a carbohydrate, into simpler sugars like maltose.

Salivary amylase works best at a slightly acidic pH of about 6.8, gastric enzymes (like pepsin) work in a highly acidic environment (pH 1-2), and intestinal enzymes work in an alkaline environment (pH 8).

The pH of human saliva typically ranges from 6.2 to 7.6, with 6.5 to 6.8 being the standard value cited for optimal salivary amylase activity.

Salivary glands secrete saliva containing enzymes like salivary amylase and lysozyme, which provides antibacterial protection. Brunner's glands secrete alkaline mucus, not amylase.

There are three pairs of salivary glands (parotid, submandibular, and sublingual), not six pairs. Therefore, the statement that there are six pairs is incorrect.

Salivary amylase has an optimum pH of approximately 6.8. A pH of 8.9 is alkaline and would inhibit the activity of salivary amylase.

'Lacrimal gland' is not a salivary gland.

Stenson's duct is associated with 'parotid gland'.

Blood is carried to the liver via two large vessels: the hepatic artery carries oxygen-rich blood from the aorta, and the portal vein carries blood containing digested food from the small intestine. The hepatic portal vein is a blood vessel that conducts blood from the gastrointestinal tract and spleen to the liver. This blood is rich in nutrients that have been extracted from food, and the liver processes these nutrients; it also filters toxins that may have been ingested with the food. The liver receives about 75% of its blood through the hepatic portal vein, with the remainder coming from the hepatic artery proper. The blood leaves the liver to the heart in the hepatic veins.

Humans produce between one-fifth and one-third of a gallon (0.75 to 1.5 liters) of saliva every day. However, saliva production mostly takes place while a person is awake. During sleep, saliva production drops to almost nothing. Most of the saliva comes from the glands at the bottom of the mouth, and the rest comes primarily from the parotid glands, near the top back of the mouth.

The rabbit has four major pairs of salivary glands: the parotid, mandibular, sublingual and zygomatic. Amylase and galactosidase are produced in the saliva, which is produced continuously by the mandibular glands and in response to food intake by the others.

Ptyalin is a form of amylase found in saliva of humans. Another name of ptyalin is salivary amylase. It is the most important amylolytic enzyme secreted in mouth (buccal cavity) by the salivary glands. The main function of ptyalin is to catalyze the hydrolysis of starch into maltose and dextrin.