Human Form & Function The urinary system

Urinary system The major structural components of the urinary system are: Kidneys Urinary bladder Ureters Urethra

Urinary system Function To rid the body of wastes, especially nitrogenous wastes such as urea. To regulate the balance of fluid, salt & pH. The blood is filtered as it passes through the kidneys. Waste substances are removed by the processes of filtration and tubular secretion. Useful substances are returned to the body by the process of selective re-absorption.

The kidneys The functional unit of the kidney is the nephron A nephron consists of a Bowman’s capsule, a renal tubule and the associated blood supply. It filters waste products out of the blood Each kidney contains about 1.2 million nephrons 2/23/2019 3HBS

The kidney Proximal convoluting tubule Glomerulus Capsule Cortex Distal convoluting tubule Medulla Renal artery Collecting duct Renal vein Loop of Henle Renal pelvis Capillaries Ureter KIDNEY A NEPHRON

The kidneys Renal medulla – loops of Henle Renal artery Renal vein Renal cortex – Bowman’s capsules Ureter – to the bladder 2/23/2019 3HBS

The nephron Common collecting duct Bowman’s capsule Renal corpuscle Distal convolute tubule Proximal convolute tubule Loop of Henle

The renal corpuscle Filtration takes place in the renal corpuscle. The renal corpuscle consists of the Bowman’s capsule and a mass of blood capillaries – the glomerulus.

The renal corpuscle Afferent arteriole Efferent arteriole Bowman’s capsule Glomerulus Proximal convolute tubule

Filtration Filtering the blood is a passive process and occurs under high pressure. The filtrate includes: Water Urea Glucose Amino acids Vitamins Salts (sodium & chlorine)

Microscopic section through a kidney Glomerulus Tubule

Photograph of a glomerulus taken with a scanning electron microscope Capillaries of the glomerulus Wellcome Images – David Gregory & Debbie Marshall

Re-absorption water salts water glucose amino acids urine vitamins Not all substances in the filtrate are waste products The nephron re-absorbes needed nutrients These include: water glucose, amino acids vitamins salts salts water glucose amino acids vitamins urine - water - urea - salts

Section through a renal tubule taken with a scanning electron microscope Wellcome Images – David Gregory & Debbie Marshall

The proximal tubule Microvilli line the proximal convolute tubule and create a brush border This greatly increases the surface area for re-absorption. Microvilli L Slomianka ANHB - UWA

Re-absorption Structure Substance Active/passive Proximal convolute tubule Water (60-70%) Passive (osmosis) Salts (60-70%) Glucose (100%) Amino acids (100%) Vitamins (100%) Active transport Loop of Henle Water (25%) Na+/Cl- (25%) Distal convolute tubule Water (5%) Na+/Cl- (5%) Collecting duct

Tubular secretion Wastes are transfered from the blood into the tubules for excretion This is an active process H+ NH4+ (ammonium) Creatinine Toxins Drugs Neurotransmitters

Tubular secretion Process Structure Substance Mode Tubular secretion Proximal collection tubule (PCT) Distal collection tubule (DCT) H+ NH4+ (ammonium) Creatinine Toxins Drugs Neurotransmitters Active transport Creatinine is a chemical waste molecule that is generated from muscle metabolism.

Filtration – a summary Blood enters the glomerulus (Bowman’s capsule) under high pressure. Water and other small molecules are forced out of the blood vessels This filtrate is collected and passes through several tubules Some water and useful substances are reabsorbed The rest passes through to the ureters and is stored in the bladder for excretion 2/23/2019 3HBS

Filtration Re-absorption + Tubular secretion Excretion Filtration – a summary Filtration Re-absorption + Tubular secretion Excretion Renal cortex Renal medulla

Deamination Definition: The stripping of nitrogen from amino acid & nitrogen bases (RNA) Deamination occurs in the liver Nitrogen occurs in the amino (NH2) part of an amino acid. Nitrogen is toxic to the human body and must be removed. The amino group Alanine

Deamination – chemical reaction Amino acid → ammonia + organic compounds (used for respiration) Ammonia (very toxic) + CO2 → urea (H2NCONH2)

Nitrogen wastes Nitrogen compound Source Amount Relative toxicity Urea Amino Acids 21 g/day Moderate Creatinine Muscle metabolism 1.8 g/day High Uric acid RNA 480mg/day Weak

Urine Urine is a clear, transparent fluid. It normally has an amber colour. It is collected in the bladder and eliminated through the urethra. The average amount of urine voided in 24 hours is about 1,200 cm3.

Composition of urine The composition of urine varies but typically contains: 95% water 5% other solutes (organic molecules) urea creatinine uric acid ions sodium & chloride ions other metabolic wastes.

Elimination vs. excretion Elimination is the removal of undigested food and waste from the body. Excretion is the removal of metabolic waste produced by cells from the body

Kidney Failure Most kidney diseases affect the glomeruli which reduces their ability to filter the blood (proteins and RBCs will be present in urine) Some lifestyle measures to reduce the risk of kidney damage include: Maintain a healthy weight Don’t smoke Drink plenty of water Alcohol only in moderation Kidney failure is when kidneys lose their ability to excrete waste and control the level of fluid in the body. 23/02/2019 Stage 2 HBS: Excretory System

Dialysis Dialysis is a method of removing wastes from the blood when kidney failure occurs. There are two types of dialysis peritoneal dialysis haemodialysis 23/02/2019 Stage 2 HBS: Excretory System

Peritoneal dialysis Peritoneal dialysis occurs inside the body using the peritoneum (a membrane that lines the inside of the abdominal cavity and covers organs such as stomach, liver and intestines) A fluid containing glucose and other substances at concentrations similar blood (and no wastes) is pumped via catheter into the abdominal cavity. Because of the concentration gradient wastes diffuse from the blood into the fluid in the abdominal cavity, useful products stay in the blood as there is not concentration gradient.

Peritoneal dialysis Peritoneal dialysis is usually done each day 23/02/2019 Stage 2 HBS: Excretory System

Haemodialysis Haemodialysis involves passing blood through an artificial kidney or dialysis machine The blood is passed through many tubes made of differentially permeable membrane and immersed in a bath of fluid. The concentration of substances in the fluid bath are similar to those in the blood (fluid has no waste) Due to concentration gradient wastes are passed from the blood into the fluid, useful substances remain in blood (no concentration gradient) 23/02/2019 Stage 2 HBS: Excretory System

Haemodialysis Haemodialysis is done for 4 to 5 hours per week. 23/02/2019 Stage 2 HBS: Excretory System