Question

Rennin and lactase, the enzymes required to digest milk, disappear in the human body by the age of
(a) Five
(b) Three
(c) Two
(d) Eight

Answer 1

Hint: Rennin and lactase are both produced in large quantities in the early years of human life when their diet is fully or partially dependent on milk. Their secretion gradually decreases and disappears when other enzymes like pepsin take over the function of protein digestion.

Complete answer:
Rennin is a proteolytic enzyme found in the gut of many animals and synthesized by the chief cells located in the mucosal epithelium of the stomach. Its function is to coagulate the proteins of milk and aid in its digestion. Milk is made up of many proteins, casein is one of them. Casein is of four major types. Kappa casein is the one that is responsible for the solubilization of all other proteins. Rennin cleaves casein and thus the proteins coagulate.
Lactase is an enzyme that is required by the body for cleaving lactose into glucose and galactose. Lactose is a sugar that is found in milk or its products. This enzyme is only found in the small intestine of mammals. Both these enzymes are abundant in infancy where the infant is highly dependent on the diet of milk. By the age of eight years, rennin and lactase disappear in the human body.

Additional Information:
- In the early years of human life, the digestive system is not very well-developed and thus it is extremely important for the milk to stay in the gut for long to stimulate effective absorption of nutrients.
- Thus, milk in its liquid form is not effective for proper absorption. Rennin and lactase convert the liquid into its semi-solid form and thus the milk stays in the stomach for a longer period of time.
- Rennin is released in its inactive form 'prorenin.’ The acidic environment produced by the HCl.
So, the correct answer is ‘(d) Eight’.

Note:
- Do not confuse rennin with renin. Renin is an enzyme secreted by the kidney where it is involved in the regulation of blood pressure by acting in concert with a peptide hormone angiotensin.
- Lactose intolerance is a disorder of the digestive system when the body produces insufficient quantities of lactase and it leads to the accumulation of undigested lactose. This causes bloating and diarrhea.