Urinary System

Urinary System

Consists of:

• Kidney(s)• Ureters• Urinary Bladder• Urethra

Functions:

• Filter gallons of fluid from bloodstream– Filter plasma 60

times/day• Responsible for

removing:– Toxins– Metabolic Wastes– Excess ions

• Regulates volume and chemical make up of blood

• Maintains the proper pH between water, salts, acids and bases– Maintains blood pH

between 7.35 – 7.45

Functions

• Regulatory functions include:– Produce hormones Renin

and erthropoietin– Renin helps regulate BP and

kidney function– Erthropoietin stimulates

RBC production in bone marrow

– Assists in metabolizing Vitamin D to its active form.

Kidney Anatomy• Kidneys are covered by

fatty tissue; anchors kidneys to posterior wall

• Internal Anatomy – 3 distinct regions– Pelvis – where kidneys

join ureters; responsible for collecting urine

– Renal Cortex – outer region; most of nephrons are found here

– Medulla – Middle region; Renal pyramids

Medulla

• Nephron – Working Unit of Kidney; Carry out processes that form urine

C o r tex

M e d u l l a

Nephron

• Glomerulus – tuft of capillaries

• Parts of Nephron– Bowman’s capsule– Renal Tubule - 3 cm in

length• Proximal Convoluted tubule

(PCT)• Loop of Henle• Distal Convoluted tubule

(DCT)– Collecting Duct

Urine Formation Involves 3 processes

• Filtrationglomerulus and Bowman’s capsule

• Renal Reabsorption

Carried out by renal tubules

• Secretion Carried out by renal tubules

• Glomerular Filtration– Blood enters via afferent

arteriole (larger diameter) and leaves via the efferent arteriole

– Difference in vessel diameter increases BP in glomerulus and assists with filtration

• Podocytes (Bowman’s capsule) – surround capillaries

• Passive, nonselective process where fluids and solutes are passed through a membrane

• Force is cause by hydrostatic pressure– What caused pressure

increase?

• GFR (Glomerular filtration rate) is the amount of filtrate produced in the kidneys in one minute.

• Renin regulates GFR by causing an increase in blood volume and blood pressure (Constricts blood vessels)

• Filtration Pressure – Increase in BP at glomerulus forces water and solutes out of blood and into capsule.

• What passes through? What remains in the blood?

Filtrate is not Urine

• Filtrate contains both wastes and needed water and solutes

• Reabsorption begins as soon as nutrients enters the PCT

• All water can’t be excreted, so tubules claim what it needs

• Why is it called reabsorption and not absorption?

What is reabsorbed?• 100 % of organic nutrients• Most electrolytes by

facilitated diffusion• Water is passively

reabsorbed– 60 – 70 % of fluid is reaborbed

by PCT

Rate and degree of reabsorption is regulated by hormones

Problems: Hyperglycemia

Where does Reabsorption occur in the nephron? • PCT are most active

reabsorbers• The descending loop of

Henle is permeable to water but not solutes

• The ascending loop of Henle is impermeable to water and most solutes– Na and Cl are actively

reabsorbed into the blood stream

• DCT is impermeable to solutes

• Reabsorption of Na, K, and water is controlled by hormones

Figure 25.18a

Cortex

Outermedulla

Innermedulla

(a)

(b)

(c)

(e)

(d)

Na+ (65%)GlucoseAmino acids

H2O (65%) and many ions (e.g.Cl– and K+)

300

Milliosmols

600

1200

Blood pH regulation

H+,NH4

+

HCO3–Some

drugs

Active transport(primary or secondary)Passive transport

(a) Proximal convoluted tubule: • 65% of filtrate volume reabsorbed • Na+, glucose, amino acids, and other nutrients actively transported; H2O and many ions follow passively • H+ and NH4

+ secretion and HCO3– reabsorption to

maintain blood pH • Some drugs are secreted

Reabsorption

(b) The descending loop of Henle

• Freely permeable to H2O• Not permeable to NaCl or

other solutes• Filtrate becomes

increasingly concentrated as H20 leaves by ____________?

Active transport(primary or secondary)Passive transport

Figure 25.18c

Na+

Urea

Cl–

Na+

Cl–

K+

(c) Ascending limb of loop of Henle • Impermeable to H2O • Permeable to NaCl • Filtrate becomes increasingly dilute as salt is reabsorbed

(a)

(b)

(c)

(e)

(d)

Cortex

Outermedulla

Innermedulla

300

Milliosmols

600

1200

Active transport(primary or secondary)Passive transport

Figure 25.16a

Loop of Henle

Osmolalityof interstitialfluid(mOsm)

Innermedulla

Outermedulla

Cortex Active transport Passive transportWater impermeable

The ascending limb:• Impermeable to H2O• Permeable to NaClFiltrate becomes increasingly dilute as NaCl leaves, eventually becoming hypo-osmotic to blood . NaCl leaving the ascending limb increases the osmolality of blood.

Filtrate entering the loop of Henle is contains many substances that are needed in the body

The descending limb:• Permeable to H2O• Impermeable to NaClAs filtrate flows, it becomes increasingly concentrated as H2Oleaves the tubule by osmosis. The filtrate osmolality increases.

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCI

NaCI

NaCI

NaCI

NaCI

What’s left in the nephron?

• Non-reabsorbed substances are:– Urea – 50 % is

reclaimed; the rest is waste

– Creatinine – a large lipid; insoluble molecule that is not reabsorbed at all

– Uric Acid – 50 % is reclaimed; waste product of RNA synthesis

Tubular Secretion – “Reabsorption in Reverse”

• Urine is formed from filtered and secreted substances

• Secretion occurs in the DCT tubules and collecting ducts – Hormones assist with

this process• ADH (antidiuretic

hormone)• Aldosterone• ANP

Figure 25.18d

Na+; aldosterone-regulatedCa2+; PTH-regulatedCl–; follows Na+

(d) Distal convoluted tubule • Na+ reabsorption regulated by aldosterone • Ca2+ reabsortion regulated by parathyroid hormone (PTH) • Cl– cotransported with Na+

(a)

(b)

(c)

(e)

(d)

Cortex

Outermedulla

Innermedulla

300

Milliosmols

600

1200

Active transport(primary or secondary)Passive transport

Figure 25.18e

Blood pHregulation

Urea;increasedby ADH

Na+

K+

H+

HCO3–

NH4+

H2O regulatedby ADH

Regulated byaldosterone:

(e) Collecting duct • H2O reabsorption regulated by ADH • Na+ reabsorption and K+ secretion regulated by aldosterone • H+ and HCO3

– reabsorption or secretion to maintain blood pH • Urea reabsorption increased by ADH Why?

(a)

(b)

(c)

(e)

(d)

Cortex

Outermedulla

Innermedulla

300

Milliosmols

600

1200

Active transport(primary or secondary) Passive transport

Substances that are not reabsorbed• Substances that lack

carry proteins along membrane– Urea– Uric acid

• Substances that are not lipid soluble

• Substances that are too large to pass– Creatinine

Label the parts of the nephron

Describe what is occurring at sections 1-6.1.

2.

3.

4.

5.

6.

1

2

34

5

6

Hormonal Control of Secretion• Osmolarity – number of

solute particles dissolved in one liter of waterAffects osmosis

• Kidneys are responsible for regulating solute concentrations in the body; the concentration of urine is regulated by hormones

• Four Hormones Control Kidney Function– Renin– Aldosterone– Atrial Natiuretic

Peptide (ANP)– Antidiuretic hormone

(ADH)

Renin• Released when

glomerular pressure is low

• Causes blood vessels to constrict; raising blood pressure in arteries

• The efferent arteriole constricts which increases glomerular pressure

• Stimulates secretion of ADH and aldosterone

Aldosterone

• Released by adrenal glands

• When secreted causes Na+ to be reabsorbed from DCT

• H20 follow Na+, so both Na+ and H2O are reabsorbed

• Eliminates K+ into urine

• Stimuli that cause the release of aldosterone– Decreased blood volume

– Decreased sodium in blood

– Increased potassium in blood (heart block)

If too much aldosterone is secreted:- Excessive Na+ and H20 retention (edema, hypertension- Accelerated secretion of K ions (muscle responsiveness)

Lasix – (Diuretic) inhibits Na from being reabsorbed; thus water is not reabsorbed.

Atrial Natiuretic Peptide (ANP)• Works against

aldosterone• Released by atrial

cardiac cells when blood volume and BP are too high.

• Why would the atrial cells detect a change in blood volume?

• When ANP is secreted:– Causes Na+ to be dumped into

tubules (urine)– H2O follows sodium into urine– Capillaries in glomerulus

dilate; increasing blood flow to Bowman’s capsule; increasing UO

– Inhibits the secretion of renin, aldosterone and ADH

– Urine contains more Na+ H2O; blood pressure and blood volume decrease

ADH (Antiduretic hormone)• When ADH is secreted,

water is reabsorbed from DCT and collecting tubules

• Person feels thirsty• When ADH is not

secreted, DCT and collecting tubules are impermeable to water, no reabsorption occurs here.

Concentration of Urine is controlled by ADH

• Dilute Urine– Na and other ions

are removed from filtrate

– Urine appears clear in color

• Concentrated Urine– ADH is secreted; distal

and collecting tubules reabsorb water

– When water leaves filtrate; urine concentration increases

W i t h o u t u s e o f h o r m o n e s , D C T a n d c o l l e c ti n g d u c t a re re l a ti v e l y i m p e r m e a b l e t o w a t e r a n d s o d i u m

Work of the Nephron with Hormone Secretion

Diuretics – chemicals which increase UO

• Any substance that is not reabsorbed and carrries water out of body– Alcohol – inhibits ADH– Caffeine – Increases

filtration rate (GFR)• Diuretic drugs are taken

for CHF, edema and to increase UO

Figure 25.17a

Active transport Passive transport

(a) Absence of ADH Large volumeof dilute urine

Collecting duct

Cortex

NaCI

NaCI

NaCI

Urea

Outermedulla

Innermedulla

DCT

H2O

H2O

Descending limbof loop of Henle

Maintaining a Balance

• Other Systems assist in excretion and affect kidney function– Integumentary– Respiratory– Digestive

• Fluid and Electrolyte Balance– Water into body = Water out

of the body– Neither a net gain or loss of

electrolytes should occur in body

• Acid-Base Balance– Blood pH ranges between

7.35 – 7.45– Kidneys will secrete H+ ions

when blood pH drops

• Acidosis – Blood pH drops below 7.35– Respiratory Acidosis

• Due to an increase of CO2

levels in body– Metabolic Acidosis

• Due to cell metabolism in the body

• Lactic acid in muscle metabolism

• Ketone bodies by the breakdown of fat

• Diabetics don’t use glucose due to lack of insulin; so cells will break down fat instead

Imbalances

Blood ph < 7.05 disrupts the stability of cell membrane, alters protein function (enzyme), causes heart arrhythmias and leads to coma

Kidney Stones• Hardened mineral

deposits that form in kidney

• Symptoms– Blood in urine– Increased need to go– Nausea and vomiting– Pain during urination– Tenderness in abdomen

and kidney region• Treatment

– Lithotripsy– Medication

Renal Failure – Kidney Failure• Nephrons in kidney stop

functioning– Unable to filter or

excrete waste– Can’t regulate

composition of body fluids

– Can’t control erythrocyte function or blood pressure

– Can’t control salt balance