Kidney-Structure, Anatomy and Function

Gross Structure

Kidneys are bean-shaped organs, about 11 cm long, 6 cm wide, 3 cm thick and weigh 150 g. They are embedded in, and held in position by, a mass of adipose tissue.
Each kidney is enclosed by a thin tough fibrous connective tissue called renal capsule that protects it from infections and injuries. Around the capsule there is a layer of fat (adipose tissue) which is further enclosed by another layer of fibrous membrane known as renal fascia. The bean shaped kidney have outer convex surface and inner concave surface.
Location: The kidneys lie on the posterior abdominal wall, one on each side of the vertebral column, behind the peritoneum and below the diaphragm.
Position: It is situated at the level of T12-L3. The right kidney is usually slightly lower than the left, probably because of the considerable space occupied by the liver.

Capsule: It is an outermost covering composed of fibrous tissue surrounding the kidney.
Cortex: It is a reddish-brown layer of tissue immediately below the capsule and outside the renal It consists of renal corpuscles and convoluted tubules.
Medulla: It is the innermost layer, consisting of conical areas called the renal pyramids separated by renal columns. There are 8-18 renal pyramids in each kidney. The apex of each pyramid is called a renal papilla, and each papilla projects into a small depression, called a minor calyx (plural calyces). Several minor calyces unite to form a major calyx. In turn, the major calyces join to form a funnel shaped structure called renal pelvis that collects urine and leads to ureter.

The renal artery enters the kidney through the hilum and then branches progressively to form the interlobar arteries arcuate arteries, interlobular arteries, and afferent arterioles, which lead to the glomerular capillaries. The distal ends of the capillaries of each glomerulus combine to form the efferent arteriole, which leads to a second capillary network, the peritubular capillaries, that surrounds the renal tubules called vasa recta. The blood vessels of the venous system progressively form the interlobular vein, arcuate vein, interlobar vein, and renal vein, which leaves the kidney beside the renal artery and ureter.

Endocrine functions: kidney is also an endocrine glands. It secretes enzymes renin, 1, 25-dihydroxycholecalciferol, erythropoietin etc.

Renin; It is an enzyme secreted by cells of juxtaglomerular apparatus which helps in regulation of blood pressure.
1, 25-dihydroxycholecalciferol; it is a biological active form of vitamin D3 found in kidney.
Erythropoietin; it is essential for RBC formation

Osmoregulation: Kidney regulate osmotic pressure in the body by regulating fluids and electrolyte balance
Homeostasis: also regulate PH balance
Excretion: metabolic wastes of the body are excreted in the form of urea, creatinine, uric acid etc in urine.
Excretion of Drugs and toxins
Selective reabsorption: glucose, amino acids, water and electrolytes etc are selectively reabsorbed in the renal tubules
Erythropoiesis: helps in RBC formation
Blood pressure regulation

https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/urinary-system-25/the-kidneys-239/internal-anatomy-of-the-kidneys-1168-4690/
https://opentextbc.ca/anatomyandphysiology/chapter/25-3-gross-anatomy-of-the-kidney/
http://www.newhealthadvisor.com/kidney-structure-and-function.html
http://www.webmd.com/urinary-incontinence-oab/picture-of-the-kidneys#1
https://www.healthpages.org/anatomy-function/kidney/
http://www.innerbody.com/image_urinov/dige05-new.html