The Urinary System

Urinary System One of the excretory systems of the body It consists of the following structures 2 kidneys – secrete urine 2 ureters – convey urine to the bladder 1 urinary bladder – stores urine temporarily 1urethra – conveys urine to the exterior Functions : homeostasis of water and electrolytes Metabolic waste products (the nitrogenous compounds like urea, uric acid excess ions and some drugs are excreted Stimulation of erythropoiesis (erythrocyte prduction) Control of blood volume Passing urine is called micturition

Kidneys Definition Bean shaped organs which secrete and excrete urine Situation On the posterior abdominal wall One on each side of the vertebral column Retroperitoneal Below diaphragm 11 cm x 6 cm x 3 cm Embedded in and surrounded by a mass of fat called the perirenal fat Renal fascia = a fibroelastic tissue sheet of tissue encloses the perirenal fat and the kidney

Relations Right Kidney Superiorly : adrenal gland Anteriorly : right lobe of liver, duodenum, hepatic flexure of colon Posteriorly : diaphragm, muscles of the posterior abdominal wall Left kidney Anteriorly : the spleen, stomach, pancreas, jejunum splenic flexure of colon Posteriorly : diaphragm, muscles of the posterior abdominal wall.

Structure Three areas : - fibrous capsule surrounding the kidney The cortex is the reddish brown layer of tissue immediately under the capsule and between the pyramids The medulla – innermost layer – pale conical shaped striations the renal pyramids Hilum – concave medial border where the nerves vessels enter The pelvis is the funnel shaped structure – receptacle for urine. It has branches called calyces (calyx) – each branch surrounds the apex of a renal pyramid – urine  through a papilla at the apex of a pyramid minor calyx major calyx  renal pelvis

Walls of pelvis contains smooth muscle fibres – lined with transitional epithelium Pacemaker cells in the walls of the calyces – peristaltic movements – started – urine propelled – intrinsic function not controlled by nerves

Microscopic Structure of the Kidney One million functional units called the nephrons Smaller number of collecting tubules Transport urine through the pyramids to the pelvis The tubules give the pyramids the striped appearance

The Nephron Consists of a tubule closed at one end The other end opens into a collecting tubule The closed end forms a cup – glomerular capsule (Bowman’s capsule) Inside a capillary network – glomerulus Walls of the glomerulus and the glomerular capsule have a single layer of flattened epithelial cells – the remainder of the nephron and the collecting tubule have a single layer of highly specialised cells

The remainder of the nephron is 3 cm has three parts:- The proximal convoluted tubule The medullary loop (the loop of Henle) The distal convoluted tubule leading into a collecting tubule

Blood Supply Arterial supply Renal artery hilum  arteriole in In the Cortex an arteriole enters the glomerular capsule – the afferent arteriole Subdivides into a cluster of capillaries – glomerulus Between the capillary loops there are connective tissue phagocytic mesangial cells The arteriole that leaves the glomerulus – the efferent arteriole

Outside the glomerulus the efferent arteriole becomes a capillary network and supplies the rest of the nephron Venous drainage Ultimately through the renal vein  IVC Nerve supply Sympathetic and parasympathetic nerves Lymphatic drainage To the paraaortic lymph nodes