Ch. 25 Urinary System

*Alcohol inhibits ADH Caffeine increases GFR

*Diuretic drugs decrease tubular reabsorption of sodium- what does that mean for water?

*In 24 hours, about 1.0 to 1.8 liters of urine are produced

*you should drink ~2.5 liters of water a day (?). Technically, you should drink as much water as you excrete.

Location of Kidneys and Features

-Against the dorsal body wall in a retroperitoneal position -At the level of the T12 to L3 Vertebrae, right slightly lower than left (due to liver)

Body Homeostasis

-Water Balance -Electrolytes -Acid-base Balance in blood -Blood Pressure -Red blood Cell Production -Activation of Vitamin D

Reabsortion by PCT cells

1. At the basolateral membrane, Na+ is pumped into the interstitial space by the Na+-K+ ATPase. Active Na+ transport creates concentration gradients that drive: 2. "Downhill" Na+ entry at the apical membrane 3. Reabsorption of organic nutrients and certain ions by co-transport at the apical membrane. 4. Reabsorption of water by osmosis through aquamarines. Water reabsorption increases the concentration of the solutes that are left behind. These solutes can then be reabsorbed as they move down their gradients: 5. Lipid-soluble substances diffuse by the transcellular route 6. Various ions (ex. Cl-, K+, Ca+) and urea diffuse by the paracellular route

The urinary system- specifically your kidneys- do all sorts of important homeostatic stuff like...

1. Regulating your water volume, ion salt concentrations, and pH levels 2. Influencing your red blood cell production and blood pressure 3. Filters toxic leftovers from your blood- like the nitrogenous waste made by metabolizing protein- and ferries it out of the body

Glomerular capsule

2 layers that surround the glomerulus Visceral layer- podocytes (cells that wrap around capillaries of the glomerulus) Parietal layer- basement membrane -Filtration slits

Renal tubule

3 parts

Distal Convoluted Tubule

Acids, toxins, ions into tubule Reabsorption of water and salt

Tubular Secretion

Additional substances are secreted and move out of the blood into renal tubular filtrate. (move into tube)

Kidney features

Adrenal gland atop each kidney Fibrous capsule surrounding each kidney

Regulation of Reabsorption and Secretion: Controlled by 5 main hormones

Angiotensin II Aldosterone ANP Parathyroid Hormone ADH *ANP: A hormone produced by the heart, atrial natriuretic peptide (ANP), increases sodium excretion and decreases blood pressure and blood volume. ANP is released into the bloodstream in response to stretching of the atrial muscle cells by increased blood volume.

Peritubular Capillary Beds

Arise from efferent arteriole of the glomerulus Normal, low pressure capillaries Adapted for absorption- reclaim most of filtrate Cling close to the renal tubule to reabsorb (reclaim) some substances from collecting tubes *Peritubular capillaries surround the proximal and distal tubules, as well as the loop of Henle, where they are known as vasa recta.*

Countercurrent Multiplication

Ascending and Descending Limbs of Nephron Loop in close proximity but go in opposite directions

When you eat, your digestive system does its thing, and all the protein gets hydrolyzed into amino acids, which get absorbed by your blood, and gets sent all over my body to build and repair cells.

Because metabolizing nutrients- especially protein- makes a mess. You may remember that amino acids are unique, in that they have nitrogen in their amine groups. And because we can't store amino acids, extra ones get processed into storable carbs or fats. But the amine group isn't used in those storage molecules, so it's converted to NH3, or ammonia, which happens to be toxic.

Glomerular Filtration

Blood is filtered and water and solutes move out forming glomerular filtrate -Nonselective passive process -Water and solutes smaller than proteins are forced through capillary walls -Proteins and blood cells are normally too large to pass through the filtration membrane -Filtrate is collected in the glomerular capsule and leaves via the renal tubule

Regulation of Glomerular Filtration

Blood is filtered and water and solutes move out forming glomerular filtrate Nonselective passive process Water and solutes smaller than proteins are forced through capillary walls Proteins and blood cells are normally too large to pass through the filtration membrane Filtrate is collected in the glomerular capsule and leaves via the renal tubule

Micturition (voiding) (aka urination)

Both sphincter muscles must open to allow voiding The internal urethral sphincter is relaxed after stretching of the bladder Pelvic splanchnic nerves initiate bladder to go into reflex contractions Urine is forced past the internal urethra sphincter and the person feels the urge to void The external urethral sphincter must be voluntarily relaxed to void

Vasa Recta

Bundle of straight vessels, concentrated urine. Surrounds the loop of henle.

Diuretics

Chemicals that increase the flow of urine (Alcohol and Caffeine)

Filtrate

Contains everything that blood plasma does (except protein)

Calyces

Cup shared structures that funnel urine towards the renal pelvis

Nephron loop (Loop of Henle)

Curves back to renal corpuscle

Perirenal fat capsule

Cushions against blows

Proximal convoluted tubule

Directly attached to glomerular capsule Cubodial Epithelial Cells Microvilli/Brush Border Mitochondria Purpose: reabsorption

Function of urine (why does the body produce it?)

Elimination of waste products from blood: nitrogenous wastes, toxins, drugs Regulation of Body Homeostasis

Most of what's in your blood is totally removed by the kidneys. Then your body pulls back what it wants to hold onto, before the rest is sent on a one-way trip to the bladder

Ex. it's kind of like when you clean out your fridge- you take out everything and then put back in everything that's still good but throw the spoiled/old things out

Urinary system

Excretion= Filtration-Reabsorption+ Secretion *Rate is the total effect of 3 different movements.

Renal column

Extensions of cortex like material inward that separate the pyramids

Glomerulus Capillary bed

Fed and drained by arterioles: -Afferent arteriole: arises from a cortical radiate artery and feeds the glomerulus -Efferent arteriole: receives blood that has passed through the glomerulus *Specialized to produce filtrate (fluid leaving glomerulus entering glomerular capsule) *High pressure forces fluid and solutes out of blood and into the glomerular capsule

Glomerular capsule (Bowman's capsule)

First part of the renal tubule

Non-filterable blood components

Formed elements (blood cells, platelets), plasma proteins

Juxtamedullary nephrons

Found in the boundary of the cortex and the medulla, cells that regulate the rate of filtrate formation

Developmental Aspects of the Urinary System

Functional kidneys are developed by the third month of fetal life Urinary system of newborn - bladder is small, urine cannot be concentrated for first two months, void 5 to 40 times per day Control of the voluntary urethral sphincter does not start until 18 months Complete nighttime control may not occur until the child is 4 years old Urinary infections are the only common problem before old age

Urine Formation

Glomerular filtration--> Tubular Reabsorption--> Tubular Secretion

Nephrons are associated with 2 capillary beds

Glomerulus and Peritubular

Renal corpuscle

Glomerulus and glomerular capsule.

Solutes NOT found in urine includes:

Glucose, blood proteins, hemoglobin, white blood cells (pus), and bile

Specialized cells

Granular cells (secrete renin when blood volume is low) and Macula dense cells (monitor NaCl content of filtrate)

Extrinsic Control

Hormonal and neural control mechanisms, major hormones - angiotensin II and atrial natiuretic peptide (opposing actions)

*In your body, a lot of the cleanup that comes after metabolism is handled by the liver, which plays a tremendous role in directing dead cells and leftover chemicals to the digestive and urinary systems.

However, your liver can't actually escort waste out of your body. Your lungs can lend a hand, exhaling carbon dioxide, and of course your colon will eventually poop out unusable stuff and old cell-parts. But much of your chemical waste still needs to be sorted and disposed of, so one system steps in to do clean-up. That is your urinary system.

Afferent arteriole

In

Where does most reabsorption take place?

In the proximal convoluted tubule (comes right after glomerular capsule and before the loop of Henle). *Thats why the PCT has microvilli

Renal pelvis

Inner collecting tube

Renal medulla

Inside the cortex of the kidney

Intrinsic control (Renal Autoregulation)

Internal mechanism of kidney to maintain constant GFR. How is this done?: Myogenic autoregulation and tubuloglomerular autoregulation (stretch receptors, vasoconstriction of arterioles, smooth muscle contraction, osmoreceptor cells - macula densa.

Renin-Angiotensin System

Juxtaglomerular complex (JG) stimulated by low blood pressure (afferent arteriole) or changes in solute concentration Release renin - series of reactions that produce angiotensin II which causes vasoconstriction and promotion of aldosterone release from adrenal cortex. Result - Blood volume and blood pressure increase Regulation of blood pressure

Organs of the Urinary System

Kidneys Ureters Urinary Bladder Urethra

Your kidneys are a pair of dark red, fist-sized, bean-shaped organs that sit on each side of your spine against the posterior body wall.

Kidneys are retroperitoneal, which means they lie between the dorsal wall and the peritoneum- the membrane that surrounds the abdominal cavity- rather than inside the cavity itself.

Glomerulus

Knot of capillaries which are covered with podocytes from the renal tubule

Cortical Nephrons

Located entirely in the cortex, includes most nephrons

Distal convoluted tubule

Merge together to form collecting ducts Cuboidal Epithelial Cells -No microvilli -Mitochondria Purpose- Ion exchange

Macula densa cells function

Monitor NaCl content of filtrate

What materials are not reabsorbed?

Nitrogenous waste products- urea, uric acid, creatinine

What is creatinine?

Nitrogenous wastes. Broken down creatine.

So, the liver converts the ammonia into a less-toxic compound, urea, which our kidneys filter out into our pee. Once out of the body, urea can degrade back into ammonia, which is why dirty, pee-soaked toilets and cat litter boxes smell like ammonia.

Now, this business of taking out the nitrogenous trash is one of the urinary system's biggest jobs. Its other major duty is to regulate the balance of salt and water in your blood, and both of these tasks are processed in the whole system of tubes that is your urinary system.

Kidney blood supply

One quarter of the total blood supply of the body passes through the kidneys each minute Renal artery provides each kidney with arterial blood supply -Renal artery divides into segmental to interlobar to arcuate to cortical radiate arteries Venous blood flow: Cortical radiate veins to arcuate to interlobar veins to inferior vena cava No segmental veins

If we were so over hydrated we had no ADH

Osmolarity of extracellular fluids--> ADH release from posterior pituitary--> Number of aquaporins (H2O channels) in collecting duct--> H2O reabsorption from collecting duct--> Large volume of dilute urine

If we were so dehydrated we had maximal ADH

Osmolarity of extracellular fluids--> ADH release from posterior pituitary--> Number of aquaporins (H2O channels) in collecting duct--> H2O reabsorption from collecting duct--> Small volume of concentrated urine

Antidiuretic Hormone

Osmoreceptors in hypothalamus react to change in blood composition Nerve impulse to posterior pituitary release of antidiuretic hormone (ADH) Prevents water loss in urine, blood volume and blood pressure increase.

Efferent arteriole

Out *(Efferent=Exit)

Renal cortex

Outer region of kidney

Renal fascia

Outermost capsule holding kidney in place (surrounds even the perirenal fat capsule)

Collecting Duct

Reabsorption of water

Juxtaglomerular complex

Regulation of blood pressure, blood volume and blood osmolarity

Main structures of the nephron

Renal corpuscle Renal tubule

Collecting ducts receives urine from many nephrons

Run through the medullary pyramids and deliver urine into the calyces and renal pelvis

Ascending

Salt out of tubule, osmotic gradient

Granular cells function

Secrete renin

Ureters

Slender tubes attaching the kidney to the bladder Continuous with the renal pelvis, enters the posterior aspect of the bladder Runs behind the peritoneum Three muscle layers *Peristalsis aids gravity in urine transport

Urinary Bladder

Smooth, collapsible, muscular sac Temporarily stores urine

Proximal Convoluted Tubule

Sodium actively reabsorbed Chloride ions follow passively Salt increases osmolarity of blood Water will follow

Solutes found in urine include...

Sodium, potassium ions, urea, uric acid, creatinine, ammonia, bicarbonate ions

Tubular Secretion- Reabsorption in reverse

Some materials move from the blood of the peritubular capillaries into the renal tubules- hydrogen and potassium ions, creatine Process is important for getting rid of substances not already in the filtrate Materials left in renal tubule move toward the ureter **In the renal system, peritubular capillaries are tiny blood vessels that travel alongside nephrons allowing reabsorption and secretion between blood and the inner lumen of the nephron.

Nephron

Structural and Functional Unit of the Kidneys Responsible for forming urine

Renal Hilum

Structures entering / exiting the kidney

Vasa recta preserve the gradient

The entire length of the vasa recta is highly permeable to water and solutes. Due to countercurrent exchanges between each section of the vasa recta and its surrounding interstitial fluid, the blood within the vasa recta remains nearly isosmotic to the surrounding fluid. As a result, the vasa recta do not undo the osmotic gradient as they remove reabsorbed water and solutes.

Homeostatic Imbalances

The kidneys prevent homeostatic imbalances by maintaining blood volume (?)

Tubular reabsorption

The peritubular capillaries reabsorb useful substances such as water, glucose, amino acids, ions. Some reabsorption is passive, most is active (move from low concentration to high concentration) *Water flows passive (using aquaporins)

Glomerular Filtration Rate (GFR)

The speed at which fluid passes out of the blood and into the glomerular capsule. Changes in physiological parameters, esp. blood pressure can influence GFR. Kidneys are able to adapt to maintain a constant GFR by controlling blood flow in and out of glomeruli, surface area of the glomerular capillary

Aging and the Urinary System

There is progressive decline in urinary function The bladder shrinks and loses bladder tone with aging Associated problems with aging - urgency, frequency, nocturne (having to pee during night-nocturnal), incontinence, urinary retention

Urethra

Thin walled tube that 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, made of smooth muscle) - external urethral sphincter (voluntary, made of skeletal muscle) Gender differences -Length Females (4 cm.), Males (20 cm.) Location - Females (anterior to vaginal opening), Males (travels through the prostate and penis) Function - Females (urine), Males (urine and sperm/semen)

Urinary Bladder Wall

Three layers of smooth muscle called the detrusor muscle, transitional epithelium

Trigone

Triangular region of the bladder base (Three openings - two from ureters, one to the urethra) In males, the prostate gland surrounds the neck of the bladder

Renal or medullary pyramids

Triangular regions of tissue in the medullary

Collecting ducts use the gradient

Under the control of antidiuretic hormone, the collecting ducts determine the final concentration and volume of urine.

Urine

Urine is what remains after the filtrate has lost most of its water, nutrients, and necessary ions through reabsorption Urine contains nitrogenous wastes and substances body does not need

Countercurrent Exchanger

Vasa recta is countercurrent exchanger by preserving the medullary gradient Pick up and remove the water but the sodium ion is not picked up so that concentration builds Blood leaving and reentering cortex via vasa recta has same solute concentration

Renal Clearance

Volume of plasma cleared of a certain substance/minute

Urinary Bladder Capacity

Walls are thick and folded in empty bladder Bladder can expand significantly without increasing internal pressure Moderately full bladder is about 5 inches long and holds about 500 ml. of urine Capable of holding twice the amount of urine

Tubular Reabsorption

Water and solutes reabsorbed from the tubular fluid and move back into blood. (move out of tube into blood)

Urine concentrated down the loop (medulla)

Water follows salt. Water back into circulatory system.

Formation of Dilute Urine

Water intake high, water loss low Absence of ADH, osmolarity falls Decrease active water channels Tubular fluid down collecting duct Decrease concentration of urine, excess water out

Formation of Concentrated Urine

Water intake low; water loss high Increased ADH levels Increase water channels Osmolarity increases, water reabsorbed Increase concentration of urine, save water

Nephron Loop

Water leaves descending limb Salt passive diffusion out of ascending limb

Descending

Water out of tubule

Filterable blood components

Water, nitrogenous wastes, nutrients, salts (ions)

Characteristics of Urine

Yellow color due to the pigment urochrome (from the destruction of hemoglobin) and solutes Sterile, slightly aromatic Normal pH around 6 (acidic bc less than 7) Specific gravity of 1.001 to 1.0035

*How many nephrons are in the kidney??

~1,000,000 (one million) nephrons in each kidney