Urinary System- Anatomy and Physiology

Functions of the Urinary system 1. Regulating blood volume and pressure 2. Regulating plasma concentrations of sodium, potassium, chloride and other ions 3. Stabilising blood pH 4. Conserving nutrients 5. Detoxifying poisons (with the liver) Functions of the Urinary system

Organisation of the Urinary System Kidneys Ureters Urinary bladder Urethra

Position of the Kidneys CT abdomen with contrast MRI coronal abdomen

Internal Structure of the Kidney

Parts of the Nephron Each nephron consists of the following parts: 1) glomerulus ; 2) Bowman’s capsule ; 3) proximal tubule ; 4) loop of Henle ; 5) distal tubule ; 6) collecting duct.

The Nephron The glomerulus is a mass of thin-walled capillaries. The Bowman’s capsule is a double-walled, cup-shaped structure. The proximal tubule leads from the Bowman’s capsule to the Loop of Henle. The loop of Henle is a long loop which extends into the medulla. The distal tubule connects the loop of Henle to the collecting duct.

Renal Corpuscle and Filtration

Only materials needed by the body are returned to bloodstream — for example, 99 % of water, all glucose and amino acids and many salts are reabsorbed. Osmosis , diffusion, and active transport draw water , glucose , amino acids and ions from filtrate into surrounding cells. Small villi like projections help in the active transport of glucose out of the filtrate and speed up the reabsorption process. From here, these components return to the bloodstream.

Nephron-Tubular System Proximal convoluted tubule Descending loop of Henle Ascending loop of Henle Distal convoluted tubule Collecting duct Nephron-Tubular System

Formation of Urine - Summary Blood enters the kidney through the renal artery at the site of the hilum The renal artery divides in to ever smaller arteries and arterioles Afferent arterioles take blood to the glomerulus to be filtered Once blood is filtered efferent arterioles take blood away from the glomerulus The PCT is concerned with reabsorption- organic nutrients are reabsorbed and water follows because there is a concentration gradient The filtered substances move into the proximal convoluted tubule Products which are filtered out: water, mineral salts, amino acids, glucose, hormones, urea, toxins The glomerulus is a network of capillaries which filters the blood Products which do not filter and remain in the blood: Leukocytes, erythrocytes, platelets, plasma proteins The remaining filtrate moves into the descending loop of henle. This is lined with thin cells so water moves out Because water has been reabsorbed the concentration of the filtrate is not very high The walls of the ascending loop of henle are lined with thicker cells, so water can’t pass in or out. Instead sodium and chloride is pumped out actively The filtrate now enters the distal convoluted tubule- is it now only 20% of what it originally was. A number of other nephrons join up to the collecting duct which travels through the medulla to the renal papilla where the filtrate is emptied in the minor calyx In the DCT the volume and composition of the filtrate can be adjusted but this is controlled by hormones From the DCT the filtrate now passes into the collecting duct. 4-5 minor calyces join up to make a major calyx 2-3 major calyces join up to form the renal pelvis The renal pelvis joins the ureter at the hilum The ureter transport the filtrate/urine from the kidney to the bladder