Urinary System REGULATING THE INTERNAL ENVIRONMENT

Organs

Kidney Functions Removal of toxins, metabolic wastes, and excess ions from the blood Regulation of blood volume, chemical composition, and pH Gluconeogenesis during prolonged fasting Endocrine functions –Renin: regulation of blood pressure and kidney function –Erythropoietin: regulation of RBC production Activation of vitamin D

Management of the body’s water content and solute composition, osmoregulation, –controlling movements of solutes between internal fluids and the external environment. –remove metabolic waste products before they accumulate to harmful levels. Accomplished by managing the composition of the internal body fluid that bathes the cells. Introduction

the waste products are either ammonia or urea Urea is far less toxic! –Urea is synthesized in the liver by combining ammonia with carbon dioxide and excreted by the kidneys. Water balance and waste disposal depend on transport epithelia

Over time, the rates of water uptake and loss must balance. Lack of balance causes cells to swell or crenate. Osmosis occurs whenever two solutions separated by a membrane differ in osmotic pressure, or osmolarity (moles of solute per liter of solution The osmolarity of human blood is about 300 mosm/L, while seawater has an osmolarity of about 1,000 mosm/L. Cells require a balance between osmotic gain and loss of water

The kidneys of vertebrates function in both osmoregulation and excretion. –We have a pair of bean-shaped kidneys. Surrounded by fat –renal artery and a renal vein supply blood –less than 1% of body weight, receive 20% of resting cardiac output. –Urine exits the kidney through a duct called the ureter, and both ureters drain through a common urinary bladder. –urine is expelled from the urinary bladder through a tube called the urethra

kidney has two regions, renal cortex and renal medulla. –Both regions are packed with microscopic excretory tubules, nephrons –Each nephron consists of a single long tubule and a ball of capillaries, called the glomerulus. –The blind end of the tubule forms a cup-shaped swelling, called Bowman’s capsule –Each human kidney packs about a million nephrons.

Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule. –capillaries, are permeable to water and small solutes but not to blood cells or large molecules such as plasma proteins. –The filtrate in Bowman’s capsule contains salt, glucose, vitamins, nitrogenous wastes, and other small molecules.

filtrate passes through three regions of the nephron: the proximal tubule; the loop of Henle, a hairpin turn with a descending limb and an ascending limb; and the distal tubule. The distal tubule empties into a collecting duct, The many collecting ducts empty into the renal pelvis, which is drained by the ureter.

Nephrons most important task is to reabsorb solutes and water. The nephrons and collecting ducts reabsorb nearly all of the sugar, vitamins, and other organic nutrients from the initial filtrate and about 99% of the water. This reduces 180 L of initial filtrate to about 1.5 L of urine to be voided. Filter all plasma 60 times a day

Physical Characteristics of Urine Color and transparency –Clear, pale to deep yellow (due to urochrome) –Drugs, vitamin supplements, and diet can alter the color –Cloudy urine may indicate a urinary tract infection

Physical Characteristics of Urine Odor –Slightly aromatic when fresh –Develops ammonia odor upon standing –May be altered by some drugs and vegetables

Physical Characteristics of Urine pH –Slightly acidic (~pH 6, with a range of 4.5 to 8.0) –Diet, prolonged vomiting, or urinary tract infections may alter pH Specific gravity –1.001 to 1.035, dependent on solute concentration

Chemical Composition of Urine 95% water and 5% solutes Nitrogenous wastes: urea, uric acid, and creatinine Other normal solutes –Na +, K +, PO 4 3–, and SO 4 2–, –Ca 2+, Mg 2+ and HCO 3 – Abnormally high concentrations of any constituent may indicate pathology

Ureters Slender tubes attaching the kidney to the bladder –Continuous with the renal pelvis –Enter the posterior aspect of the bladder Runs behind the peritoneum Peristalsis aids gravity in urine transport

Urinary Bladder Smooth, collapsible, muscular sac Temporarily stores urine Trigone made of transitional epithelium Bladder can expand significantly without increasing internal pressure

Overview

Urethra carries urine from the bladder to the outside of the body by peristalsis Release of urine is controlled by two sphincters –Internal urethral sphincter (involuntary) –External urethral sphincter (voluntary) Length –Females – 3–4 cm (1 inch) –Males – 20 cm (8 inches)