Urinary System

Food,water

Water,salt Water

Digestive tract Skin Respiratory system

Nutrients,water

Water,salt

Waste

Circulatory system

Water, solutes,wastes

Urinarysystem

Metabolicproducts, toxins Waste

Liver

Eliminationof foodresidues

Elimination ofwaste, excesssolutes, andwater

Urinary System

• Kidneys regulate water levels– Excess water excreted– Output varies from 2-1/2 liter/day to 1 liter/hour

• Kidneys regulate nitrogenous wastes and other solutes– Urea from protein metabolism– Other solutes regulated by kidneys• Sodium, chloride, potassium, calcium, hydrogen ions,

creatinine

Organs of Urinary System

• Kidneys– Principal organ of urinary system– Cortex: outer portion of the kidney– Medulla: inner region of the kidney

Organs of Urinary System

• Ureters– Transport urine from

kidneys to bladder

• Urinary bladder– Stores urine (600–1,000

ml)

• Urethra– Carries urine from body– Two sphincters control

urination

Nephrons Produce Urine

• Nephron: functional unit of the kidney

• 1 million nephrons per kidney

• Remove approximately 180 liters of fluid from the blood daily– return most of it, minus

wastes that are excreted

NephronNephron structure• Glomerulus: ball of capillaries– where filtration occurs

• Glomerular capsule: cuplike structure surrounding glomerulus

• Proximal tubule: comes off capsule• Loop of Henle: located in renal

medulla• Distal tubule: connects to collecting

duct• Collecting duct: shared by several

nephrons, empties into renal pelvis

Nephron Blood Supply• Renal artery supplies kidney• Blood vessels associated with

nephron– Afferent arteriole: enters

glomerulus– Efferent arteriole: leaves

glomerulus– Peritubular capillaries:

surround proximal and distal tubule

– Vasa recta: parallels loop of Henle

Formation of Urine1. Glomerular filtration:

movement of fluid and solutes from blood into glomerular capsule– No proteins or cells

2. Tubular reabsorption: return of fluid and solutes into blood– Stuff we want to keep

3. Tubular secretion: addition of solutes from blood into the tubule– Throwing out extra junk

Figure 15.7

a) The outer surface of several glomerular capillaries.

Podocyte

Filtrate

Proximal tubule Capillary wall

Glomerularcapsule

Glomerularspace

Glomerulus Blood flowMovement of glomerular filtrate

Afferent arteriole

Efferent arteriole

b) A highly magnified view of the inner surface of a single glomerular capillary, revealing its porous sievelike structure.

Glomerular filtration: Water, ions, glucose,amino acids, bicarbonate,and waste products(urea, creatinine) arefiltered from the glomerularcapillaries into the spacewithin the glomerular capsule.

Tubular secretion: Some drugs, waste products,and ions (primarily hydrogen,ammonium, and potassium)are actively secreted from theperitubular capillaries primarilyinto the distal tubule but alsoin other nephron segments.

Tubular reabsorption: Water, amino acids,glucose, most ions(including bicarbonate),and some urea arereabsorbed back into theperitubular capillaries,primarily in the proximaltubule but also in othernephron segments.

Glomerularcapsule

Glomerulus

Afferentarteriole

Efferentarteriole

Artery Vein

Proximal tubule

Distal tubule

Collecting duct

Urine

1

3

2

Figure 15.6

Tubular Reabsorption

• 100% of filtered glucose, amino acids, and bicarbonate (buffer)

• 65% of water reabsorbed• Most tubular reabsorption

occurs in proximal tubule

Tubular Secretion

• Movement of materials from peritubular capillaries or vasa recta into the tubule

• Purpose–Regulation of chemical levels in body– Excretion of harmful chemicals

• Substances secreted–Penicillin, cocaine, marijuana, pesticides,

preservatives, hydrogen ions, ammonium, potassium

Producing Concentrated Urine• Too little water can lead to:– lower blood volume– declining blood pressure– dehydration of body cells

• Kidneys can conserve water and produce a more concentrated urine

• Mechanism–ADH (antidiuretic hormone) secreted from

posterior pituitary gland–ADH increases permeability of collecting ducts to

water• More water reabsorbed

Producing Dilute Urine

• Excess water can:– Elevate blood pressure– Cause cells to swell and/or burst

• Kidneys respond to excess water by excreting it• Mechanism– Distal tubule is impermeable to water except when

ADH is present– Large volume of water is excreted

Micturition Reflex• Stretch receptors in bladder wall• Internal urethral sphincter– Smooth muscle, involuntary

• External urethral sphincter– Skeletal muscle, under voluntary control

• Brain can override the micturition reflex – Voluntary control becomes increasingly difficult as bladder

gets very full

Kidneys Maintain Homeostasis in Many Ways

• Maintain water balance– Adjust blood volume and blood pressure

• Aldosterone, renin, ANH help maintain salt balance in order to control blood volume

• Maintain acid-base balance and blood pH• Regulate red blood cell production via erythropoietin• Activate an inactive form of vitamin D

Water Balance Determines Blood Volume and Blood Pressure

• Involves the kidneys, hypothalamus, and posterior pituitary gland– Involves increasing or reducing ADH secretion– Involves increasing or decreasing thirst

• Diruretic: increases formation and excretion of urine– Lasix (furosemide): medication that reduces blood

volume and blood pressure– Caffeine: inhibits sodium reabsorption– Alcohol: inhibits ADH release

ADH

Save water

KidneysSavesalt

Blood volume

Increase

Set point

Decrease

Adrenal cortex

Angiotensin-converting

enzyme

Kidneys

Vasoconstriction, blood pressure

Liver

Angiotensinogen

Lungs

Reni

n

Figure 15.15

Kidneys Help Maintain Acid-Base Balance and Blood pH

• Blood pH must stay between 7.35 and 7.45• pH regulated by kidneys, buffers, lungs• Role of kidneys in pH maintenance– Reabsorption of filtered bicarbonate– Excretion of acid as ammonium

Disorders of the Urinary System

• Kidney stones– Crystallized minerals– Block urine flow

• Urinary tract infections (UTI)– Usually caused by bacteria– More common in women than

men because of shorter urethra– If untreated, bladder infections

may ascend to involve kidneys

Disorders of the Urinary System

• Acute renal failure– Short-term impairment, may be reversible– Potential causes: sustained very low blood pressure,

large kidney stones within renal pelvis, infections, transfusion reactions, severe injury, toxin exposure, drug reactions

Disorders of the Urinary System

• Chronic renal failure– Also known as end stage renal

disease (ESRD)– >70% reduction in functioning

nephrons– Causes:• Diabetes (40% will develop CRF)• Uncontrolled high BP• Glomerulonephritis• Polycystic kidney disease• Overuse of acetaminophen or

ibuprofen

Treatment of Irreversible Kidney Failure

• Dialysis• Problems:– Dialysis cannot achieve complete homeostasis of

ions and wastes– Dialysis does not replace renal hormones

Treatment of Irreversible Kidney Failure

• Kidney transplant

Kidney Transplants

• Best hope for many CRF patients• >65,000 people on waiting list for kidneys• Improvements in transplant protocols/processes

have improved outcomes– Better tissue-matching techniques– Improved anti-rejection medications– National data banks