The Urinary System

Points to ponder What are the parts and functions of the urinary system? What is the macroscopic and microscopic structure of the kidney? What are the three processes in urine formation? How is the kidney involved with regulating water- salt and acid-base balance of blood? What are the common disorders of the kidney? How can kidney failure be treated? How is the kidney involved with maintaining homeostasis along with other body systems?

What are the organs of the urinary system? Kidneys (2) – bean-shaped, fist-sized organ where urine is formed Ureters (2) – small, muscular tubes that carry urine from the kidneys to the bladder Bladder (1) – expandable organ that stores urine until it is expelled from the body Urethra (1) – tube (longer in men than women) that carries urine from the bladder to the outside of the body

Overview of the urinary system Adrenal glands produce aldosterone. renal artery 1. Kidneys produce urine. renal vein aorta inferior vena cava 2. Ureters transport urine. 3. Urinary bladder stores urine. 4. Urethra passes urine to outside. Figure 11.1 The urinary system.

What are the functions of the urinary system? Excretion of metabolic wastes Maintenance of water-salt balance Maintenance of acid-base balance Hormone secretion: renin and erythropoietin (EPO) Reabsorb filtered nutrients and synthesize vitamin D

Homeostasis The urinary system maintains homeostasis in several ways: Acts as blood filter Removal of urea (nitrogenous waste) from the bloodstream. Involved in blood pressure regulation. Release hormones: calcitriol & erythropoietin Maintain electrolyte, acid-base, and fluid balance of blood

Kidneys as Filters Diuretic- loose water; (coffee, tea, alcohol) Antidiuretic- retain water; (ADH) Aldosterone- (from pituitary gland) causes sodium & water reabsorption, and K+ excretion GFR= 180 liters (50 gal) of blood/day 178-179 liters are reabsorbed back into blood Excrete a protein free filtrate

Anatomy of the Kidney Main structures of the mammalian kidney: renal cortex renal medula renal pelvis nephrons

Urea removal

Amino acid metabolism Amino acids are the building blocks of protein. If not needed for building protein, they can be metabolized for energy, or broken apart and the carbon chains used to make fat. Metabolism requires removal of the amine unit (NH2 + H2O NH3) which becomes ammonia in water.

Ammonia and Urea Ammonia is toxic and highly water soluble. The liver turns ammonia into urea, which is less toxic and less soluble.

Anatomy of the Nephron Glomerulus Proximal tubule Loop of Henle Distal tubule

Glomerulus This is the only place in the system where the blood is actually “filtered.” Blood pressure is used to push plasma through capillary walls and into the Bowman’s capsule.

H2O ) nutrients Filtrates consist of water, salt, amino acids, creatine, urea, fatty acids, uric acid, glucose and vitamins and other nutrients. Nutrients are moved out of the tubule through active transport.

Proximal tubule Nutrients (salts, vitamins, etc.) are moved out of the tubule through active transport. Water follows the nutrients by osmosis. Wastes continue through the proximal tubule

Loop of Henle Tissue around the Loop of Henle is salty, from active transport and diffusion of sodium chloride. The salty conditions allow water to diffuse out of the loop. Urea diffuses into Loop of Henle

Loop of Henle

Loop of Henle

Distal tubule Active transport is used to move more nutrients out of the concentrated urine. Some ions, drugs, and toxins are actively pumped into the tubule.

Collecting Duct More water leaves the tube by osmosis, since the tube is surrounded by salty tissue. Some urea leaves by diffusion, and may be cycled through the system.

Which of these happens during filtration? Salt is actively pumped out. Water is removed osmotically from the filtrate. Plasma moves from capillaries into the capsule. Toxins are actively removed from plasma.

Which of these happens during filtration? Salt is actively pumped out. Water is removed osmotically from the filtrate. Plasma moves from capillaries into the capsule. Toxins are actively removed from plasma.

What drives filtration in the glomerulus? Osmosis Smooth muscle contractions Salt gradients Blood pressure

What drives filtration in the glomerulus? Osmosis Smooth muscle contractions Salt gradients Blood pressure

Which of these aids in water recovery from the filtrate? Active transport of water out of the tubules. Active transport of sodium out of the filtrate. Peristalsis in the Loop of Henle. Concentration of urea in the urine.

Which of these aids in water recovery from the filtrate? Active transport of water out of the tubules. Active transport of sodium out of the filtrate. Peristalsis in the Loop of Henle. Concentration of urea in the urine.

Why does our salty, low-vegetable American diet cause problems? Notice that sodium is actively recovered in the system, while potassium may be pumped out. A “natural” diet such as hunter-gatherers eat (mostly fresh plant material supplemented with lean meat) is low in sodium and high in potassium. How is this system adaptive when eating a “natural” diet? What is the danger of eating a high protein diet?

Water Regulation

Regulating water Antidiuretic hormone (ADH, also called vasopressin) is part of a negative feedback system that regulates water in the mammalian body. ADH increases the permeability of the distal tubule, allowing greater water recovery.

Regulating water Caffeine and alcohol are diuretics. Alcohol inhibits ADH release, while caffeine interferes with its activity. Part of the symptoms of a hangover are due to dehydration. What causes the dehydration? And why is a cup of coffee not a good cure for a hangover?

If a person were given a dose of ADH, what would happen? More water lost through kidneys. More potassium secreted by nephron. More water retained in the kidneys. More sodium secreted by nephron.

If a person were given a dose of ADH, what would happen? More water lost through kidneys. More potassium secreted by nephron. More water retained in the kidneys. More sodium secreted by nephron.

Diet Miracles? Many over-the-counter herbal diet aids claim to “detoxify” the body or “flush fat.” Many of these contain dandelion leaves, parsley, or other herbs known to be diuretics. If a person tries these products and appears to lose pounds, what is actually lost? Could there be health problems with using these products?

Final thought question The kangaroo rat is adapted to desert life. It survives on very little water. List some ways in which its kidneys might be different from the human kidney to allow it to conserve as much water as possible.

Kidneys as Filters Kangaroo rat has almost no need for water. Survives almost entirely on the water metabolized from seeds that are eaten. Kangaroo rats can extract a half gram of water out of every gram of seeds consumed. Kidneys reduce/concentrate urine to crystal-like consistency, (lots of uric acid) greatly reducing the amount of water that is lost.  Ord’s Kangaroo Rat Metabolic Water

Kidneys as Filters What could be a health risk of going on an extremely high protein diet?

Blood pressure

Renin Renin is an enzyme released by the kidneys in response to a drop in blood pressure. Renin catalyzes the production of Angiotensin Angiotensin is a hormone that causes arterioles to constrict, raises blood pressure. also causes water retention. How does this maintain homeostasis of blood pressure?

Erythropoietin A second response to low blood pressure is the release of erythropoietin, another hormone. Erythropoietin travels to the bone marrow and stimulates the production of new blood cells. How does this maintain homeostasis?

Liver Lungs Skin Kidneys removes hazardous chemicals from the blood. "detoxifies" the blood For this reason, alcoholics and other types of addicts have a higher incidence of liver disease. Some proteins & other nitrogenous compounds are broken down in the liver forming a compound call urea Lungs excrete waste like carbon dioxide and water. Skin rids waste from the body through sweat glands Kidneys