Concentration of bicarbonate ions is not controlled by PTH. Its concentration depends on the buffering capacity of blood in the form of carbonate bicarbonate buffer

The small intestine is all about maximising the surface area.

Amino acids are the chemical units or building blocks of the body that make up proteins. Protein substances make up the muscles, tendons, organs, glands, nails, and hair. The final digestion products of proteins are amino acids.

A shortage of vitamin D (calciferol) causes defective incorporation of calcium into the bones, which therefore remain soft and are easily deformed. This condition is known as 'rickets'.

Approx. 95% of the volume of normal urine is due to water. The other 5% consists of solutes (chemicals that are dissolved in the water). Some of these solutes are the result of normal biochemical activity within the cells of the body. Other solutes may be due to chemicals that originated outside of the body, such as pharmaceutical drugs.

Iron is an important component of haemoglobin, the red pigment which combines with oxygen in the red blood cells. So,it is needed by the blood.

The alveoli are tiny air pockets at the ends of the bronchioles. Oxygen from the air diffuses into the blood capillaries in their walls and carbon dioxide diffuses out.

Amount of potassium in urine varies with diet and the amount of aldosterone (a steroid hormone) in the body.

The pH of normal urine is generally in the range 4.6 - 8, a typical average being around 6.0. Much of the variation is due to diet. For example, high protein diets result in more acidic urine, but vegetarian diets generally result in more alkaline urine (both within the typical range 4.6 - 8.

The Urinary System may also be called the Renal System because this group of inter-connected body parts process a liquid substance called urine via specialist organs called the kidneys. The word renal means pertaining to the kidneys, so this group of tissues and organs is either named after the substance it processes (urine; Urinary System), or the organ that does most of the work (kidneys, Renal System).

The bladder is located on the floor of the pelvic cavity. The bladder is located anterior to (i.e. in front of) the rectum in males. In females, it is also in front of the uterus and upper vagina, so its location is described simply as anterior to the uterus and upper vagina.

The cardiovascular system transports nutrients, oxygen and hormones to the cells of the body. At the same time, it removes the wastes produced by bodily functions. These include gases such as carbon dioxide and nitrogen as well as heat that is emitted by the functions of the body.

Urinary system is also known as excretory system of human body. It is the system of production, storage and elimination of urine. Formation and elimination of urine is important for human body because urine contains nitrogenous wastes of the body that must be eliminated to maintain homeostasis.

Kidneys are the major organs of urinary system. Formation of urine takes place in kidneys which are two bean shaped organs lying close to the lumbar spine, one on each side of the body.

The innermost layer of the wall of the urinary bladder is the mucous membrane (also called the mucosa), which contains transitional epithelium tissue that can stretch. The ability of this tissue to stretch is important because it contains variable volumes of liquid - as the bladder is filled and emptied several times per day. Because it is only loosely attached to the (strong and substantial) muscular layer, the mucosa falls into many folds known as rugae when the bladder is empty or is only filled to a small extent.

Nephron is the basic structural and functional unit of the kidney. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine.

Kidneys are bean-shaped organs, each about the size of a fist. They are located near the middle of the back, just below the rib cage, one on each side of the spine. The kidneys are sophisticated reprocessing machines. Every day, a person's kidneys process about 200 quarts of blood to sift out about 2 quarts of waste products and extra water.

In addition to its excretory and homeostatic roles, the kidneys also release two important hormones into the blood. These are: 1.Erythropoietin, which acts on bone marrow to increase the production of red blood cells, and 2.Calcitriol- which promotes the absorption of calcium from food in the intestine and acts directly on bones to shift calcium into the bloodstream.

The renal capsule is the membranous covering of the kidney. It directly covers the renal cortex, which forms the outer stratum

The urinary bladder is a temporary storage reservoir for urine. It is located in the pelvic cavity, posterior to the symphysis pubis, and below the parietal peritoneum. The size and shape of the urinary bladder varies with the amount of urine it contains and with the pressure it receives from surrounding organs

The cortex of the kidney is the outer section which covers the internal medulla. The cortex is visible near the outer edge of the cross-sectioned kidney. It is composed of blood vessels and urine tubes and is supported by a fibrous matrix.

The renal pyramids are conical segments within the internal medulla of the kidney. The pyramids contain the secreting apparatus and tubules and are also known as the malphighian pyramids.

The renal column or Bertin column, or column of Bertini is a medullary extension of the renal cortex in between the renal pyramids of the kidney. It allows the cortex to be better anchored. Each column consists of lines of blood vessels and urinary tubes and a fibrous material.

The normal kidney size of an adult human is about 10 to 13 cm (4 to 5 inches) long and about 5 to 7.5 cm (2 to 3 inches) wide. It is approximately the size of a conventional computer mouse. A kidney weighs approximately 150 grams. 

One quarter of the total blood output from the heart comes to the kidneys along the renal artery. Two renal arteries arise from the abdominal section of the aorta, each artery supplies a lobe of the kidney. The incoming artery divides into four or five branches, eventually forming arterioles, each of which leads to the compact ball of capillaries called the glomerulus.