Question

1. Describe the function of calcium homeostasis, and function of calcium
   (4 marks)
2. Write Down short notes on following (4 marks)

a. Functions of pyridoxine & Folic acid

b. Visual cycle

3. Discuss gluconeogenesis and glycogenesis .
   (3 marks)
4. Descuss inborn error of aminoacid metabolism .
   (2 marks)
5. Describle fuction of thyroid hormones in human body (2 marks)

Answer 1

1. Function of calcium homeostasis:

The three factors involved in Calcium Homeostasis are: Parathyroid Hormone, Vitamin D and Calcitonin.

These act on three target organs: Intestine, bone and kidney

A) Parathyroid Hormone: The parathyroid glands (four tiny glands) located in the neck produce a hormone called parathyroid hormone (PTH). PTH raises the blood calcium level by :

i) breaking down the bone (where most of the body's calcium is stored) and causing calcium release

ii)increasing the body's ability to absorb calcium from food

iii)increasing the kidney's ability to hold on to calcium that would otherwise be lost in the urine.

B) Vitamin D: It maintains Calcium homeostasis by

i) Increasing calcium absorption from the intestine (by interacting with a calcitriol receptor located in intestinal epithelial cell)

ii )stimulating renal tubular reabsorption of Calcium.

iii) Increasing bone calcification and mineralisation(by acting on osteoclasts in the bone)

C) Calcitonin: calcitonin counteracts parathyroid hormone (PTH) and vitamin D

The hormone participates in calcium (Ca²⁺) and phosphorus metabolism. In many ways, calcitonin counteracts parathyroid hormone (PTH) and vitamin D

More specifically, calcitonin lowers blood Ca²⁺ levels in two ways:

Major effect: Inhibits osteoclast activity in bones, which break down the bone

Minor effect: Inhibits renal tubular cell reabsorption of Ca²⁺ and phosphate, allowing them to be excreted in the urine

Function of Calcium:

i) Major structural elements in bones and teeth

ii) Essential for several physiological processes such as neuromascular transmission, smooth, skeletal, and cardiac muscle contractions, nerve function, and cell division and movement

iii) Co-factor in blood coagulation

iv) Plays an important role in the action of other intracellular messanger like cyclic adenosine monophosphate and inositol triphosphate which are responsible for mediating the cellular response to various hormones including epinephrine, glucagon, ADH and secretin

iv) release of neurotransmittor and hormones

2. Function of pyridoxine: It is  needed for proper brain development (in kids) and function (for people of all ages). It helps the body make the hormones serotonin (which regulates mood) and norepinephrine (which helps your body cope with stress).It is important for protein, fat and carbohydrate metabolism and the creation of red blood cells and neurotransmitters

Function of Folic Acid: Folic acid helps our body produce and maintain new cells, and also helps prevent changes to DNA that may lead to cancer

3. Gluconeogenesis. It is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. From breakdown of proteins, these substrates include glucogenic amino acids (although not ketogenic amino acids); from breakdown of lipids (such as triglycerides), they include glycerol, odd-chain fatty acids (although not even-chain fatty acids, see below); and from other steps in metabolism they include pyruvate and lactate.

Gluconeogenesis is one of several main mechanisms used by humans and many other animals to maintain blood glucose levels, avoiding low levels (hypoglycemia)

Glycogenesis, :It is the formation of glycogen which is primary carbohydrate stored in the liver and muscle cells of animals, from glucose. Glycogenesis takes place when blood glucose levels are sufficiently high to allow excess glucose to be stored in liver and muscle cells. Glycogenesis is stimulated by the hormone insulin. Insulin facilitates the uptake of glucose into muscle cells, though it is not required for the transport of glucose into liver cells. However, insulin has profound effects on glucose metabolism in liver cells, stimulating glycogenesis and inhibiting glycogenolysis, the breakdown of glycogen into glucose.

4, Inborn error of aminoacid metabolism: They include phenylketonuria (PKU) and maple syrup urine disease. Amino acids are "building blocks" that join together to form proteins. If you have one of these disorders, your body may have trouble breaking down certain amino acids. Or there may be a problem getting the amino acids into your cells. These problems cause a buildup of harmful substances in your body. That can lead to serious, sometimes life-threatening, health problems.

These disorders are usually inherited. A baby who is born with one may not have any symptoms right away. Because the disorders can be so serious, early diagnosis and treatment are critical. Newborn babies get screened for many of them, using blood tests.

5. Function of Thyroid hormones: The thyroid hormones act on nearly every cell in the body. They act to increase the basal metabolic rate, affect protein synthesis, help regulate long bone growth (synergy with growth hormone) and neural maturation, and increase the body's sensitivity to catecholamines (such as adrenaline) by permissiveness