URINARY SYSTEM

URINARY SYSTEM

Functions

Excretory: Nitrogenous wastes, ions, toxins
Regulatory: Renin, Erythropoietin, Vitamin D

Urinary System: Consists of:

Kidneys
Ureters
Urinary Bladder
Urethra

Urinary System Gross Anatomy Online Quiz

General Overview

Kidney

Housed in fibrous capsule (adipose & fascia surround kidneys): Histology

Sinus - area where ureter, nerves, and vessels collect

Outer renal cortex

Inner renal medulla

Pyramids (base--papilla)

Form lobes (8)

Columns in between pyramids

Kidney: Gross Anatomy

Kidney: Cross Section: with link to X-ray

Kidney Anatomy Online Quiz 1
Kidney Anatomy Online Quiz 2
Kidney Anatomy Online Quiz3
Kidney Anatomy (Lab Quiz1)
Kidney Anatomy (Lab Quiz2)
Kidney Anatomy (Quiz: Plastic Model)

Collection of nephrons -- About 1 million per kidney.

2 Types or Nephrons:

cortical: short loops of Henle
juxtamedullary: long loops of Henle -- more important for concentrating urine.

Nephrons

Glomerulus: tuft of capillaries ..Histology ... Graphic

Glomerular (Bowman's) Capsule... Graphic

Renal Corpuscle = Glomerulus and Glomerular Capsule. Histology.

Tubules: Proximal convoluted tubule, Loop of Henle (descending & ascending loops), Distal convoluted tubule

Collecting Duct: empties into renal pelvis

Juxtaglomerular Apparatus:

Distal convoluted tubule interface with afferent arteriole
Juxtaglomerular cells of arteriole sense blood pressure
Macula densa cells of tubule are chemo- and osmo-receptors
Histology
Histology 2: Note large glomerulus, triangular region (jg cells) and row of macula densa cells. Compare with diagram.

Nephron: Web Anatomy Online Quiz

Urine Formation

Great Overview Site on Kidney structure and function

Urine formation consists of 3 processes:

Glomerular filtration
Tubular reabsorption
Tubular secretion

1) Glomerular Filtration

120-125 mls per minute of plasma filtrate formed
180 Liters formed per day
Kidneys use about 20-25% of body's oxygen at rest
Relatively non-selective - water and small ions pass through (Size and Electrical Charge Determine Permeability)
- Postively charged molecules pass thru more than negatively charged molecules.
Water, glucose, amino acids, nitrogenous wastes (urea) pass
Red blood cells and proteins don't pass through. Filtration Barrier.

Filtration pressure

Net (effective) Filtration Pressure (NFP)

Glomerular Hydrostatic Pressure (CHP)

Glomerular Osmotic/Oncotic Pressure (GOP)

Capsular Hydrostatic Pressure (CHP)

NFP = GHP - (GOP + CHP) = 50 - (25 + 15) = 10 mm Hg

Maintaining blood pressure is important

Low blood pressure - less filtration pressure

High blood pressure - more filtration pressure

Arterioles leading to glomerulus can dilate and constrict.

Some autoregulation

Renin-angiotensin-aldosterone system

Lecture Slides on RAAS

Low filtration flow --> macula densa cells sense slow flow or low sodium or chloride levels (low osmolarity) --> induce vasodilation. Vasoconstriction if opposite conditions exist.

Renin-angiotensin-aldosterone system. Angiotensin is a vaso-constrictor. Aldosterone leads to sodium retention.

Reduced stretch on JG cells by drop in blood pressure triggers release of renin. Vasoconstriction and sodium retention increase blood pressure.

Sympathetic NS stimulates renin release

Tubular Reabsorption

Kidney tubules reabsorb most of filtrate
Active (ATP requiring) and passive processes

Proximal convoluted tubule

Reabsorbs nutrients, electrolytes, and water.

Loop of Henle

Descending reabsorbs water by osmosis
Ascending reabsorbs sodium and chloride

Distal convoluted tubule

Sodium actively transported (aldosterone dependent)
Water via osmosis (ADH controls - increases permeability)

Collecting ducts

Sodium actively transported
Water moves via osmosis Antidiuretic Hormone (ADH) controls water permeability of collecting ducts

Tubular Secretion.

Selective excretion of certain substances: Hydrogen ions, potassium, ammonia, organic acids and bases, penicillin & histamine

Urine is concentrated by Countercurrent Multiplier System

Countercurrent Mechanism Tutorial with Animations: A Must See!!!

Other Examples of Countercurrents in Physiology

Arrangement of loops of Henle creates an osmotic gradient

Urine produced can be hypo- or hyperosmotic. Osmolarity of plasma 300-330 mOsm. Seawater is about 1000-1500 mOsm. This is about as concentrated as we can make our urine.

Other animals:

Fresh water fish and amphibians live in hypotonic environment. They need to excrete a large amount of water, so they have short loops of Henle and produce dilute urine.
Saltwater fish and desert animals need to retain fluid, so they typically have long loops of Henle and produce very concentrated urine.

Aldosterone and antidiuretic hormone regulate volume of urine.

Physiology of Urinary System Online Quiz

Ureter: tube that transports urine from kidney to bladder

Ureter Histology: X-section ; Another Image

Double Ureters

Bladder

Internal folds are called "rugae" (hey, that sounds familiar!). Allows for expansion.

Lining: transitional epithelium (collapsed bladder)

Transitional Epithelium: expanded bladder.

The Bladder: Gray's Anatomy

Urethra

Males: 3 regions

Prostatic
Membranous
Penile (spongy)

Male Bladder and urethra graphic

Females: short, typically less that 4 cm long

Female Bladder and urethra graphic.

Urination (micturition): Emptying of urinary bladder.

Micturition Reflex is a "stretch reflex" that is mediated by the parasympathetic NS.

Neurosensory loops involved in micturition reflex.

Internal sphincter (smooth muscle, involuntary control); external sphincter (skeletal muscle, voluntary control)

Graphic Normal

Artificial Urinary Sphincter

Incontinence: inability to control urination

Stress incontinence: losing urine due to a sudden increase in pressure on the bladder, such as from a cough, sneeze, or running down stairs.
There are other forms also.

Who has more of a problem with incontinence, men or women?

Review Questions for Exam

Online Exam: Overview of Urinary System

Online Exam: The Nephron

Lab Links

Online Practice Exam: Identification

Misc. Links

Urinary Tract Histology (LUMEN)

Renal Anatomy & Physiology Lecture Slides (Nursing Course)

Physiology Lecture Summaries: 4 lectures related to Urinary Physiolgy

Renal Pathology

Renal Cyst: fluid accumulation under the capsule.

Renal Physiology Outline: Nice step-by-step outline of transport and countercurrent system.

The Nephron Info Center: Good, general info on the kidney and kidney disease. Neat animations.

Kidney Stone

Kidney Stones: Causes and Treatments

UCLA Kidney Stone Treatment Center