Urinary System

Major functions of the Kindeys

1. Regulation of Blood, Electrolyte balance, Acid-base balance, and blood pressure.

2. Excretion of Metabolic products, Foreign substances, and Excess substances.

3. Secretion of Erythropoietin and Renin.

Coverage of the Kidneys

• Renal/Fibrous Capsule - prevents kidney infection.

• Perirenal Fat - cushions kidney and attaches it to the body.

• Renal Fascia - anchors the kidney.

• Pararenal Fat - external to the Renal Fascia.

Renal Structure

• Cortex

• Medulla

• Renal Column

• Renal Pyramid

• Minor Calyx

• Major Calyx

• Renal Pelvis

• Uerter

Uerters

Uerters actively propel urine to the bladder.

Uerters have a trilayered wall:

• Transistinal Epithelial Mucosa

• Smooth Muscle Muscularis

• Fibrous Connective Tissue Adventitia

Urinary Bladder

• Smooth, collapsible, muscular sac and stores urine.

• Lies on the pelvic floor posterior the public symphysis.

• connected anteriorly to the umbilicus-median.

• Collapses when empty.

• The badder expands as pressure rises.

Urinary Bladder Anatomy

Has the Destursor Muscle

Has a 3 layer wall:

• Transitional Epithelial Mucosa

• A thick muscular layer

• A Fibrous Adventitia

Urethra

A muscular tube that drains urine from bladder, out of the body. It also has 2 sphincter to help keep it close:

• Internal - INVOLUNTARY

• External - VOLUNTARY

Renal Blood Flow

Cortex

1. Perutubular Capillary

2. Distal Convoluted Tubule

3. Juxtaglomerular Apparatus

4. Bowman’s Capsule

5. Proximal Convoluted Tubule

Medulla

1. Ascending limb

2. Descending limb

3. Vasa Recta Capillary

4. Collecting duct

Vasoconstriction of AFF. Art.

VC AFF. Art. → ↓Q AFF. Art. → ↓GBF → ↓GBP → ↓GFR

Vasodilation of AFF. Art.

VD AFF. Art. → ↑Q Aff. Art. → ↑GBF → ↑GBP →↑GFR

Filtration

• First step in urine formation.

• Bulk transportation of fluid from blood to kidney tubule. (Blood cells and proteins don’t filter)

• Result of hydraulic pressure.

• GFR = 180 L/day.

Reabsorption

• Process of returning filtered material to blood stream.

• 99% of what is filtered.

• May involve transport proteins.

• Normally glucose is totally reabsorbed.

Secretion

• Material added to lumen of kidney from blood.

• Active transport of toxins and foreign substances, but also include ions.

Excretion

• Loss of fluid from body in form of urine.

JGA Feedback (↓GFR)

↓GFR → ↓Na+ in DCT → ↑NO Release → VD of Aff. Art. → ↑GBF → ↑GBP → ↑GFR

JGA Feedback (↑GFR)

↑GFR → ↑Na+ in DCT → ↑Na+ in Macula → ↑Adenosine → VC of Aff. Art. → ↓GBF → ↓GBP → ↓GFR

Response to Severe Drop in Blood Pressure

Reabsorption and Secretion

1. Primary Active Transport: actual “pump”, usually against the concentration gradient. REQUIRES ATP

2. Secondary Active Transport: moves with concentration gradient. USES ATP INDIRECTLY

3. Passive Transport: Diffusion.

4. Pinocytosis: not a major player, but useful for reacquiring larger proteins.

ADH/AVP

• VC which increases systemic BP, and decreases GFR.

• Retention of water (ONLY WATER) is controlled by ADH.

• Released in response to Hypothalami’s Stimulation (Dehydration) or increased AgII levels.

• ADH increases the number of Aquaporina incorporated into the membrane of Tubule cells.

ANP

• It is released by atrium in response to atrial stretching due to increased blood volume.

• ANP enhances Na+ and water losses by increasing glomerular flow (Aff. Art. VD).

• It also inhibits ADH secretion. Thus, it promotes sodium excretion and water excretion in urine.

Aldosterone

Sodium balance is largely controlled by Aldosterone.

• Released in response to increased AgII levels.

• The net effect of Aldosterone is to make the kidney reabsorbed Na+ (WATER FOLLOWS) and secrete K+ into the Tubule Fluid.

• Works by stimulating the Na+ and K+ ATPhase pump on the basolateral side (Back Door).

• Aldosterone also increases the Na+ permeability of the luminal side (Front Door).

AgII

• Stimulation of Aldosterone release form Adrenal Cortex.

• Stimulation of ADH/AVP release from the Post. Pit.

• VC of many systemic arterioles, increasing BP.

• VC of the Aff. Art., decreasing GFR.

Renin

It is an enzyme that catalyzes the conversation of Angiotensinogen to AgI.

Flow in the formation and releasing of urine.

1. Glomerulus (Blood)

2. Glomerulus Capsule (Filtrate)

3. PCT (Filtrate)

4. DL (Filtrate)

5. Loop  (Filtrate)

6. AL (Filtrate)

7. DCT (Filtrate)

8. Collecting Duct (Filtrate/Urine)

9. Minor Calyx (Urine)

10. Major Calyx (Urine)

11. Renal Pelvis (Urine)

12. Ureter (Urine)

13. Urinary Bladder (Urine)

14. Internal Sphincter (Sm. Muscle)

15. Urethra (Urine)

16. (External Sphincter (Sk. Muscle)

Neurological Reflex

Tubule cell that moves Na+ and K+ ions

Tubule cell that moves H+ ions

Tubule cell that creates HCO3- (Bicarbonate)

Nephron

Functions of the SNS in the Kindey

1. Reduce the GFR through VC Aff. Art.

2. Increase the Na+ reabsorption in the proximal tubules.

3. Increase the release of renin.

Maintaining BP during Dehydration